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General Validity (general + validity)
Selected AbstractsMagnetic susceptibility: Further insights into macroscopic and microscopic fields and the sphere of LorentzCONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003C.J. Durrant Abstract To make certain quantitative interpretations of spectra from NMR experiments carried out on heterogeneous samples, such as cells and tissues, we must be able to estimate the magnetic and electric fields experienced by the resonant nuclei of atoms in the sample. Here, we analyze the relationships between these fields and the fields obtained by solving the Maxwell equations that describe the bulk properties of the materials present. This analysis separates the contribution to these fields of the molecule in which the atom in question is bonded, the "host" fields, from the contribution of all the other molecules in the system, the "external" fields. We discuss the circumstances under which the latter can be found by determining the macroscopic fields in the sample and then removing the averaged contribution of the host molecule. We demonstrate that the results produced by the, so-called, "sphere of Lorentz" construction are of general validity in both static and time-varying cases. This analytic construct, however, is not "mystical" and its justification rests not on any sphericity in the system but on the local uniformity and isotropy, i.e., spherical symmetry, of the medium when averaged over random microscopic configurations. This local averaging is precisely that which defines the equations that describe the macroscopic fields. Hence, the external microscopic fields, in a suitably averaged sense, can be estimated from the macroscopic fields. We then discuss the calculation of the external fields and that of the resonant nucleus in NMR experiments. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 18A: 72,95, 2003 [source] Virulence evolution via host exploitation and toxin production in spore-producing pathogensECOLOGY LETTERS, Issue 4 2002Troy Day Many pathogens produce resilient free-living propagules that allow their dissemination in the absence of direct contact between susceptible and infected hosts. One might expect pathogens capable of producing such long-lived propagules to evolve high levels of virulence because their reproductive success is de-coupled from the survival of their host. Despite some comparative data supporting this prediction, theory has questioned its general validity. I present theoretical results that incorporate two transmission routes neglected by previous theory: death-mediated propagule production and direct host-host transmission. This theory predicts that spore-producing pathogens should evolve high levels of virulence under quite broad conditions. Moreover, a novel prediction of this theory is that the production of propagules can generate selection for the evolution of pathogen characteristics such as toxins whose sole function is to kill the host. This latter result reveals an unanticipated mechanism through which virulence is expected to evolve in spore-producing pathogens. [source] Dietary specialization and infochemical use in carnivorous arthropods: testing a conceptENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2003Johannes L. M. Steidle Abstract For the location of hosts and prey, insect carnivores (i.e., parasitoids or predators) often use infochemical cues that may originate from the host/prey itself but also from the food of the host/prey, a food plant, or another feeding substrate. These cues can be either specific for certain host/prey complexes or generally present in various complexes, and the reaction of the carnivores to these cues is either innate or learned. According to the concept on dietary specialization and infochemical use in natural enemies, the origin and specificity of the infochemical cues used and the innateness of the behavioural response are dependent on the degree of dietary specialization of the carnivore and its host/prey species. This concept has been widely adopted and has been frequently cited since its publication. Only few studies, however, have been explicitly designed to test predictions of the concept. Thus, more than 10 years after publication and despite of its broad acceptance, the general validity of the concept is still unclear. Using data from about 140 research papers on 95 species of parasitoids and predators, the present literature study comparatively scrutinises predictions from the concept. In accordance with the concept, learning to react to infochemicals and the use of general host and host plant cues was more often found in generalists than in specialists. In addition, more specialists were using specific infochemicals than generalists. In contrast to the concept, however, there was no significant difference between specialists and generalists in the proportion of carnivore species that use infochemicals during foraging and also extreme generalists are using infochemical cues for foraging. Likewise, an innate reaction to infochemicals was found in both specialists and generalists. Several reasons why infochemical use, including