2,110 research outputs found
How good are MatLab, Octave and Scilab for Computational Modelling?
In this article we test the accuracy of three platforms used in computational
modelling: MatLab, Octave and Scilab, running on i386 architecture and three
operating systems (Windows, Ubuntu and Mac OS). We submitted them to numerical
tests using standard data sets and using the functions provided by each
platform. A Monte Carlo study was conducted in some of the datasets in order to
verify the stability of the results with respect to small departures from the
original input. We propose a set of operations which include the computation of
matrix determinants and eigenvalues, whose results are known. We also used data
provided by NIST (National Institute of Standards and Technology), a protocol
which includes the computation of basic univariate statistics (mean, standard
deviation and first-lag correlation), linear regression and extremes of
probability distributions. The assessment was made comparing the results
computed by the platforms with certified values, that is, known results,
computing the number of correct significant digits.Comment: Accepted for publication in the Computational and Applied Mathematics
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The SCUBA 8-mJy survey - I: Sub-millimetre maps, sources and number counts
We present maps, source lists, and number counts from the largest, unbiassed,
extragalactic sub-mm survey so far undertaken with the SCUBA camera on the
JCMT. Our maps cover 260 sq. arcmin, to a noise level S(850)=2.5 mJy/beam. We
have reduced the data using both SURF, and our own pipeline which produces
zero-footprint maps and noise images. The uncorrelated noise maps produced by
the latter approach have allowed application of a maximum-likelihood method to
measure the statistical significance of each peak, leading to properly
quantified flux-density errors for all potential sources. We detect 19 sources
with S/N > 4, 38 with S/N > 3.5, and 72 with S/N > 3. To assess completeness
and the impact of source confusion we have applied our source extraction
algorithm to a series of simulated images. The result is a new estimate of the
sub-mm source counts in the flux-density range S(850)=5-15mJy, which we compare
with other estimates, and with model predictions. Our estimate of the
cumulative source count at S(850) > 8 mJy is 320 (+80,-100) per square degree.
Assuming that the majority of sources have z > 1.5, the co-moving number
density of high-z galaxies forming stars at a rate >1000 solar masses per year
is 10^-5 per Mpc^3, with only a weak dependence on the precise redshift
distribution. This number density corresponds to that of massive ellipticals
with L > 3-4 L* at low redshift and is also the same as the co-moving number
density of comparably massive, passively-evolving objects in the redshift band
1<z<2 inferred from recent surveys of extremely red objects. Thus the bright
sub-mm sources can plausibly account for the formation of all present-day
massive ellipticals. Improved z constraints, and a proper measurement of sub-mm
clustering can refine or refute this picture.Comment: Minor revisions. 27 pages, 13 figures. Higher resolution versions of
Figs 5,6,7 and 8 are available from the autho
A Third Exoplanetary System with Misaligned Orbital and Stellar Spin Axes
We present evidence that the WASP-14 exoplanetary system has misaligned
orbital and stellar-rotational axes, with an angle lambda = 33.1 +/- 7.4 deg
between their sky projections. The evidence is based on spectroscopic
observations of the Rossiter-McLaughlin effect as well as new photometric
observations. WASP-14 is now the third system known to have a significant
spin-orbit misalignment, and all three systems have "super-Jupiter" planets
(M_P > 3 Mjup) and eccentric orbits. This finding suggests that the migration
and subsequent orbital evolution of massive, eccentric exoplanets is somehow
different from that of less massive close-in Jupiters, the majority of which
have well-aligned orbits.Comment: 8 pages, 5 figures, 3 tables, PASP accepte
VLBI Polarimetry of 177 Sources from the Caltech-Jodrell Bank Flat-spectrum Survey
We present VLBA observations and a statistical analysis of 5 GHz VLBI
polarimetry data from 177 sources in the Caltech-Jodrell Bank flat-spectrum
(CJF) survey. The CJF survey, a complete, flux-density-limited sample of 293
extragalactic radio sources, gives us the unique opportunity to compare a broad
range of source properties for quasars, galaxies and BL Lacertae objects. We
focus primarily on jet properties, specifically the correlation between the jet
axis angle and the polarization angle in the core and jet. A strong correlation
is found for the electric vector polarization angle in the cores of quasars to
