Entropy Generation for Negative Frictional Pressure Drop in Vertical Slug and Churn Flows

It is widely accepted that the frictional pressure drop is impossible to be negative for pipe flow. However, the negative frictional pressure drops were observed for some cases of two-phase slug and churn flows in pipes, challenging the general sense of thermodynamic irreversibility. In order to solve this puzzling problem, theoretical investigations were performed for the entropy generation in slug and churn flows. It is found that the frictional pressure drop along with a buoyancy-like term contributes to the entropy generation due to mechanical energy loss for steady, incompressible slug and churn flows in vertical and inclined pipes. Experiments were conducted in a vertical pipe with diameter as 0.04 m for slug and churn flows. Most of the experimental data obtained for frictional pressure drop are negative at high gas–liquid ratios from 100 to 10,000. Entropy generation rates were calculated from experimental data. The results show that the buoyancy-like term is positive and responsible for a major part of entropy generation rate while the frictional pressure drop is responsible for a little part of entropy generation rate, because of which the overall entropy generation due to mechanical energy loss is still positive even if the frictional pressure drop is negative in vertical slug and churn flows. It is clear that the negative frictional pressure drops observed in slug and churn flows are not against the thermodynamics irreversibility.     

Conversion of a head-mounted microphone signal intocalibrated SPL units

A method is reviewed for conversion of a microphone signal into calibrated Sound Pressure Level (SPL) units. The method follows American National Standards Institute (ANSI) standard for S1.4 SPL meters and requires an accurate SPL meter and an accurate calibration sound source for conversion. Accuracy and validation data from test signals and human phonation are provided. The results indicate that under typical speech conditions, an absolute accuracy of plus or minus 1.6 dB (type I SPL meter) can be obtained with a miniature head-mounted microphone.     

Theoretical studies on the structure,sensitivity, density,thermodynamic properties and detonation performance of dinitrobitriazoles

Azodinitro- and dinitroethylene-bridged bitriazoles are of interest in the contest of high explosives, and were found to have true local energy minima at the B3LYP/aug-cc-pVDZ level of theory. The optimised structures, vibrational frequencies and thermodynamic quantities for bitriazoles were obtained in the ground state. Kamlet–Jacobs equations were used to evaluate the performance of bitriazoles based on the predicted density and the calculated heat of explosion. Detonation properties (D = 8.12 to 9.23 km s^?1 and P = 28.0 to 39.83 GPa) of bitriazoles were found to be promising compared with those of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX, D = 8.75 km s^?1 and P = 34.7 GPa) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX, D = 8.96 km s^?1 and P = 35.96 GPa). The fusion of azoles particularly appears to be a promising area for investigation, since it may lead to the desirable consequences of higher heat of explosion, higher density and thus improved detonation performance.     

化学氧碘激光器尾气主动冷却技术试验

使用主动冷却技术降低化学氧碘激光器（COIL）尾气的温度,是提高引射式压力恢复系统引射效率的一项关键技术。采用理论计算和数值模拟的方法,得出了满足技术指标要求的冷却器系统设计参数,并研制了一套以管翅式热交换器、液氮循环汽化提供制冷量的COIL尾气主动冷却试验装置。与激光器的对接试验结果表明,在COIL出光60 s试验中,热交换器可以使尾气温度从590 K降低到160 K,出口截面温度不均匀度小于21 K,经过热交换器的气流总压损失小于100 Pa。     

Microwave Plasmas at Atmospheric Pressure

Microwave plasmas at atmospheric pressure are used for surface treatments like for example cleaning, sterilization or decontamination purposes, for a pre‐treatment to increase the adhesion of lacquer, paint, or glue, and for the deposition of different kind of layers and coatings. Micro plasma jets can also be applied for biomedical applications and for treatment of small and complex geometries like for example the inside of capillaries. Larger plasma torches which exhibit higher gas temperatures can also be used for chemical syntheses like waste gas decomposition, methane pyrolysis, or carbon dioxide dissociation and for plasma spraying purposes. In the present publication an overview on the development and the investigation of the operating principle of two atmospheric pressure microwave plasma torches at frequencies of 2.45 GHz and 915 MHz will be presented. The plasma sources are based on a cylindrical resonator combined with coaxial structures. To explain how these plasma sources work, simulations of the electric field distribution will be discussed. Furthermore, some physical characteristics of an air and an Ar/H2 atmospheric plasma like gas temperatures, excitation temperatures and densities as well as the heating of the plasma by the microwave will be investigated. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-ray difffraction studies on samarium up to one megabar pressure

