Compressed Natural Gas Bus Safety: A Quantitative Risk Assessment

This study assesses the fire safety risks associated with compressed natural gas (CNG) vehicle systems, comprising primarily a typical school bus and supporting fuel infrastructure. The study determines the sensitivity of the results to variations in component failure rates and consequences of fire events. The components and subsystems that contribute most to fire safety risk are determined. Finally, the results are compared to fire risks of the present generation of diesel-fueled school buses. Direct computation of the safety risks associated with diesel-powered vehicles is possible because these are mature technologies for which historical performance data are available. Because of limited experience, fatal accident data for CNG bus fleets are minimal. Therefore, this study uses the probabilistic risk assessment (PRA) approach to model and predict fire safety risk of CNG buses. Generic failure data, engineering judgments, and assumptions are used in this study. This study predicts the mean fire fatality risk for typical CNG buses as approximately 0.23 fatalities per 100-million miles for all people involved, including bus passengers. The study estimates mean values of 0.16 fatalities per 100-million miles for bus passengers only. Based on historical data, diesel school bus mean fire fatality risk is 0.091 and 0.0007 per 100-million miles for all people and bus passengers, respectively. One can therefore conclude that CNG buses are more prone to fire fatality risk by 2.5 times that of diesel buses, with the bus passengers being more at risk by over two orders of magnitude. The study estimates a mean fire risk frequency of 2.2 x 10(-5) fatalities/bus per year. The 5% and 95% uncertainty bounds are 9.1 x 10(-6) and 4.0 x 10(-5), respectively. The risk result was found to be affected most by failure rates of pressure relief valves, CNG cylinders, and fuel piping.     

Record values of exponentially distributed random variables

A sequence {X_n, n≥1} of independent and identically distributed random variables with absolutely continuous (with respect to Lebesque measure) cumulative distribution function F(x) is considered. X_j is a record value of this sequence if X_j>max(X₁,…,X_j?1), j>1. Let {X_L(n), n≥0} with L(o)=1 be the sequence of such record values and Z_n,n?1=X_L(n)–X_L(n?1). Some properties of Z_n,n?1 are studied and characterizations of the exponential distribution are discussed in terms of the expectation and the hazard rate of z_n,n?1.     

Revisiting Fiat Regime’s Attainability of Shari’ah Objectives and Possible Futuristic Alternatives

Maqasid of Shari'ah is a millennium old theory on the higher objectives of Islamic divine law. As the discipline of Islamic economics and finance grew in politico-economic importance in the past three decades, a cathartic trend has emerged among Muslim experts to realign economic and financial practices with not merely the minimum legal requirements of religion but also the wisdom and crucial objectives of Shari'ah. An expositive example of this is the monetary economics debate of a Shari'ah consonant currency. Though vast majority of religious clerics have approbated fiat and paper currencies in strict legal terms since the 1980s, a revisionist movement since the mid-1990s seeks to counter it—some going as far as indorsing reversion to gold and silver coinage of medieval Islamic epoch of affluence. Unlike orthodox fiqhi (strict jurisprudentialism) approach that involves legalese with little leeway, Maqasid approach concerns itself with the spirit of the law. This paper operates in the exciting laboratory of Maqasidic framework to appraise the multitudinous role of fiat currency in protecting economic, political, and social public interests, prevention of harm, promotion of egalitarianism, and attainment of ultimate utopic vision of theological and spiritual demands in Shari'ah. The paper contributes, theoretically, by introducing several moral-philosophical arguments against fiat’s compatibility with Shari'ah, and, practically, by prognosticating the future course of discourse in light of advancements in technological innovations—including nascent crypto-currencies.     

On the mean residual life of records

Suppose that a technical system is subject to shocks, e.g. peaks of voltages from a sequence of identically independent voltages having a lower limit value v>0$v>0$. We propose a new definition for the mean residual life of the records of the sequence and study its various properties.