Sweep Direction Research Articles

Spectrotemporal response properties of core auditory cortex neurons in awake monkey.

So far, most studies of core auditory cortex (AC) have characterized the spectral and temporal tuning properties of cells in non-awake, anesthetized preparations. As experiments in awake animals are scarce, we here used dynamic spectral-temporal broadband ripples to study the properties of the spectrotemporal receptive fields (STRFs) of AC cells in awake monkeys. We show that AC neurons were typically most sensitive to low ripple densities (spectral) and low velocities (temporal), and that most cells were not selective for a particular spectrotemporal sweep direction. A substantial proportion of neurons preferred amplitude-modulated sounds (at zero ripple density) to dynamic ripples (at non-zero densities). The vast majority (>93%) of modulation transfer functions were separable with respect to spectral and temporal modulations, indicating that time and spectrum are independently processed in AC neurons. We also analyzed the linear predictability of AC responses to natural vocalizations on the basis of the STRF. We discuss our findings in the light of results obtained from the monkey midbrain inferior colliculus by comparing the spectrotemporal tuning properties and linear predictability of these two important auditory stages.

Characteristics of a nonlinear rotating piezoelectric energy harvester under variable rotating speeds

This paper presents a nonlinear rotating vibration energy harvester by employing a piezoelectric cantilever beam and a nonlinear magnetic force due to a pair of magnets. A mathematical model is derived for the nonlinear rotating harvester based on the Lagrange's equation and the assumed-mode method, where piezoelectric coupling behavior is also included. From the model, the potential function of the nonlinear rotating harvester is firstly studied. Then its output characteristics under rotating speeds varying linearly and nonlinearly with time are carefully examined, respectively. The effects of the distance between the two magnets, the sweep rate, the sweep direction and the growth rate of the rotating speed on the output characteristics are investigated numerically. The simulation results reveal that all these parameters have strong influences on characteristics of the rotating harvester. When an optimal distance is achieved, a nonlinear rotating energy harvester is fit for low frequency and variable rotating motion more than a linear one. All conclusions will provide guidelines for designing nonlinear rotating vibration energy harvesters.

Effects of exchange bias on magnetotransport in permalloy kagome artificial spin ice

We investigate the magnetotransport properties of connected kagome artificial spin ice networks composed of permalloy nanowires. Our data show clear evidence of magnetic switching among the wires, both in the longitudinal and transverse magnetoresistance. An unusual asymmetry with field sweep direction appears at temperatures below about 20 K that appears to be associated with exchange bias resulting from surface oxidation of permalloy, and which disappears in alumina-capped samples. These results demonstrate that exchange bias is a phenomenon that must be considered in understanding the physics of such artificial spin ice systems, and that opens up new possibilities for their control.

Feasibility of three-dimensional reconstruction and automated measurement of fetal long bones using 5D Long Bone.

ObjectiveTo evaluate the feasibility of five-dimensional Long Bone (5D LB), a new technique that automatically archives, reconstructs images, and measures lengths of fetal long bones, to assess whether the direction of volume sweep influences fetal long bone measurements in three-dimensional (3D) ultrasound and 5D LB, and to compare measurements of fetal long bone lengths obtained with 5D LB and those obtained with conventional two-dimensional (2D) and manual 3D techniques.MethodsThis prospective study included 39 singleton pregnancies at 26+0 to 32+0 weeks of gestation. Multiple pregnancies, fetuses with multiple congenital anomalies, and mothers with underlying medical diseases were excluded. Fetal long bones of the lower extremities-the femur, tibia, and fibula were measured by 2D and 3D ultrasound, and 5D LB, by an expert and non-expert examiner. First, we analyzed the 3D ultrasound and 5D LB data according to 2 different sweeping angles. We analyzed intra- and inter-observer variability and agreement between ultrasound techniques. Paired t-test, interclass correlation coefficient, and Bland-Altman plot and Passing-Bablok regression were used for statistical analysis.ResultsThere was no statistical difference between long bone measurements analyzed according to 2 different volume-sweeping angles by 3D ultrasound and 5D LB. Intra- and inter-observer variability were not significantly different among all 3 ultrasound techniques. Comparing 2D ultrasound and 5D LB, the interclass correlation coefficient for femur, tibia, and fibula was 0.91, 0.92, and 0.89, respectively.Conclusion5D LB is reproducible and comparable with conventional 2D and 3D ultrasound techniques for fetal long bone measurement.