an innate reaction to infochemicals, is adaptive in generalist carnivores are discussed . We conclude that the concept has been a useful paradigm in advancing the chemical ecology of arthropod carnivores, but needs to be modified: the use of infochemicals is expected in all arthropod carnivores, regardless of dietary specialization. [source] A mode II weight function for subsurface cracks in a two-dimensional half-spaceFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2002A. MAZZÙ ABSTRACT The general properties of a mode II Weight Function for a subsurface crack in a two-dimensional half-space are discussed. A general form for the WF is proposed, and its analytical expression is deduced from the asymptotic properties of the displacements field near the crack tips and from some reference cases obtained by finite elements models. Although the WF has general validity, the main interest is on its application to the study of rolling contact fatigue: its properties are explored for a crack depth range within which the most common failure phenomena in rolling contact are experimentally observed, and for a crack length range within the field of short cracks. The accuracy is estimated by comparison with several results obtained by FEM models, and its validity in the crack depth range explored is shown. [source] Application of possibility theory in the life-cycle inventory assessment of biofuelsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2002Raymond R. Tan Abstract Data uncertainty issues have constrained the widespread acceptance of life-cycle analysis (LCA) and related methods. This is particularly important in the LCA of fuels due to the wide range of available feedstocks and processing options. Despite recent attempts at standardization, there remain persistent doubts about the general validity of LCA results, often due to uncertainties about data quality. This paper demonstrates the application of possibility theory as a tool for handling life-cycle inventory data imprecision for the case of the net energy balance of coconut methyl ester (CME) as a biodiesel transport fuel. Results derived using a possibililistic computation are contrasted with those arrived at by probabilistic (Monte Carlo) simulation. The two approaches yield comparable results but possibilistic modelling offers significant advantages with respect to computational efficiency. The net energy balance of CME is estimated to be approximately 36 MJ kg,1, significantly higher than the 28 MJ kg,1 net energy typical of rapeseed oil methyl ester (RME) relevant to the U.K. Copyright © 2002 John Wiley & Sons, Ltd. [source] Phenotypic comparison of periodontal ligament cells in vivo and in vitroJOURNAL OF PERIODONTAL RESEARCH, Issue 2 2001P. Lekic The mammalian periodontal ligament contains heterogeneous populations of connective tissue cells, the precise function of which is poorly understood. Despite close proximity to bone and the application of high amplitude physical forces, cells in the periodontal ligament (PL) are capable of expressing regulatory factors that maintain PL width during adult life. The study of PL homeostasis and PL cell differentiation requires culture and phenotypic methods for precise characterization of PL cell populations, in particular those cells with an inherently osteogenic program. Currently it is unknown if cells cultured from the PL are phenotypically similar to the parental cells that are present in the tissues. We have compared the phenotype of cells in vivo with cells derived from the PL and expanded in vitro to assess the general validity of in vitro models for the study of phenotypic regulation in vivo. Rat PL cells were isolated by either scraping the root of the extracted first mandibular molars (Group A), or by scraping the alveolar socket following extraction of first mandibular molars (Group B), or by obtaining a mixture of cells after disaggregating a block of tissue consisting of first mandibular molar, PL and the surrounding alveolar bone (Group C). Cultured cells at confluence were fixed and immunostained for ,-smooth muscle actin (,-SMA), osteopontin (OPN), alkaline phosphatase (AP), or bone sialoprotein (BSP). For in vivo assessments, frontal sections of rat first mandibular molar were immunostained for ,-SMA, OPN, AP and BSP. We examined osteogenic differentiation of cultured PL cell cultures by bone nodule-forming assays. In vivo and at all examined sites, >68% of PL cells were immunostained for AP; ,50% and ,51% for OPN and ,-SMA (p=0.3), respectively, while only ,8% were positively stained for BSP (p<0.01). Analysis of cultured PL cells in Groups A, B and C showed 54%, 53% and 56% positive staining for ,-SMA respectively; 51%, 56%, 54% for OPN; 66%, 70%, 69% for AP and 2.2%, 1.4% and 2.8% for BSP. The mean percentage of PL cells in situ stained for the different markers was similar to that of cultured PL cells (Group A,Group B,Group C in situ for p>0.2) except for BSP which was 3 to 4 fold higher in vivo(p<0.01). PL cell cultures treated with dexamethasone showed mineralized tissue formation for all groups (A, B, C), but no mineralized tissue formation was detected in the absence of dexamethasone. As