1,608 research outputs found
Augmenter of liver regeneration enhances the success rate of fetal pancreas transplantation in rodents
Background. Treatment of fetal pancreas (FP) isografts with insulin- like growth factor-I greatly improves the rate of conversion to euglycemia in diabetic rats. Complete knowledge of other factors that may facilitate the engraftment and function of FP in vivo is still embryonic. Augmenter of liver regeneration (ALR) is a newly described polypeptide growth factor found in weanling rat livers. ALR has trophic effects on regenerating liver. We studied the effects of in situ administration of this agent on FP isografts in rats. Methods. Streptozotocin-diabetic Lewis rats (blood glucose >300 mg/dl) received 16 FP isografts transplanted intramuscularly. ALR was delivered from day 1 through day 14, in doses of 40 or 400 ng/kg/d. Animals were followed for 3 months with serial weights and blood glucose monitoring. These animals were compared with those treated with vehicle alone. Results. Of the group treated with ALR at 40 ng/kg/day for 14 days, 89% (eight of nine) were euglycemic (P=0.0003). Of the group treated with ALR at 400 ng/kg/day for 14 days, 88% (seven of eight) were euglycemic (P=0.0007). Of the group treated with vehicle alone, none of the six were euglycemic. Euglycemia is defined here as glucose<200 mg/dl for 3 days. Pathology of the intramuscular transplant site showed patches of islet tissue embedded in fat. These patches demonstrated insulin immunoreactivity. Conclusions. Diabetes was reversed in a significantly greater proportion of FP + ALR-treated recipients than those animals treated with vehicle alone. Local delivery of growth factors my be used as an adjunct to FP transplantation to improve the rate of success. This in situ model may be useful to further evaluate other soluble factors
Plant invasions, generalist herbivores, and novel defense weapons
One commonly accepted mechanism for biological invasions is that species, after introduction to a new region, leave behind their natural enemies and therefore increase in distribution and abundance. However, which enemies are escaped remains unclear. Escape from specialist invertebrate herbivores has been examined in detail, but despite the profound effects of generalist herbivores in natural communities their potential to control invasive species is poorly understood. We carried out parallel laboratory feeding bioassays with generalist invertebrate herbivores from the native (Europe) and from the introduced (North America) range using native and nonnative tetraploid populations of the invasive spotted knapweed, Centaurea stoebe. We found that the growth of North American generalist herbivores was far lower when feeding on C. stoebe than the growth of European generalists. In contrast, North American and European generalists grew equally well on European and North American tetraploid C. stoebe plants, lending no support for an evolutionary change in resistance of North American tetraploid C. stoebe populations against generalist herbivores. These results suggest that biogeographical differences in the response of generalist herbivores to novel plant species have the potential to affect plant invasions
Cluster scaling relations from cosmological hydrodynamic simulations in dark energy dominated universe
Clusters are potentially powerful tools for cosmology provided their observed
properties such as the Sunyaev-Zel'dovich (SZ) or X-ray signals can be
translated into physical quantities like mass and temperature. Scaling
relations are the appropriate mean to perform this translation. It is
therefore, important to understand their evolution and their modifications with
respect to the physics and to the underlying cosmology. In this spirit, we
investigate the effect of dark energy on the X-ray and SZ scaling relations.
The study is based on the first hydro-simulations of cluster formation for
diferent models of dark energy. We present results for four dark energy models
which differ from each other by their equations of state parameter, .
Namely, we use a cosmological constant model (as a reference), a perfect
fluid with constant equation of state parameter and one with and a scalar field model (or quintessence) with varying . We generate
N-body/hydrodynamic simulations that include radiative cooling with the public
version of the Hydra code, modified to consider an arbitrary dark energy
component. We produce cluster catalogues for the four models and derive the
associated X-ray and SZ scaling relations. We find that dark energy has little
effect on scaling laws making it safe to use the CDM scalings for
conversion of observed quantities into temperature and masses.Comment: 9 pages, 7 figures, submitted to A&
New Types of Off-Diagonal Long Range Order in Spin-Chains
We discuss new possibilities for Off-Diagonal Long Range Order (ODLRO) in
spin chains involving operators which add or delete sites from the chain. For
the Heisenberg and Inverse Square Exchange models we give strong numerical
evidence for the hidden ODLRO conjectured by Anderson \cite{pwa_conj}. We find
a similar ODLRO for the XY model (or equivalently for free fermions in one
spatial dimension) which we can demonstrate rigorously, as well as numerically.
