11,929 research outputs found
A simulation model of temperature transitory on rocks having different thermal inertia. Analysis of the theoretical capacity of rock discrimination by remote sensing data
The possibility of identifying ground surface material by measuring the surface temperature at two different and significant times of the day was investigated for the case of hypothetical island whose rocky surface contained no vegetation and consisted of dolomite, clay, and granite. The thermal dynamics of the soil surface during a day in which atmospheric conditions were average for a latitude of about 40 deg to 50 deg were numerically simulated. The line of separation between zones of different materials was delineated by the range of temperature variation. Results show that the difference between maximum and minimum value of the temperature of ground surface during the day is linked to the thermal inertia value of the material of which the rock is formed
First principles study of adsorbed Cu_n (n=1-4) microclusters on MgO(100): structural and electronic properties
We present a density functional study of the structural and electronic
properties of small Cu_n (n=1,4) aggregates on defect-free MgO(100). The
calculations employ a slab geometry with periodic boundary conditions,
supercells with up to 76 atoms, and include full relaxation of the surface
layer and of all adsorbed atoms. The preferred adsorption site for a single Cu
adatom is on top of an oxygen atom. The adsorption energy and Cu-O distance are
E_S-A = 0.99 eV and d_S-A = 2.04 Angstroems using the Perdew-Wang gradient
corrected exchange correlation functional. The saddle point for surface
diffusion is at the "hollow" site, with a diffusion barrier of around 0.45 eV.
For the adsorbed copper dimer, two geometries, one parallel and one
perpendicular to the surface, are very close in energy. For the adsorbed Cu_3,
a linear configuration is preferred to the triangular geometry. As for the
tetramer, the most stable adsorbed geometry for Cu_4 is a rhombus. The
adsorption energy per Cu atom decreases with increasing the size of the
cluster, while the Cu-Cu cohesive energy increases, rapidly becoming more
important than the adsorption energy.Comment: Major revision, Latex(2e) document, 23 pages, 11 figures, accepted
for publication in J. of Chem. Phys., paper available at
http://irrmawww.epfl.ch/vm/vm_wor
Excised acoustic black holes: the scattering problem in the time domain
The scattering process of a dynamic perturbation impinging on a draining-tub
model of an acoustic black hole is numerically solved in the time domain.
Analogies with real black holes of General Relativity are explored by using
recently developed mathematical tools involving finite elements methods,
excision techniques, and constrained evolution schemes for strongly hyperbolic
systems. In particular it is shown that superradiant scattering of a
quasi-monochromatic wavepacket can produce strong amplification of the signal,
offering the possibility of a significant extraction of rotational energy at
suitable values of the angular frequency of the vortex and of the central
frequency of the wavepacket. The results show that theoretical tools recently
developed for gravitational waves can be brought to fruition in the study of
other problems in which strong anisotropies are present.Comment: 8 pages, 9 figure
Photometric and spectroscopic study of the intermediate age open cluster NGC 3960
We present CCD UBVI photometry and high-resolution spectroscopy of the
intermediate age open cluster NGC 3960. The colour - magnitude diagrams (CMDs)
derived from the photometric data and interpreted with the synthetic CMD method
allow us to estimate the cluster parameters. We derive: age = 0.9 or 0.6 Gyr
(depending on whether or not overshooting from convective regions is included
in the adopted stellar models), distance (m-M)0 = 11.6 +/- 0.1, reddening
E(B-V) = 0.29 +/- 0.02, differential reddening Delta E(B-V) = 0.05 and
approximate metallicity between solar and half of solar. We obtained high
resolution spectra of three clump stars, and derived an average [Fe/H] = -0.12
(rms 0.04 dex), in very good agreement with the photometric determination. We
also obtained abundances of alpha-elements, Fe-peak elements, and of Ba. The
reddenings toward individual stars derived from the spectroscopic temperatures
and the Alonso et al. calibrations give further support to the existence of
significative variations across the cluster.Comment: Accepted for publication on MNRAS; fig. 3, 4, 5, 6 at degraded
resolutio
Photometric and spectroscopic study of the intermediate-age open cluster NGC 2355
In this paper we analyse the evolutionary status and properties of the old
open cluster NGC 2355, located in the Galactic anticentre direction, as a part
of the long term programme BOCCE. NGC 2355 was observed with LBC@LBT using the
Bessel , , and filters. The cluster parameters have been obtained
using the synthetic colour-magnitude diagram (CMD) method, as done in other
papers of this series. Additional spectroscopic observations with FIES@NOT of
three giant stars were used to determine the chemical properties of the
cluster. Our analysis shows that NGC 2355 has metallicity slightly less than
solar, with [Fe/H] dex, age between 0.8 and 1 Gyr, reddening
in the range 0.14 and 0.19 mag, and distance modulus of about 11 mag.
