Metallo-Anti-aromatic Al4Na4 and Al4Na3- compounds: A theoretical investigation

We propose a theoretical investigation in this paper to understand the bonding and structural properties of neutral Al4Na4 and anion Al4Na3- clusters. We show that the Al4 species in Al4Na4 and Al4Na3- clusters is a rectangular planar structure with alternate pi-bonds and hence satisfying the basic criteria for anti-aromaticity. We prove that the Al4Na4 and Al4Na3- clusters are metallo-anti-aromatic compounds

Structural, electronic and bonding properties of zeolite Sn-Beta: A periodic density functional theory study

The structural, electronic and the bonding properties of the Sn-BEA are investigated by using the periodic density functional theory. Each of the 9 different T-sites in the BEA were substituted by the Sn atom and all the 9 geometries were completely optimized using the plane wave basis set in conjunction with the ultra-soft pseudopotential. On the basis of the structural and the electronic properties, it has been demonstrated that the substitution of the Sn atom in the BEA framework is an endothermic process and hence the incorporation of the Sn in the BEA is limited. The lowest unoccupied molecular orbitals (LUMO) energies have been used to characterize the Lewis acidity of each T-site. On the basis of the relative cohesive energy and the LUMO energy, T2 site is shown to be the most favorable site for the substitution of Sn atom in the BEA framework.Comment: 17 pages, 5 figures, 2 Table

Monitoring membrane protein conformational heterogeneity by fluorescence lifetime distribution analysis using the maximum entropy method

Due to the inherent difficulty in crystallizing membrane proteins, approaches based on fluorescence spectroscopy have proved useful in elucidating their conformational characteristics. The ion channel peptide gramicidin serves as an excellent prototype for monitoring membrane protein conformation and dynamics due to a number of reasons. We have analyzed conformational heterogeneity in membrane-bound gramicidin using fluorescence lifetime distribution analysis of tryptophan residues by the maximum entropy method (MEM). MEM represents a model-free and robust approach for analyzing fluorescence lifetime distribution. In this paper, we show for the first time, that fluorescence lifetime distribution analysis using MEM could be a convenient approach to monitor conformational heterogeneity in membrane-bound gramicidin in particular and membrane proteins in general. Lifetime distribution analysis by MEM therefore provides a novel window to monitor conformational transitions in membrane proteins

Visualization of Single Molecules Building a Viral Capsid Protein Lattice through Stochastic Pathways

Direct visualization of pathways followed by single molecules while they spontaneously self-assemble into supramolecular biological machines may provide fundamental knowledge to guide molecular therapeutics and the bottom-up design of nanomaterials and nanodevices. Here, high-speed atomic force microscopy is used to visualize self-assembly of the bidimensional lattice of protein molecules that constitutes the framework of the mature human immunodeficiency virus capsid. By real-time imaging of the assembly reaction, individual transient intermediates and reaction pathways followed by single molecules could be revealed. As when assembling a jigsaw puzzle, the capsid protein lattice is randomly built. Lattice patches grow independently from separate nucleation events whereby individual molecules follow different paths. Protein subunits can be added individually, while others form oligomers before joining a lattice or are occasionally removed from the latter. Direct real-time imaging of supramolecular self-assembly has revealed a complex, chaotic process involving multiple routes followed by individual molecules that are inaccessible to bulk (averaging) techniques

Power-law corrections to entanglement entropy of horizons

We re-examine the idea that the origin of black-hole entropy may lie in the entanglement of quantum fields between inside and outside of the horizon. Motivated by the observation that certain modes of gravitational fluctuations in a black-hole background behave as scalar fields, we compute the entanglement entropy of such a field, by tracing over its degrees of freedom inside a sphere. We show that while this entropy is proportional to the area of the sphere when the field is in its ground state, a correction term proportional to a fractional power of area results when the field is in a superposition of ground and excited states. The area law is thus recovered for large areas. Further, we identify location of the degrees of freedom that give rise to the above entropy.Comment: 16 pages, 6 figures, to appear in Phys. Rev.

Seasonal evolution of oceanic upper layer processes in the northern Bay of Bengal following a single Argo float

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(10), (2019): 5369-5377, doi: 10.1029/2019GL082078.Seasonal evolution of the barrier layer (BL) and temperature inversion in the northern Bay of Bengal and their role on the mixed layer temperature (MLT) is examined using observations from a single Argo during December 2013 to July 2017. During fall, low salinity at surface generates BL in this region. It thickens to almost 80 m in winter enhanced by deepening of isothermal layer depth due to remote forcing. During winter, surface cooling lowers near‐surface temperature, and thus, the subsurface BL experiences a significant temperature inversion (~2.5 °C). This temperature inversion diffuses to distribute heat within ML and surface heating begins deep penetration of shortwave radiation through ML during spring. Hence, the ML becomes thermally well stratified, resulting in the warmest MLT. The Monin‐Obukhov length attains its highest value during summer indicating wind dominance in the ML. During spring and fall, upper ocean gains heat allowing buoyancy to dominate over wind mixing.A. S. and S. S. thank financial support from Space Application Centre (SAC), Indian Space Research Organization (ISRO), Government of India (Grant: SAC/EPSA/4.19/2016). This study was also supported by the first phase of Ministry of Earth Sciences (MoES), Government of India grant to establish a Bay of Bengal Coastal Observatory (BOBCO) at IITBBS (Grant: RP088). Authors acknowledged NCPOR Contribution number J ‐ 03/2019‐20 for this work. The authors are grateful to the reviewers and the Editor for constructive suggestions. The figures are generated using Matlab. The data source and availability are given in the Text S1.2019-10-2

Pion parameters in nuclear medium from chiral perturbation theory and virial expansion

We consider two methods to find the effective parameters of the pion traversing a nuclear medium. One is the first order chiral perturbation theoretic evaluation of the pion pole contribution to the two-point function of the axial-vector current. The other is the exact, first order virial expansion of the pion self-energy. We find that, although the results of chiral perturbation theory are not valid at normal nuclear density, those from the virial expansion may be reliable at such density. The latter predicts both the mass-shift and the in-medium decay width of the pion to be small, of about a few MeV.Comment: 9 Pages RevTex, 3 eps figure

Pion propagation in real time field theory at finite temperature

We describe how the thermal counterpart of a vacuum two-point function may be obtained in the real time formalism in a simple way by using directly the $2\times 2$ matrices that different elements acquire in this formalism. Using this procedure we calculate the analytic (single component) thermal amplitude for the pion pole term in the ensemble average of two axial-vector currents to two loops in chiral perturbation theory. The general expressions obtained for the effective mass and decay constants of the pion are evaluated in the chiral and the nonrelativistic limits. We also investigate the effect of massive states on these effective parameters.Comment: 17 pages TeX and 9 eps figure

Cherenkov Radiation from e+e−e^+e^- Pairs and Its Effect on νe\nu_e Induced Showers

We calculate the Cherenkov radiation from an $e^+e^-$ pair at small separations, as occurs shortly after a pair conversion. The radiation is reduced (compared to that from two independent particles) when the pair separation is smaller than the wavelength of the emitted light. We estimate the reduction in light in large electromagnetic showers, and discuss the implications for detectors that observe Cherenkov radiation from showers in the Earth's atmosphere, as well as in oceans and Antarctic ice.Comment: Final version, with minor changes, to appear in PRD. 5 pages with 4 figure