142 research outputs found
Surface chemistry of liquid metals
The fundamental surface chemistry of the behavior of liquid metals spreading on a solid substrate is not at all well understood. Each of these questions involves knowing the details of the structure of interfaces and their dynamics. For example the structure of a monolayer of tin oxide on pure liquid tin is unknown. This is in contrast to the relatively large amount of data available on the structure of copper oxide monolayers on solid, pure copper. However, since liquid tin has a vapor pressure below 10(exp -10)torr for a reasonable temperature range above its melting point, it is possible to use the techniques of surface science to study the geometric, electronic and vibrational structures of these monolayers. In addition, certain techniques developed by surface chemists for the study of liquid systems can be applied to the ultra-high vacuum environment. In particular we have shown that light scattering spectroscopy can be used to study the surface tension tensor of these interfaces. The tin oxide layer in particular is very interesting in that the monolayer is rigid but admits of bending. Ellipsometric microscopy allows the visualization of monolayer thick films and show whether island formation occurs at various levels of dosing
Constraints on a non-gaussian () CDM model
We consider constraints on the structure formation model based on
non-Gaussian fluctuations generated during inflation, which have
distributions. Using three data sets, the abundance of the clusters at ,
moderate and the correlation length, we show that constraints on the
non-Gaussianity and the amplitude of fluctuations and the density parameter can
be obtained. We obtain an upper bound for and a lower bound for the
non-Gaussianity and the amplitude of the fluctuations. Using the abundance of
clusters at , for the spectrum parameterized by cold dark matter
(CDM) shape parameter , we obtain an upper bound for the density
parameter and lower bounds for the amplitude and for the non-Gaussianity of fluctuations ,
where G=1 for Gaussian.Comment: 7 pages, 3 figures, MNRAS in pres
Dark energy and the evolution of spherical overdensities
We use the non-linear spherical model in cold dark matter (CDM) cosmologies
with dark energy to investigate the effects of dark energy on the growth of
structure and the formation of virialised structures. We consider dark energy
models with a constant equation of state parameter w. For -1<w<-1/3, clusters
form earlier and are more concentrated in quintessence than in LambdaCDM
models, but they form later and are less concentrated than in the corresponding
open model with the same matter density and no dark energy. We point out some
confusion in the literature around the expression of the collapse factor (ratio
of the radius of the sphere at virialisation to that at turn-around) derived
from the virial theorem. We use the Sheth & Tormen extension of the
Press-Schechter framework to calculate the evolution of the cluster abundance
in different models and show the sensitivity of the cluster abundance to both
the amplitude of the mass fluctuations, sigma8, and the sigma8-w normalisation,
selected to match either the cosmic microwave background observations or the
abundance of X-ray clusters.Comment: 9 pages, 8 figures. Accepted for publication in MNRA
TEMPERATURE AND RELATIVITY
We investigate whether inertial thermometers moving in a thermal bath behave
as being hotter or colder. This question is directly related to the classical
controversy concerning how temperature transforms under Lorentz
transformations. Rather than basing our arguments on thermodynamical
hypotheses, we perform straightforward calculations in the context of
relativistic quantum field theory. For this purpose we use Unruh-DeWitt
detectors, since they have been shown to be reliable thermometers in
semi-classical gravity. We believe that our discussion helps in definitely
clarifying this issue.Comment: 9 pages, 1 figure available upon reques
XMM-Newton Observation of a Distant X-ray Selected Cluster of Galaxies at z=1.26 with Possible Cluster Interaction
We report on the XMM-Newton (XMM) observation of RXJ1053.7+5735, one of the
most distant (z = 1.26) X-ray selected clusters of galaxies, which also shows
an unusual double-lobed X-ray morphology, indicative of possible
cluster-cluster interaction. The cluster was discovered during our ROSAT deep
pointings in the direction of the Lockman Hole. The XMM observations were
performed with the European Photon Imaging Camera (EPIC) during the performance
verification phase. Total effective exposure time was ~ 100 ksec. The best fit
temperature based on a simultaneous fit of spectra from the all EPIC cameras is
4.9(+1.5/-0.9) keV. Metallicity is poorly constrained even using the joint fit
of all spectra, with an upper limit on the iron abundance of 0.62 solar. Using
the best fit model parameters, we derived a bolometric luminosity of L(bol) =
3.4x10^44 h_{50}^-2 erg /s. Despite the fact that it was observed at fairly
large off-axis angle, the temperature errors are much smaller compared with
those of typical measurements based on ASCA or Beppo-Sax observations of z >
0.6 clusters, demonstrating the power of the XMM for determining the X-ray
temperature for high-z clusters. The measured temperature and luminosity show
that one can easily reach the intrinsically X-ray faint and cool cluster regime
comparable with those of z ~ 0.4 clusters observed by past satellites. The new
cluster temperature and L(bol) we have measured for RXJ1053.7+5735 is
consistent with a weak/no evolution of the L(bol) - Tx relation out to z ~ 1.3,
which lends support to a low Omega universe, although more data-points of z > 1
clusters are required for a more definitive statement. The caution has to be
also exercised in interpreting the result, because of the uncertainty
associated with the dynamical status of this cluster.Comment: Accepted for pubblication in A&A. 7 figures (One color figure is
changed to black and white.
