Linear consecutive-k-out-of-n: F system reliability with common-mode forced outages

This paper presents a model of consecutive-k-out-of-n: F system subject to common-mode forced outages, whose interarrival times are independent and exponentially distributed. The objective is to analytically derive the mean operating time between failures for a non-repairable component system. The average system failure time and the system availability are also considered. Then, the model is extended to a system with repairable components and unrestricted repair, in which service times are exponentially distributed.     

Energy of mixing of Al x In y Ga1 ? x ? y N compounds

The energies of mixing of quaternary compounds of the Al _x In _y Ga_{1 − x − y} N system with crystal structures of the zinc-blende type have been calculated using direct numerical simulations within the framework of the valence forced field model. An analytical approximation of the results of numerical calculations is proposed and the parameters of configurational dispersion of the mixing energy are refined, which are necessary for determining the thermodynamic functions of the quaternary compounds under consideration.     

Availability and reliability of k-out-of-(M+N):G warm standby systems

Redundancy or standby is a technique that has been widely applied to improving system reliability and availability in system design. In most cases, components in standby system are assumed to be statistically identical and independent. However, in many practical applications, not all components in standby can be treated as identical because they have different failure and repair rates. In this paper, one kind of such systems with two categories of components is studied, which is named k-out-of-(M+N):G warm standby system. In the system, one category of the components is of type 1 and the other type 2. There are M type 1 components and N type 2 components. Components of type 1 have a lower failure rate and are preferably repaired if there is one failed. There are r repair facilities available. By using Markov model, the system state transition process can be clearly illustrated, and furthermore, the solutions of system availability and reliability are obtained based on this. An example representing a power-generator and transmission system is given to illustrate the solutions of the system availability and reliability.     

Profit analysis of a k-out-of-n trichotomous system

This paper studies the profit function of a mathematical model of a k-out-of-n trichotomous system. Failure times are assumed to follow negative exponential distributions with different parameters whereas the repair time distributions are taken to be general. The analysis is carried out by using the supplementary variable technique.     

Optimal design of multi-state weighted k-out-of-n systems based on component design

This paper presents a study on design optimization of multi-state weighted k-out-of-n systems. The studied system reliability model is more general than the traditional k-out-of-n system model. The system and its components are capable of assuming a whole range of performance levels, varying from perfect functioning to complete failure. A utility value corresponding to each state is used to indicate the corresponding performance level. A widely studied reliability optimization problem is the “component selection problem”, which involves selection of components with known reliability and cost characteristics. Less adequately addressed has been the problem of determining system cost and utility based on the relationships between component reliability, cost and utility. This paper addresses this topic. All the optimization problems dealt with in this paper can be categorized as either minimizing the expected total system cost subject to system reliability requirements, or maximizing system reliability subject to total system cost limitation. The resulting optimization problems are too complicated to be solved by traditional optimization approaches; therefore, genetic algorithm (GA) is used to solve them. Our results show that GA is a powerful tool for solving these kinds of problems.     

Cost—Optimal replacement policy (N, n) for a parallel system with common cause failure

The purpose of this article is to present an improved replacement model for a parallel system of N identical units, by taking common failure and repair and maintenance costs into consideration, and to develop the methods for obtaining the (1) optimal redundant units N^* for a fixed n, (2) optimal number of repairs n^* for a fixed N, and (3) optimal pair (N^*, n^*) simultaneously, respectively, under the condition that the system is allowed to undergo at most a prefixed number of repairs before being replaced. The results are illustrated by numerical examples.     

Reliability analysis of K-out-of-N: G systems with dependent failures and imperfect coverage

This paper presents a Markov model for reliability analysis of K-out-of-N: G systems subject to dependent failures with imperfect coverage. Closed form solutions of the probabilities are used to obtain the reliability and the mean time to failure (MTTF). A numerical example is provided to illustrate the results.     

Ferroelectric transitions in valence compensated Ba1? x La x Ti1? x Cr x O3 ceramics

An attempt has been made to investigate the solid solubility limit between barium titanate, BaTiO₃ and lanthanum chromite, LaCrO₃. Compositions with x ≤ 0.15 have shown solid solution formation in the system Ba_1−x La _x Ti_1−x Cr _x O₃. Compositions with 0.01 and 0.05 are found to have a tetragonal structure, whereas those with x = 0.10 and 0.15 are found to have a cubic structure at room temperature. Dielectric measurements have been carried out at different frequencies in the temperature range 100–550 K. Plots of ε_r versus temperature for composition with x = 0.01 show dielectric anomalies at 376 K (T _C-T) and 275 (T _T-O) where T _C-T and T _T-O denote the temperature for cubic to tetragonal and tetragonal to orthorhombic transition. Dielectric anomaly corresponding to the ferroelectric to paraelectric transition has been found to shift to lower temperatures with increasing concentration of lanthanum and chromium. For compositions with x ≤ 0.05, T _C has been found to be frequency independent while for x = 0.10 and 0.15, T _C has been found to be frequency dependent in a manner similar to relaxor ferroelectrics.     

