Influence of acoustic leakage at fluid–solid interface on interferometric detection of surface acoustic wave

When using laser interferometer to detect surface acoustic wave at fluid–solid interface, there are two factors which will cause the optical path length variation of the probe laser beam: interface deformation, and refractive index changes in fluid induced by acoustic leakage. Influence of acoustic leakage on laser interferometric detection for surface acoustic wave is researched here. A metal plate immersed in an infinite fluid is used as a physical model. Interface deformation due to laser-induced acoustic wave and pressure in fluid due to acoustic leakage are computed for select cases by finite element method. The optical path length variation caused by the two factors are calculated respectively and compared. The results show that the influence of acoustic leakage increases with the increasing acoustic impedance matching of fluid and solid, the peak-to-peak of influence degree increases linearly with the increasing acoustic impedance of fluid, and that decreasing the distance between the interferometer and interface can effectively reduce the influence of acoustic leakage.     

High field imaging of the normal pancreas

Fifty MR scans conducted at 1.5 T were evaluated to assess how well the pancreas could be identified. A total of 128 sets of images were reviewed. The pancreatic head was identified in 81%, 82% and 74% of scans with T1, intermediate and T2-weighting, respectively. The body was identified in 100%, 96% and 70% and tail in 96%, 87% and 54% on those respective sequences. Relative contrast was calculated between pancreas and: liver, spleen, muscle, fat, stomach and small bowel. The variability seen in contrast compared to stomach and small bowel suggests that consistent MR visualization of the pancreas will probably necessitate the use of an oral contrast agent.     

气相井喷的泄漏源模型及其仿真

 钻井过程的井喷是气田开发中最严重的事故之一,研究气相井喷的泄漏和扩散进而为现场应急提供科学依据,必须首先明确钻井过程中井喷的泄漏源模型。采用流体力学特别是气体动力学理论与计算流体力学技术相结合的方法,分析和模拟了气相井喷的泄漏源模型。通过基于理论分析的数值仿真,得到了气相井喷的温度、静压和马赫数分布等气体动力学参数,仿真结果与理论分析以及相关实验的结论具有很好的一致性。研究表明,钻井过程中气相井喷的泄漏源可以用塞流模型表征,气相井喷可视为欠膨胀射流。     

热漏对换热器(火积)耗散最小化的影响

建立了存在热漏的换热器的传热过程模型.假定热流体与冷流体间的传热以及冷流体与外界环境间的热漏均服从牛顿传热定律,在冷流体净传热量一定的条件下,应用最优控制理论导出了换热过程(火积)耗散最小时热流体温度和冷流体温度的最优构型,并将最优路径分别与热流体温度一定和热流率一定的传统传热策略进行了比较.研究结果对于实际换热器的优化设计和最优运行具有一定的理论指导意义.     

Paramagnetic oil emulsions as oral magnetic resonance imaging contrast agents

The combination of a paramagnetic agent with an oil emulsion can uniformly enhance the small bowel. We discovered that the entire small bowel becomes homogeneously brighter than its surroundings when imaged with all commonly utilized pulse sequences. We have tried various combinations of ferric ammonium citrate, ferrous sulfate, gadolinium-DPTA and corn oil, olive oil and peanut oil. All paramagnetic oil emulsions tested were uniformly distributed throughout the small bowel, but the enhancement effect is much stronger with the ferric ammonium citrate and gadolinium-DPTA oil emulsions. We have also developed a mixture of Geritol, corn oil, ice cream and milk, which uniformly coats the small bowel wall, has good enhancement effect, tastes good, and is nutritious. With this dietary contrast, retroperitoneal structures including the pancreas can be well delineated. We conclude that the combination of a paramagnetic agent with an oil emulsion can work as a safe and effective magnetic resonance imaging (MRI) oral contrast agent with high patient acceptance.     

