电磁轨道发射器连续发射的滑动电接触

从滑动电接触电阻大小的角度,详细分析了在时序放电条件下,两颗重约为5 g的电枢,以速度为1 000 m/s,166 Hz连续发射试验。通过近似计算电流所流经轨道电阻及电枢体电阻所产生的温升,对滑动电接触电阻的影响。结果表明:连续发射运行模式下,受轨道表面温度上升的影响,第二发电枢的滑动接触电阻略高于第一发电枢的滑动接触电阻,表面滑动电接触性能受到温升的影响,在两连发的发射情况下,其影响虽不是很大,但多发高频连续发射就必须考虑热管理问题。      

Position dependence of average electron velocity in a submicrometer GaAs channel

The Monte Carlo method has been applied to obtain the average electron velocity at different positions of a submicrometer GaAs channel in the presence of a position independent electric field. Velocity-distance curves are presented for channel lengths of 0.1, 0.2, and 0.5 m and for lattice temperatures of 300 and 77 K. The curves show significant effects of collisions and boundary conditions.     

Temperature dependence of hole saturation velocity in silicon

Thep ⁺ np ⁺ diode is used to determine the hole drift velocity versus field curves in silicon as a function of temperature. By taking the analytical expression of the hole drift velocity,v=v _m (E/E _c )/(1+E/E _c ),v _m andE _c are obtained in the temperature range from 210–420 K.v _m varies from 1.04×10⁷ cm/sec at 210 K to 1.11×10⁷ cm/sec at 420 K, whileE _c increases from 1.05×10⁴ V/cm at 210 K to 5.3×10⁴ V/cm at 420 K. The curve at 300 K is very close to the result of Norris and Gibbons.     

Temperature dependence of the universal contact parameter in a unitary Fermi gas

The contact I, introduced by Tan, has emerged as a key parameter characterizing universal properties of strongly interacting Fermi gases. For ultracold Fermi gases near a Feshbach resonance, the contact depends upon two quantities: the interaction parameter 1/(k(F)a), where k(F) is the Fermi wave vector and a is the s-wave scattering length, and the temperature T/T(F), where T(F) is the Fermi temperature. We present the first measurements of the temperature dependence of the contact in a unitary Fermi gas using Bragg spectroscopy. The contact is seen to follow the predicted decay with temperature and shows how pair-correlations at high momentum persist well above the superfluid transition temperature.     

Nonlinear dependence of the contact angle of nanodroplets on contact line curvature

We have measured the contact angle of microsized and nanosized alkane droplets partially wetting a model substrate using true noncontact atomic force microscopy. The large range of droplet sizes accessible using this technique allowed us to determine the contact line curvature dependence of the contact angle with unprecedented accuracy. Whereas previous studies aimed at explaining such a dependence by a line tension effect, our results and calculations on a model system exclude such an effect and point to an extreme sensitivity to weak substrate heterogeneities confirmed by numerical simulations.     

表面黏附导致的接触行为转变

应用大规模分子动力学方法, 模拟了具有不同原子级粗糙形貌的两种刚性球形探头与弹性平面基体的黏附接触行为. 研究了载荷与真实接触面积、接触界面排斥力与真实接触面积, 以及黏附力与真实接触面积之间的关系. 分子模拟得到的载荷与真实接触面积的关系, 与连续力学接触理论预测很好地定性一致. 无论是原子级光滑探头还是粗糙探头, 黏附接触下的排斥力与真实接触面积的关系, 都与无黏附接触时的规律相一致, 即黏附力对接触行为的影响作用, 可以等效为附加在真实外载荷基础上的虚拟载荷, 将对黏附接触行为的分析转变为无黏附接触分析. 两种探头的黏附力随真实接触面积都呈幂函数形式的增长, 但是, 原子级光滑探头的幂指数大于1, 而原子级粗糙探头的幂指数小于1. 关键词： 接触行为 表面黏附 分子动力学模拟     

Intensity dependence of flow signal in slice selective velocity measurements

The quantitative determination of flow velocities using inflow-outflow techniques require slice selective excitation pulses. The intensity-velocity relationship for such methods is shown to be such that flow velocities estimated using techniques which rely on an absolute calibration of the measured intensity are sensitive to the details of the slice profile of the excited material. This can cause errors when the estimation of flow velocities is made from the image intensity. A method which provides a measure of the flow velocities and which relies only on relative variations in intensity is examined and shown to be insensitive to details of the slice profile.     

