n.

有効性、利用能、役立つこと、入手可能なこと

関: effective、effectiveness、efficacy、usefulness、validity

WordNet

capacity or power to produce a desired effect; "concern about the safety and efficacy of the vaccine" (同)efficaciousness
works well as a means or remedy; "an effective reprimand"; "a lotion that is effective in cases of prickly heat"
producing or capable of producing an intended result or having a striking effect; "an air-cooled motor was more effective than a witchs broomstick for rapid long-distance transportation"-LewisMumford; "effective teaching methods"; "effective steps toward peace"; "made an effective entrance"; "his complaint proved to be effectual in bringing action"; "an efficacious law" (同)effectual, efficacious
able to accomplish a purpose; functioning effectively; "people who will do nothing unless they get something out of it for themselves are often highly effective persons..."-G.B.Shaw; "effective personnel"; "an efficient secretary"; "the efficient cause of the revolution" (同)efficient
exerting force or influence; "the law is effective immediately"; "a warranty good for two years"; "the law is already in effect (or in force)" (同)good, in effect, in force
existing in fact; not theoretical; real; "a decline in the effective demand"; "confused increased equipment and expenditure with the quantity of effective work done"
ready for service; "the fort was held by about 100 effective soldiers"
the quality of having legal force or effectiveness (同)validness
power to be effective; the quality of being able to bring about an effect (同)effectivity, effectualness, effectuality

PrepTutorEJDIC

利用できること,有用性,利用価値
(…に対する,における)効きめ,効力《+『against』(『in』)+『名』》
『効果的な』,効きめのある / (法律などが)『有効な』,実施されている / 印象深い,感銘的な / 実際に役立つ,実動の
(理論・理由などの)『妥当性』,正当性《+of+名》 / (契約などの)有効性,合法性《+of+名》

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/11/30 18:12:21」(JST)

wiki en

[Wiki en表示]

In reliability theory and reliability engineering, the term availability has the following meanings:

The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e. a random, time. Simply put, availability is the proportion of time a system is in a functioning condition. This is often described as a mission capable rate. Mathematically, this is expressed as 100% minus unavailability.
The ratio of (a) the total time a functional unit is capable of being used during a given interval to (b) the length of the interval.

For example, a unit that is capable of being used 100 hours per week (168 hours) would have an availability of 100/168. However, typical availability values are specified in decimal (such as 0.9998). In high availability applications, a metric known as nines, corresponding to the number of nines following the decimal point, is used. With this convention, "five nines" equals 0.99999 (or 99.999%) availability.

Introduction

Availability of a system is typically measured as a factor of its reliability - as reliability increases, so does availability.

Availability of a system may also be increased by the strategy of focusing on increasing testability, diagnostics and maintainability and not on reliability. Improving maintainability during the early design phase is generally easier than reliability (and Testability & diagnostics). Maintainability estimates (item Repair [by replacement] rates) are also generally more accurate. However, because the uncertainties in the reliability estimates (and also in diagnostic times) are in most cases very large, it is likely to dominate the availability (and the prediction uncertainty) problem, even while maintainability levels are very high. Furthermore, when reliability is not under control, then many and different sorts of issues may arise, for example:

The need for complex testability (built in test sensors, hardware and software) requirements,
The need for detailed diagnostic procedures,
Manpower (maintainers / customer service capability) availability,
Spare part availability,
Dead on Arrival (DOA's) issues (non-quality impact on system availability),
Logistic delays of spares or manpower due to any reason,
Lack of repair facilities and tools - also for software (e.g. situation DoD F22 Raptor Fighter program),
Lack of repair knowledge and expert-personnel
Extensive retro-fit and complex configuration management costs and others.

The problem of unreliability may also become out of control due to the "domino effect" of maintenance induced failures after repairs and more and more increasing efforts of problem solving, re-engineering en service efforts. Only focusing on maintainability is therefore not enough!

If failures are prevented, none of the others are of any importance and therefore reliability is generally regarded as the most important part of availability!

Reliability needs to be evaluated and improved related to both availability and the cost of ownership (due to cost of spare parts, maintenance man-hours, transport costs, storage cost, part obsolete risks etc.). Often a trade-off is needed between the two. There might be a maximum ratio between availability and cost of ownership. Testability of a system should also be addressed in the availability plan as this is the link between reliability and maintainability. The maintenance strategy can influence the reliability of a system (e.g. by preventive and/or predictive maintenance), although it can never bring it above the inherent reliability. So, Maintainability and Maintenance strategies influences the availability of a system. In theory this can be almost unlimited if one would be able to always repair any fault in an infinitely short time. This is in practice impossible. Repair-ability is always limited due to testability, manpower and logistic considerations. Reliability is not limited (Reliable items can be made that outlast the life of a machine with almost 100% certainty). For high levels of system availability (e.g. the availability of engine trust in an aircraft), the use of redundacy may be the only option. Refer to reliability engineering.

