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Search Results: 1 - 10 of 118101 matches for " T. Koehler "
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Effects of delayed estrogen treatment and 20-HETE synthesis inhibition on postischemic pial artery response to acetylcholine in rats  [PDF]
Chikao Miyazaki, Emil N. Zeynalov, Raymond C. Koehler, Marguerite T. Littleton-Kearney
Open Journal of Molecular and Integrative Physiology (OJMIP) , 2014, DOI: 10.4236/ojmip.2014.41001

Relatively little is known about the effects of estrogen on postischemic cerebral vasomotor dynamics after ischemic injury. Emerging hypotheses suggest that the timing after menopause at which hormone replacement is initiated might be important and might modulate the potential benefits of estrogen on brain rescue once a cerebral ischemic event occurs. Therefore, we sought to determine if protracted hypoestrogenicity modifies estrogen’s protective effects on postischemic pial artery dilatory dysfunction and if the arachidonic acid metabolite 20-hydroxyeicosatetraeonic (20-HETE) contributes to the dysfunction. Pial artery dilation to acetylcholine was examined before and 1 hour after 15 minutes forebrain ischemia. The rat study groups included: sexually mature males (M), naive (N), OVX (OV), estrogen-treated OVX females (E1; estrogen started 1 week post ovariectomy) and delayed estrogen-treated (E10; started 10 weeks post ovariectomy) females. Postischemic responses were assessed before and after superfusion of the 20-HETE synthesis inhibitor N-hydroxy-N’-(4-butyl-2-methylphenyl)-formamidine (HET0016). Postischemic acetylcholine dilation was depressed in M, OV and E10 compared to N and E1 rats. Compared to E1, delayed estrogen replacement worsened acetylcholine-induced dilation. Postischemic microvascular estrogen receptor alpha (ERα) density was similar in the OV, E1 and E10 rats. Postischemic application of HET0016 failed to improve acetylcholine dilation. Continuous infusion of HET0016 during and after ischemia did not reverse postischemic pial vasodilatory dysfunction. Timing of estrogen replacement may be critical for vascular health after cerebral ischemic injury. Postischemic loss of acetylcholine reactivity does not appear to involve mechanisms related to 20-HETE synthesis or microvascular ERα expression.

Making Cold Molecules by Time-dependent Feshbach Resonances
P. S. Julienne,E. Tiesinga,T. Koehler
Physics , 2003, DOI: 10.1080/09500340408232491
Abstract: Pairs of trapped atoms can be associated to make a diatomic molecule using a time dependent magnetic field to ramp the energy of a scattering resonance state from above to below the scattering threshold. A relatively simple model, parameterized in terms of the background scattering length and resonance width and magnetic moment, can be used to predict conversion probabilities from atoms to molecules. The model and its Landau-Zener interpretation are described and illustrated by specific calculations for $^{23}$Na, $^{87}$Rb, and $^{133}$Cs resonances. The model can be readily adapted to Bose-Einstein condensates. Comparison with full many-body calculations for the condensate case show that the model is very useful for making simple estimates of molecule conversion efficiencies.
New Analysis of the Delta I = 1/2 Rule in Kaon Decays and the B_K Parameter
T. Hambye,G. O. Koehler,P. H. Soldan
Physics , 1999, DOI: 10.1007/s100529900084
Abstract: We present a new analysis of the Delta I = 1/2 rule in K --> pi pi decays and the B_K parameter. We use the 1/N_c expansion within the effective chiral lagrangian for pseudoscalar mesons and compute the hadronic matrix elements at leading and next-to-leading order in the chiral and the 1/N_c expansions. Numerically, our calculation reproduces the dominant Delta I = 1/2 K --> pi pi amplitude. Our result depends only moderately on the choice of the cutoff scale in the chiral loops. The Delta I = 3/2 amplitude emerges sufficiently suppressed but shows a significant dependence on the cutoff. The B_K parameter turns out to be smaller than the value previously obtained in the 1/N_c approach. It also shows a significant dependence on the choice of the cutoff scale. Our results indicate that corrections from higher order terms and/or higher resonances are large for the Delta I = 3/2 K --> pi pi amplitude and the (|Delta S| = 2) K^0 -- anti K^0 transition amplitude.
