Instantaneous Pulse Research Articles

Bremsstrahlung converter system with target in vacuum

The design of a bremsstrahlung converter for intense pulsed electron beam with total electron absorption and separated vacuum seal is investigated. The target of the converter is made of molybdenum with a thickness of 250 μm, isolated in vacuum by a titanium membrane of 60 μm thick. The article presents the experimental data of the converter tests, such as the dependence of the dose on the distance, the curve of dose rate, the image of the X-ray source obtained by the pinhole camera, and the thermal image of the converter exit window from the infrared camera. A dose of 10 mGy per pulse was demonstrated, with an instantaneous pulse dose rate of 0.1 MGy/s at a distance of 3 cm from the target plane. Reliable continuous operation for more than 1 million pulses at 10 pps has been experimentally achieved.

Cooled (4°C) lidocaine during office cystoscopy improves patient satisfaction and comfort: A prospective, randomized, double-blind, controlled study.

Office-based flexible cystoscopy is often associated with considerable discomfort in male patients. We devised this study to prospectively evaluate the efficacy of cooling intraurethral lidocaine jelly to 4°C prior to use in office-based cystoscopy in an effort to reduce male patient discomfort. A total of 600 male patients scheduled for office diagnostic cystoscopy were enrolled and randomized into three groups for a prospectively controlled, double-blind study. Each group received one of the three methods of intraurethral lubrication: plain room temperature lubricant (control) (CON), room temperature lidocaine (LI), or lidocaine at 4°C (LI4°C). Perceived pain was recorded on a Likert visual analog scale (VAS) of 1-10 where 0=no pain and 10=excruciating pain. Kruskal-Wallis test assessed the efficacy of cooling lidocaine compared to room temperature lidocaine and control. Subjective pain reporting was corroborated with instantaneous objective pulse rate recording eliminating perception bias. There was no significant difference in cystoscopy duration between all groups. Mean pain scores (mean ± standard deviation) were 4.05±0.91, 2.74±1.01, and 1.8±0.84, respectively, for groups CON, LI, and LI4°C (p=0.02). There was a 32.34% reduction in the mean pain score of LI and a further reduction of 34.3% was achieved in LI4°C when compared to CON. Body mass index (BMI) and prostate weight had a significant positive correlation with pain score, whereas no such correlation was found with age. Cooling lidocaine to 4°C provides additional analgesic benefit in men undergoing office cystoscopy and increases compliance.

具有左右分数阶导数和时滞的非瞬时脉冲微分方程非线性边值问题

具有左右分数阶导数和时滞的非瞬时脉冲微分方程非线性边值问题

Large-Scale PFN Fault Diagnosis Method Based on Multidimensional Time Series Anomaly Detection Using Convolutional Neural Network

The fast fault diagnosis of large-scale pulse-forming network (PFN) of electromagnetic rail launch system is of great significance. It is an important research direction to diagnose the PFN fault by detecting the anomaly of multidimensional time series in each pulse-formatting unit (PFU). Due to the high sampling rate of time series and the characteristics of aperiodic instantaneous pulse, the current time series diagnosis method is not suitable. Multidimensional coupling aggravates the complexity of the problem. In order to solve the problem, this article proposes a method of multidimensional time series anomaly detection based on convolutional neural network. First, the multidimensional time series is transformed into a gray-scale image, which can reflect the health status of a PFU. Second, a deep convolution neural network is constructed to identify the abnormal images based on the existing data trainers. Finally, a convolution neural network is constructed to locate the fault. The results show that the model can identify 100% of the abnormal PFU waveform, and the fault classification model can also accurately locate the fault, which proves the effectiveness of the proposed algorithm.

