10,640 research outputs found
Thermal evolution and lifetime of intrinsic magnetic fields of Super Earths in habitable zones
We have numerically studied the thermal evolution of various-mass terrestrial
planets in habitable zones, focusing on duration of dynamo activity to generate
their intrinsic magnetic fields, which may be one of key factors in
habitability on the planets. In particular, we are concerned with super-Earths,
observations of which are rapidly developing. We calculated evolution of
temperature distributions in planetary interior, using Vinet equations of
state, Arrhenius-type formula for mantle viscosity, and the astrophysical
mixing length theory for convective heat transfer modified for mantle
convection. After calibrating the model with terrestrial planets in the Solar
system, we apply it for 0.1-- rocky planets with surface
temperature of 300~\mbox{K} (in habitable zones) and the Earth-like
compositions. With the criterion for heat flux at the CMB (core-mantle
boundary), the lifetime of the magnetic fields is evaluated from the calculated
thermal evolution. We found that the lifetime slowly increases with the
planetary mass () independent of initial temperature gap at the
core-mantle boundary () but beyond a critical value
() it abruptly declines by the mantle viscosity
enhancement due to the pressure effect. We derived as a function of
and a rheological parameter (activation volume, ).
Thus, the magnetic field lifetime of super-Earths with
sensitively depends on , which reflects planetary
accretion, and , which has uncertainty at very high pressure. More
advanced high-pressure experiments and first-principle simulation as well as
planetary accretion simulation are needed to discuss habitability of
super-Earths.Comment: 19pages, 15 figures, accepted for publication in Ap
Ultrafast charge transfer and vibronic coupling in a laser-excited hybrid inorganic/organic interface
Hybrid interfaces formed by inorganic semiconductors and organic molecules are intriguing materials for opto-electronics. Interfacial charge transfer is primarily responsible for their peculiar electronic structure and optical response. Hence, it is essential to gain insight into this fundamental process also beyond the static picture. Ab initio methods based on real-time time-dependent density-functional theory coupled to the Ehrenfest molecular dynamics scheme are ideally suited for this problem. We investigate a laser-excited hybrid inorganic/organic interface formed by the electron acceptor molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) physisorbed on a hydrogenated silicon cluster, and we discuss the fundamental mechanisms of charge transfer in the ultrashort time window following the impulsive excitation. The considered interface is p-doped and exhibits charge transfer in the ground state. When it is excited by a resonant laser pulse, the charge transfer across the interface is additionally increased, but contrary to previous observations in all-organic donor/acceptor complexes, it is not further promoted by vibronic coupling. In the considered time window of 100 fs, the molecular vibrations are coupled to the electron dynamics and enhance intramolecular charge transfer. Our results highlight the complexity of the physics involved and demonstrate the ability of the adopted formalism to achieve a comprehensive understanding of ultrafast charge transfer in hybrid materials
A MATLAB/Simulink based GUI for the CERES Simulator
The Clouds and The Earth's Radiant Energy System (CERES) simulator will allow flight operational familiarity with the CERES instrument prior to launch. It will provide a CERES instrument simulation facility for NASA Langley Research Center. NASA Goddard Space Flight Center and TRW. One of the objectives of building this simulator would be for use as a testbed for functionality checking of atypical memory uploads and for anomaly investigation. For instance, instrument malfunction due to memory damage requires troubleshooting on a simulator to determine the nature of the problem and to find a solution
Further evidence for linearly-dispersive Cooper pairs
A recent Bose-Einstein condensation (BEC) model of several cuprate
superconductors is based on bosonic Cooper pairs (CPs) moving in 3D with a
quadratic energy-momentum (dispersion) relation. The 3D BEC condensate-fraction
vs. temperature (T/Tc, where Tc is the BEC transition temperature) formula
poorly fits penetration-depth data for two cuprates in the range (1/2, 1]. We
show how these fits are dramatically improved assuming cuprates to be quasi-2D,
and how equally good fits obtain for conventional 3D and quasi-1D nanotube
superconducting data, provided the correct CP dispersion is assumed in BEC at
their assumed corresponding dimensionalities. This is offered as additional
concrete empirical evidence for linearly-dispersive pairs in another recent BEC
scenario of superconductors within which a BCS condensate turns out to be a
very special case.Comment: 9 pages, 1 figur
Dual Behavior of Antiferromagnetic Uncompensated Spins in NiFe/IrMn Exchange Biased Bilayers
We present a comprehensive study of the exchange bias effect in a model
system. Through numerical analysis of the exchange bias and coercive fields as
a function of the antiferromagnetic layer thickness we deduce the absolute
value of the averaged anisotropy constant of the antiferromagnet. We show that
the anisotropy of IrMn exhibits a finite size effect as a function of
thickness. The interfacial spin disorder involved in the data analysis is
further supported by the observation of the dual behavior of the interfacial
uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we
have observed that the antiferromagnetic uncompensated spins are dominantly
frozen with nearly no rotating spins due to the chemical intermixing, which
correlates to the inferred mechanism for the exchange bias.Comment: 4 pages, 3 figure
The Higgs Boson Lineshape and Perturbative Unitarity
We discuss the lineshape of a heavy Higgs boson, and the behaviour well above
resonance. Previous studies concluded that the energy-dependent Higgs width
should be used in the resonance region, but must not be used well away from it.
We derive the full result and show that it smoothly extrapolates these limits.
It is extremely simple, and would be straightforward to implement in existing
calculations.Comment: 10 pages, 10 figures A postscript version of this paper can be
obtained http://surya11.cern.ch/users/seymour/pubs/higgswidth.ps.
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