Evolution of coercivity and its angular dependence in CoFe nanostructures subjected to field cooling

Evolution of coercivity and its angular dependence in CoFe nanostructures subjected to field cooling has been investigated in this work. Spherical CoFe grains with an average diameter of 30 nm were grown on a silicon substrate using electron beam evaporation. Further, the as‐deposited sample was subjected to field cooling. The morphology and topography of the sample before and after field cooling were characterized by atomic force microscopy and SEM. Magnetic force microscopy indicated that there is a good uniformity of magnetization throughout the sample after field cooling. Vibrating sample magnetometer measurements indicate that the coercivity in CoFe nanostructures is dependent on shape of the nanostructures. Copyright © 2013 John Wiley & Sons, Ltd.     

Measurement and modeling of the glass transition temperatures of multi-component solutions

Protein crystals are usually grown in multi-component aqueous solutions containing salts, buffers and other additives. To measure the X-ray diffraction data of the crystal, crystals are rapidly lowered to cryogenic temperatures. On flash cooling, ice frequently forms affecting the integrity of the sample. In order to eliminate this effect, substances called cryoprotectants are added to produce a glassy (vitrified) state rather than ice. Heretofore, the quantity of cryoprotectant needed to vitrify the sample has largely been established by trial and error. In this study, differential scanning calorimetry (DSC) was used to measure the melting (T_m), devitrification (T_d) and glass transition (T_g) temperatures of solutions with a range of compositions typical of those used for growing protein crystals, with the addition of glycerol as cryoprotectant. The addition of cryoprotectant raises the T_g and lowers the T_m of bulk solution thereby decreasing the cooling rates required for vitrification of protein crystals. The theoretical T_g value was calculated using the apparent volume fraction using the Miller/Fox equation extended for multi-component systems. The experimental values of T_g were within approximately ±4% of that predicted by the model. Thus, the use of the model holds the promise of a rational method for the theoretical determination of the composition of cryoprotectant requirement of protein crystallization solutions.     

Fouling Mitigation in a Heat Exchanger: High Cycles of Concentration for a Cooling-Tower Application

The purpose of the present study is to investigate the effect of a physical water treatment (PWT) technology on fouling mitigation in a simulated cooling tower operating at high cycles of concentration. Hard water was produced by evaporating pure water in a circulating open cooling tower, where dissolved calcium carbonate ions became concentrated with time. Heat transfer tests were conducted in a rectangular channel by varying the cycle of concentration (COC) from 5 to 10, and fouling resistances were measured over 270 hrs for each case with and without the PWT treatment. Another test was conducted with no blowdown case with and without the PWT treatment. The fouling resistance at 5 cycles with the PWT treatment was about 70% less than that in the case without the PWT treatment at the end of 270-hr tests. Even at 10 cycles, the PWT treatment reduced the fouling resistance by 60% from the value for the no treatment case. Thus, one can conclude that the PWT technology can help circulating cooling-tower water at relatively high COC for significant freshwater conservation, while keeping fouling resistances below industry standards.     

Cooling Characteristics During Bath Quenching of Test Probe Using Inverse Heat Transfer

It is of engineering importance to accurately predict the surface cooling characteristics in bath quenching of metals and alloys. In this investigation, the surface cooling characteristics in quenching of Wolfson probe are estimated with reasonable accuracy by solving an inverse heat conduction problem. Regularization method is used for smoothening the input temperature measurements at probe center, for superior inversion estimates. The reverse pool-boiling curve is captured on bath quenching characteristic, plotted as cooling velocity versus surface temperature. The prime advantage is the bypassing of convection coefficients, which are uncertain in pool boiling.     

Shock cooling of liquid nitrogen and superfluid helium

Abstract

Superfluid Helium (11) and liquid nitrogen are the only liquids which have been shown experimentally, to exhibit shock cooling. In the present paper we use the Landau model to demonstrate theoretically that the roton gap, which decreases with increasing density, plays the same role leading to shock cooling in liquid helium as the dissociation energy does in liquid nitrogen.     

Performance investigation of an advanced tracked prime mover on the low bearing soil

This study has presented a performance investigation of an advanced tracked prime mover for the operation of agricultural goods and other operations on peat terrain. The maximum and continuous traction torque of the prime mover has been developed by designing an advanced controller for controlling the intelligent system. The prime mover’s mobility is studied with ultrasonic displacement sensor, torque transducer, National Instrument cRIO-9004 Compact-RIO Real-time Controller Unit (RCU), a National Instrument TPC 2106T Touch Panel Control (TPC), a Trimble AG132 GPS antenna and receiver unit, and a Dlink DIR-655 router. The fuzzy logic controller (FLC) has been equipped with the prime mover hydraulic system to increase the traction torque of the hydraulic motor when the prime mover’s sinkage is more than or equal to 70 mm. The prime mover’s design demonstrates good potential in traversing peat terrain as the measured tractive effort was found to be 48% of the vehicle’s gross weight while the recommended tractive effort is in the range of 30–36% of the vehicle’s gross weight.     

真空冷却过程中实验条件对真空冷却速率的影响

以熟肉为实验材料,对实验条件对真空冷却速率的影响进行了理论分析和实验研究。实验结果表明:真空室有效容积越小、真空泵抽速越高,则真空冷却时间就会越短;冷阱温度对真空冷却速率有着明显的影响;当真空室内的最终压力在0.4～0.61kPa变化时,熟肉的表面温度一直在0℃以上,其真空冷却的时间随着真空室内压力的升高而增加。而真空室内的最终压力在0.3kPa左右时,熟肉的表面温度在真空冷却过程会低于0℃。     

Rheological Properties of Model and Crude Oil Systems when Wax Precipitate under Quiescent and Flowing Conditions

Wax precipitation and deposition is a recurring challenge in transportation of crude oil, and increased knowledge about the behavior of such systems is necessary. Microscopy and differential scanning calorimetry were used to follow the crystallisation of wax for two model systems. The amount of solid was also determined by the latter method as well. The flow and viscoelastic behavior were investigated around the wax precipitation temperature, and the yield stress was determined both after dynamic and static cooling. Interpretation of the results was carried out in view of crystal growth and microstructure of the wax crystals. The variables that were studied were wax composition, amount of wax and thermal and shear history.     

冷却速率对Lennard-Jones体系凝固过程中结构与动力学性质的影响

用分子动力学模拟方法研究了五种不同冷却速率对Lennard-Jones体系凝固过程中结构与动力学性质的影响。采用两种不同的方法来确定玻璃转变温度Tg,并且对结晶温度Tc、径向分布函数g(r)、均方位移函数MSD与扩散系数D、平均配位数进行比较分析。结果表明：冷却速率影响Lennard-Jones体系凝固过程中的结构。当使用足够高的冷却速率冷却时,体系发生玻璃化转变,而且冷却速率越快,玻璃转变温度越高;当冷却速率较小时,体系形成晶体,而且冷却速率越慢,结晶温度越高,结晶程度也越高。同时发现,冷却速率对扩散系数和平均配位数也有很大影响,二者在体系发生玻璃转变时都有一个缓变的过程,表明了过冷液相区的存在。