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Institution

University of Oklahoma

EducationNorman, Oklahoma, United States
About: University of Oklahoma is a education organization based out in Norman, Oklahoma, United States. It is known for research contribution in the topics: Population & Radar. The organization has 25269 authors who have published 52609 publications receiving 1821706 citations. The organization is also known as: OU & Oklahoma University.


Papers
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Journal ArticleDOI
TL;DR: In this article, a large sample of metal-poor giants from the Bond survey is presented, and the abundances of eight n-capture elements (Sr, Y, Zr, Ba, La, Nd, Eu, and Dy) in 43 stars have been derived from blue and red spectra.
Abstract: New abundances for neutron-capture (n-capture) elements in a large sample of metal-poor giants from the Bond survey are presented. The spectra were acquired with the KPNO 4 m echelle and coude feed spectrographs, and have been analyzed using LTE fine-analysis techniques with both line analysis and spectral synthesis. Abundances of eight n-capture elements (Sr, Y, Zr, Ba, La, Nd, Eu, and Dy) in 43 stars have been derived from blue (λλ4070-4710, R ~ 20,000, S/N ratio ~ 100-200) echelle spectra and red (λλ6100-6180, R ~ 22,000, S/N ratio ~ 100-200) coude spectra, and the abundance of Ba only has been derived from the red spectra for an additional 27 stars. Overall, the abundances show clear evidence for a large star-to-star dispersion in the heavy element-to-iron ratios. This condition must have arisen from individual nucleosynthetic events in rapidly evolving halo progenitors that injected newly manufactured n-capture elements into an inhomogeneous early Galactic halo interstellar medium. The new data also confirm that at metallicities [Fe/H] -2.4, the abundance pattern of the heavy (Z ≥ 56) n-capture elements in most giants is well-matched to a scaled solar system r-process nucleosynthesis pattern. The onset of the main r-process can be seen at [Fe/H] ≈ -2.9; this onset is consistent with the suggestion that low mass Type II supernovae are responsible for the r-process. Contributions from the s-process can first be seen in some stars with metallicities as low as [Fe/H] ~ -2.75 and are present in most stars with metallicities [Fe/H] > -2.3. The appearance of s-process contributions as metallicity increases presumably reflects the longer stellar evolutionary timescale of the (low-mass) s-process nucleosynthesis sites. The lighter n-capture elements (Sr-Y-Zr) are enhanced relative to the heavier r-process element abundances. Their production cannot be attributed solely to any combination of the solar system r- and main s-processes, but requires a mixture of material from the r-process and from an additional n-capture process that can operate at early Galactic time. This additional process could be the weak s-process in massive (~25 M☉) stars, or perhaps a second r-process site, i.e., different from the site that produces the heavier (Z ≥ 56) n-capture elements.

580 citations

Journal ArticleDOI
06 Jan 2000-Nature
TL;DR: It is reported that observed patterns of range contraction do not support the above predictions and that most species examined persist in the periphery of their historical geographical ranges, with the core populations persisting until the final stages of decline.
Abstract: As one moves from the core to the periphery of a species' geographical range, populations occupy less favourable habitats and exhibit lower and more variable densities. Populations along the periphery of the range tend to be more fragmented and, as a result, are less likely to receive immigrants from other populations. A population's probability of extinction is directly correlated with its variability and inversely correlated with density and immigration rate. This has led to the prediction that, when a species becomes endangered, its geographical range should contract inwards, with the core populations persisting until the final stages of decline. Convinced by these logical but untested deductions, conservation biologists and wildlife managers have been instructed to avoid the range periphery when planning conservation strategies or allocating resources for endangered species. We have analysed range contraction in 245 species from a broad range of taxonomic groups and geographical regions. Here we report that observed patterns of range contraction do not support the above predictions and that most species examined persist in the periphery of their historical geographical ranges.

