竖直环形通道内液氮流动沸腾的MUSIG模型分析 第二部分:径向气泡直径和界面面积浓度的预测

由于考虑了气泡的破裂和聚合,同两流体模型相比,MUSIG模型(多尺寸组模型)能更准确地描述流场内气泡直径。采用MUSIG模型详细分析了不同壁面热流量,液体入口速度,过冷度以及不同管道高度时通道内气泡相界面面积、当地气泡直径、空泡系数等参数沿径向的分布。分析结果表明,MUSIG模型可用来预测泡弹状流型转变区的流动参数,也即该模型拓展了两流体模型的使用范围。     

微矩形槽平板热管的设计制造及性能分析

目前微槽平板热管成为热管研究和开发的重点。文中简要介绍了平板热管的设计要点及制造工艺,并通过实验,对设计制作的平板热管进行了性能测试。得出如下结论:该平板热管具有良好的启动特性和工作特性;在设计中要注意工质与管壳材料的相容性;制作时要严格控制清洗、检漏、充装等关键工序以保证制作质量。     

Bekenstein-Hawking Cosmological Entropy and Correction Term Corresponding Cosmological Horizon of Rotating and Charged Black String

Utilizing the quantum statistical method and applying the new state density equation motivated by generalized uncertainty principle in quantum gravitaty, we avoid the difficulty in solving wave equation and directly calculate the partition function of bosonic and fermionic field on the background of rotating and charged black string. Then near the cosmological horizon, entropies of bosonic and fermionic field are calculated on the background of black string. When constant A introduced in generalized uncertainty principle takes a proper value, we derive Bekenstein- Hawking entropy and the correction value corresponding cosmologicaJ horizon on the background of rotating and charged black string. Because we use the new state density equation, in our calculation there are not divergent term and small mass approximation in the original brick-wall method. From the view of quantum statistic mechanics, the correction value to Bekenstein-Hawking entropy of the black string is derived. It makes people deeply understand the correction value to the entropy of the black string cosmological horizon in non-spherical coordinate spacetime.     

Bianchi Type V Magnetized String Dust Bulk Viscous Fluid Cosmological Model with Variable Magnetic Permeability

Bianchi Type V magnetized string dust bulk viscous fluid cosmological model with variable magnetic permeability, is investigated. The magnetic field is due to an electric current produced along x-axis. Thus the magnetic fields is in yz-plane and F ₂₃ is the only non-vanishing component of electromagnetic field tensor F _ij . To get the deterministic model in terms of cosmic time t, we have also assumed the condition ζ θ=constant where ζ the coefficient of bulk viscosity and θ the expansion in the model. The behaviour of the model in presence and absence of magnetic field and bulk viscosity and singularities in the model are also discussed.      

The Circular Loop Equation of a Cosmic String with Time-Varying Tension in de Sitter Spacetimes

In this work the equation of circular loops of cosmic string possessing time-dependent tension is studied in the de Sitter spacetime. We find that the cosmic string loops with initial radius r(t ₀)>0.707L, L de Sitter radius, should not collapse to form a black hole. It is also found that in the case of r(t ₀)<0.707L a loop of cosmic string whose tension depends on some power of cosmic time can not become a black hole if the power is lower than a critical value which is associated with the initial size of the loop. Our research gives rise to some important corrections to the conclusion in the case of loops of cosmic string with constant tension in the same background.     

内爆法制备双金属管复合参数的计算机辅助设计

根据爆炸复合窗口理论和内爆轰作用下管的飞行姿态计算公式,编制计算机程序来确定双金属管内爆复合的工艺参数,使得复合参数的选取大为简化。结果表明,该方法可以用于指导内爆法制备双金属管复合工艺参数的选择。     

Average-optimal string matching

The exact string matching problem is to find the occurrences of a pattern of length m from a text of length n symbols. We develop a novel and unorthodox filtering technique for this problem. Our method is based on transforming the problem into multiple matching of carefully chosen pattern subsequences. While this is seemingly more difficult than the original problem, we show that the idea leads to very simple algorithms that are optimal on average. We then show how our basic method can be used to solve multiple string matching as well as several approximate matching problems in average optimal time. The general method can be applied to many existing string matching algorithms. Our experimental results show that the algorithms perform very well in practice.     

Predictions and experimental studies of the tail pipe noise of an automotive muffler using a one dimensional CFD model

The tail pipe noise from a commercial automotive muffler was studied experimentally and numerically under the condition of wide open throttle acceleration in the present research. The engine was accelerated from 1000 to 6000 rpm in 30 s at the warm up condition. The transient acoustic characteristics of its exhaust muffler were predicted using one dimensional computational fluid dynamics. To validate the results of the simulation, the transient acoustic characteristics of the exhaust muffler were measured in an anechoic chamber according to the Japanese Standard (JIS D 1616). It was found that the results of simulation are in good agreement with experimental results at the 2nd order of the engine rotational frequency. At the high order of engine speed, differences between the computational and experimental results exist in the high revolution range (from 5000 to 6000 rpm at the 4th order, and from 4200 to 6000 rpm at the 6th order). According to these results, the differences were caused by the flow noise which was not considered in the simulation. Based on the theory of one dimensional CFD model, a simplified model which can provide an acceptable accuracy and save more than 90% of execution time compared with the standard model was proposed for the optimization design to meet the demand of time to market.     

硫化锰夹杂溶解和微生物存在对不锈钢管发生点蚀

结合发电厂凝汽器不锈钢管内壁腐蚀部位分布规律和腐蚀外貌特征,分别对腐蚀部位沉积物、内壁蚀孔附近管材成分进行扫描电子显微镜观察和能谱分析,探讨了管材中MnS溶解与微生物对凝汽器不锈钢管腐蚀的电化学反应机理,发现二者在点蚀形成过程中具有协同作用,并在综合分析影响不锈钢腐蚀的各种因素的基础上,提出了不锈钢凝汽器在运行过程中应采取的防护措施。     

Radio jets and galaxies as cosmic string probes

The lensing effect of a cosmic string is studied, and some new methods are proposed to detect the cosmic string. The technique for using jets as extended gravitational lensing probes was first explored by Kronberg.We use the “alignment-breaking parameter” ηG as a sensitive indicator of gravitational distortion by a wiggly cosmic string. Then, we applied the non-constant deflection angle to jets, and ηG of a specific jet is just related to the projected slope of the jet. At least three jets in the sample of Square Kilometer Array (SKA) would have significant signals (ηG>10°) if the wiggly infinite cosmic string existed. The distortion of elliptical object is also studied and used to do a statistical research on the directions of axes and ellipticities of galaxies. In the direction of the string, we find that galaxies appear to be more elliptical for an observer and the distribution of apparent ellipticity changes correspondingly. The ellipticity distribution of current SDSS spiral sample has the signalto-noise ratio up to 8.48 which is large enough for astronomical observations. The future survey, such as Large Synoptic Survey Telescope (LSST) and Dark Energy Survey (DES) would weaken the requirement of special geometry in the data processing. As a result, all kinds of distributions, including ellipticity axis distribution, would serve as probes to detect wiggly strings in the near future. In brief, if a wiggly cosmic string existed, these signals would be convenient to be observed with the future weak lensing survey or other surveys in the deep space. If there was no lensing signal in these distributions, it would give the upper limit of the abundance of infinite strings.