1,840 research outputs found
The Dynamics of Stellar Coronae Harboring Hot-jupiters II. A Space Weather Event on A Hot-jupiter
We carry out a numerical simulation depicting the effects of a Coronal Mass
Ejection (CME) event on a close-in giant planet in an extrasolar system. We
drive the CME in a similar manner as in simulations of space weather events on
Earth. The simulation includes the planetary orbital motion, which leads to the
forming of a comet-like planetary magnetotail which is oriented almost
perpendicular to the direction of propagation of the CME. The combination of
this feature and the fact that the CME does not expand much by the time it
reaches the planet leads to a unique CME-magnetosphere interaction, where the
CME itself is highly affected by the presence of the planetary magnetosphere.
We find that the planet is well-shielded from CME penetration, even for a
relatively weak internal magnetic field. The planetary angular momentum loss
associated with such an event is negligible compared to the total planetary
angular momentum. We also find that the energy which is deposited in the
magnetosphere is much higher than in the case of the Earth, and our simulation
suggests there is a large-scale change in the orientation of the
magnetosphere-ionosphere current system during the CME event.Comment: 16 pages, 10 figures, accepted to Ap
Interactions of the magnetospheres of stars and close-in giant planets
Since the first discovery of an extrasolar planetary system more than a
decade ago, hundreds more have been discovered. Surprisingly, many of these
systems harbor Jupiter-class gas giants located close to the central star, at
distances of 0.1 AU or less. Observations of chromospheric 'hot spots' that
rotate in phase with the planetary orbit, and elevated stellar X-ray
luminosities,suggest that these close-in planets significantly affect the
structure of the outer atmosphere of the star through interactions between the
stellar magnetic field and the planetary magnetosphere. Here we carry out the
first detailed three-dimensional MagnetoHydroHynamics (MHD) simulation
containing the two magnetic bodies and explore the consequences of such
interactions on the steady-state coronal structure. The simulations reproduce
the observable features of 1) increase in the total X-ray luminosity, 2)
appearance of coronal hot spots, and 3) phase shift of these spots with respect
to the direction of the planet. The proximate cause of these is an increase in
the density of coronal plasma in the direction of the planet, which prevents
the corona from expanding and leaking away this plasma via a stellar wind. The
simulations produce significant low temperature heating. By including dynamical
effects, such as the planetary orbital motion, the simulation should better
reproduce the observed coronal heating
Variacion espacio-temporal de la precipitacion pluvial en Mexico: Una aproximacion a la evaluacion de impactos.
A brain-sparing diphtheria toxin for chemical genetic ablation of peripheral cell lineages.
Conditional expression of diphtheria toxin receptor (DTR) is widely used for tissue-specific ablation of cells. However, diphtheria toxin (DT) crosses the blood-brain barrier, which limits its utility for ablating peripheral cells using Cre drivers that are also expressed in the central nervous system (CNS). Here we report the development of a brain-sparing DT, termed BRAINSPAReDT, for tissue-specific genetic ablation of cells outside the CNS. We prevent blood-brain barrier passage of DT through PEGylation, which polarizes the molecule and increases its size. We validate BRAINSPAReDT with regional genetic sympathectomy: BRAINSPAReDT ablates peripheral but not central catecholaminergic neurons, thus avoiding the Parkinson-like phenotype associated with full dopaminergic depletion. Regional sympathectomy compromises adipose tissue thermogenesis, and renders mice susceptible to obesity. We provide a proof of principle that BRAINSPAReDT can be used for Cre/DTR tissue-specific ablation outside the brain using CNS drivers, while consolidating the link between adiposity and the sympathetic nervous system
A complementarity-based approach to phase in finite-dimensional quantum systems
We develop a comprehensive theory of phase for finite-dimensional quantum
systems. The only physical requirement we impose is that phase is complementary
to amplitude. To implement this complementarity we use the notion of mutually
unbiased bases, which exist for dimensions that are powers of a prime. For a
d-dimensional system (qudit) we explicitly construct d+1 classes of maximally
commuting operators, each one consisting of d-1 operators. One of this class
consists of diagonal operators that represent amplitudes (or inversions). By
the finite Fourier transform, it is mapped onto ladder operators that can be
appropriately interpreted as phase variables. We discuss the examples of qubits
and qutrits, and show how these results generalize previous approaches.Comment: 6 pages, no figure
Multicomplementary operators via finite Fourier transform
A complete set of d+1 mutually unbiased bases exists in a Hilbert spaces of
