bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterogeneous discrete expenditure for diminishing returns
Authors: Hamburger Henry , Slagle James R.
Published: May 2007

A probabilistic model is developed that applies to military bombardment, advertising for a mass audience, and other kinds of situations in which striking a target means that less of it is left to strike. The model provides the basis for decision analysis based on marginal gain in such circumstances. Heterogneous resources are considered as well as composite targets. All expenditures are quantized. The model has been developed as part of a computer‐based military expert system, to replace a large complex set of expert opinions. In that application it sharply improves efficiency, yet conforms to major tenets of tactical doctrine.
Use of discounted force arrivals in static force comparisons
Authors: Lorentzen Ralph
Published: May 2007

In traditional static comparisons of two opposing forces, weapons systems on each side are added together after weighting them according to a weapon scoring system. The scoring system does not reflect the availability times of the weapon systems in a perceived conflict. In this paper it is suggested how availability times can be incorporated by introducing the net present value of force arrival patterns. The concept is extended to include the case where uncertainty concerning warning time is reflected through a probability distribution for the time of outbreak of hostilities.
Using simulated annealing to solve routing and location problems
Authors: Golden Bruce L. , Skiscim Christopher C.
Published: May 2007

In recent papers by Kirkpatrick et al., an analogy between the statistical mechanics of large multivariate physical systems and combinatorial optimization has been presented and used to develop a general strategy for solving discrete optimization problems. The method relies on probabilistically accepting intermediate increases in the objective function through a set of user‐controlled parameters. It is argued that by taking such controlled uphill steps, from time to time, a high quality solution can eventually be found in a moderate amount of computer time. In this paper, we implement this idea, apply it to the traveling salesman problem and the p‐median location problem, and test the approach extensively.
A single‐machine scheduling problem with random processing times
Authors: Chakravarthy S.
Published: May 2007

We consider the problem of scheduling n jobs with random processing times on a single machine in order to minimize the expected variance of the completion times. We prove a number of results, including one to the effect that the optimal schedule must be V shaped when the jobs have identical means or variances or have exponential processing times.
A stochastic network formulation for complex sequential processes
Authors: Lemoine Austin J.
Published: May 2007

A network model incorporating stochastic features is considered. The model represents a complex sequential process where an object or system moves through a succession of states (nodes) and operating modes (classes) in the course of carrying out its function (fulfilling its purpose). Transitions between states and operating modes occur in a possibly random manner and require (consume) some resource in randomly varying amounts. We discuss the routing behavior and resource requirements of a typical object as it moves through (and eventually out of) the network. We then shift our focus from a single object and its odyssey to the network as a whole, where time is the resource and many objects are entering the network according to a possibly nonhomogeneous Poisson pattern; in this vein, we discuss the evolution of the network over time. Finally, we consider some applications of the formulation, and results.
A forward network simplex algorithm for solving multiperiod network flow problems
Authors: Aronson Jay E. , David Chen B.
Published: May 2007

An optimization model which is frequently used to assist decision makers in the areas of resource scheduling, planning, and distribution is the minimum cost multiperiod network flow problem. This model describes network structure decision‐making problems over time. Such problems arise in the areas of production/distribution systems, economic planning, communication systems, material handling systems, traffic systems, railway systems, building evacuation systems, energy systems, as well as in many others. Although existing network solution techniques are efficient, there are still limitations to the size of problems that can be solved. To date, only a few researchers have taken the multiperiod structure into consideration in devising efficient solution methods. Standard network codes are usually used because of their availability and perceived efficiency. In this paper we discuss the development, implementation, and computational testing of a new technique, the forward network simplex method, for solving linear, minimum cost, multiperiod network flow problems. The forward network simplex method is a forward algorithm which exploits the natural decomposition of multiperiod network problems by limiting its pivoting activity. A forward algorithm is an approach to solving dynamic problems by solving successively longer finite subproblems, terminating when a stopping rule can be invoked or a decision horizon found. Such procedures are available for a large number of special structure models. Here we describe the specialization of the forward simplex method of Aronson, Morton, and Thompson to solving multiperiod network network flow problems. Computational results indicate that both the solution time and pivot count are linear in the number of periods. For standard network optimization codes, which do not exploit the multiperiod structure, the pivot count is linear in the number of periods; however, the solution time is quadratic.
Continuous quality production and machine maintenance
Authors: Tapiero Charles S.
Published: May 2007

This paper formulates a problem of continuous quality production and maintenance of a machine. Quality is assumed to be a known function of the machine's (Markov diffusion process) degradation states. Applications to a specific quality function are used to obtain analytical solutions to an open‐loop and feedback stochastic control maintenance problem.
On a large sample test for the traffic intensity in GI|G|s queue
Authors: Subba Rao S. , Harishchandra K.
Published: May 2007

