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Results for “spatial patterning”

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At least 469 records · Page 26Linked to original sources
PubMed1998

Using geographic information systems to assess spatial patterns of drug use, selection bias and attrition among a sample of injection drug users.

This study sought to assess whether frequency and type of drug use are geographically located within the city of Baltimore independent of neighborhood characteristics. The second goal was to assess geographic factors associated with sample selection and attrition. The sample consisted of 597 inner-city injection drug users who were enrolled in a HIV prevention study. The residential locations were plotted using Geographic Information Systems (GIS) software. Three patterns of drug use in the prior 6 months were examined: daily use of injection heroin, daily use of injection cocaine and any use of crack cocaine. Daily use of cocaine and any use of crack were found to be statistically associated with residing in the western portion of the city and distance from the western district sexually transmitted disease clinic. After adjusting for individual level characteristics and neighborhood level variables, as measured by 1990 census tract data, daily use of cocaine was found to be associated with residing in a more southern area of the city and distance from the western district sexually transmitted disease clinic, and any crack use was found to be associated with residing in a more western area of the city and distance from the western district sexually transmitted disease clinic. Men and younger participants were more likely to reside further away from the study clinic as were individuals who dropped out of the intervention condition. The results of this study suggest that type and frequency of drug use is associated with specific geographic areas, independent of neighborhood characteristics. These results have implications for the location of drug prevention, needle exchange and other HIV prevention activities.

Adult↗
PubMed2000

The murine cone photoreceptor: a single cone type expresses both S and M opsins with retinal spatial patterning.

Mice express S and M opsins that form visual pigments for the detection of light and visual signaling in cones. Here, we show that S opsin transcription is higher than that of M opsin, which supports ultraviolet (UV) sensitivity greater than midwavelength sensitivity. Surprisingly, most cones coexpress both S and M opsins in a common cone cell type throughout the retina. All cones express M opsin, but the levels are graded from dorsal to ventral. The levels of S opsin are relatively constant. However, in the far dorsal retina, S opsin is repressed stochastically, such that some cones express M opsin only. These observations indicate that two different mechanisms control M and S opsin expression. We suggest that a common cone type is patterned across the retinal surface to produce phenotypic cone subtypes.

Animals↗
PubMed1997

The chicken caudal genes establish an anterior-posterior gradient by partially overlapping temporal and spatial patterns of expression.

The caudal genes in vertebrates as in invertebrates assume a posterior position along the anterior-posterior axis and they appear to regulate the expression of the Hox genes. The third chicken caudal gene, Cdx-C, was cloned. Extensive comparisons of the sequence of this protein to the other known members of this homeobox family has lead to the suggestion that vertebrate genomes contain three members of the caudal homeobox family. A comparative study of the chicken Cdx-A and Cdx-C genes during gastrulation and neurulation revealed the differences between the genes. The caudal genes exhibit sequential activation in the newly formed neural plate and sequential extinction in axial midline structures during the primitive streak regression along the anterior-posterior axis. This pattern of expression suggests that the number and identity of caudal genes expressed along the anterior-posterior axis changes dynamically.

Amino Acid Sequence↗
PubMed1999

The genotype and epigenotype synergize to diversify the spatial pattern of expression of the imprinted H19 gene.

Little is known of how the genetic background effects the phenomenon of genomic imprinting. The H19 gene belongs to a cluster of imprinted genes on human chromosome 11. Here we show that the alternative splicing of a human H19 transcript is genotype-specific. Moreover, this variant transcript, which lacks exon 4, is either not found at all, is widely expressed or is confined to extra-villous cytotrophoblasts in first trimester placenta, depending on a combination of the genotype and the sex of the transmitting parent.

Alleles↗
PubMed2002

Lacunarity analysis of spatial pattern in CT images of vertebral trabecular bone for assessing osteoporosis.