Abstract

High—pressure crystal structure studies have been performed on Sm up to 100 GPa using synchrotron x-radiation and a diamond anvil cell. The structural sequence Sm-dhcp-fcc-dist.fcc has been confirmed. There is no evidence of any volume collapse. The bulk modulus and its pressure derivative have been determined (B₀ = 30.7 GPa, B₀’ = 2.5).     

Peculiarities of phase transitions when synthesizing diamond in high pressure apparatus of various types

Abstract

The influence of P, T-parmeters and duration of heat when synthesizing diamond in high pressure apparatus both of recessed anvil-type and cylindrical type (belt-type) on properties of diamond powders was studied. The dependence of pressure in reaction cells on temperature of force elements of apparatus in initial state and on efficiency of high pressure production in a reaction cell before heating was shown.     

Raman investigation of hydrostatic and nonhydrostatic compressions of OH‐ and F‐apophyllites up to 8 GPa

Layer silicates F‐ and OH‐apophyllites, KCa₄Si₈O₂₀(F, OH)·8H₂O, have been investigated by Raman spectroscopy at hydrostatic and nonhydrostatic pressures up to ~8 GPa in diamond anvil cells using a 4 : 1 methanol–ethanol mix as pressure‐transmitting medium. Our experiments show that at hydrostatic compression, apophyllites retain their crystalline states (i.e. no amorphization) up to 5 GPa. The wavenumbers of most bands exhibit linear dependences on pressure, except for a few ones, e.g. at 162 and 3565 cm^–1 in OH‐form (160.5 and 3558 cm^–1 in F‐form) that show nonlinear dependences. Nonhydrostatic compression with additional uniaxial loading induces amorphization of apophyllites. The majority of the bands in OH‐apophyllite decreases markedly in intensity and shows considerable broadening under nonhydrostatic compression up to 3–6 GPa. In addition, the wavenumbers of several bands at nonhydrostatic compression exhibit considerable nonlinear dependences on pressure with strong hysteresis. These bands are mainly associated with vibrations of the interlayer ions and molecules and also of stretching and bending silicate sheets, hence being highly sensitive to the interlayer distance. Finally, we have calculated the lattice dynamics of F‐apophyllite and interpreted the majority of bands, and these data are used to explain the complex baric behavior of the bands. Copyright © 2011 John Wiley & Sons, Ltd.     

信息安全服务外包决策分析模型研究

随着信息化的发展,信息安全得到前所未有的重视,国家主管机构的监管越来越严厉,企业在面临强制压力的合规性问题时可以选择自行部署,也可以选择服务外包.通过建立数学模型模拟了这个过程.分析结果表明:在强制压力情况下,如果用户选择外包方式,那么用户信息系统的期望值随着强制压力的提高而降低,信息安全服务供应商的利润则随着强制压力的提高而提高.     

High P–T Raman study of transitions in relaxor multiferroic Pb(Fe0.5Nb0.5)O3

The vibrational and structural properties of Pb(Fe_0.5Nb_0.5)O₃ have been investigated using Raman spectroscopy up to 40 GPa at 300 K and from 300 to 415 K at selected pressures. The measurements reveal three phase transitions, at 5.5, 8.7, and 24 GPa at room temperature. The temperature dependences of the spectra indicate transitions at 1.5 GPa, at 335 and 365 K. The results are consistent with the appearance of an intermediate tetragonal P4mm phase between the ferroelectric R3m and paraelectric Pm‐3m phases. A P–T phase diagram is proposed that allows further insight into the magnetoelectric coupling present in this material. Copyright © 2015 John Wiley & Sons, Ltd.