Unavailability Rate Research Articles

Unveiling risk factors influencing the selection of the Northern Sea Route: A conjoint analysis approach for Japanese shippers

This paper explores how Japanese corporations assess risks associated with using the Northern Sea Route (NSR) as a new maritime transport route in Asia and identifies measures to promote its usage. We address two key questions: (1) What risks influence shippers' route choices in maritime transport? (2) Does risk evaluation vary by cargo type and company size? Using choice-based conjoint analysis and a conditional logit model with online survey data, we identified five main risk factors influencing shippers: route unavailability rate, delay probability, piracy probability, transport costs, and war conditions, ranked in importance from highest to lowest as war conditions, delay probability, transport costs, route unavailability rate, and piracy probability. Additionally, the risk factors significantly influencing route selection were found to be robust, showing minimal variation across company size, type of trade (import/export), and the nature of the goods transported. Our findings suggest several policy implications. Diplomatic efforts are crucial for safe vessel navigation on the NSR. Government initiatives should focus on reducing transport delays through technology investments and implementing strategies to decrease NSR delay rates without increasing shippers' costs. Additionally, emphasizing the lower piracy risks on the NSR compared to Suez Canal Route could boost its attractiveness.

Radicals ([rad]OH, Cl[rad], ClO[rad] and Cl2[rad]−) concentration profiles in the intensified degradation of reactive green 12 by UV/chlorine process: Chemical kinetic analysis using a validated model

Understanding the production of reactive species in chlorine photolysis is critical for applying advanced oxidation processes (AOPs) in future. This paper developed a chemical kinetic model consisting of 66 chemical reactions, including many radicals and non-radical intermediates/products, to elucidate the intensified removal of reactive green 12 (RG12) dye by UV/chlorine AOP. The generated kinetic model fits our experimental data satisfactorily across a broad range of solution pH and initial chlorine concentration. The simulation process was accomplished by COPASI® software coupled with the deterministic Nelder-Mead optimization method for determining some unavailable rate constants, including the reaction of RG12 with OH (k = 1.2 × 1010 M−1 s−1), Cl (k = 2.1 × 109 M−1 s−1), Cl2− (k = 1.26 × 107 M−1 s−1) and ClO (k = 6.12 × 104 M−1 s−1). As well, the first-order rate constants of chlorine photolysis, HOCl + hv → OH + Cl and OCl− + hv → O− + Cl, were respectively (0.81–6.90) × 10−3 s−1 and (0.87–8.29) × 10−3 s−1, depending on the solution pH and chlorine dosage. The radicals concentration (and RG12 degradation rate) increased with the increase of initial chlorine dosage, whereas a solution pH of 5 is recorded for the best process efficiency (i.e., radicals’ yield and dye destruction rate). Even though the steady-state concentration of ClO (∼10−8 M) and Cl2− (∼10−11 M) are highest compared to OH (∼10−12 M) and Cl (∼10−12 M), the selectivity analysis results showed that OH radicals contributed majorly in the degradation (∼85 %) for the different investigated scenarios of pH and initial chlorine concentration. The remaining portion (∼15 %) is ensured by Cl and ClO nearly equitably. These findings were attributed to the high reactivity of RG12 toward OH rather than reactive chlorine radicals, as reflected by the initial rates of the different RG12-degradation by-products.

Research on High-Voltage Transmission System Operation on the Same Tower

The high-voltage DC adopts the simulation idea of a two-circuit system on the same convertor. The current DC system availability indicators were insufficient and proposed two reliability indicators, operating utilization and operating availability. At the same time, the active planned outage mode and the activities planned energy unavailability rate index was proposed, and the reliability evaluation program algorithm analysis based on programming developed to verify the feasibility of the power outage maintenance optimization mode, and at the same time provide certain guidance and reference significance for the subsequent design work of the same type of research. A calculation algorithm for evaluating the impact of the outage DC on the reliability of the system is proposed to calculate the value of the transmission system.

