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Is natural higgsino-only dark matter excluded?
No full textThe requirement of electroweak naturalness in supersymmetric (SUSY) models of particle physics necessitates light higgsinos not too far from the weak scale characterized by m(weak) similar to m(W,Z,h) similar to 100 GeV. On the other hand, LHC Higgs mass measurements and sparticle mass limits point to a SUSY breaking scale in the multi-TeV regime. Under such conditions, the lightest SUSY particle is expected to be a mainly higgsino-like neutralino with non-negligible gaugino components (required by naturalness). The computed thermal WIMP abundance in natural SUSY models is then found to be typically a factor 5-20 below its measured value. To gain concordance with observations, either an additional DM particle (the axion is a well-motivated possibility) must be present or additional non-thermal mechanisms must augment the neutralino abundance. We compare present direct and indirect WIMP detection limits to three natural SUSY models based on gravity-, anomaly-and mirage-mediation. We show that the case of natural higgsino-only dark matter where non-thermal production mechanisms augment its relic density, is essentially excluded by a combination of direct detection constraints from PandaX-II, LUX and Xenon-1t experiments, and by bounds from Fermi-LAT/ MAGIC observations of gamma rays from dwarf spheroidal galaxies
Design, display and immunogenicity of HIV1 gp120 fragment immunogens on virus-like particles
No full textThe broadly neutralizing antibody against HIV-1, b12, binds to the CD4 binding site (CD4bs) on the outer domain (OD) of the gp120 subunit of HIV-1 Env. We have previously reported the design of an E. coli expressed fragment of HIV-1 gp120, b122a, containing about 70% of the b12 epitope with the idea of focusing the immune response to this structure. Since the b122a structure was found to be only partially folded, as assessed by circular dichroism and protease resistance, we attempted to stabilize it by the introduction of additional disulfide bonds. One such mutant, b122a1-b showed increased stability and bound b12 with 30-fold greater affinity as compared to b122a. Various b122a and OD fragment proteins were displayed on the surface of Qp virus-like particles. Sera raised against these particles in six-month long rabbit immunization studies could neutralize Tier1 viruses across different subtypes with the best results observed with b122a1-b displayed particles. Significantly higher amounts of antibodies directed towards the CD4bs were also elicited by particles displaying b122a1-b. This study highlights the ability of fragment immunogens to focus the antibody response to the conserved CD4bs of HIV-1. (C) 2018 Elsevier Ltd. All rights reserved
Estimating anisotropic heterogeneous hydraulic conductivity and dispersivity in a layered coastal aquifer of Dakshina Kannada District, Karnataka
No full textThe solution for the inverse problem of seawater intrusion at an aquifer scale has not been studied as extensively as forward modeling, because of the conceptual and computational difficulties involved. A three-dimensional variable-density conceptual phreatic model is developed by constraining with real-field data such as layering, aquifer bottom topography and appropriate initial conditions. The initial aquifer parameters are layered heterogeneous and spatially homogeneous that are based on discrete field measurements. The developed conceptual model shows poor correlation with observed state variables (hydraulic head and solute concentration), signifying the importance of spatial heterogeneity in hydraulic conductivity and dispersivity of all the layers. The conceptual model is inverted to estimate the anisotropic spatially varying hydraulic conductivity and the longitudinal dispersivity at the pilot points by minimizing the least square error of state variables across the observation wells. The inverse calibrated model is validated for the hydraulic head at validation wells and the solute concentration is validated with equivalent solute concentration derived from the electrical resistivity, which shows good results against the field measurements. The verification of estimated anisotropic hydraulic conductivity with the electrical resistivity tomography image shows good agreement. This investigation gives an insight about constraining the highly parameterized inverse model with real-field data to estimate spatially varying aquifer parameters for an effective simulation of the seawater intrusion in a layered coastal aquifer
Phase miscibility and dynamic heterogeneity in PMMA/SAN blends through solvent free reactive grafting of SAN on graphene oxide
