Department of Physics

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The key to the survival of a species lies in understanding its evolution in an ever-changing environment. We report a theoretical model that integrates frequency-dependent selection, mutation, and asexual reproduction for understanding the biological evolution of a host species in the presence of parasites. We study the host-parasite coevolution in a one-dimensional genotypic space by considering a dynamic and heterogeneous environment modeled using a fitness landscape. It is observed that the presence of parasites facilitates a faster evolution of the host population toward its fitness maximum. We also find that the time required to reach the maximum fitness (optimization time) decreases with increased infection from the parasites. However, the overall fitness of the host population declines due to the parasitic infection. In the limit where parasites are considered to evolve much faster than the hosts, the optimization time reduces even further. Our findings indicate that parasites can play a crucial role in the survival of its host in a rapidly changing environment. © 2020 Author(s).

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Chaos

Host-parasite coevolution: Role of selection, mutation, and asexual reproduction on evolvability

The paper considers approaches to the synthesis as well as the structural and electrochemical properties of lithium and transition metals polyanionic compounds as promising cathode materials for lithium-ion battery. The characteristics of lithium and transition metals sulfates are considered, among which iron-lithium sulfate and a composite electrode material Li2Fe(SO4)2/C based on it was selected for further detailed study. The relationships between the synthesis conditions and the structural and electrochemical characteristics of the material were revealed. Based on the structural data the computational method of the bond valence strengths (BVS) applying the bond valence energy landscape algorithm (BVEL) provided activation energy maps of lithium ion migration in the Li2Fe(SO4)2 crystal structure. The method of scanning electron microscopy (SEM) made it possible to characterize the morphological state of the material, to determine the particle size distribution, which were then used to determine the geometry of the diffusion space of particles. Applying the electrochemical kinetics investigation methods (CV, GITT, EIS) the parameters of lithium ion transport in the electrodes were determined. The quasi-equilibrium E(c) dependence of the Li2Fe(SO4)2/C electrode was obtained, this dependence was simulated using an approach based on the Frumkin intercalation isotherm and the lattice gas model, and the thermodynamic characteristics of the interparticle interaction in the material were obtained. The diffusion coefficient of lithium ions D in the material was estimated using the CV method: 1.6·10− 15 cm2·s− 1 in the anodic half cycle and 10− 15 cm2·s− 1 in the cathodic half cycle, respectively. The dependences of D on the lithium ion concentration in the intercalate and electrode potential were obtained using GITT and EIS methods, a comparison of these methods results was performed. © 2020 Elsevier B.V.

Journal of Electroanalytical Chemistry

Structural and electrochemical investigation of lithium ions insertion processes in polyanionic compounds of lithium and transition metals

Quantum Dot Sensitized Solar Cells are considered as the potential third generation solar cells due to their suitable optoelectronic properties for photovoltaic response. The possibility of size and composition tunability makes quantum dots as relevant absorber materials to match the wider solar spectrum more efficiently. In conjunction, the possibility of multiple electron-hole pair generations at the cost of single photon i.e. multiple carrier generation is showing potential to overcome the theoretical single junction power conversion efficiency limitations. Quantum dot sensitized solar cells are showing power conversion efficiencies up to 12%, very close to its counterpart dye sensitized solar cells. However, QDSSCs efficiencies are still lagging behind the conventional solid state single junction solar cells. In this review, we will discuss the initial evolution of quantum dot sensitized solar cells with their microscopic working principles. The review will also address development of key building blocks and factors such as various interfaces in QDSSCs, carrier transport and recombination across different interfaces, affecting the power conversion efficiency. Further, fundamental concepts of carrier multiplication and possible theoretical models for multiple exciton generation are discussed towards their impact on the power conversion efficiencies of quantum dot sensitized solar cells. © 2020 International Solar Energy Society

Solar Energy

A review on quantum dot sensitized solar cells: Past, present and future towards carrier multiplication with a possibility for higher efficiency

