A method for predicting the internal motion resistance of rubber-tracked undercarriages,Pt. 1. A review of the state-of-the-art methods for modeling the internal resistance of tracked vehicles

This article summarizes the known methods for calculating the internal resistance of tracked undercarriages. The values of the coefficient of internal resistance for sample tracked vehicles are available in the literature and presented in this paper. Although they are suitable for simple computations, they cannot be used to optimize the energy efficiency of new generation tracked undercarriages. This problem might be solved by the models where every phenomenon leading to energy dissipation during vehicle motion is described by a separate submodel as a function of vehicle speed, track tension, undercarriage layout, design features of the undercarriage components, etc. This kind of model is still missing for vehicles with conventional rubber tracks. The article presents multiple state-of-the-art models describing rolling resistance of road wheels, bending resistance of rubber belts, etc., including the models of belt conveyors resistance. A vast majority of the phenomena discussed herein are described by several incompatible models whose parameters have not yet been determined for conventional rubber tracks. Consequently, in the second and the third part of the article, the authors have undertaken a theoretical and experimental studies on the methods for calculating and optimizing the internal motion resistance of vehicles with conventional rubber tracks.     

Densely Functionalized 2-Methylideneazetidines: Evaluation as Antibacterials

Twenty-two novel, variously substituted nitroazetidines were designed as both sulfonamide and urethane vinylogs possibly endowed with antimicrobial activity. The compounds under study were obtained following a general procedure recently developed, starting from 4-nitropentadienoates deriving from a common β-nitrothiophenic precursor. While being devoid of any activity against fungi and Gram-negative bacteria, most of the title compounds performed as potent antibacterial agents on Gram-positive bacteria (E. faecalis and three strains of S. aureus), with the most potent congener being the 1-(4-chlorobenzyl)-3-nitro-4-(p-tolyl)azetidine 22, which displayed potency close to that of norfloxacin, the reference antibiotic (minimum inhibitory concentration values 4 and 1–2 μg/mL, respectively). Since 22 combines a relatively efficient activity against Gram-positive bacteria and a cytotoxicity on eucharyotic cells only at 4-times higher concentrations (inhibiting concentration on 50% of the cultured eukaryotic cells: 36 ± 10 μM, MIC: 8.6 μM), it may be considered as a promising hit compound for the development of a new series of antibacterials selectively active on Gram-positive pathogens. The relatively concise synthetic route described herein, based on widely available starting materials, could feed further structure–activity relationship studies, thus allowing for the fine investigation and optimization of the toxico-pharmacological profile.     

微纳米电子器件散热过程中的物理问题

微纳米电子器件的散热问题是目前制约半导体工业发展的重要瓶颈。将电子器件工作时产生的热量传输到封装外壳后再耗散到环境中去需要好几个步骤,每个步骤需要不同的方法,其中有些步骤涉及到了固体中的界面热传导问题和高性能导热材料。文章先介绍了近期关于微纳米尺度器件散热问题中碰到的热传导问题在理论和实验两方面的研究进展。在热传导理论和计算方法方面,作者讨论了傅里叶定律在微纳米尺度的适用性,介绍了玻尔兹曼方程、分子动力学模拟和格林函数方法。在热传导实验方面,介绍了用扫描热显微镜测量样品表面温度和用超快激光反射法测量薄膜材料的热导率及其界面热阻。然后介绍了界面热传导问题,包括界面热阻的计算以及电子—声子相互作用对界面热阻的影响。最后作者介绍了关于高性能导热材料方面的最新进展,包括碳基导热材料、晶格结构类似于石墨烯的氮化硼材料、高分子有机材料以及界面热阻材料。     

电磁轨道发射器连续发射的滑动电接触

从滑动电接触电阻大小的角度,详细分析了在时序放电条件下,两颗重约为5 g的电枢,以速度为1 000 m/s,166 Hz连续发射试验。通过近似计算电流所流经轨道电阻及电枢体电阻所产生的温升,对滑动电接触电阻的影响。结果表明:连续发射运行模式下,受轨道表面温度上升的影响,第二发电枢的滑动接触电阻略高于第一发电枢的滑动接触电阻,表面滑动电接触性能受到温升的影响,在两连发的发射情况下,其影响虽不是很大,但多发高频连续发射就必须考虑热管理问题。      

