Temporal Waveform Research Articles

Histogram of Gradient Orientations of Signal Plots Applied to P300 Detection.

The analysis of Electroencephalographic (EEG) signals is of ulterior importance to aid in the diagnosis of mental disease and to increase our understanding of the brain. Traditionally, clinical EEG has been analyzed in terms of temporal waveforms, looking at rhythms in spontaneous activity, subjectively identifying troughs and peaks in Event-Related Potentials (ERP), or by studying graphoelements in pathological sleep stages. Additionally, the discipline of Brain Computer Interfaces (BCI) requires new methods to decode patterns from non-invasive EEG signals. This field is developing alternative communication pathways to transmit volitional information from the Central Nervous System. The technology could potentially enhance the quality of life of patients affected by neurodegenerative disorders and other mental illness. This work mimics what electroencephalographers have been doing clinically, visually inspecting, and categorizing phenomena within the EEG by the extraction of features from images of signal plots. These features are constructed based on the calculation of histograms of oriented gradients from pixels around the signal plot. It aims to provide a new objective framework to analyze, characterize and classify EEG signal waveforms. The feasibility of the method is outlined by detecting the P300, an ERP elicited by the oddball paradigm of rare events, and implementing an offline P300-based BCI Speller. The validity of the proposal is shown by offline processing a public dataset of Amyotrophic Lateral Sclerosis (ALS) patients and an own dataset of healthy subjects.

Generation of Gaussian-Shape Single Photons for High Efficiency Quantum Storage**Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0301800 and 2016YFA0302800, the National Natural Science Foundation of China under Grant Nos 11822403, 91636218, U1801661, 11704131, 11804105 and 11804104, the Natural Science Foundation of Guangdong Province under Grant Nos 2015TQ01X715 and 2018A0303130066, and the KPST of

We report the generation of heralded single photons with Gaussian-shape temporal waveforms through the spatial light modulation technique in an atomic ensemble. Both the full width at half maximum and the peak position of the Gaussian waveform can be controlled while the single photon nature holds well. We also analyze the bandwidth of the generated single photons in frequency domain and show how the sidebands of the frequency spectrum are modified by the shape of the temporal waveform. The generated single photons are especially suited for the realization of high efficiency quantum storage based on electromagnetically induced transparency.

Neural Signatures of Auditory Perceptual Bistability Revealed by Large-Scale Human Intracranial Recordings.

A key challenge in neuroscience is understanding how sensory stimuli give rise to perception, especially when the process is supported by neural activity from an extended network of brain areas. Perception is inherently subjective, so interrogating its neural signatures requires, ideally, a combination of three factors: (1) behavioral tasks that separate stimulus-driven activity from perception per se; (2) human subjects who self-report their percepts while performing those tasks; and (3) concurrent neural recordings acquired at high spatial and temporal resolution. In this study, we analyzed human electrocorticographic recordings obtained during an auditory task which supported mutually exclusive perceptual interpretations. Eight neurosurgical patients (5 male; 3 female) listened to sequences of repeated triplets where tones were separated in frequency by several semitones. Subjects reported spontaneous alternations between two auditory perceptual states, 1-stream and 2-stream, by pressing a button. We compared averaged auditory evoked potentials (AEPs) associated with 1-stream and 2-stream percepts and identified significant differences between them in primary and nonprimary auditory cortex, surrounding auditory-related temporoparietal cortex, and frontal areas. We developed classifiers to identify spatial maps of percept-related differences in the AEP, corroborating findings from statistical analysis. We used one-dimensional embedding spaces to perform the group-level analysis. Our data illustrate exemplar high temporal resolution AEP waveforms in auditory core region; explain inconsistencies in perceptual effects within auditory cortex, reported across noninvasive studies of streaming of triplets; show percept-related changes in frontoparietal areas previously highlighted by studies that focused on perceptual transitions; and demonstrate that auditory cortex encodes maintenance of percepts and switches between them.SIGNIFICANCE STATEMENT The human brain has the remarkable ability to discern complex and ambiguous stimuli from the external world by parsing mixed inputs into interpretable segments. However, one's perception can deviate from objective reality. But how do perceptual discrepancies occur? What are their anatomical substrates? To address these questions, we performed intracranial recordings in neurosurgical patients as they reported their perception of sounds associated with two mutually exclusive interpretations. We identified signatures of subjective percepts as distinct from sound-driven brain activity in core and non-core auditory cortex and frontoparietal cortex. These findings were compared with previous studies of auditory bistable perception and suggested that perceptual transitions and maintenance of perceptual states were supported by common neural substrates.

