Impact Analysis of Renewable Variabilities on Coherency Change Patterns in Power System

Ravi Yadav

Research Snippets

---

The dynamic response of a multi-machine interconnected power system to a disturbance introduces multiple electromechanical oscillatory modes within a frequency range of 0.1–2 Hz. A subset of these modes constitutes the inter-area oscillatory modes (0.1-0.7 Hz) produced by synchronous generators oscillating in unison with respect to other areas or systems [1]. These groups of generators exhibit similar dynamic behavior for a disturbance i.e., their frequency and phase-angle signals have homogeneous oscillations. Such units are referred to as “coherent” generators [2]. Identification of coherent generator groups is required for: 1) Controlled-Islanding: That limits the spread of cascading outages by partitioning the system into multiple controllable and self-sustainable islands, 2) Wide-Area damping Control: where critical inter-area oscillatory modes in a system are identified and attenuated using control strategy based on wide area measurement system data (WAMS), and 3) Dynamic equivalencing and system aggregation for dynamic vulnerability analysis.

Most of the available literature analyzes coherency patterns for only conventional synchronous generation in the power system [3]. However, high penetration of intermittent renewable energy sources can influence existing inter-area modes or introduce weakly damped modes in a system, which alters the coherency grouping of a system [4]. Depending upon the source characteristics, control topology, and location of renewable generation the coherent grouping in a power system can vary. Renewable alterations like non-uniform inertia distribution and source intermittency need to be included in the coherency pattern study for modern power systems [5]. In this work, an in-depth analysis of coherency changes patterns due to variabilities in renewable generation is presented. It raises pertinent points regarding the impact of new renewable integration, and outage of renewable sources on low-frequency power system oscillations, and the effect of dynamic renewable intermittencies on small signal stability.

Power system coherency study under different penetration levels can provide limited insight into system dynamics under renewable integration. Intermittent renewable generation can influence system dynamics in a variety of ways like non-uniform changes in inertia distribution due to: (i) a new renewable source integration at varied locations in the grid, (ii) scheduled or unscheduled outages of existing renewable plants, (iii) dynamic power flow pattern changes, and (iii) source intermittency (change in wind speed or solar insolation profiles). Each type of these variability influences the system coherency in a unique way and their effect needs to be studied for planning, wide area control, and controlled islanding applications.

Case 1: Effect of Non-uniform Inertia Distribution with Renewables
Any new large-scale renewable integration in a system could influence the existing inter-area oscillatory modes or may introduce newer oscillatory modes in the system, which can affect the system coherency. New integration can influence coherency in two ways:
(1) Spatial location of new integration or power sharing changes of participating generators.
(2) Type of renewable source or control topology.
Case 1.1: Effect new integration and power flow patterns with renewables
The location of renewable energy power plants (REPPs) and their interconnection point in a system are mostly governed by the geographical abundance of renewable sources within a geographical zone. However, depending on the interconnection nodes, the coherency grouping of an area or system can vary distinctly.

To illustrate this, two different scenarios are considered, 1) an offshore wind farm (OWF) (with back-to back voltage source converter- high voltage direct current (VSC-HVDC) link of capacity 500 MVA) is integrated while keeping the power sharing similar among the neighboring generators and 2) changing the power sharing ratio.

To simulate the first scenario, an OWF is integrated at bus-23 near generator G-07 of the IEEE-39 bus system [6]. For a trip disturbance at Line 6-11, the speed signals under base case (i.e., without OWF) and with OWF are shown in Fig. 1 (a) and (b). The disturbance excites two local oscillatory modes -0.682±8.473j (with damped frequency 1.348 Hz), and-0.5±7.100 j (with damped frequency 1.13 Hz). For both the local modes, all four generators G-04, 05, 06, and 07 participate under the base case, which changes with integration of OWF as G-07 no longer participate in these modes (refer mode shape plot of Fig. 2 (a)). A similar trend is observed for a critical inter-area mode -0.32±5.99j (damped frequency 0.955 Hz), where participation of G-07 changes with integration of OWF at bus-23 as shown in Fig. 2 (b). This shows that the participation of generator G-07 in the oscillations within the coherent area changes with the integration of OWF at bus-23 and it starts oscillating as a disassociated generator.

In the second scenario, a new OWF is integrated at bus-21, which changes the dispatched power from generators G-06 and G-07 based on their effective droop. This excites a new local oscillatory mode-1.062±10.6j (damped frequency 1.69 Hz), where only G-06 and 07 are participating, whereas an opposite trend is observed for the inter-area mode -0.346 + 6.344j (damped frequency 1.009), where G-06 and G-07 lose participation. This can be visualized from the speed signals and mode phasor plot of Fig. 3 (a) and Fig. 4. In another scenario, an OWF is integrated at bus-19 which changes the scheduled powers from G-04 and 05 in accordance with their effective droop. This excites a new local oscillatory mode -0.995+10.890j (damped frequency 1.733) with the participation of G-04 and G-05 only, whereas the same generators lose their participation in the critical inter-area mode -0.360+6.315j (refer to the speed signal and mode phasor plot in Fig. 3 (b) and Fig. 4 (b)).

The scenarios discussed above, indicate that the location of newly integrated REPP and corresponding power flow change in existing generators excite new modes within the power system and change the coherent participation of these generators in critical low-frequency inter-area modes.

For automated segregation of coherent groups, an un-supervised spectrum similarity approach method is used, which is proposed in our previous work [1]. For the case of OWF integration at bus-23, the coherency method indicates the separation of the generator G-07 from the previously coherent area (CA)-02 and forming a new coherent area CA-3 as shown in Fig. 5 (a). Whereas, in the case of OWF integration at bus-21 the coherency method indicates the separation of generators G-06 and 07 forming a new coherent area CA-2 as shown in Fig. 5 (b).

Case 1.2: Effect of Outages of Existing Renewable Sources
Planned or unplanned outages of a renewable power plant can affect system coherency depending upon the type of renewable source and location of the outage. In addition to switching outages, any reduction in dispatched power from renewable can cause a varying effect on system oscillations and therefore coherency. The outage of renewable sources can affect coherency in the following ways:
(1) Location of renewable outage/reduced dispatch
(2) Magnitude of outage/dispatch changes in the renewable source.
(2) Type of renewable source facing outage.

To illustrate this, the IEEE-39 bus system is modified to include OWF and DFIG integrations at different locations in the network as shown in Fig. 6. The wind power plants are distributed in a way that generators in all three areas have a uniform distribution of non-synchronous generation. The penetration level is 25 %, which is measured as:

As the spatial distribution of renewables is considered unform across the base case, so no apparent impact is observed on system coherency grouping. This dynamically un-changed IEEE-39 bus system with 20% renewable penetration level is subjected to renewable outages/dispatch changes to analyze their impact on system coherency. For this, two scenarios are considered. In first scenario the OWF at bus-6 suffers an outage, creating a new dynamic state of the system. For this perturbed system a line trip event at line 6-11 is simulated at 5s and oscillation trends are analyzed. The generator speed signals under base case and after outage of OWF at bus-06 for a line trip event at 6-11 are shown in Fig. 7 (a) and (b).

The outage of OWF at bus-06 increases the dispatched power from G-03, which in turn enhances the effective inertia of G-03 and changes the coherency trends for adjoining generators. For example, after an outage the participation of generator G-04 in the inter-area mode -0.345+6.045j (damped frequency 0.962 Hz) changes in a way that it starts oscillating with G-03 forming a single coherent group as shown in the mode shape plot of Fig. 8 (a). The reason for this is the increased effective inertia of G-03, which forces G-04 to oscillate in unison. It became coherent to gen-03 and formed a new coherent group leaving the existing coherency with area-02. In another scenario, an outage of the onshore wind plant (DFIG type) at bus-21 causes a change in oscillation participation of G-03, G-04, G-05, and G-07. In a way that G-04, G-05 start oscillating distinctly from the G-06, G-07 (under base case all four generators oscillate in unison for most inter-area modes). In addition, G-03 also start oscillating in unison with G-06, which was dissociated during the base case without any outage. The Speed signals and mode shape plots for this scenario are shown in Fig. 7 (c) and 8 (b). The reason for these changes is the increased effective inertia of G-06 that disturbs a delicate inertial balance in the system.

These observations are confirmed with the automated un-supervised spectrum similarity method [1]. For outage OWF at bus-06 the method correctly detects the formation of new coherent group CA-02 with G-03, G-04, G-05, G-06, and G-07 oscillating in unison as shown in Fig. 8 (a). On the other hand, for the outage of DFIG from bus-21, the generators G-07, 06, and 03 form a separate coherent group CA-2, whereas generators G-04 and 05 form another coherent group CA-3.

From these results it can be understood that outage/reduced dispatch of any renewable power plant and associated inertia change in the area, not only affects the coherency within the group but also of the adjoining coherent groups.

Case. 2: Effect of Source Intermittency Renewable energy sources like photovoltaics and wind are inherently intermittent and are non-dispatchable generations. Therefore, intermittencies associated with renewables make the effective inertia of a power system time-varying. Due to the time variation of inertia, the coherent grouping of generators becomes dynamic (the effect will be more prominent for high renewable penetration levels), which makes coherency detection a frame-to-frame operation rather than static segregation. In the work, the intermittency scenario is simulated by inducing a sudden fast ramp reduction of 20% in the detached power from DFIG at bus-19 at 7 s.

Under this scenario, the speed signals for different generators are shown in Fig. 9 (a), where due to the sudden reduction in DFIG output at bus-19, the existing generators G-04 and 05 start swinging distinctly from the generator G-06 and 07. This is confirmed from the mode participation trends, where generators G-04, 05 participate as a distinct group with respect to generators G-06 and 07 in a new inter-area mode -0.458±5.975j (damped frequency 0.975) as shown in Fig. 9 (b). This implies that fast ramp intermittency in DFIG at bus-19 caused segregation of area-02 into two coherent groups: one group with G-04 & G-05 and other groups with G-06 & G-07 generators.

The coherency results with the unsupervised clustering method for wind intermittency shown in Fig. 10, also show that the generator G-04, 05, 06, and 07 which were oscillating as a single coherent group pre-intermittency, started oscillating as two coherent groups of (G-04 & 05) and (G-06 & 07) post-intermittency.

The above analysis clearly indicates that the fast intermittencies in solar and wind power sources cause dynamic variations in system inertial patterns causing dynamic variation in the system’s oscillatory patterns and thus time-variation in coherency trends.

Conclusion
This work analyzes the impact of renewable variabilities on power system oscillation patterns and coherency trends. The work provides the following observations regarding the influence of power system coherency with renewable variabilities:
1) Renewable distribution changes at high penetration levels cause non-uniform variations in system inertia distribution resulting in the segregation of large coherent areas into small coherent groups.
2) The spatial location of renewable variability and magnitude of change in renewable power dispatched influences the mode participation trends in a power system uniquely.
3) The dynamic changes in system coherency with high renewable penetration levels make islanding, wide-area damping control, and dynamic system grouping also dynamic.
4) Distribution changes at different locations activate new and distinct inter-area modes in the system complicating the area control and islanding.
5) Fast ramp intermittencies in renewables cause dynamic variation in system coherency status for pre- and post-intermittency time periods for the same set of disturbances.

References:-

1.	R. Yadav, A. K. Pradhan and I. Kamwa, "A Spectrum Similarity Approach for Identifying Coherency Change Patterns in Power System Due to Variability in Renewable Generation," in IEEE Transactions on Power Systems, vol. 34, no. 5, pp. 3769-3779, Sept. 2019.
2.	H. You, V. Vittal, and X. Wang, “Slow coherency-based islanding,” IEEE Transactions on Power Systems, vol. 19, no. 1, pp. 483–491, Feb 2004.
3.	I. Kamwa, A. K. Pradhan, G. Joos, and S. R. Samantaray, “Fuzzy partitioning of a real power system for dynamic vulnerability assessment,” IEEE Transactions on Power Systems, vol. 24, no. 3, pp. 1356–1365, Aug 2009.
4.	M. A. M. Ariff and B. C. Pal, “Coherency identification in interconnected power system - an independent component analysis approach,” in 2013 IEEE Power Energy Society General Meeting, July 2013, pp. 1–1.
5.	R. Christie, Power systems test case archives, 1993. [Online]. Available: https://www.ee.washington.edu/research/pstca.