Network models of frequency modulated sweep detection.

Frequency modulated (FM) sweeps are common in species-specific vocalizations, including human speech. Auditory neurons selective for the direction and rate of frequency change in FM sweeps are present across species, but the synaptic mechanisms underlying such selectivity are only beginning to be understood. Even less is known about mechanisms of experience-dependent changes in FM sweep selectivity. We present three network models of synaptic mechanisms of FM sweep direction and rate selectivity that explains experimental data: (1) The ‘facilitation’ model contains frequency selective cells operating as coincidence detectors, summing up multiple excitatory inputs with different time delays. (2) The ‘duration tuned’ model depends on interactions between delayed excitation and early inhibition. The strength of delayed excitation determines the preferred duration. Inhibitory rebound can reinforce the delayed excitation. (3) The ‘inhibitory sideband’ model uses frequency selective inputs to a network of excitatory and inhibitory cells. The strength and asymmetry of these connections results in neurons responsive to sweeps in a single direction of sufficient sweep rate. Variations of these properties, can explain the diversity of rate-dependent direction selectivity seen across species. We show that the inhibitory sideband model can be trained using spike timing dependent plasticity (STDP) to develop direction selectivity from a non-selective network. These models provide a means to compare the proposed synaptic and spectrotemporal mechanisms of FM sweep processing and can be utilized to explore cellular mechanisms underlying experience- or training-dependent changes in spectrotemporal processing across animal models. Given the analogy between FM sweeps and visual motion, these models can serve a broader function in studying stimulus movement across sensory epithelia.

Hysteresis analysis of graphene transistor under repeated test and gate voltage stress

The current transport characteristic is studied systematically based on a back-gate graphene field effect transistor, under repeated test and gate voltage stress. The interface trapped charges caused by the gate voltage sweep process screens the gate electric field, and results in the neutral point voltage shift between the forth and back sweep direction. In the repeated test process, the neutral point voltage keeps increasing with test times in both forth and back sweeps, which indicates the existence of interface trapped electrons residual and accumulation. In gate voltage stress experiment, the relative neutral point voltage significantly decreases with the reducing of stress voltage, especially in −40 V, which illustrates the driven-out phenomenon of trapped electrons under negative voltage stress.

Duffing oscillation-induced reversal of magnetic vortex core by a resonant perpendicular magnetic field.

Nonlinear dynamics of the magnetic vortex state in a circular nanodisk was studied under a perpendicular alternating magnetic field that excites the radial modes of the magnetic resonance. Here, we show that as the oscillating frequency is swept down from a frequency higher than the eigenfrequency, the amplitude of the radial mode is almost doubled to the amplitude at the fixed resonance frequency. This amplitude has a hysteresis vs. frequency sweeping direction. Our result showed that this phenomenon was due to a Duffing-type nonlinear resonance. Consequently, the amplitude enhancement reduced the vortex core-switching magnetic field to well below 10 mT. A theoretical model corresponding to the Duffing oscillator was developed from the Landau–Lifshitz–Gilbert equation to explore the physical origin of the simulation result. This work provides a new pathway for the switching of the magnetic vortex core polarity in future magnetic storage devices.