The local luminosity function of QSOs and Seyfert 1 nuclei
T. Koehler,D. Groote,D. Reimers,L. Wisotzki
Physics , 1997,
Abstract: We present the analysis of a new flux-limited sample of bright quasars and Seyfert 1 galaxies in an effective area of 611 square deg, drawn from the Hamburg/ESO survey. We confirm recent claims that bright quasars have a higher surface density than previously thought. Special care was taken to avoid morphological and photometric biases against low-redshift quasars, and about 50 % of the sample objects are at z < 0.3, spanning a range of three decades in luminosity. While our derived space densities for low-luminosity Seyfert 1 nuclei are consistent with those found in the literature, we find that luminous QSOs, M_B < -24, are much more numerous in the local universe than previous surveys indicated. The optical luminosity functions of Seyfert 1 nuclei and QSOs join smoothly, and if the host galaxy contributions are taken into account, a single power-law of slope alpha = -2.2 describes the combined local luminosity function adequately, over the full range in absolute magnitude. Comparing our data with published results at higher redshifts, we can rule out pure luminosity evolution as an acceptable parametrisation; the luminosity function of quasars changes shape and slope with z, in the sense that the most luminous quasars show the weakest evolution.
Is there a plasma density gradient role on the generation of short-scale Farley-Buneman waves?
C. Haldoupis, T. Ogawa, K. Schlegel, J. A. Koehler,T. Ono
Annales Geophysicae (ANGEO) , 2005,
Abstract: The physics of the unstable E-region plasma is based on the modified two stream, or Farley-Buneman, and the gradient drift instabilities. The theory combines both mechanisms into a single dispersion relation which applies for the directly generated short-scale plasma waves, known as type 1 irregularities. In the absence of a plasma gradient it is only the two stream mechanism acting which favors wave excitation if E×B electron drifts relative to the ions exceed a threshold slightly above the ion acoustic speed. On the other hand, the theory also predicts that a destabilizing (stabilizing) electron density gradient acts to decrease (increase) the ion acoustic threshold, and hence the wave phase velocities at threshold, depending on the gradient strength and the wavelength. Given a destabilizing plasma gradient, the threshold reduction is larger at longer than shorter wavelengths and thus the best way to test the gradient role is by simultaneous observations of type 1 waves at two or more radio backscatter frequencies. The present paper relies on dual frequency backscatter observations of 1.1 m and 3.1 m type 1 irregularities made simultaneously at 144 MHz and 50 MHz, respectively, in mid-latitude sporadic E-layers. Using as typical plasma gradient scale lengths for destabilized sporadic E-layers those that are obtained from rocket electron density profiles, the radar observations are compared with the predictions of kinetic theory. The results suggest that the plasma density gradient effect on meter scale Farley-Buneman waves is not important. This is reinforced further by the analysis of backscatter from destabilized meteor trail plasma when very steep gradients are expected in electron density. The present findings, and more from past studies, question the electron density gradient role in the generation of short-scale plasma waves as predicted by the linear instability theory. This deserves attention and more study.
Digital libraries and World Wide Web sites and page persistence.
