Resolution of sensors with capacitive source impedance

A fast Thvenin equivalent model for IGBT considering the dynamic performance of both IGBT and antiparallel diode based on datasheet is proposed to increase the efficiency of power electronics transient simulation. In this paper, the conducting details of an IGBT with antiparallel diode switch are represented by a fixed topology equivalent: a voltage source in series with a constant resistance. For the first time, three devices are intergrated inside one model, and the conducting device is dynamically alternative among three statuses: IGBT, diode and open circuit, reflected in the changeable voltage source. So unchangeable admittance matrix is gained despite of the variation of conducting devices, which tremendously accelerates the calculation. A single phase half-bridge inverter circuit is tested applying the proposed model, and its accuracy and efficiency are validated.

The aim of this paper is to propose a protection strategy for the voltage generator based inverter against the large load currents. This strategy proposes an algorithm for generators output current limiting. It depends on decreasing the amplitude of the voltage reference in case of over current on generator output current. We aim to give the source a behavior similar to that of a voltage source in series with a virtual resistance. This resistance is activated only above a certain current threshold. Simulation results for the application of this strategy on resistive and resistive-inductive load will be demonstrated, in this paper. The effectiveness of the proposed current limiting method was tested on high load current resulting from the asynchronous motor startup. The last part will discuss the implementation of this current limiting strategy on real time simulation environment RT-LAB. An experimentation using Power Hardware in the Loop and realtime simulation was realized to verify the theoretical analysis.

In this article, the authors have made an attempt to promote the analysis of transmission lines containing distributed series voltage sources using Green’s function. Authors believe that this tutorial article can enrich a traditional course on transmission line theory due to the following two major value additions. Firstly, it extends the traditional transmission line theory by incorporating distributed voltage sources. Secondly, it acts as an excellent introduction to the concept of Green’s function. In this article, Green’s function for the point series voltage source is systematically derived. The 3D Electro-Magnetic tool is used to validate the analysis. A basic understanding of transmission line theory is a sufficient pre-requisite to dive into this journey.

This paper studies the use of power spectral density (PSD) and related random data analysis techniques in the test laboratory to characterize low frequency loading spectra output response, measured from a specimen, for the purpose of comparing test machine responses. In recent years digital techniques have been developed that simulate aircraft maneuver spectrum loading in the time domain. In this study one of these techniques is used to generate the input load spectrum signal to an electrohydraulic closed-loop test machine for fatigue testing of graphite/epoxy to titanium step lap bonded joints at various frequencies and PSD shapes. The output signal was measured directly from the specimen by recording on tape the dynamic strain gage signal. This signal then was processed to determine the PSD response and root mean square (RMS) time history. These data were compared with the recorded strain amplitude time history and the input load amplitude, frequency, and PSD information. A qualitative correlation was found between variations in specimen fatigue life, output signal waveform and amplitude, and variations in PSD. PSD is a measure of loading energy in the time domain and can be influenced both by load amplitude and waveform variations. Thus, the way a fatigue test machine processes an input load and frequency signal can affect the measured fatigue life of certain materials.

A method for evaluating reactor stability in boiling water reactors has been developed. The method is based on multivariate autoregressive (M-AR) modeling of steady-state neutron and process noise signals. In this method, two kinds of power spectral densities (PSDs) for the measured neutron signal and the corresponding noise source signal are separately identified by the M-AR modeling. The closed- and open-loop stability parameters are evaluated from these PSDs. The method is applied to actual plant noise data that were measured together with artificial perturbation test data. Stability parameters identified from noise data are compared to those from perturbation test data, and it is shown that both results are in good agreement. In addition to these stability estimations, driving noise sources for the neutron signal are evaluated by the M-AR modeling. Contributions from void, core flow, and pressure noise sources are quantitatively evaluated, and the void noise source is shown to be the most dominant.

