bluuebunny/crossref_metadata_2025 huggingface dataset:
Single unit responses to skin odorants from conspecifics and heterospecifics in the olfactory bulb of crucian carp Carassius carassius
Authors: Lastein Stine , Hamdani El Hassan , Døving Kjell B.
Published: October 2008

Injured fish skin leaks alarm substances that induce the fright reaction upon olfactory detection. The skin also contains a multitude of other odorants traditionally related to other behaviors, but to what extent they are detected upon injury is unknown. We have performed single unit recordings in the olfactory bulb (OB) of crucian carp while exposing the olfactory epithelium to skin extracts from conspecifics and three other species of the carp family,common carp, tench and bream. The aims were to investigate whether neural activity may be induced by different types of skin odorants and how well the odorants from injured conspecifics are distinguished from other species. The OB of crucian carp shows a clear chemotopy as units located in different regions respond to either food-related odorants, to pheromones or to alarm odorants respectively. Units in all regions responded to skin extracts, which indicate the detection of odorants usually involved in reproduction and feeding, in addition to the alarm substances. Among OB units responding to only one of the skin extracts, most were sensitive to conspecific skin extract. Furthermore, pair-wise comparisons showed that the discrimination between conspecific skin extract and skin extract from another species was in general better than the discrimination between skin extracts from two heterospecifics. The findings suggest that identification of injured fishes may be based on different groups of odorants and that the crucian carp olfactory system discriminates well between odorants from conspecifics and those from other fish species.
Functional consequences of tooth design: effects of blade shape on energetics of cutting
Authors: Anderson Philip S. L. , LaBarbera Michael
Published: October 2008

Dental structures capture, retain and fragment food for ingestion. Gnathostome dentition should be viewed in the context of the prey's material properties. Animal muscle and skin are mechanically tough materials that resist fragmentation unless energy is continually supplied directly to the tip of the fracture by some device such as a blade edge. Despite the variety of bladed tooth morphologies in gnathostomes, few studies have experimentally examined the effects of different blade designs on cutting efficiency. We tested the effects of blades with and without contained notches and in a`fang' configuration on the force and energy required to fracture raw,unprocessed biological tissues (fish and shrimp) using a double guillotine device. Blade design strongly affects the work required to fragment biological tissues. A notched blade reduced the work to fracture of tissues tested by up to 600 J m–2 (50% reduction). The specific angle of the notch had a significant effect, with acute angles more effectively reducing work to fracture. A bladed triangle matched to a notch reduced work to fracture more than a notch–straight blade pair. Strain patterns seen while cutting photoelastic gelatin indicate that the reduction in work to fracture with triangular and notched blades arises from a combination of `trapping ability'and blade approach angle causing the material to fracture at lower overall strain levels. These results show that the notched blade designs found in a wide variety of vertebrate dentitions reduce the energy expenditure (and presumably handling time) when cutting tough prey materials like animal flesh.
External gills and adaptive embryo behavior facilitate synchronous development and hatching plasticity under respiratory constraint
Authors: Rogge Jessica R. , Warkentin Karen M.
Published: October 2008

Plasticity in hatching timing allows embryos to balance egg- and larval-stage risks, and depends on the ability of hatching-competent embryos to continue developing in the egg. Hypoxia can slow development, kill embryos and induce premature hatching. For terrestrial eggs of red-eyed treefrogs, the embryonic period can extend ∼50% longer than development to hatching competence, and development is synchronous across perivitelline oxygen levels(PO2) ranging from 0.5–16.5 kPa. Embryos maintain large external gills until hatching, then gills regress rapidly. We assessed the respiratory value of external gills using gill manipulations and closed-system respirometry. Embryos without external gills were oxygen limited in air and hatched at an external PO2 of 17 kPa, whereas embryos with gills regulated their metabolism and remained in the egg at substantially lower PO2. By contrast,tadpoles gained no respiratory benefit from external gills. We videotaped behavior and manipulated embryos to test if they position gills near the air-exposed portion of the egg surface, where PO2 is highest. Active embryos remained stationary for minutes in gills-at-surface positions. After manipulations and spontaneous movements that positioned gills in the O2-poor region of the egg, however, they returned their gills to the air-exposed surface within seconds. Even neural tube stage embryos, capable only of ciliary rotation, positioned their developing head in the region of highest PO2. Such behavior may be critical both to delay hatching after hatching competence and to obtain sufficient oxygen for normal, synchronous development at earlier stages.
A microarray-based transcriptomic time-course of hyper- and hypo-osmotic stress signaling events in the euryhaline fishGillichthys mirabilis:osmosensors to effectors
Authors: Evans Tyler G. , Somero George N.
Published: October 2008

