9,908 research outputs found
First results with the boloSource() algorithm: Photometry of faint standard stars observed by Herschel/PACS
The boloSource() algorithm is a tool to separate the signal of compact
sources from that of the diffuse background in the timeline of far-infrared
measurements performed by the PACS camera of the Herschel Space Observatory. An
important characteristic and quality indicator of this method is that how well
it can reproduce the flux of faint standard stars which have reliable flux
estimates. For this propose we selected a few calibrator targets and
constructed light curves by extracting point source flux for each repetition of
the measurements independently using standard aperture photometry methods.
These were compared with the light curves obtained using the boloSource()
method on the same dataset. The results indicate that boloSource() provides a
similar level of photometric accuracy and reproducibility as the usual flux
extraction and photometry methods. This new technique will be developed further
and also tested against other methods in more complex fields with the goal to
make it usable for large-scale studies in the future.Comment: 10 pages, 7 figures, 4 table
Improving LLR Tests of Gravitational Theory
Accurate analysis of precision ranges to the Moon has provided several tests
of gravitational theory including the Equivalence Principle, geodetic
precession, parameterized post-Newtonian (PPN) parameters and ,
and the constancy of the gravitational constant {\it G}. Since the beginning of
the experiment in 1969, the uncertainties of these tests have decreased
considerably as data accuracies have improved and data time span has
lengthened. We are exploring the modeling improvements necessary to proceed
from cm to mm range accuracies enabled by the new Apache Point Observatory
Lunar Laser-ranging Operation (APOLLO) currently under development in New
Mexico. This facility will be able to make a significant contribution to the
solar system tests of fundamental and gravitational physics. In particular, the
Weak and Strong Equivalence Principle tests would have a sensitivity
approaching 10, yielding sensitivity for the SEP violation parameter
of , general relativistic effects would
be tested to better than 0.1%, and measurements of the relative change in the
gravitational constant, , would be % the inverse age of the
universe. Having this expected accuracy in mind, we discusses the current
techniques, methods and existing physical models used to process the LLR data.
We also identify the challenges for modeling and data analysis that the LLR
community faces today in order to take full advantage of the new APOLLO ranging
station.Comment: 15 pages, 3 figures, talk presented at 2003 NASA/JPL Workshop on
Fundamental Physics in Space, April 14-16, 2003, Oxnard, C
Current concepts of ectopic nodal inclusions with special emphasis on nodal nevi
Nodal inclusions of ectopic tissue within lymph nodes are seen comparatively often in
dermatopathology and general pathology. Glandular and nonglandular epithelium,
as well as melanocytic nevi can be observed within lymph nodes and represent mostly incidental findings without any relevance. The main challenge in reporting these
morphologic features is to differentiate such benign inclusions from metastatic settlements of distinct organ tumors. As sentinel node biopsy and lymph node dissection
have become standard procedure in clinical oncology and have an immense clinical
impact, the correct evaluation of these nodal inclusions is indispensable to avoid undertreatment or overtreatment of patients. In addition, the genesis of these inclusions
has not yet been satisfactorily clarified. Two concepts have been laid out: the theory
of benign metastases and the migration arrest theory. However, neither theory has so
far been able to answer the following questions: Why do we find more nodal nevi in
patients with melanoma who had a sentinel node biopsy than in patients without melanoma, and why do we not find nodal nevi in deep visceral lymph nodes? We present
a comprehensive review of the current knowledge on nodal inclusions, proposing a
concept for the pathogenesis of nodal nevi, to answer these questions
Influence of external flows on crystal growth: numerical investigation
We use a combined phase-field/lattice-Boltzmann scheme [D. Medvedev, K.
Kassner, Phys. Rev. E {\bf 72}, 056703 (2005)] to simulate non-facetted crystal
growth from an undercooled melt in external flows. Selected growth parameters
are determined numerically.
For growth patterns at moderate to high undercooling and relatively large
anisotropy, the values of the tip radius and selection parameter plotted as a
function of the Peclet number fall approximately on single curves. Hence, it
may be argued that a parallel flow changes the selected tip radius and growth
velocity solely by modifying (increasing) the Peclet number. This has
interesting implications for the availability of current selection theories as
predictors of growth characteristics under flow.
At smaller anisotropy, a modification of the morphology diagram in the plane
undercooling versus anisotropy is observed. The transition line from dendrites
to doublons is shifted in favour of dendritic patterns, which become faster
than doublons as the flow speed is increased, thus rendering the basin of
attraction of dendritic structures larger.
