4,497 research outputs found

    Detection of a dry-frozen boundary inside Martian regolith

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    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

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    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

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    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

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    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

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    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

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    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

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    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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