The structural integrity of vertebral trabecular bone is determined by the continuity of its trabecular network and the size of the holes comprising its marrow space, both of which determine the apparent size of the marrow spaces in a transaxial CT image. A model-independent assessment of the trabeculation pattern was determined from the lacunarity of thresholded CT images. Using test images of lumbar vertebrae from human cadavers, acquired at different slice thicknesses, we determined that both median thresholding and local adaptive thresholding (using a 7 x 7 window) successfully segmented the grey-scale images. Lacunarity analysis indicated a multifractal nature to the images, and a range of marrow space sizes with significant structure around 14-18 mm(2). Preliminary studies of in vivo images from a clinical CT scanner indicate that lacunarity analysis can follow the pattern of bone loss in osteoporosis by monitoring the homogeneity of the marrow spaces, which is related to the connectivity of the trabecular bone network and the marrow space sizes. Although the patient sample was small, derived parameters such as the maximum deviation of the lacunarity from a neutral (fractal) model, and the maximum derivative of this deviation, seem to be sufficiently sensitive to distinguish a range of bone conditions. Our results suggest that these parameters, used with bone mineral density values, may have diagnostic value in characterizing osteoporosis and predicting fracture risk.

Cadaver↗
PubMed2001

Helminths of the sand lizard, Lacerta agilis (Reptilia, Lacertidae), in the Palaearctic: faunal diversity and spatial patterns of variation in the composition and structure of component communities.

We studied variation in the structure of component communities of helminths in sand lizards, Lacerta agilis, from 30 localities in the Ukraine and Bulgaria. Thirty-five separate samples of lizards, with a total of 661 completely censused infracommunities, yielded 30 helminth species (4 cestodes, 10 trematodes, 3 acanthocephalans and 13 nematodes). In its range within the Ukraine, L. agilis serves as the final host for 13 species of which only 3 (S. lacertae, S. hoffmanni and P. molini) can be considered as lizard specialists. A characteristic feature of these helminth component communities was the large proportion of heteroxeneous helminth species for which L. agilis serves as paratenic host. Sand lizards in the meadow steppeland zone were primarily parasitized by larval helminths that represented a major proportion of the total number of all worms recovered while those sampled in the grassland/forest transition zone were characterized by substantially higher proportions of adult helminths using lizards as final hosts. However, L. agilis was parasitized by a much higher proportion of lizard specialists in the 'typical' habitats of the meadow steppeland zone as opposed to those located in 'marginal' habitats in the grassland/forest transition zone, where helminths were shared to a greater extent with amphibian hosts.

Animals↗
PubMed2004

Temporal and spatial patterns of nestedness in eel macroparasite communities.

A nested (non-random) species composition was observed among the intestinal macroparasite communities of European eels, Anguilla anguilla. Nestedness was observed in 8 out of 10 component community samples from the rivers Thames and Test between April 2000 and October 2001. Parasite component communities consisted of mainly generalist and specialist, but also accidental species, and included acanthocephalans, cestodes, nematodes and digeneans. Nestedness was observed when component population size differed markedly between all or most parasite species, but not when the majority of species present was similarly abundant. Nestedness could not be explained in terms of host weight, log normal distribution of parasite species, or mean intensity of infection. It is proposed that nestedness occurred as a result of a sufficiently graded abundance between parasite species, which was established early in the year by colonization processes.

Anguilla↗
PubMedDate not supplied

Temporal and spatial patterns of opsin gene expression in zebrafish (Danio rerio).

In zebrafish, the first class of cone photoreceptor to become morphologically distinct is the ultraviolet-sensitive short single cone, at 4 days postfertilization, whereas the last class, the red- and green-sensitive double cone, becomes distinct at 10 days postfertilization. We have examined the time course of visual pigment gene expression in zebrafish using whole-mount in situ hybridization. Within the retina, opsins may be detected as early as 40 h postfertilization with the ultraviolet and rod visual pigments being expressed before the blue- (48 h) and red- (60 h) sensitive pigments. In the pineal, red-sensitive opsin is expressed at 48 h postfertilization. Visual pigment expression provides a useful tool for investigations of early cell fate in zebrafish.

Animals↗
PubMedDate not supplied

Erratum: Temporal and spatial patterns of opsin gene expression in the zebrafish (Danio rerio): corrections with additions.