No full textThe spatial distribution of nanoparticles in a particular host polymer matrix can be improved by using brush coated nanoparticles. In this work we have grafted styrene-acrylonitrile (SAN) onto the surface of graphene oxide (GO) and investigated as to how the demixing temperature, morphology and volume cooperativity of PMMA/SAN blends are influenced. Grafting of polymer chains on the surface of nanoparticles usually involves the use of large amounts of solvents, many which are detrimental to the environment besides involving cumbersome processes. SAN-g-GO was prepared by a robust solvent-free strategy wherein the cyano group in SAN was replaced by oxazoline groups during melt mixing in the presence of zinc acetate and ethanol amine. These newly created oxazoline groups reacted with the COOH group of GO under melt extrusion resulting in grafting of SAN on the surface of GO sheets. The effect of SAN-g-GO nanoparticles on the demixing, local segmental motions and morphology evolution for different annealing times was carefully investigated in a classical LCST system, PMMA/SAN blend, using melt rheology, modulated DSC and AFM, respectively. The changes in viscoelastic behavior in the vicinity of demixing are investigated systematically for the control, and blends with GO and SAN-g-GO. Various models were used to gain insight into the spinodal decomposition temperatures of the blends. Interestingly, the demixing temperature determined rheologically and the spinodal decomposition temperature increased significantly in the presence of polymer grafted nanoparticles in comparison to the control and blends with GO. The evolution of the morphology, interfacial driven coarsening as a function of temperature and the localization of nanoparticles were assessed using atomic force microscopy. The cooperatively re-arranging regions estimated from calorimetric measurements begin to suggest enhanced dynamic heterogeneity in the presence of GO and SAN-g-GO in the blends. Taken together, our study reveals that the solvent-free approach of grafting SAN onto GO delays demixing, suppresses coalescence and alters cooperative relaxation in PMMA/SAN blends
Design and Analysis of the Low Device Stress Active Power Decoupling for Single-Phase Grid Connection for a Wide Range of Power Factor
No full textSingle-phase power converters suffer from the double frequency power pulsation. In voltage source inverters, the dc bus capacitor is designed to supply this double frequency current. The stringent dc bus voltage ripple specifications call for larger capacitance. This implies larger electrolytic capacitors. However, the electrolytic capacitor suffers from short-term life span, which consequently brings down the lifetime of the converter. As an alternative, active power decoupling (APD) ensures significant reduction in dc buffering requirement, thereby reducing the bus capacitance. This can make use of the film capacitors with better lifespan. In this paper, an APD scheme is designed and developed for the grid-connected system. Another important feature of the proposed scheme is that, it reduces the stress on the switches significantly while compared with existing APD solutions for all load power factors. The system is analyzed further to arrive at APD control conditions including the effect of grid filter inductance. The simulation and experimentation have been done to validate the proposed method. Additionally, the stress on the switches as a function of grid filter inductance is predicted theoretically and verified practically. The average stress on the switches is shown to be lesser than the existing solutions
A review of micromechanics based models for effective elastic properties of reinforced polymer matrix composites
No full textMicromechanics based models are used for predicting the effective mechanical properties of reinforced polymer matrix composites. This paper reviews micromechanics based models for fiber reinforced polymer composites starting with the bounds established by Voigt and Reuss models, Hashin-Shtrikman model and then on to well-known micromechanics based models like Mori-Tanaka model, Self-consistent model and Differential scheme based models. The main objective is to critically review the areas in which these micromechanics based models hold good and analyse the limitations of these models. One of the limitations of the above mentioned models is the assumption of dilute dispersion and this is overcome in this paper by revising the Mori-Tanaka model by combining the differential scheme with Eshelby's model to take into account the non-dilute dispersion effect. Numerical results are verified by finite element based simulation of the representative volume element (RVE). Experiments were carried out to estimate the effective elastic constants for different fiber volume fractions. Theoretical results are reviewed with reference to experimental measurements
Reversal of particle-hole scattering-rate asymmetry in the Anderson impurity model
