30,653 research outputs found

    Event-Driven Network Model for Space Mission Optimization with High-Thrust and Low-Thrust Spacecraft

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    Numerous high-thrust and low-thrust space propulsion technologies have been developed in the recent years with the goal of expanding space exploration capabilities; however, designing and optimizing a multi-mission campaign with both high-thrust and low-thrust propulsion options are challenging due to the coupling between logistics mission design and trajectory evaluation. Specifically, this computational burden arises because the deliverable mass fraction (i.e., final-to-initial mass ratio) and time of flight for low-thrust trajectories can can vary with the payload mass; thus, these trajectory metrics cannot be evaluated separately from the campaign-level mission design. To tackle this challenge, this paper develops a novel event-driven space logistics network optimization approach using mixed-integer linear programming for space campaign design. An example case of optimally designing a cislunar propellant supply chain to support multiple lunar surface access missions is used to demonstrate this new space logistics framework. The results are compared with an existing stochastic combinatorial formulation developed for incorporating low-thrust propulsion into space logistics design; our new approach provides superior results in terms of cost as well as utilization of the vehicle fleet. The event-driven space logistics network optimization method developed in this paper can trade off cost, time, and technology in an automated manner to optimally design space mission campaigns.Comment: 38 pages; 11 figures; Journal of Spacecraft and Rockets (Accepted); previous version presented at the AAS/AIAA Astrodynamics Specialist Conference, 201

    On green routing and scheduling problem

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    The vehicle routing and scheduling problem has been studied with much interest within the last four decades. In this paper, some of the existing literature dealing with routing and scheduling problems with environmental issues is reviewed, and a description is provided of the problems that have been investigated and how they are treated using combinatorial optimization tools

    New Product Development and Product Supply Within a Network Setting: The Case of the Chilled Ready-Meal Industry in the UK

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    This paper analyses inter-organizational networks that link together firms operating in the food processing and distribution industry in the UK. In doing so, the paper draws on insights recently developed by Mark Casson that treat inter-firm networks as an institutional response to the changing costs and opportunities of information management. Detailed analysis of product innovation and supply chain management issues within the industry, exemplified by the growth of chilled ready-meals, leads to the identification of two distinct but complementary inter-firm networks: a network of control and a network of innovation. In each case, the study finds that the critical information is derived from the retailers’ interface with consumers and thus that these information-based networks are effectively controlled by the leading supermarket chains. The study’s conclusions are considered in relation to the recent findings of the Competition Commission following its investigation into grocery retailing in the UK

    How to Improve the Capture of Urban Goods Movement Data?

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    The surveys specifically focused on the thorough knowledge of urban freight transport appeared about ten years ago. The local problematic of goods transport at local level was partially taken into account by the city planners and by the researchers: until recent years, the integration of goods transport in the total urban flows models was estimated applying a multiplying factor to car traffic. Delivering goods was not considered like a concern.Because of the quick growth of car traffic in the cities, the main stakes changed too: the fight against traffic congestion, the management of the lack of space (shipment consolidation and storage), the attempts to reduce local environmental impacts and global externalities (energy saving, reduction of greenhouse gas emissions), and economic valuation of city centres (under the pressure of a slowed down economic growth).All these changes were taking place in a context in which available rooms for manoeuvre were limited by factors such as congestion, concerns about the quality of urban life and budget restriction. It resulted in a growing unease on the freight transport industry and the city authorities, the latter having little or no data, methods and references in order to elaborate a satisfactory policy framework.surveys on urban freight transport ; urban freight movements ; urban freight data collection ; urban goods data collection ; diversity of measurement units and methods ; state of the art

    Measuring Regulatory Restrictions in Logistics Services

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    This study measures the extent of restrictions on trade in logistics services in the ASEAN+6 economies by constructing a logistics regulatory restrictiveness index for each economy that quantifies the extent of government regulations faced by logistics service providers. This is the first study of its kind to construct a regulatory index of the entire logistics sector, which includes the main modes of international transport and customs restrictions. The indices show that large differences exist in the logistics regulatory environment of ASEAN+6 economies. Many of these economies are open to trade in logistics services, while others are relatively restrictive. Malaysia, China, Indonesia, Lao PDR, the Philippines and Vietnam are the most restrictive economies of logistics services in this region. Relatively, Singapore and Australia are the most open economies for trade in logistics services, along with Japan and New Zealand. Preliminary investigations find evidence of negative relationships between logistics regulatory restrictiveness and logistics sector performance, as measured by the World Bank's Logistics Performance Index and its sub-components. These findings support that notion that a less restricted trade environment results in better performance for the logistics sector.Logistics, Transport, Government Regulation, Trade, East Asia

    Why Does cargo spend weeks in African ports ? the case of Douala, Cameroon

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    This paper investigates the main factors explaining long container dwell times in African Ports. Using original and extensive data on container imports in the Port of Douala, it seeks to provide a basic understanding of why containers stay on average more than two weeks in gateway ports in Africa while long dwell times are widely recognized as a critical hindrance to economic development. It also demonstrates the interrelationships that exist between logistics performance of consignees, operational performance of port operators and efficiency of customs clearance operations. Shipment level analysis is used to identify the main determinants of long cargo dwell times and the impact of shipment characteristics such as fiscal regime, density of value, bulking and packaging type, last port of call, and region of origin or commodity group on cargo dwell time in ports is tested. External factors, such as performance of clearing and forwarding agents, shippers and shipping line strategies, also play an important role in the determination of long dwell times. Cargo dwell time distribution has many specificities, including broad-tail, high variance or right-censoring, which requires in-depth statistical analysis prior to any design of policy recommendations.Common Carriers Industry,Transport and Trade Logistics,Transport Economics Policy&Planning,E-Business,Customs and Trade

    Purchasing Organization and Design: A Literature Review

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    This paper presents the results of a comprehensive literature review of the organization of purchasing covering the period from 1967 to 2009. The review provides a structured overview of prior research topics and findings and identifies gaps in the existing literature that may be addressed in future research. The intention of the review is to a) synthesize prior research, b) provide researchers with a structural framework on which future research on the organization of purchasing may be oriented, and c) suggest promising areas for future research.purchasing, supply, procurement, organization, institutional structure, structure, institution, design, performance, literature review

    Marketing

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    Marketing is a human activity aimed at customer satisfaction through exchange. The main objective of the course is a formation of a system of knowledge about the nature and content marketing as a philosophy of business activity in the market economy and competition in preparation for the adoption of qualified decisions in marketing
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