8,108 research outputs found
On the sensitivity of extrasolar mass-loss rate ranges: HD 209458b a case study
We present a 3D hydrodynamic study of the effects that different stellar wind
conditions and planetary wind structures have on the calculated Ly-
absorptions produced during the transit of HD 209458b. Considering a range of
stellar wind speeds [350-800] km s, coronal temperature
[3-7] K and two values of the polytropic index
[1.01-1.13], while keeping fixed the stellar mass loss rate, we found a
that a range between [3-5] g s give
account for the observational absorption in Ly- measured for the
planetary system. Also, several models with anisotropic evaporation profiles
for the planetary escaping atmosphere were carried out, showing that both, the
escape through polar regions and through the night side yields larger
absorptions than an isotropic planetary wind
Photo-ionization of planetary winds: case study HD209458b
Close-in hot Jupiters are exposed to a tremendous photon flux that ionizes
the neutral escaping material from the planet leaving an observable imprint
that makes them an interesting laboratory for testing theoretical models. In
this work we present 3D hydrodynamic simulations with radiation transfer
calculations of a close-in exoplanet in a blow-off state. We calculate the
Ly- absorption and compare it with observations of HD 209458b an
previous simplified model results.Our results show that the hydrodynamic
interaction together with a proper calculation of the photoionization proccess
are able to reproduce the main features of the observed Ly- absorption,
in particular at the blue-shifted wings of the line. We found that the ionizing
stellar flux produce an almost linear effect on the amount of absorption in the
wake. Varying the planetary mass loss rate and the radiation flux, we were able
to reproduce the absorption observed at .Comment: 9 pages, 6 figure
Attaining subclassical metrology in lossy systems with entangled coherent states
Quantum mechanics allows entanglement enhanced measurements to be performed, but loss remains an obstacle in constructing realistic quantum metrology schemes. However, recent work has revealed that entangled coherent states (ECSs) have the potential to perform robust subclassical measurements [J. Joo et al., Phys. Rev. Lett. 107, 083601 (2011)]. Up to now no read-out scheme has been devised that exploits this robust nature of ECSs, but we present here an experimentally accessible method of achieving precision close to the theoretical bound, even with loss.We show substantial improvements over unentangled classical states and highly entangled NOON states for a wide range of loss values, elevating quantum metrology to a realizable technology in the near future
Particle acceleration and radiation friction effects in the filamentation instability of pair plasmas
The evolution of the filamentation instability produced by two
counter-streaming pair plasmas is studied with particle-in-cell (PIC)
simulations in both one (1D) and two (2D) spatial dimensions. Radiation
friction effects on particles are taken into account. After an exponential
growth of both the magnetic field and the current density, a nonlinear
quasi-stationary phase sets up characterized by filaments of opposite currents.
During the nonlinear stage, a strong broadening of the particle energy spectrum
occurs accompanied by the formation of a peak at twice their initial energy. A
simple theory of the peak formation is presented. The presence of radiative
losses does not change the dynamics of the instability but affects the
structure of the particle spectra.Comment: 8 pages, 8 figures, submitted to MNRA
No role for neutrons, muons and solar neutrinos in the DAMA annual modulation results
This paper summarizes in a simple and intuitive way why the neutrons, the
muons and the solar neutrinos cannot give any significant contribution to the
DAMA annual modulation results. A number of these elements have already been
presented in individual papers; they are recalled here. Afterwards, few simple
considerations are summarized which already demonstrate the incorrectness of
the claim reported in PRL 113 (2014) 081302.Comment: 11 pages, 1 tabl
Investigating Earth shadowing effect with DAMA/LIBRA-phase1
In the present paper the results obtained in the investigation of possible
diurnal effects for low-energy single-hit scintillation events of
DAMA/LIBRA-phase1 (1.04 ton yr exposure) have been analysed in terms
of an effect expected in case of Dark Matter (DM) candidates inducing nuclear
recoils and having high cross-section with ordinary matter, which implies low
DM local density in order to fulfill the DAMA/LIBRA DM annual modulation
results. This effect is due to the different Earth depths crossed by those DM
candidates during the sidereal day.Comment: 22 pages, 9 figures, 1 table; in publication on Eur. Phys. J.
Nuclear pore complex-mediated modulation of TCR signaling is required for naïve CD4+ T cell homeostasis.
Nuclear pore complexes (NPCs) are channels connecting the nucleus with the cytoplasm. We report that loss of the tissue-specific NPC component Nup210 causes a severe deficit of naïve CD4+ T cells. Nup210-deficient CD4+ T lymphocytes develop normally but fail to survive in the periphery. The decreased survival results from both an impaired ability to transmit tonic T cell receptor (TCR) signals and increased levels of Fas, which sensitize Nup210-/- naïve CD4+ T cells to Fas-mediated cell death. Mechanistically, Nup210 regulates these processes by modulating the expression of Cav2 (encoding Caveolin-2) and Jun at the nuclear periphery. Whereas the TCR-dependent and CD4+ T cell-specific upregulation of Cav2 is critical for proximal TCR signaling, cJun expression is required for STAT3-dependent repression of Fas. Our results uncover an unexpected role for Nup210 as a cell-intrinsic regulator of TCR signaling and T cell homeostasis and expose NPCs as key players in the adaptive immune system
On the Evolution and Survival of Protoplanets Embedded in a Protoplanetary Disk
We model the evolution of a Jupiter-mass protoplanet formed by the disk
instability mechanism at various radial distances accounting for the presence
of the disk. Using three different disk models, it is found that a newly-formed
Jupiter-mass protoplanet at radial distance of 5-10 AU cannot
undergo a dynamical collapse and evolve further to become a gravitational bound
planet. We therefore conclude that {\it giant planets, if formed by the
gravitational instability mechanism, must form and remain at large radial
distances during the first 10 years of their evolution}. The
minimum radial distances in which protoplanets of 1 Saturn-mass, 3 and 5
Jupiter-mass protoplanets can evolve using a disk model with and are found to be 12, 9, and 7 AU, respectively.
The effect of gas accretion on the planetary evolution of a Jupiter-mass
protoplanet is also investigated. It is shown that gas accretion can shorten
the pre-collapse timescale substantially. Our study suggests that the timescale
of the pre-collapse stage does not only depend on the planetary mass, but is
greatly affected by the presence of the disk and efficient gas accretion.Comment: 26 pages, 2 tables, 10 figures. Accepted for publication in Ap
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