13,693 research outputs found
Expert Elicitation for Reliable System Design
This paper reviews the role of expert judgement to support reliability
assessments within the systems engineering design process. Generic design
processes are described to give the context and a discussion is given about the
nature of the reliability assessments required in the different systems
engineering phases. It is argued that, as far as meeting reliability
requirements is concerned, the whole design process is more akin to a
statistical control process than to a straightforward statistical problem of
assessing an unknown distribution. This leads to features of the expert
judgement problem in the design context which are substantially different from
those seen, for example, in risk assessment. In particular, the role of experts
in problem structuring and in developing failure mitigation options is much
more prominent, and there is a need to take into account the reliability
potential for future mitigation measures downstream in the system life cycle.
An overview is given of the stakeholders typically involved in large scale
systems engineering design projects, and this is used to argue the need for
methods that expose potential judgemental biases in order to generate analyses
that can be said to provide rational consensus about uncertainties. Finally, a
number of key points are developed with the aim of moving toward a framework
that provides a holistic method for tracking reliability assessment through the
design process.Comment: This paper commented in: [arXiv:0708.0285], [arXiv:0708.0287],
[arXiv:0708.0288]. Rejoinder in [arXiv:0708.0293]. Published at
http://dx.doi.org/10.1214/088342306000000510 in the Statistical Science
(http://www.imstat.org/sts/) by the Institute of Mathematical Statistics
(http://www.imstat.org
Bowtie models as preventive models in maritime safety
Aquest treball ha sorgit d’una proposta del Dr. Rodrigo de Larrucea que ha acabat de publicar un llibre ambiciĂłs sobre Seguretat MarĂtima. Com ell mateix diu, el tema “excedeix amb molt les potencialitats de l’autor”, aixĂ que en el meu cas això Ă©s mĂ©s cert. Es pot aspirar, però, a fer una modesta contribuciĂł a l’estudi i difusiĂł de la seguretat de la cultura marĂtima, que nomĂ©s apareix a les notĂcies quan tenen lloc desastres molt puntuals.
En qualsevol cas, el professor em va proposar que em centrĂ©s en els Bowtie Models, models en corbatĂ, que integren l’arbre de causes y el de conseqüències (en anglès el Fault Tree Analysis, FTA, i l’Event Tree Analysis, ETA). Certament, existeixen altres metodologies i aproximacions (i en el seu llibre en presenta vĂ ries, resumides), però per la seva senzillesa conceptual i possibilitat de generalitzaciĂł i integraciĂł dels resultats era una bona aposta. AixĂ, desprĂ©s d’una fase de meditaciĂł i recopilaciĂł de informaciĂł, em vaig decidir a presentar un model en corbatĂ molt general on caben les principals causes d’accidents (factores ambientals, error humĂ i fallada mecĂ nica), comptant tambĂ© que pot existir una combinaciĂł de causes.
De tota manera, a l’hora d’explotar aquest model existeix la gran dificultat de donar una probabilitat de ocurrència, un nombre entre 0 i 1, a cada branca. Normalment les probabilitats d’ocurrència sĂłn petites i degut a això difĂcils d’estimar. Cada accident Ă©s diferent, de grans catĂ strofes n’hi ha poques, i cada accident ja Ă©s estudiat de manera exhaustiva (mĂ©s exhaustiva quan mĂ©s greu Ă©s). Un altre factor que dificulta l’estima de la probabilitat de fallada Ă©s l’evoluciĂł constant del mĂłn marĂtim, tant des del punt de vista tècnic, de formaciĂł, legal i fins i tot generacional doncs cada generaciĂł de marins Ă©s diferent. Els esforços estan doncs enfocats a augmentar la seguretat, encara que sempre amb un ull posat sobre els costs. AixĂ, he presentat un model en corbatĂ pel seu valor didĂ ctic i grĂ fic però sense entrar en detalls numèrics, que si s’escau ja anirĂ© afinant i interioritzant en l’exercici de la professiĂł.
En aquest treball tambĂ© he intentat no mantenir-me totalment al costat de la teoria (ja se sap que si tot es fa bĂ©, tot surt perfecte, etc…) sinĂł presentar amb cert detall 2 casos ben coneguts d’accidents marĂtims: el petroler Exxon Valdez, el 1989 i el ferry Estonia en 1994, entre altres esmentats. SĂłn casos ja una mica vells però que van contribuir a augmentar la cultura de la seguretat, fins a arribar al nivell del que gaudim actualment, al menys als paĂŻsos occidentals. Doncs la seguretat, com esmenta Rodrigo de Larrucea “és una actitud i mai Ă©s fortuĂŻta; sempre Ă©s el resultat d’una voluntat decidida, un esforç sincer, una direcciĂł intel·ligent i una execuciĂł acurada. Sens lloc a dubtes, sempre suposa la millor alternativa”.
