50175 research outputs found
Sort by
The response of tropical precipitation to Earth's precession: the role of energy fluxes and vertical stability
No full textThe changes in Earth's precession have an impact on the tropical precipitation. This has been attributed to the changes in seasonal solar radiation at the top of the atmosphere. The primary mechanism that has been proposed is the change in thermal gradient between the two hemispheres. This may be adequate to understand the zonal mean changes, but cannot explain the variations between land and oceans. We have used a simple model of the intertropical convergence zone (ITCZ) to unravel how precipitation changes with precession. Our model attributes the changes in precipitation to the changes in energy fluxes and vertical stability. We include the horizontal advection terms in this model, which were neglected in the earlier studies. The final response of the land and oceans is a result of complex feedbacks triggered by the initial changes in the insolation. We find that the changes in precipitation over the land are mainly driven by changes in insolation, but over the oceans, precipitation changes on account of changes in surface fluxes and vertical stability. Hence insolation can be a trigger for changes in precipitation on orbital timescales, but surface energy and vertical stability play an important role too. The African monsoon intensifies during a precession minimum (higher summer insolation). This intensification is mainly due to the changes in vertical stability. The precipitation over the Bay of Bengal decreases for minimum precession. This is on account of a remote response to the enhanced convective heating to the west of the Bay of Bengal. This weakens the surface winds and thus leads to a decrease in the surface latent heat fluxes and hence the precipitation
Matrices with positive semidefinite real part
No full textMatrices with the property that the real part is positive definite, have been studied for the past five decades or more. Many results in the form of inequalities have been obtained for matrices possessing this property. In this article, a new class of matrices, viz., matrices whose real part is positive semidefinite, is considered, wherein extensions of the results in the literature are obtained
Micromechanical Damage Model for Plain Concrete Considering Propagation of Matrix Microcracks
No full textBased on the tenets of continuum micromechanics, a damage model is developed in the present work to investigate the effect of microcracking on the constitutive relations of cement based materials such as concrete. The model considers concrete as a two phase particulate composite consisting of coarse aggregates and mortar matrix. The microcracks are assumed to be present in the matrix material. Making use of Eshelby's solution for equivalent inclusion, the stress and strain fields are evaluated at the mesoscale. A two step homogenization scheme is adopted to obtain the effective response of the composite. The crack density parameter is used as a damage variable in the formulation. Strain energy release rate, obtained from the micromechanical analysis, is used as the criterion for describing the propagation of microcracks. The effect of various mesoscopic parameters, such as aggregate content, elastic properties of the phases, microcrack density and fracture resistance of the matrix, on the overall behavior of concrete is demonstrated through a parametric study
A high-performance hydrogen sensor based on a reverse-biased MoS2/GaN heterojunction
No full textWe report a MoS2/GaN heterojunction-based gas sensor by depositing MoS2 over a GaN substrate via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The microscopic and spectroscopic measurements expose the presence of highly crystalline and homogenous few atomic layer MoS2 on top of molecular beam epitaxially grown GaN film. Upon hydrogen exposure, the molecular adsorption tuned the barrier height at the MoS2/GaN interface under the reverse biased condition, thus resulting in high sensitivity. Our results reveal that temperature strongly affects the sensitivity of the device and it increases from 21% to 157% for 1% hydrogen with an increase in temperature (25-150 degrees C). For a deeper understanding of carrier dynamics at the heterointerface, we visualized the band alignment across the MoS2/GaN heterojunction having valence band and conduction band offset values of 1.75 and 0.28 eV. The sensing mechanism was demonstrated based on an energy band diagram at the MoS2/GaN interface in the presence and absence of hydrogen exposure. The proposed methodology can be readily applied to other combinations of heterostructures for sensing different gas analytes
Anisotropic Fast Electrically Switchable Emission from Composites of CsPbBr3 Perovskite Quantum Cuboids in a Nematic Liquid Crystal
No full textFast electrically switchable anisotropic photoluminescence from a nano-soft composite comprising a nematic liquid crystal (LC) and quantum cuboids of a cesium lead halide perovskite is reported. The magnitude of the anisotropy in emission appears to be dictated by the anisotropy of the LC and the capability of the cuboids to form a linear chain, the latter being evidenced through optical and electron microscopy. Application of an ac electric field of small amplitude and its consequent coupling to the LC director is employed to continuously vary the magnitude of the green emission. By appealing to a two-frequency protocol, the emission could be alternated between the anisotropic limits 40 times faster than with a standard protocol. These studies assume importance to obtain backlight sources having narrow full-width-at-half-maximum (FWHM) and polarized emission for achieving high-quality low-cost LC displays. While conventionally, the light source and the LC are separate entities, the possibility of combining the two functionalities in a single material is highly desirable from the fabrication point of view
