Hydrodynamics at the smallest scales: a solvability criterion for Navier-Stokes equations in high dimensions

Strong global solvability is difficult to prove for high-dimensional hydrodynamic systems because of the complex interplay between nonlinearity and scale invariance. We define the Ladyzhenskaya-Lions exponent α(L)(n)=(2+n)/4 for Navier-Stokes equations with dissipation -(-Δ)(α) in R(n), for all n≥2. We review the proof of strong global solvability when α≥α(L)(n), given smooth initial data. If the corresponding Euler equations for n>2 were to allow uncontrolled growth of the enstrophy (1/2)∥?u∥(L2)(2), then no globally controlled coercive quantity is currently known to exist that can regularize solutions of the Navier-Stokes equations for α<α(L)(n). The energy is critical under scale transformations only for α=α(L)(n).     

Experimental investigation of link between growth and decay of fiber Bragg gratings

We report here an experimental investigation for establishing and quantifying a link between the growth and decay characteristics of fiber Bragg gratings. One of the key aspects of our work is the determination of the defect energy distribution from the grating characteristics measured during their fabrication. We observe a strong correlation between the growth-based defect energy distribution and that obtained through accelerated aging experiments, paving the way for predicting the decay characteristics of fiber Bragg gratings from their growth data. Such a prediction is significant in simplifying the postfabrication steps required to enhance the thermal stability of fiber Bragg gratings.     

Influence of hydrogen content on impact toughness of Zr-2.5Nb pressure tube alloy

Influence of hydrogen content on the impact toughness of Zr-2.5% Nb alloy was examined by carrying out instrumented drop weight tests in the temperature range of 25-250 °C using curved Charpy specimens fabricated from unirradiated pressure tubes of Indian Pressurized Heavy Water Reactor (IPHWR). Hydrogen content of the samples was between 10 and 170 ppm by weight (wppm). Sharp ductile-to-brittle-transition behaviour was demonstrated by hydrided materials. The temperature for the onset of transition increased with the increase in the hydrogen content of the specimens. The fracture surfaces of unhydrided specimen exhibited ductile fracture caused by micro void coalescence and tear ridges at lower temperatures and by fibrous fracture at intermediate and at higher temperatures. Except for the samples tested at the upper shelf energy levels, the fracture surfaces of all hydrided samples were suggestive of hydride assisted failure. In most cases the transverse cracks observed in the fracture path matched well with the hydride precipitate distribution and orientation.     

Rheological behavior ‐ Electrical and thermal properties of polypyrrole/graphene oxide nanocomposites

Polypyrrole/graphene oxide (Ppy/GO) nanocomposites were synthesized via in situ polymerization of pyrrole in the presence of GO at various proportions (1–5%). They were characterized to determine their electrical, thermal, and rheological properties by various techniques. The aim of this study was to determine the rheological behavior of Ppy/GO nanocomposite at different mass ratios (100 : 1, 100 : 2, 100 : 3, 100 : 4, and 100 : 5%) and temperature (25–180°C) using a rotational mode in cone‐plate method. The shear stress (τ Pa) and viscosity (η Pa s) values of the nanocomposites increased with the increase in GO mass ratio added to Ppy, which was accompanied by an increased flexibility of the nanocomposites due to the higher aspect ratio of the GO sheet. Hence, it is suggested that the GO sheets are effective for the reinforcement of Ppy thereby significantly improvising its thermal stability, electrical conductivity, and rheological properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40642.     

Particulate matter air pollution disrupts endothelial cell barrier via calpain-mediated tight junction protein degradation

