Modeling and performance analysis of sequential zone picking systems

This paper develops an analytical model of sequential zone picking systems. The systems belong to the most popular internal transport and order picking systems in practice, due to their scalability, flexibility, high-throughput ability, and fit-for-use for a wide range of products and order profiles. The major disadvantage of such systems, though, is congestion and blocking under heavy use, leading to long order lead times. In order to diminish blocking and congestion most systems make use of a dynamic block-and-recirculate protocol. The various elements of the system, like conveyor lanes and the pick zones, are modeled as a network of queues with multiple order classes and with capacity constraints on subnetworks, including the dynamic block-and-recirculate protocol. Due to this protocol, however, the stationary distribution of the queueing network is highly intractable. Therefore, an innovative approximation method, using jump-over blocking is proposed to accurately assess key performance statistics such as throughput and recirculation. Multi-class jump-over networks admit a product-form stationary distribution, and can be efficiently evaluated by Mean Value Analysis (MVA) and use of Norton's theorem. The method is most suitable to support rapid and optimal design of complex zone picking systems, in terms of number of segments, number and length of zones, buffer capacities, and storage allocation of products to zones, in order to meet prespecified performance targets. Comparison of the approximation results to simulation show that for a wide range of parameters the mean relative error in the system throughput is typically less than 1%. The approximation is also applied to evaluate a real-life zone picking system of a large wholesaler supplying non-food items

The analysis of batch sojourn-times in polling systems

We consider a cyclic polling system with general service times, general switch-over times, and simultaneous batch arrivals. This means that at an arrival epoch, a batch of customers may arrive simultaneously at the different queues of the system. For the exhaustive service discipline, we study the batch sojourn-time, which is defined as the time from an arrival epoch until service completion of the last customer in the batch. We obtain exact expressions for the Laplace–Stieltjes transform of the steady-state batch sojourn-time distribution, which can be used to determine the moments of the batch sojourn-time and, in particular, its mean. However, we also provide an alternative, more efficient way to determine the mean batch sojourn-time, using mean value analysis. We briefly show how our framework can be applied to other service disciplines: locally gated and globally gated. Finally, we compare the batch sojourn-times for different service disciplines in several numerical examples. Our results show that the best performing service discipline, in terms of minimizing the batch sojourn-time, depends on system characteristics

Crime victims’ evaluations of procedural justice and police performance in relation to cooperation: a qualitative study in the Netherlands

Previous research suggests that perceived negative treatment by police officers may have consequences for victims’ willingness to share information with the police. This might explain why particularly repeat victims are less likely to cooperate with the police. The current study explores why this would be true by conducting in-depth interviews with 32 crime victims who had recently reported their victimisation of property crime or violent crime to the police. Results indicate that victims of both types of crime had similar thoughts on what was deemed fair treatment. Victims who were deeply touched by the crime and/or the offender thought it was also important that the police took a clear-stance against the crime. While rapid case handling seemed to be more important for property crime victims than police officers’ investigative actions and the outcome, victims of violent crime expected the police to find the offender to make it clear to the offender that such (law-breaking) behaviour was not tolerated. When victims of violent crime felt that the police had failed in this task, they would feel abandoned by the police. This feeling had not only negative consequences for these victims’ willingness to cooperate, but could even lead to feelings of vigilantism, particularly among victims of violent crime who knew their offender. Implications for policy and future research are discussed.NWOCriminal Justice: Legitimacy, accountability, and effectivit

A Mathematical Model for Supermarket Order Picking

Order picking consists in retrieving products from storage locations to sat- isfy independent orders from multiple customers. It is generally recognized as one of the most significant activities in a warehouse (Koster et al, 2007). In fact, order picking accounts up to 50% (Frazelle, 2001) or even 80% (Van den Berg, 1999) of the total warehouse operating costs. The critical issue in today’s business environ- ment is to simultaneously reduce the cost and increase the speed of order picking. In this paper, we address the order picking process in one of the Portuguese largest companies in the grocery business. This problem was proposed at the 92nd European Study Group with Industry (ESGI92). In this setting, each operator steers a trolley on the shop floor in order to select items for multiple customers. The objective is to improve their grocery e-commerce and bring it up to the level of the best inter- national practices. In particular, the company wants to improve the routing tasks in order to decrease distances. For this purpose, a mathematical model for a faster open shop picking was developed. In this paper, we describe the problem, our proposed solution as well as some preliminary results and conclusions.info:eu-repo/semantics/publishedVersio

