Sampling Returns for Realized Variance Calculations: Tick Time or Transaction Time?

This article introduces a new model for transaction prices in the presence of market microstructure noise in order to study the properties of the price process on two different time scales, namely, transaction time where prices are sampled with every transaction and tick time where prices are sampled with every price change. Both sampling schemes have been used in the literature on realized variance, but a formal investigation into their properties has been lacking. Our empirical and theoretical results indicate that the return dynamics in transaction time are very different from those in tick time and the choice of sampling scheme can therefore have an important impact on the properties of realized variance. For RV we find that tick time sampling is superior to transaction time sampling in terms of mean-squared-error, especially when the level of noise, number of ticks, or the arrival frequency of efficient price moves is low. Importantly, we show that while the microstructure noise may appear close to IID in transaction time, in tick time it is highly dependent. As a result, bias correction procedures that rely on the noise being independent, can fail in tick time and are better implemented in transaction time.     

时间如何前进——进化论随笔

中国古代"与时偕行"、"与时俱化"的观念,以取法天地四时的运行为基准,是一种四时循环论的变化观.我党提出的"与时俱进"思想的含义,是随着时代的前进而前进,和随着时代的变化而变化,体现了鲜明的时代创新精神,它的哲学基础是科学进化论.这一特征在语词上通过一个"进"字表达出来.虽然"与时俱进"和"与时俱化"只有一字之差,却体现了本质的超越.同时,这一表述通过对中国古代<易经>、<庄子>等经典的吸收,丰富了自身的思想内涵,也建立,了联接传统与现代的一道桥梁.当然,由于现代时间观念的一维性质,使得人们在批驳"直线进化论"的同时,易于陷入"时间进化论",而时间进化论实际上也是一种直线进化论,这也是需要警醒的.     

EFFECTS OF INTERNET USE AND SOCIAL RESOURCES ON CHANGES IN DEPRESSION

We examine how people's different uses of the Internet predict their later scores on a standard measure of depression, and how their existing social resources moderate these effects. In a longitudinal US survey conducted in 2001 and 2002, almost all respondents reported using the Internet for information, and entertainment and escape; these uses of the Internet had no impact on changes in respondents' level of depression. Almost all respondents also used the Internet for communicating with friends and family, and they showed lower depression scores six months later. Only about 20 percent of this sample reported using the Internet to meet new people and talk in online groups. Doing so changed their depression scores depending on their initial levels of social support. Those having high or medium levels of social support showed higher depression scores; those with low levels of social support did not experience these increases in depression. Our results suggest that individual differences in social resources and people's choices of how they use the Internet may account for the different outcomes reported in the literature.     

建筑与城市设计中的时间观

时间与形式、功能、空间四要素完备才能组成一个完整的建筑 ,运用时间设计的概念 ,分析和解决当今建筑界和城市规划出现的问题是现实的需要     

Communicating Global Activism

Many observers doubt the capacity of digital media to change the political game. The rise of a transnational activism that is aimed beyond states and directly at corporations, trade and development regimes offers a fruitful area for understanding how communication practices can help create a new politics. The Internet is implicated in the new global activism far beyond merely reducing the costs of communication, or transcending the geographical and temporal barriers associated with other communication media. Various uses of the Internet and digital media facilitate the loosely structured networks, the weak identity ties, and the patterns of issue and demonstration organizing that define a new global protest politics. Analysis of various cases shows how digital network configurations can facilitate: permanent campaigns; the growth of broad networks despite relatively weak social identity and ideology ties; transformation of individual member organizations and whole networks; and the capacity to communicate messages from desktops to television screens. The same qualities that make these communication-based politics durable also make them vulnerable to problems of control, decision-making and collective identity.     

论国际互联网对旅行社业的冲击

进入 2 1世纪以后 ,旅游越来越被普通老百姓所接受 ,旅行社作为旅游业的三大支柱之一 ,前景光明。但随着国际互联网的出现和广泛使用 ,给传统旅行社带来了巨大威胁。本文在详细论述互联网给旅行社带来冲击的基础上 ,指出在互联网影响下旅行社存在发展的机遇 ,提出旅行社生存发展的具体对策。     

马克思主义与时俱进的哲学思考

马克思主义具有与时俱进的理论品质。马克思主义哲学是这个理论品质的理论基础。实践与理论的矛盾运动、对真理的探求、以及创造崭新的马克思主义话语体系,都要求马克思主义与时俱进。     

Economic Determinants of Net International Migration in Western Europe

This paper aims to estimate theinfluence of economic determinants on netinternational migration in Western Europe inthe period 1960–1998. Net migration rates(i.e., population growth minus natural increase,divided by the midyear population) constitutethe dependent variable. The economicdeterminants used in this study are GDP percapita, unemployment, and average educationallevel (amount of human capital) of thepopulation. Time series regression models havebeen used in country-specific analyses. Inaddition, a pooled cross-sectional time seriesanalysis has been made. The analyses suggestthat GDP per capita has a positive effect andunemployment a negative effect on a country'snet international migration.     

Conditional Likelihood Estimators for Hidden Markov Models and Stochastic Volatility Models

ABSTRACT.  This paper develops a new contrast process for parametric inference of general hidden Markov models, when the hidden chain has a non-compact state space. This contrast is based on the conditional likelihood approach, often used for ARCH-type models. We prove the strong consistency of the conditional likelihood estimators under appropriate conditions. The method is applied to the Kalman filter (for which this contrast and the exact likelihood lead to asymptotically equivalent estimators) and to the discretely observed stochastic volatility models.     

Internet环境下的网络教学

Internet环境下的网络教学已成为人类进行终身教育和创新教育的最佳平台。文章着重论述了Internet环境下的多模式教学———讲授模式、个别辅导模式、讨论学习模式、探索学习模式、协作学习模式