be perpendicular to the jet axis. Contrary to previous claims, no correlation
is found between the jet polarization angle and the jet axis in either quasars
or BL Lac objects. With this large, homogeneous sample we are also able to
investigate cosmological issues and AGN evolution.Comment: Accepted to the Astrophysical Journal: 37 pages, 14 figure
On the Numerical Accuracy of Spreadsheets
This paper discusses the numerical precision of five spreadsheets (Calc, Excel, Gnumeric, NeoOffice and Oleo) running on two hardware platforms (i386 and amd64) and on three operating systems (Windows Vista, Ubuntu Intrepid and Mac OS Leopard). The methodology consists of checking the number of correct significant digits returned by each spreadsheet when computing the sample mean, standard deviation, first-order autocorrelation, F statistic in ANOVA tests, linear and nonlinear regression and distribution functions. A discussion about the algorithms for pseudorandom number generation provided by these platforms is also conducted. We conclude that there is no safe choice among the spreadsheets here assessed: they all fail in nonlinear regression and they are not suited for Monte Carlo experiments
Forty-Three Loci Associated with Plasma Lipoprotein Size, Concentration, and Cholesterol Content in Genome-Wide Analysis
While conventional LDL-C, HDL-C, and triglyceride measurements reflect aggregate properties of plasma lipoprotein fractions, NMR-based measurements more accurately reflect lipoprotein particle concentrations according to class (LDL, HDL, and VLDL) and particle size (small, medium, and large). The concentrations of these lipoprotein sub-fractions may be related to risk of cardiovascular disease and related metabolic disorders. We performed a genome-wide association study of 17 lipoprotein measures determined by NMR together with LDL-C, HDL-C, triglycerides, ApoA1, and ApoB in 17,296 women from the Women's Genome Health Study (WGHS). Among 36 loci with genome-wide significance (P<5×10−8) in primary and secondary analysis, ten (PCCB/STAG1 (3q22.3), GMPR/MYLIP (6p22.3), BTNL2 (6p21.32), KLF14 (7q32.2), 8p23.1, JMJD1C (10q21.3), SBF2 (11p15.4), 12q23.2, CCDC92/DNAH10/ZNF664 (12q24.31.B), and WIPI1 (17q24.2)) have not been reported in prior genome-wide association studies for plasma lipid concentration. Associations with mean lipoprotein particle size but not cholesterol content were found for LDL at four loci (7q11.23, LPL (8p21.3), 12q24.31.B, and LIPG (18q21.1)) and for HDL at one locus (GCKR (2p23.3)). In addition, genetic determinants of total IDL and total VLDL concentration were found at many loci, most strongly at LIPC (15q22.1) and APOC-APOE complex (19q13.32), respectively. Associations at seven more loci previously known for effects on conventional plasma lipid measures reveal additional genetic influences on lipoprotein profiles and bring the total number of loci to 43. Thus, genome-wide associations identified novel loci involved with lipoprotein metabolism—including loci that affect the NMR-based measures of concentration or size of LDL, HDL, and VLDL particles—all characteristics of lipoprotein profiles that may impact disease risk but are not available by conventional assay
: Pressure-dependent Changes In Light Curve Phase In Brown Dwarfs From Simultaneous and Observations
We present /IRAC Ch1 and Ch2 monitoring of six brown dwarfs during 8
different epochs over the course of 20 months. For four brown dwarfs, we also
obtained simulataneous /WFC3 G141 Grism spectra during two epochs and
derived light curves in five narrow-band filters. Probing different pressure
levels in the atmospheres, the multi-wavelength light curves of our six targets
all exhibit variations, and the shape of the light curves evolves over the
timescale of a rotation period, ranging from 1.4 h to 13 h. We compare the
shapes of the light curves and estimate the phase shifts between the light
curves observed at different wavelengths by comparing the phase of the primary
Fourier components. We use state-of-the-art atmosphere models to determine the
flux contribution of different pressure layers to the observed flux in each
filter. We find that the light curves that probe higher pressures are similar
and in phase, but are offset and often different from the light curves that
probe lower pressures. The phase differences between the two groups of light
curves suggest that the modulations seen at lower and higher pressures may be
introduced by different cloud layers.Comment: 34 pages, 22 figures, accepted for publication in Ap
Considering correlation properties on statistical simulation of clutter
