Peculiarities of Er3+ photoluminescence in halogen-doped amorphous silica

The spectra and photoluminescence kinetics of Er³⁺ ions embedded in amorphous fluorine- and chlorine-doped silica matrices synthesized by surface-plasma chemical vapor deposition were investigated at 27–300 K. Luminescence was excited with an Ar⁺ laser at a wavelength of 514.5 nm and with a diode laser at a wavelength of 975 nm. Narrow and well-expressed components of Stark sublevels with a small contribution of inhomogeneous broadening intrinsic to Er³⁺ ions in crystalline rather than amorphous matrices were revealed and identified in photoluminescence spectra. The structure of Stark sublevels was well-resolved at low temperatures. The presence of the well-resolved Stark structure in spectra was indicative of stable anion complex formation in Er³⁺ environment presumably associated with halogen incorporation. This environment was formed at a stage of the low-temperature plasma-chemical synthesis and was destroyed at glass fusion.     

Formation of a ripple pattern at a water/silicon interface using an oscillating bubble

A single femtosecond laser pulse was irradiated at a water/silicon interface, and the processed surface was investigated. Rings surrounded by ripples were found within the irradiated spot. The diameter of the rings ranged from 500 nm to 10 μm. It is proposed that acoustic waves, caused by the oscillating motion of bubbles near the water/silicon interface, deformed the melting silicon surface. In the present work, a pulse (pulse width: 150 fs) was tightly focused in water to induce optical breakdown, and a bubble was generated at an arbitrary spot. When the power density was below the ablation threshold and above the melting threshold at the silicon surface and set above the breakdown threshold at the focus in water, a pattern was generated at a specific place and with a specific size. PACS 79.20.Ds; 42.62.Cf     

Dependence of loudness growth on skirts of excitation patterns

Over a range of 50 dB, the loudness of a 100-Hz tone was measured in the presence of a broadband noise with a low-frequency cutoff at 200 Hz. The noise was varied in intensity along along with the tone so that the signal-to-noise ratio remained constant at either 0 or--10 dB. Listeners judged the loudness of the tone by loudness matching, magnitude estimation, and magnitude production. The noise markedly decreased the tone's rate of loudness growth but not the range over which loudness grows. The overall decrease in steepness of the 100-Hz loudness function was greater than that previously reported at higher frequencies. It is hypothesized that the decrease was greater because the spread of excitation at 100 Hz was more effectively contained than at higher frequencies. Support for this hypothesis is given by measures of intensity discrimination at 100 Hz.     

Pore matrices prepared at supercritical temperature by computer simulations: matrix characterization and studies of diffusion coefficients of adsorbed fluids

We present series of molecular dynamics simulations to study the structure of different porous matrix configurations. The present simulations are an extension of recently reported data at a temperature below the critical. Here, we show how temperature modifies the structure and porosity of pore matrices during their preparation in comparison with the previous work. Moreover, in these studies at a higher temperature, we studied in more detail the structure of the porous matrix. Matrices were prepared by two different processes. The first method consisted of a single Lennard-Jones fluid simulated at a fixed density and at a supercritical temperature. Then, the matrix configuration was taken from the last configuration of the fluid. The second method was prepared from a binary mixture, where one of the components served as a template material. The final porous matrix configuration was obtained by removing template particles from the mixture. Matrices were prepared at two different densities and at different matrix particle interactions. The volume distribution, the cluster formation and the connectivity between the particles in the pore matrix were investigated. The importance of using template particles was clear since they produced larger voids and higher porosities. On the other hand, the temperature of preparation seems to modify the size of the voids and the porosity in the matrices. For instance, at this high temperature, the matrix porosity is higher when template particles are present in the system. These results point in the opposite direction compared to those found in a previous paper at a lower temperature. The diffusion of fluids immersed in the different matrices was also analysed by calculating the mean square displacements of their particles. It was observed that this quantity was higher when matrices were prepared with template particles. These results also point to different directions in contrast with pore matrices prepared at a lower temperature. Finally, the results show that temperature plays an important role in the pore matrix formation.     

