4,571 research outputs found
Detection of a dry-frozen boundary inside Martian regolith
The present work investigates the time oscillations of the temperature at several depths of a Martian soil analogue made of two layers of different physical properties. The maximum temperature-time oscillation inside the Martian soil analogue, DT, and its derivative with depth, d(DT)/dz or DDT, can be analysed to understand the presence of a boundary between dry and frozen soil. The maximum temperature-time oscillation, DT, reduces by about one order of magnitude at the boundary between dry and frozen soil if a frozen layer is present. The reduction of DT at the boundary between two dry soils with different porosity is much smaller. DDT decreases by more than one order of magnitude at the boundary between dry and frozen soil if a frozen layer is present. The reduction of DDT at the boundary between two dry soils with different porosity is much smaller. (C) 2008 Elsevier Ltd. All rights reserved
Theoretical prediction ofthe thermal conductivity and temperature variation inside mars soil analogues
Mars soil analogues, in dry and frozen conditions, are investigated, as far as the thermal conductivity prediction and the temperature
variation, along its depth, are concerned. The thermal conductivity is theoretically predicted with the cubic cell model, which requires
the knowledge ofthe thermal conductivity ofthe solid particle and ofthe materials present, i.e. atmospheric gas and/or frozen ice, and
the porosity ofthe soil analogue. The soil mineral composition allows to evaluate the thermal conductivity ofthe solid particle. The heat
capacity ofthe soil analogue is evaluated with the knowledge ofits physical properties, the porosity and the speci1c heats ofthe materials
present. The thermal di2usivity is calculated as the ratio ofthe thermal conductivity and heat capacity and results to be a function ofthe
porosity and the ice mass content ofthe soil analogue. The temperature variations, in dry and partially frozen soil analogues, are predicted
during a Martian day. The temperature variation, at di2erent depth, is attenuated, as compared to the surface variation and a phase delay
is present, depending on the soil thermal properties. The temperature variation, as well as the derivative ofthe temperature variation with
the depth, is dependent on the thermal di2usivity ofthe soil analogue. In conclusion, the temperature measurement, along the depth ofa
Martian soil analogue, can be used to verify its physical status, i.e. dry or partially frozen
First-principles calculations and bias-dependent STM measurements at the alpha-Sn/Ge(111) surface: a clear indication for the 1U2D configuration
The nature of the alpha-Sn/Ge(111) surface is still a matter of debate. In
particular, two possible configurations have been proposed for the 3x3 ground
state of this surface: one with two Sn adatoms in a lower position with respect
to the third one (1U2D) and the other with opposite configuration (2U1D). By
means of first-principles quasiparticle calculations we could simulate STM
images as a function of bias voltage and compare them with STM experimental
results at 78K, obtaining an unambiguous indication that the stable
configuration for the alpha-Sn/Ge(111) surface is the 1U2D. The possible
inequivalence of the two down Sn adatoms is also discussed.Comment: Submitted to PR
Search for Higgs Bosons in SUSY Cascade Decays and Neutralino Dark Matter
The Minimal Supersymmetric Extension of the Standard Model (MSSM) is a well
motivated theoretical framework, which contains an extended Higgs sector,
including a light Higgs with Standard Model-like properties in most of the
parameter space. Due to the large QCD background, searches for such a Higgs,
decaying into a pair of bottom quarks, is very challenging at the LHC. It has
been long realized that the situation may be ameliorated by searching for Higgs
bosons in supersymmetric decay chains. Moreover, it has been recently suggested
that the bobber decay channel may be observed in standard production channels
by selecting boosted Higgs bosons, which may be easily identified from the QCD
background. Such boosted Higgs bosons are frequent in the MSSM, since they are
produced from decays of heavy colored supersymmetric particles. Previous works
have emphasized the possibility of observing boosted Higgs bosons in the light
higgsino region. In this work, we study the same question in the regions of
parameter space consistent with a neutralino dark matter relic density,
analyzing its dependence on the non-standard Higgs boson, slepton and squark
masses, as well as on the condition of gaugino mass unification. In general, we
conclude that, provided sleptons are heavier than the second lightest
neutralinos, the presence of boosted Higgs is a common MSSM feature, implying
excellent prospects for observation of the light MSSM Higgs boson in the near
future.Comment: 30 pages, 9 figures. v2: New Xenon 100 results implemented, version
to appear in PR
Sequential Flavour Symmetry Breaking
The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which
allows for independent unitary transformations of the fermion multiplets. In
the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs
boson, and the resulting fermion masses and mixing angles show a pronounced
hierarchy. In this work we connect the observed hierarchy to a sequence of
intermediate effective theories, where the flavour symmetries are broken in a
step-wise fashion by vacuum expectation values of suitably constructed spurion
fields. We identify the possible scenarios in the quark sector and discuss some
implications of this approach.Comment: 22 pages latex, no figure
Spectral Dependence of Polarized Radiation due to Spatial Correlations
We study the polarization of light emitted by spatially correlated sources.
We show that in general polarization acquires nontrivial spectral dependence
due to spatial correlations. The spectral dependence is found to be absent only
for a special class of sources where the correlation length scales as the
wavelength of light. We further study the cross correlations between two
spatially distinct points that are generated due to propagation. It is found
that such cross correlation leads to sufficiently strong spectral dependence of
polarization which can be measured experimentally.Comment: 5 pages, 4 figure
Density functional theory for strongly-correlated bosonic and fermionic ultracold dipolar and ionic gases
We introduce a density functional formalism to study the ground-state
properties of strongly-correlated dipolar and ionic ultracold bosonic and
fermionic gases, based on the self-consistent combination of the weak and the
strong coupling limits. Contrary to conventional density functional approaches,
our formalism does not require a previous calculation of the interacting
homogeneous gas, and it is thus very suitable to treat systems with tunable
long-range interactions. Due to its asymptotic exactness in the regime of
strong correlation, the formalism works for systems in which standard
mean-field theories fail.Comment: 5 pages, 2 figure
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