Performance Analyses of Graph Heuristics and Selected Trajectory Metaheuristics on Examination Timetable Problem

Examination timetabling problem is hard to solve due to its NP-hard nature, with a large number of constraints having to be accommodated. To deal with the problem effectually, frequently heuristics are used for constructing feasible examination timetable while meta-heuristics are applied for improving the solution quality. This paper presents the performances of graph heuristics and major trajectory metaheuristics or S-metaheuristics for addressing both capacitated and un-capacitated examination timetabling problem. For constructing the feasible solution, six graph heuristics are used. They are largest degree (LD), largest weighted degree (LWD), largest enrolment degree (LE), and three hybrid heuristic with saturation degree (SD) such as SD-LD, SD-LE, and SD-LWD. Five trajectory algorithms comprising of tabu search (TS), simulated annealing (SA), late acceptance hill climbing (LAHC), great deluge algorithm (GDA), and variable neighborhood search (VNS) are employed for improving the solution quality. Experiments have been tested on several instances of un-capacitated and capacitated benchmark datasets, which are Toronto and ITC2007 dataset respectively. Experimental results indicate that, in terms of construction of solution of datasets, hybridizing of SD produces the best initial solutions. The study also reveals that, during improvement, GDA, SA, and LAHC can produce better quality solutions compared to TS and VNS for solving both benchmark examination timetabling datasets

Solving Examination Timetabling Problem using Partial Exam Assignment with Great Deluge Algorithm

Constructing a quality solution for the examination timetable problem is a difficult task. This paper presents a partial exam assignment approach with great deluge algorithm as the improvement mechanism in order to generate good quality timetable. In this approach, exams are ordered based on graph heuristics and only selected exams (partial exams) are scheduled first and then improved using great deluge algorithm. The entire process continues until all of the exams have been scheduled. We implement the proposed technique on the Toronto benchmark datasets. Experimental results indicate that in all problem instances, this proposed method outperforms traditional great deluge algorithm and when comparing with the state-of-the-art approaches, our approach produces competitive solution for all instances, with some cases outperform other reported result

Concentration quenched luminescence and energy transfer analysis of Nd(3+) ion doped Ba-Al-metaphosphate laser glasses

This paper reports the dopant ion (Nd(3+)) concentration effects on its luminescence properties in a new glass system based on barium-alumino-metaphosphates. Amongst the studied concentrations range of 0.276-13.31x10(20) ions/cm(3), the glass with 2.879x10(20) ions/cm(3) (1 mol%) Nd(3+) concentration shows intense NIR emission from (4)F(3/2) excited state, followed by a decrease in emission intensity for further increase in Nd(3+) ion concentration. The observed luminescence quenching is ascribed to Nd(3+) self-quenching through the donor-donor migration assisted cross-relaxation mechanism. The microscopic energy transfer parameters for donor-acceptor energy transfer, C (DA), and donor-donor energy migration, C (DD), have been obtained from the theoretical fittings to experimental decay curves and the spectral overlap model respectively. The C (DD) parameters (x10(-39) cm(6)/sec) are found to be about three orders greater than that of C (DA) (x10(-42) cm(6)/sec) for Nd(3+) self-quenching in this host, demonstrating that the excitation energy migration among donors is due to the hopping mechanism. The energy transfer micoparameters obtained in the present study are comparable to the values reported for commercially available laser glasses LHG-8 and Q-98

Time resolved spectra and energy transfer analysis of Nd3+-Yb3+-Er3+ triply-doped Ba-Al-metaphosphate glasses for an eye safe emission (1.54 μm)

This paper reports on the development and systematic analysis of energy transfer mechanisms in Nd3+-Yb3+-Er3+ co-doped new series of barium-alumino-metaphosphate glasses. The time resolved fluorescence spectra of Nd3+ in triply doped Ba-Almetaphosaphte glasses have revealed that, Yb3+ ions could function as quite efficient bridge for an energy transfer between Nd3+ and Er3+ ions. As a result, a fourfold emission enhancement at 1.54 μm of Er3+ ions has been achieved through an excitation of 4F5/2 level of Nd3+ at 806 nm for the glass having 3 mol% Yb3+ with an energy transfer efficiency reaching up to 94%. Decay of donor (Nd3+) ion fluorescence has been analyzed based on theoretical models such as Inokuti-Hirayama, Burshtein (migration) and Yokota-Tanimoto (diffusion) and corresponding energy transfer parameters have been discussed. Primarily, electrostatic dipole-dipole (s ~ 6) interactions are found to be responsible for the occurrence of energy transfer process in theses glasses