233 research outputs found
Clustering on very small scales from a large sample of confirmed quasar pairs: Does quasar clustering track from Mpc to kpc scales?
We present the most precise estimate to date of the clustering of quasars on
very small scales, based on a sample of 47 binary quasars with magnitudes of
and proper transverse separations of \,kpc. Our
sample of binary quasars, which is about 6 times larger than any previous
spectroscopically confirmed sample on these scales, is targeted using a Kernel
Density Estimation technique (KDE) applied to Sloan Digital Sky Survey (SDSS)
imaging over most of the SDSS area. Our sample is "complete" in that all of the
KDE target pairs with \,kpc in our area
of interest have been spectroscopically confirmed from a combination of
previous surveys and our own long-slit observational campaign. We catalogue 230
candidate quasar pairs with angular separations of <8\arcsec, from which our
binary quasars were identified. We determine the projected correlation function
of quasars () in four bins of proper transverse scale over the
range \,kpc. The implied small-scale
quasar clustering amplitude from the projected correlation function, integrated
across our entire redshift range, is at \,kpc. Our sample is the first spectroscopically confirmed sample of
quasar pairs that is sufficiently large to study how quasar clustering evolves
with redshift at kpc. We find that empirical descriptions of
how quasar clustering evolves with redshift at Mpc also
adequately describe the evolution of quasar clustering at
kpc.Comment: 16 pages, 8 figures, 6 tables, Accepted for publication in MNRA
The effect of intrathecal delivery of bone marrow stromal cells on hippocampal neurons in rat model of Alzheimer�s disease
Objective(s): Intracerebral injection of bone marrow stromal cells (BMSCs) is being investigated as a therapeutic tool to prevent Alzheimer's disease (AD). Our aim was to investigate the effects of BMSCs by intrathecal injection in AD rat model. Materials and Methods: BMSCs were obtained from the bone marrow of Wistar rat and transplanted into AD rat model via intrathecal injection. The rat model had received an injection of � amyloid into the hippocampus for histological and immunohistochemical studies. Results: Histological examination of the brains in transplanted rats compared to controls demonstrated the migration of BrdU-labeled BMSCs from the site of delivery, confirmed the differentiation of BMSCs transplanted cells into the cholinergic neurons, and increased number of healthy and decreased number of dark neurons. Conclusion: Our results showed that BMSCs intratechal administration could be a promising method for treatment of Alzheimer�s disease in rat model. © 2015, Iranian Journal of Basic Medical Sciences. All rights reserved
Quasars at intermediate redshift are not special; but they are often satellites
Understanding the links between the activity of supermassive black holes
(SMBH) at the centres of galaxies and their host dark matter haloes is a key
question in modern astrophysics. The final data release of the SDSS-IV eBOSS
provides the largest contemporary spectroscopic sample of galaxies and QSOs.
Using this sample and covering the redshift interval , we have
measured the clustering properties of the eBOSS QSOs, Emission Line Galaxies
(ELGs) and Luminous Red Galaxies (LRGs). We have also measured the fraction of
QSOs as a function of the overdensity defined by the galaxy population. Using
these measurements, we investigate how QSOs populate and sample the galaxy
population, and how the host dark-matter haloes of QSOs sample the underlying
halo distribution. We find that the probability of a galaxy hosting a QSO is
independent of the host dark matter halo mass of the galaxy. We also find that
about 60\% of eBOSS QSOs are hosted by LRGs and about 20-40\% of QSOs are
hosted by satellite galaxies. We find a slight preference for QSOs to populate
satellite galaxies over central galaxies. This is connected to the host halo
mass distribution of different types of galaxies. Based on our analysis, QSOs
should be hosted by a very broad distribution of haloes, and their occurrence
should be modulated only by the efficiency of galaxy formation processes.Comment: 15 pages, 6 Figures, Data and code from this analysis is available at
https://www.roe.ac.uk/~salam/GQOD/ , submitted to MNRAS, comments and
suggestions are welcom
Remarks on the Formulation of Quantum Mechanics on Noncommutative Phase Spaces
We consider the probabilistic description of nonrelativistic, spinless
one-particle classical mechanics, and immerse the particle in a deformed
noncommutative phase space in which position coordinates do not commute among
themselves and also with canonically conjugate momenta. With a postulated
normalized distribution function in the quantum domain, the square of the Dirac
delta density distribution in the classical case is properly realised in
noncommutative phase space and it serves as the quantum condition. With only
these inputs, we pull out the entire formalisms of noncommutative quantum
mechanics in phase space and in Hilbert space, and elegantly establish the link
between classical and quantum formalisms and between Hilbert space and phase
space formalisms of noncommutative quantum mechanics. Also, we show that the
distribution function in this case possesses 'twisted' Galilean symmetry.Comment: 25 pages, JHEP3 style; minor changes; Published in JHE
Sequence Context Influences the Structure and Aggregation Behavior of a PolyQ Tract
Expansions of polyglutamine (polyQ) tracts in nine different proteins cause a family of neurodegenerative disorders called polyQ diseases. Because polyQ tracts are potential therapeutic targets for these pathologies there is great interest in characterizing the conformations that they adopt and in understanding how their aggregation behavior is influenced by the sequences flanking them. We used solution NMR to study at single-residue resolution a 156-residue proteolytic fragment of the androgen receptor that contains a polyQ tract associated with the disease spinobulbar muscular atrophy, also known as Kennedy disease. Our findings indicate that a Leu-rich region preceding the polyQ tract causes it to become α-helical and appears to protect the protein against aggregation, which represents a new, to our knowledge, mechanism by which sequence context can minimize the deleterious properties of these repetitive regions. Our results have implications for drug discovery for polyQ diseases because they suggest that the residues flanking these repetitive sequences may represent viable therapeutic targets
Noise kernel for a quantum field in Schwarzschild spacetime under the Gaussian approximation
A method is given to compute an approximation to the noise kernel, defined as
the symmetrized connected 2-point function of the stress tensor, for the
conformally invariant scalar field in any spacetime conformal to an
ultra-static spacetime for the case in which the field is in a thermal state at
an arbitrary temperature. The most useful applications of the method are flat
space where the approximation is exact and Schwarzschild spacetime where the
approximation is better than it is in most other spacetimes. The two points are
assumed to be separated in a timelike or spacelike direction. The method
involves the use of a Gaussian approximation which is of the same type as that
used by Page to compute an approximate form of the stress tensor for this field
in Schwarzschild spacetime. All components of the noise kernel have been
computed exactly for hot flat space and one component is explicitly displayed.