Analysis and design of perforated cold-formed steel tubular members

Tekcham Gishan Singh

Research Snippets

---

Cold-formed steel (CFS) tubular sections are increasingly used in construction industries, owing to their inherent high structural capacities (i.e., high tension, compression, bending and torsional resistances) as well as aesthetically appealing nature, as compared to opened cold-formed steel counterparts [1]. Unlike hot-rolled steel sections, the thickness of CFS was usually limited to 3 mm in the early 1980s so that the steel sections could be fed into cold-rolling mills. However, due to the advancement of cold-forming technology, CFS of thickness up to 25 mm can be made. In addition, due to the strength enhancement from the cold-forming process, CFS tubular sections possess higher strength and stiffness-to-weight ratios than conventional hot-rolled steel sections. Hence, because of the various advantages and other requirements, newer cold-formed steel tubular sections, such as elliptical, oval, flat-oval, semi-elliptical etc., are introduced in the market [2,3]. Despite the various research achievements detailed above, the presently available design standards do not include the strain-hardening behavior, and also, design guidelines are not included for newer steel cross-sections [4].

In steel construction, perforations (Punch holes/openings/cut-outs) of various sizes and shapes are made on the structural member for multiple needs. For example, openings are provided for air circulation, electrical wirings, material optimization (to reduce the weight of members), strength enhancement (to provide stiffness), inspection and maintenance work (in bridges, towers, ships), easy connections with other structural members, esthetics etc. However, due to the modifications made (perforations) on structural members, complex stress distributions are further introduced, thus altering the structural member's elastic stiffness and capacity. Hence it is imperative to study the structural performance of perforated structural members and further develop suitable design standards. Presently, research is being carried out to investigate the effect of perforations for various structural members subjected to different loading conditions at the Department of Civil and Infrastructure Engineering, Indian Institute of Technology Jodhpur, Rajasthan. Some key contributions in the area of perforated cold-formed steel tubular members by Dr T. G. Singh are as follows:

References:-

1.	L. Gardner, N. Saari, and F. Wang, “Comparative experimental study of hot-rolled and cold-formed rectangular hollow sections,” Thin-Walled Struct., vol. 48, no. 7, pp. 495–507, 2010.
2.	S. V. Devi and K. D. Singh, “Finite element study of lean duplex stainless steel semi-elliptical hollow section members with circular perforation subjected to torsion,” Thin-Walled Struct., vol. 146, p. 106464, 2020.
3.	J.-H. Zhu and B. Young, “Cold-formed-steel oval hollow sections under axial compression,” J. Struct. Eng., vol. 137, no. 7, pp. 719–727, 2011.
4.	T. G. Singh and K. D. Singh, “Structural performance of YSt–310 cold–formed tubular steel stub columns,” Thin-Walled Struct., vol. 121, pp. 25–40, 2017.
5.	T. G. Singh and K. D. Singh, “Experimental investigation on performance of perforated cold-formed steel tubular stub columns,” Thin-Walled Struct., vol. 131, pp. 107–121, 2018.
6.	T. G. Singh and T. M. Chan, “Effect of access openings on the buckling performance of square hollow section module stub columns,” J. Constr. Steel Res., vol. 177, p. 106438, 2021.
7.	T. G. Singh and K. D. Singh, “Design of perforated cold-formed steel hollow stub columns using direct strength method,” Thin-Walled Struct., vol. 168, p. 108265, 2021.

The smart and intelligent sensor system – Electronic Nose

Saakshi Dhanekar and Kamaljit Rangra

Research Snippets

---

Human thinking about electronics was made possible with the help of artificial systems. These systems have the capability of making decisions like humans based on their learning with the previous data. An electronic nose (e-nose) can mimic the human brain and sense different analytes/gasses/vapors. The need to detect the vapors and gasses is very well known. There are various types of sensors available, however there is a tradeoff when it comes to price and quality. Sensing materials play a major role in deciding the key parameters of sensor characterization. Many of the transition metal oxides such as ZnO, SnO2, MoS2, WO3, MoO3 and TiO2 etc. are used as potential materials as these can provide high sensitivity, durability and reusability. Unfortunately, these materials also face major challenges like specificity and functioning at high operating temperatures and so become incompatible for CMOS integration [1]. Some of the reports highlight how these can be made to function at room temperature. This saves power and adds durability to the sensor. For achieving a significant specificity, the surface of the sensor needs to be tuned; however in spite of this achieving a cent percent selectivity is not easy. Another option is to make an array of such sensors and put them together on a platform. These sensors are coached through known data sets and algorithms to develop and establish a basic capability to analyze the presence of analytes in a given environment. The system popularly known as E-nose, is an intelligent sensor based system which detects the presence of gas/vapors around it [2]–[4]. Such a system comprises an array of sensors, analog interface and data processing (neural networks). The resemblance between a human and artificial olfactory system is depicted in Fig. 1. It depicts the different stages of aroma detection by the human brain and E-nose system.

Fig. 1. Human vs Artificial Olfactory system. Adapted from [5]

There are several applications of E-nose including Food quality assessment [6], medical diagnostics [7], chemical sensors [8], cosmetics [9], environment [10], alcohol breath analyzer [11] etc. Some of the work done by the team includes fabrication of sensor arrays with different metal oxide layers [5]. This required use of electrochemical etching and deposition processes. The resistance of the sensors changed upon exposure to gas/vapors in the concentration range of 5–500 ppm and in simulated real breath conditions. This was read through the interdigitated electrodes on the deposited metal oxide films. The sensing equation used is:
S(%) = (R_a − R₀)/R₀ x 100% (1)
where R_a and R₀ are the resistance changes in presence and absence of analyte, respectively.

Fig. 2 (a) Stability and repeatability study of TiO2/PS. (b) Process scalability test. (c) Estimated and actual ppm for ethanol and acetone. (d) 2-D PCA map showing ethanol vapors discrimination by the sensor, inset shows packaged sensor. Adapted from [5].

Fig. 2a shows the repetitive and stable response received from the sensor for the sensing tests done for 6 months. Many sensors were chosen from the same wafer confirming the uniformity of the fabrication process and some were also picked up from different wafers (Fig. 2(b)). The consistency in the sensor response confirmed the good uniformity and reproducibility of the process.

To determine the concentration of the vapors, the obtained sensing data from the samples were combined using polynomial regression model given as:
ppm_gas = a1x + a₂x² +..+a_nxⁿ (2)

Here, a_i - a_n are the coefficients and x is the sensor output. These coefficients are obtained by using least-squares approximation [12]. In our case, the fourth- and third-order polynomial regression models fitted best to determine the concentration of ethanol and acetone vapors, respectively (Fig, 2(c)). Principal component analysis (PCA) was done to reduce the dimensions in the form of clusters. It clearly discriminated ethanol vapors from a group of vapors as shown in Fig. 2(d). Also other vapors like IPA, xylene, and benzene were separated with clear demarcated boundaries.

The authors would like to acknowledge Prof. Monika Agarwal, Center for Applied Research in Electronics (CARE), IIT Delhi for her contribution in data analysis and PCA.

References:-

1.	P. Dwivedi, S. Dhanekar, S. Das, and S. Chandra, “Effect of TiO2 Functionalization on Nano-Porous Silicon for Selective Alcohol Sensing at Room Temperature,” J. Mater. Sci. Technol., 2017, doi: 10.1016/j.jmst.2016.10.010.
2.	Electronic nose recognizes a variety of scents (2018, May 24) retrieved 8 December 2021 from https://phys.org/news/2018-05-electronic-nose-variety-scents.html.
3.	“Meet the E-Nose That Actually Sniffs - IEEE Spectrum.”, from https://spectrum.ieee.org/meet-the-enose-that-actually-sniffs.
4.	J. W. Gardner and P. N. Bartlett, “A brief history of electronic noses,” Sensors Actuators B. Chem., vol. 18, no. 1–3, pp. 210–211, 1994, doi: 10.1016/0925-4005(94)87085-3.
5.	S. Dhanekar, “Smart and Intelligent E‐nose for Sensitive and Selective Chemical Sensing Applications,” Smart Sensors Environ. Med. Appl., pp. 149–171, 2020, doi: 10.1002/9781119587422.ch8.
6.	W. Wojnowski, T. Majchrzak, T. Dymerski, J. Gębicki, and J. Namieśnik, “Portable Electronic Nose Based on Electrochemical Sensors for Food Quality Assessment,” Sensors (Basel)., vol. 17, no. 12, Dec. 2017, doi: 10.3390/S17122715.
7.	A. K. Pavlou and A. P. F. Turner, “Sniffing out the truth: Clinical diagnosis using the electronic nose,” in Clinical Chemistry and Laboratory Medicine, 2000, vol. 38, no. 2, pp. 99–112, doi: 10.1515/CCLM.2000.016.
8.	P. C. Chen, F. N. Ishikawa, H. K. Chang, K. Ryu, and C. Zhou, “A nanoelectronic nose: a hybrid nanowire/carbon nanotube sensor array with integrated micromachined hotplates for sensitive gas discrimination,” Nanotechnology, vol. 20, no. 12, 2009, doi: 10.1088/0957-4484/20/12/125503.
9.	A. Branca AAQC, A. Branca, P. Simonian, M. Ferrante, E. Novas, and R. Martín Negri, “Electronic Nose Based Discrimination of a Perfumery Compound in a Fragrance,” Artic. Sensors Actuators B Chem., 2003, doi: 10.1016/S0925-4005(03)00270-3.
10.	A. D. Wilson, “Review of Electronic-nose Technologies and Algorithms to Detect Hazardous Chemicals in the Environment,” Procedia Technol., vol. 1, pp. 453–463, Jan. 2012, doi: 10.1016/J.PROTCY.2012.02.101.
11.	P. Dwivedi, S. Dhanekar, M. Agrawal, and S. Das, “Interfacial Engineering in TiO2/Nano-Si Heterostructure-Based Device Prototype for E-Nose Application,” IEEE Trans. Electron Devices, vol. 65, no. 3, pp. 1127–1131, Mar. 2018, doi: 10.1109/TED.2018.2797364.
12.	D. Manolakis, V. Ingle, and S. Kogon, Statistical and adaptive signal processing: spectral estimation, signal modeling, adaptive filtering, and array processing. Artech House, 2005.

Participatory Budgeting

Pallavi Jain

Research Snippets

---

Participatory budgeting [1] is a direct democracy approach for budgeting, most often used to decide a fraction of municipal budgets. Rooted in Brazil [2], it keeps on gaining popularity as more and more cities are using it to decide on the distribution of increasing fractions of their mutual funds; in particular, it is used quite extensively in the United States [3], in Europe [4], and across the globe [5].

The most popular ballot type of Participatory Budgeting is approval voting, in which citizens are asked to approve a subset of given set of projects that they would like to be funded. More formally, in Participatory Budgeting with approval ballot, we have a set of projects, each with its cost, a collection of citizens, each approving a subset of projects, and a budget limit. We are interested in designing a mechanism to choose a subset of projects to be funded within the budget that “satisfies” the citizens. There are quite a number of aggregation methods for approval-based participatory budgeting [6, 7, 8]. One approach that is used in Paris and Warsaw is the Greedy Approval method, in which projects are ordered in decreasing order of their approval scores (i.e. the number of citizens approving each of them); then, the process is to go over the list and fund items as long as the remaining budget limit suffices.

An important aspect of Participatory budgeting which is often ignored is the interactions between projects. It is quite possible that some projects are identical to each other, and in substitution maybe because these are geographically close to each other. Therefore, funding both of these projects, is not really a good use of public finds. Similarly, it may happen that some projects are in complementarity to each other; for example, building a school, having a bust stop nearby, good roads connecting school from major part of the city, etc. Clearly, all these projects need to be funded together, especially when the school is in a remote location. We (I, along with my collaborators Krzysztof Sornat and Nimrod Talmon from Ben-Gurion University, Israel) modelled such project interactions within groups of projects by augmenting the standard model of participatory budgeting. This augmentation was done by introducing a partition over the projects and modelling the type and extent of project interactions within each part using certain functions. We study the computational complexity of finding bundles that maximize voter utility, as defined with respect to such functions. Motivated by the desire to incorporate project interactions in real-world participatory budgeting systems, we identify certain cases that admit efficient aggregation in the presence of such project interactions. Here, we assume that the partition on the projects is given by organiser, say the City Mayor. This work appeared in IJCAI 2020 [9].

