A comparison of the structures of vapour-deposited and bulk arsenic sulphide glasses

Accurate comparative measurements have been made of the X-ray diffraction pattern of a bulk arsenic sulphide glass prepared from the melt and a 250 μm film prepared by vapour deposition of the evaporated bulk. By using Ag Kα radiation, measurements have been made up to $\text{Q = 21}\text{A}\text{?}{}^{\mathrm{?1}}\text{(Q = 4π}\text{sin}\text{θ/λ)}$ so as to give good spatial resolution. Significant differences are found between bulk and film specimens, and in particular a shoulder is found on the high r side of the first peak in the distribution function for the film. Also, the film is richer in arsenic than the parent bulk. The results are compared in detail with a number of models, all of which involve covalent bonding requirements being fully satisfied, and it is concluded that there are more AsAs bonds in the film than the minimum required by stoichiometry and that a significant fraction ($\text{≈}\text{2}\text{3}$) of these are unusually long ($\text{≈2.6}\text{A}\text{?}$ compared to the more usual 2.5 Å). The most probable explanation is that the vapour contains a significant fraction of As₄S₄ species (in which the AsAs distances are $\text{≈2.6}\text{A}\text{?}$) and that the film contains a mixture of molecular species which have undergone considerable polymerization. The extent to which this results in a sheet-like structure similar to that proposed for the bulk glass remains unclear.     

On the origin of compositional fluctuations in ZnSe1- x S x alloys grown by metal-organic vapour-phase epitaxy

Periodic vertical modulations of the sulphur concentration have been observed in epitaxial layers of ZnSe_{1? x} S _x grown by metal-organic vapour-phase epitaxy. High-spatial-resolution microanalysis has shown that the sulphur variation is of the order of 1 at.% with a period of about 44 ± 0.1 nm. A detailed analysis of the possible causes of this modulation is presented which shows that periodic temperature fluctuations of the substrate are the most likely source.     

Factors affecting the correlation coefficient template matching algorithm with application to real-time 2-D coronary artery MR imaging

This paper characterizes factors affecting the accuracy of the correlation coefficient (CC) template matching algorithm, as applied to motion tracking from two-dimensional real-time coronary artery magnetic resonance images. The performance of this algorithm is analyzed in the presence of both random and systematic error. In the presence of random error, it is shown that a necessary and sufficient condition for accurate motion tracking is a large CC difference-to-noise ratio (CCDNR). The CCDNR itself is in turn affected by five factors: image and template size, image and template structure, and the magnitude of the noise. Techniques are introduced for manipulating some of these factors in order to increase the CCDNR for greater motion tracking accuracy. In the presence of superimposed systematic error it is shown that, while large CCDNR is necessary, it alone is not sufficient to ensure accurate motion tracking. Techniques are developed for improving motion tracking accuracy that minimize the effects of systematic error, while maintaining an adequate CCDNR level. The ability of these techniques to improve motion tracking accuracy is demonstrated both in phantoms and in coronary artery images.     

Experimental performance of an adaptive digital linearized poweramplifier [for cellular telephony]

Amplification of linear modulation schemes, (which exhibit fluctuating envelopes), by high power amplifiers invariably leads to the generation of distortion and intermodulation products. Recent theoretical work has suggested that a complex gain predistorter may be employed to linearize a nonlinear power amplifier. The authors present experimental results demonstrating that a reduction in out-of-band spectra in excess of 20 dB may be achieved by employing digital feedback and a complex gain predistorter     

Microwave cavity perturbation technique: Part III: Applications

The resonant cavity perturbation method as described in the preceding two parts of this series is applied to study the electrodynamical properties of different materials in the microwave and millimeter wave spectral range. We briefly discuss the relevant uncertainties which are asociated with the different measurement techniques and we find that employing the amplitude technique it is possible to measure both the width and frequency to nearly the same precision. We then demonstrate the broad range of applicability of this technique by showing results obtained on several different materials, ranging from an insulator to a superconductor. The performance limitations of this technique are discussed in detail.     

Comment on “A numerical investigation of the acoustic mode waves in a deviated borehole penetrating a transversely isotropic formation”

正In the paperA numerical investigation of the acoustic mode waves in a deviated borehole penetrating a transversely isotropic formationby Liu et al.[1]numerical experiments are reported for a dipole sonic logging scenario with a deviated borehole penetrating a VTI anisotropic medium.In such a situation it is important to clearly define the meaning of group and phase velocities as this has led to much confusion in the literature as discussed by Miller,Horne and Walsh[2].     

A perceptual learning investigation of the pitch elicited by amplitude-modulated noise

Noise that is amplitude modulated at rates ranging from 40 to 850 Hz can elicit a sensation of pitch. Here, the processing of this temporally based pitch was investigated using a perceptual-learning paradigm. Nine listeners were trained (1 hour per day for 6-8 days) to discriminate a standard rate of sinusoidal amplitude modulation (SAM) from a faster rate in a single condition (150 Hz SAM rate, 5 kHz low-pass carrier). All trained listeners improved significantly on that condition. These trained listeners subsequently showed no more improvement than nine untrained controls on pure-tone and rippled-noise discrimination with the same pitch, and on SAM-rate discrimination with a 30 Hz rate, although they did show some improvement with a 300 Hz rate. In addition, most trained, but not control, listeners were worse at detecting SAM at 150 Hz after, compared to before training. These results indicate that listeners can learn to improve their ability to discriminate SAM rate with multiple-hour training and that the mechanism that is modified by learning encodes (1) the pitch of SAM noise but not that of pure tones and rippled noise, (2) different SAM rates separately, and (3) differences in SAM rate more effectively than cues for SAM detection.