46,382 research outputs found
Analytical tools and isolation of TOF events
Analytical tools are presented in two reports. The first is a probability analysis of the orbital distribution of events in relation to dust flux density observed in Pioneer 8 and 9 distributions. A distinction is drawn between asymmetries caused by random fluctuations and systematic variations, by calculating the probability of any particular asymmetry. The second article discusses particle trajectories for a repulsive force field. The force on a particle due to solar radiation pressure is directed along the particle's radius vector, from the sun, and is inversely proportional to its distance from the sun. Equations of motion which describe both solar radiation pressure and gravitational attraction are presented
Large-scale Vortices in Protoplanetary Disks: On the observability of possible early stages of planet formation
We investigate the possibility of mapping large-scale anti-cyclonic vortices,
resulting from a global baroclinic instability, as pre-cursors of planet
formation in proto-planetary disks with the planned Atacama Large Millimeter
Array (ALMA). On the basis of three-dimensional radiative transfer simulations,
images of a hydrodynamically calculated disk are derived which provide the
basis for the simulation of ALMA. We find that ALMA will be able to trace the
theoretically predicted large-scale anti-cyclonic vortex and will therefore
allow testing of existing models of this very early stage of planet formation
in circumstellar disks.Comment: Accepted by ApJ (Letters section). A preprint version with
high-quality figures can be downloaded from
http://spider.ipac.caltech.edu/staff/swolf/homepage/public/preprints/
vortex.ps.g
Calibration update of the COMBO-17 CDFS catalogue
We present an update to the photometric calibration of the COMBO-17 catalogue
on the Extended Chandra Deep Field South, which is now consistent with the
GaBoDS and MUSYC catalogues. As a result, photometric redshifts become slightly
more accurate, with <0.01 rms and little bias in the delta_z/(1+z) of galaxies
with R<21 and of QSOs with R<24. With increasing photon noise the rms of
galaxies reaches 0.02 for R<23 and 0.035 at R~23.5. Consequences for the
rest-frame colours of galaxies at z<1 are discussed.Comment: A&A research note, resubmitted 02 Oct 2008, 4 pages in print forma
Diffuse LEED intensities of disordered crystal surfaces : II. Multiple scattering on disordered overlayers
The diffraction of low energy electrons from disordered overlayers adsorbed on ordered substrates is treated theoretically by an extension of Beeby's multiple scattering method. A lattice gas model is assumed for the disordered adsorbate layer. Multiple scattering within a certain area around each atom — each atom of the overlayer and within the ordered substrate — is treated self-consistently, the remaining contributions to the total scattering amplitude being averaged. The theory can be used in the limiting cases of random distribution and of long range order within the adsorbate layer
Estimating Functions of Probability Distributions from a Finite Set of Samples, Part 1: Bayes Estimators and the Shannon Entropy
We present estimators for entropy and other functions of a discrete
probability distribution when the data is a finite sample drawn from that
probability distribution. In particular, for the case when the probability
distribution is a joint distribution, we present finite sample estimators for
the mutual information, covariance, and chi-squared functions of that
probability distribution.Comment: uuencoded compressed tarfile, submitte
Towards time-dependent, non-equilibrium charge-transfer force fields: Contact electrification and history-dependent dissociation limits
Force fields uniquely assign interatomic forces for a given set of atomic
coordinates. The underlying assumption is that electrons are in their
quantum-mechanical ground state or in thermal equilibrium. However, there is an
abundance of cases where this is unjustified because the system is only locally
in equilibrium. In particular, the fractional charges of atoms, clusters, or
solids tend to not only depend on atomic positions but also on how the system
reached its state. For example, the charge of an isolated solid -- and thus the
forces between atoms in that solid -- usually depends on the counterbody with
which it has last formed contact. Similarly, the charge of an atom, resulting
from the dissociation of a molecule, can differ for different solvents in which
the dissociation took place. In this paper we demonstrate that such
charge-transfer history effects can be accounted for by assigning discrete
oxidation states to atoms. With our method, an atom can donate an integer
charge to another, nearby atom to change its oxidation state as in a redox
reaction. In addition to integer charges, atoms can exchange "partial charges"
which are determined with the split charge equilibration method.Comment: 11 pages, 7 figure
Diffuse LEED intensities of disordered crystal surfaces : IV. Application of the disorder theory
The principles of the statistical disorder theory are discussed briefly. The theory is applied to a model of the disordered (101)Au surface with the characteristic (1 × 2) supersstructure. A fit procedure is described, by which the experimental angular intensity profiles are used directly to determine the disorder parameters and the interaction energies between the chains of surface atoms
- …