Next, we (I, along with my collaborators Laurent Bulteau (LIGM, CNRS, Univ Gustave Eiffel, Marne-la-Vallée, France) and Nimrod Talmon (Ben-Gurion University, Israel)) considered that even partition on projects is given by the citizens. Here, the challenge is to find an aggregated partition that satisfies the citizens. We designed several aggregation methods and evaluated them by analyzing their computational complexity and their behavior with respect to certain relevant axiomatic properties. This work appeared in AAMAS 2021 [10].

Recently, we (I, along with my collaborators Krzysztof Sornat (MIT CSAIL, USA), Nimrod Talmon and Meirav Zehavi (Ben-Gurion University, Israel)) also considered that in addition to a global budget limit---there are several groupings of the projects (possibly intersecting groups), each group with its own budget limit. This work is motivated by Geometric Budgeting, Thematic Budgeting, and also non-budgeting user-cases. Considering the funding projects for a city, we would not like to spend the entire money in, say, one district. Therefore, the grouping of projects is done and every group (district, in our example) has a budget limit. Another scenario is Thematic Budgeting: Projects can usually be naturally grouped into types, e.g., educational projects, recreational projects, and so on. In such cases, it might be that groups do intersect: e.g., a recreational park might be of recreational purposes as well as for environmental purposes, thus contained in two sets of projects. Grouping of the projects is useful here: Group projects accordingly making sure that not all the budget is being spent on projects of only one type. We can also find the application in non-budgeting user-cases. E.g., to decide which processes to run on a time-limited computing server, where available processes can be naturally grouped into types and it is not desired to use all the computing power for, say, processes of only one type. We studied the computational complexity of identifying project bundles that maximize voter satisfaction while respecting all budget limits. This work has been accepted in IJCAI 2021 [11].

References:-

1.	Y. Cabannes, “Participatory budgeting: A significant contribution to participatory democracy,” Environment and Urbanization, vol. 16, no. 1, pp. 27–46, 2004.
2.	B. Wampler, Participatory Budgeting in Brazil: Contestation, Cooperation, and Accountability, Penn State Press, 2010.
3.	H. R. Gilman, “Transformative deliberations: Participatory budgeting in the United States,” Journal of Public Deliberation, vol. 8, no. 2, pp. 11:1–11:20, 2012.
4.	Y. Sintomer, C. Herzberg, and A Rocke, “Participatory budgeting in Europe: Potentials and challenges,” International Journal of Urban and Regional Research, vol. 32, no. 1, pp. 164–178, 2008.
5.	E. Ganuza and G. Baiocchi, “The power of ambiguity: How participatory budgeting travels the globe,” Journal of Public Deliberation, vol. 8, no. 2, pp. 8:1–8:12, 2012.
6.	A. Goel, A. K. Krishnaswamy, S. Sakshuwong, and T. Aitamurto. “Knapsack voting for participatory budgeting,” ACM Transactions on Economics and Computation, vol. 7, no. 2, pp. 8:1–8:27, 2019.
7.	H. Aziz, B. E. Lee, and N. Talmon, “Proportionally representative participatory budgeting: Axioms and algorithms,” in Proc. 17th International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2018), July 2018, pp. 23–31.
8.	N. Talmon and P. Faliszewski, “A framework for approval-based budgeting methods,” in Proc. Thirty-Third AAAI Conference on Artificial Intelligence (AAAI-19), 2019, pp. 2181–2188.
9.	P. Jain, K. Sornat, and N. Talmon, “Participatory Budgeting with Project Interactions,” in Proc. Twenty-Ninth International Joint Conference on Artificial Intelligence (IJCAI 2020), January 2021, pp. 386-392.
10.	P. Jain, N. Talmon, L. Bulteau, “Partition Aggregation for Participatory Budgeting,” in Proc. 20th International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2021), May 2021, pp. 665-673.
11.	P. Jain, K. Sornat, N. Talmon, and M. Zehavi, “Participatory Budgeting with Project Groups,” in 30th International Joint Conference on Artificial Intelligence (IJCAI-21), accepted.

Development of Double Diels-Alder Reaction: An Efficient Approach to Various Natural Products Synthesis

Amar Nath Singh Chauhan, Ghanshyam Mali, and Rohan D. Erande

Research Snippets

---

Environment has established a plethora of bioactive chemical compounds as natural products isolated from various natural sources such as plants, animals, microbiological and marine organisms. The preponderance of pharmaceuticals has been widely known for natural products extracted by humans since ancient times. Most of which have enormous structural complexity and intriguing chemical characteristics that play an important role in human health and prompting chemists to devise new ways to access these biologically active substances. In fact, it continues to be the leading source of new drug discovery and development, given the considerable use of molecular techniques in drug development. As a result, developing and synthesising natural products is considered to be a fantastic source of inspiration for new therapies and organic chemistry.[1,2]

Synthetic approaches for accessing biologically active molecules is a challenging endeavour that involves a thorough understanding of many facets of organic chemistry. However, several synthetic designs and modifications have already been established to access structurally sophisticated natural products.[3] Considering the high necessity of drug synthesis, number of new interventions are brought to the global market to reduce expenses of drug discovery and development.[4,5] To obtain biologically active natural compounds in a streamlined way, a variety of synthetic approaches have been devised with the cascade pericyclic reaction mainly Diels-Alder reaction being one of the most fundamental and revolutionary technique.[6] Recently, in 2020, Nishad et al. have reported a domino Diels-Alder reaction approach to the synthesized pentacyclic framework from 2-((anthracen-9-ylmethoxy)methyl)furan and DMAD.[7] In the same year, Gadigennavar and Sankararaman have described a more mature double Diels-Alder approach to the construction of V-shaped molecule cyclooctatetraene (COT) fused with aromatic wings.[8] The domino approach of Diels-Alder chemistry (cascade pericyclic approach) the double Diels-Alder strategy to access natural product scaffold remains a fascinating and fast-paced area of chemical research, not only advantageous for accessing biologically active compounds for use in biological research, but also encouraging the discovery of innovative techniques and chemically synthesized methods.[9]

Using the Double Diel-Alder approach of cascade pericyclic reaction, we highlight new synthetic accomplishments in the construction of complex biologically active scaffolds. Cascade will be presented in the context of natural product synthesis, with selected examples that address the future of these fields. The approach entails elegantly engaging out two concurrent Diels-Alder reactions, resulting in a rapid escalation in molecular complexity while potentially reducing step count. The emphasis is on leveraging the selectivity of the Diels-Alder technique to effectively create macrocyclic, bicyclic, heterocyclic, and polycyclic skeletons for structurally scenic natural product scaffolds.[10] These reactions have a variety of applications in the synthesis of complex molecular frameworks, including the synthesis of natural compounds such as: colombiasin A,[11] fluorenone derivative,[12] taxane nucleus,[13] long-chain polypropionate fragments such as Mosher's ester,[14] eleutherobin aglycone,[15] cage compounds including anthracene derivatives,[16] fullerene and benzoquinone fragmented clusters,[17] cage annulated bicyclooctenes and derivatives,[18] kekulene and other highly symmetric cages,[19] polymerized precursurs, functionalization of molecules with high symmetry, etc. The inclusion of the Diels-Alder strategy's comprehensive synthesis via cascade technique will spark new ideas in organic synthesis while also providing a platform for confronting a variety of total synthesis scaffolds for accessing bio-active natural products for drug discovery and healthcare.[20] The twofold Diels-Alder approach to total synthesis will absolutely assist in the invention of novel and efficient ways to access structurally diverse natural compounds. Under this due consideration, a consolidated Diels-Alder reaction has been designed to encapsulate biologically active scaffolds in a standardised and shortest route with total synthetic approach to their simplified-designed analogues using Diels-Alder strategy implementing well-known reactions such as Lewis-acid assistance, acid-base encouraged, and so on. Our research group is constantly motivated to acknowledge the complicated synthesis emergence of natural products, in which we used cascade strategies to access structurally diverse bis-indole alkaloids (yuchchukene natural product)[21] and generic versions, yuremamine core, pyrrolo[1,2-a]indoles, and benzofuro[2,3-b]indulines motif using cycloaddition cascade approach assisted by Lewis-acid. We're expanding our endeavours in organic chemistry to include total synthesis and method development protocols for newly identified natural compounds that have a constructive impact on humanity. Besides that, we are super motivated to observe and report spectacular switches in synthesis protocols such as regioselectivity and chemoselectivity issues in the cascade Diels-Alder reaction, influenced by a rare and limited example identified by Dethe et al, where dimerization of substituted indole-derivatives under varying reaction conditions generates three distinct natural products during the streamlined synthesis of borreverine, caulindoles, and flinderolres.[22]

References:-

1.	D. J. Newman and G. M. Cragg, “Natural products as sources of new drugs over the nearly four decades from 01/1981 to 09/2019,” Journal of Natural Products, vol. 83, no. 3, pp. 770–803, 2020.
2.	G. M. Cragg and D. J. Newman, “Nature: A vital source of leads for anticancer drug development,” Phytochemistry Reviews, vol. 8, no. 2, pp. 313–331, 2009.
3.	E. A. Anderson, “Cascade polycyclisations in natural product synthesis,” Organic & Biomolecular Chemistry, vol. 9, no. 11, p. 3997, 2011.
4.	A. G. Atanasov, S. B. Zotchev, V. M. Dirsch, and C. T. Supuran, “Natural products in drug discovery: Advances and opportunities,” Nature Reviews Drug Discovery, vol. 20, no. 3, pp. 200–216, 2021.
5.	Z. Guo, “The modification of natural products for medical use,” Acta Pharmaceutica Sinica B, vol. 7, no. 2, pp. 119–136, 2017.
6.	C. M. Reisinger, P. Rivera-Fuentes, S. Lampart, W. B. Schweizer, and F. Diederich, “Cascade pericyclic reactions of Alleno-acetylenes: Facile access to highly substituted cyclobutene, dendralene, pentalene, and indene skeletons,” Chemistry - A European Journal, vol. 17, no. 46, pp. 12906–12911, 2011.
7.	K. M. Nishad, C. S. Aswathi, P. A. Unnikrishnan, and T. S. Saumya, “Domino intermolecular and intramolecular Diels-Alder reaction sequence for expedient construction of a pentacyclic framework,” Chemical Data Collections, vol. 28, pp. 100404, 2020.
8.	S. Gadigennavar and S. Sankararaman, “Synthesis and application of 3,4,7,8-tetrakis-exo-methylenecycloocta-1,5-diene as a versatile diels–alder diene: Synthesis of V-shaped cyclooctatetraene fused acenes,” Organic & Biomolecular Chemistry, vol. 18, no. 34, pp. 6738–6744, 2020.
9.	J. D. Winkler, “Tandem Diels-Alder cycloadditions in organic synthesis,” Chemical Reviews, vol. 96, no. 1, pp. 167–176, 1996.
10.	G. Mali, A. N. Chauhan, K. A. Chavan, and R. D. Erande, “Development and applications of double Diels-Alder reaction in organic synthesis,” Asian Journal of Organic Chemistry, vol. 10, pp. 1-22, 2021.
11.	J. H. Chaplin, A. J. Edwards, and B. L. Flynn, “An enantioselective double Diels-Alder approach to the tetracyclic framework of Colombiasin a,” Org. Biomol. Chem., vol. 1, no. 11, pp. 1842–1844, 2003.
12.	G. A. Kraus and M. J. Taschner, “Timed Diels-Alder reactions,” Journal of the American Chemical Society, vol. 102, no. 6, pp. 1974–1977, 1980.
13.	J. D. Winkler, H. S. Kim, and S. Kim, “A highly efficient synthesis of taxanes via the tandem diels-alder reaction,” Tetrahedron Letters, vol. 36, no. 5, pp. 687–690, 1995.
14.	C. Marchionni, P. Vogel, and P. Roversi, “The simultaneous double Diels-Alder addition of 1,1-bis(3,5-dimethylfur-2-yl)ethane; toward a new, asymmetric synthesis of long-chain polypropionate fragments and analogues,” Tetrahedron Letters, vol. 37, no. 24, pp. 4149–4152, 1996.
15.	J. D. Winkler, K. J. Quinn, C. H. MacKinnon, S. D. Hiscock, and E. C. McLaughlin, “Tandem Diels-Alder/fragmentation approach to the synthesis of Eleutherobin,” Organic Letters, vol. 5, no. 10, pp. 1805–1808, 2003.
16.	W. R. Dolbier, Y.-A. Zhai, M. A. Battiste, K. A. Abboud, and I. Ghiviriga, “A highly pyramidalized cage alkene formed via the double diels−alder cycloaddition of syn-4,5,13,14-bis(dehydro)octafluoroparacyclophane to anthracene,” The Journal of Organic Chemistry, vol. 70, no. 25, pp. 10336–10341, 2005.
17.	J. A. Watson, R. A. Pascal, D. M. Ho, and K. V. Kilway, “Synthesis and structure of a twisted, colossal quinone,” Tetrahedron Letters, vol. 41, no. 26, pp. 5005–5008, 2000.
18.	T. C. Chou and N.-Y. Liu, “Synthesis of singly and doubly cage-annulated bicyclo[2.2.2]octenes derived from Triptycene Skeleton,” Journal of the Chinese Chemical Society, vol. 53, no. 6, pp. 1477–1490, 2006.
19.	I. Pozo, Z. Majzik, N. Pavliček, M. Melle-Franco, E. Guitián, D. Peña, L. Gross, and D. Pérez, “Revisiting kekulene: Synthesis and single-molecule imaging,” Journal of the American Chemical Society, vol. 141, no. 39, pp. 15488–15493, 2019.
20.	K. C. Nicolaou and J. S. Chen, “The art of total synthesis through Cascade reactions,” Chemical Society Reviews, vol. 38, no. 11, p. 2993, 2009.
21.	Y.-C. Kong, K.-F. Cheng, R. C. Cambie, and P. G. Waterman, “Yuehchukene: A novel indole alkaloid with anti-implantation activity,” Journal of the Chemical Society, Chemical Communications, no. 2, p. 47, 1985.
22.	D. H. Dethe, R. D. Erande, and B. D. Dherange, “Remarkable switch of regioselectivity in diels–alder reaction: Divergent total synthesis of borreverine, caulindoles, and Flinderoles,” Organic Letters, vol. 16, no. 10, pp. 2764–2767, 2014.