Cells respond to changes in osmolality with compensatory adaptations that re-establish ion homeostasis and repair disturbed aspects of cell structure and function. These physiological processes are highly complex, and require the coordinated activities of osmosensing, signal transducing and effector molecules. Although the critical role of effector proteins such as Na+, K+-ATPases and Na+/K+/Cl– co-transporters during osmotic stress are well established, comparatively little information is available regarding the identity or expression of the osmosensing and signal transduction genes that may govern their activities. To better resolve this issue, a cDNA microarray consisting of 9207 cDNA clones was used to monitor gene expression changes in the gill of the euryhaline fish Gillichthys mirabilis exposed to hyper- and hypo-osmotic stress. We successfully annotated 168 transcripts differentially expressed during the first 12 h of osmotic stress exposure. Functional classifications of genes encoding these transcripts reveal that a variety of biological processes are affected. However, genes participating in cell signaling events were the dominant class of genes differentially expressed during both hyper- and hypo-osmotic stress. Many of these genes have had no previously reported role in osmotic stress adaptation. Subsequent analyses used the novel expression patterns generated in this study to place genes within the context of osmotic stress sensing,signaling and effector events. Our data indicate multiple major signaling pathways work in concert to modify diverse effectors, and that these molecules operate within a framework of regulatory proteins.
Physiological importance of the coronary arterial blood supply to the rattlesnake heart
Authors: Hagensen Mette K. , Abe Augusto S. , Falk Erling , Wang Tobias
Published: October 2008

The reptilian heart consists of a thick inner spongy myocardium that derives its oxygen and nutrient supply directly from the blood within the ventricular cavity, which is surrounded by a thin outer compact layer supplied by coronary arteries. The functional importance of these coronary arteries remains unknown. In the present study we investigate the effects of permanent coronary artery occlusion in the South American rattlesnake (Crotalus durissus) on the ability to maintain heart rate and blood pressure at rest and during short term activity. We used colored silicone rubber(Microfil) to identify the coronary artery distribution and interarterial anastomoses. The coronary circulation was occluded and the snakes were then kept for 4 days at 30°C. Microfil injections verified that virtually all coronary arteries had successfully been occluded, but also made visible an extensive coronary supply to the outer compact layer in untreated snakes. Electrocardiogram (ECG), blood pressure (Psys) and heart rate (fH) were measured at rest and during enforced activity at day 1 and 4. Four days after occlusion of the coronary circulation, the snakes could still maintain a Psys and fH of 5.2±0.2 kPa and 58.2±2.2 beats min–1, respectively, during activity and the ECG was not affected. This was not different from sham-operated snakes. Thus, while the outer compact layer of the rattlesnake heart clearly has an extensive coronary supply, rattlesnakes sustain a high blood pressure and heart rate during activity without coronary artery blood supply.
Development of a numerical method to predict the alpine test result
Authors: Jun K-J , Park T-W , Jung S-P , Lee S-H , Yoon J-W
Published: October 2008

The alpine test, which is carried out by observing the temperature change on the brake parts of a vehicle during a high-mountain (the Gross Glockner Mountain) descent, is attracting much attention in Europe as it is conducted in extreme conditions. Consequently, many vehicle manufacturers targeting globalization are making an effort to comply with the standards of the alpine test. The test focuses on the determination of the maximum temperature of the disc and brake fluid. While rolling down a high mountain, the brake system experiences a rapid temperature change due to repetitive or continuous braking. This may in turn lead to symptoms such as fade, thermal judder, thermal crack, and vapour lock. The temperature rise is the result of the transfer of the frictional heat between the disc and pad to the brake parts. This study proposes a numerical method for predicting the temperature change of the brake system by using frictional heat division and one-dimensional heat transfer. This method can predict the temperature change not only in the disc but also in the brake fluid. Using the presented method, the alpine test result is predicted and subsequently validated by comparison with the reported experimental data.
Dynamic model of an air spring and integration into a vehicle dynamics model
Authors: Chang F , Lu Z-H
Published: October 2008

It is worthwhile to design a more accurate dynamic model for air springs, to investigate the dynamic behaviour of an air spring suspension, and to analyse and guide the design of vehicles with air spring suspensions. In this study, a dynamic model of air spring was established, considering the heat transfer process of the air springs. Two different types of air spring were tested, and the experimental results verified the effectiveness of the air spring model compared with the traditional model. The key factors affecting the computation accuracy were studied and checked by comparing the results of the experiments and simulations. The new dynamic model of the air spring was integrated into the full-vehicle multi-body dynamics model, in order to investigate the air suspension behaviour and vehicle dynamics characteristics. The co-simulation method using ADAMS and MATLAB/Simulink was applied to integration of the air spring model with the full-vehicle multi-body dynamics model.
The Eco-Industrial Complex in USA — Global Warming and Rent-Seeking Coalitions
Authors: Jankovic Ivan
Published: October 2008