Implementation of an Anaesthesia Quality Improvement Programme to Reduce Fibreoptic Bronchoscope Repair Incidents.

Background This study was aimed at investigating the effectiveness of the implementation of a comprehensive quality improvement programme (QIP) for reducing the repair rate of the fibreoptic bronchoscope (FOB). Methods A three-stage improvement strategy was implemented between January 2013 and December 2016. Stage one is the acquisition of information on violations of practice guidelines, repair rate, cost of repair, and incidence of unavailability of FOB during anaesthesia induction of the previous year through auditing. Stage two is the implementation of a quality improvement campaign (QIC) based on the results of stage one. Stage three is the programme perpetuation through monitoring compliance with policy on FOB use by regular internal audits. The effectiveness was retrospectively analyzed on a yearly basis. Results The annual repair rate, repair cost, and incidence of FOB unavailability before the QIP implementation were 1%, 18,757 USD, and 1.4%, respectively. After QIC, the repair rate in 2013 dropped by 81% (from 1% in 2012 to 0.19% in 2013, p < 0.05). The annual repair cost fell by 32% from 18,758 USD (2012) to 12,820 USD (2013). Besides, the incidence of FOB unavailability plummeted by 71% from 1.4% to 0.4% during the same period. The annual repair rates and incidence of FOB unavailability remained lower in subsequent three years than those before QIP implementation. Conclusion Implementation of a quality improvement programme was effective for reducing the rate and cost of FOB repair as well as unavailability rate, highlighting its beneficial impact on cost-effectiveness and patient safety in a tertiary referral center setting.

Reconfiguration-based methodology for improving recovery performance of faults in smart grids

This paper aims to enhance the reliability and quality of service (QoS) of power smart grids by searching and applying reconfiguration oriented solutions. A novel definition of recovery performance is provided in terms of automatic recoverability and unavailability rates. The proposed approach is based on a hierarchical and distributed multi-agent system (MAS). It involves static and mobile agents, respectively, dedicated to search for new feasible reconfigurations and to identify the consumers which may play the role of feeders over smart grids. An automatic reconfiguration corresponds to the addition of a new pertinent line in a smart grid to allow further recoveries. This paper provides the implemented communication protocol for negotiating (CPN) the resources allocation which is performed by the deployed agents. The management and assignment of the energy resources are modeled as a combinatorial optimization multiple-knapsack problem (MKP) to reach a better configuration with a higher possible recovery performance rate. To decrease the cost of automatic actions, which increases the smart grid performance and reduces the costs of the human interventions, a short list of failures is identified based on proposed relations of dominance and equivalence between observed failures. Furthermore, this work investigates the effectiveness of the designed and implemented software tool for off-line assistance-design, simulation and modeling of reconfigurable smart grids. The efficiency of the proposed strategy is validated through an experimental study performed by the developed simulator.

Modeling of correlated resources availability in distributed computing systems

Volunteer computing systems are large-scale distributed systems with large number of heterogeneous and unreliable Internet-connected hosts. Volunteer computing resources are suitable mainly to run High-Throughput Computing (HTC) applications due to their unavailability rate and frequent churn. Although they provide Peta-scale computing power for many scientific projects across the globe, efficient usage of this platform for different types of applications still has not been investigated in depth. So, characterizing, analyzing and modeling such resources availability in volunteer computing is becoming essential and important for efficient application scheduling. In this paper, we focus on statistical modeling of volunteer resources, which exhibit non-random pattern in their availability time. The proposed models take into account the autocorrelation structure in individual and subset of hosts whose availability has temporal correlation. We applied our methodology on real traces from the SETI@home project with more than 230,000 hosts. We showed that Markovian arrival process and ARIMA time series can model the availability and unavailability intervals of volunteer resources with a reasonable to excellent level of accuracy.