No full textWe study the particle-hole asymmetry of the scattering rate in strongly correlated electron systems by examining the cubic omega(3) and omega T-2 terms in the imaginary part of the self-energy of the Anderson impurity model. We show that the sign is opposite in the weak-coupling and strong-coupling limits, explaining the differences found in theoretical approaches taking the respective limits as the starting points. The sign change in fact precisely delineates the crossover between the weak- and strong-correlation regimes of the model. For weak interaction U the sign reversal occurs for small values of the doping delta = 1- n, while for interaction of order U approximate to 2 Gamma, Gamma being the hybridization strength, the crossover curve rapidly shifts to the large-doping range. This curve, based on the impurity dynamics, is genuinely different from other crossover curves defined through impurity thermodynamic and static properties
Distinguishing Intra- and Intermolecular Interactions in Liquid 1,2-Ethanediol by H-1 NMR and Ab Initio Molecular Dynamics
No full textThe central OCCO backbone of the 1,2-ethanediol molecule adopts the gauche conformer in the gaseous and crystalline states but exists in conformational equilibrium between gauche and trans in the liquid; an observation that has been attributed to the competition between intra- and intermolecular interactions. Here, we show that the nuclear Overhauser effect (NOE) has the ability to distinguish inter- from intramolecular interactions in liquid 1,2-ethanediol. We do so by exploiting the secondary isotope effect to distinguish the hydroxyl protons of HOCH2CH2OH and the deuterated HOCD2CD2OH in the H-1 NMR spectra of mixtures of the two and, in conjunction with ab initio MD simulations, show how the interplay between inter- and intramolecular interactions gives rise to the conformational isomers in the liquid state of 1,2-ethanediol
Engineering Defect Transition-Levels through the van der Waals Heterostructure
No full textTuning defect levels in 2D semiconductors without significantly altering the integrity of the materials remains one of the most difficult challenges, which critically restricts their usage in electronic and optoelectronic devices. In this study, we demonstrate that the deep levels created by a cation vacancy in a monolayer of MoS2 can be tuned to a shallow level by heterostructuring it with a monolayer of WS2, while maintaining their structural and compositional integrity intact. The overall change in dielectric constant rescales the defect transition levels in a heterostructure. As a result, the deep defect levels are shallowed by nearly 4 (VTMo-1) and 2 (V-w(-1)) times, respectively, compared to their monolayer counterparts. Our finding has the potential to revolutionize the doping strategy of the 2D materials and could pave the way for 2D electronics
Modeling how reversal of immune exhaustion elicits cure of chronic hepatitis C after the end of treatment with direct-acting antiviral agents
No full textA fraction of chronic hepatitis C patients treated with direct-acting antivirals (DAAs) achieved sustained virological responses (SVR), or cure, despite having detectable viremia at the end of treatment (EOT). This observation, termed EOT+/SVR, remains puzzling and precludes rational optimization of treatment durations. One hypothesis to explain EOT+/SVR, the immunologic hypothesis, argues that the viral decline induced by DAAs during treatment reverses the exhaustion of cytotoxic T lymphocytes (CTLs), which then clear the infection after treatment. Whether the hypothesis is consistent with data of viral load changes in patients who experienced EOT+/SVR is unknown. Here, we constructed a mathematical model of viral kinetics incorporating the immunologic hypothesis and compared its predictions with patient data. We found the predictions to be in quantitative agreement with patient data. Using the model, we unraveled an underlying bistability that gives rise to EOT+/SVR and presents a new avenue to optimize treatment durations. Infected cells trigger both activation and exhaustion of CTLs. CTLs in turn kill infected cells. Due to these competing interactions, two stable steady states, chronic infection and viral clearance, emerge, separated by an unstable steady state with intermediate viremia. When treatment during chronic infection drives viremia sufficiently below the unstable state, spontaneous viral clearance results post-treatment, marking EOT+/SVR. The duration to achieve this desired reduction in viremia defines the minimum treatment duration required for ensuring SVR, which our model can quantify. Estimating parameters defining the CTL response of individuals to HCV infection would enable the application of our model to personalize treatment durations