PL cells express quantitatively similar phenotypes in vitro and in vivo, we conclude that the in vitro models used here for assessment of PL cell differentiation appear to be appropriate and are independent of the cell sampling method. Further, dexamethasone-dependent progenitors are present both on the root and bone-related sides of the PL. [source] Biodiversity effects on ecosystem functioning: emerging issues and their experimental test in aquatic environmentsOIKOS, Issue 3 2004Paul S. Giller Recent experiments, mainly in terrestrial environments, have provided evidence of the functional importance of biodiversity to ecosystem processes and properties. Compared to terrestrial systems, aquatic ecosystems are characterised by greater propagule and material exchange, often steeper physical and chemical gradients, more rapid biological processes and, in marine systems, higher metazoan phylogenetic diversity. These characteristics limit the potential to transfer conclusions derived from terrestrial experiments to aquatic ecosystems whilst at the same time provide opportunities for testing the general validity of hypotheses about effects of biodiversity on ecosystem functioning. Here, we focus on a number of unique features of aquatic experimental systems, propose an expansion to the scope of diversity facets to be considered when assessing the functional consequences of changes in biodiversity and outline a hierarchical classification scheme of ecosystem functions and their corresponding response variables. We then briefly highlight some recent controversial and newly emerging issues relating to biodiversity-ecosystem functioning relationships. Based on lessons learnt from previous experimental and theoretical work, we finally present four novel experimental designs to address largely unresolved questions about biodiversity-ecosystem functioning relationships. These include (1) investigating the effects of non-random species loss through the manipulation of the order and magnitude of such loss using dilution experiments; (2) combining factorial manipulation of diversity in interconnected habitat patches to test the additivity of ecosystem functioning between habitats; (3) disentangling the impact of local processes from the effect of ecosystem openness via factorial manipulation of the rate of recruitment and biodiversity within patches and within an available propagule pool; and (4) addressing how non-random species extinction following sequential exposure to different stressors may affect ecosystem functioning. Implementing these kinds of experimental designs in a variety of systems will, we believe, shift the focus of investigations from a species richness-centred approach to a broader consideration of the multifarious aspects of biodiversity that may well be critical to understanding effects of biodiversity changes on overall ecosystem functioning and to identifying some of the potential underlying mechanisms involved. [source] Evaluation of three methods for the measurement of crystallinity of pet resins, preforms, and bottlesPOLYMER ENGINEERING & SCIENCE, Issue 11 2000Z. Bashir The control of crystallization is important at all processing stages of the PET bottle industry, from the manufacture of bottle resins to the fabrication of preforms and bottles. In this work, we sought to evaluate critically three methods of crystallinity measurement. We have used density, Differential Scanning Calorimetry (DSC), and Modulated Differential Scanning Calorimetry (MDSC) to study the crystallinity of PET chips, preforms, and bottles. The accuracy, precision, and general validity of each technique and the problems of interpretation are discussed. [source] Private tax collection,remnant of the past or a way forward?PUBLIC ADMINISTRATION & DEVELOPMENT, Issue 4 2006Evidence from rural Uganda Abstract This article examines the growing role and impacts of private tax collection under fiscal decentralisation in Uganda. Based on evidence from six rural councils, three aspects of privatised tax collection are examined: (i) the impact on the nature of fiscal corruption; (ii) the problem of overzealous collection; and (iii) the challenge of assessing revenue potentials. While possibly meeting short-term demands for local revenue growth and stability, the present form of private tax collection appears to transform the nature of fiscal corruption by reducing corruption at collection point and transferring the problem into the district administration. Moreover, while the charge of overzealousness permeates historical and theoretical work on privatised tax collection, the Ugandan experience casts doubt on its general validity. Instead, perverse distributional effects are the most likely cause of deteriorating state-citizen relations in rural Uganda. Finally, the article considers the merit of the prediction of private collection as a preferred contractual choice for certain indirect taxes, suggesting that problems of asymmetric information in assessing the revenue yields of most rural markets are exaggerated. Copyright © 2006 John Wiley & Sons, Ltd. [source] ENHANCEMENTS, EASY SHORTCUTS, AND THE RICHNESS OF HUMAN ACTIVITIESBIOETHICS, Issue 