3,246 research outputs found
An organ culture system to model early degenerative changes of the intervertebral disc
ABSTRACT: INTRODUCTION: Back pain, a significant source of morbidity in our society, is related to the degenerative changes of the intervertebral disc. At present, the treatment of disc disease consists of therapies that are aimed at symptomatic relief. This shortcoming stems in large part from our lack of understanding of the biochemical and molecular events that drive the disease process. The goal of this study is to develop a model of early disc degeneration using an organ culture. This approach is based on our previous studies that indicate that organ culture closely models molecular events that occur in vivo in an ex vivo setting. METHODS: To mimic a degenerative insult, discs were cultured under low oxygen tension in the presence of TNF-α, IL-1β and serum limiting conditions. RESULTS: Treatment resulted in compromised cell survival and changes in cellular morphology reminiscent of degeneration. There was strong suppression in the expression of matrix proteins including collagen types 1, 2, 6 and 9, proteoglycans, aggrecan and fibromodulin. Moreover, a strong induction in expression of catabolic matrix metalloproteinases (MMP) 3, 9 and 13 with a concomitant increase in aggrecan degradation was seen. An inductive effect on NGF expression was also noticed. Although similar, nucleus pulposus and annulus fibrosus tissues showed some differences in their response to the treatment. CONCLUSIONS: Results of this study show that perturbations in microenvironmental factors result in anatomical and gene expression change within the intervertebral disc that may ultimately compromise cell function and induce pathological deficits. This system would be a valuable screening tool to investigate interventional strategies aimed at restoring disc cell function
Optical spectroscopy of the M15 intermediate velocity cloud
We present echelle spectrograph observations in NaD, at resolutions of
6.2-8.5 km/s, for 11 stars located in the line-of-sight to the M15 intermediate
velocity cloud, which has a radial velocity of 70 km/s. This cloud is a part of
IVC Complex gp. The targets range in magnitude from V=13.3-14.8. Seven of the
observed stars are in the M15 globular cluster, the remaining four being field
stars. Column density ratios of log(N cm^-2)=11.8-12.5 are derived. Combining
the current sightlines with previously-existing data, we find the NaD/HI ratio
in the IVC varies by upto a factor of 25. One cluster star, M15 ZNG-1, was also
observed in Calcium. We find N(CaI)/N(CaII)<0.03 and NaI/CaII=0.25, similar to
values seen in the local ISM. Finally, we detect tentative evidence for IV
absorption in KI towards 3 cluster stars.Comment: A&A, in pres
Backreaction from non-conformal quantum fields in de Sitter spacetime
We study the backreaction on the mean field geometry due to a non-conformal
quantum field in a Robertson-Walker background. In the regime of small mass and
small deviation from conformal coupling, we compute perturbatively the
expectation value of the stress tensor of the field for a variety of vacuum
states, and use it to obtain explicitly the semiclassical gravity solutions for
isotropic perturbations around de Sitter spacetime, which is found to be
stable. Our results show clearly the crucial role of the non-local terms that
appear in the effective action: they cancel the contribution from local terms
proportional to the logarithm of the scale factor which would otherwise become
dominant at late times and prevent the existence of a stable self-consistent de
Sitter solution. Finally, the opposite regime of a strongly non-conformal field
with a large mass is also considered.Comment: 31 page
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
Eddington-limited accretion and the black hole mass function at redshift 6
We present discovery observations of a quasar in the Canada-France High-z
Quasar Survey (CFHQS) at redshift z=6.44. We also use near-IR spectroscopy of
nine CFHQS quasars at z~6 to determine black hole masses. These are compared
with similar estimates for more luminous Sloan Digital Sky Survey (SDSS)
quasars to investigate the relationship between black hole mass and quasar
luminosity. We find a strong correlation between MgII FWHM and UV luminosity
and that most quasars at this early epoch are accreting close to the Eddington
limit. Thus these quasars appear to be in an early stage of their life cycle
where they are building up their black hole mass exponentially. Combining these
results with the quasar luminosity function, we derive the black hole mass
function at z=6. Our black hole mass function is ~10^4 times lower than at z=0
and substantially below estimates from previous studies. The main uncertainties
which could increase the black hole mass function are a larger population of
obscured quasars at high-redshift than is observed at low-redshift and/or a low
quasar duty cycle at z=6. In comparison, the global stellar mass function is
only ~10^2 times lower at z=6 than at z=0. The difference between the black
hole and stellar mass function evolution is due to either rapid early star
formation which is not limited by radiation pressure as is the case for black
hole growth or inefficient black hole seeding. Our work predicts that the black
hole mass - stellar mass relation for a volume-limited sample of galaxies
declines rapidly at very high redshift. This is in contrast to the observed
increase at 4<z<6 from the local relation if one just studies the most massive
black holes.Comment: 16 pages, 10 figures, AJ in pres
Improving the sensitivity to gravitational-wave sources by modifying the input-output optics of advanced interferometers
We study frequency dependent (FD) input-output schemes for signal-recycling
interferometers, the baseline design of Advanced LIGO and the current
configuration of GEO 600. Complementary to a recent proposal by Harms et al. to
use FD input squeezing and ordinary homodyne detection, we explore a scheme
which uses ordinary squeezed vacuum, but FD readout. Both schemes, which are
sub-optimal among all possible input-output schemes, provide a global noise
suppression by the power squeeze factor, while being realizable by using
detuned Fabry-Perot cavities as input/output filters. At high frequencies, the
two schemes are shown to be equivalent, while at low frequencies our scheme
gives better performance than that of Harms et al., and is nearly fully
optimal. We then study the sensitivity improvement achievable by these schemes
in Advanced LIGO era (with 30-m filter cavities and current estimates of
filter-mirror losses and thermal noise), for neutron star binary inspirals, and
for narrowband GW sources such as low-mass X-ray binaries and known radio
pulsars. Optical losses are shown to be a major obstacle for the actual
implementation of these techniques in Advanced LIGO. On time scales of
third-generation interferometers, like EURO/LIGO-III (~2012), with
kilometer-scale filter cavities, a signal-recycling interferometer with the FD
readout scheme explored in this paper can have performances comparable to
existing proposals. [abridged]Comment: Figs. 9 and 12 corrected; Appendix added for narrowband data analysi
Upper limits on the strength of periodic gravitational waves from PSR J1939+2134
The first science run of the LIGO and GEO gravitational wave detectors
presented the opportunity to test methods of searching for gravitational waves
from known pulsars. Here we present new direct upper limits on the strength of
waves from the pulsar PSR J1939+2134 using two independent analysis methods,
one in the frequency domain using frequentist statistics and one in the time
domain using Bayesian inference. Both methods show that the strain amplitude at
Earth from this pulsar is less than a few times .Comment: 7 pages, 1 figure, to appear in the Proceedings of the 5th Edoardo
Amaldi Conference on Gravitational Waves, Tirrenia, Pisa, Italy, 6-11 July
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