460 research outputs found
Chemical Enrichment in Damped Lyman Alpha Systems From Hierarchical Galaxy Formation Models
We investigate chemical enrichment in Damped Lyman alpha (DLA) systems in the
hierarchical structure formation scenario using a semi-analytic model of galaxy
formation. The model developed by Nagashima, Totani, Gouda and Yoshii takes
into account various selection effects on high-redshift galaxies and can show
fundamental observational properties of galaxies, such as luminosity functions
and number-magnitude/redshift relations. DLA systems offer the possibilities of
measuring metal abundance more accurately than faint galaxies. For example,
recent measurements of zinc abundance can provide good evidence for
understanding the processes of metal pollution and star formation in DLA
systems because zinc is virtually unaffected by dust depletion. Here we focus
on this advantage for observation in order to explore the metallicity evolution
in DLA systems at high redshifts. We can consistently show the metallicity
evolution for reasonable models which also reproduce fundamental properties of
local galaxy population. This result suggests that the chemical evolution of
DLA systems can be consistently reconciled with the observational features of
typical galaxies. We also investigate other properties of DLA systems (column
density distribution and mass density of cold gas), and find that star
formation in massive galaxies should be more active than that in low-mass ones.
This is consistent with the results by Nagashima et al. and Cole et al. in
which the star formation timescale is set by reproducing cold gas mass fraction
in local spiral galaxies. Finally we discuss host galaxies associated with DLA
systems. We conclude that they primarily consist of sub-L* and/or dwarf
galaxies from the observations.Comment: 16 pages, 11 figures, Accepted for publication in Astrophsical
Journa
Formation of Sub-galactic Clouds under UV Background Radiation
The effects of the UV background radiation on the formation of sub-galactic
clouds are studied by means of one-dimensional hydrodynamical simulations. The
radiative transfer of the ionizing photons due to the absorption by HI, HeI and
HeII, neglecting the emission, is explicitly taken into account. We find that
the complete suppression of collapse occurs for the clouds with circular
velocities typically in the range V_c \sim 15-40 km/s and the 50% reduction in
the cooled gas mass with V_c \sim 20-55 km/s. These values depend most
sensitively on the collapse epoch of the cloud, the shape of the UV spectrum,
and the evolution of the UV intensity. Compared to the optically thin case,
previously investigated by Thoul & Weinberg (1996), the absorption of the
external UV photon by the intervening medium systematically lowers the above
threshold values by \Delta V_c \sim 5 km/s. Whether the gas can contract or
keeps expanding is roughly determined by the balance between the gravitational
force and the thermal pressure gradient when it is maximally exposed to the
external UV flux. Based on our simulation results, we discuss a number of
implications on galaxy formation, cosmic star formation history, and the
observations of quasar absorption lines. In Appendix, we derive analytical
formulae for the photoionization coefficients and heating rates, which
incorporate the frequency/direction-dependent transfer of external photons.Comment: 38 pages, 16 figures, accepted for publication in Ap
Dissolution dominating calcification process in polar pteropods close to the point of aragonite undersaturation
Thecosome pteropods are abundant upper-ocean zooplankton that build aragonite shells. Ocean acidification results in the lowering of aragonite saturation levels in the surface layers, and several incubation studies have shown that rates of calcification in these organisms decrease as a result. This study provides a weight-specific net calcification rate function for thecosome pteropods that includes both rates of dissolution and calcification over a range of plausible future aragonite saturation states (Omega_Ar). We measured gross dissolution in the pteropod Limacina helicina antarctica in the Scotia Sea (Southern Ocean) by incubating living specimens across a range of aragonite saturation states for a maximum of 14 days. Specimens started dissolving almost immediately upon exposure to undersaturated conditions (Omega_Ar,0.8), losing 1.4% of shell mass per day. The observed rate of gross dissolution was different from that predicted by rate law kinetics of aragonite dissolution, in being higher at Var levels slightly above 1 and lower at Omega_Ar levels of between 1 and 0.8. This indicates that shell mass is affected by even transitional levels of saturation, but there is, nevertheless, some partial means of protection for shells when in undersaturated conditions. A function for gross dissolution against Var derived from the present observations was compared to a function for gross calcification derived by a different study, and showed that dissolution became the dominating process even at Omega_Ar levels close to 1, with net shell growth ceasing at an Omega_Ar of 1.03. Gross dissolution increasingly dominated net change in shell mass as saturation levels decreased below 1. As well as influencing their viability, such dissolution of pteropod shells in the surface layers will result in slower sinking velocities and decreased carbon and carbonate fluxes to the deep ocean
