4,900 research outputs found
Properties of Galaxies in and around Voids
Two surveys for intrinsically faint galaxies towards nearby voids have been
conducted at the MPI f\"ur Astronomie, Heidelberg. One selected targets from a
new diameter limited () catalog with morphological criteria while
the other used digitized objective prism Schmidt plates to select mainly HII
dwarf galaxies. For some 450 galaxies, redshifts and other optical data were
obtained. We studied the spatial distribution of the sample objects, their
luminosity function, and their intrinsic properties. Most of the galaxies
belong to already well known sheets and filaments. But we found about a dozen
highly isolated galaxies in each sample (nearest neighborhood distance ). These tend to populate additional structures and are not
distributed homogeneously throughout the voids. As our results on 'void
galaxies' still suffer from small sample statistics, I also tried to combine
similar existing surveys of nearby voids to get further hints on the larger
structure and on the luminosity function of the isolated galaxies. No
differences in the luminosity function of sheet and void galaxies could be
found. The optical and infrared properties of both samples are in the normal
range for samples dominated by late-type dwarfs. Follow-up HI studies show that
the isolated dwarfs in both samples have unusual high amount of neutral gas for
a given luminosity.Comment: 10 pages, 4 figures, latex, to appear in the proceedings of the
'Ringberg workshop on Large Scale Structure', hold Sep. 23-28, 199
Evaluation of Two Computational Techniques of Calculating Multipath Using Global Positioning System Carrier Phase Measurements
Two computational techniques are used to calculate differential phase errors on Global Positioning System (GPS) carrier war phase measurements due to certain multipath-producing objects. The two computational techniques are a rigorous computati electromagnetics technique called Geometric Theory of Diffraction (GTD) and the other is a simple ray tracing method. The GTD technique has been used successfully to predict microwave propagation characteristics by taking into account the dominant multipath components due to reflections and diffractions from scattering structures. The ray tracing technique only solves for reflected signals. The results from the two techniques are compared to GPS differential carrier phase ns taken on the ground using a GPS receiver in the presence of typical International Space Station (ISS) interference structures. The calculations produced using the GTD code compared to the measured results better than the ray tracing technique. The agreement was good, demonstrating that the phase errors due to multipath can be modeled and characterized using the GTD technique and characterized to a lesser fidelity using the DECAT technique. However, some discrepancies were observed. Most of the discrepancies occurred at lower devations and were either due to phase center deviations of the antenna, the background multipath environment, or the receiver itself. Selected measured and predicted differential carrier phase error results are presented and compared. Results indicate that reflections and diffractions caused by the multipath producers, located near the GPS antennas, can produce phase shifts of greater than 10 mm, and as high as 95 mm. It should be noted tl the field test configuration was meant to simulate typical ISS structures, but the two environments are not identical. The GZ and DECAT techniques have been used to calculate phase errors due to multipath o the ISS configuration to quantify the expected attitude determination errors
Defects in SiO2 as the possible origin of near interface traps in the SiC∕SiO2 system: A systematic theoretical study
A systematic study of the level positions of intrinsic and carbon defects in SiO2 is presented, based on density functional calculations with a hybrid functional in an alpha-quartz supercell. The results are analyzed from the point of view of the near interface traps (NIT), observed in both SiC/SiO2 and Si/SiO2 systems, and assumed to have their origins in the oxide. It is shown that the vacancies and the oxygen interstitial can be excluded as the origin of such NIT, while the silicon interstitial and carbon dimers give rise to gap levels in the energy range inferred from experiments. The properties of these defects are discussed in light of the knowledge about the SiC/SiO2 interface
Evidence of Environmental Dependencies of Type Ia Supernovae from the Nearby Supernova Factory indicated by Local H{\alpha}
(Abridged) We study the host galaxy regions in close proximity to Type Ia
supernovae (SNe Ia) to analyze relations between the properties of SN Ia events
and environments most similar to where their progenitors formed. We focus on
local H\alpha\ emission as an indicator of young environments. The Nearby
Supernova Factory has obtained flux-calibrated spectral timeseries for SNe Ia
using integral field spectroscopy, allowing the simultaneous measurement of the
SN and its immediate vicinity. For 89 SNe Ia we measure H\alpha\ emission
