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Theoretical investigation of interstellar C-C-O and C-O-C bonding backbone molecules
No full textThere are numerous complex organic molecules containing carbon and oxygen atoms which show either C-C-O or C-O-C bonding backbone. This paper examines altogether 51 C-C-O and C-O-C bonding backbone molecules from ten different isomeric groups ( C2H2O, C3H2O, C2H4O, C2H4O2, C3H4O, C2H6O, C2H6O2, C3H6O, C3H6O2, C3H8O) to summarize the present astronomical status of these molecules. Accurate calculations of enthalpy of formation of these molecules show that the isomers with C-C-O backbone are more stable than the C-O-C backbone. Interestingly, a detailed analysis of relevant astromolecules indicates that most of the observed astromolecules have the C-C-O backbone. As a matter of fact, of all the molecules examined in this study, 80% of the astronomically observed species have the C-C-O backbone while only 20% have the C-O-C backbone. In general, interstellar abundance of a molecule is controlled by some factors such as kinetics, formation and destruction pathways, thermodynamics etc. A proper consideration of these factors could explain the observed abundances of these molecules. All these possible key factors are discussed in this paper
One-pot synthesis of Mn3O4/graphitic carbon nanoparticles for simultaneous nanomolar detection of Pb(II), Cd(II) and Hg(II)
No full textIn this paper, a facile one-step sucrose-nitrate decomposition method has been proposed to synthesis Mn3O4 nanoparticles (Mns)/graphitic carbon. The prepared material has been characterized by X-ray diffraction, Fourier transform infrared spectrometer, surface area analysis and transmission electron microscopy. The prepared Mns/graphitic carbon is drop-casted on glassy carbon electrode to allow the fabrication of electrochemical sensors for the simultaneous detection of Pb(II), Cd(II) and Hg(II) at nanomolar (nM) levels in aqueous solutions via differential pulse anodic stripping voltammetry. The proposed Mns/graphitic carbon sensors exhibit a wide linear range from 20 to 680 nM towards the simultaneous sensing of Cd(II), Pb(II) and Hg(II), and the corresponding limits of detection were found to be 0.48 x 10(-11), 9.66 x 10(-11) and 0.51 x 10(-11) M, respectively. The practical application of the proposed sensor is evaluated within a real battery, industrial and chrome plating effluents
Simplifying large spin bootstrap in Mellin space
No full textWe set up the conventional conformal bootstrap equations in Mellin space and analyse the anomalous dimensions and OPE coefficients of large spin double trace operators. By decomposing the equations in terms of continuous Hahn polynomials, we derive explicit expressions as an asymptotic expansion in inverse conformal spin to any order, reproducing the contribution of any primary operator and its descendants in the crossed channel. The expressions are in terms of known mathematical functions and involve generalized Bernoulli (Norlund) polynomials and the Mack polynomials and enable us to derive certain universal properties. Comparing with the recently introduced reformulated equations in terms of crossing symmetric tree level exchange Witten diagrams, we show that to leading order in anomalous dimension but to all orders in inverse conformal spin, the equations are the same as in the conventional formulation. At the next order, the polynomial ambiguity in the Witten diagram basis is needed for the equivalence and we derive the necessary constraints for the same
Phase Retrieval From Binary Measurements
No full textWe consider the problem of signal reconstruction from quadratic measurements that are encoded as +1 or -1 depending on whether they exceed a predetermined positive threshold or not. Binary measurements are fast to acquire and inexpensive in terms of hardware. We formulate the problem of signal reconstruction using a consistency criterion, wherein one seeks to find a signal that is in agreement with the acquired measurements. To enforce consistency, we construct a convex cost using a one-sided quadratic penalty and minimize it using an iterative accelerated projected gradient-descent technique. The projected gradient-descent (PGD) scheme reduces the cost function in each iteration, whereas incorporating momentum into PGD, notwithstanding the lack of such a descent property, exhibits faster convergence than PGD empirically. We refer to the resulting algorithm as binary phase retrieval (BPR). Considering additive white noise contamination prior to quantization, we also derive the Cramer-Rao Bound (CRB) for the binary encoding model. Experimental results demonstrate that the BPR algorithm yields a signal-to-reconstruction error ratio (SRER) of approximately 25 dB in the absence of noise. In the presence of noise prior to quantization, the SRER is within 2 to 3 dB of the CRB
Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali-Ion Batteries
No full textWe discuss here a unique flexible non-carbonaceous layered host, namely, metal titanium niobates (M-Ti-niobate, M: Al3+, Pb2+, Sb3+, Ba2+, Mg2+), which can synergistically store both lithium ions and sodium ions via a simultaneous intercalation and alloying mechanisms. M-Ti-niobate is formed by ion exchange of the K+ ions, which are specifically located inside galleries between the layers formed by edge and corner sharing TiO6 and NbO6 octahedral units in the sol-gel synthesized potassium titanium niobate (KTiNbO5). Drastic volume changes (approximately 300-400%) typically associated with an alloying mechanism of storage are completely tackled chemically by the unique chemical composition and structure of the M-Ti-niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50-75% of total K+) in the M-Ti-niobate, an efficient alloying reaction takes place directly with ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M-Ti-niobate can be cycled over a wide voltage range (as low as 0.01V) and displays remarkably stable Li+ and Na+ ion cyclability (>2 Li+/Na+ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms is also studied within the density functional theory (DFT) framework. DFT expectedly shows a very small variation in the volume of Al-titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively support the occurrence of the alloying process of Li ions with the Al ions along with the intercalation process during discharge. The M-Ti-niobates studied here demonstrate a paradigm shift in chemical design of electrodes and will pave the way for the development of a multitude of improved electrodes for different battery chemistries
Unified nonlocal rational continuum models developed from discrete atomistic equations
No full textIn this paper, a unified nonlocal rational continuum enrichment technique is presented for improving the dispersive characteristics of some well known classical continuum equations on the basis of atomistic dispersion relations. This type of enrichment can be useful in a wide range of mechanical problems such as localization of strain and damage in many quasibrittle structures, size effects in microscale elastoplasticity, and multiscale modeling of materials. A novel technique of transforming a discrete differential expression into an exact equivalent rational continuum derivative form is developed considering the Taylor's series transformation of the continuous field variables and traveling wave type of solutions for both the discrete and continuum field variables. An exact equivalent continuum rod representation of the 1D harmonic lattice with the non-nearest neighbor interactions is developed considering the lattice details. Using similar enrichment technique in the variational framework, other useful higher-order equations, namely nonlocal rational Mindlin Herrmann rod and nonlocal rational Timoshenko beam equations, are developed to explore their nonlocal properties in general. Some analytical and numerical studies on the high frequency dynamic behavior of these novel nonlocal rational continuum models are presented with their comparison with the atomistic solutions for the respective physical systems. These enriched rational continuum equations have crucial use in studying high-frequency dynamics of many nano-electro-mechanical sensors and devices, dynamics of phononic metamaterials, and wave propagation in composite structures. These new models can help to circumvent the biggest problem regarding size and time restrictions in many atomistic simulations. (C) 2017 Elsevier Ltd. All rights reserved
Hypersonic shock tunnel studies of Edney Type III and IV shock interactions
No full textOf all the possible outcomes of the shock interaction problem, Edney Type-III and Type-IV are considered to be of great importance as they lead to high heat transfer rates on the surface in the vicinity of the interaction. The enhancement in heat transfer occurs because of shear layer attachment in Type III interaction and impingement of supersonic jet in Type-IV interaction. In this study, unsteady nature of these interactions is studied in conventional shock tunnel at moderate enthalpy condition of 1.07 Mj/kg at flow Mach number of 5.62. A hemispherical model, 50 mm in diameter, mounted with thin film Platinum gauges is used along with a 25 wedge to serve as a shock generator. The schlieren images are captured along with the surface convective heat transfer rate measurements for the analysis of flowfield over the model during the test time. The pixel intensity scan is performed along several lines running horizontally to estimate the steadiness of the flowfield. These are correlated with the heat transfer rate measurements to understand the non-steady nature of the interaction during the small test times offered by the shock tunnel. (C) 2017 Elsevier Masson SAS. All rights reserved