Availability analysis of safety grade multiple redundant controller used in advanced nuclear safety systems

We analyze the availability of the Safety Programmable Logic Controller (SPLC) having multiple redundant architectures. In the SPLC, input/output and processor module are configured as triple modular redundancy (TMR), and backplane bus, power and communication modules are configured as dual modular redundancy (DMR). The voting logics for redundant architectures are based on the forwarding error detection. It means that the receivers perform the voting logics based on the status information of transmitters. To analyze the availability of SPLC, we construct the Markov model and simplify the model adopting the system unavailability rate. The results show that the fault coverage factor should be ≥0.8 and Mean Time To Repair (MTTR) should be ≤100h in order to satisfy the requirement that the availability of the safety grade PLC should be ≥0.995. Also we evaluate the availability of SPLC comparing to other PLCs such as simplex, processor DMR (pDMR) and independent TMR (iTMR) PLCs used in the existing nuclear safety systems. The availability of SPLC is higher than those of the simplex, pDMR but is lower than that of iTMR for one month which is the periodic off-line test and inspection. That’s why the number of redundant modules used in PLC is more dominant to increasing the availability than the number of fault masking methods such as voting logics used in PLC on the assumption that operation time is in the early stage. But the availability of iTMR, which has many redundant modules but has only a voting logic fast decrease and eventually is the lowest after 8000h. Also if the MTTR of each module in PLC is required to be increased to 200h, the availability of SPLC would be better than iTMR.

Adequacy assessment of a 2 area system with renewable integration

AbstractIn this paper, impacts of renewable sources on the adequacy of a 2 area system are presented. Integration of popular renewable sources like photovoltaic (PV) and wind is forcing the operational planner to operate differently. Here, an effort has been made to propose some planning scenarios for 2 area system on the basis of renewable sources integration, and reliability is evaluated corresponding to each scenario. Loss of load expectation is popular method for adequacy assessment following 2 state principle (available or unavailable) of conventional sources. Photovoltaic and wind system never follow 2 state principle unlike conventional. Existing PV module configuration determine the unavailability rate of PV plant considering component failure. Random wind speed is simulated using time series auto regressive moving average model. Wind turbine characteristics and simulated wind speed create multistate wind energy conversion system and reduced by apportioning method to predict unavailability rate. A simple 2 area system is considered to validate the efficacy of proposed theme.

Injury Patterns among Elite Football Players: A Media-based Analysis over 6 Seasons with Emphasis on Playing Position.

The study objective was to describe the types, localizations and severity of injuries among first division Bundesliga football players, and to study the effect of playing position on match and training injury incidence and severity, based on information from the public media. Exposure and injuries data from 1 448 players over 6 consecutive seasons were collected from a media-based register. In total, 3 358 injuries were documented. The incidence rate for match and training injuries was 11.5 per 1 000 match-hours (95% confidence interval [CI]: 10.9-12.2), and 61.4 per 100 player-seasons (95% CI: 58.8-64.1), respectively. Strains (30.3%) and sprains (16.7%) were the major injury types, with the latter causing significantly longer lay-off times than the former. Significant differences between the playing positions were found regarding injury incidence and injury burden (lay-off time per incidence-rate), with wing-defenders sustaining significantly lower incidence-rates of groin injuries compared to forwards (rate ratio: 0.43, 95% CI: 0.17-0.96). Wing-midfielders had the highest incidence-rate and injury burden from match injuries, whereas central-defenders sustained the highest incidence-rate and injury burden from training injuries. There were also significant differences in match availability due to an injury across the playing positions, with midfielders sustaining the highest unavailability rates from a match and training injury. Injury-risk and patterns seem to vary substantially between different playing positions. Identifying positional differences in injury-risk may be of major importance to medical practitioners when considering preventive measures.

