Assessing device reliability based on scheduled discrete degradation measurements

Degradation measurements are increasingly important in reliability studies because few failures are observed during the short time of many experiments. In this article, we assess device reliability from discrete degradation processes under scheduled inspections. In some particular situations, since the degradation quantities of the device characteristic are only observed specifically at the scheduled time points, the exact occurrence time and the corresponding damage amount of each degradation event are not recorded. For this sort of situation, there are plenty of examples such as the amount of shock damages of the database in a computer system, the amount of fatigues of the shock absorber for a car, and the amount of growth of a metal crack on an aircraft.     

Designing an optimal water quality monitoring network for river systems using constrained discrete optimization via simulation

The problem of designing a water quality monitoring network for river systems is to find the optimal location of a finite number of monitoring devices that minimizes the expected detection time of a contaminant spill event while guaranteeing good detection reliability. When uncertainties in spill and rain events are considered, both the expected detection time and detection reliability need to be estimated by stochastic simulation. This problem is formulated as a stochastic discrete optimization via simulation (OvS) problem on the expected detection time with a stochastic constraint on detection reliability; and it is solved with an OvS algorithm combined with a recently proposed method called penalty function with memory (PFM). The performance of the algorithm is tested on the Altamaha River and compared with that of a genetic algorithm due to Telci, Nam, Guan and Aral (2009) Telci, I. T., K. Nam, J. Guan, and M.M. Aral, 2009. “Optimal Water Quality Monitoring Network Design for River Systems.” Journal of Environmental Management, 90 (3–4): 2987–2998. doi: 10.1016/j.jenvman.2009.04.011[Crossref], [PubMed], [Web of Science ®] , [Google Scholar].     

Phonon emission from a discrete sine-Gordon breather

Phonon emission from a large-amplitude discrete sine-Gordon breather was studied numerically for a small degree of discreteness. In contrast to the case of highly discrete system investigated by Boesch and Peyrard (Phys. Rev. B 43 (1991) 8491), it was found that the resonance between the breather's oscillation and the phonons of the lower phonon band edge (κ=0) takes place for a small degree of discreteness.     

Sampling and electrophoretic analysis of segmented flow streams using virtual walls in a microfluidic device

A method for sampling and electrophoretic analysis of aqueous plugs segmented in a stream of immiscible oil is described. In the method, an aqueous buffer and oil stream flow parallel to each other to form a stable virtual wall in a microfabricated K-shaped fluidic element. As aqueous sample plugs in the oil stream make contact with the virtual wall, coalescence occurs and sample is electrokinetically transferred to the aqueous stream. Using this virtual wall, two methods of injection for channel electrophoresis were developed. In the first, discrete sample zones flow past the inlet of an electrophoresis channel and a portion is injected by electroosmotic flow, termed the "discrete injector". With this approach at least 800 plugs could be injected without interruption from a continuous segmented stream with 5.1% RSD in peak area. This method generated up to 1,050 theoretical plates, although analysis of the injector suggested that improvements may be possible. In a second method, aqueous plugs are sampled in a way that allows them to form a continuous stream that is directed to a microfluidic cross-style injector, termed the "desegmenting injector". This method does not analyze each individual plug but instead allows periodic sampling of a high-frequency stream of plugs. Using this system at least 1000 injections could be performed sequentially with 5.8% RSD in peak area and 53,500 theoretical plates. This method was demonstrated to be useful for monitoring concentration changes from a sampling device with 10 s temporal resolution. Aqueous plugs in segmented flows have been applied to many different chemical manipulations including synthesis, assays, sampling processing and sampling. Nearly all such studies have used optical methods to analyze plug contents. This method offers a new way to analyze such samples and should enable new applications of segmented flow systems.     

A Double Sampling Scheme for Estimating from Misclassified Multinomial Data with Applications to Sampling Inspection

In some situations, it is desired to estimate multinomial proportions from data which have been misclassified. One such area is the sampling inspection area of quality control. In this paper, it is assumed that two measuring devices are available to classify units into one of r mutually exclusive categories. The first device is an expensive procedure which classifies units correctly; the second device is a cheaper procedure which tends to misclassify units. In order to estimate the proportions p_i (i = 1,2, …, r) a double sampling scheme is presented. At the first stage, a sample of N units is taken and the fallible classifications are obtained; at the second stage a subsample of n units is drawn from the main sample and the true classifications are obtained. The maximum likelihood estimates of the p_i are derived along with their asymptotic variances. Optimum values of n and N which minimize the measurement costs for a fixed precision of estimation and which minimize the precision for fixed cost are derived. The procedures of estimation and allocation of sample size are illustrated by an example in quality control.     

