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Theoretical Work (theoretical + work)

Distribution by Scientific Domains

Life Sciences	20%
Humanities and Social Sciences	17%
Chemistry	15%
Business, Economics, Finance and Accounting	14%
Physics and Astronomy	10%
Medical Sciences	6%
Psychology	4%
Polymers and Materials Science	4%
Earth and Environmental Science	3%
2 Other Domains	7%

Distribution within Life Sciences

Ecology & Organismal Biology	30%
Evolutionary Biology	20%

Kinds of Theoretical Work

previous theoretical work

recent theoretical work

Selected Abstracts

Survey of Theoretical Work for the Proposed HEDgeHOB Experimental Schemes: HIHEX and LAPLAS

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 4-5 2007
N. A. Tahir
Abstract This paper presents a review of the theoretical work that has resulted in a scientific proposal on studies of High-Energy-Density (HED) states in matter using intense beams of energetic heavy ions that will be available at the future Facility for Antiprotons and Ion Research (FAIR) at Darmstadt [W.F. Henning, Nucl. Inst. Meth B 24 (2003) 725-729]. The proposal is named HEDgeHOB that stands for High Energy Density Matter Generated by Heavy Ion Beams. Two experimental schemes have been worked out for the HEDgeHOB experimental proposal, namely, HIHEX and LAPLAS. The first scheme allows for studies of HED states by isochoric and uniform heating of matter by an intense heavy ion beam that is followed by isentropic expansion of the heated material. Numerical simulations have shown that using the beam parameters that will be available at the FAIR, one can access all the interesting physical states of HED matter including an expanded hot liquid state, twophase liquid-gas region, critical point parameters and strongly coupled plasmas for all the materials of interest. The second scheme involves a low-entropy compression of a test material like hydrogen that is enclosed in a cylindrical shell of a high-Z material like gold or lead. The target can be driven by a hollow or a circular beam. This compression scheme relies on multiple shock reflection between the hydrogen-gold (lead) boundary and the cylinder axis. The hydrodynamic stability of the LAPLAS target has also been analyzed that shows that the implosion is completely stable to Rayleigh-Taylor and Richtmyer-Meshkov instabilities. LAPLAS implosion using a hollow beam is suitable for studying the problem of hydrogen metallization whereas the one employing a circular focal spot leads to physical conditions that are expected to exist in the interiors of the giant planets. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

2003 Nobel Prize in Physics for Theoretical Work on Superfluid 3He

CHEMPHYSCHEM, Issue 7 2004
Anthony J. Leggett Prof.
Abstract The element helium comes in two (stable) forms,4He and3He; at low temperatures and pressures both form liquids rather than solids. The liquid phase of the common isotope,4He, was realized nearly a century ago, and since 1938 has been known to show, at temperatures below about 2 K, the property of superfluidity,the ability to flow through the narrowest capillaries without apparent friction. The light isotope,3He, is believed to be of quite a different nature; however,because of its similarity to the electrons in metals, which at low temperatures sometimes form "Cooper pairs" and thereby become superconducting, theorists in the 1960s and early 1970s had speculated that something similar might happen in liquid3He, which would then also show superfluidity though for reasons rather different than4He. In 1972 nuclear magnetic resonance (NMR) experiments at Cornell University revealed the existence, below 3 millidegrees, if two new phases, one of which displayed extraordinary NMR properties. Anthony Leggett is one of the theorists who succeeded in fitting the experimental properties into the "Cooper-pairing" scenario; in particular, he explained the NMR behavior and predicted further novel NMR phenomena which were subsequently found. [source]

The ecology of virulence

ECOLOGY LETTERS, Issue 10 2006
Curtis M. Lively
Abstract Theoretical work has shown that parasites should evolve intermediate levels of virulence. Less attention has been given to the ecology of virulence. Here I explore population-dynamic models of infection in an annual host. The infection does not kill the host; but it can decrease the number of offspring produced by the host, and the magnitude of this effect depends on host population size. Hence, ,virulence' is density dependent, and is defined here as the difference in birth rates between uninfected and infected hosts, divided by the birth rate of uninfected hosts. The results suggest that infection can be highly virulent at the host's equilibrium density, even though the parasite has no effect on the host's intrinsic birth rate. The results also suggest that parasites may help to stabilize host population dynamics. In general, the impact of infection may be underestimated in natural populations. [source]

Becoming Deliberative Citizens: The Moral Learning Process of the Citizen Juror

POLITICAL STUDIES, Issue 4 2010
Shane Doheny
This article presents an analysis of qualitative interviews carried out with citizen jurors at least three years after they participated in a jury. Theoretical work on deliberation tends to emphasise the transformative effect of deliberation. Much empirical work has focused on this transformation conceived as the re-prioritisation of preferences, and examines whether and how jurors change their personal and political commitments as a result of their participation on a jury. Another approach to transformation is more discursive, and hypothesises that the concepts and perspectives that jurors use to evaluate norms may also be transformed. This article presents qualitative data that illuminate this latter hypothesis. Specifically, the article analyses the stories ex-jurors told of their participation in citizen juries, in order to chart changes in the concepts and perspectives that jurors use to evaluate norms. By analysing these stories we identify four juror roles , envoy, regulator, advocate and deliberator , and we elaborate these using Habermas' learning theory. Overall our argument is that the citizen juror is given the opportunity to undertake a learning process, and through this process they are furnished with new concepts and perspectives with which to evaluate norms. Moreover, Habermas theorises that this learning process cumulates with the formation of a deliberative citizen who thinks using the characteristics described in discourse ethics. Here we identify discourses that support this claim. [source]