A large sample test based on normal approximation for the traffic intensity parameter ρ in the cases of single and multiple‐server queues has been proposed. The test procedure is developed without imposing steady‐state assumptions and is applicable to queueing systems with general interarrival and service‐time distributions.
A note on the single‐machine scheduling problem with minimum weighted completion time and maximum allowable tardiness
Authors: Chand Suresh , Schneeberger Hans
Published: May 2007

This paper analyzes the Smith‐heuristic for the single‐machine scheduling problem where the objective is to minimize the total weighted completion time subject to the constraint that the tradiness for any job does not exceed a prespecified maximum allowable tardiness. We identify several cases of this problem for which the Smith‐heuristic is guaranteed to lead to optimal solutions. We also provide a worst‐case analysis of the Smith‐heuristic; the analysis shows that the fractional increase in the objective function value for the Smith‐heuristic from the optimal solution is unbounded in the worst case.
The matrix game derived from the many‐against‐many battle
Authors: Kikuta Kensaku
Published: May 2007

The many‐against‐many battle, which is a variant of the Friedman's one‐against‐many battle, is formulated as a two‐person constant‐sum game. It is shown that the matrix which expresses this game has a saddle point. Some cases are presented in which the payoff matrix of the game can be reduced. Finally, some parametrically special cases are analyzed.
The procurement problem: An integer programming problem well suited to a solution using duality
Authors: Gunn Eldon A. , Kusiak Andrew
Published: May 2007

A procurement problem, as formulated by Murty [10], is that of determining how many pieces of equipment units of each of m types are to be purchased and how this equipment is to be distributed among n stations so as to maximize profit, subject to a budget constraint. We have considered a generalization of Murty's procurement problem and developed an approach using duality to exploit the special structure of this problem. By using our dual approach on Murty's original problem, we have been able to solve large problems (1840 integer variables) with very modest computational effort. The main feature of our approach is the idea of using the current evaluation of the dual problem to produce a good feasible solution to the primal problem. In turn, the availability of good feasible solutions to the primal makes it possible to use a very simple subgradient algorithm to solve the dual effectively.
Survival and effectiveness of a weapon system against a superior force (guerrilla warfare)
Authors: Bache N.
Published: May 2007

Stochastic models are developed for a weapon system which attacks at a certain rate, but withdraws when attacked (guerrilla warfare). The models yield as output the distributions and mean values in closed form of the survival period and number of attacks made. As input are, for the weapon system, attack rate or amount of ammunition and time horizon, and, for the opponent, kill rate and probability of killing the weapon system, given the opponent has been attacked (strike back performance of the opponent). One model allows, however, for strike back also by the weapon system, when attacked by the opponent. This model is then used to determine, when the weapon system should strike back. The models are based on the Poisson and the binomial processes. Consistency among the models is shown and an example is provided.
An efficient algorithm for the transshipment along a single road problem
Authors: Ali Agha Iqbal
Published: May 2007

This paper presents a specialized algorithm for the transshipment along a single road problem. The problem is a specially structured network flow problem. For larger problems, the specialized algorithm is in excess of a hundred times faster than the primal simplex method on a graph.
Modified discrete preventive maintenance policies
Authors: Nakagawa Toshio
Published: May 2007

This article proposes a modified preventive maintenance (PM) policy which may be done only at scheduled times nT (n = 1,2, …): The PM is done at the next such time if and only if the total number of failures exceeds a specified number k. The optimal number k* to minimize the expected cost rate is discussed. Further, four alternative similar PM models are considered, when the system fails due to a certain number of faults, uses, shocks, and unit failures.
Rescheduling to minimize makespan on a changing number of identical processors
Authors: Tovey Craig A.
Published: May 2007

We consider the problem of rescheduling n jobs to minimize the makespan on m parallel identical processors when m changes value. We show this problem to be NP‐hard in general. Call a list schedule totally optimal if it is optimal for all m = 1, …,n. When n is less than 6, there always exists a totally optimal schedule, but for n ≥ 6 this can fail. We show that an exact solution is less robust than the largest processing time first (LPT) heuristic and discuss implications for polynomial approximation schemes and hierarchical planning models.
Algorithms for the minimax transportation problem
Authors: Ahuja R. K.
Published: May 2007

In this paper, we consider a variant of the classical transportation problem as well as of the bottleneck transportation problem, which we call the minimax transportation problem. The problem considered is to determine a feasible flow xij from a set of origins I to a set of destinations J for which max(i,j)εIxJ{cijxij} is minimum. In this paper, we develop a parametric algorithm and a primal‐dual algorithm to solve this problem. The parametric algorithm solves a transportation problem with parametric upper bounds and the primal‐dual algorithm solves a sequence of related maximum flow problems. The primal‐dual algorithm is shown to be polynomially bounded. Numerical investigations with both the algorithms are described in detail. The primal‐dual algorithm is found to be computationally superior to the parametric algorithm and it can solve problems up to 1000 origins, 1000 destinations and 10,000 arcs in less than 1 minute on a DEC 10 computer system. The optimum solution of the minimax transportation problem may be noninteger. We also suggest a polynomial algorithm to convert this solution into an integer optimum solution.
Nature of renyi's entropy and associated divergence function
Authors: Bector C. R. , Bhatia B. L.
Published: May 2007

