New classes of quasicrystals and marginal critical states

One-dimensional quasilattices, namely, the geometrical objects that represent quasicrystals, are classified into mutual local-derivability (MLD) classes. Besides the familiar class, there exist an infinite number of new MLD classes, and different MLD classes are distinguished by the inflation rules of their representatives. It has been found that electronic properties of a new MLD class are characterized by the presence of marginal critical states, which are considered to be nearly localized states.     

The masking-level difference and overall masker level: restating the internal noise hypothesis

Recent investigations of the masking-level difference (MLD) have often involved measurement of the MLD as a function of masker level. The results show, as had earlier work, that the size of the MLD decreases as the masker level decreases. These studies have usually not considered an earlier explanation of the dependency of the MLD on masker level, that is, that additive internal noise, which is partially interaurally uncorrelated, leads to decorrelated maskers at low levels of the external masking noise. Because maskers that are decorrelated yield small MLDs, the MLD is likewise small at low masker levels. This review article shows that this explanation provides a good fit to data obtained over the past four decades. It also shows that the MLD depends less on masker level with insert phones than with supraaural phones as would be predicted by the additive internal noise explanation and the observation of lower internal noise with the use of insert phones. It is concluded that the internal noise explanation should be considered when the MLD is measured as a function of masker level.     

Comodulation masking release and the masking-level difference

An experiment was performed to determine if the mechanism that mediates comodulation masking release (CMR) is associated with that used to improve detection by the masking-level difference (MLD). The experiment consisted of first improving detectability of a masked diotic tone burst by adding a synchronous noise band at another frequency region (CMR), and then measuring an MLD in the usual manner, by inverting the tone-burst signal to one ear. Results indicate that a substantial MLD can be measured for a signal whose detectability has already been improved by CMR. However, that MLD (9 dB) is smaller than that measured in random noise (14 dB). Put another way, a small CMR (4 dB) can be produced even when the detectability of a stimulus has already been improved due to the MLD. These data are in general agreement with those of Hall et al. [J. Acoust. Soc. Am. 83, 1839-1845 (1988)] and Schooneveldt and Moore [J. Acoust. Soc. Am. 85, 262-272 (1989)].     

Observation of giant magnetic linear dichroism in (Ga, Mn) As

Giant magnetic linear dichroism (MLD) is observed in the ferromagnetic semiconductor Ga(0.98)Mn(0.02)As. The contribution to this effect induced by the spontaneous magnetization can be clearly identified by azimuthal dependencies. The spectral dependence of the effect in the range from 1.4 to 2.4 eV shows that the MLD induced by the spontaneous magnetization is strongly enhanced for excitations from the electronic states that are responsible for the ferromagnetism in this material. This spectral sensitivity and the size of the effect makes MLD a powerful tool for the study of (III, Mn)V alloys and similar novel ferromagnetic semiconductors.     

Comparison of Surface Duct Energy Leakage with Bottom-Bounce Energy of Close Range Propagation

For close range(almost 8-15km) propagation,bottom-bounce energy(BBE) usually suffers from a great transmission loss due to a large grazing angle interacting with the ocean bottom,and the surface duct energy leakage(SDEL) might be able to make a significant contribution to shadow zone insonification.This study aims at making a comparison between SDEL and BBE in a shadow zone with a source depth of 50 m for close range propagation.Analysis of experimental data shows that for lower frequencies the SDEL can be comparable with the BBE up to a range of 12 km.Numerical simulations suggest that the transmission loss(TL) of 90 dB is a proper value to quantify the role of the SDEL in shadow zone insonification.When TL of the SDEL is about 90 dB,it is believed to be comparable with the BBE.Studies on the effect of mix layer depth(MLD) on the SDEL indicate that larger MLD and lower frequencies can help to create favorable conditions for SDEL and that there exists- an optimal MLD for SDEL at certain frequency.Statistics of MLD distribution in the South China Sea(SCS) show that winter is favorable for SDEL and the situation reverses in summer.Eddies are known to occur frequently in the SCS and the study on the effect of eddies on the SDEL suggests that the presence of an eddy will influence the SDEL significantly by modifying the MLD.     

