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Spatial Configuration (spatial + configuration)
Selected AbstractsGlobal physicochemical properties as activity discriminants for the mGluR1 subtype of metabotropic glutamate receptorsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2001Marta Filizola Abstract Metabotropic glutamate receptors (mGluRs) are important as candidate therapeutic targets for many neurological disorders. In the present work, the focus has been on the mGluR1 subtype, where agonists have a proconvulsant profile while antagonists exert anticonvulsant activity. Identification of molecular determinants for the inhibition of mGluR1 provides a new avenue for the discovery and development of novel anticonvulsant drugs. Spatial configuration of key groups alone cannot explain activation selectivity at this specific receptor subtype. In fact, all known agonists and antagonists acting at mGluR1 can accommodate the same critical moieties in a similar geometric arrangement that corresponds to the extended conformation of glutamate. Therefore, other factors must account for the differences in activation. This study presents the results of an analysis of a large suite of steric, topological, electrostatic, and thermodynamic molecular properties calculated for a representative set of potent mGluR1 agonists and antagonists. Global steric parameters and the total nonpolar area provide discrimination between the mGluR1 agonists and antagonists considered in the present work. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 2018,2027, 2001 [source] Plant species richness and environmental heterogeneity in a mountain landscape: effects of variability and spatial configurationECOGRAPHY, Issue 4 2006Alexia Dufour The loss of biodiversity has become a matter of urgent concern and a better understanding of local drivers is crucial for conservation. Although environmental heterogeneity is recognized as an important determinant of biodiversity, this has rarely been tested using field data at management scale. We propose and provide evidence for the simple hypothesis that local species diversity is related to spatial environmental heterogeneity. Species partition the environment into habitats. Biodiversity is therefore expected to be influenced by two aspects of spatial heterogeneity: 1) the variability of environmental conditions, which will affect the number of types of habitat, and 2) the spatial configuration of habitats, which will affect the rates of ecological processes, such as dispersal or competition. Earlier, simulation experiments predicted that both aspects of heterogeneity will influence plant species richness at a particular site. For the first time, these predictions were tested for plant communities using field data, which we collected in a wooded pasture in the Swiss Jura mountains using a four-level hierarchical sampling design. Richness generally increased with increasing environmental variability and "roughness" (i.e. decreasing spatial aggregation). Effects occurred at all scales, but the nature of the effect changed with scale, suggesting a change in the underlying mechanisms, which will need to be taken into account if scaling up to larger landscapes. Although we found significant effects of environmental heterogeneity, other factors such as history could also be important determinants. If a relationship between environmental heterogeneity and species richness can be shown to be general, recently available high-resolution environmental data can be used to complement the assessment of patterns of local richness and improve the prediction of the effects of land use change based on mean site conditions or land use history. [source] Landscape issues in plant ecologyECOGRAPHY, Issue 2 2002Sylvie De Blois In the last decade, we have seen the emergence and consolidation of a conceptual framework that recognizes the landscape as an ecological unit of interest. Plant ecologists have long emphasized landscape-scale issues, but there has been no recent attempt to define how landscape concepts are now integrated in vegetation studies. To help define common research paradigms in both landscape and plant ecology, we discuss issues related to three main landscape concepts in vegetation researches, reviewing theoretical influences and emphasizing recent developments. We first focus on environmental relationships, documenting how vegetation patterns emerge from the influence of local abiotic conditions. The landscape is the physical environment. Disturbances are then considered, with a particular attention to human-driven processes that often overrule natural dynamics. The landscape is a dynamic space. As environmental and historical processes generate heterogeneous patterns, we finally move on to stress current evidence relating spatial structure and vegetation dynamics. This relates to the concept of a landscape as a patch-corridor-matrix mosaic. Future challenges involve: 1) the capacity to evaluate the relative importance of multiple controlling processes at broad spatial scale; 2) better assessment of the real importance of the spatial configuration of landscape elements for plant species and finally; 3) the integration of natural and cultural processes and the recognition of their interdependence in relation to vegetation management issues in human landscapes. [source] Black Employment, Segregation, and the Social Organization of Metropolitan Labor MarketsECONOMIC GEOGRAPHY, Issue 3 2007Niki T. Dickerson Abstract: This broad analysis of the employment of blacks in metropolitan areas examines the role of residential segregation in comparison with four other key structural explanations for racial metropolitan inequality: industrial composition, minority concentration, immigration, and the racial disparity in skills. The goal of the analysis was to determine whether the spatial configuration of blacks relative to whites in a metropolitan area influences the employment rates of black men and black women in the context of the structural conditions of the local labor market. The study expanded the analysis of space and work beyond an emphasis on the physical distance between black communities and jobs to a broader conceptualization of residential segregation as a structural feature of the entire metropolitan labor market that is representative of its social organization with regard to race. Using a longitudinal data set of the structural characteristics of the 95 largest U.S. cities from the 1980, 1990, and 2000 decennial censuses, the study