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1

Spatial Structure of Seagrass Suggests That Size-Dependent Plant Traits Have a Strong Influence on the Distribution and Maintenance of Tropical Multispecies Meadows  

PubMed Central

Background Seagrass species in the tropics occur in multispecies meadows. How these meadows are maintained through species co-existence and what their ecological drivers may be has been an overarching question in seagrass biogeography. In this study, we quantify the spatial structure of four co-existing species and infer potential ecological processes from these structures. Methods and Results Species presence/absence data were collected using underwater towed and dropped video cameras in Pulau Tinggi, Malaysia. The geostatistical method, utilizing semivariograms, was used to describe the spatial structure of Halophila spp, Halodule uninervis, Syringodium isoetifolium and Cymodocea serrulata. Species had spatial patterns that were oriented in the along-shore and across-shore directions, nested with larger species in meadow interiors, and consisted of multiple structures that indicate the influence of 2–3 underlying processes. The Linear Model of Coregionalization (LMC) was used to estimate the amount of variance contributing to the presence of a species at specific spatial scales. These distances were <2.5 m (micro-scale), 2.5–50 m (fine-scale) and >50 m (broad-scale) in the along-shore; and <2.5 m (micro-scale), 2.5–140 m (fine-scale) and >140 m (broad-scale) in the across-shore. The LMC suggests that smaller species (Halophila spp and H. uninervis) were most influenced by broad-scale processes such as hydrodynamics and water depth whereas large, localised species (S. isoetifolium and C. serrulata) were more influenced by finer-scale processes such as sediment burial, seagrass colonization and growth, and physical disturbance. Conclusion In this study, we provide evidence that spatial structure is distinct even when species occur in well-mixed multispecies meadows, and we suggest that size-dependent plant traits have a strong influence on the distribution and maintenance of tropical marine plant communities. This study offers a contrast from previous spatial models of seagrasses which have largely focused on monospecific temperate meadows. PMID:24497978

Ooi, Jillian L. S.; Van Niel, Kimberly P.; Kendrick, Gary A.; Holmes, Karen W.

2014-01-01

2

Strong-field spatial interference in a tailored electromagnetic bath  

E-print Network

Light scattered by a regular structure of atoms can exhibit interference signatures, similar to the classical double-slit. These first-order interferences, however, vanish for strong light intensities, restricting potential applications. Here, we show how to overcome these limitations to quantum interference in strong fields. First, we recover the first-order interference in strong fields via a tailored electromagnetic bath with a suitable frequency dependence. At strong driving, the optical properties for different spectral bands are distinct, thus extending the set of observables. We further show that for a two-photon detector as, e.g., in lithography, increasing the field intensity leads to twice the spatial resolution of the second-order interference pattern compared to the weak-field case.

M. Macovei; J. Evers; G. -x. Li; C. H. Keitel

2006-06-19

3

Unusually Strong Dependence of Conformation on Solvent  

Microsoft Academic Search

Relative partition coefficients between aqueous methanol and pentane of the two stereoisomers of a series of 4-tert-butylcyclohexylamines were measured by NMR. The cis isomer shows a larger partition coefficient, with a ¢¢G°orgfaq up to 1.4 kcal\\/mol. A thermodynamic cycle relates these values to a solvent dependence of the A value for conformational equilibrium of an amino substituent. The variation with

Charles L. Perrin; Miles A. Fabian; Ignacio A. Rivero

1998-01-01

4

Frequency-dependent effective hydraulic conductivity of strongly heterogeneous media  

NASA Astrophysics Data System (ADS)

The determination of the transport properties of heterogeneous porous rocks, such as an effective hydraulic conductivity, arises in a range of geoscience problems, from groundwater flow analysis to hydrocarbon reservoir modeling. In the presence of formation-scale heterogeneities, nonstationary flows, induced by pumping tests or propagating elastic waves, entail localized pressure diffusion processes with a characteristic frequency depending on the pressure diffusivity and size of the heterogeneity. Then, on a macroscale, a homogeneous equivalent medium exists, which has a frequency-dependent effective conductivity. The frequency dependence of the conductivity can be analyzed with Biot's equations of poroelasticity. In the quasistatic frequency regime of this framework, the slow compressional wave is a proxy for pressure diffusion processes. This slow compressional wave is associated with the out-of-phase motion of the fluid and solid phase, thereby creating a relative fluid-solid displacement vector field. Decoupling of the poroelasticity equations gives a diffusion equation for the fluid-solid displacement field valid in a poroelastic medium with spatial fluctuations in hydraulic conductivity. Then, an effective conductivity is found by a Green's function approach followed by a strong-contrast perturbation theory suggested earlier in the context of random dielectrics. This theory leads to closed-form expressions for the frequency-dependent effective conductivity as a function of the one- and two-point probability functions of the conductivity fluctuations. In one dimension, these expressions are consistent with exact solutions in both low- and high-frequency limits for arbitrary conductivity contrast. In 3D, the low-frequency limit depends on the details of the microstructure. However, the derived approximation for the effective conductivity is consistent with the Hashin-Shtrikman bounds.

Caspari, E.; Gurevich, B.; Müller, T. M.

2013-10-01

5

Frequency-dependent effective hydraulic conductivity of strongly heterogeneous media.  

PubMed

The determination of the transport properties of heterogeneous porous rocks, such as an effective hydraulic conductivity, arises in a range of geoscience problems, from groundwater flow analysis to hydrocarbon reservoir modeling. In the presence of formation-scale heterogeneities, nonstationary flows, induced by pumping tests or propagating elastic waves, entail localized pressure diffusion processes with a characteristic frequency depending on the pressure diffusivity and size of the heterogeneity. Then, on a macroscale, a homogeneous equivalent medium exists, which has a frequency-dependent effective conductivity. The frequency dependence of the conductivity can be analyzed with Biot's equations of poroelasticity. In the quasistatic frequency regime of this framework, the slow compressional wave is a proxy for pressure diffusion processes. This slow compressional wave is associated with the out-of-phase motion of the fluid and solid phase, thereby creating a relative fluid-solid displacement vector field. Decoupling of the poroelasticity equations gives a diffusion equation for the fluid-solid displacement field valid in a poroelastic medium with spatial fluctuations in hydraulic conductivity. Then, an effective conductivity is found by a Green's function approach followed by a strong-contrast perturbation theory suggested earlier in the context of random dielectrics. This theory leads to closed-form expressions for the frequency-dependent effective conductivity as a function of the one- and two-point probability functions of the conductivity fluctuations. In one dimension, these expressions are consistent with exact solutions in both low- and high-frequency limits for arbitrary conductivity contrast. In 3D, the low-frequency limit depends on the details of the microstructure. However, the derived approximation for the effective conductivity is consistent with the Hashin-Shtrikman bounds. PMID:24229128

Caspari, E; Gurevich, B; Müller, T M

2013-10-01

6

Spatial Dependencies between Large-Scale Brain Networks  

PubMed Central

Functional neuroimaging reveals both increases (task-positive) and decreases (task-negative) in neural activation with many tasks. Many studies show a temporal relationship between task positive and task negative networks that is important for efficient cognitive functioning. Here we provide evidence for a spatial relationship between task positive and negative networks. There are strong spatial similarities between many reported task negative brain networks, termed the default mode network, which is typically assumed to be a spatially fixed network. However, this is not the case. The spatial structure of the DMN varies depending on what specific task is being performed. We test whether there is a fundamental spatial relationship between task positive and negative networks. Specifically, we hypothesize that the distance between task positive and negative voxels is consistent despite different spatial patterns of activation and deactivation evoked by different cognitive tasks. We show significantly reduced variability in the distance between within-condition task positive and task negative voxels than across-condition distances for four different sensory, motor and cognitive tasks - implying that deactivation patterns are spatially dependent on activation patterns (and vice versa), and that both are modulated by specific task demands. We also show a similar relationship between positively and negatively correlated networks from a third ‘rest’ dataset, in the absence of a specific task. We propose that this spatial relationship may be the macroscopic analogue of microscopic neuronal organization reported in sensory cortical systems, and that this organization may reflect homeostatic plasticity necessary for efficient brain function. PMID:24887067

Leech, Robert; Scott, Gregory; Carhart-Harris, Robin; Turkheimer, Federico; Taylor-Robinson, Simon D.; Sharp, David J.

2014-01-01

7

Coexisting orchid species have distinct mycorrhizal communities and display strong spatial segregation.  

PubMed

Because orchids are dependent on mycorrhizal fungi for germination and establishment of seedlings, differences in the mycorrhizal communities associating with orchids can be expected to mediate the abundance, spatial distribution and coexistence of terrestrial orchids in natural communities. We assessed the small-scale spatial distribution of seven orchid species co-occurring in 25 × 25 m plots in two Mediterranean grasslands. In order to characterize the mycorrhizal community associating with each orchid species, 454 pyrosequencing was used. The extent of spatial clustering was assessed using techniques of spatial point pattern analysis. The community of mycorrhizal fungi consisted mainly of members of the Tulasnellaceae, Thelephoraceae and Ceratobasidiaceae, although sporadically members of the Sebacinaceae, Russulaceae and Cortinariaceae were observed. Pronounced differences in mycorrhizal communities were observed between species, whereas strong clustering and significant segregation characterized the spatial distribution of orchid species. However, spatial segregation was not significantly related to phylogenetic dissimilarity of fungal communities. Our results indicate that co-occurring orchid species have distinctive mycorrhizal communities and show strong spatial segregation, suggesting that mycorrhizal fungi are important factors driving niche partitioning in terrestrial orchids and may therefore contribute to orchid coexistence. PMID:24325257

Jacquemyn, Hans; Brys, Rein; Merckx, Vincent S F T; Waud, Michael; Lievens, Bart; Wiegand, Thorsten

2014-04-01

8

Evolution of accelerographs, data processing, strong motion arrays and amplitude and spatial resolution in recording strong earthquake motion  

Microsoft Academic Search

This paper presents a review of the advances in strong motion recording since the early 1930s, based mostly on the experiences in the United States. A particular emphasis is placed on the amplitude and spatial resolution of recording, which both must be ‘adequate’ to capture the nature of strong earthquake ground motion and response of structures. The first strong motion

M. D. Trifunac; M. I. Todorovska

2001-01-01

9

Strong Predictability Of Spatially Distributed Physical Habitat Preferences For O. Mykiss Spawning Across Three Spatial Scales  

NASA Astrophysics Data System (ADS)

Currently accepted perception assumes Oncorhynchus mykiss prefer different ranges of similar physical habitat elements for spawning than Chinook salmon (Oncorhynchus tshawytscha), taking into account their difference in size. While there is increasing research interest regarding O. mykiss habitat use and migratory behavior, research conducted to date distinguishing the physical habitat conditions utilized for O. mykiss spawning has not provided quantified understanding of their spawning habitat preferences. The purpose of this study was to use electivity indices and other measures to assess the physical habitat characteristics preferred for O. mykiss spawning in terms of both 1-m scale microhabitat attributes, and landforms at different spatial scales from 0.1-100 times channel width. The testbed for this study was the 37.5-km regulated gravel-cobble Lower Yuba River (LYR). Using spatially distributed 2D hydrodynamic model results, substrate mapping, and a census of O. mykiss redds from two years of observation, micro- and meso-scale representations of physical habitat were tested for their ability to predict spawning habitat preference and avoidance. Overall there was strong stratification of O. mykiss redd occurrence for all representation types of physical habitat. A strong preference of hydraulic conditions was shown for mean water column velocities of 1.18-2.25 ft/s, and water depths of 1.25-2.76 ft. There was a marked preference for the two most upstream alluvial reaches of the LYR (out of 8 total reaches), accounting for 92% of all redds observed. The preferred morphological units (MUs) for O. mykiss spawning were more variable than for Chinook salmon and changed with increasing discharge, demonstrating that O. mykiss shift spawning to different MUs in order to utilize their preferred hydraulic conditions. The substrate range preferred for O. mykiss spawning was within 32-90 mm. Overall, O. mykiss spawning behavior was highly predictable and required a holistic blend of hydraulic and geomorphic representations to explain.

Kammel, L.; Pasternack, G. B.; Wyrick, J. R.; Massa, D.; Bratovich, P.; Johnson, T.

2012-12-01

10

Spatial Transport of Magnetic Flux Surfaces in Strongly Anisotropic Turbulence  

NASA Astrophysics Data System (ADS)

Magnetic flux surfaces afford familiar descriptions of spatial structure, dynamics, and connectivity of magnetic fields, with particular relevance in contexts such as solar coronal flux tubes, magnetic field connectivity in the interplanetary and interstellar medium, as well as in laboratory plasmas and dynamo problems [1-4]. Typical models assume that field-lines are orderly, and flux tubes remain identifiable over macroscopic distances; however, a previous study has shown that flux tubes shred in the presence of fluctuations, typically losing identity after several correlation scales [5]. Here, the structure of magnetic flux surfaces is numerically investigated in a reduced magnetohydrodynamic (RMHD) model of homogeneous turbulence. Short and long-wavelength behavior is studied statistically by propagating magnetic surfaces along the mean field. At small scales magnetic surfaces become complex, experiencing an exponential thinning. At large scales, instead, the magnetic flux undergoes a diffusive behavior. The link between the diffusion of the coarse-grained flux and field-line random walk is established by means of a multiple scale analysis. Both large and small scales limits are controlled by the Kubo number. These results have consequences for understanding and interpreting processes such as magnetic reconnection and field-line diffusion in plasmas [6]. [1] E. N. Parker, Cosmical Magnetic Fields (Oxford Univ. Press, New York, 1979). [2] J. R. Jokipii and E. N. Parker, Phys. Rev. Lett. 21, 44 (1968). [3] R. Bruno et al., Planet. Space Sci. 49, 1201 (2001). [4] M. N. Rosenbluth et al., Nuclear Fusion 6, 297 (1966). [5] W. H. Matthaeus et al., Phys. Rev. Lett. 75, 2136 (1995). [6] S. Servidio et al., submitted (2013).

Matthaeus, W. H.; Servidio, S.; Wan, M.; Ruffolo, D. J.; Rappazzo, A. F.; Oughton, S.

2013-12-01

11

Neighborhood dependence in Bayesian spatial models.  

PubMed

The conditional autoregressive model and the intrinsic autoregressive model are widely used as prior distribution for random spatial effects in Bayesian models. Several authors have pointed out impractical or counterintuitive consequences on the prior covariance matrix or the posterior covariance matrix of the spatial random effects. This article clarifies many of these puzzling results. We show that the neighborhood graph structure, synthesized in eigenvalues and eigenvectors structure of a matrix associated with the adjacency matrix, determines most of the apparently anomalous behavior. We illustrate our conclusions with regular and irregular lattices including lines, grids, and lattices based on real maps. PMID:19827056

Assunção, Renato; Krainski, Elias

2009-10-01

12

Efficient Estimation of Mutual Information for Strongly Dependent Variables  

E-print Network

We demonstrate that a popular class of nonparametric mutual information (MI) estimators based on k-nearest-neighbor graphs requires number of samples that scales exponentially with the true MI. Consequently, accurate estimation of MI between two strongly dependent variables is possible only for prohibitively large sample size. This important yet overlooked shortcoming of the existing estimators is due to their implicit reliance on local uniformity of the underlying joint distribution. We introduce a new estimator that is robust to local non-uniformity, works well with limited data, and is able to capture relationship strengths over many orders of magnitude. We demonstrate the superior performance of the proposed estimator on both synthetic and real-world data.

Gao, Shuyang; Galstyan, Aram

2014-01-01

13

Parity-dependent localization in N strongly coupled chains  

NASA Astrophysics Data System (ADS)

Anderson localization of wave functions at zero energy in quasi-one-dimensional (1D) systems of N disordered chains with interchain coupling t is examined. Localization becomes weaker than for the 1D disordered chain (t =0) when t is smaller than the longitudinal hopping t'=1, and localization becomes usually much stronger when t ?t'. This is not so for all N. We find "immunity" to strong localization for open (periodic) lateral boundary conditions when N is odd (a multiple of 4), with localization that is weaker than for t =0 and rather insensitive to t when t ?t'. The peculiar N dependence and a critical scaling with N are explained by a perturbative treatment in t'/t, and the correspondence to a weakly disordered effective chain is shown. Our results could be relevant for experimental studies of localization in photonic waveguide arrays.

Weinmann, Dietmar; Evangelou, S. N.

2014-10-01

14

High-spatial-resolution monitoring of strong magnetic field using Rb vapor nanometric-thin cell  

NASA Astrophysics Data System (ADS)

We have implemented the so-called ?-Zeeman technique (LZT) to investigate individual hyperfine transitions between Zeeman sublevels of the Rb atoms in a strong external magnetic field B in the range of 2500 - 5000 G (recently it was established that LZT is very convenient for the range of 10 - 2500 G). Atoms are confined in a nanometric thin cell (NTC) with the thickness L = ?, where ? is the resonant wavelength 794 nm for Rb D 1 line. Narrow velocity selective optical pumping (VSOP) resonances in the transmission spectrum of the NTC are split into several components in a magnetic field with the frequency positions and transition probabilities depending on the B-field. Possible applications are described, such as magnetometers with nanometric local spatial resolution and tunable atomic frequency references.

Hakhumyan, G.; Leroy, C.; Pashayan-Leroy, Y.; Sarkisyan, D.; Auzinsh, M.

2011-08-01

15

Spatial variability and its scale dependency of observed and modeled soil moisture over different climate regions  

NASA Astrophysics Data System (ADS)

Past studies on soil moisture spatial variability have been mainly conducted at catchment scales where soil moisture is often sampled over a short time period; as a result, the observed soil moisture often exhibited smaller dynamic ranges, which prevented the complete revelation of soil moisture spatial variability as a function of mean soil moisture. In this study, spatial statistics (mean, spatial variability and skewness) of in situ soil moisture, modeled and satellite-retrieved soil moisture obtained in a warm season (198 days) were examined over three large climate regions in the US. The study found that spatial moments of in situ measurements strongly depend on climates, with distinct mean, spatial variability and skewness observed in each climate zone. In addition, an upward convex shape, which was revealed in several smaller scale studies, was observed for the relationship between spatial variability of in situ soil moisture and its spatial mean when statistics from dry, intermediate, and wet climates were combined. This upward convex shape was vaguely or partially observable in modeled and satellite-retrieved soil moisture estimates due to their smaller dynamic ranges. Despite different environmental controls on large-scale soil moisture spatial variability, the correlation between spatial variability and mean soil moisture remained similar to that observed at small scales, which is attributed to the boundedness of soil moisture. From the smaller support (effective area or volume represented by a measurement or estimate) to larger ones, soil moisture spatial variability decreased in each climate region. The scale dependency of spatial variability all followed the power law, but data with large supports showed stronger scale dependency than those with smaller supports. The scale dependency of soil moisture variability also varied with climates, which may be linked to the scale dependency of precipitation spatial variability. Influences of environmental controls on soil moisture spatial variability at large scales are discussed. The results of this study should be useful for diagnosing large scale soil moisture estimates and for improving the estimation of land surface processes.

Li, B.; Rodell, M.

2013-03-01

16

Spatial variability and its scale dependency of observed and modeled soil moisture under different climate conditions  

NASA Astrophysics Data System (ADS)

Past studies on soil moisture spatial variability have been mainly conducted in catchment scales where soil moisture is often sampled over a short time period. Because of limited climate and weather conditions, the observed soil moisture often exhibited smaller dynamic ranges which prevented the complete revelation of soil moisture spatial variability as a function of mean soil moisture. In this study, spatial statistics (mean, spatial variability and skewness) of in situ soil moisture measurements (from a continuously monitored network across the US), modeled and satellite retrieved soil moisture obtained in a warm season (198 days) were examined at large extent scales (>100 km) over three different climate regions. The investigation on in situ measurements revealed that their spatial moments strongly depend on climates, with distinct mean, spatial variability and skewness observed in each climate zone. In addition, an upward convex shape, which was revealed in several smaller scale studies, was observed for the relationship between spatial variability of in situ soil moisture and its spatial mean across dry, intermediate, and wet climates. These climate specific features were vaguely or partially observable in modeled and satellite retrieved soil moisture estimates, which is attributed to the fact that these two data sets do not have climate specific and seasonal sensitive mean soil moisture values, in addition to lack of dynamic ranges. From the point measurements to satellite retrievals, soil moisture spatial variability decreased in each climate region. The three data sources all followed the power law in the scale dependency of spatial variability, with coarser resolution data showing stronger scale dependency than finer ones. The main findings from this study are: (1) the statistical distribution of soil moisture depends on spatial mean soil moisture values and thus need to be derived locally within any given area; (2) the boundedness of soil moisture plays a pivoting role in the dependency of soil moisture spatial variability/skewness on its mean (and thus climate conditions); (3) the scale dependency of soil moisture spatial variability changes with climate conditions.

Li, B.; Rodell, M.

2012-09-01

17

Verifying the Dependence of Fractal Coefficients on Different Spatial Distributions  

SciTech Connect

A fractal distribution requires that the number of objects larger than a specific size r has a power-law dependence on the size N(r) = C/r{sup D}propor tor{sup -D} where D is the fractal dimension. Usually the correlation integral is calculated to estimate the correlation fractal dimension of epicentres. A 'box-counting' procedure could also be applied giving the 'capacity' fractal dimension. The fractal dimension can be an integer and then it is equivalent to a Euclidean dimension (it is zero of a point, one of a segment, of a square is two and of a cube is three). In general the fractal dimension is not an integer but a fractional dimension and there comes the origin of the term 'fractal'. The use of a power-law to statistically describe a set of events or phenomena reveals the lack of a characteristic length scale, that is fractal objects are scale invariant. Scaling invariance and chaotic behavior constitute the base of a lot of natural hazards phenomena. Many studies of earthquakes reveal that their occurrence exhibits scale-invariant properties, so the fractal dimension can characterize them. It has first been confirmed that both aftershock rate decay in time and earthquake size distribution follow a power law. Recently many other earthquake distributions have been found to be scale-invariant. The spatial distribution of both regional seismicity and aftershocks show some fractal features. Earthquake spatial distributions are considered fractal, but indirectly. There are two possible models, which result in fractal earthquake distributions. The first model considers that a fractal distribution of faults leads to a fractal distribution of earthquakes, because each earthquake is characteristic of the fault on which it occurs. The second assumes that each fault has a fractal distribution of earthquakes. Observations strongly favour the first hypothesis.The fractal coefficients analysis provides some important advantages in examining earthquake spatial distribution, which are: - Simple way to quantify scale-invariant distributions of complex objects or phenomena by a small number of parameters. - It is becoming evident that the applicability of fractal distributions to geological problems could have a more fundamental basis. Chaotic behaviour could underlay the geotectonic processes and the applicable statistics could often be fractal.The application of fractal distribution analysis has, however, some specific aspects. It is usually difficult to present an adequate interpretation of the obtained values of fractal coefficients for earthquake epicenter or hypocenter distributions. That is why in this paper we aimed at other goals - to verify how a fractal coefficient depends on different spatial distributions. We simulated earthquake spatial data by generating randomly points first in a 3D space - cube, then in a parallelepiped, diminishing one of its sides. We then continued this procedure in 2D and 1D space. For each simulated data set we calculated the points' fractal coefficient (correlation fractal dimension of epicentres) and then checked for correlation between the coefficients values and the type of spatial distribution.In that way one can obtain a set of standard fractal coefficients' values for varying spatial distributions. These then can be used when real earthquake data is analyzed by comparing the real data coefficients values to the standard fractal coefficients. Such an approach can help in interpreting the fractal analysis results through different types of spatial distributions.

Gospodinov, Dragomir [Plovdiv University 'Paisii Hilendarski', 24, Tsar Asen Str., Plovdiv (Bulgaria); Geophysical Institute of Bulgarian Academy of Sciences, Akad. G. Bonchev Str., bl.3, Sofia (Bulgaria); Marekova, Elisaveta; Marinov, Alexander [Plovdiv University 'Paisii Hilendarski', 24, Tsar Asen Str., Plovdiv (Bulgaria)

2010-01-21

18

Spatial dependencies mining based on fuzzy neural networks  

NASA Astrophysics Data System (ADS)

Spatial dependency describes the relationship between one dependent spatial variable and other related spatial variables. This paper constructs two kinds of Fuzzy Neural Networks for spatial dependency mining, the modified fuzzy neural network model and the fuzzy comprehensive assessment network model. The first model is built from general fuzzy neural network model. It has four layers, input layer, fuzzy membership function layer, fuzzy reasoning layer and output layer. The second model is built based on a fuzzy comprehensive assessment algorithm. It has five layers. The first three layers are same as the first model, the fourth and the fifth layer are used to find the maximum membership degree and give the output. We develop the training algorithm for these two models based BP algorithm and genetic algorithm, respectively. This paper adopts a thematic spatial database of land evaluation to test these models. We use experiential knowledge as original rules to build initial FNN models. We can see that original rules (spatial dependencies) are corrected after training. It can be seen that these two models get almost the same revised dependencies, and this indicates that these two models both correct the original ones and get the more objective spatial dependencies. Experiments also indicate these two models are efficient.

Jiao, L. M.; Liu, Y. L.

2008-12-01

19

On the Relation between Spatial Ability Field Dependence*  

E-print Network

Field dependence and spatial ability are widely thought of as distinct psychological dimensions. We sought to evaluate the alternative hypothesis that these are, in fact, different labels for a common underlying dimension. A sample of 60 subjects was selected on the basis of scores on a test of spatial ability. These subjects completed two tests of field dependence--the Embedded Figures Test and the Rod-and-Frame Test--and two tests of spatial ability--the Spatial Relations subtests of the Multiple Aptitude Test and the Blocks Design subtest of the Wechsler Adult Intelligence Scale (WAIS). These particular tests were selected because of (1) their prevalent use in the literature and (2) their provision of paper-and-pencil and manipulative measures of each trait. Using J0reskog's (1970) method for the analysis of covariance matrices (LISREL-V), we estimated the intertrait correlation between field dependence and spatial ability to be indistinguishable from one. On this basis, we question whether field dependence should be viewed as a construct that is distinct from spatial ability. The construct of spatial ability plays a key role in theories of intelligence. Spatial ability is an individual's skill in perceiving fixed geometric/spatial relations and in applying mental transformations such as rotation or reconfiguration to existing spatial relations (cf. Anastasi, 1976). This construct holds a fundamental position in multiple-factor theories of intelligence (e.g., French, 1951; Thurstone, 1938) and in hierarchical theories of intelligence (e.g., Vernon, 1960) and has done so for a long time (see, e.g., Kelley, 1928). Furthermore, spatial ability is recognized as distinct from other fundamental dimensions of intelligence, such as verbal ability (cf. Cattell, 1971). McGee (1979) provides a thorough review of the research on spatial ability, indicating its solid footing in the psychometric literature.

Colin M. Macleod; Ross; A. Jackson; John Palmer

20

Spatial dependence of pairing in deformed nuclei  

SciTech Connect

The solution of time-dependent Hartree-Fock-Bogoliubov equations by the Wignerfunction-moments method leads to the appearance of refined low-lying modes whose description requires the accurate knowledge of the anomalous density matrix. It is shown that calculations with Woods-Saxon potential satisfy this requirement, producing an anomalous density matrix of the same quality as more complicated calculations with realistic forces.

Balbutsev, E. B.; Malov, L. A., E-mail: malov@theor.jinr.ru [Joint Institute for Nuclear Research (Russian Federation); Schuck, P. [CNRS andUniversite Paris-Sud, Institut de Physique Nucleaire (France)

2011-11-15

21

Temperature Dependence of Thermopower in Strongly Correlated Multiorbital Systems  

SciTech Connect

Temperature dependence of thermopower in the multiorbital Hubbard model is studied by using the dynamical mean-field theory with the non-crossing approximation impurity solver. It is found that the Coulomb interaction, the Hund coupling, and the crystal filed splitting bring about nonmonotonic temperature dependence of the hermopower, including its sign reversal. The implication of our theoretical results to some materials is discussed.

Sekino, M [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA); Okamoto, Satoshi [ORNL] [ORNL; Koshibae, W [RIKEN, Japan] [RIKEN, Japan; Mori, Michiyasu [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA); Maekawa, Sadamichi [Japan Atomic Energy Agency (JAEA)] [Japan Atomic Energy Agency (JAEA)

2014-01-01

22

Strong generative capacity of RST, SDRT and discourse dependency DAGSs  

E-print Network

relations but not on the distinction Nucleus/Satellite or coordinating/subordinating. This formalism only of this paper0 is to compare the discourse structures proposed in RST, SDRT and dependency DAGs which extend the semantic level of MTT for discourses. The key question is the following: do these formalisms allow the rep

Boyer, Edmond

23

Balanced Networks of Spiking Neurons with Spatially Dependent Recurrent Connections  

NASA Astrophysics Data System (ADS)

Networks of model neurons with balanced recurrent excitation and inhibition capture the irregular and asynchronous spiking activity reported in cortex. While mean-field theories of spatially homogeneous balanced networks are well understood, a mean-field analysis of spatially heterogeneous balanced networks has not been fully developed. We extend the analysis of balanced networks to include a connection probability that depends on the spatial separation between neurons. In the continuum limit, we derive that stable, balanced firing rate solutions require that the spatial spread of external inputs be broader than that of recurrent excitation, which in turn must be broader than or equal to that of recurrent inhibition. Notably, this implies that network models with broad recurrent inhibition are inconsistent with the balanced state. For finite size networks, we investigate the pattern-forming dynamics arising when balanced conditions are not satisfied. Our study highlights the new challenges that balanced networks pose for the spatiotemporal dynamics of complex systems.

Rosenbaum, Robert; Doiron, Brent

2014-04-01

24

KERNEL PARAMETER DEPENDENCE IN SPATIAL FACTOR ANALYSIS Allan A. Nielsen  

E-print Network

, Yb and Lu have been determined by instrumental neutron activation analysis. These analysesKERNEL PARAMETER DEPENDENCE IN SPATIAL FACTOR ANALYSIS Allan A. Nielsen Technical University component analysis (PCA) [1] is often used for gen- eral feature generation and linear orthogonalization

25

Strong stability of neutral equations with an arbitrary delay dependency  

E-print Network

´as Vyhl´idal Pavel Z´itek Henk Nijmeijer Didier Henrion Report TW 498, August 2007 Katholieke Universiteit´idal Pavel Z´itek Henk Nijmeijer Didier Henrion Report TW 498, August 2007 Department of Computer Science, K with an arbitrary delay dependency structure Wim Michiels, a,c Tom´as Vyhl´idal, b Pavel Z´itek, b Henk Nijmeijer, c

Henrion, Didier

26

PARTICLE CLUMPING AND PLANETESIMAL FORMATION DEPEND STRONGLY ON METALLICITY  

SciTech Connect

We present three-dimensional numerical simulations of particle clumping and planetesimal formation in protoplanetary disks with varying amounts of solid material. As centimeter-size pebbles settle to the mid-plane, turbulence develops through vertical shearing and streaming instabilities. We find that when the pebble-to-gas column density ratio is 0.01, corresponding roughly to solar metallicity, clumping is weak, so the pebble density rarely exceeds the gas density. Doubling the column density ratio leads to a dramatic increase in clumping, with characteristic particle densities more than 10 times the gas density and maximum densities reaching several thousand times the gas density. This is consistent with unstratified simulations of the streaming instability that show strong clumping in particle-dominated flows. The clumps readily contract gravitationally into interacting planetesimals on the order of 100 km in radius. Our results suggest that the correlation between host star metallicity and exoplanets may reflect the early stages of planet formation. We further speculate that initially low-metallicity disks can be particle enriched during the gas dispersal phase, leading to a late burst of planetesimal formation.

Johansen, Anders [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Youdin, Andrew [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 3H8 (Canada); Mac Low, Mordecai-Mark, E-mail: ajohan@strw.leidenuniv.n [Department of Astrophysics, American Museum of Natural History, 79th Street at Central Park West, New York, NY 10024-5192 (United States)

2009-10-20

27

Level dependence of spatial processing in the primate auditory cortex.  

PubMed

Sound localization in both humans and monkeys is tolerant to changes in sound levels. The underlying neural mechanism, however, is not well understood. This study reports the level dependence of individual neurons' spatial receptive fields (SRFs) in the primary auditory cortex (A1) and the adjacent caudal field in awake marmoset monkeys. We found that most neurons' excitatory SRF components were spatially confined in response to broadband noise stimuli delivered from the upper frontal sound field. Approximately half the recorded neurons exhibited little change in spatial tuning width over a ~20-dB change in sound level, whereas the remaining neurons showed either expansion or contraction in their tuning widths. Increased sound levels did not alter the percent distribution of tuning width for neurons collected in either cortical field. The population-averaged responses remained tuned between 30- and 80-dB sound pressure levels for neuronal groups preferring contralateral, midline, and ipsilateral locations. We further investigated the spatial extent and level dependence of the suppressive component of SRFs using a pair of sequentially presented stimuli. Forward suppression was observed when the stimuli were delivered from "far" locations, distant to the excitatory center of an SRF. In contrast to spatially confined excitation, the strength of suppression typically increased with stimulus level at both the excitatory center and far regions of an SRF. These findings indicate that although the spatial tuning of individual neurons varied with stimulus levels, their ensemble responses were level tolerant. Widespread spatial suppression may play an important role in limiting the sizes of SRFs at high sound levels in the auditory cortex. PMID:22592309

Zhou, Yi; Wang, Xiaoqin

2012-08-01

28

Spatial scale dependence of ecohydrologically mediated water balance partitioning (Invited)  

NASA Astrophysics Data System (ADS)

The difficulties in predicting whole catchment water balance from observations at patch scales motivate a search for theories that can account for the complexity of interactions in catchments. Spatial patterns of vegetation may offer a lens through which to investigate scale dependence of hydrology within catchments. Vegetation patterns are attractive because they are observable drivers of evapotranspiration, often a dominant component in catchment water balance, and because the spatial distribution of vegetation is often driven by patterns of water availability. We propose that nontrivial, scale dependent spatial patterns in both vegetation distribution and catchment water balance are generated by the presence of a convergent network of flow paths and a two way feedback between vegetation as a driver of evapotranspiration and vegetation distribution as a signature of water availability. Implementing this hypothesis via a simple network model demonstrated that such organization was controlled by catchment properties related to aridity, the network topology, the sensitivity of the vegetation response to water availability, and the point scale controls on partitioning between evapotranspiration and lateral drainage. The resulting self organization generated spatial dependence in areally averaged hydrologic variables, water balance, and parameters describing hydrological partitioning.

Thompson, S. E.; Sivapalan, M.; Harman, C. J.; Troch, P. A.; Brooks, P. D.

2013-12-01

29

Spatial clusters in a global-dependence model.  

PubMed

Spatial data often possess multiple components, such as local clusters and global clustering, and these effects are not easy to be separated. In this study, we propose an approach to deal with the cases where both global clustering and local clusters exist simultaneously. The proposed method is a two-stage approach, estimating the autocorrelation by an EM algorithm and detecting the clusters by a generalized least square method. It reduces the influence of global dependence on detecting local clusters and has lower false alarms. Simulations and the sudden infant disease syndrome data of North Carolina are used to illustrate the difference between the proposed method and the spatial scan statistic. PMID:23725886

Wang, Tai-Chi; Yue, Ching-Syang Jack

2013-06-01

30

Strong discontinuities in spatial stationary long-wave flows of an ideal incompressible fluid  

Microsoft Academic Search

Spatial stationary flows over an even bottom of a heavy ideal fluid with a free surface are considered. Jump relations for\\u000a flows with a strong discontinuity are studied. It is shown that the flow parameters behind the jump are defined by a certain\\u000a curve which is an analog of the (?, p) diagram in gas dynamics. A shock polar and

A. K. Khe

2009-01-01

31

Overnight Sleep Enhances Hippocampus-Dependent Aspects of Spatial Memory  

PubMed Central

Study Objectives: Several studies have now demonstrated that spatial information is processed during sleep, and that posttraining sleep is beneficial for human navigation. However, it remains unclear whether the effects of sleep are primarily due to consolidation of cognitive maps, or alternatively, whether sleep might also affect nonhippocampal aspects of navigation (e.g., speed of motion) involved in moving through a virtual environment. Design: Participants were trained on a virtual maze navigation task (VMT) and then given a memory test following either a day of wakefulness or a night of sleep. Subjects reported to the laboratory for training at either 10:00am or 10:00pm, depending on randomly assigned condition, and were tested 11 h later. Overnight subjects slept in the laboratory with polysomnography. Setting: A hospital-based academic sleep laboratory. Patients or Participants: Thirty healthy college student volunteers. Interventions: N/A. Measurements and Results: Point-by-point position data were collected from the VMT. Analysis of the movement data revealed a sleep-dependent improvement in maze completion time (P < 0.001) due to improved spatial understanding of the maze layout, which led to a shortening of path from start to finish (P = 0.01) rather than faster exploration speed through the maze (P = 0.7). Conclusions: We found that overnight sleep benefitted performance, not because subjects moved faster through the maze, but because they were more accurate in navigating to the goal. These findings suggest that sleep enhances participants' knowledge of the spatial layout of the maze, contributing to the consolidation of hippocampus-dependent spatial information. Citation: Nguyen ND; Tucker MA; Stickgold R; Wamsley EJ. Overnight sleep enhances hippocampus-dependent aspects of spatial memory. SLEEP 2013;36(7):1051-1057. PMID:23814342

Nguyen, Nam D.; Tucker, Matthew A.; Stickgold, Robert; Wamsley, Erin J.

2013-01-01

32

Reference frames in virtual spatial navigation are viewpoint dependent  

PubMed Central

Spatial navigation in the mammalian brain relies on a cognitive map of the environment. Such cognitive maps enable us, for example, to take the optimal route from a given location to a known target. The formation of these maps is naturally influenced by our perception of the environment, meaning it is dependent on factors such as our viewpoint and choice of reference frame. Yet, it is unknown how these factors influence the construction of cognitive maps. Here, we evaluated how various combinations of viewpoints and reference frames affect subjects' performance when they navigated in a bounded virtual environment without landmarks. We measured both their path length and time efficiency and found that (1) ground perspective was associated with egocentric frame of reference, (2) aerial perspective was associated with allocentric frame of reference, (3) there was no appreciable performance difference between first and third person egocentric viewing positions and (4) while none of these effects were dependent on gender, males tended to perform better in general. Our study provides evidence that there are inherent associations between visual perspectives and cognitive reference frames. This result has implications about the mechanisms of path integration in the human brain and may also inspire designs of virtual reality applications. Lastly, we demonstrated the effective use of a tablet PC and spatial navigation tasks for studying spatial and cognitive aspects of human memory. PMID:25249956

Torok, Agoston; Nguyen, T. Peter; Kolozsvari, Orsolya; Buchanan, Robert J.; Nadasdy, Zoltan

2014-01-01

33

Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate  

NASA Astrophysics Data System (ADS)

Planetary rotation rate is a key parameter in determining atmospheric circulation and hence the spatial pattern of clouds. Since clouds can exert a dominant control on planetary radiation balance, rotation rate could be critical for determining the mean planetary climate. Here we investigate this idea using a three-dimensional general circulation model with a sophisticated cloud scheme. We find that slowly rotating planets (like Venus) can maintain an Earth-like climate at nearly twice the stellar flux as rapidly rotating planets (like Earth). This suggests that many exoplanets previously believed to be too hot may actually be habitable, depending on their rotation rate. The explanation for this behavior is that slowly rotating planets have a weak Coriolis force and long daytime illumination, which promotes strong convergence and convection in the substellar region. This produces a large area of optically thick clouds, which greatly increases the planetary albedo. In contrast, on rapidly rotating planets a much narrower belt of clouds form in the deep tropics, leading to a relatively low albedo. A particularly striking example of the importance of rotation rate suggested by our simulations is that a planet with modern Earth's atmosphere, in Venus' orbit, and with modern Venus' (slow) rotation rate would be habitable. This would imply that if Venus went through a runaway greenhouse, it had a higher rotation rate at that time.

Yang, Jun; Boué, Gwenaël; Fabrycky, Daniel C.; Abbot, Dorian S.

2014-05-01

34

Post-starburst--AGN Connection: Spatially Resolved Spectroscopy of Hdelta-Strong AGNs  

E-print Network

Ever since the co-existence of an active galactic nucleus (AGN) and a starburst was observationally discovered, there has been a significant controversy over whether there is a physical connection between starbursts and AGNs. If yes, it is a subject of interest to reveal which one triggers another. Here we bring a unique insight onto the subject by identifying 840 galaxies with both a post-starburst signature (strong Balmer absorption lines) and an AGN (based on the emission line ratio). These poststarburst-AGNs account for the 4.2% of all the galaxies in a volume-limited sample. The presence of a post-starburst phase with an active AGN itself is of importance, suggesting that AGNs may outlive starbursts in the starburst-AGN connection. In addition, we have performed spatially resolved spectroscopy of three of our poststarbusrst-AGN galaxies, obtaining some evidence that the post-starburst region is more extended, but sharply centred around the central AGN, confirming a spatial connection between the post-starburst and the AGN.

Tomotsugu Goto

2006-05-08

35

Spatiotemporal properties of sensory responses in vivo are strongly dependent on network context  

PubMed Central

Sensory responses in neocortex are strongly modulated by changes in brain state, such as those observed between sleep stages or attentional levels. However, the specific effects of network state changes on the spatiotemporal properties of sensory responses are poorly understood. The slow oscillation, which is observed in neocortex under ketamine-xylazine anesthesia and is characterized by alternating depolarizing (up-states) and hyperpolarizing (down-states) phases, provides an opportunity to study the state-dependence of primary sensory responses in large networks. Here we used voltage sensitive dye (VSD) imaging to record the spatiotemporal properties of sensory responses and local field potential (LFP) and multiunit activity (MUA) recordings to monitor the ongoing brain state in which the sensory responses occurred. Despite a rich variability of slow oscillation patterns, sensory responses showed a consistent relationship with the ongoing oscillation and triggered a new up-state only after the termination of the refractory period that followed the preceding oscillatory cycle. We show that spatiotemporal properties of whisker-evoked responses are highly dependent on their timing with regard to the ongoing oscillation. In both the up- and down-states, responses spread across large portions of the barrel field, although the up-state responses were reduced in total area due to their sparseness. The depolarizing response in the up-state showed a tendency to propagate along the rows, with an amplitude and slope favoring the higher-numbered arcs. In the up-state, but not in the down-state, the depolarizing response was followed by a hyperpolarizing wave with a consistent spatial structure. We measured the suppression of whisker-evoked responses by a preceding response at 100 ms, and found that suppression showed the same spatial asymmetry as the depolarization. Because the resting level of cells in the up-state is likely to be closer to that in the awake animal, we suggest that the polarities in signal propagation which we observed in the up-state could be used as computational mechanisms in the behaving animal. These results demonstrate the critical importance of ongoing network activity on the dynamics of sensory responses and their integration. PMID:22509158

Civillico, Eugene F.; Contreras, Diego

2012-01-01

36

Near-field spatial mapping of strongly interacting multiple plasmonic infrared antennas.  

PubMed

Near-field dipolar plasmon interactions of multiple infrared antenna structures in the strong coupling limit are studied using scattering-type scanning near-field optical microscope (s-SNOM) and theoretical finite-difference time-domain (FDTD) calculations. We monitor in real-space the evolution of plasmon dipolar mode of a stationary antenna structure as multiple resonantly matched dipolar plasmon particles are closely approaching it. Interparticle separation, length and polarization dependent studies show that the cross geometry structure favors strong interparticle charge-charge, dipole-dipole and charge-dipole Coulomb interactions in the nanometer scale gap region, which results in strong field enhancement in cross-bowties and further allows these structures to be used as polarization filters. The nanoscale local field amplitude and phase maps show that due to strong interparticle Coulomb coupling, cross-bowtie structures redistribute and highly enhance the out-of-plane (perpendicular to the plane of the sample) plasmon near-field component at the gap region relative to ordinary bowties. PMID:24097054

Grefe, Sarah E; Leiva, Daan; Mastel, Stefan; Dhuey, Scott D; Cabrini, Stefano; Schuck, P James; Abate, Yohannes

2013-11-21

37

Plasma density inside a femtosecond laser filament in air: Strong dependence on external focusing  

E-print Network

Plasma density inside a femtosecond laser filament in air: Strong dependence on external focusing strongly influences the plasma density and the diameter of femtosecond Ti-sapphire laser filaments spectroscopy, laser induced electrical discharge, and femtosecond laser material interactions. The measurements

Becker, Andreas

38

Strong configurational dependence of elastic properties for a binary model metallic glass  

E-print Network

Strong configurational dependence of elastic properties for a binary model metallic glass Gang Duan in a Cu­Zr binary metallic glass assessed by molecular dynamics simulations is reported. By directly, the shear modulus dependence on the specific configurational inherent state of metallic glasses is shown

Goddard III, William A.

39

Strong spatial variability in trace gasdynamics following experimental drought in a humid tropical forest  

NASA Astrophysics Data System (ADS)

Soil moisture is a key driver of biogeochemical processes in terrestrial ecosystems, strongly affecting carbon (C) and nutrient availability as well as trace gas production and consumption in soils. Models predict increasing drought frequency in tropical forest ecosystems, which could feed back on future climate change directly via effects on trace gasdynamics and indirectly through changes in nutrient availability. We used throughfall exclusion shelters to determine effects of short-term (3 month) drought on trace gas fluxes and nutrient availability in humid tropical forests in Puerto Rico. Exclusion and control plots were replicated within and across three topographic zones (ridge, slope, valley) to account for spatial heterogeneity typical of these ecosystems. Throughfall exclusion reduced soil moisture in all sites and lowered exchangeable phosphorus (P) on ridges and slopes. Drought decreased soil carbon dioxide (CO2) emissions by 30% in ridge sites and 28% in slope sites, and increased net methane (CH4) consumption by 480% in valley sites. Both valley and ridge sites became net nitrous oxide (N2O) sinks in response to soil drying. Emissions of CO2 and N2O, as well as CH4 consumption were positively related to exchangeable P and the nitrate:ammonium ratio. These findings suggest that drought has the potential to decrease net trace gas emissions from humid tropical forest soils. The differential response of trace gas emissions and nutrients from different topographic zones to drought underscores the complexity of biogeochemical cycling in these ecosystems and the importance of considering spatial heterogeneity when estimating whole system responses.

Wood, Tana E.; Silver, Whendee L.

2012-09-01

40

TE-dependent spatial and spectral specificity of functional connectivity.  

PubMed

Previous studies suggest that spontaneous fluctuations in the resting-state fMRI (RS-fMRI) signal may reflect fluctuations in transverse relaxation time (T(2)(*)) rather than spin density (S(0)). However, such S(0) and T(2)(*) features have not been well characterized. In this study, spatial and spectral characteristics of functional connectivity on sensorimotor, default-mode, dorsal attention, and primary visual systems were examined using a multiple gradient-echo sequence at 3T. In the spatial domain, we found broad, local correlations at short echo times (TE ? 14 ms) due to dominant S(0) contribution, whereas long-range connections mediated by T(2)(*) became explicit at TEs longer than 22 ms. In the frequency domain, compared with the flat spectrum of S(0), spectral power of the T(2)(*)-weighted signal elevated significantly with increasing TE, particularly in the frequency ranges of 0.008-0.023 Hz and 0.037-0.043 Hz. Using the S(0) spectrum as a reference, we propose two indices to measure spectral signal change (SSC) and spectral contrast-to-noise ratio (SCNR), respectively, for quantifying the RS-fMRI signal. These indices demonstrated TE dependency of connectivity-related fluctuation strength, resembling functional contrasts in activation-based fMRI. These findings further confirm that large-scale functional circuit connectivity based on BOLD contrast may be constrained within specific frequency ranges in every brain network, and the spectral features of S(0) and T(2)(*) could be valuable for interpreting and quantifying RS-fMRI data. PMID:22119650

Wu, Changwei W; Gu, Hong; Zou, Qihong; Lu, Hanbing; Stein, Elliot A; Yang, Yihong

2012-02-15

41

Spatial Visualization Abilities of Field Dependent/Independent Preservice Teachers  

ERIC Educational Resources Information Center

Introduction: Spatial skills have been a significant area of research in educational psychology for more years and it has two major dimensions as spatial visualization and spatial orientation. Mathematics educators acknowledge the influence of cognitive styles in the learning of mathematics. There are various recognized cognitive styles in the…

Yazici, Ersen

2014-01-01

42

Exchange and spin states in quantum dots under strong spatial correlations. Computer simulation by the Feynman path integral method  

SciTech Connect

The fundamental laws in the behavior of electrons in model quantum dots that are caused by exchange and strong Coulomb correlations are studied. The ab initio path integral method is used to numerically simulate systems of two, three, four, and six interacting identical electrons confined in a three-dimensional spherical potential well with a parabolic confining potential against the background of thermal fluctuations. The temperature dependences of spin and collective spin magnetic susceptibility are calculated for model quantum dots of various spatial sizes. A basically exact procedure is proposed for taking into account the permutation symmetry and the spin state of electrons, which makes it possible to perform numerical calculations using modern computer facilities. The conditions of applicability of a virial energy estimator and its optimum form in exchange systems are determined. A correlation estimator of kinetic energy, which is an alternative to a basic estimator, is suggested. A fundamental relation between the kinetic energy of a quantum particle and the character of its virtual diffusion in imaginary time is demonstrated. The process of natural 'pairing' of electron spins during the compression of a quantum dot and cooling of a system is numerically reproduced in terms of path integrals. The temperature dependences of the spin magnetic susceptibility of electron pairs with a characteristic maximum caused by spin pairing are obtained.

Shevkunov, S. V., E-mail: shevk54@mail.ru [St. Petersburg State Polytechnic University (Russian Federation)

2013-10-15

43

Adaptive spatially dependent weighting scheme for tomosynthesis reconstruction  

NASA Astrophysics Data System (ADS)

Digital Tomosynthesis (DT) is an x-ray limited-angle imaging technique. An accurate image reconstruction in tomosynthesis is a challenging task due to the violation of the tomographic sufficiency conditions. A classical "shift-and-add" algorithm (or simple backprojection) suffers from blurring artifacts, produced by structures located above and below the plane of interest. The artifact problem becomes even more prominent in the presence of materials and tissues with a high x-ray attenuation, such as bones, microcalcifications or metal. The focus of the current work is on reduction of ghosting artifacts produced by bones in the musculoskeletal tomosynthesis. A novel dissimilarity concept and a modified backprojection with an adaptive spatially dependent weighting scheme (?BP) are proposed. Simulated data of software phantom, a structured hardware phantom and a human hand raw-data acquired with a Siemens Mammomat Inspiration tomosynthesis system were reconstructed using conventional backprojection algorithm and the new ?BP-algorithm. The comparison of the results to the non-weighted case demonstrates the potential of the proposed weighted backprojection to reduce the blurring artifacts in musculoskeletal DT. The proposed weighting scheme is not limited to the tomosynthesis limitedangle geometry. It can also be adapted for Computed Tomography (CT) and included in iterative reconstruction algorithms (e.g. SART).

Levakhina, Yulia; Duschka, Robert; Vogt, Florian; Barkhausen, JOErg; Buzug, Thorsten M.

2012-03-01

44

SPATIALLY PENALIZED REGRESSION FOR DEPENDENCE ANALYSIS OF RARE EVENTS: A STUDY IN PRECIPITATION EXTREMES  

E-print Network

SPATIALLY PENALIZED REGRESSION FOR DEPENDENCE ANALYSIS OF RARE EVENTS: A STUDY IN PRECIPITATION, USA ABSTRACT Discovery of dependence structure between precipitation extremes and other climate can be different for different locations. Secondly, the dependence structure between the precipitation

Obradovic, Zoran

45

Modeling Spatial Dependencies in High-Resolution Overhead Imagery  

SciTech Connect

Human settlement regions with different physical and socio-economic attributes exhibit unique spatial characteristics that are often illustrated in high-resolution overhead imageries. For example- size, shape and spatial arrangements of man-made structures are key attributes that vary with respect to the socioeconomic profile of the neighborhood. Successfully modeling these attributes is crucial in developing advanced image understanding systems for interpreting complex aerial scenes. In this paper we present three different approaches to model the spatial context in the overhead imagery. First, we show that the frequency domain of the image can be used to model the spatial context [1]. The shape of the spectral energy contours characterize the scene context and can be exploited as global features. Secondly, we explore a discriminative framework based on the Conditional Random Fields (CRF) [2] to model the spatial context in the overhead imagery. The features derived from the edge orientation distribution calculated for a neighborhood and the associated class labels are used as input features to model the spatial context. Our third approach is based on grouping spatially connected pixels based on the low-level edge primitives to form support-regions [3]. The statistical parameters generated from the support-region feature distributions characterize different geospatial neighborhoods. We apply our approaches on high-resolution overhead imageries. We show that proposed approaches characterize the spatial context in overhead imageries.

Cheriyadat, Anil M [ORNL] [ORNL; Bright, Eddie A [ORNL] [ORNL; Vatsavai, Raju [ORNL] [ORNL

2011-01-01

46

Angular dependence of the strong-field ionization measured in randomly oriented hydrogen molecules  

E-print Network

Angular dependence of the strong-field ionization measured in randomly oriented hydrogen molecules orientation, in excellent agreement with our ab initio theoretical model. Our results also agree separation between their rotational energy levels low rotational inertia and low polarizability anisotropy

Thumm, Uwe

47

Time-dependent variational approach to molecules in strong laser fields  

E-print Network

since our method still has a simple orbital structure and can hence be applied to realistic many-electron, the electric field by the atomic nucleus on the first bohr orbit of the hydrogen atom has a field strength of 5Time-dependent variational approach to molecules in strong laser fields Thomas Kreibich a , Robert

Gross, E.K.U.

