Hybrid Samplers for Ill-Posed Inverse Problems

Abstract.  In the Bayesian approach to ill-posed inverse problems, regularization is imposed by specifying a prior distribution on the parameters of interest and Markov chain Monte Carlo samplers are used to extract information about its posterior distribution. The aim of this paper is to investigate the convergence properties of the random-scan random-walk Metropolis (RSM) algorithm for posterior distributions in ill-posed inverse problems. We provide an accessible set of sufficient conditions, in terms of the observational model and the prior, to ensure geometric ergodicity of RSM samplers of the posterior distribution. We illustrate how these conditions can be checked in an application to the inversion of oceanographic tracer data.     

基于移动互联网的饮料瓶智能回收设备

国内饮料瓶回收主要依靠分散的人力回收,过程效率低下,流转能耗高,并且会产生二次污染。针对这一现状,提出了一种基于移动互联网的饮料瓶智能回收设备。该设备通过称量、传送、条码识别和压缩的方式对塑料瓶与易拉罐进行回收,随后用户通过微信扫描屏幕中的二维码获得微信红包。文章主要介绍了该设备的机械机构并对部分结构进行了详细的分析计算。设备不仅能够提升废旧饮料瓶的回收率,替换城市中的垃圾中转站,改善城市面貌,培养环保理念,同时挖掘互联网平台的潜在价值,让环保更加智能好玩。该设备能实现较高的社会效益和经济效益。     

ON QUANTILES OF SUMS

In this paper we investigate the relationship between the quantiles of a sum of independent continuous random variables and those of its components. Results concerning this relationship are given for the special cases of symmetric distributions, gamma distributions, and for the difference of identically distributed random variables.     

Understanding Young People and Prostitution: A Foundation for Practice?

Correspondence to Ian Shaw, School of Social and Administrative Studies, University of Wales Cardiff, 50 Park Place, Cardiff CF1 3AT, UK. Summary The practice and research literature on young people and prostitutionreflects a number of methodological challenges. This paper offersa focused review of the literature in the context of those challengesand attempts to draw conclusions that are strong enough to providea reflective and strategic approach to service planning andimplementation. Definitional issues are discussed, particularlyin relation to estimates of prevalence. The robustness of pastresearch designs and associated causal inferences are questionedand a synthesis of current explanatory accounts is offered.Risk in relation to prostitution is explored. Past service responsesare examined and a rationale for future responses is developed.     

Keeping Social Work Honest: Evaluating as Profession and Practice

Correspondence to Ian Shaw, School of Social and Administrative Studies, University of Wales Cardiff, 50 Park Place, Cardiff CF1 3AT Summary The central argument of this paper is that social work needsa radical alternative to existing options for evaluating practice.Social workers at present are offered three choices. They areinvited to choose between applying research, conducting researchor adopting specific forms of empirical research-based practice(for example Everitt et al., 1992; Thyer. 1993; Fuller and Petch,1995). We touch briefly on reasons why we believe none of these optionsprovides an adequate grounding for social work, referring especiallyto the growing call for social work to find new purpose throughan empirical, research-based practice. If alternative approachesare to be persuasive, they must be fashioned from the materialsof a new approach to research on social work practice—‘one that is exploratory rather than confirmatory, buildinga model of evaluation from the practitioners' own accounts ratherthan superimposing an ideal model’ (Elks and Kirkhart,1993, p. 555). The major part of this paper is taken up withevidence from research of this kind. The model of evaluatingin practice with which we conclude the paper is simultaneouslytrue to social workers' accounts of their practice, while offeringa critical starting point for evaluating and refashioning thatpractice.     

Reflections From the Field: the Experience of Former CSS and CQSW Students

Summary The research reported in this paper is based on the findingsof a postal questionnaire survey with former students who had,over the last seven years, successfully completed either theCertificate in Social Service (CSS) or the Certificate of Qualificationin Social Work (CQSW) at one institution of higher education. The purpose was to collect data in a systematic way about employmentcircumstances, career development, aspirations, reflectionson the course and views of the future of education for socialwork and social service. For many of these areas a lack of comparableBritish studies is noted. The findings would seem to indicate that the type of qualificationobtained is an important variable where work setting, clientgroup, perceived professional status, job choice and attitudeto certain aspects of the course are concerned. Both groupswere largely supportive of a single award for social work throughfull-time education and training, but were ambivalent aboutthere being different routes to this qualification.     

CAN THE RISK-SHIFTING EMPLOYMENT MODEL EXPLAIN FLUCTUATING EMPLOYMENT?

It is shown by numerical examples that, for the simple "two states of the world" version of Azariadis' original model of implicit labour contracts, enormous fluctuations in output price are required to generate layoffs. The paper then modifies the simple model, replacing the perfectly competitive product market specification with a sales constraint. This modification makes a significant difference; the combination of sales constraints and risk-shifting is shown to have the potential to explain layoffs. Since this sales constraint is unmotivated by micro analysis, its inclusion does not satisfy the original aim of the risk-shifting employment model to explain layoffs as based on micro foundations. A secondary aim of the paper is to make the workings of the risk-shifting employment model easier to understand by introducing a new diagrammatic analysis based on a contract curve.     

Cautionary Tales From Beginning Practitioners: The Fate of Personal Models of Social Work in Beginning Practice

Summary The relationship between professional education and beginningpractice is examined by considering whether the personal modelsof social work developed and reviewed by the individual duringsocial work education survived the transition from student toautonomous practitioner. Fifteen University of Queensland socialwork graduates were engaged in a task of making explicit theirpersonal models of social work, by way of repertory grid technique,in their first eight months of employment. The repertory gridwas used as a conversational tool to monitor the developmentof and changes in their personal models of social work. Thesocial workers were thus engaged in a process consciously reflectingon the meaning of, and the reasons for, these developments andchanges. Whilst the study found that personal models do survivethe transition to social work practice, it also highlightedareas of concern. On the whole graduates did not feel preparedfor work, and the initial period of practice was one of considerabledifficulty. Many experienced considerable difficulty in subsumingthe organizational context within their personal model of socialwork.