Role of Asian summer monsoon subsystems in the inter-hemispheric progression of deglaciation
No full textThe responses of Asian monsoon subsystems to both hemispheric climate forcing and external orbital forcing are currently issues of vigorous debate. The Indian summer monsoon is the dominant monsoon subsystem in terms of energy flux, constituting one of Earth's most dynamic expressions of ocean-atmosphere interactions. Yet, the Indian summer monsoon is grossly under-represented in Asian monsoon palaeoclimate records. Here, we present high-resolution records of Indian summer monsoon-induced rainfall and fluvial runoff recovered in a sediment core from the Bay of Bengal across Termination II, 139-127 thousand years ago, including coupled measurements of the oxygen isotopic composition and Mg/Ca, Mn/Ca, Nd/Ca and U/Ca ratios in surface-ocean-dwelling foraminifera. Our data reveal a millennial-scale transient strengthening of the Asian monsoon that punctuates Termination II associated with an oscillation of the bipolar seesaw. The progression of deglacial warming across Termination II emerges first in the Southern Hemisphere, then the tropics in tandem with Indian summer monsoon strengthening, and finally the Northern Hemisphere. We therefore suggest that the Indian summer monsoon was a conduit for conveying Southern Hemisphere latent heat northwards, thereby promoting subsequent Northern Hemisphere deglaciation
Thermal insulation of concrete and the repair material CFRP exposed to high temperature and different time intervals
No full textThe present work looks at the effectiveness of thermal insulation of concrete and repair material - CFRP wrapped around concrete cylinders, using geopolymer mortar and simwool ceramic fibre blanket. The thermal insulation tends to prevent delamination of CFRP when exposed to high temperature (400 degrees C-715 degrees C). It is observed from the results there is an improved load deformational response of concrete and CFRP wrapped cylinders due to insulation being applied using geopolymer and fibre blanket when exposed to high temperature is significant. Parametric studies were carried out using FE analysis to validate the experimental results and to study the effectiveness of insulation, for different insulation thickness of geopolymer and cermic fibre blanket
Construction of Index Codes for Interlinked Cycle Structures with Outer Cycles
No full textIndex code construction and decoding algorithm for side-information graphs called interlinked cycle (IC) structures, which generalize cycles and cliques, are given by Thapa, Ong and Johnson (Interlinked Cycles for Index Coding: Generalizing Cycles and Cliques, IEEE Trans. Inf. Theory, vol. 63, no. 6, Jun. 201
Edge Patch-Wise Local Projection Stabilized Nonconforming FEM for the Oseen Problem
No full textIn finite element approximation of the Oseen problem, one needs to handle two major difficulties, namely, the lack of stability due to convection dominance and the incompatibility between the approximating finite element spaces for the velocity and the pressure. These difficulties are addressed in this article by using an edge patch-wise local projection (EPLP) stabilization technique. The article analyses the EPLP stabilized nonconforming finite element methods for the Oseen problem. For approximating the velocity, the lowest-order Crouzeix-Raviart (CR) nonconforming finite element space is considered; whereas for approximating the pressure, two discrete spaces are considered, namely, the piecewise constant polynomial space and the lowest-order CR finite element space. The proposed discrete weak formulation is a combination of the standard Galerkin method, EPLP stabilization and weakly imposed boundary condition by using Nitsche's technique. The resulting bilinear form satisfies an inf-sup condition with respect to EPLP norm, which leads to the well-posedness of the discrete problem. A priori error analysis assures the optimal order of convergence in both the cases, that is, order one in the case of piecewise constant approximation and 3/2 in the case of CR-finite element approximation for pressure. The numerical experiments illustrate the theoretical findings
Electrical Conductivity, Selective Adhesion, and Biocompatibility in Bacteria-Inspired Peptide-Metal Self-Supporting Nanocomposites
No full textBacterial type IV pili (T4P) are polymeric protein nanofibers that have diverse biological roles. Their unique physicochemical properties mark them as a candidate biomaterial for various applications, yet difficulties in producing native T4P hinder their utilization. Recent effort to mimic the T4P of the metal-reducing Geobacter sulfurreducens bacterium led to the design of synthetic peptide building blocks, which self-assemble into T4P-like nanofibers. Here, it is reported that the T4P-like peptide nanofibers efficiently bind metal oxide particles and reduce Au ions analogously to their native counterparts, and thus give rise to versatile and multifunctional peptide-metal nanocomposites. Focusing on the interaction with Au ions, a combination of experimental and computational methods provides mechanistic insight into the formation of an exceptionally dense Au nanoparticle (AuNP) decoration of the nanofibers. Characterization of the thus-formed peptide-AuNPs nanocomposite reveals enhanced thermal stability, electrical conductivity from the single-fiber level up, and substrate-selective adhesion. Exploring its potential applications, it is demonstrated that the peptide-AuNPs nanocomposite can act as a reusable catalytic coating or form self-supporting immersible films of desired shapes. The films scaffold the assembly of cardiac cells into synchronized patches, and present static charge detection capabilities at the macroscale. The study presents a novel T4P-inspired biometallic material