Pulse Characteristics Research Articles

Automated Start‐Up and Extinction Dynamics of a Mamyshev Oscillator Based on a Temperature‐Dependent Filter

AbstractMamyshev oscillators (MOs), which are based on an effective saturable absorber that arises from offset spectral filtering, are a new type of mode‐locked fiber lasers, but experimentally verifying the theory of the evolution of various dynamic characteristics of optical pulses in MOs has remained a major challenge due to the lack of appropriate filters and the means of real‐time, single‐shot experimental measurement. Here, the starting, extinction, and output dynamics of MOs are studied by designing and using a special temperature‐sensitive band‐pass filter, whose central wavelength can be continuously and accurately adjusted with temperature. The entire automated evolution of light pulses in the MO from start‐up to stable operation and then to extinction can be observed continuously by adjusting only the filter's temperature. What is more interesting is that the start‐up and the extinction processes are mirror symmetric, and both of them experience a double Q‐switching state. Further research has shown that the maximum filter interval corresponding to MO self‐starting is related to the pump power and that the bigger the pump power, the wider the filter interval. By gradually changing the interval between the two filters, the various output characteristics of the MO are also systematically studied.

Identification and Fast Measurement Method of Open-circuit Voltage

Accurate measurement of the open-circuit voltage (OCV) promotes state of charge (SOC) accuracy. In this study, three transformation methods are employed to make the OCV identifiable, and factors affecting the accuracy of OCV identification are investigated. Furthermore, a fast OCV measurement method is proposed. The results show that the forward difference transformation and the adaptive differential evolution algorithm are more suitable for OCV identification. The accuracy of OCV identification is affected by pulse characteristics, sampling frequency, C-rate, and resting time between pulses. Positive-negative (PN) pulses of equal amplitude are more suitable for OCV identification than hybrid pulse power characteristics. A method for fast OCV measurement is developed based on the relationship between the identification error of the OCV and the number of PN pulses. A total of 57 PN pulses with an amplitude of 2 C are used to realize accurate OCV identification at various charge/discharge states, C-rate, and SOC, with an average error of −0.03% (about 1 mV). The proposed method only needs to obtain the battery voltage and current to achieve a fast measurement of OCV, which also serves as a foundation for an accurate estimation of the battery state.

An Advanced 3-D Electromagnetic Analysis and Experimental Validation of a Bipolar Subnanosecond Pulse Generation System

This article presents an advanced 3-D electromagnetic co-simulation approach developed using the CST software to evaluate the characteristics of a bipolar subnanosecond pulse forming system for application in the biomedical and defense domains. To the best of the authors’ knowledge, the simulation technique presented in this article, which integrates transient switching devices in the 3-D electromagnetic model of the bipolar subnanosecond pulse forming system, was not presented previously in the open literature. The design of the bipolar subnanosecond pulse forming system is based on a thorough analytical calculation with predictions verified using the 3-D numerical modeling to generate a voltage of up to 500 kV peak-to-peak amplitude with a duration of around 1.8 ns when connected to a 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega$</tex-math> </inline-formula> load. A good agreement between the experimental results and the CST predictions was obtained, providing the correctness of the proposed modeling technique. Future plans involve connecting the bipolar subnanosecond pulse forming system to an ultra-wideband (UWB) antenna.

Effect of Magnetic Field on Corona Discharge Under Airflow

Corona discharge under airflow is extensively researched due to its wide applications in the fields of electrostatic precipitator, flow control, thermal management, and so on. The adjustment of discharge characteristics has been an important research topic in recent years. In this article, a magnetic field is applied as a method to adjust the characteristics of corona discharge under airflow. The experimental result illustrates that the intensity and direction of the magnetic field would influence the turning point of the discharge state under airflow, and the corresponding discharge image and Trichel pulse characteristics, such as amplitude and frequency, would also be changed. The physical mechanism for this phenomenon is analyzed by considering the magnetic force of the corona discharge. With increasing magnetic field intensity, the pressure in the discharge space would change and the airflow state and the discharge process, as the ionization process and the attachment process, would be influenced. The overall characteristics of discharge under airflow would be adjusted by the magnetic field. The results illustrated that the magnetic field is possibly utilized to improve the application of corona discharge under airflow.