Regioselectivity Control in the Metal-Catalyzed Functionalization of ,-Allenols, Part,2: Theoretical Study,

CHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2009
Benito Alcaide Prof.
Abstract Calculating cyclization: Theoretical work directed towards the elucidation of the mechanisms of the gold-, palladium-, and lanthanum-catalyzed oxycyclizations (5- exo versus 6- endo versus 7- endo) of ,-allenols has been pursued in close relationship with the experimental study (Part,1, accompanying paper) and has corroborated the bench results to provide a complete study of the reactivity of ,-allenols under different metal-catalyzed conditions. The gold-, palladium- and lanthanum-catalyzed oxycyclization reactions of azetidin-2-one-tethered ,-allenol derivatives to a variety of fused enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines have been developed experimentally (Part,1, accompanying paper). The mechanisms of these regiocontrolled metal-catalyzed heterocyclization reactions have now been computationally explored at the DFT level (Part,2). The energies of the reaction intermediates and transition states for different possible pathways have been calculated in various model systems very close to the real system. Additionally, we selected the La[N(SiH3)2]3 complex to simulate the lanthanide amide precatalyst species. The agreement of theoretically predicted and experimentally observed selectivities is very good in all cases La reacción de heterociclación de , -alenoles catalizada por metales es un proceso regiocontrolado que da lugar a una amplia variedad de tetrahidrofuranos, tetrahidropiranos y tetrahidrooxepinas fusionadas enantiopuras, que contienen además un anillo ,-lactámico, que es la unidad estructural clave en productos biológicos relevantes como antibióticos e inhibidores enzimáticos. Se ha llevado a cabo un estudio teórico para la elucidación de los mecanismos de estas ciclaciones catalizadas por oro, paladio y lantano, en estrecha relación con el trabajo experimental (Parte,1, artículo anterior), corroborando los resultados obtenidos en el laboratorio. [source]

Using Population Count Data to Assess the Effects of Changing River Flow on an Endangered Riparian Plant

CONSERVATION BIOLOGY, Issue 4 2006
DIANE M. THOMSON
análisis de viabilidad poblacional; gestión ribereña; método de difusión; presas; riesgo de extinción Abstract:,Methods for using simple population count data to project extinction risk have been the focus of much recent theoretical work, but few researchers have used these approaches to address management questions. We analyzed 15 years of census data on the federally endangered endemic riparian plant Pityopsis ruthii (Small) with the diffusion approximation (DA). Our goals were to evaluate relative extinction risk among populations in two different watersheds (in Tennessee, U.S.A.) and potential effects of variation in managed river flow on population dynamics. Populations in both watersheds had high projected risks of extinction within 50 years, but the causes of this risk differed. Populations of P. ruthii on the Hiwassee River had higher initial population sizes but significantly lower average growth rates than those on the Ocoee River. The only populations with low predicted short-term extinction risk were on the Ocoee. Growth rates for populations on both rivers were significantly reduced during periods of lower river flow. We found only marginal evidence of a quadratic relationship between population performance and flow. These patterns are consistent with the idea that low flows affect P. ruthii due to growth of competing vegetation, but the degree to which very high flows may reduce population growth is still unclear. Simulations indicated that populations were most sensitive to growth rates in low-flow years, but small changes in the frequency of these periods did not strongly increase risk for most populations. Consistent with results of other studies, DA estimates of extinction risk had wide confidence limits. Still, our results yielded several valuable insights, including the need for greater monitoring of populations on the Hiwassee and the importance of low-flow years to population growth. Our work illustrates the potential value of simple methods for analyzing count data despite the challenges posed by uncertainty in estimates of extinction risk. Resumen:,Los métodos que utilizan datos de conteos simples de la población para proyectar el riesgo de extinción han sido el foco reciente de mucho trabajo teórico, pero pocos investigadores han utilizado estos métodos para responder preguntas de gestión. Analizamos 15 años de datos de censos de la planta ribereña, endémica y federalmente en peligro Pityopsis ruthii (Small) mediante el método de difusión. Nuestras metas fueron evaluar el riesgo de extinción de poblaciones en dos cuencas hidrológicas distintas y con dos efectos potenciales de la variación del flujo de agua sobre la dinámica de la población. Las poblaciones en ambas cuencas tenían alto riesgo de extinción proyectado a 50 años, pero las causas de este riesgo difirieron. Las poblaciones de P. ruthii en el Río Hiwassee tuvieron poblaciones iniciales más grandes, pero tasas de crecimiento significativamente menores, que las poblaciones en el Río Ocoee. Las únicas poblaciones con bajo riesgo de extinción pronosticado estaban en el Ocoee. Las tasas de crecimiento de las poblaciones en ambos ríos se redujeron significativamente durante períodos de bajo flujo en el río. Sólo encontramos evidencia marginal de la relación cuadrática entre el funcionamiento de la población y el flujo. Estos patrones son consistentes con la idea de que los bajos flujos afectan a P. ruthii debido al crecimiento de vegetación competitiva, pero aun no es claro el grado en que flujos muy grandes pueden reducir el crecimiento poblacional. Las simulaciones indicaron que las poblaciones son más sensibles a las tasas de crecimiento en años con bajo flujo en los ríos, pero pequeños cambios en la frecuencia de esos períodos no aumentaron el riesgo en la mayoría de las poblaciones. Consistentemente con los resultados de otros estudios, las estimaciones del riesgo de extinción mediante el método de difusión tienen amplios límites de confianza. Aun así, nuestros resultados aportaron varios conocimientos valiosos, incluyendo la necesidad de mayor monitoreo de las poblaciones en el Hiwassee y la importancia para el crecimiento poblacional de los años con bajo flujo. Nuestro trabajo ilustra el valor potencial de métodos sencillos de análisis de datos de conteo a pesar de los retos impuestos por la incertidumbre en las estimaciones del riesgo de extinción. [source]