The Oxygen Reduction Reaction in Alkaline Solution

The oxygen reduction reaction (ORR) is one of the key reactions in electrochemical energy conversion devices like fuel cells [1-3]. Recently, as the high over-potential of ORR decreases the efficiency of these devices, various carbon-supported Pt catalysts have been studied in order to lower the over-potential of the ORR [3]. The aim of this work is to determine the influence of catalyst loading on ORR. The molybdenum carbide (Mo2C) derived carbon supported Pt (20wt% metal) nanoclusters activated electrodes with catalyst loadings from 0.1 to 1.0 mg cm-2 have been tested in 0.1M KOH solution. Commercially available unmodified and modified carbons (Vulcan XC72®, 20wt% Pt- Vulcan XC72® ) were used as reference materials.Catalyst ink was prepared by suspending various powders in the mixture of Milli-Q water, isopropanol and Nafion dispersion solution (Aldrich). The loading was varied by adding different volumes of the suspending agents to the catalyst powder. The catalyst ink was pipetted onto the glassy carbon disk electrode (GCDE) surface and dried at room temperature. The flat cross-section surface (geometric) area of the composite electrode was 0.196 cm2. The loading of a catalyst was 0.1; 0.2; 0.4 or 1.0 mg cm-2.The electrochemical measurements were carried out in a three-electrode electrochemical cell. Electrochemical characteristics for catalysts were established by cyclic voltammetry (CV) and rotating disc electrode (RDE) methods. Electrochemical impedance spectroscopy was used to obtain the high-frequency series resistance (R s at ac f → ∞), i.e. the electrolyte resistance of a system. It was demonstrated that in 0.1M KOH solution the iR drop compensation is significant in the stages of mixed kinetic. Therefore, all currents presented are corrected against the ohmic potential drop.RDE data were measured at rotation rates from 0 to 3000 rpm (v=10 mV∙s-1) within the region of potentials from +0.31 to -0.55 V. The potentials were measured against Hg|HgO|0.1M KOH reference electrode. CVs were measured at potential scan rates (v mV/s) 5, 10, 20, 30, 50, 70, 100, 150 and 200. All RDE data and CVs were measured in both Ar and O2 saturated solutions. The solutions were saturated with Ar or O2 between the each measurement, respectively. All measured current densities were corrected for current densities measured in 0.1 M KOH solution saturated with Ar.The kinetics of the ORR is generally analyzed using a Tafel-like relationship, shown in Figure 1. The slopes of the Tafel-like plots have been obtained ranging from -65 to -90 mV dec-1 for various 20wt%Pt-C(Mo2C) catalyst loadings. The 20wt%Pt-C(Mo2C) catalyst showed noticeably higher activity towards ORR compared with that established for the 20wt%Pt-C(Vulcan XC72®) electrode.There are very well expressed reduction current peaks in the j c, E-curves for cathodic potential sweep direction. For all materials studied the reduction peak current density values (|j peak|) increase nearly linearly with v 1/2 (characteristic of diffusion limited process). Reduction peak current density values (|j peak|) increase with catalyst loading, shown in Figure 2 (at potential scan rate v = 30 mV/s). Same tendency has been observed at all potential scan rates. Acknowledgements This work was supported by the Estonian target research project SF0180002s08, the Estonian Centre of Excellence in Science Project TK117T "High-technology Materials for Sustainable Development", the Estonian Energy Technology Program project SLOKT10209T, the Materials Technology project SLOKT12180T. Authors thank I. Tallo for performing the high temperature chlorination synthesis of C(Mo2C).

Pulsed I –V measurement method to obtain hysteresis-free characteristics of graphene FETs

Current-voltage (I–V) characteristics of the graphene field effect transistors (GFETs) are measured by the dc, fast I–V (FIV), and pulsed I–V (PIV) methods and analyzed. The hysteresis and conductance in the dc measurement are affected by the sweeping bias range and direction. The I–V curves measured by the FIV method show reduced hysteresis and enhanced conductance at a faster sweeping rate, but are still affected by the sweeping bias range. By applying the PIV method, the hysteresis can be suppressed significantly while the conductance is improved by controlling turn-on, turn-off times (ton and toff) and the gate bias during toff (Vbase) regardless of the sweeping bias range. With short ton, long toff, and Vbase of 0 V, the hysteresis-free characteristics of GFETs are obtained.

