3,598 research outputs found
Bayesian analysis of interiors of HD 219134b, Kepler-10b, Kepler-93b, CoRoT-7b, 55 Cnc e, and HD 97658b using stellar abundance proxies
Using a generalized Bayesian inference method, we aim to explore the possible
interior structures of six selected exoplanets for which planetary mass and
radius measurements are available in addition to stellar host abundances:
HD~219134b, Kepler-10b, Kepler-93b, CoRoT-7b, 55~Cnc~e, and HD~97658b. We aim
to investigate the importance of stellar abundance proxies for the planetary
bulk composition (namely Fe/Si and Mg/Si) on prediction of planetary interiors.
We performed a full probabilistic Bayesian inference analysis to formally
account for observational and model uncertainties while obtaining confidence
regions of structural and compositional parameters of core, mantle, ice layer,
ocean, and atmosphere. We determined how sensitive our parameter predictions
depend on (1) different estimates of bulk abundance constraints and (2)
different correlations of bulk abundances between planet and host star. [...]
Although the possible ranges of interior structures are large, structural
parameters and their correlations are constrained by the sparse data. The
probability for the tested exoplanets to be Earth-like is generally very low.
Furthermore, we conclude that different estimates of planet bulk abundance
constraints mainly affect mantle composition and core size.Comment: Astronomy & Astrophysics, 597, A38 (15 pages, 9 figures
Electron impact double ionization of helium from classical trajectory calculations
With a recently proposed quasiclassical ansatz [Geyer and Rost, J. Phys. B 35
(2002) 1479] it is possible to perform classical trajectory ionization
calculations on many electron targets. The autoionization of the target is
prevented by a M\o{}ller type backward--forward propagation scheme and allows
to consider all interactions between all particles without additional
stabilization. The application of the quasiclassical ansatz for helium targets
is explained and total and partially differential cross sections for electron
impact double ionization are calculated. In the high energy regime the
classical description fails to describe the dominant TS1 process, which leads
to big deviations, whereas for low energies the total cross section is
reproduced well. Differential cross sections calculated at 250 eV await their
experimental confirmation.Comment: LaTeX, 22 pages, 10 figures, submitted to J. Phys.
A generalized bayesian inference method for constraining the interiors of super Earths and sub-Neptunes
We aim to present a generalized Bayesian inference method for constraining
interiors of super Earths and sub-Neptunes. Our methodology succeeds in
quantifying the degeneracy and correlation of structural parameters for high
dimensional parameter spaces. Specifically, we identify what constraints can be
placed on composition and thickness of core, mantle, ice, ocean, and
atmospheric layers given observations of mass, radius, and bulk refractory
abundance constraints (Fe, Mg, Si) from observations of the host star's
photospheric composition. We employed a full probabilistic Bayesian inference
analysis that formally accounts for observational and model uncertainties.
Using a Markov chain Monte Carlo technique, we computed joint and marginal
posterior probability distributions for all structural parameters of interest.
We included state-of-the-art structural models based on self-consistent
thermodynamics of core, mantle, high-pressure ice, and liquid water.
Furthermore, we tested and compared two different atmospheric models that are
tailored for modeling thick and thin atmospheres, respectively. First, we
validate our method against Neptune. Second, we apply it to synthetic
exoplanets of fixed mass and determine the effect on interior structure and
composition when (1) radius, (2) atmospheric model, (3) data uncertainties, (4)
semi-major axes, (5) atmospheric composition (i.e., a priori assumption of
enriched envelopes versus pure H/He envelopes), and (6) prior distributions are
varied. Our main conclusions are: [...]Comment: Astronomy & Astrophysics, 597, A37, 17 pages, 11 figure
Accumulation horizons and period-adding in optically injected semiconductor lasers
We study the hierarchical structuring of islands of stable periodic
oscillations inside chaotic regions in phase diagrams of single-mode
semiconductor lasers with optical injection. Phase diagrams display remarkable
{\it accumulation horizons}: boundaries formed by the accumulation of infinite
cascades of self-similar islands of periodic solutions of ever-increasing
period. Each cascade follows a specific period-adding route. The riddling of
chaotic laser phases by such networks of periodic solutions may compromise
applications operating with chaotic signals such as e.g. secure communications.Comment: 4 pages, 4 figures, laser phase diagrams, to appear in Phys. Rev. E,
vol. 7
The focus of light - linear polarization breaks the rotational symmetry of the focal spot
We experimentally demonstrate for the first time that a linearly polarized
beam is focussed to an asymmetric spot when using a high-numerical aperture
focussing system. This asymmetry was predicted by Richards and Wolf
[Proc.R.Soc.London A, 253, 358 (1959)] and can only be measured when a
polarization insensitive sensor is placed in the focal region. We used a
specially modified photodiode in a knife edge type set up to obtain highly
resolved images of the total electric energy density distribution at the focus.
