Single-unit System Research Articles

Mean residual life of coherent systems consisting of multiple types of dependent components

AbstractMean residual life is a useful dynamic characteristic to study reliability of a system. It has been widely considered in the literature not only for single unit systems but also for coherent systems. This article is concerned with the study of mean residual life for a coherent system that consists of multiple types of dependent components. In particular, the survival signature based generalized mixture representation is obtained for the survival function of a coherent system and it is used to evaluate the mean residual life function. Furthermore, two mean residual life functions under different conditional events on components’ lifetimes are also defined and studied.

Stochastic analysis of a single-unit system with repairman having multiple vacations

Stochastic analysis of a single-unit system with repairman having multiple vacations

Stochastic Behaviour of Single Unit System with Preventive Maintenance subject to Random Appearance of Server

International Journal of Computer Sciences and Engineering (A UGC Approved and indexed with DOI, ICI and Approved, DPI Digital Library) is one of the leading and growing open access, peer-reviewed, monthly, and scientific research journal for scientists, engineers, research scholars, and academicians, which gains a foothold in Asia and opens to the world, aims to publish original, theoretical and practical advances in Computer Science,Information Technology, Engineering (Software, Mechanical, Civil, Electronics & Electrical), and all interdisciplinary streams of Computing Sciences. It intends to disseminate original, scientific, theoretical or applied research in the field of Computer Sciences and allied fields. It provides a platform for publishing results and research with a strong empirical component. It aims to bridge the significant gap between research and practice by promoting the publication of original, novel, industry-relevant research.

Optimal inspection and replacement strategy for systems subject to two types of failures with adjustable inspection intervals

The inspection activities are often carried out to detect possible indication of failures in plant systems. This paper considers a single unit system subject to two types of failures, where one failure mode is the traditional 0-1 logic failure and the other failure mode is described by a two-stage failure process. Adjustable inspections are used to detect the defective stage of the latter. We assume that the inspection duration gets shorter and shorter with a constant ratio. At the same time, preventive replacement is used to avoid the possible failure due to the former failure mode. The renewal process of this system is analyzed and the expected long-run cost per unit time (ELRCUT) is derived. The optimal inspection period and the preventive replacement interval to minimize ELRCUT are studied. At last, a numerical example is presented to illustrate the proposed model.

A predictive maintenance system for hybrid degradation processes

PurposeThe purpose of this paper is to propose a predictive maintenance (PdM) system for hybrid degradation processes with continuous degradation and sudden damage to improve maintenance effectiveness.Design/methodology/approachThe PdM system updates the degradation model using partial condition monitoring information based on degradation type judgment. In addition, an extended multi-step-ahead updating stopping condition is adopted for performance enhancement of the PdM system.FindingsAn extensive numerical investigation compares the performance of the PdM system with the corresponding preventive maintenance (PM) policy. By carefully choosing the updating stopping condition, the PdM policy performs better than the corresponding PM policy.Research limitations/implicationsThe proposed PdM system is applicable to single-unit systems. And the continuous degradation process should be well modeled by the stochastic linear degradation model (Gebraeel et al., 2009).Originality/valueIn literature, there are abundant studies on PdM policies for continuous degradation processes. However, research on hybrid degradation processes still focuses on condition-based maintenance policy and a PdM policy for a hybrid degradation process is still unreported. In this paper, a PdM system for hybrid degradation processes with continuous degradation and sudden damage is proposed. The PdM system decides PM schedules by fully utilizing the condition monitoring data of each specific product, and can hopefully improve maintenance effectiveness.

Optimal maintenance strategy for systems with two failure modes

This paper considers a single-unit system subject to two types of failures: a traditional catastrophic failure and a two-stage delayed failure. Periodic inspections are carried out to identify the defective stage of the two-stage failure process, whereas preventive replacements are implemented to avoid any potential failure due to the catastrophic failure mode. We construct a basic maintenance model and then extend it to the cases of imperfect inspections (i.e., inspections that do not always notice a defective state). We analyze the renewal process of the system and establish the expected long-run cost rate (ELRCR). The optimal inspection period and preventive replacement interval are determined by minimizing the ELRCR. A case study on infusion pumps is presented to illustrate the proposed model.

