Low-temperature helium in bulk and in restricted geometries

Experiments with helium in thin films and small pores show that the bulk properties are greatly modified. With ⁴He, the onset of superfluidity is depressed and the specific heat anomaly is rounded and also depressed to lower temperatures. With ³He new features are found such as surface magnetism and free path effects. Bulk superfluid ⁴He is shown to have a sharp transition to turbulence, and bulk ³He the characteristics of a Fermi fluid.     

Degenerate symmetry-adapted perturbation theory of weak interactions between closed- and open-shell monomers: application to Rydberg states of helium hydride

Symmetry-adapted perturbation theory is extended to the (quasi) degenerate, open-shell case. The new formalism is tested in calculations of the interaction energies for a helium atom in the ground state interacting with an excited hydrogen atom. It is shown that the method gives satisfactory results if the coupling with higher Rydberg states of the dimer is small, as is the case for the A²Σ⁺,B²Π,E²Π,3²Π, and 1²Δ states of HeH. For the C²Σ⁺ state convergence of the method is very slow, but it can be improved by including the n=3 states in the model space. Received: 3 June 1998 / Accepted: 9 September 1998 / Published online: 7 December 1998     

含钼涂层钨材料在氦等离子体作用下的前期表面形貌演变研究

为了研究纳米绒毛的生成过程及内在的物理机制，采用磁控溅射镀膜的方式在钨片上镀有钼涂层 (Mo-W)。借助微观结构观察的手段分析了钨、钼块材以及钨-钼(Mo-W)样品在773K、1073K氦等离子体作用条件下的表面形貌演变过程。结果表明：钨、钼以及钨-钼(Mo-W)样品在氦等离子体作用下表面形貌演变规律基本一致；纳米绒毛及其珊瑚状前驱体是在尺寸相对较大的锥状结构上演化而来的。     

Post Recognition Speech Localization

How much does knowledge regarding a certain spoken word or phrase help with its localization? This is a very fundamental question for speech processing, and will be partially addressed in this paper. In particular, this work will utilize prior information regarding the contents of a speech signal in order to improve the artificial localization of it using Time delay of arrival (TDOA) between two microphones. The prior information, which is used to develop a very simple frequency-selective phase transform (FPT), increases the effective SNR by only using a subset of the highest SNR frequencies in the Phase Transform. Simulations in a reverberant environment show that the proposed approach can more robustly and accurately localize speech sources. For 20 ms signal segments, it is shown that using a subset of 45 percent of available speech frequency bins is superior to using 30, 60, or 100, where using 100 corresponds to the standard Phase Transform.     

Acoustic Signal Typing for Evaluation of Voice Quality in Tracheoesophageal Speech

SUMMARY: Because of the aperiodicity of many tracheoesophageal voices, acoustic analysis of the tracheoesophageal voice is less straightforward than that of the normal voice. This study presents the development and testing of an acoustic signal typing system based on visual inspection of a narrow-band spectrogram that can be used by researchers for classification of voice quality in tracheoesophageal speech. In addition to this classification system, a selection of acoustic measures [median fundamental frequency, standard deviation of fundamental frequency, jitter, percentage of voiced (%Voiced), harmonics-to-noise ratio (HNR), glottal-to-noise excitation (GNE) ratio, and band energy difference (BED)] was computed to provide more insight into the acoustic components of tracheoesophageal voice quality. For clinical relevance, relationships between the acoustic signal types and an overall judgment of the voice were investigated as well. Results showed that the four acoustic signal types form a good basis for performing more acoustic analyses and give a good impression of the overall quality of the voice.     

汉语耳语音孤立字识别研究

耳语音识别有着广泛的应用前景,是一个全新的课题.但是由于耳语音本身的特点,如声级低、没有基频等,给耳语音识别研究带来了困难.本文根据耳语音信号发音模型,结合耳语音的声学特性,建立了一个汉语耳语音孤立字识别系统.由于耳语音信噪比低,必须对其进行语音增强处理,同时在识别系统中应用声调信息提高了识别性能.实验结果说明了MFCC结合幅值包络可作为汉语耳语音自动识别的特征参数,在小字库内用HMM模型识别得出的识别率为90.4%.     

Elastically coupled molecular motors

We study the influence of filament elasticity on the motion of collective molecular motors. It is found that for a backbone flexibility exceeding a characteristic value (motor stiffness divided through the mean displacement between attached motors), the ability of motors to produce force reduces as compared to rigidly coupled motors, while the maximum velocity remains unchanged. The force-velocity-relation in two different analytic approximations is calculated and compared with Monte-Carlo simulations. Finally, we extend our model by introducing motors with a strain-dependent detachment rate. A remarkable crossover from the nearly hyperbolic shape of the Hill curve for stiff backbones to a linear force-velocity relation for very elastic backbones is found. With realistic model parameters we show that the backbone flexibility plays no role under physiological conditions in muscles, but it should be observable in certain in vitro assays. Received: 27 November 1997 / Revised: 20 February 1998 / Accepted: 27 March 1998     

线型离子阱中冷却离子所需高纯度氦气的渗透与实验

利用氦的渗透性质,向超高真空系统中充入高纯度氦缓冲气体,可以降低离子阱中囚禁离子的运动速度,减小二级多普勒频移,增加离子的存储时间,提高线型离子阱微波频标的稳定度.实验上得到了氦气渗透的实验参数、特性以及对系统真空度的影响、实现了用温度调节精确的控制充入氦气的分压强.     

Shear viscosity of hydrogen and helium fluids at extended regions of temperatures and pressures

Shear viscosities of hydrogen (H₂) and helium (He) fluids are investigated at extended regions of temperature and pressure using an improved equation of state, in which the the long-range attractive forces are incorporated into the formalism via the double Yukawa (DY) potential fitted to the empirical H₂ and He potentials. Quantum effects, which become paramount at low temperatures, are taken into account through a first-order quantum correction based on the Wigner–kirkwood expansion. The dimerization of H₂ is treated as a hard convex body for which an equation of state can be derived based on the scaled particle theory.     

Roughness measurement of metallic surfaces based on the laser speckle contrast method

A method of measuring surface roughness of flat lapped, ground and polished metallic surfaces, by the far-field speckle contrast method is presented in this paper. The laser speckle contrast technique depends on the existence of an approximately linear relationship between the speckle contrast and the roughness of the illuminated surface. Initially it was shown that the linear relationship existed up to 0.1 μm Ra (centre-line average) roughness using Helium–Neon light, after which a saturation effect was observed. The effect of varying the incident angle of illumination was investigated with a view to extending the measurement range. The use of high incident angles of illumination has been found to increase the surface roughness range up to 0.4 μm measurement Ra.