The public choice model of rent-seeking economics is used to analyze the behaviour of firms, interest groups and scientists participating in efforts to impose climate change cap-and-trade regulations of greenhouse gasses in the USA. This may serve as a case study for the entire world. Yandle's “Bootleggers and Baptists” model and McChesney's model “money for nothing” are used to explain the formation, motives and interests of the groups lobbying for or against this type of regulation. The eco-industrial complex includes firms seeking favorable treatment under cap-and-trade regime, scientists relying on the global warming panic to keep research funds flowing and environmentalist NGOs interested in setting the public agenda and attracting grants and donations. According to our analysis nuclear and renewable energy firms are acting as bootleggers (who profit from legally restricted energy market), while the oil firms are behaving as agents paying protection money) to politicians and NGOs for not demanding harmful public regulation (legal extortion, i.e. “money for nothing”).
The Impact of Flame Stabilisation and Coherent Flow Structures on the Noise Emission of Turbulent Swirl Flames
Authors: Bender Christian , Büchner Horst
Published: October 2008

The development of modern jet engine and stationary gas turbine applications is focused on the reduction of pollutants and, increasingly, on the reduction of noise emissions including combustion noise. This requires the minimization of noise sources, namely noise from the turbulent flow, combustion noise and noise caused by periodic flow and combustion instabilities or fluctuations of the ignition zone. This has to be achieved under conservation of the benefits of swirl flames, i.e. high ignition stability and broad operation ranges. The presented experimental work enables to relate the total noise generation of swirl flames to its physical sources:turbulent flow noise, combustion noise, noise caused by a lifted, unstable flame stabilization and the combustion of coherent flow structures, the latter being caused by the burners exit geometry [1, 2]. Different positions of the flame stabilization can cause an increase of combustion noise up to 3 dB. With the results it is possible to prevent additional noise to the unavoidable minimal combustion noise, evoked by stochastic, turbulent fluctuations of the mixture density, i.e. optimization of the ignition stability with a perfectly premixed pilot flame. Further insight was gained about the influence of the gas injection direction on the combustion noise, where some configurations lead to an increase up to 6 dB in comparison to the results of premixed flames [2], which in general are louder than all investigated non-premixed flames.
Knowledge Transfer: How do High Performance Coaches Access the Knowledge of Sport Scientists?
Authors: Reade Ian , Rodgers Wendy , Hall Nathan
Published: October 2008

The purpose of this research was to answer three specific questions: I) How do coaches perceive sport science research? ii) What sources do coaches consult when looking for new ideas? and iii) What barriers do coaches encounter when trying to access new information? All of the high-performance coaches involved in Canadian Interuniversity Sport (CIS) were contacted to complete an on-line survey related to these questions. There were 205 coaches who completed at least part of the questionnaire. There was a strong consensus that the CIS coaches believe that sport science makes an important contribution to high-performance sport. Gaps exist between what coaches are looking for and the research that is being conducted, especially in the area of tactics and strategies. Coaches are most likely to consult other coaches, or attend coaching conferences to get new information. Sport scientists and their publications were ranked very low by the coaches as a likely source of sport science information. The barriers to the coaches' access to sport science are the time required to find and read scientific journals, and lack of direct access to a sport scientist. Strategies to remove the barriers could include rewarding sport scientists for successful transfer of their knowledge to practice through direct communication with coaches.
Utilizing Video to Facilitate Reflective Practice: Developing Sports Coaches
Authors: Carson Fraser
Published: October 2008

The professionalization of sports coaching has led to a constant need to develop and improve coaching performance and behavior. As a result, reflective practice has become common place within coaching and relevant to the development of sports coaches. This study aims to develop on traditional reflective processes, by identifying how video can be used to assist the learning process of coaches. Nineteen inexperienced coaches recounted their experience of using a video recording of a personal coaching practice, concentrating on: (a) the reflective process, (b) the use of video to assist this process, and (c) the practicalities of video reflection. Content analysis suggests increases in cognitive understanding of the coaching process and improvement in coaching performance are experienced through this form of reflection. Initial results suggest that video reflection can help improve inexperienced sports coaches by highlighting strengths and weaknesses in performance that may be overlooked by traditional methods.
Towards an Understanding of the Barriers to Good Nutrition for Elite Athletes
Authors: Heaney Susan , O'Connor Helen , Naughton Geraldine , Gifford Janelle
Published: October 2008