Frequency shifts in distortion product otoacoustic emission evoked by fast sweeping primaries in adults and newborns

Distortion product otoacoustic emissions (DPOAEs) are a vector sum of two components, generator and reflection, which produce overall DPOAE levels with a pattern of minima and maxima across frequency referred to as fine structure. The pattern of maxima and minima shifts higher or lower in frequency dependent on sweep direction (Henin et al., 2011), consistent with cochlear scaling invariance. A break from scaling invariance occurs between 1 and 1.4 kHz in human adults. DPOAE phase at frequencies below the “break” are steeper in newborns than adults. We probed frequency shifts to up- and down-swept primaries of 1 octave/s in adults and newborns. Frequency shifts were examined for DPOAEs evoked by up-sweeps and down-sweeps using a covariate correlation function across the entire DPOAE frequency range, and above and below 2 kHz. Newborns had significantly greater frequency shifts in the reflection component below 2 kHz than adults. There was a significantly different fine structure frequency shift between the low- and high-frequency ranges in adults. In newborns, this difference in the frequency shifts for the low- and high- frequencies was significant for the reflection component. These preliminary findings suggest that frequency shifts can be used to assess potential maturational differences in cochlear mechanics.

Phase effects using chirp maskers

Schroeder-phase maskers appear to interact with the phase curvature of the basilar membrane to produce significantly different amounts of masking depending on the direction of the instantaneous frequency sweep (Oxenham and Dau, 2001). Schroeder-phase maskers may not optimally compensate for the phase-curvature of the basilar membrane, which is not assumed to be linear over its length. This study presents a comparison of masking produced by harmonic complexes that differ only in the phase relationships of their components. Four “chirp” complexes were constructed according to Elberling et al. (2007), with both positive and negative signs, and were compared to Schroeder-phase signals (Smith et al., 1986). Masking observed with pure-tones at three signal frequencies (1, 2, and 4 kHz) and with spectro-temporal burst signals (Hoglund et al., 2013) is reported at two presentation levels (50 and 60 dB SPL). The results are discussed in the context of Schroeder-phase masking and current understanding of the phase-curvature of the human basilar membrane.

Hysteresis-Free Nanosecond Pulsed Electrical Characterization of Top-Gated Graphene Transistors

We measure top-gated graphene field effect transistors (GFETs) with nanosecond-range pulsed gate and drain voltages. Due to high-k dielectric or graphene imperfections, the drain current decreases ~10% over time scales of ~10 us, consistent with charge trapping mechanisms. Pulsed operation leads to hysteresis-free I-V characteristics, which are studied with pulses as short as 75 ns and 150 ns at the drain and gate, respectively. The pulsed operation enables reliable extraction of GFET intrinsic transconductance and mobility values independent of sweep direction, which are up to a factor of two higher than those obtained from simple DC characterization. We also observe drain-bias-induced charge trapping effects at lateral fields greater than 0.1 V/um. In addition, using modeling and capacitance-voltage measurements we extract charge trap densities up to 10^12 1/cm^2 in the top gate dielectric (here Al2O3). Our study illustrates important time- and field-dependent imperfections of top-gated GFETs with high-k dielectrics, which must be carefully considered for future developments of this technology

Hidden negative differential resistance in the oxidation of formic acid on platinum

