Challenges to the Acceptance of Probabilistic Risk Analysis

This paper discusses a number of the key challenges to the acceptance and application of probabilistic risk analysis (PRA). Those challenges include: (a) the extensive reliance on subjective judgment in PRA, requiring the development of guidance for the use of PRA in risk-informed regulation, and possibly the development of robust or reference prior distributions to minimize the reliance on judgment; and (b) the treatment of human performance in PRA, including not only human error per se but also management and organizational factors more broadly. All of these areas are seen as presenting interesting research challenges at the interface between engineering and other disciplines.     

Power Assignment for <Emphasis Type="Italic">k</Emphasis>-Connectivity in Wireless Ad Hoc Networks

The problem Min-Power k-Connectivity seeks a power assignment to the nodes in a given wireless ad hoc network such that the produced network topology is k-connected and the total power is the lowest. In this paper, we present several approximation algorithms for this problem. Specifically, we propose a 3k-approximation algorithm for any k, a (k + 12H (k)) -approximation algorithm for k(2k–1) n where n is the network size, a (k+2(k + 1)/2) -approximation algorithm for 2 k7, a 6-approximation algorithm for k = 3, and a 9-approximation algorithm for k = 4.This work is supported in part by Hong Kong Research Grant Council under grant No. CityU 1149/04E.This work is partially supported by NSF CCR-0311174.     

Are g.p.a. and ethics related?

This article reports results of a study of some 200 college-aged students at California State University. Ethical values are measured using a subset of the well-known and frequently used Rokeach Value Survey. Using nonparametric statistical analysis, four value measures, and four different consistent tests of significance and probability, the research data, perhaps disappointedly for many observers including the authors, reveal that there is no relationship between college grade point average and student ethics. Statistical analysis was done on g.p.a. splits of less than 3.0 versus 3.0 or more and also on g.p.a. data for 2.5 or less versus 3.5 or more. In all cases, there are no significant relationships between high or low grade point averages and scores on ethical value rankings.     

Fundamentals of Health Risk Assessment. Use,Derivation, Validity and Limitations of Safety Indices

We investigated the way results of human health risk assessments are used, and the theory used to describe those methods, sometimes called the NAS paradigm. Contrary to a key tenet of that theory, current methods have strictly limited utility. The characterizations now considered standard, Safety Indices such as Acceptable Daily Intake, Reference Dose, and so on, usefully inform only decisions that require a choice between two policy alternatives (e.g., approve a food additive or not), decided solely on the basis of a finding of safety. Risk is characterized as the quotient of one of these Safety Indices divided by an estimate of exposure: a quotient greater than one implies that the situation may be considered safe. Such decisions are very widespread, both in the U. S. federal government and elsewhere. No current method is universal; different policies lead to different practices, for example, in California's Proposition 65, where statutory provisions specify some practices. Further, an important kind of human health risk assessment is not recognized by this theory: this kind characterizes risk as likelihood of harm, given estimates of exposure consequent to various decision choices. Likelihood estimates are necessary whenever decision makers have many possible decision choices and must weigh more than two societal values, such as in EPA's implementation of conventional air pollutants. These estimates can not be derived using current methods; different methods are needed. Our analysis suggests changes needed in both the theory and practice of human health risk assessment, and how what is done is depicted.     

Approximation Algorithms for Quadratic Programming

We consider the problem of approximating the global minimum of a general quadratic program (QP) with n variables subject to m ellipsoidal constraints. For m=1, we rigorously show that an -minimizer, where error (0, 1), can be obtained in polynomial time, meaning that the number of arithmetic operations is a polynomial in n, m, and log(1/). For m 2, we present a polynomial-time (1- )-approximation algorithm as well as a semidefinite programming relaxation for this problem. In addition, we present approximation algorithms for solving QP under the box constraints and the assignment polytope constraints.     

