Simulation of the instability of an accelerating gaseous envelope

The development of perturbations of the parameters of a dense gaseous envelope traveling with an acceleration driven by a difference in the pressures on either side is investigated numerically. Plane and axisymmetric time-dependent flows of a compressible medium are considered. The effect of both the density of the envelope and the form of the initial perturbations of its shape and motion on the mass cumulation in the compactions formed is studied. The evolutions of the perturbations of a layer and the surface of a contact discontinuity accelerated by an impinging plane shock wave are compared.     

调制不稳定性对级联放大光纤传输系统信噪比的影响

在考虑光纤损耗和级联放大器的情况下，推导了调制不稳定性的产生条件和增益的普适解析表达式，分析了调制不稳定性对信噪比的影响，给出了一个新的计算信噪比的表达式。     

Modeling film flows down inclined planes

A new model of film flow down an inclined plane is derived by a method combining results of the classical long wavelength expansion to a weighted-residuals technique. It can be expressed as a set of three coupled evolution equations for three slowly varying fields, the thickness h, the flow-rate q, and a new variable that measures the departure of the wall shear from the shear predicted by a parabolic velocity profile. Results of a preliminary study are in good agreement with theoretical asymptotic properties close to the instability threshold, laboratory experiments beyond threshold and numerical simulations of the full Navier-Stokes equations. Received: 16 April 1998 / Revised: 29 June 1998 / Accepted: 2 July 1998     

具有HfN/HfO2栅结构的p型MOSFET中的负偏置-温度不稳定性研究

研究了HfN/HfO₂高K栅结构p型金属-氧化物-半导体(MOS)晶体管(MOSFET)中，负 偏置-温度应力引起的阈值电压不稳定性(NBTI)特征.HfN/HfO₂高K栅结构的等效 氧化层厚度(EOT)为1.3nm，内含原生缺陷密度较低.研究表明，由于所制备的HfN/HfO₂ 高K栅结构具有低的原生缺陷密度，因此在p-MOSFET器件中观察到的NBTI属HfN/HfO2高K栅结构的本征特征，而非工艺缺陷引起的；进一步研究表明，该HfN/HfO₂高K栅结构中观察到的NBTI与传统的SiO₂基栅介质p-MOSFET器件中观察 到的NBTI具有类似的特征，可以被所谓的反应-扩散(R-D)模型表征： HfN/HfO₂ 栅结构p-MOSFET器件的NBTI效应的起源可以归为衬底注入空穴诱导的界面反应机理，即在负 偏置和温度应力作用下，从Si衬底注入的空穴诱导了Si衬底界面Si-H键断裂这一化学反应的 发生，并由此产生了Si^＋陷阱在Si衬底界面的积累和H原子在介质层内部的扩散 ，这种Si^＋陷阱的界面积累和H原子的扩散导致了器件NBTI效应的发生. 关键词： 高K栅介质 负偏置-温度不稳定性(NBTI) 反应-扩散(R-D)模型     

The Micro-Theory of Ultra-Short Pulse Propagating in Nonlinear Fiber

The modified quantum nonlinear Schrodinger equation of ultra-short pulse propagating in fiber is derived using dispersion relation and the Hamiltonian of the transmission system. The derived equation is solved with linearization approximation, and modulation instability is analyzed. The equation is also solved with Hartree approximation. The results indicate that pulse power, loss and self-steeping effect change the critical frequency, the maximum gain and the gain spectrum range, but the third order dispersion has no effect on modulation instability. The expectation value of optical field is average of a set of modified classical solitons, and higher order terms change the amplitude, pulse position and phase of soliton.     

The stress driven instability in elastic crystals: Mathematical models and physical manifestations

Summary Equilibrium equations and stability conditions for the simple deformable elastic body are derived by means of considering a minimum of the static energy principle. The energy is supposed to be sum of the volume (elastic) and the surface terms. The ability to change relative positions of different material particles is taken into account, and appropriate natural definitions of the first and second variations of the energy are introduced and calculated explicitly. Considering the case of negligible magnitude of the surface tension, we establish that an equilibrium state of a nonhydrostatically stressed simple elastic body (of any physically reasonable elastic energy potential and of any symmetry) possessing any small smooth part of free surface is always unstable with respect to relative transfer of the material particles along the surface. Surface tension suppresses the mentioned instability with respect to sufficiently short disturbances of the boundary surface and thus can probably provide local smoothness of the equilibrium shape of the crystal. We derive explicit formulas for critical wavelength for the simplest models of the internal and surface energies and for the simplest equilibrium configurations. We also formulate the simplest problem of mathematical physics, revealing peculiarities and difficulties of the problem of equilibrium shape of elastic crystals, and discuss possible manifestations of the above-mentioned instability in the problems of crystal growth, materials science, fracture, physical chemistry, and low-temperature physics.     