The objective of this study was to describe barriers influencing dietary practices of elite-level athletes using a focus-group design involving discussions with elite-level athletes, coaches and sports dietitians. The participants were sixteen male and thirty female elite athletes from an Australian State Institute of Sport, representing diving, netball, basketball and lawn bowls; twelve elite coaches representing swimming, diving, soccer, sailing, cycling and golf; and sixteen sports dietitians who consulted to state institutes/academies of sport with various sports. Focus groups were audio-taped and transcribed with in-depth notes also recorded during the groups. Thematic coding of transcripts and notes were undertaken by the primary coder and these themes were subsequently evaluated by the research team. A number of barriers to healthy eating were described. Lack of time for food preparation was a significant barrier raised by all groups. Financial limitations, inadequate cooking skills and difficulty with living arrangements also rated high among all three groups. Coaches were concerned with excess body weight and fat levels and perceived an impact on sports performance. Athletes reported concern about body shape due to societal pressures. Sports dietitians and coaches were concerned with issues relating to optimal dietary provision surrounding travel to and from training and competition. A range of barriers influence the diet of athletes, in particular time and financial constraints in addition to specific physique requirements. Health professionals working with elite athletes need to be aware of these barriers when assessing dietary intake, or designing nutrition interventions. Dietitians may need to advocate on behalf of athletes to facilitate increased financial or professional support to assist athletes to choose and then maintain healthy diet practices.
Fixed Order Branch-and-Bound Methods for Mixed-Integer Programming: The zoom System
Authors: Singhal Jaya , Marsten Roy E. , Morin Thomas L.
Published: October 2008

A branch-and-bound algorithm for mixed-integer programming (MIP) is presented in which a different integer variable is designated for branching at each depth in the search tree. This is done in order to achieve economies of scale in solving the linear programming relaxations to obtain bounds for the (MIP) algorithm. This algorithm is the foundation for the zoom software system, which is briefly described. Illustrative computational experience is included.

INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.
Approximation Algorithms for the Maximum Concurrent Flow Problem
Authors: Shahrokhi Farhad
Published: October 2008

The maximum concurrent flow problem (MCFP) is the optimization version of the feasibility problem in multicommodity flows. The objective is to maximize the percentage of the demands which is realizable for all commodities, subject to the capacity constraints. A fully polynomial ϵ-approximate algorithm was developed by Shahrokhi and Matula to solve the MCFP when the edge capacities are the same (the MCFP with uniform capacity). In this paper, we present an ϵ-approximate algorithm for the MCFP with uniform demand (when all demands are equal). Our ϵ-approximate algorithm employs a linear size reduction from the MCFP with uniform demand to the MCFP with uniform capacity and the fully polynomial ϵ-approximate algorithm for the MCFP with uniform capacity. The computational results indicate that the algorithm is efficient. We also present an efficient combinatorial algorithm for the MCFP in planar graphs.

INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.
Data Structures and Programming Techniques for the Implementation of Karmarkar's Algorithm
Authors: Adler Ilan , Karmarkar Narendra , Resende Mauricio G. C. , Veiga Geraldo
Published: October 2008

This paper describes data structures and programming techniques used in an implementation of Karmarkar's algorithm for linear programming. Most of our discussion focuses on applying Gaussian elimination toward the solution of a sequence of sparse symmetric positive definite systems of linear equations, the main requirement in Karmarkar's algorithm. Our approach relies on a direct factorization scheme, with an extensive symbolic factorization step performed in a preparatory stage of the linear programming algorithm. An interpretative version of Gaussian elimination makes use of the symbolic information to perform the actual numerical computations at each iteration of algorithm. We also discuss ordering algorithms that attempt to reduce the amount of fill-in in the LU factors, a procedure to build the linear system solved at each iteration, the use of a dense window data structure in the Gaussian elimination method, a preprocessing procedure designed to increase the sparsity of the linear programming coefficient matrix, and the special treatment of dense columns in the coefficient matrix.

INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.
Tabu Search—Part I
Authors: Glover Fred
Published: October 2008

This paper presents the fundamental principles underlying tabu search as a strategy for combinatorial optimization problems. Tabu search has achieved impressive practical successes in applications ranging from scheduling and computer channel balancing to cluster analysis and space planning, and more recently has demonstrated its value in treating classical problems such as the traveling salesman and graph coloring problems. Nevertheless, the approach is still in its infancy, and a good deal remains to be discovered about its most effective forms of implementation and about the range of problems for which it is best suited. This paper undertakes to present the major ideas and findings to date, and to indicate challenges for future research. Part I of this study indicates the basic principles, ranging from the short-term memory process at the core of the search to the intermediate and long term memory processes for intensifying and diversifying the search. Included are illustrative data structures for implementing the tabu conditions (and associated aspiration criteria) that underlie these processes. Part I concludes with a discussion of probabilistic tabu search and a summary of computational experience for a variety of applications. Part II of this study (to appear in a subsequent issue) examines more advanced considerations, applying the basic ideas to special settings and outlining a dynamic move structure to insure finiteness. Part II also describes tabu search methods for solving mixed integer programming problems and gives a brief summary of additional practical experience, including the use of tabu search to guide other types of processes, such as those of neural networks.

INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.
A Neural Network-Based Optimization Algorithm for the Static Weapon-Target Assignment Problem
Authors: Wacholder Eitan
Published: October 2008

A neural network-based algorithm was developed for the static weapon-target assignment problem in ballistic missile defense. An optimal assignment policy is one which allocates targets to weapon platforms such that the total expected leakage value of targets surviving the defense is minimized. This involves the minimization of a nonlinear objective function subject to inequality constraints specifying the maximum number of interceptors available to each platform and the maximum number of interceptors allowed to be fired at each target as imposed by the battle management/command control and communications system. The algorithm consists of solving a system of ordinary differential equations whose trajectories are the assignment variables of the problem. Simulations of the algorithm on PC and VAX computers were carried out using a simple numerical scheme. In all the battle instances tested, the algorithm has proven to be stable and to converge to solutions very close to global optima. The time to achieve convergence was consistently less than the time constant of the network's processing elements (neurons). This suggests that fast solutions can be realized if the algorithm is implemented in hardware circuits. Three series of battle scenarios are analyzed and discussed in detail. The main advantage of this algorithm is that it can be adapted to either a special-purpose hardware circuit or a general-purpose concurrent machine to yield fast and accurate solutions to difficult decision problems.

INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.
Anomalous Acceleration in Parallel Multiple-Cost-Row Linear Programming
Authors: Phillips Andrew T. , Ben Rosen J
Published: October 2008

Earlier parallel computational results on constrained global optimization problems have shown that speedups greater than the number of processors can occur in practice. To show how this is possible, a relatively simple example of a multiple-cost-row linear program is presented in which the parallel algorithm gives a speedup, over its sequential version, greater than the number of processors. In addition, it is shown that for a particular problem instance (taken from another special class of multiple-cost-row linear programming problems), the average parallel speedup, taken over all orderings of the cost rows, can also be greater than the number of processors.

INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.
Preprocessing in Stochastic Programming: The Case of Uncapacitated Networks
Authors: Wallace Stein W. , Wets Roger J-B
Published: October 2008

Preprocessing can speed up the solution procedures for two-stage stochastic programming. We consider the case when the second-stage problem is a pure, uncapacitated network. We describe a number of procedures to reduce the size of the recourse problem. We describe a procedure for generating efficiently the (induced) feasibility cuts, and show that further reductions are possible if more information about the node-types is taken into account. We also investigate network collapsing techniques that would simplify the work required to find both optimality cuts and feasibility cuts, if we had not yet reduced the problem to one with relatively complete recourse. Computational results confirm that substantial savings are possible.

INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.
Implementation of a Dual Affine Interior Point Algorithm for Linear Programming
Authors: Marsten Roy E. , Saltzman Matthew J. , Shanno David F. , Pierce George S. , Ballintijn J. F.
Published: October 2008

The dual affine interior point method is extended to handle variables with simple upper bounds as well as free variables. During execution, variables which appear to be going to zero are fixed at zero, and rows with slack variables bounded away from zero are removed. A variant of the big-M artificial variable method to attain feasibility is derived. The simplex method is used to recover an optimal basis upon completion of the algorithm, and the effects of scaling are discussed. Computational experience on a variety of problems is presented.

INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.
A Dual Ascent Procedure with Valid Inequalities for Designing Hierarchical Network Topologies
Authors: Mitra Sabyasachi , Murthy Ishwar
Published: October 2008

Topological design of communication networks has been well examined in the literature. However, most of these studies focus on nonhierarchical networks where all nodes are considered equivalent from a routing perspective. It is well recognized, however, that hierarchical topologies offer several advantages for remote office internetworking. In this article, we provide a mixed integer programming formulation for designing hierarchical topologies. We also provide an interesting solution strategy that incorporates valid inequalities within a dual ascent framework to obtain tight lower bounds and feasible solutions to the problem. Computational experiments with a Fortran implementation of the procedure are also reported.
Distributed State Space Generation of Discrete-State Stochastic Models
Authors: Ciardo Gianfranco , Gluckman Joshua , Nicol David
Published: October 2008