具有黏滞阻力时的最速降线

针对实际应用中存在黏滞阻力的最速降线的问题, 首先推导出适于此类问题的解除约束的广义变分原理, 它适用于具有摩擦阻尼和多自由度系统优化的问题. 得到描述有黏滞阻力情况下最速降线相关函数的微分方程, 它在黏滞阻力为零时即退化为滚轮线. 利用MATLAB数值计算给出了最速降线受黏滞阻力的影响: 在黏滞阻力系数较小时最速降线趋于变凹, 当阻力系数增大到一定值之后最速降线趋于平缓, 当阻力系数很大时最速降线趋于直线.     

高功率TEA CO2激光器气体循环系统的设计

阐述了气体循环系统对高功率TEA CO2激光器的重要作用,分析了系统参数、结构组成及其设计。以体积流量法确定放电区气体流速,采用对称式的结构布局,选用轴流压气机和板翅式热交换器,加入系统附加阻力以确定风机静压参数。研究出的气体循环系统,放电区气体平均流速84.8 m/s,流速不均匀度纵向4.2%、横向0.38%;光学支架振动加速度4×10-2 m/s2,振动位移2.6×10-7 m。在放电体积2.5×10-3 m3、单脉冲注入能量276 J、放电脉宽150 ns条件下,实现了重复频率400 Hz均匀稳定的持续辉光放电,输出了高平均功率激光。     

能量输运对柱状等离子体开关磁场穿透过程的影响

对于高密度、导通时间为μs级的柱状等离子体开关,利用磁流体动力学理论(MHD),对其导通阶段的磁场穿透过程进行了模拟,得到了磁场分布随时间的变化;研究了开关导通过程中能量输运导致的温度不均匀分布对磁场穿透过程的影响。模拟结果表明：对于高密度等离子体开关,磁场以远大于磁扩散速率的速度穿透到等离子体中;在磁压对等离子体产生的压缩效应和欧姆加热效应共同作用下,激波区域的等离子体温度显著升高,这进一步加速了磁场穿透;当考虑能量输运方程时,开关导通时间为0.87 μs,比等温模型的结果0.92 μs短,与实验结果0.87 μs相一致。     

大气压力对激光辐照双层板接触传热的影响

考虑激光辐照下结构变形对双层板接触传热影响可以更真实地反映两板间的传热情况,通过实验和数值模拟分析了大气压力对接触传热的影响。结果表明：大气压力对接触热阻影响非常明显,当大气压力超过一定值后,双层板界面始终接触,后板中心的温升阶段成类抛物形状;当大气压力在某一范围内,大气压力与温度矩产生的靶板挠度相当,接触面时分时合,后板的温升阶段成振荡式类线性增加;当大气压力小于某一特定值时,后板温度有一突跃过程,通过适当的设计有可能观测到该现象。     

A Comprehensive Experimental Investigation of Additives to Enhance Pool Boiling Heat Transfer of a Non-Azeotropic Mixture

Adding nanoparticles or surfactants to pure working fluid is a common and effective method to improve the heat transfer performance of pool boiling. The objective of this research is to determine whether additives have the same efficient impact on heat transfer enhancement of the non-azeotropic mixture. In this paper, Ethylene Glycol/Deionized Water (EG/DW) was selected as the representing non-azeotropic mixture, and a comparative experiment was carried out between it and the pure working fluid. In addition, the effects of different concentrations of additives on the pool boiling heat transfer performance under different heat fluxes were experimentally studied, including TiO₂ nanoparticles with different particle diameters, different kinds of surfactants, and mixtures of nanofluids and surfactants. The experimental results showed that the nanoparticles deteriorated the heat transfer of the EG/DW solution, while the surfactant enhanced the heat transfer of the solution when the concentration closed to a critical mass fraction (CMC). However, the improvement effect was unsteady with the increase in the heat flux density. The experimental results suggest that the mass transfer resistance of the non-azeotropic mixture is the most important factor in affecting heat transfer enhancement. Solutions with 20 nm TiO₂ obtained a steady optimum heat transfer improvement by adding surfactants.