A new evolutionary clustering search for a no-wait flow shop problem with set-up times

This paper addresses the m-machine no-wait flow shop problem where the set-up time of a job is separated from its processing time. The performance measure considered is the total flowtime. A new hybrid metaheuristic Genetic Algorithm-Cluster Search is proposed to solve the scheduling problem. The performance of the proposed method is evaluated and the results are compared with the best method reported in the literature. Experimental tests show superiority of the new method for the test problems set, regarding the solution quality. (c) 2012 Elsevier Ltd. All rights reserved.

The experiences of South Asian university students in the British education system and in their search for work

This research aimed to provide a comparative analysis of South Asian and White British students in their academic attainment at school and university and in their search for employment. Data were gathered by using a variety of methodological techniques. Completed postal questionnaires were received from 301 South Asian and White British undergraduates from 12 British universities, who were in their final year of study in 1985. In depth interviews were also conducted with 49 graduates who were a self selected group from the original sample. Additional information was also collected by using diary report forms and by administering a second postal questionnaire to selected South Asian and White British participants. It was found that while the pre-university qualifications of the White British and South Asian undergraduates did not differ considerably, many members in the latter group had travelled a more arduous path to academic success. For some South Asians, school experiences included the confrontation of racist attitudes and behaviour, both from teachers and peers. The South Asian respondents in this study were more likely than their White British counterparts, to have attempted some C.S.E. examinations, obtained some of their `O' levels in the Sixth Form and retaken their `A' levels. As a result the South Asians were on average older than their White British peers when entering university. A small sample of South Asians also found that the effects of racism were perpetuated in higher education where they faced difficulty both academically and socially. Overall, however, since going to university most South Asians felt further drawn towards their `cultural background', this often being their own unique view of `Asianess'. Regarding their plans after graduation, it was found that South Asians were more likely to opt for further study, believing that they needed to be better qualified than their White British counterparts. For those South Asians who were searching for work, it was noted that they were better qualified, willing to accept a lower minimum salary, had made more job applications and had started searching for work earlier than the comparable White British participants. Also, although generally they were not having difficulty in obtaining interviews, South Asian applicants were less likely to receive an offer of employment. In the final analysis examining their future plans, it was found that a large proportion of South Asian graduates were aspiring towards self employment.

Munkapiac keresési súrlódásokkal (Job seeking on the labour market, with frictions)

A munkapiac különleges piac, jellegzetességeinek köszönhetően számos modell elemzi. Ezek közül a legismertebbek a keresési-párosítási modellek, amelyek több egymáshoz kapcsolódó kérdéskör vizsgálatára is alkalmasak. A modellcsalád által megmagyarázható munkapiaci jelenségek széles köre, a belőlük levonható következtetések, a modellek magyarázóképességéről folytatott vita egyaránt hozzájárult, hogy a modellek kidolgozói 2010-ben közgazdasági Nobel-emlékdíjban részesültek. Modelljük kiterjeszti a munkanélküliség természetes rátájának elméletét, képes a jóléti intézkedések és intézményrendszer beépítésére. A szerző e modellek elméleti előzményei, valamint egy alapmodell ismertetése után felvázolja az újabb generációs modellek alapvonásait, a hatékonyságelemzések tanulságait, az állami intézkedések vizsgálatának lehetőségeit, valamint a Shimer-kritika alapjait. / === / The labor market is a specialized market with characteristics that have produced several different models for analysing it. One of the best known is the search and matching model, which is suitable for analysis of several related issues. The broad range of labour market phenomena that can be described by this family of models, the conclusions to be drawn from them, and the debate on their explanatory capability have all contributed to the fact that three economists who made important contributions to developing them - P. A. Diamond, D. T. Mortensen and C. A. Pissar-ides - were awarded the Nobel Prize in Economics in 2010. The DMP model named after them expands the theory of the natural rate of unemployment and is capable of integrating the analysis of welfare measures and institutions. This paper follows up on the contribution of the Nobel Prize winners by examining the theoretical preliminaries of these models, a basic search and matching model, and by looking at the typical characteristics of a new generation of models, the lessons of efficiency analyses, the possibility of investigating the role of policy measures, and the foundations of Shimer's critique.

