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A non-equilibrium thermodynamic model for viscoplasticity and damage: Two temperatures and a generalized fluctuation relation
No full textUtilizing a non-equilibrium thermodynamic setting that involves two temperatures, we present a model for ductile and brittle damage. The thermodynamic system consists of two interacting subsystems configurational and kinetic-vibrational. While the kinetic-vibrational subsystem describes fast degrees-of-freedom (DOFs) of ordinary thermal vibration, the configurational subsystem includes the slower DOFs pertaining to a slew of configurational rearrangements that characterize elasto-visco-plasticity and damage, e.g. dislocation motion, lattice stretching, void nucleation, void growth and micro-crack formation. Following statistical mechanics, an expression for the entropy of a plastically deforming metal with growing voids and micro-cracks is derived. Subsequent application of the first and second laws of thermodynamics, suitably modified for the two-temperature system, yields coupled evolution rules for dislocation density, void volume fraction, micro-crack density etc. A modified flow rule for dilatant plasticity and evolution equations for the two temperatures are also derived. Even when the two subsystems are strongly coupled, we show that a splitting of energy and entropy is feasible and that the notion of two temperatures conforms with such splitting. We conduct numerical experiments on both brittle and ductile damage to assess the predictive features of the model and validate the results against available experimental evidence. Finally, a generalized fluctuation relation is put forth for deformations with extremely high strain rates. This leads to an entirely new procedure for constitutive closure, providing valuable insights into the emergent pseudo-inertial aspects of the evolving thermodynamic states
Mycobacterium tuberculosis Rv0366c-Rv0367c encodes a non-canonical PezAT-like toxin-antitoxin pair
No full textToxin-antitoxin (TA) systems are ubiquitously existing addiction modules with essential roles in bacterial persistence and virulence. The genome of Mycobacterium tuberculosis encodes approximately 79 TA systems. Through computational and experimental investigations, we report for the first time that Rv0366c-Rv0367c is a non-canonical PezAT-like toxin-antitoxin system in M. tuberculosis. Homology searches with known PezT homologues revealed that residues implicated in nucleotide, antitoxin-binding and catalysis are conserved in Rv0366c. Unlike canonical PezA antitoxins, the N-terminal of Rv0367c is predicted to adopt the ribbon-helix-helix (RHH) motif for deoxyribonucleic acid (DNA) recognition. Further, the modelled complex predicts that the interactions between PezT and PezA involve conserved residues. We performed a large-scale search in sequences encoded in 101 mycobacterial and 4500 prokaryotic genomes and show that such an atypical PezAT organization is conserved in 20 other mycobacterial organisms and in families of class Actinobacteria. We also demonstrate that overexpression of Rv0366c induces bacteriostasis and this growth defect could be restored upon co-expression of cognate antitoxin, Rv0367c. Further, we also observed that inducible expression of Rv0366c in Mycobacterium smegmatis results in decreased cell-length and enhanced tolerance against a front-line tuberculosis (TB) drug, ethambutol. Taken together, we have identified and functionally characterized a novel non-canonical TA system from M. tuberculosis
An HIV-1 Broadly Neutralizing Antibody from a Clade C-Infected Pediatric Elite Neutralizer Potently Neutralizes the Contemporaneous and Autologous Evolving Viruses
No full textBroadly neutralizing antibodies (bNAbs) have demonstrated protective effects against HIV-1 in primate studies and recent human clinical trials. Elite neutralizers are potential candidates for isolation of HIV-1 bNAbs. The coexistence of bNAbs such as BG18 with neutralization-susceptible autologous viruses in an HIV-1-infected adult elite controller has been suggested to control viremia. Disease progression is faster in HIV-1-infected children than in adults. Plasma bNAbs with multiple epitope specificities are developed in HIV-1 chronically infected children with more potency and breadth than in adults. Therefore, we evaluated the specificity of plasma neutralizing antibodies of an antiretroviral-naive HIV-1 clade C chronically infected pediatric elite neutralizer, AIIMS_330. The plasma antibodies showed broad and potent HIV-1 neutralizing activity with >87% (29/33) breadth, a median inhibitory dilution (ID50) value of 1,246, and presence of N160 and N332 supersite-dependent HIV-1 bNAbs. The sorting of BG505.SOSIP.664.C2 T332N gp140 HIV-1 antigen-specific single B cells of AIIMS_330 resulted in the isolation of an HIV-1 N332 supersite-dependent bNAb, AIIMS-P01. The AIIMS-P01 neutralized 67% of HIV-1 cross-clade viruses, exhibited substantial indels despite limited somatic hypermutations, interacted with native-like HIV-1 trimer as observed in negative stain electron microscopy, and demonstrated high binding affinity. In addition, AIIMS-P01 neutralized the coexisting and evolving autologous viruses, suggesting the coexistence of vulnerable autologous viruses and HIV-1 bNAbs in the AIIMS_330 pediatric elite neutralizer. Such pediatric elite neutralizers can serve