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Part II: Proposals to Independently Engineer Donor and Acceptor Trap Concentrations in GaN Buffer for Ultrahigh Breakdown AlGaN/GaN HEMTs
No full textIn part I of this paper, we developed physical insights into the role and impact of acceptor and donor traps-resulting from C-doping in GaN buffer-on avalanche breakdown in AlGaN/GaN HEMT devices. It was found that the donor traps are mandatory to explain the breakdown voltage improvement. In this paper, silicon doping is proposed and explored as an alternative to independently engineer donor trap concentration and profile. Keeping in mind the acceptor and donor trap relative concentration requirement for achieving higher breakdown buffer, as depicted in part I of this paper, silicon & carbon codoping of GaN buffer is proposed and explored in this paper. The proposed improvement in breakdown voltage is supported by physical insight into the avalanche phenomena and role of acceptor/donor traps. GaN buffer design parameters and their impact on breakdown voltage as well as leakage current are presented. Finally, a modified Si-doping profile in the GaN buffer is proposed to lower the C-doping concentration near GaN channel to mitigate the adverse effects of acceptor traps in GaN buffer
A shape optimization approach for simulating contact of elastic membranes with rigid obstacles
No full textThe obstacle problem consists in computing equilibrium shapes of elastic membranes in contact with rigid obstacles. In addition to the displacement u of the membrane, the interface Gamma on the membrane demarcating the region in contact with the obstacle is also an unknown and plays the role of a free boundary. Numerical methods that simulate obstacle problems as variational inequalities share the unifying feature of first computing membrane displacements and then deducing the location of the free boundary a posteriori. We present a shape optimization-based approach here that inverts this paradigm by considering the free boundary to be the primary unknown and compute it as the minimizer of a certain shape functional using a gradient descent algorithm. In a nutshell, we compute Gamma then u, and not u then Gamma. Our approach proffers clear algorithmic advantages. Unilateral contact constraints on displacements, which render traditional approaches into expensive quadratic programs, appear only as Dirichlet boundary conditions along the free boundary. Displacements of the membrane need to be approximated only over the noncoincidence set, thereby rendering smaller discrete problems to be resolved. The issue of suboptimal convergence of finite element solutions stemming from the reduced regularity of displacements across the free boundary is naturally circumvented. Most importantly perhaps, our numerical experiments reveal that the free boundary can be approximated to within distances that are two orders of magnitude smaller than the mesh size used for spatial discretization. The success of the proposed algorithm relies on a confluence of factors- choosing a suitable shape functional, representing free boundary iterates with smooth implicit functions, an ansatz for the velocity of the free boundary that helps realize a gradient descent scheme and triangulating evolving domains with universal meshes. We discuss these aspects in detail and present numerous examples examining the performance of the algorithm
An amine functionalized zirconium metal-organic framework as an effective chemiresistive sensor for acidic gases
No full textPore surface functionalization of a metal-organic framework (MOF) with an amine moiety has turned an innocent MOF into a chemiresistive sensor for acidic gases. The Zr-NH2-benzenedicarboxylate MOF (NH2-UiO-66) proved to perform as an efficient and stable chemiresistive sensor for SO2, NO2 and CO2 at low concentrations and an operating temperature of 150 degrees C
Design, synthesis, fabrication and simulation of conjugated molecule for detection of lithium ions
No full textAlkali metal ions such as lithium, sodium and potassium are essential chemical species present in biological fluids (0.5-1.2 mM) and less hazardous quantity (0.9 mu M-12 mu M) present in drinking water. Lithium salts are used in pharmaceuticals, in ores and minerals, in Li-ion batteries. Ingestion of water source containing lithium concentration above 0.2 mM affects normal functioning of the body. Hence it is important to detect these ions in potable water. Here, a conjugated molecule based sensor for detection of lithium ion in water is developed. The conjugated molecule has a receptor moiety to capture the ion. The conjugated molecule interaction with alkali metal ions - Li+,Na+ and K+ is studied by density functional theory and interference analysis. The resistive based sensor is fabricated and device characteristics are studied. The experimental and simulation results suggest that the conjugated molecule interaction specifically with Li+ is relatively stronger. The lower limit of detection of the sensor is observed to be 0.05 mM. This limit is within the range of the lithium ion concentration found in biological fluids
Untangling the water-food-energy-environment nexus for global change adaptation in a complex Himalayan water resource system
