IP电话系统中地址映射表的创建与查询

基于十叉树的存储结构及其查询方法，提出了一种适用于VOIP系统的地址映射表创建方法及其相应的查询算法，并且以提高表的查询效率为目的，设计了地址映射表的数据类型与存储结构。实验表明，采用树形存 储结构构成的地址映射表，其相应的查询算法可以获得较短的耗费时间。     

De Facto Exchange Rate Regime Classifications: An Evaluation

There exist several statistically-based exchange rate regime classifications that disagree with one another to a disappointing degree. To what extent is this a matter of the quality of the design of these schemes, and to what extent does it reflect the need to supplement statistics with other information (as is done in the IMF’s de facto classification)? It is shown that statistical methods are good at the basics (distinguishing some type of peg from some type of float), but less helpful in other respects, such as determining whether a float is managed, particularly for countries that are not very remote from their main trading partners. Different measures of exchange rate volatility have been used but are not primarily responsible for differences between classifications. The theoretical underpinning of particular classification schemes needs to be more explicit.     

The influence of activity importance and similarity on perception of recreation substitutes

Abstract

This study examines how substitutes are selected for a fly‐angling and camping recreation activity. Results show that although people choose substitutes similar to their intended activity, the degree of similarity between substitute and original is unrelated to perceived quality of substitute. Also, both the quality of a substitute and the number of available substitutes are inversely related to the importance of an activity's attributes. The lack of a relationship between activity/substitute similarity and quality of the substitute poses problems for application of the substitutability concept.     

An analysis of air mass effects on rail ridership in three US cities

This paper examines whether daily weather affects ridership in urban transportation systems. When examining human–weather relationships, it is often advantageous to examine air masses, which take into account the entire parcel of air over a region. Spatial synoptic classification characterizes air masses based upon numerous meteorological variables at a given location. Thus, rather than examining temperature or precipitation individually, here we compare daily ridership to synoptic air mass classifications for three urban rail systems: Chicago Transit Authority (CTA), Bay Area Rapid Transit (BART), and the Hudson–Bergen light-rail line in northern New Jersey. Air masses are found to have a significant impact on daily rail ridership, with usage typically increasing on dry, comfortable days and decreasing on moist, cool ones, particularly on weekends. Although the comfort of a particular air mass changes throughout the year, seasonality is not a significant factor with respect to the air mass–ridership relationship. The results of this study can benefit rail system managers who must predict daily ridership or in the development of cost-benefit analyses for station improvements.     

Currency Prices, the Nominal Exchange Rate, and Security Prices in a Two‐Country Dynamic Monetary Equilibrium

This paper examines a continuous‐time two‐country dynamic monetary equilibrium in which countries with possibly heterogeneous tastes and endowments hold their own money for the purpose of transaction services formulated via money in the utility function. Given a price system, no‐arbitrage pricing results are provided for the price of each money and the nominal exchange rate. Characterizations are provided for equilibrium prices for general time‐additive preferences and non‐Markovian exogenous processes. Under a Markovian structure of model primitives, the currency prices are shown to solve a bivariate system of partial differential equations. Assuming that each country is endowed with heterogeneous separable power utility and the exogenous quantities all follow geometric Brownian motions, an equilibrium is shown to exist and additional characterization is provided. A further example of nonseparable Cobb–Douglas preferences is investigated. The additional features over the customary environment of homogeneous logarithmic preferences are emphasized.     

Does interdependency affect firm and industry profitability? an empirical test

Strategy researchers have argued that heterogeneity in firms' practices and profitability within and across industries may derive from industry‐level differences in the extent of interdependencies among firms' activities. Theoretical models have clarified how and why differences in the extent of the interdependencies faced by firms across industries may affect the distributions of firm profits, but the specific predictions from these models have not been empirically tested. In this paper, we present what we believe is the first large scale empirical analysis linking differences in the extent of interdependencies across industries to differences in the distribution of firm profits within and across those industries. We use survey data to measure interdependencies systematically across a wide number of industries, thus addressing the primary obstacle to incorporating interdependencies in larger scale empirical work, and find evidence consistent with the theoretical predictions: average profitability is highest in industries with moderate levels of interdependency; the dispersion of profits among firms is higher in industries with more extensive interdependencies; and industries with more extensive interdependencies have a more positively skewed performance distribution. We find that the effect of interdependencies on average industry profitability is similar in scale to the effect of patent protection and industry growth rates, placing interdependency squarely among the strategy field's central concepts. Copyright © 2009 John Wiley & Sons, Ltd.     

Evaluating foreign exchange market intervention: Self-selection,counterfactuals and average treatment effects

Estimating the effect of official foreign exchange market intervention is complicated by the fact that intervention at any point entails a “self-selection” choice made by the authorities and that no counterfactual is observed. To address these issues, we estimate the “counterfactual” exchange rate movement in the absence of intervention by introducing the method of propensity-score matching to estimate the “average treatment effect” (ATE) of intervention. To derive the propensity scores we estimate central bank intervention reaction functions. We estimate the ATE for daily official intervention in Japan over the January 1999–March 2004 period. This sample encompasses a remarkable variation in intervention frequencies as well as unprecedented frequent intervention towards the latter part of the period. We find that only sporadic and relatively infrequent intervention is effective.     

Efficiency in the international insurance industry: A cross-country comparison

The purpose of this paper is to provide new empirical evidence on frontier efficiency measurement in the international insurance industry, a topic of great interest in the academic literature during the last several years. A broad efficiency comparison of 6462 insurers from 36 countries is conducted. Different methodologies, countries, organizational forms, and company sizes are compared, considering life and non-life insurers. We find a steady technical and cost efficiency growth in international insurance markets from 2002 to 2006, with large differences across countries. Denmark and Japan have the highest average efficiency, whereas the Philippines is the least efficient. Regarding organizational form, the results are not consistent with the expense preference hypothesis, which claims that mutuals should be less efficient than stocks due to higher agency costs. Only minor variations are found when comparing different frontier efficiency methodologies (data envelopment analysis, stochastic frontier analysis).