7 2008MAARTJE SCHERMER ABSTRACT One argument that is frequently invoked against the technological enhancement of human functioning is that it is morally suspect, or even wrong, to take an easy shortcut. Some things that usually take effort, endurance or struggle can come easily with the use of an enhancer. This paper analyses the various arguments that circle round the idea that enhancement of human functioning is problematic because of the ,easy shortcut' that it offers. It discusses the concern that quick fixes lead to corrosion of character and the idea that suffering, pain, hard work and effort are essential for real and worthy achievements, and argues that these views are largely mistaken. Next, the paper argues that the core worry about taking an easy shortcut is that it makes us lose sight of the complexities of our means and ends; in other words, the argument warns against reducing the richness of human activities. A vocabulary of ,practices', ,internal goods' and ,focal engagement' will be used to articulate this argument further. The conclusion is that the easy shortcut argument has no general validity as an argument against enhancement ,as such'. The paper urges us, however, to evaluate enhancement technologies not only in terms of their efficiency in reaching certain goals but also in terms of their contribution to intrinsically worthwhile human activities. It can point out some of the caveats, as well as the opportunities, of the use of enhancement technologies. [source] Vertical product differentiation and the import demand function: theory and evidenceCANADIAN JOURNAL OF ECONOMICS, Issue 2 2002Jim Malley In this paper we use a model of vertical product differentiation to cast doubt on the general validity of the import demand function as specified in macroeconomic models. The empirical importance of our theoretical concerns is then established. According to our first hypothesis, the share of a good's imports in total imports is non-increasing in domestic wages if the country has comparative advantage in high-quality varieties of this good. The second hypothesis states that the share of a good's imports is increasing in non-wage domestic income if the country has comparative advantage in high-quality varieties of this good. JEL Classification: F4, F41 Différenciation verticale des produits et fonction de demande d'importations : théorie et résultats. Dans ce mémoire, les auteurs utilisent un modèle de différenciation verticale des produits pour jeter certains doutes sur la validité générale de la fonction de demande d'importations telle que spécifiée dans les modèles macroéconomiques. L'importance empirique de ces malaises théoriques est étudiée à l'aide de deux hypothèses. La première hypothèse suggère que la part d'un bien dans les importations totales d'un pays ne va pas croître quand les salaires du pays s'accroissent si le pays a un avantage comparatif dans les variétés de haute qualité de ce bien. La seconde hypothèse suggère que la part d'un produit qui provient de l'importation croît quand le revenu intérieur non-salarial s'accroît si le pays a un avantage comparatif dans les variétés de haute qualité de ce bien. On observe des résultats qui donnent un support empirique ferme à ces deux propositions en analysant les données en provenance de l'Allemagne, du Japon et des Etats-Unis. [source] Comparability of three-dimensional optic disc imaging with different techniquesACTA OPHTHALMOLOGICA, Issue 1 2000A study with confocal scanning laser tomography, raster tomography ABSTRACT. Purpose: We wanted to compare optic nerve head topography measurements and discrimination between normal and glaucomatous eyes with two entirely different three-dimensional optic disc imaging techniques, confocal scanning laser tomography (Heidelberg Retina Tomograph, Heidelberg Engineering) and raster tomography (Glaucoma-Scope, Ophthalmic Imaging Systems). Methods: Both eyes of 225 normal subjects and 229 eyes of 166 patients with glaucoma at different stages were imaged with the Heidelberg Retina Tomograph and the Glaucoma-Scope. Optics discs were analysed in 15° sectors around the circumference. Depth measurements were calibrated on objects with known dimensions. Results: We observed no significant differences in absolute measurements of maximum cup depth and cup area between the two instruments. We observed small differences in absolute measurements of disc anti rim area between the two instruments. Discrimination between normal and glaucomatous eyes was close to identical for the two instruments. Both instruments had the same ability to distinguish glaucomatous regional alterations of optic nerve head topography from normal disc configuration. Conclusion: Both instruments while using entirely different principles for three-dimensional optic disc imaging gave very similar results. This correspondence of results implies that the same optic disc parameters can be analysed, and the results interpreted similarly for both methods, and probably with other three-dimensional imaging instruments. It may also indicate that results of studies with one of the instruments have general validity. [source] | |||||||||||||||||||