Neutral fitness landscapes in signalling networks

Biological and technological systems process information by means of cascades of signals. Be they interacting genes, spiking neurons or electronic transistors, information travels across these systems, producing, for each set of external conditions, an appropriate response. In technology, circuits performing specific complex tasks are designed by humans. In biology, however, design has to be ruled out, confronting us with the question of how these systems could have arisen by accumulation of small changes. The key factor is the genotype-phenotype map. With the exception of RNA folding, not much is known about the exact nature of this mapping. Here, we show that structure of the genotype-phenotype map of simple feed-forward circuits is very close to the ones found in RNA; they have a large degree of neutrality, by which a circuit can be completely rewired keeping its input-output function intact, and there is a relatively small neighbourhood of a given circuit containing almost all the phenotypes.     

基于UCON的分布式数据库安全模型

针对分布式数据库系统中已发布数据难以控制的问题,结合基于角色访问控制模型(RBAC)和使用控制模型(UCON)的特点,提出一种基于UCON的分布式数据库安全模型。将分布式数据库分为服务器端和客户端,服务器端采用UCON策略,客户端采用RBAC策略。分析结果表明,该模型能有效控制分布式数据库系统中的数据。     

Collective foraging in heterogeneous landscapes

Animals foraging alone are hypothesized to optimize the encounter rates with resources through Lévy walks. However, the issue of how the interactions between multiple foragers influence their search efficiency is still not completely understood. To address this, we consider a model to study the optimal strategy for a group of foragers searching for targets distributed heterogeneously. In our model, foragers move on a square lattice containing immobile but regenerative targets. At any instant, a forager is able to detect only those targets that happen to be in the same site. However, we allow the foragers to have information about the state of other foragers. A forager who has not detected any target walks towards the nearest location, where another forager has detected a target, with a probability exp(−αd), where d is the distance between the foragers and α is a parameter characterizing the propensity of the foragers to aggregate. The model reveals that neither overcrowding (α → 0) nor independent searching (α → ∞) is beneficial for the foragers. For a patchy distribution of targets, the efficiency is maximum for intermediate values of α. In addition, in the limit α → 0, the length of the walks can become scale-free.     

The Hinterland Urbanised?

What defines the urban? And can the non-urban necessarily always be classified as rural? Neil Brenner , Director of the Urban Theory Lab at Harvard University Graduate School of Design, reflects on the lack of an overarching theory to describe these realms, and argues that what we call the countryside or the hinterland has become key to the process of capitalist urbanisation.     

Are There Counter-Landscapes? On Milk Trestles and Invisible Power Lines

The paper takes its starting point from the duality in the Estonian rural landscape shaped by social practices. On the one hand, the changes and management of landscapes follow a political decision. At the same time, the old patterns of semi-legal activity offer a resistant practice. The study is illustrated with the milk trestle, a now-disappeared symbol of recent history in the Soviet countryside. The milk trestles and their role in Estonian country life are studied from a threefold perspective—their functions, meanings and the values behind this symbol. The article is based on ethnographic field work carried out between the years of 2001 and 2002 and traces the phenomenon of how living landscape transforms into deserted landscape; in other words, how story becomes history. The paper shows how the milk trestle landscape functioned as a prolongation of the former landscape behind the ideological layers of the Soviet landscapes.     

Spatial planning for landscape: mapping the pitfalls

While welcoming the European Landscape Convention and acknowledging the successes of conservation organizations such as the National Trust in Britain, the Czech Village Restoration Scheme and the French eco‐musées, this paper identifies some of the pitfalls that must be avoided if the fine words of the Convention are to be translated into effective action. These include problems with designation, conflicts between different types of conservation, and the side effects of gentrification and increased tourism. There is a call for more research to break down barriers to understanding between countries, between disciplines, and between academics and practitioners.     

Peaceful,Pleasant and Private: The British Domestic Garden as an Ordinary Landscape

This paper uses narrative accounts of private gardens in Britain from the Mass-Observation Archive (MO) to explore ideas of landscape, privacy and attachment that emerge from daily practices and routines in these ordinary domestic spaces. We argue for the domestic garden as a vernacular or ordinary landscape that displays tensions between the private and the public nature of home within ambivalent emotional responses. Extended personal narratives offer privileged access to a site of intense engagement and carefully guarded privacy, yet with varying levels of attachment. The garden is a space well described in Britain in its public form but less well known as a private, everyday landscape. In this way a cultural landscape study becomes a contemporary critical geography of an ordinary space.     

Exploring public preferences for traditional farming landscapes

Given that an increasing share of budgetary resources are now being spent on measures aimed at protecting the visual quality of agricultural landscapes it will be important to better understand individuals’ landscape preferences and the factors that influence those preferences. Within this context, using a nationally representive survey of Irish residents, the central aim of this study was to gain more insight into people's preferences regarding traditional farming landscapes. Individuals rated agricultural landscapes in terms of beauty quite highly but given a choice prefer traditional more extensive farming landscapes over more modern intensive farming landscapes. Moreover, the results suggest that there are systematic differences in preferences for traditional farm landscapes between different demographic groupings and also depending on individuals’ environmental value orientations. Accordingly, in studying preferences for agricultural landscapes in particular areas it will be necessary to consider the social and demographic characteristics of the population as well as the physical aspects of the landscape.     

使用控制的可变性研究

在传统的访问控制模型和策略中虽有可变的特性,但属性的可变性是一个全新的概念。作为对传统访问控制的扩展,论述了使用控制模型,分析了其核心组成及特性。运用使用控制的观点,讨论了使用控制的可变性,定义了临时属性和永久属性两个可变属性。可变性是对相关主体和对象访问结果的属性更新处理,发生在授权和认证模型中,是通过在定义模型中加入更新过程实现的,使得基于历史的访问决策更容易实施。在属性可变性的基础上,进一步讨论了可变性的几种变化形式。