Evaluation of Success of Arterial Cannulation Employing the Dorsalis Pedis Artery Versus Posterior Tibial Artery: A Clinical Comparative Study.

The dorsalis pedis artery and posterior tibial artery are recognised sites for arterial cannulation. This study aimed to compare the first-attempt success rates of cannulation along with other cannulation characteristics of these 2 arteries in adult patients undergoing surgery under general anaesthesia using the conventional palpatory method. Two hundred twenty adults were allocated randomly into 2 groups. The dorsalis pedis artery and posterior tibial artery were attempted for cannulation in the dorsalis pedis artery and posterior tibial artery group, respectively. First-attempt success rates, cannulation times, number of attempts, ease of cannulation, and complications were recorded. Demographic characteristics, pulse characteristics, single-attempt success rates, ease of cannulation, reasons for failure, and complications were similar. Single-attempt success rates were similar (64.5% and 61.8%, P = .675) with equal median attempt. Easy cannulation (Visual Analogue Scale score ≤4) was the same in both groups, whereas percentages of difficult cannulation (Visual Analogue Scale scores ≥4) were 16.4% and 19.1% in the dorsalis pedis artery and posterior tibial artery groups, respectively. Cannulation time was lower in the dorsalis pedis artery group [median time in seconds: 37 (28, 63) seconds vs. 44 (29, 75) seconds, P = .027]. Single-attempt success rates were lower in the feeble pulse group as compared to the strong pulse group (48.61% vs. 70.27%, P = .002). Likewise, a higher Visual Analogue Scale of ease of cannulation (>4 score) was seen in the feeble pulse group compared to the strong pulse group (26.39% vs. 13.51%, P = .019). The single-attempt success rate was similar for both dorsalis pedis artery and posterior tibial artery. However, the time taken for cannulating the posterior tibial artery is significantly higher than that for dorsalis pedis artery.

Dynamic Photoresponse of a DNTT Organic Phototransistor.

The photosensitivity, responsivity, and signal-to-noise ratio of organic phototransistors depend on the timing characteristics of light pulses. However, in the literature, such figures of merit (FoM) are typically extracted in stationary conditions, very often from IV curves taken under constant light exposure. In this work, we studied the most relevant FoM of a DNTT-based organic phototransistor as a function of the timing parameters of light pulses, to assess the device suitability for real-time applications. The dynamic response to light pulse bursts at ~470 nm (close to the DNTT absorption peak) was characterized at different irradiances under various working conditions, such as pulse width and duty cycle. Several bias voltages were explored to allow for a trade-off to be made between operating points. Amplitude distortion in response to light pulse bursts was also addressed.

Cyanide replaces substrate in obligate-ordered addition of nitric oxide to the non-heme mononuclear iron AvMDO active site.

Thiol dioxygenases are a subset of non-heme mononuclear iron oxygenases that catalyze the O2-dependent oxidation of thiol-bearing substrates to yield sulfinic acid products. Cysteine dioxygenase (CDO) and 3-mercaptopropionic acid (3MPA) dioxygenase (MDO) are the most extensively characterized members of this enzyme family. As with many non-heme mononuclear iron oxidase/oxygenases, CDO and MDO exhibit an obligate-ordered addition of organic substrate before dioxygen. As this substrate-gated O2-reactivity extends to the oxygen-surrogate, nitric oxide (NO), EPR spectroscopy has long been used to interrogate the [substrate:NO:enzyme] ternary complex. In principle, these studies can be extrapolated to provide information about transient iron-oxo intermediates produced during catalytic turnover with dioxygen. In this work, we demonstrate that cyanide mimics the native thiol-substrate in ordered-addition experiments with MDO cloned from Azotobacter vinelandii (AvMDO). Following treatment of the catalytically active Fe(II)-AvMDO with excess cyanide, addition of NO yields a low-spin (S = 1/2) (CN/NO)-Fe-complex. Continuous wave and pulsed X-band EPR characterization of this complex produced in wild-type and H157N variant AvMDO reveal multiple nuclear hyperfine features diagnostic of interactions within the first- and outer-coordination sphere of the enzymatic Fe-site. Spectroscopically validated computational models indicate simultaneous coordination of two cyanide ligands replaces the bidentate (thiol and carboxylate) coordination of 3MPA allowing for NO-binding at the catalytically relevant O2-binding site. This promiscuous substrate-gated reactivity of AvMDO with NO provides an instructive counterpoint to the high substrate-specificity exhibited by mammalian CDO for L-cysteine.

