Superconducting state parameters of binary metallic glasses

Ashcroft’s empty core (EMC) model potential is used to study the superconducting state parameters (SSP) viz. electron–phonon coupling strength λ, Coulomb pseudopotential μ^*, transition temperature T_C, isotope effect exponent and effective interaction strength N₀V of some binary metallic glasses based on the superconducting (S), conditional superconducting (S′) and non-superconducting (NS) elements of the periodic table. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used for the first time with EMC potential in the present investigation to study the screening influence on the aforesaid properties. The T_C obtained from IU-local field correction function are found an excellent agreement with available theoretical or experimental data. In the present computation, the use of pseudo-alloy-atom model (PAA) is proposed and found successful. The present work yield results in qualitative agreement with such earlier reported values either theoretical or experimental which confirm the superconducting phase in all metallic glasses. A strong dependency of the SSP of the metallic glasses on the valence Z is found.     

System-level modeling and simulation of biochemical assays in lab-on-a-chip devices

We present a “mixed-methodology” based system-level modeling and simulation for biochemical assays in lab-on-a-chip (LoC) devices. The methodology uses a combination of numerical schemes and analytical approaches to simulate biological and physicochemical processes, specifically, an integral approach for fluid flow and electric field, method of lines (MOL) and two-compartment models for biochemical reactions, and Fourier series-based model for analyte mixing. The solution procedure begins with decomposing the LoC device into a system of inter-connected components (e.g., channels and junctions) and the models are solved in a network fashion. Models are developed to accurately capture the multi-physics (e.g., flow, mixing, and reaction) behavior of individual components. The assembly of the components is facilitated via exchange of fluid flux and Fourier series coefficients (or average concentration) of analytes between various components, which enables network solution of the models. The system models are validated against both experimental and numerical models on various biochemical assays (e.g. immunoassays and enzymatic reactions), showing significant computational speedup (100–10,000-fold depending on the assay) without appreciably compromising accuracy (<10% error relative to numerical analysis).     

An Approach for Extracting Small-Signal Equivalent Circuit of Double Heterojunction δ-Doped PHEMTs for Millimeter Wave Applications

Pseudomorphic high electron mobility transistors (PHEMTs) are very important in millimeterwave application. A simple and accurate method for extracting small-signal equivalent curcuit for Double Heterojunction δ-doped PHEMT valid up to 40GHz is presented. First, the parasitic parameters of the equivalent circuit are determined using pinch off PHEMT except for PAD capacitances. The initial intrinsic elements are then determined by conventional analytical method. Advanced Design System is then used to optimize the whole model parameters with very small dispersion of initial values. Good agreement is obtained between simulation results and measured results for a 0.25um DH PHEMT.     

Adaptive and hierarchical modelling of fatigue crack propagation

A methodology is developed to simulate adaptively and hierarchically fatigue crack growth in structural components. Cracks are modelled, by overlaying portions of the finite element mesh free of cracks with a discontinuous finite element field containing unconstrained double nodes along the discontinuity. Crack propagation is simulated by advancing the crack front in the superimposed mesh only keeping the underlying mesh fixed. Adaptivity in time and space domain together with the hierarchical nature of the method ensure both economical and reliable simulation of crack propagation. Numerical results of fatigue crack growth in the attachment lug were found to be, in good agreement with the experimental data.     

Comparison between trap and self-heating induced mobility degradation in AlGaN/GaN HEMTs

Mobility degradation due to scattering from radiation-induced defects is compared to that produced by self-heating in proton-irradiated AlGaN/GaN HEMTs using experiments and simulations. After irradiation, the mobility in the 2DEG is limited by scattering from charged traps and is temperature-limited near the gate–drain access region.     

Phase Transition Control for High Performance Ruddlesden–Popper Perovskite Solar Cells

Ruddlesden–Popper reduced‐dimensional hybrid perovskite (RDP) semiconductors have attracted significant attention recently due to their promising stability and excellent optoelectronic properties. Here, the RDP crystallization mechanism in real time from liquid precursors to the solid film is investigated, and how the phase transition kinetics influences phase purity, quantum well orientation, and photovoltaic performance is revealed. An important template‐induced nucleation and growth of the desired (BA)₂(MA)₃Pb₄I₁₃ phase, which is achieved only via direct crystallization without formation of intermediate phases, is observed. As such, the thermodynamically preferred perpendicular crystal orientation and high phase purity are obtained. At low temperature, the formation of intermediate phases, including PbI₂ crystals and solvate complexes, slows down intercalation of ions and increases nucleation barrier, leading to formation of multiple RDP phases and orientation randomness. These insights enable to obtain high quality (BA)₂(MA)₃Pb₄I₁₃ films with preferentially perpendicular quantum well orientation, high phase purity, smooth film surface, and improved optoelectronic properties. The resulting devices exhibit high power conversion efficiency of 12.17%. This work should help guide the perovskite community to better control Ruddlesden–Popper perovskite structure and further improve optoelectronic and solar cell devices.     

Single- and Two-Layer Coatings of Metal Blends onto Carbon Steel: Mechanical, Wear, and Friction Characterizations

Single- and two-layer coatings were deposited onto carbon steel using a high-velocity oxy-fuel deposition gun. The two-layer coating consisted of a top layer of tungsten carbide cobalt/nickel alloy blend that provides wear resistance and a bottom layer of iron/molybdenum blend that provides corrosion resistance. The morphological changes in the single- and two-layer coatings were examined using scanning electron microscopy. The residual stresses formed on the surface of various coatings were determined from x-ray diffraction data. Nanomechanical properties were measured using the nanoindentation technique. Microhardness and fracture toughness were measured incorporating the microindentation tests. Macrowear and macrofriction characteristics were measured using the pin-on-disk testing apparatus. The goal of this study was to ensure that the mechanical properties, friction, and wear resistance of the two-layer coating are similar to that of the single-layer coating.