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Shiv Nadar University

(SoNS) School of Natural Sciences

The ratio of two consecutive level spacings has emerged as a very useful metric in investigating universal features exhibited by complex spectra. It does not require the knowledge of density of states and is therefore quite convenient to compute in analyzing the spectrum of a general system. The Wigner-surmise-like results for the ratio distribution are known for the invariant classes of Gaussian random matrices. However, for the crossover ensembles, which are useful in modeling systems with partially broken symmetries, corresponding results have remained unavailable so far. In this work, we derive exact results for the distribution and average of the ratio of two consecutive level spacings in the Gaussian orthogonal to unitary crossover ensemble using a 3×3 random matrix model. This crossover is useful in modeling time-reversal symmetry breaking in quantum chaotic systems. Although based on a 3×3 matrix model, our results can also be applied in the study of large spectra, provided the symmetry-breaking parameter facilitating the crossover is suitably scaled. We substantiate this claim by considering Gaussian and Laguerre crossover ensembles comprising large matrices. Moreover, we apply our result to investigate the violation of time-reversal invariance in the quantum kicked rotor system. © 2020 American Physical Society.

Physics

Fulltext

Physical Review E

Distribution of the ratio of two consecutive level spacings in orthogonal to unitary crossover ensembles

Ionic liquids (ILs) are an important class of emerging compounds, owing to their widespread industrial applications in high-performance lubricants for food and cellulose processing, despite their toxicity to living organisms. It is believed that this toxicity is related to their actions on the cellular membrane. Hence, it is vital to understand the interaction of ILs with cell membranes. Here, we report on the effects of an imidazolium-based IL, 1-decyl-3-methylimidazolium tetrafluoroborate (DMIM[BF4]), on the microscopic dynamics of a membrane formed by liver extract lipid, using quasielastic neutron scattering (QENS). The presence of significant quasielastic broadening indicates that stochastic molecular motions of the lipids are active in the system. Two distinct molecular motions, (i) lateral motion of the lipid within the membrane leaflet and (ii) localized internal motions of the lipid, are found to contribute to the QENS broadening. While the lateral motion could be described assuming continuous diffusion, the internal motion is explained on the basis of localized translational diffusion. Incorporation of the IL into the liver lipid membrane is found to enhance the membrane dynamics by accelerating both lateral and internal motions of the lipids. This indicates that the IL induces disorder in the membrane and enhances the fluidity of lipids. This could be explained on the basis of its location in the lipid membrane. Results are compared with various other additives and we provide an indication of a possible correlation between the effects of guest molecules on the dynamics of the membrane and its location within the membrane. © Copyright © 2020 Sharma, Ghosh, García Sakai and Mukhopadhyay.

World University root node

Frontiers in Chemistry

Enhanced Microscopic Dynamics of a Liver Lipid Membrane in the Presence of an Ionic Liquid

Single-crystal x-ray diffraction, density-functional band-structure calculations and muon spin relaxation ($\mu$SR) are used to probe pressure evolution of the triangular spin-liquid candidate YbMgGaO$_4$. The rhombohedral crystal structure is retained up to at least 10 GPa and shows a nearly uniform compression along both in-plane and out-of-plane directions, whereas local distortions caused by the random distribution of Mg$^{2+}$ and Ga$^{3+}$ remain mostly unchanged. The $\mu$SR data confirm persistent spin dynamics up to 2.6 GPa and down to 250 mK with no change in the muon relaxation rate. Longitudinal-field $\mu$SR reveals power-law behavior of the spin-spin autocorrelation function, both at ambient pressure and upon compression.

Physical Review Research

Persistent spin dynamics in the pressurized spin-liquid candidate YbMgGaO 4

Growth of Heusler alloy films through techniques other than conventional physical vapor deposition presents a challenge for spintronic materials research. In this study an electrochemical deposition approach for these alloys is demonstrated in which sub-micron thickness control can be achieved. By using magneto optic Kerr effect and Kerr microscopy measurements a systematic study of surface magnetization reversal behavior of these films is presented. The results demonstrate that the growth of sub-micron films of Co2FeSn leads to significant enhancement in magneto optic Kerr rotation. A large Kerr rotation value up to 300 mdeg was observed for thin films of thickness ∼200 nm. The modified scheme reported here opens up a path for exploration of electrochemical method as a facile route for fabricating Heusler alloys with improved surface property. © 2020 Elsevier Ltd

Materials Today Communications

Electrodeposited Heusler alloy films with enhanced magneto-optical property

Neural codes are collective activity of the neurons which are electrically active cells in our brain. In this paper, We study the openness and closeness of the convex neural codes in one dimension. We discuss the possibilities of a convex code to be realized in dimension 1. That is conditions for the minimal embedding dimension of a neural code to be 1. © 2020 Author(s).

