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Shiv Nadar University

(SoNS) School of Natural Sciences

The recently derived distributions for the scattering-matrix elements in quantum chaotic systems are not accessible in the majority of experiments, whereas the cross sections are. We analytically compute distributions for the off-diagonal cross sections in the Heidelberg approach, which is applicable to a wide range of quantum chaotic systems. Thus, eventually, we fully solve a problem that already arose more than half a century ago in compound-nucleus scattering. We compare our results with data from microwave and compound-nucleus experiments, particularly addressing the transition from isolated resonances towards the Ericson regime of strongly overlapping ones. © 2017 American Physical Society.

Physics

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Physical Review Letters

Distribution of Off-Diagonal Cross Sections in Quantum Chaotic Scattering: Exact Results and Data Comparison

The computation of the achievable sum rate for integer-forcing (IF) linear receivers requires the search for the shortest set of linearly independent lattice vectors (SIVP). Since SIVP is considered an NP-hard problem, we propose two approximations to the IF achievable sum rate. The first approximation is suitable for systems with two antennas at both transmitter and receiver (2 × 2 arrays) and is based on the analysis of the Gauss-Lagrange algorithm. The second approximation considers n × n array systems and is based on Minkowski's second theorem. Assuming a block-fading channel with Rayleigh distribution, we have derived the exact probability density function of both approximations. We have used these results to obtain the mean sum-rate, outage probability, and outage rate for uncorrelated fading channels. For the second approximation, the effect of channel correlation on these metrics was also analyzed. An exhaustive series of simulations have been conducted to assess the tightness and robustness of both solutions. © 1972-2012 IEEE.

IEEE Transactions on Communications

Approximate Sum Rate for Integer-Forcing Receiver

We consider distributed multiple-input–multiple-output (MIMO) antenna systems, along with their certain generalizations. We show that distributed MIMO configuration can be mapped to a semicorrelated (one side correlated) Wishart model. For a given set of large-scale fading parameters, associated with the path loss and shadow fading, we derive exact and closed-form results for the marginal density of eigenvalues of H†H (or HH†), where H is the channel matrix. We also obtain exact and closed-form expressions for the ergodic channel capacity with the aid of Meijer G-function. The ergodic capacity of semicorrelated Rayleigh fading channel follows as a special case. All analytical results are validated by comparison with Monte-Carlo simulations. © 2016, Springer Science+Business Media New York.

Wireless Personal Communications

On the Ergodic Capacity of Distributed MIMO Antenna Systems

3-D vertically aligned few-layered graphene (FLGs) nanoflakes synthesised using microwave plasma enhanced chemical vapour deposition are melt-impregnated with partially reduced graphene oxide-sulfur (PrGO-S) nanocomposites for use in lithium-sulfur batteries. The aligned structure and the presence of interconnected micro voids/channels in the 3-D FLG/PrGO-S electrodes serves as template not only for the high sulfur loading (up to 80 wt\%, areal loading of 1.2 mg cm−2) but also compensates for the volume changes occurring during charge-discharge cycles. The inter-connectivity of the electrode system further facilitates fast electronic and ionic transport pathways. Consequently, the binder-free 3-D FLG/PrGO-S electrodes display a high first-cycle capacity (1320 mA h g−1 at C/20), along with excellent rate capability of ∼830 mA h g−1 and 700 mA h g−1 at 2C and 5C rates, respectively. The residual functional groups of PrGO (-OH,-C-O-C-and-COOH) facilitate fast and reversible capture of Li+ ions while confining the polysulfide shuttles, thus, contributing to excellent cycling capability and retention capacity. The 3D electrodes demonstrate excellent capacity retention of ∼80\% (1040 mA h g−1 at C/10) over 350 charge-discharge cycles. Comparatively, the 2-D planar PrGO-S electrodes displayed poor electronic conductivity and can only provide 560 mA h g−1 after 150 cycles, thereby further highlighting the vital role of the electrode morphology in improving the electrochemical performance of Li-S batteries. © The Royal Society of Chemistry.

Sustainable Energy and Fuels

3-D vertically aligned few layer graphene-partially reduced graphene oxide/sulfur electrodes for high performance lithium-sulfur batteries

In this article, we report the modification of the electronic and magnetic properties of few-layered graphene (FLG) nanoflakes by nitrogen functionalization carried out using radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) and electron cyclotron resonance (ECR) plasma processes. Even though the rf-PECVD N2 treatment led to higher N-doping levels in the FLG (4.06 atomic \%) as compared to the ECR process (2.18 atomic \%), the ferromagnetic behavior of the ECR FLG (118.62 × 10-4 emu/g) was significantly higher than that of the rf-PECVD FLG (0.39 × 10-4 emu/g) and pristine graphene (3.47 × 10-4 emu/g). Although both plasma processes introduce electron-donating N atoms into the graphene structure, distinct dominant nitrogen bonding configurations (pyridinic, pyrrolic) were observed for the two FLG types. Whereas the ECR plasma introduced more sp2-type nitrogen moieties, the rf-PECVD process led to the formation of sp3-coordinated nitrogen functionalities, as confirmed through Raman measurements. The samples were further characterized using X-ray absorption near-edge spectroscopy (XANES), and X-ray and ultraviolet photoelectron spectroscopies revealed an increased electronic density of states and a significantly higher concentration of pyrrolic groups in the rf-PECVD samples. Because of the formation of reactive edge structures and pyridinic nitrogen moieties, the ECR-functionalized FLG samples exhibited highest saturation magnetization behavior with the lowest field hysteretic features. In comparison, the rf-PECVD samples displayed the lowest saturation magnetization owing to the disappearance of magnetic edge states and formation of stable nonradical-type defects in the pyrrole type structures. Our experimental results thus provide new evidence regarding the control of the magnetic and electronic properties of few-layered graphene nanoflakes through control of the plasma-processing route. © 2017 American Chemical Society.

