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Light transmission aggregometry (LTA) is considered the gold standard method for evaluation of platelet function. However, there are a lot of variation in protocols (pre-analytical procedures and agonist concentrations) and results. The aim of our study was to establish a national LTA protocol, to investigate the effect of standardization and to define national reference values for LTA. The SSC guideline was used as base for a national procedure. Almost all recommendations of the SSC were followed e.g. no adjustment of PRP, citrate concentration of 109 mM, 21 needle gauge, fasting, resting time for whole blood and PRP, centrifugation time, speed and agonists concentrations. LTA of healthy volunteers was measured in a total of 16 hospitals with 5 hospitals before and after standardization. Results of more than 120 healthy volunteers (maximum aggregation %) were collected, with participating laboratories using 4 different analyzers with different reagents. Use of low agonist concentrations showed high variation before and after standardization, with the exception of collagen. For most high agonist concentrations (ADP, collagen, ristocetin, epinephrine and arachidonic acid) variability in healthy subjects decreased after standardization. We can conclude that a standardized Dutch protocol for LTA, based on the SSC guideline, does not result in smaller variability in healthy volunteers for all agonist concentrations. [ABSTRACT FROM AUTHOR]

In many practical instances, the choice of whether to apply family-based dispatching or not can be decided per machine. The present paper explores the impact of the location of family-based dispatching, load variations between machines and routing of jobs on the flow time effect of family-based dispatching. These factors are explored in small manufacturing cells with and without labour constraints. An industrial case motivates the study. A simulation study is performed to assess the impact of these effects. The results show that shop-floor characteristics such as routing and load variation impact the decision where to locate family-based dispatching in manufacturing cells without labour constraints. By contrast, the effect of family-based dispatching is much less vulnerable to shop-floor characteristics in cells with labour constraints. Since workers are the bottleneck in these cells, it becomes less important at what machine the set-up time involving a worker is reduced. In general, there seems to be a trade-off between the positive effect of applying family-based dispatching at a (bottleneck) machine and the possible negative effect of the more irregular job arrivals at subsequent machines. The results further indicate that family-based dispatching is more advantageous in cells with labour constraints than in cells without labour constraints, when both types of manufacturing cells have comparable machine utilizations. [ABSTRACT FROM AUTHOR]

In this paper we investigate cross-training policies in a dual resource constraint (DRC) parallel job shop where new part types are frequently introduced into the system. Each new part type introduction induces the need for workers to go through a learning curve. A cross-training policy relates to the level of multi-functionality, the pattern of skill overlaps, and the distribution of skills among workers. Our results show that the frequency of new part type introduction needs to be considered when selecting a cross-training policy. The frequency of new part type introduction has impact on the optimal level of cross-training, the relative advantage of skill overlaps, and the extent to which a cross-training policy should incorporate differences between workers. These findings are important for many DRC job shops, especially for manufacturing cells in which all changes, associated with a part type introduction, are concentrated in one cell. [ABSTRACT FROM AUTHOR]

Group Technology exploits similarities in product and process design to meet the diversity of customer demand in an economic way. In this paper we consider one of the implementations of this concept - family-based dispatching. Intrinsic to family-based dispatching is the grouping of similar types of products for joint processing. In this way the number of set-ups may be reduced. Consequently, lead-time performance of the shop can be improved. We extend existing rules for family-based dispatching by including data on upcoming job arrivals. Typically, this type of data resides in the minds of the operators, or is stored in a shop-floor control system. Its availability allows for (1) better estimates of the composition of a process batch for a family, (2) the consideration of families for which no products are available at the decision moment, and (3) the possibility to start set-ups in anticipation of future job arrivals. The potential of including forecast data in decision-making is demonstrated by an extensive simulation study of a single-machine shop. Results indicate the possibility of significant improvements of flow time performance. [ABSTRACT FROM AUTHOR]

This study investigates the performance of virtual cellular manufacturing (VCM) systems, comparing them with functional layouts (FL) and traditional, physical cellular layout (CL), in a dual-resource-constrained (DRC) system context, VCM systems employ logical cells, retaining the process layouts of job shops. Part family-based scheduling rules are applied to exploit the benefits of group technology while retaining the flexibility and functional synergies of the job shop. Past studies of VCM have been based entirely on single-resource-constrained (SRC) systems, i.e. as purely machine-limited systems, assuming that resources such as labour and tooling do not restrict the output. However, given the fact that labour forms a second major constraining resource, and many of the advantages associated with cellular manufacturing are derived from labour flexibility, it becomes necessary to extend the research to DRC systems. In this study, we assume several levels of labour flexibility in all three systems, in addition to other relevant factors such as lot size, set-up reduction, and labour assignment rules. It is shown that VCM can outperform efficiently operated FL and CL in certain parameter ranges, as preliminary research has shown so far. However, it is shown that CL tends to outperform both VCM and FL in the parameter ranges customarily advocated for CL, namely, low lot sizes, adequate levels of set-up reduction, cross training of workers, and worker mobility within cells. [ABSTRACT FROM AUTHOR]