Nature of Renyi's entropy and associated divergence function is discussed in terms of concave (convex) and pseudoconcave (pseudoconvex) functions.
Optimal replacement for fault‐tolerant systems
Authors: Taylor Howard M. , Rodriguez Beatriz E.
Published: May 2007

We consider the optimal replacement problem for a fault tolerant system comprised of N components. The components are distingushable, and the state of the system is given by knowing exactly which components are operationl and which have failed. The individual component failure rates depend on the state of the entire system. We assume that the rate at which the system produces income decreases as the system deteriorates and the system replacement cost rises. Individual components cannot be replaced. We give a greedy‐type algorithm that produces the replacement policy that maximizes the long‐run net system income per unit time.
Optimal refueling sequence for a mixed fleet with limited refuelings
Authors: Melkman Avraham A. , Stern Helman I. , Mehrez Avraham
Published: May 2007

Consider a fleet of vehicles comprised of K1 identical tankers and K2 identical nontankers (small aircraft). Tankers are capable of refueling other tankers as well as nontankers. The problem is to find that refueling sequence of the tankers that maximizes the range simultaneously attainable by all K2 nontankers. A recent paper established that the “unit refueling sequence,” comprised of one tanker refueling at each of K1 refueling operations, is optimal. The same paper also proffered the following conjecture for the case that the number of refueling operations is constrained to be less than the number of tankers: A nonincreasing refueling sequence is optimal. This article proves the conjecture.
Estimating the accuracy of the coverages of outer β‐content tolerance intervals, which control both tails of the normal distribution
Authors: Chou Youn‐Min , Owen D. B.
Published: May 2007

Tolerance limits which control both tails of the normal distribution so that there is no more than a proportion β1 in one tail and no more than β2 in the other tail with probability γ may be computed for any size sample. They are computed from X̄ ‐ k1S and X̄ ‐ k2S, where X̄ and S are the usual sample mean and standard deviation and k1 and k2 are constants previously tabulated in Odeh and Owen [3]. The question addressed is, “Just how accurate are the coverages of these intervals (– Infin;, X̄ – k1S) and (X̄ + k2S, ∞) for various size samples?” The question is answered in terms of how widely the coverage of each tail interval differs from the corresponding required content with a given confidence γ′.
Money‐wasting codes
Authors: Gilmore C. P.
Published: May 2007

One model set of performance standards deemed essential if housing needs of this era are to be met.
A study of the analysis and control of the flow of air traffic: Part I
Authors: Forys L. J. , Heffes H. , Holtzman J. M. , Horing S. , Messerli E. J. , Schwartz M. I. , Stiles J. A.
Published: May 2007

This paper contains the results of an exploratory study aimed at developing a model which could form the basis of a comprehensive analysis of the Air Traffic Control system. This model could be used to evaluate the effects of proposed changes in the system.

The results will be presented in three parts. Part I is intended to provide an overview of the results as well as a detailed description of a traffic flow model which computes the means and variances of delays experienced by individual aircraft. Since this model requires as an input a statistical description of the arrival and departure service processes, Part II describes a model which relates these processes to more basic quantities (e.g., aircraft mix, runway configuration). Since the models which are developed represent a physical system, the question of validation arises and is also discussed in Part II. Part III of the paper considers the question of designing a (real‐time) flow control system. It is formulated as a problem of minimizing a measure of system delay subject to constraints on the allowable departure and arrival times. Illustrative results are included through‐out the paper.
A decomposition approach to nonlinear programs as applied to reservoir systems
Authors: Bodin L. D. , Roefs T. G.
Published: May 2007

The problem considered in this paper is the determination of the operating policy over time of a network of water reservoirs or dams arranged according to an arbitrary topology. If streamflow was a known quantity, the problem could be formulated as a large nonlinear program (several hundred nonlinear) constraints as a minimum) and solved by the two methods proposed in this paper. Since streamflow is random, the problem becomes a large stochastic program which can be solved by a procedure given in the literature. The key step in solving this stochastic program is the solution of the nonlinear program by the methods we propose.
A study of the analysis and control of the flow of air traffic: Part III
Authors: Forys L. J. , Heffes H. , Holtzman J. M. , Horing S. , Messerli E. J. , Schwartz M. I. , Stiles J. A.
Published: May 2007

This is the third and final part of a study of the analysis and control of the flow of air traffic. Part I developed a traffic flow model to compute the means and variances of delays experienced by individual aircraft. Part II was concerned with the arrival and departure processes, and with the question of model validation. In this part, we consider an approach to the problem of designing a (real‐time) flow control system. Central to the approach is the problem of minimizing a measure of system delay subject to constraints on the allowable departure and arrival times.
Optimal flow in networks with gains and costs
Authors: Malek‐Zavarei M. , Aggarwal J. K.
Published: May 2007

