34,111 research outputs found
Chemical evolution and depletion pattern in Damped Lyman-alpha (DLA) systems
In this paper we point out a previously unnoticed anticorrelation between the
observed abundance ratio [X/Zn] (where Zn is assumed to be undepleted and X
stands for the refractories Fe, Cr and Ni) and metal column density
([Zn/H]+log(N{HI})) in DLAs. We suggest that this trend is an unambiguous sign
of dust depletion, since metal column density is a measure of the amount of
dust along the line of sight. Assuming that DLAs are (proto-)galactic disks and
using detailed chemical evolution models with metallicity dependent yields we
study chemical evolution and dust depletion patterns for alpha and iron-peak
elements in DLAs. When observational constraints on the metal column density of
DLAs are taken into account (as suggested in Boisse et al. 1998) we find that
our models reproduce fairly well the observed mild redshift evolution of the
abundances of 8 elements (Al, Si, S, Cr, Mn, Fe, Zn and Ni) as well as the
observed scatter at a given redshift. By considering the aforementioned
dependence of abundance ratios on metal column density, we further explore the
general dust depletion pattern in DLAs, comparing to our model results and to a
solar reference pattern. We suggest that further measurements of the key
elements, i.e. Zn, S and Mn, will help to gain more insight into the nature of
DLAs. In any case, the presently uncertain nucleosynthesis of Zn in massive
stars (on which a large part of these conclusions is based) should be carefully
scrutinised.Comment: 12 pages, 4 figures, Astronomy and Astrophysics, in pres
Top-Antitop-Quark Production and Decay Properties at the Tevatron
At the Tevatron, the collider experiments CDF and DO have data sets at their
disposal that comprise a few thousand reconstructed top-antitop-quark pairs and
allow for precision measurements of the cross section as well as production and
decay properties. Besides comparing the measurements to standard model
predictions, these data sets open a window to physics beyond the standard
model. Dedicated analyses look for new heavy gauge bosons, fourth generation
quarks, and flavor-changing neutral currents. In this mini-review the current
status of these measurements is summarized.Comment: Mini-review to be submitted to Mod. Phys. Lett. A, was derived from
the proceedings of the 21st Rencontres de Blois: Windows on the Universe,
Blois, France, 21. - 27. June 2009. 19 pages. 2nd revision: correct a few
minor mistakes, update references
No association of CTLA-4 polymorphisms with susceptibility to Behcet disease
Background: Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is a key negative regulator of T lymphocytes and has been shown to be associated with a number of autoimmune diseases. The present study was performed to assess the association between CTLA-4 polymorphisms and Behcet disease (BD) in Chinese patients. Methods: Two hundred and twenty-eight BD patients and 207 controls were analysed for four single nucleotide polymorphisms (SNPs) (21661A/G, 2318C/T, + 49G/A and CT60G/A) in the CTLA-4 gene by PCR-restriction fragment length polymorphism (RFLP) analysis. The association between SNP +49A/G and BD in Chinese population as well as other ethnic groups was analysed by meta-analysis. Results: No association could be detected between CTLA-4 SNPs or haplotypes and BD. Also, no association was observed between CTLA-4 polymorphisms and BD subgroups, stratified by clinical features. A meta-analysis showed that there was no heterogeneity between studies (p = 0.60, I-2 = 0%) and that CTLA-4 SNP + 49 was not associated with BD (overall effect: Z = 0.26, p = 0.79). Conclusion: This study and a meta-analysis failed to demonstrate any association between the tested CTLA-4 polymorphisms and B
Four Statements about the Fourth Generation
This summary of the Workshop "Beyond the 3-generation SM in the LHC era"
presents a brief discussion of the following four statements about the fourth
generation: 1) It is not excluded by EW precision data; 2) It addresses some of
the currently open questions; 3) It can accommodate emerging possible hints of
new physics; 4) LHC has the potential to discover or fully exclude it.Comment: Summary of the "Beyond the 3-generation SM in the LHC era" Workshop,
CERN, September 4-5, 2008; 7 pages. V2: updated bibliography and minor typos
fixed. To appear in PMC Physics
EAM Modulated DBR Laser Array for TWDM-PON Applications
4 Channel DBR laser arrays are fabricated for use in optical line terminals of TWDM-PON systems. These combine 1.4Q InGaAsP material in the DBR with EAMs using the identical active layer design. A tuning range ~10 nm and extinction ratio of >27 dB are measured
The spectral energy distribution of galaxies at z > 2.5: Implications from the Herschel/SPIRE color-color diagram
We use the Herschel SPIRE color-color diagram to study the spectral energy
distribution (SED) and the redshift estimation of high-z galaxies. We compiled
a sample of 57 galaxies with spectroscopically confirmed redshifts and SPIRE
detections in all three bands at , and compared their average SPIRE
colors with SED templates from local and high-z libraries. We find that local
SEDs are inconsistent with high-z observations. The local calibrations of the
parameters need to be adjusted to describe the average colors of high-z
galaxies. For high-z libraries, the templates with an evolution from z=0 to 3
can well describe the average colors of the observations at high redshift.
Using these templates, we defined color cuts to divide the SPIRE color-color
diagram into different regions with different mean redshifts. We tested this
method and two other color cut methods using a large sample of 783
Herschel-selected galaxies, and find that although these methods can separate
the sample into populations with different mean redshifts, the dispersion of
redshifts in each population is considerably large. Additional information is
needed for better sampling.Comment: 17 pages, 14 figures, accepted for publication in A&
On Singularity Formation of a Nonlinear Nonlocal System
We investigate the singularity formation of a nonlinear nonlocal system. This
nonlocal system is a simplified one-dimensional system of the 3D model that was
recently proposed by Hou and Lei in [13] for axisymmetric 3D incompressible
Navier-Stokes equations with swirl. The main difference between the 3D model of
Hou and Lei and the reformulated 3D Navier-Stokes equations is that the
convection term is neglected in the 3D model. In the nonlocal system we
consider in this paper, we replace the Riesz operator in the 3D model by the
Hilbert transform. One of the main results of this paper is that we prove
rigorously the finite time singularity formation of the nonlocal system for a
large class of smooth initial data with finite energy. We also prove the global
regularity for a class of smooth initial data. Numerical results will be
presented to demonstrate the asymptotically self-similar blow-up of the
solution. The blowup rate of the self-similar singularity of the nonlocal
system is similar to that of the 3D model.Comment: 28 pages, 9 figure
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