tracing ongoing star formation within a 1 kpc radius around each SN. This
constitutes the first direct study of the local environment for a large sample
of SNe Ia also having accurate luminosity, color and stretch measurements. We
find that SNe Ia with local H\alpha\ emission are redder by 0.036+/-0.017 mag,
and that the previously-noted correlation between stretch and host mass is
entirely driven by the SNe Ia coming from passive regions. Most importantly,
the mean standardized brightness for SNe Ia with local H\alpha\ emission is
0.094+/-0.031 mag fainter than for those without. This offset arises from a
bimodal structure in the Hubble residuals, that also explains the
previously-known host-mass bias. We combine this bimodality with the cosmic
star-formation rate to predict changes with redshift in the mean SN Ia
brightness and the host-mass bias. This change is confirmed using high-redshift
SNe Ia from the literature. These environmental dependences point to remaining
systematic errors in SNe Ia standardization. The observed brightness offset is
predicted to cause a significant bias in measurements of the dark energy
equation of state. Recognition of these effects offers new opportunities to
improve SNe Ia as cosmological probes - e.g. SNe Ia having local H\alpha\
emission are more homogeneous, having a brightness dispersion of 0.105+/-0.012
mag.Comment: accepted for publication in Section 3. Cosmology of A&A (The official
date of acceptance is 30/08/2013
Type Ia Supernova Hubble Residuals and Host-Galaxy Properties
Kim et al. (2013) [K13] introduced a new methodology for determining
peak-brightness absolute magnitudes of type Ia supernovae from multi-band light
curves. We examine the relation between their parameterization of light curves
and Hubble residuals, based on photometry synthesized from the Nearby Supernova
Factory spectrophotometric time series, with global host-galaxy properties. The
K13 Hubble residual step with host mass is mag for a supernova
subsample with data coverage corresponding to the K13 training; at , the step is not significant and lower than previous measurements.
Relaxing the data coverage requirement the Hubble residual step with host mass
is mag for the larger sample; a calculation using the modes of
the distributions, less sensitive to outliers, yields a step of 0.019 mag. The
analysis of this article uses K13 inferred luminosities, as distinguished from
previous works that use magnitude corrections as a function of SALT2 color and
stretch parameters: Steps at significance are found in SALT2 Hubble
residuals in samples split by the values of their K13 and
light-curve parameters. affects the light-curve width and color around
peak (similar to the and stretch parameters), and
affects colors, the near-UV light-curve width, and the light-curve decline 20
to 30 days after peak brightness. The novel light-curve analysis, increased
parameter set, and magnitude corrections of K13 may be capturing features of
SN~Ia diversity arising from progenitor stellar evolution.Comment: 17 pages, 6 figures. Accepted by Astrophysical Journa
Continuity Culture: A Key Factor for Building Resilience and Sound Recovery Capabilities
This article investigates the extent to which Jordanian service organizations seek to establish continuity culture through testing, training, and updating of their business continuity plans. A survey strategy was adopted in this research. Primary and secondary data were used. Semistructured interviews were conducted with five senior managers from five large Jordanian service organizations registered with the Amman Stock Exchange. The selection of organizations was made on the basis of simple random sampling. Interviews targeted the headquarters only in order to obtain a homogenous sample. Three out of five organizations could be regarded as crisis prepared and have better chances for recovery. The other two organizations exhibited characteristics of standard practice that only emphasizes the recovery aspect of business continuity management (BCM), while paying less attention to establishing resilient cultures and embedding BCM. The findings reveal that the ability to recover following major incidents can be improved by embedding BCM in the culture of the organization and by making BCM an enterprise-wide process. This is one of few meticulous studies that have been undertaken in the Middle East and the first in Jordan to investigate the extent to which service organizations focus on embedding BCM in the organizational culture
A Bragg glass phase in the vortex lattice of a type II superconductor
Although crystals are usually quite stable, they are sensitive to a
disordered environment: even an infinitesimal amount of impurities can lead to
the destruction of the crystalline order. The resulting state of matter has
been a longstanding puzzle. Until recently it was believed to be an amorphous
state in which the crystal would break into crystallites. But a different
theory predicts the existence of a novel phase of matter: the so-called Bragg