The problem of routing a desired flow at minimum cost through a network in which associated with each arc is a capacity, a linear cost, a fixed cost and a flow multiplier is considered. The equivalence of the problems on a general graph and a bipartite graph is shown; feasibility is discussed and properties of solutions are investigated.
Problems in the design of large power networks
Authors: Van Ness J. E.
Published: May 2007

The modern power network with its interacting generator governors and voltage regulators presents many unsolved problems. The digital computer is the major tool for solving them.
A probabilistic model of learning by means of problems
Authors: Brody J.
Published: May 2007

In this article a problem teaching situation is described and studied with the help of a mathematical model of problem presentation. Two psychological hypotheses and a difficulty function lead to an operational definition of optimal problem presentation according to the order and difficulties involved in each step. Certain properties of this model then show natural behavior and support the basic hypotheses.
An optimal schedule time of a job shop‐like disjunctive graph
Authors: Ashour S. , Chiu K. Y. , Moore T. E.
Published: May 2007

This paper considers the shop scheduling problem which involves both job precedence and machine interference constraints. Based on the graph‐theoretical representation of the problem, a branch‐and‐bound algorithm is proposed for implicitly producing an optimal schedule such that the schedule time is minimized. The algorithm utilizes a set of heuristic rules, in addition to a powerful bounding procedure, to guide the search. An upper bound is also employed to recognize an optimal solution in earlier stages. The procedure is illustrated by a sample problem and its rapid convergence is demonstrated by a set of published problems. The proposed algorithm is compared favorably with existing procedures.
Routing a fleet of M vehicles to/from a central facility
Authors: Orloff C. S.
Published: May 2007

In a previous paper, algorithms for optimally routing a single vehicle were presented. In this paper, the problem of routing a fleet of M vehicles serving fixed demand for transportation from many origins to a single destination is considered. The M vehicle General Routing Problem (abbreviated M‐GRP) is the core of many real routing problems, such as school bus routing for a single school (many‐to‐one) and garbage truck routing to a central dump. It is shown that the M‐GRP on a given graph is equivalent to a GRP on a modified graph. From this result, it is shown that single vehicle routing algorithms can be applied to the M vehicle routing problem.
Shortest path with time constraints on movement and parking
Authors: Halpern J. , Priess I.
Published: May 2007

The shortest path problem is well known and a number of methods have been proposed for its solution. In its simplest form no restrictions or special costs are placed on movement in the network. Some variations of the problem have been presented and solved, such as requirements for visiting specified nodes, turn penalties and prohibitions and time‐dependent length of arcs. In this paper we present and solve the case where we seek the shortest path when some arcs are closed for travelling during specified periods of time. We allow parking in the vertices of the network, when it is necessary to wait for an arc to be opened, but we also assume the possibility of “no‐parking” or “occupied” periods in the nodes. This type of problem emerges, for example, in the management of railway system, or a network of narrow roads with convoys moving on it.
On clique‐extremal (p,q)‐graphs
Authors: Harary F. , Lempel A.
Published: May 2007

A clique of a graph is a maximal complete subgraph. A (p,q)‐graph has p points and q lines. A clique‐extremal (p,q)‐graph has either the maximum or the minimum number of cliques among all (p,q)‐graphs. Moon and Moser have determined constructively the maximum number of cliques in a p‐point graph. The problem of studying the clique‐extremal (p,q)‐graphs is now investigated. We first develop a standard form for such extremal graphs. These standard forms are shown to have a complementary kind of analogy with respect to maximum and minimum.
A minimum‐cost multicommodity network flow problem concerning imports and exports
Authors: Golden B. L.
Published: May 2007

This paper develops an algorithm for handling nonlinear minimum‐cost multicommodity flow problems and applies it to a specific large‐scale network. The commodities will be imports and exports; the cost functions will be quadratic and convex. The setting will be a Port Planning Model which will seek to find optimal simultaneous routings through the network while fulfilling requirements both at foreign ports and at domestic hinterlands. The computer program written solves such a problem. The algorithm involves linearizing the cost function and solving the resulting linear program, which is, in fact, a series of shortest route problems. Negative cycles are studied in depth.
An algebra for determining all path‐values in a network with application to K‐shortest‐paths problems
Authors: Wongseelashote A.
Published: May 2007

This paper presents an algebra which is appropriate for the formulation and solution of k‐Shortest‐paths problems. The algebra is a generalization of “Schedule Algebra” studied by Giffler [3,4] for computing path values in a network. It is shown formally that these path values can be calculated by using direct methods of numerical linear algebra for solving systems of linear equations and an algorithm similar to the long division procedure of ordinary arithmetic. Such a method is then modified to yield an algorithm for finding k shortest elementary paths in a network.
A note on the primal‐dual and out‐of‐kilter algorithms for network optimization problems
Authors: Shapiro J. F.
Published: May 2007