Time-dependent fluid squeeze-out between solids with rough surfaces

We study the time dependency of the (average) interfacial separation between an elastic solid with a flat surface and a rigid solid with a randomly rough surface, squeezed together in a fluid. As an application we discuss fluid squeeze-out between a tire tread block and a road surface. Some implications for the leakage of seals are discussed, and experimental results are presented to test the theory. The theoretical prediction for the leak rate as a function of the fluid pressure difference is in good agreement with the experimental data for all fluid pressures up to “lift-off”, where the fluid pressure equals the nominal rubber-substrate squeezing pressure.     

叶顶间隙对离心压气机性能影响的研究

叶顶间隙的研究长期以来一直是叶轮机械研究和设计的热点和难点。本文采用CFD软件研究了进口叶尖相对马赫数分别为0．9、1．15、1．3时,有、无间隙的离心叶轮的气动性能,比较了压比、效率及流量的差别。并分析了用于 100 kW微型燃气轮机的高压比、高转速离心压气机在三种不同尺寸叶顶间隙下的性能,讨论了间隙影响的原因。数值模拟结果表明,叶顶间隙在一定范围内时,间隙主要减弱叶轮的升压能力,基本不影响效率和阻塞流量。     

Improved Aerodynamics of a Hollow-Blade Axial Flow Fan by Controlling the Leakage Flow Rate by Air Injection at the Rotating Shroud

Axial flow fans are used in many fields in order to ensure the mass and heat transfer from air, chiefly in the heating, ventilation and air conditioning industry (HVAC). A more proper understanding of the airflow behavior through the systems is necessary to manage and optimize the fan operation. Computational fluid dynamics (CFD) represents a real tool providing the ability to access flow structures in areas that measuring equipment cannot reach. Reducing the leakage flow rate, inherent in operation, by synthetic-jet techniques improves performance. This paper presents the CFD results performed on a hollow blade fan developed by our team. The leakage flow is controlled by blowing air from 16 designated circular holes and arranged on the fan shroud. We discuss the results for two rotational speeds (1000 and 2000 rpm) and two injection rates (400 and 800 L/min). The numerical results consistent with the experimental show, for the low rotation speed and high injection ratio, significant gains in power (53%), torque (80%) and leakage flow rate (80%).     

Leak rate of seals: Effective-medium theory and comparison with experiment

Seals are extremely useful devices to prevent fluid leakage. We present an effective-medium theory of the leak rate of rubber seals, which is based on a recently developed contact mechanics theory. We compare the theory with experimental results for seals consisting of silicon rubber in contact with sandpaper and sand-blasted PMMA surfaces.     

Guided waves in a transversely isotropic cylinder immersed in a fluid

Propagation of flexural guided waves in a fluid-loaded transversely isotropic cylinder is studied. Numerical results are presented for a cobalt cylinder immersed in water. The phase velocities are not significantly affected except for several modes in which the energy leakage occurs into the fluid over certain frequency ranges. Attenuation spectra for the leaking modes are plotted.     

Angiostatin抑制转移性肿瘤血液灌注和间质液输运的数值模拟

数值研究抗血管生成因子Angiostatin对转移性肿瘤微循环内血液灌注和间质液输运的抑制效应.肿瘤微血管网生成数学模型包括angiostatin的抑制效应、促血管生成因子的趋化效应和内皮细胞自身的扩散效应,血液灌注、间质液输运和跨壁流体交换分别采用Poiseuille、Darcy和Starling定律来描述.结果表明:angiostatin能抑制转移性肿瘤内外微血管网的生长速率、毛细血管芽的分叉、融合与增殖;进一步angiostatin可改善转移性肿瘤微环境内血液灌注和间质液输运的特性,从而增加微血管内外流体对流和物质交换的能力,降低肿瘤内药物输运困难,结果与实验相符,可为临床抗血管生成治疗肿瘤提供有益信息.     