glass, which is a glass and yet nearly as ordered as a perfect crystal. The
lattice of vortices that can contain magnetic flux in type II superconductors
provide a good system to investigate these ideas. Here we show that neutron
diffraction data of the vortex lattice in type II superconductors provides
unambiguous evidence for a weak, power-law decay of the crystalline order
characteristic of a Bragg glass. The theory also predicts accurately the
electrical transport properties of superconductors; it naturally explains the
observed phase transition and the dramatic jumps in the critical current
associated with the melting of the Bragg glass. Moreover the model explains
experiments as diverse as X-ray scattering in disordered liquid crystals and
conductivity of electronic crystals.Comment: 9 pages, 4 figure
Recommended from our members
Variability of dayside convection and motions of the cusp/cleft aurora
We present measurements of the ionospheric plasma flow over the range of invariant latitudes 71–76°, observed at 10-second resolution using both the EISCAT radars, with simultaneous observations of the 630 nm cusp/cleft aurora made by a meridian-scanning photometer at Ny Ålesund, Svalbard. A major increase in the trans-auroral voltage from 5 to 40 kV (associated with sunward convection in the early afternoon sector) is found to follow a southward motion of the aurora and coincide with the onset of regular transient auroral breakup events. It is shown that these observations are consistent with recent theoretical work on how ionospheric flows are excited by time-dependent reconnection at the dayside magnetopause
Measuring cosmic bulk flows with Type Ia Supernovae from the Nearby Supernova Factory
Context. Our Local Group of galaxies appears to be moving relative to the
cosmic microwave background with the source of the peculiar motion still
uncertain. While in the past this has been studied mostly using galaxies as
distance indicators, the weight of type Ia supernovae (SNe Ia) has increased
recently with the continuously improving statistics of available low-redshift
supernovae.
Aims. We measured the bulk flow in the nearby universe ()
using 117 SNe Ia observed by the Nearby Supernova Factory, as well as the
Union2 compilation of SN Ia data already in the literature.
Methods. The bulk flow velocity was determined from SN data binned in
redshift shells by including a coherent motion (dipole) in a cosmological fit.
Additionally, a method of spatially smoothing the Hubble residuals was used to
verify the results of the dipole fit. To constrain the location and mass of a
potential mass concentration (e.g., the Shapley supercluster) responsible for
the peculiar motion, we fit a Hubble law modified by adding an additional mass
concentration.
Results. The analysis shows a bulk flow that is consistent with the direction
of the CMB dipole up to , thereby doubling the volume over which
conventional distance measures are sensitive to a bulk flow. We see no
significant turnover behind the center of the Shapley supercluster. A simple
attractor model in the proximity of the Shapley supercluster is only marginally
consistent with our data, suggesting the need for another, more distant source.
In the redshift shell , we constrain the bulk flow velocity to
(68% confidence level) for the direction of the CMB
dipole, in contradiction to recent claims of the existence of a large-amplitude
dark flow.Comment: 12 pages, 5 figures, added corrigendum
(http://adsabs.harvard.edu/abs/2015A%26A...578C...1F
Improving Cosmological Distance Measurements Using Twin Type Ia Supernovae
We introduce a method for identifying "twin" Type Ia supernovae, and using
them to improve distance measurements. This novel approach to Type Ia supernova
standardization is made possible by spectrophotometric time series observations
from the Nearby Supernova Factory (SNfactory). We begin with a well-measured
set of supernovae, find pairs whose spectra match well across the entire
optical window, and then test whether this leads to a smaller dispersion in
their absolute brightnesses. This analysis is completed in a blinded fashion,
ensuring that decisions made in implementing the method do not inadvertently
bias the result. We find that pairs of supernovae with more closely matched
spectra indeed have reduced brightness dispersion. We are able to standardize
this initial set of SNfactory supernovae to 0.083 +/- 0.012 magnitudes,
implying a dispersion of 0.072 +/- 0.010 magnitudes in the absence of peculiar
velocities. We estimate that with larger numbers of comparison SNe, e.g, using
the final SNfactory spectrophotometric dataset as a reference, this method will
be capable of standardizing high-redshift supernovae to within 0.06-0.07
magnitudes. These results imply that at least 3/4 of the variance in Hubble
residuals in current supernova cosmology analyses is due to previously
unaccounted-for astrophysical differences among the supernovaeComment: 37 pages, 9 figures, 5 tables. Accepted for publication in ApJ. Fixed
typo in arXiv abstrac
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