Several components have also been computed for Schwarzschild spacetime and
again one component is explicitly displayed.Comment: 34 pages, no figures. Substantial revisions in Secs. I, IV, and V;
minor revisions elsewhere; new results include computation of the exact noise
kernel for hot flat space and an approximate computation of the noise kernel
for a thermal state at an arbitrary temperature in Schwarzschild spacetime
when the points are split in the time directio
Exponentially growing bubbles around early super massive black holes
We addressed the so far unexplored issue of outflows induced by exponentially
growing power sources, focusing on early supermassive black holes (BHs). We
assumed that these objects grow to by z=6 by
Eddington-limited accretion and convert 5% of their bolometric output into a
wind. We first considered the case of energy-driven and momentum-driven
outflows expanding in a region where the gas and total mass densities are
uniform and equal to the average values in the Universe at . We derived
analytic solutions for the evolution of the outflow, finding that, for an
exponentially growing power with e-folding time , the late time
expansion of the outflow radius is also exponential, with e-folding time of
and in the energy-driven and momentum-driven limit,
respectively.
We then considered energy-driven outflows produced by QSOs at the center of
early dark matter halos of different masses and powered by BHs growing from
different seeds. We followed the evolution of the source power and of the gas
and dark matter density profiles in the halos from the beginning of the
accretion until . The final bubble radius and velocity do not depend on
the seed BH mass but are instead smaller for larger halo masses. At z=6, bubble
radii in the range 50-180 kpc and velocities in the range 400-1000 km s
are expected for QSOs hosted by halos in the mass range
.
By the time the QSO is observed, we found that the total thermal energy
injected within the bubble in the case of an energy-driven outflow is
erg. This is in excellent agreement with the value
of erg measured through the detection of
the thermal Sunyaev-Zeldovich effect around a large population of luminous QSOs
at lower redshift. [abridged]Comment: 17 pages and 14 figures. Typos corrected. It matches the version
published in A&
The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
The Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM) is a
dedicated multi-object RM experiment that has spectroscopically monitored a
sample of 849 broad-line quasars in a single 7 deg field with the SDSS-III
BOSS spectrograph. The RM quasar sample is flux-limited to i_psf=21.7 mag, and
covers a redshift range of 0.1<z<4.5. Optical spectroscopy was performed during
2014 Jan-Jul dark/grey time, with an average cadence of ~4 days, totaling more
than 30 epochs. Supporting photometric monitoring in the g and i bands was
conducted at multiple facilities including the CFHT and the Steward Observatory
Bok telescopes in 2014, with a cadence of ~2 days and covering all lunar
phases. The RM field (RA, DEC=14:14:49.00, +53:05:00.0) lies within the CFHT-LS
W3 field, and coincides with the Pan-STARRS 1 (PS1) Medium Deep Field MD07,
with three prior years of multi-band PS1 light curves. The SDSS-RM 6-month
baseline program aims to detect time lags between the quasar continuum and
broad line region (BLR) variability on timescales of up to several months (in
the observed frame) for ~10% of the sample, and to anchor the time baseline for
continued monitoring in the future to detect lags on longer timescales and at
higher redshift. SDSS-RM is the first major program to systematically explore
the potential of RM for broad-line quasars at z>0.3, and will investigate the
prospects of RM with all major broad lines covered in optical spectroscopy.
SDSS-RM will provide guidance on future multi-object RM campaigns on larger
scales, and is aiming to deliver more than tens of BLR lag detections for a
homogeneous sample of quasars. We describe the motivation, design and
implementation of this program, and outline the science impact expected from
the resulting data for RM and general quasar science.Comment: 25 pages, submitted to ApJS; project website at http://www.sdssrm.or
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