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EFFECTIVE PROPERTY ESTIMATION OF CMC MINICOMPOSITES CONSIDERING POROSITY
No full textCeramic matrix composites (CMCs) are a promising subclass of composite materials suitable for high temperature applications. CMCs exhibit multiple damage mechanisms such as matrix cracking, interphase debonding, fiber sliding, fiber pullout, delaminations etc. Additionally, process induced defects such as matrix porosity exists at multiple length scales and has a considerable influence on the mechanical and failure behavior of CMCs. In the current work, the effect of intra-tow porosity, which exist at the micro-scale, on the mechanical behavior of CMCs has been investigated by numerical homogenization. Micro-scale response of 3 phase CMCs with intra tow pores has been obtained by finite element analysis based homogenization. Pores have been modeled as non-intersecting ellipsoids in a square unit cell representative of matrix material. The effective mechanical properties of porous matrix at the micro scale has been obtained from numerical homogenization, which are in good agreement with Mori-Tanaka mean field theory. The obtained matrix elastic properties have then been included in a three phase unit cell consisting of fiber, interphase and matrix representative of CMC microstructure. The effect of porosity volume fraction and aspect ratio on the effective elastic properties of the composite have been reported. Homogenization approach to model statistical distribution of pore size obtained from Xray computed tomography of CMC minicomposite has been proposed
Multilevel 24-Sided Polygonal Voltage-Space-Vector Structure Generation for an IM Drive Using a Single DC Source
No full textConventional two-level as well as multilevel voltage-source-inverter topologies with a hexagonal voltage-space vector structure generate low-order harmonics in the machine terminal voltages when operated beyond the linear modulation range in variable speed drive application. Progressing from hexagonal to a higher sided polygonal voltage-space-vector structure (VSVS) suppresses significant low-order harmonics throughout the modulation range. In addition, the linear modulation range will also be enhanced very near to the base speed. In this paper, for the first time, the generation of a multilevel 24-sided VSVS using a single dc source for induction-motor drives is proposed. A cascaded topology with a dc-source-fed flying-capacitor inverter and two low-voltage capacitor-fed H-bridge cells forms the power circuit. The features and advantages of the proposed scheme are validated through experimental results and discussions
Thermodynamic properties of MgGa2O4 and phase relations in the system Mg-Ga-O
No full textMaterials based on MgGa2O4 find use in microwave dielectrics, optoelectronics, spintronics and solid electrolytes for high-temperature fuel cells. For designing optimum processing conditions and evaluating interactions with other materials and environments, thermodynamic data and appropriate phase diagrams are required. As part of a larger systematic study on spinels with functional applications, thermodynamic properties of MgGa2O4 are determined in the temperature range from 875 to 1325 K using an electrochemical cell incorporating yttria-stabilized zirconia as the solid electrolyte. The Gibbs energy of formation of MgGa(2)O(4 )from its constituent binary oxides MgO with halite structure and beta-Ga2O3 with monoclinic structure is obtained: Delta G(f(ox))(0 )(+/- 135)/J mol(-1)= -39868-8.742 (T/K). The heat capacity of MgGa2O4 in the temperature range from 310 to 1200 K is measured by DSC. Both positive and negative deviations from Neumann-Kopp rule are seen in different temperature ranges. Derived from these measurements are the standard enthalpy of formation and standard entropy of MgGa2O4 at 298.15 K. The isothermal section of the phase diagram of the system Mg-Ga-O and oxygen potential-composition diagram at 1200 K are computed from thermodynamic data. (C) 2018 Elsevier B.V. All rights reserved
Characterization of elastic and electromechanical nonlinearities in piezoceramic plate actuators from vibrations of a piezoelectric-beam