Clarification is reported of the mechanism for the appearance of hidden negative differential resistance, HNDR, in the oxidation of formic acid using surface-enhanced infrared absorption spectroscopy, SEIRAS, simultaneously with electrochemical measurements. The HNDR is necessary for the appearance of potential oscillation. After holding the potential at 0.7V for 300 s, the voltammogram exhibits a long monotone current decrease, which means NDR and is named LCD, in a wide potential range between 0.5 and 0.8V. In the LCD potential range, the voltammogram is reversible with regard to potential sweep directions and there is neither adsorbed CO nor adsorbed hydroxide. The latter information is obtained by the voltammogram in the absence of formic acid and by the change in the baseline of the SEIRA spectra. We hence think that the LCD appears due to the adsorption of water, which increases in residence time on the surface with potential due to the water-surface interaction. Based on this idea, we have been able to mathematically reproduce the experimentally observed oscillation pattern. Using a pseudo-stationary voltammogram and simultaneously measured SEIRA spectra, we conclude that the HNDR appears due to the formation of adsorbed CO, which hides the LCD between 0.5 and 0.7V.

Automatic Swept Volume Decomposition based on Sweep Directions Extraction for Hexahedral Meshing

Automatic and high quality hexahedral meshing of complex solid models is still a challenging task. To guarantee the quality of the generated mesh, current commercial software normally requires users to manually decompose a complex solid model into a set of simple geometry like swept volume whose high quality hexahedral mesh can be easily generated. The manual decomposition is a time-consuming process, and its effect heavily depends on the user's experience. Therefore, to automate the solid model decomposition for hexahedral meshing is of significance. However, the efficiency of the existing algorithms are still far from expected. In this paper, an automatic swept volume decomposition approach based on sweep directions extraction is presented. The approach first extracts all the potential local sweep directions (PLSDs) of a given solid model using heuristic rules, then generates a relevant face set (RFS) for each PLSD, and incrementally determines all the swept volumes including heavily interacting ones based on PLSDs. Furthermore, to make the decomposition good for high quality hexahedral meshing, the approach constructs reasonable cutting face sets (CFSs) to split the interacting swept volumes. Experimental results show the effectiveness of our approach.

晶体硅光伏电池的标准测试

To build a standard test specification for solar cells,various kinds of affect factors on the final uncertainty of solar cell standard tests were evaluated and selected.Based on the secondary solar cell standard test equipment and devices,such as sun simulator,spectral sensitivity,IV tester and standard solar cells,several kinds of testing technologies were researched.Some effect factors in measuring processing were discussed,including the spatial uncertainty of solar cell simulator,tempo-ral stability,measuring repeatability,the uncertainty from sweep directions,the reflection and transparence of cell,the uncertainty for area and External Quantum Efficiency(EQE).Then,the measuring procedure of a high efficiency crystalline silicon solar cell was proposed and the extension test uncertainty of 3.94% was derived under the conditions of existing laboratory measurement.Based on a comparison to conventional solar cell test data,the conventional cell testing method was improved,and the uncertainty of measurement was reduced by 0.19%.Finally,a standard testing procedure for a double-side cell was proposed,which provides a reference for other related cell measurements.

全景式航空相机图像拖影与扭曲补偿系统研究

In panoramic aerial camera pendulum sweep imaging process, the dithery scanning mirror position caused by the incomplete isolation of airborne vibration environment, causes a shaking of the visual axis, which makes the image in the sweep direction produce distortion and smear. Aiming at the above problem, the geometric model is established among flight speed, altitude, target level angle and pitching axis speed compensation, with which the causes of the disturbances of image distortion and the influence of compensation precision on image smear pitching axis degree are analyzed. Through the model establishment and parameter analysis, the pitching axis control system dynamics and steady-state performance and robustness requirements are obtained. Laboratory dynamic target generator and parallel light pipe model are used to simulate the relative movement between camera and objects so as to test the precision of the control system. The exterior image in the vibration surroundings is used to test the disturbance compensation performance of the control system. Experiment results show that the steady speed error of pitching axis control system is less than 0.005/s, that almost completely suppresses the image smear phenomenon; the speed compensation residual error under 7 Hz disturbance signal is less than 0.1/s, and the system can effectively compensate the disturbance caused by the image distortions.