Development of kidney tissue in a laboratory-scale bioreactor

Prasenjit Sarkar

Research Snippets

---

While the making of kidneys in a laboratory may be termed science fiction, with the advent of embryonic stem cell research and bioreactor technology, it is poised to become a reality. The need for making kidney tissue in a bioreactor is evidenced by the increasing incidence of end-stage kidney disease worldwide as well as in India. While end-stage kidney disease can be treated with dialysis, the average lifespan of patients on dialysis is significantly lower than those with kidney transplantations. However, the number of kidneys available for transplantation is much lower than the demand for kidney transplantations. Due to the shortage of kidneys available for transplantation, recent research has focused on making kidneys in the laboratory from pluripotent stem cells with the hope that these kidneys may be transplanted into patients with end-stage kidney disease. Also, kidney tissue produced in this manner may be engrafted into patients with kidney injury to improve kidney function. Since this endeavor lies in the interface of biology and engineering, a brief description of both aspects will be provided here.

Cells are the building blocks of an organism’s body. Various types of cells are required for various types of functions in the body of an organism. For example, podocytes cells participate in forming the filtration barrier in the kidney. Some cells of the body known as stem cells possess certain unique abilities. Firstly, they can be grown indefinitely in laboratory conditions. Secondly, they can give rise to other types of cells through a process known as differentiation, when given specific signals from the environment. For example, embryonic stem cells are cells that are isolated from the ‘inner cell mass’ tissue of the embryo and can be grown indefinitely in laboratory conditions. Additionally, they can differentiate into any type of cell of the adult body, such as cells of the kidney, brain, stomach, intestines, liver, pancreas, etc. The ability of embryonic stem cells to form any tissue of the adult body can be utilized for engineering purposes to make organs in the laboratory. Current efforts to produce the kidney from embryonic stem cells will be discussed herein.

The kidney is a complex organ that filters the blood and removes toxins. The kidney comprises filtering units known as nephrons. On average, there are about a million nephrons in the adult human kidney. Nephrons themselves are made of various tissues including podocytes, proximal tubules, loops of Henle, and distal tubules. Nephrons connect to the collecting ducts, which collect urine from all the nephrons. Additionally, nephrons are interspaced by the stromal tissue. To engineer a kidney in the laboratory, all of these tissues need to be present together. Recent efforts in the direction of making kidney tissue from embryonic stem cells have achieved success in making podocytes, proximal tubules, loops of Henle, distal tubules, and stromal cells inside a kidney “organoid”. Other studies have shown the formation of collecting ducts from embryonic stem cells. Further studies have sought to combine these tissues together to engineer a kidney organoid that resembles the in vivo kidney. However, major challenges remain in making a kidney organoid that faithfully reproduces the functions of the kidney. Currently, a big challenge is that the kidney organoids produced in laboratory conditions are not suitable for engraftment into the body, as shown by engraftment experiments inside mice. When engrafted into mice, these kidney organoids undergo aberrant expansion, with the formation of unintended tissues such as cartilage. Due to such aberrant expansion of the stromal tissue in the engrafted kidney organoid, long-term engraftment of kidney organoids (>4 weeks) has not been demonstrated so far. Yet another challenge is that the engrafted kidney organoid requires requisite blood flow for the survival of the constituent tissues. While current research has demonstrated the formation of blood vessels inside the in vivo engrafted kidney organoid, the quantity of these blood vessels is inadequate. Further research needs to be conducted to increase the formation of blood vessels into the engrafted kidney organoid.

An engineering challenge in the use of kidney organoids derived from currently published methods is that the kidney organoid formed in the laboratory is 5 orders of magnitude smaller in volume than the actual human kidney. Therefore, the process of forming kidney organoids needs to be scaled up in a bioreactor. While the production of kidney organoids has been attempted in a bioreactor, these organoids were shown to be unsuitable for engraftment due to aberrant expansion of the stromal cells. Therefore, further research is required in terms of process development to make kidney organoids that are stable and do not display aberrant expansion of the stromal tissue. Additionally, further research is also required for the scale-up of kidney organoids in a bioreactor such that they may be used for the purpose of transplantation into patients. To address these engineering challenges, a molecular-level understanding of the kidney formation process is required.

At the molecular level, the process of conversion of embryonic stem cells to any other tissue is governed by environmental signals, which in most cases take the form of specific proteins present in the environment of the stem cell. Different protein signals from the environment may guide the stem cell to become different tissues. Therefore, differentiation of embryonic stem cells involves the engineering of specific protein signals that can allow the formation of the product tissue of interest. To design the differentiation process, some guidance can often be taken from the literature on the developmental biology of the tissue of interest. The differentiation process for forming kidney tissue from embryonic stem cells has been identified recently, with many research labs proposing their protocols. Common to all these protocols is the activation of the Wnt signaling pathway followed by the FGF9 signaling pathway. The Wnt signaling pathway is a set of biochemical reactions that occur when a cell is exposed to the Wnt protein. The information that the Wnt protein is present in the environment of the cell, is conveyed through this set of biochemical reactions into the cell. This process causes the cell to respond in various ways, depending on the cell type. For example, embryonic stem cells respond to the Wnt signal in the environment by differentiating, i.e. the identity of the cell changes. Embryonic stem cells can be guided through the Wnt signaling pathway and the FGF9 signaling pathway towards differentiation to the precursor of nephrons, known as nephron progenitor cells. Thereafter, activation of the Wnt signaling pathway and Notch signaling pathway is needed for induction and proper patterning of nephrons, respectively. Molecular-level studies on the Wnt and Notch signaling pathways are required to better understand the process of formation of nephrons, and to engineer stable kidney organoids in the laboratory.

The biomolecular engineering research group at IIT Jodhpur aims to conduct molecular-level studies on the Wnt and Notch signaling pathways with the goal of forming stable kidney organoids which may be used for long-term engraftment. To address the problem of long-term engraftment, a bottom-up approach will be adopted instead of the top-down approach reported in the literature. Kidney organoids will be formed that comprise of nephrons sans the stromal cells, aided by molecular-level studies on the Wnt and Notch signaling pathways. New hypotheses will be formulated and tested in order to obtain nephrons that are induced and patterned through the Wnt and Notch signaling pathways, respectively. These organoids will be engrafted into mice to study their long-term stability. Thereafter, more complexity will be added to the organoids by adding the stromal tissue and the collecting ducts. Apart from kidney organoid engineering, research will also focus on process engineering for the production of kidney tissue in a larger scale in bioreactors. Current methods for making kidney organoids are carried out in cell culture dishes which is not a scalable process. Therefore, process development will be carried out to adapt these methods to a bioreactor setting. Process parameters such as the Reynolds number and the Power number will be optimized to ensure that mass transfer limitations are minimized, localized protein concentration gradients are minimized, but cells do not die due to excessively high shear force. Kidney organoids produced in the bioreactor will be tested for long-term stability by engraftment experiments in mice.

To complete the discussion about embryonic stem cell research, ethical aspects of such research need to be addressed. Since embryonic stem cells are derived from the embryo and harvesting the inner cell mass tissue invariably leads to the destruction of the embryo, embryonic stem cell research raises ethical concerns. Moreover, kidney organoids made from embryonic stem cells cannot be engrafted into patients since they will be rejected by the immune system of the body as foreign tissue. The solution to these problems came with the discovery of induced pluripotent stem cells (iPSCs). This technology allows scientists to derive iPSCs, which are identical to embryonic stem cells in terms of their ability to be maintained indefinitely in cell culture, and their ability to form any tissue of the body. Moreover, iPSCs can be derived from other sources, such as skin cells, and therefore do not raise ethical concerns. Thus, patient-specific iPSCs can be derived, which can then be turned into kidney tissue. Such tissue will not evoke an immune response since the cells are derived from the patient’s own body. Together with this technology, it is envisioned that personalized medicine will soon become a reality.

References:-

1.	A. Kumar Gupta, P. Sarkar, J. A. Wertheim, X. Pan, T. J. Carroll, and L. Oxburgh, “Asynchronous mixing of kidney progenitor cells potentiates nephrogenesis in organoids,” Commun. Biol., vol. 3, no. 1, p. 231, May 2020, DOI: 10.1038/s42003-020-0948-7

Electrochemical Energy Storage Devices: State of the Art and Future Directions

Prashant Kumar Gupta, Praveen Kumar Sappidi

Research Snippets

---

To address the future energy demands, it is essential to develop scalable energy storage systems from abundant materials that can be integrated with renewable energy. For centuries, batteries have been known for their excellent chemical energy conversion and storage. Most portable energy storage technology is currently dominated by lithium-ion while stationary energy storage with lead acid-based technology. The intercalation-based lithium-ion technology has high energy density but is still expensive to scale up. Less abundance of lithium and the safety due to the use of liquid organic electrolytes are primary concerns. While on the other hand, conversion reaction-based lead acid batteries cause significant environmental problems with low energy density and limited cycle life require exploring an alternate energy storage technology.

The current state of the art for lithium-based technology has a positive electrode of LiCoO2 or its derivatives or spinel compound like LiMn2O4 or polyanionic compound like LiFePO4. The present research can be divided into two categories: the first one focuses on the cost and safety with the expense of energy density, while the other is to improve the energy density, whereas the demand for optimum performance lies in both. Recently, partial replacement of transition metal sites with the lithium known as lithium-rich compound showed very high capacity ~300 mAh/g but suffered from a poor cycle life [1]. Apart from lithium, other cations like K+, Na+, Zn+2, Mg+2, Al+3, etc. have been explored for energy storage. However, none were found suitable. Similar mono-valent Na and K-based ions show poor cycle life due to the bigger size of the intercalating ions. The multivalent ions, though they have an ion size close to the Li+ but high electric density due to greater charge, will result in strong electrostatic interaction with the host material, resulting in a polarization effect that sluggish the diffusion process.

The search for better technology for the future based on earth-abundant materials like Na+ and Zn+2 requires much scientific exploration to make these technologies feasible on the device level. As seawater is an infinite source of sodium elements and is an abundant material. The concentration of Na+ ions in seawater is approximately 0.47 M. It can possibly act as a Na+ ion source during the direct use of sea water in batteries. But the suitable electrode material requires more scientific examination for the commercialization of these technologies. Similarly, India lies in 7th place in terms of zinc reservoirs and 3rd place in the production of the world’s 5.3% zinc, which attracts researchers for zinc-based technology. Zinc metal has a theoretical specific capacity of 820 mAh/g. A capacity density of more than two times that of lithium, equal to 5855 mAh/cm3 makes it a potential material for energy storage application and needs to be explored [2].