On the Tightness of the Alternating-Cycle Lower Bound for Sorting by Reversals

We give a theoretical answer to a natural question arising from a few years of computational experiments on the problem of sorting a permutation by the minimum number of reversals, which has relevant applications in computational molecular biology. The experiments carried out on the problem showed that the so-called alternating-cycle lower bound is equal to the optimal solution value in almost all cases, and this is the main reason why the state-of-the-art algorithms for the problem are quite effective in practice. Since worst-case analysis cannot give an adequate justification for this observation, we focus our attention on estimating the probability that, for a random permutation of n elements, the above lower bound is not tight. We show that this probability is low even for small n, and asymptotically (1/n⁵), i.e., O(1/n⁵) and (1/n⁵). This gives a satisfactory explanation to empirical observations and shows that the problem of sorting by reversals and its alternating-cycle relaxation are essentially the same problem, with the exception of a small fraction of pathological instances, justifying the use of algorithms which are heavily based on this relaxation. From our analysis we obtain convenient sufficient conditions to test if the alternating-cycle lower bound is tight for a given instance. We also consider the case of signed permutations, for which the analysis is much simpler, and show that the probability that the alternating-cycle lower bound is not tight for a random signed permutation of m elements is asymptotically (1/m²).     

Business student ethical values anew in the 1990s

This paper uses a Rokeach Value Survey methodology to again ask the question, now in the mid 1990s, whether business student ethics are different from non-business student ethics. Additionally, the paper addresses the question of whether a course can alter or change student ethics and values during a semester. Thirdly, this paper attempts to operationalize and empirically test and measure the new ethical concepts of moral management and moral maximization.     

A comparative study of U.S. and Iraqi students

This study uses a sample comprised of U.S. students and Iraqi students to determine if differences occur over ethical perceptions based on cultural/demographic issues. Irrespective of demographics, the results of this study indicate significant cultural differences between Iraqi students and American students with regard to selected ethical issues concerning graduate education. Specifically the differences occurred in the students' perceptions of winning is everything, selling one's soul, logic before emotion, and pander to professors. Iraqi students consistently viewed these beliefs as more necessary for success in their graduate education than did their American counterparts.     

On Shortest k-Edge-Connected Steiner Networks in Metric Spaces

Given a set of points P in a metric space, let l(P) denote the ratio of lengths between the shortest k-edge-connected Steiner network and the shortest k-edge-connected spanning network on P, and let r = inf l(P) P for k 1. In this paper, we show that in any metric space, r 3/4 for k 2, and there exists a polynomial-time -approximation for the shortest k-edge-connected Steiner network, where = 2 for even k and = 2 + 4/(3k) for odd k. In the Euclidean plane, and .     

Local Optimality and Its Application on Independent Sets for k-claw Free Graphs

Given a graph G = (V,E), we define the locally optimal independent sets asfollows. Let S be an independent set and T be a subset of V such that S T = and (S) T, where (S) is defined as the neighbor set of S. A minimum dominating set of S in T is defined as T_D(S) T such that every vertex of S is adjacent to a vertex inTD(S) and TD(S) has minimum cardinality. An independent setI is called r-locally optimal if it is maximal and there exists noindependent set S V\I with |ID (S)| r such that|S| >|I (S)|.In this paper, we demonstrate that for k-claw free graphs ther-locally optimal independent sets is found in polynomial timeand the worst case is bounded by , where I and I* are a locally optimal and an optimal independent set,respectively. This improves the best published bound by Hochbaum (1983) bynearly a factor of two. The bound is proved by LP duality and complementaryslackness. We provide an efficientO(|V|^r+3) algorithm to find an independent set which is notnecessarily r-locally optimal but is guarantteed with the above bound. Wealso present an algorithm to find a r-locally optimal independent set inO(|V|^r(k-1)+3) time.     

