A new method to measure the average plasma velocity in a Hall-effect thruster is presented. The method is brought forward in virtue of the characteristics of low frequency oscillation induced by the propellant ionizat...
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A new method to measure the average plasma velocity in a Hall-effect thruster is presented. The method is brought forward in virtue of the characteristics of low frequency oscillation induced by the propellant ionization in the channel and the oriented movement feature of the plasma density out of the channel. The method, equivalent to the correlation method generally used in the signal processing field, provides a solution to the problem of specific impulse measurement on a timescale of hundreds of microseconds and makes the time evolution of average plasma velocity clear. The comparison between the measured value and the calibrated value shows that the relative error is about 3%.
In a test of the weak equivalence principle （WEP） with a rotating torsion pendulum, it is important to estimate the amplitude of the modulation signal with high precision. We use a torsional filter to remove the fre...
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In a test of the weak equivalence principle （WEP） with a rotating torsion pendulum, it is important to estimate the amplitude of the modulation signal with high precision. We use a torsional filter to remove the free oscillation signal and employ the correlation method to estimate the amplitude of the modulation signal. The data analysis of an experiment shows that the uncertainties of amplitude components of the modulation signal obtained by the correlation method are in agreement with those due to white noise. The power spectral density of the modulation signal obtained by the correlation method is about one order higher than the thermal noise limit. It indicates that the correlation method is an effective way to estimate the amplitude of the modulation signal and it is instructive to conduct a high-accuracy WEP test.
Enhanced modified moving average method (EMMAM) and correlation method (CM) for microvolt TWA identification are compared by aid of simulated ECG tracings (cases of absence of TWA and presence of stationary or time-va...
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Enhanced modified moving average method (EMMAM) and correlation method (CM) for microvolt TWA identification are compared by aid of simulated ECG tracings (cases of absence of TWA and presence of stationary or time-varying TWA) and ECG recordings from healthy subjects (H-group) and patients who survived an acute myocardial infarction (AMI-group). The two competing methods were found to be equivalent when analyzing clean ECGs affected by stationary TWA. Non-stationary TWA is correctly tracked by the CM, whereas it is identified as stationary by the EMMAM. Moreover, the EMMAM suffers for its tendency to identify as TWA noise and other kinds of repolarization variability. Such limitation is most likely the cause of its false-positive TWA production. Finally, only the CM incorporates a local threshold criterion in the TWA detection algorithm which allows better discrimination between H and AMI groups, who are well known to be at increased risk to develop TWA. (C) 2010 Elsevier Ireland Ltd. All rights reserved.
The infrared absorption spectra of the saturated vapor of isopropyl alcohol isomers and mixtures of these isomers were investigated. A method was developed for quantitative determination of the isomeric composition of...
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The infrared absorption spectra of the saturated vapor of isopropyl alcohol isomers and mixtures of these isomers were investigated. A method was developed for quantitative determination of the isomeric composition of liquid mixtures of isopropyl alcohol isomers from the absorption spectra of their vapor in the region of 1.3-1.5 mu m. Multiple linear regression was used for analysis of the experimental data. Great attention was paid to purification of the spectra from the interfering effect of atmospheric water vapor, for which a correlation method was used. The developed method of correlation purification of the spectrum from the effect of the spectra of interfering substances can be of interest not only during analysis of the composition of alcohol mixtures but also in other cases where the experimental conditions do not make it possible to free the optical channel from impurities of other substances.
The correlation method is used to determine the period of a torsion pendulum. Calculation shows that this method cannot only suppress the disturbance of white noise, but it is also insensitive to drift and damping of ...
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The correlation method is used to determine the period of a torsion pendulum. Calculation shows that this method cannot only suppress the disturbance of white noise, but it is also insensitive to drift and damping of the torsion pendulum. An estimate of the frequency based on this method is an approximative minimum variance unbiased estimator. (C) 2004 American Institute of Physics.
To meet the demand for long-distance and highly accurate detection in tunnel construction, a vibroseis source has been introduced into tunnel forward prospecting. However, serious noise in tunnels reduces the resoluti...
