On Exact Simulation of Markov Random Fields Using Coupling from the Past

A general framework for exact simulation of Markov random fields using the Propp–Wilson coupling from the past approach is proposed. Our emphasis is on situations lacking the monotonicity properties that have been exploited in previous studies. A critical aspect is the convergence time of the algorithm; this we study both theoretically and experimentically. Our main theoretical result in this direction says, roughly, that if interactions are sufficiently weak, then the expected running time of a carefully designed implementation is O ( N log N ), where N is the number of interacting components of the system. Computer experiments are carried out for random q -colourings and for the Widom–Rowlinson lattice gas model.     

Health‐Economics Analyses Applied to ELF Electric and Magnetic Fields

Extremely low frequency electric and magnetic fields (ELF EMFs) are a common exposure for modern populations. The prevailing public‐health protection paradigm is that quantitative exposure limits are based on the established acute effects, whereas the possible chronic effects are considered too uncertain for quantitative limits, but might justify precautionary measures. The choice of precautionary measures can be informed by a health‐economics analysis (HEA). We consider four such analyses of precautionary measures that have been conducted at a national or state level in California, the Netherlands, the United Kingdom, and Israel. We describe the context of each analysis, examine how they deal with some of the more significant issues that arise, and present a comparison of the input parameters and assumptions used. The four HEAs are methodologically similar. The most significant qualitative choices that have to be made are what dose‐response relationship to assume, what allowance if any to make for uncertainty, and, for a CBA only, what diseases to consider, and all four analyses made similar choices. These analyses suggest that, on the assumptions made, there are some low‐cost measures, such as rephasing, that can be applied to transmission in some circumstances and that can be justifiable in cost‐benefit terms, but that higher cost measures, such as undergrounding, become unjustifiable. Of the four HEAs, those in the United Kingdom and Israel were influential in determining the country's EMF policy. In California and Netherlands, the HEA may well have informed the debate, but the policy chosen did not stem directly from the HEA.     

SLA研究的理论模式与研究领域

第二语言习得(SLA)研究作为一门独立的学科已经有了三十多年的历史,其间理论假设层出不穷,莫衷一是。本文梳理了五种有代表性的、对外语教学有指导意义的主要SLA理论,希望能对广大的外语教学工作者有教学参考价值。     

On the Second‐Order Random Walk Model for Irregular Locations

Abstract. The second‐order random walk (RW2) model is commonly used for smoothing data and for modelling response functions. It is computationally efficient due to the Markov properties of the joint (intrinsic) Gaussian density. For evenly spaced locations the RW2 model is well established, whereas for irregularly spaced locations there is no well established construction in the literature. By considering the RW2 model as the solution of a stochastic differential equation (SDE), a discretely observed integrated Wiener process, it is possible to derive the density preserving the Markov properties by augmenting the state‐space with the velocities. Here, we derive a computationally more efficient RW2 model for irregular locations using a Galerkin approximation to the solution of the SDE without the need of augmenting the state‐space. Numerical comparison with the exact solution demonstrates that the error in the Galerkin approximation is small and negligible in applications.     

The Efficacy of Different Methods for Informing the Public About the Range Dependency of Magnetic Fields from High Voltage Power Lines

The AC electric and magnetic fields associated with high voltage power lines have become a concern as a possible health risk. In most cases the strength of these fields decreases as the inverse square of the distance from the line. In earlier work, we found that laypeople do not understand how rapidly field strength decreases with distance. Most believe that any high voltage power line they can see is exposing them to strong fields. This paper confirms the earlier finding and explores a number of strategies which might be used in risk communications to correct this misperception. We found it relatively easy to provide subjects with a better understanding of the range-dependency of magnetic field strength. Moreover, the quality of this acquisition was apparently independent of the manner in which they were instructed. Such successful instruction is markedly different from the well-established difficulty of teaching people about many qualitative domains, such as physics or ideas in probability. Clearly, while some erroneous beliefs are highly resistant to change, others can be altered quite readily. We suspect that an important distinction between knowledge about the range-dependency of power-frequency magnetic fields and less tractable topics involves the presence or absence of prior folk-theories or "mental models" of the domain.     

