479 research outputs found
Effect of High-Protein Breakfast Meals on Within-Day Appetite and Food Intake in Healthy Men and Women
The Rowett Institute and Biomathematics and Statistics Scotland are grateful to the Scottish Government for funding this work. We thank the Rowett Human Nutrition Unit staff for their technical help with the interventions. Staff members who helped include Jean Bryce, Nina Lamza and Karen Taylor. The Rowett Institute and Biomathematics and Statistics Scotland are grateful to the Scottish Government for funding this work.Peer reviewedPublisher PD
Oxygen Absorption in M87: Evidence for a Warm+Hot ISM
We present a re-analysis of the ROSAT PSPC data within the central 100 kpc of
M87 to search for intrinsic oxygen absorption similar to that recently measured
in several galaxies and groups. Using a spatial-spectral deprojection analysis
we find the strongest evidence to date for intrinsic oxygen absorption in the
hot gas of a galaxy, group, or cluster. Single-phase plasma models modified by
intervening Galactic absorption cannot fit the 0.2-2.2 keV PSPC data as they
under-predict the 0.2-0.4 keV region and over-predict the 0.5-0.8 keV region
where the emission and absorption residuals are obvious upon visual inspection
of the spectral fits. Since the excess emission between 0.2-0.4 keV rules out
intrinsic absorption from cold gas or dust, the most reasonable model for the
excess emission and absorption features is warm, collisionally ionized gas with
a temperature of ~10^6 K. Simple multiphase models (cooling flow, two phases)
modified by both intervening Galactic absorption and by a single oxygen edge
provide good fits and yield temperatures and Fe abundances of the hot gas that
agree with previous determinations by ASCA and SAX. The multiphase models of
M87 inferred from the PSPC can account for the excess EUV emission observed
with EUVE and the excess X-ray absorption inferred from EINSTEIN and ASCA data
above 0.5 keV. Although the total mass of the warm gas implied by the oxygen
absorption is consistent with the matter deposited by a cooling flow, the
suppression of the mass deposition rate and the distortion of the X-ray
isophotes in the region where the radio emission is most pronounced suggest
some feedback effect from the AGN on the cooling gas. (Abridged)Comment: 17 pages (13 figures), Accepted for Publication in The Astrophysical
Journa
The mechanism of formation of 8,8-dimethyl[4.2.1.0 3,7]nonan-6-yl acetate (fortesyl acetate) during acetolysis of nopyl toluene-psulfonate
Attempts to prepare 2-(2-hydroxyethyl)-6,6-dimethylbicyclo[3.1.1]hept-2-ene (nopol; 1) labelled with deuterium at
C-10 by a process of oxidation of the primary alcohol group of nopol to the aldehyde, followed by H/D exchange
and reduction back to alcohol, were unsuccessful because various oxidation procedures, including reaction with
N-chlorosuccinimide at 278 8C, gave instead a carboxylic acid having an oxygen at C-3. Nopol, labelled at C-11
with deuterium, was obtained through a Prins reaction of b-pinene with deuteriated paraformaldehyde. This
labelled nopol was converted into its toluene-p-sulfonate ester, and was solvolysed in acetic acid containing acetate
ion to give 8,8-dimethyltricyclo[4.2.1.03,7]nonan-6-yl acetate, which is an earlier reported novel fused ring system
(fortesyl acetate; 2 acetate). The position of the label in the product showed that the mechanism of this deep-seated
carbon skeletal rearrangement proceeds through the intermediate formation of a cyclobutane ring, followed by
shift of a methylene bridge to expand the original cyclobutane ring and then subsequent expansion of the new
cyclobutane ring. Calculations of heats of formation of possible ions involved in these shifts confirm the proposed
mechanism as the most likely pathway.Junta Nacional de Investigação CientĂfica e TecnolĂłgica.
Kuwait.
Eschenmoser Trust UK
Conduction and cooling flows
Chandra and XMM-Newton observations have confirmed the presence of large
temperature gradients within the cores of many relaxed clusters of galaxies.
