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Meandering Gate Edges for Breakdown Voltage Enhancement in AlGaN/GaN High Electron Mobility Transistors
No full textHerein, a unique device-design strategy is reported for increasing the breakdown voltage and hence Baliga figure of merit (BFOM) of III-nitride high electron mobility transistors (HEMTs) by engineering the gate edge toward the drain. The breakdown of such devices with meandering gate-drain access region (M-HEMT) are found to be 62 more compared with that of conventional HEMT whereas the on-resistance suffers by 76, leading to an overall improvement in the BFOM for by 28. The 3D technology computer-aided design simulations show that the decrease in the peak electric field at the gate edge was responsible for increased breakdown voltage
Improved corrosion response of squeeze-cast SiC nanoparticles reinforced AZ91-2.0Ca-0.3Sb alloy
No full textThe present work investigates the effect of SiC nanoparticle additions on corrosion response of the squeeze-cast AZ91 + 2.0Ca+0.3Sb (wt.) alloy subjected to immersion, hydrogen evolution, and potentiodynamic polarization scan in a 0.1 M NaCl solution. All the AZ91 + 2.0Ca+0.3Sb + xSiCnp (x = 0.5, 1.0, 2.0 (wt.)) nanocomposites demonstrate a superior corrosion resistance than the alloy, and the nanocomposite reinforced with 2.0SiCnp exhibits the highest corrosion resistance. The improved corrosion performance of the nanocomposites is attributed to the decrease in the potential difference between α-Mg and β-Mg17Al12 phases, reduced quantity of β-Mg17Al12 phase, and an increased amount of Al2Ca phase following SiC nanoparticles additions
Use of Jordan forms for convection-pressure split Euler solvers
No full textIn this study, convection-pressure split Euler flux functions which contain weakly hyperbolic convective subsystems are analyzed. A system of first-order partial differential equations (PDEs) is said to be weakly hyperbolic if the corresponding flux Jacobian does not contain a complete set of linearly independent (LI) eigenvectors. Thus, the application of existing flux difference splitting (FDS) based schemes, which depend heavily on both eigenvalues and eigenvectors, are non-trivial to such systems. In the case of weakly hyperbolic systems, a required set of LI eigenvectors can be constructed through the addition of generalized eigenvectors by utilizing the theory of Jordan canonical forms. Once this is achieved for a weakly hyperbolic convective subsystem, an upwind solver can be constructed in the splitting framework. In the present work, the above approach is used for developing two new schemes. The first scheme is based on the Zha�Bilgen type splitting while the second is based on the Toro�Vázquez splitting. Both the schemes are tested on various benchmark problems in one-dimension (1-D) and two-dimensions (2-D). The concept of generalized eigenvectors based on Jordan forms is found to be useful in dealing with the weakly hyperbolic parts of the considered Euler systems
E-Nose: Multichannel Analog Signal Conditioning Circuit with Pattern Recognition for Explosive Sensing
No full textThis paper presents E-Nose, a novel cost-effective, field-deployable portable system that constitutes a 4-channel signal conditioning circuit and multi-coated piezo-resistive micro-cantilever sensors for explosive sensing. E-Nose also features an embedded PCA and K-means based pattern recognition (PR) algorithm for the classification of explosives from non-explosives. The 4-channel configuration is a stack of two 2-channel circuits that are capable of measuring the change in the sensor resistance or capacitance in four optional modes of � R - � R, � R - � C , � C- � R , and � C - � C by using time multiplexing. The circuit uses a bidirectional AC current excitation method to drive the sensor bridge for significant reduction of DC offset errors, 1/f noise, line noise, and DC drifts. The proposed signal conditioning circuit uses the phase-sensitive synchronous rectification (PSSR) method for AC-to-DC conversion by using balanced demodulation. The circuit can measure a wide range of resistors that range from 100 Ω to 4 MΩ , with a sensitivity of 0.4mV/ppm and the worst relative error of 2.6. The capacitive measurement range is from 100pF to 100 μF with the worst relative error of 3.3. The entire data processing and the PR algorithms run on Raspberry Pi (R-Pi), which is integrated into the E-Nose system. The system performance is tested with MEMS cantilevers for the detection of explosive compounds, such as TNT and its derivatives, RDX and PETN in a controlled environment at a concentration that was as low as 16ppb TNT, 56ppb RDX and 134ppb of PETN. Measurements show that the E-Nose can detect explosives with 77 as true positive results without considering the environmental and mixed vapor effects