Wallace Koehler
Information Research: an international electronic journal , 1999,
Abstract: Web pages and Web sites, some argue, can either be collected as elements of digital or hybrid libraries, or, as others would have it, the WWW is itself a library. We begin with the assumption that Web pages and Web sites can be collected and categorized. The paper explores the proposition that the WWW constitutes a library. We conclude that the Web is not a digital library. However, its component parts can be aggregated and included as parts of digital library collections. These, in turn, can be incorporated into "hybrid libraries." These are libraries with both traditional and digital collections. Material on the Web can be organized and managed. Native documents can be collected in situ, disseminated, distributed, catalogueed, indexed, controlled, in traditional library fashion. The Web therefore is not a library, but material for library collections is selected from the Web. That said, the Web and its component parts are dynamic. Web documents undergo two kinds of change. The first type, the type addressed in this paper, is "persistence" or the existence or disappearance of Web pages and sites, or in a word the lifecycle of Web documents. "Intermittence" is a variant of persistence, and is defined as the disappearance but reappearance of Web documents. At any given time, about five percent of Web pages are intermittent, which is to say they are gone but will return. Over time a Web collection erodes. Based on a 120-week longitudinal study of a sample of Web documents, it appears that the half-life of a Web page is somewhat less than two years and the half-life of a Web site is somewhat more than two years. That is to say, an unweeded Web document collection created two years ago would contain the same number of URLs, but only half of those URLs point to content. The second type of change Web documents experience is change in Web page or Web site content. Again based on the Web document samples, very nearly all Web pages and sites undergo some form of content within the period of a year. Some change content very rapidly while others do so infrequently (Koehler, 1999a). This paper examines how Web documents can be efficiently and effectively incorporated into library collections. This paper focuses on Web document lifecycles: persistence, attrition, and intermittence. While the frequency of content change has been reported (Koehler, 1999a), the degree to which those changes effect meaning and therefore the integrity of bibliographic representation is yet not fully understood. The dynamics of change sets Web libraries apart from the traditional library
A bibliometric analysis of select information science print and electronic journals in the 1990s
Wallace Koehler
Information Research: an international electronic journal , 2000,
Abstract: This paper examines three e-journals and one paper journal begun in the 1990s within the information science genre. In addition, these journals are compared to what is perhaps the leading information science journal,one that has been published continuously for fifty years. The journals we examine are CyberMetrics, Information Research, the Journal of Internet Cataloging, Libres, and the Journal of the American Society for Information Science. We find that there are a number of important differences among the journals. These include frequency of publication, publication size, number of authors, and the funding status of articles. We also find differences among journals for distributions of authors by gender and corporate authors by region. Some of the regional differences can be explained by journal maturation -- the more mature the journal the greater the dispersion. We also find that women are more likely to publish in the newer journals than in JASIS. The fact that a journal is or is not an e-journal does not appear to affect its presence or "behaviour" as an information science journal.
A longitudinal study of Web pages continued: a consideration of document persistence. Web documents, Half-life, Linkrot, Persistence, Web citations
Wallace Koehler
Information Research: an international electronic journal , 2004,
Abstract: It is well established that Web documents are ephemeral in nature. The literature now suggests that some Web objects are more ephemeral than others. Some authors describe this in terms of a Web document half-life, others use terms like 'linkrot' or persistence. It may be that certain 'classes' of Web documents are more or less likely to persist than are others. This article is based upon an evaluation of the existing literature as well as a continuing study of a set of URLs first identified in late 1996. It finds that a static collection of general Web pages tends to 'stabilize' somewhat after it has 'aged'. However 'stable' various collections may be, their instability nevertheless pose problems for various classes of users. Based on the literature, it also finds that the stability of more specialized Web document collections (legal, educational, scientific citations) vary according to specialization. This finding, in turn, may have implications both for those who employ Web citations and for those involved in Web document collection development.
O Grande Sert o e a Literatura e o Subdesenvolvimento
Jaqueline Koehler
Revista Trías , 2012,
Abstract: Este artigo analisa o romance Grande sert o: veredas a partir da leitura do texto “Literatura e Subdesenvolvimento” de Antonio Candido. Procurando repensar o romance roseano como um retrato do país, porém sem a presen a de uma vis o historicamente presente nas literaturas latinas, da natureza como elemento romantico, mas com uma “cor local” que tem como fun o trazer um olhar crítico a respeito da realidade do país. Um exemplo discutido é o de Riobaldo, que ascende socialmente através da educa o e, com isso, reflete em toda sua narrativa a respeito da condi o social brasileira.
The Black Belt Librarian: Real-World Safety & Security (Book Review)
Abby Koehler
Journal of Library Innovation , 2012,
Abstract: A review of Warren Graham's updated The Black Belt Librarian: Real-World Safety & Security.
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