as potential candidates for isolation of novel HIV-1 pediatric bNAbs and for understanding the coevolution of virus and host immune response. IMPORTANCE More than 50% of the HIV-1 infections globally are caused by clade C viruses. To date, there is no effective vaccine to prevent HIV-1 infection. Based on the structural information of the currently available HIV-1 bNAbs, attempts are under way to design immunogens that can elicit correlates of protection upon vaccination. Here, we report the isolation and characterization of an HIV-1 N332 supersite-dependent bNAb, AIIMS-P01, from a clade C chronically infected pediatric elite neutralizer. The N332 supersite is an important epitope and is one of the current HIV-1 vaccine targets. AIIMS-P01 potently neutralized the contemporaneous and autologous evolving viruses and exhibited substantial indels despite low somatic hypermutations. Taken together with the information on infant bNAbs, further isolation and characterization of bNAbs contributing to the plasma breadth in HIV-1 chronically infected children may help provide a better understanding of their role in controlling HIV-1 infection
Photochemical degradation affects the light absorption of water-soluble brown carbon in the South Asian outflow
No full textLight-absorbing organic aerosols, known as brown carbon (BrC), counteract the overall cooling effect of aerosols on Earth's climate. The spatial and temporal dynamics of their light-absorbing properties are poorly constrained and unaccounted for in climate models, because of limited ambient observations. We combine carbon isotope forensics (delta C-13) with measurements of light absorption in a conceptual aging model to constrain the loss of light absorptivity (i.e., bleaching) of water-soluble BrC (WS-BrC) aerosols in one of the world's largest BrC emission regions-South Asia. On this regional scale, we find that atmospheric photochemical oxidation reduces the light absorption of WS-BrC by similar to 84% during transport over 6000 km in the Indo-Gangetic Plain, with an ambient first-order bleaching rate of 0.20 +/- 0.05 day(-1) during over-ocean transit across Bay of Bengal to an Indian Ocean receptor site. This study facilitates dynamic parameterization of WS-BrC absorption properties, thereby constraining BrC climate impact over South Asia
A fine-scale state-space model to understand drivers of forest fires in the Himalayan foothills
No full textThe tropical forests situated in the Himalayan foothills (terai) experience frequent wildfires which can alter the vegetation structure and composition, challenging tiger conservation efforts in this region. Hence, there is a need for better understanding of the drivers of forest fire to aid efficient management, but these efforts are hampered by the deficiency of spatial and temporal data on fire incidences. Advancement in remote sensing technology provides an opportunity to understand the spatial and temporal patterns of wildfires in relation to anthropogenic, ecological, and environmental drivers. We used MODIS fire data from 2001 to 2015 to understand fire incidences in Valmiki Tiger Reserve (VTR), an important tiger habitat area in the Himalayan terai region. We analyzed fire incidences to understand monthly and inter-annual variation of fire incidences at two spatial scales: first, using only climatic variables considering VTR as a single spatial unit and the second, to understand the fire dynamics at 1 km(2) spatial resolution using climatic, ecological, and anthropogenic variables. The results show that fire incidences occurred from January to May, 88% of which occurred in March and April. Overall, different variables affected fire incidences in March and April for both the temporal models. Precipitation had a significant negative effect on fire incidences in both March and April, but temperature had a positive effect only in March. Similarly, the fine scale temporal model showed that while ecological (litter load, NPP) and anthropogenic (distance to villages and roads) variables influenced fire incidences in March, altitude and village area surrounding the forest affected fires in April. Litter input, distance to nearest villages, and village area had a nonlinear relationship with fire incidences indicating a few inconsistencies with the global patterns of fire with human activity. We show that the Sal dominated forests and terai grasslands at low altitudes (200 m), falling within a zone of 2.5-3 km from villages and with good road connectivity are more prone to fire. The fine-scale fire prediction map of VTR will be helpful to the Tiger Reserve management in developing appropriate strategies for the fire prone areas
Exfoliation of graphite as flexible SERS substrate with high dye adsorption capacity for Rhodamine 6G