Preparation and Characterization of Pulse Electrodeposited Ni/W-SiC Nanocomposite Coating on Mild Steel Substrate

In order to improve the performances of metal containers, furnace bodies and agricultural tools manufactured by mild steels, Ni/W-SiC nanocomposites are prefabricated on mild steel substrate by the pulse electrodeposition (PED) method. The morphology, texture, microstructure, microhardness, and wear performances of Ni/W-SiC nanocomposites are examined by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), dispersive X-ray spectroscopy (EDX), hardness tester, and friction wear testing. The results indicate that the SiC size in nanocomposites is ~32.4 nm when its concentration in electrolytes is 7 g/L. The S1 and S4 nanocomposites’ microstructures (the S1 composite was prefabricated at 4 g/L, and the S4 composite was deposited at 13 g/L) reveal many large cauliflower-shaped grains. However, the S2 nanocomposite (the S2 composite was obtained at 7 g/L) demonstrates the homogeneous, finest and smoothest surface morphology. The diffraction angles of S1 nanocomposite are 41.2°, 51.7°, and 71.2° depicting the sharpest diffraction peaks, corresponding to the (1 1 1), (2 0 0), and (2 2 0) crystal planes of Ni-W grains, respectively. Moreover, the S2 nanocomposite exhibits the lowest wear depth and width of 34.2 μm and 5.5 mm, respectively. Some shallow and fine scratches on the as-described nanocomposites’ surface indicate its excellent tribological performance. However, the S4 nanocomposite exhibits a wear depth of 86.3 μm and a width of 11.9 mm.

Wide-pulse electrical stimulation of the quadriceps allows greater maximal evocable torque than conventional stimulation.

The effectiveness of a neuromuscular electrical stimulation (NMES) program has been shown to be proportional to the maximal evocable torque (MET), which is potentially influenced by pulse characteristics such as duration and frequency. The aim of this study was to compare MET between conventional and wide-pulse NMES at two different frequencies. MET-expressed as a percentage of maximal voluntary contraction (MVC) torque-and maximal tolerable current intensity were quantified on 71 healthy subjects. The right quadriceps was stimulated with three NMES protocols using different pulse duration/frequency combinations: conventional NMES (0.2ms/50Hz; CONV), wide-pulse NMES at 50Hz (1ms/50Hz; WP50) and wide-pulse NMES at 100Hz (1ms/100Hz; WP100). The proportion of subjects reaching the maximal stimulator output (100mA) before attaining maximal tolerable current intensity was also quantified. The proportion of subjects attaining maximal stimulator output was higher for CONV than WP50 and WP100 (p < 0.001). In subjects who did not attain maximal stimulator output in any protocol, MET was higher for both WP50 and WP100 than for CONV (p < 0.001). Maximal tolerable current intensity was lower for both WP50 and WP100 than for CONV and was also lower for WP100 than for WP50 (p < 0.001). When compared to conventional NMES, wide-pulse protocols resulted in greater MET and lower maximal tolerable current intensity. Overall, this may lead to better NMES training/rehabilitation effectiveness and less practical issues associated with maximal stimulator output limitations.

Highly Efficient Sum‐Frequency Generation in Niobium Oxydichloride NbOCl2 Nanosheets

AbstractParametric infrared (IR) upconversion is a process in which low‐frequency IR photons are upconverted into high‐frequency ultraviolet/visible photons through a nonlinear optical process. It is of paramount importance for a wide range of security, material science, and healthcare applications. However, in general, the efficiencies of upconversion processes are typically extremely low for nanometer‐scale materials due to the short penetration depth of the excitation fields. Here, parametric IR upconversion processes, including frequency doubling and sum‐frequency generation, are studied in layered van der Waals NbOCl2. An upconversion efficiency of up to 0.004% is attained for the NbOCl2 nanosheets, orders of magnitude higher than previously reported values for nonlinear layered materials. The upconverted signal is sensitive to layer numbers, crystal orientation, excitation wavelength, and temperature, and it can be utilized as an optical cross‐correlator for ultrashort pulse characterization.

