A review of the Tabu Search Literature on Traveling Salesman Problems

The Traveling Salesman Problem (TSP) is one of the most widely studied problems inrncombinatorial optimization. It has long been known to be NP-hard and hence research onrndeveloping algorithms for the TSP has focused on approximate methods in addition to exactrnmethods. Tabu search is one of the most widely applied metaheuristic for solving the TSP. Inrnthis paper, we review the tabu search literature on the TSP, point out trends in it, and bringrnout some interesting research gaps in this literature.

Implementing Tabu Search to Exploit Sparsity in ATSP Instances

Real life traveling salesman problem (TSP) instances are often large,sparse, and asymmetric. Conventional tabu search implementations for the TSP that have been reported in the literature, almost always deals with small, dense and symmetric instances. In this paper, we outline data structures and a tabu search implementation that takes advantage of such data structures, which can exploit sparsity of a TSP instances, and hence can solve relatively large TSP instances (with up to 3000 nodes) much faster than conventional implementations. We also provide computational experiences with this implementation.

Spatial Impact Network Exposure Model (SINEM) with Integration of Traffic Characteristics and Air Pollution Concentration

The State of Qatar has undergone rapid economic growth and urbanization during the last few decades. This has resulted in an increase in the number of motor vehicles in the country. Therefore, it is vital to monitor and manage the air pollution level in Qatar. Trafficrelated air pollutants generally have a significant contribution to air pollution especially in urban areas and they also have an adverse impact on the commuters and abutting street population. Limited study has been carried out in this area and particularly in the context of Qatar. The purpose of this research is to establish a relationship between air pollution concentration and a set of parameters related to traffic and network characteristics; such as traffic volume, speed, VCR, etc. This study aims to develop an area-wide Spatial Impact Network Exposure Model (SINEM) using Geographic Information System (GIS). The SINEM shall be developed to assess the area-wide spatial impact of trafficrelated air pollution exposure based on an aggregated approach. This model helps to predict the surrounding network exposure index which helps in the decision-making process. Interestingly, this model also has the potential to scale up as well as convert into a real-time model. It will assist relevant authorities and decision-makers to identify and initialize policy measures to reduce the exposure impact, setting up building regulations, FAR implementation and sustainable master plan development

Matroid Intersection: A Pseudo-Deterministic Parallel Reduction from Search to Weighted-Decision

We study the matroid intersection problem from the parallel complexity perspective. Given two matroids over the same ground set, the problem asks to decide whether they have a common base and its search version asks to find a common base, if one exists. Another widely studied variant is the weighted decision version where with the two matroids, we are given small weights on the ground set elements and a target weight W, and the question is to decide whether there is a common base of weight at least W. From the perspective of parallel complexity, the relation between the search and the decision versions is not well understood. We make a significant progress on this question by giving a pseudo-deterministic parallel (NC) algorithm for the search version that uses an oracle access to the weighted decision. The notion of pseudo-deterministic NC was recently introduced by Goldwasser and Grossman [Shafi Goldwasser and Ofer Grossman, 2017], which is a relaxation of NC. A pseudo-deterministic NC algorithm for a search problem is a randomized NC algorithm that, for a given input, outputs a fixed solution with high probability. In case the given matroids are linearly representable, our result implies a pseudo-deterministic NC algorithm (without the weighted decision oracle). This resolves an open question posed by Anari and Vazirani [Nima Anari and Vijay V. Vazirani, 2020]

Anisotropic surface transport in topological insulators in proximity to a helical spin density wave

We study the effects of spatially localized breakdown of time reversal symmetry on the surface of a topological insulator (TI) due to proximity to a helical spin density wave (HSDW). The HSDW acts like an externally applied one-dimensional periodic(magnetic) potential for the spins on the surface of the TI, rendering the Dirac cone on the TI surface highly anisotropic. The decrease of group velocity along the direction $\hat{x}$ of the applied spin potential is twice as much as that perpendicular to $\hat{x}$. At the Brillouin zone boundaries (BZB) it also gives rise to new semi-Dirac points which have linear dispersion along $\hat{x}$ but quadratic dispersion perpendicular to $\hat{x}$. The group velocity of electrons at these new semi-Dirac points is also shown to be highly anisotropic. Experiments using TI systems on multiferroic substrates should realize our predictions. We further discuss the effects of other forms of spin density wave on the surface transport property of topological insulator.Comment: 8 pages, 8 figure

SPECTROSCOPIC CHARACTERIZATION OF PHYTOCONSTITUENTS ISOLATED FROM A RARE MANGROVE AEGIALITIS ROTUNDIFOLIA ROXB., LEAVES AND EVALUATION OF ANTIMICROBIAL ACTIVITY OF THE CRUDE EXTRACT

Objective: The aim of the study is to isolate and characterize the phytochemicals from the leaves of a rare and unexplored mangrove Aegialitis rotundifolia and evaluate the antimicrobial properties of the crude extract. Methods: The dried powdered plant material was extracted with ethanol, and the ethanol extract obtained was dissolved in distilled water and partitioned using n-hexane first and then ethyl acetate. The ethyl acetate fraction was subjected to column chromatography for isolation of phytocompounds. The isolated compounds were characterized using infrared (IR), carbon-13 nuclear magnetic resonance (13C NMR), proton nuclear magnetic resonance (1H NMR), mass spectroscopy, and thin-layer chromatography (TLC). Antimicrobial activity of the crude extracts was performed using the well diffusion method against four bacterial strains and two fungal strains. Results: Three pure compounds were isolated from the leaves of Aegialitis rotundifolia, namely, 3,4-dimethyl benzoic acid, 3’-methoxy-4’-hydroxy-flavan-3-ol, and 3’,7-dimethoxy-dimethyl-4’,3,5-trihydroxy flavone which were confirmed by spectroscopic studies. Strong antibacterial activity was shown by the test extract against Staphylococcus aureus and Pseudomonas aeruginosa, whereas Escherichia coli and Bacillus cereus showed average and nil activity, respectively. The antifungal activity of the test extract was found to be strong for both the fungal strains, namely, Candida albicans and Aspergillus niger. Conclusion: The results of the present study show that the isolated compounds were confirmed to be 3,4-dimethyl benzoic acid, 3’-methoxy-4’- hydroxy-flavan-3-ol, and 3’,7-dimethoxy-dimethyl-4’,3,5-trihydroxy flavone and the test extracts showed potent antimicrobial activity for all the bacterial and fungal strains except E. coli and B. cereus which showed average and nil activity, respectively