Small-scale Interaction of Turbulence with Thermonuclear Flames in Type Ia Supernovae

Microscopic turbulence-flame interactions of thermonuclear fusion flames occuring in Type Ia Supernovae were studied by means of incompressible direct numerical simulations with a highly simplified flame description. The flame is treated as a single diffusive scalar field with a nonlinear source term. It is characterized by its Prandtl number, Pr << 1, and laminar flame speed, S_L. We find that if S_L ~ u', where u' is the rms amplitude of turbulent velocity fluctuations, the local flame propagation speed does not significantly deviate from S_L even in the presence of velocity fluctuations on scales below the laminar flame thickness. This result is interpreted in the context of subgrid-scale modeling of supernova explosions and the mechanism for deflagration-detonation-transitions.Comment: 8 pages, 6 figures, accepted by Astrophys.

Effect of Microwave Irradiation on the Dielectric Characteristics of Semi-Conductive Nanoparticle-Based Nanofluids: Progress towards the Microwave Synthesis

Studies on dispersing nanoparticles in base fluid to elevate its essential and critical properties have evolved significantly in the recent decade. Alongside the conventional dispersion techniques used for nanofluid synthesis, microwave energy at 2.4 GHz frequency is irradiated onto the nanofluids is experimented with in this study. The effect of microwave irradiation on the electrical and thermal properties of semi-conductive nanofluids (SNF) is investigated and presented in this article. Titanium dioxide and zinc oxide are the semi-conductive nanoparticles used for this study to synthesize the SNF, viz., titania nanofluid (TNF) and zinc nanofluid (ZNF). Flash and fire points are the thermal properties verified, and dielectric breakdown strength, dielectric constant ((Formula presented.)), and dielectric dissipation factor (tan (Formula presented.)) are the electrical properties verified in this study. AC breakdown voltage (BDV) of TNF and ZNF is improved by 16.78% and 11.25%, respectively, more than SNFs prepared without microwave irradiation. Results justify that the synergetic effect of stirring, sonication, and microwave irradiation in a rational sequence (microwave synthesis) exhibited better electrical and unaltered thermal properties. This microwave-applied nanofluid synthesis could be a simple and effective route to prepare the SNF with improved electrical properties

Cubic Augmentation of Planar Graphs

In this paper we study the problem of augmenting a planar graph such that it becomes 3-regular and remains planar. We show that it is NP-hard to decide whether such an augmentation exists. On the other hand, we give an efficient algorithm for the variant of the problem where the input graph has a fixed planar (topological) embedding that has to be preserved by the augmentation. We further generalize this algorithm to test efficiently whether a 3-regular planar augmentation exists that additionally makes the input graph connected or biconnected. If the input graph should become even triconnected, we show that the existence of a 3-regular planar augmentation is again NP-hard to decide.Comment: accepted at ISAAC 201

Yeast functional screen to identify genetic determinants capable of conferring abiotic stress tolerance in Jatropha curcas

<p>Abstract</p> <p>Background</p> <p>Environmentally inflicted stresses such as salinity and drought limit the plant productivity both in natural and agricultural system. Increasing emphasis has been directed to molecular breeding strategies to enhance the intrinsic ability of plant to survive stress conditions. Functional screens in microorganisms with heterologous genes are a rapid, effective and powerful tool to identify stress tolerant genes in plants. <it>Jatropha curcas </it>(Physic nut) has been identified as a potential source of biodiesel plant. In order to improve its productivity under stress conditions to benefit commercial plantations, we initiated prospecting of novel genes expressed during stress in <it>J. curcas </it>that can be utilized to enhance stress tolerance ability of plant.</p> <p>Results</p> <p>To identify genes expressed during salt tolerance, cDNA expression libraries were constructed from salt-stressed roots of <it>J. curcas</it>, regulated under the control of the yeast <it>GAL1 </it>system. Using a replica based screening, twenty thousand yeast transformants were screened to identify transformants expressing heterologous gene sequences from <it>J. curcas </it>with enhanced ability to tolerate stress. From the screen we obtained 32 full length genes from <it>J. curcas </it>[GenBank accession numbers <ext-link ext-link-id="FJ489601" ext-link-type="gen">FJ489601</ext-link>-<ext-link ext-link-id="FJ489611" ext-link-type="gen">FJ489611</ext-link>, <ext-link ext-link-id="FJ619041" ext-link-type="gen">FJ619041</ext-link>-<ext-link ext-link-id="FJ619057" ext-link-type="gen">FJ619057</ext-link> and <ext-link ext-link-id="FJ623457" ext-link-type="gen">FJ623457</ext-link>-<ext-link ext-link-id="FJ623460" ext-link-type="gen">FJ623460</ext-link>] that can confer abiotic stress tolerance. As a part of this screen, we optimized conditions for salt stress in <it>J. curcas</it>, defined parameters for salt stress in yeast, as well as isolated three salt hypersensitive yeast strains <it>shs-2, shs-6 </it>and <it>shs-8 </it>generated through a process of random mutagenesis, and exhibited growth retardation beyond 750 mM NaCl. Further, we demonstrated complementation of the salt sensitive phenotypes in the <it>shs </it>mutants, and analyzed the expression patterns for selected <it>J. curcas </it>genes obtained from the screen in both leaf and root tissues after salt stress treatments.</p> <p>Conclusions</p> <p>The approach described in this report provides a rapid and universal assay system for large scale screening of genes for varied abiotic stress tolerance within a short span of time. Using this screening strategy we could isolate both genes with previously known function in stress tolerance as well as novel sequences with yet unknown function in salt stress tolerance from <it>J. curcas</it>. The isolated genes could be over-expressed using plant expression system to generate and evaluate transgenic plants for stress tolerance as well as be used as markers for breeding salt stress tolerance in plants.</p

