The localization of low- and high-frequency vibrotactile stimuli

Four experiments were conducted to determine whether spatial localization on the skin varied in acuity as a function of frequency of vibratory stimulation. The glabrous skin of the palm over the hypothenar eminence was selected as the site for stimulation by two frequencies, one at 25 Hz to stimulate non-Pacinian receptors, and one at 250 Hz to excite Pacinian receptors. Because the Pacinian receptors have larger receptive fields than the non-Pacinians, it was thought that the subjects' ability to localize would be poorer when the Pacinians were the class of receptor stimulated. In addition to frequency of vibration, the presence of a surround, the site of stimulation, the separation of the stimulator pair used in the 2AFC method, and the use of an impulse stimulus were all conditions varied to determine whether a simple direct correlation exists between receptor category and spatial acuity for vibratory stimuli. A significant difference in acuity was found as a function of vibration frequency at a proximal locus on the palm, but this vanished at a distal locus. The results have been interpreted to suggest that receptor density and its gradient across the skin areas involved may be as important as receptor type in the determination of spatial acuity.     

The effect of scattering-medium parameters on signal magnitude under acousto-optic tomography

We have experimentally studied the influence of scattering anisotropy parameter g of a medium on the magnitude of signal S (visualization parameter) at an ultrasonic frequency that is registered upon acoustooptic tomography. Aqueous solutions of mixtures of cream and skimmed milk with different ratios between them were used as scattering media. The optical properties of media (absorption coefficient μ_a and reduced scattering coefficient μ′ _S ) have been measured on a spectrophotometer (Perkin-Elmer Lambda 950 UV-VIS-NIR) using the inverse adding-doubling technique. As a result of the investigation, we have found that there is a certain correlation between the value of the scattering anisotropy parameter g of aqueous solutions of investigated mixtures and the percentage of the mixture in the aqueous solution, which ensures the required small value of extinction coefficient μ of the scattering medium. An increase in signal S has been revealed with increasing anisotropy parameter g of the medium at a invariable value of extinction coefficient μ. We have concluded that, to solve an inverse problem on the acousto-optic tomography, it is necessary to take into account possible changes in the g factor in scattering media, including biological ones.     

Conditions for obtaining backward collinear isotropic acousto-optic interaction in germanium and iodic acid crystals

The possibility of experimentally obtaining backward collinear isotropic acousto-optic interaction based on bulk ultrasonic waves and terahertz electromagnetic waves is considered. The magnitudes of the acousto-optic figure of merit and the corresponding acoustic frequencies are calculated for the basic crystallographic axes in germanium and iodic acid crystals. The acousto-optic parameters of both crystals are compared.     

The quantum acousto-optic effect in Bose-Einstein condensate

We investigate the interaction between a single mode light field and an elongated cigar shaped Bose-Einstein condensate (BEC), subject to a temporal modulation of the trap frequency in the tight confinement direction. Under appropriate conditions, the longitudinal sound like waves (Faraday waves) in the direction of weak confinement acts as a dynamic diffraction grating for the incident light field analogous to the acousto-optic effect in classical optics. The change in the refractive index due to the periodic modulation of the BEC density is responsible for the acousto-optic effect. The dynamics is characterised by Bragg scattering of light from the matter wave Faraday grating and simultaneous Bragg scattering of the condensate atoms from the optical grating formed due to the interference between the incident light and the diffracted light fields. Varying the intensity of the incident laser beam we observe the transition from the acousto-optic effect regime to the atomic Bragg scattering regime, where Rabi oscillations between two momentum levels of the atoms are observed. We show that the acousto-optic effect is reduced as the atomic interaction is increased.     

Synchrosqueezing transforms: From low- to high-frequency modulations and perspectives

The general aim of this paper is to introduce the concept of synchrosqueezing transforms (SSTs) that was developed to sharpen linear time–frequency representations (TFRs), like the short-time Fourier or the continuous wavelet transforms, in such a way that the sharpened transforms remain invertible. This property is of paramount importance when one seeks to recover the modes of a multicomponent signal (MCS), corresponding to the superimposition of AM/FM modes, a model often used in many practical situations. After having recalled the basic principles of SST and explained why, when applied to an MCS, it works well only when the modes making up the signal are slightly modulated, we focus on how to circumvent this limitation. We then give illustrations in practical situations either associated with gravitational wave signals or modes with fast oscillating frequencies and discuss how SST can be used in conjunction with a demodulation operator, extending existing results in that matter. Finally, we list a series of different perspectives showing the interest of SST for the signal processing community.     

Horizontal directivity of low- and high-frequency energy in speech and singing

Speech and singing directivity in the horizontal plane was examined using simultaneous multi-channel full-bandwidth recordings to investigate directivity of high-frequency energy, in particular. This method allowed not only for accurate analysis of running speech using the long-term average spectrum, but also for examination of directivity of separate transient phonemes. Several vocal production factors that could affect directivity were examined. Directivity differences were not found between modes of production (speech vs singing) and only slight differences were found between genders and production levels (soft vs normal vs loud), more pronounced in the higher frequencies. Large directivity differences were found between specific voiceless fricatives, with /s,∫/ more directional than /f,θ/ in the 4, 8, 16 kHz octave bands.     