Copper-based chalcogenide ternary compounds are promising materials to be used as absorber layer in solar cells. In this work, we have reported the preparation of copper antimony sulfide (CAS) thin films by annealing chemically deposited multi-stack of Sb2S3-CuS and the effect of thickness ratio between two binary sulfides on the formation of different crystalline phases of Cu-Sb-S system. A series of multilayer structure was prepared with different thickness of CuS in order to study the effect of copper concentration on the structural, morphological, optical, and electrical properties of the resulting CuxSb1-xSy films. The CAS films were characterized by several techniques such as X-ray diffraction, Raman scattering, UV-visible spectroscopy, atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Hall effect measurements to evaluate their physical properties. The formation of either pure chalcostibite (CuSbS2) or mixed ternary phases containing chalcostibite, famatinite (Cu3SbS4), and tetrahedrite (Cu12Sb4S13) were detected depending on the thickness ratio of Sb2S3 and CuS. Chalcostibite films revealed desired optical and electrical values. Finally, solar cell was fabricated using the heterostructure FTO/CdS/CuSbS2/Ag and characterized by current-voltage, capacitance-voltage, and impedance-spectroscopy measurements achieving a promising ~0.8% efficiency with VOC = 0.484 V, JSC = 5.97 mA/cm2, and FF =27.34%. Impedance measurements revealed a low series resistance in the optimal solar cell, as a result, an increment in open circuit voltage. Novelty Statement: The novelty of this work is the fabrication of CuSbS2 thin films by tuning the thickness ratio of binary sulfides in Sb2S3-CuS stack followed by proper thermal annealing. Furthermore, impedance spectroscopic studies of CuSbS2 solar cell are still lacking; the present study may provide important physical insight to understand the device performance and possibilities toward any further improvement. © 2020 John Wiley & Sons Ltd

International Journal of Energy Research

Structural evolution of chemically deposited binary stacks of Sb2S3-CuS to phase-pure CuSbS2 thin films and evaluation of device parameters of CuSbS2/CdS heterojunction

Enantiomers have significant importance in pharmaceuticals, biology and modern chemistry and therefore distinguishing and quantifying the enantiomeric forms is of utmost importance. Herein, we propose diphenyl-3,3′-biphenanthryl-4,4′-diyl phosphate (R-VAPOL-PA) as a promising chiral solvating agent to discriminate amines and acids of poly-functional groups such as chiral amines, amino alcohols and hydroxy acids. The methodological approach involves using the nature of hydrogen bonds and ion pairs as a mode of weak interactions to form diastereomers where the probe is associated with enantiomers. The resulting diastereomer difference in the NMR spectrum enables the chiral discrimination with a complete baseline peak separation and an accurate enantiomeric excess (ee) analysis. We also carried out density functional theory (DFT) calculations to understand the complex formation to explain enantiodiscrimination by analysing the formation and stability of different chiral complexes. The binding energy differences between enantiomeric forms revealed by DFT calculations are qualitatively in agreement with the diastereomer difference in the NMR spectrum and unequivocally establishes the suggested experimental protocol of R-VAPOL-PA-based enantiomeric discrimination. This journal is © The Royal Society of Chemistry.

RSC Advances

R -VAPOL-phosphoric acid based 1H and 13C-NMR for sensing of chiral amines and acids

The Leggett–Garg inequalities impose restrictions on the values taken by some combinations of the two-time correlation functions of observables in order to be explainable by a noninvasive realist classical model. While in the unitary dynamics, it is straightforward to compute these correlation functions, open system effects bring in subtleties. Specifically, for non-Markovian dynamics, which involves setting up of system–bath correlations, the Leggett–Garg measurements disrupt these correlations, making a full system–bath Hamiltonian approach natural. However, here we point out that the problem can also be dealt with from a reduced dynamics perspective. The key point is that the noise superoperator acting on the system must be suitably updated after measurement interventions. Also considered is the effect of Markovian versus non-Markovian behavior as well as classically non-Markovian processes on the violation of Leggett–Garg inequalities. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.

Quantum Information Processing

Effect of memory on the violation of Leggett–Garg inequality

In this article, a comparative experimental and simulations analysis has been carried out to understand the role of tapered gap region on current density and energy of pseudospark (PS)-based electron beam emission. These studies have been performed for 5-gap and 8-gap regions in a tapered multigap multiaperture-based PS electron beam source, keeping the same electron beam fill factor, and other geometrical parameters identical. The source has been operated in a self-breakdown mode. Around four-times increase in the beam current has been observed in the 8-gap case at the fixed applied gap potential ranging between 20 and 25 kV, whereas the tapered interelectrode gap angle has been reduced from 7.5° to 4.5°. The field penetration inside the hollow cathode cavity and tapered region have also been analyzed using simulations, and the obtained results are explained based on built-up space charge in these regions. © 2020 IEEE.

