Finishing is a basic requirement for obtaining the required surface quality in the production of various components used in many industries. A relatively new finishing process, called magnetic ...abrasive finishing, is used for the finishing of complex shaped surfaces. This article presents the latest developments in magnetic abrasive polishing and describes the results obtained by various research scientists based on their experiments in the field of magnetic abrasive polishing.
The operability of the mechanism or machine design may be impaired due to premature destruction of products of this design. The article considers a method of machining products of a complex profile ...made of aluminum. The results of theoretical studies and experimental studies are presented. The problems of machining aluminum surfaces were identified. The author has proposed a method of machining aluminum products with a complex profile.
The issue of ensuring the technological quality of aluminum alloy products is considered. The problems that arise during the processing of aluminum alloys are described in detail. The results of ...various studies aimed at solving the described problem are presented. The author proposes to consider the method of magnetic abrasive machining as one of the promising methods for processing complex products.
Degradations of the pseudorange measurements, even when bounded, can lead to unacceptable positioning errors, especially when considering reduced alert limits—like those provided by GBAS, SBAS, and, ...in the future, ARAIM. The solution consists of the passive integrity method called “overbounding.” The overbounding approach allows all measurements in the position solution. The idea of the approach is to get a conservative bound for the integrity risk. The known methods of overbounding are applicable to the calculation of conservative bounds for a linear combination of several random variables. These methods are used to calculate the instantaneous integrity risk overbounding for vertical positioning, and they can be used for horizontal positioning only after some conservative steps. The original contribution is twofold: (a) new conservative upper bounds for the integrity risk in the horizontal plane; (b) new conservative upper bounds for the horizontal/vertical integrity risks per a given period of time.
This article addresses a sequential changepoint detection problem, assuming that the duration of change may be finite and unknown. This problem is of importance for many applications, e.g., for ...signal and image processing where signals appear and disappear at unknown points in time or space. In contrast to the conventional optimality criterion in quickest change detection that requires minimization of the expected delay to detection for a given average run length to a false alarm, we focus on a reliable maximin change detection criterion of maximizing the minimal probability of detection in a given time (or space) window for a given local maximal probability of false alarm in the prescribed window. We show that the optimal detection procedure is a modified CUSUM procedure. We then compare operating characteristics of this optimal procedure with popular in engineering the Finite Moving Average (FMA) detection algorithm and the ordinary CUSUM procedure using Monte Carlo simulations, which show that typically the later algorithms have almost the same performance as the optimal one. At the same time, the FMA procedure has a substantial advantage - independence to the intensity of the signal, which is usually unknown. Finally, the FMA algorithm is applied to detecting faint streaks of satellites in optical images.
The measurement system calibration includes the estimation of the sensor error models in order to get an optimal estimation of the measured parameters. The paper is devoted to the estimation of a ...nonlinear parametric model of the heteroscedasticity and its application to the calibration of measurement systems. The heteroscedasticity occurs in regression when the measurement noise variance is nonconstant. The maximum likelihood (ML) estimation of variance function parameters leads to a system of nonlinear equations. The iterative solution of these nonlinear equations is based entirely on a successful choice of initial conditions which is intractable in practice. To overcome this difficulty, another linear quasi-ML estimator is proposed. It is strongly consistent, asymptotically Gaussian, and only slightly less efficient than the Cramér-Rao lower bound. By using this estimator as an initial condition, an asymptotically efficient estimation is obtained by using one-step noniterative Newton method. The theoretical findings have been applied to the calibration of the EGNOS/GPS positioning algorithm in the (sub-)urban environments.