used a cross-sectional analysis of the cities in 2000 and a fixed-effects analysis to assess the impact of five dimensions of residential segregation and the four other structural factors on the employment of blacks across different labor markets and across time within each labor market. The results revealed that when the other structural characteristics are controlled, the employment rates of blacks are lower in more segregated cities and decrease as cities become more segregated over time. The clustering and evenness dimensions of residential segregation were the most determinative of black employment. [source] Trade Liberalization and the Geography of Production: Agglomeration, Concentration, and Dispersal in Indonesia's Manufacturing IndustryECONOMIC GEOGRAPHY, Issue 3 2004Örjan Sjöberg Abstract: The effect of the liberalization of trade on the spatial concentration of economic activities is not straightforward. It has been widely argued that protectionism increases spatial concentration as firms locate close to the main domestic markets. However, it has also been argued that an expansion of international trade primarily favors existing industrial centers and therefore leads to increased regional inequalities. Against the background of ongoing debates in both mainstream economics and in geography, we examine the spatial concentration of manufacturing in Indonesia between 1980 and 1996, a period when Indonesia substantially liberalized its trade regime. The high concentration did not decrease during this period, and establishments that engaged in international trade were actually comparably concentrated. We discuss some possible explanations for the spatial concentration in Indonesia and conclude that a host of factors may affect the outcome of trade liberalizations. In particular, the spatial configuration of the national settlement system is a potentially important factor in this regard. [source] Mixing processes in the Amazon River at the confluences of the Negro and Solimões Rivers, Encontro das Įguas, Manaus, BrazilHYDROLOGICAL PROCESSES, Issue 22 2009Alain Laraque Abstract The confluence of the rivers Negro and Solimões gives birth to the Amazon River near Manaus (Brazil). At their confluence, these two rivers with their very different physical and geochemical characteristics provide an interesting example of the mixing of waters along a reach of approximately one-hundred kilometres. The purpose of this article is to describe and explain the spatial configuration of the Solimões,Negro Rivers mixing zone, based on a systematic sampling survey carried out in September 1997, using a special sampler and an acoustic Doppler current profiler (Acoustic Doppler Current Profiler). The waters of the Negro River differ from those of the Solimões River in their lower velocity (0·3 vs 1 m s,1), conductivity (8 vs 80 µS cm,1 at 25 °C), turbidity (5 vs 80 NTU), pH (5·5 vs 7·0) and higher temperatures (by 1 °C). Due to their higher density, the waters of the Solimões River slide under those of the Negro River, and consequently, Negro River waters are located at the surface, close to the left bank, and Solimões River waters are located at the bottom, close to the right bank. The contact between the waters of the two rivers changes from a clearly defined vertical boundary to a diffuse horizontal boundary, as they move downstream. The complete mixing process takes more than 30 h and 100 km. Copyright © 2009 John Wiley & Sons, Ltd. [source] The effects of spatial configuration on preschoolers' attention strategies, selective attention, and incidental learningINFANT AND CHILD DEVELOPMENT, Issue 3 2005Fran C. Blumberg Abstract This study investigated the effects of spatial arrangement on preschool children's selective attention and incidental learning. Three- and four-year old children were shown a multi-coloured box designated as a ,special place' containing miniature chairs and models of animals. One category of objects were designated as relevant and one as irrelevant. Relevant items were placed in each of the apparatus' corners, in the middle of its walls, or in two corners and in the middle of two walls. Findings revealed that children shown relevant items in corners demonstrated the greatest number of correct relocations for relevant items while those shown relevant items in the middle of the walls showed the greatest number of correct relocations for irrelevant items. Findings also suggest that for both age groups, the ability to recall relevant items may have been independent of their ability to demonstrate a selective attention strategy. Copyright © 2005 John Wiley & Sons, Ltd. [source] Geometrically non-linear damage interface based on regularized strong discontinuityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2002Ragnar Larsson Abstract The contribution of this paper concerns the fracture modelling of an interface with a fixed internal material surface in the context of geometrically non-linear kinematics. Typical applications are composite laminates and adhesive/frictional joints in general. In the model development, a key feature is the concept of regularized strong discontinuity, which provides a regular deformation gradient within the interface. The deformation gradient within the interface is formulated in a multiplicative structure with a continuous part and a discontinuous part, whereby the interface deformation is interpreted as a transformation between the material damaged configuration and the actual spatial configuration. In analogy with the continuum formulation of hyper-inelasticity, a constitutive framework is defined for the relation between the induced material traction and the displacement jump vector, which are defined on the material damaged interface configuration. Within this framework, a simple, but yet still representative, model for the delamination problem is proposed on the basis of a damage,plasticity coupling for the interface. The model is calibrated analytically in the large deformation context with respect to energy dissipation in mode I so that a predefined amount of fracture energy is dissipated. The paper is concluded with a couple of numerical examples that display the properties of the interface. Copyright © 2002 John Wiley & Sons, Ltd. [source] Robust diagnosis and fault-tolerant control of distributed processes over communication networksINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8 2009Sathyendra Ghantasala Abstract This paper develops a robust fault detection and isolation (FDI) and fault-tolerant