887 research outputs found
Ly Leaks in the Absorption Spectra of High Redshift QSOs
Spectra of high redshift QSOs show deep Gunn-Peterson absorptions on the blue
sides of the \Lya emissions lines. They can be decomposed into components
called \Lya leaks, defined to be emissive regions in complementary to otherwise
zero-fluxed absorption gaps. Just like \Lya absorption forests at low
redshifts, \Lya leaks are both easy to find in observations and containing rich
sets of statistical properties that can be used to study the early evolution of
the IGM. Among all properties of a leak profile, we investigate its equivalent
width in this paper, since it is weakly affected by instrumental resolution and
noise. Using 10 Keck QSO spectra at , we have measured the number
density distribution function , defined to be the number of leaks per
equivalent width and per redshift , in the redshift range .
These new observational statistics, in both the differential and cumulative
forms, fit well to hydro numerical simulations of uniform ionizing background
in the CDM cosmology. In this model, Ly leaks are mainly due
to low density voids. It supports the early studies that the IGM at
would still be in a highly ionized state with neutral hydrogen fraction . Measurements of at would be effective to probe the
reionization of the IGM.Comment: 3 figs, accepted by ApJ
A WENO Algorithm of the Temperature and Ionization Profiles around a Point Source
We develop a numerical solver for radiative transfer problems based on the
weighted essentially nonoscillatory (WENO) scheme modified with anti-diffusive
flux corrections, in order to solve the temperature and ionization profiles
around a point source of photons in the reionization epoch. Algorithms for such
simulation must be able to handle the following two features: 1. the sharp
profiles of ionization and temperature at the ionizing front (I-front) and the
heating front (T-front), and 2. the fraction of neutral hydrogen within the
ionized sphere is extremely small due to the stiffness of the rate equations of
atom processes. The WENO scheme can properly handle these two features, as it
has been shown to have high order of accuracy and good convergence in capturing
discontinuities and complicated structures in fluid as well as to be
significantly superior over piecewise smooth solutions containing
discontinuities. With this algorithm, we show the time-dependence of the
preheated shell around a UV photon source. In the first stage the I-front and
T-front are coincident, and propagate with almost the speed of light. In later
stage, when the frequency spectrum of UV photons is hardened, the speeds of
propagation of the ionizing and heating fronts are both significantly less than
the speed of light, and the heating front is always beyond the ionizing front.
In the spherical shell between the I- and T-fronts, the IGM is heated, while
atoms keep almost neutral. The time scale of the preheated shell evolution is
dependent on the intensity of the photon source. We also find that the details
of the pre-heated shell and the distribution of neutral hydrogen remained in
the ionized sphere are actually sensitive to the parameters used. The WENO
algorithm can provide stable and robust solutions to study these details.Comment: 24 pages, 7 figures, accepted in New Astronom
Efficacy and Safety of Ribavirin with Sofosbuvir Plus Ledipasvir in Patients with Genotype 1 Hepatitis C: A Meta-Analysis
A WENO Algorithm for the Radiative Transfer and Ionized Sphere at Reionization
We show that the algorithm based on the weighted essentially nonoscillatory
(WENO) scheme with anti-diffusive flux corrections can be used as a solver of
the radiative transfer equations. This algorithm is highly stable and robust
for solving problems with both discontinuities and smooth solution structures.
We test this code with the ionized sphere around point sources. It shows that
the WENO scheme can reveal the discontinuity of the radiative or ionizing
fronts as well as the evolution of photon frequency spectrum with high accuracy
on coarse meshes and for a very wide parameter space. This method would be
useful to study the details of the ionized patch given by individual source in
the epoch of reionization. We demonstrate this method by calculating the
evolution of the ionized sphere around point sources in physical and frequency
spaces. It shows that the profile of the fraction of neutral hydrogen and the
ionized radius are sensitively dependent on the intensity of the source.Comment: Elsart Latex file, 20 pages, 8 figures included, accepted for
publication in New Astronom
catena-Poly[[(1,10-phenanthroline)copper(II)]-μ-oxalato]
In the title coordination polymer, [Cu(C2O4)(C12H8N2)]n, the CuII atom is six-coordinated by four O atoms from two oxalate ligands and two N atoms from one 1,10-phenanthroline (phen) ligand in a distorted octahedral coordination geometry. The oxalate anions act as bis-bidentate ligands, bridging the Cu–phen units in zigzag chains extending parallel to [100]. Interchain C—H⋯O hydrogen bonding and π–π stacking interactions [centroid–centroid distance = 3.7439 (17) Å] assemble neighboring chains, forming a three-dimensional supramolecular network
catena-Poly[(μ2-3-carboxy-5-nitrobenzoato)(μ3-5-nitrobenzene-1,3-dicarboxylato)(1,10-phenanthroline)gadolinium(III)]
The crystal structure of the title complex, [Gd(C8H3NO6)(C8H4NO6)(C12H8N2)]n, contains polymeric chains made up of GdIII atoms, 1,10-phenanthroline and fully or half-deprotonated 5-nitrobenzene-1,3-dicarboxylic acid (H2
L) ligands. The GdIII atom is coordinated in a distorted bicapped trigonal-prismatic fashion by six O atoms from two HL
− and three L
2− ligands, and by two N atoms from the 1,10-phenanthroline ligand. The L
2− ligands bridge the Gd–phenanthroline units, forming chains running parallel to [100]. O—H⋯O hydrogen bonding as well as π–π stacking interactions with an interplanar distance of 3.599 (2) Å assemble neighboring polymeric chains
21 cm Signals from Early Ionizing Sources
We investigate the 21 cm signals from the UV ionizing sources in the
reionization epoch. The formation and evolution of 21 cm emission and
absorption regions depend essentially on the kinetics of photons in the
physical and frequency spaces. To solve the radiative transfer equation, we use
the WENO algorithm, which is effective to capture the sharp ionization profile
and the cut-off at the front of light and to handle the small fraction
of neutral hydrogen and helium in the ionized sphere. We show that a spherical
shell of 21 cm emission and absorption will develop around a point source once
the speed of the ionization front (I-front) is significantly lower than the
speed of light. The 21 cm shell extends from the I-front to the front of light;
its inner part is the emission region and its outer part is the absorption
region. The 21 cm emission region depends strongly on the intensity,
frequency-spectrum and life-time of the UV ionizing source. For a source of
short life-time, no 21 cm emission region can be formed if the source dies out
before the I-front speed is significantly lower than the speed of light. Yet, a
21 cm absorption region can form and develop even after the emission of the
source ceases.Comment: 25 pages, 9 figures, accepted by Ap
Primulina anisocymosa (Gesneriaceae), a new species with a unique inflorescence structure from Guangdong, China
A new Primulina species from Guangdong, China with an unusual inflorescence is described here. Primulina anisocymosa is vegetatively most similar to P. bobaiensis. It can be distinguished from all species within Primulina morphologically by its unique zigzag monochasial cyme and infructescence. To confirm the phylogenetic relationships and generic placement of this species, not only morphological anatomical features but also chromosome and DNA sequence data were examined and analysed here. Two samples from different populations identified as Primulina anisocymosa are monophyletic and were nested in a monophyletic clade within Primulina with high branch support. The somatic chromosome number of the new species is also reported (2n = 36), supporting its placement in the genus
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