120 research outputs found
Relativistic effects and primordial non-Gaussianity in the galaxy bias
When dealing with observables, one needs to generalize the bias relation
between the observed galaxy fluctuation field to the underlying matter
distribution in a gauge-invariant way. We provide such relation at second-order
in perturbation theory adopting the local Eulerian bias model and starting from
the observationally motivated uniform-redshift gauge. Our computation includes
the presence of primordial non-Gaussianity. We show that large scale-dependent
relativistic effects in the Eulerian bias arise independently from the presence
of some primordial non-Gaussianity. Furthermore, the Eulerian bias inherits
from the primordial non-Gaussianity not only a scale-dependence, but also a
modulation with the angle of observation when sources with different biases are
correlated.Comment: 12 pages, LaTeX file; version accepted for publication in JCA
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Ex vivo normothermic perfusion of isolated segmental porcine bowel: a novel functional model of the small intestine.
BACKGROUND: There is an unmet need for suitable ex vivo large animal models in experimental gastroenterology and intestinal transplantation. This study details a reliable and effective technique for ex vivo normothermic perfusion (EVNP) of segmental porcine small intestine. METHODS: Segments of small intestine, 1.5-3.0 m in length, were retrieved from terminally anaesthetized pigs. After a period of cold ischaemia, EVNP was performed for 2 h at 37°C with a mean pressure of 80 mmHg using oxygenated autologous blood diluted with Ringer's solution. The duration of EVNP was extended to 4 h for a second set of experiments in which two segments of proximal to mid-ileum (1.5-3.0 m) were retrieved from each animal and reperfused with whole blood (control) or leucocyte-depleted blood to examine the impact of leucocyte depletion on reperfusion injury. RESULTS: After a mean cold ischaemia time of 5 h and 20 min, EVNP was performed in an initial group of four pigs. In the second set of experiments, five pigs were used in each group. In all experiments bowel segments were well perfused and exhibited peristalsis during EVNP. Venous glucose levels significantly increased following luminal glucose stimulation (mean(s.e.m.) basal level 1.8(0.6) mmol/l versus peak 15.5(5.8) mmol/l; P < 0.001) and glucagon-like peptide 1 (GLP-1) levels increased in all experiments, demonstrating intact absorptive and secretory intestinal functions. There were no significant differences between control and leucocyte-depleted animals regarding blood flow, venous glucose, GLP-1 levels or histopathology at the end of 4 h of EVNP. CONCLUSIONS: This novel model is suitable for the investigation of gastrointestinal physiology, pathology and ischaemia reperfusion injury, along with evaluation of potential therapeutic interventions
Searching for the light dark gauge boson in GeV-scale experiments
We study current constraints and search prospects for a GeV scale vector
boson at a range of low energy experiments. It couples to the Standard Model
charged particles with a strength <= 10^-3 to 10^-4 of that of the photon. The
possibility of such a particle mediating dark matter self-interactions has
received much attention recently. We consider searches at low energy high
luminosity colliders, meson decays, and fixed target experiments. Based on
available data, searches both at colliders and in meson decays can discover or
exclude such a scenario if the coupling strength is on the larger side. We
emphasize that a dedicated fixed target experiment has a much better potential
in searching for such a gauge boson, and outline the desired properties of such
an experiment. Two different optimal designs should be implemented to cover the
range of coupling strength 10^-3 to 10^-5, and < 10^-5 of the photon,
respectively. We also briefly comment on other possible ways of searching for
such a gauge boson.Comment: 33 pages, 5 figures; v2: corrected discussion of Upsilon decays,
updates to discussion of fixed-target experiments and QED constraints,
numerous minor changes, references added; v3: typo corrected relative to the
JHEP published versio
Modelling non-dust fluids in cosmology
Currently, most of the numerical simulations of structure formation use
Newtonian gravity. When modelling pressureless dark matter, or `dust', this
approach gives the correct results for scales much smaller than the
cosmological horizon, but for scenarios in which the fluid has pressure this is
no longer the case. In this article, we present the correspondence of
perturbations in Newtonian and cosmological perturbation theory, showing exact
mathematical equivalence for pressureless matter, and giving the relativistic
corrections for matter with pressure. As an example, we study the case of
scalar field dark matter which features non-zero pressure perturbations. We
discuss some problems which may arise when evolving the perturbations in this
model with Newtonian numerical simulations and with CMB Boltzmann codes.Comment: 5 pages; v2: typos corrected and refs added, submitted version; v3:
version to appear in JCA
Distribution, Elimination, and Biopersistence to 90 Days of a Systemically Introduced 30 nm Ceria-Engineered Nanomaterial in Rats
Nanoceria is used as a catalyst in diesel fuel, as an abrasive in printed circuit manufacture, and is being pursued as an antioxidant therapeutic. Our objective is to extend previous findings showing that there were no reductions of cerium in organs of the mononuclear phagocyte (reticuloendothelial) system up to 30 days after a single nanoscale ceria administration. An ~5% aqueous dispersion of citrate-stabilized 30 nm ceria, synthesized and characterized in-house, or vehicle, was iv infused into rats terminated 1, 7, 30, or 90 days later. Cageside observations were obtained daily, body weight weekly. Daily urinary and fecal cerium outputs were quantified for 2 weeks. Nine organs were weighed and samples collected from 14 tissues/organs/systems, blood and cerebrospinal fluid for cerium determination. Histology and oxidative stress were assessed. Less than 1% of the nanoceria was excreted in the first 2 weeks, 98% in feces. Body weight gain was initially impaired. Spleen weight was significantly increased in some ceria-treated groups, associated with abnormalities. Ceria was primarily retained in the spleen, liver, and bone marrow. There was little decrease of ceria in any tissue over the 90 days. Granulomas were observed in the liver. Time-dependent oxidative stress changes were seen in the liver and spleen. Nanoscale ceria was persistently retained by organs of the mononuclear phagocyte system, associated with adverse changes. The results support concern about the long-term fate and adverse effects of inert nanoscale metal oxides that distribute throughout the body, are persistently retained, and produce adverse changes
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