Detection of incremental and decremental bars at different locations across Mach bands and related stimuli

Two-alternative forced-choice procedures were used to measure the detectability of bright and dark bars at various locations across luminance patterns that produced Mach bands. Detection performance was significantly affected by both dark and bright Mach bands: poor detection performance was observed at locations near, but not in, the Mach bands; relatively good detection performance at locations within the Mach bands was caused by reliable changes in the width, depth, or symmetry of the bands produced by the signal bars. The changes were apparent with signals of lower luminance than that needed for detection in the plateau regions far from the bands, but, because the cues were not sufficiently reliable to allow errorless performance, unusually shaped psychometric functions were obtained.     

Some observations on the masking effects of Mach bands

There are 8 cycle/deg ripples or oscillations in performance as a function of location near Mach bands in experiments measuring Mach bands' masking effects on random polarity signal bars. The oscillations with increments are 180 degrees out of phase with those for decrements. The oscillations, much larger than the measurement error, appear to relate to the weighting function of the spatial-frequency-tuned channel detecting the broadband signals. The ripples disappear with step maskers and become much smaller at durations below 25 ms, implying either that the site of masking has changed or that the weighting function and hence spatial-frequency tuning is slow to develop.     

Banded structure of the electrodeposited nanocrystalline Al–Mg alloy dendrites

Nanocrystalline Al–Mg dendrites with smooth (face centered cubic (fcc)-Al(Mg)) and rough (hexagonal close packed (hcp)-Mg(Al)) globular morphology were electrodeposited. The longitudinal sections of the rough globules exhibited bright–dark banded structure possessing Mg-poor and Mg-rich compositions respectively. The banded structure was explained by considering the fluctuations in potential(E)-time curve. More negative potentials result in Mg-rich dark bands. Mg-poor bright bands appear at less negative potentials. A mechanism was proposed for the banded structure formation in Al–Mg dendrites.     

Corrosion behaviour of banded microstructure within nugget of friction stir welds in AA2024-T351

Abstract

Corrosion behaviour of the banded structure known as ‘onion ring’ in the nugget of friction stir weld AA2024-T351 was investigated to find the relation to microstructure. A micro-electrochemical cell with a 50 μm diameter glass pipette tip was used for electrochemical measurements. It was found that onion rings consisted of two bands: ‘dark’ bands that contain fewer constituent particles but show extensive precipitation of S phase and ‘light’ bands that contain fewer S phase precipitates but greater numbers of constituent particles. Electrochemical results showed that the light band has more noble (less active) open circuit potential compared to the dark band. Microstructurally, this is due to the lower number of S precipitates and therefore the possibility of higher Cu solid solution within the band compared to that of the dark band.     

Quality enhancement of image generated with bistatic ground based noise waveform SAR

A new method for quality enhancement in a noise synthetic aperture radar (SAR) image and the first results of its application to the SAR image generated with the use of a bistatic Ka-band ground-based noise waveform SAR (GB NW-SAR) are presented. A SAR image generated with a noise SAR suffers from the masking effect which is tied to residual random fluctuations in noise radar response from bright scatterers in the scene. This is similar to the masking effect present in the deterministic waveform SAR when the signal sidelobes of echoes from bright scatterers may mask the main response from a weaker target. The procedure presented is a variation of the CLEAN algorithm. Knowing precisely the emitted signal and finding positions of the strongest scatterers one may model the echo signal originated from a selected scatterer. Extraction of the modelled signal from the received one reduces the residual fluctuations and makes it possible to clean the image and increase its dynamic range. The final image is constructed from the cleaned signal and the previously removed strongest scatterers. A theoretical background is provided to the proposed procedure and its application to enhance the SAR image using simulated data as well as data generated by the Ka-band bistatic GB NW-SAR is demonstrated. The GB NW-SAR, recently developed and tested in LNDES IRE NASU, may operate in CW and pulse random signal regimes for short range applications.     

Confirmation of K-momentum dark exciton vibronic sidebands using 13C-labeled, highly enriched (6,5) single-walled carbon nanotubes