Minimal cut sets of s–t networks with k-out-of-n nodes

In this paper, we extend traditional directed s–t network by letting nodes have k-out-of-n property: To generate output flows, a node must receive at least k flows from its n input links, where k is an integer assigned for the node and its value can be any number from 1 to n. To evaluate the system reliability, minimal cut sets for the extended network are defined for nodes. Under this definition, an extended network and its sink node have the same minimal cut sets. A new algorithm is designed to generate minimal cut sets for all nodes, starting with the source node and ending with the sink node. With different initializations, the algorithm can be applied for extended s–t networks with or without node failures.     

Optimization problems in k-out-of-n systems with minimal repair

The k-out-of-n system is a system with n independent components such that the system operates if and only if at least k of these n components operate succesfully. Such a system is an important complex system and is used for mass transit, safety systems and computer systems. This paper considers what is the most economical k-out-of-n system with minimal repair. We solve two problems to minimise the long term expected cost rate per unit time; (i) the optimal number of elements, and (ii) the optimal replacement time before system failure. Finally, a numerical example is given.     

A Global/Local approach to lengthwise cracked beams: dynamic analysis

A simple model is developed for the calculation of dynamic stress intensity factors for lengthwise cracked beams subjected to impact or transient loading. The model is based on a Global/Local approach that separates the Global structural dynamics from the Local crack tip zone dominated by singular stresses. The Global model is that of connected waveguides while the Local model is based on a novel application of the J-integral that converts dynamic structural resultants directly into strain energy release rate. The accuracy of this approach is assessed by comparing it to a fully two-dimensional finite element analysis in which the modified crack closure integral is used to calculate the dynamic strain energy release rate. Both mode I and mode II examples are given, and situations with multiple wave reflections are emphasized.     

Calculation of J-integrals using experimental and numerical data: Influences of ratio (a/W) and the 3D structure

Contrary to J-integral values calculated from the 2D numerical model, calculated J-integrals [1] from 3D specimen in the numerical and experimental cases are not very close with J-integral used in the literature and two distinct points are present. The first one is according to (a/W) and can be reduced, when this ratio is inferior to 0.2. The second is a structure problem and can be explain by local three-dimensional effects surrounding the crack tip. Two applications using polymer materials for large and minor deformations are experimented. A grid method is used to experimentally determine the in-plane displacement fields around a crack tip in a Single-Edge-Notch (SEN) tensile polyurethane and PMMA specimens. This indirect method composed of experimental in-plane displacement fields and of two theoretical formulations, allows the experimental J-integral to be determined and the results obtained by the numerical simulations to be confirmed.     

Application and analysis for a consecutive-k-out-of-n:G structure

A consecutive-k-out-of-n:G system consists of an ordered sequence of n components such that the system works whenever at least k consecutive components in the system function. This study elaborates on the concept of consecutive-k-out-of-n:G systems and demonstrates an application of the basic theory of consecutive-k-out-of-n:G systems reliability to a railroad operation. The results can help in scheduling the incoming trains to utilize the station resources better.     

Configuration determination for k-out-of-n partially redundant systems

The k-out-of-n configuration is a widely adopted structure for partially redundant safety systems. This configuration ensures a high level of reliability and safety with limited financial and space resources. It also facilitates on-line Test and Maintenance (T&M) without having to shut the system down. One question a decision maker needs to answer when adopting k-out-of-n systems is: what is the best configuration for the application, i.e. how many channels in total need to be utilized and among these channels, how many channels need to function simultaneously in order for the system to function. There are various factors to consider in order to make this decision. This paper looks at this problem from a reliability engineers point of view. A quantitative analysis is performed for both unavailability and probability of spurious operation due to independent failure. In particular, the relative gain and/or loss of these quantities that occurs due to changing from one configuration to another are compared through rigorous mathematical analysis. The results provide important information that can be used when choosing system configurations to meet regulatory requirements and financial constraints. The two different configurations for shutdown systems in Nuclear Power Plants, the 2-out-of-3 system and the 2-out-of-4 system, are utilized as an example to illustrate the theoretical results.     

Exact equation and an algorithm for reliability evaluation of K-out-of-N:G system

An expression for reliability of K-out-of-N:G system is proposed. An algorithm for computing reliability of K-out-of-N system is given. It is an easy to implement, fast and memory efficient algorithm and helps to improve the computational efficiency considerably.     

