Decomposition, Reformulation, and Diving in University Course Timetabling

In many real-life optimisation problems, there are multiple interacting components in a solution. For example, different components might specify assignments to different kinds of resource. Often, each component is associated with different sets of soft constraints, and so with different measures of soft constraint violation. The goal is then to minimise a linear combination of such measures. This paper studies an approach to such problems, which can be thought of as multiphase exploitation of multiple objective-/value-restricted submodels. In this approach, only one computationally difficult component of a problem and the associated subset of objectives is considered at first. This produces partial solutions, which define interesting neighbourhoods in the search space of the complete problem. Often, it is possible to pick the initial component so that variable aggregation can be performed at the first stage, and the neighbourhoods to be explored next are guaranteed to contain feasible solutions. Using integer programming, it is then easy to implement heuristics producing solutions with bounds on their quality. Our study is performed on a university course timetabling problem used in the 2007 International Timetabling Competition, also known as the Udine Course Timetabling Problem. In the proposed heuristic, an objective-restricted neighbourhood generator produces assignments of periods to events, with decreasing numbers of violations of two period-related soft constraints. Those are relaxed into assignments of events to days, which define neighbourhoods that are easier to search with respect to all four soft constraints. Integer programming formulations for all subproblems are given and evaluated using ILOG CPLEX 11. The wider applicability of this approach is analysed and discussed.Comment: 45 pages, 7 figures. Improved typesetting of figures and table

Enabling a Just Transition: Protecting Human Rights in Renewable Energy Projects: A Briefing For Policymakers

This briefing provides guidance to policy- and decision-makers (hereafter, “policymakers”) on the benefits of and strategies for taking a human rights-based approach to renewable energy policy. It highlights the various impacts of utility-scale renewable energy projects on peoples and communities, associated risks for policymakers, and explains how national, regional, and global policies can help mitigate those impacts and risks. The briefing addresses different agents of policy- and decision-making: Host states, where renewable energy projects are proposed or located; Home states where corporations pursuing renewable energy investments, especially investments abroad, are based; Development Finance Institutions (DFIs) financing renewable energy investments, especially those required to comply with environmental and social safeguards; and Intergovernmental bodies concerned with socio-economic cooperation, which can set standards regarding the conduct of renewable energy investments. This briefing is part of a series of publications by the Columbia Center on Sustainable Investment that provide guidance on adopting a rights-based approach to renewable energy deployment

Automated generation of constructive ordering heuristics for educational timetabling

Construction heuristics play an important role in solving combinatorial optimization problems. These heuristics are usually used to create an initial solution to the problem which is improved using optimization techniques such as metaheuristics. For examination timetabling and university course timetabling problems essentially graph colouring heuristics have been used for this purpose. The process of deriving heuristics manually for educational timetabling is a time consuming task. Furthermore, according to the no free lunch theorem different heuristics will perform well for different problems and problem instances. Hence, automating the induction of construction heuristics will reduce the man hours involved in creating such heuristics, allow for the derivation of problem specific heuristics and possibly result in the derivation of heuristics that humans have not thought of. This paper presents generation construction hyper-heuristics for educational timetabling. The study investigates the automatic induction of two types of construction heuristics, namely, arithmetic heuristics and hierarchical heuristics. Genetic programming is used to evolve arithmetic heuristics. Genetic programming, genetic algorithms and the generation of random heuristic combinations is examined for the generation of hierarchical heuristics. The hyper-heuristics generating both types of heuristics are applied to the examination timetabling and the curriculum based university course timetabling problems. The evolved heuristics were found to perform much better than the existing graph colouring heuristics used for this domain. Furthermore, it was found that the while the arithmetic heuristics were more effective for the examination timetabling problem, the hierarchical heuristics produced better results than the arithmetic heuristics for the curriculum based course timetabling problem. Genetic algorithms proved to be the most effective at inducing hierarchical heuristics

Electron-impact broadening of the 3s-3p lines in low-Z Li-like ions

The collisional electron-impact line widths of the 3s-3p transitions in Li-like ions from B III to Ne VIII are calculated with the convergent close-coupling (CCC) method from the atomic collision theory. The elastic and inelastic contributions to the line broadening and their Z-scaling are discussed in detail, and comparisons with recent experimental and theoretical results are also presented. It is found that similar to our previous study of line broadening in Be-like ions, the difference between experimental and CCC results monotonically increases with the spectroscopic charge of an ion.Comment: 23 pages, 8 figures, 1 table. To be published in JQSR

