1,610 research outputs found
The dependence of the pairwise velocity dispersion on galaxy properties
(abridged) We present measurements of the pairwise velocity dispersion (PVD)
for different classes of galaxies in the Sloan Digital Sky Survey. For a sample
of about 200,000 galaxies, we study the dependence of the PVD on galaxy
properties such as luminosity, stellar mass (M_*), colour (g-r), 4000A break
strength (D4000), concentration index (C), and stellar surface mass density
(\mu_*). The luminosity dependence of the PVD is in good agreement with the
results of Jing & B\"orner (2004) for the 2dFGRS catalog. The value of
\sigma_{12} measured at k=1 h/Mpc decreases as a function of increasing galaxy
luminosity for galaxies fainter than L*, before increasing again for the most
luminous galaxies in our sample. Each of the galaxy subsamples selected
according to luminosity or stellar mass is divided into two further subsamples
according to colour, D4000, C and \mu_*. We find that galaxies with redder
colours and higher D4000, C, and \mu_* values have larger PVDs on all scales
and at all luminosities/stellar masses. The dependence of the PVD on parameters
related to recent star formation(colour, D4000) is stronger than on parameters
related to galaxy structure (C, \mu_*), especially on small scales and for
faint galaxies. The reddest galaxies and galaxies with high surface mass
densities and intermediate concentrations have the highest pairwise peculiar
velocities, i.e. these move in the strongest gravitational fields. We conclude
that the faint red population located in rich clusters is responsible for the
high PVD values that are measured for low-luminosity galaxies on small scales.Comment: 14 pages, 13 figures; reference updated and text slightly changed to
match the published version; data of measurements of power spectrum and PVD
available at http://www.mpa-garching.mpg.de/~leech/papers/clustering
Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
We present a new method for performing differential emission measure (DEM)
inversions on narrow-band EUV images from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO). The method yields positive
definite DEM solutions by solving a linear program. This method has been
validated against a diverse set of thermal models of varying complexity and
realism. These include (1) idealized gaussian DEM distributions, (2) 3D models
of NOAA Active Region 11158 comprising quasi-steady loop atmospheres in a
non-linear force-free field, and (3) thermodynamic models from a
fully-compressible, 3D MHD simulation of AR corona formation following magnetic
flux emergence. We then present results from the application of the method to
AIA observations of Active Region 11158, comparing the region's thermal
structure on two successive solar rotations. Additionally, we show how the DEM
inversion method can be adapted to simultaneously invert AIA and XRT data, and
how supplementing AIA data with the latter improves the inversion result. The
speed of the method allows for routine production of DEM maps, thus
facilitating science studies that require tracking of the thermal structure of
the solar corona in time and space.Comment: 21 pages, 18 figures, accepted for publication in Ap
Origen de la casiterita detrÃtica en los aluviones recientes de Tirados de la Vega-Golpejas (Salamanca)
9 páginas, 6 figuras, 5 tablas.[ES] En el sector Tirados de la Vega-Golpejas han sido detectadas dos anomalÃas de casiterita en los aluviones del Regato de los Lentiscos y en otros existentes al sur de Tirados de la Vega. El estudio granométrico y morfométrico de éstas casiteritas. contrastado con el de la casiterita procedente del granito de Golpejas. permite asegurar que la anomalÃa del Regato de los Lentiscos se debe a la dispersión de la casiterita de aquel granito. mientras que la de Tirados de la Vega procede de filones estannÃferos. La aplicación del análisis factoral corrobora este hecho y permite diferenciar las casiteritas que proceden de rocas granÃticas de aquellas que vienen de filones estannÃferos. Según esto se puede indicar que la capacidad de migración de la casiterita desde el yacimiento estannÃfero de Golpejas es de unos 3 Kms.[EN] Two cassiterite anomalies have been detected in the Regato de los Lentisco and Tirados de la Vega alluviums, in the Golpejas area (Salamanca). The granometric and morphometric parameters of these cassiterites have been compared with those shown by the cassiterite crystal ocurrying in the Golpejas granite. The comparison between the two groups of data allow us to conclude that the anomaly observed in the Regato de los Lentistos has been originated by the disperssion of the cassiterite from the primary deposit of Golpejas. On the contrary, the anomaly ocurring in the alloviums to the south of Tirados de la Vega shows a different origin, and is coming from stanniferous veins.
