552 research outputs found
Tunable uptake of poly(ethylene oxide) by graphite-oxide-based materials
We investigate the role of structure and chemical composition on the uptake of poly(ethylene oxide) by a series of graphite oxides (GOs) and thermally reduced GOs, leading to the formation of polymer-intercalated GO and polymer-adsorbed graphene nanostructures. To this end, a series of poly(ethylene oxide) (PEO) - GO hybrid materials exhibiting a variable degree of GO oxidation and exfoliation has been investigated in detail using a combination of techniques including X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetry, scanning-electron microscopy, and nitrogen adsorption. Intercalation of the polymer phase into well-defined GO galleries is found to correlate well with both the degree of GO oxidation and with the presence of hydroxyl groups. The latter feature is an essential prerequisite to optimize polymer uptake owing to the predominance of hydrogen-bonding interactions between intercalant and host. Unlike the bulk polymer, these intercalation compounds show neither crystallisation nor glass-transition associated with the polymer phase. Exfoliation and reduction of GO result in high-surface-area graphene layers exhibiting the highest polymer uptake in these GO-based materials. In this case, PEO undergoes surface adsorption, where we observe the recovery of glass and melting transitions associated with the polymer phase albeit at significantly lower temperatures than the bulk
X-ray Spectra of the RIXOS source sample
We present results of an extensive study of the X-ray spectral properties of
sources detected in the RIXOS survey, that is nearly complete down to a flux
limit of 3e-14 cgs (0.5-2 keV). We show that for X-ray surveys containing
sources with low count rate spectral slopes estimated using simple hardness
ratios in the ROSAT band can be biased. Instead we analyse three-colour X-ray
data using statistical techniques appropriate to the Poisson regime which
removes the effects of this bias. We have then applied this technique to the
RIXOS survey to study the spectral properties of the sample. For the AGN we
find an average energy index of 1.05+-0.05 with no evidence for spectral
evolution with redshift. Individual AGN are shown to have a range of properties
including soft X-ray excesses and intrinsic absorption. Narrow Emission Line
Galaxies also seem to fit to a power-law spectrum, which may indicate a
non-thermal origin for their X-ray emission. We infer that most of the clusters
in the sample have a bremsstrahlung temperature >3 keV, although some show
evidence for a cooling flow. The stars deviate strongly from a power-law model
but fit to a thermal model. Finally, we have analysed the whole RIXOS sample
containing 1762 sources. We find that the mean spectral slope of the sources
hardens at lower fluxes in agreement with results from other samples. However,
a study of the individual sources demonstrates that the hardening of the mean
is caused by the appearance of a population of very hard sources at the lowest
fluxes. This has implications for the nature of the soft X-ray background.Comment: 31,LaTeX file, 2 PS files with Table 2 and 22 PS figures. MNRAS in
pres
Evidence of a Critical time in Constrained Kinetic Ising models
We study the relaxational dynamics of the one-spin facilitated Ising model
introduced by Fredrickson and Andersen. We show the existence of a critical
time which separates an initial regime in which the relaxation is exponentially
fast and aging is absent from a regime in which relaxation becomes slow and
aging effects are present. The presence of this fast exponential process and
its associated critical time is in agreement with some recent experimental
results on fragile glasses.Comment: 20 Pages + 7 Figures, Revte
ROSAT PSPC spectra of X-ray selected Narrow Emission Line Galaxies
We analyse the ROSAT PSPC spectrum of 19 X-ray selected Narrow Emission Line
Galaxies (NELGs) discovered during the optical identification of sources in the
ROSAT UK Deep Survey. Their properties are compared to those of broad line
Active Galactic Nuclei (AGN) in the same sample. Counts in three spectral bands
have been extracted for all the sources, and have been fitted with a power-law
model assuming the Galactic value for NH. The average slope of NELGs is
\alpha=0.45+-0.09, whilst for the AGN it is \alpha=0.96+-0.03. The power-law
model is a good fit for ~90% of NELGs and ~75% of AGN. Recent work shows that
the fractional surface density of NELGs increases with respect to AGN at faint
fluxes. Thus they are expected to be an important component of the residual
soft (<2 keV) X--ray background. The slope of the X--ray background
(\alpha~0.4, 1-10 keV) is harder than that of AGN (\alpha~1) but our results
show that it is consistent with the summed spectrum of the NELGs in the deep
survey (\alpha~0.4). This may finally reconcile the spectrum of the background
with the properties of the sources that constitute it.Comment: Uuencoded compressed LaTex file and three PS figures plus mn.sty.