dimension d, whenever d is a power of a prime. We discuss a simple construction
of d+1 disjoint classes (each one having d-1 commuting operators) such that the
corresponding eigenstates form sets of unbiased bases. Such a construction
works properly for prime dimension. We investigate an alternative construction
in which the real numbers that label the classes are replaced by a finite field
having d elements. One of these classes is diagonal, and can be mapped to
cyclic operators by means of the finite Fourier transform, which allows one to
understand complementarity in a similar way as for the position-momentum pair
in standard quantum mechanics. The relevant examples of two and three qubits
and two qutrits are discussed in detail.Comment: 15 pages, no figure
Exact exchange-correlation potential of a ionic Hubbard model with a free surface
We use Lanczos exact diagonalization to compute the exact
exchange-correlation (xc) potential of a Hubbard chain with large binding
energy ("the bulk") followed by a chain with zero binding energy ("the
vacuum"). Several results of density functional theory in the continuum
(sometimes controversial) are verified in the lattice. In particular we show
explicitly that the fundamental gap is given by the gap in the Kohn-Sham
spectrum plus a contribution due to the jump of the xc-potential when a
particle is added. The presence of a staggered potential and a nearest-neighbor
interaction V allows to simulate a ionic solid. We show that in the ionic
regime in the small hopping amplitude limit the xc-contribution to the gap
equals V, while in the Mott regime it is determined by the Hubbard U
interaction. In addition we show that correlations generates a new potential
barrier at the surface
Continuation for thin film hydrodynamics and related scalar problems
This chapter illustrates how to apply continuation techniques in the analysis
of a particular class of nonlinear kinetic equations that describe the time
evolution through transport equations for a single scalar field like a
densities or interface profiles of various types. We first systematically
introduce these equations as gradient dynamics combining mass-conserving and
nonmass-conserving fluxes followed by a discussion of nonvariational amendmends
and a brief introduction to their analysis by numerical continuation. The
approach is first applied to a number of common examples of variational
equations, namely, Allen-Cahn- and Cahn-Hilliard-type equations including
certain thin-film equations for partially wetting liquids on homogeneous and
heterogeneous substrates as well as Swift-Hohenberg and Phase-Field-Crystal
equations. Second we consider nonvariational examples as the
Kuramoto-Sivashinsky equation, convective Allen-Cahn and Cahn-Hilliard
equations and thin-film equations describing stationary sliding drops and a
transversal front instability in a dip-coating. Through the different examples
we illustrate how to employ the numerical tools provided by the packages
auto07p and pde2path to determine steady, stationary and time-periodic
solutions in one and two dimensions and the resulting bifurcation diagrams. The
incorporation of boundary conditions and integral side conditions is also
discussed as well as problem-specific implementation issues
Search for extended gamma-ray emission from the Virgo galaxy cluster with Fermi-LAT
Galaxy clusters are one of the prime sites to search for dark matter (DM)
annihilation signals. Depending on the substructure of the DM halo of a galaxy
cluster and the cross sections for DM annihilation channels, these signals
might be detectable by the latest generation of -ray telescopes. Here
we use three years of Fermi Large Area Telescope (LAT) data, which are the most
suitable for searching for very extended emission in the vicinity of nearby
Virgo galaxy cluster. Our analysis reveals statistically significant extended
emission which can be well characterized by a uniformly emitting disk profile
with a radius of 3\deg that moreover is offset from the cluster center. We
demonstrate that the significance of this extended emission strongly depends on
the adopted interstellar emission model (IEM) and is most likely an artifact of
our incomplete description of the IEM in this region. We also search for and
find new point source candidates in the region. We then derive conservative
upper limits on the velocity-averaged DM pair annihilation cross section from
Virgo. We take into account the potential -ray flux enhancement due to
DM sub-halos and its complex morphology as a merging cluster. For DM
annihilating into , assuming a conservative sub-halo model
setup, we find limits that are between 1 and 1.5 orders of magnitude above the
expectation from the thermal cross section for
. In a more optimistic scenario, we
exclude
for for the same channel. Finally, we
derive upper limits on the -ray-flux produced by hadronic cosmic-ray
interactions in the inter cluster medium. We find that the volume-averaged
cosmic-ray-to-thermal pressure ratio is less than .Comment: 15 pages, 11 figures, 4 tables, accepted for publication in ApJ;
corresponding authors: T. Jogler, S. Zimmer & A. Pinzk
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