Phase type stress–strength models with reliability applications

The stress–strength model has attracted a great deal of attention in reliability analysis, and it has been studied under various modeling assumptions. In this article, the stress–strength reliability is studied for both single unit and multicomponent systems when stress and strength distributions are of phase type. Phase-type distributions, besides their analytical tractability, are a versatile tool for modeling a wide range of real life systems/processes. In particular, matrix-based expressions are obtained for the stress–strength reliability, and mean residual strength for an operating system. The results are illustrated for Erlang-type stress–strength distributions for a single unit system and a system having a general coherent structure. An example on the comparison of two multi-state units in stress–strength ordering is also presented.

Lateral earth pressures acting on circular shafts considering soil-structure interaction

Nowadays, there is a significant demand on developing and expanding the existing infrastructure which necessitates the implementation of fast and cost effective construction methods such as the secant pile walls. The secant pile walls constructed in a circular plan layout to form a vertical shaft provide unique advantages such as compression ring behaviour. Compression rings act as a single-unit system in resisting lateral earth pressure and converting loads from all directions to compressive forces which can be resisted only by low concrete strength. Secant pile walls require stringent drilling tolerances to be achieved in order to behave as a compression ring and to perform as an effective groundwater cut-off wall. This paper presents a parametric study that investigates various aspects of the behaviour of circular shafts constructed using secant pile walls. The aspects that are studied include the identification of the magnitude and distribution of earth pressures exerted on circular shafts by the retained material. The distribution of surcharge pressures on the shaft walls is also studied. The results showed that the surcharge pressures on the wall increased with increasing width of surcharge area; for example, the maximum surcharge pressure increased by at least 60% when surcharge width increased from W = 3 m to W = 48 m. In addition, the results indicated a decrease of the maximum surcharge pressure on the wall by almost 22% when shaft radius decreased from R = 5 m to R = 3 m for Soil 1. Unlike what is observed in plane strain conditions, distance between the surcharge and shaft wall was seen to have a small effect on the magnitude of maximum pressures. The results also showed that the theoretical estimate of pressures underestimated the calculated values at larger depths and that the horizontal extent of the spread of pressure around the shaft was significantly influenced by the type of soil as well as width of surcharge. The outcomes of this study address practical design concerns and are considered to be of interest to those involved in design and construction of vertical shafts.

Availability evaluation of repairable system requiring two types of supporting device for operations

With advancement of modern science and technology, complex systems connected to an external supporting device for their operations have been manufactured to meet the demand of industries, economic growth and populace in general. Companies and organizations heavily rely on these systems to conduct their business. This study presents the availability assessment of a single unit system connected to two types of an external supporting device for its operation. Each type of supporting device has two copies I and II. First order differential equations method is used to obtain the explicit expression for the steady-state availability. Based on assumed numerical values given to system parameters, graphical illustrations are given to highlight important results. Comparisons are performed to highlight the impact of unit failure and repair rates.

A condition-based maintenance model for a three-state system subject to degradation and environmental shocks

Condition-based maintenance (CBM) is a key measure in preventing unexpected failures caused by internal-based deterioration and external environmental shocks. This study proposes a condition-based maintenance policy for a single-unit system with two competing failure modes, i.e., degradation-based failure and shock-based failure. The failure process of the system is divided into three states, namely, normal, defective and failed, and a defective state incurs a greater degradation rate than a normal state. Random shocks arrive according to a non-homogenous Poisson process (NHPP), leading to the failure of the system immediately. The occurrence of external shocks will be affected to the degradation level of the system. Periodic inspections are performed to measure the state and the degradation level of the system, and two preventive degradation thresholds are scheduled depending on the system state. The expected cost per unit time is derived through the joint optimization of the two preventive thresholds as well as the periodic inspection interval. A numerical example is proposed to illustrate the maintenance model.

Block Inspection Policy Model with Imperfect Maintenance for Single-unit Systems

In the presented paper, authors focus on development of mathematical delay-time model for single-unit technical systems with taking into account the assumption of imperfect inspection actions performance. Thus, the briefly literature review in the area of delay-time modelling for single-unit systems is provided. This gives the possibility to present the maintenance model for the case of one component system performing with imperfect inspection. Authors also discuss the sensitivity analysis of given analytical model. The directions for further research work are defined.