48

History-dependent effects in subcycle-waveform strong-field ionization  

NASA Astrophysics Data System (ADS)

Recent developments in laser sources allow one to shape the precise electric-field waveform oscillation at the subcycle level. These waveforms may then be used to drive and control ultrafast nonlinear phenomena at the attosecond timescale. By utilizing numerical solutions of time-dependent Schrödinger equations and exact solutions of a simple quantum-mechanical system, we show that an atom driven by such sources exhibit coherent history-dependent effects. These manifest themselves in "macroscopic" quantities such as the yield in multicolor, strong-field ionization. We argue that weakly bound, metastable electronic states may enable the dependence on the system history even in long-duration, relatively weak driving waveforms.

Kolesik, M.; Brown, J. M.; Moloney, J. V.; Faccio, D.

2014-09-01

49

Pulse-shape-dependent strong-field ionization viewed with velocity-map imaging  

SciTech Connect

We explore strong field molecular ionization with velocity map imaging of fragment ions produced by dissociation following ionization. Our measurements and ab initio electronic structure calculations allow us to identify various electronic states of the molecular cation populated during ionization, with multiple pathways to individual states highlighted by the pulse shape dependence. In addition, we show that relative populations can be reconstructed from our measurements. The results illustrate how strong field molecular ionization can be complicated by the presence and interaction of multiple cationic states during ionization.

Geissler, Dominik; Weinacht, Thomas C. [Department of Physics, Stony Brook University, Stony Brook, New York 11794 (United States); Rozgonyi, Tamas [Chemical Research Center of the Hungarian Academy of Sciences, Pusztaszeri u't 59-67, Budapest, HU-1025 (Hungary); Gonzalez-Vazquez, Jesus [Instituto de Quimica Fisica Rocasolano, CSIC, C/Serrano 119, ES-28006 Madrid (Spain); Gonzalez, Leticia; Marquetand, Philipp [Institute of Theoretical Chemistry, University of Vienna, Waehringer Str. 17, 1090 Vienna (Austria)

2011-11-15

50

Parity Dependence in Strong Lens Systems as a Probe of Dark Matter Substructure  

E-print Network

The amount of mass in small, dark matter clumps within galaxies (substructure) is an important test of cold dark matter. One approach to measuring the substructure mass fraction is to analyze the fluxes of images that have been strongly lensed by a galaxy. Flux ratios between images that are anomalous with respect to smooth (no substructure) models have previously suggested that there is a greater amount of substructure than found in dark matter simulations. One measure of anomalous flux ratios is parity dependence -- that the fluxes of different images of a source are perturbed differently. In this paper, we discuss parity dependence as a probe of dark matter substructure. We find that reproducing the observed parity dependence requires a significant alignment between concentrated dark matter clumps and images. The results may imply a larger fraction of mass in substructures than suggested by some dark matter simulations and that the observed parity dependence is unlikely to be reproduced by luminous satellites of lens galaxies.

Jacqueline Chen

2008-10-11

51

Spatial aggregation, spatial dependence and predictability in the UK housing market  

Microsoft Academic Search

Most time?series studies of UK housing markets are carried out on national data. However, housing markets may be better characterised as a series of interconnected sub?national markets. In this paper, we use methods taken from the spatial econometrics literature and from cointegration to explore the nature of spatial interactions in UK regional house prices and housing starts. The three central

Geoffrey Meen

1996-01-01

52

Large-Sample Properties of Parameter Estimates for Strongly Dependent Stationary Gaussian Time Series  

Microsoft Academic Search

A strongly dependent Gaussian sequence has a spectral density $f(x, \\\\theta)$ satisfying $f(x, \\\\theta) \\\\sim |x|^{-\\\\alpha(\\\\theta)} L_\\\\theta(x)$ as $x \\\\rightarrow 0$, where $0 < \\\\alpha(\\\\theta) < 1$ and $L_\\\\theta(x)$ varies slowly at 0. Here $\\\\theta$ is a vector of unknown parameters. An estimator for $\\\\theta$ is proposed and shown to be consistent and asymptotically normal under appropriate conditions. These conditions

Robert Fox; Murad S. Taqqu

1986-01-01

53

Capacity of bioregulators of stem and progenitor cells to strongly affect liver redox-dependent processes.  

PubMed

Abstract Effects of stem and progenitor cells or their compounds on recipient cells are investigated intensively today. In spite of this, their ability to interact with native cells and the final targets affected by them, particularly biochemical parameters that characterize cell redox-dependent processes, remain little studied. We have studied how bioregulators of stem and progenitor cells affect these processes in freshly isolated liver after animal pretreatment in vivo. Cytosol of human fetal mesenchymal-mesodermal tissues (8-10 weeks gestation) was administered intravenously; the control group was treated with Hanks' solution. After 4?hr, rats were sacrificed and their livers were isolated. To evaluate liver redox-dependent state, mitochondrial respiratory activity and nitroxyl radical and Alamar Blue™ reduction rates, mitochondrial and cytosolic glycerol kinase and nicotinamide adenine dinucleotide (NADH)-dependent malate dehydrogenase activities were studied. The results obtained demonstrate that bioregulators strongly affect liver redox-dependent processes, increasing mitochondrial respiration in state III and spin probe reduction rate and enhancing Alamar Blue™ reduction by glycolytic and nonglycolytic postmitochondrial enzymes. In addition, mitochondrial glycerol kinase and both isoforms of NADH-dependent malate dehydrogenase were inhibited. These data bring us closer to understanding stem and progenitor cell effects via directed regulation of metabolic redox-dependent processes. PMID:22007912

Cherkashina, Daria V; Tkacheva, Elena N; Somov, Alexander Y; Semenchenko, Olga A; Nardid, Oleg A; Petrenko, Alexander Y

2011-12-01

54

Emotional modulation of hippocampus-dependent spatial learning  

E-print Network

by the amygdala. Anxiogenic drugs administered during acquisition in a task that can be acquired either through hippocampus-dependent �place� learning or caudate dependent �response� learning, resulted in the predominant use of response...

Elliott, Audrea Elizabeth

2006-10-30

55

Strong terahertz radiation by beating of spatial-triangular lasers in a plasma  

SciTech Connect

Resonant excitation of terahertz (THz) radiation by beating of two spatial-triangular laser beams having different frequencies and wave numbers but the same electric fields is proposed, where the ponderomotive force in the transverse direction is realized due to the beating and spatial variation of the lasers' fields. This gives rise to a stronger transient transverse current due to a sharp gradient in the laser field, and subsequently THz radiation is excited resonantly in the presence of a periodic density structure. The present scheme yields the THz field {approx}10{sup 5} kV/cm and the efficiency {approx}10{sup -2} for the laser intensity {approx}10{sup 14} W/cm{sup 2}.

Malik, Anil K.; Malik, Hitendra K. [Plasma Waves and Particle Acceleration Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi-110 016 (India); Stroth, Ulrich [Institute fuer Plasmaforschung, Universitaet Stuttgart, Stuttgart-70569 (Germany)

2011-08-15

56

Time-dependent variational approach to molecules in strong laser fields  

NASA Astrophysics Data System (ADS)

We study the dynamics of the electronic and nuclear degrees of freedom for molecules in strong laser fields using an ansatz for the wavefunction that explicitly incorporates the electron-nuclear correlation. Equations of motion for this wavefunction are derived on the basis of the stationary action principle. The method is tested on a one-dimensional model of the H 2+ molecule that can be solved essentially exactly by numerical integration of the time-dependent Schrödinger equation. By comparison with this exact solution we find that the correlated approach improves significantly on a mean-field treatment, especially for laser fields strong enough to cause substantial dissociation. These results are very promising since our method still has a simple orbital structure and can hence be applied to realistic many-electron molecules.

Kreibich, Thomas; van Leeuwen, Robert; Gross, E. K. U.

2004-09-01

57

Strong spatial variability of NO2 over polluted areas and within emission plumes observed by aircraft imaging DOAS  

NASA Astrophysics Data System (ADS)

In the troposphere, nitrogen dioxide, NO2, is mainly produced from nitric oxide, NO, emitted by combustion processes. Enhanced NO2 amounts are an indicator of air pollution and may lead to boundary layer ozone production as well as acidification and eutrophication of ecosystems. The IUP Bremen AirMAP (Airborne imaging DOAS instrument for Measurements of Atmospheric Pollution) has been used for NO2 observations over point sources and polluted areas during aircraft campaigns in 2011 and 2013. The instrument yields NO2 column densities at fine horizontal resolution, down to 30m ground pixel side length, and at good spatial coverage. Areas of several km2 are covered with NO2 measurements within a few minutes. Aircraft observations of spatial NO2 distributions are presented for different locations in Europe and different source regions, such as power plants, cities and motorways. The obtained NO2 maps reveal large spatial variability. For example, large gradients in the transition between rural and urban areas, spatial variability over cities and extended areas and, in particular, remarkably strong non-uniform distributions within individual emission plumes downwind of point sources are observed. The observations have implications for experimental emission estimates, the deduced relevance of emission sources and downwind chemistry, as well as the interpretation of satellite- and ground-based remote sensing measurements. The focus of this study is the analysis of the amounts and detailed spatial signatures in the NO2 maps, which is made possible by the favourable AirMAP imaging capabilities.

Schoenhardt, Anja; Meier, Andreas C.; Richter, Andreas; Ruhtz, Thomas; Lindemann, Carsten; Burrows, John P.

2014-05-01

58

Flavor dependence of CP asymmetries and thermal leptogenesis with strong right-handed neutrino mass hierarchy  

SciTech Connect

We prove that taking correctly into account the lepton flavour dependence of the CP asymmetries and washout processes, it is possible to obtain successful thermal leptogenesis from the decays of the second right-handed neutrino. The asymmetries in the muon and tau-flavour channels are then not erased by the inverse decays of the lightest right-handed neutrino N{sub 1}. In this way, we reopen the possibility of ''thermal leptogenesis'' in models with a strong hierarchy in the right-handed Majorana masses that is typically the case in models with up-quark neutrino-Yukawa unification.

Vives, O. [Theory Division, CERN, CH-1211, Geneva 23 (Switzerland)

2006-04-01

59

Wavelength dependence of double ionization of xenon in a strong laser field  

SciTech Connect

The wavelength dependence of double ionization of xenon in a 100-fs laser pulse (2-4x10{sup 13} W/cm{sup 2}) has been studied using photoelectron imaging and ion time-of-flight spectrometry. In the wavelength ranges between 1150 and 1560 nm and 792 and 803 nm a pronounced variation of the ratio of ion yields Xe{sup 2+}/Xe{sup +} is observed. We attribute this variation to the strong influence of a 5s{sup 2}5p{sup 5}{yields}5s5p{sup 6} transition on the dynamics of double ionization.

Kaminski, Patrick; Wiehle, Rolf; Kamke, Wolfgang; Helm, Hanspeter [Department of Molecular and Optical Physics, Albert-Ludwigs-Universitaet, 79104 Freiburg (Germany); Witzel, Bernd [Departement de physique, genie physique et optique, Universite Laval Pav. Alexandre-Vachon, Quebec G1K7P4 (Canada)

2006-01-15

60

Implementation of the time-dependent configuration-interaction singles method for atomic strong-field processes  

SciTech Connect

We present an implementation of the time-dependent configuration-interaction singles (TDCIS) method for treating atomic strong-field processes. In order to absorb the photoelectron wave packet when it reaches the end of the spatial grid, we add to the exact nonrelativistic many-electron Hamiltonian a radial complex absorbing potential (CAP). We determine the orbitals for the TDCIS calculation by diagonalizing the sum of the Fock operator and the CAP using a flexible pseudospectral grid for the radial degree of freedom and spherical harmonics for the angular degrees of freedom. The CAP is chosen such that the occupied orbitals in the Hartree-Fock ground state remain unaffected. Within TDCIS, the many-electron wave packet is expanded in terms of the Hartree-Fock ground state and its single excitations. The virtual orbitals satisfy nonstandard orthogonality relations, which must be taken into consideration in the calculation of the dipole and Coulomb matrix elements required for the TDCIS equations of motion. We employ a stable propagation scheme derived by second-order finite differencing of the TDCIS equations of motion in the interaction picture and subsequent transformation to the Schroedinger picture. Using the TDCIS wave packet, we calculate the expectation value of the dipole acceleration and the reduced density matrix of the residual ion. The technique implemented will allow one to study electronic channel-coupling effects in strong-field processes.

Greenman, Loren; Kamarchik, Eugene; Mazziotti, David A. [Department of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637 (United States); Ho, Phay J. [Argonne National Laboratory, Argonne, Illinois 60439 (United States); Pabst, Stefan [Argonne National Laboratory, Argonne, Illinois 60439 (United States); Institut fuer Theoretische Physik, Universitaet Erlangen-Nuernberg, D-91058 Erlangen (Germany); Santra, Robin [Argonne National Laboratory, Argonne, Illinois 60439 (United States); Department of Physics, University of Chicago, Chicago, Illinois 60637 (United States)

2010-08-15

61

Copulas for the description of non-Gaussian spatial dependence (Invited)  

NASA Astrophysics Data System (ADS)

Many natural processes lead to spatially distributed variables which exhibit considerable spatial variability and heterogeneous structures. The statistical description, interpolation or simulation of such fields can be done by geostatistical tools. Geostatistical methods use second order statistics, variograms and covariance functions for the description of spatial variability and the subsequent interpolation and simulation. However natural structures often exhibit non-Gaussian features both in their distributions and in their dependence. One of these is the different spatial dependence of high and low values. This kind of asymmetrical dependence is a clear sign of a non-Gaussian organization of the structure. Asymmetrical dependence is a feature which is independent of the distribution and thus can be related to the dependence described using copulas. Copulas offer a comprehensive description of spatial variability offering a framework to describe and to model asymmetrical behavior. A third order statistical function can describe asymmetrical behavior. Theoretical models allow interpolation and simulation of spatial fields. They differ from those obtained using geostatistics mainly in their uncertainty quantification. Examples from different spatial fields including topographical surfaces, rainfall and groundwater quality fields illustrate the methodology. Consequences of the models with respect to spatial scaling are also discussed.

Bardossy, A.; Guthke, P.

2013-12-01

62

Spatially dependent heating and ionization: From CME to ICME  

NASA Astrophysics Data System (ADS)

The January 21st 2005 Interplanetary Coronal Mass Ejection (ICME) observed by multiple spacecraft at L1 was also observed further out in the heliosphere at Ulysses (~3.25 AU). Previous multi-spacecraft studies of this ICME found evidence suggesting that the flanks of a magnetic cloud like structure associated with this ICME were observed at L1 while a more central cut through the associated magnetic cloud was observed at Ulysses. This event presents a unique opportunity to study the spatial variation of the ionic composition contained within a single ICME and relate it to the eruption at the Sun. Using SWICS, we compare and contrast the heavy ion composition across the two different observations cuts through the ICME. We will compare the results from ACE and Ulysses with predictions from ionization models in the corona and with remote observations of phenomena indicative of electron heating in the inner corona.

Lepri, S. T.; Laming, J.; Rakowski, C. E.

2010-12-01

63

Spatial and gender-dependent variations in perioral pinprick sensitivity.  

PubMed

Twenty-eight right-handed young adults participated in a sensory testing experiment to evaluate pinprick sensitivity at ten spatially matched sites on the right and left sides of the face. Stimuli were provided by a sharp-pointed dental explorer on which a rubber eraser had been positioned to minimize variations in the extent to which the skin was indented. Sharpness was defined as the magnitude at which abrupt, localized pricking/stinging sensations were evoked. A magnitude matching procedure was used to reduce among-subject variability in the data. Specifically, each estimate of sharpness was adjusted (i.e., divided) by the subject's mean estimate of the brightness of a visual stimulus. Prior to data collection, subjects were carefully instructed on the use of a common numerical scale for assignment of values of sharpness and brightness. Repeated-measures analysis of variance of the adjusted estimates of sharpness revealed a non-significant effect of gender (p > 0.4), a highly significant effect of side (p < 0.0001), and a highly significant effect of test site (p < 0.0001). Pinprick percepts were sharper on the left side of the face than on the right. Moreover, the vermilion of the upper lip exhibited the greatest sensitivity to pinprick; the vermilion of the lower lip exhibited the least sensitivity. These results suggest that use of a patient's sensitivity to pinprick during clinical neurosensory examination must be undertaken in an informed manner. A conclusion of pathological alteration in sensation can be made only after consideration of the normal spatial variations in the percept of sharpness. PMID:8360364

Lee, J; Essick, G K

1993-08-01

64

Strong density-dependent competition and acquired immunity constrain parasite establishment: implications for parasite aggregation.  

PubMed

The vast majority of parasites exhibit an aggregated frequency distribution within their host population, such that most hosts have few or no parasites while only a minority of hosts are heavily infected. One exception to this rule is the trophically transmitted parasite Pterygodermatites peromysci of the white-footed mouse (Peromyscus leucopus), which is randomly distributed within its host population. Here, we ask: what are the factors generating the random distribution of parasites in this system when the majority of macroparasites exhibit non-random patterns? We hypothesise that tight density-dependent processes constrain parasite establishment and survival, preventing the build-up of parasites within individual hosts, and preclude aggregation within the host population. We first conducted primary infections in a laboratory experiment using white-footed mice to test for density-dependent parasite establishment and survival of adult worms. Secondary or challenge infection experiments were then conducted to investigate underlying mechanisms, including intra-specific competition and host-mediated restrictions (i.e. acquired immunity). The results of our experimental infections show a dose-dependent constraint on within-host-parasite establishment, such that the proportion of mice infected rose initially with exposure, and then dropped off at the highest dose. Additional evidence of density-dependent competition comes from the decrease in worm length with increasing levels of exposure. In the challenge infection experiment, previous exposure to parasites resulted in a lower prevalence and intensity of infection compared with primary infection of naïve mice; the magnitude of this effect was also density-dependent. Host immune response (IgG levels) increased with the level of exposure, but decreased with the number of worms established. Our results suggest that strong intra-specific competition and acquired host immunity operate in a density-dependent manner to constrain parasite establishment, driving down aggregation and ultimately accounting for the observed random distribution of parasites. PMID:21215747

Luong, Lien T; Vigliotti, Beth A; Hudson, Peter J

2011-04-01

65

At least three scales of convection in a mantle with strongly temperature-dependent viscosity  

NASA Astrophysics Data System (ADS)

We studied the convective patterns developing at high Rayleigh numbers and intermediate viscosity ratios in a fluid with a strongly temperature-dependent viscosity. Within this sluggish lid regime, three different scales of convection develop. The largest convective scale is cellular, with cold downwelling sheets of viscous fluid encasing hotter, less viscous, parts of the tank. Within each of those cells develop several (typically 3-7) hot 3D upwelling plumes. Upon impinging under the cold thermal boundary layer, each plume in turn generates locally a small ring of cold material which does not reach the bottom of the tank. Applying those results to the Earth's mantle, we suggest that the large-scale features of mantle convection and the co-existence of several scales of convection, i.e. slabs and plumes, are produced by thermal convection in a mantle with high Rayleigh number and a strongly temperature-dependent viscosity material. This generates a convective pattern in two large-scale cells : the Pacific and the Indo-Atlantic "boxes". Our experiments further suggest that what has been named the two hot superplumes, i.e. the two seismically slow regions encased within the subduction rings, are in fact each constituted of several hot instabilities. Moreover, plumes impacts under the lithosphere should be surrounded by cold rings of small extent. The asthenosphere appears therefore as the graveyard of both small-scale convection and hot plumes generated in the system.

Androvandi, Sophie; Davaille, Anne; Limare, Angela; Foucquier, Aurélie; Marais, Catherine

2011-10-01

66

Standardized LM Tests for Spatial Error Dependence in Linear or Panel Regressions  

Microsoft Academic Search

The robustness of the LM tests for spatial error dependence of Burridge (1980) for the linear regression model and Anselin (1988) for the panel regression model are examined. While both tests are asymptotically robust against distributional misspecification, their finite sample behavior can be sensitive to the spatial layout. To overcome this shortcoming, standardized LM tests are suggested. Monte Carlo results

Badi H. Baltagi; Zhenlin Yang

2010-01-01

67

Temperature dependence, spatial scale, and tree species diversity in eastern Asia and North America  

E-print Network

Temperature dependence, spatial scale, and tree species diversity in eastern Asia and North America in eastern Asia and North America to investigate the roles of environmental temperature and spatial scale and temperature is much steeper in eastern Asia than in North America: in cold climates at high latitudes

Brown, James H.

68

Acute Effects of Alcohol on Intrusive Memory Development and Viewpoint Dependence in Spatial  

E-print Network

Acute Effects of Alcohol on Intrusive Memory Development and Viewpoint Dependence in Spatial Memory the effect of alcohol on intrusive memories and, concurrently, on egocentric and allocentric spatial memory. Methods: With a double-blind independent group design participants were administered alcohol (.4 or .8 g

Burgess, Neil

69

Path dependence and the validation of agent-based spatial models of DANIEL G. BROWN*{{, SCOTT PAGE{, RICK RIOLO{,  

E-print Network

Path dependence and the validation of agent-based spatial models of land use DANIEL G. BROWN dependence arises from negative and positive feedbacks. Negative feedbacks in the form of spatial dis-amenities

Brown, Daniel G.

70

Runoff source or sink? Biocrust hydrological function strongly depends on the relative abundance of mosses  

NASA Astrophysics Data System (ADS)

The redistribution of water in semi-arid environments is critical for overall ecosystem productivity. To a large degree, ecosystem engineers may determine the redistribution of water. Biological soil crusts (biocrusts) are one such group of ecosystem engineers. Their effects on infiltration have been somewhat controversial, varying from place to place and ranging from strongly positive to strongly negative. In addition, they coexist with and are modified by additional ecosystem engineers. We used a systems approach to examine the interactive effects of multiple engineers on infiltration processes across two analogous sets of interactors. First in Spain, we examined interactions among Stipa tenacissima, biocrusts, and the European rabbit; and in Australia, the interaction between biocrusts and the bilby (a rabbit-like marsupial). We focused on the effects of particular community properties of biocrusts such as species richness, total cover, species composition, and spatial patterning to characterize their variable effects on infiltration. We measured the early (sorptivity) and later (steady-state infiltration) stages of infiltration at two supply potentials using disk permeameters, which allowed us to determine the relative effects of different engineers and soil micropores on water flow through large macropores. In the Spanish case, structural equation modeling showed that both Stipa and biocrust cover exerted substantial and equal positive effects on infiltration under ponding, whereas indirectly, rabbit disturbance negatively affected infiltration by reducing crust cover; rabbits had negligible direct effects. The biocrust influence could be partitioned roughly equally between total cover and composition. All lichen species were negatively related to infiltration and almost all mosses were positively related to infiltration. In the Australian study, bilby forage pits had a direct and strong positive influence on steady state infiltration under ponding and most infiltration variables, and moderate effects on biocrust properties. Biocrust total cover and composition were again the most influential of biocrust community properties on infiltration, especially in the case of the composition effect on steady state infiltration under ponding. The key difference was that the Australian biocrusts primarily decreased infiltration. On dune runoff zones, later successional biocrusts (lichens, mosses, dark cyanobacterial crusts) of any type decreased infiltration rates compared to early successional crusts. On swale run-on zones, lichens impeded infiltration and mosses did not. These results highlight the importance of biocrusts as key players in the redistribution of water, and demonstrate the modulating role played by animal ecosystem engineers through their localized surface disturbances. Our studies highlight the central role of the relative abundance of mosses compared to other biocrust organisms as an underappreciated, and perhaps a key, determinant of biocrust hydrology.

Bowker, M. A.; Eldridge, D. J.; Maestre, F. T.

2012-04-01

71

Color Dependence in the Spatial Distribution of Satellite Galaxies  

E-print Network

We explore the color dependence of the radial profile of satellite galaxies around isolated parent galaxies. Samples of potential satellites selected from large galaxy redshift surveys are significantly contaminated by interlopers -- objects not bound to the parent galaxy. We use the Sloan Digital Sky Survey to estimate the interloper fraction in samples of candidate satellite galaxies. We show that samples of red and blue satellites have different interloper populations: a larger fraction of blue galaxies are likely to be interlopers compared to red galaxies. Both with and without interloper subtraction, the radial profile of blue satellites is significantly shallower than that of red satellites. In addition, while red and blue primaries have different interloper fractions, the slope of the corrected radial profiles are consistent after interloper correction. We discuss the implications of these results for galaxy formation models.

Jacqueline Chen

2007-11-07

72

Exact probabilistic solution of spatial-dependent stochastics and associated spatial potential landscape for the bicoid protein  

NASA Astrophysics Data System (ADS)

We investigated the spatial-dependent stochastic effects originating from the finite number of bicoid proteins in Drosophila melanogaster, which are crucial to cell development. We obtained an exact solution to the spatial-dependent stochastic chemical master equation and recovered the usual reaction-diffusion solution for the average of the bicoid concentration, valid in the bulk. We also used the steady state probability to get the spatial potential landscape. The stochastic effects are captured by the Poisson distribution; so, as the average of the bicoid concentration decreases from the anterior (A) to the posterior (P) of the embryo, the statistical fluctuations also decrease. An alternative way of interpreting this is that the shape of the spatial potential landscape shrinks from A to P. While the mathematical result is known, we offer a simple approach to understanding why it is what it is and give associated physical intuitions. The approach can be generalized and applied to any problem with a particle that diffuses, decays, and has a stochastic source.

Lepzelter, David; Wang, Jin

2008-04-01

73

Extraordinary photoluminescence and strong temperature/angle-dependent Raman responses in few-layer phosphorene.  

PubMed

Phosphorene is a new family member of two-dimensional materials. We observed strong and highly layer-dependent photoluminescence in few-layer phosphorene (two to five layers). The results confirmed the theoretical prediction that few-layer phosphorene has a direct and layer-sensitive band gap. We also demonstrated that few-layer phosphorene is more sensitive to temperature modulation than graphene and MoS2 in Raman scattering. The anisotropic Raman response in few-layer phosphorene has enabled us to use an optical method to quickly determine the crystalline orientation without tunneling electron microscopy or scanning tunneling microscopy. Our results provide much needed experimental information about the band structures and exciton nature in few-layer phosphorene. PMID:25188827

Zhang, Shuang; Yang, Jiong; Xu, Renjing; Wang, Fan; Li, Weifeng; Ghufran, Muhammad; Zhang, Yong-Wei; Yu, Zongfu; Zhang, Gang; Qin, Qinghua; Lu, Yuerui

2014-09-23

74

Experimental investigation of the energy dependence of the strong coupling strength  

NASA Astrophysics Data System (ADS)

The energy dependence of the relative production rate of three-jet events is studied in hadronic e +e - annihilation events at center of mass energies between 22 and 46.7 GeV. Three-jet events are defined by a jet finding algorithm which is closely related to the definition of resolvable jets used in O( ?s2) perturbative QCD calculations, where the relative production rate of three-jet events is roughly proportional to the size of the strong coupling strength. The production rates of three-jet events in the data decrease significantly with increasing centre of mass energy. The experimental rates, which are independent of fragmentation model calculations, can be directly compared to theoretically calculated jet production rates and are in good agreement with the QCD expectations of a running coupling strength. The hypothesis of an energy independent coupling constant can be excluded with a significance of four standard derivations.

Bethke, S.; Allison, J.; Ambrus, K.; Barlow, R. J.; Bartel, W.; Bowdery, C. K.; Cartwright, S. L.; Chrin, J.; Clarke, D.; Dieckmann, A.; Duerdoth, I. P.; Eckerlin, G.; Elsen, E.; Felst, R.; Finch, A. J.; Foster, F.; Greenshaw, T.; Hagemann, J.; Haidt, D.; Heintze, J.; Heinzelmann, G.; Hellenbrand, K. H.; Hill, P.; Hughes, G.; Kado, H.; Kawagoe, K.; Kleinwort, C.; Knies, G.; Kobayashi, T.; Komamiya, S.; Krehbiel, H.; von Krogh, J.; Kuhlen, M.; Loebinger, F. K.; Macbeth, A. A.; Magnussen, N.; Marshall, R.; Meinke, R.; Middleton, R. P.; Minowa, M.; Murphy, P. G.; Naroska, B.; Nye, J. M.; Olsson, J.; Ould-Saada, F.; Petersen, A.; Ramcke, R.; Rieseberg, H.; Schmidt, D.; Schmitt, H. vd.; Smolik, L.; Schneekloth, U.; Skard, J. A. J.; Spitzer, J.; Steffen, P.; Stephens, K.; Wagner, A.; Walker, I. W.; Warming, P.; Weber, G.; Zimmer, M.; Zorn, G. T.; JADE Collaboration

1988-10-01

75

Strong selection or rejection of spatially periodic patterns in degenerate bifurcations  

NASA Astrophysics Data System (ADS)

When studying bifurcating space-periodic solutions one often has a situation, common in many problems of fluid dynamics, in which in the R-k plane ( R a control parameter such as Reynolds number, k wave number) the passage from linear stability to instability is characterized by a parabola-like curve, having a minimum at Rc, kc. We analyse classes of problems in which the coefficients of nonlinear terms in the amplitude equation go through zero near kc. Various examples of such degenerate problems can be found in the literature, but have not been studied yet. We give an extensive classification of bifurcation pictures, which display rather unusual behaviour. We further study the stability of these periodic solutions subject to quite general perturbation. We find as a general result that all bifurcating solutions are unstable except for a small neighbourhood of a curve ? in the R-k plane. There is hence a strong selection mechanism of (periodic) patterns, which fixes, for each value of R, with a very small uncertainty, the wave number of the stable bifurcating periodic solution. For one class of problems the curve ? continues to exist for all values of R for which our theory is consistent. For another class the curve stops at a value R ? > R c. For R > R ? all bifurcating periodic solutions are unstable. In this case instability provides a mechanism of rejection of all periodic patterns. In the last section we analyse the particular case of the Blasius boundary-layer flow.

Eckhaus, Wiktor; Iooss, Gérard

1989-10-01

76

Gas depletion in cluster galaxies depends strongly on their internal structure  

NASA Astrophysics Data System (ADS)

We analyse galaxies in 300 nearby groups and clusters identified in the Sloan Digital Sky Survey using a photometric gas mass indicator that is useful for estimating the degree to which the interstellar medium of a cluster galaxy has been depleted. We study the radial dependence of inferred gas mass fractions for galaxies of different stellar masses and stellar surface densities. At fixed cluster-centric distance and at fixed stellar mass, lower density galaxies are more strongly depleted of their gas than higher density galaxies. An analysis of depletion trends in the two-dimensional plane of stellar mass M* and stellar mass surface density ?* reveals that gas depletion at fixed cluster-centric radius is much more sensitive to the density of a galaxy than to its mass. We suggest that low-density galaxies are more easily depleted of their gas, because they are more easily affected by ram-pressure and/or tidal forces. We also look at the dependence of our gas fraction/radius relations on the velocity dispersion of the cluster, finding no clear systematic trend.

Zhang, Wei; Li, Cheng; Kauffmann, Guinevere; Xiao, Ting

2013-03-01

77

Ascaroside Expression in Caenorhabditis elegans Is Strongly Dependent on Diet and Developmental Stage  

PubMed Central

Background The ascarosides form a family of small molecules that have been isolated from cultures of the nematode Caenorhabditis elegans. They are often referred to as “dauer pheromones” because most of them induce formation of long-lived and highly stress resistant dauer larvae. More recent studies have shown that ascarosides serve additional functions as social signals and mating pheromones. Thus, ascarosides have multiple functions. Until now, it has been generally assumed that ascarosides are constitutively expressed during nematode development. Methodology/Principal Findings Cultures of C. elegans were developmentally synchronized on controlled diets. Ascarosides released into the media, as well as stored internally, were quantified by LC/MS. We found that ascaroside biosynthesis and release were strongly dependent on developmental stage and diet. The male attracting pheromone was verified to be a blend of at least four ascarosides, and peak production of the two most potent mating pheromone components, ascr#3 and asc#8 immediately preceded or coincided with the temporal window for mating. The concentration of ascr#2 increased under starvation conditions and peaked during dauer formation, strongly supporting ascr#2 as the main population density signal (dauer pheromone). After dauer formation, ascaroside production largely ceased and dauer larvae did not release any ascarosides. These findings show that both total ascaroside production and the relative proportions of individual ascarosides strongly correlate with these compounds' stage-specific biological functions. Conclusions/Significance Ascaroside expression changes with development and environmental conditions. This is consistent with multiple functions of these signaling molecules. Knowledge of such differential regulation will make it possible to associate ascaroside production to gene expression profiles (transcript, protein or enzyme activity) and help to determine genetic pathways that control ascaroside biosynthesis. In conjunction with findings from previous studies, our results show that the pheromone system of C. elegans mimics that of insects in many ways, suggesting that pheromone signaling in C. elegans may exhibit functional homology also at the sensory level. In addition, our results provide a strong foundation for future behavioral modeling studies. PMID:21423575

Kaplan, Fatma; Srinivasan, Jagan; Mahanti, Parag; Ajredini, Ramadan; Durak, Omer; Nimalendran, Rathika; Sternberg, Paul W.; Teal, Peter E. A.; Schroeder, Frank C.; Edison, Arthur S.; Alborn, Hans T.

2011-01-01

78

Compton scattering in strong magnetic fields: Spin-dependent influences at the cyclotron resonance  

NASA Astrophysics Data System (ADS)

The quantum electrodynamical (QED) process of Compton scattering in strong magnetic fields is commonly invoked in atmospheric and inner magnetospheric models of x-ray and soft gamma-ray emission in high-field pulsars and magnetars. A major influence of the field is to introduce resonances at the cyclotron frequency and its harmonics, where the incoming photon accesses thresholds for the creation of virtual electrons or positrons in intermediate states with excited Landau levels. At these resonances, the effective cross section typically exceeds the classical Thomson value by over 2 orders of magnitude. Near and above the quantum critical magnetic field of 44.13 TeraGauss, relativistic corrections must be incorporated when computing this cross section. This profound enhancement underpins the anticipation that resonant Compton scattering is a very efficient process in the environs of highly magnetized neutron stars. This paper presents formalism for the QED magnetic Compton differential cross section valid for both subcritical and supercritical fields, yet restricted to scattered photons that are below pair creation threshold. Calculations are developed for the particular case of photons initially propagating along the field, and in the limit of zero vacuum dispersion, mathematically simple specializations that are germane to interactions involving relativistic electrons frequently found in neutron star magnetospheres. This exposition of relativistic, quantum, magnetic Compton cross sections treats electron spin dependence fully, since this is a critical feature for describing the finite decay lifetimes of the intermediate states. Such lifetimes are introduced to truncate the resonant cyclotronic divergences via standard Lorentz profiles. The formalism employs both the traditional Johnson and Lippmann (JL) wave functions and the Sokolov and Ternov (ST) electron eigenfunctions of the magnetic Dirac equation. The ST states are formally correct for self-consistently treating spin-dependent effects that are so important in the resonances. It is found that the values of the polarization-dependent differential cross section depend significantly on the choice of ST or JL eigenstates when in the fundamental resonance but not outside of it, a characteristic that is naturally expected. Relatively compact analytic forms for the cross sections are presented that will prove useful for astrophysical modelers.

Gonthier, Peter L.; Baring, Matthew G.; Eiles, Matthew T.; Wadiasingh, Zorawar; Taylor, Caitlin A.; Fitch, Catherine J.

2014-08-01

79

Pump power dependence of the spatial gating properties of femtosecond optical Kerr effect measurements  

NASA Astrophysics Data System (ADS)

The pump power dependence of the spatial gating properties of femtosecond optical Kerr gate (OKG) was investigated using coaxial two-color optical Kerr measurements in CS2. As the pump power increased, the spatial pattern of the optical Kerr signals changed from a Gaussian spot to a ring form, and then a spot surrounded by a concentric ring, successively. By comparing the experimental data with the calculation results and measuring the pump power dependence of the OKG signal intensity, we demonstrated that the spatial variation of OKG transmittance could be attributed to the non-uniform spatially distributed phase change of the probe beam, due to the transient birefringence effect induced by pump beam with transverse mode of a Gaussian distribution.

Wang, Xiaofang; He, Pengchao; Yan, Lihe; Si, Jinhai; Chen, Feng; Hou, Xun

2013-08-01

80

Area dependence of interlayer tunneling in strongly correlated bilayer two-dimensional electron systems at T=1  

E-print Network

Area dependence of interlayer tunneling in strongly correlated bilayer two-dimensional electron­16 Electrons are just as strongly correlated with their neighbors in their own layer as they are with elec.35.Lk Bilayer two-dimensional electron systems 2DESs in a large perpendicular magnetic field B support

Eisenstein, Jim

81

The Efficiency of Magma Ocean Cumulate Overturn using a strong temperature-dependent Viscosity  

NASA Astrophysics Data System (ADS)

The impact heat accumulated during the late stage of the planetary accretion can melt a significant part or even the entire mantle of a planetary body - producing a global magma ocean. The subsequent cooling of the interior causes the magma ocean to freeze rapidly from the core-mantle boundary to the surface due to the steeper slope of the mantle adiabat compared to the slope of the solidus. Freezing of a magma ocean is a highly complex process, which has been investigated by several authors [e.g. 1, 2]. In the present work, we assume fractional crystallization of such a magma ocean. For fractional crystallization, dense cumulates are produced with time close to the surface, largely due to iron enrichment in the evolving magma ocean liquid [2]. A gravitationally unstable mantle forms, which is prone to overturn. We investigate the cumulate overturn and its influence on the thermal evolution of Mars using the 3D spherical/2D cylindrical mantle convection code Gaia [3, 4]. We present different simulations using the initial conditions from [2] and a strong temperature dependence of the viscosity. Our simulations show that using a rather weak temperature dependence of the viscosity (e.g. using an activation energy of 100 kJ/mol as in [2]) results in a complete overturn (i.e. dense cumulates from the surface sink to the core mantle boundary). A stable density gradient evolves in the mantle, in which the convection ceases and cannot be rejuvenated during the entire evolution of Mars even with heating by radioactive elements. The lack of convection, however, is not compatible with the observed long-standing volcanic activity and elastic thickness estimates on Mars. When using a strongly temperature dependent viscosity (e.g. typical activation energy for mantle material of 300 kJ/mol), a stagnant lid forms rapidly on top of the convective interior preventing the uppermost dense cumulates to overturn. The formation of the lid is also given assuming the high surface temperatures due to the efficient greenhouse effect caused by the degassing of the freezing magma ocean [2]. Below the dense stagnant lid, an initially stable density gradient settles which is, however, less steep than in the previous case. In that case, convection continues and the mantle is continuously remixed. The convection pattern is dominated by small scale structures, which is not consistent with the large scale volcanic surface structures. Moreover, the global primordial high density crust as suggested by this scenario is at odds with the assumed low density of the southern hemisphere [5]. We conclude that a fractionated global and deep magma ocean seems to be difficult to reconcile with observations. Further investigations assuming for instance a hemispherical or shallow magma ocean will be studied.

Plesa, A.-C.; Breuer, D.

2012-04-01

82

Visualisation of structural inhomogeneities in strongly scattering media using the method of spatially-resolved reflectometry: Monte Carlo simulation  

SciTech Connect

Two-dimensional spatial intensity distributions of diffuse scattering of near-infrared laser radiation from a strongly scattering medium, whose optical properties are close to those of skin, are obtained using Monte Carlo simulation. The medium contains a cylindrical inhomogeneity with the optical properties, close to those of blood. It is shown that stronger absorption and scattering of light by blood compared to the surrounding medium leads to the fact that the intensity of radiation diffusely reflected from the surface of the medium under study and registered at its surface has a local minimum directly above the cylindrical inhomogeneity. This specific feature makes the method of spatially-resolved reflectometry potentially applicable for imaging blood vessels and determining their sizes. It is also shown that blurring of the vessel image increases almost linearly with increasing vessel embedment depth. This relation may be used to determine the depth of embedment provided that the optical properties of the scattering media are known. The optimal position of the sources and detectors of radiation, providing the best imaging of the vessel under study, is determined. (biophotonics)

Bykov, A V; Priezzhev, A V; Myllylae, Risto A

2011-06-30

83

Restricted dispersal reduces the strength of spatial density dependence in a tropical bird population  

PubMed Central

Spatial processes could play an important role in density-dependent population regulation because the disproportionate use of poor quality habitats as population size increases is widespread in animal populations—the so-called buffer effect. While the buffer effect patterns and their demographic consequences have been described in a number of wild populations, much less is known about how dispersal affects distribution patterns and ultimately density dependence. Here, we investigated the role of dispersal in spatial density dependence using an extraordinarily detailed dataset from a reintroduced Mauritius kestrel (Falco punctatus) population with a territorial (despotic) breeding system. We show that recruitment rates varied significantly between territories, and that territory occupancy was related to its recruitment rate, both of which are consistent with the buffer effect theory. However, we also show that restricted dispersal affects the patterns of territory occupancy with the territories close to release sites being occupied sooner and for longer as the population has grown than the territories further away. As a result of these dispersal patterns, the strength of spatial density dependence is significantly reduced. We conclude that restricted dispersal can modify spatial density dependence in the wild, which has implications for the way population dynamics are likely to be impacted by environmental change. PMID:18285284

Burgess, Malcolm D; Nicoll, Malcolm A.C; Jones, Carl G; Norris, Ken

2008-01-01

84

Need for Space: The Key Distance Effect Depends on Spatial Stimulus Configurations  

PubMed Central

In numerous psychological experiments, participants classify stimuli by pressing response keys. According to Lakens, Schneider, Jostmann, and Schubert (2011), classification performance is affected by physical distance between response keys – indicating a cognitive tendency to represent categories in spatial code. However, previous evidence for a key distance effect (KDE) from a color-naming Stroop task is inconclusive as to whether: (a) key separation automatically leads to an internal spatial representation of non-spatial stimulus characteristics in participants, or if the KDE rather depends on physical spatial characteristics of the stimulus configuration; (b) the KDE attenuates the Stroop interference effect. We therefore first adopted the original Stroop task in Experiment 1, confirming that wider key distance facilitated responses, but did not modulate the Stroop effect as was previously found. In Experiments 2 and 3 we controlled potential mediator variables in the original design. When we did not display instructions about stimulus-response mappings, thereby removing the unintended spatial context from the Stroop stimuli, no KDE emerged. Presenting the instructions at a central position in Experiment 4 confirmed that key separation alone is not sufficient for a KDE, but correspondence between spatial configurations of stimuli and responses is also necessary. Evidence indicates that the KDE on Stroop performance is due to known mechanisms of stimulus-response compatibility and response discriminability. The KDE does, however, not demonstrate a general disposition to represent any stimulus in spatial code. PMID:24642888

Stephan, Julia; Franz, Volker H.

2014-01-01

85

Modeling Spatial and Temporal Dependencies of User Mobility in Wireless Mobile Networks  

E-print Network

1 Modeling Spatial and Temporal Dependencies of User Mobility in Wireless Mobile Networks Wei-Jen Hsu, Thrasyvoulos Spyropoulos, Konstantinos Psounis and Ahmed Helmy Dept. of Computer and Information--Realistic mobility models are fundamental to eval- uate the performance of protocols in mobile ad hoc networks

86

Representing genetic variation as continuous surfaces: an approach for identifying spatial dependency in landscape genetic studies  

E-print Network

dependency in landscape genetic studies Melanie A. Murphy, Jeffrey S. Evans, Samuel A. Cushman and Andrew ecology and population genetics, has great potential to influence our understanding of habitat ecological data, spatial incorpora- tion of neutral multilocus genetic data presents two unique complexities

Storfer, Andrew

87

ASSESSING FINGERPRINT INDIVIDUALITY USING EPIC: A CASE STUDY IN THE ANALYSIS OF SPATIALLY DEPENDENT MARKED  

E-print Network

ASSESSING FINGERPRINT INDIVIDUALITY USING EPIC: A CASE STUDY IN THE ANALYSIS OF SPATIALLY DEPENDENT MARKED PROCESSES By Chae Young Lim and Sarat C. Dass Michigan State University Fingerprint individuality refers to the extent of uniqueness of finger- prints and is governed by the distribution of fingerprint

Dass, Sarat C.

88

Spatial Learning Depends on Both the Addition and Removal of New Hippocampal Neurons  

E-print Network

neurogenesis to a developmental phenomenon has, however, been challenged by the discovery that new neuronsSpatial Learning Depends on Both the Addition and Removal of New Hippocampal Neurons David Dupret1 development. Learning promotes survival of relatively mature neurons, apoptosis of more immature cells

Boyer, Edmond

89

Drivers of bacterial -diversity depend on spatial scale Jennifer B. H. Martinya,1  

E-print Network

. As observed in studies of macroorganisms, the drivers of salt marsh bacterial -diversity depend on spatial diversification of ammonia-oxidizing bacteria taxa at the continental scale, de- spite an overall relationship). Understanding the mechanisms that gen- erate and maintain biodiversity is thus key to predicting ecosystem

German, Donovan P.

90

Time-dependent spatial amplitude patterns of harmonic tremor at Arenal volcano, Costa Rica  

E-print Network

Time-dependent spatial amplitude patterns of harmonic tremor at Arenal volcano, Costa Rica: seismic´afico Nacional, 28014 Madrid, Spain 4 Escuela Centroamericana de Geolog´ia, Universidad de Costa Rica, AP 214-2060 San Jos´e, Costa Rica 5 Institut des Sciences de la Terre, Universit´e de Savoie, CNRS, F-73376 Le

Paris-Sud XI, Université de

91

Plume formation in strongly temperature-dependent viscosity fluids: Application to early Mars  

NASA Astrophysics Data System (ADS)

One of the most prominent features of Mars is the hemispherical dichotomy. The Martian surface consists of a heavily cratered elevated southern hemisphere and a resurfaced depressed northern hemisphere. The dichotomy seems to have formed very early in the history of the planet. Another interesting feature is a remnant magnetization of the crust, which suggests that early Mars had a magnetic field. Investigation of the origin of these features provides insights into the early history of Mars as well as other terrestrial planets including Earth. We develop a hypothesis that the dichotomy is caused by an early transient superplume produced by a hot Martian core. At first glance, the superplume hypothesis seems unlikely because the number of plumes in typical fluids heated from below is very large and the plumes are relatively small. However, solid rocks are rather unusual fluids whose viscosity varies with temperature by many orders of magnitude. Plume formation in such fluids is a complex and poorly understood phenomena. Thus, we begin with a systematic two- dimensional numerical and theoretical investigation of plume formation in strongly temperature-dependent viscosity fluids. Then we extend both the numerical calculations and the theory to fully three-dimensional geometry. We find the conditions under which a single transient superplume forms. One of the most important conditions is the requirement that the core was at least several hundred degrees Kelvin hotter than the mantle. Geophysical data and theoretical models of core formation suggest that this is likely to be the case. We find that the superplume can easily satisfy the timing constraints on the formation of the dichotomy. In the last part we consider the coupled core-mantle thermal evolution and investigate the cooling of the initially superheated core and the generation of the magnetic field on early Mars. We show that the core cooling is sufficiently rapid to induce convection inside the core and allow the operation of the magnetic dynamo. In our models, the magnetic field exists for millions to hundreds of millions of years after planetary formation, which is consistent with observations.

Ke, Yun

92

Multi-scale Convection in a Mantle with Strongly Temperature-dependent Rheology  

NASA Astrophysics Data System (ADS)

Owing to the heterogeneity and complex rheology of mantle material, several scales of convection coexist in the Earth's mantle, producing cold linear slabs, mid-ocean ridges, 3D superswells and hot spots. However, if those features have individually been generated and studied in numerical and laboratory experiments, the exact conditions for their coexistence in a self-consistent convective model have remained elusive. We studied the characteristics of thermal instabilities developping when a layer of sugar syrup, a fluid with a strongly temperature-dependent viscosity and high Prandtl number (> 7000), is heated from below and cooled from above. A new visualization technique allowed to determine both the temperature and velocity fields inside the experimental tank. We focuss on high Rayleigh numbers (1.7x106 to 3.3x107) and intermediate viscosity ratios (7 to 4100). For this parameter range, "sluggish lid" convection occurs, in which three different scales of convection develop. Owing to the viscosity increase with decreasing temperature, the tank thermal structure becomes asymmetric: thermal boundary layer (TBL) instabilities, typical of high Rayleigh number convection, develop under the coldest, therefore most viscous, part of the upper thermal boundary layer which cannot move as fast as the less viscous fluid. The largest convective scale is therefore cellular, with cold downwelling sheets of viscous fluid encasing hotter parts of the tank. Within each of those cells develop several (typically 3 to 7) hot 3D upwelling plumes. Upon impinging under the cold TBL, each plume in turn generates locally a small ring of cold material which does not reach the bottom of the tank. The introduction of a denser layer at the bottom of the tank can vary the morphology of the hot instabilities but has no influence on the existence of the large-scale cold circulation. Hence high Rayleigh thermal convection in the sluggish lid regim can produce large-scale cells delimited by cold subducting slabs, within which several 3D plumes develop. On Earth, two of such cells exist, the Pacific and the Indo-Atlantic boxes. Our experiments further suggest that what has been named the two "hot superplumes", i.e. the two seismically slow regions encased within the subduction rings, are in fact each constitued of several hot instabilities.

Androvandi, S.; Davaille, A.

2007-12-01

93

Scale dependency of fracture energy and estimates thereof via dynamic rupture solutions with strong thermal weakening  

NASA Astrophysics Data System (ADS)

Seismological estimates of fracture energy show a scaling with the total slip of an earthquake [e.g., Abercrombie and Rice, GJI 2005]. Potential sources for this scale dependency are coseismic fault strength reductions that continue with increasing slip or an increasing amount of off-fault inelastic deformation with dynamic rupture propagation [e.g., Andrews, JGR 2005; Rice, JGR 2006]. Here, we investigate the former mechanism by solving for the slip dependence of fracture energy at the crack tip of a dynamically propagating rupture in which weakening takes place by strong reductions of friction via flash heating of asperity contacts and thermal pressurization of pore fluid leading to reductions in effective normal stress. Laboratory measurements of small characteristic slip evolution distances for friction (~10 ?m at low slip rates of ?m-mm/s, possibly up to 1 mm for slip rates near 0.1 m/s) [e.g., Marone and Kilgore, Nature 1993; Kohli et al., JGR 2011] imply that flash weakening of friction occurs at small slips before any significant thermal pressurization and may thus have a negligible contribution to the total fracture energy [Brantut and Rice, GRL 2011; Garagash, AGU 2011]. The subsequent manner of weakening under thermal pressurization (the dominant contributor to fracture energy) spans a range of behavior from the deformation of a finite-thickness shear zone in which diffusion is negligible (i.e., undrained-adiabatic) to that in which large-scale diffusion obscures the existence of a thin shear zone and thermal pressurization effectively occurs by the heating of slip on a plane. Separating the contribution of flash heating, the dynamic rupture solutions reduce to a problem with a single parameter, which is the ratio of the undrained-adiabatic slip-weakening distance (?c) to the characteristic slip-on-a-plane slip-weakening distance (L*). However, for any value of the parameter, there are two end-member scalings of the fracture energy: for small slip, the undrained-adiabatic behavior expectedly results in fracture energy scaling as G ~ ?^2, and for large slip (where TP approaches slip on a plane) we find that G ~ ?^(2/3). This last result is a slight correction to estimates made assuming a constant, kinematically imposed slip rate and slip-on-a-plane TP resulting in G ~ ?^(1/2) [Rice, JGR 2006]. We compile fracture energy estimates of both continental and subduction zone earthquakes. In doing so, we incorporate independent estimates of fault prestress to distinguish fracture energy G from the parameter G' defined by Abercrombie and Rice [2005], which represents the energetic quantity that is most directly inferred following seismological estimates of radiated energy, seismic moment and source radius. We find that the dynamic rupture solutions (which account for the variable manner of thermal pressurization and result in a self-consistent slip rate history) allow for a close match of the estimated fracture energy over several orders of total event slip, further supporting the proposed explanation that fracture energy scaling may largely be attributed to a fault strength that weakens gradually with slip, and additionally, the potential prevalence of thermal pressurization.

Viesca, R. C.; Garagash, D.

2013-12-01

94

Gaze-dependent spatial updating of tactile targets in a localization task  

PubMed Central

There is concurrent evidence that visual reach targets are represented with respect to gaze. For tactile reach targets, we previously showed that an effector movement leads to a shift from a gaze-independent to a gaze-dependent reference frame. Here we aimed to unravel the influence of effector movement (gaze shift) on the reference frame of tactile stimuli using a spatial localization task (yes/no paradigm). We assessed how gaze direction (fixation left/right) alters the perceived spatial location (point of subjective equality) of sequentially presented tactile standard and visual comparison stimuli while effector movement (gaze fixed/shifted) and stimulus order (vis-tac/tac-vis) were varied. In the fixed-gaze condition, subjects maintained gaze at the fixation site throughout the trial. In the shifted-gaze condition, they foveated the first stimulus, then made a saccade toward the fixation site where they held gaze while the second stimulus appeared. Only when an effector movement occurred after the encoding of the tactile stimulus (shifted-gaze, tac-vis), gaze similarly influenced the perceived location of the tactile and the visual stimulus. In contrast, when gaze was fixed or a gaze shift occurred before encoding of the tactile stimulus, gaze differentially affected the perceived spatial relation of the tactile and the visual stimulus suggesting gaze-dependent coding of only one of the two stimuli. Consistent with previous findings this implies that visual stimuli vary with gaze irrespective of whether gaze is fixed or shifted. However, a gaze-dependent representation of tactile stimuli seems to critically depend on an effector movement (gaze shift) after tactile encoding triggering spatial updating of tactile targets in a gaze-dependent reference frame. Together with our recent findings on tactile reaching, the present results imply similar underlying reference frames for tactile spatial perception and action. PMID:24575060

Mueller, Stefanie; Fiehler, Katja

2014-01-01

95

Aphid and ladybird beetle abundance depend on the interaction of spatial effects and genotypic diversity.  