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To meet the demand for long-distance and highly accurate detection in tunnel construction, a vibroseis source has been introduced into tunnel forward prospecting. However, serious noise in tunnels reduces the resolution of vibroseis signals, and small-scale structure recognition in tunnels requires higher signal resolution. Thus, we develop a time-frequency domain correlation method based on the synchrosqueezed wavelet transform for tunnel vibroseis data. Time-frequency domain correlation may capture more information than a single time or frequency domain correlation method, and its effectiveness depends on the time-frequency transformation method. The synchrosqueezed wavelet transform allows us to obtain high-resolution time-frequency spectra and thus helps to extract high-resolution effective signals. The advantages and disadvantages of different correlation methods are highlighted using numerical examples, in which the high resolution and strong robustness of the time-frequency domain correlation method based on the synchrosqueezed wavelet transform are demonstrated. A detailed field case study in an iron mine tunnel further demonstrates the reliability of the time-frequency domain correlation method based on the synchrosqueezed wavelet transform for practical data.
s In the displacement measurement using digital speckle correlation method, significant measuring error due to the multi-peak nature of the correlation coefficient function is a critical issue as sometimes the seconda...
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s In the displacement measurement using digital speckle correlation method, significant measuring error due to the multi-peak nature of the correlation coefficient function is a critical issue as sometimes the secondary peak can be wrongly determined as the maximum instead of the highest peak. In the multi-frequency harmonic wave correlation method (MHCM) as proposed in this work, for speckle patterns before and after the displacement, correlation calculations were performed on corresponding sets of data matrices assembled by amplitudes/intensities obtained from harmonic waves with different frequencies. The calculated maximum correlation coefficients were compared with each other to locate the maximum in order to measure the displacement. Both ultrasonic speckle MHCM and laser speckle MHCM were applied to the displacement measurement respectively. Measured results indicated that MHCM effectively helps to ensure the correct determination of the maximum correlation coefficient, to avoid random errors caused by other factors and improves the measurement accuracy in the meanwhile. (C) 2016 Elsevier Ltd. All rights reserved.
The efficient identification of the unbalanced responses in the inner and outer rotors from the beat vibration is the key step in the dynamic balancing of a dual-rotor system with a slight rotating speed difference. T...
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The efficient identification of the unbalanced responses in the inner and outer rotors from the beat vibration is the key step in the dynamic balancing of a dual-rotor system with a slight rotating speed difference. This paper proposes a non-whole beat correlation method to identify the unbalance responses whose integral time is shorter than the whole beat correlation method. The principle, algorithm and parameter selection of the proposed method is emphatically demonstrated in this paper. From the numerical simulation and balancing experiment conducted on horizontal decanter centrifuge, conclusions can be drawn that the proposed approach is feasible and practicable. This method makes important sense in developing the field balancing equipment based on portable Single Chip Microcomputer (SCMC) with low expense. (C) 2012 Elsevier Ltd. All rights reserved.
With the rapid development of additive manufacturing (AM), materials used in AM increase year by year, generating a large amount of discarded waste materials. Some of these waste materials are hazardous to the environ...
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With the rapid development of additive manufacturing (AM), materials used in AM increase year by year, generating a large amount of discarded waste materials. Some of these waste materials are hazardous to the environment and the human body. Facing this problem, it is crucial to reduce material usage in AM technologies by recycling. Up until now, extensive attentions have been attracted on material reuse/recycling in AM tech-nologies, however, comparisons of material reuse degree (MRD) are still lacking. Aiming at addressing MRD issues, we developed an improved resolution coefficient grey correlation (IRCGC) method to evaluate MRD in four representative AM technologies, including fused deposition modeling (FDM), stereolithography (SLA), se-lective laser sintering (SLS), and laminated object manufacturing (LOM). In such an IRCGC method, a grey correlation optimization model was established and a combined analytic hierarchy process and entropy weight method was employed to obtain weights. Afterwards, MRD in 4 AM technologies were assessed by an evaluation system and then were clustered using data analysis software. Experimental results show that among the 4 AM technologies, the FDM technology demonstrated the highest MRD, whereas, the SLA technology exhibited the lowest MRD. The SLS and the LOM AM technologies are classified into the good level.
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