Cloud microphysical effects of turbulent mixing and entrainment

Turbulent mixing and entrainment at the boundary of a cloud is studied by means of direct numerical simulations that couple the Eulerian description of the turbulent velocity and water vapor fields with a Lagrangian ensemble of cloud water droplets that can grow and shrink by condensation and evaporation, respectively. The focus is on detailed analysis of the relaxation process of the droplet ensemble during the entrainment of subsaturated air, in particular the dependence on turbulence time scales, droplet number density, initial droplet radius and particle inertia. We find that the droplet evolution during the entrainment process is captured best by a phase relaxation time that is based on the droplet number density with respect to the entire simulation domain and the initial droplet radius. Even under conditions favoring homogeneous mixing, the probability density function of supersaturation at droplet locations exhibits initially strong negative skewness, consistent with droplets near the cloud boundary being suddenly mixed into clear air, but rapidly approaches a narrower, symmetric shape. The droplet size distribution, which is initialized as perfectly monodisperse, broadens and also becomes somewhat negatively skewed. Particle inertia and gravitational settling lead to a more rapid initial evaporation, but ultimately only to slight depletion of both tails of the droplet size distribution. The Reynolds number dependence of the mixing process remained weak over the parameter range studied, most probably due to the fact that the inhomogeneous mixing regime could not be fully accessed when phase relaxation times based on global number density are considered.Comment: 17 pages, 10 Postscript figures (figures 3,4,6,7,8 and 10 are in reduced quality), to appear in Theoretical Computational Fluid Dynamic

The Rapid Evaluation of COVID-19 Vaccination in Emergency Departments for Underserved Patients Study

Early evidence has suggested a high prevalence of acute pulmonary embolism (PE) in Coronavirus 19 (COVID). However, the bulk of existing data evaluates the population of COVID patients admitted to an intensive care unit (ICU). There has been limited evidence in the emergency department (ED) population and as a result, there is variability in diagnostic evaluation for patients presenting with COVID. The objective of this study was to describe the diagnostic evaluation of both COVID positive and negative patients in the ED

Polynomial time algorithms to determine weakly reversible realizations of chemical reaction networks

Weak reversibility is a crucial structural property of chemical reaction networks (CRNs) with mass action kinetics, because it has major implications related to the existence, uniqueness and stability of equilibrium points and to the boundedness of solutions. In this paper, we present two new algorithms to find dynamically equivalent weakly reversible realizations of a given CRN. They are based on linear programming and thus have polynomial time-complexity. Hence, these algorithms can deal with large-scale biochemical reaction networks, too. Furthermore, one of the methods is able to deal with linearly conjugate networks, too. © 2014 Springer International Publishing Switzerland

Statistical Properties of Turbulence: An Overview

We present an introductory overview of several challenging problems in the statistical characterisation of turbulence. We provide examples from fluid turbulence in three and two dimensions, from the turbulent advection of passive scalars, turbulence in the one-dimensional Burgers equation, and fluid turbulence in the presence of polymer additives.Comment: 34 pages, 31 figure