PubMed

Intraspecific variation and genotypic diversity of host-plants can affect the structure of associated arthropod communities and the dynamics of populations. Similarly, neighboring plants can also affect interactions between host-plants and their associated arthropods. However, most studies on the effects of host-plant genotypes have largely ignored the potential effects of neighboring host-plants on arthropod communities. In this study, we used a common garden experiment to ask how spatial effects of neighboring patches, along with genotype identity and genotypic diversity in tall goldenrod (Solidago altissima), affect the abundances of a common goldenrod herbivore (Uroleucon nigrotuberculatum) and their dominant predator (Harmonia axyridis, a ladybird beetle). Aphid abundance varied 80-fold among genotypes, while ladybird beetle abundance was not affected by genotype identity. Additionally, there were strong effects of neighboring plots: aphid abundance in a focal plot was positively correlated to aphid abundance in nearby plots, suggesting strong spatial patterning in the abundance of aphids. Neither aphid nor ladybird beetle abundance was affected by genotypic diversity. However, focal plot genotypic diversity mediated the strength of the neighborhood effect (i.e., strong effects for genotype polyculture focal plots and weak effects for genotype monoculture focal plots). Our results show that aphids were directly influenced by host-plant genotype identity while ladybird beetles responded mainly to prey abundance, and suggest that genotypic diversity can influence the effects of spatial processes on the plant-herbivore interactions. PMID:21805301

Genung, Mark A; Crutsinger, Gregory M; Bailey, Joseph K; Schweitzer, Jennifer A; Sanders, Nathan J

2012-01-01

96

Hippocampus-dependent place learning enables spatial flexibility in C57BL6/N mice  

PubMed Central

Spatial navigation is a fundamental capability necessary in everyday life to locate food, social partners, and shelter. It results from two very different strategies: (1) place learning which enables for flexible way finding and (2) response learning that leads to a more rigid “route following.” Despite the importance of knockout techniques that are only available in mice, little is known about mice' flexibility in spatial navigation tasks. Here we demonstrate for C57BL6/N mice in a water-cross maze (WCM) that only place learning enables spatial flexibility and relearning of a platform position, whereas response learning does not. This capability depends on an intact hippocampal formation, since hippocampus lesions by ibotenic acid (IA) disrupted relearning. In vivo manganese-enhanced magnetic resonance imaging revealed a volume loss of ?60% of the hippocampus as a critical threshold for relearning impairments. In particular the changes in the left ventral hippocampus were indicative of relearning deficits. In summary, our findings establish the importance of hippocampus-dependent place learning for spatial flexibility and provide a first systematic analysis on spatial flexibility in mice. PMID:23293591

Kleinknecht, Karl R.; Bedenk, Benedikt T.; Kaltwasser, Sebastian F.; Grunecker, Barbara; Yen, Yi-Chun; Czisch, Michael; Wotjak, Carsten T.

2012-01-01

97

Effects of the symmetry energy on strongly-magnetized neutron stars in the density-dependent RMF model  

NASA Astrophysics Data System (ADS)

We investigate the structure of neutron stars with strong magnetic fields by using a density-dependent relativistic mean field model. The coupling constant between nucleons and the rho meson in the model is obtained by using the polytropic formula for the symmetry energy in the neutron star. With the density-dependent coupling constant, the effects of the symmetry energy on strongly-magnetized neutron stars are considered in detail for particle fractions and the equation of state. The consequent changes in the masses and the radii of the neutron star are discussed by using the roles of the symmetry energy in the neutron star.

Ryu, Chung-Yeol; Cheoun, Myung-Ki

2013-07-01

98

Spatial resolution is dependent on image content for SPECT with iterative reconstruction incorporating distance dependent resolution (DDR) correction.  

PubMed

The aim of this study is to determine the dependence of single photon emission computed tomography (SPECT) spatial resolution on the content of images for iterative reconstruction with distance dependent resolution (DDR) correction. An experiment was performed using a perturbation technique to measure change in resolution of line sources in simple and complex images with iterative reconstruction with increasing iteration. Projections of the line sources were reconstructed alone and again after the addition of projections of a uniform flood or a complex phantom. An alternative experiment used images of a realistic brain phantom and evaluated an effective spatial resolution by matching the images to the digital version of the phantom convolved with 3D Gaussian kernels. The experiments were performed using ordered subset expectation maximisation iterative reconstruction with and without the use of DDR correction. The results show a significant difference in reconstructed resolution between images of line sources depending on the content of the added image. The full width at half maximum of images of a line source reconstructed using DDR correction increased by 20-30 % when the added image was complex. Without DDR this difference was much smaller and disappeared with increasing iteration. Reported SPECT resolution should be taken as indicative only with regard to clinical imaging if the measurement is made using a point or line source alone and an iterative reconstruction algorithm is used. PMID:25005848

Badger, Daniel; Barnden, Leighton

2014-09-01

99

Group velocity of acoustic waves in strongly scattering media: Dependence on the volume fraction of scatterers  

Microsoft Academic Search

We study, both experimentally and theoretically, the ballistic propagation of ultrasonic wave pulses through a random strongly scattering medium as a function of the volume fraction of the scatterers. The scattering medium consists of a liquid suspension of monodisperse glass beads, whose concentration is varied by controlling the upward flow of the liquid in a fluidized bed. At intermediate frequencies,

M. L. Cowan; K. Beaty; J. H. Page; Zhengyou Liu; Ping Sheng

1998-01-01

100

Transition from the strong-to the weak-coupling regime in semiconductor microcavities: Polarization dependence  

E-print Network

is a structure formed by high reflecting dielectric mirrors distributed Bragg reflectors on the two sides described in the framework of the weak-coupling WC and strong-coupling SC regimes.7 If the cavity- mirror of fosc ex at high car- rier density: the blocking mechanism due to the Pauli exclu- sion principle phase

Viña, Luis

101

Folding Study of Venus Reveals a Strong Ion Dependence of Its Yellow Fluorescence under Mildly Acidic Conditions*S  

E-print Network

Folding Study of Venus Reveals a Strong Ion Dependence of Its Yellow Fluorescence under Mildly- cencethatisrelativelyinsensitivetochangesinpHandionconcen- trations. Here, we present a detailed study of the stability and fold- ing of Venus. By following hydrogen-deuterium exchange of 15 N-labeled Venus using NMR spectroscopy over 13 months, residue

Jackson, Sophie

102

Luteolin Inhibits Microglia and Alters Hippocampal-Dependent Spatial Working Memory in Aged Mice123  

PubMed Central

A dysregulated overexpression of inflammatory mediators by microglia may facilitate cognitive aging and neurodegeneration. Considerable evidence suggests the flavonoid luteolin has antiinflammatory effects, but its ability to inhibit microglia, reduce inflammatory mediators, and improve hippocampal-dependent learning and memory in aged mice is unknown. In initial studies, pretreatment of BV-2 microglia with luteolin inhibited the induction of inflammatory genes and the release of inflammatory mediators after lipopolysaccharide (LPS) stimulation. Supernatants from LPS-stimulated microglia caused discernible death in Neuro.2a cells. However, treating microglia with luteolin prior to LPS reduced neuronal cell death caused by conditioned supernatants, indicating luteolin was neuroprotective. In subsequent studies, adult (3–6 mo) and aged (22–24 mo) mice were fed control or luteolin (20 mg/d)-supplemented diet for 4 wk and spatial working memory was assessed as were several inflammatory markers in the hippocampus. Aged mice fed control diet exhibited deficits in spatial working memory and expression of inflammatory markers in the hippocampus indicative of increased microglial cell activity. Luteolin consumption improved spatial working memory and restored expression of inflammatory markers in the hippocampus compared with that of young adults. Luteolin did not affect either spatial working memory or inflammatory markers in young adults. Taken together, the current findings suggest dietary luteolin enhanced spatial working memory by mitigating microglial-associated inflammation in the hippocampus. Therefore, luteolin consumption may be beneficial in preventing or treating conditions involving increased microglial cell activity and inflammation. PMID:20685893

Jang, Saebyeol; Dilger, Ryan N.; Johnson, Rodney W.

2010-01-01

103

Nicotine dependence more strongly correlates with psychological distress in disadvantaged areas of Kazakhstan than Germany.  

PubMed

The aim of this study was to describe the association of current smoking and nicotine dependence with psychological distress in socially disadvantaged urban areas of Germany and Kazakhstan. Random samples of people living in disadvantaged areas of Berlin, Germany, and Almaty, Kazakhstan, were assessed using the General Health Questionnaire with 28 items and the Fagerström Test for Nicotine Dependence. The association of both current smoking and nicotine dependence with psychological distress was assessed for each sample using linear regression analyses and compared between the two samples calculating t-values for the comparison of B-coefficients. Current smoking was equally associated with psychological distress in both countries, whereas the association of nicotine dependence and psychological distress was only seen for the Kazakh sample and significantly stronger than for the German sample. The results could not be explained by social characteristics. Possibly due to the lack of outpatient community mental health services for the treatment of common mental disorders, nicotine dependence was associated with psychological distress in the disadvantaged area of Kazakhstan. PMID:23807567

Ignatyev, Yuriy; Mundt, Adrian P

2014-10-01

104

The Mechano-Stability of Isolated Focal Adhesions is Strongly Dependent on pH  

PubMed Central

SUMMARY This report demonstrates that the mechanical stability of focal adhesions exhibits a biphasic and sensitive pH dependence. These studies used isolated focal adhesions, which retain many of the properties of the intracellular structures, including protein composition and force-dependent reinforcement by cytosolic proteins. The focal adhesion structures are least stable to applied force at a pH of 6.4, and significantly more stable at slightly higher and lower pH values. This trend is consistent with previous work that characterized the pH dependence of cell migration and may therefore be relevant to controlling the invasiveness of metastatic cancer cells. This approach is significant because it allows biochemical studies of large protein complexes previously studied only in cell culture, and therefore offers new opportunities for performing mechanistic studies of a range of factors that contribute to focal adhesion stability. PMID:22726685

Beaumont, Kristin Grant; Mrksich, Milan

2012-01-01

105

Native Birds and Alien Insects: Spatial Density Dependence in Songbird Predation of Invading Oak Gallwasps  

PubMed Central

Revealing the interactions between alien species and native communities is central to understanding the ecological consequences of range expansion. Much has been learned through study of the communities developing around invading herbivorous insects. Much less, however, is known about the significance of such aliens for native vertebrate predators for which invaders may represent a novel food source. We quantified spatial patterns in native bird predation of invading gall-inducing Andricus wasps associated with introduced Turkey oak (Quercus cerris) at eight sites across the UK. These gallwasps are available at high density before the emergence of caterpillars that are the principle spring food of native insectivorous birds. Native birds showed positive spatial density dependence in gall attack rates at two sites in southern England, foraging most extensively on trees with highest gall densities. In a subsequent study at one of these sites, positive spatial density dependence persisted through four of five sequential week-long periods of data collection. Both patterns imply that invading galls are a significant resource for at least some native bird populations. Density dependence was strongest in southern UK bird populations that have had longest exposure to the invading gallwasps. We hypothesise that this pattern results from the time taken for native bird populations to learn how to exploit this novel resource. PMID:23342048

Schönrogge, Karsten; Begg, Tracey; Stone, Graham N.

2013-01-01

106

Consistent order selection with strongly dependent data and its application to efficient estimation  

Microsoft Academic Search

Order selection based on criteria by Akaike (IEEE Trans. Automat. Control AC-19 (1974) 716), AIC, Schwarz (Ann. Stat. (1978) 461), BIC or Hannan and Quinn's (J. R. Stat. Soc. Ser. B (1979) 190) HIC is often applied in empirical examples. They have been used in the context of order selection of weakly dependent ARMA models, AR models with unit or

Javier Hidalgo

2002-01-01

107

Strong voltage-dependent inward rectification of inward rectifier K + channels is caused by intracellular spermine  

Microsoft Academic Search

Inward rectifier K+ channels mediate the K+ conductance at resting potential in many types of cell. Since these K+ channels do not pass outward currents (inward rectification) when the cell membrane is depolarized beyond a trigger threshold, they play an important role in controlling excitability. Both a highly voltage-dependent block by intracellular Mg2+ and an endogenous gating process are presently

B Fakler; U Brändle; E Glowatzki; S Weidemann; H.-P Zenner; J. P Ruppersberg

1995-01-01

108

Light-dependent induction of strongly increased microalgal growth by methanol  

Microsoft Academic Search

Low methanol concentrations (about 0.5% v\\/v) induce biomass production in cultures of the unicellular green alga Scenedesmus obliquus by more than 300%, compared to controls without this solvent. This effect on the microalgal growth was found to be dependent on the solvent concentration, the packed cell volume (PCV), light intensity and light quality. It could be shown that methanol addition

A. Theodoridou; D. Dornemann; K. Kotzabasis

2002-01-01

109

Depth of convection in a fluid with strongly temperature and pressure dependent viscosity  

SciTech Connect

We discuss the equations describing convective motion of a fluid with temperature and pressure dependent rheology. By combining observational constraints from plate tectonics with theoretical constraints deduced from the model equations and parameter values, we are led to the conclusion that shallow upper mantle convection is consistent with the equations of fluid dynamics.

Fowler, A.C.

1982-08-01

110

Physiological Mechanisms of the Effectiveness of Bilateral Stereotactic Cingulotomy against Strong Psychological Dependence in Drug Addicts  

Microsoft Academic Search

It is now generally believed that psychological dependence in drug addicts is determined not only socially, but also physiologically. At the Institute of the Human Brain (Russian Academy of Sciences), bilateral stereotactic cryocingulotomy has been used for treatment of drug addiction since 1998. To date, the surgery has been performed on 348 patients, which has made it possible to study

S. V. Medvedev; A. D. Anichkov; Yu. I. Polyakov

2003-01-01

111

Ideal gas in a strong gravitational field: Area dependence of entropy  

SciTech Connect

We study the thermodynamic parameters like entropy, energy etc. of a box of gas made up of indistinguishable particles when the box is kept in various static background spacetimes having a horizon. We compute the thermodynamic variables using both statistical mechanics as well as by solving the hydrodynamical equations for the system. When the box is far away from the horizon, the entropy of the gas depends on the volume of the box except for small corrections due to background geometry. As the box is moved closer to the horizon with one (leading) edge of the box at about Planck length (L{sub p}) away from the horizon, the entropy shows an area dependence rather than a volume dependence. More precisely, it depends on a small volume A{sub perpendicular}L{sub p}/2 of the box, up to an order O(L{sub p}/K){sup 2} where A{sub perpendicular} is the transverse area of the box and K is the (proper) longitudinal size of the box related to the distance between leading and trailing edge in the vertical direction (i.e. in the direction of the gravitational field). Thus the contribution to the entropy comes from only a fraction O(L{sub p}/K) of the matter degrees of freedom and the rest are suppressed when the box approaches the horizon. Near the horizon all the thermodynamical quantities behave as though the box of gas has a volume A{sub perpendicular}L{sub p}/2 and is kept in a Minkowski spacetime. These effects are: (i) purely kinematic in their origin and are independent of the spacetime curvature (in the sense that the Rindler approximation of the metric near the horizon can reproduce the results) and (ii) observer dependent. When the equilibrium temperature of the gas is taken to be equal to the horizon temperature, we get the familiar A{sub perpendicular}/L{sub p}{sup 2} dependence in the expression for entropy. All these results hold in a D+1 dimensional spherically symmetric spacetime. The analysis based on methods of statistical mechanics and the one based on thermodynamics applied to the gas treated as a fluid in static geometry, lead to the same results showing the consistency. The implications are discussed.

Kolekar, Sanved; Padmanabhan, T. [IUCAA, Pune University Campus, Ganeshkhind, Pune 411007 (India)

2011-03-15

112

How strongly does dating meteorites constrain the time-dependence of the fine-structure constant?  

E-print Network

We review our argument on the nature of the so-called meteorite constraint on the possible time-dependence of the fine-structure constant, emphasizing that dating meteorites at the present time is different in principle from searching directly for the traces in the past, as in the Oklo phenomenon and the QSO absorption lines. In the related literature, we still find some arguments not necessarily consistent with this difference to be taken properly into account. It does not immediately follow that any model-dependent approaches are useless in practice, though we cannot help suspecting that dating meteorites is no match for the Oklo and the QSO in probing the time-variability of the fine-structure constant, at this moment. Some of the relevance to the QSO data particularly in terms of the scalar field will be discussed.

Yasunori Fujii; Akira Iwamoto

2005-08-05

113

Laser based imaging of time depending microscopic scenes with strong light emission  

NASA Astrophysics Data System (ADS)

Investigating volume scatterometry methods based on short range LIDAR devices for non-static objects we achieved interesting results aside the intended micro-LIDAR: the high speed camera recording of the illuminated scene of an exploding wire -intended for Doppler LIDAR tests - delivered a very effective method of observing details of objects with extremely strong light emission. As a side effect a schlieren movie is gathered without any special effort. The fact that microscopic features of short time processes with high emission and material flow might be imaged without endangering valuable equipment makes this technique at least as interesting as the intended one. So we decided to present our results - including latest video and photo material - instead of a more theoretical paper on our progress concerning the primary goal.

Hahlweg, Cornelius; Wilhelm, Eugen; Rothe, Hendrik

2011-10-01

114

Compton scattering in strong magnetic fields: Spin-dependent influences at the cyclotron resonance  

E-print Network

The quantum electrodynamical (QED) process of Compton scattering in strong magnetic fields is commonly invoked in atmospheric and inner magnetospheric models of x-ray and soft gamma-ray emission in high-field pulsars and magnetars. A major influence of the field is to introduce resonances at the cyclotron frequency and its harmonics, where the incoming photon accesses thresholds for the creation of virtual electrons or positrons in intermediate states with excited Landau levels. At these resonances, the effective cross section typically exceeds the classical Thomson value by over 2 orders of magnitude. Near and above the quantum critical magnetic field of 44.13 TeraGauss, relativistic corrections must be incorporated when computing this cross section. This paper presents formalism for the QED magnetic Compton differential cross section valid for both subcritical and supercritical fields, yet restricted to scattered photons that are below pair creation threshold. Calculations are developed for the particular c...

Gonthier, Peter L; Eiles, Matthew T; Wadiasingh, Zorawar; Taylor, Caitlin A; Fitch, Catherine J

2014-01-01

115

Evidence for Two Populations of Classical Transneptunian Objects: The Strong Inclination Dependence of Classical Binaries  

E-print Network

We have searched 101 Classical transneptunian objects for companions with the Hubble Space Telescope. Of these, at least 21 are binary. The heliocentric inclinations of the objects we observed range from 0.6-34 degrees. We find a very strong anticorrelation of binaries with inclination. Of the 58 targets that have inclinations of less than 5.5 degrees, 17 are binary, a binary fraction of 29 +7/-6%. All 17 are similar-brightness systems. On the contrary, only 4 of the 42 objects with inclinations greater than 5.5 degrees have satellites and only 1 of these is a similar-brightness binary. This striking dichotomy appears to agree with other indications that the low eccentricity, non-resonant Classical transneptunian objects include two overlapping populations with significantly different physical properties and dynamical histories.

Keith S. Noll; William M. Grundy; Denise C. Stephens; Harold F. Levison; Susan D. Kern

2007-11-09

116

Transport lattice models of heat transport in skin with spatially heterogeneous, temperature-dependent perfusion  

PubMed Central

Background Investigation of bioheat transfer problems requires the evaluation of temporal and spatial distributions of temperature. This class of problems has been traditionally addressed using the Pennes bioheat equation. Transport of heat by conduction, and by temperature-dependent, spatially heterogeneous blood perfusion is modeled here using a transport lattice approach. Methods We represent heat transport processes by using a lattice that represents the Pennes bioheat equation in perfused tissues, and diffusion in nonperfused regions. The three layer skin model has a nonperfused viable epidermis, and deeper regions of dermis and subcutaneous tissue with perfusion that is constant or temperature-dependent. Two cases are considered: (1) surface contact heating and (2) spatially distributed heating. The model is relevant to the prediction of the transient and steady state temperature rise for different methods of power deposition within the skin. Accumulated thermal damage is estimated by using an Arrhenius type rate equation at locations where viable tissue temperature exceeds 42°C. Prediction of spatial temperature distributions is also illustrated with a two-dimensional model of skin created from a histological image. Results The transport lattice approach was validated by comparison with an analytical solution for a slab with homogeneous thermal properties and spatially distributed uniform sink held at constant temperatures at the ends. For typical transcutaneous blood gas sensing conditions the estimated damage is small, even with prolonged skin contact to a 45°C surface. Spatial heterogeneity in skin thermal properties leads to a non-uniform temperature distribution during a 10 GHz electromagnetic field exposure. A realistic two-dimensional model of the skin shows that tissue heterogeneity does not lead to a significant local temperature increase when heated by a hot wire tip. Conclusions The heat transport system model of the skin was solved by exploiting the mathematical analogy between local thermal models and local electrical (charge transport) models, thereby allowing robust, circuit simulation software to obtain solutions to Kirchhoff's laws for the system model. Transport lattices allow systematic introduction of realistic geometry and spatially heterogeneous heat transport mechanisms. Local representations for both simple, passive functions and more complex local models can be easily and intuitively included into the system model of a tissue. PMID:15548324

Gowrishankar, TR; Stewart, Donald A; Martin, Gregory T; Weaver, James C

2004-01-01

117

Modeling the spatial and temporal dependence in fMRI data  

PubMed Central

Summary Functional magnetic resonance imaging (fMRI) data sets are large and characterized by complex dependence structures driven by highly sophisticated neurophysiology and aspects of the experimental designs. Typical analyses investigating task-related changes in measured brain activity use a two-stage procedure in which the first stage involves subject-specific models and the second-stage specifies group (or population) level parameters. Customarily, the first-level accounts for temporal correlations between the serial scans acquired during one scanning session. Despite accounting for these correlations, fMRI studies often include multiple sessions and temporal dependencies may persist between the corresponding estimates of mean neural activity. Further, spatial correlations between brain activity measurements in different locations are often unaccounted for in statistical modeling and estimation. We propose a two-stage, spatio-temporal, autoregressive model which simultaneously accounts for spatial dependencies between voxels within the same anatomical region and for temporal dependencies between a subject’s estimates from multiple sessions. We develop an algorithm that leverages the special structure of our covariance model, enabling relatively fast and efficient estimation. Using our proposed method, we analyze fMRI data from a study of inhibitory control in cocaine addicts. PMID:19912175

Derado, Gordana; Bowman, F. DuBois; Kilts, Clinton D.

2010-01-01

118

Colour cues or spatial cues? Context-dependent preferences in the European greenfinch (Carduelis chloris).  

PubMed

Using featural cues such as colour to identify ephemeral food can increase foraging efficiency. Featural cues may change over time however; therefore, animals should use spatial cues to relocate food that occurs in a temporally stable position. We tested this hypothesis by measuring the cue preferences of captive greenfinches Carduelis chloris when relocating food hidden in a foraging tray. In these standardised associative learning trials, greenfinches favoured colour cues when returning to a foraging context that they had encountered before only once ("one-trial test") but switched to spatial cues when they had encountered that scenario on ten previous occasions ("repeated-trial test"). We suggest that repeated encounters generated a context in which individuals had a prior expectation of temporal stability, and hence context-dependent cue selection. Next, we trained birds to find food in the absence of colour cues but tested them in the presence of visual distracters. Birds were able to learn spatial cues after one encounter, but only when visual distracters were identical in colouration. When a colourful distracter was present in the test phase, cue selection was random. Unlike the first one-trial test, birds were not biased towards this colourful visual distracter. Together, these results suggest that greenfinches are able to learn both cue types, colour cue biases represent learning, not simply distraction, and spatial cues are favoured over colour cues only in temporally stable contexts. PMID:21170666

Herborn, Katherine; Alexander, Lucille; Arnold, Kathryn E

2011-03-01

119

Hydration-dependent dynamics of deeply cooled water under strong confinement.  

PubMed

We have measured the hydration-level dependence of the single-particle dynamics of water confined in the ordered mesoporous silica MCM-41. The dynamic crossover observed at full hydration is absent at monolayer hydration. The monolayer dynamics are significantly slower than those of water in a fully hydrated pore at ambient temperatures. At low temperatures, the opposite is found to be true. These results underscore the importance of water's tetrahedral hydrogen-bond network in accounting for its low temperature dynamic properties. PMID:23679419

Bertrand, C E; Liu, K-H; Mamontov, E; Chen, S-H

2013-04-01

120

Strong field ionization rates simulated with time-dependent configuration interaction and an absorbing potential  

NASA Astrophysics Data System (ADS)

Ionization rates of molecules have been modeled with time-dependent configuration interaction simulations using atom centered basis sets and a complex absorbing potential. The simulations agree with accurate grid-based calculations for the ionization of hydrogen atom as a function of field strength and for charge resonance enhanced ionization of H_2^+ as the bond is elongated. Unlike grid-based methods, the present approach can be applied to simulate electron dynamics and ionization in multi-electron polyatomic molecules. Calculations on HCl+ and HCO+ demonstrate that these systems also show charge resonance enhanced ionization as the bonds are stretched.

Krause, Pascal; Sonk, Jason A.; Schlegel, H. Bernhard

2014-05-01

121

Natal departure timing from spatially varying environments is dependent of individual ontogenetic status.  

PubMed

Natal departure timing represents one of the first crucial decisions for juveniles born in spatially varying environments that ultimately disappear, but our knowledge on its determinants is limited. The present study aimed at understanding the determinants of juvenile natal departure by releasing individually tagged juvenile pike (Esox lucius L.) with variable body size and trophic position in a temporary flooded grassland. Specifically, we investigated whether natal departure depends on individual competitive status ('competition hypothesis'), physiological tolerance to environmental conditions ('physiological hypothesis') or individual trophic position and the spatial heterogeneity of trophic resources ('trophic hypothesis'). The results indicated that departure timing was negatively correlated with body size at release, showing that the dominance status among competing individuals was not the main trigger of juvenile departure. A positive correlation between departure timing and individual body size at departure was observed, suggesting that inter-individual variability in physiological tolerance did not explain departure patterns. While individual growth performances were similar irrespective of the timing of natal departure, stable isotope analyses revealed that juveniles with higher trophic position departed significantly earlier than individuals with lower trophic position. Therefore, the trade-off driving the use of spatially varying environments was most likely dependent upon the benefits associated with energetic returns than the costs associated with inter-individual competition or physiological stress. This result highlighted how ontogeny, and particularly ontogenetic niche shift, can play a central role in juvenile's decision to depart from natal habitats in a predatory species. PMID:23812603

Cucherousset, Julien; Paillisson, Jean-Marc; Roussel, Jean-Marc

2013-08-01

122

Natal departure timing from spatially varying environments is dependent of individual ontogenetic status  

NASA Astrophysics Data System (ADS)

Natal departure timing represents one of the first crucial decisions for juveniles born in spatially varying environments that ultimately disappear, but our knowledge on its determinants is limited. The present study aimed at understanding the determinants of juvenile natal departure by releasing individually tagged juvenile pike ( Esox lucius L.) with variable body size and trophic position in a temporary flooded grassland. Specifically, we investigated whether natal departure depends on individual competitive status (`competition hypothesis'), physiological tolerance to environmental conditions (`physiological hypothesis') or individual trophic position and the spatial heterogeneity of trophic resources (`trophic hypothesis'). The results indicated that departure timing was negatively correlated with body size at release, showing that the dominance status among competing individuals was not the main trigger of juvenile departure. A positive correlation between departure timing and individual body size at departure was observed, suggesting that inter-individual variability in physiological tolerance did not explain departure patterns. While individual growth performances were similar irrespective of the timing of natal departure, stable isotope analyses revealed that juveniles with higher trophic position departed significantly earlier than individuals with lower trophic position. Therefore, the trade-off driving the use of spatially varying environments was most likely dependent upon the benefits associated with energetic returns than the costs associated with inter-individual competition or physiological stress. This result highlighted how ontogeny, and particularly ontogenetic niche shift, can play a central role in juvenile's decision to depart from natal habitats in a predatory species.

Cucherousset, Julien; Paillisson, Jean-Marc; Roussel, Jean-Marc

2013-08-01

123

Linking the allee effect, sexual reproduction, and temperature-dependent sex determination via spatial dynamics.  

PubMed

We develop a spatially explicit, two-sex, individual-based model (IBM) and a derived spatially homogeneous model (SHM) to describe the Allee effect due to scarcity of mating possibilities at low population sizes or densities. The SHM, based on coupled difference equations, represents the first spatially homogeneous approach to this phenomenon, which differentiates between sexes and relies only on measurable population parameters. The IBM reinforces the findings of the SHM by adopting more realistic mate search strategies of diffusive movement and active search. Both models are characterized by a hyperbolic-shaped extinction boundary in the male-female state space, which contrasts with a linear boundary in one-dimensional models of the Allee effect. We examine how the position of the extinction boundary depends on population demography (primary sex ratio, reproduction and mortality probabilities) and adopted mate search strategies. The investigation of different phases in the IBM dynamics emphasizes the differences between local and global densities and shows the importance of scale when assessing the Allee effect. To demonstrate the potential application of our models, we combine the SHM and available data to predict the impact of environmental temperature changes on two turtle species with temperature-dependent sex determination. PMID:18707273

Berec, L; Boukal, D S; Berec, M

2001-02-01

124

The spatial frequency tuning of optic-flow-dependent behaviors in the bumblebee Bombus impatiens  

PubMed Central

Insects use visual estimates of flight speed for a variety of behaviors, including visual navigation, odometry, grazing landings and flight speed control, but the neuronal mechanisms underlying speed detection remain unknown. Although many models and theories have been proposed for how the brain extracts the angular speed of the retinal image, termed optic flow, we lack the detailed electrophysiological and behavioral data necessary to conclusively support any one model. One key property by which different models of motion detection can be differentiated is their spatiotemporal frequency tuning. Numerous studies have suggested that optic-flow-dependent behaviors are largely insensitive to the spatial frequency of a visual stimulus, but they have sampled only a narrow range of spatial frequencies, have not always used narrowband stimuli, and have yielded slightly different results between studies based on the behaviors being investigated. In this study, we present a detailed analysis of the spatial frequency dependence of the centering response in the bumblebee Bombus impatiens using sinusoidal and square wave patterns. PMID:20435814

Dyhr, Jonathan P.; Higgins, Charles M.

2010-01-01

125

Sensitive Polarization Dependence for Helium Rydberg Atoms Driven by Strong Microwave Fields  

NASA Astrophysics Data System (ADS)

We prepare n^3S He Rydberg atoms with selected values n>=25 in a fast beam using CO2 lasers and double-resonance excitation. They then fly through a TE_121 mode cavity, exposing them to a half-sine pulse (about 350 field osc.) of 9.904 GHz electric field whose polarization can be varied: linear (LP), elliptical (EP), and circular (CP). Making EP close to LP can lead to substantial changes in microwave-power-dependent transitions to nearby bound states. In at least one case, a sharp dip in the LP signal( W. van de Water et al., Phys. Rev. A 42), 572 (1990) is transformed by EP into a pattern reminiscent of Stueckelberg oscillations, previously observed with LP at higher frequencies.( S. Yoakum et al., Phys. Rev. Lett. 69), 1919 (1992) Calculations suggest that pulse-shape-induced dynamics at Floquet avoided-crossing(s) explain the LP behavior. Changing the field to EP clearly must modify this behavior. We will discuss this kind of data as well as the polarization dependence of microwave ionization of n^3S He Rydberg atoms.

Zelazny, S. A.; Bellermann, M. R. W.; Smith, L. L.; Koch, P. M.

1996-05-01

126

Hepcidin Induction by Pathogens and Pathogen-Derived Molecules Is Strongly Dependent on Interleukin-6  

PubMed Central

Hepcidin, the iron-regulatory hormone, is increased during infection or inflammation, causing hypoferremia. This response is thought to be a host defense mechanism that restricts iron availability to invading pathogens. It is not known if hepcidin is differentially induced by bacterial versus viral infections, whether the stimulation of pattern recognition receptors directly regulates hepcidin transcription, or which of the proposed signaling pathways are essential for hepcidin increase during infection. We analyzed hepcidin induction and its dependence on interleukin-6 (IL-6) in response to common bacterial or viral infections in mice or in response to a panel of pathogen-derived molecules (PAMPs) in mice and human primary hepatocytes. In wild-type (WT) mice, hepcidin mRNA was induced several hundred-fold both by a bacterial (Streptococcus pneumoniae) and a viral infection (influenza virus PR8) within 2 to 5 days. Treatment of mice and human primary hepatocytes with most Toll-like receptor ligands increased hepcidin mRNA within 6 h. Hepcidin induction by microbial stimuli was IL-6 dependent. IL-6 knockout mice failed to increase hepcidin in response to S. pneumoniae or influenza infection and had greatly diminished hepcidin response to PAMPs. In vitro, hepcidin induction by PAMPs in primary human hepatocytes was abolished by the addition of neutralizing IL-6 antibodies. Our results support the key role of IL-6 in hepcidin regulation in response to a variety of infectious and inflammatory stimuli. PMID:24478088

Rodriguez, Richard; Jung, Chun-Ling; Gabayan, Victoria; Deng, Jane C.; Ganz, Tomas; Nemeth, Elizabeta

2014-01-01

127

Numerical simulations of three-dimensional thermal convection in a fluid with strongly temperature-dependent viscosity  

Microsoft Academic Search

A numerical simulation of three-dimensional thermal-convection structure in a fluid with strongly temperature-dependent viscosity filling a bottom-heated rectangular box is presented. It is shown that the convective flow patterns obtained in the numerical simulation are consistent with predictions of Busse and Frick (1985). The planform of the convection obtained for a fluid in a bottom-heated box of aspect ratio a(x)

Masaki Ogawa; Gerald Schubert; Abdelfattah Zebib

1991-01-01

128

Band theory for strongly-correlated electron systems: an orbital-dependent exchange and correlation energy functional  

Microsoft Academic Search

An explicitly orbital-dependent correlation energy functional is proposed in a form of the modified second-order perturbation terms. The expression encourages the hybridization between the different kinds of orbitals in the vicinity of the Fermi level. We incorporate the present correlation energy functional into the relativistic linear augmented-plane-wave method in view of the application to the strongly correlated electron systems.

Masahiko Higuchi; Hiroshi Yasuhara

2002-01-01

129

Carrier type dependence on spatial asymmetry of unipolar resistive switching of metal oxides  

NASA Astrophysics Data System (ADS)

We report a carrier type dependence on the spatial asymmetry of unipolar resistive switching for various metal oxides, including NiOx, CoOx, TiO2-x, YSZ, and SnO2-x. n-type oxides show a unipolar resistive switching at the anode side whereas p-type oxides switch at the cathode side. During the forming process, the electrical conduction path of p-type oxides extends from the anode to cathode while that of n-type oxides forms from the cathode to anode. The carrier type of switching oxide layer critically determines the spatial inhomogeneity of unipolar resistive switching during the forming process possibly triggered via the oxygen ion drift.

Nagashima, Kazuki; Yanagida, Takeshi; Kanai, Masaki; Celano, Umberto; Rahong, Sakon; Meng, Gang; Zhuge, Fuwei; He, Yong; Ho Park, Bae; Kawai, Tomoji

2013-10-01

130

Concentration dependence of femtosecond coherent anti-Stokes Raman scattering in the presence of strong absorption  

NASA Astrophysics Data System (ADS)

We study near-resonant femtosecond coherent anti-Stokes Raman scattering (CARS) of dipicolinic acid (DPA) by exciting the molecular system with a pair of visible pump and Stokes pulses and probing the resultant molecular coherence with a time-delayed UV probe pulse. We record the generated Stokes and anti-Stokes pulse energies as functions of DPA concentration. We observe that the CARS signal has a maximum and the power-law dependence is steeper than the well-known quadratic one. We present a model that describes the propagation of the generated signal through the medium. From this model, we derive an analytical expression that closely agrees with our experimental data. Since DPA serves as a marker molecule for bacterial spores, our results help to establish the detectability limits for a lethal spore dosage when the present technique is applied.

Zhi, Miaochan; Pestov, Dmitry; Wang, Xi; Murawski, Robert K.; Rostovtsev, Yuri V.; Sariyanni, Zoe E.; Sautenkov, Vladimir A.; Kalugin, Nikolai G.; Sokolov, Alexei V.

2007-05-01

131

Strong asymmetrical bias dependence of magnetoresistance in organic spin valves: the role of ferromagnetic/organic interfaces  

NASA Astrophysics Data System (ADS)

We report a highly asymmetric magnetoresistance (MR) bias dependence, with the inverse MR peaking at a negative bias and a sign reversal occurring at a positive bias in prototypical La0.7Sr0.3MnO3 (LSMO)/Alq3/Co organic spin valve (OSV) with a tunnel barrier between LSMO and Alq3. This behavior is in strong contrast with the commonly found inverse MR in entire bias range for LSMO/Alq3/Co OSVs. The MR bias voltage dependence is independent on the type of the tunnel barrier, either SrTiO3 or Al2O3. Together with first-principle calculations, we demonstrate that the strongly hybridized Co d-states with Alq3 molecules at the interface are responsible for the efficient d-states spin injection and the observed MR bias dependence is originated from the energy dependent density of states of Co d-states. These findings open up new possibilities to engineer interfacial bonding between ferromagnetic materials and a wide variety of molecule selections for the desired spin transport properties.

Jiang, S. W.; Shu, D. J.; Lin, L.; Shi, Y. J.; Shi, J.; Ding, H. F.; Du, J.; Wang, M.; Wu, D.

2014-01-01

132

Spatial organization and time dependence of Jupiter's tropospheric temperatures, 1980-1993  

NASA Technical Reports Server (NTRS)

The spatial organization and time dependence of Jupiter's temperature near 250-millibar pressure were measured through a jovian year by imaging thermal emission at 18 micrometers. The temperature field is influenced by seasonal radiative forcing, and its banded organization is closely correlated with the visible cloud field. Evidence was found for a quasi-periodic oscillation of temperatures in the Equatorial Zone, a correlation between tropospheric and stratospheric waves in the North Equatorial Belt, and slowly moving thermal features in the North and South Equatorial Belts. There appears to be no common relation between temporal changes of temperature and changes in the visual albedo of the various axisymmetric bands.

Orton, Glenn S.; Friedson, A. James; Yanamandra-Fisher, Padmavati A.; Caldwell, John; Hammel, Heidi B.; Baines, Kevin H.; Bergstralh, Jay T.; Martin, Terry Z.; West, Robert A.; Veeder, Glenn J., Jr.

1994-01-01

133

The time dependent propensity function for acceleration of spatial stochastic simulation of reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

The inhomogeneous stochastic simulation algorithm (ISSA) is a fundamental method for spatial stochastic simulation. However, when diffusion events occur more frequently than reaction events, simulating the diffusion events by ISSA is quite costly. To reduce this cost, we propose to use the time dependent propensity function in each step. In this way we can avoid simulating individual diffusion events, and use the time interval between two adjacent reaction events as the simulation stepsize. We demonstrate that the new algorithm can achieve orders of magnitude efficiency gains over widely-used exact algorithms, scales well with increasing grid resolution, and maintains a high level of accuracy.

Fu, Jin; Wu, Sheng; Li, Hong; Petzold, Linda R.

2014-10-01

134

Spatial-spectral volume holographic systems: resolution dependence on effective thickness.  

PubMed

The resolution dependence of spatial-spectral volume holographic imaging systems on angular and spectral bandwidth of nonuniform gratings is investigated. Modeling techniques include a combination of the approximate coupled-wave analysis and the transfer-matrix method for holograms recorded in absorptive media. The effective thickness of the holograms is used as an estimator of the resolution of the imaging systems. The methodology, which assists in the design and optimization of volume holographic simulation results based on our approach, are confirmed with experiments and show proof of consistency and usefulness of the proposed models. PMID:21364728

Castro, Jose M; Brownlee, John; Luo, Yuan; de Leon, Erich; Barton, Jennifer K; Barbastathis, George; Kostuk, Raymond K

2011-03-01

135

Constrained variants of the gravity model and spatial dependence: model specification and estimation issues  

NASA Astrophysics Data System (ADS)

In this paper, we distinguish three constrained variants of the gravity model of spatial interaction: doubly constrained, production constrained and attraction constrained exponential gravity models. These model variants include origin- and/or destination-specific balancing factors that act as constraints to ensure that the estimated rows and columns of the flow data matrix sum to the observed row and column totals. Because flows are typically counts, the Poisson rather than the normal probability model specification furnishes the appropriate statistical distribution, and parameter estimation can be achieved via Poisson regression. This probability model specification motivates the use of origin and/or destination fixed effects or—under certain conditions—the use of origin- and/or destination-specific random effects for model estimation. The paper establishes theoretical connections between balancing factors, fixed effects represented by binary indicator variables and random effects. The results pertaining to both the doubly and singly constrained cases of spatial interaction are illustrated with an empirical example while accounting for spatial dependence between flows from locations neighbouring both the origins and destinations during estimation.

Griffith, Daniel A.; Fischer, Manfred M.

2013-07-01

136

Spatial dependency of cholera prevalence on potential cholera reservoirs in an urban area, Kumasi, Ghana  

NASA Astrophysics Data System (ADS)

Cholera has been a public health burden in Ghana since the early 1970s. Between 1999 and 2005, a total of 25,636 cases and 620 deaths were officially reported to the WHO. In one of the worst affected urban cities, fecal contamination of surface water is extremely high, and the disease is reported to be prevalent among inhabitants living in close proximity to surface water bodies. Surface runoff from dump sites is a major source of fecal and bacterial contamination of rivers and streams in the study area. This study aims to determine (a) the impacts of surface water contamination on cholera infection and (b) detect and map arbitrary shaped clusters of cholera. A Geographic Information System (GIS) based spatial analysis is used to delineate potential reservoirs of the cholera vibrios; possibly contaminated by surface runoff from open space refuse dumps. Statistical modeling using OLS model reveals a significant negative association between (a) cholera prevalence and proximity to all the potential cholera reservoirs ( R2 = 0.18, p < 0.001) and (b) cholera prevalence and proximity to upstream potential cholera reservoirs ( R2 = 0.25, p < 0.001). The inclusion of spatial autoregressive coefficients in the OLS model reveals the dependency of the spatial distribution of cholera prevalence on the spatial neighbors of the communities. A flexible scan statistic identifies a most likely cluster with a higher relative risk (RR = 2.04, p < 0.01) compared with the cluster detected by circular scan statistic (RR = 1.60, p < 0.01). We conclude that surface water pollution through runoff from waste dump sites play a significant role in cholera infection.

Osei, Frank B.; Duker, Alfred A.; Augustijn, Ellen-Wien; Stein, Alfred

2010-10-01

137

Angular dependence of magnetoresistance in strongly anisotropic quasi-two-dimensional metals: Influence of Landau-level shape  

NASA Astrophysics Data System (ADS)

We present the quantum-mechanical calculation of the angular dependence of interlayer conductivity ?zz(? ) in a tilted magnetic field in quasi-two-dimensional (quasi-2D) layered metals. Our calculation is applicable for arbitrary density of electron states and shows that the shape of Landau levels (LLs) is important for this angular dependence. We derive simple analytical formulas for ?zz(? ) in the particular cases of Gaussian and dome-shaped LLs. Since in strongly anisotropic quasi-two-dimensional metals in a high magnetic field the LL shape is closer to dome-like or Gaussian, this analytical formula replaces the traditionally used one, derived for Lorentzian LL shape. The amplitude of angular magnetoresistance oscillations (AMRO) is considerably stronger for the dome-like or Gaussian than for the traditionally used Lorentzian LL shape. The ratio ?zz(? =0)/?zz(? ?±90?) is also several times smaller for the Lorentzian LL shape at the same LL width. The field dependence of ?zz(? ?±90?) provides useful information about the electron mean free time. AMRO and Zeeman energy splitting lead to a spin current. For typical organic metals and for a medium magnetic field of 10 T this spin current is only a few percent of the charge current. However, the spin current may almost reach the charge current for special tilt angles of the magnetic field. The spin current has strong angular oscillations, which are phase-shifted as compared to the usual AMRO.

Grigoriev, P. D.; Mogilyuk, T. I.

2014-09-01

138

Time-dependent density-functional theory of strong-field ionization of atoms by soft x rays  

NASA Astrophysics Data System (ADS)

We demonstrate the capabilities of time-dependent density functional theory (TDDFT) for strong-field, short-wavelength (soft x-ray) physics, as compared to a formalism based on rate equations. We find that TDDFT provides a very good description of the total and individual ionization yields for Ne and Ar atoms exposed to strong laser pulses. We assess the reliability of different adiabatic density functionals and conclude that an accurate description of long-range interactions by the exchange and correlation potential is crucial for obtaining the correct ionization yield over a wide range of intensities (from 1013 to 5×1015W/cm2). Our TDDFT calculations disentangle the contribution from each ionization channel based on the Kohn-Sham wave functions.

Crawford-Uranga, A.; De Giovannini, U.; Räsänen, E.; Oliveira, M. J. T.; Mowbray, D. J.; Nikolopoulos, G. M.; Karamatskos, E. T.; Markellos, D.; Lambropoulos, P.; Kurth, S.; Rubio, A.

2014-09-01

139

Time-Dependent Density-Functional Theory of Strong-Field Ionization of Atoms under Soft X-Rays  

E-print Network

We demonstrate the capabilities of time-dependent density functional theory (TDDFT) for strong-field, short wavelength (soft X-ray) physics, as compared to a formalism based on rate equations. We find that TDDFT provides a very good description of the total and individual ionization yields for Ne and Ar atoms exposed to strong laser pulses. We assess the reliability of different adiabatic density functionals and conclude that an accurate description of long-range interactions by the exchange and correlation potential is crucial for obtaining the correct ionization yield over a wide range of intensities ($10^{13}$ -- $5 \\times 10^{15}$ W/cm$^2$). Our TDDFT calculations disentangle the contribution from each ionization channel based on the Kohn-Sham wavefunctions.

Crawford-Uranga, Alison; Räsänen, Esa; de Oliveira, Micael Jose Tourdot; Mowbray, Duncan John; Nikolopoulos, George M; Karamatskos, Evangelos T; Markellos, Dimitris; Lambropoulos, Peter; Kurth, Stefan; Rubio, Angel

2014-01-01

140

Comparison of strong gravitational lens model software I. Redshift and model dependence of time delay and mass calculations  

NASA Astrophysics Data System (ADS)

Analysis of strong gravitational lensing depends on software analysis of observational data. The purpose of this study is to evaluate the behavior of strong gravitational lens modeling software with changes in redshift. Four different strong gravitational lens software modeling codes are directly compared (Lenstool/glafic, two light traces mass codes, and GRALE/PixeLens, two non-light traces mass codes) in the analysis of a mock model as well as analysis of SDSSJ1004 + 4112. The calculated time delay is proportional to DdDs/Dds. The percent change in time delays calculated at each redshift tested is compared with percent change in DdDs/Dds. A mock model with a singular isothermal ellipsoid and four images is tested with each code. Five models are used with a constant zlens and a varying zsource, and five models with a constant zsource and a varying zlens. The effects of changing geometry are similarly investigated for SDSSJ1004 + 4112. In general, the changes in time delay are of a similar magnitude and direction, although some calculated time delays did not follow changes in DdDs/Dds. This variation is explained by changes in image position calculated by glafic and GRALE, which varied according to Dds/Ds. Changes in enclosed mass for the mock model with a constant zsource are similar to changes in DdDs/Dds for three of the four codes tested. These data demonstrate the effect of changes in redshift on parameters calculated by each of the codes as compared to changes in DdDs/Dds. The paucity of comparative studies in strong gravitational lensing suggests the need for further studies. These results show that small changes in redshift affect the calculated time delay and mass, and that the effect on the calculations is dependent on the particular software used.

Lefor, A. T.; Futamase, T.

2014-10-01

141

Potential and flux field landscape theory. I. Global stability and dynamics of spatially dependent non-equilibrium systems  

NASA Astrophysics Data System (ADS)

We established a potential and flux field landscape theory to quantify the global stability and dynamics of general spatially dependent non-equilibrium deterministic and stochastic systems. We extended our potential and flux landscape theory for spatially independent non-equilibrium stochastic systems described by Fokker-Planck equations to spatially dependent stochastic systems governed by general functional Fokker-Planck equations as well as functional Kramers-Moyal equations derived from master equations. Our general theory is applied to reaction-diffusion systems. For equilibrium spatially dependent systems with detailed balance, the potential field landscape alone, defined in terms of the steady state probability distribution functional, determines the global stability and dynamics of the system. The global stability of the system is closely related to the topography of the potential field landscape in terms of the basins of attraction and barrier heights in the field configuration state space. The effective driving force of the system is generated by the functional gradient of the potential field alone. For non-equilibrium spatially dependent systems, the curl probability flux field is indispensable in breaking detailed balance and creating non-equilibrium condition for the system. A complete characterization of the non-equilibrium dynamics of the spatially dependent system requires both the potential field and the curl probability flux field. While the non-equilibrium potential field landscape attracts the system down along the functional gradient similar to an electron moving in an electric field, the non-equilibrium flux field drives the system in a curly way similar to an electron moving in a magnetic field. In the small fluctuation limit, the intrinsic potential field as the small fluctuation limit of the potential field for spatially dependent non-equilibrium systems, which is closely related to the steady state probability distribution functional, is found to be a Lyapunov functional of the deterministic spatially dependent system. Therefore, the intrinsic potential landscape can characterize the global stability of the deterministic system. The relative entropy functional of the stochastic spatially dependent non-equilibrium system is found to be the Lyapunov functional of the stochastic dynamics of the system. Therefore, the relative entropy functional quantifies the global stability of the stochastic system with finite fluctuations. Our theory offers an alternative general approach to other field-theoretic techniques, to study the global stability and dynamics of spatially dependent non-equilibrium field systems. It can be applied to many physical, chemical, and biological spatially dependent non-equilibrium systems.

Wu, Wei; Wang, Jin

2013-09-01

142

Potential and flux field landscape theory. I. Global stability and dynamics of spatially dependent non-equilibrium systems.  

PubMed

We established a potential and flux field landscape theory to quantify the global stability and dynamics of general spatially dependent non-equilibrium deterministic and stochastic systems. We extended our potential and flux landscape theory for spatially independent non-equilibrium stochastic systems described by Fokker-Planck equations to spatially dependent stochastic systems governed by general functional Fokker-Planck equations as well as functional Kramers-Moyal equations derived from master equations. Our general theory is applied to reaction-diffusion systems. For equilibrium spatially dependent systems with detailed balance, the potential field landscape alone, defined in terms of the steady state probability distribution functional, determines the global stability and dynamics of the system. The global stability of the system is closely related to the topography of the potential field landscape in terms of the basins of attraction and barrier heights in the field configuration state space. The effective driving force of the system is generated by the functional gradient of the potential field alone. For non-equilibrium spatially dependent systems, the curl probability flux field is indispensable in breaking detailed balance and creating non-equilibrium condition for the system. A complete characterization of the non-equilibrium dynamics of the spatially dependent system requires both the potential field and the curl probability flux field. While the non-equilibrium potential field landscape attracts the system down along the functional gradient similar to an electron moving in an electric field, the non-equilibrium flux field drives the system in a curly way similar to an electron moving in a magnetic field. In the small fluctuation limit, the intrinsic potential field as the small fluctuation limit of the potential field for spatially dependent non-equilibrium systems, which is closely related to the steady state probability distribution functional, is found to be a Lyapunov functional of the deterministic spatially dependent system. Therefore, the intrinsic potential landscape can characterize the global stability of the deterministic system. The relative entropy functional of the stochastic spatially dependent non-equilibrium system is found to be the Lyapunov functional of the stochastic dynamics of the system. Therefore, the relative entropy functional quantifies the global stability of the stochastic system with finite fluctuations. Our theory offers an alternative general approach to other field-theoretic techniques, to study the global stability and dynamics of spatially dependent non-equilibrium field systems. It can be applied to many physical, chemical, and biological spatially dependent non-equilibrium systems. PMID:24089732

Wu, Wei; Wang, Jin

2013-09-28

143

A study of charge dependence of particle transport using impurity pellet injection and high-spatial resolution bremsstrahlung measurement on the Large Helical Device  

NASA Astrophysics Data System (ADS)

The spatial structure and Z dependence of transport coefficient were studied by injecting impurity pellets (C, Al, and Ti) and measuring high-spatial resolution bremsstrahlung in steady-state neutral beam heated plasmas on the Large Helical Device [A. Iiyoshi et al., Fusion Techol. 17, 169 (1990)]. The D and V were evaluated from a diffusive/convective model with minimizing the residual error between the experimental and computational bremsstrahlung intensities taking the recycling rate into account. As a result, the existence of an inward convection was observed at ?>0.6, and no convection was required at ?<0.6. Furthermore, it is found that the dependence of D on the electron density, the species and charge state of impurity is weak [typically D=0.15-0.25 (m2/s) in the range of ne=1.4-5.2×1019 (m-3)], but the inward convection has a strong dependence not only on the electron density but also the charge state. The spatial structure and Z dependence of the convective velocity for carbon and titanium ions were evaluated.

Nozato, H.; Morita, S.; Goto, M.; Takase, Y.; Ejiri, A.; Amano, T.; Tanaka, K.; Inagaki, S.

