Mathematical expression of pressure gradient in the flow of spherical capsules less dense than water

This study yielded a mathematical expression to calculate the pressure gradient (ΔP/L)_m of the flow of a spherical capsule train. An experimental investigation was carried out to determine pressure drops of two-phase mixture flow of spherical ice capsules and water inside the pipelines of cooling systems. Instead of ice capsules, spherical capsules made of polypropylene material whose density (870 kg/m³) is similar to that of ice were used in the experiments. Flow behavior of the spherical capsules, 0.08 m outer diameter, was observed in the measuring section inside plexiglass pipes, 0.1 m inner diameter (ID) and 6 m in length; pressure drops were measured on the 4 m section. The investigation was carried out in the 1.2 × 10⁴ < Re < 1.5 × 10⁵ range and under transport concentration (C_tr) by 5–30%. Dimensionless numbers of the physical event were found out by conducting a dimensional analysis, so that mixture density was expressed in terms of specific gravity and in situ concentration. After arriving at certain conclusions based on the relevant experimental findings and observations, empirical and mathematical models which can be used for calculation of the pressure gradient were developed. Comparison of the mathematical model with the experimental findings revealed that pressure drop values deviated by 2.7% on average for 2.5 × 10⁴ < Re < 1.5 × 10⁵.     

爆炸成型弹丸的试验研究

本文主要介绍了在炸药爆炸驱动下形成EFP的装药结构设计，并对爆炸形成EFP过程进行了必要的光测和电测，得到EFP运动过程的分幅照片，EFP速度－距离曲线。对钢板叠靶及混凝土靶进行了模拟实验，并对破坏效果进行了分析与讨论。     

方管在高速撞击下的能量吸收能力

本文报导了速度约为100m/sec的子弹高速撞击铝合金方管的实验,表明在这种撞击条件下仍与准静态实验中一样,方管仍呈现“开裂与卷曲”的变形破坏模式,并证实了在高速碰撞下方管仍是一种极好的能量吸收装置.理论分析表明,在这种撞击条件下惯性力仍是不重要的;计入了应变率效应之后,理论预计的方管承载能力与实验符合良好.     

列车编组对桥梁振动响应影响的试验研究

通过对两座桥梁振动测试结果的分析，发现列车编组对桥梁振动响应很有影响，且这一现象过去常常被忽略。本文详细研究了列车编组与桥梁横向振动响应之间的关系，同时还就一座桥梁加固后的试验结果进行分析，指出用改善列车编组的方法提高桥梁动态性能的必要性和可行性。     

加载功率与壳温对AlGaN/GaN高速电子迁移率晶体管器件热阻的影响

结温是制约器件性能和可靠性的关键因素, 通常利用热阻计算器件的工作结温. 然而, 器件的热阻并不是固定值, 它随器件的施加功率、温度环境等工作条件的改变而变化. 针对该问题, 本文以CREE公司生产的高速电子迁移率晶体管(HEMT)器件为研究对象, 利用红外热像测温法与Sentaurus TCAD模拟法相结合, 测量研究了AlGaN/GaN HEMT器件在不同加载功率以及管壳温度下热阻的变化规律. 研究发现: 当器件壳温由80 ℃升高至130 ℃时, 其热阻由5.9 ℃/W变化为6.8 ℃/W, 增大15%, 其热阻与结温呈正反馈效应; 当器件的加载功率从2.8 W增加至14 W时, 其热阻从5.3 ℃/W变化为6.5 ℃/W, 增大22%. 对其热阻变化机理的研究发现: 在不同的管壳温度以及不同的加载功率条件下, 由于材料导热系数的变化导致其热阻随温度与加载功率的变化而变化.     

Linear Response of General Observables in Spiking Neuronal Network Models

We establish a general linear response relation for spiking neuronal networks, based on chains with unbounded memory. This relation allow us to predict the influence of a weak amplitude time dependent external stimuli on spatio-temporal spike correlations, from the spontaneous statistics (without stimulus) in a general context where the memory in spike dynamics can extend arbitrarily far in the past. Using this approach, we show how the linear response is explicitly related to the collective effect of the stimuli, intrinsic neuronal dynamics, and network connectivity on spike train statistics. We illustrate our results with numerical simulations performed over a discrete time integrate and fire model.     

磁浮轨道交通的专利技术发展态势

利用专利数据和文献数据分析工具,对德温特数据库(DII)和WOS核心数据库中磁浮轨道交通产业技术的相关专利进行检索和系统分析,以了解目前全球磁浮轨道交通产业技术领域的发展现状、研发热点、技术分布情况和专利权人格局,以及通过对全球磁浮轨道交通产业技术的论文数量、研究机构、研究热点等方面的计量分析,探寻中国发展磁浮轨道交通产业技术面临的机会与挑战,以期为中国磁浮轨道交通产业的发展提供决策参考及依据.     

Rapid large-scale preparation of polysaccharides from jackfruit peel waste by high-speed countercurrent chromatography and their antioxidant and hypoglycemic activities

Polysaccharides with antioxidant and hypoglycemic activities were first isolated from jackfruit (Artocarpus heterophyllus Lam.) peel through the one-step high-speed countercurrent chromatography. The separation process was completed using the polymer two-phase aqueous system constituted by PEG1000-K₂HPO₄-KH₂PO₄-H₂O (0.8:1.25:1.25:6.5, w/w). For every separation process, two main polysaccharides, namely, fraction-1 and fraction-2 (165 and 225 mg, respectively) were obtained from a 2.0 g crude sample. As suggested by high-performance gel permeation chromatography, jackfruit peel polysaccharides had the mean molecular weight values of 113.3 and 174.3 kDa, separately. Physicochemical analysis suggested that two polysaccharides were dominant in galacturonic acid, galactose, rhamnose, arabinose, glucose, mannose, as well as fucose, which were highly esterified. Biological activity analysis showed that fraction-1 exhibited stronger antioxidant activity in vitro and hypoglycemic activity in streptozotocin-induced diabetic mice compared with fraction-2. The results suggest that polysaccharide fraction-1 may be developed as a potential functional food supplement.     

隧道中高速列车空气阻力的数值计算

对高速列车在隧道中行驶时所引起的湍流场进行了数值模拟，计算了列车所受到的空气阻力。数值计算采用变密度、轴对称的ｋ～ε模型和ＰＩＳＯ算法，并将粗糙面速度分布公式和尼古拉兹公式引入壁函数法中，以反映壁面粗糙度的影响，提出了对不规则边界的速度修正法。针对不同的车速、阻塞比和车头细长比，分别进行了模拟，获得了全场的压力分布，以及空气阻力与基本参数的关系，并与传统的经典方法阻力计算结果进行了对比分析。     

High-speed observation of ultrahigh-speed submerged water jets

Some peculiar phenomena occur around ultrahigh-speed submerged water jets accompanied by very severe cavitation erosion. Using the flow visualization technique with a xenon flash, the water jets were carefully observed, and the spatial distributions of highly erosive impulsive pressures around the jets were measured by means of a pressure-sensitive film technique. The effects of the injection pressure and the nozzle configuration are systematically clarified. Thus, the characteristics and structures of ultrahigh-speed submerged water jets are clearly shown.