The anomalous temperature dependence of the sound velocity in water

The quantum yields of naphthalene vapour fluorescence at 225°c and of phenanthrene vapour fluorescence at 365°c excited by the Hg 313 μ line are independent of concentration up to 0·014 and 0·007 moles/l. respectively; this is attributed to fast dissociation relaxation of the excimer at these temperatures.

The fluorescence of naphthacene vapour excited at temperatures of 355–435°c by the group of Hg lines at 365 μ decreases with increasing pressure at pressures below that at which absorption of the incident radiation is virtually complete, and is attributed to a combination of self-quenching and reabsorption of fluorescence. An analysis of the data for the limiting cases of complete and negligible fluorescence reabsorption provides upper and lower limits for self-quenching constant which are consistent with unit collisional quenching efficiency and a lifetime of 5·3 ± 2·2 + 10^-9 sec at 355°c.     

电磁轨道发射器连续发射的滑动电接触

从滑动电接触电阻大小的角度,详细分析了在时序放电条件下,两颗重约为5 g的电枢,以速度为1 000 m/s,166 Hz连续发射试验。通过近似计算电流所流经轨道电阻及电枢体电阻所产生的温升,对滑动电接触电阻的影响。结果表明:连续发射运行模式下,受轨道表面温度上升的影响,第二发电枢的滑动接触电阻略高于第一发电枢的滑动接触电阻,表面滑动电接触性能受到温升的影响,在两连发的发射情况下,其影响虽不是很大,但多发高频连续发射就必须考虑热管理问题。      

Sliding electrical contact performance of electromagnetic launcher system in rapid fire mode

从滑动电接触电阻大小的角度,详细分析了在时序放电条件下,两颗重约为5 g的电枢,以速度为1 000 m/s,166 Hz连续发射试验.通过近似计算电流所流经轨道电阻及电枢体电阻所产生的温升,对滑动电接触电阻的影响.结果表明:连续发射运行模式下,受轨道表面温度上升的影响,第二发电枢的滑动接触电阻略高于第一发电枢的滑动接触电阻,表面滑动电接触性能受到温升的影响,在两连发的发射情况下,其影响虽不是很大,但多发高频连续发射就必须考虑热管理问题.     

Determination of light velocity dependence on direction of propagation

A high precision experiment is reported showing that the phase velocity of light does not depend on direction.     

Continuum electron capture dependence on projectileZ and velocity

Continuum electrons centered in velocity about that of the projectile and ejected near zero degrees in the laboratory frame have been observed for collisions of highly stripped C^q+ and O^q+ ions incident on Argon. For fully stripped projectile ions, the Z dependence and the velocity dependence of the continuum capture cross section have been determined for beam energies of 1.6 to 2.8 MeV/amu. Striking disagreements are noted between some results of this work and present theoretical predictions.     

Spatial dependence of correlation functions in the decay problem for a passive scalar in a large-scale velocity field

Statistical characteristics of a passive scalar advected by a turbulent velocity field are considered in the decay problem with a low scalar diffusivity κ (large Prandtl number v/κ, where v is kinematic viscosity). A regime in which the scalar correlation length remains smaller than the velocity correlation length is analyzed. The equal-time correlation functions of the scalar field are found to vary according to power laws and have angular singularities reflecting locally layered distribution of the scalar in space.     

Single atomic contact adhesion and dissipation in dynamic force microscopy

By combining dynamic force microscopy experiments and first-principles calculations, we have studied the adhesion associated with a single atomic contact between a nanoasperity--the tip apex--and a semiconductor surface--the Ge(111)-c(2 x 8). The nanoasperity's termination has been atomically characterized by extensive comparisons of the measured short-range force at specific sites with the chemical forces calculated using many atomic models that vary in structure, composition, and relative orientation with respect to the surface. This thorough characterization has allowed us to explain the dissipation signal observed in atomic-resolution images and force spectroscopic measurements, as well as to identify a dissipation channel and the associated atomic processes.     

The velocity andZ dependence of the transient magnetic field in iron

The velocity dependence of the transient magnetic field in iron has been investigated for¹³⁴Ba at four initial velocities betweenv _i=0.8v ₀ andv _i=3.6v ₀ (v ₀=c/137). The present work confirms the linearv-dependence found for light ions (Z34). Existing data on transient fields were reanalyzed assuming a general validity of the linearv-dependence. The extractedZ-dependence shows a smooth, almost linearZ-dependence for ions withZ12. From the present work, with the calibration of the transient field from systematics, theg-factor of the first excited 2⁺ state in¹³⁴Ba is determined to beg=0.41(6).