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PubMed2003

[Spatial heterogeneity of vegetation and soil characteristics in oasis-desert ecotone].

The spatial distribution of bio- and abiotic factors in ecosystem has the features of spatial heterogeneity in general, and spatial heterogeneity is important in the function and process of ecosystem at a variety of scales. In this paper, semivariance theory and methods were used to study the degree, composition, scale and pattern of spatial heterogeneity of vegetation coverage and soil environment factors, and their relationships in the Fukang oasis-desert ecotone of Xinjiang. With block kriging in the studied area of sampling, the spatial pattern of each factor was expressed in three dimensions as well. The results indicated that except the little spatial autocorrelation of salt salinity, there existed a spatial autocorrelation above mean of the other factors, and the spatial variation was mainly limited to smaller scales. The vegetation coverage, for which auto-correlated spatial heterogeneity was a main component, had a high degree of spatial heterogeneity with obvious spatial pattern at the scale of 3 km. From the perspective of spatial distributions, there existed a remarkable difference between soil holard and soil pH value in the studied area. Besides this, the higher value areas interleaved with the lower ones, significant positive correlations were observed between herbage coverage and soil factors (surface SH and SPH), and shrub coverage depended on the deep SH. The difference of spatial heterogeneity and pattern between SC and HC indicated the different ecological function and process in the ecosystem.

Desert Climate↗
PubMed1995

The prothymosin alpha gene is specifically expressed in ectodermal and mesodermal regions during early postimplantation mouse embryogenesis.

Prothymosin alpha (ProT alpha) is a highly acidic nuclear protein, once believed to have an extracellular immunoregulatory role but more recently implicated in cell proliferation and/or differentiation. Several recent studies have revealed that ProT alpha mRNA is present during embryogenesis. However, these studies did not investigate the spatial distribution of ProT alpha mRNA in the embryo. Here we present a detailed study of the spatial distribution of ProT alpha mRNA during the early stages of postimplantation development (6.5-12.5 dpc) of the mouse. Three findings are of particular interest. First, ProT alpha mRNA levels increase during the early postimplantation stages (6.5-8.5 dpc) of mouse embryogenesis. Second, ProT alpha mRNA is not uniformly distributed in the mouse embryo, but is present in a spatially specific manner. Third, we have observed that the mouse ProT alpha gene is expressed almost exclusively in ectodermal and mesoderm-derived structures, and not in cells which give rise to the definitive endoderm.

Animals↗
PubMed2000

Relation of cortical language distribution and cognitive function in surgical epilepsy patients.

PURPOSE: To investigate the relation between the number and spatial distribution of language sites and specific patient-and epilepsy-related variables. METHODS: Patients with stimulation-induced reading or naming errors from anterior or inferior temporal cortex (i.e., atypical temporal language sites) were compared with those with language sites confined to Wernicke's area (WA) in the posterosuperior temporal and inferior parietal perisylvian area. In a consecutive series of 44 left hemisphere language dominant patients with complex partial seizures before left temporal lobectomy, correlations were compared between cortical language distribution and measures of cognitive function. RESULTS: Patients with atypical temporal language sites (group 1) had significantly fewer years of education that did patients with language sites in WA (group 2). Patients in group 1 had poorer verbal learning and fluency than did patients in group 2. Patients with IQ <80 were significantly more likely to have multiple sites where stimulation disrupted language than did patients with normal IQ. Number of language sites had significant negative correlations with full-scale IQ, and measures of confrontation naming, verbal fluency, and immediate verbal memory. CONCLUSIONS: Language cortex has a wider spatial distribution in epilepsy surgery patients with lower intelligence, poorer education, and worse verbal and memory skills.

Adult↗
PubMed2006

Effect of heterogeneity on the quantitative determination of trace elements in concrete.