Temperature dependence of interband transition energy in InGaAsN strain-compensated quantum-well and ridge-waveguide lasers fabricated with pulsed anodic oxidation

Ridge-waveguide InGaAsN triple-quantum-well strain-compensated lasers grown by metal organic chemical vapor deposition were fabricated with pulsed anodic oxidation. The laser’s output power reached 145 mW in continuous-wave mode at room temperature for a 4-?m -stripe-width laser. Continuous-wave single longitudinal mode operation was maintained at a high injection current level with a wavelength of 1287.3 nm at room temperature. Single longitudinal mode operation at 1317.2 nm was achieved at twice the threshold current at 100 °C. The band gap of InGaAsN in the quantum wells at different temperatures was calculated and compared to the measured temperature-dependent laser wavelength.     

Trapping of positive muons by vacancies in non-stoichiometric compounds

A direct evidence for trapping of positive muons by vacancies was found by using the longitudinal field method., 65.5 at. %Cu-34.5 at. %Al, 51at. %Al-49at. %Ni and 52 at. %Al-48at. %Ni polycrystalline samples were studied. The forward/backward asymmetry was measured as a function of time at room temperature changing the magnetic field from 0 to 70 Oe. At H=0, a relaxation function of Kubo-Toyabe type was found. Analysing the data, it was found that positive muons are trapped by vacancies in these materials.     

Field ion microscope observations of surface rearrangement and oxide formation at clean rhenium surfaces heated in oxygen

The interaction between oxygen and clean, well-ordered rhenium surfaces has been investigated in the field ion microscope over a wide range of temperatures. The surface structure of vacuum annealed specimens was extensively modified by the presence of adsorbed oxygen. At partial monolayer coverages, surface metal atom rearrangement was inhibited, particularly at {112?2}, but at coverages near saturation, facets were produced at {101?0} at a lower temperature than on the clean surface, resulting in the exposure of an increased proportion of closepacked surface structures and suggesting a change in the rearrangement mechanism at high coverages. The production of facets at the major poles was temperature and coverage dependent as a result of the varying influence of adsorbed oxygen on surface free energy. A decrease in oxygen coverage was observed at 1200–1300 K on near-saturated surfaces, which may be associated with the formation of volatile ReO₃ from regions where oxygen concentration exceeds a critical value. There was little evidence of the production of a discrete surface oxide phase formed on specimens heated in the presence of gas phase oxygen, but a reduction in specimen radius as a result of volatile oxide formation was observed at pressures greater than 10^?4 Torr and temperatures above 1400 K. It is concluded that the final structure of rhenium surfaces heated in oxygen is dependent upon the rate of oxide formation, the effective oxygen coverage during oxidation, and the extent of surface rearrangement.     

Study on cross-section clad profile in coaxial single-pass cladding with a low-power laser

In this paper, a model of cross-section clad profile on the substrate in coaxial single-pass cladding with a low-power laser was studied. The static model of powder mass concentration distribution at cold-stream conditions was defined as a Gaussian function. In coaxial single-pass cladding with a low-power laser, since the influence of surface tension, gravity and gas flow on the clad bead could be neglected, the cross-section profile of the clad bead deposited by a low-power laser on the substrate was dominated by the powder concentration at each point on the pool and the time when the material was liquid at this point. The height of each point on the cross-section clad profile was defined as a definite integration of a Gaussian function from the moment at which the melt pool was just arriving at the point to the moment at which the point left the melt pool. In the presented experiment, powder of Steel 63 (at 0.63 wt% C) was deposited on a substrate of Steel 20 (at 0.20 wt% C) at the laser power of 135 W. The experimental results testified the model.     

Laser Doppler velocimetry measurement at a hard-to-reach intake port of a two-stroke engine

To understand better the complex scavenging process in ported two-stroke engines, optical set-ups were designed for velocity measurements at the exit of an intake port of a motoring and firing single-cylinder propane-fueled two-stroke engine by laser Doppler velocimetry. The radial velocity component was measured at the center of one port at engine speeds of 600, 900, and 1200 rpm. Laser beams entered the engine from the top through a quartz window and the light scattered by the seed particles was collected at 90° through the exhaust ports and a side window. The noise produced by the piston head was analyzed and separated from the signal generated by the seed particles. Analysis of the results from this engine showed that, in general, differences in both magnitude and the shape of the plotted results were observed when the engine was firing. A backflow into the intake system was observed at 600 rpm; this backflow decreased in strength, shifted in crank angle at 900 rpm, and eventually was eliminated at an engine speed of 1200 rpm.     