Approximate Bayesian Inference for Survival Models

Abstract. Bayesian analysis of time‐to‐event data, usually called survival analysis, has received increasing attention in the last years. In Cox‐type models it allows to use information from the full likelihood instead of from a partial likelihood, so that the baseline hazard function and the model parameters can be jointly estimated. In general, Bayesian methods permit a full and exact posterior inference for any parameter or predictive quantity of interest. On the other side, Bayesian inference often relies on Markov chain Monte Carlo (MCMC) techniques which, from the user point of view, may appear slow at delivering answers. In this article, we show how a new inferential tool named integrated nested Laplace approximations can be adapted and applied to many survival models making Bayesian analysis both fast and accurate without having to rely on MCMC‐based inference.     

"美色"探秘的旅程

20多年前,鲁晨光先生对语言称呼和颜色视觉的一致性提出质疑,指出色觉差异或颠倒的可能性,且并不影响称呼和交流.这有悖于人们的惯常思维引起了论争,由此开始了作者与鲁先生在空间时分时合,跨国越洋;在时间上断续的、跨世纪的探索.从<潜科学>"是否存在标准色觉";<自然信息>"试析达尔文留下的香甜美难题";<学术界>"论第二物性感知差异"等,直到今天,终于形成了哲学的两亩地--新著<色觉奥妙和哲学基本问题>和<美感奥妙和需求进化>."美色"探秘的旅程,正是这哲学两亩地栽培浇灌,发芽结果的来龙去脉.     

Institutional Pressures and Organizational Capacity: The Case of Outcome Measurement1

A central claim of new institutional theory is that organizations in a field come to exhibit shared characteristics over time. Recent literature emphasizes variation across field members, but has yet to concur on why differences occur. This study tests institutional explanations for the uneven implementation of one organizational practice—outcome measurement, an evaluative technique used to assess the impact of an organization’s programs. We analyze data from a new survey investigating the practices of nonprofit organizations (N = 379) and argue for the inclusion of the concept of organizational capacity to account for the uneven implementation of outcome measurement. As predicted by new institutional theory, organizations are more likely to adopt outcome measurement if key actors promulgate its use. However, the implementation of outcome measurement is best explained by the addition of the concept of organizational capacity alongside variables drawn from new institutionalism. Nonprofits with adequate organizational capacity, operationalized—following Weber’s concept of bureaucracy—as the presence of written rules and members with specialized knowledge, are better able to respond to isomorphic pressures to implement a new organizational practice. Our findings expand scholarship that examines the intersection of institutional dynamics and organizational traits in accounting for patterns of implementation of practices across an organizational field.     

Memory properties and aggregation of spatial autoregressive models

A random field displays long (resp. short) memory when its covariance function is absolutely non-summable (resp. summable), or alternatively when its spectral density (spectrum) is unbounded (resp. bounded) at some frequencies. Drawing on the spectrum approach, this paper characterizes both short and long memory features in the spatial autoregressive model. The data generating process is presented as a sequence of spatial autoregressive micro-relationships. The study elaborates the exact conditions under which short and long memories emerge for micro-relationships and for the aggregated field as well. To study the spectrum of the aggregated field, we develop a new general concept referred to as the ‘root order of a function’. This concept might be usefully applied in studying the convergence of some special integrals. We illustrate our findings with simulation experiments and an empirical application based on Gross Domestic Product data for 100 countries spanning over 1960–2004.     

Commodification of rural places: A narrative of social fields,rural development,and football

One of the most significant recent elements of restructuring in rural areas is the transition from an economy based on agricultural production to an economy based on the countryside as a form of commodity. In this transition process, different narratives or images of an area are produced to promote villages and other places in the countryside as commodities. Much of the literature takes it for granted that outsiders control the processes of branding rural areas, but our case study demonstrates that the producers (as well as potential consumers) of the countryside as a commodity can be insiders within a community. In this paper, we demonstrate how a local football club can take a leading role in the process of commodification of rural places in the post-modern era. Football clubs are presented as commodities to attract investors, sponsors, and expertise from private businesses. In both commodification of rural places and football, the challenge is to construct narratives or images that correspond to the pre-existing expectations of consumers, whoever they might be. Our theory-informed empirical analyses illustrate the way in which the Norwegian football club Sogndal Football has been instrumental in the restructuring of the Sogndal community.