A detailed knowledge of the manifold of both bright and dark excitons in single-walled carbon nanotubes (SWCNTs) is critical to understanding radiative and nonradiative recombination processes. Exciton-phonon coupling opens up additional absorption and emission channels, some of which may "brighten" the sidebands of optically forbidden (dark) excitonic transitions in optical spectra. In this report, we compare (12)C and (13)C-labeled SWCNTs that are highly enriched in the (6,5) species to identify both absorptive and emissive vibronic transitions. We find two vibronic sidebands near the bright (1)E(11) singlet exciton, one absorptive sideband ~200 meV above, and one emissive sideband ~140 meV below, the bright singlet exciton. Both sidebands demonstrate a ~50 cm(-1) isotope-induced shift, which is commensurate with exciton-phonon coupling involving phonons of A[Formula: see text] symmetry (D band, ω ~ 1330 cm(-1)). Independent analysis of each sideband indicates that both sidebands arise from the same dark exciton level, which lies at an energy approximately 25 meV above the bright singlet exciton. Our observations support the recent prediction of, and mounting experimental evidence for, the dark K-momentum singlet exciton lying ~25 meV (for the (6,5) SWCNT) above the bright Γ-momentum singlet. This study represents the first use of (13)C-labeled SWCNTs highly enriched in a single nanotube species to unequivocally confirm these sidebands as vibronic sidebands of the dark K-momentum singlet exciton.     

Mach bands and airplane shadows cast on dry terrain

Luminous rings are often seen surrounding the shadow of a high-flying airplane. Some of these phenomena are due to water droplets (glories, the Heiligenschein), but a different sort of explanation is required when a luminous ring (sometimes simply a bright spot) is seen while the plane is flying over dry terrain. Demonstrations involving distances and shadows manyfold smaller than those of an airliner's shadow show that Mach bands can produce illusory luminance phenomena that greatly resemble those associated with a plane's shadow over dry terrain. Luminance rings have recently also been observed over dry, sparsely vegetated terrain, around the shadow of an adjacent airplane (i.e., far from the observer's antisolar point), thereby excluding all previous alternative interpretations; Mach bands are thus a likely explanation for at least some instances of dry-terrain luminous rings around airplane shadows.     

Method for measuring veiling glare in high-performance display devices

An experimental method for measuring the veiling glare characteristics of display devices is presented. The measured veiling glare ratio (G) is taken to be the luminance in the surrounding bright field divided by the luminance in a dark circle. The method is based on a collimated conic probe that minimizes signal contamination from bright surroundings allowing for measurements of low luminance in a circular dark spot of a test pattern. A correction factor computed with test patterns having opaque spots is introduced. The factor is expressed as a bivariate function of the dark-spot radius and the distance between the probe and the emissive surface. We studied the uncertainty introduced by the method by measuring veiling glare test patterns printed on radiographic film for which the transmission of the dark spots was determined experimentally. Performance characterization measurements show that signal contamination is less than 10(-4) of the bright field surrounding a dark circle. Our results show that G of a few hundred can be measured with an uncertainty of a few percent, and ratios of approximately 10(3) can be reported within 10%. Finally, we demonstrate the method by measuring G for a high-performance monochrome cathode-ray tube display.     

Foveal contour interaction: detection and discrimination

Contour interaction, the detrimental effect of flanking features on the discrimination of optotypes, has been studied mainly close to the visual acuity limit. We were interested to know how these results compare with those for the detection of targets. According to the simplest model of contour interaction, comparable detection effects would be expected. The case for low-level masking would be further strengthened if the form and nature of the dependence on flank separation and flank polarity followed that typically found in studies of lateral spatial masking [Vision Res. 33, 993 (1993)]. Landolt Cs subtending a visual angle of 0.25 degrees, 0.5 degrees, and 1.0 degrees were presented and contrast thresholds for detecting the presence of the Landolt C and discriminating its orientation were measured in five normal subjects as a function of flank separation and flank polarity. The results obtained for the relationship between detection and discrimination depend on the size of the target used. For small letters, discrimination but not detection was significantly affected by flanking bars. For large letters, detection and discrimination were affected to the same extent. However, in this case the effectiveness of opposite-polarity flanks and the finding that facilitation occurred at close, not far, flank separations suggests that the simplest explanation in terms of masking may not be applicable.     

Deep-level studies in GaN layers grown by epitaxial lateral overgrowth

The electrical properties, deep-level spectra, microcathodoluminescence (MCL) spectra and diffusion lengths of minority charge carriers were measured in GaN films grown by the epitaxial lateral overgrowth (ELOG) technique. The results are compared to the properties of GaN layers grown in a standard fashion without masking of the initial template. MCL and electron beam induced current (EBIC) imaging of the laterally overgrown regions revealed the presence of dark spots with density of 1-5 × 10⁶ cm^− 2 that are associated with individual dislocations. The concentration of deep electron and hole traps was found to be much higher in the standard material than in the ELOG material. Diffusion lengths of minority carriers determined from EBIC signal profiling gave values of 0.8-1 μm along the bright regions and 0.4-0.5 μm in the dark regions of the ELOG samples. Similar measurements on metal organic chemical vapor deposition templates gave a diffusion length of 0.4-0.5 μm, close to the diffusion length in the dark stripes of the ELOG samples.     