A connection to the singlet pair correlations in one dimensional models of
interacting electrons is made and briefly discussed.Comment: 13 pages, Revtex v3.0, 2 PostScript figures include
Role of phason-defects on the conductance of a 1-d quasicrystal
We have studied the influence of a particular kind of phason-defect on the
Landauer resistance of a Fibonacci chain. Depending on parameters, we sometimes
find the resistance to decrease upon introduction of defect or temperature, a
behavior that also appears in real quasicrystalline materials. We demonstrate
essential differences between a standard tight-binding model and a full
continuous model. In the continuous case, we study the conductance in relation
to the underlying chaotic map and its invariant. Close to conducting points,
where the invariant vanishes, and in the majority of cases studied, the
resistance is found to decrease upon introduction of a defect. Subtle
interference effects between a sudden phason-change in the structure and the
phase of the wavefunction are also found, and these give rise to resistive
behaviors that produce exceedingly simple and regular patterns.Comment: 12 pages, special macros jnl.tex,reforder.tex, eqnorder.tex. arXiv
admin note: original tex thoroughly broken, figures missing. Modified so that
tex compiles, original renamed .tex.orig in source
AGN Jet-induced Feedback in Galaxies. II. Galaxy colours from a multicloud simulation
We study the feedback from an AGN on stellar formation within its host
galaxy, mainly using one high resolution numerical simulation of the jet
propagation within the interstellar medium of an early-type galaxy. In
particular, we show that in a realistic simulation where the jet propagates
into a two-phase ISM, star formation can initially be slightly enhanced and
then, on timescales of few million years, rapidly quenched, as a consequence
both of the high temperatures attained and of the reduction of cloud mass
(mainly due to Kelvin-Helmholtz instabilities). We then introduce a model of
(prevalently) {\em negative} AGN feedback, where an exponentially declining
star formation is quenched, on a very short time scale, at a time t_AGN, due to
AGN feedback. Using the Bruzual & Charlot (2003) population synthesis model and
our star formation history, we predict galaxy colours from this model and match
them to a sample of nearby early-type galaxies showing signs of recent episodes
of star formation (Kaviraj et al. 2007). We find that the quantity t_gal -
t_AGN, where t_gal is the galaxy age, is an excellent indicator of the presence
of feedback processes, and peaks significantly around t_gal - t_AGN \approx
0.85 Gyr for our sample, consistent with feedback from recent energy injection
by AGNs in relatively bright (M_{B} \lsim -19) and massive nearby early-type
galaxies. Galaxies that have experienced this recent feedback show an
enhancement of 3 magnitudes in NUV(GALEX)-g, with respect to the unperturbed,
no-feedback evolution. Hence they can be easily identified in large combined
near UV-optical surveys.Comment: 18 pages, 16 figures, accepted for publication on MNRAS. This version
includes revisions after the referee's repor
Deep Chandra X-ray Imaging of a Nearby Radio Galaxy 4C+29.30: X-ray/Radio Connection
We report results from our deep Chandra X-ray observations of a nearby radio
galaxy, 4C+29.30 (z=0.0647). The Chandra image resolves structures on
sub-arcsec to arcsec scales, revealing complex X-ray morphology and detecting
the main radio features: the nucleus, a jet, hotspots, and lobes. The nucleus
is absorbed (N(H)=3.95 (+0.27/-0.33)x10^23 atoms/cm^2) with an unabsorbed
luminosity of L(2-10 keV) ~ (5.08 +/-0.52) 10^43 erg/s characteristic of Type 2
AGN. Regions of soft (<2 keV) X-ray emission that trace the hot interstellar
medium (ISM) are correlated with radio structures along the main radio axis
indicating a strong relation between the two. The X-ray emission beyond the
radio source correlates with the morphology of optical line-emitting regions.