We also investigated the abundances of O, Na, Al, , iron-peak, and
neutron capture elements, showing that NGC 2355 falls within the abundance
distribution of similar clusters (same age and metallicity). The Galactocentric
distance of NGC~2355 places it at the border between two regimes of metallicity
distribution; this makes it an important cluster for the study of the chemical
properties and evolution of the disc.Comment: 20 pages, 11 figures, Accepted on MNRA
Many-body effective mass enhancement in a two-dimensional electron liquid
Motivated by a large number of recent magnetotransport studies we have
revisited the problem of the microscopic calculation of the quasiparticle
effective mass in a paramagnetic two-dimensional (2D) electron liquid (EL). Our
systematic study is based on a generalized approximation which makes use
of the many-body local fields and takes advantage of the results of the most
recent QMC calculations of the static charge- and spin-response of the 2D EL.
We report extensive calculations for the many-body effective mass enhancement
over a broad range of electron densities. In this respect we critically examine
the relative merits of the on-shell approximation, commonly used in
weak-coupling situations, {\it versus} the actual self-consistent solution of
the Dyson equation. We show that already for and higher, a
solution of the Dyson equation proves here necessary in order to obtain a well
behaved effective mass. Finally we also show that our theoretical results for a
quasi-2D EL, free of any adjustable fitting parameters, are in good qualitative
agreement with some recent measurements in a GaAs/AlGaAs heterostructure.Comment: 12 pages, 3 figures, CMT28 Conference Proceedings, work related to
cond-mat/041226
The Chemical Evolution of the Milky Way
The field of chemical evolution modeling of the Galaxy is experiencing in the
last years a phase of high activity and important achievements. There are,
however, several open questions which still need to be answered. In this review
I summarize what have been the most important achievements and what are some of
the most urgent questions to be answered.Comment: 10 pages including 3 figs, to appear in "The Chemical Evolution of
the Milky Way. Stars vs Clusters", Proceedings of the Sept.1999 Vulcano
Workshop, F.Giovannelli and F.Matteucci eds (Kluwer, Dordrecht) in pres
Heat Capacity Mapping Mission (HCMM) program: Study of geological structure of Sicily and other Italian areas
The usefulness of thermal inertia mapping in discriminating geolithological units was investigated using Sardinia and the Gulf of Orosei as test sites. Software designed for LANDSAT data were modified and improved for HCMM tapes. A first attempt was made to compare the geological cross section, the topography, the IR radiance, and the thermal inertia along selected profiles of the test site. Thermal inertia profiles appear smoothed in comparison with the thermal radiance. The lowest apparent thermal inertia (ATI) was found on granitic and basaltic outcrops where their image is of sufficient extent, while ATI is higher on carbonatic and dolomitic or moist deposits. Almost every fault is marked by a jump of ATI, the interval being sometimes of the order of one pixel. This seems to demonstrate the ability of ATI to detect contacts or tectonically disturbed zones with a good resolution. It seems more difficult to measure the differences in ATI between homogeneous materials having different lithology. Ground surveys conducted and a simulation model of diurnal temperatures of rocks having different thermal inertia are discussed
Self-consistent Overhauser model for the pair distribution function of an electron gas at finite temperature
We present calculations of the spin-averaged pair distribution function
in a homogeneous gas of electrons moving in dimensionality D=3 or D=2 at
finite temperature. The model involves the solution of a two-electron
scattering problem via an effective potential which embodies many-body effects
through a self-consistent Hartree approximation, leading to two-body wave
functions to be averaged over a temperature-dependent distribution of relative
momentum for electron pairs. We report illustrative numerical results for
in an intermediate-coupling regime and interpret them in terms of
changes of short-range order with increasing temperature.Comment: 6 pages, 5 figures, submitted to Solid State Communication
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