This paper compares and contrasts two distinct primal‐dual methods to network optimization, including the out‐of‐kilter method. A hybrid approach combining the two methods is suggested.
On kernels in strongly connected graphs
Authors: Anciaux‐Mundeleer M. , Hansen P.
Published: May 2007

Two theorems on the existence of kernels and of complementary kernels in strongly connected graphs are presented.
Minimal ratio spanning trees
Authors: Chandrasekaran R.
Published: May 2007

Given an undirected graph G: (N;E) with a node set N and an edge set E and numbers Ce and De, e ϵ E, we provide a polynominally bounded algorithm to solve the problem: Find a spanning tree T such that the ratio magnified image is minimized. An extension to finding bases in matroids that minimize such ratio functions is immediate. It is shown that an algorithm that is “greedy,” in the sense of Edmonds [2], will not work for this problem.
Bounding distributions for a stochastic pert network
Authors: Shogan A. W.
Published: May 2007

Consider a PERT network with stochastic activity durations. This paper presents a new method for obtaining probability distributions that bound the exact probability distribution of the project duration from above and below. The expected values of these bounding distributions then furnish lower and upper bounds on the expected project duration. As illustrated by computational experience, these bounds are tighter than those obtained from methods currently in use. The paper concludes by describing similar results for stochastic shortest‐route networks.
A decomposition algorithm for network reliability analysis
Authors: Shogan A. W.
Published: May 2007

Consider a directed, source‐sink network whose arcs either function or fail with known probabilities. This paper presents a decomposition algorithm for the exact computation of the reliability of such a network; that is, the probability that there exists a path from the network's source to its sink, consisting only of functioning arcs. The decomposition algorithm, which can be used even after the network can undergo no further modular decomposition, is based on a partitioning of the nodes of the network into subsets that can be sequentially analyzed. The algorithm permits arbitrary dependence among arcs that terminate at nodes belonging to the same subset of the partition but requires two arcs terminating at nodes belonging to different subsets to be independent. Computational experience from a computer implementation of the algorithm is also reported.
A generalized dynamic flows problem
Authors: Halpern J.
Published: May 2007

The original maximal dynamic flows problem is to find the maximal flow that may be transferred within a given period of time, from the source to the destination of a network with constant edge capacities and lengths. This paper generalizes the problem in two ways. First, the edge's capacity is time dependent, and secondly, the heldover of flows in the vertices may be prohibited during certain intervals of time. The presence of these two additional features implies that cycling of flows may be necessary in order to generate an optimal solution, an impossible result in the original problem. The generalized maximal dynamic flows problem requires, therefore, a special method of solution, and the paper presents a suitable algorithm which solves the problem.
Realization of a symmetric terminal capacity matrix by a tree with the minimum diameter
Authors: Ozawa T.
Published: May 2007

Trees realizing a terminal capacity matrix (TCM) have a unique layer structure. An algorithm making use of this layer structure is presented for construction of a tree which realizes the TCM with the smallest possible diameter. This minimum‐diameter tree has layers of stars. An upper bound on the minimum diameter is given for a prescribed number of vertices. Also presented are algorithms to construct a star and a tree of diameter 3 which realize the TCM as a minimum requirement matrix.
A more compact formulation of the symmetric multiple traveling salesman problem with fixed charges
Authors: Discenza Joseph Henry
Published: May 2007

The multiple traveling salesman problem with fixed charges (MTSPF) is an extension of the standard traveling salesman problem (TSP). Previous work by Hong and Padberg showed how to transform to a TSP with n + m + 4 nodes, where m is the number of salesmen. The four extra nodes were included to prevent the transformed problem from escaping part of the fixed costs. This paper shows that two of these nodes can be eliminated without sacrificing the formulation as a TSP. Further, all four extra nodes can be replaced by a pair of simple constraints. All formulations produce equivalent solutions.
Combinatorial optimization and vehicle fleet planning: Perspectives and prospects
Authors: Magnanti T. L.
Published: May 2007

As a well‐structured and costly activity that pervades industries in both the public and private sector, vehicle fleet management would appear to be a splendid candidate for model‐based planning and optimization. And yet, until recently the combinatorial intricacies of vehicle routing and of vehicle scheduling have precluded the widespread use of optimization (exact) methods for this problem class. Our discussion in this paper identifies the extent and nature of these problem complexities and draws contrasts with other applications of combinatorial optimization. It also summarizes a number of successful uses of optimization for vehicle fleet planning and highlights potentially fruitful avenues for algorithmic development. In particular, we describe several alternative models and novel algorithms for the vehicle routing problem, show how various modeling approaches for this problem are intimately related, and illustrate the interplay between model formulations and the algorithms that they suggest. This discussion shows that prospects for applying exact methods, possibly in conjunction with heuristics, are far from fully realized and points to vehicle fleet planning as a tempting target of opportunity for further investigation.
Finding a minimum equivalent graph of a digraph
Authors: Martello Silvano , Toth Paolo
Published: May 2007