Study on the systematic approach of Markov modeling for dependability analysis of complex fault-tolerant features with voting logics

The Markov analysis is a technique for modeling system state transitions and calculating the probability of reaching various system states. While it is a proper tool for modeling complex system designs involving timing, sequencing, repair, redundancy, and fault tolerance, as the complexity or size of the system increases, so does the number of states of interest, leading to difficulty in constructing and solving the Markov model. This paper introduces a systematic approach of Markov modeling to analyze the dependability of a complex fault-tolerant system. This method is based on the decomposition of the system into independent subsystem sets, and the system-level failure rate and the unavailability rate for the decomposed subsystems. A Markov model for the target system is easily constructed using the system-level failure and unavailability rates for the subsystems, which can be treated separately. This approach can decrease the number of states to consider simultaneously in the target system by building Markov models of the independent subsystems stage by stage, and results in an exact solution for the Markov model of the whole target system. To apply this method we construct a Markov model for the reactor protection system found in nuclear power plants, a system configured with four identical channels and various fault-tolerant architectures. The results show that the proposed method in this study treats the complex architecture of the system in an efficient manner using the merits of the Markov model, such as a time dependent analysis and a sequential process analysis.

Switching‐based state tracking of model reference adaptive control systems in the presence of intermittent failures of all actuators

SUMMARYThis paper investigates the state tracking problem for a class of model reference adaptive control systems with intermittent failures of all actuators. We consider the case that all actuators may suffer failures simultaneously. The concepts of failure frequency and unavailability rate are introduced to describe the failures. Because of the actuator failures, the error system is modeled as a switched system. Then, the notion of global practical stability of switched systems is presented, and sufficient conditions are provided to guarantee the global practical stability of the error system. An example of HiMAT vehicle and the simulation results demonstrate the feasibility and effectiveness of the proposed design method. Copyright © 2013 John Wiley &amp; Sons, Ltd.

State Tracking of MRAC Systems in the Presence of Controller Temporary Failure Based on a Switching Method

The state tracking problem for a class of model reference adaptive control (MRAC) systems in the presence of controller temporary failures is studied. Due to the controller temporary failure, the considered system is viewed as an error switched system. The properties of Lyapunov function candidates without switching are described. Then the notion of global practical stability of switched systems is presented, and sufficient conditions for global practical stability of the error system under the restrictions of controller failure frequency and unavailability rate are provided. An example is presented to demonstrate the feasibility and effectiveness of the proposed method.

Global synchronization of complex dynamical networks with network failures

AbstractNetwork failure refers to the case that parts or all of the connections in the network become disconnected. In this paper, the global synchronization of complex dynamical networks with network failures is studied based on the framework of switching system. For simplicity, assume that the network becomes totally unavailable when network failures happen and it takes a period of time to fix the network. In order to ensure the global synchronization of CDNs with network failures, the upper bounds of both the unavailability rate of the network and the frequency of network failures are obtained, respectively. Illustrated examples and the simulation results also show the effectiveness of the proposed result. Copyright © 2009 John Wiley &amp; Sons, Ltd.

The impact of an electronic prescribing and administration system on the safety and quality of medication administration

