Failure Rate Estimation Research Articles

A methodology to include real-life failure data in the failure rate estimation of power distribution systems

A methodology to include real-life failure data in the failure rate estimation of power distribution systems

Using field feedback to estimate failure rates of safety-related systems

The IEC 61508 and IEC 61511 functional safety standards encourage the use of field feedback to estimate the failure rates of safety-related systems, which is preferred than generic data. In some cases (if “Route 2H” is adopted for the "hardware safety integrity constraints”), this is even a requirement. This paper presents how to estimate the failure rates from field feedback with confidence intervals, depending if the failures are detected on-line (called "detected failures", e.g. by automatic diagnostic tests) or only revealed by proof tests (called "undetected failures"). Examples show that for the same duration and number of failures observed, the estimated failure rates are basically higher for “undetected failures” because, in this case, the duration observed includes intervals of time where it is unknown that the elements have failed. This points out the need of using a proper approach for failure rates estimation, especially for failures that are not detected on-line. Then, this paper proposes an approach to use the estimated failure rates, with their uncertainties, for PFDavg and PFH assessment with upper confidence bounds, in accordance with IEC 61508 and IEC 61511 requirements. Examples finally show that the highest SIL that can be claimed for a safety function can be limited by the 90% upper confidence bound of PFDavg or PFH. The requirements of the IEC 61508 and IEC 61511 relating to the data collection and analysis should therefore be properly considered for the study of all safety-related systems.

Implications of employer coverage of contraception: Cost‐effectiveness analysis of contraception coverage under an employer mandate

ObjectivesMandatory employer-based insurance coverage of contraception in the US has been a controversial component of the Affordable Care Act (ACA). Prior research has examined the cost‐effectiveness of contraception in general; however, no studies have developed a formal decision model in the context of the new ACA provisions. As such, this study aims to estimate the relative cost‐effectiveness of insurance coverage of contraception under employer-sponsored insurance coverage taking into consideration newer regulations allowing for religious exemptions. Study designA decision model was developed from the employer perspective to simulate pregnancy costs and outcomes associated with insurance coverage. Method-specific estimates of contraception failure rates, outcomes and costs were derived from the literature. Uptake by marital status and age was drawn from a nationally representative database. ResultsProviding no contraception coverage resulted in 33 more unintended pregnancies per 1000 women (95% confidence range: 22.4; 44.0). This subsequently significantly increased the number of unintended births and terminations. Total costs were higher among uninsured women owing to higher costs of pregnancy outcomes. The effect of no insurance was greatest on unmarried women 20–29 years old. ConclusionsDenying female employees' full coverage of contraceptives increases total costs from the employer perspective, as well as the total number of terminations. ImplicationsInsurance coverage was found to be significantly associated with women's choice of contraceptive method in a large nationally representative sample. Using a decision model to extrapolate to pregnancy outcomes, we found a large and statistically significant difference in unintended pregnancy and terminations. Denying women contraception coverage may have significant consequences for pregnancy outcomes.

Investigation of maintenance performance for a gasification process unit using Weibull analysis

Purpose – The purpose of this paper is to investigate maintenance performance of a gasification process unit by identifying reliability, failure and hazard rate. The prediction on the number of preventive maintenance (PM) activities and size of labour are being analysed. Design/methodology/approach – The study collects maintenance data for 4,000 hours operation to perform Weibull analysis in order to determine two key factors which are beta shape factor, β and characteristic life, η. Findings – The results for estimation of failure, reliability and hazard rate show that the pump was most likely contributed to the biggest failure. On the other hand, reaction chamber was able to maintain the longest operation among other components. It is estimated that the total PM activities should be within 20-50 activities per month for whole processing plant. Meanwhile, the estimation of size of labour should be within the range of 60-130 numbers of workers per month for all components. Originality/value – The method of Weibull analysis for investigating current maintenance performance has been analysed using real case study data. The data collection is obtained from a typical gasification process unit.