Single-longitudinal mode laser structure based on a very narrow filtering technique
A narrow filtering technique based on the spectral overlapping of two uniform FBGs and applied to obtain a Single Longitudinal Mode (SLM) laser is proposed and demonstrated in this work. The two FBGs are spectrally detuned to reduce their coincident reflection response narrowing the equivalent filter bandwidth. A proof-of-concept linear laser has been built and tested exhibiting SLM operation even with temperature and strain variations.The authors are grateful to the Spanish government project TEC2010-20224-C02, to the Spanish Ministry of Education and Culture, and to the grant AP2009-1403
Periostin as a modulator of chronic cardiac remodeling after myocardial infarction
OBJECTIVE: After acute myocardial infarction, during the cardiac repair phase, periostin is released into the infarct and activates signaling pathways that are essential for the reparative process. However, the role of periostin in chronic cardiac remodeling after myocardial infarction remains to be elucidated. Therefore, the objective of this study was to investigate the relationship between tissue periostin and cardiac variables in the chronic cardiac remodeling induced by myocardial infarction. METHODS: Male Wistar rats were assigned to 2 groups: a simulated surgery group (SHAM; n = 8) and a myocardial infarction group (myocardial infarction; n = 13). After 3 months, morphological, functional and biochemical analyses were performed. The data are expressed as means±SD or medians (including the lower and upper quartiles). RESULTS: Myocardial infarctions induced increased left ventricular diastolic and systolic areas associated with a decreased fractional area change and a posterior wall shortening velocity. With regard to the extracellular matrix variables, the myocardial infarction group presented with higher values of periostin and types I and III collagen and higher interstitial collagen volume fractions and myocardial hydroxyproline concentrations. In addition, periostin was positively correlated with type III collagen levels (r = 0.673, p = 0.029) and diastolic (r = 0.678, p = 0.036) and systolic (r = 0.795, p = 0.006) left ventricular areas. Considering the relationship between periostin and the cardiac function variables, periostin was inversely correlated with both the fractional area change (r = -0.783, p = 0.008) and the posterior wall shortening velocity (r = -0.767, p = 0.012). CONCLUSIONS: Periostin might be a modulator of deleterious cardiac remodeling in the chronic phase after myocardial infarction in rats
First-line treatment and outcome of elderly patients with primary central nervous system lymphoma (PCNSL)—a systematic review and individual patient data meta-analysis
Evidence for prognosis and treatment of elderly patient with primary central nervous system is limited. High-dose methotrexate should be applied whenever possible, especially combination with oral alkylating agents is a promising approach. Further combinations with other intravenous drugs do not seem to improve outcome. More prospective trials designed for elderly PCNSL patients are warrante
Two-Photon Dichroic Atomic Vapor Laser Lock Using Electromagnetically Induced Transparency and Absorption
We demonstrate a technique to lock the frequency of a laser to a transition
between two excited states in Rb vapor in the presence of a weak magnetic
field. We use a ladder configuration from specific hyperfine sublevels of the
5S 1/2, 5P 3/2, and 5D 5/2 levels. This atomic configuration can show
Electromagnetically Induced Transparency and Absorption processes. The error
signal comes from the difference in the transparency or absorption felt by the
two orthogonal polarizations of the probe beam. A simplified model is in good
quantitative agreement with the observed signals for the experimental
parameters. We have used this technique to lock the frequency of the laser up
to 1.5 GHz off atomic resonance.Comment: 6 pages, 8 figures. Last version for publication in J. Opt. Soc. Am.
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