A harmony search algorithm for nurse rostering problems

Harmony search algorithm (HSA) is a relatively new nature-inspired algorithm. It evolves solutions in the problem search space by mimicking the musical improvisation process in seeking agreeable harmony measured by aesthetic standards. The nurse rostering problem (NRP) is a well-known NP-hard scheduling problem that aims at allocating the required workload to the available staff nurses at healthcare organizations to meet the operational requirements and a range of preferences. This work investigates research issues of the parameter settings in HSA and application of HSA to effectively solve complex NRPs. Due to the well-known fact that most NRPs algorithms are highly problem (or even instance) dependent, the performance of our proposed HSA is evaluated on two sets of very different nurse rostering problems. The first set represents a real world dataset obtained from a large hospital in Malaysia. Experimental results show that our proposed HSA produces better quality rosters for all considered instances than a genetic algorithm (implemented herein). The second is a set of well-known benchmark NRPs which are widely used by researchers in the literature. The proposed HSA obtains good results (and new lower bound for a few instances) when compared to the current state of the art of meta-heuristic algorithms in recent literature

What do Spanish men know about menopause?

Objective: The aim of the study is to evaluate the knowledge that men have about menopause and to analyze whether sociodemographic aspects influence in this knowledge. Methods: 560 consecutive surveys were collected during 2019. The surveys were completed anonymously, voluntarily and without incentives by men. A maximum score of 45 points was considered for the knowledge analysis. Results: The mean age was 49.13 ± 11.1 years. The most frequent source of information to obtain knowledge about menopause were friends (61.4%). The mean of the questionnaire score was 20.69 ± 6.1. The most frequent symptoms associated with menopause were hot flashes and vaginal dryness (93.7%; 48%) and the best-known treatment to improve vaginal health was lubricants at 69.5%. The most common treatment men know for improving menopause symptoms was menopause hormone treatment; however, 27.9% of men think there is no treatment for menopause. Differences between ages in numbers and grades were found (p=0.032). The scores by levels of study showed statistically differences (primary school, high school, professional training and university education (men with a higher level of education had significantly more knowledge) (p=0.013). Differences were showed in men who obtained information from health staff with respect to other sources (p<0.001). Conclusions: The knowledge in men in this sample is limited. Differences between ages, level of education and sources of information were found. No differences were found between public and private hospitals. The teaching of this knowledge should be carried out by trained personnel, preferably health staff.pre-print224 K

What is the optimum time to start antiretroviral therapy in people with HIV and tuberculosis coinfection? A systematic review and meta-analysis

Background: HIV and tuberculosis are frequently diagnosed concurrently. In March 2021, World Health Organization recommended that antiretroviral therapy (ART) should be started within two weeks of tuberculosis treatment start, at any CD4 count. We aimed to assess whether earlier ART improved outcomes in people with newly diagnosed HIV and tuberculosis. Methods: We did a systematic review by searching nine database for for trials that compared earlier ART to later ART initiation in people with HIV and tuberculosis. We included studied published from database inception to 12 March 2021. We compared ART within four weeks vs. ART more than four weeks after TB treatment, and ART within two weeks vs. ART between two and eight weeks, and stratified analysis by CD4 count. The main outcome was death; secondary outcomes included IRIS and AIDS-defining events. We used random effects meta-analysis to pool effect estimates. Results: 2468 abstracts were screened, from which we identified nine trials. Among people with all CD4 counts, there was no difference in mortality by earlier ART (≤ 4 week) vs. later ART (> 4 week) (risk difference [RD] 0%; 95% confidence interval [CI] -2% to +1%). Among people with CD4 count ≤50 cells/mm3, earlier ART (≤4 weeks) reduced risk of death (RD -6%; -10% to -1%). Among people with all CD4 counts earlier ART (≤4 weeks) increased the risk of IRIS (RD +6%, 95% CI +2% to +10%) and reduced the incidence of AIDS defining events (RD -2%, 95% CI -4% to 0%). Results were similar when trials were restricted to the five trials which permitted comparison of ART within two weeks to ART between two and eight weeks. Discussion: Earlier ART did not alter risk of death overall among people living with HIV who had TB disease. Trials were conducted between 2004 and 2014, before recommendations to treat HIV at any CD4 count or to rapidly start ART in people without TB. No trials included children or pregnant women. No trials included integrase inhibitors in ART regimens. For logistical and patient preference reasons, earlier ART initiation for everyone with TB and HIV may be preferred to later ART