Laser-induced breakdown spectroscopy has been used for quantitative measurement of trace elements, e.g. sulfur and chlorine, in concrete. Chloride and sulfate ions have a large effect on the durability of concrete structures, and quantitative measurement is important for condition assessment and quality assurance. Concrete is a highly heterogeneous material in composition and grain-size distribution, i.e. the spatial distribution of elements. Calibration plots were determined by use of laboratory-made reference samples consisting of pressings of cement powder, hydrated cement, cement mortar, and concrete, in which the heterogeneity of the material is increasing because of the aggregates. Coarse aggregate and cement paste are distinguishable by the intensity of the Ca spectral lines. More advanced evaluation is necessary to account for the effect of the fine aggregate. The three series of reference samples enable systematic study of the effects of heterogeneity on spectral intensity, signal fluctuation, uncertainty, and limits of detection. Spatially resolved measurements and many spectra enable statistical evaluation of the data. The heterogeneity has an effect on measurement of the sulfur and chlorine content, because both occur mainly in the cement matrix. Critical chloride concentrations are approximately 0.04% (m/m). The chlorine spectral line at 837.6 nm is evaluated. The natural sulfur content of concrete is approximately 0.1% (m/m). The spectral line at 921.3 nm is evaluated. One future application may be simultaneous determination of the amount of damaging trace elements and the cement content of the concrete.

Journal Article↗
PubMed1988

Pattern of transcription of the homeo gene Hox-3.1 in the mouse embryo.

A cDNA from the Hox-3.1 locus, isolated from a 10.5-day postcoitum (p.c.) mouse embryo cDNA library, and the putative encoded protein are described. The spatial distribution of Hox-3.1 gene transcripts from late gastrulation to embryonic day 14.5 p.c. was monitored by in situ hybridization, using a cDNA probe. When first detectable in 8.5-day p.c. embryos, the transcripts are distributed in all the tissues of the posterior end. At later stages, the distribution becomes progressively spatially restricted and tissue specific. By 12.5 days p.c., transcription is localized most intensely in the neural tube region lying above the heart. The early transcription pattern thus appears to be compatible with a regionalizing role for the Hox-3.1 gene.

Amino Acid Sequence↗
PubMed2005

[A new precipitation distribution hydrological model and its application].

In distribution hydrological models, precipitation is the key input data for analyzing and computing hydrological processes. Finding a way to produce distribution precipitation data is a hotspot in hydrological research. This paper presented the hypothesis that the distribution of precipitation on the earth surface is the result of the effects of atmosphere system and terrain. Moreover, the spatial distribution of natural precipitation is a group of concentric ovals on the flat earth surface, and has a definite centre with maximum precipitation not affected by terrain. Supporting by the hypothesis, this paper established a new precipitation distribution hydrological model which could simulate the spatial distribution of precipitation, and modified the terrain effect on precipitation through Newton interpolation. The position of the precipitation centre and its precipitation amount were simulated in first time, and thus, the model could have a practical value in basin storm analysis and real-time runoff forecasting. The model was tested by the precipitation data of the Xichuan river basin in the Loess Plateau, which indicated that the model had a high precision.

Chemical Precipitation↗
PubMed2005

Adaptive migratory divergence among sympatric brook charr populations.

Ecological processes clearly contribute to population divergence, yet how they interact over complex life cycles remains poorly understood. Notably, the evolutionary consequences of migration between breeding and non-breeding areas have received limited attention. We provide evidence for a negative association between interpopulation differences in migration (between breeding and feeding areas, as well as within each) and the amount of gene flow (m) among three brook charr (Salvelinus fontinalis) populations inhabiting Mistassini Lake, Quebec, Canada. Individuals (n = 1166) captured throughout lake feeding areas over two consecutive sampling years were genotyped (10 microsatellites) and assigned to one of the three populations. Interpopulation differences in migration were compared based on spatial distribution overlap, habitat selection, migration distance within feeding areas, and morphology. We observed a temporally stable, heterogeneous spatial distribution within feeding areas among populations, with the extent of spatial segregation related to differential habitat selection (represented by littoral zone substrate). Spatial segregation was lowest and gene flow highest (m = 0.015) between two populations breeding in separate lake inflows. Segregation was highest and gene flow was lowest (mean m = 0.007) between inflow populations and a third population breeding in the outflow. Compared to outflow migrants, inflow migrants showed longer migration distances within feeding areas (64-70 km vs. 22 km). After entering natal rivers to breed, inflow migrants also migrated longer distances (35-75 km) and at greater elevations (50-150 m) to breeding areas than outflow migrants (0-15 km; -10-0 m). Accordingly, inflow migrants were more streamlined with longer caudal regions, traits known to improve swimming efficiency. There was no association between the geographic distance separating population pairs and the amount of gene flow they exchanged. Collectively, our results are consistent with the hypothesis that reduced gene flow between these brook charr populations results from divergent natural selection leading to interpopulation differences in migration. They also illustrate how phenotypic and genetic differentiation may arise over complex migratory life cycles.

