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Background Conditions (background + condition)

Distribution by Scientific Domains

Life Sciences	33%
Humanities and Social Sciences	22%
Earth and Environmental Science	22%

Selected Abstracts

Contribution of voltage-gated sodium channels to the b-wave of the mammalian flash electroretinogram

THE JOURNAL OF PHYSIOLOGY, Issue 10 2008
Deb Kumar Mojumder
Voltage-gated sodium channels (Nav channels) in retinal neurons are known to contribute to the mammalian flash electroretinogram (ERG) via activity of third-order retinal neurons, i.e. amacrine and ganglion cells. This study investigated the effects of tetrodotoxin (TTX) blockade of Nav channels on the b-wave, an ERG wave that originates mainly from activity of second-order retinal neurons. ERGs were recorded from anaesthetized Brown Norway rats in response to brief full-field flashes presented over a range of stimulus energies, under dark-adapted conditions and in the presence of steady mesopic and photopic backgrounds. Recordings were made before and after intravitreal injection of TTX (,3 ,m) alone, 3,6 weeks after optic nerve transection (ONTx) to induce ganglion cell degeneration, or in combination with an ionotropic glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 200 ,m) to block light-evoked activity of inner retinal, horizontal and OFF bipolar cells, or with the glutamate agonist N -methyl- d -aspartate (NMDA, 100,200 ,m) to reduce light-evoked inner retinal activity. TTX reduced ERG amplitudes measured at fixed times corresponding to b-wave time to peak. Effects of TTX were seen under all background conditions, but were greatest for mesopic backgrounds. In dark-adapted retina, b-wave amplitudes were reduced only when very low stimulus energies affecting the inner retina, or very high stimulus energies were used. Loss of ganglion cells following ONTx did not affect b-wave amplitudes, and injection of TTX in eyes with ONTx reduced b-wave amplitudes by the same amount for each background condition as occurred when ganglion cells were intact, thereby eliminating a ganglion cell role in the TTX effects. Isolation of cone-driven responses by presenting test flashes after cessation of a rod-saturating conditioning flash indicated that the TTX effects were primarily on cone circuits contributing to the mixed rod,cone ERG. NMDA significantly reduced only the additional effects of TTX on the mixed rod,cone ERG observed under mesopic conditions, implicating inner retinal involvement in those effects. After pharmacological blockade with CNQX, TTX still reduced b-wave amplitudes in cone-isolated ERGs indicating Nav channels in ON cone bipolar cells themselves augment b-wave amplitude and sensitivity. This augmentation was largest under dark-adapted conditions, and decreased with increasing background illumination, indicating effects of background illumination on Nav channel function. These findings indicate that activation of Nav channels in ON cone bipolar cells affects the b-wave of the rat ERG and must be considered when analysing results of ERG studies of retinal function. [source]

Ethnic Inequalities in the Public Sector: A Comparative Analysis

DEVELOPMENT AND CHANGE, Issue 2 2006
Yusuf Bangura
This article uses empirical data to discuss the links between ethnicity, inequality and governance in a framework that divides countries according to their levels of ethnic polarization. It makes three main arguments. First, types of diversity, not the existence of diversity per se, explain potentials for conflict or cohesion in multiethnic societies. Ethnic cleavages are configured differently in different social structures and are less conflictual in some countries than in others. Second, relative balance has been achieved in the public sectors of countries that are highly fragmented or those with ethnicity-sensitive policies, but not in those with ethnicity-blind policies. Third, the article is critical of institutional approaches to conflict management that underplay background conditions in shaping choices. Consociational arrangements may not be relevant in unipolar ethnic settings or fragmented multiethnic societies, where governments may be ethnically inclusive under democratic conditions. They seem unavoidable in ethnic settings with two or three main groups or in settings with strong ethnic/regional clusters. [source]

Environmental links to reduced tropical cyclogenesis over the south-east Caribbean

