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Search Results: 1 - 10 of 143 matches for " Bunker "
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Luminosities, Masses and Star Formation Rates of Galaxies at High Redshift (IAU279 conference proceedings)
Andrew Bunker
Physics , 2013, DOI: 10.1017/S1743921312012963
Abstract: There has been great progress in recent years in discovering star forming galaxies at high redshifts (z>5), close to the epoch of reionization of the intergalactic medium (IGM). The WFC3 and ACS cameras on the Hubble Space Telescope have enabled Lyman break galaxies to be robustly identified, but the UV luminosity function and star formation rate density of this population at z=6-8 seems to be much lower than at z=2-4. High escape fractions and a large contribution from faint galaxies below our current detection limits would be required for star-forming galaxies to reionize the Universe. We have also found that these galaxies have blue rest-frame UV colours, which might indicate lower dust extinction at z>5. There has been some spectroscopic confirmation of these Lyman break galaxies through Lyman-alpha emission, but the fraction of galaxies where we see this line drops at z>7, perhaps due to the onset of the Gunn-Peterson effect (where the IGM is opaque to Lyman-alpha).
Near-Infrared Emission Line Searches for High-Redshift Galaxies
Andrew Bunker
Physics , 1999,
Abstract: In this article I review recent developments in near-infrared emission line searches for star-forming galaxies at high redshift. Using the J-, H- & K-bands we can potentially chart the history of star formation over the range 110, the next frontier in the Hy-Redshift Universe.
Democracia comunal en Chile, 1992-2008
Bunker, Kenneth;Navia, Patricio;
Política y gobierno , 2010,
Abstract: since first held in post-dictatorship chile in 1992, municipal elections have consolidated as an essential component of chilean democracy. in this article we assess whether decentralization in chile has helped redefine and re-articulate political practices and if the party system has reproduced the existing patterns at the local level. we evaluate three scenarios. first, if the behavior of voters in local elections is similar to their behavior in legislative elections. second, if municipal election results are independent of national political processes. third, if the average tenure of mayors and their reelection rates are similar to those of deputies. we conclude by suggesting that the development of local institutions have tended to reproduce the practices and characteristics of the national political system rather than to redefine the balance of power between the executive and legislative bodies, or to allow the emergence of new patterns in the political careers of democratically elected representatives.
Epidemiological Risk Factors For Breast Cancer – A Review
MN Okobia, CH Bunker
Nigerian Journal of Clinical Practice , 2005,
Abstract: The rising global incidence, morbidity and mortality from breast cancer has led to intensified efforts in the search for etiological factors of the disease. While international variations in the incidence of the disease may implicate a role for environmental factors, available evidence indicates that lifetime estrogen exposure may be a critical factor in breast carcinogenesis. While increase age and the female sex are well-recognized risk factors, reproductive characteristics such as age at menarche and menopause, menstrual irregularity, age at first and last childbirth, parity and breastfeeding have also been linked to breast carcinogenesis. Early menarche and late menopause are associated with increased lifetime exposure to estrogens. In addition, a long period from Tanner stage breast-2 to onset of ovulatory cycles and a long period of luteal inadequacy anovulatory cycles characteristic of the perimenopausal years creates long estrogen windows favorable for tumor induction. The intense differentiation of the terminal duct lobular unit associated with each full term pregnancy and release of various hormones, autocrine and paracrine growth factors during lactation may explain the protective effects the protective effects of early age at first full term pregnancy, parity and lactation of breast cancer risk. A protective role for xenoestgrogens has been postulated and evidence is emerging in support of an increased breast cancer risk with abortion and prolonged use of postmenopausal hormone replacement therapy. Appreciating relevant risk factors for breast cancer in the population is central to any preventive and control program aimed at reducing the burden of disease through the design and implementation of culturally sensitive interventions. Key Words: Breast cancer, risk factors, estrogens, parity Nigerian Journal of Clinical Practice Vol 8(1) 2005: 35-42
The Aetiopathogenesis of Male Genital Lichen Sclerosus (MGLSc)
TN Shim,CB Bunker
Nepal Journal of Dermatology, Venereology & Leprology , 2013, DOI: 10.3126/njdvl.v11i1.7929
Abstract: DOI: http://dx.doi.org/10.3126/njdvl.v11i1.7929
A Matched Catalogue of z> 5.9 Galaxies in the WFC3 Hubble Ultra Deep Field
Andrew Bunker,Stephen Wilkins
Physics , 2009,
Abstract: There have been several independent analyses of the recent Wide Field Camera 3 images of the Hubble Deep Field, selecting galaxies at z>6 through the Lyman break technique. Presented here is a matched catalogue of objects in common between the analyses posted to this preprint server, listing the different catalogue names associated with the same sources.