Animal Migration↗
PubMed1997

Straight-line movement and competitive mate searching in prairie rattlesnakes, Crotalus viridis viridis

Males compete in various ways for mating and reproductive success. Phylogenetic factors and local ecology affect female spatial and temporal distributions, which in turn influence the form of male competition, sexual selection and mating systems. In prairie rattlesnake, Crotalus viridis viridispopulations where (1) males seek females during a brief reproductive period, (2) females are relatively few, and (3) females are widely and unpredictably distributed spatially into small discrete clusters, males should show efficient mate searching more so than time-consuming 'handling' (e.g. fighting, mate persuasion). Natural history studies and computer and mathematical modelling generate this expectation. This long-term field study of prairie rattlesnakes in Wyoming indicated that straight-line (i.e. fixed-bearing) movement by males is critical for mate location and, thus, for mating success. Males that searched along straight-line paths located and mated with more females than those having less straight movement paths. Fighting was observed rarely, and no relationship was found between males' success at mate location and body mass and/or snout-vent length. Thus a range of traits may mediate competition and mating success among male snakes.

Journal Article↗
PubMed1992

The effects of selective glutamate receptor antagonists on synchronized firing bursts in layer III of rat visual cortex.

In the rat visual cortex in vitro, single-shock stimulations applied to the border between layer VI and the white matter evoke synchronized burst-firing by units in layer III. We have examined the effects of glutamate receptor antagonists on this activity, with antagonists applied via the bath to allow correlation of effects with concentrations. All synaptically driven components (recorded extracellularly as field potential 'S2' spikes, dipoles 'W1' and 'W2', and coinciding single-unit spikes) were inhibited by greater than 90% in 1.0 mM kynurenic acid and in 3 or 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, which selectively blocks AMPA/kainate receptors). S2 spike amplitudes were reduced by half in 0.7 microM CNQX. 2-Amino-5-phosphonovalerate (APV), a specific blocker of NMDA receptors, did not prevent S2 spike burst or horizontal spread of bursting within layer III. However, APV reduced the duration of synchronized bursts and the slower potentials which followed. In Mg(2+)-free medium, new components appeared which were APV-sensitive: (1) low amplitude spikes, distributed spatially like S2 spike, but recurring more slowly, and (2) slow potentials, distributed spatially like W1 and W2 potentials, but lasting for hundreds of milliseconds. The amplitudes of these spikes were reduced by half in 3 microM D-APV. Our data imply that: (1) glutamate receptors play a major role in mediating local, excitatory neurotransmission in the supragranular layers of neocortex, with NMDA and AMPA/kainate subtypes each subserving somewhat different functions; (2) AMPA/kainate receptors mediate rapid excitatory transmission between layer III neurons, responsible for driving the first 15 ms of synchronized bursts; (3) currents gated by NMDA receptors determine the duration of coherent firing bursts, and drive asynchronous neuronal firing following bursts; and (4) under conditions which circumvent block by extracellular Mg2+, activation of NMDA receptors greatly enhances and prolongs the response to single-shock stimulations. In vivo, activation of layer III neurons is likely to depend significantly upon currents gated by NMDA receptors whenever repetitively firing excitatory inputs summed over several tens of milliseconds provide enough depolarization to lift block by extracellular Mg2+.