ABSTRACT: BACKGROUND: : Exposure to particulate matter (PM) is a significant risk factor for increased cardiopulmonary morbidity and mortality. The mechanism of PM-mediated pathophysiology remains unknown. However, PM is proinflammatory to the endothelium and increases vascular permeability in vitro and in vivo via ROS generation. OBJECTIVES: We explored the role of tight junction proteins as targets for PM-induced loss of lung endothelial cell (EC) barrier integrity and enhanced cardiopulmonary dysfunction. METHOD: S: Changes in human lung EC monolayer permeability were assessed by Transendothelial Electrical Resistance (TER) in response to PM challenge (collected from Ft. McHenry Tunnel, Baltimore, MD, particle size >0.1 um). Biochemical assessment of ROS generation and Ca2+ mobilization were also measured. RESULTS: : PM exposure induced tight junction protein ZO-1 relocation from the cell periphery, which was accompanied by significant reductions in ZO-1 protein levels but not in adherens junction proteins (VE-cadherin and beta-catenin). N-acetyl-cysteine (NAC, 5mM) reduced PM-induced ROS generation in ECs, which further prevented TER decreases and atteneuated ZO-1 degradation. PM also mediated intracellular calcium mobilization via the transient receptor potential cation channel M2 (TRPM2), in a ROS-dependent manner with subsequent activation of the Ca2+-dependent protease calpain. PM-activated calpain is responsible for ZO-1 degradation and EC barrier disruption. Overexpression of ZO-1 attenuated PM-induced endothelial barrier disruption and vascular hyperpermeability in vivo and in vitro. CONCLUSIONS: : These results demonstrate that PM induces marked increases in vascular permeability via ROS-mediated calcium leakage via activated TRPM2, and via ZO-1 degradation by activated calpain. These findings support a novel mechanism for PM-induced lung damage and adverse cardiovascular outcomes.     

Fatigue behaviour of post weld heat treated electron beam welded AA2219 aluminium alloy joints

This paper reports the effect of post weld heat treatment on fatigue behaviour of electron beam welded AA2219 aluminium alloy. An attempt has been made to enhance the fatigue strength of the electron beam welded joints through post weld heat treatment methods such as solution treatment, artificial aging, solution treatment and artificial aging. Electron beam welding machine with 100 kV capacity has been used to fabricate the square butt joints. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN has been used to evaluate the fatigue life of the welded joints. Of the three post weld heat treated joints, the solution treated and aged joints are enduring higher number of cycles under the action of cyclic loads.     

Microwave-assisted rapid synthesis of anisotropic Ag nanoparticles by solid state transformation

Anisotropic silver nanoparticles (NPs) have been synthesized rapidly using microwave irradiation by the decomposition of silver oxalate in a glycol medium using polyvinyl pyrolidone (PVP) as the capping agent. The obtained Ag nanoparticles have been characterized by UV-visible spectroscopy, powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) studies. Anisotropic Ag nanoparticles of average size around 30?nm have been observed in the case of microwave irradiation for 75?s whereas spherical particles of a size around 5-6?nm are formed for 60?s of irradiation. The texture coefficient and particle size calculated from XRD patterns of anisotropic nanoparticles reveal the preferential orientation of (111) facets in the Ag sample. Ethylene glycol is found to be a more suitable medium than diethylene glycol. A plausible mechanism has been proposed for the formation of anisotropic Ag nanoparticles from silver oxalate.     

Fluorescence changes of aflatoxins B1 and G1.

The effects of various factors, such as pH, buffer, sodiumchloride and ultra-violet radiation on the fluorescence of aflatoxins B1 and G1 have been studied. The fluorescence characteristics of aflatoxins B1 and G1 underwent a marked change at pH values above 7.2. Prolonged exposure to ultra-violet radiation lead to some degradation of aflatoxins and the extent of degradation was dependent upon the nature of the solvent. Sodium chloride partially protected the toxins from degradation by ultra-violet radiation or alkaline conditions.     

Flicker noise in CMOS transistors from subthreshold to stronginversion at various temperatures

Flicker noise is the dominant noise source in silicon MOSFET's. Even though considerable amount of work has been done in investigating the noise mechanism, controversy still exists as to the noise origin. In this paper, a systematic study of flicker noise in CMOS transistors from twelve different fabricators is reported under various bias conditions corresponding to the gate voltage changing from subthreshold to strong inversion, and the drain voltage changing from linear to saturation regions of operation. The measurement temperature was varied from room temperature down to 5 K. Experimental results consistently suggest that 1/f noise in n-channel devices is dominated by carrier-density fluctuation while in p-channel devices the noise is mainly due to mobility fluctuation