We investigated the dependence of the parameters of the segments of spiral arms of the Galaxy on the age of classical Cepheids. The catalog of Cepheids (Mel'nik et al.) was divided into two samples- ...relatively young (P > 9d) and relatively old (P < 9d) objects. The parameters of the spiral structure were determined both for two samples separately and jointly for the combination of two systems of segments traced by young and old objects. For most of the segments, their parameters for young and old objects differ significantly. Taking into account the difference between the two segment systems, we obtained the estimate R0 equal to 7.23−0.18+0.19 kpc, which in the modern Large Magellanic Cloud (LMC) calibration corresponds to the value of R0=8.08−0.20+0.21|stat.−0.36+0.38|cal. kpc. It is shown that the displacement between the segments is not reduced to the effect of differential rotation only. To interpret this displacement for objects of Perseus and Sagittarius-2 segments, we carried out a dynamic modeling of the change in the position of the segment points when moving in the smooth gravitational field of the Galaxy. At the angular velocity of rotation of the spiral pattern Ωp = 25.2 ± 0.5 km s−1 kpc−1 (Dambis et al.) the observed displacement between segments on young and old objects can be explained by the amplitude of spiral perturbations of the radial velocity of u = 10 ± 1.5 km s−1. For the constructed double system of spiral segments, it is demonstrated that the assumption of constancy of the pitch angles within each segment and the assumption that the pole of the spiral pattern is in the direction of the nominal center of the Galaxy do not contradict the data within the range of uncertainty.
Two Strategies in Transient Change Detection Egea-Roca, Daniel; Guepie, Blaise Kevin; Lopez-Salcedo, Jose A. ...
IEEE transactions on signal processing,
2022, Letnik:
70
Journal Article
Recenzirano
The paper addresses the transient change detection (TCD) problem, assuming that the duration of change is finite. The TCD criterion minimizes the worst-case probability of missed detection among all ...tests with a prescribed worst-case probability of false alarm. We study the fixed sample size (FSS) test as a solution to the TCD problem. First, the operating characteristics of the FSS test have been established for arbitrary pre- and post-change distributions. Next, a numerical method of the sample (block) size optimization has been considered for three particular log-likelihood ratio distributions, i.e., Gaussian, <inline-formula><tex-math notation="LaTeX">\chi ^{2}</tex-math></inline-formula> and exponential. Moreover, simple asymptotic equations for the optimal operating characteristics and block size have been proposed in the Gaussian case. Numerical results are provided to confirm the theoretical findings for the above-mentioned distributions. The accuracy and sharpness of the asymptotic analytical equation is analyzed in the Gaussian case. Finally, the FSS test is compared to the finite moving average (FMA) test obtained by optimizing the CUSUM-type test with respect to the TCD optimality criterion for the above-mentioned distributions. The application of the FSS and FMA tests to the radio-navigation integrity monitoring is also considered.
This paper addresses the detection of a suddenly arriving dynamic profile of a finite duration often called a transient change. In contrast to the traditional abrupt change detection, where the ...post-change period is assumed to be infinitely long, the detection of a suddenly arriving transient change should be done before it disappears. The detection of transient changes after their disappearance is considered as missed. Hence, the traditional quickest change detection criterion, minimizing the average detection delays provided a prescribed false alarm rate, is compromised. The proposed optimality criterion minimizes the worst case probability of missed detection provided that the worst case probability of false alarm during a certain period is upper bounded. A suboptimal CUSUM-type transient change detection algorithm, based on a subclass of truncated Sequential Probability Ratio Tests, is proposed. The optimization of the proposed algorithm in this subclass leads to a specially designed Finite Moving Average Test. The proposed method is analyzed theoretically and by simulation. A special attention is paid to the case of Gaussian observations with a dynamic profile.
Anomaly detection is addressed within a statistical framework. Often the statistical model is composed of two types of parameters: the informative parameters and the nuisance ones. The nuisance ...parameters are of no interest for detection but they are necessary to complete the model. In the case of unknown, non-random and non-bounded nuisance parameters, their elimination is unavoidable. Some approaches based on the assumption that the nuisance parameters belonging to a subspace interfere with the informative ones in a linear manner, use the theory of invariance to reject the nuisance. Unfortunately, this can lead to a serious degradation of the detector capacity because some anomalies are masked by nuisance parameters. Nevertheless, in many cases the physical nature of nuisance parameters is (partially) known, and this a priori knowledge permits to define lower and upper bounds for the nuisance parameters. The goal of this paper is to study the statistical performances of the constrained generalized likelihood ratio test used to detect an additive anomaly in the case of bounded nuisance parameters. An example of the integrity monitoring of GNSS train positioning illustrates the relevance of the proposed method.
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