Extension of the measuring range of balances

The basic principle of comparing the sample mass with the mass of a reference body in equilibrium gives the equal-armed beam balance a unique accuracy. Main parameters characterising the suitability of the instrument are measuring range, resolution and relative sensitivity (resolution/maximum load). The historical development of the values of these parameters achieved depended strongly on the practical need in those times. Technically unfavourable scales of the oldest Egyptian dynasties (~3000 BC) could resolve mass differences of 1 g and had a relative sensitivity of at least 10^–3. More sophisticated instruments from the 18^th Dynasty (~1567–1320 BC) achieved a relative sensitivity of 10^–4 independent of the size of the instrument. In 350 BC Aristotle clarified the theory of the lever and at about 250 BC Archimedes used the balance for density determinations of solids. The masterpiece of a hydrological balance was Al Chazini’s 'Balance of Wisdom’ built about 1120. Its relative sensitivity was 2⋅10^–5. Real progress took place when scientists like Lavoisier (1743–1794) founded modern chemistry. At the end of the 19^th century metrological balances reached a relative sensitivity of 10^–9 with a maximum load of several kilogrammes. That seems to be the high end of sensitivity of the classical mechanical beam balance with knife edges. Improvements took place by electrodynamic compensation (Emich, Gast). In 1909 Ehrenhaft and Millikan could weigh particles of 10^–15 g by means of electrostatic suspension. In 1957 Sauerbrey invented the oscillating quartz crystal balance. By observing the frequency shift of oscillating carbon nanotubes or of silica nanorods, masses or mass changes in the attogram or zeptogram have been observed recently.     

中学生营养平衡米膳食最佳模式评价

根据中国营养学会推荐的热量标准,研制了中学生营养平衡米膳食最佳模式。按该模式,中学生每日应摄入的膳食品种及其数量如下:主食:营养平衡米,初中男生510~597g,女生468~510g;高中男生618~683g,女生532~575g;副食相同:青菜或水果500g或600g,鱼或肉100g或50g,蛋类40g,大豆制品30g,花生油12.5g,盐6g。调查结果表明,蛋白质、脂肪、碳水化合物,热量摄入量全部达标准要求。Q(蛋白质)∶Q(脂肪)∶Q(碳水化合物):高中男女生为16∶20∶64,初中男、女生分别为17∶20∶63。提示中学生营养平衡米膳食最佳模式使中学生达到营养平衡,建议推广食用。     

The characterization of the capability of a balance

A survey is given on important standardized definitions by which the capability of balances may be characterized. Some modifications are proposed with regard to the use of mass sensors for the continuous determination of mass variations. An important supplement is the relative resolution introduced by Jenemann. Optimum values are presented.I am indepted to H. R. Jenemann for his critical remarks.     

共混合聚(醚-酯)多嵌段共聚物的表面表征及其血液相容性研究

本文通过X-射线光电子能谱(XPS)、表面接触角、表面ξ电位和血液相容性实验,研究了聚(醚-酯)多嵌段共聚物及其共混物的表面组成和性质与血液相容性的关系。实验结果表明,疏水性的PET-PTMO多嵌段共聚物的血液相容性很差,并且与表相中软段的富集量无关;当亲水性的PET-PEO多嵌段共聚物与疏水性的PET-PTMO多嵌段共聚物共混后,发现存在着一个最佳的共混比例,此时材料表面的血小板粘附量大大降低。对于共混物,表相△[C—O)/[C—O]和表面ξ电位可以较好地与血小板粘附量相关联。以上结果清楚地表明,材料表面的亲-疏水性平衡、软段深度层次分布及表面电位是影响血液相容性的重要因素。