Polarity assignment in ZnTe, GaAs, ZnO, and GaN-AlN nanowires from direct dumbbell analysis

Aberration corrected scanning transmission electron microscopy (STEM) with high angle annular dark field (HAADF) imaging and the newly developed annular bright field (ABF) imaging are used to define a new guideline for the polarity determination of semiconductor nanowires (NWs) from binary compounds in two extreme cases: (i) when the dumbbell is formed with atoms of similar mass (GaAs) and (ii) in the case where one of the atoms is extremely light (N or O: ZnO and GaN/AlN). The theoretical fundaments of these procedures allow us to overcome the main challenge in the identification of dumbbell polarity. It resides in the separation and identification of the constituent atoms in the dumbbells. The proposed experimental via opens new routes for the fine characterization of nanostructures, e.g., in electronic and optoelectronic fields, where the polarity is crucial for the understanding of their physical properties (optical and electronic) as well as their growth mechanisms.     

Phase control of six-wave mixing from circularly polarized light

We investigate the phase control of six-wave mixing (SWM) in atomic system with multi-Zeeman levels theoretically and experimentally. With the relative phase varying, the switch between bright and dark state can appear in probe transmission signal. Then we demonstrate the evolution of six-wave mixing generated in bright and dark states by scanning the frequency detuning of the dressing field at different polarized probe field. Meanwhile, by utilizing the strong dressing effect of circular polarized light, we observe pure dark state switched to pure bright state in terms of energy level splitting, and compare different phases under different detuning of circularly polarized light. Theoretical calculations are in well agreement with the experimental observations.     

Thermally Activated Photoluminescence in Lead Selenide Colloidal Quantum Dots

The thermal activation processes in PbSe colloidal quantum dots and their influence on the ground‐state exciton emission are discussed. Activation of a dark exciton occurs at 1.4–7 K, assisted by an acoustic phonon coupling. Activation of a bright exciton occurs at 100–200 K, which appears as a sudden change in the photoluminescence band intensity, energy, and full width at half maximum. This activation overcomes the dark–bright‐state splitting, when the activation temperature increases with the decrease of the dots' size. The dark exciton lifetime is found to be ≈6–12 µs at 1.4 K, while the bright exciton lifetime at 300 K evaluated as 450 ns varies slightly with the change in the size of the dots. In addition, the emission quantum yield of these dots, measured at a variety of temperatures when dissolved in various solvents, reveals information about the influence of the environment on the recombination processes.     

Spatial frequency tuning of brightness polarity identification

Recent studies have shown that cells in the primary visual cortex can, in addition to borders, also encode surface brightness. Whether the brightness is encoded by a large extraclassical receptive field or by a filling-in type mechanism activated by the luminance border is not known. These explanations imply different spatial frequency tunings for the underlying mechanism. In a psychophysical masking paradigm we measured spatial frequency tuning functions for identification of both luminance polarity (bright/dark) and luminance border orientation of oval and circular luminance patches with variable diameters (0.2-10 deg). For both tasks we obtained nearly overlapping narrow (1.5 octave) bandpass masking tuning functions centered at 1.5-5.0 c/deg. Stimulus size and shape had only minimal effect on the tuning functions. The results favor the idea of brightness filling-in and suggest that the cells activated by the luminance border modulate the activity of the cells signaling surface brightness. Further, the brightness processing mechanism is spatial frequency selective.     

Cracking of a Tool Steel Guide Roller in a Bar Mill

Failure analysis of a guide roller used in a bar mill of an integrated steel plant has been presented. The guide rollers are positioned at the entry of rolling stands and act as guide in the multi-grooved pass for aligning the hot bars and hold the twisted oval bar while it enters a round pass. The hot bar is at a temperature of ??1100°C, and the rollers are water cooled. The component is subjected to cyclic thermal stress depending on the mill operating conditions. The rollers are cracking longitudinally leading to failure. The investigation consists of visual inspection, chemical analysis, fractography, characterization of microstructures using optical and scanning electron microscopes (SEM), energy dispersive spectroscopy (EDS) analysis, and measurement of micro-hardness. The chemical analysis indicates the material as AISI D2 grade of cold work tool steel. Visual observation of the failed component shows multiple longitudinal cracks on the roller surface associated with a dark circular band of oxidation. The fracture surface shows a dark oxidized area propagating from the roller surface followed by flat bright appearance indicating final brittle fracture. Fractography of the dark surface from where the crack initiates shows fatigue striations. Microstructural examination under optical and SEM shows a network of coarse carbide particles at the grain boundary as well as uniformly distributed fine carbide precipitates within the martensite matrix. Multiple cracks are observed to initiate and propagate from the surface through the clusters of grain boundary carbides. EDS analysis and elemental mapping suggest the carbides to be chromium carbides. SEM shows micro-cracking of carbide particles associated with the crack. Clustered distribution of carbides deteriorates toughness and initiates cracking at the roller surface subjected to thermal cycling because of their differential thermal expansion coefficient leading to the failure of the component.     