Ionic Diffusion and Drug Release Behavior of Core-Shell-Functionalized Alginate-Chitosan-Based Hydrogel
No full textThis paper reports the core-shell structure effects in calcium alginate (CaALG) microbeads due to the threshold water level for phase transition and correlates these properties with respect to pH and electrical conductivity. Further, in this study, we used a novel microfluidic device for drug release testing to study the programmed release of risedronate (RIS-anti-osteoporotic drug) encapsulated in pH-responsive CaALG-chitosan (CHT) microbeads. Our microfluidic device contains a single straight microchannel containing a steplike barrier design used to restrict the mobility of the microbeads at the sample detection zone. For optical and fluorescence microscopy, single fluorescently labeled CaALG-CHT microbead containing RIS was placed in the sample detection zone by flowing through the inlet port with ultrapure water. The RIS release behavior from the microbeads at different pH (2.1, 4, 6.8, and 7.4) conditions was determined by using a spectrophotometer connected to the outlet port of the device. Results of our first study showed that the decrease in the concentration of CaCl2 increases the swelling rate in CaALG microbeads. Maximum swelling was achieved with the lowest molar concentration of CaCl2 used for fabrication of CaALG microbeads. Further, electrical current-voltage characteristic shows the nature of ionic mobility with respect to varying levels of pH indicating electrokinetic forces developed in the CaALG microbeads. By using a microfluidic device for drug release testing, we demonstrated that a sustained release delivery system for RIS can be prepared by coating with pH-sensitive and biodegradable CaALG-CHT. The CaALG-CHT microbeads used for encapsulating RIS are resistant to the acidic environment of the stomach. This may improve the therapeutic effectiveness and reduce the gastric adverse effects associated with RIS by preventing its decomposition in the acidic condition of stomach. The newly developed microfluidic device for drug release testing may find applications in screening novel drugs and delivery systems
Dynamical control by water at a molecular level in protein dimer association and dissociation
No full textWater, often termed as the �lubricant of life,� is expected to play an active role in navigating protein dissociation�association reactions. In order to unearth the molecular details, we first compute the free-energy surface (FES) of insulin dimer dissociation employing metadynamics simulation, and then carry out analyses of insulin dimerization and dissociation using atomistic molecular-dynamics simulation in explicit water. We select two sets of initial configurations from 1) the dissociated state and 2) the transition state, and follow time evolution using several long trajectories (�1�2 μs). During the process we not only monitor configuration of protein monomers, but also the properties of water. Although the equilibrium structural properties of water between the two monomers approach bulklike characteristics at a separation distance of �5 nm, the dynamics differ considerably. The complex association process is observed to be accompanied by several structural and dynamical changes of the system, such as large-scale correlated water density fluctuations, coupled conformational fluctuation of protein monomers, a dewettinglike transition with the change of intermonomeric distance RMM from �4 to �2 nm, orientation of monomers and hydrophobic hydration in the monomers. A quasistable, solvent-shared, protein monomer pair (SSPMP) forms at around 2 nm during association process which is a local free-energy minimum having �50�60 of native contacts. Simulations starting with arrangements sampled from the transition state (TS) of the dimer dissociation reveal that the final outcome depends on relative orientation of the backbone in the �hotspot� region
Hand-powered elastomeric pump for microfluidic point-of-care diagnostics
No full textThe pumping of fluids into microfluidic channels has become almost an unavoidable operation in all microfluidic applications. Such a need has seen an outburst of several techniques for pumping, out of which the majority of techniques involve complicated fabrication, as they require the introduction of electrodes, valves, piezoelectric materials, acoustic transducers, etc., into the microfluidic device. In addition to the complexity, this also escalates the cost incurred per device. Further, the use of stable external power supplies to produce such a pumping action adds to the bulkiness of the pumps, making them unsuitable for point-of-care diagnostic (POCD) applications. This paper reports a technique of pumping that is simple to realize and does not require external electric/magnetic power, but exploits the elastic properties of materials to achieve the pumping action. This mechanism of pumping ensured the cost per pump to less than 4 USD and can be used for at least 500 times. Several simulations, validation, and characterization experiments were performed on the developed pump to establish its functionality and suitability for use in POCD applications