Simultaneous production of low- and high-frequency sounds by neonatal finless porpoises

Phocoenids are generally considered to be nonwhistling species that produce only high-frequency pulsed sounds. Here our results show that neonatal finless porpoises (Neophocaena phocaenoides) frequently produce clear low-frequency (2-3 kHz) pulsed signals, without distinct high-frequency energy, just after birth and can produce both low- (2-3 kHz) and high-frequency (>100 kHz) pulsed signals simultaneously until about 20 days postnatal. The results indicate that low-frequency signals of neonatal finless porpoises are not an early form of high-frequency signals and suggest that low- and high-frequency signals may be produced by different sound production mechanisms.     

Epitaxially grown zinc oxide films for electro-optic and acousto-optic interactions

Measurements of acoustic surface waves (ASW) and optical guided waves (OGW) wave properties have been carried out on chemical vapor deposited (CVD) epitaxial zinc oxide (ZnO) films on sapphire (Al₂O₃) substrates of different orientations. Surface preparation and orientation effects have been studied. Untuned acoustic insertion loss of 40 dB at 160 MHz and optical propagation loss of better than 5 dB/cm at 6328Å for the TE₀ mode were obtained in a 2μm thick (11$\text{2}$4) ZnO film deposited on a (0001) sapphire substrate.     

Laser Doppler anemometry and the acousto-optic effect

This paper deals with the effect of phase variations along the paths of the laser beams due to refractive index changes caused by the acousto-optic effect, when an LDA system is used to measure sound waves. Theoretical and experimental results will be discussed. A theoretical expression will be developed for the movement of the fringes in terms of the angle of the sound wave, the wavenumber and the distance of propagation of the laser beams. Results will show that as the wavenumber increases, the angle at which the maximum amplitude of the fringe movement occurs tends away from π/2 to the laser beam bisector, and towards the angle of the laser beams. It will also be shown that the phase modulations detected experimentally are in reasonable agreement with those predicted theoretically.     

Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions

It is well known that noncentral nuclear forces, such as the spin–orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known because only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may convey useful information about the in-medium properties of noncentral nuclear interactions, besides earlier studies using the time-dependent Hartree–Fock approach to understand the effects of spin–orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore the dynamical effects of noncentral nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focus of these studies has been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent single-nucleon potential. Interestingly, some useful probes were identified in the model studies but so far there are still no data to compare with. In this brief review, we summarize the main physics motivations as well as the recent progress in understanding the spin dynamics and identifying spin-sensitive observables in heavy-ion reactions at intermediate energies. We hope the interesting, important, and new physics potentials identified in the spin dynamics of heavy-ion collisions will stimulate more experimental work in this direction.     

The interaction of two collinear cracks in a rectangular superconductor slab under an electromagnetic force

The interaction of two collinear cracks is obtained for a type-II superconducting under electromagnetic force. Fracture analysis is performed by means of finite element method and the magnetic behavior of superconductor is described by the critical-state Bean model. The stress intensity factors at the crack tips can be obtained and discussed for decreasing field after zero-field cooling. It is revealed that the stress intensity factor decreases as applied field increases. The crack-tip stress intensity factors decrease when the distance between the two collinear cracks increases and the superconductors with smaller crack has more remarkable shielding effect than those with larger cracks.     

声光布喇格衍射场光能量分布及光斑形状设计

本文在一维布喇格衍射分析方法的基础上,导出了两维时的衍射场光能量分布,给出了相应的实验结果.分析了影响衍射光光斑能量分布的主要因素,最后提出了综合考虑衍射效率,上升时间、光斑形状的新的设计思想.     

The effect of repulsive interactions on Bose-Einstein condensation

One-dimensional Bose gases that interact via a repulsive two-body interaction and show Bose-Einstein condensation at the free level are studied. It is shown that the introduction of this interaction, however small, destroys the condensate. It is also shown that the free energy of an interacting Bose gas does not depend on the boundary conditions(including attractive boundary conditions) in the van der Waals limit.     

The effect of three-body interactions on thermal desorption spectra

Thermal desorption spectra are calculated for a one-dimensional chain and for a two-dimensional square lattice using the transfer-matrix technique and Monte Carlo simulations. Lateral interactions of adsorbed particles cause a splitting of spectra. The repulsive three-body interactions are shown to lead to an inequality of the integral intensities of the thermal desorption peaks.     

The averaged Lagrangian and high-frequency gravitational waves

The averaged Lagrangian technique of Whitham is applied to the second variation Lagrangian for the perturbations of a general-relativistic spacetime. This gives a variational principle for (sums of) approximately periodic gravitational waves which in turn leads to the rederivation of some results of Isaacson. Examples of the use of the method are discussed.Supported by National Science Foundation grant GP-31358.     

The influence of high-frequency phase distortion on the phase correction effect in atmospheric turbulence

By using the method of the power-spectrum inversion, the turbulence phase screen has been built up, and the propagation characteristics of high-frequency phase of laser beam in atmospheric turbulence have been analyzed; in addition, the phase correction effect of laser beams by using the adaptive deformable mirror has been simulated, and its affecting factors in turbulence have also been analyzed quantitatively. The results show that the phase correction effect of laser beams in turbulence is mostly determined by the percent of high-frequency phase in distorted wavefront. With the increase of the intensity of atmospheric turbulence and the propagation distance in turbulence, the percent of high-frequency phase in distorted wavefront increases, resulting in the degradation of the phase correction effect.