26,714 research outputs found
Spot evolution in the eclipsing binary CoRoT 105895502
Stellar activity is ubiquitous in late-type stars. The special geometry of
eclipsing binary systems is particularly advantageous to study the stellar
surfaces and activity. We present a detailed study of the 145 d CoRoT light
curve of the short-period eclipsing binary CoRoT 105895502. By means of
light-curve modeling with Nightfall, we determine the orbital period, effective
temperature, Roche-lobe filling factors, mass ratio, and orbital inclination of
CoRoT 105895502 and analyze the temporal behavior of starspots in the system.
Our analysis shows one comparably short-lived (about 40 d) starspot, remaining
quasi-stationary in the binary frame, and one starspot showing prograde motion
at a rate of 2.3 deg per day, whose lifetime exceeds the duration of the
observation. In the CoRoT band, starspots account for as much as 0.6 % of the
quadrature flux of CoRoT 105895502, however we cannot attribute the spots to
individual binary components with certainty. Our findings can be explained by
differential rotation, asynchronous stellar rotation, or systematic spot
evolution.Comment: Accepted in A&
Response of Bose gases in time-dependent optical superlattices
The dynamic response of ultracold Bose gases in one-dimensional optical
lattices and superlattices is investigated based on exact numerical time
evolutions in the framework of the Bose-Hubbard model. The system is excited by
a temporal amplitude modulation of the lattice potential, as it was done in
recent experiments. For regular lattice potentials, the dynamic signatures of
the superfluid to Mott-insulator transition are studied and the position and
the fine-structure of the resonances is explained by a linear response
analysis. Using direct simulations and the perturbative analysis it is shown
that in the presence of a two-colour superlattice the excitation spectrum
changes significantly when going from the homogeneous Mott-insulator the quasi
Bose-glass phase. A characteristic and experimentally accessible signature for
the quasi Bose-glass is the appearance of low-lying resonances and a
suppression of the dominant resonance of the Mott-insulator phase.Comment: 20 pages, 9 figures; added references and corrected typo
Doubly Charmed Baryons in COMPASS
The search for doubly charmed baryons has been a topic for COMPASS from the
beginning. Requiring however a complete spectrometer and highest possible
trigger rates this measurement has been postponed. The scenario for such a
measurement in the second phase of COMPASS is outlined here. First studies of
triggering and simulation of the setup have been performed. New rate estimates
based on recent measurements from SELEX at FNAL are presented.Comment: 13 pages, 15 figures, contribution to the Workshop on Future Physics
at COMPASS, CERN, Geneva, September 26-27 2002, to appear as CERN Yellow
Repor
Mesogranular structure in a hydrodynamical simulation
We analyse mesogranular flow patterns in a three-dimensional hydrodynamical
simulation of solar surface convection in order to determine its
characteristics. We calculate divergence maps from horizontal velocities
obtained with the Local Correlation Tracking (LCT) method. Mesogranules are
identified as patches of positive velocity divergence. We track the
mesogranules to obtain their size and lifetime distributions. We vary the
analysis parameters to verify if the pattern has characteristic scales. The
characteristics of the resulting flow patterns depend on the averaging time and
length used in the analysis. We conclude that the mesogranular patterns do not
exhibit intrinsic length and time scales
К вопросу о кипении жидкости с подводом тепла через стенку
The application of digital holographic microscopy offers quantitative phase contrast imaging of reflective and (partially) transparent samples. Low coherent light sources enable an increased resolution in phase shifting digital holography by the reduction of stray light and multiple reflections in the experimental interferometer setup. Therefore light emitting diodes (LED) are utilized. Here, the effects on the reconstruction quality by considering the whole spectrum of the light source are investigated. Furthermore, the propagation of the complex wave fronts, which are determined by digital holography, and used for re- and multifocusing, is modified to light sources with a spectral width wider than that of typical laser light sources. Therefore, the propagation algorithm using the convolution method as a solution of the Fresnel-Kirchhoff diffraction integral according to the first Rayleigh-Sommerfeld approximation is extended by an additional integral to take into account the spectral width of low coherent light sources. Numerically, in the new approach the supplementary integral is realized by a discrete sum considering a finite set of wavelengths. Specifically, the results of the modified algorithm are compared with common algorithms with respect to resolution and image sharpness
CVT/GPL phase 3 integrated testing
The hardware for 20 candidate shuttle program life sciences experiments was installed in the GPL and experiments were conducted during a 5-day simulated mission. The experiments involved humans, primates, rats, chickens, and marigold plants. All experiments were completed to the satisfaction of the experimenters. In addition to the scientific data gathered for each experiment, information was obtained concerning experiment hardware design and integration, experiment procedures, GPL support systems, and test operations. The results of the integrated tests are presented
Magnetic field control of cycloidal domains and electric polarization in multiferroic BiFeO
The magnetic field induced rearrangement of the cycloidal spin structure in
ferroelectric mono-domain single crystals of the room-temperature multiferroic
BiFeO is studied using small-angle neutron scattering (SANS). The cycloid
propagation vectors are observed to rotate when magnetic fields applied
perpendicular to the rhombohedral (polar) axis exceed a pinning threshold value
of 5\,T. In light of these experimental results, a phenomenological model
is proposed that captures the rearrangement of the cycloidal domains, and we
revisit the microscopic origin of the magnetoelectric effect. A new coupling
between the magnetic anisotropy and the polarization is proposed that explains
the recently discovered magnetoelectric polarization to the rhombohedral axis
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