Prevalence and determinants of noise-induced hearing loss among workers in the automotive industry in China: A pilot study.

ObjectiveData on noise‐induced hearing loss (NIHL) in the automotive industry are rare. This pilot study aimed to investigate the prevalence and determinants of NIHL among workers in the automotive industry in China.MethodsA cross‐sectional survey was conducted with 6557 participants from the automotive industry. The questionnaire survey was administered, and individual noise exposure level (LAeq.8h) and hearing loss level were measured.ResultsOf participants, 96.43% were male; the median age was 27.0 years and 28.82% had NIHL defined as adjusted high‐frequency noise‐induced hearing loss (AHFNIHL). Concerning individual noise levels (LAeq.8h), 62.53% exceeded 85 dB(A), which were mainly concentrated in various jobs, including metal cutting, surface treatment, stamping, welding, grinding, assembly, plastic molding, and forging. Each typical noise source generated its own unique temporal waveform shape with the type of non‐Gaussian noise. Of workers, 53.15% regularly used hearing protector devices (HPD), and the proportion of regular HPD use increased with LAeq.8h. The trend test showed that the prevalence of AHFNIHL in male workers significantly increased with an increase in LAeq.8h at <94 dB(A) and cumulative noise exposure (CNE) in each age group (P < 0.05 or P < 0.01). A logistic regression analysis showed that CNE and HPD usage frequency were important factors contributing to AHFNIHL.ConclusionsCNE and HPD usage frequency were the determinants for NIHL. Much more human surveys are needed to understand the prevalence and determinants of NIHL in the automotive industry in China.

2.24-Tb/s Physical Random Bit Generation With Minimal Post-Processing Based on Chaotic Semiconductor Lasers Network

Multi-channel physical random bit generator (RBG) based on a chaotic semiconductor lasers (SLs) network is proposed and experimentally demonstrated. In experiments, a small ring network consisting of three SLs mutually coupled with heterogeneous delays is constructed to obtain chaotic temporal waveforms. The results show that the time-delay signature of chaotic intensities in all the three SLs can be well concealed over wide range of parameters. Through linear combination of the three chaotic outputs, seven channels of chaotic entropy sources can be obtained. Furthermore, by introducing a minimal post-processing technique and directly extracting four least significant bits at 80-GS/s sampling rate, seven channel random bit sequences with verified randomness can be simultaneously achieved, and the total bit rate is 2.24 Tb/s. The proposed RBGs enabling such high generation rate have potential applications in the one-time pad encryption for the high-speed optical communication networks.

Two dimensional electron transports for terahertz emission fromIn0.53Ga0.47As/In0.52Al0.48Asmultilayer structures illuminated by 1.55 μm-laser

Two dimensional electron gas (2DEG) transports in In0.53Ga0.47As/In0.52Al0.48As multilayer structure (MLS) illuminated by an ultrashort optical pulse with the central wavelength at 1.55 μm is investigated by ensemble Monte Carlo simulations. Terahertz (THz) pulses are calculated according to the transient photocurrent in the InGaAs layers. It is found that InGaAs/InAlAs MLS with narrower InGaAs layers has an advantage in generating large temporal change in the transient photocurrent, which thereby is able to increase the intensity of THz emission. Beryllium (Be)-doping in InGaAs layers provides a scattering channel to speed the decay of photocurrent, and is shown to be a factor in shaping the bipolar structure of THz temporal waveforms. Bandwidth of the generated THz emission is found to be mainly controlled by the laser pulse duration at low doping level, but at high doping level, the bandwidth is determined together by laser pulse duration and doping density.

1-bit photon cross-correlation-based phase-modulation fluorometer using an OFDM signal-modulated excitation light source

We propose a phase-modulation fluorometer, which is a combination of a 1-bit photon cross-correlator constructed using a field-programmable gate array and an excitation light source modulated by an orthogonal frequency-division multiplexing signal. Such multiplexing allows us to use multiple modulation frequencies efficiently and selectively within a given baseband. Defined as the inverse of its fundamental frequency, the symbol length of the multiplexing is set equal to the width of the time window of the cross-correlator. Therefore, all temporal waveforms of the subcarriers in the baseband are connected smoothly at both ends of the symbol interval; hence, no spurious sidebands appear in the frequency domain of the subcarriers. The 1-bit cross-correlator brings about fluorescence lifetimes in the photon-counting realm. From a phase difference spectrum between the fluorescence and the reference signal, fluorescence lifetimes for each frequency may be obtained with precision simultaneously. The resolution time and the width of the time window of the cross-correlator are 2.0 ns and 256 ns, respectively. As a proof-of-principle experiment, we measured the fluorescence lifetimes of some standard samples.

