An improved theoretical model for the dynamics of a free–clamped cylinder in axial flow

A new, improved linear analytical model is presented in this paper for the dynamics of a slender cantilevered cylinder with an ogival free end, subjected to axial flow directed from its free end towards the clamped one. In the present model the fluid-dynamic forces at the free end of the cylinder are analysed in a meticulous manner. The model predicts that the cylinder loses stability at relatively low flow velocity by flutter, and then at higher flow velocity by static divergence. This agrees with the dynamical behaviour observed in experiments. Moreover, quantitative agreement in the critical flow velocities for flutter and divergence between this improved theory and experiment is fairly good.     

Isotopic effects on the control of molecular handedness of H 2 POSH by ultrashort laser pulses

The selective preparation of an enantiomer starting from a pure state of H₂POSH representing a 50%:50% mixture of two enantiomers with opposite chiralities is extended to its deuterated counterpart, H₂POSD. A one-dimensional model involving the torsional angle of S-H/D around a pre-oriented P-S axis is used. The design of an appropriate sequence of ultrashort infrared laser pulses to achieve molecular handedness for H₂POSH/D is based on the characteristic level splitting and tunneling times of both molecules. A simple scheme of two linearly polarized laser pulses involving a three level system serves to convert the different isotopomers to opposite enantiomers, for any given mixture of H₂POSH and H₂POSD molecules. Received 31 August 2000 and Received in final form 23 November 2000     

What does an observed quantum system reveal to its observer?

The evolution of a quantum system under observation becomes retarded or even impeded. We review this “quantum Zeno effect” in the light of the criticism that has been raised upon a previous attempt to demonstrate it, of later reexaminations of both the projection postulate and the significance of the observations, and of the results of a recent experiment on an individual cold atom. Here, the micro-state of the quantum system gets unveiled with the observation, and the effect of measurement is no longer mixed up with dephasing the object's wave function by the reactive effect of the detection. A procedure is outlined that promises to provide, by observation, an upper limit for the delay of even an exponential decay. Received 11 January 2001 and Received in final form 28 February 2001     

Quantum theory of van der Waals interactions between excited atoms and birefringent dielectric surfaces

A theory of van der Waals (vdW) interaction between an atom (in ground or excited state) and a birefringent dielectric surface with an arbitrary orientation of the principal optic axis (C-axis) is presented. Our theoretical approach is based on quantum-mechanical linear response theory, using generalized susceptibilities for both atom and electromagnetic field. Resonant atom-surface coupling is predicted for excited-state atoms interacting with a dispersive dielectric surface, when an atom de-excitation channel gets into resonance with a surface polariton mode. In the non-retarded regime, this resonant coupling can lead to enhanced attractive or repulsive vdW surface forces, as well as to a dissipative coupling increasing the excited-state relaxation. We show that the strongly non-scalar character of the interaction with the birefringent surface produces a C-axis-dependent symmetry-breaking of the atomic wavefunction. Changes of the C-axis orientation may also lead to a frequency shift of the surface polariton mode, allowing for tuning on or off the resonant coupling, resulting in a special type of engineering of surface forces. This is analysed here in the case of cesium 6D _3/2 level interacting with a sapphire interface, where it is shown that an adequate choice of the sapphire C-axis orientation allows one to transform vdW surface attraction into repulsion, and to interpret recent experimental observations based on selective reflection methods [H. Failache etal., Phys. Rev. Lett. 83, 5467 (1999)]. Received 24 January 2001     

Radiation pressure induced instabilities in laser interferometric detectors of gravitational waves

The large scale interferometric gravitational wave detectors consist of Fabry-Perot cavities operating at very high powers ranging from tens of kW to MW for next generations. The high powers may result in several nonlinear effects which would affect the performance of the detector. In this paper, we investigate the effects of radiation pressure, which tend to displace the mirrors from their resonant position resulting in the detuning of the cavity. We observe a remarkable effect, namely, that the freely hanging mirrors gain energy continuously and swing with increasing amplitude. It is found that the “time delay”, that is, the time taken for the field to adjust to its instantaneous equilibrium value, when the mirrors are in motion, is responsible for this effect. This effect is likely to be important in the optimal operation of the full-scale interferometers such as VIRGO and LIGO. Received 12 July 1999     

虚拟数字电路实验室系统的研究与实现

讨论了数字电路的逻辑级模拟中元件传输延迟模型、元件状态值模型的建立,逻辑模拟的算法以及元件计算的方法．在此基础上,运用面向对象的编程方法．实现了一个虚拟数字电路实验室系统．该系统打破了传统实验教学中地域、时间、经费等方面的限制,有利于更好的培养学生的独立研究和创新的能力．     

Introduction to a field-theoretical treatment of neutrino oscillations

We discuss the main features of the field-theoretical approach to neutrino oscillations where one combines neutrino production and detection processes in a single Feynman graph. The ‘oscillating neutrinos’ are represented by inner lines of this graph and appear in the calculation of the cross section of the total process as propagators of the neutrino mass eigenfields. We show that this field-theoretical approach leads to a transparent treatment of neutrino oscillations without ambiguities and provides the correct answer in cases where the standard approach fails.     

医用物理实验的考试初探

本就医用物理实验课设置考试的必要性和具体实施过程作了介绍。对提高学生素质收效良好。