11,306 research outputs found
Incorporating scatter search and threshold accepting in finding maximum likelihood estimates for the multinomial probit model
No full text[[abstract]]This paper presents a procedure that incorporates scatter search and threshold accepting to find the maximum likelihood estimates for the multinomial probit (MNP) model. Scatter search, widely used in optimization-related studies, is a type of evolutionary algorithm that uses a small set of solutions as the selection pool for mating and generating new solutions to search for a globally optimal solution. Threshold accepting is applied to the scatter search to improve computational efficiency while maintaining the same level of solution quality. A set of numerical experiments, based on synthetic data sets with known model specifications and error structures, were conducted to test the effectiveness and efficiency of the proposed framework. The results indicated that the proposed procedure enhanced performance in terms of likelihood function value and computational efficiency for MNP model estimation as compared to the original scatter search framework. (C) 2010 Elsevier B.V. All rights reserved.[[note]]SC
Diversified local search strategy under scatter search framework for the probabilistic traveling salesman problem
No full text[[abstract]]This paper focuses on introducing a concept of diversified local search strategy under the scatter search framework for the probabilistic traveling salesman problem (PTSP). Different combinations of three commonly used local search methods in the PTSP, i.e., 1-shift, 2-opt, and 3-opt, were used to investigate its effects. A set of numerical experiments were conducted to test the validity of the proposed strategy based on randomly generated test instances. The numerical results and the permutation test showed that the diversified local search strategy, especially by combining I-shift and 2-opt algorithms, can most effectively solve the homogeneous and heterogeneous PTSP in most of the tested instances in comparison with the single local search strategy under scatter search framework. (C) 2007 Elsevier B.V. All rights reserved.[[note]]SC
A genetic local search algorithm with a threshold accepting mechanism for solving the runway dependent aircraft landing problem
No full text[[abstract]]As the demand for air transportation continues to grow, some flights cannot land at their preferred landing times because the airport is near its runway capacity. Extra fuel consumption and air pollution are then caused by the landing delays. Moreover, such delays may possibly yield extra costs for both passengers and airline companies that result from rescheduling transfer passengers and crew members. Consequently, how to increase the handling efficiency of congested airports is a crucial management issue. Building new runways at existing airports is often not feasible due to environmental, financial and geographical constraints. Therefore, devising a method for tackling the aircraft landing problem (ALP) in order to optimize the usage of existing runways at airports is the focus of this paper. This paper aims to develop a solution procedure based on a genetic local search (GLS) algorithm for solving the ALP with runway dependent attributes. A set of numerical experiments were conducted to test the validity of the proposed algorithm based on five test instances created and investigated by previous studies. The numerical results showed that the proposed GLS algorithm can effectively and efficiently determine the runway allocation, sequence and landing time for arriving aircraft for the five test cases by minimizing total delays under the separation constraints in comparison with the outcomes yielded by previous studies.[[note]]SC
Different initial solution generators in genetic algorithms for solving the probabilistic traveling salesman problem
No full text[[abstract]]The probabilistic traveling salesman problem (PTSP) is a topic of theoretical and practical importance in the study of stochastic network problems. It provides researchers with a modeling framework for exploring the stochastic effects in routing problems. This paper proposed three initial solution generators (NN1, NN2, RAN) under a genetic algorithm (GA) framework for solving the PTSP. A set of numerical experiments based on heterogeneous and homogeneous PTSP instances were conducted to test the effectiveness and efficiency of the proposed algorithms. The results from the heterogeneous PTSP show that the average E[tau] values obtained by the three generators under a GA framework are similar to those obtained by the "Previous Best," but with an average computation time saving of 50.2%. As for the homogeneous PTSP instances, NN1 is a relatively better generator among the three examined, while RAN consistently performs worse than the other two generators in terms of average E[tau] values. Additionally, as compared to previously reported studies, no one single algorithm consistently outperformed the others across all homogeneous PTSP instances in terms of the best E[tau] values. The fact that no one initial solution generator consistently performs best in terms of the E[tau] value obtained across all instances in heterogeneous cases, and that the performance of each examined algorithm is dependent on the number of nodes (n) and probability (p) for homogeneous cases, suggest the possibility of context- dependent phenomenon. Finally, to obtain valid results, researchers are advised to include at least a certain amount of test instances with the same combination of n and p when conducting PTSP experiments. (C) 2010 Elsevier Inc. All rights reserved.[[note]]SC
Reduction of acute respiratory illness (ARI) due to a voluntary workplace influenza vaccination program: Who are more likely to get the benefit?
No full textA hybrid scatter search for the probabilistic traveling salesman problem
No full text[[abstract]]The probabilistic traveling salesman problem (PTSP) is an important theoretical and practical topic in the study of stochastic network problems. It provides researchers with a modeling framework for exploring the stochastic effects in routing problems. This paper focuses on developing the hybrid scatter search (HSS) by incorporating the nearest neighbor rule (NNR), threshold accepting (TA) and edge recombination (ER) crossover into a scatter search conceptual framework to solve the PTSP. A set of numerical experiments were conducted to test the validity of the HSS based on the test problems from Tang and Miller-Hooks' study. The numerical results showed that the HSS can effectively solve the PTSP in most of the tested cases in terms of objective function value. Moreover, the results also indicated that incorporating threshold accepting into the scatter search framework can further increase the computation efficiency while maintaining solution quality. These findings show the potential of the proposed HSS in solving the large-scale PTSP. (c) 2005 Elsevier Ltd. All rights reserved.[[note]]SC
Creating a psychologically safe online space for a student-generated questions learning activity via different identity revelation modes
No full text[[abstract]]This study focuses on mitigating evaluation apprehension, which is usually unavoidable in identifiable social situations, via the constructive use of prominent features of networked technologies. Specifically, this study investigated learners' attitudes towards different user-identity revelation modes, namely, real-identity, anonymity and created-identity, in an online question-construction and peer-assessment context. Forty university freshmen, taking a physics laboratory course, participated for one semester in 2007. A learning system called The Question Authoring and Reasoning Knowledge System which allowed students to contribute and benefit from cyclic process of constructing and reviewing questions, was devised. Analysis of the data gathered found that students reacted statistically differently to the modes of real name, anonymity and nickname. Furthermore, participating students adjusted their preferred mode in different roles and circumstances. The data obtained suggest that program developers should embed flexible and versatile capabilities of computer and communication technologies by allowing individuals the opportunity not to be identified or only be identified via a nickname of their choice, so as to help eliminate feelings of embarrassment and uneasiness, which are not psychologically sound and may hinder the learning process.[[note]]SSC
Synthesis and characterization of ruthenium complexes with two fluorinated amino alkoxide chelates. The quest to design suitable MOCVD source reagents
No full textStable organic blue-light-emitting devices prepared from poly[spiro(fluorene-9,9’-xanthene)]
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