Insights into location dependent loss-of-coolant-accident (LOCA) frequency assessment for GSI-191 risk-informed applications

As a tribute to the published work by S.H. Bush, S. Beliczey and H. Schulz, this paper assesses the progress with methods and techniques for quantifying the reliability of piping systems in commercial nuclear power plants on the basis of failure rate estimates derived from field experience data in combination with insights and results from probabilistic fracture mechanics analyses and expert elicitation exercises. This status assessment is made from a technical perspective obtained through development of location-specific loss-of-coolant-accident (LOCA) frequencies for input to risk-informed resolution of the generic safety issue (GSI) 191. The methods and techniques on which these GSI-191 applications are based build on a body of work developed by the authors during a period spanning more than two decades. The insights that are presented and discussed in this paper cover today’s knowledge base concerning how to utilize a risk-informed approach to the assessment of piping reliability in the context of probabilistic risk assessment (PRA) in general and the resolution of GSI-191 in particular. Specifically the paper addresses the extent to which LOCA frequencies vary from location to location within a reactor coolant system pressure boundary (RCPB) for a given plant as well as vary from plant to plant, and the reasons for these variabilities. Furthermore, the paper provides the authors’ perspectives on interpretations and applications of information extracted from an expert elicitation process to obtain LOCA frequencies as documented in NUREG-1829 and how to apply this information to GSI-191. Finally, this paper documents technical insights relative to mitigation of material degradation mechanisms and on effective strategies to manage the risks of debris-induced failures during a LOCA.

Failure of antibiotics in cellulitis trials: a systematic review and meta-analysis

ObjectivesThe objectives of the study are to quantify trial-to-trial variability in antibiotic failure rates, in randomized clinical trials of cellulitis treatment and to provide a point estimate for the treatment failure rate across trials. MethodsWe conducted a structured search for clinical trials evaluating antibiotic treatment of cellulitis, indexed in PubMed by August 2015. We included studies published in English and excluded studies conducted wholly outside of developed countries because the pathophysiology of cellulitis is likely to be different in such settings. Two authors reviewed all abstracts identified for possible inclusion. Of studies identified initially, 5% met the selection criteria. Two reviewers extracted data independently, and data were pooled using the Freeman-Tukey transformation under a random-effects model. Our primary outcome was the summary estimate of treatment failure across intent-to-treat and clinically evaluable participants. ResultsWe included 19 articles reporting data from 20 studies, for a total of 3935 patients. Treatment failure was reported in 6% to 37% of participants in the 9 trials reporting intent-to-treat results, with a summary point estimate of 18% failing treatment (95% confidence interval, 15%-21%). In the 15 articles evaluating clinically evaluable participants, treatment failure rates ranged from 3% to 42%, and overall, 12% (95% confidence interval, 10%-14%) were designated treatment failures. ConclusionsTreatment failure rates vary widely across cellulitis trials, from 6% to 37%. This may be due to confusion of cellulitis with its mimics and perhaps problems with construct validity of the diagnosis of cellulitis. Such factors bias trials toward equivalence and, in routine clinical care, impair quality and antibiotic stewardship. Objective diagnostic tools are needed.

Validity testing and neuropsychology practice in the VA healthcare system: results from recent practitioner survey

Objective: A survey of neuropsychologists in the Veterans Health Administration examined symptom/performance validity test (SPVT) practices and estimated base rates for patient response bias. Method: Invitations were emailed to 387 psychologists employed within the Veterans Affairs (VA), identified as likely practicing neuropsychologists, resulting in 172 respondents (44.4% response rate). Practice areas varied, with 72% at least partially practicing in general neuropsychology clinics and 43% conducting VA disability exams. Results: Mean estimated failure rates were 23.0% for clinical outpatient, 12.9% for inpatient, and 39.4% for disability exams. Failure rates were the highest for mTBI and PTSD referrals. Failure rates were positively correlated with the number of cases seen and frequency and number of SPVT use. Respondents disagreed regarding whether one (45%) or two (47%) failures are required to establish patient response bias, with those administering more measures employing the more stringent criterion. Frequency of the use of specific SPVTs is reported. Conclusions: Base rate estimates for SPVT failure in VA disability exams are comparable to those in other medicolegal settings. However, failure in routine clinical exams is much higher in the VA than in other settings, possibly reflecting the hybrid nature of the VA’s role in both healthcare and disability determination. Generally speaking, VA neuropsychologists use SPVTs frequently and eschew pejorative terms to describe their failure. Practitioners who require only one SPVT failure to establish response bias may overclassify patients. Those who use few or no SPVTs may fail to identify response bias. Additional clinical and theoretical implications are discussed.

