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First Observations on the Trap-Induced Avalanche Instability and Safe Operating Area Concerns in AlGaN/GaN HEMTs
No full textThis paper reports the very first systematic study on the physics of avalanche instability and safe operating area (SOA) reliability in AlGaN/GaN high-electron-mobility transistor (HEMT) using submicroseconds pulse characterization, poststress degradation analysis, well-calibrated TCAD simulations, and failure analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Impacts of electrical and thermal effects on SOA boundary and avalanche instability are investigated. Trap-induced cumulative nature of degradation is studied in detail. The root cause for avalanche instability in AlGaN/GaN HEMTs is investigated. Postfailure SEM, energy dispersive X-ray (EDX), and TEM analysis reveal distinct failure modes in the presence and absence of carrier trapping
Analytical modelling of spatial deformation pathways in planar and spatial shallow bistable arches
No full textWe analyse spatial bistable arches and present an analytical model incorporating axial, two transverse bending and torsion energy components. We extend the St. Venant and Michell relationship used in flexural-torsional buckling of planar arches and use it in modelling spatial arches. We study deformation pathways in spatial arches and their effect on critical characteristics of bistability such as back and forth switching forces, and the distance travelled by a point of the arch. We show that not considering spatial deformation leads to incorrect inferences concerning the bistability of planar arches too. Thus, this model serves as a generalized framework for the existing analysis on planar arches since they belong to a subset of spatial arches. Additionally, the effects of eccentric loading on spatial deformations are explored for arches with a range of as-fabricated shapes and boundary conditions, and the results are validated with finite-element analysis
Transport, multifractality, and the breakdown of single-parameter scaling at the localization transition in quasiperiodic systems
No full textThere has been a revival of interest in localization phenomena in quasiperiodic systems with a view to examining how they differ fundamentally from such phenomena in random systems. Motivated by this, we study transport in the quasiperiodic, one-dimensional Aubry-Andre model and its generalizations to two and three dimensions. We study the conductance of open systems, connected to leads, as well as the Thouless conductance, which measures the response of a closed system to boundary perturbations. We find that these conductances show signatures of a metal-insulator transition from an insulator, with localized states, to a metal, with extended states having (a) ballistic transport (one dimension), (b) superdiffusive transport (two dimensions), or (c) diffusive transport (three dimensions); precisely at the transition, the system displays subdiffusive critical states. We calculate the beta function beta(g) = d ln(g)/d ln(L) and show that, in one and two dimensions, single-parameter scaling is unable to describe the transition. Furthermore, the conductances show strong nonmonotonic variations with L and an intricate structure of resonant peaks and subpeaks. In one dimension the positions of these peaks can be related precisely to the properties of the number that characterizes the quasiperiodicity of the potential; and the L dependence of the Thouless conductance is multifractal. We find that, as dimension increases, this nonmonotonic dependence of g on L decreases and, in three dimensions, our results for beta(g) are reasonably well approximated by single-parameter scaling
Electrochemical Energy Storage Properties of Ni-Mn-Oxide Electrodes for Advance Asymmetric Supercapacitor Application
No full textIn this work, we report a facile one-spot synthesis process and the influence of compositional variation on the electrochemical performance of Ni-Mn-oxides (Ni:Mn = 1:1, 1:2, 1:3, and 1:4) for high-performance advanced energy storage applications. The crystalline structure and the morphology of these synthesized nanocomposites have been demonstrated using X-ray diffraction, field emission scanning electron microscopy, and transmission electron Microscopy. Among these materials, Ni-Mn-oxide with Ni:Mn = 1:3 possesses a large Brunauer-Emmett-Teller specific surface area (127 m(2) g(-1)) with pore size 8.2 nm and exhibits the highest specific capacitance of 1215.5 F g(-1) at a scan rate 2 mV s(-1) with an excellent long-term cycling stability (similar to 87.2% capacitance retention at 10 A g(-1) over 5000 cycles). This work also gives a comparison and explains the influence of different compositional ratios on the electrochemical properties of Ni-Mn-oxides. To demonstrate the possibility of commercial application, an asymmetric supercapacitor device has been constructed by using Ni-Mn-oxide (Ni:Mn = 1:3) as a positive electrode and activated carbon (AC) as a negative electrode. This battery-like device achieves a maximum energy density of 132.3 W h kg(-1) at a power density of 1651 W kg(-1) and excellent coulombic efficiency of 97% over 3000 cycles at 10 A g(-1)
Bridging the gap between diffusivities from experiment and molecular dynamics: n-hexane and 2,2-dimethyl butane in zeolite BEA
No full textWhen do molecular dynamics (MD) simulations yield better agreement with experimental macroscopic measurements of diffusivities of guest molecules in zeolites? We report studies to show that simulations of n-hexane and 2,2-dimethyl butane in `powder' samples of zeolite BEA (as compared to single-crystal sample) lead to a better agreement with ZLC diffusivity measurements previously reported by Barcia et al. The results suggest that main reason why MD simulations until now could not reproduce the measurement from macroscopic techniques such as uptake and gas chromatography is because all simulations employed `single-crystal' sample. Implications of these results on `sample preparation' which is considered very important in experiments but never planned in simulations are discussed. The results further demonstrate that the changes in diffusivities, as well as activation energies that are observed between single crystal and `powder' sample are not only dependent on the nature of the zeolite sample, but also on the type of guest molecule, i.e., the changes on going from `single crystal' to `powder' sample for n-hexane and 2,2-dimethyl butane are not the same