With the advancement of computer’s power will help design and analyze experiments via computations to better understand the underlying physicochemical factors, which will result in the development of next-generation energy storage devices, electrode materials and solid and liquid electrolytes. The rate of charging and discharging, stability, and overall efficiency of any battery is highly dependent on the structural and transport properties of the electrolytes. The atomistic and molecular level simulations would help understand the Ion hopping (Li+, Na+, Mg2+, Zn2+, and Al3+, etc.), ion dynamics, ionic conductivity, transference number, and solvation thermodynamic properties in different electrolytes and electrode materials. On the other hand, it is known that solvated ions in the liquid electrolytes influence the overall reaction rate and selectivity. Thus, fundamental gaps such as accurate understanding of the reaction kinetics in different electrolyte materials and their effects due to different perturbations are challenging, which need to be understood in more detail. A combination of atomic-level simulations such as Density Functional Theory (DFT), Molecular dynamics (MD) simulations, and Coarse-grained (CG) simulations along with the experimental benchmarks, will help in developing the next-generation batteries. Figure 1 presents research directions towards the combined computational and experimental approach toward this multi-dimensional battery material development problem.

Figure 1. Combined computational and experimental approach towards the development of battery materials.

Further, to enhance the battery performance, different electrolytes are being considered such as water-in-salt electrolytes [3], polymer electrolytes [4], etc. However, there are challenges such as developing enhanced sampling techniques for the electrochemical reactions in the solid-liquid interfaces, implementing Machine Learning (ML) approaches to understand the physicochemical properties of liquid electrolytes [5], and estimating the lifetime of both electrolyte and electrode materials. Considering modern computing resources such as GPUs and web-based cloud technologies, this combination of approaches would enable the researchers to solve this complex problem.

References:-

1.	P. Roziera, and J. M. Tarascon. Li-Rich Layered Oxide Cathodes for Next-Generation Li-Ion Batteries: Chances and Challenges. Journal of The Electrochemical Society, 162 (14) A2490-A2499, 2015
2.	A. Konarov, N. Voronina, J. H. Jo, Z. Bakenov, Y. K. Sun, and S. T. Myung. Present and Future Perspective on Electrode Materials for Rechargeable Zinc-Ion Batteries. ACS Energy Letter, 3, 2620−2640, 2018
3.	T. Liang, R. Hou, Q. Dou, H. Zhang, X. Yan. The Applications of Water‐in‐Salt Electrolytes in Electrochemical Energy Storage Devices. Advanced Functional Materials, 31(3), pp. 2006749, 2021.
4.	K. D. Fong, J. Self, B. D. McCloskey, and K. A. Persson. Ion Correlations and Their Impact on Transport in Polymer-Based Electrolytes. Macromolecules, 54(6), pp. 2575-2591, 2021
5.	Y. Shao, L. Knijff, F. M. Dietrich, K. Hermansson, C. Zhang. Modelling Bulk Electrolytes and Electrolyte Interfaces with Atomistic Machine Learning. Batteries & Supercaps, 4(4), pp. 585-595, 2021.

On Dynamics of Non-Autonomous Dynamical Systems

Puneet Sharma

Research Snippets

---

Non-autonomous Dynamical Systems have been investigated to characterize the qualitative behavior of several natural and physical systems around us. The studies have resulted in better characterization of various systems like population models, weather prediction, investigation of stability of general Hamiltonian systems and motion of electric charges in time varying electromagnetic fields. In this work, we investigate the topological dynamics of a general non-autonomous dynamical system. In particular, we investigate the cases when the system is generated by a uniformly convergent sequence of maps. We relate the dynamics of the system in this case with the rate of convergence of the generating family. We prove that if the sequence of functions in the generating family is commutative and converges “fast enough” (with order >O (1/n)), the dynamics of the non-autonomous system can be characterized in terms of the dynamics of the limiting function. In the process, we investigate dynamical behavior of the system through properties like equicontinuity, minimality, transitivity, stronger forms of mixing, sensitivity, Li-Yorke sensitivity, Li-Yorke chaos, periodicity, existence of proximal pairs and topological entropy. We prove that the dynamics of the non-autonomous system can be characterized in terms of the limiting function if the generating family exhibits “collective convergence”. We prove that if the system is generated by a commutative family of self-maps and converges at a “sufficiently fast rate” then it exhibits collective convergence and hence the condition derived is indeed more general condition establishing the dynamics of non-autonomous system in terms of the limiting system. We further prove that if the limiting function is a isometry, “fast rate of convergence” is sufficient to characterize the dynamics of the non-autonomous system under consideration.

Another important case is when the non-autonomous system is generated by a finite family of continuous self-maps. In such a setting, it is important to investigate the effect of the dynamics of the individual components on the overall dynamics of the system. Addressing the problem, we relate the dynamics of the non-autonomous system under consideration with the dynamics of the individual members of the family of the generating maps. We prove that if the maps are “well behaved”, the dynamics of the non-autonomous system can be characterized using an autonomous system. During the study, we obtain natural extensions of many of the results known for the autonomous case. We proved that for a commutative finite family, some of the stronger notions of mixing for the non-autonomous system can be studied using autonomous systems. We also establish that the characterization of properties like weakly mixing and topological mixing also holds analogously in the non-autonomous case, if the generating family is commutative. Such an implication simplifies the investigation of qualitative behavior of a non-autonomous system. In general it is observed that the dynamics of the non-autonomous system generated by the family F cannot be characterized in terms of the dynamics of the generating functions. While the non-autonomous system can exhibit a certain dynamical behavior without any of the generating functions exhibiting the same, a non-autonomous system may fail to exhibit a dynamical behavior even if all the generating functions exhibit the same.

As a natural question arising from the setting, we also investigated the relation of alterations and rearrangements to the generating family to the dynamics of the non-autonomous system under consideration. We prove that while insertion/deletion of a map in the generating family of maps can disturb the dynamics of a system, the dynamics of the system does not change if the map inserted/deleted is feeble open. In the process, we prove that if the inserted/deleted map is feeble open, the altered system exhibits any form of mixing/sensitivity if and only if the original system exhibits the same. We extend our investigations to obtain conditions under which properties like equicontinuity, minimality, proximality, various notions of mixing and different forms of sensitivities are equivalent for the two systems. We prove that while properties like minimality and equicontinuity are preserved under alterations unconditionally, various forms of mixing and sensitivities are equivalent for the two systems when the generating family is feeble open. We prove that proximal pairs are preserved between a system and its alteration when the non-autonomous system is generated by a commutative injective family. We also give examples to establish the necessity of the conditions imposed. We generalize our investigations to the case when the alteration is a rearrangement of the original system. We prove that the results obtained hold good when the family is a finite rearrangement of the original system. We give an example to prove that the results obtained cannot be extended when the modified system is an infinite rearrangement of the given system. We also give examples to show that the dynamical behavior of a system need be not be preserved under infinite rearrangement.

References:-

1.	Dvorakova J., Chaos in nonautonomous discrete dynamical systems, Communications in Nonlinear Science and Numerical Simulation 17 (2012), 4649-4652.
2.	Manish Raghav, Puneet Sharma, Alterations and Rearrangements of a Non-Autonomous Dynamical System, Bulletin of Iranian Mathematical Society, vol. 45 (2019), 1431-1441
3.	S. Kolyada, L.Snoha, Topological entropy of Nonautonomous Dynamical Systems, Random and Computational Dynamics,4(2\&3) (1996), 205-233
4.	S. Kolyada, L.Snoha, S.Trofimchuk, On minimality of Non-autonomous Dynamical Systems, Nonlinear Oscillations, vol. 7, Issue 1 (2004), 83-89
5.	P.Sharma, M.Raghav, Dynamics Of Non-Autonomous Discrete Dynamical Systems, Topology Proceedings vol. 52 (2018), 45-59
5.	Puneet Sharma, Manish Raghav; On Dynamics Generated by a Uniformly Convergent Sequence of Maps", Topology and its Applications, 247 (2018), 81-90.

Main Group Metal Complexes as Molecular Materials

Abhishek Mishra and Ramesh K. Metre

Research Snippets

---

Nanomaterials have overpowered the electronic and advanced material industry in past few decades because of their uncountable properties originating from the smaller size and low band gap.¹ More recently, coordination complexes of transition and lanthanide metal ions were explored as molecular materials in electronic devices.^2,3 These organometallic molecular complexes are considered as potential candidates for electronic and electrical devices in recent time due to their discrete size, controllable design, and ease of handling. Literature shows numerous example of organometallic complexes successfully used as molecular materials in various devices such as OLEDs (organic light emitting devices)⁴, molecular switches⁵, molecular wires⁶, memristive devices⁷, dye sensitized solar cells⁸, etc.

However, intriguing research is still underway for developing new strategies and molecular architectures for these advanced functional molecular materials. Organometallic complexes of main group metals have, with their recently reported properties, been considered as promising molecular materials. Main group organometallic complexes have proven their suitability for being molecular materials in terms of their solution processable synthesis, versatile design, solubility, flexibility, stability, and ease of processing etc. Recent literature reports on “the rearrangement of NHC to abnormal NHC by an organotin sulphide cation⁹, a photon up-conversion of IR light into a broad white light spectrum using [(R^delocSn)₄S₆] (R^deloc = 4–(CH₂=CH)–C₆H₄)¹⁰, an interesting Zn metal trapping phenomenon by functionalizing the organotin sulfide cage¹¹, and a molecular precursor based on Zn/Sn/S ternary complex for CZTS (Cu₂ZnSnS₄) i.e., a potential material for thin film solar cells¹²”, provides further evidence of their wide range of interesting properties.

Recently, we have reported a tetranuclear monoorganotin sulfide cage [(RSn^IV)₄(μ-S)₆]·2CHCl₃·4H₂O (1) (R = 2-phenylazophenyl) exploiting the intramolecular N→Sn coordination. The complex 1 is further explored as active material for the fabrication of solution-processable resistive memory switching device. The current-voltage (I-V) characteristics of the device showed an excellent memory behaviour with low write voltage i.e., -1.4 V. The device also displayed a good ON/OFF ratio of 10³ with retention time of 10000s. The complex 1 is the first organotin complex to exhibit the memristive behaviour.¹³ On the other hand, we reported another hydroxido-bridged dinuclear monoorganostannoxane [(RSn^IV)₂(μ-OH)(μ-OMe)Cl₄]·CH₃OH (R = 2-phenylazophenyl) (2) which was explored as active material for NDR (negative differential resistance) device. The I−V characteristic studies performed on the device made using 2 found to exhibit excellent NDR behavior in the region of 1.5−2.5 V.¹⁴

References:-

1.	Wu, W. Nanoscale, 2017,9, 7342-7372
2.	Derrat, H. S.; Robertson, C. C.; Meijer, A. J. H. M.; Thomas, J. A. Dalt. Trans. 2018, 47 (35), 12300-12307
3.	Dickie, C. M.; Laughlin, A. L.; Wofford, J. D.; Bhuvanesh, N. S.; Nippe, M. Chem. Sci. 2017, 8 (12), 8039-8049
4.	Zhao, Y. W.; Zhang, F. Q.; Zhang, X. M. ACS Appl. Mater. Interfaces 2016, 8 (36), 24123-24130
5.	Cheng, H. B.; Zhang, H. Y.; Liu, Y. J. Am. Chem. Soc. 2013, 135, 28, 10190�10193.
6.	Liu, X.; Tan, Y.; Ma, Z.; Pei, Y. J. Phys. Chem. C 2016, 120 (49), 27980-27988
7.	Hong, E. Y. H.; Poon, C. T.; Yam, V. W. W. J. Am. Chem. Soc. 2016, 138 (20), 6368-6371
8.	Green, M. A. Prog. Photovoltaics 2009, 17, 183-189.
9.	Wagner, M.; Z�ller, T.; Hiller, W.; Prosenc, M. H.; Jurkschat, K. Chem. Commun. 2013, 49, 8925�8927
10.	Rosemann, N. W.; Eu�ner, J. P.; Beyer, A.; Koch, S. W.; Volz, K.; Dehnen, S.; Chatterjee, S. Science 2016, 352, 1301�1304
11.	Geringer, E.; Leusmann, E.; Tambornino, F.; Gerhard, M.; Koch, M.; Dehnen, S. Chem. Commun. 2020, 56, 4769-4772.
12.	Fuhrmann, D.; Dietrich, S.; Krautscheid, H. Inorg. Chem. 2017, 56, 13123�13131.
13.	Mishra, A.; Betal, A.; Pal, N.; Kumar, R.; Lama, P.; Sahu, S.; Metre, R. K. ACS Appl. Electron. Mater. 2020, 2, 220-229
14.	Mishra, A.; Betal, A.; Kumar, R.; Lama, P.; Sahu, S.; Metre, R. K. ACS Appl. Electron. Mater. 2021, 3, 203-210

How it all began? : A brief introduction to Asian American literature

Rima Bhattacharya

Research Snippets

---

Short Overview of Asian American Immigration A precise understanding of what constitutes the literature of immigration in America, its modes of representation, and its themes requires a clear knowledge of the history of immigration, the nation’s attitude towards immigrants and its cultural mythology that leads to the formation of the so-called American national character. Immigration to the United States occurred in three great waves. Immigrants who came to the U.S. in the mid-nineteenth century were mostly from northern and western Europe, specifically the British Isles, including Ireland, Germany, and Scandinavia. Assimilated into the melting pot of America’s immigrant populations, these Europeans contributed significantly to the nation’s economic and social growth. However, public attitude toward immigrants in America began to change in the latter part of the nineteenth century with the arrival of millions of poor and uneducated people from southern and eastern Europe, specifically from Italy, Greece, and the Slavic countries. These immigrants not only dressed differently but also followed religions that were different from the Protestant majority of the native-born American contemporaries. Consequently, they were considered inferior and made into victims of prejudice and racism in America (Payant xvii).