基于Kriging代理模型的DBD等离子体控制叶顶泄漏流动研究

本文采用数值方法研究了布置于涡轮动叶叶顶的多个等离子体激励器组合对间隙泄漏流动的影响。结果表明:不同的极板数目和位置组合对间隙泄漏流量有着十分明显的影响。在叶顶沿吸力边布置等离子体激励器的最佳位置在大约55%S/Sps处,布置相同数目的等离子体激励器,在靠近尾缘处的控制效果要远好于在前缘附近的控制效果;等离子体激励器在叶顶靠近吸力边处产生诱导涡,阻碍了间隙内流体的流动,使泄漏流体的速度降低。同时还会使得分离泡的破碎提前,有利于减小掺混损失;对泄漏流动的控制效果不会随着等离子体极板数增加而持续增强,而存在一定限度,最优布置方式的泄漏流量较原型下降约46%,相应的出口截面能量损失下降了15.7%。     

Lagging ignition of combustible fluids in porous media—effect of fuel supply rate*

The effect of fluid leakage into insulation material is considered, where the combustible fluid spread over the inner fibres of the material is both slowly oxidizing and undergoing evaporation/desorption. It is found, in particular, that the constant supply of fuel can lead to unexpected oscillatory behaviour in regions of parameter space which would otherwise have been considered safe. In particular, the case of an extremely slow rate of supply of fluid can be the most deceptive in terms of the possibility of ignition.     

Instability and reconstruction of a thin fluid film under inversion conditions

The development of mechanical instability of a neutral fluid film (liquid helium or hydrogen) under inversion conditions (it does not lie on a solid substrate but hangs from a ceiling) is discussed. Critical parameters of such an instability and the character of surface reconstruction under the action of van der Waals forces, bubble pressure, and gravitational forces are determined. The interrelation with the well-known Frenkel problem of a drop on a solid substrate is pointed out. An electrostatic mechanism is proposed for the stimulation of instability of a thin helium film. This mechanism is promising for the problem of superfluid helium leakage.     

高磁场中纳升(Nanoliter)生物组织固态氢谱及代谢研究

在高磁场21.1 T（900 MHz ¹H NMR)的快速魔角旋转条件下,采用商业化的1.6 mm探头, 生物样品可以在≤1 μL(150 nL,约0.15 mg）和较短的时间（数分钟）内获得满意的代谢产物的固体高分辨氢谱,且仅需对1.6 mm样品管稍作改进. 防止生物样品的泄漏和污染是实验成功的关键因素,因此对于生物样品的封装进行了讨论, 同时对于微量生物样品在高磁场下信噪比的优化策略也进行了理论和实验的探讨. 该文介绍了生物样品的高磁场固体NMR谱学方法在代谢组学的应用,并总结了此领域里的最新研究进展.     

A collagen based vitro model of angiogenesis designed for tissue-engineering material

Angiogenesis is central importance to tissue-engineering. Many vitro models are developed to study the mechanism of angiogenesis, making a great deal of contribution to drug development against tumor, and often may be expensive, time-consuming. Till now, few reported models have been applied to evaluating the effect of degradation fluid of tissue-engineering material to angiogenesis. In present study, we used ECV304 cell as the model cell line, type I collagen matrix that contained no stimulatory factors as a culture substratum to develop a testing model. Tube-like structure (TLS) formed within 8 h on lower density of collagen (0.2, 0.5 mg/ml), which is not found on dense collagen (1, 2 mg/ml). After ECV304 cells were seeded on the surface of collagen matrix, adherence occurred within 1 h. Soon afterwards, ECV304 cells migrated into cell aggregates, then sent out elongated cell processes to form TLS by cytoplasmic anastomosis. Proliferation was obviously perceived during the course. To investigate the efficiency of the model, we took poly(lactic acid) (PLA) degradation fluid with degradation time varying from 1 to 120 days as the testing material. TLS formation is enhanced by ECV304 cells exposed to early degradation fluid before 50-day point, and the trend of inhibition grew as the degradation time increased. Further, no formation was found in degradation fluid after 90-day point. The model is sensitive to the surrounding environment, and can demonstrate the effects of testing material quantitatively to angiogenesis. In summary, the simplicity, reproducibility and miniaturized character of the model described here may make it highly useful as a medium to test the effect of degradation fluid of tissue-engineering material to angiogenesis.     