Convective heat transfer from a partially premixed impinging flame jet. Part II: Time-resolved results

Firstly,Power Spectral Density( PSD) is proposed for mirror surface figure evaluation in the large aperture telescope system as for some difficulties for Root Mean Square( RMS) in the evaluation of large scale variety and disadvantage of robust for rigid body displacement. Then,the decomposition arithmetic of PSD is analyzed with Zernike polynomial,and Zernike polynomial spectrum energy distribution is analyzed in some order. The algorithm has been used in the surface figure evaluation of a Φ 500 mm mirror,and energy distribution in the frequency domain of the actual mirror surface has been obtained. The experimental results indicate that the evaluation of PSD is more practical when used in large aperture mirror for their manufacture and testing and for the error budget allocation in telescope system. Finally,a kind of noncorrelative sub-aperture stitching method for evaluation of reflective mirror shape based on PSD is proposed which can be used in the large aperture telescope.

Data-driven prediction of aerodynamic noise of transonic buffeting over an airfoil

The dense seismic array in Long Beach, California is located in an urban environment along the Pacific Ocean. There are a variety of noise sources influencing the ambient seismic noise field, both natural (such as the Pacific Ocean) and anthropogenic (such as traffic) in origin. To understand the temporal and spatial influences of these sources, we calculate noise power spectral densities (PSD). From spatial maps of noise PSD, we find that energy from the Pacific Ocean dominates the noise field at frequencies below 2 Hz, while energy from roads and Interstate 405 dominate the noise field at frequencies above 2 Hz. From maps of noise PSD over time, or spectrograms, we observe diurnal fluctuations in energy that are in accord with expected fluctuations in human activity. We expect the noise source distribution to be more homogeneous at higher frequencies, and this is in agreement with ambient noise cross-correlation results at frequencies spanning 0.5 Hz to 2 Hz and 2 Hz to 4 Hz.

We propose a technique of multi-channel speech enhancement based on integration of beamforming and statistical model-based speech enhancement to clearly extract the target speech, even in very noisy environments. Conventional microphone array-based techniques estimate speech and noise power spectral densities (PSDs) from the spatial cues of the sound sources; however, their estimation errors dramatically increase when there are many noise sources. We integrated clean speech models trained in advance and the noise PSDs estimated in beamspace to compose observation models and designed a precise Wiener filter. Experiments under adverse noise conditions showed that the proposed technique significantly improved the signal-to-noise ratios (SNRs) compared with the conventional microphone array processing technique.

It is today generally accepted that to carry‐out realistic transport simulation trials, field data must be acquired from vehicles travelling on the actual route(s) to be used for a particular distribution environment. This approach requires time, effort, access to data recording equipment as well as the necessary expertise to analyse the collected data. Often, this is out of reach of smaller operators who want a reasonable approximation without the time and expense. Currently, the only available option is the adoption of generic test spectra and levels that have been shown to be approximate representations of distribution environments. This paper discusses an alternative and practical method that uses some knowledge of the dynamic characteristics of various vehicle types along with an assessment of the types of roads (road roughness) to be encountered along a particular route. The method exploits the fact that the spectral characteristics (power spectral density) of road profiles are well known. The paper shows how this road surface elevation spectral function is combined with a numerical model of a particular vehicle type and speed to produce a target vibration power spectral density suitable for vibration test systems. One added benefit is that the method is capable of calculating the variations in root mean square levels of the response vibrations. This is presented as the root mean square distribution which, when coupled with the target power spectral density, can be used to synthesize realistic random vibrations that bear statistical similitude with real, field vibrations. Copyright © 2012 John Wiley & Sons, Ltd.

Scale-dependent surface roughness strongly affects critical surface properties of materials, including adhesion, wettability, and optical/thermal properties. As a particular example, tuning the ratio of the true to nominal area—a parameter that depends on the root mean square (RMS) local slope of the finest scales of topography—is an effective approach to tailor the wetting characteristics of solid surfaces. While power spectral density (PSD) analysis of atomic force microscopy (AFM) topographic images allows for directly assessing the scale-dependence of surface roughness, this approach to analyze AFM height maps requires power-law modeling and extrapolation of a PSD with inherently non-normal error distributions. Here, we use a Monte Carlo approach based on synthetic AFM images of known input power-law parameters to (1) evaluate the accuracy of fitting techniques based on the expected distribution of the PSD; (2) evaluate the error propagation from the standard errors of the fitted power-law parameters to the computed RMS slope and area ratio; and (3) evaluate the statistical power of various PSD regression techniques when differentiating surfaces. The results indicated that standard error for ordinary least squares on a log-log PSD (log OLS) underpredicts the observed variance by ∼50%. This underprediction can be eliminated by implementing a log-link gamma regression. Moreover, when propagating the standard error to derived parameters (e.g., the RMS slope), the propagated error is generally conservative relative to the observed variance and closely predicts the observed variance when extrapolating to the finest scale. This result demonstrates the possibility of accurately estimating roughness parameters that are critical for evaluating surface phenomena on the basis of fitting and extrapolating AFM data using self-affine models. Finally, our results provided evidence for the possibility of statistically differentiating surfaces with similar power-law parameters when using weighted gamma regression with a mean of 10 images, as opposed to unweighted log-OLS that requires as many as 10 000 images to differentiate images.