Typical-use contraceptive failure rates in 43 countries with Demographic and Health Survey data: summary of a detailed report

BackgroundWhile most unintended pregnancies occur because couples do not use contraception, contraceptive failure is also an important underlying cause. However, few recent studies outside of the United States have estimated contraceptive failure rates, and most such studies have been restricted to married women, to a limited number of countries and to 12-month failure rate estimates. MethodsUsing self-reported data from 43 countries with Demographic and Health Survey data, we estimated typical-use contraceptive failure rates for seven contraceptive methods at 12, 24 and 36months of use. We provide a median estimate for each method across 43 countries overall, in seven subregions and in individual countries. We assess differences by various demographic and socioeconomic characteristics. Estimates are not corrected for potential errors in retrospective reporting contraceptive use or potential underreporting of abortion, which may vary by country and subgroups within countries. ResultsAcross all included countries, reported 12-month typical-use failure rates were lowest for users of longer-acting methods such as implants (0.6 failures per 100 episodes of use), intrauterine devices (1.4) and injectables (1.7); intermediate for users of short-term resupply methods such as oral contraceptive pills (5.5) and male condoms (5.4); and highest for users of traditional methods such as withdrawal (13.4) or periodic abstinence (13.9), a group largely using calendar rhythm. ConclusionsOur findings help us to highlight those methods, subregions and population groups that may be in need of particular attention for improvements in policies and programs to address higher contraceptive failure rates.

A failure rate interaction model for two-component systems based on copula function

Failure rate estimation of a component or a system plays an important role for reliability analysis and maintenance decision-making. In some systems, failure mechanisms from different components interact with each other, and the interaction may accelerate the failure procedure of a certain component. Therefore, it is necessary to consider the correlation of failures from different components for obtaining an accurate reliability prediction. In this article, a failure rate interaction model for two components based on copula function is proposed. In this model, the failure correlation of two components in the same system is estimated using copula function. Then, the joint failure probability distribution function of the two components and the conditional failure probability distribution of failures for each component are determined. Finally, the failure rate is calculated considering the correlation of failures between components, and the failure rate estimation of the oil pump and oil seal is presented and discussed to illustrate the validity of the proposed method.

Advantages and disadvantages of emergency postcoital contraception

Emergency postcoital contraception (EPC) also known as 'emergency contraception' and 'morning after pill' is an easy way to prevent conceiving and it can be purchased in many countries without any prescription. EPC offers an important chance to prevent an unintended pregnancy when a regular method fails, no method was used, or sex was forced. The currently available options include an estrogen-progestin combination (ethinyl estradiol with levonorgestrel), progestin alone (levonorgestrel), the ulipristal acetate, the antiprogestin synthetic steroid mifepristone (RU-486), estrogen alone (high-dose ethinyl estradiol) and the Copper T intrauterine device (IUD). EPC pills, which may be more accessible than an emergency IUD, reduce the chance that pregnancy will happen after a single act of intercourse by at least 50 percent. The Copper T IUD is the most effective form of emergency contraception with an estimated failure rate of less than 1%. EPC is a simple safe emergency method to reduce the chance of pregnancy and EPC pills do not harm an existing pregnancy. EPC is not suitable for women who cannot take birth control pills, it does not protect against sexually transmitted infections and should not be used as a regular method of birth control. The sooner the pills are taken, the better it is. The effect or the potential of EPC diminishes over time. It may have some temporary side effects such as nausea and vomiting, delay in menses, irregular vaginal bleeding, abdominal pain, headache, dizziness, and fatigue. If these side effects occur, they generally resolve within 24 hours of the pill use. Side effects of the copper-containing IUD are also rare, but may include menstrual cramping or increased menstrual flow.

Survival analysis of wide dental implant: systematic review and meta-analysis.