2004-05-01

144

Effector movement triggers gaze-dependent spatial coding of tactile and proprioceptive-tactile reach targets.  

PubMed

Reaching in space requires that the target and the hand are represented in the same coordinate system. While studies on visually-guided reaching consistently demonstrate the use of a gaze-dependent spatial reference frame, controversial results exist in the somatosensory domain. We investigated whether effector movement (eye or arm/hand) after target presentation and before reaching leads to gaze-dependent coding of somatosensory targets. Subjects reached to a felt target while directing gaze towards one of seven fixation locations. Touches were applied to the fingertip(s) of the left hand (proprioceptive-tactile targets) or to the dorsal surface of the left forearm (tactile targets). Effector movement was varied in terms of movement of the target limb or a gaze shift. Horizontal reach errors systematically varied as a function of gaze when a movement of either the target effector or gaze was introduced. However, we found no effect of gaze on horizontal reach errors when a movement was absent before the reach. These findings were comparable for tactile and proprioceptive-tactile targets. Our results suggest that effector movement promotes a switch from a gaze-independent to a gaze-dependent representation of somatosensory reach targets. PMID:25084225

Mueller, Stefanie; Fiehler, Katja

2014-09-01

145

Thermal maps of Jupiter - Spatial organization and time dependence of stratospheric temperatures, 1980 to 1990  

NASA Astrophysics Data System (ADS)

The spatial organization and time dependence of Jupiter's stratospheric temperatures have been measured by observing thermal emission from the 7.8-micrometer CH4 band. These temperatures, observed through the greater part of a Jovian year, exhibit the influence of seasonal radiative forcing. Distinct bands of high temperature are located at the poles and midlatitudes, while the equator alternates between warm and cold with a period of approximately 4 years. Substantial longitudinal variability is often observed within the warm midlatitude bands, and occasionally elsewhere on the planet. This variability includes small, localized structures, as well as large-scale waves with wavelengths longer than about 30,000 kilometers. The amplitudes of the waves vary on a time scale of about 1 month; structures on a smaller scale may have lifetimes of only days. Waves observed in 1985, 1987, and 1988 propagated with group velocities less than + or - 30 meters/sec.

Orton, G. S.; Friedson, A. J.; Caldwell, J.; Hammel, H. B.; Baines, K. H.; Bergstralh, J. T.; Martin, T. Z.; Malcom, M. E.; West, R. A.; Golisch, W. F.; Griep, D. M.; Kaminski, C. D.; Tokunaga, A. T.; Baron, R.; Shure, M.

1991-04-01

146

Thermal maps of Jupiter - Spatial organization and time dependence of stratospheric temperatures, 1980 to 1990  

NASA Technical Reports Server (NTRS)

The spatial organization and time dependence of Jupiter's stratospheric temperatures have been measured by observing thermal emission from the 7.8-micrometer CH4 band. These temperatures, observed through the greater part of a Jovian year, exhibit the influence of seasonal radiative forcing. Distinct bands of high temperature are located at the poles and midlatitudes, while the equator alternates between warm and cold with a period of approximately 4 years. Substantial longitudinal variability is often observed within the warm midlatitude bands, and occasionally elsewhere on the planet. This variability includes small, localized structures, as well as large-scale waves with wavelengths longer than about 30,000 kilometers. The amplitudes of the waves vary on a time scale of about 1 month; structures on a smaller scale may have lifetimes of only days. Waves observed in 1985, 1987, and 1988 propagated with group velocities less than + or - 30 meters/sec.

Orton, Glenn S.; Friedson, A. James; Baines, Kevin H.; Martin, Terry Z.; West, Robert A.; Caldwell, John; Hammel, Heidi B.; Bergstralh, Jay T.; Malcolm, Michael E.

1991-01-01

147

Strong topographic sheltering effects lead to spatially complex treeline advance and increased forest density in a subtropical mountain region.  

PubMed

Altitudinal treelines are typically temperature limited such that increasing temperatures linked to global climate change are causing upslope shifts of treelines worldwide. While such elevational increases are readily predicted based on shifting isotherms, at the regional level the realized response is often much more complex, with topography and local environmental conditions playing an important modifying role. Here, we used repeated aerial photographs in combination with forest inventory data to investigate changes in treeline position in the Central Mountain Range of Taiwan over the last 60 years. A highly spatially variable upslope advance of treeline was identified in which topography is a major driver of both treeline form and advance. The changes in treeline position that we observed occurred alongside substantial increases in forest density, and lead to a large increase in overall forest area. These changes will have a significant impact on carbon stocking in the high altitude zone, while the concomitant decrease in alpine grassland area is likely to have negative implications for alpine species. The complex and spatially variable changes that we report highlight the necessity for considering local factors such as topography when attempting to predict species distributional responses to warming climate. PMID:25141823

Greenwood, Sarah; Chen, Jan-Chang; Chen, Chaur-Tzuhn; Jump, Alistair S

2014-12-01

148

He?2++ molecular ion in a strong time-dependent magnetic field: a current-density functional study.  

PubMed

The He?2++ molecular ion exposed to a strong ultrashort time-dependent (TD) magnetic field of the order of 10(9) G is investigated through a quantum fluid dynamics (QFD) and current-density functional theory (CDFT) based approach using vector exchange-correlation (XC) potential and energy density functional that depend not only on the electronic charge-density but also on the current density. The TD-QFD-CDFT computations are performed in a parallel internuclear-axis and magnetic field-axis configuration at the field-free equilibrium internuclear separation R = 1.3 au with the field-strength varying between 0 and 10(11) G. The TD behavior of the exchange- and correlation energy of the He?2++ is analyzed and compared with that obtained using a [B-TD-QFD-density functional theory (DFT)] approach based on the conventional TD-DFT under similar computational constraints but using only scalar XC potential and energy density functional dependent on the electronic charge-density alone. The CDFT based approach yields TD exchange- and correlation energy and TD electronic charge-density significantly different from that obtained using the conventional TD-DFT based approach, particularly, at typical magnetic field strengths and during a typical time period of the TD field. This peculiar behavior of the CDFT-based approach is traced to the TD current-density dependent vector XC potential, which can induce nonadiabatic effects causing retardation of the oscillating electronic charge density. Such dissipative electron dynamics of the He?2++ molecular ion is elucidated by treating electronic charge density as an electron-"fluid" in the terminology of QFD. PMID:21598275

Vikas

2011-08-01

149

Wavelength dependence of sub-laser-cycle few-electron dynamics in strong-field multiple ionization  

NASA Astrophysics Data System (ADS)

Recoil-ion momentum distributions for double and triple ionization of Ne and Ar, as well as for double ionization of N2 molecule by intense (0.3 0.5 PW cm-2), short (~35 40 fs) laser pulses have been recorded in a so far unexplored long laser-wavelength regime at 1300 nm. Compared to earlier results at 800 nm, the direct (e, ne) ionization pathway during recollision is strongly enhanced manifesting itself in a pronounced double-hump structure in the longitudinal ion momentum spectra not only for Ne, but also surprisingly distinct for Ar and, found for the first time, for molecules. Observed wavelength dependence of the sub-laser-cycle correlated few-electron dynamics might be of paramount importance for possible future applications in attosecond science, in particular, for imaging of ultrafast molecular processes via recollision-induced fragmentation.

Herrwerth, O.; Rudenko, A.; Kremer, M.; de Jesus, V. L. B.; Fischer, B.; Gademann, G.; Simeonidis, K.; Achtelik, A.; Ergler, Th; Feuerstein, B.; Schröter, C. D.; Moshammer, R.; Ullrich, J.

2008-02-01

150

Strong-field ionization rates of linear polyenes simulated with time-dependent configuration interaction with an absorbing potential  

NASA Astrophysics Data System (ADS)

The strong field ionization rates for ethylene, trans 1,3-butadiene, and trans,trans 1,3,5-hexatriene have been calculated using time-dependent configuration interaction with single excitations and a complex absorbing potential (TDCIS-CAP). The calculations used the aug-cc-pVTZ basis set with a large set of diffuse functions (3 s, 2 p, 3 d, and 1 f) on each atom. The absorbing boundary was placed 3.5 times the van der Waals radius from each atom. The simulations employed a seven-cycle cosine squared pulse with a wavelength of 800 nm. Ionization rates were calculated for intensities ranging from 0.3 × 1014 W/cm2 to 3.5 × 1014 W/cm2. Ionization rates along the molecular axis increased markedly with increasing conjugation length. By contrast, ionization rates perpendicular to the molecular axis were almost independent of the conjugation length.

Krause, Pascal; Schlegel, H. Bernhard

2014-11-01

151

Azimuth-dependent amplification of weak and strong ground motions within a fault zone (Nocera Umbra, central Italy)  

NASA Astrophysics Data System (ADS)

During three moderate-magnitude earthquakes occurred in September-October 1997 in the central Apennines, Italy, accelerations larger than 0.5 g were recorded in the town of Nocera Umbra, 10 to 15 km N-NW of the epicenters. The accelerograph is sited in a fault zone, close to a N30°E tectonic contact. Six temporary seismological stations installed across the fault recorded 82 aftershocks occurred in two seismogenic zones: the Colfiorito-Sellano area, S-SE of the array, and the Gualdo Tadino area, to the north. The array data reveal large variations in terms of both peak ground motions and spectral amplitudes. Within the fault zone, amplifications show a strong dependence on the source azimuth. At the accelerograph site, the effects are particularly large for events from S-SE: peak ground motions are a factor of 14 larger than those of a reference site and conventional spectral ratios attain amplitudes as large as 50 at 7 Hz along the N30°E direction of motion, parallel to the strike of the fault. Nineteen strong motion accelerograms were then used to compare ground motion properties between weak and strong events up to M0 = 1.2 × 1025 dyn cm. A particle motion analysis shows that the directional effect is also present in the strongest motions, even though the amplification of peak ground motion decreases when M0 increases. Results from stochastic simulations indicate that such a behavior is not due to nonlinearity: applying the empirical weak motion transfer functions in a purely linear model the observed peak ground motions of the largest events are fit satisfactorily.

Cultrera, Giovanna; Rovelli, Antonio; Mele, Giuliana; Azzara, Riccardo; Caserta, Arrigo; Marra, Fabrizio

2003-03-01

152

Strong spin-orbit coupling and Zeeman spin splitting in angle dependent magnetoresistance of Bi2Te3  

NASA Astrophysics Data System (ADS)

We have studied angle dependent magnetoresistance of Bi2Te3 thin film with field up to 9 T over 2-20 K temperatures. The perpendicular field magnetoresistance has been explained by the Hikami-Larkin-Nagaoka theory alone in a system with strong spin-orbit coupling, from which we have estimated the mean free path, the phase coherence length, and the spin-orbit relaxation time. We have obtained the out-of-plane spin-orbit relaxation time to be small and the in-plane spin-orbit relaxation time to be comparable to the momentum relaxation time. The estimation of these charge and spin transport parameters are useful for spintronics applications. For parallel field magnetoresistance, we have confirmed the presence of Zeeman effect which is otherwise suppressed in perpendicular field magnetoresistance due to strong spin-orbit coupling. The parallel field data have been explained using both the contributions from the Maekawa-Fukuyama localization theory for non-interacting electrons and Lee-Ramakrishnan theory of electron-electron interactions. The estimated Zeeman g-factor and the strength of Coulomb screening parameter agree well with the theory. Finally, the anisotropy in magnetoresistance with respect to angle has been described by the Hikami-Larkin-Nagaoka theory. This anisotropy can be used in anisotropic magnetic sensor applications.

Dey, Rik; Pramanik, Tanmoy; Roy, Anupam; Rai, Amritesh; Guchhait, Samaresh; Sonde, Sushant; Movva, Hema C. P.; Colombo, Luigi; Register, Leonard F.; Banerjee, Sanjay K.

2014-06-01

153

Up, down, and all around: scale-dependent spatial variation in rocky-shore communities of Fildes Peninsula, King George Island, Antarctica.  

PubMed

Understanding the variation of biodiversity along environmental gradients and multiple spatial scales is relevant for theoretical and management purposes. Hereby, we analysed the spatial variability in diversity and structure of intertidal and subtidal macrobenthic Antarctic communities along vertical environmental stress gradients and across multiple horizontal spatial scales. Since biotic interactions and local topographic features are likely major factors for coastal assemblages, we tested the hypothesis that fine-scale processes influence the effects of the vertical environmental stress gradients on the macrobenthic diversity and structure. We used nested sampling designs in the intertidal and subtidal habitats, including horizontal spatial scales ranging from few centimetres to 1000s of metres along the rocky shore of Fildes Peninsula, King George Island. In both intertidal and subtidal habitats, univariate and multivariate analyses showed a marked vertical zonation in taxon richness and community structure. These patterns depended on the horizontal spatial scale of observation, as all analyses showed a significant interaction between height (or depth) and the finer spatial scale analysed. Variance and pseudo-variance components supported our prediction for taxon richness, community structure, and the abundance of dominant species such as the filamentous green alga Urospora penicilliformis (intertidal), the herbivore Nacella concinna (intertidal), the large kelp-like Himantothallus grandifolius (subtidal), and the red crustose red alga Lithothamnion spp. (subtidal). We suggest that in coastal ecosystems strongly governed by physical factors, fine-scale processes (e.g. biotic interactions and refugia availability) are still relevant for the structuring and maintenance of the local communities. The spatial patterns found in this study serve as a necessary benchmark to understand the dynamics and adaptation of natural assemblages in response to observed and predicted environmental changes in Antarctica. PMID:24956114

Valdivia, Nelson; Díaz, María J; Holtheuer, Jorge; Garrido, Ignacio; Huovinen, Pirjo; Gómez, Iván

2014-01-01

154

Up, Down, and All Around: Scale-Dependent Spatial Variation in Rocky-Shore Communities of Fildes Peninsula, King George Island, Antarctica  

PubMed Central

Understanding the variation of biodiversity along environmental gradients and multiple spatial scales is relevant for theoretical and management purposes. Hereby, we analysed the spatial variability in diversity and structure of intertidal and subtidal macrobenthic Antarctic communities along vertical environmental stress gradients and across multiple horizontal spatial scales. Since biotic interactions and local topographic features are likely major factors for coastal assemblages, we tested the hypothesis that fine-scale processes influence the effects of the vertical environmental stress gradients on the macrobenthic diversity and structure. We used nested sampling designs in the intertidal and subtidal habitats, including horizontal spatial scales ranging from few centimetres to 1000s of metres along the rocky shore of Fildes Peninsula, King George Island. In both intertidal and subtidal habitats, univariate and multivariate analyses showed a marked vertical zonation in taxon richness and community structure. These patterns depended on the horizontal spatial scale of observation, as all analyses showed a significant interaction between height (or depth) and the finer spatial scale analysed. Variance and pseudo-variance components supported our prediction for taxon richness, community structure, and the abundance of dominant species such as the filamentous green alga Urospora penicilliformis (intertidal), the herbivore Nacella concinna (intertidal), the large kelp-like Himantothallus grandifolius (subtidal), and the red crustose red alga Lithothamnion spp. (subtidal). We suggest that in coastal ecosystems strongly governed by physical factors, fine-scale processes (e.g. biotic interactions and refugia availability) are still relevant for the structuring and maintenance of the local communities. The spatial patterns found in this study serve as a necessary benchmark to understand the dynamics and adaptation of natural assemblages in response to observed and predicted environmental changes in Antarctica. PMID:24956114

Valdivia, Nelson; Diaz, Maria J.; Holtheuer, Jorge; Garrido, Ignacio; Huovinen, Pirjo; Gomez, Ivan

2014-01-01

155

Propagation of sound waves through a spatially homogeneous but smoothly time-dependent medium  

SciTech Connect

The propagation of sound through a spatially homogeneous but non-stationary medium is investigated within the framework of fluid dynamics. For a non-vortical fluid, especially, a generalized wave equation is derived for the (scalar) potential of the fluid velocity distribution in dependence of the equilibrium mass density of the fluid and the sound wave velocity. A solution of this equation for a finite transition period ? is determined in terms of the hypergeometric function for a phenomenologically realistic, sigmoidal change of the mass density and sound wave velocity. Using this solution, it is shown that the energy flux of the sound wave is not conserved but increases always for the propagation through a non-stationary medium, independent of whether the equilibrium mass density is increased or decreased. It is found, moreover, that this amplification of the transmitted wave arises from an energy exchange with the medium and that its flux is equal to the (total) flux of the incident and the reflected wave. An interpretation of the reflected wave as a propagation of sound backward in time is given in close analogy to Feynman and Stueckelberg for the propagation of anti-particles. The reflection and transmission coefficients of sound propagating through a non-stationary medium is analyzed in more detail for hypersonic waves with transition periods ? between 15 and 200 ps as well as the transformation of infrasound waves in non-stationary oceans. -- Highlights: •Analytically exact study of sound propagation through a non-stationary medium. •Energy exchange between the non-stationary medium and the sound wave. •Transformation of hypersonic and ultrasound frequencies in non-stationary media. •Propagation of sound backward in time in close analogy to anti-particles. •Prediction of tsunamis both in spatially and temporally inhomogeneous oceans.

Hayrapetyan, A.G., E-mail: armen@physi.uni-heidelberg.de [Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg (Germany); Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Grigoryan, K.K.; Petrosyan, R.G. [Yerevan State University, 1 Alex Manoogian Str., 0025 Yerevan (Armenia)] [Yerevan State University, 1 Alex Manoogian Str., 0025 Yerevan (Armenia); Fritzsche, S. [Helmholtz-Institut Jena, Fröbelstieg 3, D-07743 Jena (Germany) [Helmholtz-Institut Jena, Fröbelstieg 3, D-07743 Jena (Germany); Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena (Germany)

2013-06-15

156

Spatially resolved frequency-dependent elasticity measured with pulsed force microscopy and nanoindentation.  

PubMed

Recently several atomic force microscopy (AFM)-based surface property mapping techniques like pulsed force microscopy (PFM), harmonic force microscopy or Peakforce QNM® have been introduced to measure the nano- and micro-mechanical properties of materials. These modes all work at different operating frequencies. However, complex materials are known to display viscoelastic behavior, a combination of solid and fluid-like responses, depending on the frequency at which the sample is probed. In this report, we show that the frequency-dependent mechanical behavior of complex materials, such as polymer blends that are frequently used as calibration samples, is clearly measurable with AFM. Although this frequency-dependent mechanical behavior is an established observation, we demonstrate that the new high frequency mapping techniques enable AFM-based rheology with nanoscale spatial resolution over a much broader frequency range compared to previous AFM-based studies. We further highlight that it is essential to account for the frequency-dependent variation in mechanical properties when using these thin polymer samples as calibration materials for elasticity measurements by high-frequency surface property mapping techniques. These results have significant implications for the accurate interpretation of the nanomechanical properties of polymers or complex biological samples. The calibration sample is composed of a blend of soft and hard polymers, consisting of low-density polyethylene (LDPE) islands in a polystyrene (PS) surrounding, with a stiffness of 0.2 GPa and 2 GPa respectively. The spring constant of the AFM cantilever was selected to match the stiffness of LDPE. From 260 Hz to 1100 Hz the sample was imaged with the PFM method. At low frequencies (0.5-35 Hz), single-point nanoindentation was performed. In addition to the material's stiffness, the relative heights of the LDPE islands (with respect to the PS) were determined as a function of the frequency. At the lower operation frequencies for PFM, the islands exhibited lower heights than when measured with tapping mode at 120 kHz. Both spring constants and heights at the different frequencies clearly show a frequency-dependent behavior. PMID:22331128

Sweers, Kim K M; van der Werf, Kees O; Bennink, Martin L; Subramaniam, Vinod

2012-03-21

157

Spatially resolved frequency-dependent elasticity measured with pulsed force microscopy and nanoindentation  

NASA Astrophysics Data System (ADS)

Recently several atomic force microscopy (AFM)-based surface property mapping techniques like pulsed force microscopy (PFM), harmonic force microscopy or Peakforce QNM® have been introduced to measure the nano- and micro-mechanical properties of materials. These modes all work at different operating frequencies. However, complex materials are known to display viscoelastic behavior, a combination of solid and fluid-like responses, depending on the frequency at which the sample is probed. In this report, we show that the frequency-dependent mechanical behavior of complex materials, such as polymer blends that are frequently used as calibration samples, is clearly measurable with AFM. Although this frequency-dependent mechanical behavior is an established observation, we demonstrate that the new high frequency mapping techniques enable AFM-based rheology with nanoscale spatial resolution over a much broader frequency range compared to previous AFM-based studies. We further highlight that it is essential to account for the frequency-dependent variation in mechanical properties when using these thin polymer samples as calibration materials for elasticity measurements by high-frequency surface property mapping techniques. These results have significant implications for the accurate interpretation of the nanomechanical properties of polymers or complex biological samples. The calibration sample is composed of a blend of soft and hard polymers, consisting of low-density polyethylene (LDPE) islands in a polystyrene (PS) surrounding, with a stiffness of 0.2 GPa and 2 GPa respectively. The spring constant of the AFM cantilever was selected to match the stiffness of LDPE. From 260 Hz to 1100 Hz the sample was imaged with the PFM method. At low frequencies (0.5-35 Hz), single-point nanoindentation was performed. In addition to the material's stiffness, the relative heights of the LDPE islands (with respect to the PS) were determined as a function of the frequency. At the lower operation frequencies for PFM, the islands exhibited lower heights than when measured with tapping mode at 120 kHz. Both spring constants and heights at the different frequencies clearly show a frequency-dependent behavior.

Sweers, Kim K. M.; van der Werf, Kees O.; Bennink, Martin L.; Subramaniam, Vinod

2012-03-01

158

Field Observations Of The 29 September Tsunami In American Samoa: Spatial Variability And Indications Of Strong Return Flow  

NASA Astrophysics Data System (ADS)

The 29 September 2009 tsunami caused 181 fatalities and displaced more than 5000 people on the islands of Samoa, American Samoa, and Tonga. This is the first tsunami to cause significant damage and fatalities on U.S. soil in more than 30 years. Scientists from around the world quickly mobilized to help document the tsunami water levels before this ephemeral data was forever lost as recovery activities and natural processes overtook the effected area. A USGS team collected data in American Samoa from October 6-22 and November 5-12, 2009. The tsunami was large, reaching elevations of greater than 15 m, however wave heights and devastation varied from village to village in American Samoa. Even within villages, some structures were completely destroyed, some flooded and left standing, and others barely touched. Wave heights, flow depths, runup heights, inundation distances, and flow directions were collected for use in ground-truthing inundation models. The team also collected nearshore bathymetry, topography and reef flat elevation, sediment samples, and documented the distribution and characteristics of both sand and boulder deposits. Eyewitness accounts of the tsunami were also videotaped. One striking aspect of this tsunami was the abundance of indicators of strong return flow. For example at Poloa in the northwest of Tutuila, where the runup was greater than 11 m along a 300-m stretch of coast and flow depths exceeded 4 m, the coral reef flat was strewn with debris including chairs, desks, and books from a school. On land, River channels were excavated and new channels formed as return flow scoured sediment and transported it offshore. Possible causes for the strong return flow and the relation between the stength of the return flow, inundation distance, and runup in American Samoa are presented. These relationships and others based on data collected by field survey teams will ultimately reduce loss of life and destruction from tsunamis in the Pacific and elsewhere.

Jaffe, B. E.; Richmond, B. M.; Gelfenbaum, G. R.; Watt, S.; Apotsos, A. A.; Buckley, M. L.; Dudley, W. C.; Peck, B.

2009-12-01

159

Strong Decoherence  

Microsoft Academic Search

We introduce a condition for the strong decoherence of a set of alternative histories of a closed quantum-mechanical system such as the universe. The condition applies, for a pure initial state, to sets of homogeneous histories that are chains of projections, generally branch-dependent. Strong decoherence implies the consistency of probability sum rules but not every set of consistent or even

Murray Gell-Mann; James B. Hartle

1995-01-01

160

Facile synthesis and strongly microstructure-dependent electrochemical properties of graphene/manganese dioxide composites for supercapacitors  

NASA Astrophysics Data System (ADS)

Graphene has attracted much attention since it was firstly stripped from graphite by two physicists in 2004, and the supercapacitor based on graphene has obtained wide attention and much investment as well. For practical applications of graphene-based supercapacitors, however, there are still many challenges to solve, for instance, to simplify the technological process, to lower the fabrication cost, and to improve the electrochemical performance. In this work, graphene/MnO2 composites are prepared by a microwave sintering method, and we report here a relatively simple method for the supercapacitor packaging, i.e., dipping Ni-foam into a graphene/MnO2 composite solution directly for a period of time to coat the active material on a current collector. It is found that the microwave reaction time has a significant effect on the microstructure of graphene/MnO2 composites, and consequently, the electrochemical properties of the supercapacitors based on graphene/MnO2 composites are strongly microstructure dependent. An appropriately longer microwave reaction time, namely, 15 min, facilitates a very dense and homogeneous microstructure of the graphene/MnO2 composites, and thus, excellent electrochemical performance is achieved in the supercapacitor device, including a high specific capacitance of 296 F/g and a high capacitance retention of 93% after 3,000 times of charging/discharging cycles.

Zhang, Caiyun; Zhu, Xiaohong; Wang, Zhongxing; Sun, Ping; Ren, Yinjuan; Zhu, Jiliang; Zhu, Jianguo; Xiao, Dingquan

2014-09-01

161

Facile synthesis and strongly microstructure-dependent electrochemical properties of graphene/manganese dioxide composites for supercapacitors  

PubMed Central

Graphene has attracted much attention since it was firstly stripped from graphite by two physicists in 2004, and the supercapacitor based on graphene has obtained wide attention and much investment as well. For practical applications of graphene-based supercapacitors, however, there are still many challenges to solve, for instance, to simplify the technological process, to lower the fabrication cost, and to improve the electrochemical performance. In this work, graphene/MnO2 composites are prepared by a microwave sintering method, and we report here a relatively simple method for the supercapacitor packaging, i.e., dipping Ni-foam into a graphene/MnO2 composite solution directly for a period of time to coat the active material on a current collector. It is found that the microwave reaction time has a significant effect on the microstructure of graphene/MnO2 composites, and consequently, the electrochemical properties of the supercapacitors based on graphene/MnO2 composites are strongly microstructure dependent. An appropriately longer microwave reaction time, namely, 15 min, facilitates a very dense and homogeneous microstructure of the graphene/MnO2 composites, and thus, excellent electrochemical performance is achieved in the supercapacitor device, including a high specific capacitance of 296 F/g and a high capacitance retention of 93% after 3,000 times of charging/discharging cycles. PACS 81.05.ue; 78.67.Sc; 88.80.fh

2014-01-01

162

nature neuroscience volume 1 no 7 november 1998 563 Nervous system signaling depends on the spatially and tempo-  

E-print Network

on the spatially and tempo- rally coordinated function of a variety of voltage- and ligand- gated ion channels- and ligand-gated ion channels depends on interactions with intra- cellular proteins, which are enriched in the postsynaptic density and provide a link to the cytoskeleton. For example, at glyciner- gic inhibitory synapses

Luscher, Bernhard

163

Processing of Location-Dependent Continuous Queries on Real-Time Spatial Data: The View from RETINA  

E-print Network

Processing of Location-Dependent Continuous Queries on Real-Time Spatial Data: The View from RETINA Indian Institute of Technology Bombay Mumbai, INDIA Abstract In this paper, using RETINA, a real. In this paper, we introduce our system, called RETINA, which is an abbreviation of REal-Time TraffIc NAvigation

Ramamritham, Krithi

164

Spatial Dependence and Heterogeneity in Bayesian Factor Analysis: A Cross-National Investigation of Schwartz Values  

ERIC Educational Resources Information Center

In this article, we present a Bayesian spatial factor analysis model. We extend previous work on confirmatory factor analysis by including geographically distributed latent variables and accounting for heterogeneity and spatial autocorrelation. The simulation study shows excellent recovery of the model parameters and demonstrates the consequences…

Stakhovych, Stanislav; Bijmolt, Tammo H. A.; Wedel, Michel

2012-01-01

165

Scale-dependent proximity of wildlife habitat in a spatially-neutral Bayesian model  

Microsoft Academic Search

Organisms may be constrained by the energetic costs incurred while obtaining resources in fragmented landscapes. We used a spatially neutral model of deer wintering habitat to evaluate the effects of landscape fragmentation on the aggregation of deer habitat. The spatially neutral model used Bayesian probabilities to predict where deer wintering areas occurred. The probabilities were conditional on 12 landscape variables

Bruce T. Milne; Kevin M. Johnston; Richard T. T. Forman

1989-01-01

166

Spatially dependent Rabi oscillations: An approach to sub-diffraction-limited coherent anti-Stokes Raman-scattering microscopy  

SciTech Connect

We present a theoretical investigation of coherent anti-Stokes Raman scattering (CARS) that is modulated by periodically depleting the ground-state population through Rabi oscillations driven by an additional control laser. We find that such a process generates optical sidebands in the CARS spectrum and that the frequency of the sidebands depends on the intensity of the control laser light field. We show that analyzing the sideband frequency upon scanning the beams across the sample allows one to spatially resolve emitter positions where a spatial resolution of 65 nm, which is well below the diffraction limit, can be obtained.

Beeker, Willem P.; Lee, Chris J.; Boller, Klaus-Jochen; Gross, Petra; Cleff, Carsten; Fallnich, Carsten; Offerhaus, Herman L.; Herek, Jennifer L. [Laser Physics and Nonlinear Optics Group, MESA Research Institute for Nanotechnology, University of Twente, P.O. Box 217, Enschede NL-7500 AE (Netherlands); Institut fuer Angewandte Physik, Westfaelische Wilhelms-Universitaet, D-48149 Muenster (Germany); Optical Sciences Group, MESA Research Institute for Nanotechnology, University of Twente, P.O. Box 217, Enschede NL-7500 AE (Netherlands)

2010-01-15

167

Transport lattice models of heat transport in skin with spatially heterogeneous, temperature-dependent perfusion  

E-print Network

Background: Investigation of bioheat transfer problems requires the evaluation of temporal and spatial distributions of temperature. This class of problems has been traditionally addressed using the Pennes bioheat equation. ...

Martin, Gregory T

168

Brazilian spatial dynamics in the long term (1872-2000): ``path dependency'' or ``reversal of fortune''?  

NASA Astrophysics Data System (ADS)

This paper analyzes the spatial dynamics of Brazilian regional inequalities between 1872 and 2000 using contemporary tools. The first part of the paper provides new estimates of income per capita in 1872 by municipality using census and electoral information on income by occupation. The level of analysis is the Minimum Comparable Areas 1872-2000 developed by Reis et al. (Áreas mínimas comparáveis para os períodos intercensitários de 1872 a 2000, 2007). These areas are the least aggregation of adjacent municipalities required to allow consistent geographic area comparisons between census years. In the second section of the paper, Exploratory Spatial Data Analysis, Markov chains and stochastic kernel techniques (spatially conditioned) are applied to the dataset. The results suggest that, in broad terms, the spatial pattern of income distribution in Brazil during that period of time has remained stable.

Monasterio, Leonardo Monteiro

2010-03-01

169

Reconstructing land use drivers and their spatial scale dependence for Costa Rica (1973 and 1984)  

Microsoft Academic Search

Costa Rican land use and cover (in 1973 and 1984) were investigated using a nested scale analysis. Spatial distributions of potential biophysical and human land use\\/cover drivers were statistically related to the distribution of pastures, arable lands, permanent crops, natural and secondary vegetation, for 0.1° grid units and five artificially aggregated spatial scales. Multiple regression models describing land use\\/cover variability

A. Veldkamp; L. O. Fresco

1997-01-01

170

Species richness effects on ecosystem multifunctionality depend on evenness, composition and spatial pattern  

USGS Publications Warehouse

1.?Recent studies have suggested that the simultaneous maintenance of multiple ecosystem functions (multifunctionality) is positively supported by species richness. However, little is known regarding the relative importance of other community attributes (e.g. spatial pattern, species evenness) as drivers of multifunctionality. 2.?We conducted two microcosm experiments using model biological soil crust communities dominated by lichens to: (i) evaluate the joint effects and relative importance of changes in species composition, spatial pattern (clumped and random distribution of lichens), evenness (maximal and low evenness) and richness (from two to eight species) on soil functions related to nutrient cycling (?-glucosidase, urease and acid phosphatase enzymes, in situ N availability, total N, organic C, and N fixation), and (ii) assess how these community attributes affect multifunctionality. 3.?Species richness, composition and spatial pattern affected multiple ecosystem functions (e.g. organic C, total N, N availability, ?-glucosidase activity), albeit the magnitude and direction of their effects varied with the particular function, experiment and soil depth considered. Changes in species composition had effects on organic C, total N and the activity of ?-glucosidase. Significant species richness × evenness and spatial pattern × evenness interactions were found when analysing functions such as organic C, total N and the activity of phosphatase. 4.?The probability of sustaining multiple ecosystem functions increased with species richness, but this effect was largely modulated by attributes such as species evenness, composition and spatial pattern. Overall, we found that model communities with high species richness, random spatial pattern and low evenness increased multifunctionality. 5.?Synthesis. Our results illustrate how different community attributes have a diverse impact on ecosystem functions related to nutrient cycling, and provide new experimental evidence illustrating the importance of the spatial pattern of organisms on ecosystem functioning. They also indicate that species richness is not the only biotic driver of multifunctionality, and that particular combinations of community attributes may be required to maximize it.

Maestre, F.T.; Castillo-Monroy, A. P.; Bowker, M.A.; Ochoa-Hueso, R.

2012-01-01

171

Luminance-dependence of spatial vision in budgerigars (Melopsittacus undulatus) and Bourke's parrots (Neopsephotus bourkii).  

PubMed

Budgerigars (Melopsittacus undulatus) and Bourke's parrots (Neopsephotus bourkii) are closely related birds with different activity patterns. Budgerigars are strictly diurnal while Bourke's parrots are active in dim twilight. Earlier studies show that the intensity threshold of colour vision is similar in both species while Bourke's parrots have larger eyes with a higher density of rods than budgerigars. In this study, we investigate whether this could be an adaptation for better spatial vision in dim light. We used two alternative forced-choice experiments to determine the spatial acuity of both species at light intensities ranging from 0.08 to 73 cd/m(2). We also determined the spatial contrast sensitivity function (CSF) for bright light in Bourke's parrots and compare it to existing data for budgerigars. The spatial acuity of Bourke's parrots was found to be similar to that of budgerigars at all light levels. Also the CSF of Bourke's parrots is similar to that of budgerigars with a sensitivity peak located between 2.1 and 2.6 cycles/degree. Our findings do not support the hypothesis that Bourke's parrots have superior spatial acuity in dim light compared to budgerigars and the adaptive value of the relatively rod-rich and large eyes of Bourke's parrots remains unclear. PMID:22001888

Lind, Olle; Sunesson, Tony; Mitkus, Mindaugas; Kelber, Almut

2012-01-01

172

The dependence of exciton transport efficiency on spatial patterns of correlation within the spectral bath  

NASA Astrophysics Data System (ADS)

Spatial correlations in spectral bath motions have been proposed to explain long-lived coherence in exciton transport. Systems of interest, ranging from photosynthetic complexes to organic photovoltaics, contain inhomogeneous environments. We consider the possibility that the degree of spatial correlation varies throughout an exciton transport system. We model exciton transport in the Fenna-Matthews-Olson complex (FMO), a photosynthetic light-harvesting complex. Although it remains unclear whether significant spatial correlations exist in FMO, its very high exciton transport efficiency makes it an interesting case for studies of exciton transport. We also simulate a highly symmetric ten-site model system. We use an extension of the environment-assisted quantum transport model to simulate transport, allowing the spatial correlation function to vary throughout the system. We demonstrate both via analysis and via simulation that exciton transport efficiency is most sensitive to changes in correlation between the site coupled to the trap and its neighboring sites. This asymmetry in sensitivity is highly robust and appears irrespective of changes in parameters such as transition dipole orientations and initial conditions. Our results suggest that in the design of exciton transport systems, efforts to increase efficiency by controlling spatial correlation should be focused on the region near the site of exciton trapping.

Pelzer, Kenley M.; Fidler, Andrew F.; Griffin, Graham B.; Gray, Stephen K.; Engel, Gregory S.

2013-09-01

173

Site-dependent spectra from the 1999 Turkey earthquakes considering different sets of strong-motion data  

Microsoft Academic Search

In the last decade extensive strong-motion measurements were carried out by the reconnaissance team of the German TaskForce for Earthquakes. Aftershocks were recorded by a mesh of temporarily installed strong-motion recorders during the field surveys to Turkey in 1998 (Adana\\/Ceyhan), 1999 (Izmit\\/Kocaeli and Duezce\\/Bolu) and 2002 (Sultandagi\\/Afyon). Particularly the two missions in 1999 provided a unique and comprehensive database of

J. Schwarz; C. Ende; J. Habenberger; D. H. Lang

2003-01-01

174

The spatial scale of density-dependent growth and implications for dispersal from nests in juvenile Atlantic salmon  

Microsoft Academic Search

By dispersing from localized aggregations of recruits, individuals may obtain energetic benefits due to reduced experienced\\u000a density. However, this will depend on the spatial scale over which individuals compete. Here, we quantify this scale for juvenile\\u000a Atlantic salmon (Salmo salar) following emergence and dispersal from nests. A single nest was placed in each of ten replicate streams during winter, and

Sigurd Einum; Grethe Robertsen; Keith H. Nislow; Simon McKelvey; John D. Armstrong

2011-01-01

175

Spatially dependent parameter estimation and nonlinear data assimilation by autosynchronization of a system of partial differential equations  

NASA Astrophysics Data System (ADS)

Given multiple images that describe chaotic reaction-diffusion dynamics, parameters of a partial differential equation (PDE) model are estimated using autosynchronization, where parameters are controlled by synchronization of the model to the observed data. A two-component system of predator-prey reaction-diffusion PDEs is used with spatially dependent parameters to benchmark the methods described. Applications to modeling the ecological habitat of marine plankton blooms by nonlinear data assimilation through remote sensing are discussed.

Kramer, Sean; Bollt, Erik M.

2013-09-01

176

Designing MAC Protocols for Spread Spectrum Ad Hoc Networks: Thinning versus Spatial State-Dependent Packing  

Microsoft Academic Search

Achieving high spatial reuse in ad hoc networks ex- ploiting a spread spectrum physical layer can be quite challeng- ing. Designing a MAC protocol for such systems must take into account the physical layer characteristics. Most existing MAC designs for spread spectrum ad hoc networks perform contention resolution to thin the intended transmissions. This is fundamen- tally similar to the

X. Yang; A. Hasan; G. de Veciana; J. G. Andrews

177

A biologically-inspired clustering algorithm dependent on spatial data in sensor networks  

Microsoft Academic Search

Sensor networks in environmental monitoring applications aim to provide scientists with a useful spatio- temporal representation of the observed phenomena. This helps to deepen their understanding of the environmental signals that cover large geographic areas. In this paper, the spatial aspect of this data handling requirement is met by creating clusters in a sensor network based on the rate of

Ibiso Wokoma; Lan Ling Shum; Lionel Sacks; Ian Marshall

2005-01-01

178

A CONTENT-DEPENDENT SPATIALLY LOCALIZED VIDEO WATERMARK FOR RESISTANCE TO COLLUSION AND INTERPOLATION ATTACKS  

E-print Network

. We introduce the notion of a watermark foot- print, the spatial locations over which its energy frame, current image wa- termarking techniques can immediately be applied at the subframe-level. We are that the watermarked media must be perceptually equivalent to the original, and the watermark should be robust

Kundur, Deepa

179

Frequency and wave number dependence of the shear correlator in strongly coupled hot Yang-Mills theory  

NASA Astrophysics Data System (ADS)

We use AdS/QCD duality to compute the finite temperature Green’s function G(?,k;T) of the shear operator T12 for all ?, k in hot Yang-Mills theory in the strongly coupled domain. The goal is to assess how the existence of scales like the transition temperature and glueball masses affect the correlator computed in the scalefree conformal N=4 supersymmetric Yang-Mills theory. We observe sizeable effects for T close to Tc which rapidly disappear with increasing T. Quantitative agreement of these predictions with future lattice Monte Carlo data would suggest that QCD matter in this temperature range is strongly interacting.

Kajantie, K.; Krššák, Martin; Vepsäläinen, M.; Vuorinen, Aleksi

2011-10-01

180

Strong Libraries, Strong Scores  

ERIC Educational Resources Information Center

This article talks about the first-ever Texas Conference on School Libraries on April 6, 2005 that was attended by one hundred thirty-five school administrators and trustees. The miniconference, entitled Strong Libraries, Strong Scores, was held at the Austin Hilton, Austin, Texas during the Texas Library Association's Annual Conference and was…

Gray, Carlyn

2006-01-01

181

Dynamical modeling of viral spread in spatially distributed populations: stochastic origins of oscillations and density dependence  

Microsoft Academic Search

In order to understand the spatio-temporal structure of epidemics beyond that permitted with classical SIR (susceptible-infective- recovered)-type models, a new mathematical model for the spread of a viral disease in a population of spatially distributed hosts is described. The positions of the hosts are randomly generated in a rectangular habitat. Encounters between any pair of individuals are according to a

Henry C. Tuckwell; Laurent Toubiana

182

Spatial analysis of soil surface hydraulic properties: Is infiltration method dependent?  

Microsoft Academic Search

The management of irrigated agricultural fields requires reliable information about soil hydraulic properties and their spatio-temporal variability. The spatial variability of saturated hydraulic conductivity, Ks and the alpha-parameter ?vG-2007 of the van Genuchten equation was reviewed on an agricultural loamy soil after a 17-year period of repeated conventional agricultural practices for tillage and planting. The Beerkan infiltration method and its

Ibrahim Mubarak; Rafael Angulo-Jaramillo; Jean Claude Mailhol; Pierre Ruelle; Mohammadreza Khaledian; Michel Vauclin

2010-01-01

183

Time-dependent theory of Auger decay induced by ultra-short pulses in a strong laser field  

Microsoft Academic Search

A quantum mechanical theory of a laser-assisted Auger process in atoms excited by an ultra-short (attosecond) electromagnetic pulse in the field of a few-cycle strong laser pulse is presented. It is based on the non-stationary Schrödinger equation, which describes the photoionization of an inner atomic shell and the decay of the created vacancy, while the Auger electron is treated in

A K Kazansky; I P Sazhina; N M Kabachnik

2009-01-01

184

Spatial Analysis to Quantify Numerical Model Bias and Dependence: How Many Climate Models Are There?  

E-print Network

are not strongly related. KEY WORDS: Cross-covariance model; Intergovernmental Panel on Climate Change; Kernel [Intergovernmental Panel on Climate Change (IPCC) 2001], related to increas- ing anthropogenic emissions the Earth's atmosphere, ocean, and land processes are the primary tool to study how climate may change over

Jun, Mikyoung

185

Accuracy of spatial localization depending on head posture in a perturbed gravitoinertial force field.  

PubMed

Spatial orientation is crucial when subjects have to accurately reach memorized visual targets. In previous studies modified gravitoinertial force fields were used to affect the accuracy of pointing movements in complete darkness without visual feedback of the moving limb. Target mislocalization was put forward as one hypothesis to explain this decrease in accuracy of pointing movements. The aim of this study was to test this hypothesis by determining the accuracy of spatial localization of memorized visual targets in a perturbed gravitoinertial force field. As head orientation is involved in localization tasks and carrying relevant sensory systems (visual, vestibular and neck muscle proprioceptive), we also tested the effect of head posture on the accuracy of localization. Subjects (n=10) were seated off-axis on a rotating platform (120 degrees s(-1)) in complete darkness with the head fixed (head-fixed session) or free to move (head-free session). They were required to report verbally the egocentric spatial localization of visual memorized targets. They gave the perceived target location in direction (i.e. left or right) and in amplitude (in centimeters) relative to the direction they thought to be straight ahead. Results showed that the accuracy of visual localization decreased when subjects were exposed to inertial forces. Moreover, subjects localized the memorized visual targets more to the right than their actual position, that was in the direction of the inertial forces. With further analysis, it appeared that this shift of localization was concomitant with a shift of the visual straight ahead (VSA) in the opposite direction. Thus, the modified gravitoinertial force field led to a modification in the orientation of the egocentric reference frame. Furthermore, this shift of localization increased when the head was free to move while the head was tilted in roll toward the center of rotation of the platform and turned in yaw in the same direction. It is concluded that the orientation of the egocentric reference frame was influenced by the gravitoinertial vector. PMID:15578170

Prieur, J-M; Bourdin, C; Vercher, J-L; Sarès, F; Blouin, J; Gauthier, G M

2005-03-01

186

Variant 22: Spatially-Dependent: Transient Processes in MOX Fueled Core  

SciTech Connect

This work is a part of Joint U.S./Russian Project with Weapons-Grade Plutonium Disposition in VVER Reactors and presents the results of spatial kinetics calculational benchmarks. The examinations were carried out with the following purposes: to verify one of spatial neutronic kinetics model elaborated in KI, to understand sensibility of the model to neutronics difference of UOX and MOX cores, and to compare in future point and spatial kinetics models (on the base of a set of selected accidents) in view of eventual creation of RELAP option with 3D kinetics. The document contains input data and results of model operation of three emergency dynamic processes in the VVER-1000 core: (1) Central control rod ejection by pressure drop caused by destroying of the moving mechanism cover. (2) Overcooling of the reactor core caused by steam line rupture and non-closure of steam generator stop valve. (3) The boron dilution of coolant in part of the VVER-1000 core caused by penetration of the distillate slug into the core at start up of non-working loop. These accidents have been applied to: (1) Uranium reference core that is the so-called Advanced VVER-1000 core with Zirconium fuel pins claddings and guide tubes. A number of assemblies contained 18 boron BPRs while first year operating. (2) MOX core with about 30% MOX fuel. At a solving it was supposed that MOX-fuel thermophysical characteristics are identical to uranium fuel ones. The calculations were carried out with the help of the program NOSTRA/1/, simulating VVER dynamics that is briefly described in Chapter 1. Chapter 3 contains the description of reference Uranium and MOX cores that are used in calculations. The neutronics calculations of MOX core with about 30% MOX fuel are named ''Variant 2 1''. Chapters 4-6 contain the calculational results of three above mentioned benchmark accidents that compose in a whole the ''Variant 22''.

Pavlovichev, A.M.

2001-09-28

187

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster  

E-print Network

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental infrared the isotopically labeled systems arises from an analysis of the simulated cluster spectroscopy and leads

Iyengar, Srinivasan S.

188

Spatial heterogeneity in the effects of climate and density-dependence on dispersal in a house sparrow metapopulation  

PubMed Central

Dispersal plays a key role in the response of populations to climate change and habitat fragmentation. Here, we use data from a long-term metapopulation study of a non-migratory bird, the house sparrow (Passer domesticus), to examine the influence of increasing spring temperature and density-dependence on natal dispersal rates and how these relationships depend on spatial variation in habitat quality. The effects of spring temperature and population size on dispersal rate depended on the habitat quality. Dispersal rate increased with temperature and population size on poor-quality islands without farms, where house sparrows were more exposed to temporal fluctuations in weather conditions and food availability. By contrast, dispersal rate was independent of spring temperature and population size on high-quality islands with farms, where house sparrows had access to food and shelter all the year around. This illustrates large spatial heterogeneity within the metapopulation in how population density and environmental fluctuations affect the dispersal process. PMID:21613299

Parn, Henrik; Ringsby, Thor Harald; Jensen, Henrik; Saether, Bernt-Erik

2012-01-01

189

Evaluation of TRMM Multi-satellite Precipitation Analysis (TMPA) performance in the Central Andes region and its dependency on spatial and temporal resolution  

NASA Astrophysics Data System (ADS)

Climate time series are of major importance for base line studies for climate change impact and adaptation projects. However, in mountain regions and in developing countries there exist significant gaps in ground based climate records in space and time. Specifically, in the Peruvian Andes spatially and temporally coherent precipitation information is a prerequisite for ongoing climate change adaptation projects in the fields of water resources, disasters and food security. The present work aims at evaluating the ability of Tropical Rainfall Measurement Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) to estimate precipitation rates at daily 0.25° × 0.25° scale in the Central Andes and the dependency of the estimate performance on changing spatial and temporal resolution. Comparison of the TMPA product with gauge measurements in the regions of Cuzco, Peru and La Paz, Bolivia were carried out and analysed statistically. Large biases are identified in both investigation areas in the estimation of daily precipitation amounts. The occurrence of strong precipitation events was well assessed, but their intensities were underestimated. TMPA estimates for La Paz show high false alarm ratio. The dependency of the TMPA estimate quality with changing resolution was analysed by comparisons of 1-, 7-, 15- and 30-day sums for Cuzco, Peru. The correlation of TMPA estimates with ground data increases strongly and almost linearly with temporal aggregation. The spatial aggregation to 0.5°, 0.75° and 1° grid box averaged precipitation and its comparison to gauge data of the same areas revealed no significant change in correlation coefficients and estimate performance. In order to profit from the TMPA combination product on a daily basis, a procedure to blend it with daily precipitation gauge measurements is proposed. Different sources of errors and uncertainties introduced by the sensors, sensor-specific algorithm aspects and the TMPA processing scheme are discussed. This study reveals the possibilities and restrictions of the use of TMPA estimates in the Central Andes and should assist other researchers in the choice of the best resolution-accuracy relationship according to requirements of their applications.

Scheel, M. L. M.; Rohrer, M.; Huggel, C.; Santos Villar, D.; Silvestre, E.; Huffman, G. J.

2010-10-01

190

Evaluation of TRMM Multi-satellite Precipitation Analysis (TMPA) performance in the Central Andes region and its dependency on spatial and temporal resolution  

NASA Astrophysics Data System (ADS)

Climate time series are of major importance for base line studies for climate change impact and adaptation projects. However, for instance, in mountain regions and in developing countries there exist significant gaps in ground based climate records in space and time. Specifically, in the Peruvian Andes spatially and temporally coherent precipitation information is a prerequisite for ongoing climate change adaptation projects in the fields of water resources, disasters and food security. The present work aims at evaluating the ability of Tropical Rainfall Measurement Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) to estimate precipitation rates at daily 0.25° × 0.25° scale in the Central Andes and the dependency of the estimate performance on changing spatial and temporal resolution. Comparison of the TMPA product with gauge measurements in the regions of Cuzco, Peru and La Paz, Bolivia were carried out and analysed statistically. Large biases are identified in both investigation areas in the estimation of daily precipitation amounts. The occurrence of strong precipitation events was well assessed, but their intensities were underestimated. TMPA estimates for La Paz show high false alarm ratio. The dependency of the TMPA estimate quality with changing resolution was analysed by comparisons of 1-, 7-, 15- and 30-day sums for Cuzco, Peru. The correlation of TMPA estimates with ground data increases strongly and almost linearly with temporal aggregation. The spatial aggregation to 0.5°, 0.75° and 1° grid box averaged precipitation and its comparison to gauge data of the same areas revealed no significant change in correlation coefficients and estimate performance. In order to profit from the TMPA combination product on a daily basis, a procedure to blend it with daily precipitation gauge measurements is proposed. Different sources of errors and uncertainties introduced by the sensors, sensor-specific algorithm aspects and the TMPA processing scheme are discussed. This study reveals the possibilities and restrictions of the use of TMPA estimates in the Central Andes and should assist other researchers in the choice of the best resolution-accuracy relationship according to requirements of their applications.

Scheel, M. L. M.; Rohrer, M.; Huggel, Ch.; Santos Villar, D.; Silvestre, E.; Huffman, G. J.

2011-08-01

191

A System of Repressor Gradients Spatially Organizes the Boundaries of "Morphogen-dependent" Target Genes  

PubMed Central

Summary The homeodomain (HD) protein Bicoid (Bcd) is thought to function as a gradient morphogen that positions boundaries of target genes via threshold-dependent activation mechanisms. Here we analyze 66 Bcd-dependent regulatory elements, and show that their boundaries are positioned primarily by repressive gradients that antagonize Bcd-mediated activation. A major repressor is the pair-rule protein Runt, which is expressed in an opposing gradient, and is necessary and sufficient for limiting Bcd-dependent activation. Evidence is presented that Runt functions with the maternal repressor Capicua and the gap protein Kruppel as the principal components of a repression system that correctly orders boundaries throughout the anterior half of the embryo. These results put conceptual limits on the Bcd morphogen hypothesis, and demonstrate how the Bcd gradient functions within the gene network that patterns the embryo. PMID:22541432

Chen, Hongtao; Xu, Zhe; Mei, Constance; Yu, Danyang; Small, Stephen

2012-01-01

192

Energy Dependence of Localization Length of Two-Dimensional Electron System Moving in a Random Potential under Strong Magnetic Fields  

Microsoft Academic Search

From self-consistent determination of the dynamical diffusion coefficient, the Fermi energy dependence of the localization length, xi(EF), is obtained for the case where the Fermi energy, EF, lies near the center of the lowest Landau subband. If the energy is measured from the point where the real part of the retarded Green's function vanishes, xi(EF) for small |EF| is expected

Yoshiyuki Ono

1982-01-01

193

Time-dependent analytical R-matrix approach for strong-field dynamics. I. One-electron systems  

NASA Astrophysics Data System (ADS)

We develop a flexible analytical approach to describe strong-field dynamics in atoms and molecules. The approach is based on the ideas of the R-matrix method. Here, we illustrate and validate our approach by applying it to systems with one active electron bound by the Coulomb potential and benchmark our results against the standard theory of Perelomov, Popov, and Terent'ev [Sov. Phys. JETP0021-903710.1007/BF01132710 23, 924 (1966)]. We discuss corrections to the ionization amplitude associated with the interplay of the Coulomb potential and the laser field on the sub-laser cycle time scale and the shape of the tunneling wave packets associated with different instants of ionization.

