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Critical Dependence (critical + dependence)

Distribution by Scientific Domains

Earth and Environmental Science	40%

Selected Abstracts

Reference Minerals for the Microanalysis of Light Elements

GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2-3 2001
M. Darby Dyar
tourmaline; danburite; spodumène; muscovite; isotopes The quantitative determination of light element concentrations in geological specimens represents a major analytical challenge as the electron probe is generally not suited to this task. With the development of new in situ analytical techniques, and in particular the increasing use of secondary ion mass spectrometry, the routine determination of Li, Be and B contents has become a realistic goal. However, a major obstacle to the development of this research field is the critical dependence of SIMS on the availability of well characterized, homogeneous reference materials that are closely matched in matrix (composition and structure) to the sample being studied. Here we report the first results from a suite of large, gem crystals which cover a broad spectrum of minerals in which light elements are major constituents. We have characterized these materials using both in situ and wet chemical techniques. The samples described here are intended for distribution to geochemical laboratories active in the study of light elements. Further work is needed before reference values for these materials can be finalized, but the availability of this suite of materials represents a major step toward the routine analysis of the light element contents of geological specimens. La détermination quantitative des concentrations en éléments légers dans les échantillons géologiques représente un défi analytique majeur, la sonde électronique ne convenant généralement pas pour ce travail. Avec le développement de nouvelles techniques analytiques in situ, en particulier l'utilisation grandissante de la spectrométrie ionique secondaire, la détermination en routine des teneurs en Li, Be et B est devenue un objectif réaliste. Toutefois, un obstacle majeur dans le développement de cette recherche subsiste : la technique SIMS est dépendante de la disponibilité de matériaux de référence bien caractérisés et homogènes proches en composition et en structure de l'échantillon étudié. Nous rapportons ici les premiers résultats obtenus à partie d'un groupe de grands cristaux de qualité gemme recouvrant un large spectre de minéraux composés essentiellement d'éléments légers. Nous avons caractérisé ces matériaux en utilisant à la fois des techniques in situ et par voie humide. Les échantillons décrits ici vont être distribués dans les laboratoires de géochimie spécialisés dans l'étude des éléments légers. Avant la conclusion des valeurs de référence de ces matériaux, des travaux ultérieurs seront nécessaires, mais la disponibilité de l'ensemble de ces matériaux représente une étape importante vers l'analyse en routine des teneurs en éléments légers d'échantillons géologiques. [source]

Governance of Higher Education in Britain: The Significance of the Research Assessment Exercises for the Funding Council Model

HIGHER EDUCATION QUARTERLY, Issue 1 2004
Ted Tapper
This article uses the political struggles that have enveloped the research assessment exercises (RAEs) to interpret the UK's current funding council model of governance. Ironically, the apparently widespread improvement in the research performance of British universities, as demonstrated by RAE 2001, has made it more difficult to distribute research income selectively, which was supposedly the central objective of the whole evaluative process. Whilst enhanced research ratings may be seen as a cause for celebration in the universities, the failure to anticipate this outcome and, more significantly, to plan for its financial implications is seen in political circles as a failure of higher education management. The article explores the alternative models of governance that are likely to emerge as a consequence of this crisis and, in particular, whether the funding councils can have much freedom of action, given the tighter political control of policy goals and their critical dependence upon the academic profession for the conduct of the evaluative process. [source]

The North Atlantic Oscillation and European vegetation dynamics

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2008
Célia Gouveia
Abstract The relationship between vegetation greenness and the North Atlantic Oscillation (NAO) is assessed over Europe. The study covers the 21-year period from 1982 to 2002 and is based on monthly composites of the Normalised Difference Vegetation Index (NDVI) and Brightness Temperature from the Global Inventory Monitoring and Modelling System (GIMMS) as well as on monthly precipitation from the Global Precipitation Climatology Centre (GPCC). A systematic analysis is first performed of point correlation fields over the 21-year period between the winter NAO index and spring and summer NDVI, followed by an assessment of the vegetation response to precipitation and temperature conditions in winter, over two contrasting regions, namely the Iberian Peninsula and Northeastern Europe. Finally, the impact of NAO on vegetation dynamics over the two regions is evaluated by studying the corresponding annual cycles of NDVI and comparing their behaviour for years associated with opposite NAO phases. Over the Iberian Peninsula there is strong evidence that positive (negative) values of winter NAO induce low (high) vegetation activity in the following spring and summer seasons. This feature is mainly associated with the impact of NAO on winter precipitation, together with the strong dependence of spring and summer NDVI on water availability during the previous winter. Northeastern Europe shows a different behaviour, with positive (negative) values of winter NAO inducing high (low) values of NDVI in spring, but low (high) values of NDVI in summer. This behaviour mainly results from the strong impact of NAO on winter temperature, associated with the critical dependence of vegetation growth on the combined effect of warm conditions and water availability during the winter season. Copyright © 2008 Royal Meteorological Society [source]

Lattice modes in a system of charge rotators in a plasma environment

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004
S. V. Vladimirov
Abstract Three dimensional rotatory modes of oscillations in a one-dimensional chain of rod-like charged particles or dust grains in a plasma are investigated. An oscillatory dependence on wavenumber and a critical dependence on the relative strengths of the confining potential is found. The characteristic frequency range for the oscillatory modes is of the order of the dust plasma frequency. The azimuthal and colatitudinal modes show opposite characteristics in the near and far interparticle distance regimes, respectively. The rods are shown to move, or switch to the relevant equilibrium, dependind on the confining parameters. This is an example of a phase change phenomenon which is analogous to that observed in liquid crystals. The ability to line up rods in different directions, by alternating the relative sizes of the confining potentials, is a powerful tool for applications. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Thermotropic Lipid Phase Transition and the Behavior of Hydrolytic Enzymes in the Kidney Cortex Brush Border Membrane

CHEMISTRY & BIODIVERSITY, Issue 10 2006
Sankar
Abstract Functional interactions of lipids and proteins were examined in brush-border membranes isolated from the kidney cortex by studying the temperature dependence of the hydrolytic enzyme activities. A close relationship was observed for the membrane proteins and the thermotropic lipid phase transitions. Three lines of evidences were provided for such dependence: a) Arrhenius relationship of the membrane-bound enzyme activities, and the effect of temperature in native and partially delipidated membranes, b) differential scanning calorimetric study of the membrane lipid phase transitions in the native and delipidated membranes, multilamellar vesicles prepared from the membrane extracted lipids, and in vesicles from dimyristoyl phosphatidylcholine, and c) the excimer (dimer)-formation studies of the membrane extrinsic fluorescent probe, pyrene, and the resultant membrane microviscosity. The brush-border membranes were partially delipidated with BuOH and 2,2,2-trifluoroethanol. The functional interactions of the delipidated membranes, which were greatly lost on lipid removal, were largely restored by the addition of exogenous lipids in the reconstitution process, which indicate the critical dependence of the membrane integral proteins on the neighboring lipid molecules in the bulk lipid phase. [source]