High-level formalisms such as stochastic Petri nets can be used to model complex systems. Analysis of logical and numerical properties of these models often requires the generation and storage of the entire underlying state space. This imposes practical limitations on the types of systems that can be modeled. Because of the vast amount of memory consumed, we investigate distributed algorithms for the generation of state space graphs. The distributed construction allows us to take advantage of the combined memory readily available on a network of workstations. The key technical problem is to find effective methods for on-the-fly partitioning, so that the state space is evenly distributed among processors. In this article we report on the implementation of a distributed state space generator that may be linked to a number of existing system modeling tools. We discuss partitioning strategies in the context of Petri net models, and report on performance observed on a network of workstations, as well as on a distributed memory multicomputer.
On the Performance of Heuristics on Finite and Infinite Fractal Instances of the Euclidean Traveling Salesman Problem
Authors: Moscato Pablo , Norman Michael G.
Published: October 2008

We show how, by a constructive process, we can generate arbitrarily large instances of the Traveling Salesman Problem (TSP) using standard fractals such as those of Peano, Koch, or Sierpinski. We show that optimal solutions for these TSPs can be known a priori, and thus, they provide us with new nontrivial TSP instances offering the possibility of testing heuristics well beyond the scope of testbed instances which have been solved by exact numerical methods. Furthermore, instances may be constructed with different features, for example, with different fractal dimensions. To four of these fractal TSPs we apply three standard constructive heuristics, namely Multiple Fragment, Nearest Neighbor, and Farthest Insertion from Convex-Hull, which have efficient general-purpose implementations. The ability of different algorithms to solve these different fractal TSPs gives us significant insight into the nature of TSP heuristics in a way which is complementary to approaches such as worst-case or average-case analysis.
Approximating Shortest Paths in Large-Scale Networks with an Application to Intelligent Transportation Systems
Authors: Chou Yu-Li , Romeijn H. Edwin , Smith Robert L.
Published: October 2008

We propose a hierarchical algorithm for approximating shortest paths between all pairs of nodes in a large-scale network. The algorithm begins by extracting a high-level subnetwork of relatively long links (and their associated nodes) where routing decisions are most crucial. This high-level network partitions the shorter links and their nodes into a set of lower-level subnetworks. By fixing gateways within the high-level network for entering and exiting these subnetworks, a computational savings is achieved at the expense of optimality. We explore the magnitude of these tradeoffs between computational savings and associated errors both analytically and empirically with a case study of the Southeast Michigan traffic network. An order-of-magnitude drop in computation times was achieved with an on-line route guidance simulation, at the expense of less than 6% increase in expected trip times.
Using Variable Redefinition for Computing Lower Bounds for Minimum Spanning and Steiner Trees with Hop Constraints
Authors: Gouveia Luis
Published: October 2008

We use variable redefinition (see R. Martin, 1987. Generating Alternative Mixed-Integer Programming Models Using Variable Redefinition, Operations Research 35, 820–831) to strengthen a multicommodity flow (MCF) model for minimum spanning and Steiner trees with hop constraints between a root node and any other node. Hop constraints model quality of service constraints. The Lagrangean dual value associated with one Lagrangean relaxation derived from the MCF formulation dominates the corresponding LP value. However, the lower bounds given after a reasonable number of iterations of the associated subgradient optimization procedure are, for several cases, still far from the theoretical best limit. Martin's variable redefinition technique is used to obtain a generalization of the MCF formulation whose LP bound is equal to the previously mentioned Lagrangean dual bound. We use a set of instances with up to 100 nodes, 50 basic nodes, and 350 edges for comparing an LP approach based on solving the LP relaxation of the new model with the equivalent Lagrangean scheme derived from MCF.
An Incremental Branch-and-Bound Method for the Satisfiability Problem
Authors: Bennaceur Hachemi , Gouachi Idir , Plateau Gérard
Published: October 2008

The satisfiability problem is to check whether a set of clauses in propositional logic is satisfiable. If it is satisfiable, the incremental satisfiability problem is then to check whether satisfiability remains given additional clauses. This paper deals with an incremental branch-and-bound method which solves exactly both problems. This method includes flexible Lagrangean relaxations, metaheuristics, and judicious jumping back. This leads to an efficient implementation which compares favorably with the classical Davis-Putnam-Loveland procedure and its incremental version designed by Hooker. Numerous computational results are detailed.
Online Scheduling with Lookahead: Multipass Assembly Lines
Authors: Motwani Rajeev , Saraswat Vijay , Torng Eric
Published: October 2008

This article describes our use of competitive analysis and the on-line model of computation in a product development setting; specifically, we use competitive analysis to evaluate on-line scheduling strategies for controlling a new generation of networked reprographic machines (combination printer-copier-fax machines servicing a network) currently being developed by companies such as Xerox Corporation. We construct an abstract machine model, the multipass assembly line, which not only models networked reprographic machines but also models several common manufacturing environments such as a robotic assembly line or a mixed product assembly line. We consider on-line algorithms with finite lookahead because these machines typically have limited knowledge of the future. We first prove some lower bounds on the performance of any on-line algorithm with finite lookahead. We then show that simple greedy algorithms achieve competitive ratios that are close to these general lower bounds. In particular, we show that lookahead improves the competitive ratio of these simple greedy algorithms from approximately 2 (with no lookahead) to being arbitrarily close to 1 (for large lookahead). This implies these simple greedy algorithms are realistic candidates for field use in future reprographic products.
An Approximate Analysis of a UNIX Macro Process Scheduler
Authors: Benhenni Robert A.
Published: October 2008