Torlina, Lisa; Smirnova, Olga

2012-10-01

194

Electronic Supplementary Information for Probe Dependence of Spatially Heterogeneous Dynamics in Supercooled Glycerol as Revealed by  

E-print Network

in Supercooled Glycerol as Revealed by Single Molecule Microscopy Stephan A. Mackowiak, Lindsay M. Leone of the viscosity of Supplementary Material for PCCP This journal is © The Owner Societies 2011 #12;2 glycerol. The temperature dependence of glycerol's viscosity is known to vary with temperature according to the Vogel

Kaufman, Laura

195

Bound state of solution of Dirac-Coulomb problem with spatially dependent mass  

E-print Network

The bound state solution of Coulomb Potentials in the Dirac equation is calculated for position dependent mass function M(r) within the framework of asymptotic iteration method (AIM). The eigenfunctions are derived in terms of hypergeometric function and function generator equation of AIM.

Eser Olgar; Hayder M. Dhahir; H. Mutaf

2014-09-24

196

A spin-dependent Popov-Fedotov trick and a new loop expansion for the strong coupling negative U Hubbard model  

Microsoft Academic Search

We calculate fluctuation effects on Bose condensation type superconductivity in the strong coupling negative U Hubbard model by means of a new loop expansion. Our method is based on a spin-dependent modification of the Popov-Fedotov trick. We replace the Popov-Fedotov chemical potential by a fictitious imaginary magnetic field. This field is absorbed in spindependent semionic Matsubara frequencies, which allows for

J. Stein; R. Oppermann

1991-01-01

197

Hippocampal dysregulation of neurofibromin-dependent pathways is associated with impaired spatial learning in engrailed 2 knock-out mice.  

PubMed

Genome-wide association studies indicated the homeobox-containing transcription factor Engrailed-2 (En2) as a candidate gene for autism spectrum disorders (ASD). Accordingly, En2 knock-out (En2(-/-)) mice show anatomical and behavioral "ASD-like" features, including decreased sociability and learning deficits. The molecular pathways underlying these deficits in En2(-/-) mice are not known. Deficits in signaling pathways involving neurofibromin and extracellular-regulated kinase (ERK) have been associated with impaired learning. Here we investigated the neurofibromin-ERK cascade in the hippocampus of wild-type (WT) and En2(-/-) mice before and after spatial learning testing. When compared with WT littermates, En2(-/-) mice showed impaired performance in the Morris water maze (MWM), which was accompanied by lower expression of the activity-dependent gene Arc. Quantitative RT-PCR, immunoblotting, and immunohistochemistry experiments showed a marked downregulation of neurofibromin expression in the dentate gyrus of both naive and MWM-treated En2(-/-) mice. ERK phosphorylation, known to be induced in the presence of neurofibromin deficiency, was increased in the dentate gyrus of En2(-/-) mice after MWM. Treatment of En2(-/-) mice with lovastatin, an indirect inhibitor of ERK phosphorylation, markedly reduced ERK phosphorylation in the dentate gyrus, but was unable to rescue learning deficits in MWM-trained mutant mice. Further investigation is needed to unravel the complex molecular mechanisms linking dysregulation of neurofibromin-dependent pathways to spatial learning deficits in the En2 mouse model of ASD. PMID:25274808

Provenzano, Giovanni; Pangrazzi, Luca; Poli, Andrea; Pernigo, Mattia; Sgadò, Paola; Genovesi, Sacha; Zunino, Giulia; Berardi, Nicoletta; Casarosa, Simona; Bozzi, Yuri

2014-10-01

198

Spatial volume dependence for 2+1 dimensional SU(N) Yang-Mills theory  

NASA Astrophysics Data System (ADS)

We study the 2+1 dimensional SU(N) Yang-Mills theory on a finite two-torus with twisted boundary conditions. Our goal is to study the interplay between the rank of the group N , the length of the torus L and the Z N magnetic flux. After presenting the classical and quantum formalism, we analyze the spectrum of the theory using perturbation theory to one-loop and using Monte Carlo techniques on the lattice. In perturbation theory, results to all orders depend on the combination x = ? N L and an angle defined in terms of the magnetic flux (? is `t Hooft coupling). Thus, fixing the angle, the system exhibits a form of volume independence ( N L dependence). The numerical results interpolate between our perturbative calculations and the confinement regime. They are consistent with x-scaling and provide interesting information about the k-string spectrum and effective string theories. The occurrence of tachyonic instabilities is also analysed. They seem to be avoidable in the large N limit with a suitable scaling of the magnetic flux.

Pérez, Margarita García; González-Arroyo, Antonio; Okawa, Masanori

2013-09-01

199

Quantitative determination of valproic acid in postmortem blood samples--evidence of strong matrix dependency and instability.  

PubMed

Most of the daily work of forensic toxicologists deals with fatal cases resulting from overdoses of licit and illicit drugs. However, another reason for fatalities in patients suffering from epilepsy can be undetectable or subtherapeutic levels of antiepileptic drugs. Some studies have shown a correlation between "sudden unexpected death in epilepsy" (SUDEP) and the ineffective treatment of epilepsy. Low levels of antiepileptic drugs may be a risk factor for SUDEP. The death of a psychiatric patient also suffering from epilepsy inspired the investigation. Subsequent to the death of the patient, the doctor was accused of providing inadequate therapy for epilepsy. The patient was to be treated with valproic acid. We developed and validated a simple method of determining valproic acid levels by gas chromatography-mass spectrometry for serum, but a transfer of the method from serum to postmortem whole blood failed. The method had to be modified and revalidated for postmortem whole blood specimens. A stability study of valproic acid in postmortem blood was conducted, showing a decline of valproic acid levels by 85 % after storage at room temperature for 28 days. During the storage time, the blood samples showed changes in consistency. Depending on the stage of decomposition, it is necessary to perform a determination by standard addition with an equilibration time of 4 h before extraction to achieve reliable results. For a proper interpretation of quantitative results, it is necessary to keep the postmortem decline of valproic acid concentrations in mind. PMID:23536197

Kiencke, Verena; Andresen-Streichert, Hilke; Müller, Alexander; Iwersen-Bergmann, Stefanie

2013-11-01

200

The Effect of Opium Dependency of Parent (s) on Offspring’s Spatial Learning & Memory in Adult Male Rats  

PubMed Central

Objective(s): As far as we know, there has been no report regarding the effects of opium addiction or dependency of both parents on the learning and memory process in offspring. The aim of this study was to examine the learning and memory changes of adult male offspring whose mothers, fathers and/or both parents had dependency to opium before and during pregnancy. Materials and Methods : All experiments were carried out on Wistar rats. Opium dependency was induced by daily injections of opium (10 mg/kg/SC, bid/10 d) before mating. The presence of a vaginal plug was designated as gestation day. Treatment with opium continued through breeding and gestation until parturition. Spatial memory was tested in male offspring of control, saline and prenatal opium treated groups by a training trial and the probe test in the Morris water maze. Swimming escape latency in the maze and the ability to find the platform in the training trial were recorded. The time spent in the trigger zone and number of times the rats crossed the platform during the probe phase and swimming speed were measured. Results: The data revealed increased escape latency and a greater distance traveled to find the hidden platform in the offspring’s whose mother, father and /or both parents were exposed to opium. Crossings to target quadrant at probe trials was significantly reduced in all of the prenatal opium exposed offsprings. The swimming speed showed a significant increase in father and parent’s opium exposed offspring. Conclusion: Prenatal opium exposure of either parent may cause deficits in spatial learning, but the precise mechanism(s) remain largely unknown. PMID:23826491

Saberi Moghadam, Arezoo; Sepehri, Gholamreza; Sheibani, Vahid; Haghpanah, Tahereh; Divsalar, Kouros; Hajzadeh, Mousa-Al-Reza; Afarineshkhaki, Mohammadreza

2013-01-01

201

Temporal and spatial distribution of tropospheric NO2 over arid areas of Central Asia by OMI Satellite observations: Evidence for a strong contribution of soil biogenic nitric oxide  

NASA Astrophysics Data System (ADS)

We present results observations of tropospheric NO2 carried out by Ozone Monitoring Instrument (OMI) over the Central Asian arid areas from 2005 to 2011. We selected 8 oases (Ruoqiang, Milan, Waxxari, Qiemo, Minfeng, Shache, Awati and Kuche) in Taklimakan desert (part of the great Central Asian deserts). For these, spatial distributions, seasonal variations, and trends of tropospheric NO2 Vertical Column Densities (VCDs) retrieved are discussed. In the Taklimakan desert, oases are the centers of all human activities and the economy of the selected oases are dominated by oasis agriculture. Irrigation and fertilization favor the microbial production of nitric oxide in soils, which after emission is converted to NO2 by ozone. Consequently, tropospheric NO2-VCDs are a good proxy for biogenic NO emissions from soils. For contrast, we examined also the NO2-VCDs in the area of the growing megacity Urumqi (43.85°N, 87.62°E), which is known as an anthropogenic highly polluted city in the Central Asian deserts. For 2005-2011, all selected oases are hot spots of NO/NO2 in the Taklimakan desert. Higher NO2-VCDs were observed during growing seasons over all 8 oases. NO2-VCDs observed in summer generally increased from 2005 to 2011. NO2-VCDs over Urumqi were generally at least 1 order of magnitude higher than those over the oases. In contrast to the oases, wintertime NO2-VCDs over Urumqi are higher than in summer. We evaluated governmental statistical agricultural data of the 8 oasis, and compared the trends with corresponding summertime NO2-VCDs. Inter-annual trends of NO2-VCDs over the oases show similar patterns to those of N-fertilizer application and sown (and irrigated) areas. Highest NO2-VCDs observed in summer for agriculturally dominated oases are a strong indication that soil biogenic NO emission is the main contributor to the tropospheric NO2 over all 8 oases, while in Urumqi fossil fuel combustion, particularly during winter, is the main source for NO/NO2. With regard to recent/future agriculture development in the Taklimakan oases (80% of the current Chinese cotton production originates from there), biogenic NO emission from soils will provide an increasing contribution to tropospheric NO2 over Central Asia.

Mamtimin, Buhalqem; Qi, Yue; Beirle, Steffen; Wagner, Thomas; Meixner, Franz X.

2013-04-01

202

Differential neuronal representation of spatial attention dependent on relative target locations during multiple object tracking.  

PubMed

Humans can simultaneously track multiple moving objects with attention. The number of objects that can be tracked is known to be larger when visual stimuli are presented bilaterally rather than presented unilaterally. To elucidate the underlying neuronal mechanism, we trained monkeys to covertly track a single or multiple object(s). We found that neurons in the lateral prefrontal cortex exhibited greater activity for the target passing through the receptive field (RF) than for distractors. During multiple-object tracking, response enhancement for one target presented in the RF was stronger when the other target was located in the opposite than the same visual hemifield. Because the neuronal modulation did not differ depending on relative target locations with respect to upper and lower visual hemifields, the distance between the targets does not explain the results. We propose that inherent, anatomical separation of visual processing for contralateral and ipsilateral visual fields might constrain cognitive capacity. PMID:25057198

Matsushima, Ayano; Tanaka, Masaki

2014-07-23

203

Nonlinear frequency-dependent effects in the dc magnetization of uniaxial magnetic nanoparticles in superimposed strong alternating current and direct current fields  

NASA Astrophysics Data System (ADS)

The dc component of the magnetization of noninteracting fine magnetic particles possessing simple uniaxial anisotropy and subjected to strong ac and dc bias magnetic fields is calculated via the magnetic Langevin equation. In the presence of an ac driving field, the dc component of the magnetization of uniaxial particles alters drastically leading to new nonlinear effects; in particular, it becomes frequency-dependent. In axial symmetry, where the strong ac field is parallel to the easy axis of a particle, two distinct dispersion regions in the dc magnetization at low and mid-frequencies emerge, corresponding to longitudinal overbarrier and intrawell relaxation modes. Such frequency-dependent behavior allows one to estimate the magnetization reversal time via the half-width of the low-frequency dispersion band. Otherwise, by applying the strong ac field at an angle to the easy axis of a particle so breaking the axial symmetry, a third high-frequency nonlinear resonant dispersion in the dc component of the magnetization appears accompanied by parametric resonance behavior due to excitation of transverse modes with frequencies close to the precession frequency.

Wei, Nijun; Byrne, Declan; Coffey, William T.; Kalmykov, Yuri P.; Titov, Serguey V.

2014-11-01

204

THE SPATIAL AND TEMPORAL DEPENDENCE OF CORONAL HEATING BY ALFVEN WAVE TURBULENCE  

SciTech Connect

The solar atmosphere may be heated by Alfven waves that propagate up from the convection zone and dissipate their energy in the chromosphere and corona. To further test this theory, we consider wave heating in an active region observed on 2012 March 7. A potential field model of the region is constructed, and 22 field lines representing observed coronal loops are traced through the model. Using a three-dimensional (3D) reduced magnetohydrodynamics code, we simulate the dynamics of Alfven waves in and near the observed loops. The results for different loops are combined into a single formula describing the average heating rate Q as a function of position within the observed active region. We suggest this expression may be approximately valid also for other active regions, and therefore may be used to construct 3D, time-dependent models of the coronal plasma. Such models are needed to understand the role of thermal non-equilibrium in the structuring and dynamics of the Sun's corona.

Asgari-Targhi, M.; Van Ballegooijen, A. A.; Cranmer, S. R.; DeLuca, E. E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS-15, Cambridge, MA 02138 (United States)

2013-08-20

205

Developmental plasticity of spatial hearing following asymmetric hearing loss: context-dependent cue integration and its clinical implications  

PubMed Central

Under normal hearing conditions, comparisons of the sounds reaching each ear are critical for accurate sound localization. Asymmetric hearing loss should therefore degrade spatial hearing and has become an important experimental tool for probing the plasticity of the auditory system, both during development and adulthood. In clinical populations, hearing loss affecting one ear more than the other is commonly associated with otitis media with effusion, a disorder experienced by approximately 80% of children before the age of two. Asymmetric hearing may also arise in other clinical situations, such as after unilateral cochlear implantation. Here, we consider the role played by spatial cue integration in sound localization under normal acoustical conditions. We then review evidence for adaptive changes in spatial hearing following a developmental hearing loss in one ear, and show that adaptation may be achieved either by learning a new relationship between the altered cues and directions in space or by changing the way different cues are integrated in the brain. We next consider developmental plasticity as a source of vulnerability, describing maladaptive effects of asymmetric hearing loss that persist even when normal hearing is provided. We also examine the extent to which the consequences of asymmetric hearing loss depend upon its timing and duration. Although much of the experimental literature has focused on the effects of a stable unilateral hearing loss, some of the most common hearing impairments experienced by children tend to fluctuate over time. We therefore propose that there is a need to bridge this gap by investigating the effects of recurring hearing loss during development, and outline recent steps in this direction. We conclude by arguing that this work points toward a more nuanced view of developmental plasticity, in which plasticity may be selectively expressed in response to specific sensory contexts, and consider the clinical implications of this. PMID:24409125

Keating, Peter; King, Andrew J.

2013-01-01

206

Spatially-resolved mapping of history-dependent coupled electrochemical and electronical behaviors of electroresistive NiO.  

PubMed

Bias-induced oxygen ion dynamics underpins a broad spectrum of electroresistive and memristive phenomena in oxide materials. Although widely studied by device-level and local voltage-current spectroscopies, the relationship between electroresistive phenomena, local electrochemical behaviors, and microstructures remains elusive. Here, the interplay between history-dependent electronic transport and electrochemical phenomena in a NiO single crystalline thin film with a number of well-defined defect types is explored on the nanometer scale using an atomic force microscopy-based technique. A variety of electrochemically-active regions were observed and spatially resolved relationship between the electronic and electrochemical phenomena was revealed. The regions with pronounced electroresistive activity were further correlated with defects identified by scanning transmission electron microscopy. Using fully coupled mechanical-electrochemical modeling, we illustrate that the spatial distribution of strain plays an important role in electrochemical and electroresistive phenomena. These studies illustrate an approach for simultaneous mapping of the electronic and ionic transport on a single defective structure level such as dislocations or interfaces, and pave the way for creating libraries of defect-specific electrochemical responses. PMID:25335689

Sugiyama, Issei; Kim, Yunseok; Jesse, Stephen; Strelcov, Evgheni; Kumar, Amit; Tselev, Alexander; Rahani, Ehasan Kabiri; Shenoy, Vivek B; Yamamoto, Takahisa; Shibata, Naoya; Ikuhara, Yuichi; Kalinin, Sergei V

2014-01-01

207

Spatially-resolved mapping of history-dependent coupled electrochemical and electronical behaviors of electroresistive NiO  

NASA Astrophysics Data System (ADS)

Bias-induced oxygen ion dynamics underpins a broad spectrum of electroresistive and memristive phenomena in oxide materials. Although widely studied by device-level and local voltage-current spectroscopies, the relationship between electroresistive phenomena, local electrochemical behaviors, and microstructures remains elusive. Here, the interplay between history-dependent electronic transport and electrochemical phenomena in a NiO single crystalline thin film with a number of well-defined defect types is explored on the nanometer scale using an atomic force microscopy-based technique. A variety of electrochemically-active regions were observed and spatially resolved relationship between the electronic and electrochemical phenomena was revealed. The regions with pronounced electroresistive activity were further correlated with defects identified by scanning transmission electron microscopy. Using fully coupled mechanical-electrochemical modeling, we illustrate that the spatial distribution of strain plays an important role in electrochemical and electroresistive phenomena. These studies illustrate an approach for simultaneous mapping of the electronic and ionic transport on a single defective structure level such as dislocations or interfaces, and pave the way for creating libraries of defect-specific electrochemical responses.

Sugiyama, Issei; Kim, Yunseok; Jesse, Stephen; Strelcov, Evgheni; Kumar, Amit; Tselev, Alexander; Rahani, Ehasan Kabiri; Shenoy, Vivek B.; Yamamoto, Takahisa; Shibata, Naoya; Ikuhara, Yuichi; Kalinin, Sergei V.

2014-10-01

208

Spatially-resolved mapping of history-dependent coupled electrochemical and electronical behaviors of electroresistive NiO  

PubMed Central

Bias-induced oxygen ion dynamics underpins a broad spectrum of electroresistive and memristive phenomena in oxide materials. Although widely studied by device-level and local voltage-current spectroscopies, the relationship between electroresistive phenomena, local electrochemical behaviors, and microstructures remains elusive. Here, the interplay between history-dependent electronic transport and electrochemical phenomena in a NiO single crystalline thin film with a number of well-defined defect types is explored on the nanometer scale using an atomic force microscopy-based technique. A variety of electrochemically-active regions were observed and spatially resolved relationship between the electronic and electrochemical phenomena was revealed. The regions with pronounced electroresistive activity were further correlated with defects identified by scanning transmission electron microscopy. Using fully coupled mechanical-electrochemical modeling, we illustrate that the spatial distribution of strain plays an important role in electrochemical and electroresistive phenomena. These studies illustrate an approach for simultaneous mapping of the electronic and ionic transport on a single defective structure level such as dislocations or interfaces, and pave the way for creating libraries of defect-specific electrochemical responses. PMID:25335689

Sugiyama, Issei; Kim, Yunseok; Jesse, Stephen; Strelcov, Evgheni; Kumar, Amit; Tselev, Alexander; Rahani, Ehasan Kabiri; Shenoy, Vivek B.; Yamamoto, Takahisa; Shibata, Naoya; Ikuhara, Yuichi; Kalinin, Sergei V.

2014-01-01

209

Comparison of the strong-field ionization of N{sub 2} and F{sub 2}: A time-dependent density-functional-theory study  

SciTech Connect

We compare strong-field ionization probabilities of N{sub 2} and F{sub 2} molecules using time-dependent density functional theory calculations. Accurate nuclear potentials and ground vibrational wave functions are incorporated into our study. For both molecules, the effect of molecular vibration is small, while that of the molecular orientation is significant. When compared to the ionization probability of a molecule at the equilibrium geometry, we estimate the effect of the ground state vibration to be within 3% for N{sub 2} and within 6% for F{sub 2} in the intensity range from 1 to 5x10{sup 14} W/cm{sup 2}. The molecular-orientation-dependent ionization probabilities for both molecules at various intensities are presented. They are strongly dependent on the laser intensity, and the anisotropy diminishes when the laser intensity is high. For laser intensities of 1.6 and 2.2x10{sup 14} W/cm{sup 2} we find ionization probability ratios of 5.9 and 4.3, respectively, for the parallel versus perpendicular orientation of N{sub 2}. This is reasonably consistent with experimental measurements. For randomly oriented molecules, the ratio of the probabilities for N{sub 2} and F{sub 2} increases from about 1 at 10{sup 14} W/cm{sup 2} to 2 at 4x10{sup 14} W/cm{sup 2}, which agrees well with experimental results.

Chu Xi; McIntyre, Melissa [Department of Chemistry and Biochemistry, University of Montana, Missoula, Montana 59812 (United States)

2011-01-15

210

Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field  

NASA Astrophysics Data System (ADS)

Evolution of the helium atom in a strong time-dependent (TD) magnetic field ( B) of strength up to 1011 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schrödinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >109 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >109 G, the conventional TD-DFT based approach differs "dynamically" from the CDFT based approach under similar computational constraints.

Vikas, Hash(0x125f4490)

2011-02-01

211

Spatial dependence and mitigation of radiation damage by a line-focus mini-beam.  

SciTech Connect

Recently, strategies to reduce primary radiation damage have been proposed which depend on focusing X-rays to dimensions smaller than the penetration depth of excited photoelectrons. For a line focus as used here the penetration depth is the maximum distance from the irradiated region along the X-ray polarization direction that the photoelectrons penetrate. Reported here are measurements of the penetration depth and distribution of photoelectron damage excited by 18.6 keV photons in a lysozyme crystal. The experimental results showed that the penetration depth of {approx}17.35 keV photoelectrons is 1.5 {+-} 0.2 {micro}m, which is well below previous theoretical estimates of 2.8 {micro}m. Such a small penetration depth raises challenging technical issues in mitigating damage by line-focus mini-beams. The optimum requirements to reduce damage in large crystals by a factor of 2.0-2.5 are Gaussian line-focus mini-beams with a root-mean-square width of 0.2 {micro}m and a distance between lines of 2.0 {micro}m. The use of higher energy X-rays (>26 keV) would help to alleviate some of these requirements by more than doubling the penetration depth. It was found that the X-ray dose has a significant contribution from the crystal's solvent, which initially contained 9.0%(w/v) NaCl. The 15.8 keV photoelectrons of the Cl atoms and their accompanying 2.8 keV local dose from the decay of the resulting excited atoms more than doubles the dose deposited in the X-ray-irradiated region because of the much greater cross-section and higher energy of the excited atom, degrading the mitigation of radiation damage from 2.5 to 2.0. Eliminating heavier atoms from the solvent and data collection far from heavy-atom absorption edges will significantly improve the mitigation of damage by line-focus mini-beams.

Finfrock, Y.; Stern, E.; Yacoby, Y.; Alkire, R.; Evans-Lutterodt, K.; Stein, A.; Isakovic, A. F.; Kas, J.; Joachimiak, A.; Biosciences Division; Univ. of Washington; Hebrew Univ.; BNL

2010-12-01

212

Spatial Dependence and Mitigation of Radiation Damage by a Line Focus Mini Beam  

SciTech Connect

Recently, strategies to reduce primary radiation damage have been proposed which depend on focusing X-rays to dimensions smaller than the penetration depth of excited photoelectrons. For a line focus as used here the penetration depth is the maximum distance from the irradiated region along the X-ray polarization direction that the photoelectrons penetrate. Reported here are measurements of the penetration depth and distribution of photoelectron damage excited by 18.6 keV photons in a lysozyme crystal. The experimental results showed that the penetration depth of {approx}17.35 keV photoelectrons is 1.5 {+-} 0.2 {micro}m, which is well below previous theoretical estimates of 2.8 {micro}m. Such a small penetration depth raises challenging technical issues in mitigating damage by line-focus mini-beams. The optimum requirements to reduce damage in large crystals by a factor of 2.0-2.5 are Gaussian line-focus mini-beams with a root-mean-square width of 0.2 {micro}m and a distance between lines of 2.0 {micro}m. The use of higher energy X-rays (>26 keV) would help to alleviate some of these requirements by more than doubling the penetration depth. It was found that the X-ray dose has a significant contribution from the crystal's solvent, which initially contained 9.0%(w/v) NaCl. The 15.8 keV photoelectrons of the Cl atoms and their accompanying 2.8 keV local dose from the decay of the resulting excited atoms more than doubles the dose deposited in the X-ray-irradiated region because of the much greater cross-section and higher energy of the excited atom, degrading the mitigation of radiation damage from 2.5 to 2.0. Eliminating heavier atoms from the solvent and data collection far from heavy-atom absorption edges will significantly improve the mitigation of damage by line-focus mini-beams.

Finfrock, Y.Z.; Evans-Lutterodt, K.; Stern, E.A.; Yacoby, Y.; Alkire, R.W.; Stein, A.; Isakovic, A.F.; Kas, J. J.; Joachimiak, A.

2010-09-14

213

Observation of a strong inverse temperature dependence for the opacity of atmospheric water vapor in the mm continuum near 280 GHz  

NASA Technical Reports Server (NTRS)

Results are presented of the field measurements of atmospheric opacity at 278 GHz (9.3/cm) conducted at the McMurdo Station (Antarctica) during the austral springs of 1986 and 1987, in conjunction with balloon measurements of water vapor profile and total column density, showing a strong inverse temperature dependence when normalized to precipitable water vapor. The value of measured opacity per mm of precipitable water vapor (PWV) is roughly two times greater at -35 C than at -10 C and three times greater than measurements at +25 C reported by Zammit and Ade (1981). Various theories proposed to explain excess absorption in continuum regions are reviewed.

Emmons, Louisa K.; De Zafra, Robert L.

1990-01-01

214

Expression of Na+-dependent citrate transport in a strongly metastatic human prostate cancer PC-3M cell line: regulation by voltage-gated Na+ channel activity.  

PubMed

Prostate is a unique organ which synthesizes and releases large amounts of citrate. It has been shown that in metastatic prostate cancer, the amount of citrate in prostatic fluid is significantly reduced, approaching the level normally found in blood. In our previous study, we characterized electrophysiologically the mechanism of citrate transport in a normal prostatic epithelial (PNT2-C2) cell line. It was concluded that the cells expressed a novel transporter carrying 1 citrate3- together with 4 K+, primarily out of cells. In the present study, we aimed similarly to characterize the mechanism(s) of citrate transport in a strongly metastatic human prostate cancer (PC-3M) cell line and to compare this with the previous data. Citrate transport in PC-3M cells was found to be both Na+ and K+ dependent. Intracellular application of citrate produced an outward current that was primarily K+ dependent whilst extracellular citrate elicited an inward current that was mainly Na+ dependent. The electrophysiological and pharmacological characteristics of the citrate outward current were similar to the K+-dependent citrate transporter found in the PNT2-C2 cells. On the other hand, the inward citrate current had a markedly different reversal potential, ionic characteristics, inhibitor profile and pH sensitivity. Preincubation of the PC-3M cells (24 or 48 h) with the voltage-gated Na+ channel (VGSC) blocker tetrodotoxin (TTX) significantly reduced the Na+ sensitivity of the citrate current, up-regulated VGSC mRNA expression but did not change the partial permeability of the membrane to Na+. It was concluded (a) that PC-3M cells express a K+-dependent transporter (carrying citrate outward), similar to that found in normal prostate epithelial cells, as well as (b) a Na+-dependent transporter (carrying citrate inward). The molecular nature of the latter was investigated by RT-PCR; the three known Na+-dependent citrate/dicarboxylate transporters could not be detected. VGSC activity, which itself has been associated with metastatic prostate cancer, had a differential effect on the two citrate transporters, down-regulating the expression of the Na+-dependent component whilst enhancing the K+-dependent citrate transporter. PMID:15611019

Mycielska, Maria E; Palmer, Christopher P; Brackenbury, William J; Djamgoz, Mustafa B A

2005-03-01

215

Expression of Na+-dependent citrate transport in a strongly metastatic human prostate cancer PC-3M cell line: regulation by voltage-gated Na+ channel activity  

PubMed Central

Prostate is a unique organ which synthesizes and releases large amounts of citrate. It has been shown that in metastatic prostate cancer, the amount of citrate in prostatic fluid is significantly reduced, approaching the level normally found in blood. In our previous study, we characterized electrophysiologically the mechanism of citrate transport in a normal prostatic epithelial (PNT2-C2) cell line. It was concluded that the cells expressed a novel transporter carrying 1 citrate3? together with 4 K+, primarily out of cells. In the present study, we aimed similarly to characterize the mechanism(s) of citrate transport in a strongly metastatic human prostate cancer (PC-3M) cell line and to compare this with the previous data. Citrate transport in PC-3M cells was found to be both Na+ and K+ dependent. Intracellular application of citrate produced an outward current that was primarily K+ dependent whilst extracellular citrate elicited an inward current that was mainly Na+ dependent. The electrophysiological and pharmacological characteristics of the citrate outward current were similar to the K+-dependent citrate transporter found in the PNT2-C2 cells. On the other hand, the inward citrate current had a markedly different reversal potential, ionic characteristics, inhibitor profile and pH sensitivity. Preincubation of the PC-3M cells (24 or 48 h) with the voltage-gated Na+ channel (VGSC) blocker tetrodotoxin (TTX) significantly reduced the Na+ sensitivity of the citrate current, up-regulated VGSC mRNA expression but did not change the partial permeability of the membrane to Na+. It was concluded (a) that PC-3M cells express a K+-dependent transporter (carrying citrate outward), similar to that found in normal prostate epithelial cells, as well as (b) a Na+-dependent transporter (carrying citrate inward). The molecular nature of the latter was investigated by RT-PCR; the three known Na+-dependent citrate/dicarboxylate transporters could not be detected. VGSC activity, which itself has been associated with metastatic prostate cancer, had a differential effect on the two citrate transporters, down-regulating the expression of the Na+-dependent component whilst enhancing the K+-dependent citrate transporter. PMID:15611019

Mycielska, Maria E; Palmer, Christopher P; Brackenbury, William J; Djamgoz, Mustafa BA

2005-01-01

216

Spatial dependence and the relationship of soil organic carbon and soil moisture in the Luquillo Experimental Forest, Puerto Rico  

Microsoft Academic Search

We used geo-spatial statistical techniques to examine the spatial variation and relationship of soil organic carbon (SOC) and soil moisture (SM) in the Luquillo Experimental Forest (LEF), Puerto Rico, in order to test the hypothesis that mountainous terrain introduces spatial autocorrelation and crosscorrelation in ecosystem and soil properties. Soil samples (n = 100) were collected from the LEF in the

Hongqing Wang; Charles A. S. Hall; Joseph D. Cornell; Myrna H. P. Hall

2002-01-01

217

Wavelength-dependent study of trapping molecules in an excited electronic state of I{sub 2}{sup 2+} with strong laser fields  

SciTech Connect

Using the B {sup 3{Pi}}{sub u}{sup +} state of neutral I{sub 2} as an intermediate state, we populate an excited electronic state, designated as (2,0), of I{sub 2}{sup 2+} in its bound region of internuclear separation with short laser pulses. Trapping of the molecules in the (2,0) state is deduced from the disappearance of the (2,0) dissociation signal when populated at large internuclear separation, and wavelength-dependent results rule out electron localization as an alternative explanation for this disappearance. The wavelength dependence also firmly establishes the B state as the intermediate state. Moreover, simulation results are consistent with the experiments, which confirm the previously measured (2,0) potential curve. The (2,0) state correlates to the I{sup 2+}+I{sup 0+} dissociation limit and has played an important role in strong field physics. It is also the lowest lying truly bound (not metastable) state of the dication. In addition, the potential curve of the I{sub 2}{sup 3+} ground-state manifold is measured. Finally, calculations show a general picture of the wavelength dependence for trapping molecules in potential wells using intermediate states.

Fang, L.; Gibson, G. N. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)

2010-03-15

218

Strong excitation intensity dependence of the photoluminescence line shape in GaAs{sub 1-x}Bi{sub x} single quantum well samples  

SciTech Connect

A set of high quality single quantum well samples of GaAs{sub 1-x}Bi{sub x} with bismuth concentrations not exceeding 6% and well widths ranging from 7.5 to 13 nm grown by molecular beam epitaxy on a GaAs substrate at low temperature is studied by means of photoluminescence (PL). It is shown that the PL line shape changes when the exciton reduced mass behavior changes from an anomalous increase (x < 5%) to a conventional decrease (x > 5%). Strongly non-monotonous PL bandwidth dependence on the excitation intensity is revealed and interpreted in terms of optically unresolved contributions from the saturable emission of bound free excitons.

Mazur, Yu. I.; Dorogan, V. G.; Ware, M. E.; Salamo, G. J. [Department of Physics, University of Arkansas, 226 Physics Building, Fayetteville, Arkansas 72701 (United States); Schmidbauer, M. [Leibniz-Institute for Crystal Growth, Max-Born-Str. 2, D-12489 Berlin (Germany); Tarasov, G. G. [Institute of Semiconductor Physics, National Academy of Sciences, pr. Nauki 45, Kiev 03028 (Ukraine); Johnson, S. R.; Lu, X. [Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287-6206 (United States); Yu, S.-Q. [Department of Electrical Engineering, University of Arkansas, 3217 Bell Engineering, Fayetteville, Arkansas 72701 (United States); Tiedje, T. [Department of Electrical and Computer Engineering, University of Victoria, Victoria, British Columbia V8W 3P6 (Canada)

2013-04-14

219

Verification test problems for the calculation of probability of loss of assured safety in temperature-dependent systems with multiple weak and strong links.  

SciTech Connect

Four verification test problems are presented for checking the conceptual development and computational implementation of calculations to determine the probability of loss of assured safety (PLOAS) in temperature-dependent systems with multiple weak links (WLs) and strong links (SLs). The problems are designed to test results obtained with the following definitions of loss of assured safety: (1) Failure of all SLs before failure of any WL, (2) Failure of any SL before failure of any WL, (3) Failure of all SLs before failure of all WLs, and (4) Failure of any SL before failure of all WLs. The test problems are based on assuming the same failure properties for all links, which results in problems that have the desirable properties of fully exercising the numerical integration procedures required in the evaluation of PLOAS and also possessing simple algebraic representations for PLOAS that can be used for verification of the analysis.

Johnson, Jay Dean (ProStat, Mesa, AZ); Oberkampf, William Louis; Helton, Jon Craig (Arizona State University, Tempe, AZ)

2006-06-01

220

Stable and efficient momentum-space solutions of the time-dependent Schrödinger equation for one-dimensional atoms in strong laser fields  

NASA Astrophysics Data System (ADS)

One-dimensional model systems have a particular role in strong-field physics when gaining physical insight by computing data over a large range of parameters, or when performing numerous time propagations within, e.g., optimal control theory. Here we derive a scheme that removes a singularity in the one-dimensional Schrödinger equation in momentum space for a particle in the commonly used soft-core Coulomb potential. By using this scheme we develop two numerical approaches to the time-dependent Schrödinger equation in momentum space. The first approach employs the expansion of the momentum-space wave function over the eigenstates of the field-free Hamiltonian, and it is shown to be more efficient for laser parameters usual in strong field physics. The second approach employs the Crank-Nicolson scheme or the method of lines for time-propagation. The both methods are readily applicable for large-scale numerical simulations in one-dimensional model systems.

Shvetsov-Shilovski, N. I.; Räsänen, E.

2014-12-01

221

D-Serine Augments NMDA-NR2B Receptor-Dependent Hippocampal Long-Term Depression and Spatial Reversal Learning  

Microsoft Academic Search

The contributions of hippocampal long-term depression (LTD) to explicit learning and memory are poorly understood. Electrophysiological and behavioral studies examined the effects of modulating NMDA receptor-dependent LTD on spatial learning in the Morris water maze (MWM). The NMDA receptor co-agonist D-serine substantially enhanced NR2B-dependent LTD, but not long-term potentiation (LTP) or depotentiation, in hippocampal slices from adult wild type mice.

Steven Duffy; Viviane Labrie; John C Roder

2008-01-01

222

The roles of scene gist and spatial dependency among objects in the semantic guidance of attention in real-world scenes.  

PubMed

A previous study (Vision Research 51 (2011) 1192-1205) found evidence for semantic guidance of visual attention during the inspection of real-world scenes, i.e., an influence of semantic relationships among scene objects on overt shifts of attention. In particular, the results revealed an observer bias toward gaze transitions between semantically similar objects. However, this effect is not necessarily indicative of semantic processing of individual objects but may be mediated by knowledge of the scene gist, which does not require object recognition, or by known spatial dependency among objects. To examine the mechanisms underlying semantic guidance, in the present study, participants were asked to view a series of displays with the scene gist excluded and spatial dependency varied. Our results show that spatial dependency among objects seems to be sufficient to induce semantic guidance. Scene gist, on the other hand, does not seem to affect how observers use semantic information to guide attention while viewing natural scenes. Extracting semantic information mainly based on spatial dependency may be an efficient strategy of the visual system that only adds little cognitive load to the viewing task. PMID:25199610

Wu, Chia-Chien; Wang, Hsueh-Cheng; Pomplun, Marc

2014-12-01

223

Scale-dependent relationships between the spatial distribution of a limiting resource and plant species diversity in an African grassland ecosystem  

Microsoft Academic Search

One cornerstone of ecological theory is that nutrient availability limits the number of species that can inhabit a community. However, the relationship between the spatial distribution of limiting nutrients and species diversity is not well established because there is no single scale appropriate for measuring variation in resource distribution. Instead, the correct scale for analyzing resource variation depends on the

T. Michael Anderson; Samuel J. McNaughton; Mark E. Ritchie

2004-01-01

224

A linear stability analysis on the onset of thermal convection of a fluid with strongly temperature-dependent viscosity in a spherical shell  

NASA Astrophysics Data System (ADS)

A linear stability analysis was performed in order to study the onset of thermal convection in the presence of a strong viscosity variation, with a special emphasis on the condition for the stagnant-lid (ST) convection where a convection takes place only in a sublayer beneath a highly viscous lid of cold fluid. We consider the temporal evolution (growth or decay) of an infinitesimal perturbation superimposed to a Boussinesq fluid with an infinite Prandtl number which is in a static (motionless) and conductive state in a basally heated planar layer or spherical shell. The viscosity of the fluid is assumed to be exponentially dependent on temperature. The linearized equations for conservations of mass, momentum, and internal (thermal) energy are numerically solved for the critical Rayleigh number, Ra c , as well as the radial profiles of eigenfunctions for infinitesimal perturbations. The above calculations are repeatedly carried out by systematically varying (i) the magnitude of the temperature dependence of viscosity, E, and (ii) the ratio of the inner and outer radii of the spherical shell, ?. A careful analysis of the vertical structure of incipient flows demonstrated that the dominance of the ST convection can be quantitatively identified by the vertical profile of ? h (a measure of conversion between horizontal and vertical flows), regardless of the model geometries. We also found that, in the spherical shell relevant to the Earth's mantle ( ? = 0.55), the transition into ST convection takes place at the viscosity contrast across the layer {r_?˜eq10^4} . Taken together with the fact that the threshold value of r ? falls in the range of r ? for a so-called sluggish-lid convection, our finding suggests that the ST-mode of convection with horizontally elongated convection cells is likely to arise in the Earth's mantle solely from the temperature-dependent viscosity.

Kameyama, Masanori; Ichikawa, Hiroki; Miyauchi, Arata

2013-02-01

225

Hippocampally dependent and independent chronic spatial navigational deficits following parasagittal fluid percussion brain injury in the rat  

Microsoft Academic Search

Previous reports have documented spatial navigational deficits following experimental traumatic brain injury (TBI), although the majority of the work to date has involved assessment at acute intervals following TBI, and has focused on tasks sensitive to hippocampal dysfunction. The present experiments were designed to investigate the chronic consequences of TBI, and the possible contribution of extrahippocampal dysfunction to TBI-induced spatial

H. M Bramlett; E. J Green; W. Dalton Dietrich

1997-01-01

226

Low levels of realized seed and pollen gene flow and strong spatial genetic structure in a small, isolated and fragmented population of the tropical tree Copaifera langsdorffii Desf  

PubMed Central

Over the past century, the Brazilian Atlantic forest has been reduced to small, isolated fragments of forest. Reproductive isolation theories predict a loss of genetic diversity and increases in inbreeding and spatial genetic structure (SGS) in such populations. We analysed eight microsatellite loci to investigate the pollen and seed dispersal patterns, genetic diversity, inbreeding and SGS of the tropical tree Copaifera langsdorffii in a small (4.8?ha), isolated population. All 112 adult trees and 128 seedlings found in the stand were sampled, mapped and genotyped. Seedlings had significantly lower levels of genetic diversity (A=16.5±0.45, mean±95% s.e.; He=0.838±0.006) than did adult trees (A=23.2±0.81; He=0.893±0.030). Parentage analysis did not indicate any seed immigration (mseeds=0) and the pollen immigration rate was very low (mpollen=0.047). The average distance of realized pollen dispersal within the stand was 94?m, with 81% of the pollen travelling <150?m. A significant negative correlation was found between the frequency and distance of pollen dispersal (r=?0.79, P<0.01), indicating that short-distance pollinations were more frequent. A significant SGS for both adults (?50?m) and seedlings (?20?m) was also found, indicating that most of the seeds were dispersed over short distances. The results suggested that the spatial isolation of populations by habitat fragmentation can restrict seed and pollen gene flow, increase SGS and affect the genetic diversity of future generations. PMID:20372183

Sebbenn, A M; Carvalho, A C M; Freitas, M L M; Moraes, S M B; Gaino, A P S C; da Silva, J M; Jolivet, C; Moraes, M L T

2011-01-01

227

The combination of energy-dependent internal adaptation mechanisms and external factors enables Listeria monocytogenes to express a strong starvation survival response during multiple-nutrient starvation.  

PubMed

The goal of this study was to characterize the starvation survival response (SSR) of a wild-type Listeria monocytogenes 10403S and an isogenic DeltasigB mutant strain during multiple-nutrient starvation conditions over 28 days. This study examined the effects of inhibitors of protein synthesis, the proton motive force, substrate level phosphorylation, and oxidative phosphorylation on the SSR of L. monocytogenes 10403S and a DeltasigB mutant during multiple-nutrient starvation. The effects of starvation buffer changes on viability were also examined. During multiple-nutrient starvation, both strains expressed a strong SSR, suggesting that L. monocytogenes possesses SigB-independent mechanism(s) for survival during multiple-nutrient starvation. Neither strain was able to express an SSR following starvation buffer changes, indicating that the nutrients/factors present in the starvation buffer could be a source of energy for cell maintenance and survival. Neither the wild-type nor the DeltasigB mutant strain was able to elicit an SSR when exposed to the protein synthesis inhibitor chloramphenicol within the first 4 h of starvation. However, both strains expressed an SSR when exposed to chloramphenicol after 6 h or more of starvation, suggesting that the majority of proteins required to elicit an effective SSR in L. monocytogenes are likely produced somewhere between 4 and 6 h of starvation. The varying SSRs of both strains to the different metabolic inhibitors under aerobic or anaerobic conditions suggested that (1) energy derived from the proton motive force is important for an effective SSR, (2) L. monocytogenes utilizes an anaerobic electron transport during multiple-nutrient starvation conditions, and (3) the glycolytic pathway is an important energy source during multiple-nutrient starvation when oxygen is available, and less important under anaerobic conditions. Collectively, the data suggest that the combination of energy-dependent internal adaptation mechanisms of cells and external nutrients/factors enables L. monocytogenes to express a strong SSR. PMID:20001327

Lungu, Bwalya; Saldivar, Joshua C; Story, Robert; Ricke, Steven C; Johnson, Michael G

2010-05-01

228

CLASSSTRONG: Classical simulations of strong field processes  

NASA Astrophysics Data System (ADS)

A set of Mathematica functions is presented to model classically two of the most important processes in strong field physics, namely high-order harmonic generation (HHG) and above-threshold ionization (ATI). Our approach is based on the numerical solution of the Newton-Lorentz equation of an electron moving on an electric field and takes advantage of the symbolic languages features and graphical power of Mathematica. Like in the Strong Field Approximation (SFA), the effects of atomic potential on the motion of electron in the laser field are neglected. The SFA was proven to be an essential tool in strong field physics in the sense that it is able to predict with great precision the harmonic (in the HHG) and energy (in the ATI) limits. We have extended substantially the conventional classical simulations, where the electric field is only dependent on time, including spatial nonhomogeneous fields and spatial and temporal synthesized fields. Spatial nonhomogeneous fields appear when metal nanosystems interact with strong and short laser pulses and temporal synthesized fields are routinely generated in attosecond laboratories around the world. Temporal and spatial synthesized fields have received special attention nowadays because they would allow to exceed considerably the conventional harmonic and electron energy frontiers. Classical simulations are an invaluable tool to explore exhaustively the parameters domain at a cheap computational cost, before massive quantum mechanical calculations, absolutely indispensable for the detailed analysis, are performed.

Ciappina, M. F.; Pérez-Hernández, J. A.; Lewenstein, M.

2014-01-01

229

Excision efficiency is not strongly coupled to transgenic rate: cell type-dependent transposition efficiency of sleeping beauty and piggyBac DNA transposons.  

PubMed

The Sleeping Beauty (SB) and piggyBac (PB) DNA transposons represent an emerging new gene delivery technology, potentially suitable for human gene therapy applications. Previous studies pointed to important differences between these transposon systems, depending on the cell types examined and the methodologies applied. However, efficiencies cannot always be compared because of differences in applications. In addition, "overproduction inhibition," a phenomenon believed to be a characteristic of DNA transposons, can remarkably reduce the overall transgenic rate, emphasizing the importance of transposase dose applied. Therefore, because of lack of comprehensive analysis, researchers are forced to optimize the technology for their own "in-house" platforms. In this study, we investigated the transposition of several SB (SB11, SB32, SB100X) and PB (mPB and hyPB) variants in various cell types at three levels: comparing the excision efficiency of the reaction by real-time PCR, testing the overall transgenic rate by detecting cells with stable integrations, and determining the average copy number when using different transposon systems and conditions. We concluded that high excision activity is not always followed by a higher transgenic rate, as exemplified by the hyperactive transposases, indicating that the excision and the integration steps of transposition are not strongly coupled as previously thought. In general, all levels of transposition show remarkable differences depending on the transposase used and cell lines examined, being the least efficient in human embryonic stem cells (hESCs). In spite of the comparably low activity in those special cell types, the hyperactive SB100X and hyPB systems could be used in hESCs with similar transgenic efficiency and with reasonably low (2-3) transgene copy numbers, indicating their potential applicability for gene therapy purposes in the future. PMID:25045962

Kolacsek, Orsolya; Erdei, Zsuzsa; Apáti, Agota; Sándor, Sára; Izsvák, Zsuzsanna; Ivics, Zoltán; Sarkadi, Balázs; Orbán, Tamás I

2014-08-01

230

Hormonal regulation of gluconeogenesis in cereal aleurone is strongly cultivar-dependent and gibberellin action involves SLENDER1 but not GAMYB.  

PubMed

Storage oil is a major constituent in the cereal aleurone layer. The aim of this study was to investigate how gibberellin (GA) and abscisic acid (ABA) regulate conversion of oil to sugar in barley aleurone. The activity of the glyoxylate cycle enzyme isocitrate lyase (ICL) was surveyed in eight barley cultivars. Surprisingly, some cultivars do not require GA for the induction of ICL (e.g. Himalaya), whereas some do (e.g. Golden Promise). Furthermore, in Golden Promise, GA also stimulates triacylglycerol breakdown and enhances the net flux of carbon from acetate to sugar. In contrast, ABA strongly represses ICL activity and the flux of carbon from oil to sugar in both Golden Promise and Himalaya. Biolistics using a promoter reporter showed that GA and ABA regulate ICL at the level of transcription. Studies using barley and rice mutants and pharmacological agents show that GA-dependent induction of ICL activity is mediated by SLENDER1 and requires cGMP, but does not involve the transcription factor GAMYB. Gibberellin and ABA therefore act antagonistically to regulate gluconeogenesis in the aleurone layer as well as controlling the production and secretion of hydrolases into the starchy endosperm. We suggest that the variation between different barley cultivars might be a result of selective breeding to alter seed dormancy. PMID:16236157

Eastmond, Peter J; Jones, Russell L

2005-11-01

231

Effect of delayed link failure on probability of loss of assured safety in temperature-dependent systems with multiple weak and strong links.  

SciTech Connect

Weak link (WL)/strong link (SL) systems constitute important parts of the overall operational design of high consequence systems, with the SL system designed to permit operation of the system only under intended conditions and the WL system designed to prevent the unintended operation of the system under accident conditions. Degradation of the system under accident conditions into a state in which the WLs have not deactivated the system and the SLs have failed in the sense that they are in a configuration that could permit operation of the system is referred to as loss of assured safety. The probability of such degradation conditional on a specific set of accident conditions is referred to as probability of loss of assured safety (PLOAS). Previous work has developed computational procedures for the calculation of PLOAS under fire conditions for a system involving multiple WLs and SLs and with the assumption that a link fails instantly when it reaches its failure temperature. Extensions of these procedures are obtained for systems in which there is a temperature-dependent delay between the time at which a link reaches its failure temperature and the time at which that link actually fails.

Johnson, J. D. (ProStat, Mesa, AZ); Oberkampf, William Louis; Helton, Jon Craig (Arizona State University, Tempe, AZ)

2007-05-01

232

Glucuronidation Converts Clopidogrel to a Strong Time-Dependent Inhibitor of CYP2C8: A Phase II Metabolite as a Perpetrator of Drug-Drug Interactions.  

PubMed

Cerivastatin and repaglinide are substrates of cytochrome P450 (CYP)2C8, CYP3A4, and organic anion-transporting polypeptide (OATP)1B1. A recent study revealed an increased risk of rhabdomyolysis in patients using cerivastatin with clopidogrel, warranting further studies on clopidogrel interactions. In healthy volunteers, repaglinide area under the concentration-time curve (AUC0-?) was increased 5.1-fold by a 300-mg loading dose of clopidogrel and 3.9-fold by continued administration of 75?mg clopidogrel daily. In vitro, we identified clopidogrel acyl-?-D-glucuronide as a potent time-dependent inhibitor of CYP2C8. A physiologically based pharmacokinetic model indicated that inactivation of CYP2C8 by clopidogrel acyl-?-D-glucuronide leads to uninterrupted 60-85% inhibition of CYP2C8 during daily clopidogrel treatment. Computational modeling resulted in docking of clopidogrel acyl-?-D-glucuronide at the CYP2C8 active site with its thiophene moiety close to heme. The results indicate that clopidogrel is a strong CYP2C8 inhibitor via its acyl-?-D-glucuronide and imply that glucuronide metabolites should be considered potential inhibitors of CYP enzymes. PMID:24971633

Tornio, A; Filppula, A M; Kailari, O; Neuvonen, M; Nyrönen, T H; Tapaninen, T; Neuvonen, P J; Niemi, M; Backman, J T

2014-10-01

233

DEFINITION OF MULTIVARIATE GEOCHEMICAL ASSOCIATIONS WITH POLYMETALLIC MINERAL OCCURRENCES USING A SPATIALLY DEPENDENT CLUSTERING TECHNIQUE AND RASTERIZED STREAM SEDIMENT DATA - AN ALASKAN EXAMPLE.  

USGS Publications Warehouse

The application of an unsupervised, spatially dependent clustering technique (AMOEBA) to interpolated raster arrays of stream sediment data has been found to provide useful multivariate geochemical associations for modeling regional polymetallic resource potential. The technique is based on three assumptions regarding the compositional and spatial relationships of stream sediment data and their regional significance. These assumptions are: (1) compositionally separable classes exist and can be statistically distinguished; (2) the classification of multivariate data should minimize the pair probability of misclustering to establish useful compositional associations; and (3) a compositionally defined class represented by three or more contiguous cells within an array is a more important descriptor of a terrane than a class represented by spatial outliers.

Jenson, Susan, K.; Trautwein, C. M.

1984-01-01

234

Strong Interaction  

SciTech Connect

We will give here an overview of our theory of the strong interactions, Quantum Chromo Dynamics (QCD) and its properties. We will also briefly review the history of the study of the strong interactions, and the discoveries that ultimately led to the formulation of QCD. The strong force is one of the four known fundamental forces in nature, the others being the electromagnetic, the weak and the gravitational force. The strong force, usually referred to by scientists as the 'strong interaction', is relevant at the subatomic level, where it is responsible for the binding of protons and neutrons to atomic nuclei. To do this, it must overcome the electric repulsion between the protons in an atomic nucleus and be the most powerful force over distances of a few fm (1fm=1 femtometer=1 fermi=10{sup -15}m), the typical size of a nucleus. This property gave the strong force its name.

Karsch, F.; Vogelsang, V.