Wide-diameter implants are frequently placed in molar sites to obtain appropriate restoration profiles, to rescue implants that lack stability, and to engage bone in extraction sites. However, studies of wide-diameter implant placement have provided conflicting evidence regarding clinical outcomes. This systematic review aims to analyze survival rates of wide-diameter implants (platform diameter ≥5mm) and assess clinical variables potentially affecting failure rates. Electronic search was conducted using MEDLINE (PubMed), Cochrane Central Register of Controlled Trials (CENTRAL) and EMBASE from January 1980 to October 2014. Publication screening, data extraction, and quality assessment were performed. Failure rate per implant-year was analyzed using mix-effects Poisson regression model to obtain summary estimates of the 5-year survival rate. Relative risk (RR) was calculated to evaluate the association of different clinical variables with estimated failure rates. Eleven retrospective studies and eight prospective studies having at least 1-year follow-up period were included in the analysis. The estimated 5-year survival rate was 92.67% (95% confidence interval: [79.60, 97.50]) in the retrospective studies and 97.76% (Confidence interval: [93.25, 99.27]) in the prospective studies. Implant surface and implant diameter were significantly associated with the failure events in the retrospective studies. Placement of wide-diameter implants demonstrated a promising survival rate during 5-year follow-up. Further controlled trials with the control group and longer follow-up period are needed to provide the direct evidence comparing survival rates of wide implants with survival rates of narrower implants.

Long-Term Performance of the Riata/ST Implantable Cardioverter–Defibrillator Lead

Riata and Riata ST implantable cardioverter-defibrillator leads are prone to structural and electrical failure (EF). Our objective was to evaluate Riata/ST lead performance over a long-term follow-up. Of 184 patients having undergone Riata/ST and Riata ST Optim lead implantation from September 2003 to June 2008, 154 patients were evaluated for EF and radiographic conductor externalization (CE). Survival analysis for EF was performed for Riata/ST leads, both for failure-free lead survival and cumulative hazard. Subanalysis on 7Fr leads was performed to evaluate EF and CE rates both for different Riata ST lead management (monitoring vs proactive) and between Riata ST and Riata ST Optim leads. During a mean follow-up of 7 years, Riata/ST lead EF rate was 13% overall. Similar failure-free survival rate was noted for 7Fr as for 8Fr leads (log-rank, p = 0.63). Of all failed leads, 64% failed only after 5 years of follow-up. Compared with the absolute failure rate of 1.84% per device year, cumulative hazard analysis for leads surviving past 5 years revealed an estimated failure rate of 7% per year. No clinical or procedural predictors for EF were found. The subanalysis on 7Fr leads showed an excellent outcome both for a proactive lead management approach as for Optim leads. In conclusion, long-term survival of the Riata/ST lead is impaired with an accelerating EF risk over time. An initial exponential trend was followed by a linear lead failure pattern for leads surviving past 5 years, corresponding to an estimated 7% annual EF rate. These findings may have repercussions on the lead management strategy in patients currently surviving with a Riata/ST lead to prevent significant clinical events like inappropriate shocks or failed device interventions.

Abstract 19880: High Failure Rate of Linox Defibrillator Leads

Introduction: Recent lead failures have resulted in large recalls with a significant global impact, not only financially, but also physically and mentally for those carrying an implantable cardiac defibrillator (ICD). Following the introduction of the ‘Linox S’ and ‘Linox SD’ ICD leads in 2006 by manufacturer ‘Biotronik’, we observed several cases with early failure. The objective of this study was to determine the failure rate of ‘Biotronik Linox’ leads implanted at our centre, and to compare them with the performance of two comparators, the Durata (St. Jude Medical) and the Endotak (Boston Scientific) lead. Methods: As of 2012, all ‘Linox S or SD’ (n=408), Durata (model 7122, n=340) and Endotak (model 0125, 0138 and 0158, n=343) leads were identified form the Erasmus MC prospective ICD registry. Lead failure was defined by low/high-voltage impedance, failure to capture, sense or defibrillate, or the presence of non-physiological signals not due to external interference. Results: A total of 1091 high-voltage defibrillation leads were implanted between April 2000 and May 2012 in 1066 patients (78% males, median age 62 years). The median time from implantation to lead failure was 3.6 years (IQR, 1.5 to 4.8 years). ‘Linox’ leads demonstrated a sudden increase in failure at 3-3.5 years after implantation and their estimated failure rates were 5.5% and 10.1%, at 5 and 8 years after implantation, respectively. Durata and Endotak demonstrated gradual malfunction and failure rates were 2.1% and 2.1%, and 0.4% and 0.8%, at 5 and 8 years, respectively. The mechanism of failure was noise in the majority of failed leads (50%) followed by impedance out-of-range (29%). Conclusions: ‘Linox S/SD’ leads demonstrate a significant high failure rate. Remote monitoring is reasonable as electrical dysfunction (noise or impedance out-of-range) is observed in the majority of cases. National device safety and advisory committees worldwide might be facing a new challenge.