Ethical Futures and Public-Private Partnerships: Peering Far Down the Track

This article employs an institutional perspective in formulating predictions about the ethical futures of privatization partnerships. Although this paper focuses on ethical concerns in the U.S. public sector, it incorporates a multinational dimension in (a) comparing the meaning of privatization among societies and (b) probing privatization financing in the global economy. Five assumptions that flow from institutional reasoning are made explicit as supports for subsequent predictions. The institutional logic shifts privatization conversation away from conventional debate about competition and efficiency toward centralizing forces in both sectors in response to globalization. In that regard, this study identifies the systemic erosion of (local) community integrity as the key privatization problem of the future.     

Examining the link between social responsibility and decision styles

The paper examines the factors that influence socially responsible decision making by individuals. The study found four social responsibility styles: Playing it Safe, Weather The Storm, Problem to Solve, and Hope it Goes Away. These styles describe individuals on the basis of decision style, propensity for risk, and coping style. The styles explain why people with different values might come to the same decision in the same circumstances.     

Zeroing in on leadership effectiveness: The methodological challenges of benchmarking leadership practices

Business success in the 21st century will be based on the widespread mastery of leadership roles, rather than on the directives of a professional or leadership elite. The first step for systematically enacting a leadership development agenda for our nation is to identify the factors, values or qualities most important to leadership effectiveness. Next, we must improve our understanding of how these guiding ideas and insights translate into what successful leaders do. As we perfect this understanding, we will need to operationally define the best practices of successful leaders. These best practices must then become benchmarks for intensive leadership development efforts.This article considers nine methodological challenges of the first agenda item-identification of the factors, values or qualities most important to leadership effectiveness. To illustrate these challenges, the authors use their own business leadership research as a case study. This research surveys 127 chairmen, chief executive officers, and presidents-a cross section of successful U.S.A. business leaders, including men and women from all parts of the nation who have diverse industry, racial, ethnic and religious backgrounds. The authors identify where methodological improvements are needed to cope with the challenges of leadership research. They suggest important directions for methodological development and propose three minimum standards for future leadership research.     

Human Interindividual Variability in Parameters Related to Health Risks

This paper reviews existing data on the variability in parameters relevant for health risk analyses. We cover both exposure-related parameters and parameters related to individual susceptibility to toxicity. The toxicity/susceptibility data base under construction is part of a longer term research effort to lay the groundwork for quantitative distributional analyses of non-cancer toxic risks. These data are broken down into a variety of parameter types that encompass different portions of the pathway from external exposure to the production of biological responses. The discrete steps in this pathway, as we now conceive them, are:Contact Rate (Breathing rates per body weight; fish consumption per body weight)Uptake or Absorption as a Fraction of Intake or Contact RateGeneral Systemic Availability Net of First Pass Elimination and Dilution via Distribution Volume (e.g., initial blood concentration per mg/kg of uptake)Systemic Elimination (half life or clearance)Active Site Concentration per Systemic Blood or Plasma ConcentrationPhysiological Parameter Change per Active Site Concentration (expressed as the dose required to make a given percentage change in different people, or the dose required to achieve some proportion of an individual's maximum response to the drug or toxicant)Functional Reserve Capacity–Change in Baseline Physiological Parameter Needed to Produce a Biological Response or Pass a Criterion of Abnormal FunctionComparison of the amounts of variability observed for the different parameter types suggests that appreciable variability is associated with the final step in the process–differences among people in functional reserve capacity. This has the implication that relevant information for estimating effective toxic susceptibility distributions may be gleaned by direct studies of the population distributions of key physiological parameters in people that are not exposed to the environmental and occupational toxicants that are thought to perturb those parameters. This is illustrated with some recent observations of the population distributions of Low Density Lipoprotein Cholesterol from the second and third National Health and Nutrition Examination Surveys.     