2-Amino-5-phosphonovalerate↗
PubMed2003

Statistical properties of BOLD magnetic resonance activity in the human brain.

We investigated the random variability of BOLD (blood oxygen level dependent) activation during rest, or null-hypothesis, conditions in which the observers were neither receiving controlled sensory stimuli nor performing cognitive tasks. The data indicate that the distributions for the BOLD variation across space are skewed, with non-Gaussian tails, while the distributions for the temporal variation within individual voxels are predominantly Gaussian. The proportion of voxels that show non-Gaussian properties is highly correlated with the magnitude of head movement of the observers. In all observers, the white matter showed less variability than the gray matter. The distributions for the spatial and the temporal variations are robust across observers despite differences in the data acquisition methods (EPI vs. spiral) and magnetic field strength (1.5 vs. 3 T). In most cases, the non-Gaussian tails of the spatial distribution can be eliminated by normalizing the amplitude in each voxel to its standard deviation before cumulating across voxels. We therefore recommend such a normalization procedure before any data manipulations are performed on fMRI data.

Adult↗
PubMed2006

Structure of liquid water at ambient temperature from ab initio molecular dynamics performed in the complete basis set limit.

Structural properties of liquid water at ambient temperature were studied using Car-Parrinello [Phys. Rev. Lett. 55, 2471 (1985)] ab initio molecular dynamics (CPAIMD) simulations combined with the Kohn-Sham (KS) density functional theory and the BLYP exchange-correlation functional for the electronic structure. Unlike other recent work on the same subject, where plane-wave (PW) or hybrid Gaussian/plane-wave basis sets were employed, in the present paper, a discrete variable representation (DVR) basis set is used to expand the KS orbitals, so that with the real-space grid adapted in the present work, the properties of liquid water could be obtained very near the complete basis set limit. Structural properties of liquid water were extracted from a 30 ps CPAIMD-BLYP/DVR trajectory at 300 K. The radial distribution functions (RDFs), spatial distribution functions, and hydrogen bond geometry obtained from the CPAIMD-BLYP/DVR simulation are generally in good agreement with the most up to date experimental measurements. Compared to recent ab initio MD simulations based on PW basis sets, less significant overstructuring was found in the RDFs and the distributions of hydrogen bond angles, suggesting that previous plane-wave and Gaussian basis set calculations have exaggerated the tendency toward overstructuring.

Journal Article↗
PubMed2003

Oculomotor control and the maintenance of spatially and temporally distributed events in visuo-spatial working memory.

Previous studies have demonstrated that working memory for spatial location can be significantly disrupted by concurrent eye or limb movement (Baddeley, 1986; Smyth, Pearson, & Pendleton, 1988). Shifts in attention alone can also interfere with spatial span (Smyth & Scholey, 1994), even with no corresponding movement of the eyes or limbs (Smyth, 1996). What is not clear from these studies is how comparable is the magnitude of effect caused by different forms of spatial disrupter. Recently, it has been demonstrated that limb movements produce as much interference with spatial span as do reflexive saccades (Lawrence, Myerson, Oonk, & Abrams, 2001). In turn this has led to the hypothesis that all spatially directed movement can produce similar effects in visuo-spatial working memory. This paper reports the results of five experiments that have contrasted the effect of concurrent eye movement, limb movement, and covert attention shifts on participants' working memory for sequences of locations. All conditions involving concurrent eye movement produced significantly greater reduction in span than equivalent limb movement or covert attention shifts with eyes fixated. It is argued that these results demonstrate a crucial role for oculomotor control processes during the rehearsal of location-specific representations in working memory.

Adult↗
PubMed2000

Experience-dependent plasticity of rat barrel cortex: redistribution of activity across barrel-columns.