Accepted in MNRA
Influence of solvent on poly(2-(dimethylamino)ethyl methacrylate) dynamics in polymer-concentrated mixtures: a combined neutron scattering, dielectric spectroscopy and calorimetric study
We have investigated the dynamical processes-α-relaxation, local motions of the side-groups, and methyl group rotations-in poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) in the dry state and in mixtures (at 70 wt% polymer concentration) with tetrahydrofuran (THF) and water, to address the question as to how these polymer motions are affected by plasticizers interacting in different ways with the polymer. Differential scanning calorimetry, dielectric spectroscopy, and neutron scattering techniques on labeled samples (with deuterated solvents to isolate the signal of the polymer component) have been combined. The α-relaxation is drastically affected, with similar shifts of the glass-transition temperature for both solvents. Effects of compositional heterogeneities and reduction of the fragility are also observed. On the contrary, methyl-group dynamics are unaffected by the presence of solvent. Regarding side-group local motions (β-relaxation), two kinds of components-a slow and a fast one-could be identified in the dry state. On the basis of the spatial information provided by neutron scattering, a model for the geometry of the motions involved in the fast component has been proposed. Adding solvent, this process would remain essentially unaltered, but the population involved in the slower one would be reduced. With THF as solvent, this reduction would be complete, but with water it would be only partial. This could be attributed to rather heterogeneous distribution of water molecules in the polymer likely associated with the presence of water clusters. Such a scenario would also explain the much more pronounced broadening of the glass-transition region observed for the polymer in the aqueous mixture with respect to that induced by THF.Financial support from the Projects MAT2012-31088 (Spanish MINECO and EU) and IT-654-13 (Basque Government) is acknowledged. This work is based on experiments performed at FOCUS (SINQ, Paul Scherrer Institute, Villigen, Switzerland), and at TOFTOF and SPHERES (Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany), and has been supported by the European Commission under the seventh Framework
Programme through the “Research Infrastructures” action of the “Capacities” Programme, NMI3-II Grant Number 283883.Peer Reviewe
Primary herpes simplex virus type 1 infection with acute liver failure in solid organ transplantation: Report of three cases and review
Herpes virus infections is not uncommon in solid organ transplantation patients. We report 3 cases with primary Herpes simplex virus type-1 (HSV1) infection with acute liver failure (ALF). This is a rare and potentially fatal entity that could be a donor-derived infection. Although the initial clinical presentation is non-specific, it should be considered as a differential diagnosis in HSV-negative serology patients with liver failure and empirical treatment must be started in combination with a drastic reduction of immunosuppression. A strategy of HSV prophylaxis for pre-transplant HSV seronegative patients must be stablished in order to reduce the risk of clinical disease.© 2022 Published by Elsevier Ltd
NGC 7582: The Prototype Narrow-Line X-ray Galaxy
NGC 7582 is a candidate prototype of the Narrow Line X-ray Galaxies (NLXGs)
found in deep X-ray surveys. An ASCA observation shows the hard (> 3 keV) X-ray
continuum of NGC 7582 drops 40% in ~6 ks, implying an AGN, while the soft band
(< 3 keV) does not drop in concert with the hard continuum, requiring a
separate component. The X-ray spectrum of NGC 7582 also shows a clear 0.5-2 keV
soft (kT = 0.8 (+0.9,-0.3) keV or Gamma = 2.4 +/- 0.6; L(X) = 6 x 10**40 ergs
s**-1) low--energy component, in addition to a heavily absorbed [N(H) = (6 +/-
2)\times 10**22 cm**-2 ] and variable 2-10 keV power law [Gamma = 0.7
(+0.3,-0.4); L(X) = (1.7-2.3) x 10**42 ergs s**-1]. This is one of the flattest
2-10 keV slopes in any AGN observed with ASCA. (The ROSAT HRI image of NGC 7582
further suggests extent to the SE.)
These observations make it clear that the hard X-ray emission of NGC 7582,
the most "narrow-line" of the NLXGs, is associated with an AGN. The strong
suggestion is that all NLXGs are obscured AGNs, as hypothesized to explain the
X-ray background spectral paradox. The separate soft X-ray component makes NGC
7582 (and by extension other NLXGs) detectable as a ROSAT source.Comment: text: Latex2e 10 pages, including 1 table, and 2 postscript figures
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