Significantly, the liberal social and political climate of the American sixties saw some major changes taking place in the immigration policies allowing many more immigrants, even from non-European countries. During this period, immigrants arrived in the United States mainly from underdeveloped nations such as Mexico, China, Vietnam, India, Poland, Ukraine, El Salvador, Ireland, the Philippines, and the Dominican Republic. With this third wave of immigration, the gap between the native-born Americans and immigrants grew wider. Coming from non-European backgrounds, carrying a wide variety of cultural baggage, practising various religions, conversing in their native language, following different customs and, most importantly, being “coloured,” these immigrants had almost no similarity with their American counterparts.

These newer immigrants differed from the immigrants of the earlier waves in their wish to retain ties to their native lands and cultures, rather than completely renounce their ethnicity for the sake of assimilation. Unlike the earlier immigrants who were forced to sever all ties with their home, these newer immigrants used modern communications and technological advancement to retain connections with their native countries through brief but frequent visits. Significantly, this new “transnationalism” of the newer immigrants which allowed them to simultaneously enjoy the benefits of dual citizenship and a multicultural lifestyle in the United States complicated their process of assimilation. Consequently, many of these people preferred to live in ethnic enclaves, follow the customs of their native lands, and reject certain aspects of the American lifestyle that they thought were damaging their families, even while considering themselves American.

In order to understand the political significance of Asian American literature, it is necessary to trace the emergence of the category of immigrants called “Asian American.” Asians in America often considered as representatives of distant and exotic civilizations, suppliers of cheap labour, racially corrupting presences, and unsolicited invaders became a visible threat to the national character of America when their population started growing. Ready to work for meagre returns, Asian Americans soon began to undermine white Americans’ job security. Significantly, the seemingly useful categorization of Asian Americans into a “model minority,” is, in reality, reductive and pernicious in unacceptably simplifying the experiences of Asian Americans and also creating divisions between Asian Americans and other coloured groups of America. In order to counter this adverse and abridged discursive history, several Asian American writers, artists, activists and historians developed an alternative understanding of their community comprising its diverse geographies, journeys, and experiences that resist simplistic representation.

The category “Asian American” emerged in the history of U.S. immigration in the late 1960s and 1970s with the arrival of immigrants specifically from East Asia (China, Korea, and Japan) and the Philippines. The later addition of groups from Southeast Asia, South Asia, and West Asia both problematized and developed the field of Asian American writing. Paradoxically, the terrain of Asian American writing that attempts to challenge the marginalization of Asian Americans within the U.S. history, politics, and culture culminated in creating divisions within its own domain. The early Asian Americans who were mainly Chinese, Japanese, Korean, and Filipino sought full and unquestioned membership in the U.S. body politic. Ironically, if on the one hand, their desire to be acknowledged as a part of the U.S. was being fulfilled by the retraction of exclusionary immigration laws, on the other, they themselves were disowning immigrants from other parts of Asia by confining the notion of being Asian American mostly to immigrants from East Asia and Philippines. However, despite the early Asian Americans’ attempt to tighten the boundaries of their domain, the arrival of a growing number of immigrants from South Asian countries such as Bangladesh, Bhutan, India, the Maldives, Nepal, Pakistan, Sri Lanka and, later on, refugees from Vietnam, Cambodia, and Laos soon began to challenge such a narrow definition.

Asian American Literature and Literary Criticism

Much like the U.S. immigration policy, the literature of immigration in America has undergone several transformations reflecting the historical and social contexts from which it emerged. In the later decades of the twentieth century, immigrant literature evolved from being multicultural to transnational in the hands of a new wave of immigrant writers who celebrated and nurtured their ethnicity. One must remember that Asian American literature does not merely refer to artistically constructed texts by American authors of Asian ancestry. It also refers to a counter discourse developed by early writers such as Sui Sin Far, Carlos Bulosan, and John Okada who wrote before the Asian American movement of the 1960s. The later writers of the tradition such as Onoto Watanna, Jade Snow Wong, Amy Tan and Bharati Mukherjee have received a more ambivalent response from the critics of Asian American literature. While the former set of writers were quite explicit in acknowledging ethnicity and confronting discriminations, the later ones embraced the political ideologies of their literary antecedents and reinvented those systems to suit the times. However, regardless of their differences from the early Asian American writers, the works of later authors continue to share the preoccupations of the earlier writings such as an emphasis on resistance, and identity issues.

Along with the literature, Asian American literary criticism has also undergone a transition from an ideologically driven emergent phase that lasted from the 1970s to the 1990s to the institutionally-driven established phase of criticism. When the civil rights movement of the 1960s gave birth to the notion of “new ethnicity” in the 1970s, ethnicity suddenly became tolerable and even preferable in some circles. Sociologists such as Michael Novak, Nathan Glazer and Daniel Moynihan disparaged the “myth of the melting pot,” and advocated the need to acknowledge “the ethnic pattern [as] American, more American than […] assimilationist,” for America to become a diverse but collective society (Novak 71, Glazer and Moynihan xxii-xxiv). Besides the sociologists, several literary critics began to express their interest in studying ethnic literature, including the literature of immigration. For instance, Werner Sollors and William Boelhower argued that literature of immigration had much in common with the mainstream American culture than its authors would agree. In 1987, William Boelhower in Through a Glass Darkly claimed that in the United States ethnicity is flexible rather than reified by a cultural essence (31-32). Werner Sollors further underscored the dynamics of ethnicity in Beyond Ethnicity (1986) and The Invention of Ethnicity (1989), in arguing that ethnicity is continuously reinvented and reinterpreted by not only each generation of immigrants but also by each individual immigrant. Gradually literary critics developed a particular interest in the works of young writers from the “new” immigrant groups, comprising mostly of non-European and non-white stock, which had been immigrating to America since 1965. This newly developed branch of Asian American literature sought to address key issues regarding the assimilatory pattern of immigrants in America. The impression of uprooted and alien immigrants arriving in the strange land of America to be thrown together into a stew pot, yet not assimilating into the American society until their second generation, is a theme that is found in many works of recent non-European immigrants.

It is not surprising that authors of Asian American literature directed their critique mostly towards the nation-state to which they desired to belong to but which refused to acknowledge them. The co-editors of Aiiieeeee! An Anthology of Asian American Writers, one of the first works to demand recognition of the growing number of Asians in the United States and acknowledgment of their contributions to the nation, often expressed their disdain over Asian American writers’ attempt to inveigle the attention of mainstream American white-readers by using formulaic or stereotypical elements in their fictions. The first major academic work to outline Asian American literature was Elaine Kim’s Asian American Literature: An Introduction to the Writings and their Social Contexts. As an early critic, Kim played a significant role in establishing Asian American literature as an important corpus of work worthy of scholarly attention. In contrast to the rebellious and polemical language of Aiiieeeee!, Kim’s book retooled the arguments of Asian American literary critics into academic conventions of methodology and discourse.

The anti-exclusionary dynamics of claiming America marked the emergent phase of Asian American literature. Asian American writers and critics harped on the importance of recording the experiences of Asian American immigrants which had been, for a long time, excluded from American history and culture. Most of the prominent works of Asian American literary critics that emerged after Kim’s book, covertly or overtly agreed on the fixing of a national boundary for Asian American literary studies. Sau-ling Wong’s Reading Asian American Literature that offers a close and textured reading of some of the key Asian American literary works is the best possible representation of this strategy. Some other notable works that defined Asian American literature in terms of national boundaries were David Leiwei Li’s Imagining the Nation, Jinqi Ling’s Narrating Nationalisms, and Rachel C. Lee’s The Americas of Asian American Literature. Though critics, then, were mostly trying to limit the field of Asian American literature nationally, the specifications of an Asian American writer and the privileges and limitations imposed on a writer by such specifications continued to be debated. In this respect, Susan Koshy’s focus on the transnational aspects of Asian American literature in her essay “The Fiction of Asian American Literature,” rejected Wong’s argument to make the case that the nationalist orientation of Asian American literary criticism, which had sustained since Aiiieeeee!, would no longer be unquestionably accepted.

In her pivotal work, Immigrant Acts, Lisa Lowe decentralizes the nation-centred logic through which Asian American literature was for long defined. The exclusion of Asian immigrants in the United States, argued Lowe, was paradoxically responsible for uniting them and also for making them critically aware of their exclusion. Lowe’s thesis marked the completion of the emergent phase of Asian American literary criticism and also offered a strong theoretical foundation for the political functions of Asian American literature. Although, the later critics of Asian American literature rejected the U.S. centrism while articulating Asian American differences, not many changes took place in the manner in which America constituted the subjectivities of Asian Americans. King-Kok Cheung’s Interethnic Companion to Asian American Literature provides an apt instance of how, despite their diverse existence, Asian Americans continue to articulate their differences through their national or communal spaces. Therefore, at one level, by remaining immutable, the category “Asian American” allows one to thematically organize a group of texts according to the authors’ ethnicity and national origins. It is necessary to gauge the contributions of Asian American literary criticism in the making of a successful Asian American writer. For instance, although a bestselling author is more famous than any critic of Asian American literature, many mainstream readers may not necessarily recognize that author as an Asian American writer or her works as integral to Asian American literature. Literary criticism in legitimizing a piece of writing can add to the accomplishments of an author.