The survival of direct composite restorations in the management of severe tooth wear including attrition and erosion: A prospective 8-year study

ObjectivesSurvival of directly placed composite to restore worn teeth has been reported in studies with small sample sizes, short observation periods and different materials. This study aimed to estimate survival for a hybrid composite placed by one clinician up to 8-years follow-up. MethodsAll patients were referred and recruited for a prospective observational cohort study. One composite was used: Spectrum® (DentsplyDeTrey). Most restorations were placed on the maxillary anterior teeth using a Dahl approach. ResultsA total of 1010 direct composites were placed in 164 patients. Mean follow-up time was 33.8 months (s.d. 27.7). 71 of 1010 restorations failed during follow-up. The estimated failure rate in the first year was 5.4% (95% CI 3.7–7.0%). Time to failure was significantly greater in older subjects (p=0.005) and when a lack of posterior support was present (p=0.003). Bruxism and an increase in the occlusal vertical dimension were not associated with failure. The proportion of failures was greater in patients with a Class 3 or edge-to-edge incisal relationship than in Class 1 and Class 2 cases but this was not statistically significant. More failures occurred in the lower arch (9.6%) compared to the upper arch (6%) with the largest number of composites having been placed on the maxillary incisors (n=519). ConclusionThe worn dentition presents a restorative challenge but composite is an appropriate restorative material. Clinical significanceThis study shows that posterior occlusal support is necessary to optimise survival.

Hazard Function Models to Estimate Mortality Rates Affecting Fish Populations with Application to the Sea Mullet (Mugil cephalus) Fishery on the Queensland Coast (Australia)

Fisheries management agencies around the world collect age data for the purpose of assessing the status of natural resources in their jurisdiction. Estimates of mortality rates represent a key information to assess the sustainability of fish stocks exploitation. Contrary to medical research or manufacturing where survival analysis is routinely applied to estimate failure rates, survival analysis has seldom been applied in fisheries stock assessment despite similar purposes between these fields of applied statistics. In this paper, we developed hazard functions to model the dynamic of an exploited fish population. These functions were used to estimate all parameters necessary for stock assessment (including natural and fishing mortality rates as well as gear selectivity) by maximum likelihood using age data from a sample of catch. This novel application of survival analysis to fisheries stock assessment was tested by Monte Carlo simulations to assert that it provided un-biased estimations of relevant quantities. The method was applied to data from the Queensland (Australia) sea mullet (Mugil cephalus) commercial fishery collected between 2007 and 2014. It provided, for the first time, an estimate of natural mortality affecting this stock: 0.22 $\pm$ 0.08 year$^{-1}$.

Irrigation and Debridement Before a 2-Stage Revision Total Knee Arthroplasty Does Not Increase Risk of Failure

BackgroundStudies have suggested that the success of 2-stage revision total knee arthroplasty (rTKA) may be compromised by a prior failed irrigation and debridement (I&D). The purpose of this study was to use 2 large state inpatient databases to compare the 2-stage rTKA failure rates for those patients with and without a prior I&D. MethodsThis retrospective, longitudinal study used inpatient discharge data from the State Inpatient Database of 2 states (California and New York) from 2005 to 2011. A combination of International Classification of Diseases, Ninth Revision, diagnosis and procedure codes was used to identify rTKA patients and compare failure rates for rTKA patients with and without prior I&D. The primary outcome was failure of the staged revision, which was defined as subsequent surgery due to infection within 4 years of the 2-stage rTKA. ResultsOf the 750 patients who underwent 2-stage rTKA, 57 had undergone a prior I&D. In all, 126 patients failed rTKA. After 4 years, the estimated failure rate was 8.7% (95% confidence interval [CI], 1.9%-16.9%) in the group with prior I&D and 17.5% (95% CI, 14.7%-20.4%) in the group without prior I&D. After adjusting for sex, race, insurance, median household income, and comorbidities, the hazard ratio for the group with a failed I&D was 0.49 (P = .122; 95% CI, 0.20-1.20), which indicated a lower risk of failure compared to the group without prior I&D. ConclusionThese findings indicate that the failure rate of 2-stage rTKA is not increased by prior failed I&D.