580 citations

Journal ArticleDOI
23 Feb 1990-Science
TL;DR: The snail Physella virgata virGata, a widely distributed freshwater pulmonate, was observed to change its life-history characteristics in the presence of the crayfish Orconectes virilis in spring-fed Oklahoma streams, indicating that the life histories of these snails are phenotypically plastic.
Abstract: The snail Physella virgata virgata, a widely distributed freshwater pulmonate, was observed to change its life-history characteristics in the presence of the crayfish Orconectes virilis in spring-fed Oklahoma streams. These changes were apparently initiated by a water-borne cue released when crayfish fed on conspecific snails. In the presence of the cue, snails exhibited rapid growth rates and little reproduction until they reached a size of about 10 mm after 8 months. In the absence of the cue, snails typically grew to about 4 mm (3.5 months) and then began reproduction. The chemically inducible shift indicates that the life histories of these snails are phenotypically plastic. By increasing the variance associated with size and age of maturity, prey may increase the likelihood of coexisting with seasonal predators.

578 citations

Journal ArticleDOI
TL;DR: A new, monophyletic taxonomy for dendrobatids is proposed, recognizing the inclusive clade as a superfamily (Dendrobatoidea) composed of two families (one of which is new), six subfamilies (three new), and 16 genera (four new).
Abstract: The known diversity of dart-poison frog species has grown from 70 in the 1960s to 247 at present, with no sign that the discovery of new species will wane in the foreseeable future. Although this growth in knowledge of the diversity of this group has been accompanied by detailed investigations of many aspects of the biology of dendrobatids, their phylogenetic relationships remain poorly understood. This study was designed to test hypotheses of dendrobatid diversification by combining new and prior genotypic and phenotypic evidence in a total evidence analysis. DNA sequences were sampled for five mitochondrial and six nuclear loci (approximately 6,100 base pairs [bp]; x¯ = 3,740 bp per terminal; total dataset composed of approximately 1.55 million bp), and 174 phenotypic characters were scored from adult and larval morphology, alkaloid profiles, and behavior. These data were combined with relevant published DNA sequences. Ingroup sampling targeted several previously unsampled species, including Ar...

577 citations

Journal ArticleDOI
TL;DR: This is the first comprehensive microarray currently available for studying biogeochemical processes and functional activities of microbial communities important to human health, agriculture, energy, global climate change, ecosystem management, and environmental cleanup and restoration.
Abstract: Owing to their vast diversity and as-yet uncultivated status, detection, characterization and quantification of microorganisms in natural settings are very challenging, and linking microbial diversity to ecosystem processes and functions is even more difficult. Microarray-based genomic technology for detecting functional genes and processes has a great promise of overcoming such obstacles. Here, a novel comprehensive microarray, termed GeoChip, has been developed, containing 24 243 oligonucleotide (50 mer) probes and covering 410 000 genes in 4150 functional groups involved in nitrogen, carbon, sulfur and phosphorus cycling, metal reduction and resistance, and organic contaminant degradation. The developed GeoChip was successfully used for tracking the dynamics of metal-reducing bacteria and associated communities for an in situ bioremediation study. This is the first comprehensive microarray currently available for studying biogeochemical processes and functional activities of microbial communities important to human health, agriculture, energy, global climate change, ecosystem management, and environmental cleanup and restoration. It is particularly useful for providing direct linkages of microbial genes/populations to ecosystem processes and functions.

576 citations


Authors

Showing all 25490 results

NameH-indexPapersCitations
Ronald C. Kessler2741332328983
Michael A. Strauss1851688208506
Derek R. Lovley16858295315
Ashok Kumar1515654164086
Peter J. Schwartz147647107695
Peter Buchholz143118192101
Robert Hirosky1391697106626
Elizabeth Barrett-Connor13879373241
Brad Abbott137156698604
Lihong V. Wang136111872482
Itsuo Nakano135153997905
Phillip Gutierrez133139196205
P. Skubic133157397343
Elizaveta Shabalina133142192273
Richard Brenner133110887426
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
202392
2022348
20212,425
20202,481
20192,433
20182,396