control (FTC) structure for distributed processes modeled by nonlinear parabolic partial differential equations (PDEs) with control constraints, time-varying uncertain variables, and a finite number of sensors that transmit their data over a communication network. The network imposes limitations on the accuracy of the output measurements used for diagnosis and control purposes that need to be accounted for in the design methodology. To facilitate the controller synthesis and fault diagnosis tasks, a finite-dimensional system that captures the dominant dynamic modes of the PDE is initially derived and transformed into a form where each dominant mode is excited directly by only one actuator. A robustly stabilizing bounded output feedback controller is then designed for each dominant mode by combining a bounded Lyapunov-based robust state feedback controller with a state estimation scheme that relies on the available output measurements to provide estimates of the dominant modes. The controller synthesis procedure facilitates the derivation of: (1) an explicit characterization of the fault-free behavior of each mode in terms of a time-varying bound on the dissipation rate of the corresponding Lyapunov function, which accounts for the uncertainty and network-induced measurement errors and (2) an explicit characterization of the robust stability region where constraint satisfaction and robustness with respect to uncertainty and measurement errors are guaranteed. Using the fault-free Lyapunov dissipation bounds as thresholds for FDI, the detection and isolation of faults in a given actuator are accomplished by monitoring the evolution of the dominant modes within the stability region and declaring a fault when the threshold is breached. The effects of network-induced measurement errors are mitigated by confining the FDI region to an appropriate subset of the stability region and enlarging the FDI residual thresholds appropriately. It is shown that these safeguards can be tightened or relaxed by proper selection of the sensor spatial configuration. Finally, the implementation of the networked FDI,FTC architecture on the infinite-dimensional system is discussed and the proposed methodology is demonstrated using a diffusion,reaction process example. Copyright © 2008 John Wiley & Sons, Ltd. [source] Fast gradual matching measure for image retrieval based on visual similarity and spatial relationsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 7 2006Jean-Franēois Omhover In this article, we propose a new method to retrieve images containing a request set of regions. The user is asked to specify a set of regions belonging to a single image. Then this request set of regions is compared to the sets of the regions of the images in the database. We propose a comparison measure that not only evaluates the similarity of regions one to the other, but that also takes into account the spatial configuration of the regions. The spatial structure of the regions is represented by means of fuzzy spatial relations, like horizontal and vertical disposal and connexity. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 711,723, 2006. [source] A compact spin-free combinatoric open-shell coupled cluster theory applied to single-reference doubletsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2008Dipayan Datta Abstract In this article, we present an explicitly spin-free compact coupled cluster (CC) theory for simple open-shell systems, e.g., doublets, biradicals, which can be described either by a single open-shell determinant or by a configuration state function (CSF) which corresponds to a single spatial configuration but is a linear combination of determinants with different spin allocations. A new cluster expansion Ansatz for the wave-operator is introduced, in which the spin-free cluster operators are either of the form of closed-shell-like n hole-n particle excitations or contain valence excitations, which may involve exchange spectator scatterings. These latter type of operators are allowed to contract among themselves through the spectator orbitals. The novelty of the Ansatz is in the choice of a suitable automorphic factor accompanying each composite of noncommuting operators, ensuring that each such composite appears only once. The resulting CC equations consist of two types of terms: one is direct and the other is folded and the latter involves the effective Hamiltonian operator. We emphasize that while the direct term terminates exactly at the quartic power of the cluster amplitudes, termination of the folded term is dictated by the valence rank of the effective Hamiltonian operator, just as in the spin-free open-shell CC theory with a normal ordered exponential Ansatz. Example applications are presented by computing the core and valence-ionized state energies of H2O molecule and comparing the results with benchmark full CI results. The results show the efficacy of the method. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Multidimensional scaling of fragrances: A comparison between the verbal and non-verbal methods of classifying fragrances1JAPANESE PSYCHOLOGICAL RESEARCH, Issue 1 2004Takahiro Higuchi Abstract:,Higuchi, Shoji, and Hatayama (2002) selected nine sense-descriptive adjectives (e.g., sweet, clear) to describe the olfactory properties of fragrances. In order to clarify the ability of these adjectives to classify fragrances, the present study used a non-verbal sorting of fragrances that has been widely accepted in previous studies as a method of classifying fragrance. Interfragrance similarities obtained from the non-verbal sorting were then compared with those obtained from the adjective rating based on a two-dimensional spatial configuration of fragrances created by a multidimensional scaling (MDS) analysis. The similarities of the two MDS configurations, obtained from the verbal and non-verbal sorting, were estimated by the correlation of interfragrance distances on the spatial configuration. The correlation coefficient was 0.61, indicating that the ability of the sense-descriptive adjectives to classify fragrances is nearly the same as that of the non-verbal sorting. [source] Simulating forest ecosystem response to climate warming incorporating spatial effects in north-eastern ChinaJOURNAL OF BIOGEOGRAPHY, Issue 12 2005Hong S. He Abstract Aim, Predictions of ecosystem responses to climate warming are often made using gap models, which are among the most effective tools for assessing the effects of climate change on forest composition and structure. Gap