Survey of Theoretical Work for the Proposed HEDgeHOB Experimental Schemes: HIHEX and LAPLAS

Corporate socially responsible (CSR) practices in the context of Greek industry

CORPORATE SOCIAL RESPONSIBILITY AND ENVIRONMENTAL MANAGEMENT, Issue 1 2003
Dr Constantina Bichta
This paper sets out to describe the level of corporate environmental responsibility of the Greek industrial sector. While the level of corporate socially responsible behaviour has been widely explored in the context of Northern European industry, the theoretical work surrounding the level of CSR practices of Greek industry is underdeveloped. A qualitative study was designed to increase awareness about the level of environmental responsibility of two Greek firms, which represented the chemical/fertilizer and metal sectors. The empirical findings suggest that a number of factors, both internal and external, determine the level of environmental policy and performance of the two companies. The environmental policy of the companies appears also to relate to the sector of operation. The paper concludes that the Greek business actor should look at his workforce in order to accelerate the environmental activities of the organization. With regard to the theory of CSR, it is argued that the development of a model of CSR is aided by the study and identification of factors that support and/or undermine the socially responsible behaviour of the European corporate sector. Copyright © 2003 John Wiley & Sons, Ltd. and ERP Environment. [source]

The effect of bidirectional flow on tidal channel planforms

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2004
Sergio Fagherazzi
Abstract Salt marsh tidal channels are highly sinuous. For this project, ,eld surveys and aerial photographs were used to characterize the planform of tidal channels at China Camp Marsh in the San Francisco Bay, California. To model the planform evolution, we assume that the topographic curvature of the channel centreline is a key element driving meander migration. Extraction of curvature data from a planimetric survey, however, presents certain problems because simple calculations based on equally distanced points on the channel axis produce numerical noise that pollutes the ,nal curvature data. We found that a spline interpolation and a polynomial ,t to the survey data provided us with a robust means of calculating channel curvature. The curvature calculations, combined with data from numerous cross-sections along the tidal channel, were used to parameterize a computer model. With this model, based on recent theoretical work, the relationship between planform shape and meander migration as well as the consequences of bidirectional ,ow on planform evolution have been investigated. Bank failure in vegetated salt marsh channels is characterized by slump blocks that persist in the channel for several years. It is therefore possible to identify reaches of active bank erosion and test model predictions. Our results suggest that the geometry and evolution of meanders at China Camp Marsh, California, re,ect the ebb-dominated regime. Copyright © 2004 John Wiley & Sons, Ltd. [source]

The spatial spread of invasions: new developments in theory and evidence

ECOLOGY LETTERS, Issue 1 2005
Alan Hastings
Abstract We review and synthesize recent developments in the study of the spread of invasive species, emphasizing both empirical and theoretical approaches. Recent theoretical work has shown that invasive species spread is a much more complex process than the classical models suggested, as long range dispersal events can have a large influence on the rate of range expansion through time. Empirical work goes even further, emphasizing the role of spatial heterogeneity, temporal variability, other species, and evolution. As in some of the classic work on spread, the study of range expansion of invasive species provides unique opportunities to use differences between theory and data to determine the important underlying processes that control spread rates. [source]

Income Variance Dynamics and Heterogeneity

ECONOMETRICA, Issue 1 2004
Costas Meghir
Recent theoretical work has shown the importance of measuring microeconomic uncertainty for models of both general and partial equilibrium under imperfect insurance. In this paper the assumption of i.i.d. income innovations used in previous empirical studies is removed and the focus of the analysis is placed on models for the conditional variance of income shocks, which is related to the measure of risk emphasized by the theory. We first discriminate amongst various models of earnings determination that separate income shocks into idiosyncratic transitory and permanent components. We allow for education- and time-specific differences in the stochastic process for earnings and for measurement error. The conditional variance of the income shocks is modelled as a parsimonious ARCH process with both observable and unobserved heterogeneity. The empirical analysis is conducted on data drawn from the 1967,1992 Panel Study of Income Dynamics. We find strong evidence of sizeable ARCH effects as well as evidence of unobserved heterogeneity in the variances. [source]