An availability plan should clearly provide a strategy for availability control. Whether only Availability or also Cost of Ownership is more important depends on the use of the system. For example, a system that is a critical link in a production system - e.g. a big oil platform – is normally allowed to have a very high cost of ownership if this translates to even a minor increase in availability, as the unavailability of the platform results in a massive loss of revenue which can easily exceed the high cost of ownership. A proper reliability plan should always address RAMT analysis in its total context. RAMT stands in this case for Reliability, Availability, Maintainability/Maintenance and Testability in context to the customer needs.

Representation

The most simple representation for availability is as a ratio of the expected value of the uptime of a system to the aggregate of the expected values of up and down time, or

If we define the status function as

X(t)= \begin{cases} 1, & \mbox{sys functions at time } t\\ 0, & \mbox{otherwise} \end{cases}

therefore, the availability A(t) at time t>0 is represented by

A(t)=\Pr[X(t)=1]=E[X(t)].

Average availability must be defined on an interval of the real line. If we consider an arbitrary constant , then average availability is represented as

A_c = \frac{1}{c}\int_0^c A(t)\,dt.

Limiting (or steady-state) availability is represented by^{[citation needed]}

A = \lim_{c \rightarrow \infty} A_c.

Limiting average availability is also defined on an interval as,

A_{\infty}=\lim_{c \rightarrow \infty} A_c = \lim_{c \rightarrow \infty}\frac{1}{c}\int_0^c A(t)\,dt,\quad c > 0.

Availability is the probability that an item will be in an operable and commitable state at the start of a mission when the mission is called for at a random time, and is generally defined as uptime divided by total time (uptime plus downtime).

Definitions within Systems Engineering

Availability, Inherent (Ai) ^[1] The probability that an item will operate satisfactorily at a given point in time when used under stated conditions in an ideal support environment. It excludes logistics time, waiting or administrative downtime, and preventive maintenance downtime. It includes corrective maintenance downtime. Inherent availability is generally derived from analysis of an engineering design and is calculated as the mean time to failure (MTTF) divided by the mean time to failure plus the mean time to repair (MTTR). It is based on quantities under control of the designer.

Availability, Achieved (Aa) ^[2] The probability that an item will operate satisfactorily at a given point in time when used under stated conditions in an ideal support environment (i.e., that personnel, tools, spares, etc. are instantaneously available). It excludes logistics time and waiting or administrative downtime. It includes active preventive and corrective maintenance downtime.

Availability, Operational (Ao) ^[3] The probability that an item will operate satisfactorily at a given point in time when used in an actual or realistic operating and support environment. It includes logistics time, ready time, and waiting or administrative downtime, and both preventive and corrective maintenance downtime. This value is equal to the mean time between failure (MTBF) divided by the mean time between failure plus the mean downtime (MDT). This measure extends the definition of availability to elements controlled by the logisticians and mission planners such as quantity and proximity of spares, tools and manpower to the hardware item.

Refer to Systems Engineering for more details

Example

If we are using equipment which has a mean time to failure (MTTF) of 81.5 years and mean time to repair (MTTR) of 1 hour:

MTTF in hours = 81.5*365*24=713940 (This is a reliability parameter and often has a high level of uncertainty!)

Inherent Availability (Ai) = MTTF/(MTTF+MTTR) = 713940/713941 =99.999859%

Inherent Unavailability = 0.000141%

Outage due to equipment in hours per year = 1/rate = 1/MTTF = 0.01235 hours per year.

Literature

Availability is well established in the literature of stochastic modeling and optimal maintenance. Barlow and Proschan [1975] define availability of a repairable system as "the probability that the system is operating at a specified time t." Blanchard [1998] gives a qualitative definition of availability as "a measure of the degree of a system which is in the operable and committable state at the start of mission when the mission is called for at an unknown random point in time." This definition comes from the MIL-STD-721. Lie, Hwang, and Tillman [1977] developed a complete survey along with a systematic classification of availability.

Availability measures are classified by either the time interval of interest or the mechanisms for the system downtime. If the time interval of interest is the primary concern, we consider instantaneous, limiting, average, and limiting average availability. The aforementioned definitions are developed in Barlow and Proschan [1975], Lie, Hwang, and Tillman [1977], and Nachlas [1998]. The second primary classification for availability is contingent on the various mechanisms for downtime such as the inherent availability, achieved availability, and operational availability. (Blanchard [1998], Lie, Hwang, and Tillman [1977]). Mi [1998] gives some comparison results of availability considering inherent availability.

Availability considered in maintenance modeling can be found in Barlow and Proschan [1975] for replacement models, Fawzi and Hawkes [1991] for an R-out-of-N system with spares and repairs, Fawzi and Hawkes [1990] for a series system with replacement and repair, Iyer [1992] for imperfect repair models, Murdock [1995] for age replacement preventive maintenance models, Nachlas [1998, 1989] for preventive maintenance models, and Wang and Pham [1996] for imperfect maintenance models.