Stochastic simulation of velocity pulses of near-fault ground motions based on multivariate copula modeling

Due to the featured high-amplitude, long-period pulses in velocity or displacement time–history, the near-fault ground motion may have a stronger destructive effect on engineering structures. Therefore, studying velocity pulses modeling of near-fault ground motions has been an important topic in the earthquake engineering community. However, the variability and probabilistic correlation of pulse model parameters have not received enough attention. To this end, an elegant method for stochastic simulation of velocity pulses of near-fault ground motions is proposed based on the classical Gabor wavelet modeling and probabilistic correlation analysis of associated model parameters by multivariate copula modeling. Especially, an efficient scheme of iteratively determining the optimal copulas pertinent to edges of a complex vine structure is developed, and two parameters relevant to the near-fault ground motion records, i.e., the rupture distance and the strongest pulse orientation, are introduced which provides a physical basis for addressing the dependence structure among variables. For illustrative purposes, the ground accelerograms recorded by near-fault instruments in the 1999 Chi-Chi earthquake are used. It is shown that the multivariate copula modeling enables the efficient representation of probabilistic correlation between model parameters which is consistent with their physical mechanism. The time histories and spectral characteristics of velocity pulses of near-fault ground motions and their stochastic fluctuations with respect to the rupture distance are well simulated. While the empirical linear regression model does not meet the requirements of random vibration analysis and thus cannot guide the safety design of seismic structures.

A novel scheme for ultrashort terahertz pulse generation over a gapless wide spectral range: Raman-resonance-enhanced four-wave mixing

Ultrashort energetic terahertz (THz) pulses have created an exciting new area of research on light interactions with matter. For material studies in small laboratories, widely tunable femtosecond THz pulses with peak field strength close to MV cm−1 are desired. Currently, they can be largely acquired by optical rectification and difference frequency generation in crystals without inversion symmetry. We describe in this paper a novel scheme of THz pulse generation with no frequency tuning gap based on Raman-resonance-enhanced four-wave mixing in centrosymmetric media, particularly diamond. We show that we could generate highly stable, few-cycle pulses with near-Gaussian spatial and temporal profiles and carrier frequency tunable from 5 to >20 THz. They had a stable and controllable carrier-envelop phase and carried ~15 nJ energy per pulse at 10 THz (with a peak field strength of ~1 MV cm−1 at focus) from a 0.5-mm-thick diamond. The measured THz pulse characteristics agreed well with theoretical predictions. Other merits of the scheme are discussed, including the possibility of improving the THz output energy to a much higher level.

Gain characteristics of stimulated Brillouin scattering in fused silica.

Stimulated Brillouin scattering (SBS) is a non-linear process which has the capacity to improve the beam quality and pulse characteristics of laser beams. In this paper, we theoretically and experimentally study the process of SBS in fused silica. In particular, we examine the energy reflection and pulse compression of input laser pulses as functions of focus position, pump energy and beam diameter. We utilized coupled wave equations and a distributed noise model to simulate the reflected energy and time waveform under different gain parameters. An experimental system is constructed and used to qualify the numerical simulations. The results reveal that the threshold for the SBS process and the energy reflectivity significantly change with laser focus position under the same pump and focusing parameters. Ultimately, the gain characteristics of the SBS material is the primary factor that influences the SBS output. This work presented here offers insight into the operation of short-length solid-state SBS lasers and serves as a basis for the design and optimization of such systems.

Wavelength and pulse width programmable mode-locked Yb fiber laser.

To the best of our knowledge, this study is the first demonstration of a mode-locked polarization-maintaining Yb fiber laser that incorporates a liquid-crystal-on-silicon-based electrically programmable filter into the cavity. The intracavity filter continuously tunes pulse characteristics, such as a wavelength tunable range of 1018-1065 nm and pulse width tunable range of 0.3-2.6 ps. Further, numerical simulations of the laser oscillator results were consistent with the experimental results and confirmed the mode-locked pulse generation regime. The proposed technique is expected to have great potential as a seed laser for multifunctional ultrashort-pulse lasers.