models do not generally account for broad-scale effects such as the spatial configuration of the simulated forest ecosystems, disturbance, and seed dispersal, which extend beyond the simulation plots and are important under changing climates. In this study we incorporate the broad-scale spatial effects (spatial configurations of the simulated forest ecosystems, seed dispersal and fire disturbance) in simulating forest responses to climate warming. We chose the Changbai Natural Reserve in China as our study area. Our aim is to reveal the spatial effects in simulating forest responses to climate warming and make new predictions by incorporating these effects in the Changbai Natural Reserve. Location, Changbai Natural Reserve, north-eastern China. Method, We used a coupled modelling approach that links a gap model with a spatially explicit landscape model. In our approach, the responses (establishment) of individual species to climate warming are simulated using a gap model (linkages) that has been utilized previously for making predictions in this region; and the spatial effects are simulated using a landscape model (LANDIS) that incorporates spatial configurations of the simulated forest ecosystems, seed dispersal and fire disturbance. We used the recent predictions of the Canadian Global Coupled Model (CGCM2) for the Changbai Mountain area (4.6 °C average annual temperature increase and little precipitation change). For the area encompassed by the simulation, we examined four major ecosystems distributed continuously from low to high elevations along the northern slope: hardwood forest, mixed Korean pine hardwood forest, spruce-fir forest, and sub-alpine forest. Results, The dominant effects of climate warming were evident on forest ecosystems in the low and high elevation areas, but not in the mid-elevation areas. This suggests that the forest ecosystems near the southern and northern ranges of their distributions will have the strongest response to climate warming. In the mid-elevation areas, environmental controls exerted the dominant influence on the dynamics of these forests (e.g. spruce-fir) and their resilience to climate warming was suggested by the fact that the fluctuations of species trajectories for these forests under the warming scenario paralleled those under the current climate scenario. Main conclusions, With the spatial effects incorporated, the disappearance of tree species in this region due to the climate warming would not be expected within the 300-year period covered by the simulation. Neither Korean pine nor spruce-fir was completely replaced by broadleaf species during the simulation period. Even for the sub-alpine forest, mountain birch did not become extinct under the climate warming scenario, although its occurrence was greatly reduced. However, the decreasing trends characterizing Korean pine, spruce, and fir indicate that in simulations beyond 300 years these species could eventually be replaced by broadleaf tree species. A complete forest transition would take much longer than the time periods predicted by the gap models. [source] Modelling the spatial configuration of refuges for a sustainable control of pests: a case study of Bt cottonJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2003C. Vacher Abstract The ,high-dose-refuge' (HDR) strategy is widely recommended by the biotechnology industry and regulatory authorities to delay pest adaptation to transgenic crops that produce Bacillus thuringiensis (Bt) toxins. This involves cultivating nontoxic plants (refuges) in close proximity to crops producing a high dose of Bt toxin. The principal cost associated with this strategy is due to yield losses suffered by farmers growing unprotected, refuge plants. Using a population genetic model of selection in a spatially heterogeneous environment, we show the existence of an optimal spatial configuration of refuges that could prevent the evolution of resistance whilst reducing the use of costly refuges. In particular, the sustainable control of pests is achievable with the use of more aggregated distributions of nontransgenic plants and transgenic plants producing lower doses of toxin. The HDR strategy is thus suboptimal within the context of sustainable agricultural development. [source] Deletion of N-terminus of human tyrosine hydroxylase type 1 enhances stability of the enzyme in AtT-20 cellsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 1 2005Akira Nakashima Abstract Wildtype human tyrosine hydroxylase (TH) type 1 and 4 mutants (del-52, a form with the first 52 amino acid residues deleted; del-157, one with the first 157 amino acid residues deleted; RR-EE, one in which Arg37 -Arg38 was replaced by Glu37 -Glu38; and S40D, one in which Ser40 was replaced by Asp40) were expressed in AtT-20 mouse neuroendocrine cells in order to clarify how deeply the N-terminus of TH is involved in the efficient production of dopamine (DA) in mammalian cells. The amounts of DA that accumulated in AtT-20 cells expressing these human TH type 1 (hTH1) phenotypes were in the following order: del-52 = del-157 = RR-EE > S40D > wildtype, although the enzyme activities of del-52 and del-157 were lower than those of wildtype, RR-EE, and S40D. The observation on immunoblot analyses that the N-terminus-deleted hTH1 mutants were much more stable than wildtype can reconcile the discrepant results. Computer-assisted analysis of the spatial configuration of hTH1 identified five newly recognized PEST motifs, one of which was located in the N-terminus sequence of Met1 -Lys12 and predicted that deletion of the N-terminus region would alter the secondary structure within the catalytic domain. Collectively, the high stability of the N-terminus-deleted hTH1 mutants can be generated by the loss of a PEST motif in their N-termini and the structural change in the catalytic domain, which would promise an efficient production of DA in mammalian cells expressing N-terminus deleted hTH1. © 2005 Wiley-Liss, Inc. [source] Evaluating land use/land cover changes and fragmentation in the Camili forest planning unit of northeastern Turkey from 1972 to 2005LAND DEGRADATION AND DEVELOPMENT, Issue 4 2007F. Sivrikaya Abstract Changes in land use/land cover have important consequences on the management of natural resources including soil and water quality, global climatic systems and biodiversity. This study analysed the spatial and temporal pattern of land use/land cover change in the Camili forest planning unit that includes the Camili Biosphere Reserve Area within the