See the light: Optimization of put-to-light order picking systems

Put-to-light order picking systems invert the basic logic of conventional picker-to-parts systems. Instead of successively visiting the storage positions of the stock keeping units (SKUs) when collecting picking orders, an order picker accompanies successive bins each containing multiple items of a specific SKU along a lane of subsequent orders. Whenever the picker passes an order requiring the current SKU, which is indicated by a light signal, she puts the requested number of items into the bin associated with the order. Such an order picking system is well-suited if the assortment is not overly large and all orders demand similar SKUs, so that it is mainly applied in distribution centers of brick-and-mortar retail chains. This paper evaluates four different setups of put-to-light systems, which, during operations, require the solution of different storage assignment and SKU sequencing problems. We formulate these problems, prove computational complexity, and suggest suited solution algorithms. By applying these algorithms in a comprehensive computational study, we benchmark the impact of the four different setups on picking performance. In this way, warehouse managers receive decision support on how to set up their put-to-light systems.     

WHILE WAITING FOR THE PROTOCOL

The Biological Weapons Convention (BWC) regime currently suffers from a lack of effective compliance procedures. Because a legally binding compliance protocol to the BWC is not available, other measures are needed to stabilize the regime against the risk of violations of its rules. The Treaty on the Non-Proliferation of Nuclear Weapons, the Chemical Weapons Convention, and the experiences of UN inspection teams show that among the necessary components of effective compliance mechanisms are an intermediary level between bilateral consultations of states parties and involvement of the UN Security Council as well as independent assessment capabilities. This article suggests that the UN Secretary General could assume such an intermediary function and, using the authority contained in Article 99 of the UN Charter, could investigate not only alleged use of biological weapons but also alleged breaches of the BWC. A standing expert unit in the Department for Disarmament Affairs could provide the independent expertise necessary for such investigations. Such a compliance mechanism could provisionally help stabilize the BWC regime until a permanent compliance system can be agreed.     

MILITARY EXPENDITURE AND ECONOMIC GROWTH IN MIDDLE EASTERN COUNTRIES: A DYNAMIC PANEL DATA ANALYSIS

Defence expenditures have both costs and benefits to the economy. The costs of defence expenditures are mainly emphasized as opportunity costs. On the other hand, defence spending may have growth‐promoting potential benefits: a rise in defence spending may result in a higher aggregate demand, production and employment. This paper examines empirically the effects of military expenditures on economic growth for Middle Eastern countries and Turkey, for the time‐period 1989–1999. The relationship between military expenditure and economic growth is investigated by using cross‐section and dynamic panel estimation techniques. Empirical analysis indicates that military expenditure enhances economic growth in the Middle Eastern countries and Turkey as a whole.     

AFRICA'S NEW SECURITY THREAT

HIV/AIDS is not a traditional security threat but the consequences are just as serious. That it is non-violent serves only to disguise its devastation. HIV/AIDS overwhelms health services, shortens lives, destabilises governments and disrupts societies; sometimes to the extent that major conflict ensues. The extent of the virus is far more serious than initially anticipated. Infection rates in Southern Africa indicate that huge numbers of people will die over the next 10 years, affecting the basic functioning of society. The ability to produce and distribute food will be reduced. The skills and human resources needed for effective government will become even more scarce. Political instability may result in complex humanitarian emergencies and crime; neither of which can be addressed without effective government. While the populations of Southern Africa have proved resilient in the past, it is certain that the virus will extract a huge cost from the people of the region in the future.     

ANALYSING THE DETERMINANTS OF TERRORISM IN TURKEY USING GEOGRAPHICALLY WEIGHTED REGRESSION

This paper investigates the determinants of provincial terrorism in Turkey taking spatial dimension into account for the time period 1990–2006. Following a traditional global regression analysis, spatial variations in the relationships are examined with geographically weighted regression (GWR) to obtain locally different parameter estimates. Empirical results indicate that increases in income and schooling ratio tend to reduce the provincial average level of terrorism, whereas an increase in unemployment enhances it. Moreover, GWR results indicate that the provincial effects of per capita income and education are more pronounced for the Eastern and South Eastern provinces compared to the Western provinces.     

URBAN FORTRESSES

One of the consequences of the state's inability to protect the life and property of all its citizens—especially in developing countries—is the formation of private alternatives to crime prevention and control. Gated communities, or enclosed neighbourhoods, are one such popular alternative. This article compares the phenomenon of gated communities in two developing countries: South Africa and Brazil. Both countries are plagued by violent crime and share key human development indicators. The article also explores key issues that have been raised around gated communities in both countries. Gated communities can contribute to spatial fragmentation in urban areas, and reflect increased polarisation, fragmentation and diminished solidarity within society. By excluding other urban residents and people from surrounding neighbourhoods, gated communities can contribute to social exclusion, inhibiting the construction of social networks that form the basis of social and economic activities.     

Formulations for dynamic lot sizing with service levels

In this article, we study deterministic dynamic lot‐sizing problems with a service‐level constraint on the total number of periods in which backlogs can occur over a finite planning horizon. We give a natural mixed integer programming formulation for the single item problem (LS‐SL‐I) and study the structure of its solution. We show that an optimal solution to this problem can be found in \begin{align*}\mathcal O(n^2\kappa)\end{align*} time, where n is the planning horizon and \begin{align*}\kappa=\mathcal O(n)\end{align*} is the maximum number of periods in which demand can be backlogged. Using the proposed shortest path algorithms, we develop alternative tight extended formulations for LS‐SL‐I and one of its relaxations, which we refer to as uncapacitated lot sizing with setups for stocks and backlogs. {We show that this relaxation also appears as a substructure in a lot‐sizing problem which limits the total amount of a period's demand met from a later period, across all periods.} We report computational results that compare the natural and extended formulations on multi‐item service‐level constrained instances. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013     

Comprehensive approaches,diverse coherences: the different levels of policy coherence in the Dutch 3D approach in Afghanistan

Since 2000, international organisations such as the UN, NATO and the EU, but also countries, have started to apply what has been called the comprehensive approach to crisis management. This article unpacks this comprehensive approach implemented by the Dutch in Uruzgan province, Afghanistan. It first borrows and expands a conceptual framework developed by De Coning and Friis. Subsequently, it maps the different sorts of coherence in the mission by applying the framework. It shows how in practice there was not one single comprehensive approach, but many different forms of interaction between a number of organisational units. Each interaction had its own distinct issues and its own level of coherence. The level of coherence differed depending on the level at which the interaction took place – strategic at headquarters level versus operational at field level – and at what point in the mission it happened – in most cases it moved towards more cohesion.     

Scheduling twin robots on a line

This article introduces the twin robots scheduling problem (TRSP), in which two robots positioned at the opposite ends of a rail are required to deliver items to positions along the rail, and the objective is to minimize the makespan. A proof of ‐hardness of the TRSP is presented, along with exact and heuristic algorithms. Computational results on challenging instances are provided.Copyright © 2014 Wiley Periodicals, Inc. Naval Research Logistics 61: 119–130, 2014