No full textHolistic water management approaches are essential under future climate and socio-economic changes, especially while trying to achieve inter-disciplinary societal goals such as the Sustainable Development Goals (SDGs) of clean water, hunger eradication, clean energy and life on land. Assessing water resources within a water-food-energy-environment nexus approach enables the relationships between water-related sectors to be untangled while incorporating impacts of societal changes. We use a systems modelling approach to explore global change impacts on the nexus in the mid-21st century in a complexwestern Himalayanwater resource system in India, considering a range of climate change and alternative socio-economic development scenarios. Results show that future socio-economic changes will have a much stronger impact on the nexus compared to climate change. Hydropower generation and environmental protection represent the major opportunities and limitations for adaptation in the studied system and should, thereby, be the focus for actions and systemic transformations in pursue of the SDGs. The emergence of scenario-specific synergies and trade-offs between nexus component indicators demonstrates the benefits that water resource systems models canmake to designing better responses to the complex nexus challenges associated with future global change. (c) 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY licens
Study of the influence of Zr on the mechanical properties and functional response of Ti-Nb-Ta-Zr-O alloy for orthopedic applications
No full textIn Ti-Nb-Ta-Zr based beta-titaniumalloys intended for orthopedic applications, Zr does not affect the stability of low modulus beta-phase, unlike Nb and Ta. The present study attempts to investigate the influence of Zr on the overall mechanical and functional responses of a Ti-Nb-Ta-Zr-O alloy in contrast to a new Ti-Nb-Ta-O alloy. In each material, different crystallographic textures were produced by varying the processing route. While both alloys were found to show low elastic modulus values due to their beta-only microstructures, Ti-Nb-Ta-O alloy had lower elastic modulus because of its favorable crystallographic orientation caused by absence of Zr. The tensile strength values were remarkably high for both due to the presence of interstitial oxygen. The hardening effect of Zr was also evident from the higher strength of Ti-Nb-Ta-Zr-O as compared to Ti-Nb-Ta-O alloy. Although the corrosion resistance and in vitro biological behavior of the two alloys were satisfactory, the Ti-Nb-Ta-Zr-O alloy showed lower corrosion rate and improved osteoblast attachment than the Ti-Nb-Ta-Oalloy. Thus, whereas the two alloys show promising performance in terms of their mechanical and functional response, presence of Zr marginally improves the performance in the Ti-Nb-Ta-Zr-O for orthopedic applications. (C) 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
Measurements of the Higgs boson width and anomalous HVV couplings from on-shell and off-shell production in the four-lepton final state
No full textStudies of on-shell and off-shell Higgs boson production in the four-lepton final state are presented, using data from the CMS experiment at the LHC that correspond to an integrated luminosity of 80.2 fb(-1) at a center-of-mass energy of 13 TeV. Joint constraints are set on the Higgs boson total width and parameters that express its anomalous couplings to two electroweak vector bosons. These results are combined with those obtained from the data collected at center-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 5.1 and 19.7 fb(-1), respectively. Kinematic information from the decay particles and the associated jets are combined using matrix element techniques to identify the production mechanism and to increase sensitivity to the Higgs boson couplings in both production and decay. The constraints on anomalous HVV couplings are found to be consistent with the standard model expectation in both the on-shell and off-shell regions. Under the assumption of a coupling structure similar to that in the standard model, the Higgs boson width is constrained to be 3.2(-2.2)(+2.8)MeV while the expected constraint based on simulation is 4.1(-4.0)(+5.0) MeV. The constraints on the width remain similar with the inclusion of the tested anomalous HVV interactions
Electrochemical sensing and photocatalytic degradation of methylene blue (MB) dye by cobalt-beta hydroxy benzoate complex
No full textIn this work describes the cobalt-beta hydroxyl benzoate (Co-bhb), Cobalt based complex has been synthesized by solvothermal method and verified for the application detection and removal of environmentally hazardous molecule like methylene blue. The Co-bhb sample were characterized by various techniques like FTIR, PXRD, MS-Mass analysis, NMR, and SEM, EDX, ES-TEM,XPS, PL and BET surface area measurement. The Co-bhb/cp electrode was prepared and electrochemical performance was carried out to explore the electrical activity of the complex for dye sensor application. The Cyclic voltammetry studies were made in 0.05M K4Fe (CN)(6) solution and electrochemical sensing experiments were performed in 0.05M H2SO4. An excellent response resulted of the Co-bhb/cpe for sensing the dye at very low concentrations. In addition the photocatalytic activity of degradation of Methylene blue has been performed. The results have showed that the Co-bhb is a promising candidate for electrochemical and catalytic properties
A New Formula for Predicting Solar Cycles
No full textA new formula for predicting solar cycles based on the current theoretical understanding of the solar cycle from the flux transport dynamo is presented. Two important processes-fluctuations in the Babcock-Leighton (BL) mechanism and variations in the meridional circulation (MC), which are believed to be responsible for irregularities of the solar cycle-are constrained using observational data. We take the polar field near minima of the cycle as a measure of the randomness in the BL process, and the decay rate near the minima as a consequence of the change in MC. We couple these two observationally derived quantities into a single formula to predict the amplitude of the future solar cycle. Our new formula suggests that cycle 25 would be a moderate cycle. Whether this formula for predicting the future solar cycle can be justified theoretically is also discussed using simulations from the flux transport dynamo model