A Combined Theoretical and Experimental Research Project into the Aminolysis of ,-Lactam Antibiotics: The Importance of Bifunctional Catalysis

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2003
Natalia Díaz
Abstract This paper reports the results of experimental work on the aminolysis of penicillin (6-APA) and monobactam (aztreonam) antibiotics by propylamine or ethanolamine. In general, aztreonam is slightly more reactive than 6-APA, despite the common assumption that the amide bond should be less activated in monobactams. Intriguingly, when ethanolamine acts as the nucleophile, the corresponding rate law has a kinetic term proportional to [RNH2][RNH3+]. To complement the experimental observations, the rate-determining free energy barriers in aqueous solution for various mechanistic pathways were computed by standard quantum chemical methodologies. From previous theoretical work it was assumed that the aminolysis of ,-lactams proceeds through mechanisms in which either a water molecule or a second amine molecule may act as bifunctional catalysts, assisting proton transfer from the attacking amine molecule to the leaving amino group. The energy barriers as computed have moderate values (ca. 26,34 kcal·mol,1) and reproduce most of the experimentally observed kinetic trends. Furthermore, the calculations predict that positively charged ethanolamine molecules can act as bifunctional catalysts as well, thus explaining the presence of the kinetic term proportional to [RNH2][RNH3+] in the rate law. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

ALLEE EFFECT AND SELF-FERTILIZATION IN HERMAPHRODITES: REPRODUCTIVE ASSURANCE IN DEMOGRAPHICALLY STABLE POPULATIONS

EVOLUTION, Issue 12 2004
Pierre-Olivier Cheptou
Abstract The fact that selfing increases seed set (reproductive assurance) has often been put forward as an important selective force for the evolution of selfing. However, the role of reproductive assurance in hermaphroditic populations is far from being clear because of a lack of theoretical work. Here, I propose a theoretical model that analyzes selffertilization in the presence of reproductive assurance. Because reproductive assurance directly influences the per capita growth rate, I developed an explicit demographic model for partial selfers in the presence of reproductive assurance, specifically when outcrossing is limited by the possibility of pollen transfer (Allee effect). Mating system parameters are derived as a function of the underlying demographical parameters. The functional link between population demography and mating system parameters (reproductive assurance, selfing rate) can be characterized. The demographic model permits the analysis of the evolution of self-fertilization in stable populations when reproductive assurance occurs. The model reveals some counterintuitive results such as the fact that increasing the fraction of selfed ovules can, in certain circumstances, increase the fraction of outcrossed ovules. Moreover, I demonstrate that reproductive assurance per se cannot account for the evolution of stable mixed selfing rates. Also, the model reveals that the extinction of outcrossing populations depends on small changes in population density (ecological perturbations), while the transition from outcrossing to selfing can, in certain cases, lead the population to extinction (evolutionary suicide). More generally, this paper highlights the fact that self-fertilization affects both the dynamics of individuals and the dynamics of selfing genes in hermaphroditic populations. [source]

Why we're still arguing about the Pleistocene occupation of the Americas

EVOLUTIONARY ANTHROPOLOGY, Issue 2 2007
Nicole M. Waguespack
Abstract Although empirical issues surround the when, how, and who questions of New World colonization, much of current debate hinges on theoretical problems because it has become clear that our understanding of New World colonization is not resolute.1 In fact, the central issues of debate have remained essentially unchanged for the last eighty years. The now classic and probably incorrect story of New World colonization begins in Late Pleistocene Siberia, with small a population of foragers migrating across Beringia (,13,500 calendar years before present (CYBP) (Box 1) through an ice-free corridor and traveling through the interior of North America. High mobility and rapid population growth spurred southward expansion into increasingly distant unoccupied regions, culminating in the settlement of the Southern Cone of South America. Armed with the skills and weapons needed to maintain a megafauna-based subsistence strategy, early colonists necessarily had the adaptive flexibility to colonize a diverse array of Pleistocene landscapes. For a time, this scenario seemed well substantiated. The earliest sites in South America were younger than their northern counterparts, fluted artifacts were found across the Americas within a brief temporal window, and projectile points capable of wounding elephant-sized prey were commonly found in association with proboscidean remains. The Bering Land Bridge connecting Asia to Alaska and an ice-free corridor providing passage between the Pleistocene ice masses of Canada seemed to provide a clear route of entry for Clovis colonists. However, recent archeological, paleoenvironmental, biological, and theoretical work largely questions the plausibility of these events. [source]

Simplified yet highly accurate enzyme kinetics for cases of low substrate concentrations