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2007
Alexandros P. Georgiadis
Abstract Tropical cyclone formation over the Caribbean is not evenly distributed across the basin. Previous work identified the south-western sector as the area that dominates the hurricane activity of the whole basin. The south-eastern sector, in contrast, exhibits a distinct suppression in cyclogenesis. This study seeks to identify the restricting factors that differentiate the cyclogenesis climatology in the south-east Caribbean. It is based on statistical analysis of eight environmental variables using principal component analysis. The first three components are examined in detail. The first component, accounting for 31.7% of the variance within the data, differentiates the Caribbean from the rest of the subtropical Atlantic, primarily in terms of an increased thermodynamic potential for cyclogenesis and enhanced atmospheric humidity in the boundary layer. The second component, accounting for 31% of the variance, marks the south-west Caribbean as the only sub-region within the area of analysis where the easterlies curve southwards and the relative vorticity is cyclonic. The third component, accounting for 20.3% of the variance, differentiates the South Caribbean from the rest of the Atlantic, indicating it to be a region of increased spatial variation in the intensity of the easterlies and in absolute vorticity. The variance of cyclogenesis within the Caribbean is greatest along the second and third components. Thus, the genesis pattern in the basin is likely associated with the low-level wind-field and absolute vorticity. The divergence of the flow, when combined with the vorticity of the wind-field over the Caribbean, renders the background conditions of the eastern sector less prone to developing disturbances than is the case in the western Caribbean. Copyright © 2006 Royal Meteorological Society [source]

Agricultural Biotechnology and Regime Formation: A Constructivist Assessment of the Prospects

INTERNATIONAL STUDIES QUARTERLY, Issue 4 2002
William D. Coleman
Controversies surrounding the appropriate use and diffusion of agricultural biotechnologies are giving rise to questions about governance at the international level. This article investigates the likelihood that a single, international regime or multiple regimes governing this technology will form by way of negotiation. We show that four normative,institutional arrangements, organized around distinct general principles, have a potential governance role: world food security and safety, liberalized trade, protection of intellectual property, and conservation and sustainable use of biodiversity. We argue that an adequate amount of compatibility between the principles and norms of these arrangements is required to support the type of communicative action or truth,seeking needed to develop the intersubjective understanding for a regime. Using a framework for assessing normative compatibility, we find not one, but two nascent understandings rooted in the trade and biodiversity areas competing to form the foundation for governance. Further analysis of levels of institutional density between the two developing regimes reveals they are presently too low to support a negotiated resolution of normative conflict. Finally, we demonstrate that recent framing attempts at the international level to decrease areas of tension and incompatibility in principles/norms between the regimes have neglected to create the crucial normative background conditions needed to avert a scenario of increased political conflict in the near future. [source]

The Odyssey of Senior Public Service: What Memoirs Can Teach Us

PUBLIC ADMINISTRATION REVIEW, Issue 1 2003
J. Patrick Dobel
This article examines the political, psychological, and moral challenges of senior public service in the executive office. The study uses memoirs published by members of the Clinton administration. The memoirs discuss the consistent background conditions of senior public service as the personality of the chief executive, the vagaries of election cycles, the tension between staff and agency executives, and the role of the media. Senior executives adopt a number of stances to address the tension between the realities of public service and the ideals they bring. The memoirs suggest several stances, such as politics as original sin, seduction, hard work and compromise, and game. The memoirs demonstrate the high cumulative cost that public service exacts on the health and personal lives of senior officials. Finally, the study reveals a number of consistent themes about how senior appointed public officials can navigate the dilemmas and challenges of senior public service at all levels of government. [source]

Contribution of voltage-gated sodium channels to the b-wave of the mammalian flash electroretinogram