Journal of Physical Chemistry C

Tuning the Electronic and Magnetic Properties of Nitrogen-Functionalized Few-Layered Graphene Nanoflakes

Catalytic cerium chloride was found to activate 2-iodoxybenzoic acid (IBX) for the oxidative dehydrogenation of tetrahydroisoquinolines, tetrahydro-β-carbolines, and thiazolidines to their dehydrogenated and aromatic forms at room temperature in moderate to excellent yields. The robustness of the protocol was demonstrated by scaling up the reactions to multigram quantities. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Chemistry

European Journal of Organic Chemistry

Cerium Chloride Catalyzed, 2-Iodoxybenzoic Acid Mediated Oxidative Dehydrogenation of Multiple Heterocycles at Room Temperature

We study the stability of drum-shaped transition metal (TM)-doped boron clusters, M@Bn with n = 14 and 16, and M = 3d, 4d, and 5d TM atom using ab initio calculations. Our results show that drum-shaped M@B14 clusters are favored for M = Cr, Mn, Fe, Co, and Ni, while in other cases, open conical or bowl shaped structures become more favorable. The isoelectronic Ni@B14 and Co@B14- clusters have large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps and these are magic clusters. Their stability has been correlated with the occurrence of magic behavior with 24 valence electrons in a disk jellium model, while for Fe@B14 case the drum structure is deformed and the stability occurs at 22 delocalized valence electrons. The bonding nature in these clusters has been studied by analyzing the electron density at bond and ring critical points, the Laplacian distribution of the electron density, the electron localization function, the source function, and electron localization-delocalization indices, all of which suggest two- and three-center σ bonding within and between the two B7 rings, respectively, and hybridization between the TM d orbitals and the π bonded molecular orbitals of the drum. The infrared and Raman spectra of these magic clusters show all real frequencies, suggesting the dynamical stability of the drum-shaped structures. There is a low frequency mode associated with the M atom. Results of the electronic spectra of the anion clusters are also presented that may help to identify these species in future experiments. Further, we discuss the stability of 24 delocalized valence electron systems Mn@B16 anion, Fe@B16, Co@B16 cation, and other related clusters. Assembly of Co@B14 clusters has been shown to stabilize a carbon nanotube-like nanotube of boron with Co atomic nanowire inside while a nanotube of boron with triangular network has been obtained with the assembly of Fe@B16 drum-shaped clusters. Both the nanotubes are metallic. © 2017 American Chemical Society.

Center for Informatics

Electronic Origin of the Stability of Transition-Metal-Doped B14 Drum-Shaped Boron Clusters and Their Assembly into a Nanotube

Lignin is an amorphous biopolymer consisting of hydroxyphenyl propane units, which are interlinked with ether and biphenyl linkages. The widespread abundance and variation in the substitution of phenolic units in the nature of plant species present them as a viable source for phenolic raw materials. This chapter aims to list the major phenolic components available from lignin and its utility as a synthon for benzoxazine monomer synthesis. The presence of additional functionalities in the monomer dictates the polymer properties and its utility in various applications. © 2017 Elsevier Inc. All rights reserved.

Advanced and Emerging Polybenzoxazine Science and Technology

Lignin-Based Phenols: Potential Feedstock for Renewable Benzoxazines

Using thermodynamic measurements, neutron diffraction, nuclear magnetic resonance and muon spin relaxation, we establish putative quantum spin-liquid behavior in Ba 3 InIr 2 O 9 , where unpaired electrons are localized on mixed-valence Ir 2 O 9 dimers with Ir 4.5+ ions. Despite the antiferromagnetic Curie-Weiss temperature on the order of 10 K, neither long-range magnetic order nor spin freezing are observed down to at least 20mK, such that spins are short-range correlated and dynamic over nearly three decades in temperature. Quadratic power-law behavior of both the spin-lattice relaxation rate and specific heat indicates the gapless nature of the ground state. We envisage that this exotic behavior may be related to an unprecedented combination of the triangular and buckled honeycomb geometries of nearest-neighbor exchange couplings in the mixed-valence setting.

Physical Review B

Persistent low-temperature spin dynamics in the mixed-valence iridate Ba3InIr2O9

The acid/base-catalysed Kemp elimination of 5-nitro-benzisoxazole forming 2-cyano-4-nitrophenol has long served as a design platform of enzymes with non-natural reactions, providing new mechanistic insights in protein science. Here we describe an alternative concept based on redox catalysis by P450-BM3, leading to the same Kemp product via a fundamentally different mechanism. QM/MM computations show that it involves coordination of the substrate's N-atom to haem-Fe(II) with electron transfer and concomitant N-O heterolysis liberating an intermediate having a nitrogen radical moiety Fe(III)-N· and a phenoxyl anion. Product formation occurs by bond rotation and H-transfer. Two rationally chosen point mutations cause a notable increase in activity. The results shed light on the prevailing mechanistic uncertainties in human P450-catalysed metabolism of the immunomodulatory drug leflunomide, which likewise undergoes redox-mediated Kemp elimination by P450-BM3. Other isoxazole-based pharmaceuticals are probably also metabolized by a redox mechanism. Our work provides a basis for designing future artificial enzymes. © The Author(s) 2017.