A Joint Inspection-Based Preventive Maintenance and Spare Ordering Optimization Policy Using a Three-Stage Failure Process

Separated decision-making for maintenance and spare ordering is unrealistic in the industry, so this paper aims to optimize them together. A joint policy of inspection-based preventive maintenance (PM) and spare ordering considering two modes of spare ordering, namely, a regular order and an emergency order, is proposed for single-unit systems using a three-stage failure process. If the system is recognized to be in the minor defective stage, the original inspection interval is shortened and a regular order is placed. However, replacement is undertaken preventively or correctively if the severe defective stage is identified or a failure occurs. Depending on the system state and the state of the regular ordered spare when replacement is needed, all possible scenarios are considered to construct optimization model I. The decision variables are the optimal inspection interval and the times of shortening the original inspection interval. Additionally, model II on the basis of an assumption that the spare is always ordered at time 0 is also developed. The results from a numerical example illustrated the applicability and the effectiveness of model I compared to model II, and the irregular inspection policy is validated to be cost-saving compared to the regular inspection policy.

A preventive maintenance policy based on dependent two-stage deterioration and external shocks

This paper proposes a preventive maintenance policy for a single-unit system whose failure has two competing and dependent causes, i.e., internal deterioration and sudden shocks. The internal failure process is divided into two stages, i.e. normal and defective. Shocks arrive according to a non-homogeneous Poisson process (NHPP), leading to the failure of the system immediately. The occurrence rate of a shock is affected by the state of the system. Both an age-based replacement and finite number of periodic inspections are schemed simultaneously to deal with the competing failures. The objective of this study is to determine the optimal preventive replacement interval, inspection interval and number of inspections such that the expected cost per unit time is minimized. A case study on oil pipeline maintenance is presented to illustrate the maintenance policy.

Optimal preventive and opportunistic maintenance policy for a two-unit system

This paper presents a new optimal opportunistic and preventive maintenance policy for a two-unit model with economic dependency applicable to the electric power distribution systems. Unlike the previous optimal maintenance policies which considered mainly single unit systems or no opportunistic maintenance for two-unit systems, we consider a two-unit system with economic dependency, where unit 1 is subject to condition monitoring and soft failure and unit 2 is subject to hard failure. Unit 1 is gradually deteriorating and unit 2 has a general life time distribution. Condition of unit 1 is monitored periodically and it is considered as failed when its deterioration level reaches a critical level N. At the failure time of unit 2 system is considered as failed, although unit 1 is working, and unit 2 will be correctively replaced by the next inspection epoch. Units 1 or 2 are preventively replaced when deterioration level of unit 1 or age of unit 2 reaches or exceeds the related PM levels. At the time of corrective or preventive replacement of a unit, there is an opportunity to replace also the other unit. A mathematical model is derived to find the preventive and opportunistic replacement levels for units 1 and 2 that minimize the long run expected average cost per unit time. The problem is formulated and solved in the semi-Markov decision process (SMDP) framework. Numerical example is provided to illustrate the performance of the proposed model and a comparison of the proposed model with other policies is carried out.

Analysis of a Single-Unit System with Weibull Failure and Repair densities Subject to Server Failure

The main concentration in the present paper is to analyze a single- unit system using the concepts of inspection, degradation, preventive maintenance, and server failure. A single repair facility inspect the original and degraded unit upon failure to check the feasibility of repair. The repair facility may fail during maintenance, repair and inspection and undergoes for treatment with Weibull probability density function. The unit after repair becomes degraded. Switch devices are perfect. All random variables like repair time, failure time, inspection time and treatment rate are independent and statistically independent. For the analysis of the system various measures of system effectiveness are obtained by using semi-Markov processes and regenerative point technique. With the help of numerical and graphical results for MTSF, availability and profit functions it is concluded that present system is more reliable, available and profitable, when random variables have less vale of shape parameters. Keywords: System, Availability, Inspection, Degradation and Preventive Maintenance