Caucasian hotspot, in the northeast corner of Turkey. To assess the patterns during a 33-year period, the necessary data were obtained from forest stand maps and evaluated with Geographic Information Systems and FRAGSTATS. Results showed that the total forested areas increased from 19,946·5,ha (78·6% of the study area) in 1972 to 20,797·3,ha (81·9 per cent) in 2005 with a slight net increase of 851,ha. Softwood cover types (411·8,ha) completely transitioned to other cover types over 33-year period. In terms of spatial configuration, the total number of forest fragments increased from 172 to 608, and mean size of forest patch (MPS) decreased from 147·7,ha to 41·8,ha during the period. Nearly 84 per cent of the patches in 1972 and 93 per cent of them in 2005 generally seem to concentrate into 0,100,ha patch size class, indicating more fragmented landscape over time that might create a risk for the maintenance of biodiversity of the area. There were apparent trends in the temporal structure of forest landscape, some of which may issue from mismanagement of the area, social conflict, and illegal utilization of forest resources due to ineffective forest protection measurements. The study revealed that it is important to understand both spatial and temporal changes of land use/land cover and their effects on landscape pattern to disclose the implications for land use planning and management. Copyright © 2007 John Wiley & Sons, Ltd. [source] A method for the tribological testing of thin, hard coatingsLUBRICATION SCIENCE, Issue 2 2002R. Michalczewski Abstract A new method has been developed for tribological testing of thin, hard antiwear coatings, using a ball-on-disc tribosystem, under conditions of dry sliding. In this, an Al2O3 ball is pressed against a coated steel disc. Wear debris is removed from the contact zone by a stream of dry argon in this novel method. This improves the stability of the tribological properties and the repeatability of the test results. All test conditions are precisely defined, in particular: the type of motion, air relative humidity, ambient temperature, sliding speed, load, tribosystem spatial configuration, substrate material, substrate hardness and roughness, and coating thickness. The method developed has been used to test various physical vapour deposition coatings (deposited by the vacuum arc method), i. e., single-layer TiN, Ti(C,N), CrN, and Cr(C,N), and multilayer Cr(C,N)/CrN/Cr and Cr(C,N)/(CrN+Cr2N)/CrN/Cr. It is shown that CrN coatings exhibit the best antiwear properties, and Ti(C,N) the worst. Friction coefficients for CrN and Cr(C,N) coatings are much lower than for the more commonly used TiN. Multilayer coatings have better antiwear properties than single-layer ones. [source] Consequences of forest fragmentation for polyporous fungi at two spatial scalesOIKOS, Issue 2 2006R. Penttilä Greatly reduced area of old-growth forests and the very low amount of dead wood in managed forests in northern Europe have caused a marked decline in the populations of saproxylic species. It is less clear at which spatial and temporal scales these adverse changes are taking place, and more information is needed to reliably predict which species are especially sensitive to loss and fragmentation of habitat. Here we compare species richness, incidence of occurrence in forest fragments, and abundance of polyporous fungal species and species groups between two regions in Finland with contrasting histories of forestry and a marked difference in the amount and spatial configuration of old-growth forests. We also analyse the consequences of increasing loss of connectivity on the presence and abundance of polypores in a study region with a documented short-term history of old-growth fragmentation. Our results show that the species number, incidence of occurrence, and abundance of especially the rare, threatened, and near-threatened species are much lower in the old-growth fragments in Häme in southern Finland in comparison with Kuhmo in eastern Finland, most probably because of the longer history of intensive forestry in Häme. Among the rare species, the species that show the greatest difference between the two regions (at the scale of 500 km) also tended to respond most strongly to the more recent forest fragmentation within the study region in Kuhmo (at the scale of 50 km). Polypores associated with spruce seem to be more strongly affected by forestry than species associated with pine, possibly reflecting the differences in the natural dynamics of spruce-dominated and pine-dominated forests. [source] L- and M-cone input to 12Hz and 30Hz flicker ERGs across the human retinaOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2010N. K. Challa Abstract We recorded L- and M-cone isolating ERGs from human subjects using a silent substitution technique at temporal rates of 12 and 30 Hz. These frequencies isolate the activity of cone-opponent and non-opponent post-receptoral mechanisms, respectively. ERGs were obtained using a sequence of stimuli with different spatial configurations comprising; (1) circular stimuli of different sizes which increased in 10° steps up to 70°diameter, or (2) annular stimuli with a 70° outer diameter but with different sized central ablations from 10° up to 60°. L- and M-cone isolating ERGs were obtained from five colour normal subjects using a DTL fibre electrode. Fourier analysis of the ERGs was performed and we measured the amplitude of the first harmonic of the response. For 12 Hz ERGs the L:M cone response amplitude ratio (L:MERG) was close to unity and remained stable irrespective of the spatial configuration of the stimulus. The maintenance of this balanced ratio points to the existence of cone selective input across the human retina for the L-M cone opponent mechanism. For 30 Hz the L:MERG ratio was greater than unity but varied depending upon which region of the retina was being stimulated. This variation we consider to be a consequence of the global response properties of M-cone ERGs rather than representing a real variation in L:M cone ratios across the retina. [source] Economic geography: the rising star of the social sciencesOXONOMICS, Issue 1-2 2007Ashby H. B. Monk The study of economic geography is concerned with explaining the spatial configuration of economic activity; considering the extent of the world's economic growth over the last half century, the relevance of the discipline is clear. Economic geography is undeniably a ,new star' in the social sciences, a status confirmed by the success of the Journal