Multi-Morphological Pulse Signal Feature Point Recognition Based on One-Dimensional Deep Convolutional Neural Network

Radial pulse signals are produced by the periodic ejection of blood from the heart, and physiological and pathological information of the human body can be analyzed by extracting the time-domain characteristics of pulse waves. However, since pulse signals are weak physiological signals on the body surface and complex, the acquisition of pulse characteristics using the traditional curvature method will produce a large error, which cannot meet the needs of pulse wave analysis in current clinical practice. To solve this problem, a multi-morphological pulse signal feature recognition algorithm based on the one-dimensional deep convolutional neural network (1D-DCNN) model is proposed. We used the multi-channel pulse diagnosis instrument independently developed by the team to collect radial pulse signals under continuous pressure of the test subjects and collected 115 subjects and extracted a total of 1300 single-cycle pulse signals and then divided these pulse signals into 6 different forms. Five types of pulse signal time-domain feature points were labeled, and five independent feature point datasets were labeled and formed five customized neural network models that were generated to train and identify the pulse feature point datasets independently. The results show that the correction coefficient (Radjusted2) of the multi-class pulse signal processing algorithm proposed in this paper for each type of feature point recognition reaches more than 0.92. The performance is significantly better than that of the traditional curvature method, which shows the accuracy and superiority of the proposed method. Therefore, the multi-class pulse signal characteristic parameter recognition model based on the 1D-DCNN model proposed in this paper can efficiently and accurately identify pulse time-domain characteristic parameters, which can be applied to discriminate time-domain pulse information in clinical practice and assist doctors in diagnosis.

Laser-pulse characterization using strong-field autocorrelation patterns and random-forest-based machine learning

Building on the strategy presented in Opt. Lett. 47, 3992 (2022), we demonstrate an efficient alternative approach for the in situ characterization of ultrashort low-frequency laser pulses. In this context, we employ first-principles quantum-mechanical calculations to model the strong-field ionization of rare-gas atoms and produce autocorrelation patterns for a set of few-femtosecond near-infrared laser pulses. We explore the nonperturbative and nonlinear dependence of the autocorrelation patterns on the pulse characteristics and postulate an analytical function describing these patterns. For every laser pulse considered, we employ the parameters appearing in this analytical function, together with the underlying pulse parameters for supervised machine learning. Specifically, we use the random-forest technique for retrieving key laser pulse parameters from autocorrelation patterns produced via strong-field ionization. The current approach offers advantages for application to experimental data.

The current pulses characteristics of the negative corona discharge in SF6/CF4 mixtures

This paper presents the results of numerical investigation of the current pulses characteristics in SF6/CF4 mixtures for the negative point-plane corona discharge. The pressure and the temperature of gas mixtures are 0.4 MPa and 300 K, respectively. The CF4 content varies from 20% to 80%. The 2D axisymmetric geometry with point-plane electrodes is investigated, and the three drift-diffusion equations are solved to predict the characteristics of the negative corona discharge. In addition, Poisson’s equation is coupled with the above three continuity equations to calculate the electric field. In order to calculate the electron impact coefficients, including the Townsend ionization and attachment coefficients, as well as the mobilities and diffusion coefficients for electrons, the two-term Boltzmann equation is solved. The characteristics of three ionic species at five stages of the first current pulse in 60%SF6-40%CF4 and 20%SF6-80%CF4 mixtures are selected to discuss the development mechanism of current pulses. Moreover, the reduced electric field strengths at the corresponding time instants are presented to help understand the discharge process. The current waveform and the total number of three species are compared in all the cases to analyze the effects of the CF4 content on the discharge. The reduced electric field strength is also helpful in understanding the effects of CF4 content. When the CF4 content increases to 80%, the discharge is more intensive and the pulse frequency also increases.

The Effect of Lifting-and-Thrusting Laser Acupuncture on Electrodermal Activity of Acupoints, Pulse Characteristics, and Brainwave.