The work has been inspired in its initial aspects by the book of my tutor Jaime Rodrigo de Larrucea, that presents a state of the art of all the maritime aspects related to safety. Evidently, since it covers all the topics, it cannot deepen on every topic. It was my opportunity to deepen in the Bowtie Model but finally I have also covered a wide variety of topics.
Later, when I began to study the topics, I realized that the people in the maritime world usually do not understand to a great extent statistics. Everybody is concerned about safety but few nautical students take a probabilistic approach to the accidents. For this it is extremely important to study the population that is going to be studied: in our case the SOLAS ships
Also, during my time at Riga, I have been very concerned with the most diverse accidents, some of them studied during the courses at Barcelona. I have seen that it is difficult to model mathematically the accidents, since each one has different characteristics, angles, and surely there are not 2 equal.
Finally, it was accorded that I should concentrate on the Bowtie Model, which is not very complex from a statistical point of view. It is simply a fault tree of events model and a tree of effects. I present some examples in this Chapter 2. The difficulty I point out is to try to estimate the probabilities of occurrence of events that are unusual.
We concentrated at major accidents, those that may cause victims or heavy losses. Then, for the sake of generality, at Chapter 4, I have divided the causes in 4 great classes: Natural hazards, human factor, mechanical failure and attacks (piracy and terrorism). The last concern maybe should not be included beside the others since terrorism and piracy acts are not accidents, but since there is an important code dedicated to prevent security threats, ISPS, it is example of design of barriers to prevent an undesired event (although it gives mainly guidelines to follow by the States, Port Terminals and Shipping Companies). I have presented a detailed study of the tragedy of the Estonia, showing how a mechanical failure triggered the failure of the ferry, by its nature a delicate ship, but there were other factors such as poor maintenance and heavy seas.
At the next Chapter, certain characteristics of error chains are analyzed. Finally, the conclusions are drawn, offering a pretty optimistic view of the safety (and security) culture at the Western World but that may not easily permeate the entire World, due to the associated costs
Impact Of Content Features For Automatic Online Abuse Detection
Online communities have gained considerable importance in recent years due to
the increasing number of people connected to the Internet. Moderating user
content in online communities is mainly performed manually, and reducing the
workload through automatic methods is of great financial interest for community
maintainers. Often, the industry uses basic approaches such as bad words
filtering and regular expression matching to assist the moderators. In this
article, we consider the task of automatically determining if a message is
abusive. This task is complex since messages are written in a non-standardized
way, including spelling errors, abbreviations, community-specific codes...
First, we evaluate the system that we propose using standard features of online
messages. Then, we evaluate the impact of the addition of pre-processing
strategies, as well as original specific features developed for the community
of an online in-browser strategy game. We finally propose to analyze the
usefulness of this wide range of features using feature selection. This work
can lead to two possible applications: 1) automatically flag potentially
abusive messages to draw the moderator's attention on a narrow subset of
messages ; and 2) fully automate the moderation process by deciding whether a
message is abusive without any human intervention
Finding Street Gang Members on Twitter
Most street gang members use Twitter to intimidate others, to present
outrageous images and statements to the world, and to share recent illegal
activities. Their tweets may thus be useful to law enforcement agencies to
discover clues about recent crimes or to anticipate ones that may occur.
Finding these posts, however, requires a method to discover gang member Twitter
profiles. This is a challenging task since gang members represent a very small
population of the 320 million Twitter users. This paper studies the problem of
automatically finding gang members on Twitter. It outlines a process to curate
one of the largest sets of verifiable gang member profiles that have ever been
studied. A review of these profiles establishes differences in the language,
images, YouTube links, and emojis gang members use compared to the rest of the
Twitter population. Features from this review are used to train a series of
supervised classifiers. Our classifier achieves a promising F1 score with a low
false positive rate.Comment: 8 pages, 9 figures, 2 tables, Published as a full paper at 2016
IEEE/ACM International Conference on Advances in Social Networks Analysis and
Mining (ASONAM 2016
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