No full textAdsorption is one of the most important processes in wastewater treatment, especially for dye removal. In addition to adsorption, there must be a vigilant technique, such as Surface Enhanced Raman spectroscopy (SERS), for detection of low concentration of dye molecules to detect water foiling. Herein, we report a simple, low cost, rapid and efficient technique for the production of exfoliated graphite (EG) under microwave irradiation at 800 W in 1 min, as excellent adsorption material for Rhodamine 6G (R6G) dye. The effect of adsorption process parameters such as pH, contact time, isotherm models (Langmuir and Freundlich) and kinetic models (pseudo-first and pseudo-second-order) on dye removal under aqueous solutions, were investigated. The maximum adsorption capacity for R6G dye is 212.72 (+/- 5.3) mg/g. Meanwhile compressing of EG, into a flexible graphite sheet (FGS) demonstrates responsive SEAS for R6G molecules up to detection limit of 10(-7) mol/L. However, with silver nanoparticle incorporation, the detection limit increases up to 10(-)(12) mol/L. Performance of flexible sheet checked over a month by rubbing sheet through paper and cloth doesn't have any impact on the synthesis of exfoliated graphite. Aging factor of the sheet also shows reproducible SEAS spectra after a month. These are the highest reported values fill today, for adsorption of R6G dye on Exfoliated graphite, with reasonable SEAS detection
ON EXTREME CONTRACTIONS AND THE NORM ATTAINMENT SET OF A BOUNDED LINEAR OPERATOR
No full textIn this paper we completely characterize the norm attainment set of a bounded linear operator between Hilbert spaces. In fact, we obtain two different characterizations of the norm attainment set of a bounded linear operator between Hilbert spaces. We further study the extreme contractions on various types of finite-dimensional Banach spaces, namely Euclidean spaces, and strictly convex spaces. In particular, we give an elementary alternative proof of the well-known characterization of extreme contractions on a Euclidean space, which works equally well for both the real and the complex case. As an application of our exploration, we prove that it is possible to characterize real Hilbert spaces among real Banach spaces, in terms of extreme contractions on their 2-dimensional subspaces
High-power, widely wavelength tunable, grating-free Raman fiber laser based on filtered feedback
No full textThe cascaded Raman fiber laser is a proven technology that provides wavelength agile high-power fiber lasers outside the rare-earth emission windows. However, conventional cascaded Raman fiber lasers lack wavelength agility due to the use of fixed wavelength fiber Bragg gratings. Recently, proposed cascaded Raman fiber lasers based on random distributed feedback have provided a grating-free solution enabling wavelength agility. With these lasers, wide wavelength tunability has been achieved. However, there are still limitations in scaling output power while maintaining high spectral purity of wavelength conversion. Spectral purity is characterized by the in-band power ratio, which is the ratio of the output power in the required wavelength to the total power. The origin of this limitation arises from the inability to efficiently terminate the Raman cascade at a specific wavelength with increasing power. In this Letter, we propose a novel filtered distributed feedback mechanism to terminate the Raman cascade at any desired wavelength, enabling power scaling with high spectral purity. Output power up to 28 W has been achieved with >85% in-band power ratio and >400 nm tuning range from 1118 to 1535 nm. (C) 2019 Optical Society of Americ
Geometry dependent crossover of Barkhausen statistics in iron thin films
No full textWe report the crossover of Barkhausen noise statistics upon a change in the measurement geometry. The behaviour is akin to the angle dependent critical to sub-critical crossover of avalanche statistics as present in avalanche models with random anisotropy directions. The samples studied were 15-25 nm thin films of iron, grown on (001) GaAs by pulsed laser ablation. Use of planar Hall effect as a probe for the magnetic state facilitated this work, which would be impractical to do in a MOKE setup. We compare our data with simulations of a random anisotropy Ising model, and demonstrate striking similarity between experimental and simulated avalanche size distributions. Further, through micromagnetic simulations, we conclude that crystallite misorientations were the origin of domain wall pinning in our system leading to Barkhausen noise
Kinetic study of Z-scheme C3N4/CuWO4 photocatalyst towards solar light inactivation of mixed populated bacteria
No full textIn the present work, Z-scheme composite C3N4/CuWO(4 )was synthesised by sol-gel method for the photocatalytic degradation of a mixed population of Gram-positive bacteria (S. attreus) and Gram-negative bacteria (E. coli). The effect of the photoinactivation was observed for two different types of bacteria in the same medium together and individually in the absence of the nutrients. The lattice structures and phase purities were determined by X-ray diffraction. For morphological and topographical features, SEM and TEM imaging were performed. The oxidation states of the elements and band edges of the semiconductor were determined by XPS and UPS, respectively. The lifetime of the charge carriers and band gap of the semiconductors were determined by time resolved florescence spectroscopy and diffused reflectance spectroscopy, respectively. The photocatalytic experiments were performed for different weight ratios of C3N4 and CuWO4. Scavenger experiments were performed to investigate the exact mechanism and major responsible radicals for photocatalysis. The rate constants and order of the inactivation reactions were obtained by power law kinetics. The rate followed by the inactivation for E. coli and S. aureus were analysed. For E. coli, the order of inactivation reaction is 1.15 while S. aureus inactivation reaction order is 0.9