1,108 research outputs found
Bias in Matter Power Spectra ?
We review the constraints given by the linear matter power spectra data on
cosmological and bias parameters, comparing the data from the PSCz survey
(Hamilton et al., 2000) and from the matter power spectrum infered by the study
of Lyman alpha spectra at z=2.72 (Croft et al., 2000). We consider
flat-- cosmologies, allowing , and to vary, and we
also let the two ratio factors and () vary independently. Using a simple
minimisation technique, we find confidence intervals on our parameters for each
dataset and for a combined analysis. Letting the 5 parameters vary freely gives
almost no constraints on cosmology, but requirement of a universal ratio for
both datasets implies unacceptably low values of and . Adding
some reasonable priors on the cosmological parameters demonstrates that the
power derived by the PSCz survey is higher by a factor compared to
the power from the Lyman forest survey.Comment: Accepted in A&
The cyclooxygenase-2 selective inhibitor NS-398 does not influence trabecular or cortical bone gain resulting from repeated mechanical loading in female mice.
SUMMARY:
A single injection of the cyclooxygenase-2 (COX-2) selective inhibitor NS-398 reduces bone’s osteogenic response to a single period of mechanical loading in female rats, while women taking COX-2 selective inhibitors do not have lower bone mass. We show that daily NS-398 injection does not influence bone gain from repeated loading in female mice.
INTRODUCTION:
Prostaglandins are mediators of bone cells’ early response to mechanical stimulation. COX-2 expression is up-regulated by exposure of these cells to mechanical strain or fluid flow, and the osteogenic response to a single loading period is reduced by COX-2 inhibition. This study determined, in female mice in vivo, the effect of longer term COX-2 inhibition on adaptive (re)modelling of cortical and trabecular bone in response to repeated loading.
METHODS:
Nineteen-week-old female C57BL/6 mice were injected with vehicle or NS-398 (5 mg/kg/day) 5 days a week for 2 weeks. On three alternate days each week, the right tibiae/fibulae were axially loaded [40 cycles (7 min)/day] three hours after injection. Left limbs acted as internal controls. Changes in three-dimensional bone architecture were analysed by high-resolution micro-computed tomography.
RESULTS:
In control limbs NS-398 was associated with reduced trabecular number but had no influence on cortical bone. In loaded limbs trabecular thickness and cortical periosteally enclosed volume increased. NS-398 showed no effect on this response.
CONCLUSION:
Pharmacological inhibition of COX-2 by NS-398 does not affect trabecular or cortical bone’s response to repeated mechanical loading in female mice and thus would not be expected to impair the functional adaptation of bone to physical activity in women
Bones' adaptive response to mechanical loading is essentially linear between the low strains associated with disuse and the high strains associated with the lamellar/woven bone transition.
There is a widely held view that the relationship between mechanical loading history and adult bone mass/strength includes an adapted state or "lazy zone" where the bone mass/strength remains constant over a wide range of strain magnitudes. Evidence to support this theory is circumstantial. We investigated the possibility that the "lazy zone" is an artifact and that, across the range of normal strain experience, features of bone architecture associated with strength are linearly related in size to their strain experience. Skeletally mature female C57BL/6 mice were right sciatic neurectomized to minimize natural loading in their right tibiae. From the fifth day, these tibiae were subjected to a single period of external axial loading (40, 10-second rest interrupted cycles) on alternate days for 2 weeks, with a peak dynamic load magnitude ranging from 0 to 14 N (peak strain magnitude: 0-5000 µε) and a constant loading rate of 500 N/s (maximum strain rate: 75,000 µε/s). The left tibiae were used as internal controls. Multilevel regression analyses suggest no evidence of any discontinuity in the progression of the relationships between peak dynamic load and three-dimensional measures of bone mass/strength in both cortical and cancellous regions. These are essentially linear between the low-peak locomotor strains associated with disuse (∼300 µε) and the high-peak strains derived from artificial loading and associated with the lamellar/woven bone transition (∼5000 µε). The strain:response relationship and minimum effective strain are site-specific, probably related to differences in the mismatch in strain distribution between normal and artificial loading at the locations investigated
A common behavior of thermoelectric layered cobaltites: incommensurate spin density wave states in [CaCoCuO][CoO] and [CaCoO][CoO]
Magnetism of a misfit layered cobaltite
[CaCoCuO][CoO] ( 0.62, RS
denotes a rocksalt-type block) was investigated by a positive muon spin
rotation and relaxation (SR) experiment. A transition to an
incommensurate ({\sf IC}) spin density wave ({\sf SDW}) state was found below
180 K (= ); and a clear oscillation due to a static
internal magnetic field was observed below 140 K (= ). Furthermore,
an anisotropic behavior of the zero-field SR experiment indicated that
the {\sf IC-SDW} propagates in the - plane, with oscillating moments
directed along the c axis. These results were quite similar to those for the
related compound [CaCoO][CoO], {\sl i.e.},
CaCoO. Since the {\sf IC-SDW} field in
[CaCoCuO][CoO] was approximately
same to those in pure and doped [CaCoO][CoO], it
was concluded that the {\sf IC-SDW} exist in the [CoO] planes.Comment: 15 pages, 6 figures. accepted for publication in J. Phys.: Condens.
