Derivative procedure for bem based computation of change in natural frequency with crack size

An efficient boundary element method (BEM) based computation of change in natural frequencies with crack size is proposed. The accuracy of the method demonstrated through three case studies is found to be good. The results are not so dependent on the type of element used around the crack tip

Stress enhanced calcium kinetics in a neuron

Accurate modeling of the mechanobiological response of a Traumatic Brain Injury is beneficial toward its effective clinical examination, treatment and prevention. Here, we present a stress history-dependent non-spatial kinetic model to predict the microscale phenomena of secondary insults due to accumulation of excess calcium ions (Ca) induced by the macroscale primary injuries. The model is able to capture the experimentally observed increase and subsequent partial recovery of intracellular Ca concentration in response to various types of mechanical impulses. We further establish the accuracy of the model by comparing our predictions with key experimental observations

Improved structural and optical properties of Cu2ZnSnS4 thin films via optimized potential in single bath electrodeposition

Here we report on the preparation of high quality Cu2ZnSnS4 thin films using single bath electrodeposition process via an optimized deposition potential. X-ray diffraction and Raman analysis validated the formation of kesterite phase of CZTS without any secondary phases at an optimized deposition potential of -1.4V vs. Ag/AgCl. As a signature of highly pure crystalline films of CZTS kesterite phase, we observed a characteristic Raman peak at 338 cm(-1) that corresponds to the vibration of sulfur atoms. Elemental analysis using energy dispersion analysis of X-rays (EDX) reveals a near ideal composition ratio of 2:1:1:4 for these films, and indicates the formation of the ideal stoichiometric compound. Furthermore, X-ray photoelectron spectroscopy analysis of the grown films illustrates an appropriate chemical composition and valence states of the constituent elements without a trace of free sulfur. Using the chrono- amperometry data and the Scharifker and Hill model we found that the nucleation mechanism for CZTS thin film is instantaneous. Optical properties demonstrated the optimum band gap of 1.5 eV for kesterite CZTS film prepared from a precursor electrodeposited at -1.4 V vs. Ag/AgCl. Mott-Schottky electrical measurements confirm the p-type nature of the film with a carrier concentration of 10(17) cm(-3), a flat band potential of V-FB = 0.7V and space charge region width of 0.2 mu m. (C) 2014 Published by Elsevier Ltd

Cation/Anion Substitution in Cu2ZnSnS4 for Improved Photovoltaic Performance

Cations and anions are replaced with Fe, Mn, and Se in CZTS in order to control the formations of the secondary phase, the band gap, and the micro structure of Cu2ZnSnS4. We demonstrate a simplified synthesis strategy for a range of quaternary chalcogenide nanoparticles such as Cu2ZnSnS4 (CZTS), Cu2FeSnS4 (CFTS), Cu2MnSnS4 (CMTS), Cu2ZnSnSe4 (CZTSe), and Cu2ZnSn(S0.5Se0.5)(4) (CZTSSe) by thermolysis of metal chloride precursors using long chain amine molecules. It is observed that the crystal structure, band gap and micro structure of the CZTS thin films are affected by the substitution of anion/cations. Moreover, secondary phases are not observed and grain sizes are enhanced significantly with selenium doping (grain size similar to 1 mu m). The earth-abundant Cu2MSnS4/Se-4 (M = Zn, Mn and Fe) nanoparticles have band gaps in the range of 1.04-1.51 eV with high optical-absorption coefficients (similar to 10(4) cm(-1)) in the visible region. The power conversion efficiency of a CZTS solar cell is enhanced significantly, from 0.4% to 7.4% with selenium doping, within an active area of 1.1 +/- 0.1 cm(2). The observed changes in the device performance parameters might be ascribed to the variation of optical band gap and microstructure of the thin films. The performance of the device is at par with sputtered fabricated films, at similar scales

Enzymatic and non-enzymatic electrochemical glucose sensor based on carbon nano-onions

A high sensitive glucose sensing characteristic has been realized in carbon nano-onions (CNOs). The CNOs of mean size 30 nm were synthesized by an energy-efficient, simple and inexpensive combustion technique. These as-synthesized CNOs could be employed as an electrochemical sensor by covalently immobilizing the glucose oxidase enzyme on them via carbodiimide chemistry. The sensitivity achieved by such a sensor is 26.5 mu A mM (1) cm (2) with a linear response in the range of 1-10 mM glucose. Further to improve the catalytic activity of the CNOs and also to make them enzyme free, platinum nanoparticles of average size 2.5 nm are decorated on CNOs. This sensor fabricated using Pt-decorated CNOs (Pt@CNOs) nanostructure has shown an enhanced sensitivity of 21.6 mu A mM (1) cm (2) with an extended linear response in the range of 2-28 mM glucose. Through these attempts we demonstrate CNOs as a versatile biosensing platform. (C) 2018 Elsevier B.V. All rights reserved

Strong Depletion in Hybrid Perovskite p–n Junctions Induced by Local Electronic Doping

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A semiconductor p–n junction typically has a doping-induced carrier depletion region, where the doping level positively correlates with the built-in potential and negatively correlates with the depletion layer width. In conventional bulk and atomically thin junctions, this correlation challenges the synergy of the internal field and its spatial extent in carrier generation/transport. Organic–inorganic hybrid perovskites, a class of crystalline ionic semiconductors, are promising alternatives because of their direct badgap, long diffusion length, and large dielectric constant. Here, strong depletion in a lateral p–n junction induced by local electronic doping at the surface of individual CH3NH3PbI3 perovskite nanosheets is reported. Unlike conventional surface doping with a weak van der Waals adsorption, covalent bonding and hydrogen bonding between a MoO3 dopant and the perovskite are theoretically predicted and experimentally verified. The strong hybridization-induced electronic coupling leads to an enhanced built-in electric field. The large electric permittivity arising from the ionic polarizability further contributes to the formation of an unusually broad depletion region up to 10 µm in the junction. Under visible optical excitation without electrical bias, the lateral diode demonstrates unprecedented photovoltaic conversion with an external quantum efficiency of 3.93% and a photodetection responsivity of 1.42 A W−1

Using optical spectroscopy to probe the impact of atomic disorder on the Heusler alloy Co2MnGa

The exceptional electronic and spintronic properties of magnetic Heusler alloys, which include half-metals and Weyl semimetals, are strongly sensitive to deviations from the ideal atomic structure. To ensure that these materials have been produced with the desired properties, it is necessary to determine both the structural ordering and the electronic structure, which can be challenging. Here, we present the results of a far-infrared-to-visible optical spectroscopy study of films of room-temperature ferromagnetic Weyl semimetal Co2MnGa. Combined with a determination of the level of ordering from x-ray diffraction, we have investigated near Fermi energy valence and conduction band intra- and interband transitions and their dependence on the atomic order. Motivated by band structure calculations, we have modeled our optical spectra with two Drude terms and two Lorentz oscillators, where the latter are assigned to interband transitions. The scattering rate of the itinerant carriers, determined from the width of the Drude term, increases threefold with increasing disorder, while the carrier density to effective mass ratio is unchanged. Based on our band structure and the joint density of states calculations, we have assigned the oscillator that dominates the interband spectral region near 1 eV to transitions across the minority spin gap along the Γ-X direction. It is found that the energy of this transition is strongly sensitive to the degree of order and decreases rapidly with increasing disorder as states fill a decreasing minority spin gap. Our results demonstrate optical spectroscopy is a sensitive way to fingerprint structural order in the technologically relevant near Fermi level electronic states in Heusler alloys