| Agriculture sector has been playing an important role in economic system of China, domestic and international trading volume of agricultural products increases at a high speed year after year, leading to a huge market need of fresh agricultural products. However, the idea of "product fisrt, circulation second" has been restricting the safe and quick distribution of fresh agricultural products. Due to the backward logistics system for agricultural products, the logistics chain composed of produce, supply and marketing disconnects frequently and leads to low circulation efficiency. In recent years, logistics cost of fresh agricultural products stays at a high level; facilities and infrastructure for logistics operation are out of date; operation and management level of logistics lags far behind that of some developed countries. In all, at present, relatively perfect logistics platform for fresh agricultural products has not been constructed and logistics enterprises do things in one' own way.At present, food safety has become a new focus all over the world. But, more attentions are paid for the operation process consisting of produce, processing and sale than that for some problems related to the safety of agricultural products. Agricultural products supply characterizes with traditional mode made of storage and transport; enterprises at different stages lack enough coordination; related departments at different levels of government pay little attentions to the supervision of food safety during logistics process; a wholesome cold chain system has not come into being; the proportion of fresh agricultural products under the conditions of refrigerated storage and transport is very low. All of these lead to a great deal of loss and accidents related to food safety during operation process of fresh agricultural products logistics.On the basis of the investigation and analysis of fresh agricultural products logistics both at home and from abroad, systemic studies are carried out from different aspects including the formation mechanism and layout optimization of the logistics network for fresh agricultural products based on cold chain, as well as the control mechanism of logistic safety and risk, detailed studies are listed as follows:(1) The formation mechanism of logistics network for fresh agricultural products based on cold chainBased on the developing process and current conditions of cold chain in China and some other developed countries, according to two-dimension space model, the types of operators at produce, supply and sale stages are classified, the self-organizing process of the corresponding three subsystems are analyzed in detail by the theories of Synergetics and self-organization. Furthermore, the formation mechanism of logistics network for fresh agricultural products based on cold chain are presented and interpreted by the Brussel model in the theory system of Dissipation Structure, according to the investigations in Guangzhou and Changsha , forward logistics network for fresh agricultural products based on cold chain in big cities in China are developed, and, the cause of formation of corresponding reverse logistics is analyzed and some characteristics are presented at the same time.(2) Layout optimization of logistics network for fresh agricultural productsAccording to the investigation results, the steps and content of the plan and design of logistics network for fresh agricultural products based on cold chain are presented. The three-level logistics network covering different regions for fresh agricultural products including producing places, pre-cooling stations and collection-distribution points is studied in detail, based on the problem description and basic presumptions, from the point view of both strategic plan and practical operation, to determine the scales, amounts and locations of pre-cooling stations and wholesale markets or distribution centers, as well as procurement periods of pre-cooling stations, a non-line mix integer programming model containing two assignment models is constructed, combined with a specific numerical example, the design and plan problem is solved and analyzed step by step by genetic algorithm. (3) Optimization on distribution system for fresh agricultural products based on cold chainThe basic framework for the distribution of fresh agricultural products is put forward, the necessity to optimize distribution system is analyzed, of which vehicle routing operation and management is especially critical, aiming at the distribuation operation with relatively biger pick-up quantity than distribution quantity, a kind of vehicle routing problem with simultaneous delivery and pick-up is studied, by the comparison and analysis of two insertion criterions with a given instance, a new residual load based heuristics is put forward to make full use of refrigerated vehicle space.(4) Control and management of the risk related to the logistics safety of fresh agricultural productsAiming at existing logistics networks in China, according to related researches, the concept of logistics safety of fresh agricultural products as well risk control and management mechanism are put forward for the first time. With the help of the theories such as system safety engineering, risk management control and system reliability, the basic control principle, step and content are analyzed in detail, and, some optional methods used for risk analysis and evaluation are compared.(5) Risk analysis and evaluation of the logistics system of fresh agricultural products According to the detailed investigation in Changsha, taking vegetable logistics as an example, the operating process of fresh agricultural products logistic covering several regions are analyzed, elementary risk analysis on logistics system with partial cold chain is presented by risk coordinate graph method, and, risk levels of vegetable logistics system in complete cold chain environment as well as partial cold chain are evaluated by GO-FLOW method, evaluation results are compared and analyzed in detail. Based on related investigations in Guangzhou, the risk type during sale logistic process and critical factors affecting logistics safety are presented by the idea of HACCP, a relatively sound index system for logistics safety evaluation is established, combined with the evaluation grades from experts in practical operation and theory research fields, the weights of first-level indices are determined by AHP(The Analytic Hierarchy Process), risk level of sale logistics for fresh agricultural products is evaluated by combined fuzzy evaluation method.
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