Matte
Hidden magnetic transitions in thermoelectric layered cobaltite, [CaCoO][CoO]
A positive muon spin rotation and relaxation (SR) experiment on
[CaCoO][CoO], ({\sl i.e.}, CaCoO, a layered
thermoelectric cobaltite) indicates the existence of two magnetic transitions
at 100 K and 400 - 600 K; the former is a transition from a paramagnetic
state to an incommensurate ({\sf IC}) spin density wave ({\sf SDW}) state. The
anisotropic behavior of zero-field SR spectra at 5 K suggests that the
{\sf IC-SDW} propagates in the - plane, with oscillating moments directed
along the c-axis; also the {\sf IC-SDW} is found to exist not in the
[CaCoO] subsystem but in the [CoO] subsystem. In addition, it is
found that the long-range {\sf IC-SDW} order completes below 30 K,
whereas the short-range order appears below 100 K. The latter transition is
interpreted as a gradual change in the spin state of Co ions %% at temperatures
above 400 K. These two magnetic transitions detected by SR are found to
correlate closely with the transport properties of
[CaCoO][CoO].Comment: 7 pages, 8 figures. to be appeared in Phys. Rev.
Incremental Grid-like Layout Using Soft and Hard Constraints
We explore various techniques to incorporate grid-like layout conventions
into a force-directed, constraint-based graph layout framework. In doing so we
are able to provide high-quality layout---with predominantly axis-aligned
edges---that is more flexible than previous grid-like layout methods and which
can capture layout conventions in notations such as SBGN (Systems Biology
Graphical Notation). Furthermore, the layout is easily able to respect
user-defined constraints and adapt to interaction in online systems and diagram
editors such as Dunnart.Comment: Accepted to Graph Drawing 201
Host Galaxies of Gamma-Ray Bursts and their Cosmological Evolution
We use numerical simulations of large scale structure formation to explore
the cosmological properties of Gamma-Ray Burst (GRB) host galaxies. Among the
different sub-populations found in the simulations, we identify the host
galaxies as the most efficient star-forming objects, i.e. galaxies with high
specific star formation rates. We find that the host candidates are low-mass,
young galaxies with low to moderate star formation rate. These properties are
consistent with those observed in GRB hosts, most of which are sub-luminous,
blue galaxies. Assuming that host candidates are galaxies with high star
formation rates would have given conclusions inconsistent with the
observations. The specific star formation rate, given a galaxy mass, is shown
to increase as the redshift increases. The low mass of the putative hosts makes
them difficult to detect with present day telescopes and the probability
density function of the specific star formation rate is predicted to change
depending on whether or not these galaxies are observed.Comment: 11 pages, 10 figures. Accepted for publication in MNRA
Heterotic strings on G_2 orbifolds
We study compactification of heterotic strings to three dimensions on
orbifolds of G_2 holonomy. We consider the standard embedding and show that the
gauge group is broken from E_8 x E_8 or SO(32) to F_4 x E_8 or SO(25)
respectively. We also compute the spectrum of massless states and compare with
the results obtained from reduction of the 10-dimensional fields. Non-standard
embeddings are discussed briefly. For type II compactifications we verify that
IIB and IIA have equal massless spectrum.Comment: LaTex, 21 page
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