Analysis of facility protection strategies against an uncertain number of attacks: The stochastic R-interdiction median problem with fortification

We present the Stochastic R-Interdiction Median Problem with Fortification (S-RIMF). This model optimally allocates defensive resources among facilities to minimize the worst-case impact of an intentional disruption. Since the extent of terrorist attacks and malicious actions is uncertain, the problem deals with a random number of possible losses. A max-covering type formulation for the S-RIMF is developed. Since the problem size grows very rapidly with the problem inputs, we propose pre-processing techniques based on the computation of valid lower and upper bounds to expedite the solution of instances of realistic size. We also present heuristic approaches based on heuristic concentration-type rules. The heuristics are able to find an optimal solution for almost all the problem instances considered. Extensive computational testing shows that both the optimal algorithm and the heuristics are very successful at solving the problem. Finally, a discussion of the importance of recognizing the stochastic nature of the number of possible attacks is provided.     

Redundancy in logic II: 2CNF and Horn propositional formulae

We report results about the redundancy of formulae in 2CNF form. In particular, we give a slight improvement over the trivial redundancy algorithm and give some complexity results about some problems related to finding Irredundant Equivalent Subsets (i.e.s.) of 2CNF formulae. The problems of checking whether a 2CNF formula has a unique i.e.s. and checking whether a clause in is all its i.e.s.'s are polynomial. Checking whether a 2CNF formula has an i.e.s. of a given size and checking whether a clause is in some i.e.s.'s of a 2CNF formula are polynomial or NP-complete depending on whether the formula is cyclic. Some results about Horn formulae are also reported.     

Critical Path Analysis With Fuzzy Activity Times

Fuzzy logic has been proposed as an alternate approach for quantifying uncertainty relating to project activity duration. The fuzzy logic approach may be suitable in the situations where past data are either unavailable or not relevant, the definition of the activity itself is somewhat unclear, or the notion of the activity's completion is vague. The purpose of this paper is to present a new methodology for fuzzy critical path analysis that is consistent with the extension principle of fuzzy logic. It is the direct generalization of critical path analysis to the fuzzy domains, and resolves some of the problems expressed in the fuzzy critical path literature, especially in computing the fuzzy backward pass of the project network and fuzzy activity criticality. Here the uncertainty is represented by three possible time estimates in a way that is similar to the well-known program evaluation and review technique (PERT) approach. Another important advantage of the proposed approach is that one integrated procedure determines both the fuzzy set of critical path lengths and fuzzy activity criticality. The proposed approach constructs the membership function for the fuzzy set of critical path lengths and the fuzzy activity criticality by solving a series of mathematical programming problems. The proposed method is successfully tested on well-known problem sets, and is shown to offer computation times that should allow it to help project managers better understand and manage project schedule uncertainty.     

Location and Calibration of Valves in Water Distribution Networks Using a Scatter-Search Meta-heuristic Approach

Recently, there has been an increase in the use of meta-heuristic techniques addressing water distribution network design and management optimization problems. The meta-heuristic approach applied to water distribution systems has provided interesting results both for optimum pipe diameter sizing and for the location and management of network pressure control devices (i.e., pumps and valves). Regarding the insertion and calibration of pressure regulation valves, the use of meta-heuristic techniques is relatively recent. We search to strategically placing the valves in order to achieve pressure control in the network and, therefore, the valves must be calibrated in relation to water demand trends over time. In the Pressure Reference Method (PRM) described in this paper, the search for valve location is restricted to pipe-branch sets defined on the basis of hydraulic analysis and considering the range between minimum and maximum acceptable pressures in the network. In the PRM approach, the Scatter-Search (Glover and Laguna, 1997) meta-heuristic procedures are applied to obtain the optimal location and calibration of valves in the water distribution network.     

Project Management in Construction: Software Use and Research Directions

This paper focuses on future research and the use of project management software in the construction industry. Data are drawn from an empirical study of project management professionals that yielded 240 replies (35% response rate), 42 of which were from the construction industry. Data were collected on: demographics and work environment, project management software usage patterns, analytical technique usage, data management, and suggestions for future research. The results indicate that construction professionals have different characteristics, needs and preferences, as compared to the overall sample. The study shows that construction professionals are more experienced and educated than the respondents in the overall study, they tend to work on fewer projects with larger numbers of activities, and they are more likely to use Primavera (Primavera, Inc., Bala Cynwyd, Pa.) than Microsoft Project (Microsoft Corp., Redmond, Wash.). Construction respondents are heavy users of critical path analysis for planning and control, resource scheduling for planning, and earned value analysis for control. The number of activities in a typical project and the use of software for all active projects were the key determinants of the usage of specific analytical techniques. These factors are also significant determinants of the types of information entered and updated, although the effect is weaker. Although construction professionals are generally satisfied with the quality of schedules produced by the software, they still expressed a clear interest in future research on resource scheduling∕leveling in general and a net present value option in particular. To maximize the impact on practice, development of new planning and control methods should include their integration into project management software.     