Reliability Estimation from Linear Degradation and Failure Time Data With Competing Risks Under a Step-Stress Accelerated Degradation Test

The accelerated degradation test (ADT) has become critical for product reliability assessment. In performing the ADT for newly developed products, a constant-stress ADT may be impractical or sometimes impossible where the available size of testing units and the testing duration are heavily bounded to meet the short development period of the products. As an alternative, a step-stress accelerated degradation test (SSADT) can be a useful tool for satisfying the test limitation, and for making up for uncertainty in selecting appropriate levels of stress. Occasionally, the elevated stress under SSADT not only accelerates the performance degradation of products, but it may also expedite traumatic failures. This paper proposes a modeling approach to simultaneously analyze linear degradation data and traumatic failures with competing risks in an SSADT experiment. Under the modeling approach, a cumulative exposure model is considered. The failure rate corresponding to each failure mode is described as a function of the degradation level at the moment of failure. No parametric assumptions are made regarding the failure-time distribution to extend the proposed method to more general cases. We derive maximum likelihood estimates of the model parameters, then estimate failure rates and product reliability based on the degradation level to failure. Asymptotic properties of the maximum likelihood estimates are also discussed. The proposed model is applied to accelerated degradation data from plastic substrate active matrix light-emitting diodes (AMOLEDs), along with sensitivity analysis.

Validation Techniques for Fault Emulation of SRAM-based FPGAs

A variety of fault emulation systems have been created to study the effect of single-event effects (SEEs) in static random access memory (SRAM) based field-programmable gate arrays (FPGAs). These systems are useful for augmenting radiation-hardness assurance (RHA) methodologies for verifying the effectiveness for mitigation techniques; understanding error signatures and failure modes in FPGAs; and failure rate estimation. For radiation effects researchers, it is important that these systems properly emulate how SEEs manifest in FPGAs. If the fault emulation systems does not mimic the radiation environment, the system will generate erroneous data and incorrect predictions of behavior of the FPGA in a radiation environment. Validation determines whether the emulated faults are reasonable analogs to the radiation-induced faults. In this paper we present methods for validating fault emulation systems and provide several examples of validated FPGA fault emulation systems.

Multi‐objective design of advanced power distribution networks using restricted‐population‐based multi‐objective seeker‐optimisation‐algorithm and fuzzy‐operator

This study proposes a method for designing advanced power distribution system (PDS) including distributed generations, using a combination of fundamental loop generator and multi-objective seeker-optimisation algorithm (MOSOA). The proposed approach reduces the searching space using fundamental loop generator technique to obtain initial feasible solutions which is further improved by SOA to generate new set of solutions with improved aptitude. The proposed methodology uses a contingency-load-loss-index for reliability evaluation, which is independent of the estimation of failure rate and fault repair duration of feeder branches. This planning strategy includes distribution automation devices such as automatic reclosers (RAs) to enhance the reliability of PDS. The proposed algorithm generates a set of non-dominated solution by simultaneous optimisation of two conflicting objectives (economic cost and system reliability) using Pareto-optimality-based trade-off analysis including a fuzzy-operation to automatically select the most suitable solution over the Pareto-front. The performance of the proposed approach is assessed and illustrated on 54-bus and 100-bus PDS, considering realtime design practices. Extensive comparisons are made against some well-known and efficient MO algorithms such as fast non-dominated sorting genetic algorithm-II, MO particle- swarm-optimisation and MO immunised-particleswarm-optimisation. Simulation results show that the proposed approach is accurate and efficient, and a potential candidate for large-scale PDS planning.

A novel model of failure rate prediction for circular electrical connectors

The reliability of electrical connectors has critical impact on electronic systems. It is usually characterized by failure rate prediction value according to standard MIL-HDBK-217 (or GJB-299C in Chinese) in engineering practice. Given to their limitations and mislead results, a new failure rate prediction models needs to be presented. The presented model aims at the mechanism of increase of film thickness which leads to the increase of contact resistance. The estimated failure rate value can be given at different environmental conditions, and some of the factors affecting the reliability are taken into account. Accelerated degradation test (ADT) was conducted on GJB599III series electrical connector. The failure rate prediction model can be simply formed and convenient to calculate the expression of failure rate changing with time at various temperature and vibration conditions. This model gives an objective assessment in short time, which makes it convenient to be applied to the engineering.