2009-09-29

235

Hippocampal-Dependent Spatial Memory in the Water Maze is Preserved in an Experimental Model of Temporal Lobe Epilepsy in Rats  

PubMed Central

Cognitive impairment is a major concern in temporal lobe epilepsy (TLE). While different experimental models have been used to characterize TLE-related cognitive deficits, little is known on whether a particular deficit is more associated with the underlying brain injuries than with the epileptic condition per se. Here, we look at the relationship between the pattern of brain damage and spatial memory deficits in two chronic models of TLE (lithium-pilocarpine, LIP and kainic acid, KA) from two different rat strains (Wistar and Sprague-Dawley) using the Morris water maze and the elevated plus maze in combination with MRI imaging and post-morten neuronal immunostaining. We found fundamental differences between LIP- and KA-treated epileptic rats regarding spatial memory deficits and anxiety. LIP-treated animals from both strains showed significant impairment in the acquisition and retention of spatial memory, and were unable to learn a cued version of the task. In contrast, KA-treated rats were differently affected. Sprague-Dawley KA-treated rats learned less efficiently than Wistar KA-treated animals, which performed similar to control rats in the acquisition and in a probe trial testing for spatial memory. Different anxiety levels and the extension of brain lesions affecting the hippocampus and the amydgala concur with spatial memory deficits observed in epileptic rats. Hence, our results suggest that hippocampal-dependent spatial memory is not necessarily affected in TLE and that comorbidity between spatial deficits and anxiety is more related with the underlying brain lesions than with the epileptic condition per se. PMID:21829459

Inostroza, Marion; Cid, Elena; Brotons-Mas, Jorge; Gal, Beatriz; Aivar, Paloma; Uzcategui, Yoryani G.

2011-01-01

236

Endogenous proteolytic cleavage of disease-associated prion protein to produce C2 fragments is strongly cell- and tissue-dependent.  

PubMed

The abnormally folded form of the prion protein (PrP(Sc)) accumulating in nervous and lymphoid tissues of prion-infected individuals can be naturally cleaved to generate a N-terminal-truncated fragment called C2. Information about the identity of the cellular proteases involved in this process and its possible role in prion biology has remained limited and controversial. We investigated PrP(Sc) N-terminal trimming in different cell lines and primary cultured nerve cells, and in the brain and spleen tissue from transgenic mice infected by ovine and mouse prions. We found the following: (i) the full-length to C2 ratio varies considerably depending on the infected cell or tissue. Thus, in primary neurons and brain tissue, PrP(Sc) accumulated predominantly as untrimmed species, whereas efficient trimming occurred in Rov and MovS cells, and in spleen tissue. (ii) Although C2 is generally considered to be the counterpart of the PrP(Sc) proteinase K-resistant core, the N termini of the fragments cleaved in vivo and in vitro can actually differ, as evidenced by a different reactivity toward the Pc248 anti-octarepeat antibody. (iii) In lysosome-impaired cells, the ratio of full-length versus C2 species dramatically increased, yet efficient prion propagation could occur. Moreover, cathepsin but not calpain inhibitors markedly inhibited C2 formation, and in vitro cleavage by cathepsins B and L produced PrP(Sc) fragments lacking the Pc248 epitope, strongly arguing for the primary involvement of acidic hydrolases of the endolysosomal compartment. These findings have implications on the molecular analysis of PrP(Sc) and cell pathogenesis of prion infection. PMID:20154089

Dron, Michel; Moudjou, Mohammed; Chapuis, Jérôme; Salamat, Muhammad Khalid Farooq; Bernard, Julie; Cronier, Sabrina; Langevin, Christelle; Laude, Hubert

2010-04-01

237

Age, sex and spatial dependent variations in heavy metals levels in the Glaucous Gulls ( Larus hyperboreus ) from the Bjørnøya and Jan Mayen, Arctic  

Microsoft Academic Search

Heavy metals (Cd, Cu, Fe, Mn and Zn) concentrations were determined in different tissues (muscle, kidney, liver, brain, gonads,\\u000a heart and feathers) of Glaucous Gulls (Larus hyperboreus) from Bjørnøya and Jan Mayen. The age and spatial dependent variations in heavy metals were quantified and interpreted in\\u000a view of the three chemometric techniques, i.e. non-parametric Mann–Whitney U test, redundancy gradient analysis

Micha? Malinga; Piotr Szefer; Geir W. Gabrielsen

2010-01-01

238

Survival and spatial fidelity of moufl on ( Ovis gmelini ): A Bayesian analysis of an age-dependent capture-recapture model  

Microsoft Academic Search

We study the influence of age and sex on survival and spatial fidelity of moufl on (Ovis gmelini) in the Caroux-Espinouse massif. Survival and movement probabilities are estimated through a Bayesian analysis of an age-dependent\\u000a capture-recapture model. Prior information is based on external data, namely on radio-tracked animals. Recapture rates differed\\u000a between age, sexes, and areas. Whatever the area, survival

Jerôme Dupuis; Jacques Badia; Marie-Line Maublanc; Richard Bon

2002-01-01

239

GENDER AND ADOLESCENT ALCOHOL USE DISORDERS ON BOLD (BLOOD OXYGEN LEVEL DEPENDENT) RESPONSE TO SPATIAL WORKING MEMORY  

Microsoft Academic Search

Aims: To determine how alcohol use differentially affects brain functioning in male and female adolescents. Methods: Adolescents with alcohol use disorders (AUDs; 7 female, 11 male) and control adolescents without AUDs (9 female, 12 male), aged 14-17 years, performed spatial working memory and vigilance tasks during functional magnetic resonance imaging. Results: Gender, AUD and their interaction were significantly associated with

LISA C. CALDWELL; ALECIA D. SCHWEINSBURG; BONNIE J. NAGEL; VALERIE C. BARLETT; SANDRA A. BROWN; SUSAN F. TAPERT

2005-01-01

240

Sex-specific dispersal in spatially varying environments leads to habitat-dependent evolutionarily stable offspring sex ratios  

Microsoft Academic Search

When the environment varies spatially, so that some habitats are more favorable to reproduction than others, an individual should attempt to increase the number of offspring establishing in high-quality habitats. Hence, if male and female dispersal behavior differ, it may be adaptive to produce more offspring of the more dispersing sex in low-quality habitats, since these offspring are likely to

Romain Julliard

2000-01-01

241

Spatial Patterns of Seed Dispersal by White-Faced Capuchins in Costa Rica: Evaluating Distant-Dependent Seed Mortality  

E-print Network

Spatial Patterns of Seed Dispersal by White-Faced Capuchins in Costa Rica: Evaluating Distant dispersal by white- faced capuchin monkeys Cebus capucinus in Santa Rosa National Park, Costa Rica of the Area de Conservacion Guanacaste (ACG), in north- western Costa Rica (101500

Fedigan, Linda M.

242

Bond-length dependence of charge-transfer excitations and stretch phonon modes in perovskite ruthenates: Evidence of strong pd hybridization effects  

E-print Network

to be a useful method to investigate the bonding natures in the strongly correlated electron systems. In cuprates for Strongly Correlated Materials Research, Seoul National University, Seoul 151-747, Korea C. B. Eom Transition metal oxides are an intriguing material system where bondings between the outer most electron

Eom, Chang Beom

243

Speech Cues Contribute to Audiovisual Spatial Integration  

PubMed Central

Speech is the most important form of human communication but ambient sounds and competing talkers often degrade its acoustics. Fortunately the brain can use visual information, especially its highly precise spatial information, to improve speech comprehension in noisy environments. Previous studies have demonstrated that audiovisual integration depends strongly on spatiotemporal factors. However, some integrative phenomena such as McGurk interference persist even with gross spatial disparities, suggesting that spatial alignment is not necessary for robust integration of audiovisual place-of-articulation cues. It is therefore unclear how speech-cues interact with audiovisual spatial integration mechanisms. Here, we combine two well established psychophysical phenomena, the McGurk effect and the ventriloquist's illusion, to explore this dependency. Our results demonstrate that conflicting spatial cues may not interfere with audiovisual integration of speech, but conflicting speech-cues can impede integration in space. This suggests a direct but asymmetrical influence between ventral ‘what’ and dorsal ‘where’ pathways. PMID:21909378

Bishop, Christopher W.; Miller, Lee M.

2011-01-01

244

Multielectron effects on the orientation dependence and photoelectron angular distribution of multiphoton ionization of CO{sub 2} in strong laser fields  

SciTech Connect

We perform an ab initio study of multiphoton ionization (MPI) of carbon dioxide in intense linearly polarized laser pulses with arbitrary molecular orientation by means of a time-dependent density-functional theory (TDDFT) with proper long-range potential. We develop a time-dependent Voronoi-cell finite difference method with highly adaptive molecular grids for accurate solution of the TDDFT equations. Our results demonstrate that the orientation dependence of MPI is determined by multiple orbital contributions and that the electron correlation effects are significant. The maximum peak of MPI is predicted to be at 40 deg. in good agreement with recent experimental data. Photoelectron angular distribution reveals the delicate relation between the orientation dependence and the molecular orbital symmetry.

Son, Sang-Kil [Department of Chemistry, University of Kansas, Lawrence, Kansas 66045 (United States); Chu, S.-I [Department of Chemistry, University of Kansas, Lawrence, Kansas 66045 (United States); Center for Quantum Science and Engineering, Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China)

2009-07-15

245

1564 IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 17, NO. 5, OCTOBER 2009 Modeling Spatial and Temporal Dependencies of  

E-print Network

and Temporal Dependencies of User Mobility in Wireless Mobile Networks Wei-Jen Hsu, Member, IEEE, Thrasyvoulos Spyropoulos, Member, IEEE, Konstantinos Psounis, Senior Member, IEEE, and Ahmed Helmy, Member, IEEE Abstract--Realistic mobility models are fundamental to evaluate the performance of protocols in mobile ad hoc networks. Unfortu

246

Distance-dependence in two Amazonian palms: effects of spatial and temporal variation in seed predator communities  

Microsoft Academic Search

Animals aid population growth and fitness in tropical forest communities through dispersal and negatively impact populations through seed predation. The interaction between dispersal and seed predation can produce distance- or density-dependence; powerful mechanisms for maintaining species diversity incorporated in the Janzen–Connell model. Large mammals, the highest biomass seed predators of intact Amazonian communities and at risk due to human disturbance,

Julie L. Wyatt; Miles R. Silman

2004-01-01

247

Abnormal temperature dependence of band-gap energies observed in (InAs)\\/(GaAs) and (InP)\\/(GaP) superlattices with strong lateral composition modulation  

Microsoft Academic Search

An abnormal variation of the band-gap energy with temperature was observed in both the (InAs)2.2\\/(GaAs)2 and (InP)2\\/(GaP)2 short-period-superlattice (SPS) structures. Strong lateral composition modulation induced two horizontally adjacent regions with different In content in the SPS regions. Due to the difference of thermal expansion coefficients among the substrate and the two adjacent regions in the SPS structures, it is proposed

Shu-Tsun Chou

2000-01-01

248

Role of Voltage-Dependent Calcium Channel Long-Term Potentiation (LTP) and NMDA LTP in Spatial Memory  

Microsoft Academic Search

This experiment explores the role of two forms of long-term potentiation (LTP) in behavioral memory. NMDA and\\/or voltage- dependent calcium channels (VDCCs) were antagonized phar- macologically at levels that block nmdaLTP and vdccLTP, re- spectively, in rats learning an eight-arm radial maze task. Animals were trained twice a day for 11 d under the systemic influence of MK-801, verapamil, both

Albert M. Borroni; Harlan Fichtenholtz; Brian L. Woodside; Timothy J. Teyler

249

Temporal and spatial gait parameters in patients dependent on walking assistance after stroke: reliability and agreement between simple and advanced methods of assessment.  

PubMed

The aim of this study was to investigate the reliability of temporal and spatial gait parameters in patients dependent on walking assistance after severe stroke, and to examine agreement between simple and advanced methods. Twenty-one patients, admitted for in-patient multidisciplinary rehabilitation, were assessed repeatedly for walking function, both in a test corridor and a gait laboratory (3D camera system) before and after 11 weeks of rehabilitation. The test-retest reliability was examined using intraclass correlation (ICC1.1), and measurement error was reported by within-subject standard deviation (Sw). The agreement between different methods for assessing walking speed, cadence and step length was explored by Bland-Altman plots. High to excellent test-retest reliability was found between trials, both when assessed in the corridor (ICC: 0.93-0.99) and in the laboratory (ICC: 0.88-0.99). Agreement between methods was satisfactory at baseline and was higher after the rehabilitation period. Agreement was found to be slightly better at lower walking speeds and for shorter step lengths. The results implicate that temporal-spatial gait parameters may be measured reliably by both simple and advanced methods in dependent walkers after stroke. A high level of agreement was found between the two methods for walking speed, cadence and average step length at both test points. PMID:24726190

Høyer, Ellen; Opheim, Arve; Strand, Liv Inger; Moe-Nilssen, Rolf

2014-05-01

250

Sex and dose-dependent effects of developmental exposure to bisphenol A on anxiety and spatial learning in deer mice (Peromyscus maniculatus bairdii) offspring.  

PubMed

Bisphenol A (BPA) is a widely produced, endocrine disrupting compound that is pervasive in the environment. Data suggest that developmental exposure to BPA during sexual differentiation of the brain leads to later behavioral consequences in offspring. Outbred deer mice (Peromyscus maniculatus bairdii) are an excellent animal model for such studies as they exhibit well-defined sex- and steroid-dependent behaviors. Here, dams during gestation and lactation were fed with a phytoestrogen-free control diet, the same diet supplemented with either ethinyl estradiol (0.1 ppb), or one of the three doses of BPA (50 mg, 5 mg, 50 ?g/kg feed weight). After weaning, the pups were maintained on control diet until they reached sexual maturity and then assessed for both spatial learning capabilities and anxiety-like and exploratory behaviors. Relative to controls, males exposed to the two upper but not the lowest dose of BPA demonstrated similar impairments in spatial learning, increased anxiety and reduced exploratory behaviors as ethinyl estradiol-exposed males, while females exposed to ethinyl estradiol, but not to BPA, consistently exhibited masculinized spatial abilities. We also determined whether dams maintained chronically on the upper dose of BPA contained environmentally relevant concentrations of BPA in their blood. While serum concentrations of unconjugated BPA in controls were below the minimum level of detection, those from dams on the BPA diet were comparable (5.48±2.07 ng/ml) to concentrations that have been observed in humans. Together, these studies demonstrate that developmental exposure to environmentally relevant concentrations of BPA can disrupt adult behaviors in a dose- and sex-dependent manner. PMID:23051835

Jašarevi?, Eldin; Williams, Scott A; Vandas, Gregory M; Ellersieck, Mark R; Liao, Chunyang; Kannan, Kurunthachalam; Roberts, R Michael; Geary, David C; Rosenfeld, Cheryl S

2013-01-01

251

Cell-cycle-dependent spatial sequestration of the DnaA replication initiator protein in Bacillus subtilis.  

PubMed

Initiation of DNA replication must be restricted to occur only once per cell cycle. In most bacteria, DnaA protein binds replication origins and promotes the initiation of DNA replication. We have found that in Bacillus subtilis, DnaA only colocalizes with origin regions at early or late stages of the cell cycle, when the replication machinery is assembling or disassembling, respectively. In contrast, DnaA colocalizes with the DNA replication machinery during most of the cell cycle. Indeed, we present evidence that a primary function of YabA, a negative regulator of replication initiation, is to tether DnaA to the polymerase-clamp protein DnaN. Thus, YabA ensures that once the origin is duplicated, it moves away from the replisome and from DnaA. We propose that DnaA colocalization with origins is specific to the time of initiation, and that replisome/YabA-mediated spatial sequestration of DnaA prevents inappropriate reinitiation of DNA replication. PMID:19081080

Soufo, Clarisse Defeu; Soufo, Hervé Joël Defeu; Noirot-Gros, Marie-Françoise; Steindorf, Astrid; Noirot, Philippe; Graumann, Peter L

2008-12-01

252

Bayesian Spatial Quantile Regression  

PubMed Central

Tropospheric ozone is one of the six criteria pollutants regulated by the United States Environmental Protection Agency under the Clean Air Act and has been linked with several adverse health effects, including mortality. Due to the strong dependence on weather conditions, ozone may be sensitive to climate change and there is great interest in studying the potential effect of climate change on ozone, and how this change may affect public health. In this paper we develop a Bayesian spatial model to predict ozone under different meteorological conditions, and use this model to study spatial and temporal trends and to forecast ozone concentrations under different climate scenarios. We develop a spatial quantile regression model that does not assume normality and allows the covariates to affect the entire conditional distribution, rather than just the mean. The conditional distribution is allowed to vary from site-to-site and is smoothed with a spatial prior. For extremely large datasets our model is computationally infeasible, and we develop an approximate method. We apply the approximate version of our model to summer ozone from 1997–2005 in the Eastern U.S., and use deterministic climate models to project ozone under future climate conditions. Our analysis suggests that holding all other factors fixed, an increase in daily average temperature will lead to the largest increase in ozone in the Industrial Midwest and Northeast. PMID:23459794

Reich, Brian J.; Fuentes, Montserrat; Dunson, David B.

2013-01-01

253

Understanding China’s recent growth experience: A spatial econometric perspective  

Microsoft Academic Search

This study reconsiders the question of China’s recent growth experience from a spatial econometric perspective. An empirical model of Chinese output growth using cross provincial data over the 1978–1998 period is specified, but a spatial econometric analysis of the specification reveals strong evidence of misspecification due to ignored spatial lag dependence. The subsequent estimating using Anselin’s spatial lag model determines

Long Gen Ying

2003-01-01

254

Strong-Field Kapitza-Dirac Scattering of Neutral Atoms  

NASA Astrophysics Data System (ADS)

Laser induced strong-field phenomena in atoms and molecules on the femtosecond (fs) time scale have been almost exclusively investigated with traveling wave fields. In almost all cases, approximation of the strong electromagnetic field by an electric field purely oscillating in time suffices to describe experimental observations. Spatially dependent electromagnetic fields, as they occur in a standing light wave, allow for strong energy and momentum transfer and are expected to extend strong-field dynamics profoundly. Here we report a strong-field version of the Kapitza-Dirac effect for neutral atoms where we scatter neutral He atoms in an intense short pulse standing light wave with fs duration and intensities well in the strong-field tunneling regime. We observe substantial longitudinal momentum transfer concomitant with an unprecedented atomic photon scattering rate greater than 1016s-1.

Eilzer, S.; Zimmermann, H.; Eichmann, U.

2014-03-01

255

Strong-field Kapitza-Dirac scattering of neutral atoms.  

PubMed

Laser induced strong-field phenomena in atoms and molecules on the femtosecond (fs) time scale have been almost exclusively investigated with traveling wave fields. In almost all cases, approximation of the strong electromagnetic field by an electric field purely oscillating in time suffices to describe experimental observations. Spatially dependent electromagnetic fields, as they occur in a standing light wave, allow for strong energy and momentum transfer and are expected to extend strong-field dynamics profoundly. Here we report a strong-field version of the Kapitza-Dirac effect for neutral atoms where we scatter neutral He atoms in an intense short pulse standing light wave with fs duration and intensities well in the strong-field tunneling regime. We observe substantial longitudinal momentum transfer concomitant with an unprecedented atomic photon scattering rate greater than 10(16)s(-1). PMID:24702358

Eilzer, S; Zimmermann, H; Eichmann, U

2014-03-21

256

Outcome of treatment of human HeLa cervical cancer cells with roscovitine strongly depends on the dosage and cell cycle status prior to the treatment.  

PubMed

Exposure of asynchronously growing human HeLa cervical carcinoma cells to roscovitine (ROSC), a selective cyclin-dependent kinases (CDKs) inhibitor, arrests their progression at the transition between G(2)/M and/or induces apoptosis. The outcome depends on the ROSC concentration. At higher dose ROSC represses HPV-encoded E7 oncoprotein and initiates caspase-dependent apoptosis. Inhibition of the site-specific phosphorylation of survivin and Bad, occurring at high-dose ROSC treatment, precedes the onset of apoptosis and seems to be a prerequisite for cell death. Considering the fact that in HeLa cells the G(1)/S restriction checkpoint is abolished by E7, we addressed the question whether the inhibition of CDKs by pharmacological inhibitors in synchronized cells would be able to block the cell-cycle in G(1) phase. For this purpose, we attempted to synchronize cells by serum withdrawal or by blocking of the mitotic apparatus using nocodazole. Unlike human MCF-7 cells, HeLa cells do not undergo G(1) block after serum starvation, but respond with a slight increase of the ratio of G(1) population. Exposure of G(1)-enriched HeLa cells to ROSC after re-feeding does not block their cell-cycle progression at G(1)-phase, but increases the ratio of S- and G(2)-phase, thereby mimicking the effect on asynchronously growing cells. A quite different impact is observed after treatment of HeLa cells released from mitotic block. ROSC prevents their cell cycle progression and cells transiently accumulate in G(1)-phase. These results show that inhibition of CDKs by ROSC in cells lacking the G(1)/S restriction checkpoint has different outcomes depending on the cell-cycle status prior to the onset of treatment. PMID:19180585

Wesierska-Gadek, Józefa; Borza, Andreea; Walzi, Eva; Krystof, Vladimir; Maurer, Margarita; Komina, Oxana; Wandl, Stefanie

2009-04-01

257

Cyclophilin-D binds strongly to complexes of the voltage-dependent anion channel and the adenine nucleotide translocase to form the permeability transition pore.  

PubMed

A cyclophilin-D affinity matrix was employed to isolate components of the mitochondrial permeability transition pore. A cDNA encoding cyclophilin-D was cloned from a rat liver library and ligated into pGEX to allow expression of a glutathione S-transferase/cyclophilin-D fusion protein in Escherichia coli XL1 cells. The cyclophilin-D in the fusion was functionally normal as judged by its peptidylprolyl cis-trans-isomerase activity and its inhibition by cyclosporin A. The fusion protein was bound to glutathione-agarose to form the cyclophilin-D affinity matrix. The matrix selectively bound 32-kDa proteins of mitochondrial membrane extracts, but no H2O-soluble proteins were bound. The 32-kDa band on SDS/PAGE resolved into a doublet and reacted with antibodies against the voltage-dependent anion channel (porin) and the adenine nucleotide translocase. These two proteins were also selectively retained by the affinity matrix in the presence of cyclosporin A. The thus-purified voltage-dependent anion channel, adenine nucleotide translocase and the fusion protein were incorporated into phosphatidylcholine liposomes containing fluorescein sulphonate. The proteoliposomes were permeabilized by Ca2+ plus phosphate, and this was blocked completely by cyclosporin A. These properties are identical to those of the permeability transition pore in mitochondria. It is concluded that the basic permeability transition pore structure comprises the voltage-dependent anion channel (outer membrane), adenine nucleotide translocase (inner membrane) and cyclophilin-D, and forms at contact sites between the two membranes. PMID:9874241

Crompton, M; Virji, S; Ward, J M

1998-12-01

258

Silencing Nicotiana attenuata calcium-dependent protein kinases, CDPK4 and CDPK5, strongly up-regulates wound- and herbivory-induced jasmonic acid accumulations.  

PubMed

The plant hormone jasmonic acid (JA) plays a pivotal role in plant-insect interactions. Herbivore attack usually elicits dramatic increases in JA concentrations, which in turn activate the accumulation of metabolites that function as defenses against herbivores. Although almost all enzymes involved in the biosynthesis pathway of JA have been identified and characterized, the mechanism by which plants regulate JA biosynthesis remains unclear. Calcium-dependent protein kinases (CDPKs) are plant-specific proteins that sense changes in [Ca(2+)] to activate downstream responses. We created transgenic Nicotiana attenuata plants, in which two CDPKs, NaCDPK4 and NaCDPK5, were simultaneously silenced (IRcdpk4/5 plants). IRcdpk4/5 plants were stunted and aborted most of their flower primordia. Importantly, after wounding or simulated herbivory, IRcdpk4/5 plants accumulated exceptionally high JA levels. When NaCDPK4 and NaCDPK5 were silenced individually, neither stunted growth nor high JA levels were observed, suggesting that NaCDPK4 and NaCDPK5 have redundant roles. Attack from Manduca sexta larvae on IRcdpk4/5 plants induced high levels of defense metabolites that slowed M. sexta growth. We found that NaCDPK4 and NaCDPK5 affect plant resistance against insects in a JA- and JA-signaling-dependent manner. Furthermore, IRcdpk4/5 plants showed overactivation of salicylic-acid-induced protein kinase, a mitogen-activated protein kinase involved in various stress responses, and genetic analysis indicated that the increased salicylic-acid-induced protein kinase activity in IRcdpk4/5 plants was a consequence of the exceptionally high JA levels and was dependent on CORONATINE INSENSITIVE1. This work reveals the critical roles of CDPKs in modulating JA homeostasis and highlights the complex duet between JA and mitogen-activated protein kinase signaling. PMID:22715110

Yang, Da-Hai; Hettenhausen, Christian; Baldwin, Ian T; Wu, Jianqiang

2012-08-01

259

Strong optical nonlinearity of CVD-grown MoS2 monolayer as probed by wavelength-dependent second-harmonic generation  

NASA Astrophysics Data System (ADS)

While noncentrosymmetric MoS2 monolayer is known to exhibit efficient second-harmonic generation (SHG), there is currently no agreement on its absolute nonlinear susceptibility ?(2), varying over three orders of magnitude according to recent experiments. In order to resolve this conflicting issue, we have studied the nonlinear optical properties of MoS2 monolayer grown by chemical vapor deposition. The polycrystalline nature of the monolayer was directly probed by the SHG polarization dependence across the grain boundaries using femtosecond pulses. Broadband wavelength-dependent SHG response (? =1.1-2.0?m) using picosecond pulses was studied by comparing the relative SHG counts of MoS2 to quartz and incorporating the structural and optical characteristics of the monolayer. Significant nonlinear optical dispersion gives rise to ?(2)˜430 pm/V at 580 nm, where SHG is neither affected by any excitonic absorption/resonance nor by fundamental absorption. We also show that ?(2) must be derived from a thin bulk (sheet) optical nonlinearity and that the previous measurements are in fact all consistent, together with our measurements and first-principle calculations.

Clark, D. J.; Senthilkumar, V.; Le, C. T.; Weerawarne, D. L.; Shim, B.; Jang, J. I.; Shim, J. H.; Cho, J.; Sim, Y.; Seong, M.-J.; Rhim, S. H.; Freeman, A. J.; Chung, K.-H.; Kim, Y. S.

2014-09-01

260

Solute-dependent activation of cell motility in strongly hypertonic solutions in Dictyostelium discoideum, human melanoma HTB-140 cells and walker 256 carcinosarcoma cells.  

PubMed

Published data concerning the effects of hypertonicity on cell motility have often been controversial. The interpretation of results often rests on the premise that cell responses result from cell dehydration, i.e. osmotic effects. The results of induced hypertonicity on cell movement of Dictyostelium discoideum amoebae and human melanoma HTB-140 cells reported here show that: i) hypertonic solutions of identical osmolarity will either inhibit or stimulate cell movement depending on specific solutes (Na(+) or K(+), sorbitol or saccharose); ii) inhibition of cell motility by hypertonic solutions containing Na(+) ions or carbohydrates can be reversed by the addition of calcium ions; iii) various cell types react differently to the same solutions, and iv) cells can adapt to hypertonic solutions. Various hypertonic solutions are now broadly used in medicine and to study modulation of gene expression. The observations reported suggest the need to examine whether the other responses of cells to hypertonicity can also be based on the solute-dependent cell responses besides cell dehydration due to the osmotic effects. PMID:21614489

Korohoda, W?odzimierz; Kucia, Magdalena; Wybieralska, Ewa; Wianecka-Skocze?, Magdalena; Waligórska, Agnieszka; Druka?a, Justyna; Madeja, Zbigniew

2011-09-01

261

Self-intermediate scattering function of strongly interacting three-dimensional lattice gases: Time- and wave-vector-dependent tracer diffusion coefficient  

NASA Astrophysics Data System (ADS)

We investigate the self-intermediate scattering function (SISF) in a three-dimensional (3D) cubic lattice fluid (interacting lattice gas) with attractive nearest-neighbor interparticle interactions at a temperature slightly above the critical one by means of Monte Carlo simulations. A special representation of SISF as an exponent of the mean tracer diffusion coefficient multiplied by the geometrical factor and time is considered to highlight memory effects that are included in time and wave-vector dependence of the diffusion coefficient. An analytical expression for the diffusion coefficient is suggested to reproduce the simulation data. It is shown that the particles' mean-square displacement is equal to the time integral of the diffusion coefficient. We make a comparison with the previously considered 2D system on a square lattice. The main difference with the two-dimensional case is that the time dependence of particular characteristics of the tracer diffusion coefficient in the 3D case cannot be described by exponentially decreasing functions, but requires using stretched exponentials with rather small values of exponents, of the order of 0.2. The hydrodynamic values of the tracer diffusion coefficient (in the limit of large times and small wave vectors) defined through SIFS simulation results agree well with the results of its direct determination by the mean-square displacement of the particles in the entire range of concentrations and temperatures.

Skarpalezos, Loukas; Argyrakis, Panos; Vikhrenko, Vyacheslav S.

2014-05-01

262

Strong growth orientation dependence of strain relaxation in epitaxial (Ba,Sr)TiO3 films and the resulting dielectric properties  

NASA Astrophysics Data System (ADS)

The growth orientation dependence of strain relaxation and the dielectric properties were investigated for (001)- and (111)-epitaxial (Ba,Sr)TiO3 films. The films were deposited on SrRuO3/SrTiO3 and SrTiO3 substrates using rf magnetron sputtering. The residual strain was found to be remarkably different between the two orientations, although these lattice mismatches are identical; the strain relaxation of the (001)-epitaxial films is significantly slower than that of the (111)-epitaxial films and is promoted only when the growth rate is very low (?5 nm/h). The observed orientation dependence is discussed with the surface energy for both growth orientations, which influences the growth mode of the films. Due to the large contrast of the strain in the (001)- and (111)-epitaxial films, the paraelectric to ferroelectric phase transition temperature of the (001)-epitaxial films is much higher than that of unstrained bulks, while the (111)-epitaxial films show a phase transition temperature corresponding to that of unstrained bulks regardless of the growth rates.

Yamada, Tomoaki; Kamo, Takafumi; Funakubo, Hiroshi; Su, Dong; Iijima, Takashi

2011-05-01

263

Endocytotic routes of cobra cardiotoxins depend on spatial distribution of positively charged and hydrophobic domains to target distinct types of sulfated glycoconjugates on cell surface.  

PubMed

Cobra cardiotoxins (CTX) are a family of three-fingered basic polypeptides known to interact with diverse targets such as heparan sulfates, sulfatides, and integrins on cell surfaces. After CTX bind to the membrane surface, they are internalized to intracellular space and exert their cytotoxicity via an unknown mechanism. By the combined in vitro kinetic binding, three-dimensional x-ray structure determination, and cell biology studies on the naturally abundant CTX homologues from the Taiwanese cobra, we showed that slight variations on the spatial distribution of positively charged or hydrophobic domains among CTX A2, A3, and A4 could lead to significant changes in their endocytotic pathways and action mechanisms via distinct sulfated glycoconjugate-mediated processes. The intracellular locations of these structurally similar CTX after internalization are shown to vary between the mitochondria and lysosomes via either dynamin2-dependent or -independent processes with distinct membrane cholesterol sensitivity. Evidence is presented to suggest that the shifting between the sulfated glycoconjugates as distinct targets of CTX A2, A3, and A4 might play roles in the co-evolutionary arms race between venomous snake toxins to cope with different membrane repair mechanisms at the cellular levels. The sensitivity of endocytotic routes to the spatial distribution of positively charged or hydrophobic domains may provide an explanation for the diverse endocytosis pathways of other cell-penetrating basic polypeptides. PMID:24898246

Lee, Shao-Chen; Lin, Chien-Chu; Wang, Chia-Hui; Wu, Po-Long; Huang, Hsuan-Wei; Chang, Chung-I; Wu, Wen-guey

2014-07-18

264

Luminosity dependence of the spatial and velocity distributions of galaxies: Semi-analytic models versus the Sloan Digital Sky Survey  

E-print Network

By comparing semi-analytic galaxy catalogues with data from the Sloan Digital Sky Survey (SDSS), we show that current galaxy formation models reproduce qualitatively the dependence of galaxy clustering and pairwise peculiar velocities on luminosity, but some subtle discrepancies with the data still remain. The comparisons are carried out by constructing a large set of mock galaxy redshift surveys that have the same selection function as the SDSS Data Release Four (DR4). The mock surveys are based on two sets of semi-analytic catalogues presented by Croton et al. and Kang et al. From the mock catalogues, we measure the redshift-space projected two-point correlation function, the power spectrum, and the pairwise velocity dispersion (PVD) in Fourier space and in configuration space, for galaxies in different luminosity intervals. We then compare these theoretical predictions with the measurements derived from the SDSS DR4. On large scales and for galaxies brighter than L*, both sets of mock catalogues agree well with the data. For fainter galaxies, however, both models predict stronger clustering and higher pairwise velocities than observed. We demonstrate that this problem can be resolved if the fraction of faint satellite galaxies in massive haloes is reduced by ~30% compared to the model predictions. A direct look into the model galaxy catalogues reveals that a signifcant fraction (15%) of faint galaxies ($-1810^{13}\\msun$, and this population is predominantly red in colour. These faint red galaxies are responsible for the high PVD values of low-luminosity galaxies on small scales.

Cheng Li; Y. P. Jing; Guinevere Kauffmann; Gerhard Boerner; Xi Kang; Lan Wang

2007-01-09

265

Spectral type dependent rotational braking and strong magnetic flux in three components of the late-M multiple system LHS 1070  

E-print Network

We show individual high resolution spectra of components A, B, and C of the nearby late-M type multiple system LHS 1070. Component A is a mid-M star, B and C are known to have masses at the threshold to brown dwarfs. From our spectra we measure rotation velocities and the mean magnetic field for all three components individually. We find magnetic flux on the order of several kilo-Gauss in all components. The rotation velocities of the two late-M objects B and C are similar (vsini = 16km/s), the earlier A component is spinning only at about half that rate. This suggests weakening of net rotational braking at late-M spectral type, and that the lack of slowly rotating late-M and L dwarfs is real. Furthermore, we found that magnetic flux in the B component is about twice as strong as in component C at similar rotation rate. This indicates that rotational braking is not proportional to magnetic field strength in fully convective objects, and that a different field topology is the reason for the weak braking in low mass objects.

Ansgar Reiners; Andreas Seifahrt; Hans Ulrich Käufl; Ralf Siebenmorgen; Alain Smette

2007-06-14

266

Temperature dependence of silicate weathering in nature: How strong a negative feedback on long-term accumulation of atmospheric CO2 and global greenhouse warming?  

NASA Astrophysics Data System (ADS)

Estimation of the temperature dependence of natural feldspar weathering in two catchments at different elevations yields an apparent Arrhenius activation energy of 18.4 kcal/mol (77.0 kJ/mol), much higher than most laboratory values. This finding supports recent suggestions that hydrolytic weathering of silicate minerals may consume carbonic acid and thereby remove atmospheric carbon dioxide more rapidly with increasing temperature than previously thought. This result provides a stronger negative feedback on long-term greenhouse warming than has been assumed in most models of global carbon cycling. The present estimate was determined from the ratio of feldspar weathering rates (determined by geochemical mass balance) in the southern Blue Ridge Mountains of North Carolina, United States. Temperature (a function of elevation) is the only factor that differs between the two catchments; parent rock type, aspect, hillslope hydrology, and vegetation type and successional stage are the same in both.

Velbel, Michael Anthony

1993-12-01

267

Spatially distributed assessment of solar resources for energy applications in Slovakia  

Microsoft Academic Search

Spatial and temporal distribution of available solar energy depends on several factors. Besides latitude and astronomical factors it is strongly influenced by climate factors (e.g. cloudiness, turbidity) and topography. This paper presents a solar database of Slovakia containing spatially-distributed solar energy resource data necessary for planning, sitting and forecasting of solar device installations. The database consists of several data sets

Jaroslav HOFIERKA

2008-01-01

268

Isolation by distance in a continuous population: reconciliation between spatial autocorrelation analysis and population genetics models  

Microsoft Academic Search

Analysis of the spatial genetic structure within continuous populations in their natural habitat can reveal acting evolutionary processes. Spatial autocorrelation statistics are often used for this purpose, but their relationships with population genetics models have not been thoroughly established. Moreover, it has been argued that the dependency of these statistics on variation in mutation rates among loci strongly limits their

OLIVIER J. HARDY; XAVIER VEKEMANS

1999-01-01

269

Vestibular modulation of spatial perception  

PubMed Central

Vestibular inputs make a key contribution to the sense of one’s own spatial location. While the effects of vestibular stimulation on visuo-spatial processing in neurological patients have been extensively described, the normal contribution of vestibular inputs to spatial perception remains unclear. To address this issue, we used a line bisection task to investigate the effects of galvanic vestibular stimulation (GVS) on spatial perception, and on the transition between near and far space. Brief left-anodal and right-cathodal GVS or right-anodal and left-cathodal GVS were delivered. A sham stimulation condition was also included. Participants bisected lines of different lengths at six distances from the body using a laser pointer. Consistent with previous results, our data showed an overall shift in the bisection bias from left to right as viewing distance increased. This pattern suggests leftward bias in near space, and rightward bias in far space. GVS induced strong polarity dependent effects in spatial perception, broadly consistent with those previously reported in patients: left-anodal and right-cathodal GVS induced a leftward bisection bias, while right-anodal and left-cathodal GVS reversed this effect, and produced bisection bias toward the right side of the space. Interestingly, the effects of GVS were comparable in near and far space. We speculate that vestibular-induced biases in space perception may optimize gathering of information from different parts of the environment. PMID:24133440

Ferre, Elisa R.; Longo, Matthew R.; Fiori, Federico; Haggard, Patrick

2013-01-01

270

Spatial Dependence of Heat Flux Transients and Wetting Behavior During Immersion Quenching of Inconel 600 Probe in Brine and Polymer Media  

NASA Astrophysics Data System (ADS)

Cooling curve analysis of Inconel 600 probe during immersion quenching in brine and polymer quench media was carried out. Thermal histories at various axial and radial locations were recorded using a high-speed data acquisition system and were input to an inverse heat-conduction model for estimating the metal/quenchant heat flux transients. A high performance smart camera was used for online video imaging of the immersion quenching process. Solution to two-dimensional inverse heat-conduction problem clearly brings out the spatial dependence of boundary heat flux transients for a Inconel 600 probe with a simple cylindrical geometry. The estimated heat flux transients show large variation on axial as well as radial directions of quench probe surface for brine quenching. Polymer quenching showed less variation in metal/quenchant heat flux transients. Shorter durations of vapor film, higher rewetting temperatures, and faster movement of wetting front on quench probe surface were observed with brine quenching. Measurement of dynamic contact angle showed better spreading and good wettability for polymer medium as compared to brine quenchant. The solid-liquid interfacial tension between polymer medium and Inconel substrate was lower compared with that of solution. Rewetting and boiling processes were nonuniform and faster on quench probe surface during immersion quenching in brine solution. For the polymer quench medium, slow rewetting, uniform boiling and repeated wetting were observed.

Ramesh, G.; Narayan Prabhu, K.

2014-08-01

271

3?5?-Pregnanolone glutamate, a use-dependent NMDA antagonist, reversed spatial learning deficit in an animal model of schizophrenia.  

PubMed

Neuroactive steroids modulate receptors for neurotransmitters in the brain and thus might be efficacious in the treatment of various diseases of the central nervous system such as schizophrenia. We have designed and synthetized a novel use-dependent NMDA receptor antagonist 3?5?-pregnanolone glutamate (3?5?-P-Glu). In this study, we evaluate procognitive properties of 3?5?-P-Glu in an animal model of schizophrenia induced by systemic application of MK-801. The procognitive properties were evaluated using active place avoidance on a rotating arena (Carousel maze). We evaluated effects of 3?5?-P-Glu on the avoidance, on locomotor activity, and anxiety. 3?5?-P-Glu alone altered neither spatial learning nor locomotor activity in control animals. In the model animals, 3?5?-P-Glu reversed the MK-801-induced cognitive deficit without reducing hyperlocomotion. The highest dose of 3?5?-P-Glu also showed anxiolytic properties. Taken together, 3?5?-P-Glu may participate in the restoration of normal brain functioning and these results may facilitate the development of new promising drugs improving cognitive functioning in schizophrenia. PMID:22820236

Vales, Karel; Rambousek, Lukas; Holubova, Kristina; Svoboda, Jan; Bubenikova-Valesova, Vera; Chodounska, Hana; Vyklicky, Ladislav; Stuchlik, Ales

2012-11-01

272

Age, sex and spatial dependent variations in heavy metals levels in the Glaucous Gulls (Larus hyperboreus) from the Bjørnøya and Jan Mayen, Arctic.  

PubMed

Heavy metals (Cd, Cu, Fe, Mn and Zn) concentrations were determined in different tissues (muscle, kidney, liver, brain, gonads, heart and feathers) of Glaucous Gulls (Larus hyperboreus) from Bjørnøya and Jan Mayen. The age and spatial dependent variations in heavy metals were quantified and interpreted in view of the three chemometric techniques, i.e. non-parametric Mann-Whitney U test, redundancy gradient analysis and detrended correspondence analysis. The Glaucous Gulls from Bjørnøya contained significantly higher (p < 0.05) levels of Cd, Cu and Zn than those inhabited Jan Mayen. Adult birds were characterized by greater (p < 0.01) concentration of muscle, hepatic and renal heavy metals in comparison to chicks. Insignificantly higher slope constant Zn/Cd for the liver than for the kidney may reflect insignificant Cd exposure. Estimate of transfer factor (TF) allows us to assess variations in heavy metal concentrations during the individual development of Glaucous Gulls. It may be stated that there is a distinct increase of bioaccumulation of all the studied metals during subsequent stages of the bird life. PMID:19847662

Malinga, Micha?; Szefer, Piotr; Gabrielsen, Geir W

2010-10-01

273

Spatial Domain Interactions between Ultraweak Optical Beams  

NASA Astrophysics Data System (ADS)

We have observed spatial interactions between two ultraweak optical beams that are initially collinear and nonoverlapping. The weak beams are steered towards each other by a spatially varying cross-Kerr refractive index waveguide written by a strong laser beam in a three-level coherently prepared atomic medium. After fusing together, the combined beam shows controllable phase-dependent behaviors. This is the first observation of solitonlike interactions between weak beams and can be useful for all-optically tunable beam combining, switching, and gating for weak photonic signals.

Khadka, Utsab; Sheng, Jiteng; Xiao, Min

2013-11-01

274

A gender-and sexual orientation-dependent spatial attentional effect of invisible images Yi Jiang, Patricia Costello, Fang Fang, Miner Huang, and Sheng He  

E-print Network

) erotic pictures, can direct the distribution of spatial attention. Furthermore, invisible erotic that subliminal presentation of emotional stimuli can modulate activity of the amygdala (4, 5), a subcortical

He, Sheng

275

The spatial resolving power of earth resources satellites: A review  

NASA Technical Reports Server (NTRS)

The significance of spatial resolving power on the utility of current and future Earth resources satellites is critically discussed and the relative merits of different approaches in defining and estimating spatial resolution are outlined. It is shown that choice of a particular measure of spatial resolution depends strongly on the particular needs of the user. Several experiments have simulated the capabilities of future satellite systems by degradation of aircraft images. Surprisingly, many of these indicated that improvements in resolution may lead to a reduction in the classification accuracy of land cover types using computer assisted methods. However, where the frequency of boundary pixels is high, the converse relationship is found. Use of imagery dependent upon visual interpretation is likely to benefit more consistently from higher resolutions. Extraction of information from images will depend upon several other factors apart from spatial resolving power: these include characteristics of the terrain being sensed, the image processing methods that are applied as well as certain sensor characteristics.

Townshend, J. R. G.

1980-01-01

276

Spatial variation of total column ozone on a global scale  

Microsoft Academic Search

The spatial dependence of total column ozone varies strongly with latitude, so that homogeneous models (invariant to all rotations) are clearly unsuitable. However, an assumption of axial symmetry, which means that the process model is invariant to rotations about the Earth’s axis, is much more plausible and considerably simplifies the modeling. Using TOMS (Total Ozone Mapping Spectrometer) measurements of total

Michael L. Stein

2007-01-01

277

Temporal scaling properties and spatial synchronization of spontaneous blood oxygenation level-dependent (BOLD) signal fluctuations in rat sensorimotor network at different levels of isoflurane anesthesia.  

PubMed

Spontaneous fluctuations in the blood oxygenation level-dependent (BOLD) MRI signal during the resting state are increasingly being studied in healthy and diseased brain in humans and animal models. Yet, the relationship between functional brain status and the characteristics of spontaneous BOLD fluctuations remains poorly understood. In order to obtain more insights into this relationship and, in particular, the effects of anesthesia thereupon, we investigated the spatial and temporal correlations of spontaneous BOLD fluctuations in somatosensory and motor regions of rat brain at different inhalation levels of the frequently applied anesthetic isoflurane. We found that the temporal scaling, characterized by the Hurst exponent (H), showed persistent behavior (H?>?0.5) at 0.5-1.0% isoflurane. Furthermore, low-pass-filtered spontaneous BOLD oscillations were correlated significantly in bilateral somatosensory and bilateral motor cortices, reflective of interhemispheric functional connectivity. Under 2.9% isoflurane anesthesia, the temporal scaling characteristics approached those of Gaussian white noise (H?=?0.5), the relative amplitude of BOLD low-frequency fluctuations declined, and cross-correlations of these oscillations between functionally connected regions decreased significantly. Loss of interhemispheric functional connectivity at 2.9% isoflurane anesthesia was stronger between bilateral motor regions than between bilateral somatosensory regions, which points to distinct effects of anesthesia on differentially organized neuronal networks. Although we cannot completely rule out a possible contribution from hemodynamic signals with a non-neuronal origin, our results emphasize that spatiotemporal characteristics of spontaneous BOLD fluctuations are related to the brain's specific functional status and network organization, and demonstrate that these are largely preserved under light to mild anesthesia with isoflurane. PMID:20669170

Wang, Kun; van Meer, Maurits P A; van der Marel, Kajo; van der Toorn, Annette; Xu, Lijuan; Liu, Yingjun; Viergever, Max A; Jiang, Tianzi; Dijkhuizen, Rick M

2011-01-01

278

Analysis of the spatial distribution between successive earthquakes.  

PubMed

Spatial distances between subsequent earthquakes in southern California exhibit scale-free statistics, with a critical exponent delta approximately 0.6, as well as finite size scaling. The statistics are independent of the threshold magnitude as long as the catalog is complete, but depend strongly on the temporal ordering of events, rather than the geometry of the spatial epicenter distribution. Nevertheless, the spatial distance and waiting time between subsequent earthquakes are uncorrelated with each other. These observations contradict the theory of aftershock zone scaling with main shock magnitude. PMID:15783608

Davidsen, Jörn; Paczuski, Maya

2005-02-01

279

The role of habituation in hippocampus-dependent spatial working memory tasks: Evidence from GluA1 AMPA receptor subunit knockout mice  

PubMed Central

Spatial alternation, win-shift behavior has been claimed to be a test of working memory in rodents that requires active maintenance of relevant, trial-specific information. In this review, we describe work with GluA1 AMPA receptor subunit knockout mice that show impaired spatial alternation, but normal spatial reference memory. Due to their selective impairment on spatial alternation, GluA1 knockout mice provide a means by which the psychological processes underlying alternation can be examined. We now argue that the spatial alternation deficit in GluA1 knockout mice is due to an inability to show stimulus-specific, short-term habituation to recently experienced stimuli. Short-term habituation involves a temporary reduction in attention paid to recently presented stimuli, and is thus a distinct process from those that are involved in working memory in humans. We have recently demonstrated that GluA1 knockout mice show impaired short-term habituation, but, surprisingly, show enhanced long-term spatial habituation. Thus, GluA1 deletion reveals that there is competition between short-term and long-term processes in memory. © 2010 Wiley Periodicals, Inc. PMID:21125585

Sanderson, David J; Bannerman, David M

2012-01-01

280

STRONG FERTILITY CENTER Strong Fertility Center  

E-print Network

STRONG FERTILITY CENTER Strong Fertility Center Women's Lifestyle Center The Women's Lifestyle with the improved lifestyle. Also, we work together with the Strong Fertility Center to coordinate your fertility fertility treatments. · A complete nutritional consultation with our registered dietician, Tracy Cherry, RD

Goldman, Steven A.

281

Modelling the spread of Wolbachia in spatially heterogeneous environments.  

PubMed

The endosymbiont Wolbachia infects a large number of insect species and is capable of rapid spread when introduced into a novel host population. The bacteria spread by manipulating their hosts' reproduction, and their dynamics are influenced by the demographic structure of the host population and patterns of contact between individuals. Reaction-diffusion models of the spatial spread of Wolbachia provide a simple analytical description of their spatial dynamics but do not account for significant details of host population dynamics. We develop a metapopulation model describing the spatial dynamics of Wolbachia in an age-structured host insect population regulated by juvenile density-dependent competition. The model produces similar dynamics to the reaction-diffusion model in the limiting case where the host's habitat quality is spatially homogeneous and Wolbachia has a small effect on host fitness. When habitat quality varies spatially, Wolbachia spread is usually much slower, and the conditions necessary for local invasion are strongly affected by immigration of insects from surrounding regions. Spread is most difficult when variation in habitat quality is spatially correlated. The results show that spatial variation in the density-dependent competition experienced by juvenile host insects can strongly affect the spread of Wolbachia infections, which is important to the use of Wolbachia to control insect vectors of human disease and other pests. PMID:22675165

Hancock, Penelope A; Godfray, H Charles J

2012-11-01

282

Spatially and Temporally Varying Associations between Temporary Outmigration and Natural Resource Availability in Resource-Dependent Rural Communities in South Africa: A Modeling Framework  

PubMed Central

Migration-environment models tend to be aspatial within chosen study regions, although associations between temporary outmigration and environmental explanatory variables likely vary across the study space. This research extends current approaches by developing migration models considering spatial non-stationarity and temporal variation – through examination of the migration-environment association at nested geographic scales (i.e. whole-population, village, and subvillage) within a specific study site. Demographic survey data from rural South Africa, combined with indicators of natural resource availability from satellite imagery, are employed in a nested modeling approach that brings out distinct patterns of spatial variation in model associations derived at finer geographic scales. Given recent heightened public and policy concern with the human migratory implications of climate change, we argue that consideration of spatial variability adds important nuance to scientific understanding of the migration-environment association. PMID:23008525

Leyk, Stefan; Maclaurin, Galen J.; Hunter, Lori M.; Nawrotzki, Raphael; Twine, Wayne; Collinson, Mark; Erasmus, Barend

2012-01-01

283

Topographic Controls on Spatial Patterns of Soil Texture and Moisture in a Semi-arid Montane Catchment with Aspect-Dependent Vegetation  

Microsoft Academic Search

Soil moisture exerts significant control over the partitioning of latent and sensible energy fluxes, the magnitude of both vertical and lateral water fluxes, the physiological and water-use characteristics of vegetation, and nutrient cycling. Considerable progress has been made in determining how soil characteristics, topography, and vegetation influence spatial patterns of soil moisture in humid environments at the catchment, hillslope, and

B. M. Lehman; J. D. Niemann

2008-01-01

284

Evaluation of TRMM Multi-satellite Precipitation Analysis (TMPA) performance in the Central Andes region and its dependency on spatial and temporal resolution  

Microsoft Academic Search

Climate time series are of major importance for base line studies for climate change impact and adaptation projects. However, for instance, in mountain regions and in developing countries there exist significant gaps in ground based climate records in space and time. Specifically, in the Peruvian Andes spatially and temporally coherent precipitation information is a prerequisite for ongoing climate change adaptation

M. L. M. Scheel; M. Rohrer; Ch. Huggel; D. Santos Villar; E. Silvestre; G. J. Huffman

2011-01-01

285

Evaluation of TRMM Multi-satellite Precipitation Analysis (TMPA) performance in the Central Andes region and its dependency on spatial and temporal resolution  

Microsoft Academic Search

Climate time series are of major importance for base line studies for climate change impact and adaptation projects. However, in mountain regions and in developing countries there exist significant gaps in ground based climate records in space and time. Specifically, in the Peruvian Andes spatially and temporally coherent precipitation information is a prerequisite for ongoing climate change adaptation projects in

M. L. M. Scheel; M. Rohrer; C. Huggel; D. Santos Villar; E. Silvestre; G. J. Huffman

2010-01-01

286

Strongly Driven Crystallization Processes in a Metallic Glass  

SciTech Connect

The crystallization of amorphous NiTi thin films was studied in situ using pulsed laser heating in a dynamic transmission electron microscope. A single pulse can crystallize small areas of the film within 2 {micro}s. The crystallized volume fraction and morphology depend strongly on the laser energy, the laser spatial profile, and the heat transport in the film. As compared to slower furnace and continuous wave laser annealing, pulsed laser heating produces a dramatically different microstructure. Higher than expected crystallization rates were observed under pulsed irradiation that do not correlate with kinetic data obtained from the slow-heating crystallization experiments.

LaGrange, T; Grummon, D S; Reed, B W; Browning, N D; King, W E; Campbell, G H

2009-02-09

287

Strong polaritonic interaction between flux-flow and phonon resonances in Bi2Sr2CaCu2O8+x intrinsic Josephson junctions: Angular dependence and the alignment procedure  

NASA Astrophysics Data System (ADS)

Bi2Sr2CaCu2O8+x single crystals represent natural stacks of atomic scale intrinsic Josephson junctions, formed between metallic CuO2-Ca-CuO2 and ionic insulating SrO-2BiO-SrO layers. Electrostriction effect in the insulating layers leads to excitation of c-axis phonons by the ac-Josephson effect. Here we study experimentally the interplay between and velocity matching (Eck) electromagnetic resonances in the flux-flow state of small mesa structures with c-axis optical phonons. A very strong interaction is reported, which leads to formation of phonon-polaritons with infrared and Raman-active transverse optical phonons. A special focus in this work is made on analysis of the angular dependence of the resonances. We describe an accurate sample alignment procedure that prevents intrusion of Abrikosov vortices in fields up to 17 T, which is essential for achieving high-quality resonances at record high frequencies up to 13 THz.