Parallel Excluded Volume Tempering for Polymer Melts
Alex Bunker,Burkhard Duenweg
Physics , 2000, DOI: 10.1103/PhysRevE.63.016701
Abstract: We have developed a technique to accelerate the acquisition of effectively uncorrelated configurations for off-lattice models of dense polymer melts which makes use of both parallel tempering and large scale Monte Carlo moves. The method is based upon simulating a set of systems in parallel, each of which has a slightly different repulsive core potential, such that a thermodynamic path from full excluded volume to an ideal gas of random walks is generated. While each system is run with standard stochastic dynamics, resulting in an NVT ensemble, we implement the parallel tempering through stochastic swaps between the configurations of adjacent potentials, and the large scale Monte Carlo moves through attempted pivot and translation moves which reach a realistic acceptance probability as the limit of the ideal gas of random walks is approached. Compared to pure stochastic dynamics, this results in an increased efficiency even for a system of chains as short as $N = 60$ monomers, however at this chain length the large scale Monte Carlo moves were ineffective. For even longer chains the speedup becomes substantial, as observed from preliminary data for $N = 200$.
Galaxy Morphology in the GTO-NICMOS Northern Hubble Deep Field
Andrew J. Bunker
Physics , 1999,
Abstract: The increased incidence of morphologically peculiar galaxies at faint magnitudes in the optical could be attributable either to "morphological k-corrections" (the change in appearance when viewing high-z objects at shorter rest-frame wavelengths), or an increase in the incidence of truly irregular systems with redshift. The deep, high-resolution GTO-NICMOS near-IR imaging of a portion of the northern Hubble Deep Field has been combined with the WFPC2 data and photometric redshift estimates to study the redshift evolution of morphology, comparing galaxy appearance at the same rest-wavelengths (Bunker, Spinrad & Thompson 1999). It appears that morphological k-corrections are only significant in a minority of cases, and that once these are accounted for, evolution is still demanded - galaxies were smaller and more irregular in the past, with some of the peculiarities probably merger-related. This multi-waveband data set also enables a study of the spatially-resolved stellar populations in distant galaxies. A near-infrared analysis of some of the brighter spirals shows more pronounced barred structure than in the optical, indicating that the apparent decline in barred spirals at faint magnitudes in the optical HDF may be due to band-shifting effects at the higher redshifts, rather than intrinsic evolution.
Longitudinal magnetic excitations in classical spin systems
Alex Bunker,D. P. Landau
Physics , 1999, DOI: 10.1103/PhysRevLett.85.2601
Abstract: Using spin dynamics simulations we predict the splitting of the longitudinal spin wave peak in all antiferromagnets with single site anisotropy into two peaks separated by twice the energy gap at the Brillouin zone center. This phenomenon has yet to be observed experimentally but can be easily investigated through neutron scattering experiments on MnF$_2$ and FeF$_2$. We have also determined that for all classical Heisenberg models the longitudinal propagative excitations are entirely multiple spin-wave in nature.
Estrogen Metabolism and Breast Cancer Risk – A Review
M N Okobia, C H Bunker
African Journal of Reproductive Health , 2006,
Abstract: The standard paradigm providing a general mechanistic explanation for the association of cumulative, excessive estrogen exposure and breast cancer risk is that estrogen and perhaps progesterone affect the rate of cell division, and thus manifest their effect on the risk of breast cancer by causing proliferation of breast epithelial cells. Proliferating cells are susceptible to genetic errors during DNA replication which, if uncorrected, can ultimately lead to a malignant phenotype. This standard paradigm has recently been expanded to encompass emerging research data supporting a complementary genotoxic pathway mediated by the generation and redox cycling of reactive oxygen species through the metabolic effects of estrogens metabolites such 4 and 16a-hydroxy catechols. This paradigm shift is necessitated by evidence of estrogen induced carcinogenesis in several animal and human models following exposure to these estrogen metabolites. This review examines some of the available evidence relating these estrogen metabolites to animal and human breast carcinogenesis African Journal of Reproductive Health Vol. 10 (1) 2006: pp. 13-25
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