The redistribution of neuronal activity across rat barrel cortex following an alteration in whisker usage has been investigated. In adult rats, two mystacial vibrissae - D(2) and one neighbor, D(1) or D(3) - were left intact while all other vibrissae on that side of the snout were clipped. Neurons in contralateral barrel cortex were sampled with a microelectrode array 3.5 days later. Stimulation of clipped vibrissae produced a narrow spatial distribution of cortical activity, whereas stimulation of intact vibrissae produced a widened spatial distribution. Simultaneous recordings from multiple cortical barrel-columns suggest that changes in the effective connectivity between barrel-columns may partially account for this redistribution of sensory responses. Evidence is also presented for a second mechanism, a release from inhibition in sensory-deprived cortical areas. A model is therefore proposed where these two mechanisms operate together to regulate the cortical distribution of evoked activity.

Action Potentials↗
PubMed2005

BDNF-modulated spatial organization of Cajal-Retzius and GABAergic neurons in the marginal zone plays a role in the development of cortical organization.

The present study utilizes nestin-BDNF transgenic mice, which offer a model for early increased brain-derived neurotrophic factor (BDNF) signalling, to examine the role of BDNF in the development of cortical architecture. Our results demonstrate that the premature and homogeneous expression of BDNF, while preserving tangential migration from the ganglionic eminence to the cortex, impairs the final radial migration of GABAergic neurons, as well as their integration in the appropriate cortical layers. Moreover, Cajal-Retzius (CR) cells and GABAergic neurons segregate in the cortical marginal zone (MZ) in response to BDNF signalling, leading to an alternating pattern and a columnar cortical organization, within which the migration of different neuronal populations is specifically affected. These results suggest that both CR and GABAergic neurons play a role in directing the radial migration of late-generated cortical neurons, and that the spatial distribution of these cells in the MZ is critical for the development of correct cortical organization. In addition, reelin secreted by CR cells in the MZ is not sufficient to direct the migration of late-born neurons to the upper cortical layers, which most likely requires the presence of reelin-secreting interneurons in layers V-VI. We propose that in addition to modulating reelin expression, BDNF regulates the patched distribution of CR and GABAergic neurons in the MZ, and that this spatial distribution is involved in the formation of anatomical and/or functional columns and convoluted structures.

Animals↗
PubMed1994

Minimal angle of resolution in monocular, single-colour vision and the TAIS model.

The mathematical model TAIS simulates visual perception of single-colour or black-and-white, non-moving objects. It makes an analysis of the luminance spatial distribution in an optional direction and describes it in linguistic terms. The model comprises three modules that successively convolve the luminance distribution with a spatial filter (a normalized Gaussian function), calculate the second derivative of the convolution and, with use of context-free and context-sensitive grammars, generate a string of symbols. The string of symbols contains the information, simplified in form and rectified from visual noise, about perceived spatial changes of brightness. The model simulates various visual phenomena, e.g. edge detection and spatial resolution, and it predicts the resolving power dependence on the light source size. The model-generated dependence of minimal angle of resolution on the light source width fits the experimental data with linear correlation coefficients in the range 0.70-0.94. The diagram consists of decreasing and constant parts, its shape adjusted to experimental data through selection of the Gaussian filter parameter and second derivative threshold.

Adaptation, Ocular↗
PubMedDate not supplied

[Population dynamics in Serbia--present status and problems at the end of the 20th century].

INTRODUCTION: Population changes in Serbia in the last hundred years were very intensive in all fields of demographic development. They were positive, because the movement trend was basically up-to-date and as such responded to the needs and requirements of the problems in regard to population time. However, what was the intensity of these changes? What kinds of problems does Serbia face at the end of the 20th century? Methodology In order to establish precise data and isolate basic problems the following components were analyzed: fertility, mortality and population growth, age and ethnic distribution, migrations and spatial distribution. Data were taken from official vital statistics, censuses, censuses of people from the territory of former Yugoslavia, population projections and secondary analysis of relevant scientific findings. RESULTS: Serbia is faced with a number of problems in almost all segments of demographic development at the end of the 20th century. This primarily includes dual types of reproduction, open depopulation and fast population growth, reversible mortality trends of certain age-sex groups, a large number of refugees, pronounced emigration, especially of young and educated people, and greater or smaller distortions in the territorial distribution and in the development of certain subpopulations. DISCUSSION: Changes in population of Serbia have been intensive in all areas of demographic development giving it to a lesser or greater extent characteristics of contemporary population of developed countries. These changes, however, were either slow or began later, or too intensive and elemental, causing a series of distortions in the population development. CONCLUSION: The existence of demographic problems poses numerous questions. The basic one is to what extent do demographic distortions slow down the development of a country as a whole; how may the extreme differences in the population fertility levels represent a source of conflict, crises and instability, to questions concerning solutions and probabilities of strong political response. However, there is no dilemma that a population policy is necessary.