Geomagnetic signal de-noising method based on improved empirical mode decomposition and morphological filtering

To solve the problem that geomagnetic signals are susceptible to random noise and instantaneous pulse interference in geomagnetic navigation, a geomagnetic signal de-noising method based on improved empirical mode decomposition (IEMD) and morphological filtering (MF) is proposed. The instantaneous pulse interference is eliminated by designing different structural elements according to the characteristics of the pulse signal. The signal after filtering the instantaneous pulse interference is decomposed by EMD, and the intrinsic mode functions (IMFs) obtained from the decomposition are determined as two modes (i.e. noise IMFs and mixed IMFs) by the cross-correlation coefficient criterion. The noise IMFs are removed directly, and a normalized least means square filter (NLMS) is designed to remove noise from mixed IMFs, which can adaptively adjust the filtering parameters according to the noise level of different IMF components. The noise-reduced mixed IMFs and residual are reconstructed to obtain the final geomagnetic signal. Experiment results illustrate that the proposed MF-IEMD method can effectively achieve noise reduction. Comparing with the traditional EMD and MF-EMD de-noising methods, the root mean square errors(RMSE) decreased by 49.27% and 24.79%, respectively.

Development of arbitrary waveform torsional vibration signal generator

In order to more accurately evaluate or calibrate the electronic torsional vibration test analyzer and analysis method, a torsional vibration signal generator is developed in the present study. The developed device generates a tooth pulse interval sequence based on the inverse solution of the shaft torsional equation. Moreover, a single-frequency signal, inter-harmonic signal, time-varying harmonic signal, and noise-containing time-varying inter-harmonic signal are simulated. The pulse width modulation module of TMS320F28335 is used to generate the instantaneous speed gear pulse signal, while the external expanded digital to analog conversion module is utilized to generate the corresponding speed analog signal. The hardware structure of the proposed generator has remarkable advantages, including simple structure, low-cost operation and easy to use interface. Moreover, it can be applied to evaluate or calibrate the torsional vibration test analyzer and analytical methods.

Accurately accounting for effects on times-of-flight caused by finite field-transition times during the ejection of ions from a storage trap: A study for single-reference TOF and MRTOF mass spectrometry

In applied forms of time-of-flight mass spectrometry utilizing ion storage devices prior to an analysis device, a non instantaneous electric ejection pulse applied in the region of ion storage is used to accelerate ions into the time-of-flight analyzer. The calculated mass value of the ions from the time-of-flight is dependent on the duration of the field transition up to full strength. For novel applications dedicated to precision measurements, such as multi-reflection time-of-flight mass spectrometry of short-lived isotopes, the goal is to continuously decrease the measurement uncertainty while providing a mass accuracy on the same order. Even though dynamic-field models for time-of-flight mass spectrometry have been considered in the past for technological advances, it is important to study the accuracy of the measured mass in this context. Using a simplified linear model for the field transition, we provide a basic investigation of the scenario, and discuss the deviation from the classical “mass-over-charge” dependency of the ions’ time-of-flight, which becomes violated. The emerging mass discrepancy depends on the distance between the mass of the ion used for calibration and that of the ion of interest and, in extreme cases, can increase to about one percent for systems with short times-of-flight. However, for typical conditions in single-reference multi-reflection time-of-flight mass spectrometry, mass deviations caused by this effect typically remain below the 1ppm level. If a mass calibration using two or more ion species is possible during the measurement, the effect becomes negligible for appropriate choices of reference masses.

Research on Time-Domain Transfer Impedance Measurement Technology for High Frequency Current Transformers in Partial Discharge Detection of Cables

We focus on the high frequency current method which is widely applied in the partial discharge (PD) detection of cables. Aiming at guaranteeing the accuracy of this method, we study an innovative time-domain technology for effectively measuring the transfer impedance of the high frequency current transformers (HFCTs). The proposed technology called pulse injection method obtains the system response under the excitation of the wide-band instantaneous pulse signal. Firstly, by studying the working principle of HFCTs, we summarize that the bandwidth of the selected signal acquisition device should be at least 100MHz to ensure measurement accuracy. Secondly, Gauss pulse and square wave pulse are generated to determine the effects of different sources. The measurement results indicate that Gauss pulse is more suitable for pulse injection method, and the rise time should be under 10 ns to improve the starting frequency of oscillation distortion. Finally, the transfer impedance curves of five types of HFCTs are acquired by both pulse injection and traditional point-frequency methods. The measurement results show a remarkable consistency between two methods. However, pulse injection method requires the simpler operation and has a higher resolution, obviously improving the measurement efficiency and better displaying the details of the transfer impedance curves.

