49 research outputs found
Performance of N/p silicon and cadmium sulfide solar cells as affected by hypervelocity particle impact
Simulated micrometeoroid impact effect on silicon and cadmium sulfide solar cell performance
Three-Dimensional Identification and Reconstruction of Galaxy Systems within Deep Redshift Surveys
We have developed a new geometrical method for identifying and reconstructing
a homogeneous and highly complete set of galaxy groups in the next generation
of deep, flux-limited redshift surveys. Our method combines information from
the three-dimensional Voronoi diagram and its dual, the Delaunay triangulation,
to obtain group and cluster catalogs that are remarkably robust over wide
ranges in redshift and degree of density enhancement. Using the mock DEEP2
catalogs, we demonstrate that the VDM algorithm can be used to identify a
homogeneous set of groups in a magnitude-limited sample (I\sbr{AB}\le23.5)
throughout the survey redshift window . The actual group
membership can be effectively reconstructed even in the distorted redshift
space environment for systems with line of sight velocity dispersion
greater than \kms. By comparing the galaxy cluster
catalog derived from the mock DEEP2 observations to the underlying distribution
of clusters found in real space with much fainter galaxies included (which
should more closely trace mass in the cluster), we can assess completeness in
velocity dispersion directly. We conclude that the recovered DEEP2 group and
cluster sample should be statistically complete for
\kms. Finally, we argue that the reconstructed bivariate distribution of
systems as a function of redshift and velocity dispersion reproduces with high
fidelity the underlying real space distribution and can thus be used robustly
to constrain cosmological parametersComment: Latex, 21 pages, ApJ submitte
The COVID-19 pandemic and the future of telecommuting in the United States
This study focuses on an important transport-related long-term effect of the COVID-19 pandemic in the United States: an increase in telecommuting. Analyzing a nationally representative panel survey of adults, we find that 40â50% of workers expect to telecommute at least a few times per month post-pandemic, up from 24% pre-COVID. If given the option, 90â95% of those who first telecommuted during the pandemic plan to continue the practice regularly. We also find that new telecommuters are demographically similar to pre-COVID telecommuters. Both pre- and post-COVID, higher educational attainment and income, together with certain job categories, largely determine whether workers have the option to telecommute. Despite growth in telecommuting, approximately half of workers expect to remain unable to telecommute and between 2/3 and 3/4 of workers expect their post-pandemic telecommuting patterns to be unchanged from their pre-COVID patterns. This limits the contribution telecommuting can make to reducing peak hour transport demand
The VIMOS VLT Deep Survey: the group catalogue
[Abridged] We present a homogeneous and complete catalogue of optical groups
identified in the purely flux limited (17.5<=I<=24.0) VIMOS-VLT Deep Survey
(VVDS). We use mock catalogues extracted from the MILLENNIUM simulation, to
correct for potential systematics that might affect the overall distribution as
well as the individual properties of the identified systems. Simulated samples
allow us to forecast the number and properties of groups that can be
potentially found in a survey with VVDS-like selection functions. We use them
to correct for the expected incompleteness and also to asses how well galaxy
redshifts trace the line-of-sight velocity dispersion of the underlying mass
overdensity. In particular, we train on these mock catalogues the adopted
group-finding technique (the Voronoi-Delaunay Method, VDM). The goal is to
fine-tune its free parameters, recover in a robust and unbiased way the
redshift and velocity dispersion distributions of groups and maximize the level
of completeness (C) and purity (P) of the group catalogue. We identify 318 VVDS
groups with at least 2 members within 0.2<=z<=1.0, among which 144 (/30) with
at least 3 (/5) members. The sample has globally C=60% and P=50%. Nearly 45% of
the groups with at least 3 members are still recovered if we run the algorithm
with a parameter set which maximizes P (75%). We exploit the group sample to
study the redshift evolution of the fraction f_b of blue galaxies (U-B<=1)
within 0.2<=z<=1. We find that f_b is significantly lower in groups than in the
whole ensemble of galaxies irrespectively of their environment. These
quantities increase with redshift, with f_b in groups showing a marginally
significant steeper increase. We also confirm that, at any explored redshift,
f_b decreases for increasing group richness, and we extend towards fainter
luminosities the magnitude range over which this result holds.Comment: Submitted to A&A, revised version after referee comments, Table 5
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Validity and reliability of a novel 3D scanner for assessment of the shape and volume of amputeesâ residual limb models
Objective assessment methods to monitor residual limb volume following lower-limb amputation are required to enhance practitioner-led prosthetic fitting. Computer aided systems, including 3D scanners, present numerous advantages and the recent Artec Eva scanner, based on laser free technology, could potentially be an effective solution for monitoring residual limb volumes.
The aim of this study was to assess the validity and reliability of the Artec Eva scanner (practical measurement) against a high precision laser 3D scanner (criterion measurement) for the determination of residual limb model shape and volume. Three observers completed three repeat assessments of ten residual limb models, using both the scanners. Validity of the Artec Eva scanner was assessed (mean percentage error <2%) and Bland-Altman statistics were adopted to assess the agreement between the two scanners. Intra and inter-rater reliability (repeatability coefficient <5%) of the Artec Eva scanner was calculated for measuring indices of residual limb model volume and shape (i.e. residual limb cross sectional areas and perimeters). Residual limb model volumes ranged from 885 to 4399 ml. Mean percentage error of the Artec Eva scanner (validity) was 1.4% of the criterion volumes. Correlation coefficients between the Artec Eva and the Romer determined variables were higher than 0.9. Volume intra-rater and inter-rater reliability coefficients were 0.5% and 0.7%, respectively. Shape percentage maximal error was 2% at the distal end of the residual limb, with intra-rater reliability coefficients presenting the lowest errors (0.2%), both for cross sectional areas and perimeters of the residual limb models.
The Artec Eva scanner is a valid and reliable method for assessing residual limb model shapes and volumes. While the method needs to be tested on human residual limbs and the results compared with the current system used in clinical practice, it has the potential to quantify shape and volume fluctuations with greater resolution
An optical group catalogue to z = 1 from the zCOSMOS 10k sample
We present a galaxy group catalogue spanning the redshift range 0.1 <~ z <~ 1
in the ~1.7 deg^2 COSMOS field, based on the first ~10,000 zCOSMOS spectra. The
performance of both the Friends-of-Friends (FOF) and Voronoi-Delaunay-Method
(VDM) approaches to group identification has been extensively explored and
compared using realistic mock catalogues. We find that the performance improves
substantially if groups are found by progressively optimizing the group-finding
parameters for successively smaller groups, and that the highest fidelity
catalogue, in terms of completeness and purity, is obtained by combining the
independently created FOF and VDM catalogues. The final completeness and purity
of this catalogue, both in terms of the groups and of individual members,
compares favorably with recent results in the literature. The current group
catalogue contains 102 groups with N >= 5 spectroscopically confirmed members,
with a further ~700 groups with 2 <= N <= 4. Most of the groups can be assigned
a velocity dispersion and a dark-matter mass derived from the mock catalogues,
with quantifiable uncertainties. The fraction of zCOSMOS galaxies in groups is
about 25% at low redshift and decreases toward ~15% at z ~ 0.8. The zCOSMOS
group catalogue is broadly consistent with that expected from the semi-analytic
evolution model underlying the mock catalogues. Not least, we show that the
number density of groups with a given intrinsic richness increases from
redshift z ~ 0.8 to the present, consistent with the hierarchical growth of
structure.Comment: 20 pages, 19 figures, accepted for publication in Ap