Analysis of a single-unit system with degradation and maintenance

A single-unit system is analyzed by considering the concepts of degradation and maintenance subjected to random shocks. A single server is called immediately to do repair activities. The maintenance of system is done by the server if it is suffered by the impact of shock. However, upon failure server repairs the unit. Repair of the unit is not perfect and it does not work as new after repair so called a degraded unit. The degraded unit is replaced by new one in case it is affected by the impact of shock. Server conducts inspection of degraded failed unit upon its failure to check the possibility of its repair. If repair of the unit is not possible, it is replaced by new one with some replacement time. Repair, maintenance, inspection, and replacement times all are arbitrary distributed whereas failure and shock times of the unit are exponentially distributed. Using regenerative point technique and semi-Markov process recurrence relations for several reliability measures are obtained. The numerical results for MTSF, steady state availability and profit functions are obtained with respect to shock rate.

Formulation, Development and Characterization of Floating Beads of Diltiazem Hydrochloride

The main goal of any drug delivery system is to achieve desired concentration of the drug in blood or tissue, which is therapeutically effective and nontoxic for a prolonged period. Various attempts have been made to develop gastroretentive delivery systems such as high density system, swelling, floating system. The recent developments of FDDS including the physiological and formulation variables affecting gastric retention, approaches to design single-unit and multiple-unit floating systems, and their classification and formulation aspects are covered in detail. Gastric emptying is a complex process and makes in vivo performance of the drug delivery systems uncertain. In order to avoid this variability, efforts have been made to increase the retention time of the drug-delivery systems for more than 12 hours. The floating or hydrodynamically controlled drug delivery systems are useful in such application. Background of the research: Diltiazem HCL (DTZ), has short biological half life of 3-4 h, requires rather high frequency of administration. Due to repeated administration there may be chances of patient incompliance and toxicity problems. Objective: The objective of study was to develop sustained release alginate beads of DTZ for reduction in dosing frequency, high bioavailability and better patient compliance. Methodology: Five formulations prepared by using different drug to polymer ratios, were evaluated for relevant parameters and compared. Alginate beads were prepared by ionotropic external gelation technique using CaCl2 as cross linking agent. Prepared beads were evaluated for % yield, entrapment efficiency, swelling index in 0.1N HCL, drug release study and SEM analysis. In order to improve %EE and drug release, LMP and sunflower oil were used as copolymers along with sodium alginate.

Comparative study between a single unit system and a two-unit cold standby system with varying demand.

The concerned paper illustrates the comparison of two stochastic models of a cable manufacturing plant with varying demand. Here, it shows the comparison between a single unit system (Model 1) and a two-unit cold standby system (Model 2). In Model 1, the system is either in working state on some demand or put to shut down mode on no demand. In Model 2, at initial stage, one of the units is operative while the other is kept as cold standby. At times when the operative unit stops working due to some breakdown/failure, the standby unit instantaneously becomes operative while the repairman repairs the failed unit. In this working model, only one unit remains operative at a time. However, there may be a state when both the units fail. The comparison of systems is done by means of MTSF (mean time to system failure), steady state availability and profit function using Laplace transforms and software package Code-Blocks 13.12. Different graphs have been plotted to discover which model is superior to the other model under the given conditions. The system is analysed by making use of semi-Markov processes and regenerative point technique.

СУЧАСНИЙ СТАН СТВОРЕННЯ, ВИРОБНИЦТВА ТА ДОСЛІДЖЕННЯ ТАБЛЕТОВАНИХ ЛІКАРСЬКИХ ПРЕПАРАТІВ Повідомлення 19. Сучасний стан розробки та дослідження мультипартикулярних пелетних систем.