A UNIX macro process scheduler, referred to as the Fair Share Scheduler (FSS), is a UNIX scheduling algorithm that allocates different shares of the processor capacity to different groups of processes. First, the scheduling algorithm is approximated by a generalized processor-sharing discipline. Then, a second approximation is made to derive the mean response times of the different groups and the optimal allocation of shares among the groups. Finally, an application is shown where substantial performance improvements are observed.
Rejoinder—OR/MS, Electronic Commerce, and the Virtual INFORMS Community
Authors: Bhargava Hemant K. , Krishnan Ramayya
Published: October 2008

We would like to begin by thanking all the commentators for their careful review and thoughtful comments. We see three themes related to OR/MS and the Web in the various comments and suggestions made by the commentators. The first relates to electronic commerce, the second to enabling technology infrastructure, and the third to the role of the Web in serving the INFORMS community. We respond to each of these points in turn.
Lifted Cover Inequalities for 0-1 Integer Programs: Computation
Authors: Gu Zonghao , Nemhauser George L. , Savelsbergh Martin W. P.
Published: October 2008

We investigate the algorithmic and implementation issues related to the effective and efficient use of lifted cover inequalities and lifted GUB cover inequalities in a branch and cut algorithm for 0-1 integer programming. We have tried various strategies on several test problems and we identify the best ones for use in practice.
Localizer: A Modeling Language for Local Search
Authors: Michel Laurent , Van Hentenryck Pascal
Published: October 2008

Local search is a traditional technique to solve combinatorial search problems and has raised much interest in recent years. The design and implementation of local search algorithms is not an easy task in general and may require considerable experimentation and programming effort. However, contrary to global search, little support is available to assist the design and implementation of local search algorithms. This paper is an attempt to support the implementation of local search. It presents the preliminary design of LOCALIZER, a modeling language which makes it possible to express local search algorithms in a notation close to their informal descriptions in scientific papers. Experimental results on our first implementation show the feasibility of the approach.
Analysis of Stochastic Assembly with GI-Distributed Assembly Time
Authors: Wilhelm W. E. , Som Pradip
Published: October 2008

In this article, we study an assembly system that supplies an end-product inventory. We allow assembly operation times to be general, independent (GI) distributed and analyze the system as a Markov renewal process, deriving a closed-form expression for long-run Palm probabilities of both kit and end-product inventory positions. We then present a numerical procedure to obtain various performance measures using the matrix-geometric approach. Finally, we describe insights about the operation of the assembly system that are made possible by our analysis, in particular, showing the effects of kit buffer capacity on kit and end-product inventory positions.
Lifted Cover Inequalities for 0-1 Integer Programs: Complexity
Authors: Gu Zonghao , Nemhauser George L. , Savelsbergh Martin W. P.
Published: October 2008

We investigate several complexity issues related to branch-and-cut algorithms for 0-1 integer programming based on lifted-cover inequalities (LCIs). We show that given a fractional point, determining a violated LCI over all minimal covers is NP-hard. The main result is that there exists a class of 0-1 knapsack instances for which any branch-and-cut algorithm based on LCIs has to evaluate an exponential number of nodes to prove optimality.
Improvement Procedures for the Undirected Rural Postman Problem
Authors: Hertz Alain , Laporte Gilbert , Hugo Pierrette Nanchen
Published: October 2008

This article describes new construction and postoptimization heuristics for the Undirected Rural Postman Problem. Extensive computational tests indicate that some combinations of these heuristics consistently produce optimal or high-quality solutions.
Analyzing Infeasible Mixed-Integer and Integer Linear Programs
Authors: Guieu Olivier , Chinneck John W.
Published: October 2008

Algorithms and computer-based tools for analyzing infeasible linear and nonlinear programs have been developed in recent years, but few such tools exist for infeasible mixed-integer or integer linear programs. One approach that has proven especially useful for infeasible linear programs is the isolation of an Irreducible Infeasible Set of constraints (IIS), a subset of the constraints defining the overall linear program that is itself infeasible, but for which any proper subset is feasible. Isolating an IIS from the larger model speeds the diagnosis and repair of the model by focussing the analytic effort. This paper describes and tests algorithms for finding small infeasible sets in infeasible mixed-integer and integer linear programs; where possible these small sets are IISs.
Computing Minimum-Weight Perfect Matchings
Authors: Cook William , Rohe André
Published: October 2008