Bioelectrical signals such as electrocardiogram (ECG) and flow cytometry signals are often affected by both low-frequency and high frequency perturbations during data acquisition. It is necessary to remove these interferences from the acquired data so that the pertinent information needed from these signals can be obtained. Methods for detrending and denoising in ECG are well established, but in the context of impedance cytometry data, there lacks a body of literature available that provides guidance as to a robust methodology for processing the data. For the first time in the context of impedance cytometry, to the best of our knowledge, in this work we systematically studied and compared the performance of different algorithms for detrending and denoising, and developed a procedure to analyze impedance cytometry data with minimal error. This work can serve as guidance to select the optimal algorithm based on the following parameters: Standard Deviation, Correlation Coefficient, Power Spectral Density (PSD), Root Mean Square Error (RMSE) and Root Mean Square Difference (RMSD). The approaches discussed conventional filtering techniques such as: Butterworth Filtering, Chebyshev Filtering, as well as the thresholding techniques in the Discrete Wavelet Transform (DWT). The procedure of selecting the mother wavelet basis functions and the four different thresholding methods are discussed and compared. The performance of the optimized algorithm is compared with the pClamp10 commercially available cytometry analysis software resulting in 19.2% improvement in amplitude preservation, 18.4% improvement in area preservation and more than 50% improvement in the peak-search error rate.

Supercontinuum (SC) light sources are nowadays a very common way to access a large span of wavelengths, usually ranging from the near ultraviolet (around 400 nm) to the infrared (around 2.4 μm). It corresponds to a range of interest for many applications in optics for measuring transmission, dispersion, or in biophotonics for achieving fluorescencemicroscopy, optical coherence tomography... Indeed these sources are really promising because they should allow to replace the N laser sources used in these experimental setups to access to all theses wavelengths by a single broad one and a spectral filtering apparatus. Most of these results have been obtained by using powerful pump lasers of several kilo-Watts peak power, operating from the femtosecond (Titane:Saphire) to the nanosecond regimes (Nd:YAG), launched in the low dispersion region of a microstructured optical fiber. Although these fibers are short enough (typically from 1 to 10 m) to neglect the linear absorption during the propagation of the pump, the spectral power density is relatively low (few hundreds of μw/nm)which could limit the implementation of SC sources inmany application devices. This is related to a technological limitation of the pump source because it is not easy to combine strong peak power and high average power. One of the simplest solutions to increase the the spectral power density of SC sources is to replace pulsed sources with continuous-wave (CW) light sources whose available average powers are much more important. Wewill see that the dynamics of SC formation is considerably different in this case, requiring to perform intensive numerical studies to optimize the fiber parameters. Indeed, longer fibers are required (from tens to hundreds of meters) which heightens sensitivity to fiber attenuation, namely of the OHpic absorption, that strongly impacts the soliton evolution. However extremely powerful SCs have been reported with more than 10 mW/nm of spectral power density. Furthermore, these pump sources are usually all-fiber that leads to a second advantage against most of pulsed SC because CW pump can be directly spliced on the PCF. It is also important to point out that these SC sources have different temporal properties than the ones of pulsed SCs. The first experimental demonstration of CW SC have been realized at the end of the nineties with a Raman laser launched in a standard telecommunication fiber. The spectral broadening was relatively restricted (around 200 nm) because it was mainly due to Raman effect Gonzalez-Herraez et al. (2003); Persephonis et al. (1996); Prabhu et al. (2000). A breakthrough was reached a few years later when stronger pump lasers (from more than one order of magnitude) based on Ytterbium doped fibers were combined with photonic crystal fibers 4

Effect of the combustion chamber length in combustion instability of low-toxic hypergolic thruster