4,299 research outputs found
Angular separations of the lensed QSO images
We have analyzed the observed image separations of the gravitationally lensed
images of QSOs for a possible correlation with the source redshift. Contrary to
the previously noted anti-correlation based on a smaller data set, no
correlation is found for the currently available data. We have calculated the
average image separations of the lensed QSOs as a function of source redshifts,
for isothermal spheres with cores in a flat universe, taking into account the
amplification bias caused by lensing. The shape of the distribution of average
image separation as a function of redshift is very robust and is insensitive to
most model parameters. Observations are found to be roughly consistent with the
theoretical results for models which assume the lens distribution to be (i)
Schechter luminosity function which, however, can not produce images with large
separation and (ii) the mass condensations in a cold dark matter universe, as
given by the Press-Schechter theory if an upper limit of 1-7
M is assumed on the mass of the condensations.Comment: 20 pages, 7 postscript figures, accepted for publication in The
Astrophysical Journa
Atomistic Aspects of Diffusion and Growth on the Si and Ge (111) Surfaces
The stability of interfaces and the mechanisms of thin film growth on
semiconductors are issues of central importance in electronic devices. These
issues can only be understood through detailed study of the relevant
microscopic processes. Experimental studies are able to provide detailed,
atomic scale information for model systems. Theoretical analysis of
experimental results is essential in explaining certain surprising observations
and in providing guidance for optimizing conditions and methods of growth. We
review recent theoretical work on the diffusion of adatoms, the structure of
adsorbate monolayers, and their implications for growth on the Si and Ge (111)
surfaces. The theoretical analysis consists of first-principles calculations of
the total-energy and entropy factors for stable, metastable and saddle-point
configurations. These calculations are supplemented by Monte Carlo simulations
of simple models that afford direct contact with experimental observations.Comment: 30 pages, 11 figures (sent upon request, non-standard format
Ram pressure drag - the effects of ram pressure on dark matter and stellar disk dynamics
We investigate the effects of ram pressure stripping on gas-rich disk
galaxies in the cluster environment. Ram pressure stripping principally effects
the atomic gas in disk galaxies, stripping away outer disk gas to a truncation
radius. We demonstrate that the drag force exerted on truncated gas disks is
passed to the stellar disk, and surrounding dark matter through their mutual
gravity. Using a toy model of ram pressure stripping, we show that this can
drag a stellar disk and dark matter cusp off centre within it's dark matter
halo by several kiloparsecs. We present a simple analytical description of this
process that predicts the drag force strength and its dependency on ram
pressures and disk galaxy properties to first order. The motion of the disk can
result in temporary deformation of the stellar disk. However we demonstrate
that the key source of stellar disk heating is the removal of the gas potential
from within the disk. This can result in disk thickening by approximately a
factor of two in gas-rich disks.Comment: Accepted by MNRAS (Oct 2011) 17 pages, 11 figures, 1 tabl
Factors Influencing The Practice Of Exclusive Breastfeeding In Three Regions Of Nigeria
Background: Breastfeeding is the super food for babies and is sufficient if given exclusively in the first six months of a baby's life. In Nigeria, the practice of breastfeeding is high but Exclusive Breastfeeding (EBF) rates remain low at 13%. Several interrelating factors directly or indirectly affect the decision or ability of mothers to practice EBF. The objective of this study was to assess the factors influencing EBF in Nigeria.Methodology: A cross sectional survey among 433 mothers of children between six and twenty-four months old was conducted in urban and peri-urban/rural parts of Zaria, Abakaliki, and Ibadan. The study adopted a mixed research methodology that consisted of key informant interviews, structured questionnaires, and focus group discussions. Descriptive statistic was used to analyze the quantitative data while the themes in the qualitative data were analyzed using manual content analysis.Results: Approximately 90% of all mothers interviewed had heard about EBF, although with variations in the exact definition of EBF as many interpreted it to be just till the start of 6 months. The practice of EBF is low - Ibadan (16%), Abakaliki (10%) and Zaria (2%).Inaccurate knowledge of EBF, occupation, antenatal care attendance, age of mothers, supportive environment from stakeholders are some factors associated with the practice of EBF.Conclusion: The findings in this study indicate that several factors affect the practice of EBF in Nigeria. Improving the practice of EBF in the country will require a multifaceted approach and concerted efforts from stakeholders to address the deterring factors limiting its practice.Keywords: Exclusive Breastfeeding, Interrelating factors, social activity and significant others, and Nigeri
Measuring and Modelling the Redshift Evolution of Clustering: the Hubble Deep Field North
(abridged) The evolution of galaxy clustering from z=0 to z=4.5 is analyzed
using the angular correlation function and the photometric redshift
distribution of galaxies brighter than I_{AB}\le 28.5 in the HDF North. The
reliability of the photometric redshift estimates is discussed on the basis of
the available spectroscopic redshifts, comparing different codes and
investigating the effects of photometric errors. The redshift bins in which the
clustering properties are measured are then optimized to take into account the
uncertainties of the photometric redshifts. The results show that the comoving
correlation length has a small decrease in the range 0<z<1 followed by an
increase at higher z. We compare these results with the theoretical predictions
of a variety of cosmological models belonging to the general class of CDM. The
comparison with the expected mass clustering evolution indicates that the
observed high-redshift galaxies are biased tracers of the dark matter with an
effective bias b strongly increasing with redshift. Assuming an Einstein-de
Sitter universe, we obtain b\simeq 2 at z=2 and b\simeq 5 at z=4. A comparison
of the clustering amplitudes that we measured at z=3 with those reported for
LBG suggests that the clustering depends on the abundance of the objects: more
abundant objects are less clustered, as expected in the paradigm of
hierarchical galaxy formation. The strong clustering and high bias measured at
z=3 are consistent with the expected density of massive haloes predicted for
the various cosmologies here considered. At z=4, the strong clustering observed
in the HDF requires a significant fraction of massive haloes to be already
formed by that epoch. This feature could be a discriminant test for the
cosmological parameters if confirmed by future observations.Comment: 23 pages, Latex using MN style, figures enclosed. Version accepted
for publication in MNRA
IL-36 Induces Bisphosphonate-Related Osteonecrosis of the Jaw-Like Lesions in Mice by Inhibiting TGF-β-Mediated Collagen Expression
Long-term administration of nitrogen-containing bisphosphonates can induce detrimental side effects such as bisphosphonate-related osteonecrosis of the jaw (BRONJ) in human. Although inflammation is known to be associated with BRONJ development, the detailed underlying mechanism remains unknown. Here, we report that the pro-inflammatory cytokine IL-36α is, in part, responsible for the BRONJ development. We found a notably higher level of IL-36α and lower level of collagen in the BRONJ lesions in mice. We also found that IL-36α remarkably suppressed TGF-β-mediated expression of Collα1 and α-Sma via the activation of Erk signaling pathway in mouse gingival mesenchymal stem cells. When IL-36 signaling was abrogated in vivo, development of BRONJ lesions was ameliorated in mice. Taken together, we showed the pathologic role of IL-36α in BRONJ development by inhibiting collagen expression and demonstrated that IL-36α could be a potential marker and a therapeutic target for the prevention and treatment of BRONJ
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