Statistical properties of image data are of paramount importance in the design of pattern recognition technics and the interpretation of their outputs. Image simulation allows quantification of method?s error and accuracy. In the case of SAR images, the contamination they suffer from a particular kind of noise, called speckle, which does not follow the classical hypothesis of entering the signal in an additive manner and obeying the Gaussian law, make them require a more careful treatment. Since the seminal work of Frery et al. (1997) a great variety of studies have been made targeting the specification of statistical properties of SAR data beyond classical assumptions. The G distribution family proposed by Frery has been proved a flexible tool for the design of pattern recognition algorithms based on statistical modeling. Nevertheless, most of such work does not consider correlation present in the data as significant, which introduces an error in the model of particular regions of the imagery. The autocorrelation function can represent the structure of sea waves and the random variation made by the height and width of trees, along with the variability introduced in forests by the variation of wind intensity. Using the roughness parameter of the G family for target discrimination alleviates this modeling error, since it was shown by Frery et al. (1997) that it characterizes heterogeneity in data. Classification accuracy is then tied to parameter estimation, which in this case it has been proved difficult, Lucini (2002), Bustos et al. (2002). In this paper we review some of our own simulation techniques to generate SAR clutter with pre-specified correlation properties, Flesia (1999), Bustos et al. (2001), Bustos et al. (2009), and release a new set of routines in R for simulation studies based on such techniques. We give an example of the code versatility studying the change in accuracy of non-parametric techniques when correlated data is classified, compared with classification of uncorrelated data simulated with the same parameters. All code is available for download from AGF?s Reproducible Research website, Flesia (2014).This work was financially supported by grants from SeCyT-UNC, Argentina. AGF, MML are careermembers of CONICET.Fil: Flesia, Ana Georgina. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentina.Fil: Flesia, Ana Georgina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro de Investigaciones y Estudios de Matemática; Argentina.Fil: Pérez, DarÃo Javier. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentina.Fil: Pérez, DarÃo Javier. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro de Investigaciones y Estudios de Matemática; Argentina.Fil: Lucini, MarÃa Magdalena. Universidad Nacional de Nordeste. Facultad de Ciencias Exactas, Naturales y Agrimensura; Argentina.Fil: Lucini, MarÃa Magdalena. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina.Ciencias de la Información y Bioinformática (desarrollo de hardware va en 2.2 "IngenierÃa Eléctrica, Electrónica y de Información" y los aspectos sociales van en 5.8 "Comunicación y Medios"
The Diversity of Diffuse Ly Nebulae around Star-Forming Galaxies at High Redshift
We report the detection of diffuse Ly emission, or Ly halos
(LAHs), around star-forming galaxies at and in the NOAO
Deep Wide-Field Survey Bo\"otes field. Our samples consist of a total of
1400 galaxies, within two separate regions containing spectroscopically
confirmed galaxy overdensities. They provide a unique opportunity to
investigate how the LAH characteristics vary with host galaxy large-scale
environment and physical properties. We stack Ly images of different
samples defined by these properties and measure their median LAH sizes by
decomposing the stacked Ly radial profile into a compact galaxy-like
and an extended halo-like component. We find that the exponential scale-length
of LAHs depends on UV continuum and Ly luminosities, but not on
Ly equivalent widths or galaxy overdensity parameters. The full
samples, which are dominated by low UV-continuum luminosity Ly emitters
(), exhibit LAH sizes of 5kpc. However, the
most UV- or Ly-luminous galaxies have more extended halos with
scale-lengths of 7kpc. The stacked Ly radial profiles decline
more steeply than recent theoretical predictions that include the contributions
from gravitational cooling of infalling gas and from low-level star formation
in satellites. On the other hand, the LAH extent matches what one would expect
for photons produced in the galaxy and then resonantly scattered by gas in an
outflowing envelope. The observed trends of LAH sizes with host galaxy
properties suggest that the physical conditions of the circumgalactic medium
(covering fraction, HI column density, and outflow velocity) change with halo
mass and/or star-formation rates.Comment: published in ApJ, minor proof corrections applie
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