FEBS JOURNAL, Issue 19 2009
Hanna M. Härdin
Much of enzyme kinetics builds on simplifications enabled by the quasi-steady-state approximation and is highly useful when the concentration of the enzyme is much lower than that of its substrate. However, in vivo, this condition is often violated. In the present study, we show that, under conditions of realistic yet high enzyme concentrations, the quasi-steady-state approximation may readily be off by more than a factor of four when predicting concentrations. We then present a novel extension of the quasi-steady-state approximation based on the zero-derivative principle, which requires considerably less theoretical work than did previous such extensions. We show that the first-order zero-derivative principle, already describes much more accurately the true enzyme dynamics at enzyme concentrations close to the concentration of their substrates. This should be particularly relevant for enzyme kinetics where the substrate is an enzyme, such as in phosphorelay and mitogen-activated protein kinase pathways. We illustrate this for the important example of the phosphotransferase system involved in glucose uptake, metabolism and signaling. We find that this system, with a potential complexity of nine dimensions, can be understood accurately using the first-order zero-derivative principle in terms of the behavior of a single variable with all other concentrations constrained to follow that behavior. [source]

Beam to String Transition of Vibrating Carbon Nanotubes Under Axial Tension

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009
Xianlong Wei
Abstract State-of-the-art nanoelectromechanical systems have been demonstrated in recent years using carbon nanotube (CNT) based devices, where the vibration of CNTs is tuned by tension induced through external electrical fields. However, the vibration properties of CNTs under axial tension have not been quantitatively determined in experiments. Here, a novel in situ method for precise and simultaneous measurement of the resonance frequency, the axial tension applied to individual CNTs and the tube geometry is demonstrated. A gradual beam-to-string transition from multi-walled CNTs to single-walled CNTs is observed with the crossover from bending rigidity dominant regime to extensional rigidity dominant regime occur much larger than that expected by previous theoretical work. Both the tube resonance frequency under tension and transition of vibration behavior from beam to string are surprisingly well fitted by the continuum beam theory. In the limit of a string, the vibration of a CNT is independent of its own stiffness, and a force sensitivity as large as 0.25,MHz (pN),1 is demonstrated using a 2.2,nm diameter single-walled CNT. These results will allow for the designs of CNT resonators with tailored properties. [source]

A Micro-Simulation Approach to Modelling Spatial Unemployment Disparities

GROWTH AND CHANGE, Issue 3 2010
DAVID PHILIP MCARTHUR
ABSTRACT This paper aims to construct a comprehensive model capable of simulating spatial unemployment disparities. The key feature of the model is that it simultaneously deals with commuting and migration. Much of the existing literature simply models one adjustment mechanism at a time. This paper adopts a micro-simulation approach to build a model which can deal with equilibrium and disequilibrium unemployment disparities in a context where commuting and migration are possible. The model is then used to demonstrate the importance of considering both types of flows and to guide future empirical and theoretical work in the area. [source]

Electronic and Magnetic Properties of SrTiO3/LaAlO3 Interfaces from First Principles

ADVANCED MATERIALS, Issue 26-27 2010
Hanghui Chen
Abstract A number of intriguing properties emerge upon the formation of the epitaxial interface between the insulating oxides LaAlO3 and SrTiO3. These properties, which include a quasi two-dimensional conducting electron gas, low temperature superconductivity, and magnetism, are not present in the bulk materials, generating a great deal of interest in the fundamental physics of their origins. While it is generally accepted that the novel behavior arises as a result of a combination of electronic and atomic reconstructions and growth-induced defects, the complex interplay between these effects remains unclear. In this report, we review the progress that has been made towards unraveling the complete picture of the SrTiO3/LaAlO3 interface, focusing primarily on present ab initio theoretical work and its relation to the experimental data. In the process, we highlight some key unresolved issues and discuss how they might be addressed by future experimental and theoretical studies. [source]

Lesions of the mammillary body region alter hippocampal movement signals and theta frequency: Implications for path integration models

HIPPOCAMPUS, Issue 9 2008
Patricia E. Sharp
Abstract Cells throughout the hippocampal formation are involved in processing spatial information. These same cells also show an influence of locomotor activity, and these movement signals are thought to be critical for the path integration abilities of these cells. Nuclei in the mammillary region provide ascending influences to the hippocampal formation and have been implicated in influencing both hippocampal spatial and theta signals. Here, we report the effects of mammillary lesions on movement-related signals in several hippocampal subregions. We find first, as predicted by earlier work, these lesions cause an approximately 1 Hz reduction in the frequency of theta modulation of cell firing. According to recent theoretical work, this might, in turn, be expected to influence the size of hippocampal place fields. Our data do not confirm this prediction for any of the hippocampal regions examined. Second, we report lesion effects on the relationship between firing rate and running speed for the hippocampal cells. These lesions caused a reduction in both the slope and intercept of rate-by-speed functions for cells in the hippocampus and postsubiculum. Surprisingly, cells in subiculum showed an opposite effect, so that the excitatory influence of locomotion was enhanced. Path integration theories predict that the speed at which path integration occurs is related to the strength of this movement signal. In remarkable accordance with this prediction, we report that the timing of the place cell signals is slowed following mammillary lesions for hippocampal and postsubicular cells, but, in contrast, is speeded up for subicular cells. In fact, the timing for place signals across lesion condition and brain region is predicted by a single linear function which relates timing to the strength of the running speed signal. Thus, these data provide remarkable support for some aspects of current path integration theory, while posing a challenge for other aspects of these same theories. © 2008 Wiley-Liss, Inc. [source]