NUMERICAL ANALYSIS OF SAFETY ZONE OF A LARGE FLAT-PLATE BOUNDED-WAVE EMP SIMULATOR.

The safety zone of a large flat-plate bounded-wave electromagnetic pulse simulator was analyzed using the 3D electromagnetic simulation software Computer Simulation Technology. First, the double-limit requirement cited from the GB 8702 for an instantaneous pulse was clarified compared with the International Commission on Non-Ionizing Radiation Protection guidelines. This means that both the amplitude of the time-domain waveforms and all frequency components should be satisfied with the respective exposure limits. Then, the leakage field of a large flat-plate bounded-wave simulator was simulated. After analyzing the peak amplitude of an instantaneous electric field in a certain area, the observation points along six directions were specified, and the corresponding amplitudes were given. Furthermore, it was verified that the time-domain electric field of the critical points was satisfied with the frequency-domain exposure limits. Finally, the safety distances lower than the reference levels were given, and the safety zones corresponding to the three common exposure limits were obtained.

Observation of dark and bright pulses in q-switched erbium doped fiber laser using graphene nano-platelets as saturable absorber

In this paper, a passively Q-switched Erbium doped fiber laser (EDFL) by residing Graphene nanoplatelets (GnPs) embedded in polyvinyl alcohol (PVA) based saturable absorber (SA) is demonstrated. To aid the dispersion of GNPs, a surfactant is used and then it is mixed with polyvinyl alcohol (PVA) as host polymer to develop GnPs-PVA film based passive SA. The GnPs-PVA based film then integrated in laser cavity in ring cavity configuration for pulse laser generation. The experimental works show that the proposed passive SA operates at input pump power range from 77 mW to 128 mW with a tunable repetition rate from 78.4 kHz to 114.8 kHz and a shortest pulse width of 3.69 µs. The laser produces maximum instantaneous output peak power and pulse energy of 7.3 mW and 30.46 nJ, respectively and accompanied by signal to noise ratio (SNR) of 64 dB.

Assessment of RANS turbulence models and Zwart cavitation model empirical coefficients for the simulation of unsteady cloud cavitation

The numerical simulation of unsteady cavitation flows is sensitive to the selected models and associated parameters. Consequently, three Reynolds Average Navier-Stokes (RANS) turbulence models and the Zwart cavitation model were selected to assess their performance for the simulation of cloud cavitation on 2D hydrofoils. The experimental cavitation tests from a NACA65012 hydrofoil at different hydrodynamic conditions were used as a reference to tune the modeling parameters and the experimental tests from a NACA0015 were finally used to validate them. The effects of near wall grid refinement, time step, iterations and mesh elements were also investigated. The results indicate that the Shear Stress Transport (SST) model is sensitive to near wall grid resolution which should be fine enough. Moreover, the cavitation morphology and dynamic behavior are sensitive to the selection of the Zwart empirical vaporization, Fv , and condensation, Fc , coefficients. Therefore, a multiple linear regression approach with the single objective of predicting the shedding frequency was carried out that permitted to find the range of coefficient values giving the most accurate results. In addition, it was observed that they provided a better prediction of the vapor volume fraction and of the instantaneous pressure pulse generated by the main cloud cavity collapse.

Graphene in chitin based passive Q-switcher

Many materials have been utilized as saturable absorbers in generating pulsed lasers. By incorporating them with host polymers such as polymethylmethacrylate (PMMA), polyvinyl alcohol (PVA) and polyethylene oxide (PEO), the process of saturable absorber integration into the laser cavity is made easier. This work reported the generation of Q-switched pulsed lasers based on graphene embedded in chitin saturable absorber. Graphene: chitin with a concentration of 1:1 and 1.5:1 are integrated into a fiber laser cavity and the laser performance of both SAs are recorded and compared. The graphene chitin SA of 1:1 concentration produces a higher repetition rate and shorter pulse duration of 111.77 kHz and 1.328 μs, respectively. However, the SA with higher graphene content operated at a larger range of input pump power yielding a higher instantaneous peak power and pulse energy of 7.29 mW, and 14.37 nJ, respectively. This work introduces chitin as a potentially excellent natural host polymer as an alternative to conventional ones such as polyvinyl alcohol (PVA) and polyethylene oxide (PEO).