The problem considered is that of removing the maximum number of edges from a digraph without affecting its reachability properties. The worst‐case performance of algorithms from the related literature is analyzed; it is found that Hsu's method contains some mistakes. A new algorithm is presented, based on a reduction procedure and on a branch and bound search; its efficiency is studied both theoretically and through computational experiments.
Maximum flow in networks with a small number of random arc capacities
Authors: Somers J. E.
Published: May 2007

In a directed, capacitated network with single source and sink in which the capacities of some of the arcs are random variables, the max‐flow value is also a random variable. I propose a new approach to the problem of computing its distribution and expected value via a corollary of the max‐flow min‐cut theorem, and implement it explicitly for small numbers of random capacities. I consider the error obtained in estimating the expected max‐flow value by setting some of the random capacities equal to their means. When the flows are restructed by lower bounds, I give the probability of existence of a feasible flow.
On‐line connectivity algorithms
Authors: Cheston Grant A.
Published: May 2007

The problem is to be able to respond to inquiries of the form “Are vertices u and v of graph G connected?” as quickly as possible in an on‐line situation where edges are being inserted into and deleted from the graph. Recently Even and Shiloach presented a data structure and algorithm involving three synchronized processes to handle the deletion case. An alternative algorithm, LEVELS, is presented to update their data structure. This algorithm is more efficient than theirs and has the further feature of not requiring synchronized processes, so that it is much easier to implement. Finally the LEVELS algorithm is compared to and contrasted with an algorithm using a spanning‐forest data structure for both edge insertion and deletion. The LEVELS algorithm appears to be better for deletion, while the spanning‐forest algorithm is better for insertion.
Mesh association by projection along smoothed‐normal‐vector fields: Association of closed manifolds
Authors: van Brummelen E. H.
Published: May 2007

The necessity to associate two geometrically distinct meshes arises in many engineering applications. Current mesh‐association algorithms have generally been developed for piecewise‐linear geometry approximations, and their extension to the high‐order geometry representations corresponding to high‐order finite element methods is nontrivial. In the present work, we therefore propose a mesh‐association method for high‐order geometry representations. The associative map defines the image of a point on a mesh as its projection along a so‐called smoothed‐normal‐vector field onto the other mesh. The smoothed‐normal‐vector field is defined by the solution of a modified Helmholtz equation with right‐hand‐side data corresponding to the normal‐vector field. Classical regularity theory conveys that the smoothed‐normal‐vector field is continuously differentiable, which renders it well suited for a projection‐based association. Moreover, the regularity of the smoothed‐normal‐vector field increases with the regularity of the normal‐vector field and, hence, the smoothness of the association increases with the smoothness of the geometry representations. The proposed association method thus accommodates the higher regularity that can be provided by high‐order geometry representations. Several important properties of smoothed‐normal‐projection association are established by analysis and by numerical experiments on closed manifolds. Copyright © 2007 John Wiley & Sons, Ltd.
Effect of grafting alkoxysilane on the surface properties of Kevlar fiber
Authors: Ai Tao , Wang Rumin , Zhou Wenying
Published: May 2007

This research applied the methodology of metalation and grafting alkoxysilane to modify the surface of Kevlar‐29 fiber. The surface properties of the modified Kevlar fiber were characterized by scanning electron microscopy, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, and Brunauer‐Emmett‐Teller isothermal adsorption analysis. The relationship between surface characteristics of Kevlar fiber and its interfacial adhesion of Kevlar fiber‐reinforced epoxy resin composites was also discussed. Compared with the untreated fiber, the surface of the modified Kevlar fiber was much rougher, its oxygen content increased by about 12%, the surface area enlarged about 10 times, and the wetting behavior improved. Due to the modification of the fiber, the adhesion between the fiber and the resin matrix was markedly improved and the Interlaminar Shear Strength of its epoxy composites increased by about 57%. POLYM. COMPOS. 28:412–416, 2007. © 2007 Society of Plastics Engineers.
Screen‐print selective diffusions for high‐efficiency industrial silicon solar cells
Authors: Edwards Matthew , Bocking Jonathan , Cotter Jeffrey E. , Bennett Neil
Published: May 2007

Screen‐print diffusion pastes present an industrially applicable alternative to conventional techniques of dopant deposition. Several commercially available screen‐print dopant pastes are assessed for their suitability in forming heavy selective diffusions for use under metal contacts in silicon solar cells. Pastes are assessed in terms of their ease of application, their ability to form heavy diffusions with low sheet resistances, and their ability to maintain high post‐diffusion wafer lifetimes. Potential for the use of dopant pastes in high‐efficiency solar cell devices is investigated using photoconductance (PC) measurements and photoluminescence (PL) images. It is found that under certain conditions, screen‐print dopant pastes, particularly phosphorus paste, have potential to form effective selective diffusions without significantly compromising performance in high‐efficiency solar cells. Copyright © 2007 John Wiley & Sons, Ltd.
Morphology control in polystyrene/poly(methyl methacrylate) composite latex particles
Authors: Herrera Virginia , Pirri Rosangela , Asua José M. , Leiza Jose R.
Published: May 2007