Expressing the Not-Said: Art and Design and the Formation of Sexual Identities

INTERNATIONAL JOURNAL OF ART & DESIGN EDUCATION, Issue 1 2005
Nicholas Addison
Central to this paper is an analysis of the work produced by a year 10 student in response to the ,Expressive Study' of the art and design GCSE (AQA 2001). I begin by examining expressivism within art education and turn to the student's work partly to understand whether the semi-confessional mode she chose to deploy is encouraged within this tradition. The tenets of expressivism presuppose the possibility that through the practice of art young people might develop the expressive means to give ,voice' to their feelings and come to some understanding of self. I therefore look at the way she took ownership of the ,expressive' imperative of the title by choosing to explore her emerging lesbian identity and its position within the normative, binary discourses on sex and sexual identity that predominate in secondary schools. Within schooling there is an absence of formal discussion around sex, sexual identity and sexuality other than in the context of health and moral education and, to some extent, English. This is surprising given the emphasis on self-exploration that an art and design expressive study would seem to invite. In order to consider the student's actions as a situated practice I examine the social and cultural contexts in which she was studying. With reference to visual semiotics and the theoretical work of Judith Butler, I interpret the way she uses visual resources not only to represent her emerging sexual identity but to counter dominant discourses around homosexuality in schools. I claim that through her art practice she enacts the ,name of the law' to refute the binary oppositions that underpin sex education in schools. This act questions the assumptions about the purpose of expressive activities in art education with its psychologically inflected rhetoric of growth and selfhood and offers a mode of expressive practice that is more socially engaged and communicative. [source]

Sensitivity of the southern African circulation to dipole sea-surface temperature patterns in the south Indian Ocean

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2002
C. J. C. Reason
Abstract Previous observational work suggests that when sea-surface temperature (SST) is warm (cool) in the southwest Indian Ocean and cool (warm) in the southeast Indian Ocean, increased (decreased) summer rains may occur over large areas of southeastern Africa. In this study, an atmospheric general circulation model is used to investigate the sensitivity of the regional circulation and rainfall over southern Africa to these dipole SST anomalies in the subtropical south Indian Ocean. When the model is forced with positive SST anomalies in the west and negative SST anomalies in the east, increased rainfall occurs over southeastern Africa as a result of the enhanced convergence of moister than average air over the region. Enhanced evaporation occurs over the warm pole in the southwest Indian Ocean and this moist air is advected towards southeastern Africa as a result of the low-pressure anomaly generated over this pole, which strengthens the onshore flow. Increased and more intense extra-tropical cyclones occur to the southeast of South Africa, favourable for tropical,temperate trough formation. When the SST poles are reversed in sign, decreased precipitation occurs over southeastern Africa as a result of increased low-level divergence of low-level flow and this flow being drier than average. Weaker and fewer extra-tropical cyclones occur southeast of South Africa in this case. The model results are sensitive to the proximity of the southwest Indian Ocean pole to southeastern Africa. There is also sensitivity in the model low-level wind changes and precipitation anomaly over low-latitude southern Africa (but not over South Africa to any significant extent) to the presence or absence of the SST pole over the southeast Indian Ocean. Although the model resolution does not capture the details of the local SST and topographic gradients as well as one would like, the changes in model circulation and precipitation in the experiments with different SST anomalies are consistent with previous observational and theoretical work, hence increasing confidence in the robustness of the results. Copyright © 2002 Royal Meteorological Society [source]

Two-Level Security Management and the Prospects for New Democracies: A Simulation Analysis

INTERNATIONAL STUDIES QUARTERLY, Issue 3 2000
Marc V. Simon
Most new democracies face serious internal, ethnic/separatist conflicts; in addition, some face international threats. The literature on the growth of democracy in the global system and its impact on world politics does not fully account for the dual threats all states must address in managing their security. Based on theoretical work by Starr (1994) which describes the "common logic" of conflict processes in war and revolution, we outline a model of how states respond to security threats from both external and internal sources. Using computer simulation, we analyze the model and evaluate the relative importance for state security of factors such as system size, numbers of democracies in the system, extraction/allocation strategy pursued by new democracies, and government legitimacy level. Our results show that new democracies thrive in systems that are predominantly democratic. Also, ally support can provide crucial resources for new democracies facing internal threats. Finally, "endangered" democracies can recover security by attempting to buy off domestic threats rather than deter them, and by improving legitimacy. [source]

