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3819 items in total found

Journal Articles | 2019

Design, modeling, and analysis of vertical robotic storage and retrieval systems

Debjit Roy, Kaveh Azadeh, and Rene De Koster

Transportation Science

Autonomous vehicle-based storage and retrieval systems are commonly used in many fulfillment centers (e.g., e-commerce warehouses), because they allow a high- and flexible-throughput capacity. In these systems, roaming robots transport loads between a storage location and a workstation. Two main variants exist: horizontal, where the robots only move horizontally and use lifts for vertical transport, and a new variant vertical, where the robots can also travel vertically in the rack. This paper builds a framework to analyze the performance of the vertical system and compare its throughput capacity with the horizontal system. We build closed queueing network models for this that, in turn, are used to optimize the design. The results show that the optimal height-to-width ratio of a vertical system is around one. Because a large number of system robots may lead to blocking and delays, we compare the effects of different robot blocking protocols on the system throughput: robot Recirculation and Wait-on-Spot. The Wait-on-Spot policy produces a higher system throughput when the number of robots in the system is small. However, for a large number of robots in the system, the Recirculation policy dominates the Wait-on-Spot policy. Finally, we compare the operational costs of the vertical and horizontal transport systems. For systems with one load/unload (L/U) point, the vertical system always produces a similar or higher system throughput with a lower operating cost compared with the horizontal system with a discrete lift. It also outperforms the horizontal system with a continuous lift in systems with two L/U points.

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Journal Articles | 2019

Inventory allocation in robotic mobile fulfillment systems

Tim Lamballais Tessensohn, Debjit Roy, and Rene B M De Koster

IISE Transactions

A Robotic Mobile Fulfillment System is a recently developed automated, parts-to-picker material handling system. Robots can move storage shelves, also known as inventory pods, between the storage area and the workstations and can continually reposition them during operations. This article shows how to optimize three key decision variables: (i) the number of pods per SKU; (ii) the ratio of the number of pick stations to replenishment stations; and (iii) the replenishment level per pod. Our results show that throughput performance improves substantially when inventory is spread across multiple pods, when an optimum ratio between the number of pick stations to replenishment stations is achieved and when a pod is replenished before it is completely empty. This article contributes methodologically by introducing a new type of Semi-Open Queueing Network (SOQN): cross-class matching multi-class SOQN, by deriving necessary stability conditions, and by introducing a novel interpretation of the classes.

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Journal Articles | 2019

Integrated storage-order picking systems: Technology, performance models, and design insights

ElenaTappiaa, Debjit Roy, MarcoMelacini, and René De Koster

European Journal of Operational Research

In many warehouses shuttle-based technologies have replaced the traditional AS/R system based storage technologies. The impact these systems have on downstream order picking performance is largely unknown. To study the interactions between upstream storage and downstream picking systems, we develop a novel analytical model for integrated storage and order picking systems. The resulting semi-open queuing model is solved using the matrix-geometric method. Using the queuing network model, we are able to study the effect of storage system technology on order throughput times, and the effect of the picking station input buffer size on order picking performance. Further, we analyze the effect of a constant work-in-process (CONWIP) control for orders on system performance. Our results indicate that using SBS/R instead of AS/R-based storage systems yields investment cost savings (i.e., fewer aisles in the storage area and fewer picking stations), paired with a lower total throughput time at a given order arrival rate. Numerical studies show how the total throughput time, first, benefits and then becomes stable by increasing the input buffer size at the picking stations. Retrieving item tote at the storage system in advance with respect to the picker availability is also advantageous, especially in the SBS/R system.

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Journal Articles | 2019

From courts to markets: New evidence on enforcement of pharmaceutical bans in India

Chirantan Chatterjee, Debi Prasad Mohapatra, and Manuel Estay

Social Science & Medicine

Regulatory enforcement of product safety standards given health concerns, whether it is in romaine lettuce, smartphones or cars, is emerging to be a challenge for global public health. This is particularly true for developing economies with fragile institutions. In this context, recent studies on Indian pharmaceutical markets provide evidence suggesting that the sector is a hub for substandard quality of medicines. Departing from these prior studies which use randomly collected samples, we reinvestigate this question using novel pan-India market sales data of banned medicines from 0.75 million pharmacists and chemists in India. We find that indeed such medicines get sold in India even after bans are imposed on them in the period 2007 to 2013. However, there is a general decline in demand post ban for our focal molecules suggesting broad adherence to bans. We also observe regional heterogeneity in prevalence of banned medicines sold between rich and poor regions of India with the former counterintuitively showing more sales. That said, while Ozawa et al. (2018) argue that prevalence of substandard medicines is around 13% in low and middle-income countries, we find an infringement ratio which is more muted in India at about 5%. Finally, a regression-based examination suggests that prior firm presence in therapeutic markets and popularity of molecules positively impact the likelihood of sale of banned medicines in India. Our results are robust to alternative explanations and are substantiated with a theoretical set up examining firm trade-offs in the decision to infringe. India has recently been under the lens of the global access to medicines debate and our findings have important policy implications for global health.

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Journal Articles | 2019

Did India's price policy for coronary stents create unintended consequences?