For small anisotropy and Prandtl number, we find oscillations of the tip
velocity in the presence of flow. On increasing the fluid viscosity or
decreasing the flow velocity, we observe a reduction in the amplitude of these
oscillations.Comment: 10 pages, 7 figures, accepted for Physical Review E; size of some
images had to be substantially reduced in comparison to original, resulting
in low qualit
Large size and slow rotation of the trans-Neptunian object (225088) 2007 OR10 discovered from Herschel and K2 observations
We present the first comprehensive thermal and rotational analysis of the
second most distant trans-Neptunian object (225088) 2007 OR10. We combined
optical light curves provided by the Kepler space telescope -- K2 extended
mission and thermal infrared data provided by the Herschel Space Observatory.
We found that (225088) 2007 OR10 is likely to be larger and darker than derived
by earlier studies: we obtained a diameter of d=1535^{+75}_{-225} km which
places (225088) 2007 OR10 in the biggest top three trans-Neptunian objects. The
corresponding visual geometric albedo is p_V=0.089^{+0.031}_{-0.009}. The light
curve analysis revealed a slow rotation rate of P_rot=44.81+/-0.37 h,
superseded by a very few objects only. The most likely light-curve solution is
double-peaked with a slight asymmetry, however, we cannot safely rule out the
possibility of having a rotation period of P_rot=22.40+/-0.18 h which
corresponds to a single-peaked solution. Due to the size and slow rotation, the
shape of the object should be a MacLaurin ellipsoid, so the light variation
should be caused by surface inhomogeneities. Its newly derived larger diameter
also implies larger surface gravity and a more likely retention of volatiles --
CH_4, CO and N_2 -- on the surface.Comment: Accepted for publication in AJ, 8 pages in emulateapj styl
Structure prediction based on ab initio simulated annealing for boron nitride
Possible crystalline modifications of chemical compounds at low temperatures
correspond to local minima of the energy landscape. Determining these minima
via simulated annealing is one method for the prediction of crystal structures,
where the number of atoms per unit cell is the only information used. It is
demonstrated that this method can be applied to covalent systems, at the
example of boron nitride, using ab initio energies in all stages of the
optimization, i.e. both during the global search and the subsequent local
optimization. Ten low lying structure candidates are presented, including both
layered structures and 3d-network structures such as the wurtzite and zinc
blende types, as well as a structure corresponding to the beta-BeO type
Fock terms in the quark-meson coupling model
The mean field description of nuclear matter in the quark-meson coupling
model is improved by the inclusion of exchange contributions (Fock terms). The
inclusion of Fock terms allows us to explore the momentum dependence of
meson-nucleon vertices and the role of pionic degrees of freedom in matter. It
is found that the Fock terms maintain the previous predictions of the model for
the in-medium properties of the nucleon and for the nuclear incompressibility.
The Fock terms significantly increase the absolute values of the
single-particle, four-component scalar and vector potentials, a feature that is
relevant for the spin-orbit splitting in finite nuclei.Comment: RevTex, 17 pages, 4 Postscript figures, version to appear in Nucl.
Phys.
Catalogue of ISO LWS observations of asteroids
(Abridged) The Long Wavelength Spectrometer (LWS) onboard the Infrared Space
Observatory (ISO) observed the four large main-belt asteroids (1) Ceres, (2)
Pallas, (4) Vesta, and (10) Hygiea multiple times. The photometric and
spectroscopic data cover the wavelength range between 43 and 197 um, and are a
unique dataset for future investigations and detailed characterisations of
these bodies. The standard ISO archive products, produced through the last
post-mission LWS pipeline, were still affected by instrument artefacts. Our
goal was to provide the best possible data products to exploit the full
scientific potential of these observations. We performed a refined reduction of
all measurements, corrected for various instrumental effects, and re-calibrated
the data. We outline the data reduction process and give an overview of the
available data and the quality of the observations. We apply a thermophysical
model to the flux measurements to derive far-IR based diameter and albedo
values of the asteroids. The measured thermal rotational lightcurve of (4)
Vesta is compared to model predictions. The absolute photometric accuracy of
the data products was foubd to be better than 10%. The calibrated spectra will
serve as source for future mineralogical studies of dwarf planets and dwarf
planet candidates.Comment: 11 pages, 6 figures, accepted for publication in A&
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