3,968 research outputs found
Some criteria for determining recognizability of a set
Let an be the number of strings of length n in a set A â â*, where â is a finite alphabet. Several criteria for determining that a set is not recognizable by a finite automaton are given, based solely on the sequence {an}. The sequence {an} is also used to define a finitely addititive probability measure on all recognizable sets
Galactic Extinction from Colors and Counts of Field Galaxies in WFPC2 Frames: An Application to GRB 970228
We develop the ``simulated extinction method'' to measure average foreground
Galactic extinction from field galaxy number-counts and colors. The method
comprises simulating extinction in suitable reference fields by changing the
isophotal detection limit. This procedure takes into account selection effects,
in particular, the change in isophotal detection limit (and hence in isophotal
magnitude completeness limit) with extinction, and the galaxy color--magnitude
relation.
We present a first application of the method to the HST WFPC2 images of the
gamma-ray burster GRB 970228. Four different WFPC2 high-latitude fields,
including the HDF, are used as reference to measure the average extinction
towards the GRB in the F606W passband. From the counts, we derive an average
extinction of A_V = 0.5 mag, but the dispersion of 0.4 mag between the
estimates from the different reference fields is significantly larger than can
be accounted by Poisson plus clustering uncertainties. Although the counts
differ, the average colors of the field galaxies agree well. The extinction
implied by the average color difference between the GRB field and the reference
galaxies is A_V = 0.6 mag, with a dispersion in the estimated extinction from
the four reference fields of only 0.1 mag. All our estimates are in good
agreement with the value of 0.81\pm0.27 mag obtained by Burstein & Heiles, and
with the extinction of 0.78\pm0.12 measured by Schlegel et al. from maps of
dust IR emission. However, the discrepancy between the widely varying counts
and the very stable colors in these high-latitude fields is worth
investigating.Comment: 14 pages, 2 figures; submitted to the Astrophysical Journa
Faint K Selected Galaxy Correlations and Clustering Evolution
Angular and spatial correlations are measured for K-band--selected galaxies,
248 having redshifts, 54 with z>1, in two patches of combined area 27 arcmin^2.
The angular correlation for K<=21.5 mag is (theta/1.4+/-0.19 arcsec
e^{+/-0.1})^{-0.8}. From the redshift sample we find that the real-space
correlation, calculated with q_0=0.1, of M_K<=-23.5 mag galaxies (k-corrected)
is \xi(r) = (r/2.9e^{+/-0.12}1/h Mpc)^{-1.8} at a mean z= 0.34,
(r/2.0e^{+/-0.15}1/h Mpc)^{-1.8} at z= 0.62, (r/1.4e^{+/-0.15}1/h Mpc)^{-1.8}
at z= 0.97, and (r/1.0e^{+/-0.2}1/h Mpc)^{-1.8} at z= 1.39, the last being a
formal upper limit for a blue-biased sample. In general, these are more
correlated than optically selected samples in the same redshift ranges. Over
the interval 0.32 AB
mag, have \xi(r)=(r/2.4e^{+/-0.14}1/h Mpc)^{-1.8} whereas bluer galaxies, which
have a mean B of 23.7 mag and mean [OII] equivalent width W_{eq} = 41=\AA, are
very weakly correlated, with \xi(r)=(r/0.9e^{+/-0.22}1/h Mpc)^{-1.8}. For our
measured growth rate of clustering, this blue population, if non-merging, can
grow only into a low-redshift population less luminous than 0.4L_\ast. The
cross-correlation of low- and high-luminosity galaxies at z=0.6 appears to have
an excess in the correlation amplitude within 100/h kpc. The slow redshift
evolution is consistent with these galaxies tracing the mass clustering in low
density, Omega= 0.2, relatively unbiased, sigma_8=0.8, universe, but cannot yet
exclude other possibilities.Comment: to be published in the Aug 1 ApJ, 20 pages as a uuencoded postscript
file Postscript with all figures is available at
http://manaslu.astro.utoronto.ca/~carlberg/paper
The distortion of distant galaxy images by large-scale structure
Inhomogeneity in the distribution of mass in the universe on scales âČ 100 Mpc can generate a coherent shear distortion or polarization of the images of background galaxies. This distortion may be measurable over patches of the sky up to a few square degrees in size. If this distortion is measured, or conversely, if its magnitude is limited, it should help us understand the degree to which luminosity traces the underlying mass over cosmological scales. A prescription is given for quantifying the galaxy distortion and a propagation equation for its evolution in an inhomogeneous universe is derived. The creation of shear by inhomogeneity is illustrated using model kinematic universes comprising random distributions of point masses, spheres and circular discs designed to simulate the superclusters, voids and âwallsâ reported in galaxy velocity surveys. Using these simulations, we estimate that an rms induced ellipticity of |p|_(rms) Ë 0.2Ω_(LSS) (where Ω_(LSS) is the fraction of the mass of the universe clustered on the large scale) will be produced. The angular correlation length is Ë 1.6°.