Mechanical and thermal properties, and comparative life-cycle impacts, of stabilised earth building products
No full textThe study presented here investigates the use of alkali-activation and waste materials in stabilised compressed earth construction products. Experimental results for mechanical and thermal properties are presented. Environmental impacts are also compared in a Life Cycle Assessment together with a wider discussion of construction practicalities. Construction and demolition waste shows potential as an aggregate, with processed ground blast furnace slag, together with fly ash, particularly promising for alkali-activated stabilisation. Thermal conductivities of materials using the processed ground blast furnace slag were noticeably lower. Alkali-activated compressed earth blocks appear most promising for reducing the global warming potential of stabilised earth construction
Structural elucidation, theoretical insights and thermal properties of three novel multicomponent molecular forms of gallic acid with hydroxypyridines
No full textDevelopment of novel drug for manipulating the physicochemical properties of the API by obtaining their multicomponent forms is a challenging task in the pharmaceutical industry. Novel multicomponent crystal forms of gallic acid with three hydroxypyridines have been prepared by liquid assisted grinding and slow evaporation of the solvent. Preliminary PXRD and FTIR characterizations were carried out to confirm the interactions between the components, then the three dimensional molecular structures were confirmed through single crystal X-ray diffraction method. Structural studies clearly revealed the three distinct molecular crystal forms of gallic acid with hydroxypyridines. The molecular structures exhibit O�H�O, N�H�O and C�H�O intermolecular hydrogen bond interactions, which results different supramolecular motifs. Further, intermolecular interactions were quantified through Hirshfeld surface analysis, which revealed the dominance of O�H and H�H interactions. Computation of interaction energies between the molecules and analysis of three dimensional energy frameworks quantifies the molecular packing. The density functional theory calculations were employed to optimize the structural coordinates, which substantiate the experimental results. Low value of HOMO-LUMO energy gap signifies the promising electronic properties of the molecules. The chemical reactive sites were further identified on the molecular electrostatic potential surface. Finally, thermal properties of the crystals were studied using thermogravimetric analysis
Surface mechanical attrition treatment of low modulus Ti-Nb-Ta-O alloy for orthopedic applications
No full textSurface mechanical attrition treatment (SMAT) is recognized as a surface severe plastic deformation (SPD) method that is effective in improving the surface-dependent mechanical and functional properties of conventional metallic biomaterials. In this study, we aimed to systemically investigate the effect of SMAT on the physical, electrochemical, tribological and biological performances of a newly developed low modulus β Ti-Nb-Ta-O alloy with two different microstructures, namely, single phase β-treated and dual phase β + α aged. The microhardness results showed considerable hardening for the β-treated condition due to formation of deformation substructures; that was associated with increased corrosion resistance resulting from a stronger and denser passive layer on the surface, as revealed by Tafel polarization, impedance studies and Mott-Scottky plots. The wear volume loss during fretting in serum solution was found to decrease by 46 while friction coefficient decreased only marginally, due to presence of a harder and more brittle surface. In the β + α condition of the alloy, minimal hardening was observed due to coarsening of the precipitates during SMAT. However, this also reduced the number of α-β interfaces, which in turn minimized the tendency for galvanic corrosion resulting in lower corrosion rate after SMAT. Wear resistance was enhanced after SMAT, with 32 decrease in wear volume loss and 21 decrease in friction coefficient resulted due to improved ductility on the surface. The attachment and growth of osteoblasts on the alloys in vitro were not affected by SMAT and was comparable to that on commercially pure Ti. Taken together, these results provide new insights into the effects of surface SPD of low modulus β- Ti alloys for orthopedic applications and underscore the importance of the initial microstructure in determining the performance of the alloy