Instantaneous Pulse Power Compensator for High-Density Single-Phase Inverters

In this paper, instantaneous pulse power compensator (IPPC) method is proposed to achieve power pulsation decoupling function for single-phase inverter applications. A smaller capacitor is placed in series with the traditional dc-link capacitor, and this smaller capacitor voltage is controlled using pulse currents to cancel out the dc-link voltage ripple. Unlike twice-line-frequency power decoupling method, the proposed IPPC method can compensate the pulsating power with all the orders harmonics on the dc-link line, not only the second-order component. Both modeling and simulation results show that IPPC method can achieve nearly zero voltage ripple for the dc-link capacitor since the pulse current is fully compensated. Whereas twice-line-frequency power decoupling method has limit in voltage ripple reduction, especially in small dc-link capacitance conditions. The experimental results based on a full-bridge topology decoupling circuit and a single-phase inverter application show consistent results with simulation results. A 16% reduction of the prototype size, i.e., 16% higher power density with only ∼1% efficiency penalty can be achieved by the proposed IPPC method when compared to the second-order power decoupling method.

An improved single probe method for sap flow measurements using finite heating duration

Because of its low cost and simple fabrication, it is easy to advocate for the single probe method as a method of choice in sap flow studies. An improved single probe method with finite heating duration (F-SPHP) is verified both in cut stem segments and in the field using mature beech (Fagus sylvatica L.) trees. The F-SPHP method is based on an analytical solution of the partial differential equation for combined heat conduction and convection, which shows large relative sensitivity to thermal conductivity (K). The F-SPHP method is able to measure sap flux densities (SFD) between 2 and 36 cm3 cm−2 h−1 (heat pulse velocity (Vh): 3–60 cm h−1) in the cut stem segment experiment. This is an improvement compared to the instantaneous single probe heat pulse (I-SPHP) method which cannot accurately measure low (Vh < 20 cm h−1) sap flow. Sapflow+ (a four-needle heat pulse method) is used for field validation, and when compared with gravimetric measurements, slopes of 0.853 and 0.730 are obtained for F-SPHP and Sapflow+, respectively. Patterns measured with F-SPHP and Sapflow+ in mature beech trees in the forest are similar at all measurement positions and temperature correction is needed for both methods when natural temperature gradients are steep. Compared with multi-probe methods, the single probe method with finite heating duration has the advantage of causing less damage to conductive tissue.

High-energy low-temporal-coherence instantaneous broadband pulse system

We propose and experimentally demonstrate a scheme of achieving high-energy low-temporal-coherence instantaneous broadband light pulses. The low-temporal-coherence instantaneous broadband pulse with a large bandwidth (10.2 nm) and high energy (35 J) in the high gain (more than 107 times) laser system was safely created. The coherence time of the output pulse is 318 fs with a 3 ns pulse duration. The excellent near-field beam quality and focusability of the pulse can be comparable to that of conventional coherent lasers. To the best of our knowledge, this is the highest energy of a low-temporal-coherence instantaneous broad-bandwidth pulse reported thus far.

Comparison of Measurement Sites in Instantaneous Orthostatic Pulse Rate Measurement

Comparison of Measurement Sites in Instantaneous Orthostatic Pulse Rate Measurement

Double‐ended travelling‐wave fault location based on residual analysis using an adaptive EKF

This paper presents the estimated residuals for detecting the traveling wave front using an adaptive extended Kalman filter based on the maximum likelihood (EKF-ML), which uses the maximum likelihood method to adaptively optimize the error covariance matrices and the initial conditions. In some situations, such as faults close to the bus or close to zero inception angle, or faults with high fault resistances, the transient waves can become weak and even become lost in the noise, which makes the discrimination of the traveling wave front become more difficult. Aiming at this, residuals between the observed values and the estimated values using the adaptive EKF exhibit remarkable singularities, and can be used for exactly determining the wave front. Thus, the exact arrival time of the initial wave head can be determined and then the fault distance can be calculated precisely. The effectiveness of exacting mutation feature using the proposed method has been demonstrated by a simulated instantaneous pulse. And it has been tested with different types of faults using ATP simulation. Simulation results verify that the estimated residuals are highly sensitive to traveling wave front and less sensitive to modeling uncertainty (such as noise disturbance).