Optical double-image cryptography based on diffractive imaging with a laterally-translated phase grating

In this paper, we propose a method using structured-illumination-based diffractive imaging with a laterally-translated phase grating for optical double-image cryptography. An optical cryptosystem is designed, and multiple random phase-only masks are placed in the optical path. When a phase grating is laterally translated just before the plaintexts, several diffraction intensity patterns (i.e., ciphertexts) can be correspondingly obtained. During image decryption, an iterative retrieval algorithm is developed to extract plaintexts from the ciphertexts. In addition, security and advantages of the proposed method are analyzed. Feasibility and effectiveness of the proposed method are demonstrated by numerical simulation results.     

The discrete null space method for the energy consistent integration of constrained mechanical systems. Part II: multibody dynamics

In the present work, rigid bodies and multibody systems are regarded as constrained mechanical systems at the outset. The constraints may be divided into two classes: (i) internal constraints which are intimately connected with the assumption of rigidity of the bodies, and (ii) external constraints related to the presence of joints in a multibody framework. Concerning external constraints lower kinematic pairs such as revolute and prismatic pairs are treated in detail. Both internal and external constraints are dealt with on an equal footing. The present approach thus circumvents the use of rotational variables throughout the whole time discretization. After the discretization has been completed a size‐reduction of the discrete system is performed by eliminating the constraint forces. In the wake of the size‐reduction potential conditioning problems are eliminated. The newly proposed methodology facilitates the design of energy–momentum methods for multibody dynamics. The numerical examples deal with a gyro top, cylindrical and planar pairs and a six‐body linkage. Copyright © 2006 John Wiley & Sons, Ltd.     

Strategy for repetitive pinched injections on a microfluidic device

A microfluidic valve was fabricated with a cross intersection and two tee intersections in close proximity and evaluated for repetitive pinched injections. Electrokinetic forces were used to mobilize the sample and control diffusive transport at a cross intersection to produce sample plugs of short axial extent in an analysis channel similar to the standard pinched valve. The addition of a tee intersection in the sample channel maintained the sample close to the injection valve under "pullback"conditions allowing more rapid loading into the cross intersection. A second tee intersection allowed unidirectional transport in the analysis channel enabling loading of subsequent injections during an analysis. The two tee intersections were each located 80 microm from the cross intersection. Injection frequencies of 1, 2.5, 5, and 10 Hz were tested with a duty cycle of 0.5 for sample loading and dispensing. With 1 kV applied to the microchip during dispensing, the relative standard deviation of the peak areas for 15 injections was 1.6%. The peak width (4sigma) for the repetitive injections increased from 71 to 96 microm compared to a standard pinched injection due to the presence of the tee intersection in the analysis channel.     

数据采集的自适应采样策略研究

本文介绍自适应采样策略的实现方案,提出了数据压缩来解决采样频率与有限存储容量之间的矛盾,并提出LZW算法是综合性能较好的一种数据压缩算法.     

Stress trajectories element method for stress determination from discrete data on principal directions

This paper presents a Trefftz-element numerical method for the reconstruction of stress trajectories and the determination of full stress tensors in two-dimensional elastic bodies from discrete data on principal directions. The conventional techniques cannot be used because neither displacements nor tractions are specified on the boundary. The proposed approach involves the subdivision of the domain into smaller subdomains and the introduction of the Cauchy integrals with unknown densities on element boundaries in order to approximate complex potentials within the elements. For polynomial approximations of the densities, this leads to piecewise polynomial approximations for the complex potentials within the entire domain and, therefore, all elasticity equations are automatically satisfied as in the Trefftz method. Continuity of the complex potentials is forced at the collocation points, which forms the first group of equations. The second group is formed by satisfying the data on principal directions known in some locations. All these equations are homogeneous; therefore, it is assumed that the average value of the maximum shear stresses at data points is unity. This guarantees the existence of a non-trivial solution of the system; however it addresses the non-uniqueness of the reconstruction of the full stress tensor. The technique is validated by reconstructing stress trajectories and determining maximum shear stresses from synthetic and photoelasticity data. It has been applied to reconstruction of tectonic stresses in the Australian region and the results were compared with previous approaches.     

Variance Reduction Techniques for Monte Carlo Sampling from Student Distributions

A Monte Carlo design is presented for estimating the variance and cumulative distribution function of translation and scale invariant statistics based on independent Student random variables. One obvious application is studying estimates of the location parameter from a symmetric, possibly long-tailed distribution. The method itself amounts to suppressing some of the variability in the sampled objects by integrating these objects over appropriate regions of the underlying probability space. Indications are that, in cases of interest, the variability is thereby considerably reduced, as is illustrated in an application concerning trimmed and Winsorieed means.