References:-

1.	Payant, Katherine B. “Introduction.” The Immigrant Experience in North American Literature: Carving out a Niche, edited by Katherine B. Payant and Toby Rose, Greenwood Press, 1999, pp. xiii–xxvii.
2.	Novak, Michael. The Rise of the Unmeltable Ethnics: Politics and Culture in the Seventies. Macmillan, 1972.
3.	Glazer, N., and Daniel Patrick Moynihan. Beyond the Melting Pot. 2nd ed., M.I.T Press, 1970
4.	Boelhower, William. Through a Glass Darkly: Ethnic Semiosis in American Literature. Oxford UP, 1987

Source of the figure used along with the article: Immigrants make America great (Source: Wikimedia Commons, Photo by: Paul Sableman). URL: (https://commons.wikimedia.org/wiki/File:Immigrants_Make_America_Great_(32611307221).jpg)

Development of cascade reactions for the synthesis of biologically active indole alkaloids

Ghanshyam Mali, Amar Nath Singh Chauhan, Kailas Arjun Chavan and Rohan D. Erande

Research Snippets

---

Nature produces numerous structurally complex and fascinating molecules that play an extremely supreme role in human health additionally as conjointly attract chemists to develop ways to access such biologically active compounds. Humankind has been used largely natural products as a source of traditional medicines for thousands of years and still represents the primary source of new drug development. The chemistry of Indole based alkaloids is one the most exciting research area owing to a wide range of biological activity and one of the prominent needs of medicinal chemistry.[1] Indole alkaloids are the classic example of structurally diverse architecture which shows the variety of biological activity. The synthesis of biologically active indole alkaloids is a challenging task that requires expertise in various aspects of organic synthesis. Numbers of synthesis designs and modifications already addressed various natural product scaffolds to serve humanity. Here, we highlight unique synthetic developments towards the construction of complexed biologically active scaffolds and application towards drug discovery using cascade approach to access biologically active indole-based alkaloids, the execution of cascade within the context of natural product synthesis with selected examples that address the future of this field. Cascade reactions (Domino or Tandem reactions) is an efficient methodology for the synthesizing core of structurally complex molecules therefore they received huge attention in a couple of decades. The continuously growing importance of cascade reactions impart synthetic chemists to achieve efficiency in synthesizing natural product scaffold. The cascade reactions have many benefits including atomic economy, time economy, resource management, besides this cascade process offers an economical and environmentally friendly approach for generating molecular complexity.[2][3] Because of their promising advantages, these reactions have found various applications in the synthesis of complex molecular frameworks such as in synthesizing natural products: (-)-3-O-methyl-10,11-demethoxychippiine, (-)-3-hydroxy-3,4-secocoronaridine, (-)-dippinine B, (+)- dippinine C, (-)-demethoxychippiine,[4] (-)-tubifoline, (+)-condyfoline, (+)-1,2-dehydroa- spidospermidine,[5] (±)-dehaloperophoramidine,[6] (−)-jerantinines A,C,E, (−)-16-methoxytabersonine, (+)-vinblastine,[7] lysergic acid,[8] (+)-tronocarpine,[9] and (+)-strychnine[10] etc. Introducing the total synthesis by cascade approach will empower the new thinking in organic synthesis and also provide a platform to approach a variety of scaffolds in total synthesis. Learning the unique approach to access structurally diverse natural products definitely can illuminate the area of chemistry of total synthesis. In the field of natural products and total synthesis, cascade reaction provides a great power of process to construct complex molecules and the core of the natural product in a single step.[11] Inspired by the distinctive biological activity of various indole-based alkaloids, like voacamine,[12] villalstonine,[13] toxiferine,[14] vinblastine,[15] ajmalicine[16] and catarantine,[17] our aim is to develop cascade methodology towards attempting the total synthesis of structurally complex molecules, along with discovery of novel potent drug candidates to cure mankind. To understand the basic evolution and early detection of disease, many attempts, clinical trials and potential strategies are being planned based on the immense interest in chemistry and biology. In this regard, a unified approach has been designed to synthesis effectively indole-based alkaloids and their simplified-designed analogues using a cascade approach incorporating well-known photochemical, cycloadditions, and Lewis-acid catalyzed reactions.

We have also developed a cascade approach to synthesize a bis-indole alkaloid yuchchukene natural product (antifertility and estrogenic activity) and its analogues (known for potent antiimplantation activity in rats as well as potential fertility regulatory agents), Yuremamine core (a new phytoindole),[18] pyrrolo[1,2-a]indoles and benzofuro[2,3-b]indulines motif utilizing Lewis-acid catalyzed cycloaddition. We extended our work for the total synthesis of recently isolated natural product such as shearilicine and paspalinine-13-ene along with previously reported paspalicine, paspalinine (low micromolar to nanomolar against various cancer cell lines).[19] Furthermore, our research group continuously looking forward to synthesis such promising scaffolds of the natural products of immense importance by the development of cascade approach.

References:-

1.	R. A. Khan, "Natural products chemistry: The emerging trends and prospective goals," Saudi Pharm. J., vol. 26, no. 5, pp. 739-753, 2018, doi: https://doi.org/10.1016/j.jsps.2018.02.015.
2.	K. C. Nicolaou and J. S. Chen, "The art of total synthesis through cascade reactions," Chem. Soc. Rev., vol. 38, no. 11, pp. 2993-3009, 2009, doi: 10.1039/B903290H.
3.	K. C. Nicolaou, D. J. Edmonds, and P. G. Bulger, "Cascade Reactions in Total Synthesis,"Angew. Chemie Int. Ed., vol. 45, no. 43, pp. 7134-7186, Nov. 2006, doi: https://doi.org/10.1002/anie.200601872.
4.	J. Zhou, D.-X. Tan, and F.-S. Han, "A Divergent Enantioselective Total Synthesis of Post-Iboga Indole Alkaloids," Angew. Chemie Int. Ed., vol. 59, no. 42, pp. 18731-18740, Oct. 2020, doi: https://doi.org/10.1002/anie.202008242.
5.	B. Delayre, C. Piemontesi, Q. Wang, and J. Zhu, "TiCl3-Mediated Synthesis of 2,3,3-Trisubstituted Indolenines: Total Synthesis of (+)-1,2-Dehydroaspidospermidine, (+)-Condyfoline, and (-)-Tubifoline," Angew. Chemie Int. Ed., vol. 59, no. 33, pp. 13990-13997, Aug. 2020, doi: https://doi.org/10.1002/anie.202005380.
6.	A. Hoang, K. Popov, and P. Somfai, "An Efficient Synthesis of (+_)-Dehaloperophoramidine," J. Org. Chem., vol. 82, no. 4, pp. 2171-2176, Feb. 2017, doi: 10.1021/acs.joc.6b02969
7.	N. Wang, J. Liu, C. Wang, L. Bai, and X. Jiang, "Asymmetric Total Syntheses of (-)-Jerantinines A, C, and E, (-)-16-Methoxytabersonine, (-)-Vindoline, and (+)-Vinblastine," Org. Lett., vol. 20, no. 1, pp. 292-295, Jan. 2018, doi: 10.1021/acs.orglett.7b03694.
8.	A. Iwata, S. Inuki, S. Oishi, N. Fujii, and H. Ohno, "Formal Total Synthesis of (+)-Lysergic Acid via Zinc(II)-Mediated Regioselective Ring-Opening Reduction of 2-Alkynyl-3-indolyloxirane," J. Org. Chem., vol. 76, no. 13, pp. 5506-5512, Jul. 2011, doi: 10.1021/jo2008324
9.	D.-X. Tan, J. Zhou, C.-Y. Liu, and F.-S. Han, "Enantioselective Total Synthesis and Absolute Configuration Assignment of (+)-Tronocarpine Enabled by an Asymmetric Michael/Aldol Reaction," Angew. Chemie Int. Ed., vol. 59, no. 10, pp. 3834-3839, Mar. 2020, doi: https://doi.org/10.1002/anie.201914868.
10.	L. He et al., "Asymmetric Total Synthesis of (+)-Strychnine," Org. Lett., vol. 21, no. 1, pp. 252-255, Jan. 2019, doi: 10.1021/acs.orglett.8b03686.
11.	V. F. V. and S. Balalaie*, "Cascade Reaction in the Synthesis of Heterocyclic Natural Products," Current Organic Chemistry, vol. 21, no. 15. pp. 1393-1426, 2017, doi: http://dx.doi.org/10.2174/1385272820666160603114213.
12.	J. LA BARRE and L. GILLO, "About the cardiotonic properties of voacangine and voacanginine" Bull. Acad. R. Med. Belg., vol. 20, no. 5, pp. 194-216, Jan. 1955, [Online]. Available: https://www.unboundmedicine.com/medline/citation/13260772/ About_the_cardiotonic_properties_of_voacangine_and_voacanginine.3260772/ About_the_cardiotonic_properties_of_voacangine_and_voacanginine.
13.	L. Pan et al., "Bioactive indole alkaloids isolated from Alstonia angustifolia," Phytochem. Lett., vol. 10, pp. 54-59, Dec. 2014, doi: 10.1016/j.phytol.2014.06.010.
14.	A. R. Battersby and H. F. Hodson, "152. Alkaloids of calabash curare and strychnos species. Part I. Chemistry and structure of hemitoxiferine-I and toxiferine-I, including the preparation of toxiferine-I," J. Chem. Soc., no. 0, pp. 736-741, 1960, doi: 10.1039/JR9600000736.
15.	A. G. Atanasov et al., "Discovery and resupply of pharmacologically active plant-derived natural products: A review," vol. 33, pp. 1582-1614, 2015
16.	T. J. M. Blom et al., "Uptake and accumulation of ajmalicine into isolated vacuoles of cultured cells of Catharanthus roseus (L.) G. Don. and its conversion into serpentine," Planta, vol. 183, no. 2, pp. 170-177, 1991, doi: 10.1007/BF00197785
17.	G. C. Coatti, J. C. Marcarini, D. Sartori, Q. C. Fidelis, D. T. Ferreira, and M. S. Mantovani, "Cytotoxicity, genotoxicity and mechanism of action (via gene expression analysis) of the indole alkaloid aspidospermine (antiparasitic) extracted from Aspidosperma polyneuron in HepG2 cells," Cytotechnology, vol. 68, no. 4, pp. 1161-1170, Aug. 2016, doi: 10.1007/s10616-015-9874-9.
18.	J. J. Vepsalainen, S. Auriola, M. Tukiainen, N. Ropponen, and J. C. Callaway, "Isolation and Characterization of Yuremamine, a New Phytoindole," Planta Med, vol. 71, no. 11, pp. 1053-1057, 2005.
19.	N. P. Ariantari et al., "Indole Diterpenoids from an Endophytic Penicillium sp.," J. Nat. Prod., vol. 82, no. 6, pp. 1412-1423, Jun. 2019, doi: 10.1021/acs.jnatprod.8b00723.

Damage Tolerant High Entropy Alloys: Technological Possibility for Sustainable Human Life

Saurabh Sanjay Nene

Research Snippets

---

Introduction of metals to the mankind was a major breakthrough to levitate the human life by overcoming environmental as well as economical concerns. However, most of these metals either exhibit very high strength or exceptional ductility as a result of strength-ductility tradeoff. All the existing materials such as steels, Al alloys and Ti alloys which are getting frequently used in a day-to-day application display this inverse strength-ductility relation which result in sudden failures of these materials during service [1-2]. As a result, material designers worked in this direction so that a cost-effective strategy can be developed for realizing strong as well as ductile material for engineering applications to minimize/delay failures in them during service. This attempt gave birth to very advanced materials for the human community such as advanced high strength steels, Twinning/Transformation induced plasticity assisted steels, ultralight Mg-Al-Ca alloys and so on. However, they also exhibited strength-ductility dilemma though in a minimized way [1-2].

Continuous evolution in the alloy design research focusing on this everlasting issue in metallic materials led to discovery of all together new class of metallic alloys termed as High Entropy Alloys (HEAs). The entire effort of high entropy alloy (HEA) design was based on obtaining an alloy composition that have higher tensile strengths with greater elongations. Conventional materials failed to attain these unconventional properties; hence, the concept of the equiatomic addition of elements attracted researchers in a very short time span. Earlier work on equiatomic HEAs showed uncommon mechanical, wear and fatigue properties that were attributed mainly to the complex concentrated solid solutions formed (by suppressing brittle intermetallic compounds) in the material [2-3]. Further development in this field brought to the floor dual-phase non-equiatomic HEAs, that displayed extraordinary work hardening because of the synergistic activation of dislocation, transformation and twinning effects during deformation. An additional benefit of non-equiatomic HEA design was to devise a huge compositional space (away from the centre of the phase diagram) for developing new alloys which was not explored before. Therefore, researchers realized that, non-equiatomic HEA design approach will enable the material to deform with multiple deformation mechanisms at room temperature so that it will not only show higher strength but also work hardening ability which is necessary for having good ductility. Thus, various attempts were made towards this direction giving rise to various types of HEAs such as FeMnCoCrNi based equiatomic HEAs, AlxCoCrFeNi based, FeMnCoCr based and FeMnCoCrSi based non-equiatomic HEAs [2-4].

Recent work by Z. Li, D. Raabe and his Group [4] at Germany utilized the metastability of phases synergized with high entropy to tune the deformation mechanisms and thereby yield an extraordinary combination of strength and ductility for non-equiatomic dual-phase HEAs (DP-HEAs). Thus, they claimed that the material can be ductilized with steady increase in strength through sustained work hardening (WH) during deformation. Our work further elevated this effort by redefining the metastable dual-phase high entropy alloys (HEAs) design with a motive that they would exhibit properties of stainless steel, TRIP steel and electrical steel in synergy in a cost-effective manner. This was realized by adding light weight non-transition element Si into Fe-Mn-Co-Cr matrix with further alteration with minor additions of Cu and Al. The alloy chemistry in combination with friction stir processing, showed an excellent combination of strength, ductility and corrosion resistance and concurred the conventional strength-ductility tradeoff as shown in Figs. 1 (a-e) [1-8]. We attributed these unconventional properties of these HEAs to the adaptive phase evolution in them leading to optimum grain and phase proportions of ϒ-f.c.c. and ε-h.c.p. phases in the microstructures with varying alloy chemistry (Figs. 1 (a-d)) as well as processing conditions (Fig. 1). This adaptive phase stability not only promoted the flexibility in microstructural evolution but also empowered the material in selection of multiple deformation mechanisms for attaining good plasticity at room temperature [5-10].