We make several observations on the implementation of Edmonds' blossom algorithm for solving minimum-weight perfect-matching problems and we present computational results for geometric problem instances ranging in size from 1,000 nodes up to 5,000,000 nodes. A key feature in our implementation is the use of multiple search trees with an individual dual-change ε for each tree. As a benchmark of the algorithm's performance, solving a 100,000-node geometric instance on a 200 Mhz Pentium-Pro computer takes approximately 3 minutes.
A Set-Partitioning-Based Heuristic for the Vehicle Routing Problem
Authors: Kelly James P. , Xu Jiefeng
Published: October 2008

We develop a generic tabu search heuristic for solving the well-known vehicle routing problem. This algorithm explores the advantages of simple local search and improvement heuristics as well as a complex meta-heuristic. The solutions generated by these heuristics are selected and assembled by a set-partitioning model to produce superior solutions. Computational experience on standard benchmark problems is discussed and comparisons with other up-to-date heuristic methods are provided.
Parallel Complexity of Additive Location Problems
Authors: Averbakh Igor , Berman Oded
Published: October 2008

Parallel NC-algorithms for a general class of multifacility location problems on a tree with identical facilities and the minisum objective function are presented. The class includes the p-median problem, the p-coverage problem, and the uncapacitated plant location problem.
Heuristic and Metaheuristic Approaches for a Class of Two-Dimensional Bin Packing Problems
Authors: Lodi Andrea , Martello Silvano , Vigo Daniele
Published: October 2008

Two-dimensional bin packing problems consist of allocating, without overlapping, a given set of small rectangles (items) to a minimum number of large identical rectangles (bins), with the edges of the items parallel to those of the bins. According to the specific application, the items may either have a fixed orientation or they can be rotated by 90°. In addition, it may or not be imposed that the items are obtained through a sequence of edge-to-edge cuts parallel to the edges of the bin. In this article, we consider the class of problems arising from all combinations of the above requirements. We introduce a new heuristic algorithm for each problem in the class, and a unified tabu search approach that is adapted to a specific problem by simply changing the heuristic used to explore the neighborhood. The average performance of the single heuristics and of the tabu search are evaluated through extensive computational experiments.
Exact and Approximate Nondeterministic Tree-Search Procedures for the Quadratic Assignment Problem
Authors: Maniezzo Vittorio
Published: October 2008

This article introduces two new techniques for solving the Quadratic Assignment Problem. The first is a heuristic technique, defined in accordance with the Ant System metaphor, and includes as a distinctive feature the use of a new lower bound at each constructive step. The second is a branch-and-bound exact approach, containing some elements introduced in the Ant algorithm. Computational results prove the effectiveness of both approaches.
A Bundle Type Dual-Ascent Approach to Linear Multicommodity Min-Cost Flow Problems
Authors: Frangioni Antonio , Gallo Giorgio
Published: October 2008

We present a Cost Decomposition approach for the linear Multicommodity Min-Cost Flow problem, where the mutual capacity constraints are dualized and the resulting Lagrangean Dual is solved with a dual-ascent algorithm belonging to the class of Bundle methods. Although decomposition approaches to block-structured Linear Programs have been reported not to be competitive with general-purpose software, our extensive computational comparison shows that, when carefully implemented, a decomposition algorithm can outperform several other approaches, especially on problems where the number of commodities is “large” with respect to the size of the graph. Our specialized Bundle algorithm is characterized by a new heuristic for the trust region parameter handling, and embeds a specialized Quadratic Program solver that allows the efficient implementation of strategies for reducing the number of active Lagrangean variables. We also exploit the structural properties of the single-commodity Min-Cost Flow subproblems to reduce the overall computational cost. The proposed approach can be easily extended to handle variants of the problem.
Propagation of Interval Values in Simple Processing Networks
Authors: Schug Brett W. , Realff Matthew J.
Published: October 2008

Process network optimization problems are prevalent in the processing industries. Streams of differing compositions undergo mixing and splitting steps to attain product streams of desired properties. Constraint propagation of system variable bounds across a process network allows identification of system capabilities prior to optimization, and expedites solution of the optimization itself. In this article, an improved generalized algorithm for interval propagation in simple networks, and an extension of the model structure of the pooling problem beyond that of simple pools and streams, are presented. An application of preprocessing to a branch-and-bound approach to process network NLP global optimization is given. The importance of model structure to tightness of derived bounds is illustrated. This work demonstrates that knowledge of the problem structure may be used to integrate reasoning and optimization, and that specialized structures and specific domain constraints can lead to customized algorithms that are significantly more efficient than general algorithms.