In an alternative prescription, the universe is modelled using a power spectrum of density fluctuations and the mean correlation function is computed both analytically and numerically. In these simulations we find that |p|_(rms) Ë0.02 for biased cold dark matter models of an EinsleinâDe Sitter universe, and the effective correlation length is Ξ_(1/2) Ë 0.5^ΰ. For a hot dark matter dominated universe the correlation length is Ξ_(1/2) Ë 0.7^ΰ.
The faint, blue galaxies discovered by Tyson and collaborators have a surface density of Ë 3 Ă 10^5 deg^(â2) and should provide an ideal set of sources for measuring this effect
XROMM analysis of tooth occlusion and temporomandibular joint kinematics during feeding in juvenile miniature pigs
Like humans, domestic pigs are omnivorous and thus are a common model for human masticatory function. Prior attempts to characterize foodâtooth interactions and jaw movements associated with mastication have been limited to aspects of the oral apparatus that are visible externally (with videography) and/or to 2D movements of oral structures (with monoplanar videofluoroscopy). We used XROMM, a 3D technique that combines CT-based morphology with biplanar videofluoroscopy, to quantify mandibular kinematics, tooth occlusion and mandibular condylar displacements within the temporomandibular joint (TMJ) during feeding. We observed that the pig TMJ moved detectably in only three of six possible degrees of freedom during mastication: two rotations, pitch and yaw; and one translation, protractionâretraction. Asymmetrical yaw around a dorsoventral axis produced the observed alternating leftâright chewing cycles responsible for food reduction. Furthermore, the relative motions of the upper and lower premolars contained a substantial mesiodistal component in addition to the buccolingual component, resulting in an oblique (rather than a strictly transverse) power stroke. This research demonstrates the capacity of XROMM to explore the kinematic underpinnings of key masticatory movements, such as the occlusal power stroke, by integrating tooth, joint and rigid body jaw movements. XROMM also allowed us to test kinematic hypotheses based on skeletal anatomy with actual kinematics observed during naturalistic feeding behaviors. We observed that the soft tissue structures of the TMJ appear to play a significant role in limiting the range of motion of a joint, and thus analyses based solely on osseous morphology may over-estimate joint mobility
Measuring the Angular Correlation Function for Faint Galaxies in High Galactic Latitude Fields
A photometric survey of faint galaxies in three high Galactic latitude fields
(each ) with sub-arcsecond seeing is used to study the
clustering properties of the faint galaxy population. Multi-color photometry of
the galaxies has been obtained to magnitude limits of , and
. Angular correlation analysis is applied to magnitude-limited and
color-selected samples of galaxies from the three fields for angular
separations ranging from . General agreement is obtained with other
recent studies which show that the amplitude of the angular correlation
function, , is smoothly decreasing as a function of limiting
magnitude. The observed decline of rules out the viability of
``maximal merger'' galaxy evolution models. Using redshift distributions
extrapolated to faint magnitude limits, models of galaxy clustering evolution
are calculated and compared to the observed I-band . Faint
galaxies are determined to have correlation lengths and clustering evolution
parameters of either and ;
and ; or and
, assuming and with . The latter case is for clustering fixed in co-moving
coordinates and is probably unrealistic since most local galaxies are observed
to be more strongly clustered. No significant variations in the clustering
amplitude as a function of color are detected, for all the color-selected
galaxy samples considered. (Abridged)Comment: LaTeX (aaspp4.sty), 54 pages including 15 postscript figures; 3
additional uuencoded, gzipped postscript files (~300 kb each) of Figs. 1, 2
and 3 available at ftp://ftp.astro.ubc.ca/pub/woods ; To be published in the
Nov. 20, 1997 issue of The Astrophysical Journa
The non-Gaussian tail of cosmic-shear statistics
Due to gravitational instability, an initially Gaussian density field
develops non-Gaussian features as the Universe evolves. The most prominent
non-Gaussian features are massive haloes, visible as clusters of galaxies. The