Acupuncture has been shown as an effective traditional Chinese medicine treatment method, especially for pain relief. Recently, laser acupuncture is becoming increasingly popular, thanks to its noninvasive and painless nature and effectiveness in treating diseases, proven by many studies (for example, some previous studies showed that low-power laser stimulation is able to increase the power of alpha rhythms and theta waves). In our prior work, we developed a novel laser acupuncture model that emulates lifting-and-thrusting operation commonly used in traditional needle acupuncture and showed its benefit in improving cardiac output and peripheral circulation. By extending our previous studies, in this work, we perform extensive experiments to understand the effect of such a system on electrodermal activity (EDA) of acupoints, pulse characteristics, and brainwave, to further verify its efficacy. In particular, we found that laser stimulation could cause significant changes in EDA of acupoints, pulse amplitude, pulse-rate-variability (PRV), and acupoint conductance, as a function of laser power and stimulation time. In addition, laser acupuncture with the lifting-and-thrusting operation has more significant effect on increasing the power of alpha and theta frequency bands as compared to laser acupuncture without the lifting-and-thrusting operation. Finally, given sufficient stimulation time (e.g., > 20 min), the performance of a low-powered laser acupuncture with the lifting-and-thrusting operation could be comparable to that of traditional needle acupuncture.

Phase-matching free pulse retrieval based on plasma-induced defocusing

A phase-matching free pulse retrieval technique based on plasma-induced defocusing in a rare gas is presented. Based on a pump-probe setup, this technique uses a moderately intense pump laser pulse for ionizing the medium, creating in turn an ultrafast defocusing lens. While a coronagraph blocks out the probe pulse in absence of ionization, the plasma lens leads to increase the probe beam size in the far field. By measuring the spectrum of the probe propagating around the coronagraph as a function of the pump-probe delay π, a bi-dimensional trace (ω,π) is obtained. This enables to fully characterize the temporal and spectral characteristics of the probe pulse through a method that is free of phase matching constraints. Demonstrated both in the near-infrared (800 nm) and in the ultraviolet (266 nm), the present technique is potentially suited for characterizing pulses in the whole transparency region of the used gas, i.e., from the deep-ultraviolet to the far-infrared.

Увеличение эффективности обнаружения воздушных судов на догонных курсах в импульсно-доплеровских бортовых РЛС с малой высотой полета носителя

Problem statement. The effectiveness of solving the problem of warning about possible collisions of small aircraft or unmanned aerial vehicles intended for the development of hard-to-reach territories depends on the time of early detection of another aircraft on intersecting trajectories. As a result of the comparative analysis of radar detection methods carried out in the article, taking into account the differences in the signal-interference situation characteristic of on-board pulse−Doppler radars for targets on catch-up courses in versions "multiple input - multiple output", "with joint a posteriori processing of results" and in traditional radar with active or passive phased antenna arrays have shown that the latter have energy advantages. Therefore, for this category of pulse-Doppler radars, a method for estimating the detection range on several frames is presented, which allows you to choose the logic of operation with an increase in the detection range. Research methods. The theory of antenna arrays and the theory of radar detection for pulse-Doppler radars were actively used in the work with the specified requirements for the probabilities of correct detection, false alarm and the selected model of fluctuations of the reflected useful signal. Purpose. To substantiate the advantages of technical solutions based on a traditional technical solution with phased antenna arrays for detection on catch-up courses and to develop recommendations for finding conditions that allow to increase the detection range. Results. The simulation results are presented, showing an improvement in the conditions for radar detection in onboard pulse-Doppler radars when finding the spectrum of the reflected radar signal in the Doppler frequency range, on which the spectrum of the reflected signal from the Earth's surface is superimposed when using radar with phased antenna arrays compared with spatial processing methods in MIMO and radars with joint a posteriori processing of results. A method for calculating the detection range on several adjacent frames has been developed and it is shown that in this case a longer range is achieved compared to the case of detection on a single frame. Practical significance. The results of the work can be used in small-sized onboard pulse radars of low-altitude carriers in order to increase the time of early warning of the presence of other aircraft on the flight path. This task seems to be especially relevant when flying radar carriers in hard-to-reach, developed territories.