Here we investigate whether thermal conduction operating over those gradients
can supply sufficient heat to offset radiative cooling. Narayan & Medvedev
(2001) and Gruzinov (2002) have noted, using published results on cluster
temperatures, that conduction within a factor of a few of the Spitzer rate is
sufficient to balance bremsstrahlung cooling. From a detailed study of the
temperature and emission measure profiles of Abell 2199 and Abell 1835, we find
that the heat flux required by conduction is consistent with or below the rate
predicted by Spitzer in the outer regions of the core. Conduction may therefore
explain the lack of observational evidence for large mass cooling rates
inferred from arguments based simply on radiative cooling, provided that
conductivity is suppressed by no more than a factor of three below the full
Spitzer rate. To stem cooling in the cluster centre, however, would necessitate
conductivity values at least a factor of two larger than the Spitzer values,
which we consider implausible. This may provide an explanation for the observed
star formation and optical nebulosities in cluster cores. The solution is
likely to be time dependent. We briefly discuss the possible origin of the
cooler gas and the implications for massive galaxies.Comment: 5 pages, 4 figures, accepted by MNRAS. Minor changes following
referee's comment
ROSAT Evidence for Intrinsic Oxygen Absorption in Cooling Flow Galaxies and Groups
Using spatially resolved, deprojected ROSAT PSPC spectra of 10 of the
brightest cooling flow galaxies and groups with low Galactic column densities
we have detected intrinsic absorption over energies ~0.4-0.8 keV in half of the
sample. Since no intrinsic absorption is indicated for energies below ~0.4 keV,
the most reasonable model for the absorber is collisionally ionized gas at
temperatures T=10^{5-6} K with most of the absorption arising from ionized
states of oxygen but with a significant contribution from carbon and nitrogen.
The soft X-ray emission of this warm gas can explain the sub-Galactic column
densities of cold gas inferred within the central regions of most of the
systems. Attributing the absorption to ionized gas reconciles the large columns
of cold H and He inferred from EINSTEIN and ASCA with the lack of such columns
inferred from ROSAT. Within the central ~10-20 kpc, where the constraints are
most secure, the estimated mass of the ionized absorber is consistent with most
(perhaps all) of the matter deposited by a cooling flow over the lifetime of
the flow. Since the warm absorber produces no significant H or He absorption
the large absorber masses are consistent with the negligible atomic and
molecular H inferred from HI and CO observations of cooling flows. It is also
found that if T > ~2x10^5 K then the optical and UV emission implied by the
warm gas does not violate published constraints. Finally, we discuss how the
prediction of warm ionized gas as the product of mass drop-out in these and
other cooling flows can be verified with new CHANDRA and XMM observations.
(Abridged)Comment: 17 pages (5 figures), Accepted for publication in ApJ, expanded
discussion of multiphase spectral models, theoretical implications of warm
gas in cooling flows, and the statistical significance of the oxygen
absorptio
Investigations into the mechanism of action of nitrobenzene as a mild dehydrogenating agent under acid-catalysed conditions
Protonated nitrobenzene can be used to dehydrogenate a range of hydrocarbons, which already possess at least one double bond. Kinetic and spectroscopic results, together with known electrode potentials, yield approximate limits within which protonated nitrobenzenes can be expected to effect dehydrogenation of hydroaromatic compounds. A
high yielding synthesis of benzo[ j ]fluoranthene is described
Filtering Genes for Cluster and Network Analysis
<p>Abstract</p> <p>Background</p> <p>Prior to cluster analysis or genetic network analysis it is customary to filter, or remove genes considered to be irrelevant from the set of genes to be analyzed. Often genes whose variation across samples is less than an arbitrary threshold value are deleted. This can improve interpretability and reduce bias.</p> <p>Results</p> <p>This paper introduces modular models for representing network structure in order to study the relative effects of different filtering methods. We show that cluster analysis and principal components are strongly affected by filtering. Filtering methods intended specifically for cluster and network analysis are introduced and compared by simulating modular networks with known statistical properties. To study more realistic situations, we analyze simulated "real" data based on well-characterized E. coli and S. cerevisiae regulatory networks.</p> <p>Conclusion</p> <p>The methods introduced apply very generally, to any similarity matrix describing gene expression. One of the proposed methods, SUMCOV, performed well for all models simulated.</p
WFPC2 Observations of the Cooling Flow Elliptical in Abell 1795
We present WFPC2 images of the core of the cooling flow cD galaxy in Abell
1795. An irregular, asymmetric dust lane extends 7 \h75 kpc in projection to
the north-northwest. The dust shares the morphology observed in the H
and excess UV emission. We see both diffuse and knotty blue emission around the
dust lane, especially at the ends. The dust and emission features lie on the
edge of the radio lobes, suggesting star formation induced by the radio source
or the deflection of the radio jets off of pre-existing dust and gas. We
measure an apparent R significantly less than 3.1, implying that the
extinction law is not Galactic in the dust lane, or the presence of line
emission which is proportional to the extinction. The dust mass is at least
2 M\solar\ and is more likely to be 6.5 M\solar.Comment: 14 pages, LaTeX, Figure 4 included, Postscript Figs. 1-3 available at
ftp://astro.nmsu.edu/pub/JASON/A1795/, accepted for publication in ApJ
Letter
Toxicity Profile and Pharmacokinetic Study of A Phase I Low-Dose ScheduleâDependent Radiosensitizing Paclitaxel Chemoradiation Regimen for Inoperable NonâSmall-Cell Lung Cancer
We report the toxicity profile and pharmacokinetic data of a schedule-dependent chemoradiation regimen using pulsed low-dose paclitaxel for radiosensitization in a phase I study for inoperable non-small cell lung cancer (NSCLC)
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