基于支持向量机的分布式光纤泄漏检测定位系统及实验分析

针对基于Sagnac和Mach-Zehnder混合干涉仪的分布式光纤管道泄漏检测定位系统进行了泄漏实验,采用在1 km~9 km之间的20组泄漏点样本,依据支持向量机建立样本数据的回归模型,对支持向量机的相关调整参数进行了优化,对系统的灵敏度进行了分析。实验结果表明,经SVM回归分析可得,处理后样本比实验所得泄漏点位置更接近实际泄漏点位置,传统定位方法得到的泄漏点位置平均绝对误差为118.85 m,经过回归分析后样本的平均绝对误差为92.01 m,定位精确度达99.85%,定位精度提高;当泄漏点距法拉第旋转镜的距离越远,检测系统的灵敏度越小,当泄漏点位置超过10 km时,系统的灵敏度低于0.5 Hz/m。     

分布式负载垂直极化有界波电磁脉冲模拟器外泄场的规律分析

将基于MPI平台的并行时域有限差分(FDTD)方法与基于完全磁导体(PMC)镜像法相结合,并结合CST模拟软件,模拟给出分布式负载垂直极化有界波电磁脉冲(EMP)的外泄场(包括侧泄场和后泄场)的分布规律。模拟结果与实验结果符合得很好。研究表明:在高度方向上,地面附近的外泄场峰值最大,但远离模拟器时,在1.5 m高的高度范围内,外泄场的峰值差别不大;不管采用何种双指数脉冲源,距离模拟器边缘位置比较近的测点在传输线段的侧泄场的幅值大于分布式负载段侧泄场的幅值,且两者都大于分布式负载末端的后泄场幅值,但随着测点与模拟器边缘的垂直距离的增加,分布式负载段的后泄场可能会比侧泄场大;对于电压峰值相同的双指数激励源而言,所含的高频分量越多,在一定范围内,从其分布式负载末端外泄的后泄场更大;模拟器下方大地的电导率增加,模拟器的外泄场增加。     

考虑中子泄漏修正的快堆蒙特卡罗少群截面参数制作与验证方法

一种基于B1均匀化方程的泄漏修正模型在连续能量蒙特卡罗程序TRIPOLI4中得以实现并且用于制作少群截面参数。此蒙卡泄漏修正模型通过在连续能量的蒙卡模拟以及求解B1均匀化方程之间迭代,最终得到蒙卡模拟下的临界状态。通过此方法得到的少群截面参数较其他蒙卡以及确定论方法有两点显著优势:用于求解B1均匀化方程的少群常数是用通过临界状态的通量谱得到的;考虑了泄漏效应的蒙卡模拟可以更真实地反映组件计算时的能谱状态。为验证此泄漏修正模型,一个由连续能量的TRIPOLI4模拟而得到的数值临界实验被用于分析与比较。通过与其他蒙卡程序SERPENT以及确定论程序ECCO进行结果对比,可证明此B1泄漏修正方法能够给出更精确的用于堆芯计算的少群截面参数。     

Enteric MRI contrast agents: comparative study of five potential agents in humans.

We compared the effectiveness of 1 mM Geritol, 12% corn oil emulsion, Kaolin-pectin, single contrast oral barium sulfate, and effervescent granules as enteric magnetic resonance imaging (MRI) contrast agents. Five volunteers were recruited. Each volunteer ingested for examinations, separated by at least one week, either 500 ml of each of the liquid preparations or two packets of the CO2 granules (producing 400 ml of CO2 per packet). Abdominal MR images were then obtained using a 1.5 T Magnetom imager and SE 550/22, SE 2000/45/90 and FISP 40/18/40 degrees pulse sequences. The oil emulsions were best tolerated. Barium sulfate caused the greatest amount of nausea, followed by Geritol and Kaolin-pectin. With FISP 40/18/40 degrees, 60%-80% of the small bowel was well delineated using oil emulsion, Kaolin-pectin, or barium sulfate. We conclude that oil emulsion was by far the best enteric MR contrast agent in our study. Good delineation of the small bowel and pancreas can be achieved using oil emulsion and gradient echo pulse sequences. The lack of side-effects and the excellent taste make it highly acceptable to human subjects.