Motzkau, H.; Katterwe, S. O.; Rydh, A.; Krasnov, V. M.

2013-08-01

288

Do spatial patterns of clonal fragments and architectural responses to defoliation depend on the structural blue-print? An experimental test with two rhizomatous Cyperaceae  

Microsoft Academic Search

Clonal architecture is involved in performance of clonal fragments, as it determines spatial distribution of ramets. It is\\u000a expected to rely on the species-specific expression of several architectural traits (structural blue-print). However, in contrasting\\u000a environments, realized clonal architectures may differ, due to phenotypic plasticity. In this paper, we compared clonal architectures\\u000a between two rhizomatous ecologically close Cyperaceae (Carex divisa and

Marie-Lise Benot; Anne Bonis; Cendrine Mony

2010-01-01

289

Gender-Dependent Frequency–Spatial Organization of the Brain Cortex Activity during Convergent and Divergent Thinking: I. Analysis of the EEG Power  

Microsoft Academic Search

The frequency–spatial organization of the brain cortex activity of men and women was studied during convergent (CTh) and divergent (DTh) thinking by means of EEG power mapping in a broad frequency band. Right-handed 17- to 23-year-old students (36 men and 30 women) participated in the study. Mental arithmetic was used as a model of CTh. Functional changes in the EEG

O. M. Razoumnikova

2004-01-01

290

A smoothed particle hydrodynamics-based fluid model with a spatially dependent viscosity: application to flow of a suspension with a non-Newtonian fluid matrix  

Microsoft Academic Search

A smoothed particle hydrodynamics approach is utilized to model a non-Newtonian fluid with a spatially varying viscosity.\\u000a In the limit of constant viscosity, this approach recovers an earlier model for Newtonian fluids of Español and Revenga (Phys\\u000a Rev E 67:026705, 2003). Results are compared with numerical solutions of the general Navier–Strokes equation using the “regularized” Bingham model\\u000a of Papanastasiou (J

Nicos S. Martys; William L. George; Byong-Wa Chun; Didier Lootens

2010-01-01

291

Spatially embedded growing small-world networks  

PubMed Central

Networks in nature are often formed within a spatial domain in a dynamical manner, gaining links and nodes as they develop over time. Motivated by the growth and development of neuronal networks, we propose a class of spatially-based growing network models and investigate the resulting statistical network properties as a function of the dimension and topology of the space in which the networks are embedded. In particular, we consider two models in which nodes are placed one by one in random locations in space, with each such placement followed by configuration relaxation toward uniform node density, and connection of the new node with spatially nearby nodes. We find that such growth processes naturally result in networks with small-world features, including a short characteristic path length and nonzero clustering. We find no qualitative differences in these properties for two different topologies, and we suggest that results for these properties may not depend strongly on the topology of the embedding space. The results do depend strongly on dimension, and higher-dimensional spaces result in shorter path lengths but less clustering. PMID:25395180

Zitin, Ari; Gorowara, Alexander; Squires, Shane; Herrera, Mark; Antonsen, Thomas M.; Girvan, Michelle; Ott, Edward

2014-01-01

292

Spatially embedded growing small-world networks.  

PubMed

Networks in nature are often formed within a spatial domain in a dynamical manner, gaining links and nodes as they develop over time. Motivated by the growth and development of neuronal networks, we propose a class of spatially-based growing network models and investigate the resulting statistical network properties as a function of the dimension and topology of the space in which the networks are embedded. In particular, we consider two models in which nodes are placed one by one in random locations in space, with each such placement followed by configuration relaxation toward uniform node density, and connection of the new node with spatially nearby nodes. We find that such growth processes naturally result in networks with small-world features, including a short characteristic path length and nonzero clustering. We find no qualitative differences in these properties for two different topologies, and we suggest that results for these properties may not depend strongly on the topology of the embedding space. The results do depend strongly on dimension, and higher-dimensional spaces result in shorter path lengths but less clustering. PMID:25395180

Zitin, Ari; Gorowara, Alexander; Squires, Shane; Herrera, Mark; Antonsen, Thomas M; Girvan, Michelle; Ott, Edward

2014-01-01

293

Discovery of Spatial Association Rules in Geographic Information Databases  

Microsoft Academic Search

. Spatial data mining, i.e., discovery of interesting, implicitknowledge in spatial databases, is an important task for understandingand use of spatial data- and knowledge-bases. In this paper, an efficientmethod for mining strong spatial association rules in geographic informationdatabases is proposed and studied. A spatial association rule is arule indicating certain association relationship among a set of spatial andpossibly some nonspatial

Krzysztof Koperski; Jiawei Han

1995-01-01

294

Spatial-visual skills and engineering design  

E-print Network

The purpose of this study was to determine whether students with strong spatial-visual skills tend to design more complex mechanisms for the undergraduate course Design and Manufacturing I. The Purdue Spatial Visualization ...

Tseng, Tiffany

2009-01-01

295

Spared unconscious influences of spatial memory in diencephalic amnesia  

PubMed Central

Spatial memory is crucial to our daily lives and in part strongly depends on automatic, implicit memory processes. This study investigates the neurocognitive basis of conscious and unconscious influences of object–location memory in amnesic patients with Korsakoff’s syndrome (N = 23) and healthy controls (N = 18) using a process-dissociation procedure in a computerized spatial memory task. As expected, the patients performed substantially worse on the conscious memory measures but showed even slightly stronger effects of unconscious influences than the controls. Moreover, a delayed test administered after 1 week revealed a strong decline in conscious influences in the patients, while unconscious influences were not affected. The presented results suggest that conscious and unconscious influences of spatial memory can be clearly dissociated in Korsakoff’s syndrome. PMID:18560813

Antonides, Rémy; Wester, Arie J.; Kessels, Roy P. C.

2008-01-01

296

Higgs-induced spectroscopic shifts near strong gravity sources  

SciTech Connect

We explore the consequences of the mass generation due to the Higgs field in strong gravity astrophysical environments. The vacuum expectation value of the Higgs field is predicted to depend on the curvature of spacetime, potentially giving rise to peculiar spectroscopic shifts, named hereafter 'Higgs shifts'. Higgs shifts could be searched through dedicated multiwavelength and multispecies surveys with high spatial and spectral resolution near strong gravity sources such as Sagittarius A* or broad searches for signals due to primordial black holes. The possible absence of Higgs shifts in these surveys should provide limits to the coupling between the Higgs particle and the curvature of spacetime, a topic of interest for a recently proposed Higgs-driven inflationary model. We discuss some conceptual issues regarding the coexistence between the Higgs mechanism and gravity, especially for their different handling of fundamental and composite particles.

Onofrio, Roberto [Dipartimento di Fisica 'Galileo Galilei', Universita di Padova, Via Marzolo 8, Padova 35131 (Italy) and ITAMP, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)

2010-09-15

297

Yugoslav strong motion network  

Microsoft Academic Search

Data concerning ground motion and the response of structures during strong earthquakes are necessary for seismic hazard evaluation and the definition of design criteria for structures to be constructed in seismically active zones. The only way to obtain such data is the installation of a strong-motion instrument network. The Yugoslav strong-motion programme was created in 1972 to recover strong-motion response

Vladimir Mihailov

1985-01-01

298

Synesthesia: Strong and Weak  

Microsoft Academic Search

In this review, we distinguish strong and weak forms of synesthesia. Strong synesthesia is characterized by a vivid image in one sensory modality in response to stimulation in another one. Weak synesthesia is characterized by cross-sensory correspondences expressed through language, perceptual similarity, and perceptual interactions during information processing. Despite important phenomenological dissimilarities between strong and weak synesthesia, we maintain that

Gail Martino; Lawrence E. Marks

2001-01-01

299

Spatial and temporal variation in the relative contribution of density dependence, climate variation and migration to fluctuations in the size of great tit populations  

Microsoft Academic Search

1. The aim of the present study is to model the stochastic variation in the size of five populations of great tit Parus major in the Netherlands, using a combination of individual-based demographic data and time series of population fluctuations. We will examine relative contribution of density-dependent effects, and variation in climate and winter food on local dynamics as well

Vidar Grøtan; B. E. Sæther; Steinar Engen; Balen van J. H; Albert C. Perdeck; Marcel E. Visser

2009-01-01

300

Gender-Dependent Frequency-Spatial Organization of the Brain Cortex Activity during Convergent and Divergent Thinking: II. Analysis of the EEG Coherence  

Microsoft Academic Search

The gender dependence of inter- and intrahemispheric interactions of neuronal assemblies during convergent (CTh) and divergent (DTh) thinking was studied on the basis of analysis of coherence (Coh) of cortical potentials in a broad frequency band. CTh was studied with a model of mental arithmetic, and DTh, with a heuristic task. Right-handed subjects were examined. The distinctive feature of CTh

O. M. Razoumnikova

2005-01-01

301

Interaction dynamics of spatially separated cavitation bubbles in water.  

PubMed

We present a high-speed photographic analysis of the interaction of cavitation bubbles generated in two spatially separated regions by femtosecond laser-induced optical breakdown in water. Depending on the relative energies of the femtosecond laser pulses and their spatial separation, different kinds of interactions, such as a flattening and deformation of the bubbles, asymmetric water flows, and jet formation were observed. The results presented have a strong impact on understanding and optimizing the cutting effect of modern femtosecond lasers with high repetition rates (>1 MHz). PMID:21198216

Tinne, Nadine; Schumacher, Silvia; Nuzzo, Valeria; Arnold, Cord L; Lubatschowski, Holger; Ripken, Tammo

2010-01-01

302

Enhanced spin Hall effect in strong magnetic disorder  

NASA Astrophysics Data System (ADS)

We consider a two-dimensional electron gas in an inversion asymmetric layer and in the presence of spatially distributed magnetic impurities. We investigate the relationship between the geometrical properties of the wave function and the system's spin-dependent transport properties. A localization transition, arising when disorder is increased, is exhibited by the appearance of a fractal state with finite inverse participation ratio. Below the transition, interference effects modify the carrier's diffusion, as revealed by the dependence on the scattering time of the power law exponents characterizing the spreading of a wave packet. Above the transition, in the strong disorder regime, we find that the states are spin polarized and localized around the impurities. A significant enhancement of the spin current develops in this regime.

van den Berg, T. L.; Raymond, L.; Verga, A.

2012-12-01

303

Spatial dependency of Buruli ulcer prevalence on arsenic-enriched domains in Amansie West District, Ghana: implications for arsenic mediation in Mycobacterium ulcerans infection  

PubMed Central

Background In 1998, the World Health Organization recognized Buruli ulcer (BU), a human skin disease caused by Mycobacterium ulcerans (MU), as the third most prevalent mycobacterial disease. In Ghana, there have been more than 2000 reported cases in the last ten years; outbreaks have occurred in at least 90 of its 110 administrative districts. In one of the worst affected districts, Amansie West, there are arsenic-enriched surface environments resulting from the oxidation of arsenic-bearing minerals, occurring naturally in mineral deposits. Results Proximity analysis, carried out to determine spatial relationships between BU-affected areas and arsenic-enriched farmlands and arsenic-enriched drainage channels in the Amansie West District, showed that mean BU prevalence in settlements along arsenic-enriched drainages and within arsenic-enriched farmlands is greater than elsewhere. Furthermore, mean BU prevalence is greater along arsenic-enriched drainages than within arsenic-enriched farmlands. Conclusion The results suggest that arsenic in the environment may play a contributory role in MU infection. PMID:15369592

Duker, Alfred A; Carranza, Emmanuel JM; Hale, Martin

2004-01-01

304

The differential spatial distribution of secondary metabolites in Arabidopsis leaves reacting hypersensitively to Pseudomonas syringae pv. tomato is dependent on the oxidative burst.  

PubMed

Secondary metabolites (SMs) play key roles in pathogen responses, although knowledge of their precise functions is limited by insufficient characterization of their spatial response. The present study addressed this issue in Arabidopsis leaves by non-targeted and targeted metabolite profiling of Pseudomonas syringae pv. tomato (Pst-AvrRpm1) infected and adjacent uninfected leaf tissues. While overlap was observed between infected and uninfected areas, the non-targeted metabolite profiles of these regions differed quantitatively and clustering analysis underscores a differential distribution of SMs within distinct metabolic pathways. Targeted metabolite profiling revealed that infected tissues accumulate more salicylic acid and the characteristic phytoalexin of Arabidopsis, camalexin, than uninfected adjacent areas. On the contrary, the antioxidant coumarin derivative, scopoletin, was induced in infected tissues while its glucoside scopolin predominated in adjacent tissues. To elucidate the still unclear relationship between the accumulation of SMs and reactive oxygen species (ROS) accumulation and signalling, a catalase-deficient line (cat2) in which ROS signalling is up-regulated, was used. Metabolic analysis of cat2 suggests that some SMs have important interactions with ROS in redox homeostasis during the hypersensitive response to Pst-AvrRpm1. Overall, the study demonstrates that ROS availability influences both the amount and the pattern of infection-induced SM accumulation. PMID:20530195

Simon, Clara; Langlois-Meurinne, Mathilde; Bellvert, Floriant; Garmier, Marie; Didierlaurent, Laure; Massoud, Kamal; Chaouch, Sejir; Marie, Arul; Bodo, Bernard; Kauffmann, Serge; Noctor, Graham; Saindrenan, Patrick

2010-07-01

305

Double Dissociations in Visual and Spatial Short-Term Memory  

ERIC Educational Resources Information Center

A visual short-term memory task was more strongly disrupted by visual than spatial interference, and a spatial memory task was simultaneously more strongly disrupted by spatial than visual interference. This double dissociation supports a fractionation of visuospatial short-term memory into separate visual and spatial components. In 6 experiments,…

Klauer, Karl Christoph; Zhao, Zengmei

2004-01-01

306

Self-interaction-free time-dependent density-functional theory for molecular processes in strong fields: High-order harmonic generation of H2 in intense laser fields  

Microsoft Academic Search

We present a self-interaction-free time-dependent density-functional theory (TDDFT) for nonperturbative treatment of multiphoton processes of many-electron molecular systems in intense laser fields. The time-dependent exchange-correlation (xc) energy potential with proper short- and long-range potential is constructed by means of the time-dependent optimized effective potential (OEP) method and the incorporation of an explicit self-interaction-correction (SIC) term. The resulting time-dependent OEP\\/SIC equations

Xi Chu; Shih-I. Chu

2001-01-01

307

Characterization of spatial intrafield gate CD variability, its impact on circuit performance, and spatial mask-level correction  

Microsoft Academic Search

The authors present a comprehensive characterization method applied to the study of the state-of-the-art 18-?m CMOS process. Statistical characterization of gate CD reveals a large spatial intrafield component, strongly dependent on the local layout patterns. The authors describe the statistical analysis of this data and demonstrate the need for such comprehensive characterization. They describe the experimental setup of the novel

Michael Orshansky; Linda Milor; Chenming Hu

2004-01-01

308

X-ray scanner for the visualization of the spatial distribution of nanometer-scale roughness  

Microsoft Academic Search

In the x-ray region, the reflection efficiency of a superpolished surface strongly depends on its roughness. This effect may be used to obtain a 2D map of the roughness spatial distribution for flat surfaces with a rms. roughness height of the order of one nanometer. The basic components of such a device are a precision mechanical 1D scanning stage and

Vladimir V. Protopopov; Kamil A. Valiev; Rafik M. Imamov

1998-01-01

309

Testing the spatial distribution of economic activity in Jiangsu province by means of spatial association methods  

NASA Astrophysics Data System (ADS)

The new economic geography theory suggests that regional development is strongly dependent on market access. Due to a snowball effect, spatial clusters of employment and firms might induce regional income increases. In order to identify explicit patterns of regional development, this study makes the empirical attempts by applying spatial association methods for estimating and distinguishing various spatial patterns of economic activities for three county-level factors, namely income, employment and firms of Jiangsu in 2004. The conclusions in this study reveal that on the whole, there is significant, positive correlation of income, employment and firms between regions over the whole space in that year. Moreover, regional income can be to a large extent explained by the market potentials of its neighbors. Apart from market access, regional incomes might be affected by other factors such as local amenities or technology spillover. Also, highly agglomerated clusters of employment and firms give rise to high regional incomes. Strong spatial heterogeneity of employment and firms indicates that firms locate first, anticipating the subsequent consumers' locations and demand functions. Thus, the mobility of firms and employment can induce the highly agglomeration of income.

Ge, Ying; Wang, Weina; Zhang, Shuhui; Yan, Weibiao

2007-06-01

310

Spatial Displays and Spatial Instruments  

NASA Technical Reports Server (NTRS)

The conference proceedings topics are divided into two main areas: (1) issues of spatial and picture perception raised by graphical electronic displays of spatial information; and (2) design questions raised by the practical experience of designers actually defining new spatial instruments for use in new aircraft and spacecraft. Each topic is considered from both a theoretical and an applied direction. Emphasis is placed on discussion of phenomena and determination of design principles.

Ellis, Stephen R. (editor); Kaiser, Mary K. (editor); Grunwald, Arthur J. (editor)

1989-01-01

311

Strong-field physics: Displaced creation  

NASA Astrophysics Data System (ADS)

The ionization of atoms and molecules by strong laser fields has become a core technique in modern laser physics. Now, the electrons emerging from ionized molecules are shown to exhibit a memory of the ionization process, resulting in a spatial phase that may influence the interpretation of imaging data.

Küpper, Jochen

2014-08-01

312

The spatial scaling of habitat selection by African elephants.  

PubMed

1. Understanding and accurately predicting the spatial patterns of habitat use by organisms is important for ecological research, biodiversity conservation and ecosystem management. However, this understanding is complicated by the effects of spatial scale, because the scale of analysis affects the quantification of species-environment relationships. 2. We therefore assessed the influence of environmental context (i.e. the characteristics of the landscape surrounding a site), varied over a large range of scales (i.e. ambit radii around focal sites), on the analysis and prediction of habitat selection by African elephants in Kruger National Park, South Africa. 3. We focused on the spatial scaling of the elephants' response to their main resources, forage and water, and found that the quantification of habitat selection strongly depended on the scales at which environmental context was considered. Moreover, the inclusion of environmental context at characteristic scales (i.e. those at which habitat selectivity was maximized) increased the predictive capacity of habitat suitability models. 4. The elephants responded to their environment in a scale-dependent and perhaps hierarchical manner, with forage characteristics driving habitat selection at coarse spatial scales, and surface water at fine spatial scales. 5. Furthermore, the elephants exhibited sexual habitat segregation, mainly in relation to vegetation characteristics. Male elephants preferred areas with high tree cover and low herbaceous biomass, whereas this pattern was reversed for female elephants. 6. We show that the spatial distribution of elephants can be better understood and predicted when scale-dependent species-environment relationships are explicitly considered. This demonstrates the importance of considering the influence of spatial scale on the analysis of spatial patterning in ecological phenomena. PMID:21054380

de Knegt, Henrik J; van Langevelde, Frank; Skidmore, Andrew K; Delsink, Audrey; Slotow, Rob; Henley, Steve; Bucini, Gabriela; de Boer, Willem F; Coughenour, Michael B; Grant, Cornelia C; Heitkönig, Ignas M A; Henley, Michelle; Knox, Nicky M; Kohi, Edward M; Mwakiwa, Emmanuel; Page, Bruce R; Peel, Mike; Pretorius, Yolanda; van Wieren, Sipke E; Prins, Herbert H T

2011-01-01

313

Strongly correlated electron systems  

Microsoft Academic Search

This special section is dedicated to the Strongly Correlated Electron Systems Conference (SCES) 2011, which was held from 29 August–3 September 2011, in Cambridge, UK. SCES'2011 is dedicated to 100 years of superconductivity and covers a range of topics in the area of strongly correlated systems. The correlated electronic and magnetic materials featured include f-electron based heavy fermion intermetallics and

Siddharth S Saxena; P B Littlewood

2012-01-01

314

The Relation Between Sandstorms and Strong Winds in Xinjiang, China  

Microsoft Academic Search

With observational data spanning 1961–1999 from 90 meteorological stations in Xinjiang, China, the spatial and temporal characteristics of sandstorms and strong winds, and the contribution of strong winds to the occurrence of sandstormsare analyzed. Moreover, the dominant wind direction and minimumwind speeds during sandstorm periods are discussed. The research shows that although possessing similar climatic trends, sandstorms and strong winds

Xu Wang; Yu Ma; Hongwu Chen; Gang Wen; Shoujun Chen; Zuyu Tao; Yong-Seung Chung

2003-01-01

315

Bioelasticity imaging:II. Spatial resolution  

NASA Astrophysics Data System (ADS)

The large elasticity contrast possible with strain imaging promises new diagnostic information to augment x-ray, MRI, and ultrasound for the detection of tumors in soft tissue. In the past, we described the design of an elastographic system using the Fourier crosstalk concept introduced by Barrett and Gifford. The diagonal of the crosstalk matrix is related to the pre-sampled modulation transfer function (MTF) of the strain image. Another approach to measuring the spatial resolution of an elasticity image employs a linear frequency- modulated (chirp) strain pattern imposed upon a simulated ultrasonic echo field to study the strain modulation over a range of spatial frequencies in the image. In experiments, high contrast inclusions positioned at varying separations were imaged to apply the Rayleigh criterion for resolution measurement. We measured MTF curves that fell to 0.2 at a spatial frequency of 0.5 mm-1 to 1 mm-1 under realistic conditions. The spatial resolution for ultrasonic strain imaging strongly depends on the transducer properties and deformation patterns applied to the object. Experiments with tissue-like phantoms mimicking the properties of early breast cancer show that 2 mm spheres three times stiffer than the background can be readily resolved. Thus, the potential for using elasticity imaging to detect early breast cancers is excellent.

Cook, Larry T.; Zhu, Yanning; Hall, Timothy J.; Insana, Michael F.

2000-04-01

316

Nova Spatial  

NSDL National Science Digital Library

Nova Spatial is a software firm which has developed GIS software for the Android (TM) mobile device platform. Products include pcMapper Lite and extensions that allow for creation of GIS shape files using just a standard smartphone.

Llc, Nova S.

317

REGULAR ARTICLE Reproductive Numbers for Nonautonomous Spatially  

E-print Network

REGULAR ARTICLE Reproductive Numbers for Nonautonomous Spatially Distributed Periodic SIS Models, aggregated, system. We derive global reproduction numbers governing the general spatially distributed and the frequency dependent transmission law are considered. Comparing these global reproductive numbers

Bravo de la Parra, Rafael

318

Implications of Strong-Rate-Weakening Friction  

E-print Network

Implications of Strong-Rate- Weakening Friction for the Length-Scale Dependence of the Strength · Rapid transitions between high static friction and very low dynamic friction · Leads to slip-pulse rupture · Slip pulses are extremely localized and have strong positive feedback between friction and slip

Greer, Julia R.

319

LHC Phenomenology and Lattice Strong Dynamics  

NASA Astrophysics Data System (ADS)

While the LHC experimentalists work to find evidence of physics beyond the standard model, lattice gauge theorists are working as well to characterize the range of possible phenomena in strongly-coupled models of electroweak symmetry breaking. I will summarize the current progress of the Lattice Strong Dynamics (LSD) collaboration on the flavor dependence of SU(3) gauge theories.

Fleming, G. T.

2013-03-01

320

High-resolution delineation of chlorinated volatile organic compounds in a dipping, fractured mudstone: Depth- and strata-dependent spatial variability from rock-core sampling  

NASA Astrophysics Data System (ADS)

Synthesis of rock-core sampling and chlorinated volatile organic compound (CVOC) analysis at five coreholes, with hydraulic and water-quality monitoring and a detailed hydrogeologic framework, was used to characterize the fine-scale distribution of CVOCs in dipping, fractured mudstones of the Lockatong Formation of Triassic age, of the Newark Basin in West Trenton, New Jersey. From these results, a refined conceptual model for more than 55 years of migration of CVOCs and depth- and strata-dependent rock-matrix contamination was developed. Industrial use of trichloroethene (TCE) at the former Naval Air Warfare Center (NAWC) from 1953 to 1995 resulted in dense non-aqueous phase liquid (DNAPL) TCE and dissolved TCE and related breakdown products, including other CVOCs, in underlying mudstones. Shallow highly weathered and fractured strata overlie unweathered, gently dipping, fractured strata that become progressively less fractured with depth. The unweathered lithology includes black highly fractured (fissile) carbon-rich strata, gray mildly fractured thinly layered (laminated) strata, and light-gray weakly fractured massive strata. CVOC concentrations in water samples pumped from the shallow weathered and highly fractured strata remain elevated near residual DNAPL TCE, but dilution by uncontaminated recharge, and other natural and engineered attenuation processes, have substantially reduced concentrations along flow paths removed from sources and residual DNAPL. CVOCs also were detected in most rock-core samples in source areas in shallow wells. In many locations, lower aqueous concentrations, compared to rock core concentrations, suggest that CVOCs are presently back-diffusing from the rock matrix. Below the weathered and highly fractured strata, and to depths of at least 50 meters (m), groundwater flow and contaminant transport is primarily in bedding-plane-oriented fractures in thin fissile high-carbon strata, and in fractured, laminated strata of the gently dipping mudstones. Despite more than 18 years of pump and treat (P&T) remediation, and natural attenuation processes, CVOC concentrations in aqueous samples pumped from these deeper strata remain elevated in isolated intervals. DNAPL was detected in one borehole during coring at a depth of 27 m. In contrast to core samples from the weathered zone, concentrations in core samples from deeper unweathered and unfractured strata are typically below detection. However, high CVOC concentrations were found in isolated samples from fissile black carbon-rich strata and fractured gray laminated strata. Aqueous-phase concentrations were correspondingly high in samples pumped from these strata via short-interval wells or packer-isolated zones in long boreholes. A refined conceptual site model considers that prior to P&T remediation groundwater flow was primarily subhorizontal in the higher-permeability near surface strata, and the bulk of contaminant mass was shallow. CVOCs diffused into these fractured and weathered mudstones. DNAPL and high concentrations of CVOCs migrated slowly down in deeper unweathered strata, primarily along isolated dipping bedding-plane fractures. After P&T began in 1995, using wells open to both shallow and deep strata, downward transport of dissolved CVOCs accelerated. Diffusion of TCE and other CVOCs from deeper fractures penetrated only a few centimeters into the unweathered rock matrix, likely due to sorption of CVOCs on rock organic carbon. Remediation in the deep, unweathered strata may benefit from the relatively limited migration of CVOCs into the rock matrix. Synthesis of rock core sampling from closely spaced boreholes with geophysical logging and hydraulic testing improves understanding of the controls on CVOC delineation and informs remediation design and monitoring.

Goode, Daniel J.; Imbrigiotta, Thomas E.; Lacombe, Pierre J.

2014-12-01

321

Task-dependent encoding of space and events by striatal neurons is dependent on neural subtype  

PubMed Central

The dorsal striatum plays a critical role in procedural learning and memory. Current models of basal ganglia assume that striatal neurons and circuitry are critical for the execution of over-learned, habitual sequences of action. However, less is known about how the striatum encodes task information that guides the performance of actions in procedural tasks. To explore the striatal encoding of task information, we compared the behavioral correlates of striatal neurons tested in two tasks: a Multiple-T-maze task in which reward delivery was entirely predictable based on spatial cues (the Multiple-T task), and a task in which rats ran on a rectangular track, but food delivery depended on the distance traveled on the track and was not dependent solely on spatial location (the Take-5 task). Striatal cells recorded on these tasks were divisible into three cell types: phasic-firing neurons (PFNs), tonically firing neurons (TFNs), and high-firing neurons (HFNs) and similar proportions of each cell type were found in each task. However, the behavioral correlates of each cell type were differentially sensitive to the type of task rats were performing. PFNs were responsive to specific task-parameters on each task. TFNs showed reliable burst-and-pause responses following food delivery and other events that were consistent with tonically active-neurons (TANs) on the Take-5 (non-spatial) task but not on the Multiple-T (spatial) task. HFNs showed spatial oscillations on the Multiple-T (spatial) task but not the Take-5 (non-spatial) task. Reconstruction of the rats’ position on the maze was highly accurate when using striatal ensembles recorded on the Multiple-T (spatial) task, but not when using ensembles recorded on the Take-5 (non-spatial) task. In contrast, reconstruction of time following food delivery was successful in both tasks. The results indicated a strong task dependency of the quality of the spatial, but not the reward-related, striatal representations on these tasks. These results suggest that striatal spatial representations depend on the degree to which spatial task-parameters can be unambiguously associated with goals. PMID:18406064

Schmitzer-Torbert, Neil C.; Redish, A. David

2013-01-01

322

Functional optical metamaterials employing spatial dispersion and absorption  

NASA Astrophysics Data System (ADS)

Functional optical metamaterials usually consist of absorbing, anisotropic and often non-centrosymmetric structures of a size that is only a few times smaller than the wavelength of visible light. If the structures would be substantially smaller, excitation of higher-order electromagnetic multipoles in them, including magnetic dipoles, would be inefficient. As a result, the material would act as an ordinary electric-dipole material. The required non-negligible size of metamolecules, however, makes the material spatially dispersive, so that its optical characteristics depend on light propagation direction. This phenomenon significantly complicates the description of metamaterials in terms of conventional electric permittivity and magnetic permeability tensors. In this work, we present a simple semianalytical method to describe such spatially dispersive metamaterials, which are also allowed to be optically anisotropic and non-centrosymmetric. Applying the method, we show that a strong spatial dispersion, combined with absorption and optical anisotropy, can be used to efficiently control propagational characteristics of optical beams.

Shevchenko, A.; Grahn, P.; Kaivola, M.

2014-09-01

323

Quantum Hydrodynamical Formulation of Time-Dependent Density Functional Theory for Probing Strong-Field Multiphoton Processes: Application to the Study of High-Order Harmonic Generation of He and Ne in Intense Laser Fields  

NASA Astrophysics Data System (ADS)

We extend the quantum hydrodynamical (QFD) formulation of time-dependent density functional theory (TDDFT) to the study of multiphoton processes of many-electron atomic systems in intense laser fields (A. K. Roy and S. I. Chu, Phys. Rev. A (in press).). The QFD-TDDFT formulation results in a single generalized nonlinear Schrodinger equation (GNLSE) and includes the many-body effects through a local time-dependent exchange-correlation (xc) potential. The GNLSE is solved by the time- dependent generalized pseudospectral method (X. M. Tong and S.I. Chu, Chem. Phys. 217) (1997) 119. (X. Chu and S. I. Chu, Phys. Rev. A 63) (2001) 023411.. The procedure is applied to the study of multiphoton ionization (MPI) and high harmonic generation (HHG) of He and Ne in intense laser fields. Four different xc energy functionals are used in the study with an aim to explore the roles of exchange and correlation ovn MPI/HHG processes in details ^1.

Roy, A. K.; Chu, Shih-I.

2002-05-01

324

Spatial Mass  

E-print Network

In analogy to the transverse mass constructed from two objects, we define the spatial mass constructed from the input objects 3-vector momenta. This observable is insensitive to jet mass scale and resolution uncertainties when constructed from small-radius hadronic jets. Thus it improves the effective resolution on multijet masses for searches and measurements in hadronic final states. To illustrate the efficacy of the spatial mass, we consider a top quark mass measurement at the Large Hadron Collider (LHC) in the 3-jet final state. The reduction in uncertainty comes with a negligible cost in sensitivity.

Nachman, Benjamin

2014-01-01

325

Spatial Mass  

E-print Network

In analogy to the transverse mass constructed from two objects, we define the spatial mass constructed from the input objects 3-vector momenta. This observable is insensitive to jet mass scale and resolution uncertainties when constructed from small-radius hadronic jets. Thus it improves the effective resolution on multijet masses for searches and measurements in hadronic final states. To illustrate the efficacy of the spatial mass, we consider a top quark mass measurement at the Large Hadron Collider (LHC) in the 3-jet final state. The reduction in uncertainty comes with a negligible cost in sensitivity.

Benjamin Nachman; Ariel Schwartzman

2014-07-08

326

Spatial propagation of protein polymerization.  

PubMed

We consider the spatial dependence of filamentous protein self-assembly. Through studying the cases where the spreading of aggregated material is dominated either by diffusion or by growth, we derive analytical results for the spatial evolution of filamentous protein aggregation, which we validate against Monte Carlo simulations. Moreover, we compare the predictions of our theory with experimental measurements of two systems for which we identify the propagation as either growth or diffusion controlled. Our results connect the macroscopic observables that characterize the spatial propagation of protein self-assembly with the underlying microscopic processes and provide physical limits on spatial propagation and prionlike behavior associated with protein aggregation. PMID:24655282

Cohen, S I A; Rajah, L; Yoon, C H; Buell, A K; White, D A; Sperling, R A; Vendruscolo, M; Terentjev, E M; Dobson, C M; Weitz, D A; Knowles, T P J

2014-03-01

327

Strong Autonomy and Education.  

ERIC Educational Resources Information Center

Suggests that the possibilities available to autonomy- oriented educators may be quite limited and fall far short of what they think them to be, discussing independence and autonomy, knowledge and autonomy, weak and strong autonomy, and autonomy and education, and concluding that the anti-perfectionist liberal policy is not committed to the…

Winch, Christopher

2002-01-01

328

Strong Colorings of Hypergraphs  

Microsoft Academic Search

A strong vertex coloring of a hypergraph assigns distinct col- ors to vertices that are contained in a common hyperedge. This captures many previously studied graph coloring problems. We present nearly tight upper and lower bound on approximating general hypergraphs, both oine and online. We then consider various parameters that make coloring easier, and give a unied treatment. In particular,

Geir Agnarsson; Magnús M. Halldórsson

2004-01-01

329

Spatial networks  

NASA Astrophysics Data System (ADS)

Complex systems are very often organized under the form of networks where nodes and edges are embedded in space. Transportation and mobility networks, Internet, mobile phone networks, power grids, social and contact networks, and neural networks, are all examples where space is relevant and where topology alone does not contain all the information. Characterizing and understanding the structure and the evolution of spatial networks is thus crucial for many different fields, ranging from urbanism to epidemiology. An important consequence of space on networks is that there is a cost associated with the length of edges which in turn has dramatic effects on the topological structure of these networks. We will thoroughly explain the current state of our understanding of how the spatial constraints affect the structure and properties of these networks. We will review the most recent empirical observations and the most important models of spatial networks. We will also discuss various processes which take place on these spatial networks, such as phase transitions, random walks, synchronization, navigation, resilience, and disease spread.

Barthélemy, Marc

2011-02-01

330

Strong nonlocal interaction stabilizes cavity solitons with a varying size plateau  

NASA Astrophysics Data System (ADS)

Cavity solitons are localized light peaks in the transverse section of nonlinear resonators. These structures are usually formed under a coexistence condition between a homogeneous background of radiation and a self- organized patterns resulting from a Turing type of instabilities. In this issue, most of studies have been realized ignoring the nonlocal e?ects. Non-local e?ects can play an important role in the formation of cavity solitons in optics, population dynamics and plant ecology. Depending on the choice of the nonlocal interaction function, the nonlocal coupling can be strong or weak. When the nonlocal coupling is strong, the interaction between fronts is controlled by the whole non-local interaction function. Recently it has shown that this type of nonlocal coupling strongly a?ects the dynamics of fronts connecting two homogeneous steady states and leads to the stabilization of cavity solitons with a varying size plateau. Here, we consider a ring passive cavity filled with a Kerr medium like a liquid crystal or left-handed materials and driven by a coherent injected beam. We show that cavity solitons resulting for strong front interaction are stable in one and two-dimensional setting out of any type of Turing instability. Their spatial profile is characterized by a varying size plateau. Our results can apply to large class of spatially extended systems with strong nonlocal coupling.

Fernandez-Oto, Cristian; Tlidi, Mustapha; Escaff, Daniel; Clerc, Marcel; Kockaert, Pascal

2014-05-01

331

One spatial map or many? Spatial coding of connected environments.  

PubMed

We investigated how humans encode large-scale spatial environments using a virtual taxi game. We hypothesized that if 2 connected neighborhoods are explored jointly, people will form a single integrated spatial representation of the town. However, if the neighborhoods are first learned separately and later observed to be connected, people will form separate spatial representations; this should incur an accuracy cost when inferring directions from one neighborhood to the other. Interestingly, our data instead suggest that people have a very strong tendency to form local representations, regardless of whether the neighborhoods were learned together or separately. Only when all visible distinctions between neighborhoods were removed did people behave as if they formed one integrated spatial representation. These data are broadly consistent with evidence from rodent hippocampal place cell recordings in connected boxes, and with hierarchical models of spatial coding. PMID:24364723

Han, Xue; Becker, Suzanna

2014-03-01

332

Spatially confined assembly of nanoparticles.  

PubMed

Conspectus The ability to assemble NPs into ordered structures that are expected to yield collective physical or chemical properties has afforded new and exciting opportunities in the field of nanotechnology. Among the various configurations of nanoparticle assemblies, two-dimensional (2D) NP patterns and one-dimensional (1D) NP arrays on surfaces are regarded as the ideal assembly configurations for many technological devices, for example, solar cells, magnetic memory, switching devices, and sensing devices, due to their unique transport phenomena and the cooperative properties of NPs in assemblies. To realize the potential applications of NP assemblies, especially in nanodevice-related applications, certain key issues must still be resolved, for example, ordering and alignment, manipulating and positioning in nanodevices, and multicomponent or hierarchical structures of NP assemblies for device integration. Additionally, the assembly of NPs with high precision and high levels of integration and uniformity for devices with scaled-down dimensions has become a key and challenging issue. Two-dimensional NP patterns and 1D NP arrays are obtained using traditional lithography techniques (top-down strategies) or interfacial assembly techniques (bottom-up strategies). However, a formidable challenge that persists is the controllable assembly of NPs in desired locations over large areas with high precision and high levels of integration. The difficulty of this assembly is due to the low efficiency of small features over large areas in lithography techniques or the inevitable structural defects that occur during the assembly process. The combination of self-assembly strategies with existing nanofabrication techniques could potentially provide effective and distinctive solutions for fabricating NPs with precise position control and high resolution. Furthermore, the synergistic combination of spatially mediated interactions between nanoparticles and prestructures on surfaces may play an increasingly important role in the controllable assembly of NPs. In this Account, we summarize our approaches and progress in fabricating spatially confined assemblies of NPs that allow for the positioning of NPs with high resolution and considerable throughput. The spatially selective assembly of NPs at the desired location can be achieved by various mechanisms, such as, a controlled dewetting process, electrostatically mediated assembly of particles, and confined deposition and growth of NPs. Three nanofabrication techniques used to produce prepatterns on a substrate are summarized: the Langmuir-Blodgett (LB) patterning technique, e-beam lithography (EBL), and nanoimprint lithography (NPL). The particle density, particle size, or interparticle distance in NP assemblies strongly depends on the geometric parameters of the template structure due to spatial confinement. In addition, with smart design template structures, multiplexed NPs can be assembled into a defined structure, thus demonstrating the structural and functional complexity required for highly integrated and multifunction applications. PMID:25244100

Jiang, Lin; Chen, Xiaodong; Lu, Nan; Chi, Lifeng

2014-10-21

333

Natural auditory scene statistics shapes human spatial hearing  

PubMed Central

Human perception, cognition, and action are laced with seemingly arbitrary mappings. In particular, sound has a strong spatial connotation: Sounds are high and low, melodies rise and fall, and pitch systematically biases perceived sound elevation. The origins of such mappings are unknown. Are they the result of physiological constraints, do they reflect natural environmental statistics, or are they truly arbitrary? We recorded natural sounds from the environment, analyzed the elevation-dependent filtering of the outer ear, and measured frequency-dependent biases in human sound localization. We find that auditory scene statistics reveals a clear mapping between frequency and elevation. Perhaps more interestingly, this natural statistical mapping is tightly mirrored in both ear-filtering properties and in perceived sound location. This suggests that both sound localization behavior and ear anatomy are fine-tuned to the statistics of natural auditory scenes, likely providing the basis for the spatial connotation of human hearing. PMID:24711409

Parise, Cesare V.; Knorre, Katharina; Ernst, Marc O.

2014-01-01

334

Contextual neural gas for spatial clustering and analysis  

Microsoft Academic Search

This study aims to introduce contextual Neural Gas (CNG), a variant of the Neural Gas algorithm, which explicitly accounts for spatial dependencies within spatial data. The main idea of the CNG is to map spatially close observations to neurons, which are close with respect to their rank distance. Thus, spatial dependency is incorporated independently from the attribute values of the

Julian Hagenauer; Marco Helbich

2012-01-01

335

The effect of grazing on the spatial heterogeneity of vegetation  

Microsoft Academic Search

Grazing can alter the spatial heterogeneity of vegetation, influencing ecosystem processes and biodiversity. Our objective was to identify why grazing causes increases in the spatial heterogeneity of vegetation in some cases, but decreases in others. The immediate effect of grazing on heterogeneity depends on the interaction between the spatial pattern of grazing and the pre-existing spatial pattern of vegetation. Depending

P. B. Adler; D. A. Raff; W. K. Lauenroth

2001-01-01

336

Strong Imbalanced Turbulence  

E-print Network

We consider stationary, forced, imbalanced, or cross-helical MHD Alfvenic turbulence where the waves traveling in one direction have higher amplitudes than the opposite waves. This paper is dedicated to so-called strong turbulence, which cannot be treated perturbatively. Our main result is that the anisotropy of the weak waves is stronger than the anisotropy of a strong waves. We propose that critical balance, which was originally conceived as a causality argument, has to be amended by what we call a propagation argument. This revised formulation of critical balance is able to handle the imbalanced case and reduces to old formulation in the balanced case. We also provide phenomenological model of energy cascading and discuss possibility of self-similar solutions in a realistic setup of driven turbulence.

A. Beresnyak; A. Lazarian

2007-09-05

337

Strong Electroweak Symmetry Breaking  

E-print Network

Models of spontaneous breaking of electroweak symmetry by a strong interaction do not have fine tuning/hierarchy problem. They are conceptually elegant and use the only mechanism of spontaneous breaking of a gauge symmetry that is known to occur in nature. The simplest model, minimal technicolor with extended technicolor interactions, is appealing because one can calculate by scaling up from QCD. But it is ruled out on many counts: inappropriately low quark and lepton masses (or excessive FCNC), bad electroweak data fits, light scalar and vector states, etc. However, nature may not choose the minimal model and then we are stuck: except possibly through lattice simulations, we are unable to compute and test the models. In the LHC era it therefore makes sense to abandon specific models (of strong EW breaking) and concentrate on generic features that may indicate discovery. The Technicolor Straw Man is not a model but a parametrized search strategy inspired by a remarkable generic feature of walking technicolor,...

Grinstein, Benjamin

2011-01-01

338

Strongly interacting Higgs bosons  

Microsoft Academic Search

The sensitivity of present-energy weak interactions to a strongly interacting heavy-Higgs-boson sector is discussed. The gauged nonlinear sigma model, which is the limit of the linear model as the Higgs-boson mass goes to infinity, is used to organize and catalogue all possible heavy-Higgs-boson effects. As long as the SU(2)L×SU(2)R symmetry of the Higgs sector is preserved, these effects are found

Thomas Appelquist; Claude Bernard

1980-01-01

339

Living Bones, Strong Bones  

NSDL National Science Digital Library

In this activity about engineering, nutrition, and physical activity, learners design and build a healthy bone model of a space explorer which is strong enough to withstand increasing amounts of weight. This activity contains several engaging mini-activities and stresses the importance of the scientific method. Learners can complete this activity as part of NASA's Fit Explorer Challenge, in which learners train like astronauts, set goals, track their progress, and accumulate points to progress through Exploration Levels and earn certificates.

Center, Nasa J.

2012-06-26

340

Strong-motion seismology  

Microsoft Academic Search

Although this is the first review on this topic to appear in a quadrennial report, the roots of strong-motion seismology extend back to at least 1932, when far-sighted engineers in the Seismological Field Survey of the U. S. Coast and Geodetic Survey installed rugged, fieldworthy instruments designed to make on-scale recordings of large earthquakes (Carder, 1964); these instruments are called

David M. Boore

1983-01-01

341

Spatial anxiety relates to spatial abilities as a function of working memory in children  

Microsoft Academic Search

Spatial ability is a strong predictor of students' pursuit of higher education in science and mathematics. However, very little is known about the affective factors that influence individual differences in spatial ability, particularly at a young age. We examine the role of spatial anxiety in young children's performance on a mental rotation task. We show that even at a young

Gerardo Ramirez; Elizabeth A. Gunderson; Susan C. Levine; Sian L. Beilock

2012-01-01

342

Spatial Variability of Snowpack Properties On Small Slopes  

NASA Astrophysics Data System (ADS)

The spatial variability of alpine snowpacks is created by a variety of parameters like deposition, wind erosion, sublimation, melting, temperature, radiation and metamor- phism of the snow. Spatial variability is thought to strongly control the avalanche initi- ation and failure propagation processes. Local snowpack measurements are currently the basis for avalanche warning services and there exist contradicting hypotheses about the spatial continuity of avalanche active snow layers and interfaces. Very little about the spatial variability of the snowpack is known so far, therefore we have devel- oped a systematic and objective method to measure the spatial variability of snowpack properties, layering and its relation to stability. For a complete coverage, the analysis of the spatial variability has to entail all scales from mm to km. In this study the small to medium scale spatial variability is investigated, i.e. the range from centimeters to tenths of meters. During the winter 2000/2001 we took systematic measurements in lines and grids on a flat snow test field with grid distances from 5 cm to 0.5 m. Fur- thermore, we measured systematic grids with grid distances between 0.5 m and 2 m in undisturbed flat fields and on small slopes above the tree line at the Choerbschhorn, in the region of Davos, Switzerland. On 13 days we measured the spatial pattern of the snowpack stratigraphy with more than 110 snow micro penetrometer measure- ments at slopes and flat fields. Within this measuring grid we placed 1 rutschblock and 12 stuffblock tests to measure the stability of the snowpack. With the large num- ber of measurements we are able to use geostatistical methods to analyse the spatial variability of the snowpack. Typical correlation lengths are calculated from semivari- ograms. Discerning the systematic trends from random spatial variability is analysed using statistical models. Scale dependencies are shown and recurring scaling patterns are outlined. The importance of the small and medium scale spatial variability for the larger (kilometer) scale spatial variability as well as for the avalanche formation are discussed. Finally, an outlook on spatial models for the snowpack variability is given.

Pielmeier, C.; Kronholm, K.; Schneebeli, M.; Schweizer, J.

343

Strong interaction and QFD  

NASA Astrophysics Data System (ADS)

With an assumed weak multiplet structure for bosonic hadrons, which is consistent with the ?I = {1}/{2} rule, it is shown that the strong interaction effective hamiltonian is compatible with the weak SU(2) × U(1) gauge transformation. Especially the ?-meson transformation as a triplet under SU(2) W, and this is the origin of the ?-photon analogy. It is also shown that the existence of the non-vanishing Cabibbo angle is a necessary condition for the absence of the exotic hadrons.

Ebata, Takeshi

1981-08-01

344

Time Dependence Time Dependence  

E-print Network

Time Dependence 1/60 #12;Time Dependence deadline:= t + 5 2/60 #12;Time Dependence deadline:= t + 5 no problem 3/60 #12;Time Dependence deadline:= t + 5 no problem if t ;Time Dependence deadline:= t + 5 no problem if t Time

Hehner, Eric C.R.

345

LETTER Communicated by Bruno Averbeck Stimulus-Dependent Correlations and Population Codes  

E-print Network

of additional strong spatial decay of correla- tions, such stimulus dependence may have a negative impact in the neural response have the potential to both positively and negatively affect the ability of a population Computation 21, 2774­2804 (2009) C 2009 Massachusetts Institute of Technology #12;Stimulus

Doiron, Brent

346

Strongly correlating liquids and their isomorphs  

E-print Network

This paper summarizes the properties of strongly correlating liquids, i.e., liquids with strong correlations between virial and potential energy equilibrium fluctuations at constant volume. We proceed to focus on the experimental predictions for strongly correlating glass-forming liquids. These predictions include i) density scaling, ii) isochronal superposition, iii) that there is a single function from which all frequency-dependent viscoelastic response functions may be calculated, iv) that strongly correlating liquids are approximately single-parameter liquids with close to unity Prigogine-Defay ratio, and v) that the fictive temperature initially decreases for an isobaric temperature up jump. The "isomorph filter", which allows one to test for universality of theories for the non-Arrhenius temperature dependence of the relaxation time, is also briefly discussed.

Ulf R. Pedersen; Nicoletta Gnan; Nicholas P. Bailey; Thomas B. Schröder; Jeppe C. Dyre

2010-04-07

347

Relaxation polarizations: Strong and weak processes  

NASA Astrophysics Data System (ADS)

It has been shown that the through conductivity can differently affect the frequency dependences of the dielectric loss tangent of dielectrics with relaxation polarization. According to this difference, the relaxations in dielectrics are divided into two types: strong and weak. In the case of strong relaxations, the frequency dependences of the imaginary part of the complex conductivity exhibit extrema. Strong and weak relaxations have been investigated in Debye and in non-Debye dielectrics in order to determine the boundary between these processes and explain the existence of relaxations of two types. It has been established that the relaxations in dielectrics can be separated because of the different ratios of the contributions to the polarization of dielectrics from the fast and relaxation polarizations. The corresponding data in the literature are reviewed and the data on the development of strong relaxations in heterogeneous dielectrics are reported.

Bogatin, A. S.

2012-01-01

348

Identity Crises and Strong Compactness II: Strong Cardinals  

E-print Network

the general field of "identity crisis studies", there has been additional, extensive resear* *ch done Identity Crises and Strong Compactness II: Strong Cardinals of Magidor, that the class of strongly compact cardinals can assume yet another identity. Specifically, we

Cummings, James

349

Strongly correlated materials.  

PubMed

Strongly correlated materials are profoundly affected by the repulsive electron-electron interaction. This stands in contrast to many commonly used materials such as silicon and aluminum, whose properties are comparatively unaffected by the Coulomb repulsion. Correlated materials often have remarkable properties and transitions between distinct, competing phases with dramatically different electronic and magnetic orders. These rich phenomena are fascinating from the basic science perspective and offer possibilities for technological applications. This article looks at these materials through the lens of research performed at Rice University. Topics examined include: Quantum phase transitions and quantum criticality in "heavy fermion" materials and the iron pnictide high temperature superconductors; computational ab initio methods to examine strongly correlated materials and their interface with analytical theory techniques; layered dichalcogenides as example correlated materials with rich phases (charge density waves, superconductivity, hard ferromagnetism) that may be tuned by composition, pressure, and magnetic field; and nanostructure methods applied to the correlated oxides VO? and Fe?O?, where metal-insulator transitions can be manipulated by doping at the nanoscale or driving the system out of equilibrium. We conclude with a discussion of the exciting prospects for this class of materials. PMID:22893361

Morosan, Emilia; Natelson, Douglas; Nevidomskyy, Andriy H; Si, Qimiao

2012-09-18

350

Strong Electroweak Symmetry Breaking  

E-print Network

Models of spontaneous breaking of electroweak symmetry by a strong interaction do not have fine tuning/hierarchy problem. They are conceptually elegant and use the only mechanism of spontaneous breaking of a gauge symmetry that is known to occur in nature. The simplest model, minimal technicolor with extended technicolor interactions, is appealing because one can calculate by scaling up from QCD. But it is ruled out on many counts: inappropriately low quark and lepton masses (or excessive FCNC), bad electroweak data fits, light scalar and vector states, etc. However, nature may not choose the minimal model and then we are stuck: except possibly through lattice simulations, we are unable to compute and test the models. In the LHC era it therefore makes sense to abandon specific models (of strong EW breaking) and concentrate on generic features that may indicate discovery. The Technicolor Straw Man is not a model but a parametrized search strategy inspired by a remarkable generic feature of walking technicolor, that technivector mesons are light, narrow and decay readily into electroweak vector mesons and photons. While walking technicolor is popular among practitioners, alternatives exist and the Straw Man may not lead to their discovery.