of Economic Geography. Under the surface, however, economists and geographers disagree frequently about ontology and methodology. If used to enhance and improve ideas, these divisions will ultimately lead to better research and even greater success. [source] Synthesis, characterization, and its PL dynamics of colloidal type II CdTe/CdSe nanocrystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Masaru Oda Abstract We describe our improved synthesis and optical properties of high quality type II CdTe/CdSe nanocrystals (NCs). Specifically, clear shell-thickness dependences have been observed in the absorption and photoluminescence (PL) spectra and PL decay profiles as well. The magnitude of the lowest absorption band decreases drastically with large redshift as the shell thickness increases. The origin will be discussed on the bases of the model where the spatial configuration of the lowest electron-hole pair in the NCs changes from that of type I to type II as the shell thickness increases. As for the PL lifetime of the lowest electron-hole excitations, substantial increase is observed with increasing shell thickness. This can also be understood by considering the spatial configuration; spatial overlap between electron and hole wavefunctions decreases with increasing shell thickness, thus the lifetime increases. As for the NCs with extremely thin shell (,1 ML; 1 ML = 0.35 nm), the PL lifetime seems much longer than expected. This suggests that the thin shells seem imperfect and work rather a kind of trap sites than layers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of natural barriers on the spillover of a marine mollusc: implications for fisheries reservesAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2003Alexander Tewfik Abstract 1.The movement of organisms and dispersal of propagules is fundamental to the maintenance of populations over time. However, the existence of barriers, created through the spatial configuration of habitats, may significantly affect dispersal patterns and thus influence community dynamics and resource sustainability. 2.Within marine environments unstructured or open habitats may form partial or complete ecological barriers due to elevated risk of predation or physical stresses associated with them. The existence and effects of such barriers may be of particular importance when considering the establishment of marine protected areas with a fisheries enhancement focus. 3.In this paper, the spillover of post-settlement queen conch (Strombus gigas) from a protected area in the Turks and Caicos Islands is investigated. It is hypothesized that the reserve boundaries overlap with a series of shallow, sand habitats that effectively enclose the protected population, reducing the spillover of conch into the adjacent fished areas. 4.To test this, density gradient maps for juvenile and adult conch populations were constructed using underwater visual survey data at 68 sites within and surrounding the protected area. These maps illustrate very low densities coinciding with poor, shallow sand habitats along the two marine boundaries of the reserve where spillover is expected to take place. 5.These sand habitats are thought to create ecological barriers to a slow, sedentary gastropod largely due to their shallowness (physical stresses of solar exposure or anoxia) and lack of food reducing the tendency of individuals to move across these areas, despite the 10-times higher density of adult queen conch observed in the protected area compared with outside. Copyright © 2003 John Wiley & Sons, Ltd. [source] Connectivity and patch area in a coastal marine landscape: Disentangling their influence on local species richness and compositionAUSTRAL ECOLOGY, Issue 6 2009ANA INÉS BORTHAGARAY Abstract Landscape ecology emerged as a terrestrial discipline to evaluate the effect of spatial configuration of natural systems on ecological patterns. The advances in marine systems have been comparatively scarce perhaps as a consequence of a long-standing view about the greater dispersal potential of marine species and its effect on the spatial homogenization of marine landscapes. Herein we used an intertidal rocky system as a model to analyse the effect of landscape attributes on local species richness and composition. We evaluated the effect of patch area, landscape connectivity and salinity gradient on local species richness of macro-invertebrates, and the effect of geographic distance on species similarity. We sampled 19 rocky patches along the Uruguayan Atlantic coast one time during the spring of 2003. The relative contribution of the variables assessed on specific richness of sessile, mobile and total macrofauna was analysed with a stepwise multiple linear regression. For the mobile macrofaunal richness, we also incorporated the sessile macrofaunal richness as another independent variable. The effect of geographic distance on biological similarity was assessed by a Mantel test. We showed that landscape connectivity, as a descriptor of the average physical isolation of a biological community in the landscape, is an important factor explaining the community species richness for sessile macrofauna, what indirectly increases the mobile macrofaunal richness. The geographic distance between sites was negatively related to species similarity. We suggest that at the landscape scale, connectivity among sites can be important to understand the local structure of marine communities, particularly in rocky intertidal systems. Also the distance-decay of similarity in community composition provides a useful descriptor of how biological composition varies along a physical gradient. Our results contribute to reinforce the view that mesoscale connectivity (101,2 km) in coastal marine landscapes plays a more important role in local community structure than previously assumed. [source] Sedimentary Response of Different Fan Types to the Paleogene,Neogene Basin Transformation in the Kuqa Depression, Tarim Basin, Xinjiang ProvinceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Zhiyong GAO Abstract: A group of alluvial fans formed in the early Paleogene represent marginal sedimentary facies at the foot of the South Tianshan Mountain, Kuqa Depression, Tarim Basin, Xinjiang province. Two types of fans occurred in the middle,late Paleogene Kumugeliemu and Suweiyi formations: one alluvial, and the other fan delta deposited in a lacustrine setting. Within the early Neogene Jidike Formation, coastal subaqueous fans developed, probably in a deeper water lacustrine