Algorithms for scheduling parallel batch processing machines with non-identical job ready times

This research is motivated by a practical application observed at a printed circuit board (PCB) manufacturing facility. After assembly, the PCBs (or jobs) are tested in environmental stress screening (ESS) chambers (or batch processing machines) to detect early failures. Several PCBs can be simultaneously tested as long as the total size of all the PCBs in the batch does not violate the chamber capacity. PCBs from different production lines arrive dynamically to a queue in front of a set of identical ESS chambers, where they are grouped into batches for testing. Each line delivers PCBs that vary in size and require different testing (or processing) times. Once a batch is formed, its processing time is the longest processing time among the PCBs in the batch, and its ready time is given by the PCB arriving last to the batch. ESS chambers are expensive and a bottleneck. Consequently, its makespan has to be minimized. ^ A mixed-integer formulation is proposed for the problem under study and compared to a formulation recently published. The proposed formulation is better in terms of the number of decision variables, linear constraints and run time. A procedure to compute the lower bound is proposed. For sparse problems (i.e. when job ready times are dispersed widely), the lower bounds are close to optimum. ^ The problem under study is NP-hard. Consequently, five heuristics, two metaheuristics (i.e. simulated annealing (SA) and greedy randomized adaptive search procedure (GRASP)), and a decomposition approach (i.e. column generation) are proposed—especially to solve problem instances which require prohibitively long run times when a commercial solver is used. Extensive experimental study was conducted to evaluate the different solution approaches based on the solution quality and run time. ^ The decomposition approach improved the lower bounds (or linear relaxation solution) of the mixed-integer formulation. At least one of the proposed heuristic outperforms the Modified Delay heuristic from the literature. For sparse problems, almost all the heuristics report a solution close to optimum. GRASP outperforms SA at a higher computational cost. The proposed approaches are viable to implement as the run time is very short. ^

Makespan minimization in a job shop with a batch processing machine

A job shop with one batch processing and several discrete machines is analyzed. Given a set of jobs, their process routes, processing requirements, and size, the objective is to schedule the jobs such that the makespan is minimized. The batch processing machine can process a batch of jobs as long as the machine capacity is not violated. The batch processing time is equal to the longest processing job in the batch. The problem under study can be represented as Jm:batch:Cmax. If no batches were formed, the scheduling problem under study reduces to the classical job shop scheduling problem (i.e. Jm:: Cmax), which is known to be NP-hard. This research extends the scheduling literature by combining Jm::Cmax with batch processing. The primary contributions are the mathematical formulation, a new network representation and several solution approaches. The problem under study is observed widely in metal working and other industries, but received limited or no attention due to its complexity. A novel network representation of the problem using disjunctive and conjunctive arcs, and a mathematical formulation are proposed to minimize the makespan. Besides that, several algorithms, like batch forming heuristics, dispatching rules, Modified Shifting Bottleneck, Tabu Search (TS) and Simulated Annealing (SA), were developed and implemented. An experimental study was conducted to evaluate the proposed heuristics, and the results were compared to those from a commercial solver (i.e., CPLEX). TS and SA, with the combination of MWKR-FF as the initial solution, gave the best solutions among all the heuristics proposed. Their results were close to CPLEX; and for some larger instances, with total operations greater than 225, they were competitive in terms of solution quality and runtime. For some larger problem instances, CPLEX was unable to report a feasible solution even after running for several hours. Between SA and the experimental study indicated that SA produced a better average Cmax for all instances. The solution approaches proposed will benefit practitioners to schedule a job shop (with both discrete and batch processing machines) more efficiently. The proposed solution approaches are easier to implement and requires short run times to solve large problem instances.