Crystallization Behavior of Amorphous Poly(l-Lactide)

Amorphous poly(l-lactide) (PLLA) was annealed in two different ways: amorphous samples were heated at a given temperature to induce crystallization (one-step annealing); and amorphous samples were first crystallized at a low temperature and subsequently annealed at a higher temperature than the crystallization temperature. Samples thus prepared were measured by DSC. The original amorphous sample exhibited an exothermic peak at about 100°C (exothermic peak I), an exothermic peak just below the melting point (exothermic peak II), and an endothermic peak when it was melted. Exothermic peak I was caused by cold crystallization. When the melting points of PLLA samples, heat-treated in various ways, were plotted as a function of annealing temperature, there was discontinuity at about 120°C. From analyses of wide-angle X-ray diffraction patterns, it was found that when amorphous PLLA was crystallized at a temperature below 120°C, crystallites of the β-form formed, and when annealed at a temperature above 120°C, crystallites of the α-form grew. Thus, exothermic peak I was attributed to cold crystallization of the β-form, and peak II was caused by the phase transition of the β-form to a more stable form.     

Temporal integration in the presence of off-frequency maskers

Temporal integration was measured at a relatively low and a relatively high signal frequency under conditions of off-frequency masking. The masker was typically gated for 300 ms, and the signal was presented 70 ms after masker onset. In experiment 1, the signal frequency was 500 or 2000 Hz. Temporal integration was measured in quiet and in the presence of a masker whose frequency was lower or higher than the signal frequency. In all listening situations, there was less integration at 2000 Hz than at 500 Hz. This effect of frequency was particularly dramatic in the presence of a lower frequency masker, where there was almost no integration at 2000 Hz. Experiment 2 showed that this dramatic effect of frequency cannot be understood in terms of the underlying psychometric functions. Experiment 3 measured temporal integration at 750 and 2000 Hz for a large number of masker-signal frequency separations for both a tonal and a noise masker, and in conditions where the masker was gated or continuous. The results with the gated tonal masker largely confirmed the results of experiment 1. The results with the continuous tonal masker and the gated or continuous noise masker, however, were quite different. In those cases, the amount of temporal integration at both signal frequencies was more or less independent of the masker-signal separation; the masked temporal integration was nearly equal to the integration in quiet. Thus based on the conditions evaluated here, off-frequency masked temporal integration differs substantially from integration in quiet only for gated tonal maskers located considerably lower in frequency than the signal. It is unclear how to account for this finding, although it may be related to attentional factors.     

Production of powerful electron beams in dense gases

Subnanosecond electron beams with the record current amplitude (～70 A in air and ～200 A in helium) were produced at atmospheric pressure. The optimal generator open-circuit voltage was found for which the electron-beam current amplitude produced in a gas diode was maximal behind a foil. It was established that the electron beam was produced at the stage when the cathode plasma closely approaches the anode. It was shown that a high-current beam can be produced at high pressures because of the presence of the upper branches in the curves characterizing the electron-escape (runaway) criterion and the discharge-ignition criterion (Paschen curve).     

8.30 μm singly resonant ZnGeP2 optical parametric oscillators pumped by a Tm,Ho:GdVO4 laser

A single resonator 8.30 μm ZnGeP₂ (ZGP) optical parametric oscillators (OPO) was reported in the paper. The OPO was pumped by a 10.2-W Tm,Ho:GdVO₄ laser at 8 kHz in a Q-switch mode, a 170-mW idler was obtained at 8.30 μm, and the output power of the idler and signal wave was 1.0 W, corresponding to an optical-optical conversion efficiency of 10.3% and a slope efficiency of 20.9%. Tm,Ho:GdVO₄ laser was pumped by a 30-W fiber-coupled laser diode (LD) at the center wavelength of 801 nm. The output wavelength of Tm,Ho:GdVO₄ laser was at 2.05 μm, and the energy per pulse of 1.28 mJ in 18 ns was achieved at 8 kHz with the peak power of 71.1 kW.     