Point-spread function of the ocean color bands of the Moderate Resolution Imaging Spectroradiometer on Aqua

The Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua platform has nine spectral bands with center wavelengths from 412 to 870 nm that are used to produce the standard ocean color data products. Ocean scenes usually contain high contrast due to the presence of bright clouds over dark water. About half of the MODIS Aqua ocean pixels are flagged as spatial stray light contaminated. The MODIS has been characterized for stray light effects prelaunch. In this paper, we derive point-spread functions for the MODIS Aqua ocean bands based on prelaunch line-spread function measurements. The stray light contamination of ocean scenes is evaluated based on artificial test scenes and on-orbit data.     

The thickness of defect bands in high-pressure die castings

Defect bands following the casting contour are often observed in high-pressure die cast (HPDC) components. In this article, suitable methods for measuring the thickness (w) and grain size in the bands (d_sb) in HPDCs have been developed. The w/d_sb relationship of defect bands has been investigated in HPDC specimens from a range of alloys, casting geometries and band locations within castings. Samples include aluminum alloy, AlSi4MgMn and AlMg5Si2Mn, tensile test bars cast by cold-chamber (cc) HPDC and a magnesium alloy, AM50, hot-chamber (hc) HPDC steering-wheel component. The band thicknesses were measured to be in the range 7–18 mean grains wide. This is substantial evidence that defect bands form due to strain localization in partially solidified alloys during cc and hc HPDC. Additionally, within this range, the w/d_sb ratio decreases with increasing distance from the casting center in a cross-section containing multiple bands.     

Magnetic brightening of carbon nanotube photoluminescence through symmetry breaking

We report that symmetry breaking by a magnetic field can drastically increase the photoluminescence quantum yield of single-walled carbon nanotubes, by as much as a factor of 6, at low temperatures. To explain this we have developed a theoretical model based on field-dependent exciton band structure and the interplay of Coulomb interactions and the Aharonov-Bohm effect. This conclusively explains our data as the first experimental observation of dark excitons 5-10 meV below the bright excitons.     

Interaction of bright-dark solitons in a silicon-on-insulator optical waveguide

In this paper, we use a distributed Fourier transform to simulate the interaction effects of bright and dark solitons numerically through a nonlinear coupled-wave Schrödinger equation satisfied by the TE and TM mode direction of silicon-on-insulator waveguides. The simulation shows that an increase in the relative polarization angle of bright and dark solitons reduces the influence of bright solitons on dark solitons but increases the influence of dark solitons on bright solitons when the nonlinear effect is constant. At the appropriate polarization angle, the dark soliton will show a quasi-soliton waveform under the influence of a bright soliton. When the power is similar, the interaction is most obvious. An increase in the bright soliton pulse width can increase its effective transmission distance and is greatly affected by dark solitons at short distances. A change in the dark soliton pulse width has little effect on the interaction. Changing the delay difference can change the position and peak of a quasi-soliton in a dark soliton. An appropriate delay difference can improve the effective transmission distance of the bright soliton and increase its stability in a short distance.     

电子雷管和导爆管雷管起爆的振动信号时频特性对比

为了对比电子雷管和导爆管雷管两种起爆方式的爆破振动信号,开展了某露天采石矿两种雷管起爆的深孔爆破振动测试。基于小波分析方法和Matlab程序小波工具箱,对爆破振动信号按照频率划分为10个频带,分析各频带能量和峰值质点速度(peak partide velocity,PPV)的分布特征及随爆心距的变化。结果表明:采用电子雷管和导爆管雷管起爆时,90%的爆破振动能量分布在2~6频带（9.77~312.50 Hz）和2~7频带（9.77~625.00 Hz）,且PPV分布在3~4频带（19.53~78.13 Hz）和4~5频带（39.06~126.25 Hz）,即电子雷管起爆的爆破地震波能量和PPV均向低频带分布,且信号的PPV更小;中、高频带能量大小与段药量成正比,与爆心距成反比;各频带能量占比和PPV大小是反映爆破振动强度的重要指标,采用电子雷管能有效地减少爆破振动。