The factor anylisis corroborates the differentiation mentionated above, and indicates a migration capacite of about 3 kms. from the stannifeous deposits of Golpejas for the alluvial cassiterite.Peer reviewe
3D Surface Measurement for Medical Application—Technical Comparison of Two Established Industrial Surface Scanning Systems
In 3D mapping of flexible surfaces (e.g. human faces) measurement errors due to movement or positioning occur. Aggravated by equipment- or researcher-caused mistakes considerable deviations can result. Therefore first the appliances' precision handling and reliability in clinical environment must be established. Aim of this study was to investigate accuracy and precision of two contact-free 3D measurement systems (white light vs. laser). Standard specimens of known diameter for sphere deviation, touch deviation and plane deviation were tested. Both systems are appropriate for medical application acquiring solid data (<mm). The more complex white-light system shows better accuracy at 0.2s measuring time. The laser system is superior concerning robustness, while accuracy is poorer and input time (1.5-2.5s) longer. Due to the clinical demand the white-light system is superior in a laboratory environment, while the laser system is easier to handle under non-laboratory condition
Certainty Closure: Reliable Constraint Reasoning with Incomplete or Erroneous Data
Constraint Programming (CP) has proved an effective paradigm to model and
solve difficult combinatorial satisfaction and optimisation problems from
disparate domains. Many such problems arising from the commercial world are
permeated by data uncertainty. Existing CP approaches that accommodate
uncertainty are less suited to uncertainty arising due to incomplete and
erroneous data, because they do not build reliable models and solutions
guaranteed to address the user's genuine problem as she perceives it. Other
fields such as reliable computation offer combinations of models and associated
methods to handle these types of uncertain data, but lack an expressive
framework characterising the resolution methodology independently of the model.
We present a unifying framework that extends the CP formalism in both model
and solutions, to tackle ill-defined combinatorial problems with incomplete or
erroneous data. The certainty closure framework brings together modelling and
solving methodologies from different fields into the CP paradigm to provide
reliable and efficient approches for uncertain constraint problems. We
demonstrate the applicability of the framework on a case study in network
diagnosis. We define resolution forms that give generic templates, and their
associated operational semantics, to derive practical solution methods for
reliable solutions.Comment: Revised versio
Electrodynamics with Lorentz-violating operators of arbitrary dimension
The behavior of photons in the presence of Lorentz and CPT violation is
studied. Allowing for operators of arbitrary mass dimension, we classify all
gauge-invariant Lorentz- and CPT-violating terms in the quadratic Lagrange
density associated with the effective photon propagator. The covariant
dispersion relation is obtained, and conditions for birefringence are
discussed. We provide a complete characterization of the coefficients for
Lorentz violation for all mass dimensions via a decomposition using
spin-weighted spherical harmonics. The resulting nine independent sets of
spherical coefficients control birefringence, dispersion, and anisotropy. We
discuss the restriction of the general theory to various special models,
including among others the minimal Standard-Model Extension, the isotropic
limit, the case of vacuum propagation, the nonbirefringent limit, and the
vacuum-orthogonal model. The transformation of the spherical coefficients for
Lorentz violation between the laboratory frame and the standard Sun-centered
frame is provided. We apply the results to various astrophysical observations
and laboratory experiments. Astrophysical searches of relevance include studies
of birefringence and of dispersion. We use polarimetric and dispersive data
from gamma-ray bursts to set constraints on coefficients for Lorentz violation
involving operators of dimensions four through nine, and we describe the mixing
of polarizations induced by Lorentz and CPT violation in the cosmic-microwave
background. Laboratory searches of interest include cavity experiments. We
present the theory for searches with cavities, derive the experiment-dependent
factors for coefficients in the vacuum-orthogonal model, and predict the
corresponding frequency shift for a circular-cylindrical cavity.Comment: 58 pages two-column REVTeX, accepted in Physical Review
The Evolution of PSR J0737-3039B and a Model for Relativistic Spin Precession
We present the evolution of the radio emission from the 2.8-s pulsar of the
double pulsar system PSR J0737-3039A/B. We provide an update on the Burgay et
al. (2005) analysis by describing the changes in the pulse profile and flux
density over five years of observations, culminating in the B pulsar's radio
disappearance in 2008 March. Over this time, the flux density decreases by
0.177 mJy/yr at the brightest orbital phases and the pulse profile evolves from
a single to a double peak, with a separation rate of 2.6 deg/yr. The pulse
profile changes are most likely caused by relativistic spin precession, but can
not be easily explained with a circular hollow-cone beam as in the model of
Clifton & Weisberg (2008). Relativistic spin precession, coupled with an
elliptical beam, can model the pulse profile evolution well. This particular
beam shape predicts geometrical parameters for the two bright orbital phases
which are consistent and similar to those derived by Breton et al. (2008).
However, the observed decrease in flux over time and B's eventual disappearance
cannot be easily explained by the model and may be due to the changing
influence of A on B.Comment: 20 pages, 18 figures, Accepted by ApJ on 2 August 201
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