Intersubjectivity: Towards a Dialogical Analysis

JOURNAL FOR THE THEORY OF SOCIAL BEHAVIOUR, Issue 1 2010
ALEX GILLESPIE
Intersubjectivity refers to the variety of possible relations between perspectives. It is indispensable for understanding human social behaviour. While theoretical work on intersubjectivity is relatively sophisticated, methodological approaches to studying intersubjectivity lag behind. Most methodologies assume that individuals are the unit of analysis. In order to research intersubjectivity, however, methodologies are needed that take relationships as the unit of analysis. The first aim of this article is to review existing methodologies for studying intersubjectivity. Four methodological approaches are reviewed: comparative self-report, observing behaviour, analysing talk and ethnographic engagement. The second aim of the article is to introduce and contribute to the development of a dialogical method of analysis. The dialogical approach enables the study of intersubjectivity at different levels, as both implicit and explicit, and both within and between individuals and groups. The article concludes with suggestions for using the proposed method for researching intersubjectivity both within individuals and between individuals and groups. [source]

Fatigue in children with long-term conditions: an evolutionary concept analysis

JOURNAL OF ADVANCED NURSING, Issue 8 2009
Margaret McCabe
Abstract Title.,Fatigue in children with long-term conditions: an evolutionary concept analysis. Aim., This paper is a report of a concept analysis of fatigue in children with long-term conditions. Background., There is little research focused on the experience of fatigue in children. Previous work has focused primarily on children living with cancer. It is necessary to clarify and refine the concept, and add to the knowledge base that supports ongoing theoretical work in order to improve the clinical care of children with long-term conditions who experience fatigue. Method., English language literature published from 1989 to 2007 was searched using the CINAHL, Medline and PsychINFO data bases. Sixty-two papers and two book chapters were used in this concept analysis. Rodgers' method of evolutionary concept analysis was used. This inductive method helps us to view the concept in a sociocultural and temporal context. Findings., The number of publications focusing on fatigue in children is increasing. The analysis yielded two surrogate terms, five attributes, three antecedents and seven consequences. Based on this analysis, fatigue in children with long-term conditions appears to be a subjective experience of tiredness or exhaustion that is multidimensional and includes physical, mental, and emotional aspects. Conclusions., Evidence suggesting children with long-term conditions experience fatigue is increasing, but conceptual gaps remain. This analysis has yielded a view of fatigue in children that illustrates healthcare professionals' limited yet growing awareness of the symptom. Ongoing study as a means to refine our understanding of the concept could potentially lead to important contributions to clinical care of children with long-term conditions. [source]

Academics' perceptions of the professional or clinical doctorate: findings of a national survey

JOURNAL OF CLINICAL NURSING, Issue 12 2007
BSc(Hons), Lorraine Ellis PhD
Aims and objectives., The aim of this study was to report the perceptions of senior academics' working in institutions of higher education towards professional doctorates for the health and social care professions. Background., The professional doctorate is a product of its time introduced for the purpose of developing and improving clinical practice. The extent to which this has been realised, however, has yet to be determined, there being little empirical or theoretical work in this field. This research is an attempt to begin to produce an evidence base in this area by reporting the views of those stakeholders responsible for delivering the curriculum and its intended aim of improving clinical practice. Design., A modified version of illuminative evaluation was designed to map the range of perceptions and intended outcomes of the professional doctorate. Methods., Fifty-five academics from 41 institutions of higher education were telephone interviewed and their perceptions of the professional doctorate elicited, together with a content analysis of the curriculum documents. Results., Academics' views fell into one of three broad categories: enthusiastic, ambivalent and sceptical. Conclusions and relevance to practice., Academics' perceptions of the professional doctorate may have a bearing on whether the stated aim of the curriculum and improvements in clinical practice is realised. Academics are responsible for the recruitment of students and the quality of the educational experience. Respondents' perceptions raise questions about their commitment to professional doctorates relative to PhD, factors that will be considered during stages two and three of this research where the views of students and sponsors will be reported. [source]

A comparison of predicted and experimental vibrational spectra in some small fluorocarbons

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2002
He Jiang
Abstract The vibrational assignments of difluoromethane, cis and trans 1,2-difluoroethylene, trifluoroethylene, 2-fluoropropene, 1,1-difluoroethylene, and tetrafluoroethylene have been reassessed in the light of recent theoretical work. Inconsistent experimental wave number values and assignments have been clarified, and some changes to the experimental assignments are proposed. The assignments compare favorably with recent scaled density functional theory calculations using the hybrid three-parameter B3-PW91 density functional. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 1220,1225, 2002 [source]

Inclusion of biotic stress (consumer pressure) alters predictions from the stress gradient hypothesis

JOURNAL OF ECOLOGY, Issue 6 2009
Christian Smit
Summary 1. ,The stress gradient hypothesis (SGH) predicts a shift from net negative interactions in benign environments towards net positive in harsh environments in ecological communities. While several studies found support for the SGH, others found evidence against it, leading to a debate on how nature and strength of species interactions change along stress gradients, and to calls for new empirical and theoretical work. 2. ,In the latest attempt in this journal, it is successfully argued how the SGH should be expanded by considering different life strategies of species (stress tolerance versus competitive ability) and characteristics of abiotic stress (resource versus non-resource based) over wider stress gradients (opposed to low,high contrasts), but the crucial role of biotic stress by consumers is largely ignored in this refinement. 3. ,We point out that consumers strongly alter the outcome of species interactions in benign and harsh environments, and show how inclusion of consumer-incurred biotic stress alters the predicted outcome of interactions along resource- and non-resource-based stress gradients for stress-tolerant and competitive benefactors and beneficiaries. 4. ,Synthesis. New studies should include stress gradients consisting of both abiotic and biotic components to disentangle their impacts, and to improve our understanding of how species interactions change along environmental gradients. [source]

