Home  About us  Contact
 

Practical Limits (practical + limit)

Distribution by Scientific Domains
Humanities and Social Sciences33%

Selected Abstracts

Practical limits of resolution in confocal and non-linear microscopy

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2004
Guy Cox
Abstract Calculated and measured resolution figures are presented for confocal microscopes with different pinhole sizes and for nonlinear (2-photon and second harmonic) microscopes. A modest degree of super-resolution is predicted for a confocal microscope but in practice this is not achievable and confocal fluorescence gives little resolution improvement over widefield. However, practical non-linear microscopes do approach their theoretical resolution and therefore show no resolution disadvantage relative to confocal microscopes in spite of the longer excitation wavelength. Microsc. Res. Tech. 63:18,22, 2004. © 2003 Wiley-Liss, Inc. [source]

Assessment of the nitrogen status of grassland

GRASS & FORAGE SCIENCE, Issue 2 2004
A. Farruggia
Abstract Two types of diagnostics are used for N management in grasslands: diagnostics based on N concentration of shoots and diagnostics based on soil mineral N. The Nitrogen Nutrition Index (NNI) is an example of the first type. However, its evaluation requires the determination of shoot dry weight per unit area and, thus, constitutes a practical limit to its utilization in the context of farm studies. In order to simplify its evaluation, a method based on the N concentration of the upper sward layer (Nup) has been proposed. The objectives of this study were to test the relationship between NNI and Nup in the context of permanent grassland and to examine the relationship between Nup and soil mineral status. The study was conducted as two experiments, one on small cut-plots receiving contrasting rates of mineral N fertilization, and a second on plots of an existing field-scale lysimeter experiment. In each plot and at several dates, shoot biomass within quadrats was measured, N concentration was determined on the upper leaves and on the entire shoots, and mineral nitrogen of the soil below the vegetation sampled was determined. N concentration of the upper lamina layer of the canopy was linearly related to the NNI determined on the entire shoots. Therefore, determining N concentration in leaves at the top of canopy appears to be an alternative means to evaluate NNI without having to measure shoot biomass. The absence of an overall significant correlation between soil mineral N content and sward N index, observed over the two studies, indicates that each of these two indicators has to be considered specifically in relation to the objective of the diagnostic procedure. As sward N index may vary independently of soil mineral N content, the sward N indicator does not appear to be a suitable indicator for diagnosis of environmental risks related to nitrate leaching. However, soil mineral N content does not allow the prediction of sward N status and thus is not a suitable indicator of sward growth rate. Although soil mineral N content is an important environmental indicator for nitrate-leaching risks during potential drainage periods, it has a limited diagnosis value with respect to the herbage production function of grasslands. [source]

Managing very large distributed data sets on a data grid

CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 11 2010
Miguel Branco
Abstract In this work we address the management of very large data sets, which need to be stored and processed across many computing sites. The motivation for our work is the ATLAS experiment for the Large Hadron Collider (LHC), where the authors have been involved in the development of the data management middleware. This middleware, called DQ2, has been used for the last several years by the ATLAS experiment for shipping petabytes of data to research centres and universities worldwide. We describe our experience in developing and deploying DQ2 on the Worldwide LHC computing Grid, a production Grid infrastructure formed of hundreds of computing sites. From this operational experience, we have identified an important degree of uncertainty that underlies the behaviour of large Grid infrastructures. This uncertainty is subjected to a detailed analysis, leading us to present novel modelling and simulation techniques for Data Grids. In addition, we discuss what we perceive as practical limits to the development of data distribution algorithms for Data Grids given the underlying infrastructure uncertainty, and propose future research directions. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Napoleon and the Universal Monarchy

HISTORY, Issue 319 2010
PHILIP DWYER
Although the idea of ,Universal Monarchy' has existed since the early middle ages, the term started to be used pejoratively from the sixteenth century onwards. This article looks at the manner in which contemporaries perceived Napoleon's actions on the international scene, and how they used the term in relation to his foreign policy. Most of Europe's political elite believed that Napoleon was bent on some sort of ,universal domination', and that it was not limited to Europe. That perception was a direct result of an aggressive, expansionist French foreign policy. Napoleon's intentions, on the other hand, are more ambiguous. While at times he adopted a rhetoric which informed contemporary fears, the practical limits to his foreign policy were such that ,Universal Monarchy' could never be anything more than an ephemeral dream. [source]

Identification of hemes and related cyclic tetrapyrroles by matrix-assisted laser desorption/ionization and liquid secondary ion mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2002
Hyung-Sun Youn
Mass spectrometry has proven to be a powerful technique applicable on trace amounts for the identification of known hemes and cyclic tetrapyrroles, and for providing critical information for the structure of new and novel versions. This report describes investigations of the practical limits of detection for such bioinorganic prosthetic groups, primarily by liquid secondary ion mass spectrometry (LSIMS) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), including a survey of the utility of common matrices. The lower limit of detection under favorable conditions extends to low picomole amounts. Certain derivatization techniques, such as methyl esterification and chelation to zinc, both increase the sensitivity of analyses and provide spectroscopic signatures that enable heme/cyclic tetrapyrrole ions to be identified in the presence of contaminants. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Science against modernism: the relevance of the social theory of Michael Polanyi

THE BRITISH JOURNAL OF SOCIOLOGY, Issue 1 2001
Charles Thorpe
ABSTRACT Science, as an institution, is widely taken by sociologists to exemplify the modern tendency towards vesting trust and authority in impersonal offices and procedures, rather than in embodied human individuals. Such views of science face an important challenge in the social philosophy of Michael Polanyi. His work provides important insights into the continuing role of embodied personal authority and tradition in science and, hence, in late modernity. I explicate Polanyi's relevance for social theory, through a comparison with Weber's essay ,Science as a Vocation'. An understanding of the personal dimensions of trust and authority in science suggests practical limits to the position of Giddens on the disembedding of social relations and on the scepticism and reflexivity of modernity. [source]