Certain Segments (certain + segment)

Distribution by Scientific Domains
Humanities and Social Sciences33%
Earth and Environmental Science33%

Selected Abstracts

Validation of plant functional types across two contrasting landscapes

JOURNAL OF VEGETATION SCIENCE, Issue 2 2002
Michael Kleyer
Disturbance; Fertility; Logistic regression; Trait; Urban landscape Abstract. The validation of plant functional type models across contrasting landscapes is seen as a step towards the claim that plant functional types should recur regionally or even globally. I sampled the vegetation of an urban landscape on a range of sites representing gradients of resource supply and disturbance intensity. A group of plants with similar attributes was considered a ,functional type', if the species significantly co-occurred in a certain segment of the gradient plane of resource supply and disturbance intensity. Vegetative and regeneration traits were considered. A similar study was performed in a nearby agricultural landscape (Kleyer 1999). The logistic regression models from the urban landscape were applied to the data set of the agricultural landscape and vice versa. Although the overall environment of the two landscapes was very different, recurrent patterns of several functional types were found. At high fertility and high disturbance levels, annual species predominated with a persistent seed bank, high seed output, and short vertical expansion. When disturbances changed from below-ground to above-ground, the sexual regeneration mode was replaced by the vegetative mode, while vertical expansion remained low. At medium disturbance intensities, the vertical expansion and vegetative regeneration increased with fertility, while the seed bank remained mostly transient to short-term persistent and lateral expansion and sexual regeneration was intermediate. At low disturbances and low resource supplies, seed bank longevity, and vertical and lateral expansion tended to be long. Diversity of groups of plants with similar attributes was highest at intermediate disturbance levels and low fertility. These results correspond with Grime's humped-back model and Connell's intermediate disturbance hypothesis. [source]

Half a Century of Public Software Institutions: Open Source as a Solution to Hold-Up Problem

JOURNAL OF PUBLIC ECONOMIC THEORY, Issue 4 2010
MICHAEL SCHWARZ
We argue that the intrinsic inefficiency of proprietary software has historically created a space for alternative institutions that provide software as a public good. We discuss several sources of such inefficiency, focusing on one that has not been described in the literature: the underinvestment due to fear of hold-up. An inefficient hold-up occurs when a user of software must make complementary investments, when the return on such investments depends on future cooperation of the software vendor, and when contracting about a future relationship with the software vendor is not feasible. We also consider how the nature of the production function of software makes software cheaper to develop when the code is open to the end users. Our framework explains why open source dominates certain sectors of the software industry (e.g., programming languages), while being almost non existent in some other sectors (e.g., computer games). We then use our discussion of efficiency to examine the history of institutions for provision of public software from the early collaborative projects of the 1950s to the modern "open source" software institutions. We look at how such institutions have created a sustainable coalition for provision of software as a public good by organizing diverse individual incentives, both altruistic and profit-seeking, providing open source products of tremendous commercial importance, which have come to dominate certain segments of the software industry. [source]

How about alternatives to phthalate plasticizers?

JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2003
Leonard G. Krauskopf
Phthalate plasticizers have historically served as the preferred plasticizers to impart flexibility to PVC and several other polar polymers. They provide a desirable balance of cost and performance properties. Their acceptable and safe use is unmatched in medical appliances, food processing, and packaging applications, as well as in many other end uses. Potential alternatives do not have the historical record of acceptable performance found with phthalate plasticizers. Nevertheless, the "Precautionary Principle" has caused certain segments of society to clamor for alternates to phthalate plasticizers. This paper reviews known "non-phthalate" plasticizers and provides comparisons to the traditional "General Purpose" (GP) phthalate plasticizers; "General Purpose" plasticizers are those that impart optimum overall performance properties in PVC at lowest cost. [source]

Death at the Border: Efficacy and Unintended Consequences of US Immigration Control Policy