The effect of the presence of different amounts of block copolymers [polystyrene‐block‐poly(methyl methacrylate)] on the morphology of polystyrene/poly (methyl methacrylate) composite latex particles was investigated. The block copolymers were produced in situ by controlled radical polymerization (CRP) through the addition of the second monomer to a seed prepared by miniemulsion polymerization with a certain amount of a CRP agent. With an increase in the amounts of the block copolymers, the particle morphology changed from a hemisphere morphology (for a latex without block copolymers, i.e., without the use of a CRP agent during the polymerization) to clear core–shell morphologies as a result of decreasing polymer–polymer interfacial tension © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2484–2493, 2007
Fixing moduli in exact Type IIA flux vacua
Authors: Benini F. , Acharya B.S. , Valandro R.
Published: May 2007

Type IIA flux compactifications with O6‐planes have been argued from a four dimensional effective theory point of view to admit stable, moduli free solutions. We discuss in detail the ten dimensional description of such vacua and present exact supersymmetric solutions in the case when the O6‐charge is smoothly distributed: the geometry is Calabi‐Yau and the dilaton is constant. In the localized case, the solution is a half‐flat, non‐Calabi‐Yau metric but still with constant dilaton. Finally, using the ten dimensional description we show how all moduli are stabilized and reproduce precisely the results of de Wolfe et al. [arXiv:hep‐th/0505160]. This talk is based on [arXiv:hep‐th/0607223].
A note on the string dual of 𝒩 = 1 SQCD‐like theories
Authors: Casero R. , Paredes A.
Published: May 2007

In this note we describe how 𝒩 = 1 SQCD‐like theories with a large number of flavors can be given a dual description in terms of a string background containing a large number of additional D5‐branes. The dual geometries account for the backreaction of the additional branes: they depend on the ratio between the number of flavors and colors of the gauge theory. This note is based on [1]. We present here also a new set of solutions, which are not included in the original paper.
AdS spacetimes in M‐theory
Authors: Gauntlett J.P. , Mac Conamhna O.A.P. , Mateos T. , Waldram D.
Published: May 2007

We review recent progress in the classification and construction of supersymmetric AdS solutions of M‐theory. The AdS supersymmetry conditions are derived by taking the near‐horizon limit of M‐fivebranes wrapping supersymmetric cycles in manifolds of G2 or SU(N) holonomy, N = 2, 3, 4. The new explicit solutions we find are AdS3 solutions arising in the near‐horizon limit of M‐fivebranes wrapping Kähler four‐cycles in Calabi‐Yau four‐folds, intersecting membranes in a string, and dual to 𝒩 = (2,0) conformal field theories in two dimensions. Eight doubly countably infinite families of these solutions are reduced and dualised to IIB, and the central charge of the dual field theories computed. Some future directions are briefly discussed.
Exact discreteness and mass gap of N = 1 symplectic Yang‐Mills from M‐theory
Authors: Boulton L. , García del Moral M.P. , Restuccia A.
Published: May 2007

In this note we summarize some of the results found recently in [1]. We show the pure discreteness of the non‐perturbative quantum spectrum of a symplectic Yang‐Mills theory defined on a Riemann surface of positive genus, living in a target space that, in particular, can be 4D. This theory corresponds to the membrane with central charges. The presence of the central charge induces a confinement in the phase at zero temperature. When the energy rises, the center of the group breaks and the theory enters in a quark‐plasma phase after a topological transition, corresponding to the N = 4 wrapped supermembrane.
Supersymmetric D‐branes on flux backgrounds
Authors: Martucci L.
Published: May 2007

Several aspects concerning the physics of D‐branes in Type II flux compactifications preserving minimal 𝒩 = 1 supersymmetry in four dimensions are considered. It is shown how these vacua are completely characterized in terms of properly defined generalized calibrations for D‐branes and the relation with Generalized Complex Geometry is discussed. General expressions for superpotentials and D‐terms associated with the 𝒩 = 1 four‐dimensional description of space‐time filling D‐branes are presented. The massless spectrum of calibrated D‐branes can be characterized in terms of cohomology groups of a differential complex canonically induced on the D‐branes by the underlying generalized complex structure.
Classification of supersymmetric backgrounds of string theory
Authors: Gran U. , Gutowski J. , Papadopoulos G. , Roest D.
Published: May 2007

We review the recent progress made towards the classification of supersymmetric solutions in ten and eleven dimensions with emphasis on those of IIB supergravity. In particular, the spinorial geometry method is outlined and adapted to nearly maximally supersymmetric backgrounds. We then demonstrate its effectiveness by classifying the maximally supersymmetric IIB G‐backgrounds and by showing that N = 31 IIB solutions do not exist.
N = 1 domain wall solutions of massive type II supergravity and the issue of mirror symmetry
Authors: Vaulà S.
Published: May 2007

