8,493 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
Particle density and non-local kinetic energy density functional for two-dimensional harmonically confined Fermi vapors
We evaluate analytically some ground state properties of two-dimensional
harmonically confined Fermi vapors with isotropy and for an arbitrary number of
closed shells. We first derive a differential form of the virial theorem and an
expression for the kinetic energy density in terms of the fermion particle
density and its low-order derivatives. These results allow an explicit
differential equation to be obtained for the particle density. The equation is
third-order, linear and homogeneous. We also obtain a relation between the
turning points of kinetic energy and particle densities, and an expression of
the non-local kinetic energy density functional.Comment: 7 pages, 2 figure
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
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
Escape and fractionation of volatiles and noble gases from Mars-sized planetary embryos and growing protoplanets
Planetary embryos form protoplanets via mutual collisions, which can lead to
the development of magma oceans. During their solidification, large amounts of
the mantles' volatile contents may be outgassed. The resulting HO/CO
dominated steam atmospheres may be lost efficiently via hydrodynamic escape due
to the low gravity and the high stellar EUV luminosities. Protoplanets forming
later from such degassed building blocks could therefore be drier than
previously expected. We model the outgassing and subsequent hydrodynamic escape
of steam atmospheres from such embryos. The efficient outflow of H drags along
heavier species (O, CO, noble gases). The full range of possible EUV
evolution tracks of a solar-mass star is taken into account to investigate the
escape from Mars-sized embryos at different orbital distances. The envelopes
are typically lost within a few to a few tens of Myr. Furthermore, we study the
influence on protoplanetary evolution, exemplified by Venus. We investigate
different early evolution scenarios and constrain realistic cases by comparing
modeled noble gas isotope ratios with observations. Starting from solar values,
consistent isotope ratios (Ne, Ar) can be found for different solar EUV
histories, as well as assumptions about the initial atmosphere (either pure
steam or a mixture with accreted H). Our results generally favor an early
accretion scenario with a small amount of accreted H and a low-activity Sun,
because in other cases too much CO is lost during evolution, which is
inconsistent with Venus' present atmosphere. Important issues are likely the
time at which the initial steam atmosphere is outgassed and/or the amount of
CO which may still be delivered at later evolutionary stages. A late
accretion scenario can only reproduce present isotope ratios for a highly
active young Sun, but then very massive steam atmospheres would be required.Comment: 61 pages, 7 figures, 3 tables, accepted to Icaru
Bulk and surface energetics of lithium hydride crystal: benchmarks from quantum Monte Carlo and quantum chemistry
We show how accurate benchmark values of the surface formation energy of
crystalline lithium hydride can be computed by the complementary techniques of
quantum Monte Carlo (QMC) and wavefunction-based molecular quantum chemistry.
To demonstrate the high accuracy of the QMC techniques, we present a detailed
study of the energetics of the bulk LiH crystal, using both pseudopotential and
all-electron approaches. We show that the equilibrium lattice parameter agrees
with experiment to within 0.03 %, which is around the experimental uncertainty,
and the cohesive energy agrees to within around 10 meV per formula unit. QMC in
periodic slab geometry is used to compute the formation energy of the LiH (001)
surface, and we show that the value can be accurately converged with respect to
slab thickness and other technical parameters. The quantum chemistry
calculations build on the recently developed hierarchical scheme for computing
the correlation energy of a crystal to high precision. We show that the
hierarchical scheme allows the accurate calculation of the surface formation
energy, and we present results that are well converged with respect to basis
set and with respect to the level of correlation treatment. The QMC and
hierarchical results for the surface formation energy agree to within about 1
%.Comment: 16 pages, 4 figure
The habitability of a stagnant-lid Earth
Plate tectonics is a fundamental component for the habitability of the Earth.
Yet whether it is a recurrent feature of terrestrial bodies orbiting other
stars or unique to the Earth is unknown. The stagnant lid may rather be the
most common tectonic expression on such bodies. To understand whether a
stagnant-lid planet can be habitable, i.e. host liquid water at its surface, we
model the thermal evolution of the mantle, volcanic outgassing of HO and
CO, and resulting climate of an Earth-like planet lacking plate tectonics.
We used a 1D model of parameterized convection to simulate the evolution of
melt generation and the build-up of an atmosphere of HO and CO over 4.5
Gyr. We then employed a 1D radiative-convective atmosphere model to calculate
the global mean atmospheric temperature and the boundaries of the habitable
zone (HZ). The evolution of the interior is characterized by the initial
production of a large amount of partial melt accompanied by a rapid outgassing
of HO and CO. At 1 au, the obtained temperatures generally allow for
liquid water on the surface nearly over the entire evolution. While the outer
edge of the HZ is mostly influenced by the amount of outgassed CO, the
inner edge presents a more complex behaviour that is dependent on the partial
pressures of both gases. At 1 au, the stagnant-lid planet considered would be
regarded as habitable. The width of the HZ at the end of the evolution, albeit
influenced by the amount of outgassed CO, can vary in a non-monotonic way
depending on the extent of the outgassed HO reservoir. Our results suggest
that stagnant-lid planets can be habitable over geological timescales and that
joint modelling of interior evolution, volcanic outgassing, and accompanying
climate is necessary to robustly characterize planetary habitability
Biphoton compression in standard optical fiber: exact numerical calculation
Generation of two-photon wavepackets, produced by spontaneous parametric down
conversion in crystals with linearly chirped quasi-phase matching grating, is
analyzed. Although being spectrally broad, two-photon wavepackets produced this
way are not Fourier transform limited. In the paper we discuss the temporal
compression of the wavepackets, exploiting the insertion of a standard optical
fiber in the path of one of the two photons. The effect is analyzed by means of
full numerical calculation and the exact dispersion dependencies in both the
crystal and the fiber are considered. The study opens the way to the practical
realization of this idea.Comment: 10 pages, 16 figure
How large are present-day heat flux variations across the surface of Mars?
International audienc
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