POPULATION AND DEVELOPMENT REVIEW, Issue 4 2001
Wayne A. Cornelius
This article assesses the efficacy of the strategy of immigration control implemented by the US government since 1993 in reducing illegal entry attempts, and documents some of the unintended consequences of this strategy, especially a sharp increase in mortality among unauthorized migrants along certain segments of the Mexico,US border. The available data suggest that the current strategy of border enforcement has resulted in rechanneling flows of unauthorized migrants to more hazardous areas, raising fees charged by people-smugglers, and discouraging unauthorized migrants already in the US from returning to their places of origin. However, there is no evidence that the strategy is deterring or preventing significant numbers of new illegal entries, particularly given the absence of a serious effort to curtail employment of unauthorized migrants through worksite enforcement. An expanded temporary worker program, selective legalization of unauthorized Mexican workers residing in the United States, and other proposals under consideration by the US and Mexican governments are unlikely to reduce migrant deaths resulting from the current strategy of border enforcement. [source]

Fluid Geoanalysis in the Chinese Continental Scientific Drilling Project

GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2 2004
Liqiang Luo
fluides; géochimie; analyse en ligne; analyse in situ; forage scientifique continental chinois Mass spectrometry and chromatography were used in the on-line and in situ analysis of fluids in the Chinese continental scientific drilling project. The drilling processes and mud have great effects on the identification of fluids. After considering the effects of air components and artefacts on the deep fluids, we have found that in some segments, helium, methane and carbon dioxide are the main gas components that should originate from the deep Earth. The correlations among gas components are discussed and the fluid profiles in the hole are presented. La spectrométrie de masse et la chromatographie ont été utilisées pour l'analyse in situ et en ligne de fluides dans le cadre d'un projet scientifique de forage continental chinois. Les techniques de forage et la boue ont des effets importants sur l'identification des fluides. Après avoir étudié les effets liés aux composants de l'air et les artefacts dans les fluides profonds, nous avons découvert que, dans certains segments, l'hélium, le méthane et le gaz carbonique étaient les gaz principaux dont l'origine était profonde. Les corrélations entre les composants gazeux sont discutées et les profils des fluides dans le forage sont présentés. [source]

The co-optation of squatters in Amsterdam and the emergence of a movement meritocracy: a critical reply to Pruijt

INTERNATIONAL JOURNAL OF URBAN AND REGIONAL RESEARCH, Issue 3 2004
Justus Uitermark
This article explains how and why the relationship between the Amsterdam squatter movement and the local government has changed over the last decade. Besides reassessing Pruijt's analysis of the Amsterdam squatter movement in a recent issue of this journal, the article also engages with the post-Fordist literature on social movements. This literature is largely based on the assumption that a subversive identity is incompatible with co-optation. However, as such ,soft factors' as culture gain more importance in urban growth strategies, it is likely that some segments of urban movements may become co-opted while retaining their subversive identity. It is hypothesized that we are witnessing the emergence of a movement meritocracy: with the rise of soft neoliberal urban policies, the way in which the local polity delivers incentives follows an increasingly discriminatory pattern, giving a place to those segments that contribute to the cultural vibrancy of the city whilst ignoring segments that struggle for basic provisions. These processes are probably not peculiar to Amsterdam and there is an urgent need for post-Fordist and other social movement theory to investigate what are the consequences of these shifts for government-movement interactions. Comment et pourquoi la relation entre le mouvement des squatters d'Amsterdam et le gouvernement local a-t-elle changé au cours de la dernière décennie? Outre l'examen de l'analyse qu'a faite Pruijt du mouvement des squatters d'Amsterdam dans un récent numéro de cette revue, l'article s'appuie sur la littérature post-fordiste des mouvements sociaux. Celle-ci se fonde surtout sur l'hypothèse qu'une identité subversive est incompatible avec une cooptation. Or, comme les ,facteurs intangibles' tels que la culture prennent de l'importance dans les stratégies d'expansion urbaine, il est probable que certains segments des mouvements urbains pourront être cooptés tout en gardant leur nature subversive. On suppose l'apparition d'une méritocratie des mouvements: avec l'essor des politiques urbaines néolibérales de compromis, la manière dont le gouvernement local propose des mesures d'incitation suit un modèle de plus en plus discriminatoire, donnant une place aux segments qui contribuent à la vibration culturelle de la ville, tout en ignorant ceux qui luttent pour des services de base. Les processus n'étant sans doute pas propres à Amsterdam, il est urgent que les théories des mouvements sociaux, post-fordistes ou autres, étudient les conséquences de ces changements dans les interactions entre gouvernement et mouvements. [source]