Optimization of thin-film design for multi-layer dielectric grating

Thin-film design used to fabricate multi-layer dielectric (MLD) gratings should provide high transmittance during holography exposure, high reflectance at use wavelength and sufficient manufacturing latitude of the grating design making the MLD grating achieve both high diffraction efficiency and low electric field enhancement. Based on a (HLL)⁹H design comprising of quarter-waves of high-index material and half-waves of low-index material, we obtain an optimum MLD coating meeting these requirements by inserting a matching layer being half a quarter-wave of Al₂O₃ between the initial design and an optimized HfO₂ top layer. The optimized MLD coatings exhibits a low reflectance of 0.017% under photoresist at the exposure angle of 17.8° for 413 nm light and a high reflectance of 99.61% under air at the use angle of 51.2° for 1053 nm light. Numerical calculation of intensity distribution in the photoresist coated on the MLD film during exposure shows that standing-wave patterns are greatly minimized and thus simulation profile of photoresist gratings after development demonstrates smoother shapes with lower roughness. Furthermore, a MLD gratings with grooves etched into the top layer of this MLD coating provides a high diffraction efficiency of 99.5% and a low electric field enhancement ratio of 1.53. This thin-film design shows perfect performances and can be easily fabricated by e-beam evaporation.     

Linear and quadratic magneto-optical effects observed in La0.7Sr0.3MnO3 thin films in transmitted light

Magnetic linear dichroism (MLD) is observed in polycrystalline La_0.7Sr_0.3MnO₃ films in transmitted light. The spectral and temperature dependences of the MLD are determined for the energy E of the light wave ranging from 1.5 to 3.5 eV. The experimental spectra are fitted by a sum of Lorentzian curves. The MLD spectrum exhibits more features in comparison to the spectra of magnetic circular dichroism (MCD), which we measured earlier using the same film samples. Various temperature behaviors of the intensities of the Lorentzian components centered at different E values have been revealed. This can be related to the effect of the surface states on the magneto-optical characteristics of the samples.     

Temporal structure model of binaural masking level difference.

It is shown that a simple cross-correlation model is not adequate to explain both binaural masking level difference (MLD) and spatial selective attention. The reason is that for a low-intensity signal in NoS(pi) condition the maximal activity in the binaural analyzer as a function of interaural delay in single spectral channel is independent of signal intensity. On the other hand, if detection ability is associated with the isolation of tonically firing units, MLD is simply explained as the increase in firing synchronization as a function of the signal's interaural phase difference (IPD). Quantitatively results are presented based on numerical solutions of the model.     

Binaural modulation masking

Modulation thresholds were measured in three subjects for a sinusoidally amplitude-modulated (SAM) wideband noise (the signal) in the presence of a second amplitude-modulated wideband noise (the masker). In monaural conditions (Mm-Sm) masker and signal were presented to only one ear; in binaural conditions (M0-S pi) the masker was presented diotically while the phase of modulation of the SAM noise signal was inverted in one ear relative to the other. In experiment 1 masker modulation frequency (fm) was fixed at 16 Hz, and signal modulation frequency (fs) was varied from 2-512 Hz. For monaural presentation, masking generally decreased as fs diverged from fm, although there was a secondary increase in masking for very low signal modulation frequencies, as reported previously [Bacon and Grantham, J. Acoust. Soc. Am. 85, 2575-2580 (1989)]. The binaural masking patterns did not show this low-frequency upturn: binaural thresholds continued to improve as fs decreased from 16 to 2 Hz. Thus, comparing masked monaural and masked binaural thresholds, there was an average binaural advantage, or masking-level difference (MLD) of 9.4 dB at fs = 2 Hz and 5.3 dB at fs = 4 Hz. In addition, there were positive MLDs for the on-frequency condition (fm = fs = 16 Hz: average MLD = 4.4 dB) and for the highest signal frequency tested (fs = 512 Hz: average MLD = 7.3 dB). In experiment 2 the signal was a SAM noise (fs = 16 Hz), and the masker was a wideband noise, amplitude-modulated by a narrow band of noise centered at fs. There was no effect on monaural or binaural thresholds as masker modulator bandwidth was varied from 4 to 20 Hz (the average MLD remained constant at 8.0 dB), which suggests that the observed "tuning" for modulation may be based on temporal pattern discrimination and not on a critical-band-like filtering mechanism. In a final condition the masker modulator was a 10-Hz-wide band of noise centered at the 64-Hz signal modulation frequency. The average MLD in this case was 7.4 dB. The results are discussed in terms of various binaural capacities that probably play a role in binaural release from modulation masking, including detection of varying interaural intensity differences (IIDs) and discrimination of interaural correlation.     

