Node-weighted Steiner tree approximation in unit disk graphs

Given a graph G=(V,E) with node weight w:V→R ⁺ and a subset S⊆V, find a minimum total weight tree interconnecting all nodes in S. This is the node-weighted Steiner tree problem which will be studied in this paper. In general, this problem is NP-hard and cannot be approximated by a polynomial time algorithm with performance ratio aln n for any 0<a<1 unless NP⊆DTIME(n ^O(log n)), where n is the number of nodes in s. In this paper, we are the first to show that even though for unit disk graphs, the problem is still NP-hard and it has a polynomial time constant approximation. We present a 2.5ρ-approximation where ρ is the best known performance ratio for polynomial time approximation of classical Steiner minimum tree problem in graphs. As a corollary, we obtain that there is a polynomial time (9.875+ε)-approximation algorithm for minimum weight connected dominating set in unit disk graphs, and also there is a polynomial time (4.875+ε)-approximation algorithm for minimum weight connected vertex cover in unit disk graphs.     

我国电子商务用户网上购物行为的影响因素及其演变:基于2006年与2009年数据的实证研究

网上购物近年来发展迅速,以美国为主的西方社会已经针对网络购物行为接受度开展了广泛研究,但是有关网络购物行为接受度的动态演变的研究还不充分。同时,由于存在文化的差异,相关研究成果尚须通过我国数据的验证才能得以确认。本研究基于技术接受度模型(TAM),在2006年和2009年两个时间点,以中国网民中最具代表性的高等院校大学生群体为调查对象,分别通过311份和319份有效样本数据,运用结构方程模型来分析消费者感知网上购物的有用性、易用性和安全性对其态度和意向的影响变化。该研究验证了网上购物接受模型在中国情境下的适用性,并为网上零售商提出了有针对性的营销建议。     

社会网络、 先前经验与创业风险识别

无法识别创业风险是导致创业失败的主要原因之一,如何有效识别并管理创业风险是新创企业健康成长的关键.社会网络能够弥补创业者在识别风险过程中的信息劣势,但既有研究极少探索社会网络是否以及如何影响创业风险识别.为弥补这个研究空白,文章利用信息处理理论为研究框架,构建了创业风险识别模型.具体而言,结构洞和网络强度有利于创业者获取更多、高质量与风险相关的信息,进而识别更多的创业风险;获取信息的数量在网络强度与创业风险识别关系之间发挥完全中介作用;创业者的先前经验正向影响创业风险识别,并对结构洞与获取信息的数量之间关系起调节作用.文章讨论了研究结果的理论贡献与实践启发.     

汇率变动对中国物价的传递效应——从成本角度分析

本文利用反映加工贸易的非竞争型投入产出模型和计量经济模型相结合的方法,综合考虑进口品对国内品的替代作用和部门间的价格传导效应,从生产成本角度分情景测算了人民币升值对中国CPI和PPI的影响。测算结果表明,人民币升值可以有效缓解国内的通胀水平,但其传导效应并非是完全的,对CPI和PPI的传递率分别约为13.64%和17.80%。     

Is there an Expectations Gap in the Roles of Independent Directors? An Explorative Study of Listed Chinese Companies

This paper investigates whether an expectations gap exists in the control, strategic and resource provision roles that independent directors play in the corporate governance of listed Chinese firms and the factors that affect their performance of these roles. For this purpose, we interviewed Chinese executive directors, independent directors, institutional investors and stock exchange regulators. We find a performance gap but no reasonableness gap with respect to the control and strategic roles. The results suggest that the performance gap may be attributed to such factors as the ill‐defined roles, independent directors' limited amount of time commitment and their lack of competence and objectivity. Interestingly, there is disagreement over the protection of minority interest as the objective of the control role. We find no consensus on the desirability, reasonableness and effectiveness of independent directors' resource provision role, perhaps because of a pejorative interpretation of this role as an exercise of guanxi.     