IEEE Transactions on Electron Devices

Effect of Tapered Interelectrode Gap Region on Pseudospark-Sourced Electron Beam Emission

In this work, a microhollow cathode variant consisting of cylindrical cathode structure and a coaxial anode, with a layer of dielectric barrier on the inner wall of the cathode cavity, has been investigated. This arrangement allows the device to be operated at atmospheric pressure reaching electron densities up to 1018 m-3 in the microhollow cathode cavity. The discharge initiates from the narrow gap region between the cathode and the anode, followed by hollow cathode discharge. The presence of the anode in the discharge cavity causes the discharge electrons to be absorbed by the anode. A theoretical approach has been followed and it establishes a criterion for sustenance of this discharge in the microhollow cathode cavity. This criterion resulted from the fact that for discharge to be sustained in the hollow cathode cavity, the generation of electrons should be balanced by the absorption of electrons. Both these phenomena have been quantitatively explained by electron multiplication quotient and a multipass parameter for hollow cathode discharge has been evaluated. © 1973-2012 IEEE.

Department of Electrical Engineering

IEEE Transactions on Plasma Science

Investigations of Discharge Sustenance in a Dielectric Barrier-Based Microhollow Cathode

The investigation addresses the influence of tensile deformation on the magnetic properties of 304SS samples in their as-received state as well as those with martensite content of 12 and 17%. Non-destructive electromagnetic techniques like magnetic Barkhausen emission (MBE) and magnetic hysteresis loop have been used to measure variation in MBE voltage and coercivity, respectively, during plastic deformation through tensile loading. As both the techniques use surface probe, the present investigation will be useful for in situ evaluation of structural components. With progressive plastic deformation, those measurements revealed different stages of deformation indicated by change in MBE signal and magnetic coercivity. The stages of magnetoelastic response, strain-induced martensitic transformation, dislocation pile-ups and formation of voids reflected different patterns of magnetic Barkhausen emission and magnetic coercivity variation with progressive straining of austenitic stainless steel samples. The changes in true strain with variation in martensite content along gauge length of fractured samples have been analyzed with respect to martensite transformation kinetics. Mathematical fitting methodology has been adopted to distinguish as-received and pre-strained martensitic transformation characteristics. In situ magnetic NDE and associated martensitic transformation parameters may be useful for structural health monitoring of in-service components. © 2020, ASM International.

Journal of Materials Engineering and Performance

Impact of Pre-formed Martensite on the Electromagnetic Properties and Martensitic Transformation Kinetics of Uniaxially Tensile Loaded 304 Stainless Steel

Glass forming ability (GFA) and soft-magnetic behaviour of melt-spun Fe69C5.5P11.5Mn0.4Si2.3Cr1.8Mo1B8.5 (alloy 2) and Fe68C9P12Mn1Si3Nb2B5, (alloy 3) alloys prepared using high phosphorous pig iron (h-PI, Fe80C14P2.2Mn0.4Si3.4) has been studied. The glass formation, thermo-physical and soft-magnetic properties of the alloys were analyzed for different quenching rates by varying wheel speed as 23, 26, 33, 39 and 43 m/s. The simultaneous incorporation of alloying elements (Cr, Mo, Nb) and metalloids (C, B, P, Si) transforms h-PI to complete glassy alloy, even at low quenching rates. The melt quenching rate influences the thermal parameters and Curie temperature of glassy ribbons in an opposite way. Amongst all, FeCPMnSiCrMoB glassy alloy show superior combination of higher glass transition temperature of 788 K, super cooled region of 34 K, glass Curie temperature of 552 K, coercivity less than 13 A/m and maximum saturation magnetization of 1.1 T. In addition, the annealing treatment at 758 K improves magnetic softness (1.7 A/m) of the alloy by relaxation of quenched-in stresses. The comparison of developed glassy alloy with similar Fe-glassy alloys and SENNTIX type alloys show best combination of thermo-physical and magnetic properties. The glassy alloy prepared using blast furnace high phosphorous pig iron can be used for uniformly gapped soft-magnetic cores. © 2019 Elsevier B.V.