Mathematics

AIP Conference Proceedings

Convex realizations of neural codes in one dimension

The potential biomedical applications of ionic liquids (ILs) need an understanding of the effects of the molecules in living organisms. Researchers are still exploring the molecular level description of this interaction. Any foreign molecule affecting a living organism has to interact first with the outer layer of a cell, which is mainly composed of a phospholipid bilayer. Here, to understand the membrane-IL interaction, a zwitterionic lipid has been chosen to prepare multilamellar vesicles (MLVs) which are the model cellular membranes. Small angle x-ray diffraction study has revealed the change in inter-bilayer spacing in the presence of imidazolium based ILs in the ripple phase of the bilayer. The investigation was extended further to understand the role of a negatively charged lipid in the MLVs. This study indicates that the cations of an IL screen electrostatic repulsion between the negatively charged lipids and induce the formation of a vesicle. © 2020 American Institute of Physics Inc.. All rights reserved.

Effect of ionic liquids on the structures of ripple phases of model cellular membranes

Here, an excellent cavitation erosion-corrosion resistance of stainless steel using a novel severe surface deformation technique, reciprocating friction processing (RFP) was demonstrated. The RFP treated stainless steel showed nano-grained, nano-twinned microstructure along with high dislocation density. The RFP treated steel significantly surpassed the performance of advanced structural materials including high entropy alloy (Al0.1CoCrFeNi) and complex concentrated alloy (SiC reinforced Al0.1CoCrFeNi), demonstrating the lowest cavitation erosion and cavitation erosion-corrosion rates for this class of materials. The RFP treated steel demonstrated outstanding corrosion behavior in 3.5\% NaCl solution as well. The unusual performance of RFP treated steel is attributed to its excellent mechanical strength and strong passivating behavior. © 2020 Elsevier B.V.

Mechanical Engineering

(SoE) School of Engineering

Wear

Cavitation erosion-corrosion resilient surfaces through reciprocating friction processing

We investigate the spectral fluctuations and electronic transport properties of chaotic mesoscopic cavities using Kwant, an open source Python programming language based package. Discretized chaotic billiard systems are used to model these mesoscopic cavities. For the spectral fluctuations, we study the ratio of consecutive eigenvalue spacings, and for the transport properties, we focus on Landauer conductance and shot noise power. We generate an ensemble of scattering matrices in Kwant, with desired number of open channels in the leads attached to the cavity. The results obtained from Kwant simulations, performed without or with magnetic field, are compared with the corresponding random matrix theory predictions for orthogonally and unitarily invariant ensembles. These two cases apply to the scenarios of preserved and broken time-reversal symmetry, respectively. In addition, we explore the orthogonal to unitary crossover statistics by varying the magnetic field and examine its relationship with the random matrix transition parameter. © 2020 Author(s).

Chaos

Electronic transport in chaotic mesoscopic cavities: A Kwant and random matrix theory based exploration

Superhydrophobic surfaces with high adhesion have attracted huge attention in recent research works due to their versatile applications including transportation of microdroplet without any loss. Modification of metallic surfaces to achieve such properties is important to extend their applications. Especially, the superhydrophobic surfaces with very low bacterial adhesion have attracted intense attention in medical, food, and pharmaceutical industries. Here, we have fabricated different micropatterns on aluminium surfaces using a simple and cost-effective micro-imprinting technique. The surface chemistry was modified through a coating of low surface energy material 1H, 1H, 2H, 2H-perfluorooctyl-trichlorosilane (FOTS) using vapor deposition technique. Surface morphology of the samples was investigated using scanning electron microscopy (SEM) and contact profilometer. Results show a significant influence of the surface morphology on the wetting, adhesion and anti-bacterial properties. Surfaces composed of discrete micropillars showed higher de-wetting compared to surface containing continuous zig-zag micro lines even despite lower roughness factor. However, the opposite trend was observed in case of adhesion. These results are explained based on wetting state and difference in liquid-air interface pinning. Further, the developed samples showed higher water-retaining ability compared to rose-petal along with superhydrophobicity. The surface with micropillar structures with higher roughness factor exhibited improved non-fouling behavior which has been quantified by spot assay and atomic force microscopy (AFM). This study opens up the possibility of fabricating multifunctional metal surfaces on a large scale by a cost-effective, environment friendly and easily scalable processing route. © 2020 IOP Publishing Ltd.

Surface Topography: Metrology and Properties

Effect of topography and chemical treatment on the hydrophobicity and antibacterial activities of micropatterned aluminium surfaces

Direct synthesis of a nano-structured carbon hybrid consisting of vertically aligned carbon nanograsses on top of boron-doped nanocrystalline diamond is demonstrated and the carbon hybrid is further applied as an electrode material for the fabrication of supercapacitors. The hybrid film combines the dual advantages of sp2 (carbon nanograss) and sp3 (nanocrystalline diamond) bonded carbon, possessing not only the excellent electrical characteristics of sp2 carbon but also the exceptional electrochemical stability of sp3 carbon. As a result, the specific capacitance of the as-prepared hybrid material reaches up to 0.4 F cm-2, one of the highest reported in diamond-based supercapacitors. The entire electrochemical results exhibit enhanced electron transfer efficiency with remarkable stability of 95\% of capacitance retention even after 10 000 cycles.