Symmetrized dot pattern analysis for the unsteady vibration state in a Sirocco fan unit

Sirocco fan units, also known as squirrel cage fans, are usually installed at the air conditioning systems of vehicles used in public transport. They must provide an accurate ventilation flow rate, with high efficiency and performance, but also without operative problems like underperforming, outages or breakdowns, which usually lead to compromise the comfort and quietness of the passengers. Due to their heavy duty, they are susceptible of such problems which finally cause poor ventilation, magnified in highly crowded situations, and important noise generation with uncomfortable vibrations. Periodic maintenance and regular monitoring are thus essential to control that the fan operative range ensures a correct operation.This paper deals with a series of working failures, typically encountered in industrial applications with Sirocco fans, like impeller unbalances, obstructed channels or blocked inlets. A database with vibration signals has been measured experimentally to obtain the forced response of the fan as a function of the flow rate for different troubled scenarios. Following, a Symmetrized Dot Pattern (SDP) technique, that transforms the temporal waveforms into polar maps, is employed to generate dot patterns which can discriminate between different working conditions and failures, allowing an easy visual identification. The final objective is to show the potentiality of this technique as a fault diagnosis methodology for typical squirrel cage fans, providing optimal parameters for its use. The results obtained are also compared with other diagnosis techniques, previously employed by the authors, for a complementary analysis of the vibrating condition of these centrifugal fans.

Improved impulse noise modeling for indoor narrow-band power line communication

This paper presents a novel low-complexity fully parametric frequency-dependent impulse noise model for Narrow-Band PLC in the frequency band below 500 kHz. The statistical characterization of measured noise in terms of impulse temporal waveform and the average PSD allowed to confirm the limitations of the commonly used Middleton class-A model due to its flat PSD that is not matching measurements results. To improve the impulse noise model matching with measurement results, a two-state model using impulses in the form of damped sinusoids is proposed. Comparison of the time and frequency characteristics of the proposed model with measurement show the presence of modeled pulses with shapes close to the measured noise, as well as a good matching in the average PSD. Simulation results in using the proposed model for FSK and OFDM systems design show good accuracy to the measured noise, in terms of detector outputs in 2-FSK, bit error rates and fraction of errors per sub-band in the OFDM-based transmission.

Efficient quantum memory for single-photon polarization qubits

A quantum memory, for storing and retrieving flying photonic quantum states, is a key interface for realizing long-distance quantum communication and large-scale quantum computation. While many experimental schemes of high storage-retrieval efficiency have been performed with weak coherent light pulses, all quantum memories for true single photons achieved so far have efficiencies far below 50%, a threshold value for practical applications. Here, we report the demonstration of a quantum memory for single-photon polarization qubits with an efficiency of >85% and a fidelity of >99 %, basing on balanced two-channel electromagnetically induced transparency in laser-cooled rubidium atoms. For the single-channel quantum memory, the optimized efficiency for storing and retrieving single-photon temporal waveforms can be as high as 90.6 %. Our result pushes the photonic quantum memory closer to its practical applications in quantum information processing.

An algorithmic approach to single-probe Cherenkov removal in pulsed x-ray beams.

The removal of Cherenkov light in an optical dosimetry system is an important process to ensure accurate dosimetry without compromising spatial resolution. Many solutions have been presented in the literature, each with advantages and disadvantages. We present a methodology to remove Cherenkov light from a scintillator fiber optic dosimeter in a pulsed megavoltage x-ray beam using the temporal waveform across the pulse. A sample waveform of Cherenkov light can be measured by exposing only the fiber to the beam. By assuming that the Cherenkov waveform closely matches the intensity of incident radiation, this waveform can be convoluted with the instantaneous scintillation response function to generate an expected scintillation signal. By finding the least-squares fit between these two functions and the experimental data, the estimated Cherenkov contribution can be subtracted off the net signal. This can be applied for arbitrarily complex Cherenkov waveforms (within the 2ns timing resolution of the data acquisition), and in fact, the results suggest more fluctuations in the waveforms provide a better fit to data. Four beam profiles for different field sizes and energies were found with this method. They closely matched references data measured with ionization chamber with average differences across the beam no more than 4%. Noisy waveforms are assumed to be the primary cause of differences between the analyzed scintillator and IC results. We propose methods for improving the results and optimizing the data acquisition and analysis processes. These results demonstrate that it is possible and effective with a single probe to use function fitting of expected data to experimental to remove a complicated Cherenkov signal from the net light signal in pulsed-beam optical dosimetry.

