共查询到20条相似文献,搜索用时 15 毫秒
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L. Mray O. Demny 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2001,460(2-3):472-474
A new method suitable for reducing the limit of the detection and the decision threshold is presented. It is suitable for determining the level of confidence concerning analytical results in gamma spectrometry, taking into consideration the detector-response function. 相似文献
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Reliability certification is set as a problem of Bayesian Decision Analysis. Uncertainties about the system reliability are quantified by assuming the parameters of the models describing the stochastic behavior of components as random variables. A utility function quantifies the relative value of each possible level of system reliability after having been accepted or the opportunity loss of the same level if the system has been rejected. A decision about accepting or rejecting the system can be made either on the basis of the existing prior assessment of uncertainties or after obtaining further information through testing of the components or the system at a cost. The concepts of value of perfect information, expected value of sample information and the expected net gain of sampling are specialized to the reliability of a multicomponent system to determine the optimum component testing scheme prior to deciding on the system's certification. A component importance ranking is proposed on the basis of the expected value of perfect information about the reliability of each component. The proposed approach is demonstrated on a single component system failing according to a Poisson random process and with natural conjugate prior probability density functions (pdf) for the failure rate and for a multicomponent system under general assumptions. 相似文献
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I. Verpoest E. Aernoudt A. Deruyttere M. De Bondt 《International Journal of Fatigue》1985,7(4):199-214
To test the hypothesis that fatigue cracks in drawn, pearlitic steel wire propagate from pre-existing surface defects which can be treated as cracks, the fatigue limits of five different wires have been statistically determined. The fatigue thresholds were measured using a new AC potential drop method and the initial defect depths then calculated using the equation ao=1π(ΔKth/2σe)2 and compared with observed values.
For higher strength steel wires (σu>1800 MPa) the agreement was very good; for the lower strength steel wire (σu=1469 MPa), however, the observed values were smaller than the calculated ones. The reasons for this discrepancy are discussed. A quantitative model is developed from the hypothesis and the influence of residual tensile stresses, decarburization and polishing on the fatigue limit of drawn steel wire is assessed. 相似文献
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Active Personal Dosemeters (APDs) are widely used in real-time personal dosimetry. Their performance, operational characteristics and limitations, as well as their calibration should be routinely checked to assure satisfactory operation and safe use. This study summarises the results of such type tests and calibrations performed in almost 4750 dosemeters at Ionising Radiation Calibration Laboratory (HIRCL) of Greek Atomic Energy Commission (GAEC). About 13.8% of the pencil type and 4.3% of the electronic dosemeters were found to be out of limits of acceptable performance. For the pencil type dosemeters, the mean calibration factor (CF+/-SD) for high- and low-dose categories was found to be 1.014+/-0.102 (range 0.793-1.458) and 0.995+/-0.059 (range 0.794-1.311), respectively. Of these >85% of them had reproducibility better than 90%, while <1% showed remarkable non-linearity and approximately 10% of them failed to retain the dose reading within the limits after 24 h. For the electronic dosemeters, the mean CF was 1.034+/-0.046 (range 0.967-1.238). The majority of them showed good reproducibility and linearity results while, after irradiation, the dose readings were not shifted through time. The energy response varies with the dosemeter type, reaching in one dosemeter type down to 50%. Both electronic and pencil did not showed electronic equilibrium problems. 相似文献
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Recent years have seen the increasing use of passive dosemeters that have high sensitivities and, in laboratory conditions, detection limits of <10 μSv. However, in real operational use the detection limits will be markedly higher, because a large fraction of the accrued dose will be due to natural background, and this must be subtracted in order to obtain the desired occupational dose. No matter how well known the natural background is, the measurement uncertainty on doses of a few tens of microsieverts will be large. Individual monitoring services need to recognise this and manage the expectations of their clients by providing sufficient information. 相似文献
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《Reliability Engineering》1984,7(3):181-191
In this paper, a new Bayesian approach proposed in a previous work is used to formulate point and interval estimators of shape parameter and reliable life of the two-parameter Weibull model with both parameters unknown. The Jeffreys' non-informative joint prior was also used and the corresponding estimation results were compared with those obtained by the proposed method.By means of a large Monte Carlo simulation, the proposed estimators are shown to possess good properties when a minimum of prior knowledge actually exists. 相似文献
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After cylinder notch fatigue specimens of 40 CrNiMo steel were rolled, their fatigue limit increased by 41%. The rolled specimens did not fracture, even though they had been loaded for 107 cycles under fatigue limit stress, but a non-propagating fatigue crack was generated. Thus the value of the fatigue limit depends on the fatigue threshold value ΔKth of the metal of the rolled layer. Plastic deformation increased ΔKth in these experiments. It can be inferred that ΔKth of the rolled layer increases from the occurrence of plastic deformation and microvoids on the layer. Calculation of the effect of residual stress in the crack wake on the stress intensity factor ΔK indicates that residual compression stress decreases ΔK by 21.5 MPa √M. It was calculated that rolling induced both the length of the non-propagating crack and the increase of fatigue limit. The calculated values are in accord with experiment. Analysis and calculations indicate that the non-propagating crack is generated on the rolled layer. Thus the fatigue limit is improved because rolling produces residual compression stress in the layer (which decreases the stress intensity factor), and increases ΔKth of the layer. 相似文献
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In this paper, we develop a Bayesian analysis of a threshold autoregressive model with exponential noise. An approximate Bayes
methodology, which is introduced here, and the Gibbs sampler are used to compute marginal posterior densities for the parameters
of the model, including the threshold parameter, and to compute one-step-ahead predictive density functions. The proposed
methodogy is illustrated with a simulation study and a real example. 相似文献
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The relationship between the fatigue limit stress range, Δσw, the threshold stress intensity factor, ΔKth, and microstructure of low-carbon 12CrNi3A steel has been investigated. Non-propagating microcracks were observed on the surface of smooth specimens which has been subjected to at least 5 × 106 cycles at the fatigue limit stress. The size of the cracks depended on the characteristic sizes of the microstructure of the material. Scanning electron microscopy showed that the fractographic characteristics in the near-threshold region of fatigue macrocrack growth were similar to those in the fatigue microcrack initiation region. This implies that the fatigue limit and fatigue threshold of the material have a similar physical meaning, both signifying the resistance of the material to the propagation of fatigue cracks. The relationship ΔKth = 1.12ΔσW √πα was shown to be valid, where a is a material parameter relating to microstructure, rather than to the length of a macrocrack. The results also showed that the value of a depends on the material and microstructure, and that both ΔσW and ΔKth will change if the microstructural characteristics of the material change. 相似文献
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G. N. Solopchenko 《Measurement Techniques》1996,39(10):988-992
We compare two distribution-independent methods for determining confidence intervals for the characteristics of systematic
and random error and for interquantile intervals of complete error, the methods compared are the bootstrap and L0 methods. We compare the properties of computational difficulty and reliability. Both methods have approximately the same
reliability, but the bootstrap methods requires 4–5 times as much work.