Cu–Zn–Al based catalysts for low temperature bioethanol steam reforming by solar energy

Bioethanol steam reforming is one of the most promising route to produce hydrogen from a renewable liquid biofuel. Activity of two Cu–Zn–Al based catalysts was investigated at low temperatures, ranging from 420 to 500 °C, in view of temperature limitations associated with solar energy supply by parabolic trough technology. At 450 °C the space velocity effect was also investigated, by varying the weight hourly space velocity (WHSV) from 1.67 to 3.32 h⁻¹. In each experimental conditions, together with the expected hydrogen and carbon dioxide, also methane, ethylene, acetaldehyde and diethylether were detect as products, so indicating the presence of several parallel reaction pathways. A good selectivity to ethanol reforming was obtained only at 500 °C (with values of the H₂/CO₂ mol ratio of 3.4 and 4.5) with both catalysts, while at lower temperatures alcohol dehydration into acetaldehyde seemed to be the main reaction.     

Complexity and compilability of diagnosis and recovery of graph‐based systems

This article reports complexity results on diagnosis of systems modeled as graphs. In this model introduced by Rao and Viswanadham, each component is a node of a graph, and an edge indicates that faults propagate from one component to the other one. The basic problem of diagnosis is known to be polynomial and NP‐complete in the cases of single faults and multiple faults, respectively. We extend the complexity analysis to the case of faulty alarms, and also consider the problem of limiting the propagation of faults. We show that none of the considered diagnosis problems can be simplified by preprocessing the graph. © 2005 Wiley Periodicals, Inc. Int J Int Syst 20: 1053–1076, 2005.     

Prevalence of diphtheria toxin antibodies in human sera from a cross-section of the Italian population

A polycentric study was carried out between 1993 and 1995 in order to evaluate diphtheria immunity on a representative sample of population from different areas of Italy. To determine diphtheria antitoxin, sera from 5187 apparently healthy subjects, divided according to sex and age groups, were titrated using an ELISA indirect method. A basic protective titre of diphtheria antitoxin (> 0.01 IU ml-1) was found in 4080 (78.6%) subjects. No statistically significant differences between males and females were observed. Our findings show that the proportion of susceptibles increases with age and a high proportion of adults no longer has diphtheria antitoxin at protective levels since toxigenic C. diphtheriae circulation is presently lacking in Italy.     

Arbitration (or how to merge knowledge bases)

Knowledge-based systems must be able to “intelligently” manage a large amount of information coming from different sources and at different moments in time. Intelligent systems must be able to cope with a changing world by adopting a “principled” strategy. Many formalisms have been put forward in the artificial intelligence (AI) and database (DB) literature to address this problem. Among them, belief revision is one of the most successful frameworks to deal with dynamically changing worlds. Formal properties of belief revision have been investigated by Alchourron, Gardenfors, and Makinson, who put forward a set of postulates stating the properties that a belief revision operator should satisfy. Among these properties, a basic assumption of revision is that the new piece of information is totally reliable and, therefore, must be in the revised knowledge base. Different principles must be applied when there are two different sources of information and each one has a different view of the situation-the two views contradicting each other. If we do not have any reason to consider any of the sources completely unreliable, the best we can do is to “merge” the two views in a new and consistent one, trying to preserve as much information as possible. We call this merging process arbitration. In this paper, we investigate the properties that any arbitration operator should satisfy. In the style of Alchourron, Gardenfors, and Makinson we propose a set of postulates, analyze their properties, and propose actual operators for arbitration     

Redundancy in logic I: CNF propositional formulae

A knowledge base is redundant if it contains parts that can be inferred from the rest of it. We study some problems related to the redundancy of a CNF formula. In particular, any CNF formula can be made irredundant by deleting some of its clauses: what results is an irredundant equivalent subset. We study the complexity of problems related to irredundant equivalent subsets: verification, checking existence of an irredundant equivalent subset with a given size, checking necessary and possible presence of clauses in irredundant equivalent subsets, and uniqueness. We also consider the problem of redundancy with different definitions of equivalence.