Minimizing makespan for hybrid flowshops with batch, discrete processing machines and arbitrary job sizes

This research aims at a study of the hybrid flow shop problem which has parallel batch-processing machines in one stage and discrete-processing machines in other stages to process jobs of arbitrary sizes. The objective is to minimize the makespan for a set of jobs. The problem is denoted as: FF: batch1,sj:Cmax. The problem is formulated as a mixed-integer linear program. The commercial solver, AMPL/CPLEX, is used to solve problem instances to their optimality. Experimental results show that AMPL/CPLEX requires considerable time to find the optimal solution for even a small size problem, i.e., a 6-job instance requires 2 hours in average. A bottleneck-first-decomposition heuristic (BFD) is proposed in this study to overcome the computational (time) problem encountered while using the commercial solver. The proposed BFD heuristic is inspired by the shifting bottleneck heuristic. It decomposes the entire problem into three sub-problems, and schedules the sub-problems one by one. The proposed BFD heuristic consists of four major steps: formulating sub-problems, prioritizing sub-problems, solving sub-problems and re-scheduling. For solving the sub-problems, two heuristic algorithms are proposed; one for scheduling a hybrid flow shop with discrete processing machines, and the other for scheduling parallel batching machines (single stage). Both consider job arrival and delivery times. An experiment design is conducted to evaluate the effectiveness of the proposed BFD, which is further evaluated against a set of common heuristics including a randomized greedy heuristic and five dispatching rules. The results show that the proposed BFD heuristic outperforms all these algorithms. To evaluate the quality of the heuristic solution, a procedure is developed to calculate a lower bound of makespan for the problem under study. The lower bound obtained is tighter than other bounds developed for related problems in literature. A meta-search approach based on the Genetic Algorithm concept is developed to evaluate the significance of further improving the solution obtained from the proposed BFD heuristic. The experiment indicates that it reduces the makespan by 1.93 % in average within a negligible time when problem size is less than 50 jobs.

Developing physical and physiological employment standards: translation of job analysis findings to assessments and performance standards - a systematic review

Physical employment standards (PES) are developed with the aim of ensuring that an employee's physical and physiological capacities are commensurate with the demands of their occupation. While previous commentaries and narrative reviews have provided frameworks for the development of PES, this is the first systematic review of the methods used to translate job analysis findings to PES tests and performance standards for physically demanding occupations. A search of PubMed and Google Scholar was conducted for research articles published in English up to and including March 2015. Two authors independently reviewed and extracted data.

The search yielded 87 potentially eligible papers, including 60 peer reviewed journal articles and 17 technical reports. 57 papers were excluded leading to a final data set of 31 papers, representing 22 studies. Job analysis was most commonly conducted through subjective determination of job tasks followed by objective quantification and validation. Determination of criterion tasks was evenly distributedthrough subjective and objective methods with criterion tasks being defined most commonly as most demanding, critical and/or frequent. Generic predictive and task-related predictive tests were more commonly observed in isolation or in combination when compared to task simulation tests. Performance standards were more commonly criterion-referenced than norm-referenced with a variety of statistical methods utilised. This review provides recommendations for researchers when developing physical employment standards for a variety of occupations.

Employability and job status as moderators of the effects of job insecurity on work outcomes

Despite greater use of temporary employment contracts, little is known about how employees react to job length uncertainty. Individual careers within the safety of one or two primary organisations are no longer the norm. This study investigates the effects of job insecurity and employment status (temporary/permanent) on work outcomes. Three hundred and ninety-one employees (122 temporary and 269 permanent) in low to medium level non-academic positions from two Australian universities completed a survey. The results show that a belief that comparable employment is easily available did not alleviate the negative effects of job insecurity. Work attitudes for temporaries and permanents though were differentially influenced by employee perceptions of their own employability.