Temporal and spatial genetic variation in a metapopulation of the annual Erysimum cheiranthoides on stony river banks

JOURNAL OF ECOLOGY, Issue 1 2009
Olivier Honnay
Summary 1Metapopulation dynamics , the recurrent extinction and colonization in spatially discrete habitats , is expected to strongly affect within and between population genetic diversity. So far, however, accounts of true plant metapopulations are extremely scarce. 2We monitored the colonization and extinction dynamics of an assemblage of populations of the annual Erysimum cheiranthoides on stony river banks during three consecutive years. Each year, winter flooding drives some populations to extinction, while vacant banks may become colonized. We describe the dynamics of these ephemeral populations using amplified fragment length polymorphism (AFLP) markers to quantify changes in the metapopulation genetic structure over time, and assessing the direction and relative amount of migration and colonization events. 3Average extinction and colonization rates were high (0.39 and 0.34, respectively). While population genetic differentiation (FST) tripled from 0.06 in 2005 to 0.17 in 2007, total metapopulation genetic diversity remained fairly constant through the years. Genetic assignment analyses allowed assigning more than 50% of the genotyped individuals to populations extant the year before. Colonizing individuals originated from different source populations (, << 1) and there was considerable evidence of upstream seed dispersal. 4The degree and pattern of spatial genetic structure varied between years and was related to variation in the flooding intensity of the Meuse River through the years. Possibly, activation of the soil seed bank also played a role in structuring the genetic make-up of the populations. 5Because migration and colonization events were qualitatively equal, and colonizing individuals originated from different sources, the increase in FST was in agreement with previous theoretical work. Very high migration and colonization rates, and the short monitoring period, may explain why there was no loss of genetic diversity from the metapopulation through recurrent extinction and colonization events. 6Synthesis. This study gives one of the first accounts of the dynamics of a true plant metapopulation. Temporal monitoring of genetic variation gave evidence of extensive and bidirectional seed dispersal, highly variable and increasing genetic differentiation, and rather constant within population genetic diversity. An important suggestion from this research is to include a dormant seed stage in further theoretical work on (meta) population genetics. [source]

Carbon Taxes and Carbon Emissions Trading

JOURNAL OF ECONOMIC SURVEYS, Issue 3 2001
Paul Elkins
This paper surveys the literature on, and examples of current implementation of, carbon taxes and carbon emission permits. It sets out the theoretical basis for these instruments, with special reference to the revenue-recycling and tax interaction effects. This theoretical work concludes that instruments which raise revenue which can be recycled so as to reduce pre-existing distortionary taxes are significantly less costly than those which do not. The paper then reviews the sizable literature on the distributional effects of these instruments, especially with regard to industrial competitiveness and regressive effects on low-income groups, evaluating attempts to mitigate these where they are perceived as unacceptable. The paper concludes that such efforts at mitigation, while possible, can substantially reduce the efficiency benefits of the instruments. The projected costs of carbon taxes depend on a wide range of assumptions. This is still a contested area, but the paper concludes that, on a range of plausible assumptions, these costs need not be high. Finally the paper notes that early evaluations of the environmental effectiveness of carbon taxes have been generally positive. This suggests that, if concern about anthropogenic climate change continues to increase, more countries will introduce carbon taxes and emission permits, with the latter increasingly auctioned. [source]

The Determinants of Organizational Change and Structural Inertia: Technological and Organizational Factors

JOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 4 2002
Massimo G. Colombo
There are a growing body of theoretical work, wide anecdotal evidence, and a few large-scale empirical studies supporting the view that business firms quite rarely change their organizational structure, a phenomenon usually referred to in the literature as structural inertia. The present paper aims to analyze empirically the determinants of structural inertia and organizational change. As far as we know, this work constitutes the first attempt to directly address such issues through econometric estimates based on a large, longitudinal dataset at plant level. For this purpose, we consider changes of the organizational structure within a sample composed of 438 Italian manufacturing plants observed from 1975 to 1996. More precisely, we specify and test a duration model of the likelihood of an individual plant changing the number of hierarchical tiers after a spell r, provided that no change has occurred up to T. We also analyze the direction of change, distinguishing increases from decreases of the number of managerial layers. We consider a set of plant- and industry-specific explanatory variables that are expected to induce or oppose organizational change. The findings show that the adoption of advanced manufacturing technologies and new human-resources management practices favors organizational change. On the contrary, the presence of sunk costs and the extent of influence activities figure prominently in explaining structural inertia of business organizations. [source]