We report on Domain Wall solution of Calabi–Yau compactifications with general fluxes and their application to the study of mirror symmetry in generalized backgrounds. We address, in particular, to the issue of magnetic NSNS fluxes. We show that the Domain Wall gradient flow equations can be interpreted as a set of generalized Hitchin's flow equations of a manifold with SU(3) × SU(3) structure fibered along the direction transverse to the Domain wall.
Analysis of biaxial strain in InN(0001) epilayers grown by molecular beam epitaxy
Authors: Dimakis E. , Domagala J. , Iliopoulos E. , Adikimenakis A. , Georgakilas A.
Published: May 2007

The in‐plane lattice parameters of InN, GaN and Al2O3 in a InN/GaN/Al2O3(0001) heterostructure have been measured as a function of temperature in the range of 25–350 °C, using high resolution X‐ray diffraction. The results reveal that both the GaN and InN crystals follow the in‐plane thermal expansion of the Al2O3 substrate's lattice and there is no rearrangement of misfit dislocations at the InN/GaN and GaN/Al2O3 interfaces. It was also found that either compressive or tensile character of residual biaxial strain is possible for the InN films, depending on the two‐dimensional (2D) or three‐dimensional (3D) growth mode of InN on the GaN(0001) buffer layer. The tensile strain is inherent to the nucleation and coalescence of 3D islands. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fisher information and quantum–classical field theory: classical statistics similarity
Authors: Syska J.
Published: May 2007

The classical statistics indication for the impossibility to derive quantum mechanics from classical mechanics is proved. The formalism of the statistical Fisher information is used. Next the Fisher information as a tool of the construction of a self‐consistent field theory, which joins the quantum theory and classical field theory, is proposed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Proteins and Carbon Nanotubes: Close Encounter in Water
Authors: Nepal Dhriti , Geckeler Kurt E.
Published: May 2007

The interactions between biological substances and carbon nanotubes (CNTs) and their effect on the nanotubes are of significant importance in this emerging era of nanobiotechnology. Consequently, highly stable dispersions of debundled CNTs in aqueous solution are an important prerequisite for their applications and for the development of nanotube‐based molecular electronic and nanobiomedical devices. Here, we report that proteins can work as tools to this end if their primary structure and the pH value of the system are chosen appropriately. Proteins containing a large number of basic residues, for example, histone, are found to be the most promising protein tools for the dispersion of nanotubes. Apart from other interactions, the polarity of the protein seems to play a vital role in obtaining high yields of debundled nanotubes. In addition, an enrichment of metallic nanotubes in the products is observed, which offers a facile approach for separating nanotubes according to their electronic properties in the bulk.
The effect of nicotine on striatal dopamine release in man: A [11C]raclopride PET study
Authors: Montgomery Andrew J. , Lingford‐Hughes Anne R. , Egerton Alice , Nutt David J. , Grasby Paul M.
Published: May 2007

In common with many addictive substances and behaviors nicotine activates the mesolimbic dopaminergic system. Brain microdialysis studies in rodents have consistently shown increases in extrasynaptic DA levels in the striatum after administration of nicotine but PET experiments in primates have given contradicting results. A recent PET study assessing the effect of smoking in humans showed no change in [11C]raclopride binding in the brain, but did find that “hedonia” correlated with a reduction in [11C]raclopride binding suggesting that DA may mediate the positive reinforcing effects of nicotine. In this experiment we measured the effect of nicotine, administered via a nasal spray, on DA release using [11C]raclopride PET, in 10 regular smokers. There was no overall change in [11C]raclopride binding after nicotine administration in any of the striatal regions examined. However, the individual change in [11C]raclopride binding correlated with change in subjective measures of “amused” and “happiness” in the associative striatum (AST) and sensorimotor striatum (SMST). Nicotine concentration correlated negatively with change in BP in the limbic striatum. Nicotine had significant effects on cardiovascular measures including pulse rate, systolic blood pressure (BPr), and diastolic BPr. Baseline [11C]raclopride binding potential (BP) in the AST correlated negatively with the Fagerström score, an index of nicotine dependence. These results support a role for the DA system in nicotine addiction, but reveal a more complex relationship than suggested by studies in animals. Synapse 61:637–645, 2007. © 2007 Wiley‐Liss, Inc.
Developments in HIV medicine
Authors: Jones Rachael , Nelson Mark , Gazzard Brian
Published: May 2007

With HIV‐infected patients living longer since the introduction of antiretroviral therapy, the emphasis now is on improving adherence and reducing the toxicities and side‐effects associated with long‐term treatment. Other developments include new guidance on post‐exposure prophylaxis and treatment of patients co‐infected with HIV and hepatitis C. Copyright © 2007 Wiley Interface Ltd
Recent technological developments in the management of urinary tract stones
Authors: Choong Simon
Published: May 2007

In the 1980s, the advent of non‐invasive techniques, such as lithotripsy, ureteroscopy and percutaneous nephrolithotomy, revolutionised the treatment of urinary tract stones. Since then, technological advances have been at the forefront of improvements in stone management.