Factors affecting thresholds for sinusoidal signals in narrow-band maskers with fluctuating envelopes

When a signal is higher in frequency than a narrow-band masker, thresholds are lower when the masker envelope fluctuates than when it is constant. This article investigates the cues used to achieve the lower thresholds, and the factors that influence the amount of threshold reduction. In experiment I the masker was either a sinusoid (constant envelope) or a pair of equal-amplitude sinusoids (fluctuating envelope) centered at the same frequency as the single sinusoid (250, 1000, 3000, or 5275 Hz). The signal frequency was 1.8 times the masker frequency. At all center frequencies, thresholds were lower for the two-tone masker than for the sinusoidal masker, but the effect was smaller at the highest and lowest frequencies. The reduced effect at high frequencies is attributed to the loss of a cue related to phase locking in the auditory nerve. The reduced effect at low frequencies can be partly explained by reduced slopes of the growth-of-masking functions. In experiment II the masker was a sinusoid amplitude modulated at an 8-Hz rate. Masker and signal frequencies were the same as for the first experiment. Randomizing the modulation depth between the two halves of a forced-choice trial had no effect on thresholds, indicating that changes in modulation depth are not used as a cue for signal detection. Thresholds in the modulated masker were higher than would be predicted if they were determined only by the masker level at minima in the envelope, and the threshold reduction produced by modulating the master envelope was less at 250 Hz than at higher frequencies. Experiments III and IV reveal two factors that contribute to the reduced release from masking at low frequencies: The rate of increase of masked threshold with decreasing duration is greater at 250 Hz than at 1000 Hz; the amount of forward masking, relative to simultaneous masking, is greater at 250 Hz than at 1000 Hz. The results are discussed in terms of the relative importance of across-channel cues and within-channel cues.     

Effects of speaking rate on tongue position and velocity of movement in vowel production

This study used glossometry to examine the position of the tongue and the velocity of its movements in vowels spoken normally and at a self-selected fast rate. The subject in experiment 1 showed lingual undershoot for stressed vowels in "a big again" and "a bob again." The tongue was lower for /I/ and higher for /a/ at the fast rate than at the normal rate. The stressed vowels exerted an affect on unstressed vowels: The tongue was lower in the schwas that preceded and followed /a/ than /I/. Only one of the three subjects in experiment 2 showed no lingual undershoot for fast-rate /I/. The tongue was higher at the fast rate than at the normal rate in the schwas flanking /I/ so that the displacement was less at the fast rate than at the normal rate. Another talker increased the peak velocity of tongue movements at the fast rate and showed no undershoot for /a/. Multiple regression analyses showed that the timing of movements for successive phonetic segments accounted well for undershoot in only one of the three subjects. The results suggest that in order to model the effects of speaking rate on the tongue movements used in forming stressed vowels, it will be necessary to take into account: (1) how much vowels are shortened at a fast rate: (2) how much the peak velocity of tongue movements is increased, if at all; and (3) the position of the tongue before and after the stressed vowels. All three factors are likely to be influenced by how clearly the talker wishes to speak.     

Effect of pulse polarity and energy on ultrasound-induced lung hemorrhage in adult rats

The objective of this study was to further assess the role of inertial cavitation in ultrasound-induced lung hemorrhage by examining the effect of pulse polarity at a common in situ (at the lung surface) peak rarefactional pressure [pr(in situ)] and at a common in situ pulse intensity integral (PII(in situ)). A total of 60 rats was divided into three experimental groups of 20 animals per group and randomly exposed to pulsed ultrasound. The groups were exposed as follows: Group 1 to 0 degree polarity pulses (compression followed by rarefraction) at a pr(in situ) of 3.48 MPa and a PII(in situ) of 4.78 Ws/m2, group 2 to 180 degree polarity pulses (rarefraction followed by compression) at a pr(in situ) of 3.72 MPa and a PII(in situ) of 2.55 Ws/m2, and group 3 to 180 degree polarity pulses at a pr(in situ) of 4.97 MPa and a PII(in situ) of 4.79 Ws/m2. For all experimental groups, the frequency was 2.46 MHz, the exposure duration was 240 s, the pulse repetition frequency was 2.5 kHz, and the pulse duration was 0.42 micros. Six sham animals were also randomly distributed among the experimental animals. The lesion surface area and depth were determined for each rat as well as lesion occurrence (percentage of rats with lesions) per group. It was found that lesion occurrence and size correlated better with PII(in situ) than with pr(in situ), suggesting that a mechanism other than inertial cavitation was responsible for the damage.     