We report here a reexamination of the developmental expression of cone opsins in the zebrafish retina. The red- and blue-sensitive opsins appear at 51 h postfertilization (hpf) whereas ultraviolet (UV) opsin is not seen until after 55 hpf. More cells show red cone opsin expression than blue at 51 and 55 hpf, indicating the sequence of cone opsin expression in zebrafish is first red, then blue, and finally UV. Curiously, morphological development of the cones is in reverse order; UV cones appear quite mature by day 6-7 postfertilization (pf), but morphologically, red cones do not appear adult-like until 15-20 days pf.

Animals↗
PubMed2001

Mercury accumulation rates and spatial patterns in lake sediments from west Greenland: a coast to ice margin transect.

The Arctic is recognized as an important focus for long-range transport of contaminants, such as mercury (Hg), from industrial regions at lower latitudes. In addition to large geographic gaps, there are few long-term retrospective time trends in arctic research, besides the Greenland ice record, to assess the onset of atmospheric pollution as well as to establish the rates of change in the terrestrial environment. In a study of sediments from 21 lakes along a 150 km transect from the coast to the ice sheet margin in the Søndre Strømfjord (Kangerlussuaq) region, we present stratigraphic evidence for elevated Hg inputs to this ice-free region on Greenland's west coast. Nineteen study lakes showed Hg concentration enrichments (HgEFconc) in surface compared to deeper sediments, with a mean HgEFconc of 3. Higher HgEFconc are found in lakes closest to the ice margin. The existence of this Hg gradient is supported by pollution Hg inventories in three 210Pb-dated cores. While 210Pb inventories and Pb pollution are higher at the coast, pollution Hg inventories are nearly 3-fold higher at the ice margin (570 micrograms m-2) than at the coast (210 micrograms m-2). These dated cores also indicate an onset of Hg pollution in the region beginning at least by the late 19th century but possibly as early as the 17th century.

Environmental Pollutants↗
PubMed2005

Stationary spatial patterns during bulk CO electrooxidation on platinum.

We present experimental studies and mathematical modeling on pattern formation during bulk CO electrooxidation on Pt ring electrodes. Profiles of the interfacial potential drop in front of the working electrode were recorded with a potential probe. Stationary self-organized potential patterns were observed under potentiostatic conditions in dilute acidic and basic supporting electrolytes. The amplitude and shape of these potential patterns can be modified by an appropriate local perturbation of the interfacial potential drop. A mathematical model of the formation of these patterns reveals that the homogeneous state becomes unstable through a subcritical Turing-like bifurcation and that several patterned electrode states coexist in wide parameter ranges.

Journal Article↗
PubMed2005

Formation of spatially patterned colloidal photonic crystals through the control of capillary forces and template recognition.

We report the formation of microscopic patterns of substrate-supported, 3D planar colloidal crystals using physical confinement in conjunction with surfaces displaying predetermined binary patterns of hydropholicity. The formation process involves a primary self-assembly wherein nano- and microscale colloids order into a photonic fcc lattice via capillary interactions followed by a secondary template-induced crystal cleavage step. Following this method, arbitrary arrays of pattern elements, which preserve structural and orientational properties of the parent crystal, can be easily obtained.

Journal Article↗
PubMed2003

Spatial patterns of nitrate, chloride, sulfate, and fluoride concentrations in the Woodbine Aquifer of north-central Texas.

A geographic information system was used to map and analyze nitrate, chloride, sulfate, and fluoride concentrations in 110 wells tapping the Woodbine Aquifer. The study area, covering nine counties in north-central Texas, includes large percentages of both urban and agricultural land uses. Land use maps were compared with solute concentration data, and statistics were applied to detect associations between solutes, well depth, and land use. Anthropogenic sources such as fertilizer applications and natural sources such as gypsum, lignite, and clay deposits controlled nitrate, chloride, and sulfate concentrations, each inversely correlated with well depth. However, only one nitrate observation--from a shallow well in the aquifer's outcrop zone--surpassed the maximum contaminant level (MCL) of 44.3 mg L(-1). By comparison, nearly half of the sulfate and several of the chloride observations surpassed the MCL of 250 mg L(-1) for each of those ions. Volcanic ash deposits influenced fluoride concentrations, which directly correlated with well depth. There were no statistically significant associations between solute concentrations and land use. Low recharge rates and confining layers have mitigated anthropogenic impacts on solute levels in the aquifer.