We measured the ISM temperature in several regions across the galaxy to be kT ~
0.5 with slightly higher temperatures (of a few keV) in the center and in the
vicinity of the radio hotspots. Assuming these regions were heated by weak
shocks driven by the expanding radio source, we estimated the corresponding
Mach number of 1.6 in the southern regions. The thermal pressure of the X-ray
emitting gas in the outermost regions suggest the hot ISM is slightly
under-pressured with respect to the cold optical-line emitting gas and
radio-emitting plasma, which both seem to be in a rough pressure equilibrium.
We conclude that 4C+29.30 displays a complex view of interactions between the
jet-driven radio outflow and host galaxy environment, signaling feedback
processes closely associated with the central active nucleus.Comment: ApJ in pres
Expression of a type B RIFIN in Plasmodium falciparum merozoites and gametes
BACKGROUND: The ability of Plasmodium falciparum to undergo antigenic variation, by switching expression among protein variants encoded by multigene families, such as var, rif and stevor, is key to the survival of this parasite in the human host. The RIFIN protein family can be divided into A and B types based on the presence or absence of a 25 amino acid motif in the semi-conserved domain. A particular type B RIFIN, PF13_0006, has previously been shown to be strongly transcribed in the asexual and sexual stages of P. falciparum in vitro. METHODS: Antibodies to recombinant PF13_0006 RIFIN were used in immunofluorescence and confocal imaging of 3D7 parasites throughout the asexual reproduction and sexual development to examine the expression of PF13_0006. Furthermore, reactivity to recombinant PF13_0006 was measured in plasma samples collected from individuals from both East and West African endemic areas. RESULTS: The PF13_0006 RIFIN variant appeared expressed by both released merozoites and gametes after emergence. 7.4% and 12.1% of individuals from East and West African endemic areas, respectively, carry plasma antibodies that recognize recombinant PF13_0006, where the antibody responses were more common among older children. CONCLUSIONS: The stage specificity of PF13_0006 suggests that the diversity of RIFIN variants has evolved to provide multiple specialized functions in different stages of the parasite life cycle. These data also suggest that RIFIN variants antigenically similar to PF13_0006 occur in African parasite populations
Galaxy And Mass Assembly (GAMA): the 0.013 < z < 0.1 cosmic spectral energy distribution from 0.1 m to 1 mm
We use the Galaxy And Mass Assembly survey (GAMA) I data set combined with GALEX, Sloan Digital Sky Survey (SDSS) and UKIRT Infrared Deep Sky Survey (UKIDSS) imaging to construct the low-redshift (z < 0.1) galaxy luminosity functions in FUV, NUV, ugriz and YJHK bands from within a single well-constrained volume of 3.4 Ă 105 (Mpcâhâ1)3. The derived luminosity distributions are normalized to the SDSS data release 7 (DR7) main survey to reduce the estimated cosmic variance to the 5âper cent level. The data are used to construct the cosmic spectral energy distribution (CSED) from 0.1 to 2.1 ÎŒm free from any wavelength-dependent cosmic variance for both the elliptical and non-elliptical populations. The two populations exhibit dramatically different CSEDs as expected for a predominantly old and young population, respectively. Using the Driver et al. prescription for the azimuthally averaged photon escape fraction, the non-ellipticals are corrected for the impact of dust attenuation and the combined CSED constructed. The final results show that the Universe is currently generating (1.8 ± 0.3) Ă 1035âh W Mpcâ3 of which (1.2 ± 0.1) Ă 1035âh W Mpcâ3 is directly released into the inter-galactic medium and (0.6 ± 0.1) Ă 1035âh W Mpcâ3 is reprocessed and reradiated by dust in the far-IR. Using the GAMA data and our dust model we predict the mid- and far-IR emission which agrees remarkably well with available data. We therefore provide a robust description of the pre- and post-dust attenuated energy output of the nearby Universe from 0.1 ÎŒm to 0.6âmm. The largest uncertainty in this measurement lies in the mid- and far-IR bands stemming from the dust attenuation correction and its currently poorly constrained dependence on environment, stellar mass and morphology
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