distortion of high-redshift galaxy images due to the tidal gravitational field
of the large-scale matter distribution, called cosmic shear, can be used to
investigate the statistical properties of the LSS. In particular, non-Gaussian
properties of the LSS will lead to a non-Gaussian distribution of cosmic-shear
statistics. The aperture mass () statistics, recently introduced as
a measure for cosmic shear, is particularly well suited for measuring these
non-Gaussian properties. In this paper we calculate the highly non-Gaussian
tail of the aperture mass probability distribution, assuming Press-Schechter
theory for the halo abundance and the `universal' density profile of haloes as
obtained from numerical simulations. We find that for values of
much larger than its dispersion, this probability distribution is closely
approximated by an exponential, rather than a Gaussian. We determine the
amplitude and shape of this exponential for various cosmological models and
aperture sizes, and show that wide-field imaging surveys can be used to
distinguish between some of the currently most popular cosmogonies. Our study
here is complementary to earlier cosmic-shear investigations which focussed
more on two-point statistical properties.Comment: 9 pages, 5 figures, submitted to MNRA
Development of intuitive rules: Evaluating the application of the dual-system framework to understanding children's intuitive reasoning
This is an author-created version of this article. The original source of publication is Psychon Bull Rev. 2006 Dec;13(6):935-53
The final publication is available at www.springerlink.com
Published version: http://dx.doi.org/10.3758/BF0321390
Cosmic Shear from STIS Pure Parallels: Analysis
The measurement of cosmic shear requires deep imaging with high image quality
on many lines of sight to sample the statistics of large-scale structure. The
expected distortion of galaxy images by cosmic shear on the STIS angular scale
is a few percent, therefore the PSF anisotropy has to be understood and
controlled to an accuracy better than 1%. In this poster we present the
analysis of the PSF of STIS and a preliminary cosmic shear measurement using
archival data from the STIS pure parallel program to show that the STIS camera
on-board HST is well suited for our project. The data reduction and catalog
production are described in an accompanying paper (astro-ph/0102330).Comment: 4 pages, 5 figures, to appear in the proceedings of the STScI 2001
spring symposium "The Dark Universe: Matter, Energy and Gravity" Baltimore
April 2-5 2001, acknowledgements adde
Cold collapse and the core catastrophe
We show that a universe dominated by cold dark matter fails to reproduce the
rotation curves of dark matter dominated galaxies, one of the key problems that
it was designed to resolve. We perform numerical simulations of the formation
of dark matter halos, each containing \gsim 10^6 particles and resolved to
0.003 times the virial radius, allowing an accurate comparison with rotation
curve data. A good fit to both galactic and cluster sized halos can be achieved
using the density profile rho(r) \propto [(r/r_s)^1.5(1+(r/r_s)^1.5)]^-1, where
r_s is a scale radius. This profile has a steeper asymptotic slope, rho(r)
\propto r^-1.5, and a sharper turnover than found by lower resolution studies.
The central structure of relaxed halos that form within a hierarchical universe
has a remarkably small scatter (unrelaxed halos would not host disks). We
compare the results with a sample of dark matter dominated, low surface
brightness (LSB) galaxies with circular velocities in the range 100-300 km/s.
The rotation curves of disks within cold dark matter halos rise too steeply to
match these data which require a constant mass density in the central regions.
The same conclusion is reached if we compare the scale free shape of observed
rotation curves with the simulation data. It is important to confirm these
results using stellar rather than HI rotation curves for LSB galaxies. We test
the effects of introducing a cut-off in the power spectrum that may occur in a
universe dominated by warm dark matter. In this case halos form by a monolithic
collapse but the final density profile hardly changes, demonstrating that the
merger history does not play a role in determining the halo structure.Comment: Latex 13 pages, 4 figures. Submitted to MNRAS. High resolution colour
version of figure 4 and other N-body images here:
http://star-www.dur.ac.uk:80/~moore/images
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