Chlorides↗
PubMed2004

Plant vascular architecture and within-plant spatial patterns in resource quality following herbivory.

In this study, we used plant vascular architecture as a framework from which to predict induced changes in resource quality for Lema trilinea feeding on the host plant Solanum dulcamara at both low and high levels of herbivory. The systemic patterns of allocation of dye from a capillary tube inserted onto the petiole of the first true leaf and sections of the stem were used to establish the degree of vascular connectivity among different leaf positions. Induced changes in the activity of two defensive proteins, proteinase inhibitor (PI) and polyphenol oxidase (PPO), as well as larval L. trilinea performance, were measured in weakly or strongly connected leaves on plants with the first leaf damaged or undamaged by adult L. trilinea. At high levels of herbivory, larval performance decreased on the sixth leaf, which has strong vascular connections to the first leaf, yet increased on the fifth leaf, which has weak vascular connections to the first leaf. PPO activity increased in both the fifth and sixth leaf, while PI activity decreased in the fifth leaf although remaining unchanged in the sixth leaf. At low levels of herbivory, a decrease in larval performance was observed in the sixth leaf, but no change occurred in the weakly connected fifth leaf. Hence, plant vascular architecture clearly predicted within-plant changes in resource quality following only small amounts of herbivore damage.

Animals↗
PubMed1985

Odor-related bulbar EEG spatial pattern analysis during appetitive conditioning in rabbits.

Mildly thirsty rabbits were classically conditioned by reinforcement with water to give a discriminative licking response to the presentation of odors. The jaw movement component of the licking conditioned response (JM CR) was elicited only by the reinforced odor; an increase in the relative frequency of sniffing (RR CR) occurred to both reinforced (CS+) and nonreinforced (CS-) odors. Oscillatory electroencephalographic bursts of high-frequency (40-80 Hz) potentials were recorded epidurally from the lateral olfactory bulb with 64-electrode arrays (8 X 8, 3.5 X 3.5 mm) chronically implanted. Emphasis was on comparing bursts during odor presentation with bursts preceding odor arrival on each trial. A "detection" burst was characterized as occurring immediately after odor arrival and before the sniff response. "Discrimination" bursts occurred during the RR CR and before the JM CR onset. Significant air-odor burst differences (together with sniffing) occurred through up to six sessions for both CS+ and CS- odors for "discrimination" bursts but not for "detection" bursts.

Animals↗
PubMed1988

Two-tiered regulation of spatially patterned engrailed gene expression during Drosophila embryogenesis.

A regulatory cascade, initiated during the syncytial stage of embryogenesis, culminates in the striped pattern of engrailed gene expression at the cellular blastoderm stage. The early regulatory genes, for example the pair-rule genes, are expressed transiently and as their products decay a distinct regulatory programme involving segment polarity genes takes over. This late programme maintains and perhaps modifies the striped pattern of engrailed expression through interactions that may involve cell communication.

Animals↗
PubMed2000

Soil pathogens and spatial patterns of seedling mortality in a temperate tree.

The Janzen-Connell hypothesis proposes that host-specific, distance- and/or density-dependent predators and herbivores maintain high tree diversity in tropical forests. Negative feedback between plant and soil communities could be a more effective mechanism promoting species coexistence because soil pathogens can increase rapidly in the presence of their host, causing conditions unfavourable for local conspecific recruitment. Here we show that a soil pathogen leads to patterns of seedling mortality in a temperate tree (Prunus serotina) as predicted by the Janzen-Connell hypothesis. In the field, the mean distance to parent of seedling cohorts shifted away from maternal trees over a period of 3 years. Seedlings were grown in soil collected 0-5 m or 25-30 m from Prunus trees. Sterilization of soil collected beneath trees improved seedling survival relative to unsterilized soil, whereas sterilization of distant soil did not affect survival. Pythium spp., isolated from roots of dying seedlings and used to inoculate healthy seedlings, decreased survival by 65% relative to controls. Our results provide the most complete evidence that native pathogens influence tree distributions, as predicted by the Janzen-Connell hypothesis, and suggest that similar ecological mechanisms operate in tropical and temperate forests.

Biological Evolution↗