Conveyor merges in zone picking systems: A tractable and accurate approximate model

. Sequential zone picking systems are popular conveyor-based picker-to-parts order picking systems that divide the order picking area in work zones. When designing a zone picking system, it is important to know whether the throughput capability of the system can meet customer demand. However, the performance and maximum throughput capability of a zone picking system is largely determined by congestion and blocking that occur at the various conveyor merges in the system. In this paper we develop an analytical model to study the impact of conveyor merges in sequential zone picking systems. Because of finite buffers, blocking, recirculation, and merging, the resulting queueing model does not have a product-form stationary queue-length distribution which makes exact analysis practically infeasible. Therefore, we develop an approximate solution by using an aggregation technique and matrix-geometric methods to study the throughput capability of the system. The model is suitable to support rapid design of complex zone picking systems, in terms of number and length of zones, input and output buffer capacities, and storage allocation of products to zones to meet prespecified performance targets. Comparison of the approximation results to simulation show that for a wide range of parameters the mean relative error in the system throughput is typically less than 5%. The model accurately predicts the loss in throughput due to congestion and blocking at the merges, and can be used to allocate input and output buffer spaces to maximize the throughput capability of the system

How does cultural capital keep you thin? Exploring unique aspects of cultural class that link social advantage to lower body mass index

A widely used indicator for cultural class is strongly related to a lower body mass index (BMI): cultural capital measured as ‘highbrow' taste. This study’s objective was to theorise and measure aspects of cultural class that are more plausibly linked to low BMI, and subsequently explore their relevance. Building on Bourdieusian theory we derive four of those aspects: ‘refinement’ (valuing form and appearance over function and substance), ‘asceticism’ (self-imposed constraints), ‘diversity’ (appreciation of variety in and of itself) and ‘reflexivity’ (reflexive deliberation and internal dialogue). Using standardised interviews with 597 participants in the Dutch GLOBE study in 2016, we subsequently demonstrate: (i) newly developed survey items can reliably measure four aspects of cultural class: ‘asceticism’, ‘general refinement’, ‘food refinement’ and ‘reflexivity’ (Cronbach’s alphas between 0.67–0.77); (ii) embodied/objectified cultural capital (i.e. ‘highbrow’ taste) was positively associated with gene

Sequencing of neuroblastoma identifies chromothripsis and defects in neuritogenesis genes

Neuroblastoma is a childhood tumour of the peripheral sympathetic nervous system. The pathogenesis has for a long time been quite enigmatic, as only very few gene defects were identified in this often lethal tumour. Frequently detected gene alterations are limited to MYCN amplification (20%) and ALK activations (7%). Here we present a whole-genome sequence analysis of 87 neuroblastoma of all stages. Few recurrent amino-acid-changing mutations were found. In contrast, analysis of structural defects identified a local shredding of chromosomes, known as chromothripsis, in 18% of high-stage neuroblastoma. These tumours are associated with a poor outcome. Structural alterations recurrently affected ODZ3, PTPRD and CSMD1, which are involved in neuronal growth cone stabilization. In addition, ATRX, TIAM1 and a series of regulators of the Rac/Rho pathway were mutated, further implicating defects in neuritogenesis in neuroblastoma. Most tumours with defects in these genes were aggressive high-stage neuroblastomas, but did not carry MYCN amplifications. The genomic landscape of neuroblastoma therefore reveals two novel molecular defects, chromothripsis and neuritogenesis gene alterations, which frequently occur in high-risk tumours