Internationalization and Indigenous Technological Efforts of Emerging Economy Firms: The Effect of Multiple Knowledge Sources

Getting engaged in competitive international markets motivates exporting firms to enhance their technological competitiveness and invest in research and development (R&D). While in-house R&D investment is important for getting advanced technologies, the technologies needed by exporters located in emerging economies (EEs) typically readily exist overseas. Drawing on organizational learning literature, we argue that the R&D intensity stimulated by exporting may be reduced when 1) EE exporters are better prepared and motivated to absorb foreign knowledge, 2) foreign sources of knowledge are more available, and/or 3) local technology supply is poor. An analysis on 5592 automobile parts and component manufacturers in China during 2005–2007 supports these arguments. To compete in markets abroad, Chinese firms' R&D intensity increases with export intensity when their export intensity is low. As the export intensity exceeds a certain threshold, their R&D intensity starts to decrease as intensive exporters are better prepared and motivated to acquire knowledge from foreign sources. When substitutive foreign knowledge sources such as foreign parents and FDI spillovers in the local industry is available, firms' R&D intensity stimulated by exporting can be further reduced. Better local technology supply can increase the R&D intensity stimulated by exporting.     

Assessment of Catastrophic Risk Using Bayesian Network Constructed from Domain Knowledge and Spatial Data

Prediction of natural disasters and their consequences is difficult due to the uncertainties and complexity of multiple related factors. This article explores the use of domain knowledge and spatial data to construct a Bayesian network (BN) that facilitates the integration of multiple factors and quantification of uncertainties within a consistent system for assessment of catastrophic risk. A BN is chosen due to its advantages such as merging multiple source data and domain knowledge in a consistent system, learning from the data set, inference with missing data, and support of decision making. A key advantage of our methodology is the combination of domain knowledge and learning from the data to construct a robust network. To improve the assessment, we employ spatial data analysis and data mining to extend the training data set, select risk factors, and fine‐tune the network. Another major advantage of our methodology is the integration of an optimal discretizer, informative feature selector, learners, search strategies for local topologies, and Bayesian model averaging. These techniques all contribute to a robust prediction of risk probability of natural disasters. In the flood disaster's study, our methodology achieved a better probability of detection of high risk, a better precision, and a better ROC area compared with other methods, using both cross‐validation and prediction of catastrophic risk based on historic data. Our results suggest that BN is a good alternative for risk assessment and as a decision tool in the management of catastrophic risk.     

Models for measuring and benchmarking olympics achievements

As demonstrated in several recent studies, data envelopment analysis (DEA) is a useful tool for evaluating and comparing the performance of nations competing in the Olympic Games. Assurance regions (ARs) have been used to further refine the DEA results. These AR DEA models assume that ARs apply uniformly across all nations. Such models can have shortcomings in the sense that different nations may impose different ARs, as nations may value gold, silver, and bronze medals differently. This paper extends previous DEA studies by incorporating multiple sets of nation-specific ARs into the DEA. By doing so, we establish fair models for measuring and benchmarking the performance of nations at six summer Olympic Games.     

Analysis of postponement strategy by EPQ-based models with planned backorders

This paper develops economic production quantity (EPQ)-based models with planned backorders to evaluate the impact of the postponement strategy on a manufacturer in a supply chain. We derive the optimal total average costs per unit time for producing and keeping n end-products in a postponement system and a non-postponement system, respectively. By comparing the optimal total average costs of the two systems, we evaluate the impact of postponement on the manufacturer under four circumstances. Our results show that postponement strategy can give a lower total average cost under certain circumstances. We also find that the key factors in postponement decisions are the variance of the machine utilization rates and the variance of the backorder costs.     

电子市场中时间价格敏感需求下的交货期定价决策

电子市场中,如何通过交货期报价来增大需求、提高收益,对于网络营销企业来说是至关重要的.本文假定在一个包含网络营销企业与其客户的运作系统中,需求同时对价格与时间都敏感的条件下,以最优化自身收益为目标、以满足必须达到规定的服务水平为主要约束条件,构建了交货期定价决策模型.通过数值算例,探讨了在电子市场中消费者为价格敏感或交货期敏感时,网络营销企业的最优定价策略.上述结论可以为网络营销企业在电子市场中的定价决策提供有益的指导.