The response of the coupled tropical ocean,atmosphere to westerly wind bursts

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 579 2002
Alexey V. Fedorov
Abstract Two different perspectives on El Niño are dominant in the literature: it is viewed either as one phase of a continual southern oscillation (SO), or alternatively as the transient response to the sudden onset of westerly wind bursts (WWBs). Occasionally those bursts do indeed have a substantial effect on the SO,the unusual strength of El Niño of 1997/98 appears to be related to a sequence of bursts,but frequently the bursts have little or no impact. What processes cause some bursts to be important, while others remain insignificant? The question is addressed by using a simple coupled tropical ocean,atmosphere model that simulates a continual, possibly attenuating, oscillation to study the response to WWBs. The results show that the impact of WWBs depends crucially on two factors: (i) the background state of the system as described by the mean depth of the thermocline and intensity of the mean winds, and (ii) the timing of the bursts with respect to the phase of the SO. Changes in the background conditions alter the sensitivity of the system, so that the impact of the bursts on El Niño may be larger during some decades than others. Changes in the timing of WWBs affect the magnitude and other characteristics of the SO by modifying the energetics of the ocean,atmosphere interactions. A reasonable analogy is a swinging pendulum subject to modest blows at random times,those blows can either magnify or diminish the amplitude, depending on their timing. It is demonstrated that a WWB can increase the strength of El Niño significantly, if it occurs 6 to 10 months before the peak of warming, or can reduce the intensity of the subsequent El Niño, if it occurs during the cold phase of the continual SO. Copyright © 2002 Royal Meteorological Society. [source]

Spectroscopy of solar neutrinos

ASTRONOMISCHE NACHRICHTEN, Issue 5 2010
M. Wurm
Abstract In the last years, liquid-scintillator detectors have opened a new window for the observation of low-energetic astrophysical neutrino sources. In 2007, the solar neutrino experiment Borexino began its data-taking in the Gran Sasso underground laboratory. High energy resolution and excellent radioactive background conditions in the detector allow the first-time spectroscopic measurement of solar neutrinos in the sub-MeV energy regime. The experimental results of the Beryllium 7 neutrino flux measurements (Arpesella et al. 2008b) as well as the prospects for the detection of solar Boron 8, pep and CNO neutrinos are presented in the context of the currently discussed ambiguities in solar metallicity. In addition, the potential of the future SNO+ and LENA experiments for high-precision solar neutrino spectroscopy will be outlined (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Trophic-dynamic considerations in relating species diversity to ecosystem resilience

BIOLOGICAL REVIEWS, Issue 3 2000
KRIS H. JOHNSON
ABSTRACT Complexity in the networks of interactions among and between the living and abiotic components forming ecosystems confounds the ability of ecologists to predict the economic consequences of perturbations such as species deletions in nature. Such uncertainty hampers prudent decision making about where and when to invest most intensively in species conservation programmes. Demystifying ecosystem responses to biodiversity alterations may be best achieved through the study of the interactions allowing biotic communities to compensate internally for population changes in terms of contributing to ecosystem function, or their intrinsic functional redundancy. Because individual organisms are the biologically discrete working components of ecosystems and because environmental changes are perceived at the scale of the individual, a mechanistic understanding of functional redundancy will hinge upon understanding how individuals' behaviours influence population dynamics in the complex community setting. Here, I use analytical and graphical modelling to construct a conceptual framework for predicting the conditions under which varying degrees of interspecific functional redundancy can be found in dynamic ecosystems. The framework is founded on principles related to food web successional theory, which provides some evolutionary insights for mechanistically linking functional roles of discrete, interacting organisms with the dynamics of ecosystems because energy is the currency both for ecological fitness and for food web commerce. Net productivity is considered the most contextually relevant ecosystem process variable because of its socioeconomic significance and because it ultimately subsumes all biological processes and interactions. Redundancy relative to productivity is suggested to manifest most directly as compensatory niche shifts among adaptive foragers in exploitation ecosystems, facilitating coexistence and enhancing ecosystem recovery after disturbances which alter species' relative abundances, such as extinctions. The framework further explicates how resource scarcity and environmental stochasticity may constitute ,ecosystem legacies' influencing the emergence of redundancy by shaping the background conditions for foraging behaviour evolution and, consequently, the prevalence of compensatory interactions. Because it generates experimentally testable predictions for a priori hypothesis testing about when and where varying degrees of functional redundancy are likely to be found in food webs, the framework may be useful for advancing toward the reliable knowledge of biodiversity and ecosystem function relations necessary for prudent prioritization of conservation programmes. The theory presented here introduces explanation of how increasing diversity can have a negative influence on ecosystem sustainability by altering the environment for biotic interactions - and there by changing functional compensability among biota - under particular conditions. [source]