Characteristics of Turbulent Aeolian Sand Movement Over Straw Checkerboard Barriers and Formation Mechanisms of Their Internal Erosion Form

AbstractStraw checkerboard barrier (SCB) array is one of the most effective and widely used measures for antidesertification projects. The efficiency and durability of SCB are greatly influenced by the features of wind field and sand particle motion. Unfortunately, very few studies have explored the characteristics of turbulent flow and the internal erosional form inside the barrier cell, because of the complexity of turbulent flow and the sand particle motion around the surface of SCBs. In this paper, we simulated the wind‐sand flow around SCBs using 3‐D hybrid Reynolds‐averaged Navier‐Stokes/large eddy simulation method and Lagrangian particle tracing method to analyze the characteristics of turbulent flow, particle motion, and internal erosional form of SCBs. The results show that the vast majority of particles fall into SCB cells from their middle and posterior parts when wind‐sand flow passes SCBs, due to the impact of gravity and subsidence flow. It indicates that SCBs could effectively prevent sand flow‐induced hazards. The turbulent flow in SCBs has great instantaneous pulse velocity, resulting in retransfer of sand particles in SCBs. Analysis of the mean flow field in SCB found one huge streamwise vortex that filled the SCB cells and two spanwise vortexes in the back of SCB cells. These vortexes will drive particles inside SCBs to move toward the front and side walls, making the erosional form of SCB cells low in the middle and high near all the sides.

Revisitation of the dipole tracer test for heterogeneous porous formations

Abstract In this paper, a new analytical solution for interpreting dipole tests in heterogeneous media is derived by associating the shape of the tracer breakthrough curve with the log-conductivity variance. It is presented how the solution can be used for interpretation of dipole field test in view of geostatistical aquifer characterization on three illustrative examples. The analytical solution for the tracer breakthrough curve at the pumping well in a dipole tracer test is developed by considering a perfectly stratified formation. The analysis is carried out making use of the travel time of a generic solute particle, from the injection to the pumping well. Injection conditions are adapted to different possible field setting. Solutions are presented for resident and flux proportional injection mode as well as for an instantaneous pulse of solute and continuous solute injections. The analytical form of the solution allows a detailed investigation on the impact of heterogeneity, the tracer input conditions and ergodicity conditions at the well. The impact of heterogeneity manifests in a significant spreading of solute particles that increases the natural tendency to spreading induced by the dipole setup. Furthermore, with increasing heterogeneity the number of layers needed to reach ergodic conditions become larger. Thus, dipole test in highly heterogeneous aquifers might take place under non-ergodic conditions giving that the log-conductivity variance is underestimated. The method is a promising geostatistical analyzing tool being the first analytical solution for dipole tracer test analysis taking heterogeneity of hydraulic conductivity into account.

Conductive graphene as passive saturable absorber with high instantaneous peak power and pulse energy in Q-switched regime

Abstract The Q-switched pulse regime is demonstrated by integrating conductive graphene as passive saturable absorber producing relatively high instantaneous peak power and pulse energy. The fabricated conductive graphene is investigated using Raman spectroscopy. The single wavelength Q-switching operates at 1558.28 nm at maximum input pump power of 151.47 mW. As the pump power is increased from threshold power of 51.6 mW to 151.47 mW, the pulse train repetition rate increases proportionally from 47.94 kHz to 67.8 kHz while the pulse width is reduced from 9.58 μs to 6.02 μs. The generated stable pulse produced maximum peak power and pulse energy of 32 mW and 206 nJ, respectively. The first beat node of the measured signal-to-noise ratio is about 62 dB indicating high pulse stability.