The who-rule is a labour allocation rule used in labour and machine-limited dual resource constrained (DRC) systems. A who-rule selects one worker out of several workers to be transferred to a work centre. By means of a practical instance, the paper shows that the who-rule plays a role in the daily practice of worker assignment. Previous simulation studies, however, either have not mentioned the who-rule or have treated it as a fixed factor. The present study will explore the need of including the who-rule in simulation studies. It will describe in detail at what decision moments the who-rule needs to be applied in simulation. Further, it will explore the flow time effects of applying different who-rules in several DRC systems where labour flexibility is limited and workers differ with respect to task proficiencies, the number of skills they possess and the loads of work centres for which they are responsible. As with other labour allocation rules, the impact of the who-rule depends on the specific DRC shop modelled. The paper will show that the average labour utilization, and the types and extent of worker differences, determine the impact of the who-rule on shop performance. [ABSTRACT FROM AUTHOR]

A hierarchical methodology for the design of manufacturing cells is proposed, which includes labour-grouping considerations in addition to part–machine grouping. It is empirically driven and designed for an interactive decision environment, with an emphasis on fast execution times. The method synthesizes the capabilities of neural network methods for rapid clustering of large part–machine data sets, with multi-objective optimization capabilities of mathematical programming. The procedure includes three phases. In Phase I, part families and associated machine types are identified through neural network methods. Phase II involves a prioritization of part families identified, along with adjustments to certain load-related parameters. Phase III involves interactive goal programming for regrouping machines and labour into cells. In machine grouping, factors such as capacity constraints, cell size restrictions, minimization of load imbalances, minimization of intercell movements of parts, minimization of new machines to be purchased, provision of flexibility, etc. are considered. In labour grouping, the functionally specialized labour pools are partitioned and regrouped into cells. Factors such as minimization of hiring and cross-training costs, ensuring balanced loads for workers, minimization of intercell movements of workers, providing adequate levels of labour flexibility, etc. are considered in a pragmatic manner. [ABSTRACT FROM AUTHOR]

This study addresses the problem of identifying families of parts having a similar sequence of operations. This is a prerequisite for the implementation of cellular manufacturing, group technology, just-in-time manufacturing systems, and for streamlining material flows in general. A pattern recognition approach based on artificial neural networks is proposed, and it is shown that the Fuzzy ART neural network can be effectively utilized for this application. First, a representation scheme for operation sequences is developed, followed by an illustrative example. A more comprehensive experimental verification, based on the mixture-model approach is then performed to evaluate its performance. The experimental factors include size of the part-machine matrix, proportion of voids, proportion of exceptional elements, and vigilance threshold. It is shown that this neural network is effective in identifying good clustering solutions, consistently and with relatively fast execution times. [ABSTRACT FROM AUTHOR]

This study deals with workforce flexibility defined in terms of 'multifunctionality' and 'redundancy'. These concepts refer, respectively, to the number of different tasks a worker has mastered and the number of workers that are qualified to do a specific task. A third factor to be considered is worker efficiency. These elements of workforce flexibility support a team of workers in dealing with absenteeism and a fluctuating mix in the demand of human resources. The main focus of this study is on the impact of the distribution of workforce flexibility among workers on team performance. In this study, team performance is measured as the shortage of labour capacity, the minimum time needed to perform all tasks (e.g. the timespan) and the total cumulative production time. Two extreme assignment methods, which include a linear goal-programming formulation that minimizes the shortage, makespan and production time, are used in a full orthogonal factorial experimental design (2.2.5.5). The MANOVA results show that a uniform distribution of multifunctionality results in a shorter makespan and lower total production time. The more absenteeism, the stronger these effects. Absenteeism has a very negative impact on all performance measures, independent of the distribution of flexibility. This study shows that, in cases of absenteeism, the workload of the bottleneck worker will increase relatively more than the workload of the remaining operators. Since the bottleneck worker determines the makespan, there will be greater waiting time for the other team members. This may be contra to intuition which tells us that absenteeism will increase the relative workload (or utilization level) of the remaining workers. With respect to the distribution of redundancy, our study shows that each task should be mastered by at least two workers in order to reduce the negative impact of low to moderate levels of absenteeism. Above this minimal level of task redundancy, labour flexibility... [ABSTRACT FROM AUTHOR]

In this paper, a hierarchical methodology for the design of manufacturing cells is proposed, synthesizing the capabilities of new pattern recognition methods for rapid clustering of large part-machine data sets, with multi-objective optimization capabilities of mathematical programming. The procedure includes three phases. In Phase I, part families and associated machine types are identified through neural network methods for pattern recognition. Phase II is a celt formation phase that involves the assignment of part families and individual machines to create independent cells. It takes into account several factors such as capacity constraints, cell size restrictions, minimization of load imbalances and provision of flexibility. Phase III attempts to minimize inter-cell traffic further for families that may still have to be processed in more than one cell. The methodology is illustrated using several examples. [ABSTRACT FROM AUTHOR]

This paper presents three quasi on-line scheduling procedures for FMSs consisting of work stations, transport devices, and operators. In the scheduling, different types of decisions are taken to perform a particular operation, i.e. the selection of (a) a work station, (b) a transport device and (c) an operator. Further, (d) the scheduling sequence of the operations has to be determined. The three developed procedures differ in the way these four decision problems arc solved hierarchically. Several dispatching rules (SPT, SPT.TOT, SPT/TOT and EFTA) are available to solve the last mentioned decision problem. Limited buffer capacities in an FMS may cause deadlock in the procedures as well as in practice. The scheduling procedures involve a buffer handling method to avoid deadlock. A case study is presented to demonstrate the three procedures and to show some of its properties. Based on simulation tests, some conclusions are drawn about the performance of the scheduling procedures and the various dispatching rules. [ABSTRACT FROM AUTHOR]