Mixed conducting oxides Y x Zr1? x ? y Ti y O2? x /2 (YZT) and corresponding Ni/YZT cermets as anode materials in an SOFC

The physical properties of mixed-conducting oxides in the ternary system Y₂O₃–ZrO₂–TiO₂ with the general formula Y _x Zr_1−x−y Ti _y O_2−x/2 (YZT, where 0.133 < x < 0.25 and 0 < y < 0.15) are presented and evaluated in terms of an application as anode materials in solid oxide fuel cells (SOFCs). The total electrical conductivity of the ceramics with cubic fluorite structure in air mainly depends on the Ti content and decreases at 900 °C by about one order of magnitude from y = 0 to y = 0.15. Comparing the conductivity of contributions at 900 °C in Ar/4% H₂ the highest contributions of electronic conductivity were obtained for y = 0.15. For the Ni/YZT cermets, the enhanced adherence at the metal/ceramic interface, compared to Ni/8YSZ (8 mol% yttria stabilised zirconia), results in a better long-term stability in terms of electrical conductivity and microstructure after 1,000 h of annealing at 1,000 °C in reducing atmosphere. The electrochemical performance, tested in fuel cells with Ni/8YSZ, Ni/Y_0.20Zr_0.75Ti_0.05O_1.9 and Ni/Y_0.20Zr_0.70Ti_0.10O_1.9 anodes, decreased for Ni/Y_0.20Zr_0.70Ti_0.10O_1.9 under steam reforming conditions, most likely due to the reduced ionic conductivity of this specific YZT ceramic.     

s -Wave Symmetry Along the c -Axis and s + d In-plane Superconductivity in Bulk YBa2Cu4O8

To clarify the order parameter symmetry of cuprates, the magnetic penetration depth λ was measured along the crystallographic directions a, b, and c in single crystals of YBa₂Cu₄O₈ via muon spin rotation. This method is direct, bulk sensitive, and unambiguous. The temperature dependences of λ _a ⁻² and λ _b ⁻² exhibit an inflection point at low temperatures as is typical for two-gap superconductivity (TGS) with s+d-wave character in the planes. Perpendicular to the planes a pure s-wave gap is observed thereby highlighting the important role of c-axis effects. We conclude that these are generic and universal features in the bulk of cuprates.     

epoline electronic Online Filing (eOLF)

An office-wide project set up in 1999, epoline^® has been designed to improve the efficiency of the EPO and the range of services it offers to its customers, the intellectual property community. This article, the second in a special series on epoline^®, presents the epoline^® electronic Online Filing service, enabling applicants and attorneys to submit patent applications and documents to the EPO electronically. The history of the system is outlined, as well as the way it works and its advantages. In conclusion, the scheduled enhancements to the system are described.     

Study on dielectric ageing behaviour of antiferroelectric (Pb1? x Ba x )ZrO3 (0≤ x ≤0.10) ceramics

Ageing phenomena on dielectric constant and dielectric losses of pure and compositionally modified PbZrO₃ by Ba²⁺ ions are presented both in antiferrolelectric and ferroelectric phases. It is shown that the room temperature stable antiferroelectric phase of the samples gets inhibited on cooling after a heating cycle. The phase recovers from metastable ferroelectric phase on long-term ageing at room temperature. The antiferroelectric (Pb_1−x Ba _x )ZrO₃ system having higher internal stress has a great driving force for higher ageing rate. It is also shown that the ageing process is more pronounced if the sample is thermally activated and the room temperature ageing leads to linear dependence of dielectric constant and dielectric losses upon logarithmic of time. It is proposed that the decrease in dielectric constant with time is due to the motion of domain walls coming from the domain nucleation as well as the stress relaxation.     

Crystal structure and IR spectra of Sr1? x La x Fe1? x Cd x O3?δ

Sr_1−x La _x Fe_1−x Cd _x O_3−δ solid solutions with x = 0.1 and 0.5 prepared at 1270 K are shown to have a cubic perovskite structure and the SrLaFeO₄ structure, respectively. In the range x = 0.25-0.4, the samples consist of a perovskite phase and SrLaFeO₄. As x increases from 0.2 to 0.5, the content of the perovskite phase gradually decreases, and that of the phase isostructural with SrLaFeO₄ increases. The IR spectra of the samples with x = 0.3−0.5 are similar to the spectrum of SrLaFeO₄. The Sr_2/3La_1/3FeO_3−δ ferrite has the perovskite structure, rather than the Sr₂LaFe₃O₈ structure. The synthesis of this ferrite proceeds through the formation of SrFeO_3−δ and LaFeO₃, followed by the mutual dissolution of these orthoferrites. Original Russian Text ? S.V. Smolenchuk, L.A. Bashkirov, M.V. Bushinskii, S.S. Dorofeichik, 2007, published in Neorganischeskie Materialy, 2007, Vol. 43, No. 5, pp. 621–625.