光纤激光共孔径光谱合成实现5kW高效优质输出

采用多层介质膜衍射光栅实现多路高功率光纤激光共孔径光谱合成有望成为光纤激光同时实现高功率、高效率和高光束质量的最具发展潜力的技术途径。搭建了一套基于双光栅色散补偿设计的5kW共孔径光谱合成系统。采用国产多层介质膜衍射光栅实现了5路kW级窄谱子束激光的高效优质共孔径光谱合成,最大输出功率达5.07kW,光束质量因子(M2)小于3,合成效率达到91.2%。初步研究表明:多层介质膜衍射光栅在较高功率水平、较宽光谱范围内均能保持较高衍射效率,是实现高功率光纤激光高效率光谱合成的重要器件;参与合成的子束自身的光束质量水平和线宽是影响合成输出光束质量的重要因素,光谱合成系统的输出功率主要受限于窄谱子束的输出功率和合成路数,增加窄谱子束的功率或合成路数均可进一步提升系统的输出功率。     

The effect of masker interaural phase on the detection of a monaural signal

The masking-level difference (MLD) for a 500-Hz monaural pure-tone signal was examined as a function of the interaural phase shift of a 100-Hz-wide noise band centered on 500 Hz. Results indicated that the MLD decreased in magnitude as the interaural phase shift of the masker increased. In a second experiment, the 100-Hz-wide noise band was used as both the masker and the signal in order to examine the detection cues of interaural time difference and interaural level difference separately. Again, the interaural phase of the masker was varied, and an Sm signal was presented. Results indicated that the MLD decreased as a function of increasing masker interaural temporal difference for the time cue, but that the MLD did not change systematically for the level cue. The deterioration of binaural detection as a function of increasing masker interaural phase difference was not as great as that which has been reported in localization and lateralization experiments.     

The role of monaural frequency selectivity in binaural analysis

The relation between the monaural critical band and binaural analysis was examined using an NoSm MLD paradigm, in order to resolve ambiguities about the width of the masking spectrum important for binaural detection. A 500-Hz pure-tone signal was presented with a 600-Hz-wide band of masking noise to the signal ear. Bands of noise ranging in width from 25 to 600 Hz, or noise notches (imposed on a 600-Hz-wide band centered on the signal frequency) ranging in width from 0 to 600 Hz were presented to the nonsignal ear. All noise bands and notches were centered on 500 Hz, the frequency of the signal. The effects of varying bandwidth were radically different from those of varying notchwidth: the MLD changed from zero to approximately 8 dB over a bandwidth range of 400 Hz; for notchwidths, however, the MLD changed 8 dB over a range of only 50 Hz. The results support an interpretation that the fine frequency selectivity of monaural analysis is preserved in peripheral binaural interaction, but that a relatively wide frequency range of critical bands is scanned at a later stage of binaural processing. It was suggested that the wide spectral range of binaural analysis may provide a background against which binaural differences due to the signal are detected.     

提高多层介质膜脉宽压缩光栅阈值的清洗方法

采用HPM溶液（盐酸、双氧水和去离子水的混合液）结合氧等离子体对多层介质膜脉宽压缩光栅进行清洗研究。用X射线光电子能谱检测光栅表面的元素成分及其原子含量的变化。实验结果表明,氧等离子体处理能有效去除光栅表面残留光刻胶和碳氟化合物; 再经HPM溶液清洗,反应离子束刻蚀和氧等离子体处理过程产生的金属污染物被进一步去除。经过上述清洗工艺处理后,光栅一级衍射效率仍保持在95%以上,光栅表面激光诱导损伤阈值达到1.6 J/cm2 (1053 nm, 10 ps)。实验结果说明了氧等离子体和HPM溶液相结合能有效清洗多层介质膜脉宽压缩光栅,并显著提高光栅损伤阈值。     

The masking level difference for signals placed in masker envelope minima and maxima

Previous data on the masking level difference (MLD) have suggested that NoSpi detection for a long-duration signal is dominated by signal energy occurring in masker envelope minima. This finding was expanded upon using a brief 500-Hz tonal signal that coincided with either the envelope maximum or minimum of a narrow-band Gaussian noise masker centered at 500 Hz, and data were collected at a range of masker levels. Experiment 1 employed a typical MLD stimulus, consisting of a 30-ms signal and a 50-Hz-wide masker with abrupt spectral edges, and experiment 2 used stimuli generated to eliminate possible spectral cues. Results were quite similar for the two types of stimuli. At the highest masker level the MLD for signals coinciding with masker envelope minima was substantially larger than that for signals coinciding with envelope maxima, a result that was primarily due to decreased NoSpi thresholds in masker minima. For most observers this effect was greatly reduced or eliminated at the lowest masker level. These level effects are broadly consistent with the presence of physiological background noise and with a level-dependent binaural temporal window. Comparison of these results with predictions of a published model suggest that basilar-membrane compression alone does not account for this level effect.     