No full textPiezoceramic actuators have been observed to exhibit nonlinear behaviour even when subjected to weak electric fields. The experimental observations necessitate the need for a nonlinear constitutive equation, to aptly describe the behaviour of the piezoelectric actuators. The nonlinear response could have been effected due to a nonlinear behaviour in the mechanical domain (nonlinear elastic behaviour), or due to a nonlinear electromechanical coupling, or due to a combination of both the nonlinear elastic behaviour and nonlinear electromechanical coupling. To locate the source of nonlinearity and to identify the nature of the nonlinearity, a two-step experimental procedure is proposed in this article, wherein experiments were conducted on a cantilever duralumin beam with a pair of surface bonded PZT-5H piezoelectric patches. The source of the nonlinearity in the piezoelectric actuators (as to whether it is from the mechanical domain, or in the electromechanical coupling) can be directly identified from the experimental results obtained from this procedure. The nature of the contribution of each domain, to the overall nonlinear behaviour, can be deduced from the backbone curves obtained from the piezoelectric-beam vibrations. The first-step of the experimental procedure was aimed at investigating only the mechanical domain of the piezoelectric actuator. This was achieved by short circuiting the PZT-5H patches and obtaining the displacement frequency response curves of the piezoelectric-beam by base excitation. The second-step of experiments were aimed to investigate the presence of non linearity in the electromechanical coupling. Here, the piezoelectric-beam was excited by the PZT-5H actuator to get a similar set of displacement frequency response curves for the first, second and third modes. The nonlinear constitutive equation was established from the profile of the backbone curves of the displacement frequency response plots obtained from the experiments. It was observed that, apart from the linear terms, both quadratic and cubic strain terms were required to represent the stress in the piezoelectric material. The electromechanical coupling too required a nonlinear representation whereby, aside from the linear relation the stress was equal to the product of cubic strain and the electric field. (C) 2018 Elsevier Ltd. All rights reserved
Synthesis, structural studies, molecular docking and DNA binding studies of N-4-substituted hydrazinecarbothioamides
No full textThree thiosemicarbazones of general formulae, H5C2(Ph)-CH=N-NH-C(S)-NHR R = H (L-1), CH3 (L-2), C2H5 (L-3)] were synthesized on condensation between 4-ethylbenzaldehyde and N-4-substituted-thiosemicarbazide 2HN-NH-C(S)-NHR] and characterized using X-ray single-crystal diffraction, elemental analysis, infra red, NMR spectral analysis. Single crystal data indicates that the ligands L-1 and L-3 crystallized in monoclinic system with space group P2(1/c) and crystal L-2 in triclinic system with space group P-1 The interactions of the ligands with calf-thymus-Deoxyribo Nucleic Acid (CT-DNA) were investigated by spectrophotometric method and the results indicated that ligands bound to Deoxyribo Nucleic Acid (DNA) by groove binding mode. The docking studies of ligands with glucosamine-6-phosphate synthase revealed that the ligands are potent as a drug for target enzyme. (C) 2018 Elsevier B.V. All rights reserved
Functional annotation of putative fadE9 of Mycobacterium tuberculosis as isobutyryl-CoA dehydrogenase involved in valine catabolism
No full textMembers of the Acyl-CoA dehydrogenase (ACADs) family of enzymes play a crucial role in cholesterol and steroid catabolism and are widely studied in the oldest known human pathogen, Mycobacterium tuberculosis (Mtb). However, there is a paucity of information on ACADs involved in branched chain amino acid catabolism. Here we characterized one of the putative ACAD enzyme, fadE9, as ``Isobutyryl CoA Dehydrogenase (IBDH)'' using a combined computational and experimental approach, guided by homology modeled structural information, affirming its role in valine catabolism. Multiple sequence alignment and phylogenetic analysis place it in a separate cluster from a recently identified family of alpha(2)beta(2)-heterotetramer ACADs in Mtb, based on the position of the conserved Arg247 and catalytic Glu368 residues. The conserved Arg247 was predicted to play an essential role at the center of H-bonding network of reaction center and was confirmed by the reduced activity of R247K mutant Thus, in addition to the finding of an architecturally distinct alpha(2)beta(2)-heterotetramer among ACADs, these studies also highlight the differences between MtIBDH, fadE9 from the other ACADs that are involved in cholesterol and steroid catabolism of Mtb. (C) 2018 Published by Elsevier B.V