setting. The three types of fans are stacked vertically in outcrop with the sequence in ascending order: bottom alluvial, middle fan-delta, and top subaqueous. The subaqueous is a typical coarse-fan deposit occurring in the glutinite member of the Jidike Formation in some wells. Laterally, from the foreland to the lacustrine settings, the distribution pattern of sedimentary facies represents the same three fan types sequentially. The spatial distribution of these fans was controlled by the Paleogene,Neogene Basin transformation, and evolution with different types of fans developed in the Kuqa Depression in response. In the Paleogene, the Kuqa Depression was a rift basin where an alluvial fan was deposited in the foreland setting, which, by early Neogene, became a foreland basin when the lake level changed. With any rise in lake level, fan-deltas migrated from lacustrine to foreland settings, whereas when the lake level fell, fan migration was reversed. In the early Neogene, with increasing slope and rising lake level, fans progressed and covered the previous fan-delta and lacustrine mudstone. Eventually, subaqueous fans developed, forming the present spatial configuration of these three fan types. [source] The role of vegetation patterns in structuring runoff and sediment fluxes in drylandsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2005Juan Puigdefįbregas Abstract The dynamics of vegetation-driven spatial heterogeneity (VDSH) and its function in structuring runoff and sediment fluxes have received increased attention from both geomorphological and ecological perspectives, particularly in arid regions with sparse vegetation cover. This paper reviews the recent findings in this area obtained from field evidence and numerical simulation experiments, and outlines their implications for soil erosion assessment. VDSH is often observed at two scales, individual plant clumps and stands of clumps. At the patch scale, the local outcomes of vegetated patches on soil erodibility and hydraulic soil properties are well established. They involve greater water storage capacity as well as increased organic carbon and nutrient inputs. These effects operate together with an enhanced capacity for the interception of water and windborne resources, and an increased biological activity that accelerates breakdown of plant litter and nutrient turnover rates. This suite of relationships, which often involve positive feedback mechanisms, creates vegetated patches that are increasingly different from nearby bare ground areas. By this way a mosaic builds up with bare ground and vegetated patches coupled together, respectively, as sources and sinks of water, sediments and nutrients. At the stand scale within-storm temporal variability of rainfall intensity controls reinfiltration of overland flow and its decay with slope length. At moderate rainfall intensity, this factor interacts with the spatial structure of VDSH and the mechanism of overland flow generation. Reinfiltration is greater in small-grained VDSH and topsoil saturation excess overland flow. Available information shows that VDSH structures of sources and sinks of water and sediments evolve dynamically with hillslope fluxes and tune their spatial configurations to them. Rainfall simulation experiments in large plots show that coarsening VDSH leads to significantly greater erosion rates even under heavy rainfall intensity because of the flow concentration and its velocity increase. Copyright © 2005 John Wiley & Sons, Ltd. [source] Simulating forest ecosystem response to climate warming incorporating spatial effects in north-eastern ChinaJOURNAL OF BIOGEOGRAPHY, Issue 12 2005Hong S. He Abstract Aim, Predictions of ecosystem responses to climate warming are often made using gap models, which are among the most effective tools for assessing the effects of climate change on forest composition and structure. Gap models do not generally account for broad-scale effects such as the spatial configuration of the simulated forest ecosystems, disturbance, and seed dispersal, which extend beyond the simulation plots and are important under changing climates. In this study we incorporate the broad-scale spatial effects (spatial configurations of the simulated forest ecosystems, seed dispersal and fire disturbance) in simulating forest responses to climate warming. We chose the Changbai Natural Reserve in China as our study area. Our aim is to reveal the spatial effects in simulating forest responses to climate warming and make new predictions by incorporating these effects in the Changbai Natural Reserve. Location, Changbai Natural Reserve, north-eastern China. Method, We used a coupled modelling approach that links a gap model with a spatially explicit landscape model. In our approach, the responses (establishment) of individual species to climate warming are simulated using a gap model (linkages) that has been utilized previously for making predictions in this region; and the spatial effects are simulated using a landscape model (LANDIS) that incorporates spatial configurations of the simulated forest ecosystems, seed dispersal and fire disturbance. We used the recent predictions of the Canadian Global Coupled Model (CGCM2) for the Changbai Mountain area (4.6 °C average annual temperature increase and little precipitation change). For the area encompassed by the simulation, we examined four major ecosystems distributed continuously from low to high elevations along the northern slope: hardwood forest, mixed Korean pine hardwood forest, spruce-fir forest, and sub-alpine forest. Results, The dominant effects of climate warming were evident on forest ecosystems in the low and high elevation areas, but not in the mid-elevation areas. This suggests that the forest ecosystems near the southern and northern ranges of their distributions will have the strongest response to climate warming. In the mid-elevation areas, environmental controls exerted the dominant influence on the dynamics of these forests (e.g. spruce-fir) and their resilience to climate warming was suggested by the fact that the fluctuations of species trajectories for these forests under the warming scenario paralleled those under the current climate scenario. Main conclusions, With the spatial effects incorporated, the disappearance of tree species in this region due to the climate warming would not be expected within the 300-year period covered by the simulation. Neither Korean pine nor spruce-fir was completely replaced by broadleaf species during the simulation period. Even