Benjamin Grinstein

2011-02-19

351

PREFACE: Strongly correlated electron systems Strongly correlated electron systems  

NASA Astrophysics Data System (ADS)

This special section is dedicated to the Strongly Correlated Electron Systems Conference (SCES) 2011, which was held from 29 August-3 September 2011, in Cambridge, UK. SCES'2011 is dedicated to 100 years of superconductivity and covers a range of topics in the area of strongly correlated systems. The correlated electronic and magnetic materials featured include f-electron based heavy fermion intermetallics and d-electron based transition metal compounds. The selected papers derived from invited presentations seek to deepen our understanding of the rich physical phenomena that arise from correlation effects. The focus is on quantum phase transitions, non-Fermi liquid phenomena, quantum magnetism, unconventional superconductivity and metal-insulator transitions. Both experimental and theoretical work is presented. Based on fundamental advances in the understanding of electronic materials, much of 20th century materials physics was driven by miniaturisation and integration in the electronics industry to the current generation of nanometre scale devices. The achievements of this industry have brought unprecedented advances to society and well-being, and no doubt there is much further to go—note that this progress is founded on investments and studies in the fundamentals of condensed matter physics from more than 50 years ago. Nevertheless, the defining challenges for the 21st century will lie in the discovery in science, and deployment through engineering, of technologies that can deliver the scale needed to have an impact on the sustainability agenda. Thus the big developments in nanotechnology may lie not in the pursuit of yet smaller transistors, but in the design of new structures that can revolutionise the performance of solar cells, batteries, fuel cells, light-weight structural materials, refrigeration, water purification, etc. The science presented in the papers of this special section also highlights the underlying interest in energy-dense materials, which make use of 'small' electrons packed to the highest possible density. These are by definition 'strongly correlated'. For example: good photovoltaics must be efficient optical absorbers, which means that photons will generate tightly bound electron-hole pairs (excitons) that must then be ionised at a heterointerface and transported to contacts; efficient solid state refrigeration depends on substantial entropy changes in a unit cell, with large local electrical or magnetic moments; efficient lighting is in a real sense the inverse of photovoltaics; the limit of an efficient battery is a supercapacitor employing mixed valent ions; fuel cells and solar to fuel conversion require us to understand electrochemistry on the scale of a single atom; and we already know that the only prospect for effective high temperature superconductivity involves strongly correlated materials. Even novel IT technologies are now seen to have value not just for novel function but also for efficiency. While strongly correlated electron systems continue to excite researchers and the public alike due to the fundamental science issues involved, it seems increasingly likely that support for the science will be leveraged by its impact on energy and sustainability. Strongly correlated electron systems contents Strongly correlated electron systemsSiddharth S Saxena and P B Littlewood Magnetism, f-electron localization and superconductivity in 122-type heavy-fermion metalsF Steglich, J Arndt, O Stockert, S Friedemann, M Brando, C Klingner, C Krellner, C Geibel, S Wirth, S Kirchner and Q Si High energy pseudogap and its evolution with doping in Fe-based superconductors as revealed by optical spectroscopyN L Wang, W Z Hu, Z G Chen, R H Yuan, G Li, G F Chen and T Xiang Structural investigations on YbRh2Si2: from the atomic to the macroscopic length scaleS Wirth, S Ernst, R Cardoso-Gil, H Borrmann, S Seiro, C Krellner, C Geibel, S Kirchner, U Burkhardt, Y Grin and F Steglich Confinement of chiral magnetic modulations in the precursor region of FeGeH Wilhelm, M Baenitz, M Schmidt, C Naylor, R Lortz, U

Saxena, Siddharth S.; Littlewood, P. B.

2012-07-01

352

Phase transitions driven by state-dependent poisson noise.  

PubMed

Nonlinear systems driven by state-dependent Poisson noise are introduced to model the persistence of climatic anomalies in land-atmosphere interaction caused by the soil-moisture dependence of the frequency of rainfall events. It is found that these systems may give rise to bimodal probability distributions, while the state variable randomly persists around the preferential states because of transient dynamics that are opposite to the long-term behavior. Mean-field analysis and numerical simulations of the spatially distributed systems reveal a symmetry-breaking bifurcation for sufficiently strong spatial diffusive couplings and intermediate noise intensities. In such conditions, the initial development of spatial patterns is followed by a stable configuration, selected on the bases of the initial conditions in correspondence of the remnants of the modes of the uncoupled system. PMID:15089118

Porporato, Amilcare; D'Odorico, Paolo

2004-03-19

353

Numerical micromagnetism of strong inhomogeneities  

E-print Network

The size of micromagnetic structures, such as domain walls or vortices, is comparable to the exchange length of the ferromagnet. Both, the exchange length of the stray field $l_s$ and the magnetocrystalline exchange length $l_k$ are material-dependent quantities that usually lie in the nanometer range. This emphasizes the theoretical challenges associated with the mesoscopic nature of micromagnetism: the magnetic structures are much larger than the atomic lattice constant, but at the same time much smaller than the sample size. In computer simulations, the smallest exchange length serves as an estimate for the largest cell size admissible to prevent appreciable discretization errors. This general rule is not valid in special situations where the magnetization becomes particularly inhomogeneous. When such strongly inhomogeneous structures develop, micromagnetic simulations inevitably contain systematic and numerical errors. It is suggested to combine micromagnetic theory with a Heisenberg model to resolve such...

Andreas, Christian; Hertel, Riccardo

2014-01-01

354

Strong, Lightweight, Porous Materials  

NASA Technical Reports Server (NTRS)

A new class of strong, lightweight, porous materials has been invented as an outgrowth of an effort to develop reinforced silica aerogels. The new material, called X-Aerogel is less hygroscopic, but no less porous and of similar density to the corresponding unmodified aerogels. However, the property that sets X-Aerogels apart is their mechanical strength, which can be as much as two and a half orders of magnitude stronger that the unmodified aerogels. X-Aerogels are envisioned to be useful for making extremely lightweight, thermally insulating, structural components, but they may also have applications as electrical insulators, components of laminates, catalyst supports, templates for electrode materials, fuel-cell components, and filter membranes.

Leventis, Nicholas; Meador, Mary Ann B.; Johnston, James C.; Fabrizio, Eve F.; Ilhan, Ulvi

2007-01-01

355

Numerical micromagnetism of strong inhomogeneities  

NASA Astrophysics Data System (ADS)

The size of micromagnetic structures, such as domain walls or vortices, is comparable to the exchange length of the ferromagnet. Both, the exchange length of the stray field ls and the magnetocrystalline exchange length lk, are material-dependent quantities that usually lie in the nanometer range. This emphasizes the theoretical challenges associated with the mesoscopic nature of micromagnetism: the magnetic structures are much larger than the atomic lattice constant, but at the same time much smaller than the sample size. In computer simulations, the smallest exchange length serves as an estimate for the largest cell size admissible to prevent appreciable discretization errors. This general rule is not valid in special situations where the magnetization becomes particularly inhomogeneous. When such strongly inhomogeneous structures develop, micromagnetic simulations inevitably contain systematic and numerical errors. It is suggested to combine micromagnetic theory with a Heisenberg model to resolve such problems. We analyze cases where strongly inhomogeneous structures pose limits to standard micromagnetic simulations, arising from fundamental aspects as well as from numerical drawbacks.

Andreas, Christian; Gliga, Sebastian; Hertel, Riccardo

2014-08-01

356

Spatial autocorrelation in farmland grasshopper assemblages (Orthoptera: Acrididae) in western France.  

PubMed

Agricultural intensification in western Europe has caused a dramatic loss of grassland surfaces in farmlands, which have resulted in strong declines in grassland invertebrates, leading to cascade effects at higher trophic levels among consumers of invertebrates. Grasshoppers are important components of grassland invertebrate assemblages in European agricultural ecosystems, particularly as prey for bird species. Understanding how grasshopper populations are distributed in fragmented landscapes with low grassland availability is critical for both studies in biodiversity conservation and insect management. We assessed the range and strength of spatial autocorrelation for two grasshopper taxa (Gomphocerinae subfamily and Calliptamus italicus L.) across an intensive farmland in western France. Data from surveys carried out over 8 yr in 1,715 grassland fields were analyzed using geostatistics. Weak spatial patterns were observed at small spatial scales, suggesting important local effects of management practices on grasshopper densities. Spatial autocorrelation patterns for both grasshopper taxa were only detected at intermediate scales. For Gomphocerinae, the range of spatial autocorrelation varied from 802 to 2,613 m according to the year, depending both on grasshopper density and on grassland surfaces in the study site, whereas spatial patterns for the Italian locust were more variable and not related to grasshopper density or grassland surfaces. Spatial patterns in the distribution of Gomphocerinae supported our hypothesis that habitat availability was a major driver of grasshopper distribution in the landscape, and suggested it was related to density-dependent processes such as dispersal. PMID:23068160

Badenhausser, I; Gouat, M; Goarant, A; Cornulier, T; Bretagnolle, V

2012-10-01

357

Explosion Source Strong Ground Motions in the Mississippi Embayment  

Microsoft Academic Search

Two strong-motion arrays were deployed for the October 2002 Embay- ment Seismic Excitation Experiment to study the spatial variation of strong ground motions in the deep, unconsolidated sediments of the Mississippi embayment because there are no comparable strong-motion data from natural earthquakes in the area. Each linear array consisted of eight three-component K2 accelerographs spaced 15 m apart situated 1.2

Charles A. Langston; Paul Bodin; Christine Powell; Mitch Withers; Steve Horton; Walter Mooney

2006-01-01

358

Spatial effects in real networks: Measures, null models, and applications  

NASA Astrophysics Data System (ADS)

Spatially embedded networks are shaped by a combination of purely topological (space-independent) and space-dependent formation rules. While it is quite easy to artificially generate networks where the relative importance of these two factors can be varied arbitrarily, it is much more difficult to disentangle these two architectural effects in real networks. Here we propose a solution to this problem, by introducing global and local measures of spatial effects that, through a comparison with adequate null models, effectively filter out the spurious contribution of nonspatial constraints. Our filtering allows us to consistently compare different embedded networks or different historical snapshots of the same network. As a challenging application we analyze the World Trade Web, whose topology is known to depend on geographic distances but is also strongly determined by nonspatial constraints (degree sequence or gross domestic product). Remarkably, we are able to detect weak but significant spatial effects both locally and globally in the network, showing that our method succeeds in retrieving spatial information even when nonspatial factors dominate. We finally relate our results to the economic literature on gravity models and trade globalization.

Ruzzenenti, Franco; Picciolo, Francesco; Basosi, Riccardo; Garlaschelli, Diego

2012-12-01

359

Communication with spatially modulated Light through turbulent Air across Vienna  

E-print Network

The transverse spatial modes of light offer a large state-space with interesting physical properties. For exploiting it in future long-distance experiments, spatial modes will have to be transmitted over turbulent free-space links. Numerous recent lab-scale experiments have found significant degradation in the mode quality after transmission through simulated turbulence and consecutive coherent detection. Here we experimentally analyze the transmission of one prominent class of spatial modes, the orbital-angular momentum (OAM) modes, through 3 km of strong turbulence over the city of Vienna. Instead of performing a coherent phase-dependent measurement, we employ an incoherent detection scheme which relies on the unambiguous intensity patterns of the different spatial modes. We use a pattern recognition algorithm (an artificial neural network) to identify the characteristic mode pattern displayed on a screen at the receiver. We were able to distinguish between 16 different OAM mode superpositions with only ~1.7% error, and use them to encode and transmit small grey-scale images. Moreover, we found that the relative phase of the superposition modes is not affected by the atmosphere, establishing the feasibility for performing long-distance quantum experiments with the OAM of photons. Our detection method works for other classes of spatial modes with unambiguous intensity patterns as well, and can further be improved by modern techniques of pattern recognition.

Mario Krenn; Robert Fickler; Matthias Fink; Johannes Handsteiner; Mehul Malik; Thomas Scheidl; Rupert Ursin; Anton Zeilinger

2014-02-11

360

Strong-interaction nonuniversality  

SciTech Connect

The universal QCD color theory is extended to an SU(3)/sub 1//direct product/SU(3)/sub 2//direct product/SU(3)/sub 3/ gauge theory, where quarks of the /ital i/th generation transform as triplets under SU(3)/sub /ital i// and singlets under the other two factors. The usual color group is then identified with the diagonal subgroup, which remains exact after symmetry breaking. The gauge bosons associated with the 16 broken generators then form two massive octets under ordinary color. The interactions between quarks and these heavy gluonlike particles are explicitly nonuniversal and thus an exploration of their physical implications allows us to shed light on the fundamental issue of strong-interaction universality. Nonuniversality and weak flavor mixing are shown to generate heavy-gluon-induced flavor-changing neutral currents. The phenomenology of these processes is studied, as they provide the major experimental constraint on the extended theory. Three symmetry-breaking scenarios are presented. The first has color breaking occurring at the weak scale, while the second and third divorce the two scales. The third model has the interesting feature of radiatively induced off-diagonal Kobayashi-Maskawa matrix elements.

Volkas, R. R.; Foot, R.; He, X.; Joshi, G. C.

1989-07-01

361

Invasion and adaptive evolution for individual-based spatially structured populations.  

PubMed

The interplay between space and evolution is an important issue in population dynamics, that is particularly crucial in the emergence of polymorphism and spatial patterns. Recently, biological studies suggest that invasion and evolution are closely related. Here, we model the interplay between space and evolution starting with an individual-based approach and show the important role of parameter scalings on clustering and invasion. We consider a stochastic discrete model with birth, death, competition, mutation and spatial diffusion, where all the parameters may depend both on the position and on the phenotypic trait of individuals. The spatial motion is driven by a reflected diffusion in a bounded domain. The interaction is modelled as a trait competition between individuals within a given spatial interaction range. First, we give an algorithmic construction of the process. Next, we obtain large population approximations, as weak solutions of nonlinear reaction-diffusion equations. As the spatial interaction range is fixed, the nonlinearity is nonlocal. Then, we make the interaction range decrease to zero and prove the convergence to spatially localized nonlinear reaction-diffusion equations. Finally, a discussion of three concrete examples is proposed, based on simulations of the microscopic individual-based model. These examples illustrate the strong effects of the spatial interaction range on the emergence of spatial and phenotypic diversity (clustering and polymorphism) and on the interplay between invasion and evolution. The simulations focus on the qualitative differences between local and nonlocal interactions. PMID:17554541

Champagnat, Nicolas; Méléard, Sylvie

2007-08-01

362

CMEIAS-aided microscopy of the spatial ecology of individual bacterial interactions involving cell-to-cell communication within biofilms.  

PubMed

This paper describes how the quantitative analytical tools of CMEIAS image analysis software can be used to investigate in situ microbial interactions involving cell-to-cell communication within biofilms. Various spatial pattern analyses applied to the data extracted from the 2-dimensional coordinate positioning of individual bacterial cells at single-cell resolution indicate that microbial colonization within natural biofilms is not a spatially random process, but rather involves strong positive interactions between communicating cells that influence their neighbors' aggregated colonization behavior. Geostatistical analysis of the data provide statistically defendable estimates of the micrometer scale and interpolation maps of the spatial heterogeneity and local intensity at which these microbial interactions autocorrelate with their spatial patterns of distribution. Including in situ image analysis in cell communication studies fills an important gap in understanding the spatially dependent microbial ecophysiology that governs the intensity of biofilm colonization and its unique architecture. PMID:22969336

Dazzo, Frank B

2012-01-01

363

Spatial distribution of absorption in plasmonic thin film solar cells.  

PubMed

The spatial dependence of absorption in a structured thin film solar cell is investigated through the rigorous coupled-wave analysis method. The investigated structure allows strong localized surface plasmon and surface plasmon polaritons, simultaneously. The absorptance of silver and amorphous silicon can be separately accounted for by calculating the time-averaged energy dissipation although only the absorption of amorphous silicon contributes to the photocurrent. In our studied case, the metallic material absorbs around 15%-20% of the total impinging sunlight while the active layer absorbs only approximately 50%. PMID:20589037

Chao, Chien-Chang; Wang, Chih-Ming; Chang, Jenq-Yang

2010-05-24

364

Interplay between mutational pathway and spatial drug distribution controls time to evolution of drug resistance  

E-print Network

Spatial gradients of drug concentration are believed to play an important role in the evolution of drug resistance. We use a stochastic model to show that in a growing population of malignant cells the effect of a spatially non-uniform drug distribution depends critically on the mutational pathway leading to resistance. A non-uniform drug concentration can strongly accelerate the emergence of resistance when the pathway involves a sequence of mutants with increasing resistance, but slows it down if the pathway crosses a fitness valley. Our results suggest that the design of better strategies to combat the emergence of resistance may require detailed knowledge of the mutational pathways involved.

Greulich, Philip; Allen, Rosalind J

2012-01-01

365

Visualizations in Spatial Algorithm Development  

NASA Astrophysics Data System (ADS)

Spatial algorithms as used in Geographic Information Systems (GIS) can be difficult to understand and use, both for the developers and users. Knowledge transfer between developers and GIS enabled application users is often inadequate, incomprehensible or non-existent. Novel approaches for spatially indexing and searching data involve trade-offs; all have their limitations and advantages. Effectively communicating these trade-offs is a challenge. Both the limitations and strong points of any algorithms used in scientific applications must be explained to end-users in an easily understood and digestible manner. Written documentation is only one way of describing an algorithm. Images, animations, and interactive demos have long been used to aid in understanding spatial algorithms but their adoption and use could be increased. This session demonstrates how to include interactive visualizations from a project's inception and outlines the possibility of using these visualizations not only as eventual documentation, but also as verification criteria for spatial algorithm development. Interactive tools, such as Google Earth, can be used to create and visualize inputs to spatial algorithms and validate results. During development, a developer can benefit from constant feedback and the ability to quickly test changes and new code. This session will also demonstrate methods of documenting spatial algorithms for end users. The use of literate programming tools such as docco, http:// jashkenas.github.com/docco/, and spatial visualizations document the code and aid in producing documentation for scientists and developers.

Gilman, J.; Pilone, D.; Mitchell, A. E.; Baynes, K.

2012-12-01

366

Achieving a strongly temperature-dependent Casimir effect.  

PubMed

We propose a method of achieving large temperature T sensitivity in the Casimir force that involves measuring the stable separation between dielectric objects immersed in a fluid. We study the Casimir force between slabs and spheres using realistic material models, and find large >2??nm/K variations in their stable separations (hundreds of nanometers) near room temperature. In addition, we analyze the effects of Brownian motion on suspended objects, and show that the average separation is also sensitive to changes in T. Finally, this approach also leads to rich qualitative phenomena, such as irreversible transitions, from suspension to stiction, as T is varied. PMID:20867961

Rodriguez, Alejandro W; Woolf, David; McCauley, Alexander P; Capasso, Federico; Joannopoulos, John D; Johnson, Steven G

2010-08-01

367

Strong, Time-Dependent Electromagnetic Fields in the  

E-print Network

, and Formation · Four topics, from the outer jet lobes to the hole formation ­ M87 knots as MHD shocks" (hot spot) & forward "bow" shocks produced a hot cocoon of post-shock jet material that surrounded the jet FR II sources, therefore look like hydrodynamic (HD) jets Reverse Shock (Mach disk) Bow Shock

Maryland at College Park, University of

368

Preserving speckle statistics in minimum-variance beamformed images: the effectiveness of spatial compounding  

Microsoft Academic Search

Data-dependent apodization techniques such as the minimum-variance beamformer (MVB) can beat the diffraction limit of the conventional Delay-and-Sum (DAS) beamformer, yielding enhanced resolution and contrast. However, the MVB algorithm strongly increases the speckle variance. This needs to be compensated in order for the MVB algorithm to be clinically successful. This paper shows that combining the MVB with spatial compounding yields

Francois G. Vignon; Michael R. Burcher

2009-01-01

369

Clustering multivariate spatial data based on local measures of spatial autocorrelation  

Microsoft Academic Search

A growing interest in clustering spatial data is emerging in several areas, from local economic development to epidemiology, from remote sensing data to environment analyses. However, methods and procedures to face such problem are still lacking. Local measures of spatial autocorrelation aim at identifying patterns of spatial dependence within the study region. Mapping these measures provide the basic building block

Luca Scrucca

2005-01-01

370

Cooking with Strong Lenses and Other Ingredients  

NASA Astrophysics Data System (ADS)

Strong lensing offers the most direct method for constraining the distribution of mass in galaxies at cosmological distances. The combination of strong lensing with other observables increases its power, but often in ways that are model-dependent and resistant to intuition. In this talk, I will unpack the information content of spectroscopic, photometric, kinematic, and strong-lensing observables as they translate into constraints on the macroscopic distribution of luminous and dark matter in massive elliptical galaxies. I will also highlight how the choice of priors and analysis methods affects the conclusions drawn from a given set of observations. Finally, in this context I will present the latest results from observational efforts to extend strong-lensing analyses to lower mass galaxies in the Sloan Lens ACS Survey (SLACS) and to earlier cosmic times in the BOSS Emission-Line Lens Survey (BELLS).

Bolton, Adam; SLACS; BELLS; SDSS-III

2013-07-01

371

The Impact of Spatial Incongruence on an Auditory-Visual Illusion  

PubMed Central

Background The sound-induced flash illusion is an auditory-visual illusion – when a single flash is presented along with two or more beeps, observers report seeing two or more flashes. Previous research has shown that the illusion gradually disappears as the temporal delay between auditory and visual stimuli increases, suggesting that the illusion is consistent with existing temporal rules of neural activation in the superior colliculus to multisensory stimuli. However little is known about the effect of spatial incongruence, and whether the illusion follows the corresponding spatial rule. If the illusion occurs less strongly when auditory and visual stimuli are separated, then integrative processes supporting the illusion must be strongly dependant on spatial congruence. In this case, the illusion would be consistent with both the spatial and temporal rules describing response properties of multisensory neurons in the superior colliculus. Methodology/Principal Findings The main aim of this study was to investigate the importance of spatial congruence in the flash-beep illusion. Selected combinations of one to four short flashes and zero to four short 3.5 KHz tones were presented. Observers were asked to count the number of flashes they saw. After replication of the basic illusion using centrally-presented stimuli, the auditory and visual components of the illusion stimuli were presented either both 10 degrees to the left or right of fixation (spatially congruent) or on opposite (spatially incongruent) sides, for a total separation of 20 degrees. Conclusions/Significance The sound-induced flash fission illusion was successfully replicated. However, when the sources of the auditory and visual stimuli were spatially separated, perception of the illusion was unaffected, suggesting that the “spatial rule” does not extend to describing behavioural responses in this illusion. We also find no evidence for an associated “fusion” illusion reportedly occurring when multiple flashes are accompanied by a single beep. PMID:19649293

Innes-Brown, Hamish; Crewther, David

2009-01-01

372

Temporal consistency of spatial pattern in growth of the mussel, Mytilus edulis: Implications for predictive modelling  

NASA Astrophysics Data System (ADS)

Human pressures on coastal seas are increasing and methods for sustainable management, including spatial planning and mitigative actions, are therefore needed. In coastal areas worldwide, the development of mussel farming as an economically and ecologically sustainable industry requires geographic information on the growth and potential production capacity. In practice this means that coherent maps of temporally stable spatial patterns of growth need to be available in the planning process and that maps need to be based on mechanistic or empirical models. Therefore, as a first step towards development of models of growth, we assessed empirically the fundamental requirement that there are temporally consistent spatial patterns of growth in the blue mussel, Mytilus edulis. Using a pilot study we designed and dimensioned a transplant experiment, where the spatial consistency in the growth of mussels was evaluated at two resolutions. We found strong temporal and scale-dependent spatial variability in growth but patterns suggested that spatial patterns were uncoupled between growth of shell and that of soft tissue. Spatial patterns of shell growth were complex and largely inconsistent among years. Importantly, however, the growth of soft tissue was qualitatively consistent among years at the scale of km. The results suggest that processes affecting the whole coastal area cause substantial differences in growth of soft tissue among years but that factors varying at the scale of km create strong and persistent spatial patterns of growth, with a potential doubling of productivity by identifying the most suitable locations. We conclude that the observed spatial consistency provides a basis for further development of predictive modelling and mapping of soft tissue growth in these coastal areas. Potential causes of observed patterns, consequences for mussel-farming as a tool for mitigating eutrophication, aspects of precision of modelling and sampling of mussel growth as well as ecological functions in general are discussed.

Bergström, Per; Lindegarth, Susanne; Lindegarth, Mats

2013-10-01

373

Identity Crises and Strong Compactness II: Strong Cardinals  

E-print Network

was groundbreaking and established the general #12;eld of \\identity crisis studies", there has been additionalIdentity Crises and Strong Compactness II: Strong Cardinals Arthur W. Apter #3; Department of Magidor, that the class of strongly compact cardinals can assume yet another identity. Speci#12;cally, we

Cummings, James

374

Cosmography with cluster strong lensing  

E-print Network

By stacking an ensemble of strong lensing clusters, we demonstrate the feasibility of placing constraints on the dark energy equation of state. This is achieved by using multiple images of sources at two or more distinct redshift planes. The sample of smooth clusters in our simulations is based on observations of massive clusters and the distribution of background galaxies is constructed using the Hubble Deep Field. Our source distribution reproduces the observed redshift distribution of multiply imaged sources in Abell 1689. The cosmology recovery depends on the number of image families with known spectroscopic redshifts and the number of stacked clusters. Our simulations suggest that constraints comparable to those derived from other competing established techniques on a constant dark energy equation of state can be obtained using 10 to 40 clusters with 5 or more families of multiple images. We have also studied the observational errors in the image redshifts and positions. We find that spectroscopic redshifts and high resolution {\\it Hubble Space Telescope} images are required to eliminate confidence contour relaxation relative to the ideal case in our simulations. This suggests that the dark energy equation of state, and other cosmological parameters, can be constrained with existing {\\it Hubble Space Telescope} images of lensing clusters coupled with dedicated ground-based arc spectroscopy.

James Gilmore; Priyamvada Natarajan

2006-05-10

375

Regulation of Spatial Selectivity by Crossover Inhibition  

PubMed Central

Signals throughout the nervous system diverge into parallel excitatory and inhibitory pathways that later converge on downstream neurons to control their spike output. Converging excitatory and inhibitory synaptic inputs can exhibit a variety of temporal relationships. A common motif is feedforward inhibition, in which an increase (decrease) in excitatory input precedes a corresponding increase (decrease) in inhibitory input. The delay of inhibitory input relative to excitatory input originates from an extra synapse in the circuit shaping inhibitory input. Another common motif is push-pull or “crossover” inhibition, in which increases (decreases) in excitatory input occur together with decreases (increases) in inhibitory input. Primate On midget ganglion cells receive primarily feedforward inhibition and On parasol cells receive primarily crossover inhibition; this difference provides an opportunity to study how each motif shapes the light responses of cell types that play a key role in visual perception. For full-field stimuli, feedforward inhibition abbreviated and attenuated responses of On midget cells, while crossover inhibition, though plentiful, had surprisingly little impact on the responses of On parasol cells. Spatially structured stimuli, however, could cause excitatory and inhibitory inputs to On parasol cells to increase together, adopting a temporal relation very much like that for feedforward inhibition. In this case, inhibitory inputs substantially abbreviated a cell’s spike output. Thus inhibitory input shapes the temporal stimulus selectivity of both midget and parasol ganglion cells, but its impact on responses of parasol cells depends strongly on the spatial structure of the light inputs. PMID:23575830

Cafaro, Jon; Rieke, Fred

2013-01-01

376

Steering neutral atoms in strong laser fields  

NASA Astrophysics Data System (ADS)

The seminal strong-field tunnelling theory introduced by L V Keldysh plays a pivotal role. It has shaped our understanding of atomic strong-field processes, where it represents the first step in complex ionisation dynamics and provides reliable tunnelling rates. Tunnelling rates, however, cannot be necessarily equated with ionisation rates. Taking into account the electron dynamics in the Coulomb potential following the tunnelling process, the process of frustrated tunnelling ionisation has been found to lead to excited Rydberg atoms. Here, we excite He atoms in the strong-field tunnelling regime into Rydberg states. A high percentage of these Rydberg atoms survive in high intensity laser fields. We exploit this fact together with their high polarisability to kinematically manipulate the Rydberg atoms with a second elliptically polarised focused strong laser field. By varying the spatial overlap of the two laser foci, we are able to selectively control the deflection of the Rydberg atoms. The results of semi-classical calculations, which are based on the frustrated tunnelling model and on the ponderomotive acceleration, are in accord with our experimental data.

Eilzer, S.; Eichmann, U.

2014-10-01

377

Excitation wavelength dependent photoluminescence in structurally non-uniform Si/SiGe-island heteroepitxial multilayers  

SciTech Connect

In nanometer-size Si/SiGe-island heteroepitxial multilayers grown on Si(001), low temperature photoluminescence spectra are observed that strongly depend on the excitation wavelength and show a strong correlation with structural properties revealed by transmission electron microscopy. These experimental results can be explained by assuming that the optically created carriers are strongly localized at Si/SiGe island heterointerfaces. We show that electron-hole pairs are generated and recombine within spatial regions mainly defined by the photoexcitation penetration depth, and that the estimated exciton diffusion length is notably short and comparable with the SiGe-island average size.

Modi, N.; Tsybeskov, L. [Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102 (United States); Lockwood, D. J.; Wu, X.; Baribeau, J.-M. [Institute for Microstructural Sciences, National Research Council, Ottawa, Ontario K1A 0R6 (Canada)

2012-06-01

378

Individual Differences in Visual Imagery and Spatial Ability.  

ERIC Educational Resources Information Center

To explore the relationship between spatial ability and both image quality and image process efficiency, 79 subjects completed spatial tests, imagery questionnaires, and laboratory tasks. Laboratory measures of process efficiency and image quality were strongly related to spatial test performance and weakly related to one another. (Author/BW)

Poltrock, Steven E.; Brown, Polly

1984-01-01

379

On the growth of locally interacting plants: differential equations for the dynamics of spatial moments.  

PubMed

Ecologists are faced with the challenge of how to scale up from the activities of individual plants and animals to the macroscopic dynamics of populations and communities. It is especially difficult to do this in communities of plants where the fate of individuals depends on their immediate neighbors rather than an average over a larger region. This has meant that algorithmic, agent-based models are typically used to understand their dynamics, although certain macroscopic models have been developed for neighbor-dependent, birth death processes. Here we present a macroscopic model that, for the first time, incorporates explicit, gradual, neighbor-dependent plant growth, as a third fundamental process of plant communities. The model is derived from a stochastic, agent-based model, and describes the dynamics of the first and second spatial moments of a multispecies, spatially structured plant community with neighbor-dependent growth, births, and deaths. A simple example shows that strong neighborhood space-filling during tree growth in an even-aged stand of Scots pine is well captured by the spatial-moment model. The space-filling has a spatial signature consistent with that observed in several field studies of forests. Small neighborhoods of interaction, nonuniform spacing of trees, and asymmetric competition all contribute to the buildup of a wide range of tree sizes with some large dominant individuals and many smaller ones. PMID:24597220

Adams, Thomas P; Holland, E Penelope; Law, Richard; Plank, Michael J; Raghib, Michael

2013-12-01

380

Optimal configurations of spatial scale for grid cell firing under noise and uncertainty.  

PubMed

We examined the accuracy with which the location of an agent moving within an environment could be decoded from the simulated firing of systems of grid cells. Grid cells were modelled with Poisson spiking dynamics and organized into multiple 'modules' of cells, with firing patterns of similar spatial scale within modules and a wide range of spatial scales across modules. The number of grid cells per module, the spatial scaling factor between modules and the size of the environment were varied. Errors in decoded location can take two forms: small errors of precision and larger errors resulting from ambiguity in decoding periodic firing patterns. With enough cells per module (e.g. eight modules of 100 cells each) grid systems are highly robust to ambiguity errors, even over ranges much larger than the largest grid scale (e.g. over a 500 m range when the maximum grid scale is 264 cm). Results did not depend strongly on the precise organization of scales across modules (geometric, co-prime or random). However, independent spatial noise across modules, which would occur if modules receive independent spatial inputs and might increase with spatial uncertainty, dramatically degrades the performance of the grid system. This effect of spatial uncertainty can be mitigated by uniform expansion of grid scales. Thus, in the realistic regimes simulated here, the optimal overall scale for a grid system represents a trade-off between minimizing spatial uncertainty (requiring large scales) and maximizing precision (requiring small scales). Within this view, the temporary expansion of grid scales observed in novel environments may be an optimal response to increased spatial uncertainty induced by the unfamiliarity of the available spatial cues. PMID:24366144

Towse, Benjamin W; Barry, Caswell; Bush, Daniel; Burgess, Neil

2014-02-01

381

Optimal configurations of spatial scale for grid cell firing under noise and uncertainty  

PubMed Central

We examined the accuracy with which the location of an agent moving within an environment could be decoded from the simulated firing of systems of grid cells. Grid cells were modelled with Poisson spiking dynamics and organized into multiple ‘modules’ of cells, with firing patterns of similar spatial scale within modules and a wide range of spatial scales across modules. The number of grid cells per module, the spatial scaling factor between modules and the size of the environment were varied. Errors in decoded location can take two forms: small errors of precision and larger errors resulting from ambiguity in decoding periodic firing patterns. With enough cells per module (e.g. eight modules of 100 cells each) grid systems are highly robust to ambiguity errors, even over ranges much larger than the largest grid scale (e.g. over a 500 m range when the maximum grid scale is 264 cm). Results did not depend strongly on the precise organization of scales across modules (geometric, co-prime or random). However, independent spatial noise across modules, which would occur if modules receive independent spatial inputs and might increase with spatial uncertainty, dramatically degrades the performance of the grid system. This effect of spatial uncertainty can be mitigated by uniform expansion of grid scales. Thus, in the realistic regimes simulated here, the optimal overall scale for a grid system represents a trade-off between minimizing spatial uncertainty (requiring large scales) and maximizing precision (requiring small scales). Within this view, the temporary expansion of grid scales observed in novel environments may be an optimal response to increased spatial uncertainty induced by the unfamiliarity of the available spatial cues. PMID:24366144

Towse, Benjamin W.; Barry, Caswell; Bush, Daniel; Burgess, Neil

2014-01-01

382

Two-dimensional Laguerre-Gaussian soliton family in strongly nonlocal nonlinear media  

SciTech Connect

We have studied Laguerre-Gaussian spatial solitary waves in strongly nonlocal nonlinear media analytically and numerically. An exact analytical solution of two-dimensional self-similar waves is obtained. Furthermore, a family of different spatial solitary waves has been found. It is interesting that the spatial soliton profile and its width remain unchanged with increasing propagation distance. The theoretical predictions may give new insights into low-energetic spatial soliton transmission with high fidelity.

Zhong Weiping [State Key Laboratory of Laser Technology, Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Department of Electronic Engineering, Shunde College, Shunde 528300 (China); Yi Lin [State Key Laboratory of Laser Technology, Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

2007-06-15

383

Stochastic stability in spatial games Jacek Miekisz  

E-print Network

. John Maynard Smith [17, 18] has refined the concept of equilibrium to include the stability of Nash of spatial games with multiple Nash equilibria is analyzed. In particular, we construct an example of a spatial game with three strategies, where stochastic stability of Nash equilibria depends on the number

Miekisz, Jacek

384

Spatial Convergence in China: 1952-99  

Microsoft Academic Search

The purpose of this paper is to examine the convergence process in China by taking into account the spatial interaction between factors. The paper shows that there has been a dramatic increase in the spatial dependence of China's per capita GDP in the last 20 years. The consequence of space plays an important role, which is reflected in the influence

Patricio Aroca; Dong Guo; Geoffrey J. D. Hewings

2006-01-01

385

Spatial memory, recognition memory, and the hippocampus  

E-print Network

Spatial memory, recognition memory, and the hippocampus Nicola J. Broadbent*, Larry R. Squire. Squire, August 27, 2004 There is wide agreement that spatial memory is dependent on the integrity recognition memory is not as clear. We examined the relationship between hippocampal lesion size and both

Squire, Larry R.

386

Spatial Uncertainty Analysis of Ecological Models  

SciTech Connect

The authors evaluated the sensitivity of a habitat model and a source-sink population model to spatial uncertainty in landscapes with different statistical properties and for hypothetical species with different habitat requirements. Sequential indicator simulation generated alternative landscapes from a source map. Their results showed that spatial uncertainty was highest for landscapes in which suitable habitat was rare and spatially uncorrelated. Although, they were able to exert some control over the degree of spatial uncertainty by varying the sampling density drawn from the source map, intrinsic spatial properties (i.e., average frequency and degree of spatial autocorrelation) played a dominant role in determining variation among realized maps. To evaluate the ecological significance of landscape variation, they compared the variation in predictions from a simple habitat model to variation among landscapes for three species types. Spatial uncertainty in predictions of the amount of source habitat depended on both the spatial life history characteristics of the species and the statistical attributes of the synthetic landscapes. Species differences were greatest when the landscape contained a high proportion of suitable habitat. The predicted amount of source habitat was greater for edge-dependent (interior) species in landscapes with spatially uncorrelated(correlated) suitable habitat. A source-sink model demonstrated that, although variation among landscapes resulted in relatively little variation in overall population growth rate, this spatial uncertainty was sufficient in some situations, to produce qualitatively different predictions about population viability (i.e., population decline vs. increase).

Jager, H.I.; Ashwood, T.L.; Jackson, B.L.; King, A.W.

2000-09-02

387

Concepts in strong Langmuir turbulence theory  

SciTech Connect

Some of the basic concepts of strong Langmuir turbulence (SLT) theory are reviewed. In SLT system, a major fraction of the turbulent energy is carried by local, time-dependent, nonlinear excitations called cavitons. Modulational instability, localization of Langmuir fields by density fluctuations, caviton nucleation, collapse, and burnout and caviton correlations are reviewed. Recent experimental evidence will be presented for SLT phenomena in the interaction of powerful HF waves with the ionosphere and in laser-plasma interaction experiments. 38 refs., 11 figs.

DuBois, D.F.; Rose, H.A.

1990-01-01

388

EDITORIAL: Strongly correlated electron systems Strongly correlated electron systems  

Microsoft Academic Search

Strongly correlated electrons is an exciting and diverse field in condensed matter physics. This special issue aims to capture some of that excitement and recent developments in the field. Given that this issue was inspired by the 2010 International Conference on Strongly Correlated Electron Systems (SCES 2010), we briefly give some history in order to place this issue in context.

Filip Ronning; Cristian Batista

2011-01-01

389

Strongly Fault Secure Logic Networks  

Microsoft Academic Search

Strongly fault secure logic networks are defined and are shown to include totally self-checking networks as a special case. Strongly fault secure networks provide the same protection against assumed faults as totally self-checking networks, and it is shown that when stuck-at faults are assumed a strongly fault secure network can be easily modified to form a totally self-checking network. A

James E. Smith; Gernot Metze

1978-01-01

390

Capacity of MIMO free space optical communications using multiple partially coherent beams propagation through non-Kolmogorov strong turbulence.  

PubMed

We study the average capacity performance for multiple-input multiple-output (MIMO) free-space optical (FSO) communication systems using multiple partially coherent beams propagating through non-Kolmogorov strong turbulence, assuming equal gain combining diversity configuration and the sum of multiple gamma-gamma random variables for multiple independent partially coherent beams. The closed-form expressions of scintillation and average capacity are derived and then used to analyze the dependence on the number of independent diversity branches, power law ?, refractive-index structure parameter, propagation distance and spatial coherence length of source beams. Obtained results show that, the average capacity increases more significantly with the increase in the rank of MIMO channel matrix compared with the diversity order. The effect of the diversity order on the average capacity is independent of the power law, turbulence strength parameter and spatial coherence length, whereas these effects on average capacity are gradually mitigated as the diversity order increases. The average capacity increases and saturates with the decreasing spatial coherence length, at rates depending on the diversity order, power law and turbulence strength. There exist optimal values of the spatial coherence length and diversity configuration for maximizing the average capacity of MIMO FSO links over a variety of atmospheric turbulence conditions. PMID:23842307

Deng, Peng; Kavehrad, Mohsen; Liu, Zhiwen; Zhou, Zhou; Yuan, Xiuhua

2013-07-01

391

Attosecond near-threshold photoionization in a strong laser field  

NASA Astrophysics Data System (ADS)

A drastic modification of the conventional streaking patterns of double differential cross section for attosecond near-threshold ionization of atoms in a strong infrared (IR) field is theoretically investigated. Rescattering of slow electrons from the ionic core leads to appearance of the interference fringes and strong diffraction maxima in the spectra of photoelectrons at small energies. The computations based on solving the time-dependent Schrödinger equation show that both these spectral features strongly depend on the IR intensity and frequency. Investigations of low-energy streaking can provide unique information on slow photoelectron dynamics in combined fields of ionic core and strong IR laser.

Kazansky, A. K.; Bozhevolnov, A. V.; Sazhina, I. P.; Kabachnik, N. M.

2014-09-01

392

Octopus arm choice is strongly influenced by eye use.  

PubMed

This study aims to investigate the octopus' eye and arm coordination and raises the question if visual guidance determines choice of arm use. Octopuses possess eight seemingly identical arms but have recently been reported to show a preference as to which arm they use to initiate contact with objects. These animals also exhibit lateralized eye use, therefore, a connection between eye and arm preference seems possible. Seven Octopus vulgaris were observed during approach, contact initiation and exploration of plastic objects that were positioned on three different levels in the water column. The subjects most commonly used an arm to initiate contact with an object that was in a direct line between the eye used to look at the object, and the object itself. This indicates that choice of arm use is spatially rather opportunistic when depending on visual guidance. Additionally, first contact with an object was usually established by the central third of the arm and in arm contact sequences neighboring arms were the most likely to follow an arm already touching the object. Although results point towards strong eye/arm coordination, we did not find lateralized behavior in this experiment. Results are discussed from a neuro-anatomical, behavioral and ecological perspective. PMID:16797740

Byrne, Ruth A; Kuba, Michael J; Meisel, Daniela V; Griebel, Ulrike; Mather, Jennifer A

2006-09-25

393

Strong Dynamical Heterogeneity and Universal Scaling in Driven Granular Fluids  

NASA Astrophysics Data System (ADS)

Large-scale simulations of two-dimensional bidisperse granular fluids allow us to determine spatial correlations of slow particles via the four-point structure factor S4(q,t). Both cases, elastic (?=1) and inelastic (?<1) collisions, are studied. As the fluid approaches structural arrest, i.e., for packing fractions in the range 0.6???0.805, scaling is shown to hold: S4(q,t)/?4(t)=s(q?(t)). Both the dynamic susceptibility ?4(??) and the dynamic correlation length ?(??) evaluated at the ? relaxation time ?? can be fitted to a power law divergence at a critical packing fraction. The measured ?(??) widely exceeds the largest one previously observed for three-dimensional (3d) hard sphere fluids. The number of particles in a slow cluster and the correlation length are related by a robust power law, ?4(??)??d -p(??), with an exponent d-p?1.6. This scaling is remarkably independent of ?, even though the strength of the dynamical heterogeneity at constant volume fraction depends strongly on ?.

Avila, Karina E.; Castillo, Horacio E.; Fiege, Andrea; Vollmayr-Lee, Katharina; Zippelius, Annette

2014-07-01

394

Kubo conductivity of a strongly magnetized two-dimensional plasma.  

NASA Technical Reports Server (NTRS)

The Kubo formula is used to evaluate the bulk electrical conductivity of a two-dimensional guiding-center plasma in a strong dc magnetic field. The particles interact only electrostatically. An ?anomalous' electrical conductivity is derived for this system, which parallels a recent result of Taylor and McNamara for the coefficient of spatial diffusion.

Montgomery, D.; Tappert, F.

1971-01-01

395

Spatially resolved ultrasonic attenuation in resistance spot welds: implications for nondestructive testing.  

PubMed

Spatial variation of ultrasonic attenuation and velocity has been measured in plane parallel specimens extracted from resistance spot welds. In a strong weld, attenuation is larger in the nugget than in the parent material, and the region of increased attenuation is surrounded by a ring of decreased attenuation. In the center of a stick weld, attenuation is even larger than in a strong weld, and the low-attenuation ring is absent. These spatial variations are interpreted in terms of differences in grain size and martensite formation. Measured frequency dependences indicate the presence of an additional attenuation mechanism besides grain scattering. The observed attenuations do not vary as commonly presumed with weld quality, suggesting that the common practice of using ultrasonic attenuation to indicate weld quality is not a reliable methodology. PMID:18325561

Mozurkewich, George; Ghaffari, Bita; Potter, Timothy J

2008-09-01

396

Spatially resolved measurement of high doses in microbeam radiation therapy using samarium doped fluorophosphate glasses  

SciTech Connect

The measurement of spatially resolved high doses in microbeam radiation therapy has always been a challenging task, where a combination of high dose response and high spatial resolution (microns) is required for synchrotron radiation peaked around 50 keV. The x-ray induced Sm{sup 3+}{yields} Sm{sup 2+} valence conversion in Sm{sup 3+} doped fluorophosphates glasses has been tested for use in x-ray dosimetry for microbeam radiation therapy. The conversion efficiency depends almost linearly on the dose of irradiation up to {approx}5 Gy and saturates at doses exceeding {approx}80 Gy. The conversion shows strong correlation with x-ray induced absorbance of the glass which is related to the formation of phosphorus-oxygen hole centers. When irradiated through a microslit collimator, a good spatial resolution and high ''peak-to-valley'' contrast have been observed by means of confocal photoluminescence microscopy.

Okada, Go; Morrell, Brian; Koughia, Cyril; Kasap, Safa [Department of Electrical and Computer Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9 (Canada); Edgar, Andy; Varoy, Chris [School of Chemical and Physical Sciences and MacDiarmid Institute, Victoria University of Wellington, Kelburn Parade (New Zealand); Belev, George; Wysokinski, Tomasz [Canadian Light Source Inc., University of Saskatchewan, Saskatoon, SK S7N 0X4 (Canada); Chapman, Dean [Department of Anatomy and Cell Biology, University of Saskatchewan, Saskatoon, SK S7N 5E5 (Canada)

2011-09-19

397

Strongly invariant subgroups Grigore Calugareanu  

E-print Network

Strongly invariant subgroups Grigore Calugareanu Abstract As a special case of fully invariant subgroups, strongly invariant sub- groups are introduced and studied for Abelian groups. 1 Introduction and let f be an endomorphism of G. If H is fully invariant in G then, by restriction, f in- duces

Cãlugãreanu, Grigore

398

Strong-back safety latch  

SciTech Connect

The calculation decides the integrity of the safety latch that will hold the strong-back to the pump during lifting. The safety latch will be welded to the strong-back and will latch to a 1.5-in. dia cantilever rod welded to the pump baseplate. The static and dynamic analysis shows that the safety latch will hold the strong-back to the pump if the friction clamps fail and the pump become free from the strong-back. Thus, the safety latch will meet the requirements of the Lifting and Rigging Manual for under the hook lifting for static loading; it can withstand shock loads from the strong-back falling 0.25 inch.

DeSantis, G.N.

1995-03-06

399

Multi-parameter high-resolution spatial maps of a CdZnTe radiation detector array  

SciTech Connect

Resistivity results from a 48x48 pixelated CdZnTe (CZT) radiation detector array are presented alongside X-ray topography and detector mapping with a collimated gamma-ray beam. By using a variety of measurements performed on the same sample and registering each data set relative to the others, the spatial dependence of relationships between them was examined. The local correlations between resistivity and one measure of detector performance were strongly influenced by the positions of grain boundaries and other gross crystal defects in the sample. These measurements highlight the need for material studies of spatially heterogeneous CZT to record position information along with the parameters under study.

N. R. Hilton; H. B. Barber; B. A. Brunett; J. D. Eskin; M. S. Goorsky; R. B. James; J. C. Lund; D. G. Marks; T. E. Schlesinger; T. M.Teska; J. M. Van Scyoc; J.M. Woolfenden; H. Yoon

1998-11-07

400

Approximate spatial reasoning  

NASA Technical Reports Server (NTRS)

A model for approximate spatial reasoning using fuzzy logic to represent the uncertainty in the environment is presented. Algorithms are developed which can be used to reason about spatial information expressed in the form of approximate linguistic descriptions similar to the kind of spatial information processed by humans. Particular attention is given to static spatial reasoning.

Dutta, Soumitra

1988-01-01

401

TeachSpatial  

NSDL National Science Digital Library

The TeachSpatial collection assembles digital teaching resources relevant to spatial cognition, spatial learning, and spatial literacy across multiple STEM disciplines for middle school, high school, and undergraduate learners. Common topics include physical geography, GIS (Geographic Information Systems), and map reading skills (population demographics, geographic coordinates, etc.). Resources are indexed by the core spatial concepts and principles found in the 1996 National Science Education Standards and contain comments and ratings from a community of users. TeachSpatial is a project of the Center for Spatial Studies at the University of California, Santa Barbara.

2012-01-13

402

Recent advances of strong-strong beam-beam simulation  

SciTech Connect

In this paper, we report on recent advances in strong-strong beam-beam simulation. Numerical methods used in the calculation of the beam-beam forces are reviewed. A new computational method to solve the Poisson equation on nonuniform grid is presented. This method reduces the computational cost by a half compared with the standard FFT based method on uniform grid. It is also more accurate than the standard method for a colliding beam with low transverse aspect ratio. In applications, we present the study of coherent modes with multi-bunch, multi-collision beam-beam interactions at RHIC. We also present the strong-strong simulation of the luminosity evolution at KEKB with and without finite crossing angle.

Qiang, Ji; Furman, Miguel A.; Ryne, Robert D.; Fischer, Wolfram; Ohmi,Kazuhito

2004-09-15

403

Strong selection barriers explain microgeographic adaptation in wild salamander populations.  

PubMed

Microgeographic adaptation occurs when populations evolve divergent fitness advantages across the spatial scales at which focal organisms regularly disperse. Although an increasing number of studies find evidence for microgeographic adaptation, the underlying causes often remain unknown. Adaptive divergence requires some combination of limited gene flow and strong divergent natural selection among populations. In this study, we estimated the relative influence of selection, gene flow, and the spatial arrangement of populations in shaping patterns of adaptive divergence in natural populations of the spotted salamander (Ambystoma maculatum). Within the study region, A. maculatum co-occur with the predatory marbled salamander (Ambystoma opacum) in some ponds, and past studies have established a link between predation risk and adaptive trait variation in A. maculatum. Using 14 microsatellite loci, we found a significant pattern of genetic divergence among A. maculatum populations corresponding to levels of A. opacum predation risk. Additionally, A. maculatum foraging rate was strongly associated with predation risk, genetic divergence, and the spatial relationship of ponds on the landscape. Our results indicate the sorting of adaptive genotypes by selection regime and strongly suggest that substantial selective barriers operate against gene flow. This outcome suggests that microgeographic adaptation in A. maculatum is possible because strong antagonistic selection quickly eliminates maladapted phenotypes despite ongoing and substantial immigration. Increasing evidence for microgeographic adaptation suggests a strong role for selective barriers in counteracting the homogenizing influence of gene flow. PMID:23730765

Richardson, Jonathan L; Urban, Mark C

2013-06-01

404

Effects of spatial variability of soil hydraulic properties on water dynamics  

NASA Astrophysics Data System (ADS)

Soil hydraulic properties may present spatial variability and dependence at the scale of watersheds or fields even in man-made single soil structures, such as cranberry fields. The saturated hydraulic conductivity (Ksat) and soil moisture curves were measured at two depths for three cranberry fields (about 2 ha) at three different sites near Québec city, Canada. Two of the three studied fields indicate strong spatial dependence for Ksat values and soil moisture curves both in horizontal and vertical directions. In the summer of 2012, the three fields were equipped with 55 tensiometers installed at a depth of 0.10 m in a regular grid. About 20 mm of irrigation water were applied uniformly by aspersion to the fields, raising soil water content to near saturation condition. Soil water tension was measured once every hour during seven days. Geostatistical techniques such as co-kriging and cross-correlograms estimations were used to investigate the spatial dependence between variables. The results show that soil tension varied faster in high Ksat zones than in low Ksatones in the cranberry fields. These results indicate that soil water dynamic is strongly affected by the variability of saturated soil hydraulic conductivity, even in a supposed homogenous anthropogenic soil. This information may have a strong impact in irrigation management and subsurface drainage efficiency as well as other water conservation issues. Future work will involve 3D numerical modeling of the field water dynamics with HYDRUS software. The anticipated outcome will provide valuable information for the understanding of the effect of spatial variability of soil hydraulic properties on soil water dynamics and its relationship with crop production and water conservation.

Gumiere, Silvio Jose; Caron, Jean; Périard, Yann; Lafond, Jonathan

2013-04-01

405

Time-dependent convection with non-Newtonian viscosity  

NASA Technical Reports Server (NTRS)

A numerical model of bottom-heated, two-dimensional convection in boxes of aspect ratios 2.5 and 4.0 was used to study the differences in time-dependent convection between Newtonian and stress-dependent viscosity. The onset of time dependence due to boundary layer instability is found at approximately the same effective Rayleigh number for both rheologies. However, with increasing Rayleigh number, the temporal and spatial fluctuations in the flow field become much more pronounced with non-Newtonian rheology; also, the tendency for breakup of long cells into smaller ones is stronger. The presence of stress-dependent rheology can cause long-wavelength lateral viscosity variations up to an order of magnitude; this result could have strong implications for the interpretation of mantle viscosity from postglacial rebound.

Christensen, Ulrich R.; Yuen, David A.

1989-01-01

406

Titanium: light, strong, and white  

USGS Publications Warehouse

Titanium (Ti) is a strong silver-gray metal that is highly resistant to corrosion and is chemically inert. It is as strong as steel but 45 percent lighter, and it is twice as strong as aluminum but only 60 percent heavier. Titanium dioxide (TiO2) has a very high refractive index, which means that it has high light-scattering ability. As a result, TiO2 imparts whiteness, opacity, and brightness to many products. ...Because of the unique physical properties of titanium metal and the whiteness provided by TiO2, titanium is now used widely in modern industrial societies.

Woodruff, Laurel; Bedinger, George

2013-01-01

407

Optimization of the dynamic behavior of strongly nonlinear heterogeneous materials  

E-print Network

boundaries. Fabrication of sonic crystals have been shown toof the sonic vacuum type phononic crystals with ancrystals has a strong dependence on the amplitude represented by Eqs. (2.4) and (2.5) for sonic

Herbold, Eric B.

2008-01-01

408

Hydrological networks and associated topographic variation as templates for the spatial organization of tropical forest vegetation.  

PubMed

An understanding of the spatial variability in tropical forest structure and biomass, and the mechanisms that underpin this variability, is critical for designing, interpreting, and upscaling field studies for regional carbon inventories. We investigated the spatial structure of tropical forest vegetation and its relationship to the hydrological network and associated topographic structure across spatial scales of 10-1000 m using high-resolution maps of LiDAR-derived mean canopy profile height (MCH) and elevation for 4930 ha of tropical forest in central Panama. MCH was strongly associated with the hydrological network: canopy height was highest in areas of positive convexity (valleys, depressions) close to channels draining 1 ha or more. Average MCH declined strongly with decreasing convexity (transition to ridges, hilltops) and increasing distance from the