Applications

Availability is used extensively in power plant engineering. For example, the North American Electric Reliability Corporation implemented the Generating Availability Data System in 1982.^[4]

References

^ "Inherent Availability (AI)". Glossary of Defense Acquisition Acronyms and Terms. Department of Defense. Retrieved 10 April 2014.
^ "Achieved Availability (AI)". Glossary of Defense Acquisition Acronyms and Terms. Department of Defense. Retrieved 10 April 2014.
^ "Operational Availability (AI)". Glossary of Defense Acquisition Acronyms and Terms. Department of Defense. Retrieved 10 April 2014.
^ "Mandatory Reporting of Conventional Generation Performance Data" (PDF). Generating Availability Data System. North American Electric Reliability Corporation. July 2011. pp. 7, 17. Retrieved 13 March 2014.

This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).

External links

Reliability and Availability Basics
System Reliability and Availability
Availability and the Different Ways to Calculate It

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 脳炎または髄膜炎患者における単純ヘルペスウイルスの診断のためのPCR検査 pcr testing for the diagnosis of herpes simplex virus in patients with encephalitis or meningitis
2. 甲状腺ホルモンの作用 thyroid hormone action
3. β‐サラセミアメジャーにおける造血細胞移植の有効性 efficacy of hematopoietic cell transplantation in beta thalassemia major
4. 錠剤を嚥下できないHIV感染成人患者の治療：液剤、チュアブル、および砕くことができる剤形の薬剤 treatment of hiv infected adults who have trouble swallowing pills liquid chewable and crushable formulations
5. サンゴヘビによる咬傷の評価およびマネージメント evaluation and management of coral snakebites

English Journal

Do Differential Response Rates to Patient Surveys Between Organizations Lead to Unfair Performance Comparisons?: Evidence From the English Cancer Patient Experience Survey.

Saunders CL1, Elliott MN, Lyratzopoulos G, Abel GA.
Medical care.Med Care.2016 Nov 24. [Epub ahead of print]
BACKGROUND: Patient surveys typically have variable response rates between organizations, leading to concerns that such differences may affect the validity of performance comparisons.OBJECTIVE: To explore the size and likely sources of associations between hospital-level survey response rates and pa
PMID 26595223

Differential detection of a surrogate biological threat agent (Bacillus globigii) with a portable surface plasmon resonance biosensor.

Adducci BA1, Gruszewski HA1, Khatibi PA1, Schmale DG 3rd2.
Biosensors & bioelectronics.Biosens Bioelectron.2016 Apr 15;78:160-6. doi: 10.1016/j.bios.2015.11.032. Epub 2015 Nov 14.
New methods and technology are needed to quickly and accurately detect potential biological warfare agents, such as Bacillus anthracis, causal agent of anthrax in humans and animals. Here, we report the detection of a simulant of B. anthracis (B. globigii) alone and in a mixture with a different spe
PMID 26606307

A high-throughput liquid bead array-based screening technology for Bt presence in GMO manipulation.

Fu W1, Wang H1, Wang C1, Mei L1, Lin X1, Han X2, Zhu S3.
Biosensors & bioelectronics.Biosens Bioelectron.2016 Mar 15;77:702-8. doi: 10.1016/j.bios.2015.10.043. Epub 2015 Oct 23.
The number of species and planting areas of genetically modified organisms (GMOs) has been rapidly developed during the past ten years. For the purpose of GMO inspection, quarantine and manipulation, we have now devised a high-throughput Bt-based GMOs screening method based on the liquid bead array.
PMID 26499065

Japanese Journal

Thick-target yields of radioactive targets deduced from inverse kinematics

Aikawa M.,Ebata S.,Imai S.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 353, 1-3, 2015-06-15
… We apply the method to the natCu(12C,X)24Na reaction to confirm availability. …
NAID 120005602532

パブリッククラウドにおけるL2TPv3を用いたサーバ高可用性の評価

松本直人
情報処理学会研究報告. IOT, [インターネットと運用技術] 2015-IOT-29(33), 1-3, 2015-05-14
インターネットを介して計算機資源を利用するパブリッククラウドは日々拡大を続けている.しかしパブリッククラウドの多くはトラフィック制限により IPUnicast のみクラウドネットワーク上で利用可能であり,IPMulticast を用いた VRRP など高可用性を実現するプロトコルを使うことができない.本稿では,パブリッククラウド上の仮想マシンにおいて L2TPv3 プロトコルを有効とし,OSPFv …
NAID 110009900818

パブリッククラウドにおけるL2TPv3を用いたサーバ高可用性の評価

松本直人
情報処理学会研究報告. CSEC, [コンピュータセキュリティ] 2015-CSEC-69(33), 1-3, 2015-05-14
インターネットを介して計算機資源を利用するパブリッククラウドは日々拡大を続けている.しかしパブリッククラウドの多くはトラフィック制限により IPUnicast のみクラウドネットワーク上で利用可能であり,IPMulticast を用いた VRRP など高可用性を実現するプロトコルを使うことができない.本稿では,パブリッククラウド上の仮想マシンにおいて L2TPv3 プロトコルを有効とし,OSPFv …
NAID 110009900784