1,351 research outputs found
Validation of fluorescence transition probability calculations
A systematic and quantitative validation of the K and L shell X-ray
transition probability calculations according to different theoretical methods
has been performed against experimental data. This study is relevant to the
optimization of data libraries used by software systems, namely Monte Carlo
codes, dealing with X-ray fluorescence. The results support the adoption of
transition probabilities calculated according to the Hartree-Fock approach,
which manifest better agreement with experimental measurements than
calculations based on the Hartree-Slater method.Comment: 8 pages, 21 figures and images, 3 tables, to appear in proceedings of
the Nuclear Science Symposium and Medical Imaging Conference 2009, Orland
Morphology and properties evolution upon ring-opening polymerization during extrusion of cyclic butylene terephthalate and graphene-related-materials into thermally conductive nanocomposites
In this work, the study of thermal conductivity before and after in-situ
ring-opening polymerization of cyclic butylene terephthalate into poly
(butylene terephthalate) in presence of graphene-related materials (GRM) is
addressed, to gain insight in the modification of nanocomposites morphology
upon polymerization. Five types of GRM were used: one type of graphite
nanoplatelets, two different grades of reduced graphene oxide (rGO) and the
same rGO grades after thermal annealing for 1 hour at 1700{\deg}C under vacuum
to reduce their defectiveness. Polymerization of CBT into pCBT, morphology and
nanoparticle organization were investigated by means of differential scanning
calorimetry, electron microscopy and rheology. Electrical and thermal
properties were investigated by means of volumetric resistivity and bulk
thermal conductivity measurement. In particular, the reduction of nanoflake
aspect ratio during ring-opening polymerization was found to have a detrimental
effect on both electrical and thermal conductivities in nanocomposites
Tracing the Mass-Assembly History of Galaxies with Deep Surveys
We use the optical and near-infrared galaxy samples from the Munich
Near-Infrared Cluster Survey (MUNICS), the FORS Deep Field (FDF) and GOODS-S to
probe the stellar mass assembly history of field galaxies out to z ~ 5.
Combining information on the galaxies' stellar mass with their star-formation
rate and the age of the stellar population, we can draw important conclusions
on the assembly of the most massive galaxies in the universe: These objects
contain the oldest stellar populations at all redshifts probed. Furthermore, we
show that with increasing redshift the contribution of star-formation to the
mass assembly for massive galaxies increases dramatically, reaching the era of
their formation at z ~ 2 and beyond. These findings can be interpreted as
evidence for an early epoch of star formation in the most massive galaxies in
the universe.Comment: 3 pages, 2 figures; published in B. Aschenbach, V. Burwitz, G.
Hasinger, B. Leibundgut (eds.): "Relativistic Astrophysics and Cosmology -
Einstein's Legacy. Proceedings of the Conference held in Munich, 2006", ESO
Astrophysics Symposia, Springer Verlag, 2007, p. 310. Replaced to match final
published versio
Effect of processing conditions on the thermal and electrical conductivity of poly (butylene terephthalate) nanocomposites prepared via ring-opening polymerization
Successful preparation of polymer nanocomposites, exploiting graphene-related
materials, via melt mixing technology requires precise design, optimization and
control of processing. In the present work, the effect of different processing
parameters during the preparation of poly (butylene terephthalate)
nanocomposites, through ring-opening polymerization of cyclic butylene
terephthalate in presence of graphite nanoplatelets (GNP), was thoroughly
addressed. Processing temperature (240{\deg}C or 260{\deg}C), extrusion time (5
or 10 minutes) and shear rate (50 or 100 rpm) were varied by means of a full
factorial design of experiment approach, leading to the preparation of
polybutylene terephthalate/GNP nanocomposite in 8 different processing
conditions. Morphology and quality of GNP were investigated by means of
electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry and
Raman spectroscopy. Molecular weight of the polymer matrix in nanocomposites
and nanoflake dispersion were experimentally determined as a function of the
different processing conditions. The effect of transformation parameters on
electrical and thermal properties was studied by means of electrical and
thermal conductivity measurement. Heat and charge transport performance
evidenced a clear correlation with the dispersion and fragmentation of the GNP
nanoflakes; in particular, gentle processing conditions (low shear rate, short
mixing time) turned out to be the most favourable condition to obtain high
conductivity values
Effect of morphology and defectiveness of graphene-related materials on the electrical and thermal conductivity of their polymer nanocomposites
In this work, electrically and thermally conductive poly (butylene
terephthalate) nanocomposites were prepared by in-situ ring-opening
polymerization of cyclic butylene terephthalate (CBT) in presence of a
tin-based catalyst. One type of graphite nanoplatelets (GNP) and two different
grades of reduced graphene oxide (rGO) were used. Furthermore, high temperature
annealing treatment under vacuum at 1700{\deg}C was carried out on both RGO to
reduce their defectiveness and study the correlation between the
electrical/thermal properties of the nanocomposites and the nanoflakes
structure/defectiveness. The morphology and quality of the nanomaterials were
investigated by means of electron microscopy, x-ray photoelectron spectroscopy,
thermogravimetry and Raman spectroscopy. Thermal, mechanical and electrical
properties of the nanocomposites were investigated by means of rheology,
dynamic mechanical thermal analysis, volumetric resistivity and thermal
conductivity measurements. Physical properties of nanocomposites were
correlated with the structure and defectiveness of nanoflakes, evidencing a
strong dependence of properties on nanoflakes structure and defectiveness. In
particular, a significant enhancement of both thermal and electrical
conductivities was demonstrated upon the reduction of nanoflakes defectiveness
IR Colors and Sizes of Faint Galaxies
We present J and Ks band galaxy counts down to J=24 and Ks=22.5 obtained with
the new infrared imager/spectrometer, SOFI, at the ESO New Technology
Telescope. The co-addition of short, dithered, images led to a total exposure
time of 256 and 624 minutes respectively, over an area of arcmin
centered on the NTT Deep Field. The total number of sources with S/N is
1569 in the J sample and 1025 in the Ks-selected sample. These are the largest
samples currently available at these depths. A d/d relation with slope
of in J and in Ks is found with no evident sign of a
decline at the magnitude limit. The observed surface density of ``small''
sources is much lower than ``large'' ones at bright magnitudes and rises more
steeply than the large sources to fainter magnitudes. Fainter than
and Ks, small sources dominate the number counts. Galaxies get redder
in J-K down to
J and Ks. At fainter magnitudes, the median color becomes
bluer with an accompanying increase in the compactness of the galaxies. We show
that the blue, small sources which dominate the faint IR counts are not
compatible with a high redshift () population. On the contrary, the
observed color and compactness trends, together with the absence of a turnover
at faint magnitudes and the dominance of small sources, can be naturally
explained by an increasing contribution of sub- galaxies when going to
fainter apparent magnitudes. Such evidence strongly supports the existence of a
steeply rising () faint end of the local infrared luminosity
function of galaxies - at least for luminosities .Comment: Accepted for publication on A&A; 15 pages, 13 figure
Non-linear Matter Spectra in Coupled Quintessence
We consider cosmologies in which a dark-energy scalar field interacts with
cold dark matter. The growth of perturbations is followed beyond the linear
level by means of the time-renormalization-group method, which is extended to
describe a multi-component matter sector. Even in the absence of the extra
interaction, a scale-dependent bias is generated as a consequence of the
different initial conditions for baryons and dark matter after decoupling. The
effect is enhanced significantly by the extra coupling and can be at the 2-3
percent level in the range of scales of baryonic acoustic oscillations. We
compare our results with N-body simulations, finding very good agreement.Comment: 20 pages, 6 figures, typo correcte
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