Chonemorpha grandiflora extract mediated synthesis of Ag-ZnO nanoparticles for its anticancer, electrical and dielectric applications
No full textA phytosynthesis method is a nontoxic and environmentally friendly approach. We successfully synthesized the spherical Ag-ZnO nanoparticles via phytosynthesis method using Chonemorpha grandiflora leaf extract. The Scherrer's equation revealed the average crystallite size in the range of 20-35 nm which is in good agreement with TEM results. Adsorption peak was found at 380 nm using Diffused reflectance spectra and energy band gap is found to be 3.08-3.18 eV using Kubelka-Munk function. In vitro viability studies on MCF7, HCT116 and A 549 cell lines showed dose-dependent toxicity. Dielectric applications were investigated in the frequency range from 100 Hz to 8MHzat room temperature using LCR meter. The dielectric parameters of Ag-ZnO nanoparticles increased with Ag concentration and decrease with frequency. This behavior may be due to the decrease in the concentration of Ag in ZnO host material. Further, there is an increase inAC electrical conductivity with adding Ag concentration and at higher frequencies which is due to the increase of available charge carriers. The DC conductivity of samples increases from 2.6. x. 10(-5) Sm-1 to 2 x 10(-4) Sm-1 with the increasing Ag content and is highest for 0.1 content
Role of geography and climatic oscillations in governing into-India dispersal of freshwater snails of the family: Viviparidae
No full textThe indian subcontinent has experienced numerous paleogeological and paleoclimatic events during the Cenozoic which shaped the biotic assembly over time in the subcontinent. The role of these events in governing the biotic exchange between Southeast Asia and Indian subregion is underexplored. We aimed to uncover the effects the collision of the Indian and Asian plate, marine transgression in the Bengal basin as well as the paleoclimatic changes in the subcontinent and adjoining regions, on the dispersal of freshwater snail family Viviparidae from Southeast Asia (SEA) to Indian subregion. Extensive sampling was carried out throughout the Indian subcontinent to capture the current diversity of the targeted lineages. Three mitochondrial and two nuclear markers were sequenced from these samples and combined with published sequences to reconstruct global phylogeny of Viviparidae. Molecular dating and ancestral range estimation were undertaken to obtain the time frame for the dispersal events. Results from these analyses were contrasted with paleoclimate and paleogeology to better understand the biogeography of Indian viviparids. Results support at least two dispersal events into India from Southeast Asia. The earlier event is likely to have occurred during a warm and humid Eocene period before a permanent land connection was established between the two landmasses. While the more recent dispersal occurred post-suturing and overlapped with a time in late Tertiary to Quaternary when arid climate prevailed. However, we could not firmly establish how the marine transgressions influenced the dispersal events. Even though most biotic exchange between India and SEA are noted to be post-suturing, our results add to a growing body of work that suggests faunal exchange pre-suturing probably mediated by intermittent land connections
An NMR View of Protein Dynamics in Health and Disease
No full textBiological molecules are often highly dynamic, and this flexibility can be critical for function. The large range of sampled timescales and the fact that many of the conformers that are continually explored are only transiently formed and sparsely populated challenge current biophysical approaches. Solution nuclear magnetic resonance (NMR) spectroscopy has emerged as a powerful method for characterizing biomolecular dynamics in detail, even in cases where excursions involve short-lived states. Here, we briefly review a number of NMR experiments for studies of biomolecular dynamics on the microsecond-to-second timescale and focus on applications to protein and nucleic acid systems that clearly illustrate the functional relevance of motion in both health and disease
Effect of magnetic dipolar interactions and size dispersity on the origin of steady state magnetomechanical response in bidisperse Mn-Zn ferrite spherical particle based magnetorheological fluids
No full textMagnetorheological fluids have tunable magneto-mechanical strength. We report the magneto-mechanical (steady-state shear) response of magnetorheological fluids (MRFs) containing bi-disperse Mn-Zn ferrite (Mn0.7Zn0.3Fe2O4) spherical particles synthesized by a solvothermal method. Using a model of magnetic dipolar interactions between the particles, we have explained the origin of the magneto-mechanical response of the MRFs. The observed yield strength values of our MRFs increase with the applied magnetic field strength and the concentration of the ferrite particles in the fluid due to the formation of strong columnar structures which resist the shear. Moreover, the yield strength of the MRFs was found to depend strongly on the particle size, size distribution and the magnetic nature (saturation) of the particles. We have demonstrated that a bi-disperse size distribution of particles in the fluid imparts superior yield strength to the MRF compared to that of the mono-disperse particles. Unlike conventional metallic iron particles, which lead to dispersion instability and are prone to corrosion and thermo-oxidative failures, the low-density corrosion-resistant soft-ferrimagnetic Mn-Zn ferrite particles make our MRF system dependable for various technological applications demanding shock absorption and vibration isolation
Stereoselective Conjugate Addition of the Lithium Anion of N-Allyl lmine to Unsaturated Esters: Application to the Enantiospecific Total Synthesis of (-)-Epibatidine
No full textA regio- and diastereoselective conjugate addition of the lithium anion of N-allyl imine (prepared from allylamine and benzophenone) to alpha,beta-unsaturated esters in good yields is reported. The reaction was general and provided the gamma-amino esters resulting from the regioselective C-C bond formation between the alpha-carbon to the nitrogen in the imine and the beta-carbon of the unsaturated ester. Synthetic utility of the formed products was illustrated in the nonracemic total synthesis of the bioactive alkaloid (-)-epibatidine