Search for supersymmetry in events with a photon, a lepton, and missing transverse momentum in proton-proton collisions at s√=13 TeV
No full textResults of a search for supersymmetry are presented using events with a photon, an electron or muon, and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 35.9 fb−1 of proton-proton collisions at s√=13 TeV, produced by the LHC and collected with the CMS detector in 2016. Theoretical models with gauge-mediated supersymmetry breaking predict events with photons in the final state, as well as electroweak gauge bosons decaying to leptons. Searches for events with a photon, a lepton, and missing transverse momentum are sensitive probes of these models. No excess of events is observed beyond expectations from standard model processes. The results of the search are interpreted in the context of simplified models inspired by gauge-mediated supersymmetry breaking. These models are used to derive upper limits on the production cross sections and set lower bounds on masses of supersymmetric particles. Gaugino masses below 930 GeV are excluded at the 95% confidence level in a simplified model with electroweak production of a neutralino and chargino. For simplified models of gluino and squark pair production, gluino masses up to 1.75 TeV and squark masses up to 1.43 TeV are excluded at the 95% confidence level
Quantitative vapour concentration measurements in n-dodecane and n-hexadecane sprays
No full textQuantitative vapour concentration measurements in evaporating sprays of n-dodecane and n-hexadecane at high pressure and temperature are presented in this paper. These two liquids have been selected as they represent realistic fuels such as diesel and biodiesel, and exhibit significantly different boiling points. The objective of this study is to understand the effect of boiling point on vapour distribution in evaporating sprays. The experiments are performed in a high pressure spray chamber with optical access filled with nitrogen and heated to reach a pressure of 50-bar and temperature of 900 K. Two injection pressures of 1000 and 1500-bar are considered. Planar laser induced fluorescence (PLIF) of an exciplex tracer system consisting of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and a-methyl naphthalene has been used for vapour concentration measurements. A calibration point relating the TMPD concentration and PLIF signal is obtained by using a fuel vapour jet at a known temperature. Various corrections to the PLIF signal are performed. The vapour mixture fraction (or vapour mass fraction) obtained from the experimental data is compared for the two liquids. It is observed that the mixture fractions for both liquids are very close to each other. An analytical model is used to explain this trend by estimating the variation of mixture fraction along centerline for the two liquids. The model shows the predominance of the density ratio, which is similar for both liquids leading to similarity in the experimental data of mixture fraction. Also, the measurements provide a comprehensive dataset for assessment of CFD simulations of single component evaporating sprays in terms of predicting vapour-air mixing
Hydrogenation of CO2, carbonyl and imine substrates catalyzed by IrH3((PNP)-P-Ph-P-H)] complex
No full textA series of iridium and rhodium complexes M(COD)((PNP)-P-Ph-P-H)]Cl {M = Ir (1), Rh (2)}, MH2Cl((PNP)-P-Ph-P-H)] {M = Ir (3), Rh (4)} and IrH3((PNP)-P-Ph-P-H)] (6) supported by pincer ligand HeN(CH2CH2PPh2)(2) {(PNP)-P-Ph-P-H} have been synthesized and characterized. All complexes were isolated in good yields. The iridium trihydride complex IrH3((PNP)-P-Ph-P-H)] (6) was found to be an active catalyst for the hydrogenation of CO2 in 1 M aqueous KOH solution. It also acts as a catalyst for the base-free hydrogenation of carbonyl and imine substrates in MeOH. Under similar hydrogenation conditions, 2-cyclohexen-1-one undergoes solvent assisted tandem Michael addition-reduction mediated by bifunctional Lewis-acid-catalyst IrH3((PNP)-P-Ph-P-H)] in ROH (R = Me, Et) at room temperature. The complexes 1, 3, 4, and 6 were characterized by X-ray crystallography. Extensive hydrogen bonding interactions N-H center dot center dot center dot H-Ir (2.15 angstrom), N-H center dot center dot center dot center dot Cl (2.370 angstrom) were noted in the crystal structures of these complexes. (C) 2018 Elsevier B.V. All rights reserved