Demography↗
PubMed1999

Neuroimage of voluntary movement: topography of the Bereitschaftspotential, a 64-channel DC current source density study.

The Bereitschaftspotential (BP) was recorded at 56 scalp positions when 17 healthy subjects performed brisk extensions of the right index finger. Aim of the study was to contribute to our understanding of the physiology underlying the BP and, in particular, to specify the situation at BP onset. For this purpose, the spatial pattern of the BP was analyzed in short time intervals (35 and/or 70 ms) starting 2.51 s before movement onset. For each time segment a spherical model of the BP was calculated by using spline interpolation. Then the spatial distribution of the electric potential at the scalp surface was transformed into a spatial distribution of current source densities (CSD map). Onset times of the BP and onset times of initial CSD-activity ranged between 2.23 and 1.81 s before movement onset. We selected a time window between 1.6 and 1.5 s before movement onset in order to analyze the spatial CSD pattern in each subject. In 10 subjects there was a significant current sink in the scalp area located over medial-wall motor areas (pre-SMA, SMA proper and anterior cingulate cortex: electrode positions C1, C2, FCz, Cz) in the absence of a significant current sink over the primary motor cortex (MI: electrode positions C3, CP3, and CP5). In three subjects significant current sinks were present at both sites and in another three subjects a current sink only over the lateral motor cortex was observed. In one subject no significant current sinks were measured. It is concluded that there is a large group of subjects (13/17) in whom BP at onset is associated with a current sink over medial-wall motor areas. At a later time interval (0.6 to 0.5 s before movement onset), significant current sinks were found in 13 subjects in medial and in 10 subjects in lateral recordings. These data were considered to be consistent with the hypothesis that, at least in a majority of subjects, medial-wall motor areas are activated earlier than lateral motor areas when organizing the initiation of a simple self-paced movement. Surface-recordings of the EEG do not allow further specification of cortical areas, which contribute to the current sinks. But in context with the current literature of the electrophysiology of nonhuman primates and of brain imaging in humans it is suggested that SMA and anterior cingulate cortex contribute to the current sink, the fronto-central midline, and that the primary motor cortex (MI) contributes to the current sink in the scalp area, which is located above MI and closely posterior to it.

Adult↗
PubMed2006

Development of optimal models of porous media by combining static and dynamic data: the porosity distribution.

This paper is part of a project, the goal of which is the development of the optimal spatial distributions of the porosity and permeability of a large-scale porous medium by using complementary static and dynamic data for the medium. The data include limited measurements of the porosity, which the method honors (preserves) in the optimal model and utilizes its correlation function, together with the first-arrival (FA) times, at a certain number of receivers, of seismic waves that have propagated in the medium and the time dependence of the pressure of a fluid flowing in the medium. The method uses the simulated-annealing (SA) technique in order to develop the optimal model. In the present paper we utilize the porosity and FA times data in order to develop the optimal spatial distribution of the porosity. This is accomplished by combining the SA method with a simulator that solves for the numerical solution of the acoustic-wave equation from which the FA times are estimated, limited porosity, and FA times data. We show that the optimal model not only honors the data, but also provides accurate estimates of the porosities in the rest of the porous medium. The efficiency of the computations is discussed in detail.

Journal Article↗