Suppression of FM-to-AM conversion in a broadband Nd:glass regenerative amplifier with an intracavity birefringent filter.

In order to suppress the frequency modulation to amplitude modulation (FM-to-AM) conversion induced by a Nd:glass regenerative laser amplifier, a birefringent quartz crystal was designed by theoretical simulation and inserted into the regenerative amplifier. A broadband Nd:glass regenerative laser amplifier with a flattop region of ∼3.7 nm in the gain spectrum was developed. An all-fiber front-end system was used to generate a 2 ns shaped pulse with a spectral width of ∼0.5 nm, which was broadened by a two-stage phase modulator. Then, the laser pulse was amplified by a spectral-broadened regenerative amplifier. The amplified output temporal waveform modulation depth was reduced from a maximum of 47.7% to 17.3% at a center wavelength of 1053.328 nm. The experimental results show that the FM-to-AM conversion can be effectively suppressed in the spectral-broadened Nd:glass regenerative laser amplifier, which indicates that it has potential application as a preamplifier of large-scale laser facilities.

Effects of Axisymmetric Square-Wave Excitation on Transverse Jet Structure and Mixing

The influence of temporal square-wave excitation on structural and mixing characteristics of an equidensity, gaseous jet in crossflow (JICF) was explored in the present study. As in separate unforced and sinusoidally excited JICF experiments, acetone planar laser-induced fluorescence imaging enabled this detailed quantification for the JICF for mean jet-to-crossflow momentum flux ratios ranging from (with a convective unstable upstream shear layer, or USL, in the absence of forcing) to (with a globally unstable USL). Such square-wave excitation of the jet fluid required adaptive feedforward control, not only to create more accurate temporal square waveforms but to enable more accurate comparison among alternative forcing conditions. Square-wave excitation of the JICF demonstrated a significant influence on the naturally globally unstable JICF, where specific nondimensional stroke ratios within -dependent ranges could produce deeply penetrating, periodic vortices with improved jet penetration and spread. Enhanced jet penetration did not always correlate with better molecular mixing, however; there was a stronger correlation of improved mixing at higher values with creation of a more symmetric jet cross section via square-wave excitation, especially one with a clear counter-rotating vortex pair structure.

Numerical Investigation on the Transient Evolution Mechanisms of Nonlinear Phenomena in a Helium Dielectric Barrier Discharge at Atmospheric Pressure

In this paper, the evolution and transition mechanisms of typical nonlinear phenomena in an atmospheric pressure helium dielectric barrier discharge (DBD) are investigated from the perspective of transient evolution properties through fluid modeling. By gradually up-regulating the interelectrode gap width, the discharge (steady state) evolves from symmetric single-period (SP1), through asymmetric single-period (AP1), into Period-2 (P2) state. Similar evolution trace can also be obtained when increasing the driving frequency. Right after the initial breakdown, the discharge goes through several transient periods featuring unstable asymmetric current pulses before the establishment of steady-state discharge. As the bifurcation parameter increases in excess of the critical value, the discrepancy between the seed electron level of positive and negative discharges accumulates over the transient periods, switching the discharge into AP1 state. After then, a further elevation in the gas gap width (or driving frequency) leads to the generation of a “moderate intensity” positive pulse. With the “moderate intensity” positive pulse and a stronger positive pulse emerging alternatively in the temporal waveform sequence, the discharge evolves into P2 state. Finally, based on the transient evolution mechanisms, a preliminary state-controlling method regarding the use of a first-peak-leveled applied voltage is proposed, which may shed light on the modification of nonlinear states in some practical DBD application scenarios.

Simulation Platform of Photoacoustic Imaging Based on Finite Element and k-space Pseudospectral Method

Numerical simulation is a powerful technology for photoacoustic imaging (PAI) in both theory studies and practical applications. In this paper, a simulation platform for PAI was designed and implemented based on Matlab. The simulation platform utilized finite element method (FEM) and k-space pseudospectral method to calculate the forward and inverse problem of PAI. And a graphical user interface (GUI) was realized. Structural design, work process and other operating details of the platform was also provided. By compared with theoretical temporal waveform of photoacoustic signal and reconstruction results of COMSOL, the validity and reliability was verified. And a reliable simulation tool was proposed for PAI.