Abstract Objective To assess the effect of an electronic prescribing and administration system on the safety and quality of medication administration in a UK hospital. Setting Surgical ward in a teaching hospital. Method Data were collected before and after introducing a closed-loop system comprising electronic prescribing, automated dispensing, barcode patient identification and electronic medication administration records (ServeRx, MDG Medical). We observed medication administration during drug rounds and assessed medication administration error (MAE) rates for ward-stock and non-ward-stock drugs, accuracy of medication administration documentation, timeliness of administration, administration of medication from unlocked areas and supervision of patients taking oral medication by nursing staff. Key findings Pre- and post-intervention MAE rates were 6.4 and 2.3% respectively for ward-stock drugs (95% confidence interval for the difference (CI) −5.8 to −2.4%), and 14.6 and 13.7% for non-ward-stock drugs (CI −6.5 to 4.7%). Excluding omissions due to unavailability, pre- and post-intervention MAE rates were 6.2 and 2.2% respectively for ward-stock drugs (CI −5.7 to −2.3%), and 9.2 and 3.5% for non-ward-stock drugs (CI −9.3 to −2.1%). Pre-intervention, 2086 doses (96.3%) were documented correctly and 1557 (95.9%) post-intervention (CI −1.6 to 0.8%). There were five clinically significant documentation discrepancies pre-intervention (0.2%), and 33 (2.0%) afterwards (CI 1.1 to 2.5%). Timeliness of administration improved post-intervention (P &amp;lt; 0.001; Chi-square test), as did administration of medication from unlocked areas (CI 4.7 to 7.3%) and supervision of patients taking oral medication (CI 17 to 23%). Conclusion Reductions in MAEs, excluding omissions due to unavailability, occurred for both ward-stock and non-ward-stock drugs. The system also improved timeliness and security of drug administration. However, there was an increase in potentially significant documentation discrepancies.

Controller Failure Analysis for Systems with Interval Time-Varying Delay: A Switched Method

This paper studies the problem of controller failure analysis for a class of interval time-varying delay systems with a predesigned state feedback controller. Our objective is to establish conditions concerning controller failure time, under which the systems still keep exponentially stable. For this purpose, the systems with controller failures are first formulated as a class of switched delay systems. Next, based on a piecewise Lyapunov functional method, the exponential stability of such systems is guaranteed by restricting the unavailable rate and failure frequency of the controller. All the results are presented in terms of linear matrix inequalities. Two examples are provided to demonstrate the effectiveness of the proposed technique.

Unavailability of wind turbines due to wind-induced accelerations

The malfunctioning of acceleration-sensitive equipment in wind turbines has the potential to affect their annual failure rates during normal operating conditions. Current protective measures for wind turbines are triggered by wind speed. However, this option neglects the structural response of the wind turbines, and limits the possibility of effectively controlling accelerations at the top of the wind towers. In this study, a dynamic model of the wind tower/rotor blade system is used to estimate the acceleration response at the top of the towers. This model is coupled with a probabilistic description of the dynamic properties of the wind turbines, and an annual distribution of the wind hazard to obtain a distribution of the acceleration response for various levels of wind speed. This distribution is used to develop wind-induced acceleration fragility curves for typical wind turbines. Acceleration thresholds of 10, 15, and 20 m/s 2 are likely to be exceeded at the onset of protective cut out wind speeds of 25 m/s, with probabilities as high as 64%, 48%, and 37%, respectively. Several wind turbine subcomponents are sensitive to these levels of acceleration. Some examples, in decreasing order of acceleration susceptibility, include generators, brakes, yaw systems, inverters, mechanical controls, electrical controls, hydraulic systems, gearboxes, shafts, and physical/electrical connections to the power grid. By weighting the fragility curves with the likelihood of observing specific wind speeds during any given year, this study provides unconditional probabilities of failure that represent annual unavailability rates for wind turbines. Exceeding any of the acceleration levels between 10 m/s 2 and 20 m/s 2 has probabilities of 47% and 49% at two locations with different wind regimens: Western Texas, USA, and Northern Ireland. This annual unavailability rate indicates that almost half the units of a wind farm at either location are likely to experience abnormal operation owing to the demands on acceleration-sensitive equipment. The use of fragility curves and the risk of unavailability for wind turbines will continue to grow because they allow performance assessment of future systems which favor larger, more flexible, more massive, and more complex wind turbine units. These new generation units will be able to operate at higher wind speeds and more demanding environmental conditions. A short- term option to reduce acceleration-induced failures in built systems is to establish shutdown criteria based on acceleration, rather than just wind speed. However, long-term handling of acceleration-sensitive equipment requires fragility and reliability analysis at the design stage, and the use of actively controlled protective devices.

