Long-run urban dynamics: understanding local housing market change in London

Abstract

Recently, a literature has emerged using empirical techniques to study the evolution of international cities over many centuries; however, few studies examine long-run change within cities. Conventional models and concepts are not always appropriate and data issues make long-run neighbourhood analysis particularly problematic. This paper addresses some of these points. First, it discusses why the analysis of long-run urban change is important for modern urban policy and considers the most important concepts. Second, it constructs a novel data set at the micro level, which allows consistent comparisons of London neighbourhoods in 1881 and 2001. Third, the paper models some of the key factors that affected long-run change, including the role of housing. There is evidence that the relative social positions of local urban areas persist over time but, nevertheless, at fine spatial scales, local areas still exhibit change, arising from aggregate population dynamics, from advances in technology, and also from the effects of shocks, such as wars. In general, where small areas are considered, long-run changes are likely to be greater, because individuals are more mobile over short than long distances. Finally, the paper considers the implications for policy.     

Adding Support for Persistence to CLOS via Its Metaobject Protocol

Language-level support for object persistence frees programmers from having to confront a broad class of database issues from within their applications. By virtue of its metaobject protocol, CLOS is a language whose semantics can be tailored by individual programmers. We used the metaobject protocol to extend CLOS with support for object persistence. Our goal was to obtain a version of CLOS with persistence to which we could easily port a commercial geometric CAD modeling system. We describe the design and implementation of our persistence extension and highlight the strengths and weaknesses exhibited by the CLOS metaobject protocol during our experiment. For many aspects of the implementation we found that the metaobject protocol was ideal. In other cases we had to choose among paying a large performance penalty, extending the protocol, and bypassing the protocol by modifying the language implementation directly.     

An entropy-based persistence barcode

In persistent homology, the persistence barcode encodes pairs of simplices meaning birth and death of homology classes. Persistence barcodes depend on the ordering of the simplices (called a filter) of the given simplicial complex. In this paper, we define the notion of “minimal” barcodes in terms of entropy. Starting from a given filtration of a simplicial complex K, an algorithm for computing a “proper” filter (a total ordering of the simplices preserving the partial ordering imposed by the filtration as well as achieving a persistence barcode with small entropy) is detailed, by way of computation, and subsequent modification, of maximum matchings on subgraphs of the Hasse diagram associated to K. Examples demonstrating the utility of computing such a proper ordering on the simplices are given.     

基于J2EE的O/R(Object-Relation)映射方案研究

对象模型和关系模型是两种完全不同的模式,在开发中如何实现对象到关系的映射是一个关键的问题,分析了对象关系映射不匹配的各个方面,以及当前的各种持久化解决方案,并重点分析了透明对象关系映射的特点,最后对如何实现对象关系映射的关键技术进行了研究.     

Recursive identification of switched ARX systems

We consider the problem of recursively identifying the parameters of a deterministic discrete-time Switched Auto-Regressive eXogenous (SARX) model, under the assumption that the number of models, the model orders and the mode sequence are unknown. The key to our approach is to view the identification of multiple ARX models as the identification of a single, though more complex, lifted dynamical model built by applying a polynomial embedding to the input/output data. We show that the dynamics of this lifted model do not depend on the value of the discrete state or the switching mechanism, and are linear on the so-called hybrid model parameters. Therefore, one can identify the parameters of the lifted model using a standard recursive identifier applied to the embedded input/output data. The estimated hybrid model parameters are then used to build a polynomial whose derivatives at a regressor give an estimate of the parameters of the ARX model generating that regressor. The estimated ARX model parameters are shown to converge exponentially to their true values under a suitable persistence of excitation condition on a projection of the embedded input/output data. Such a condition is a natural generalization of the well known result for ARX models. Although our algorithm is designed for perfect input/output data, our experiments also evaluate its performance as a function of the level of noise for different choices of the number of models and model orders. We also present an application to temporal video segmentation.     

基于JPA的数据持久化模型设计与实现

基于SQL的JDBC持久化技术和基于对象/关系映射（ORM）的面向对象持久化技术都会导致系统紧耦合。针对上述问题,通过研究Java持久化API（JPA）ORM技术、JPA模型和JPA接口,提出并实现一种灵活的数据持久化模型。该模型与ORM框架松耦合,可以简化对象持久化的开发,加快应用系统的开发速度。     

A synergistic model-driven approach for persistence modeling with UML

The Model Driven Development (MDD) approach proposes that models (and model-to-model transformations) play the main role on system development. However, there is not a consensual notation to model persistence based upon object-relational mapping frameworks: while UML lacks specific resources for persistence modeling, the entity-relationship model does not make reference to the dynamic concepts existing in UML.This paper proposes MD-JPA, a UML profile for persistence modeling based on the well-known Java Persistence API 2 (JPA) standard for object-relational mapping, pursuing the modeling of transient and persistent elements in a more coherent and synergistic way. This paper describes the main characteristics of MD-JPA as well as the way that models that adopt such profile can them be used to generate a Java implementation by the application of the proposed model transformations on a MDD approach. Finally, an open source tool was developed to make the results of this work available to the community.     

基于Java的分布式应用程序的开发机制-RMI

从单机系统到Ｃ／Ｓ结构的盛行,应用程序体系结构已经发展到了如今的分布式计算模型。在分布式计算中,Ｊａｖａ的ＲＭＩ无疑是其中的佼佼者。文章首先从应用程序体系结构的发展历史入手,深入探讨了ＲＭＩ的相关概念以及通信结构,最后以一个简单的例子论述了如何编写ＲＭＩ应用程序。     

Cyber-harassment victimization in Portugal: Prevalence,fear and help-seeking among adolescents

Cyber-harassment is one of today's problems in adolescent health. This study aimed to determine the prevalence of cyber-victimization among Portuguese adolescents. It also explored its nature, patterns and victim's reactions of fear and help-seeking. A representative sample of 627 adolescents, aged 12–16, enrolled in schools from northern Portugal and Azores answered an online survey. Cyber-victimization was widely experienced by these adolescents, mainly among older adolescents. Results evidenced a high prevalence rate of adolescents (66.1%) double involved as both cyber-victim and cyber-aggressor. Although not all adolescents reported fear (37%) or sought help (45.9%), persistent victimization increased fear. In turn, fear increased help-seeking behaviors. Cyber-victims were more afraid encountering unknown cyber-aggressors (vs. acquainted) and when victimized by older males (vs. younger females cyber-aggressors). Younger girls reported more fear and more help-seeking behaviors while older boys were more often victim-aggressors. The subgroup of victim-aggressors was both the target of a higher diversity of cyber-victimization behaviors than the victim-only subgroup and also engaged in fewer help-seeking behaviors. Those adolescents who sought help considered it helpful. Implications for educational, social and political practices are discussed.     

Ethanol consumption in Brazil: Empirical facts based on persistence,seasonality and breaks

This paper investigates the consumption of sugar cane ethanol in Brazil for the time period from January 2000 to December 2012. We examine ethanol and gasoline consumption along with the price ratio series. Two important features of the data are analyzed, in particular, its degree of persistence and the seasonality. The results show that the two series of consumption are fractionally integrated with orders of integration smaller than 1 implying that shocks in the series will disappear in the long run. On the other hand, the price ratio series displays an order of integration higher than 1 implying lack of mean reversion behavior. This suggests that strong policy measures must be adopted on prices in the event of shocks since they do not recover by themselves in the long run.