Atomistic phenomena in dense fluid shock waves

The shock structure problem is one of the classical problems of fluid mechanics and at least for non-reacting dilute gases it has been considered essentially solved. Here we present a few recent findings, to show that this is not the case. There are still new physical effects to be discovered provided that the numerical technique is general enough to not rule them out a priori. While the results have been obtained for dense fluids, some of the effects might also be observable for shocks in dilute gases.     

复流形局部q-凸楔形上带权的同伦公式

本文得到复流形局部q-凸楔形上(r,s)型微分形式的带权的同伦公式和(r,s)型的方程的带权的连续解,并给出(r,s)型微分形式的不含边界积分的新的带权的同伦公式和(r,s)型的方程的新的带权的连续解.这些新的带权公式尤其适用于具有非光滑边界的局部q-凸楔形,这时不但可以避免边界积分的复杂估计,而且积分密度也不必在边界有定义,只要在区域上有定义就行.其次,引进权因子,带权的积分公式在应用上(比如在函数的插值方面)具有更大的灵活性.     

全变差有界函数列的一致(R)可积性

给出了一致有界单调函数列一致可积性定理 ,由此得出全变差序列有界的收敛函数列的一致可积性 .说明了该结论可判断一些非一致收敛函数列的逐项积分性质 .     

Synthesis of endogenous sperm-activating and attracting factor isolated from ascidian Ciona intestinalis

A chemoattractant candidate named sperm-activating and attracting factor (SAAF) from the eggs of ascidian Ciona intestinalis, was synthesized from chenodeoxycholic acid in 16 steps. The present synthesis led to the unambiguous structure determination of SAAF to be (3R,4R,7R,25S)-3,4,7,26-tetrahydroxycholestane-3,26-disulfate. The synthetic pure specimen was also used to confirm the dual sperm-activating and attracting activity.     

双阱结构含时量子输运的微扰论及输运方程

利用Lewis-Riesenfeld不变量理论和与不变量有关的幺正变换方法研究了双阱结构含时量子 输运的微扰论.获得了双阱内含时薛定谔方程的精确解的完备集，在此基础上，把双阱与左 右热库的相互作用作为微挠，获得了双阱结构一阶近似下的输运方程，并在绝热近似下提供 了一种用于研究量子输运过程中几何相因子(Berry相因子)的方法. 关键词： 含时量子输运 输运方程 不变量 几何相因子     

Probing proton halo of the exotic nucleus28S by elastic electron scattering

Elastic electron scattering on the exotic light nucleus²⁸S is investigated in the plane wave Born approximation. The variation of the squared form factors of²⁸S with momentum transfer is compared with that of³²S. It is found that the behavior of the form factors near the second minimum (with a moderate momentum transfer) is sensitive to the alteration of the charge density distribution of halo protons in²⁸S. This indicates that elastic electron scattering can be a good probe of the structure of proton-halo nuclei.     

Calculation of the Safety Factor of the Ohmic HL-2A Single Null Divertor Discharge

The safety most important factor profile is one of the the plasma discharge. For limiter configuration, people usually use the following cylindrical approximation formula to calculate it q（r）=5r^2BT/RIp where r is the minor radius of the plasma toms, R is the major radius （in m） , BT is the toroidal magnetic field （in T）, Ip is the total toroidal current（in MA）.     

Spectral Domain Analysis of Coaxial Cavities

Coaxial cavities are used in high power gyrotrons as the beam-wave interaction structure. Much research has been devoted to their mode selective properties. A coaxial cavity lacks a sharp boundary at its open end, so it has some physical features that can only be observed using a spectral model, such as frequency-dependent field profiles and mode overlapping effects. These properties are important since cold tests are usually conducted in the frequency domain. This study applies the incident/reflected wave boundary condition to the wave equation of a weakly irregular coaxial waveguide. The resistivity of the wall is considered in the analysis. Calculations reveal that the fixed-position spectrum yields an uncertain resonant frequency and quality factor. Although the maximum-field spectrum can uniquely determine the properties of the coaxial cavity, the resonant frequency obtained using the maximum-field spectral model is inconsistent with that obtained using the temporal model. The field-energy spectrum explains the low Q nature of the coaxial cavity. Moreover, resonant frequencies evaluated using the field-energy spectrum agree precisely with those evaluated using the temporal model.     

Experimental Evaluation of Strain Shielding in Distal Femur in Revision TKA

Theoretical concerns about the use of cemented and press-fit stems in revision total knee arthroplasty (TKA) include stress shielding with adverse effects on prosthesis fixation. Radiological studies have showed distal femoral bone resorption after revision TKA. The revision with use of stems can place abnormal stresses. These stresses can promote the effect of bone stress shielding and may contribute to bone loss. Experimental quantification of strain shielding in the distal synthetic femur following TKA is the main purpose of the present study. Three different constructs of TKA were assessed. The first construct included a stemless femoral component. The other two included a press-fit and a cemented femoral stem. Cortical bone strains were measured experimentally with tri-axial strain gauges in synthetic femurs before and after in-vitro knee surgery. The difference between principal strains of implanted and intact femur was calculated for each strain gauge position. This study indicates that the use of stems in distal femur changes the distribution and magnitude of bone strains. The press-fit stem provoked relevant bone area (stem length) subjected to strain shielding and also originated the highest reduction of strains in the distal region, which can potentially induce bone resorption. The stemless implanted femur produced minor bone strain changes relatively to the intact femur. The use of distal femur stems increases initial stability in the bone, but the observed reduction of strains in this region, relative to the intact femur, provokes strain shielding that can induce bone resorption and may compromise the long term implant stability.     

Effect of Pressure on Fluid Damping in MEMS Torsional Resonators with Flow Ranging from Continuum to Molecular Regime

High quality factor of dynamic structures at micro and nano scale is exploited in various applications of micro electro-mechanical systems (MEMS) and nano electro-mechanical system. The quality factor of such devices can be very high in vacuum. However, when vacuum is not desirable or not possible, the tiny structures must vibrate in air or some other gas at pressure levels that may vary from atmospheric to low vacuum. The interaction of the surrounding fluid with the vibrating structure leads to dissipation, thus bringing down the quality factor. Depending on the ambient fluid pressure or the gap between the vibrating and the fixed structure, the fluid motion can range from continuum flow to molecular flow giving a wide range of dissipation. The relevant fluid flow characteristics are determined by the Knudsen number which is the ratio of the mean free path of the gas molecule to the characteristic flow length of the device. This number is very small for continuum flow and reasonably big for molecular flow. In this paper, we study the effect of fluid pressure on the quality factor by carrying out experiments on a MEMS device that consists of a double gimbaled torsional resonator. Such devices are commonly used in optical cross-connects and switches. We only vary fluid pressure to make the Knudsen number go through the entire range of continuum flow, slip flow, transition flow, and molecular flow. We experimentally determine the quality factor of the torsional resonator at different air pressures ranging from 760 Torr to 0.001 Torr. The variation of this pressure over six orders of magnitude ensures required rarefaction to range over all flow conditions. Finally, we get the variation of quality factor with pressure. The result indicates that the quality factor, Q, follows a power law, Q ∝P ^–r , with different values of the exponent r in different flow regimes. In the second part of the paper, we propose the use of effective viscosity for considering velocity slip conditions in solving Navier–Stokes equation numerically. This concept is validated with analytical results for a simple case and then compared with the experimental results presented in this paper. The study shows that the effective viscosity concept can be used effectively even for the molecular regime if the air-gap to length ratio is sufficiently small (h ₀/L<0.01). As this ratio increases, the range of validity decreases.