The results are in good agreement with the predictions of a vectorial focussing
theory.Comment: to be published in "Journal of Modern Optics
Semiclassical Analysis of String/Gauge Duality on Non-commutative Space
We use semiclassical method to study closed strings in the modified AdS_5*S^5
background with constant B-fields. The point-like closed strings and the
streched closed strings rotating around the big circle of S^5 are considered.
Quantization of these closed string leads to a time-dependent string spectrum,
which we argue to correspond to the RG-flow of the dual noncommutative Yang
Mills theory.Comment: 19 pages, 1 figure, revtex4. minor corrections. references adde
Recoil-Ion and Electron Momentum Spectroscopy: Reaction-Microscopes
Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to 4 and superior momentum resolutions around a few per cent of an atomic unit (a.u.) are typically reached in state-of-the art machines, so-called reaction-microscopes. Evolving from recoil-ion and cold target recoil-ion momentum spectroscopy (COLTRIMS), reaction-microscopes—the `bubble chambers of atomic physics'—mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields. This paper concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of high-intensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using reaction-microscopes. Third, for electron and ion-impact, the investigation of two-electron reactions has matured to a state such that the first fully differential cross sections (FDCSs) are reported. Fourth, comprehensive sets of FDCSs for single ionization of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is briefly envisaged
Impact of the measured parameters of exoplanets on the inferred internal structure
Exoplanet characterization is one of the main foci of current exoplanetary
science. For super-Earths and sub-Neptunes, we mostly rely on mass and radius
measurements, which allow to derive the body's mean density and give a rough
estimate of the planet's bulk composition. However, the determination of
planetary interiors is a very challenging task. In addition to the uncertainty
in the observed fundamental parameters, theoretical models are limited due to
the degeneracy in determining the planetary composition. We aim to study
several aspects that affect internal characterization of super-Earths and
sub-Neptunes: observational uncertainties, location on the M-R diagram, impact
of additional constraints as bulk abundances or irradiation, and model
assumptions. We use a full probabilistic Bayesian inference analysis that
accounts for observational and model uncertainties. We employ a Nested Sampling
scheme to efficiently produce the posterior probability distributions for all
the planetary structural parameter of interest. We include a structural model
based on self-consistent thermodynamics of core, mantle, high-pressure ice,
liquid water, and H-He envelope. Regarding the effect of mass and radius
uncertainties on the determination of the internal structure, we find three
different regimes: below the Earth-like composition line and above the
pure-water composition line smaller observational uncertainties lead to better
determination of the core and atmosphere mass respectively, and between them
structure characterization only weakly depends on the observational
uncertainties. We show that small variations in the temperature or entropy
profiles lead to radius variations that are comparable to the observational
uncertainty, suggesting that uncertainties linked to model assumptions can
become more relevant to determine the internal structure than observational
uncertainties.Comment: 12 pages, 12 figure
Video thoracoscopic surgery used to manage tuberculosis in thoracic surgery
Background: The aim of this study was to evaluate the indications and results of video-assisted thoracic surgery (VATS) for the management of tuberculosis in 10 patients with unusual clinical and radiologic presentation for the disease. Methods: From March 2000 to March 2002, 96 diagnostic VATS operations for unclear thoracic lesions were performed at the authors' institution. Their final diagnosis for 10 (10.4%) of these patients was tuberculosis. The suspected preoperative diagnoses were pancoast tumour (n = 1), pericardial effusion (n = 1), pleural mesothelioma (n = 1), pleural empyema (n = 2), mediastinal lymphoma (n = l), and lung cancer (n = 4). Results: For all the patients, the diagnosis of tuberculosis was achieved by VATS. The duration of drainage was 2.5 days. There have been neither morbidity nor mortality since surgery. The hospital stay was 3 to 5 days. Conclusion: Thoracoscopy is a safe and effective procedure for the management of tuberculosis. Tuberculosis should be kept in mind during the differential diagnosis of unknown thoracic lesions, and also for patients who live in economically well developed countries and are not immune compromise
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