非静止轨道卫星系统考虑通信中断的服务质量分析

基于Globalstar和Odyssey两个Walker delta星座,建立星间链路网络,重点分析网络中的不同轨道间星间链的动态特性,特别是与星上跟瞄系统密切相关的俯仰角、方位角和链路长度变化,为卫星网络路由提供依据.对传统的卫星路由策略作了改进,利用卫星系统的冗余覆盖的特性,选择不同策略下的最优路径.针对用户不能忍受通信中断的情况,提出考虑消除中断的路由策略,进行服务质量的分析比较.同时也比较在消除中断的路由策略下,LEO同MEO网络差异之处.消除通信中断是以其它QoS性能下降为代价.     

美军战术数据链格式化消息标准的发展

首先介绍了战术数据链及格式化消息的概念、特点及消息体系的层次结构,在此基础上对美军战术数据链格式化消息标准的发展历程及为满足信息化战争的需要而不断完善和发展的新趋势进行了详细分析,最后对我国战术数据链格式化消息标准的发展提出了建议。     

Modelling Risk Perceptions of Stakeholders in Public–Private Partnership Toll Road Contracts

This paper investigates the risk perceptions of key stakeholder groups typically involved in public–private partnership (PPP) toll roads. Risk perceptions have an important impact on these PPP schemes for investing in public infrastructure. However, the nature and extent of risk associated with the specification of a PPP contract that commits contracting parties to deliver on their obligations remain unclear. In the context of major transport infrastructure, such as a new toll road, the often‐cited key risk to investors is the traffic (and hence demand) risk. There are, however, other risks, including political risk and media risk, the latter often causing untold harm resulting in modifications to the planned infrastructure. This paper develops a method to capture evidence on how public sector and private sector partners involved in previous PPPs perceive the levels of risk associated with each risk attribute, as a way of identifying the ex ante risk setting brought to negotiations in PPP toll road investments. Using a sample of 101 experts with contract experience in 32 countries, we develop a stated choice experiment and estimate a discrete choice model to quantify a risk profile index (RPI) to capture the perceived (relative) influence of each dimension of risk, and then identify sources of systematic differences in the RPI as a way of understanding the influence of personal traits and contextual and contractual factors.     

一种基于DS-FFH/MSK调制的数据链抗干扰性能分析

提出了DS-FFH/MSK调制方式的一种实现方案,并在多种干扰环境下,从信源误比特率的角度对基于该实现方案的Link16战术数据链的抗干扰性能进行了系统分析,推导了几种不同干扰条件下数据链的误比特率表达式,并给出了计算机仿真结果.     

Assessing Industrial Buyer Preferences: Using the Swait-Louviere Test to Test the Key Informant Assumption

When using professional buyers to study an organizations buying behavior an important consideration is whether their preferences reflect those of the organization. Since this is a key informant problem, the present article focuses on the issue of the degree to which key informants can be used to provide insights into their own organizations preferences. We conduct a direct test of the key informant assumption using the Swait-Louviere test. In this test preferences from a choice experiment using actual buyers, and from market decisions made by the organization, are estimated separately, then jointly in multinomial logit models. We found that buyers experimental preferences were similar to estimates obtained from the market decisions. Buyers preferences were closer to the intuitive preferences of the organizations top executives than the estimates based on past market decisions, although a model based on the combined data outperformed either. We discuss the implications of these results for industrial buying research.This revised version was published online in May 2005 with a corrected cover date.     

虚拟企业伙伴选择方法的研究

选择正确的合作伙伴是虚拟企业组建的关键步骤之一,也是虚拟企业成功运作的首要前提。针对某一具体案例,从目前虚拟企业伙伴选择的几种典型方法入手,运用系统研究方法,对各方法的具体思路作一总结,并提出了各方法的适用范围、优势与弊端,同时,找出了它们之间的差异所在。     

农户民间借贷需求影响因素的经验分析——基于河南省的调查

采用河南省农村的社会调查资料,运用Logit模型,对农户民间借贷需求影响因素进行了实证检验。结果表明:社会资本拥有量、家庭状况和信贷环境均是影响农户民间借贷需求的主要因素。尤其,具有一定社会地位的家庭、收入水平较高的家庭、负担水平较重的家庭以及所在村存在"高利贷"等因素对农户获得民间借贷的可能性具有非常显著的作用。     

Valuation of nature-based tourism resources using dichotomous choice contingent valuation method

The purpose of this paper is to measure the potential revenue from nature-based tourism resources in the environmentally sensitive area of Mt Minju, South Korea. A dichotomous choice contingent valuation method was employed to estimate the mean willingness-to-pay, contingent on a hypothetical market scenario. The empirical results show that the economic value of nature-based tourism resources was estimated at 5905 Won (ca US$ 7) per visitor. This implies that the significant economic value of natural resources will be lost from any large-scale development by degrading natural environments. In addition to the value of natural resources, nature-based tourism also provides the locally owned small tourist businesses with lower leakages than the externally owned large-scale ones. Low leakage implies that local residents gain more direct income from nature-based tourism.     

Estimating Discrete Joint Probability Distributions for Demographic Characteristics at the Store Level Given Store Level Marginal Distributions and a City-Wide Joint Distribution

This paper provides a solution to the problem of estimating a joint distribution using the associated marginal distributions and a related joint distribution. The particular application we have in mind is estimating joint distributions of demographic characteristics corresponding to market areas for individual retail stores. Marginal distributions are generally available at the census tract level, but joint distributions are only available for Metropolitan Statistical Areas which are generally much larger than the market for a single retail store. Joint distributions over demographics are an important input into mixed logit demand models for aggregate data. Market shares that vary systematically with demographics are essential for relieving the restrictions imposed by the Independence from Irrelevant Alternative property of the logit model.We approach this problem by formulating a parametric function that incorporates both the city-wide joint distributional information and marginal information specific to the retail stores market area. To estimate the function, we form moment conditions equating the moments of the parametric function to observed data, and we input these into a GMM objective. In one of our illustrations we use four marginal demographic distributions from each of eight stores in Dominicks Finer Foods data archive to estimate a four dimensional joint distribution for each store. Our results show that our GMM approach produces estimated joint distributions that differ substantially from the product of marginal distributions and emit marginals that closely match the observed marginal distributions. Mixed logit demand estimates are also presented which show the estimates to be sensitive to the formulation of the demographics distribution.The views expressed are not purported to reflect those of the United States Department of Justice