全固态激光中的光谱合成技术

对多种全固态激光中的光谱合成技术进行了探讨和研究,包括光纤激光、Yb:YAG板条激光和半导体激光。对于光纤激光,探讨了基于单个多层介质膜（MLD）光栅、一对MLD光栅、多个体布拉格光栅三种衍射光学元件的光谱合成技术中色散造成的光束质量退化问题,指出子束光谱线型的二阶矩全宽决定了光束质量的退化量,但所允许的光谱宽度又依赖于具体的技术选择途径。进而比较了三种光谱合成方案的优缺点。对于固体激光,实验演示了基于Yb:YAG晶体的板条激光实现光谱合成的原理可行性。通过设计一个基于MLD光栅的振荡器内的光谱合成装置,实现了7束子激光最高241 W的光谱合成输出,合成后光束质量β因子约4.1,表明大功率Yb:YAG板条激光具有通过光谱合束技术实现功率进一步提升的潜力。对于半导体激光,提出并设计了大模场外腔半导体激光+快轴光谱合成的技术。实验演示了9个1 mm宽LD芯片沿快轴方向的光谱合成,用β因子评价合成后的光束质量,在慢轴方向β≈6.3,在快轴方向β≈1.6,表明快轴光谱合成造成的光束质量退化是完全可控的。     

Individual differences in the masking level difference with a narrowband masker at 500 or 2000 Hz

The masking level difference (MLD) for a narrowband noise masker is associated with marked individual differences. This pair of studies examines factors that might account for these individual differences. Experiment 1 estimated the MLD for a 50 Hz wide band of masking noise centered at 500 or 2000 Hz, gated on for 400 ms. Tonal signals were either brief (15 ms) or long (200 ms), and brief signals were coincident with either a dip or peak in the masker envelope. Experiment 2 estimated the MLD for both signal and masker consisting of a 50 Hz wide bandpass noise centered on 500 Hz. Signals were generated to provide only interaural phase cues, only interaural level cues, or both. The pattern of individual differences was dominated by variability in NoSpi thresholds, and NoSpi thresholds were highly correlated across all conditions. Results suggest that the individual differences observed in Experiment 1 were not primarily driven by differences in the use of binaural fine structure cues or in binaural temporal resolution. The range of thresholds obtained for a brief NoSpi tonal signal at 500 Hz was consistent with a model based on normalized interaural correlation. This model was not consistent for analogous conditions at 2000 Hz.     

Killing pairs constructed from a recurrent vector field

Killing pairs are investigated under the assumption that one member of the pair is a known recurrent vector field. This reduces the equation determining the other member of the pair to a linear equation. The conditions for such a Killing pair to exist are obtained for a well known class of spacetimes admitting a recurrent vector field.     

Predicted new class of hadrons and the average parton charge

A semiempirical mass formula of a particular parton model, in which it is assumed that partons are highly charged, requires the existence of a new class of hadrons, at least one of which must be absolutely stable and whose masses are of the order of a few GeV. Several experiments (with accelerators and cosmic rays) appear to support the notions that partons are highly charged and that a new class of hadrons exists. The recently reported particle of Niu et al., with an apparent lifetime ～10^?13 sec, may be a member of the new predicted class.     

Surface antiferromagnetic domain structures of NiO (0 0 1) studied using UV photoemission electron microscope

Direct observation of the antiferro (AF) magnetic domain structures of a NiO (0 0 1) surface is found to be possible using a spectroscopy photoelectron low-energy electron microscope (SPELEEM) and a commercial UV Hg excitation light source without using any polarizers. The principle is based on the magnetic linear dichroism (MLD) effect, where different domain contrasts are produced according to the relative angle between the antiferromagnetic axis and the linearly polarized light. The observed AF magnetic domain structures are strongly affected by both bulk AF magnetic domain structures and the stresses induced during the sample cleaving process. Moreover, the AF magnetic domain structures are found to be irreversible when the sample is heated to over its Néel temperature and then cooled. The possibility of imaging AF magnetic domain structures without using synchrotron radiation or a polarizer is attractive.