Translated from Izmiritel'naya Tekhnika, No. 10, pp. 9–12, October, 1996. 相似文献
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Cynthia R. Lovelace James J. Swain Hisham Zeinelabdin Jatinder N. D. Gupta 《Quality and Reliability Engineering International》2009,25(6):663-700
Many organizations use a single estimate of Cp and/or Cpk for process benchmarking, without considering the sampling variability of the estimators and how that impacts the probability of meeting minimum index requirements. Lower confidence limits have previously been determined for the Cp and Cpk indices under the standard assumption of independent data, which are based on the sampling distributions of the index estimators. In this paper, lower 100(1‐α)% confidence limits for Cp and Cpk were developed for autocorrelated processes. Simulation was used to generate the empirical sampling distribution of each estimator for various combinations of sample size (n), autoregressive parameter (?), true index value (Cp or Cpk), and confidence level. In addition, the minimum values of the estimators required in order to meet quality requirements with 100(1‐α)% certainty were also determined from these empirical sampling distributions. These tables may be used by practitioners to set minimum capability requirements for index estimators, rather than true values, for the autocorrelated case. The implications of these results for practitioners will be discussed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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The fundamental limits for detection and characterization of fluorescent (phosphorescent) inhomogeneities embedded in tissuelike highly scattering turbid media are investigated. The absorption and fluorescence contrast introduced by exogenous fluorophores are also compared. Both analyses are based on practical signal-to-noise ratio considerations. For an object with fivefold fluorophore concentration and lifetime contrast with respect to the background tissue, we find the smallest detectable fluorescent object at 3-cm depth in tissuelike turbid media to be ~0.25 cm in radius, whereas the smallest characterizable object size is ~0.75 cm in radius, given a model with 1% amplitude and 0.5 degrees phase noise. We also find that, for fluorescence extinction coefficients epsilon = 0.5 x 10(5) cm(-1) M(-1), the fluorescence measurement mode is superior to the absorption mode for detecting an inhomogeneity. The optimal choice of modulation frequency for the frequency-domain fluorescence measurements is also discussed. 相似文献
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Zero-current ion fluxes through polymer membranes of ion-selective electrodes (ISEs) may lead to biased endpoints of potentiometric titrations. The bias is eliminated, and the sensitivity of the end-point detection is improved through reducing transmembrane ion fluxes by an appropriate choice of the inner solution. Surprisingly, ISE membranes that have a significant primary ion flux toward the inner solution show much larger sensitivities than expected by titration theory; however, depending on the experimental conditions, their application may bias the endpoint. With the optimal systems, endpoint detection is now possible with total sample concentrations below 10(-6) M, as demonstrated by the titration of EDTA with a Pb2+ solution. 相似文献
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Galleani L 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2011,58(8):1550-1558
The dynamic Allan variance (DAVAR) is a surface which describes the stability of a high-precision clock with respect to time. When the DAVAR is evaluated from experimental data, its surface shows random fluctuations caused by the estimation process. It is fundamental to assign a statistical significance to these fluctuations, so that they can be differentiated from the variations of the surface caused by clock anomalies. First, we develop confidence surfaces to assign a statistical significance to the random fluctuations of the DAVAR estimator. Then, we introduce detection surfaces to reveal the variations of the surface caused by clock anomalies. We validate the obtained results through numerical simulations. 相似文献
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Moving object detection is a challenging task in many computer vision applications. In this paper, we propose a robust background modelling method for this task. First, the background is updated by an adaptive strategy based on Centre-symmetric Local Binary Patterns. Then, background subtraction is used for detecting moving object. Although the traditional background subtraction technique uses the difference value between the current pixel and its corresponding background pixel for objection detection, our method utilises the confidence factor to determine whether the current pixel is a background or foreground pixel. The confidence factor of the current pixel is calculated in term of the difference values of its neighbourhood pixels. In the experiments, the proposed algorithm is tested on several challenging datasets such as PETS 2009, BMC 2012 and SABS. The experimental results demonstrate that our algorithm can robustly detect moving object under various scenes. 相似文献