<p align="center"><strong>MODERN STATE OF CREATION, PRODUCTION AND RESEARCH OF DRUGS</strong></p><p align="center"><strong>M</strong><strong>.</strong><strong>B</strong><strong>. </strong><strong>Demchuk</strong><strong>, </strong><strong>S</strong><strong>.</strong><strong>M</strong><strong>. </strong><strong>Gureyeva</strong><strong><sup>1</sup></strong><strong>, </strong><strong>T</strong><strong>.</strong><strong>A</strong><strong>. </strong><strong>Hroshovyi</strong><strong></strong></p><p>TernopilStateMedicalUniversityby I.Ya. Horbachevsky</p><p><sup>1</sup>JSC “Farmak”</p><p><strong>Noti</strong><strong>ce</strong><strong> 19.</strong> The current state of development and research of multiple unit pellet systems.</p><p><strong>Summary: </strong>the literature on technological aspects of creations of pellets, features of compression pellet to obtain multiple unit pellet systems are summarized<strong>.</strong></p><p><strong>Keywords: </strong>pellets, methods of pellets, pellet pressing, multiple unit pellet systems.</p><p><strong>Introduction. </strong>Oral modified-release multiple-unit dosage forms have always been more effective therapeutic alternative to conventional or immediate release single-unit dosage forms. With regards to the final dosage form, the multiparticulates are usually formulated into single-unit dosage forms such as filling them into hard gelatin capsules or compressing them into tablets.</p><p>Pelletization is a technique that enables the formation of spherical beads or pellets with a mean diameter usually ranging from 0.5 to2.0 mm. These pellets can evantually be coated and very often used in controlled-release dosage forms. The use of pelletization and pellets leads to an improvement in the flowability, appearance and mixing properties, thus avoiding excessive dust and reducing segregation and, generally, eliminating undesirable properties and improving the physical or chemical properties of fine powders.</p><p>The pharmaceutical industry has developed a great interest in pelletization due to a variety of reasons:</p><p>– prevention of segregation of co-agglomerated components, resulting in an improvement of the uniformity of the content;</p><p>– prevention of dust formation;</p><p>– increasing bulk density and decreasing bulk volume;</p><p>– the defined shape and weight improves the appearance of the product;</p><p>– improvement of the handling properties, due to the free-flowing properties;</p><p>– improvement of the hardness and friability of pellets;</p><p>– controlled release application of pellets due to the ideal low surface area-to-volume ratio that provides an ideal shape for the application of film coatings.</p><p>Pellets are prepared by different techniques, such as extrusion and spheronisation, rotogranulation, solution, suspension or powder layering, spray-drying or spray-congealing.</p><p>Extrusion / spheronisation is a multistage process for obtaining pellets with uniform size from wet granulates (extrudates). The process is more labour-intensive and more expensive than the conventional wet-granulation technique, as its use should be limited only to the production of spherical pellets for controlled release of drugs.</p><p>The fluid-bed granulation consists in the spraying of a granulation solution onto the suspended particles, which then are dried rapidly in the hot air stream.</p><p>Rotogranulation is one of the most recent methods for the production of spheroids. The single-unit spheronizing system can be described using terms like centrifugal granulator, rotary fluidized-bed granulator, rotary fluid bed, rotary processor or rotor granulator.</p><p>Layering a suspension or a solution of a drug on a seed material (usually, a coarse crystal or nonpareil) can produce pellets that are uniform in size distribution and generally posess very good surphace morphology. These characteristics are especially desirable when pellets will be coated for the purpose of achieving a controlled release.</p><p>Dry powder layering is similar to the solution or suspension layering. Instead of these dispersions, the layering is performed using a drug powder.</p><p>Spray-drying represents another process with limited application in the development of pharmaceutical pelletized products, based on globulation. During spray-drying, a drug solution or suspension is sprayed, with or without excipients, into a hot-air stream, generating dry and highly spherical particles.</p><p>Spray-congealing (spray-chilling) is a technique similar to spray-drying. Spray-congealing is a process in which a drug is allowed to melt, disperse or dissolve in hot melts of gums, waxes, fatty acids or other melting solids. The dispersion is then sprayed into a stream of air and other gases with a temperature below the melting point of the formulation components.</p><p><strong>Conclusions.</strong> The basic requirements and approaches to development multiple unit pellet system, aspects and examples receipt of pellets and tablets based on them are described.</p>

Probabilistic analysis of two reliability models of a single-unit system with preventive maintenance beyond warranty and degradation

Probabilistic analysis of two reliability models of a single-unit system with preventive maintenance beyond warranty and degradation