Effects of stoichiometry, purity, etching and distilling on resistance of MgB2 pellets and wire segments

We present a study of the effects of non-stoichiometry, boron purity, wire diameter and post-synthesis treatment (etching and Mg distilling) on the temperature dependent resistance and resistivity of sintered MgB2 pellets and wire segments. Whereas the residual resistivity ratio (RRR) varies between RRR \~ 4 to RRR > 20 for different boron purity, it is only moderately affected by non-stoichiometry (from 20% Mg deficiency to 20% Mg excess) and is apparently independent of wire diameter and presence of Mg metal traces on the wire surface. The obtained set of data indicates that RRR values in excess of 20 and residual resistivities as low as rho{0} ~ 0.4 mu Ohm cm are intrinsic material properties of high purity MgB2

Effect of sintering temperature under high pressure in the uperconductivity for MgB2

We report the effect of the sintering temperature on the superconductivity of MgB2 pellets prepared under a high pressure of 3 GPa. The superconducting properties of the non-heated MgB2 in this high pressure were poor. However, as the sintering temperature increased, the superconducting properties were vastly enhanced, which was shown by the narrow transition width for the resistivity and the low-field magnetizations. This shows that heat treatment under high pressure is essential to improve superconducting properties. These changes were found to be closely related to changes in the surface morphology observed using scanning electron microscopy.Comment: 3 Pages including 3 figure

Conceptual Design of a Manufacturing Process for an Automotive Microchannel Heat Exchanger

Calls for higher fuel efficiency in the United States and Europe are driving the need for waste heat recovery in automotive markets. While conventional heat exchangers can be designed to meet the heat duty requirement, the resulting volume, weight, and thermal mass are too large for rapid transient response and packaging of the device. The lightweight, compact form factor of microchannel heat exchangers with submillimeter flow passages is attractive for automotive applications. However, the industrial use of microchannel heat exchangers continues to be inhibited by high manufacturing costs. The objective of this paper is to develop a microchannel heat exchanger concept capable of meeting the cost and performance goals for an automotive application. So-called printed-circuit microchannel heat exchangers are produced using a stacked-lamina approach in which individual metal laminae are photochemically machined and diffusion bonded. Here, the conceptual design of a microchannel heat exchanger produced using more conventional stamping and joining technologies is discussed for an automotive application. The device is sized to provide waste heat recovery from an exhaust stream to engine coolant for a representative passenger vehicle with acceptable pressure loss. Using the specified design, a process-based cost model is presented showing cost modeling efforts to date including the capital investment and cost-of-goods-sold as a function of annual production volume. The initial results show a pathway for the cost effective integration of compact microchannel heat exchangers into advanced vehicle thermal management systems

Performance evaluation of water-repellent combat uniforms using a static manikin and human subjects under a rainfall tower system

The purpose of the present study was to evaluate the water-repellent properties of newly-developed combat uniforms using a rainfall tower system. Two types of water-repellent- combat uniforms with an identical level of water repellency through textile tests (WR_M and WR_T) were compared with an untreated-combat uniform (Control). A static manikin was used to evaluate water-repellent properties in a standing position and eight male subjects participated to test walking effects under artificial rainfall. The results showed that it took to saturate the upper body was longer for WR_T than WR_M and Control in the standing position for both normal and heavy rain conditions (P < 0.05). The lower body in WR_T was rarely wet in the standing position after 60 min, whereas the lower body was partially wet while walking within 30 min. Changes in clothing weight after the rainfall test were 729 ± 21, 256 ± 36 and 137 ± 25 g per trial for Control, WR_M, and WR_T, respectively (P < 0.001). Subjects expressed better tactile, less colder, less heavier, and less humid sensations and less uncomfortable feeling for WR_T than Control or WR_M (P < 0.05), while WR_M was better only for tactile sensation and heaviness than Control (P < 0.05). Ten-time-washes had not impaired the water-repellent properties of WR_M or WR_T. These results indicated that the rainfall tower test is valid to verify water-repellent property of clothing ensemble and suggest a possibility of classifying the water repellency of clothing ensemble into sub-levels of an excellent and a fair class. Further studies on wider range of experimental conditions to validate the current results are required.This study is funded by Defense Agency for Technology and Quality (20190907EA7-00

Low frequency oscillations assessed by diffuse speckle contrast analysis for foot angiosome concept

An angiosome refers to a 3D tissue volume that is vascularized by a single artery and is a relatively new concept that is useful in vascular surgery; however, the direct relationship between arterial blood flow and micro-perfusion is still controversial. Here, we propose a diffuse speckle contrast analysis (DSCA), which is an emerging tissue perfusion monitoring modality, to investigate the correlations among low frequency oscillations (LFOs) measured from different areas on the feet of healthy subjects. We obtained reproducible results from the correlation analyses of LFOs, and their physiological implications were discussed. In order to confirm the changes in the frequency oscillations, we analyzed and compared the power spectral density changes due to heart rate variability in the electrocardiographic signal during reactive hyperemia and head-up tilt protocols. © 2020, The Author(s).1