Stability and ℒ2 Gain Analysis for Discrete-Time LTI Systems with Controller Failures

In this paper, we analyze stability and ℒ2 gain properties for discrete-time linear time-invariant (LTI) systems controlled by a pre-designed dynamical output feedback controller which fails from time to time due to physical or purposeful reason. Our aim is to find conditions concerning controller failure time, under which the system's stability and ℒ2 gain properties are preserved to a desired level. For stability, by using a piecewise Lyapunov function, we show that if the unavailability rate of the controller is smaller than a specified constant and the average time interval between controller failures (ATBCF) is large enough, then global exponential stability of the system is guaranteed. For ℒ2 gain, also by using a piecewise Lyapunov function, we show that if the unavailability rate of the controller is smaller than a specified constant, then the system with an ATBCF achieves a reasonable weighted ℒ2 gain level, and the weighted ℒ2 gain approaches normal ℒ2 gain when the ATBCF is sufficiently large.

Controller failure time analysis for symmetric control systems

In this paper, we consider a controller failure time analysis problem for a class of symmetric linear time-invariant (LTI) systems controlled by a pre-designed symmetric static output feedback controller. We assume that the controller fails from time to time due to a physical or purposeful reason, and we analyse stability and disturbance attenuation properties of the entire system. Our aim is to find conditions concerning controller failure time, under which the system's stability and disturbance attenuation properties are preserved to a desired level. For both stability and disturbance attenuation analysis, we show that if the unavailability rate of the controller is smaller than a specified constant, then global exponential stability of the entire system and a reasonable disturbance attenuation level is achieved. The key point is to establish a common quadratic Lyapunov-like function for the entire system in two different situations.

STABILITY AND H∞ DISTURBANCE ATTENUATION ANALYSIS FOR LTI CONTROL SYSTEMS WITH CONTROLLER FAILURES

ABSTRACTIn this paper, we analyze stability and H∞ disturbance attenuation properties for linear time‐invariant (LTI) systems controlled by a pre‐designed dynamical output feedback controller which fails from time to time due to physical or purposeful reasons. Our aim is to find conditions concerning the controller failure time, under which the system's stability and H∞ disturbance attenuation properties are preserved to a desired level. For stability, by using a piecewise Lyapunov function, we show that if the unavailability rate of the controller is smaller than a specified constant and the average time interval between controller failures (ATBCF) is large enough, then the global exponential stability of the system is guaranteed. For H∞ disturbance attenuation, also by using a piecewise Lyapunov function, we show that if the unavailability rate of the controller is smaller than a specified constant, then a system with an ATBCF achieves a reasonable weighted H∞ disturbance attenuation level, and the weighted H∞ disturbance attenuation approaches normal H∞ disturbance attenuation when the ATBCF is sufficiently large.

The National Marrow Donor Program. Meeting the needs of the medically underserved.

The National Marrow Donor Program operates the world's largest registry of volunteer unrelated stem cell donors. In recent years, the program has focused on building a large and diverse donor file. After initial recruitment, however, months or years may elapse before a potential donor is contacted on behalf of a searching patient. Here, the author begins to explore factors that influence donor availability at the confirmatory typing stage of the search process. Over a 1-year period from March 1, 1999 through February 29, 2000, the author evaluated donor unavailability rates at the confirmatory typing stage of the search process. Unavailability rates by donor racial/ethnic group and by donor center were evaluated. To determine the consistency within individual donor centers, the author compared donor unavailability during the first 6 months of the observation period with unavailability during the second 6 months. Donor unavailability at confirmatory typing was higher among donors registered with domestic (U.S.) donor centers. The self-identified racial or ethnic group of the donor also affected the likelihood the donor will be available when requested. Between individual donor centers, there were large differences in the overall donor unavailability. Rates of donor unavailability tended to remain consistent at individual centers over time. This study suggests that procedures used at individual donor centers may dramatically impact donor unavailability. Future initiatives should undertake to identify best practice models for donor recruitment, retention, and subsequent contacts.