Sarang Deo, Hanu Tyagi, Chirantan Chatterjee, and Himasagar Molakapuri

Social Science & Medicine

In February 2017, India capped the retail price of coronary stents and restricted the channel margin to bring Percutaneous Transluminal Coronary Angioplasty (PTCA) procedure, which uses coronary stents, within reach of millions of patients who previously could not afford it. Prior research shows that care providers respond to such regulations in a way that compensates for their loss in profits because of price control. Therefore, price control policies often introduce unintended consequences, such as distortions in clinical decision making. We investigate such distortions through empirical analysis of claims data from a representative public insurance program in the Indian state of Karnataka. Our data comprises 25,769 insurance claims from 69 private and seven public hospitals from February 2016 to February 2018. The public insurance context is ideal for investigating distortions in clinical decisions as the price paid by patients, and thereby access to the treatment, does not change after price control. We find that the change in the average volume of PTCA procedures per hospital per month after price control disproportionately increased when compared to the change in the clinical alternative – Coronary Artery Bypass Graft (CABG) procedures. This increase corresponds to 6% of the average number of PTCA procedures and 28% of the average number of CABG procedures before the price control. In addition, disproportionate increase in PTCA procedures occurred only among private hospitals, indicating the possibility of profit-maximization intentions driving the clinical choices. Such clinical distortions can have negative implications for patient health outcomes in the long run. We discuss alternative policies to improve access and affordability to healthcare products and services which are likely to not suffer from similar distortions.

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Journal Articles | 2019

Corpus linguistics, newspaper archives and historical research methods

Chinmay Tumbe

Journal of Management History

Purpose

The purpose of this paper is to demonstrate the utility of corpus linguistics and digitised newspaper archives in management and organisational history.

Design/methodology/approach

The paper draws its inferences from Google NGram Viewer and five digitised historical newspaper databases – The Times of India, The Financial Times, The Economist, The New York Times and The Wall Street Journal – that contain prints from the nineteenth century.

Findings

The paper argues that corpus linguistics or the quantitative and qualitative analysis of large-scale real-world machine-readable text can be an important method of historical research in management studies, especially for discourse analysis. It shows how this method can be fruitfully used for research in management and organisational history, using term count and cluster analysis. In particular, historical databases of digitised newspapers serve as important corpora to understand the evolution of specific words and concepts. Corpus linguistics using newspaper archives can potentially serve as a method for periodisation and triangulation in corporate, analytically structured and serial histories and also foster cross-country comparisons in the evolution of management concepts.

Research limitations/implications

The paper also shows the limitation of the research method and potential robustness checks while using the method.

Practical implications

Findings of this paper can stimulate new ways of conducting research in management history.

Originality/value

The paper for the first time introduces corpus linguistics as a research method in management history.

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Journal Articles | 2019

Broker imposed precarity of Indian technical immigrants

Shrihari S. Sohani andBiju Varkkey

Industrial Relations Journal

The primary purpose of this article is to investigate the labour supply chain of Indian technical immigrants in the United States. The two important findings that emerge are as follows: First, the study unearths a latent phenomenon of broker-induced precarity that results from the labour supply chain and explores how aspirational jobs are becoming precarious ones. Second, the study provides a foundation for devising policies and interventions to make the process of the labour supply chain less detrimental to the Indian technical immigrants. This article draws on a seven-month-long field-based qualitative study and ensures a meticulous triangulation of the findings through an analysis of archival data and actual artefacts related to manpower movement across the labour supply chain.

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Journal Articles | 2019

Framework for sustainable maintenance system: ISM fuzzy MICMAC and TOPSIS approach

Rajesh Kumar Singh and Ayush Gupta (FPM)

Annals of Operations Research

Due to the increasing complexity of manufacturing processes and automation, maintenance of all machines and equipments has become challenging task for production managers today. Due to lack of sensitivity for maintenance, share of maintenance cost in total product cost is also increasing along with decreased productivity. Organizations are either quite slow or getting failed in updating their maintenance systems with time. Keeping in view the importance of maintenance in today’s context, this study has tried to develop a framework for a sustainable maintenance system for manufacturing organizations. Usually organizations are not able to identify critical factors for effective maintenance. Therefore, in this context, the study has identified fourteen factors for the effective maintenance management from the literature review. Some of these factors are process oriented and some are result oriented. Interpretive structural modeling approach is applied for the development of structural relationship among the factors from a strategic perspective. Fuzzy MICMAC analysis is then carried out to categorize these factors based on their driving and dependence value. Further to prioritise major driving factors, Technique for order preferences by similarity of an ideal solution approach has been also applied. It is observed that top management support and commitment, strategic planning and implementation, continuous upgradation of maintenance system to reduce manufacturing lead time and cost are major factors to ensure the sustainable competitive advantage.

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Journal Articles | 2019

Identifying defective network components through restricted group testing

Diptesh Ghosh

OPSEARCH

In this paper, we consider a network of switches in which some of the switches may malfunction. Our aim is to find out efficiently (a) if any of the switches in a network of switches are defective, and (b) if there are defective switches, to identify those switches. We find an optimal solution for the first problem and a heuristic solution to the second, and demonstrate the feasibility of our approach through computational experiments.

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Journal Articles | 2019

Attitudinal choice models with applications in human decision making

Manish Aggarwal

International Journal of Intelligent Systems

A new family of attitudinal discrete choice models is proposed by considering the attitudinal character and the weight vector, both of which are specific to a decision maker (DM). Given the attribute values of different alternatives, the proposed models give varying choice probabilities, as per the DM's-specific attitudinal character and the weight vector. It is also shown that the conventional discrete choice models are the special cases of the proposed attitudinal models. The proposed choice models are also generalized through an additional parameter to add to their capabilities. An application on real data is included to demonstrate their usefulness in the real world.

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