Fig. 1: (a-d) Design of microstructurally flexible high Entropy alloys namely, Fe₅₀Mn₃₀Co₁₀Cr₁₀ (DP-HEA), Fe₄₀Mn₂₀Co₂₀Cr₁₅Si₅ (CS-HEA)_,  Fe₃₉Mn₂₀Co₂₀Cr₁₅Si₅Al₁ (Al-HEA) and Fe_38.5Mn₂₀Co₂₀Cr₁₅Si₅Cu_1.5 (Cu-HEA). (All elemental content is in atomic %), (e) Tensile properties of all these HEA after perfoming friction stir processing at 350 rotations per minute (RPM) [5]. 

Moreover, we found that these materials exhibited extremely high resistance to failure under cyclic loading due to localized ϒ→ ε transformation within the crack tip plastic zone which delayed the crack propagation and improved the fatigue life. This controlled transformation activity was mainly attributed to the engineered  matrix stability and stress concentration within the crack tip plastic zone. Fig.2 (a) display the dramatically improved fatigue endurance limit of the Fe_38.5Mn₂₀Co₂₀Cr₁₅Si₅Cu_1.5 HEA whereas Fig. 2 (b) display the localized ϒ→ ε transformation near the fatigue crack tip in the interrupted fatigue specimen of the same HEA in electron back scattered diffraction (EBSD) phase map (Figs 2 b₁-b₃). Fig. 2 (c-c₁) clearly indicates the crack path deviation supporting the region-specific plastic deformation during fatigue deformation by dual phase strengthening within the crack tip plastic zone [11].

Fig. 2: (a) S-N curve for ultrafine grained Fe_38.5Mn₂₀Co₂₀Cr₁₅Si₅Cu_1.5 HEA, (b) EBSD image quality, and (b₁-b₃) phase map showing localizedϒ → ε transformation near the fatigue crack tip, (c) EBSD phase, and (c1) IPF map showing crack path deviation [11].

I am currently working towards correlating this metastable HEA design approach with the defects inherently present in the material for realizing new damage tolerant materials. All the metallic materials inherently contain defects which are known to be sites for local stress concentration. In metastable HEAs, this local variation in stress near the defects can additionally activate ϒ → ε transformation based on the tuned metastability of the matrix phase. As a result, this localized phase transformation would deviate the crack path due to increased strength of the region via plastic deformation ahead of the crack front. This crack path deviation can cause crack branching at the crack front during the propagation which can further delay the overall fracture in the material. Therefore, this minor increase in plasticity before failure due to the presence of peculiar type of defects in these metastable HEAs is termed as defect induced plasticity (DIP). This DIP effect in these metastable HEAs not only enhances the damage tolerance of the material but also delays the sudden failures in materials like Fatigue. This work thus will involve synergistic research done by mechanical engineering, computational materials and metallurgical community such that a new material can be designed in a most effective way. Further, this work can be easily extended to metal additive manufacturing research since defects are inherently present in all 3D printed products and hence limit their usability in engineering applications.

In summary, DIP effect in metastable HEAs gives the benefit to utilize defects (which are considered as detrimental sites for failure in conventional materials) for improving their failure resistance in engineering applications for sustainable human life.

References:-

1.	W. J. Larke Iron and steel, Nature, 136 (1935) 20-26.
2.	J.W. Yeh, et al. Nanostructured high entropy alloys with multiple component elements: novel alloy design concepts and outcomes, Advanced Engineering Materials 6 (2004) 299 - 303
3.	D.B. Miracle, O.N. Senkov, A critical review of high entropy alloys and related concepts, Acta Materialia 122 (2017) 448-511
4.	Z. Li, et al. Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off. Nature 534 (2016) 227 - 230.
5.	S.S. Nene, M. Frank, P. Agrawal, S. Sinha, K. Liu, S. Shukla, R.S. Mishra, B. A. McWilliams, K. C. Cho, Microstructurally flexible high entropy alloys: Linkages between alloy design and deformation behavior, Materials and Design 194 (2020) 108968.
6.	S.S. Nene, K. Liu, M. Frank, R.S. Mishra, R. E. Brennan, K. C. Cho, Z. Li, D. Raabe, Enhanced strength and ductility in a friction stir processing engineered dual phase high entropy alloy, Scientific Reports 7 (2017) 16167.
7.	S.S. Nene, K. Liu, M. Frank, R.S. Mishra, B. A. McWilliams, K. C. Cho, Extremely high strength and work hardenability in metastable high entropy alloy, Scientific Reports 8 (2018) 9920.
8.	S.S. Nene, M. Frank, K. Liu, S. Sinha, R.S. Mishra, B. A. McWilliams, K. C. Cho, Reversed strength-ductility relationship in microstructurally flexible high entropy alloy, Scripta Materialia 154 (2018) 163 - 167.
9.	S.S. Nene, S. Sinha, M. Frank, K. Liu, R.S. Mishra, B. A. McWilliams, K. C. Cho, Unexpected strength-ductility response in an annealed, metastable, high entropy alloy, Applied Materials Today 13 (2018) 196 - 206.
10.	S.S. Nene, M. Frank, K. Liu, S. Sinha, R.S. Mishra, B. A. McWilliams, K. C. Cho, Corrosion resistant high entropy alloy with high strength and ductility, Scripta Materialia 166 (2019) 168-172.
11.	K. Liu, S.S. Nene, M. Frank, S. Sinha, R.S. Mishra, Extremely high fatigue resistance in ultrafine grained high entropy alloy at ambient temperature, Applied Materials Today 15 (2019) 525-530.

Design of Mechanically Tunable Wide Phononic Band Gaps in Soft Laminates by Means of Topology Optimization

Atul Kumar Sharma

Research Snippets

---

The propagation of elastodynamic waves in periodic composite materials, also known as phononic crystals (PnCs), has gained increasing attention in the recent past [1,2]. PnCs possess the promising characteristic of exhibiting band gaps within which the propagation of acoustic/elastic waves in certain frequency ranges is prohibited. Due to this characteristic, PnCs have been implemented in a wide range of engineering applications such as frequency filters, vibration isolators, acoustic diodes, noise suppressors, and among many others [3,4].

Soft active materials, such as tissues, dielectric elastomers, and magnetorheological elastomers, etc. have been of particular interest due to their characteristic of undergoing large deformation when actuated by mechanical, electrical, magnetic, thermal fields [5]. The constitutive behavior of such materials is nonlinear and material properties are a function of mechanical, electrical, or magnetic loading. These features made them attractive for tunable band gap structures. In this regard, a significant effort has been made to investigate the wave propagation and band gaps in the periodic composite structures or PnCs made up of soft active materials [3,6,7]. However, in several of these applications, the position and width of the band gaps of PnCs play a crucial role. Thus, it is necessary to design a periodic structure that possesses the desired position and width of the band gap. The design of PnCs with tunable band gaps has been the topic of continued interest and investigation [1]. A large volume of literature expounds on designing the topologies of PnCs made up of hard materials such as Aluminium/Epoxy, for widening the band gap width [1,2]. In contrast, not much work has been done on topology optimization of PnCs made up of soft materials [8]. To this end, this paper reports a gradient-based topology optimization framework for designing wide and mechanically tunable soft band gap structures.

Consider an infinite periodic laminated composite composed of perfectly boded two different soft compressible phases denoted by a and b as shown in Fig. 1. In the undeformed configuration, the thickness of the unit cell is . For tuning the band gaps, laminate is subjected to fixed equi-biaxial prestretch in the lateral directions and the pre-stress in the longitudinal direction. In the deformed configuration, the thickness of the unit cell becomes and is related to undeformed thickness as with p=(a,b) and being the stretch ratio in the longitudinal direction for pth phase. Considering that the phases are made up of compressible neo-Hookean materials, the nonlinear constitutive relation relating the applied prestress and longitudinal prestretch is given as

Figure 1: Schematic of an infinite two-phase soft phononic crystal subjected to prestress in the longitudinal direction and the corresponding undeformed unit cell.

This paper is restricted to investigate the longitudinal waves propagating in the x3 direction of the deformed phononic crystal. The finite deformation field theory presented in Ref. [9] is used for studying the incremental elastic longitudinal wave propagation superimposed on the static deformation induced by the applied prestress . The incremental equation governing the longitudinal waves propagating in the x3 is obtained as

Next, the standard finite element method with Bloch periodic boundary conditions [10] is adopted to find the band diagrams of the infinite periodic soft laminate. Considering time-harmonic excitation, the resulting finite element equations for modeling the infinite periodic soft laminate is given as

where denotes the spatially dependent nodal incremental displacement vector, K and M are the stiffness and mass matrices, respectively, and k is the wave vector. The eigenvalue problem (Eq. 2) along with the Bloch periodic boundary condition is solved for extracting the longitudinal band diagram.

This paper aims to find the optimal distribution of soft compressible phases a and b in the unit cell that maximizes the band gap width in the pre-stressed configuration. The mathematical formulation of the topology optimization problem for maximizing the band gap width in the pre-stressed configuration is defined as

The finite element eigenvalue problem and the topology optimization problem presented in this paper are implemented by developing an in-house MATLAB code. The unit cell is assumed to be made up of two compressible neo-Hookean hyperelastic phases a and b whose material properties are listed in Table 1. In the undeformed configuration, the size of the unit cell is taken to be 1mm and discretized into 200 linear bar elements. The longitudinal band structures are obtained by sweeping the wave vector in the irreducible first Brillouin zone . For convenience, the frequency is normalized as and the wave vector is normalized as kh.

In conclusion, a gradient-based topology optimization framework is presented for maximizing the longitudinal band gap width in soft compressible laminated phononic crystals. The topology optimization and finite element framework presented for extracting band gap diagrams is implemented using an in-house MATLAB code. The higher compression prestress is found to have a favourable impact on the optimized band gap characteristics. The present gradient-based framework can be extended for designing wide tunable band gaps for anti-plane and in-plane waves of general propagation direction in two-dimensional and three-dimensional soft composites.

References:-

1.	G. Yi, Y. C. Shin, H. Yoon, S.-H. Jo, B. D. Youn, Topology optimization for phononic band gap maximization considering a target driving frequency, JMST Advances 1 (1) (2019) 153-159.
2.	W. Li, F. Meng, Y. Chen, Y. f. Li, X. Huang, Topology optimization of photonic and phononic crystals and metamaterials: a review, Advanced Theory and Simulations 2 (7) (2019) 1900017.
3.	Y. Chen, B. Wu, Y. Su, W. Chen, Tunable two-way unidirectional acoustic diodes: Design and simulation, Journal of Applied Mechanics 86 (3) (2019)
4.	Z.-G. Chen, J. Zhao, J. Mei, Y. Wu, Acoustic frequency filter based on anisotropic topological phononic crystals, Scientific reports 7 (1) (2017) 1-6.
5.	J. Kim, J. W. Kim, H. C. Kim, L. Zhai, H.-U. Ko, R. M. Muthoka, Review of soft actuator materials, International Journal of Precision Engineering and Manufacturing 20 (12) (2019) 2221-2241.
6.	R. Getz, D. M. Kochmann, G. Shmuel, Voltage-controlled complete stopbands in two-dimensional soft dielectrics, International Journal of Solids and Structures 113 (2017) 24-36.
7.	A. Bayat, F. Gordaninejad, Band-gap of a soft magnetorheological phononic crystal, Journal of vibration and acoustics 137 (1) (2015).
8.	E. Bortot, O. Amir, G. Shmuel, Topology optimization of dielectric elastomers for wide tunable band gaps, International Journal of Solids and Structures 143 (2018) 262-273.
9.	A. Dorfmann, R. W. Ogden, Electroelastic waves in a finitely deformed electroactive material, IMA Journal of Applied Mathematics 75 (4) (2010) 603-636.
10.	C. Kittel, Introduction to solid state physics, John Wiley & Sons, Inc., New York (2005).
11.	K. Svanberg, The method of moving asymptotes—a new method for structural optimization, International journal for numerical methods in engineering 24 (2) (1987) 359-373.