Context in the Risk Assessment of Digital Systems

As the use of digital computers for instrumentation and control of safety-critical systems has increased, there has been a growing debate over the issue of whether probabilistic risk assessment techniques can be applied to these systems. This debate has centered on the issue of whether software failures can be modeled probabilistically. This paper describes a context-based approach to software risk assessment that explicitly recognizes the fact that the behavior of software is not probabilistic. The source of the perceived uncertainty in its behavior results from both the input to the software as well as the application and environment in which the software is operating. Failures occur as the result of encountering some context for which the software was not properly designed, as opposed to the software simply failing randomly. The paper elaborates on the concept of error-forcing context as it applies to software. It also illustrates a methodology which utilizes event trees, fault trees, and the Dynamic Flowgraph Methodology (DFM) to identify error-forcing contexts for software in the form of fault tree prime implicants.     

A Survey of Approaches for Assessing and Managing the Risk of Extremes

In this paper, we review methods for assessing and managing the risk of extreme events, where extreme events are defined to be rare, severe, and outside the normal range of experience of the system in question. First, we discuss several systematic approaches for identifying possible extreme events. We then discuss some issues related to risk assessment of extreme events, including what type of output is needed (e.g., a single probability vs. a probability distribution), and alternatives to the probabilistic approach. Next, we present a number of probabilistic methods. These include: guidelines for eliciting informative probability distributions from experts; maximum entropy distributions; extreme value theory; other approaches for constructing prior distributions (such as reference or noninformative priors); the use of modeling and decomposition to estimate the probability (or distribution) of interest; and bounding methods. Finally, we briefly discuss several approaches for managing the risk of extreme events, and conclude with recommendations and directions for future research.     

A Probabilistic Analysis of the Capacitated Facility Location Problem

The solution value of a stochastic version of the capacitated facility location problem is studied. It is shown that, for large numbers of customers n, the value of can be closely approximated by , where the constant is identified as a function of the parameters of the underlying stochastic model. Furthermore, an extensive probabilistic analysis is performed on the difference that includes an exponential inequality on the tail distribution, a classification of the speed of convergence and a central limit theorem.     

A Further Improved Approximation Algorithm for Breakpoint Graph Decomposition

Breakpoint graph decomposition is a crucial step in all recent approximation algorithms for SORTING BY REVERSALS, which is one of the best-known algorithmic problems in computational molecular biology. Caprara and Rizzi recently improved the approximation ratio for breakpoint graph decomposition from to + 1.4348 + , for any positive . In this paper, we extend the techniques of Caprara and Rizzi and incorporate a balancing argument to further improve the approximation ratio to + 1.4193 + , for any positive . These improvements imply improved approximation results for SORTING BY REVERSALS for almost all random permutations.     

The Rhetoric and Reality of Public-Private Partnerships

Public-private partnership (or PPP) is now a very-fashionable concept in discourse about public sector management. For many, following a British lead, it focuses on attracting private financing for public projects. However there are several other forms of public-private mix that are also often described as partnerships, and some of them are not nearly so new. This article notes that several nodes of interest have developed to explore these mixes/partnerships, and raises some questions about them. We should consider whether all such mixes can properly be described as partnerships. Also we need to know more about their long history, to investigate the possibility of developing a classificatory system to help us better understand the various forms, and to consider what conditions are necessary for successful mixing or partnering, in particular for protecting the public interest at a time when market forces exercise great power.     

On Combinatorial Approximation of Covering 0-1 Integer Programs and Partial Set Cover

The problems dealt with in this paper are generalizations of the set cover problem, min{cx | Ax b, x {0,1}ⁿ}, where c Q₊ⁿ, A {0,1}^{m × n}, b 1. The covering 0-1 integer program is the one, in this formulation, with arbitrary nonnegative entries of A and b, while the partial set cover problem requires only m–K constrains (or more) in Ax b to be satisfied when integer K is additionall specified. While many approximation algorithms have been recently developed for these problems and their special cases, using computationally rather expensive (albeit polynomial) LP-rounding (or SDP-rounding), we present a more efficient purely combinatorial algorithm and investigate its approximation capability for them. It will be shown that, when compared with the best performance known today and obtained by rounding methods, although its performance comes short in some special cases, it is at least equally good in general, extends for partial vertex cover, and improves for weighted multicover, partial set cover, and further generalizations.