for the sub-alpine forest, mountain birch did not become extinct under the climate warming scenario, although its occurrence was greatly reduced. However, the decreasing trends characterizing Korean pine, spruce, and fir indicate that in simulations beyond 300 years these species could eventually be replaced by broadleaf tree species. A complete forest transition would take much longer than the time periods predicted by the gap models. [source] A Cooperative Game Theory of Noncontiguous AlliesJOURNAL OF PUBLIC ECONOMIC THEORY, Issue 4 2001Daniel G. Arce M. This paper develops a cooperative game-theoretic representation of alliances with noncontiguous members that is based on cost savings from reducing overlapping responsibilities and sequestering borders. For various scenarios, three solutions (the Shapley value, nucleolus, and core's centroid) are found and compared. Even though their underlying ethical norm varies, the solutions are often identical for cases involving contiguous allies and for rectangular arrays of noncontiguous allies. When transaction costs and/or alternative spatial configurations are investigated, they may then differ. In all cases the cooperative approach leads to a distribution of alliance costs that need not necessarily coincide with the traditional emphasis on gross domestic product size as a proxy for deterrence value (the exploitation hypothesis). Instead, burdens can now be defined based upon a country's spatial and strategic location within the alliance. [source] Access and Agency in Elizabeth Cary's The Tragedy of Mariam: Early Modern Closet Drama and the Spatialization of Power1LITERATURE COMPASS (ELECTRONIC), Issue 2 2006Carol Mejia-LaPerle This essay was runner-up in the 2005 Literature Compass Graduate Essay Prize, Renaissance Section. Numerous critics have explored the stoic sentiments in Elizabeth Cary's The Tragedy of Mariam (1613), especially the ways in which female characters negotiate the demands of patriarchal force, while expressing a conscience contrary to those demands. However, this essay examines the material conditions necessary for pursuing stoic ideals, prompted by the fact that Cary uniquely depicts female resistance of tyrannical conditions in distinctly spatial terms. Her closet drama consistently deploys literary representations of space to ask important questions about gendered subjects: How is space an expression and enforcement of power upon women? How can spatial configurations be manipulated to alter or circumvent the effects of tyranny? This essay argues that Cary's closet drama depicts power as a force that organizes environments; that is, spatial arrangements that regulate characters' behaviors are also the material manifestations of authority through which the discourses expressing female agency are constructed and contained. Since closet dramas were not written for public performance but for consumption within a domestic setting, spatial arrangements are apprehended through, indeed are never prior to, the act of reading. The reader perceives the play's landscape , the play's space , through the characters' language. This study tests the reciprocity between space and words, specifically the way spatialization in the play facilitates the processes and practices of female speech. [source] The discordance of diversification: evolution in the tropical-montane frogs of the Eastern Arc Mountains of TanzaniaMOLECULAR ECOLOGY, Issue 18 2010LUCINDA P. LAWSON Abstract Species with similar geographical distribution patterns are often assumed to have a shared biogeographical history, an assumption that can be tested with a combination of molecular, spatial, and environmental data. This study investigates three lineages of Hyperolius frogs with concordant ranges within the Eastern Afromontane Biodiversity Hotspot to determine whether allopatric populations of co-distributed lineages shared a parallel biogeographical response to their shared paleoclimatic histories. The roles of refugial distributions, isolation, and climate cycles in shaping their histories are examined through Hierarchical Approximate Bayesian Computation, comparative phylogeography, and comparisons of current and past geographical distributions using ecological niche models. Results from these analyses show these three lineages to have independent evolutionary histories, which current spatial configurations of sparsely available habitat (montane wetlands) have moulded into convergent geographical ranges. In spite of independent phylogeographical histories, diversification events are temporally concentrated, implying that past vicariant events were significant at the generic level. This mixture of apparently disparate histories is likely due to quantifiably different patterns of expansion and retreat among species in response to past climate cycles. Combining climate modelling and phylogeographical data can reveal unrecognized complexities in the evolution of co-distributed taxa. [source] L- and M-cone input to 12Hz and 30Hz flicker ERGs across the human retinaOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2010N. K. Challa Abstract We recorded L- and M-cone isolating ERGs from human subjects using a silent substitution technique at temporal rates of 12 and 30 Hz. These frequencies isolate the activity of cone-opponent and non-opponent post-receptoral mechanisms, respectively. ERGs were obtained using a sequence of stimuli with different spatial configurations comprising; (1) circular stimuli of different sizes which increased in 10° steps up to 70°diameter, or (2) annular stimuli with a 70° outer diameter but with different sized central ablations from 10° up to 60°. L- and M-cone isolating ERGs were obtained from five colour normal subjects using a DTL fibre electrode. Fourier analysis of the ERGs was performed and we measured the amplitude of the first harmonic of the response. For 12 Hz ERGs the L:M cone response amplitude ratio (L:MERG) was close to unity and remained stable irrespective of the spatial configuration of the stimulus. The maintenance of this balanced ratio points to the existence of cone selective input across the human retina for the L-M cone opponent mechanism. For 30 Hz the L:MERG ratio was greater than unity but varied depending upon which region of the retina was being stimulated. This variation we consider to be a consequence of the global response properties of M-cone ERGs rather than representing a real variation in L:M cone ratios across the retina. [source] | |||||||||||||||||||||||||||||||||||||||||||