Influence of substrate bias voltage on crystallographic structure, optical and electronic properties of Al/(Ta2O5)(0.85)(TiO2)(0.15)/p-Si MIS Schottky barrier diodes fabricated by dc magnetron sputtering
No full textThin films of (Ta2O5)(0.85)(TiO2)(0.15) were prepared on p-Si and quartz substrates by reactive magnetron sputtering and the influence of substrate bias voltage (V-b) on their structural and electrical properties was studied. The crystal structure of the prepared films was elucidated by X-ray diffraction (XRD) studies. The structure of the as deposited films was found to be amorphous and the surface roughness of the films was found to be low. The crystallinity of the films was observed to be improved by increasing the substrate bias voltage. The XPS results revealed that the composition of the films were nearly stoichiometric with V-b at 0 V and -150 V. The optical properties of the films at various substrate bias voltages were also studied. The optical band gap of the films formed at various V-b values from 0 to -150 V decreased from 4.49 to 4.39 eV as revealed from the optical transmission spectra. The fabricated Al/(Ta2O5)(0.85)(TiO2)(0.15)/p-Si metal-insulator-semiconductor (MIS) Schottky diodes leakage currents at -1.5 V decreased from 4.65 x 10(-6) A (unbiased) to 3.73 x 10(-8) A (V-b = -100 V). On the other hand, the sample biased at V-b = -150 V exhibited an increase in leakage current (2.99 x 10(-4) A) when compared to all other prepared samples. Furthermore, the electrical parameters such as Schottky barrier height and ideality factor were calculated for the Al/(Ta2O5)(0.85)(TiO2)(0.15)/p-Si MIS Schottky structure and systematically investigated as a function of substrate bias voltage using current-voltage (I-V) and capacitance- voltage (C-V) characteristics
Advances in understanding combustion phenomena using non-premixed and partially premixed counterflow flames: A review
No full textCounterflow flames provide an ideal platform for understanding the flame structure and as a model to study the effect of physical and chemical perturbations on the flame structure. This article reviews the advances made in the understanding of combustion dynamics and chemistry through experimental and numerical studies in counterflow non-premixed and partially premixed flames. Key contributions on fundamental aspects such as extinction, ignition and effect of perturbations on the stability of diffusion flames are first summarized and analysed. The review then focuses on the progress made in the understanding of the effect of inert particles and flame suppressants on the flame characteristics. A review of detailed studies on edge flames facilitates further understanding of local quenching and re-ignition phenomena in highly turbulent flames. The influence of radiation model and unsteady flow-conditions on the flame kinetics and dynamics along with work on NOx kinetics has been discussed. The review also outlines that specific experiments need to be carried out over a wide range of conditions for further understanding and validation of numerical models
PLHINT: A knowledge-driven computational approach based on the intermolecular H bond interactions at the protein-ligand interface from docking solutions
No full textThe tendency of docking scoring functions to generate crystal close conformations of ligands bound to protein structures face limitations in not reproducing the exact crystal intermolecular contacts in dock poses. Intermolecular H bond contacts enumerated at the protein-docked ligand interface can be used to train scoring models and improve virtual screening performance. There is a need to incorporate additional knowledge of protein-ligand H bond contacts in extension to crystal contacts from docking solutions within the reproducibility efficiency of the docking program. A computational approach PLHINT (Protein-ligand H bond interaction pattern) is presented here which extracts intermolecular H bond interactions from native-like docked ligand poses, transform into the scoring scheme and apply over the virtual screening results of database molecules. The basic premise of the PLHINT approach is to score the most observed H bond patterns with the high score to achieve high recovery rates. Tested on ten diverse DUD-E benchmark datasets, the approach has demonstrated better overall performance and ligand enrichment competency over virtual screening results generated by three genetic algorithm-based docking programs viz. AutoDock Vina, FIexAID and PLANTS. Furthermore, the approach has successfully recovered the poor and random virtual screening results with better enrichments. (C) 2017 Elsevier Inc. All rights reserved