Alternating current operation of low-Mg-doped p-GaN Schottky diodes

Current–voltage (I–V) characteristics with variations of voltage sweep speed (vsweep) and changing sweep directions, and alternating current (AC) operation of low-Mg-doped p-GaN Schottky contacts were analyzed. In the I–V characteristics, conventional memory effect, due to carrier capture and emission from acceptor-type deep-level defects, was seen for all the measurement conditions. In addition, proportional relationship between vsweep and current, and polarity inversion of the current were observed when the applied voltage was low, which indicates the existence of a displacement current, because the Schottky barrier height is so high and a true current is significantly small. In the AC operations under the square- and sinusoidal-wave input, a conventional rectifying operation was observed when the input voltage was relatively high. However, we found differential operation in the output current when the input voltage was low, where the displacement current was dominant. Such a unique functional operation was achieved by only one Schottky diode.

Measuring stimulus-frequency otoacoustic emissions using swept tones

Although stimulus-frequency otoacoustic emissions (SFOAEs) offer compelling advantages as noninvasive probes of cochlear function, they remain underutilized compared to other evoked emission types, such as distortion-products (DPOAEs), whose measurement methods are less complex and time-consuming. Motivated by similar advances in the measurement of DPOAEs, this paper develops and characterizes a more efficient SFOAE measurement paradigm based on swept tones. In contrast to standard SFOAE measurement methods, in which the emissions are measured in the sinusoidal steady-state using discrete tones of well defined frequency, the swept-tone method sweeps rapidly across frequency (typically at rates of 1 Hz/ms or greater) using a chirp-like stimulus. Measurements obtained using both swept- and discrete-tone methods in an interleaved suppression paradigm demonstrate that the two methods of measuring SFOAEs yield nearly equivalent results, the differences between them being comparable to the run-to-run variability encountered using either method alone. The match appears robust to variations in measurement parameters, such as sweep rate and direction. The near equivalence of the SFOAEs obtained using the two measurement methods enables the interpretation of swept-tone SFOAEs within existing theoretical frameworks. Furthermore, the data demonstrate that SFOAE phase-gradient delays-including their large and irregular fluctuations across frequency-reflect actual physical time delays at different frequencies, showing that the physical emission latency, not merely the phase gradient, is inherently irregular.

Environmental effects on the electrical behavior of pentacene thin-film transistors with a poly(methyl methacrylate) gate insulator

The electrical properties of top-contact pentacene thin-film transistors (TFTs) with a poly(methyl methacrylate) (PMMA) gate dielectric were analyzed in air and vacuum environments. Compared to the vacuum case, the pentacene TFT in air exhibited lower drain currents and more pronounced shifts in the threshold voltage upon reversal of the gate voltage sweep direction, together with a decrease in the field-effect mobility. These characteristic variations were explained in terms of two distinctive actions of polar H2O molecules in pentacene TFT. H2O molecules were suggested to diffuse under the source and drain contacts and interrupt the charge injection into the pentacene film, whereas those that permeate at the pentacene/PMMA interface retard hole depletion in and around the TFT channel. The diffusion process was much slower than the permeation process. The degraded TFT characteristics in air could be recovered mostly by storing the device under vacuum, which suggests that the air instability of TFTs is due mainly to the physical adsorption of H2O molecules within the pentacene film.

Two-dimensional spatial-frequency-modulated imaging through parallel acquisition of line images

This Letter demonstrates a two-dimensional imaging technique that uses a line scan camera to resolve one spatial dimension and temporal modulation to resolve the perpendicular dimension. A temporal intensity modulation, which increases linearly in frequency along one direction is applied to an illumination beam. The modulated light distribution is imaged onto an object then onto a line scan camera oriented perpendicularly to the direction of the modulation sweep. A line diffuser is placed shortly before the line scan camera and diffuses light along the direction of modulation so that each pixel collects all modulation frequencies.