Removal of rain video based on temporal intensity and chromatic constraint of raindrops

An improved algorithm of frame time difference is proposed and applied to raindrops removal of video image.This paper analyzes the temporal intensity waveform and chromatic constraint properties of raindrops, and the method is optimized by these two properties. We make use of the difference between rain and non-rain moving objects in the pixels’ intensity changes, which realized a broad classification between the rain and non-rain moving object pixel. The candidate raindrops pixels are optimized in combination with the chromatic constraint property. The experimental results show that the proposed algorithm has a better effect of rainy day in video image restoration than Garg’s, and it is simple and effective. The algorithm has a strong applicability, and it can be further used for many applications, such as air pollution control, management, outdoor surveillance, remote sensing and intelligent vehicles.

Space-time duality and quantum temporal imaging

Using the space-time analogy, we compare the performance of quantum temporal imaging with its classical counterpart. We consider a temporal imaging scheme, based on the sum-frequency generation (SFG) time lens, but our results can be applied to other temporal imaging schemes such as, for instance, four-wave mixing. Extending the theory presented in our previous publications, in this paper we take into account the finite time aperture of the imaging system, characterized by its pupil function. Using the quantum theory, we obtain a unitary transformation of the quantum field from the input to the output of the imaging scheme and identify the contribution of the vacuum fluctuations missing in the classical theory. This contribution plays a key role in the quantum temporal imaging of nonclassical temporal waveforms, characterized by nonclassical fluctuations of the electromagnetic field. As an example, we consider quantum temporal imaging of broadband squeezed light and formulate the criteria for conservation of its squeezing properties at the output of the system.

Calibration of the field strength of broadband terahertz radiation in air coherent detection technique

In the air coherent detection of the terahertz (THz) technique, a high voltage signal with a square waveform offers a modulated biased field over the air sensor. In this technique, a temporal THz waveform can be obtained routinely. However, its field strength has to be calibrated separately by other techniques. In this paper, we propose a method to calibrate the field strength of the THz pulse by means of applying a positive square wave instead of an alternating square wave as the modulated biased field. In this method, the ratio of the THz signal to the background signal is used for the calibration of the field strength of the THz pulse. Using this method, both the waveform and the electric field strength of the THz pulse can be easily obtained.

All-optical characterization of the two-dimensional waveform and the Gouy phase of an infrared pulse based on plasma fluorescence of gas.

The characterization of the temporal waveform of few-cycle laser pulses is an indispensable part in strong-field physics and attosecond science. Recently, a simple waveform-characterization technique called TIPTOE (tunneling ionization with a perturbation for the time-domain observation of an electric field) has been demonstrated for measuring linearly polarized few-cycle pulses. We theoretically and experimentally show that TIPTOE can be extended to resolve more characteristics of an optical waveform: the two-dimensional polarization and the Gouy phase. Based on the plasma fluorescence of a gaseous medium, we achieve all-optical and spatially resolved measurements of the waveform of an infrared pulse. This detection method enables the remote characterization of a waveform without the need to place an apparatus near the focal point of the laser beam. The proposed approach represents a simple and powerful method for conducting waveform diagnostics on few-cycle laser sources.

Knee motion and muscle activation patterns are altered in hip osteoarthritis: The effect of severity on walking mechanics

BackgroundKnee function is impaired in individuals with moderate hip osteoarthritis. How this extends to those undergoing total hip arthroplasty is unknown despite the common requirement for knee arthroplasty in this population. The study purpose was to determine whether sagittal plane knee joint movements and quadriceps and hamstring activation patterns differ between individuals with either moderate or severe unilateral hip osteoarthritis, and between ipsilateral and contralateral knees. Methods20 individuals with moderate osteoarthritis and 20 with severe osteoarthritis were recruited. Sagittal knee motion and surface electromyograms from the hamstrings and quadriceps were collected during treadmill walking at a self-selected speed. Principal component analysis captured amplitude and temporal sagittal plane motion and EMG waveform features. Student's t-tests and Analysis of Variance determined between group differences and within/between group leg differences. FindingsThe severe groups' contralateral knee was in greater flexion at initial contact and demonstrated a movement profile of a longer stance phase (p < 0.001). The severe group had reduced sagittal plane knee motion (p < 0.0001); more so in the ipsilateral knee (p < 0.0001). The severe group had greater hamstring (p = 0.009) and quadriceps activation (p < 0.001) overall, specifically mid-stance quadriceps bilaterally (p = 0.002). Ipsilateral sagittal plane knee motion was reduced in both groups. Compared with those with moderate osteoarthritis, individuals with severe osteoarthritis walk with reduced sagittal plane knee motion bilaterally, suggesting prolonged contralateral stance, and elevated mid-stance hamstring and quadriceps activation. InterpretationAltered kinematics and muscle activity could contribute to a greater mechanical demand on the contralateral knee in those with more severe hip osteoarthritis.