The mass and temperature functions in a moving barrier model
In this paper, I use the extension of the excursion set model of Sheth &
Tormen (2002) and the barrier shape obtained in Del Popolo & Gambera (1998) to
calculate the unconditional halo mass function, and the conditional mass
function in several cosmological models. I show that the barrier obtained in
Del Popolo & Gambera (1998), which takes account of tidal interaction between
proto-haloes, is a better description of the mass functions than the spherical
collapse and is in good agreement with numerical simulations (Tozzi & Governato
1998, and Governato et al. 1999). The results are also in good agreement with
those obtained by Sheth & Tormen (2002), only slight differences are observed
expecially at the low mass end. I moreover calculate, and compare with
simulations, the temperature function obtained by means of the mass functions
previously calculated and also using an improved version of the M-T relation,
which accounts for the fact that massive clusters accrete matter
quasi-continuously, and finally taking account of the tidal interaction with
neighboring clusters. Even in this case the discrepancy between the
Press-Schecter predictions and simulations is considerably reduced.Comment: 23 pages; 11 encapsulated figures. Accepted for publication in MNRA
Clusters of Galaxies and the Diffuse Gamma Ray Background
We discuss the diffuse emission of gamma rays and neutrinos from galaxy
clusters in the viable models for structure formation in the universe. We use a
self-consistent picture for cluster formation and evolution starting from a
primordial density perturbation spectrum, and a realistic modelling for the
distribution of the intergalactic medium which is abundantly present within
galaxy clusters. We find that an evolving population of clusters can produce a
fraction of the diffuse gamma-ray background (DGRB)
observed by EGRET. This result is robust and is weakly dependent on the
cosmological scenario and on the degree of evolution of the inter galactic
medium (IGM) in distant clusters, because the bulk of the sources contributing
to the DGRB is located at redshifts z \simlt 0.2. We also found a correlation
between the non-thermal, gamma-ray and the thermal X-ray emissions from these
structures. Using this result, we derived a list of gamma-ray clusters
observable with the next generation -ray detectors. Finally, we briefly
discuss the possible relevance of galaxy clusters for neutrino astronomy and
for very high energy particle astronomy.Comment: 37 pages, 9 Figures, Latex (using elsart,epsfig), to appear in
Astroparticle Physics. Send comments to S.Colafrancesco:
[email protected]
The Nature, Evolution, Clustering and X-ray Properties of Extremely Red Galaxies in the CDFS/GOODS field
We identify a deep sample of 198 extremely red objects (EROs) in (50.4 sq.
arcmin of) the Chandra Deep Field South, selected as I-K>3.92 galaxies to a
limit K=22. The ERO number counts remain well below the predictions for pure
luminosity evolution, and fall below even a non-evolving model, suggesting the
comoving number density of passive/very red galaxies decreases with redshift.
The angular correlation function of these EROs indicates stronger clustering
than that of other galaxies at the same magnitudes, and is best-fitted by
models in which the EROs have a comoving correlation radius 12.5/h Mpc, or
21.4/h Mpc in a stable clustering model. We find a 40-arcsec diameter grouping
of 10 EROs, centered on the Chandra source (and ERO) XID:58, with colours
suggesting a cluster of mostly passive EROs at approx. z=1.5. The 942 ksec
Chandra survey detected 73 X-ray sources in the area of our ERO sample, of
which 17 coincide with EROs. Of these sources, 13 have X-ray properties
indicative of obscured AGN, while the faintest 4 may be starburst galaxies. In
addition, we find evidence that Chandra sources and EROs are positively
cross-correlated at non-zero (2-20 arcsec) separations, implying that they tend
to trace the same large-scale structures.Comment: 17 pages, latex, 14 figures, accepted for publication in MNRAS. Major
revisions from original version, with a new, reselected sample of ERO
Mixed Models with n>1 and Large Scale Structure constraints
Recent data on CBR anisotropies show a Doppler peak higher than expected in
CDM cosmological models, if the spectral index . However, CDM and LCDM
models with n>1 can hardly be consistent with LSS data. Mixed models, instead,
whose transfer function is naturally steeper because of free--streaming in the
hot component, may become consistent with data if n>1, when Omega_h is large.
This is confirmed by our detailed analysis, extended both to models with a hot
component whose momentum space distribution had a thermal origin (like massive
neutrinos), and to models with a non--cold component arising from heavier
particle decay. In this work we systematically search models which fulfill all
constraints which can be implemented at the linear level. We find that a
stringent linear constraint arises from fitting the extra-power parameter
Gamma. Other significant constraints arise comparing the expected abundances of
galaxy clusters and high-z systems with observational data. Keeping to models
with Gamma \geq 0.13, a suitable part of the space parameter still allows up to
\sim 30% of hot component (it is worth outlining that our stringent criteria
allow only models with 0.10 \mincir Omega_h \mincir 0.16, if n \leq 1). We also
outline that models with such large non--cold component would ease the solution
of the so--called baryon catastrophe in galaxy clusters.Comment: 28 pages + 9 figures, uses elsart.sty, to be published in New
Astronom
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