Carrier-dependent temporal processing in an auditory interneuron

Signal processing in the auditory interneuron Omega Neuron 1 (ON1) of the cricket Teleogryllus oceanicus was compared at high- and low-carrier frequencies in three different experimental paradigms. First, integration time, which corresponds to the time it takes for a neuron to reach threshold when stimulated at the minimum effective intensity, was found to be significantly shorter at high-carrier frequency than at low-carrier frequency. Second, phase locking to sinusoidally amplitude modulated signals was more efficient at high frequency, especially at high modulation rates and low modulation depths. Finally, we examined the efficiency with which ON1 detects gaps in a constant tone. As reflected by the decrease in firing rate in the vicinity of the gap, ON1 is better at detecting gaps at low-carrier frequency. Following a gap, firing rate increases beyond the pre-gap level. This "rebound" phenomenon is similar for low- and high-carrier frequencies.     

STM studies of the reconstructed Au(1 1 1) thin-film at elevated temperatures

High temperature scanning tunneling microscope (HT-STM) was used to investigate a reconstructed Au(1 1 1) film evaporated on mica. The experiment was carried out at elevated temperatures in the range of 300-500 K. A herringbone reconstruction was observed at a wide range of temperatures. However, at the highest temperatures studied a break down of the reconstruction long range order was noticed. Finally, the presence of a triangular-like reconstruction was reported. Changes in the reconstruction were explained in terms of the change in surface stress arising as a result of the tension at the gold-mica interface.     

Monaural level discrimination under dichotic conditions

The ability to make judgments about the stimulus at one ear when a stimulus is simultaneously presented to the other ear was tested. Specifically, subjects discriminated the level of a 600 Hz target tone presented at the left ear while an identical-frequency distractor was simultaneously presented at the other ear. When there was no distractor, threshold was 0.7 dB. Threshold increased to 1.1 dB when a distractor with a fixed phase and level was introduced contra-aurally to the target. Further increases in threshold were observed when an across-presentation variability was introduced into the distractor phase (threshold of 1.6 dB) or level (threshold of 5.8 dB). When both the distractor level and phase varied, the largest threshold of 7.3 dB was obtained. These increases in threshold cannot be predicted by common binaural models, which assume that a target stimulus at one ear can be processed without interference from the stimulus at the nontarget ear. The measured thresholds are consistent with a model that utilizes two binaural dimensions that roughly correspond to the loudness and the position of a fused binaural image. The results show that, with binaurally fused tonal stimuli, subjects are unable to listen to one ear.     

XPS studies for NaCl deposited on the Ni(111) surface

Vapor deposited NaCl on the Ni(111) surface was characterized by XPS. Three types of NaCl were found on the surface. First, the NaCl interacted strongly with Ni giving the Nals peak at 1072.2 eV, the C12p peak at 198.8 eV and the NaKLL peak at 494.3 eV. The 494.3 eV peak shifted to 493.4 eV when measured at ∼ 500 K. The energy of the NaKLL peak and the modified Auger parameter for sodium were nearer to those for Na metal than to those for bulk NaCl. The species was assigned to NaCl which was freed from the potential of the NaCl crystal and which had a weakened NaCl bond. The other types were characterized by using H₂O as a probe. One set of the peaks, the Nals peak at 1072.8 eV, the C12p peak at 199.6 eV and the NaKLL peak at 497.7 eV, was assigned to NaCl which was in the form of a very thin crystal. The other set, the Nals peak at 1073.5 eV, the C12p peak at 200.1 eV and the NaKLL peak at 498.5 eV, was obtained during crystal growth of NaCl as large islands upon annealing. The energies suffered from the charging effect. The effect of coadsorbing oxygen was also studied.