4,595 research outputs found
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Shared Autonomous Mobility Services Show Promise for Increasing Access to Employment in Southern California
Workers in Southern California currently face transportationrelated challenges accessing employment opportunities, including but not limited to high parking costs and/or limited parking availability in dense employment and residential areas; long commute distances between residential areas and employment opportunities; and poor transit service quality in many areas. These challenges are particularly burdensome for low-income households that may not have access to a personal vehicle and/or live in jobpoor neighborhoods, as having a personal vehicle may be the only viable way to get to work
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Assessment of the Employment Accessibility Benefits of Shared Autonomous Mobility Services
The goal of this study is to assess and quantify the potential employment accessibility benefits of Shared Autonomous Mobility Service (SAMS) commute modes across a large diverse metropolitan region considering heterogeneity in the working population. To meet this goal, this study employs a welfare-based (i.e. logsum-based) measure of accessibility, obtained via estimating a hierarchical work destination-commute mode choice model. The employment accessibility logsum measure incorporates the spatial distribution of worker residences and employment opportunities, the attributes of the available commute modes, and the characteristics of individual workers. This research further captures heterogeneity of workers using latent class analysis (LCA). The LCA model inputs include the socio-demographic characteristics of workers to subsequently account for different worker clusters valuing different types of employment opportunities differently. The accessibility analysis results indicate: (i) the accessibility benefit differences across latent classes are modest but young workers and low-income workers do see higher benefits than high- and middle-income workers; (ii) there are substantial spatial differences in accessibility benefits with workers living in lower density areas benefiting more than workers living in high-density areas; (iii) nearly all the accessibility benefits come from the SAMS-only mode as opposed to the SAMS+Transit mode; and (iv) the SAMS cost per mile assumption significantly impacts the magnitude of the overall employment accessibility benefits
Infrared Gluon and Ghost Propagators from Lattice QCD. Results from large asymmetric lattices
We report on the infrared limit of the quenched lattice Landau gauge gluon
and ghost propagators as well as the strong coupling constant computed from
large asymmetric lattices. The infrared lattice propagators are compared with
the pure power law solutions from Dyson-Schwinger equations (DSE). For the
gluon propagator, the lattice data is compatible with the DSE solution. The
preferred measured gluon exponent being , favouring a null zero
momentum propagator. The lattice ghost propagator shows finite volume effects
and, for the volumes considered, the propagator does not follow a pure power
law. Furthermore, the strong coupling constant is computed and its infrared
behaviour investigated.Comment: Talk given at QNP06; final version with improved english, accepted
for publication at EPJ
Oscillation dynamics of embolic microspheres in flows with red blood cell suspensions
Dynamic nature of particle motion in blood flow is an important determinant of embolization based cancer therapy. Yet, the manner in which the presence of high volume fraction of red blood cells influences the particle dynamics remains unknown. Here, by investigating the motions of embolic microspheres in pressure-driven flows of red blood cell suspensions through capillaries, we illustrate unique oscillatory trends in particle trajectories, which are not observable in Newtonian fluid flows. Our investigation reveals that such oscillatory behavior essentially manifests when three simultaneous conditions, namely, the Reynolds number beyond a threshold limit, degree of confinement beyond a critical limit, and high hematocrit level, are fulfilled simultaneously. Given that these conditions are extremely relevant to fluid dynamics of blood or polymer flow, the observations reported here bear significant implications on embolization based cancer treatment as well as for complex multiphase fluidics involving particle
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Direct Laser Fabrication of a Gas Turbine Engine Component - Microstructure and Properties - Part I
This paper presents the development of a new technique for the production of abrasive
turbine blade tips by direct laser processing. This superalloy cermet component is an integral part
of the low pressure turbine sealing system in a demonstrator engine. Direct laser fabrication of
this component fiom a bed a loose powder results in significant cost savings and improved
performance over the currently employed production technique. The technology has been
demonstrated by fabricating a prototype lot of 100 blade tips, which will be subjected to an engine
test. This is the first instance of a direct fabrication method applied to the production of functional
engine hardware. This research was funded by the United States Air Force contract F33615-94-
C-2424 titled "Affordable Turbine Blade Tips".Mechanical Engineerin
Gas-Liquid Nucleation in Two Dimensional System
We study the nucleation of the liquid phase from a supersaturated vapor in
two dimensions (2D). Using different Monte Carlo simulation methods, we
calculate the free energy barrier for nucleation, the line tension and also
investigate the size and shape of the critical nucleus. The study is carried
out at an intermediate level of supersaturation(away from the spinodal limit).
In 2D, a large cut-off in the truncation of the Lennard-Jones (LJ) potential is
required to obtain converged results, whereas low cut-off (say, is
generally sufficient in three dimensional studies, where is the LJ
diameter) leads to a substantial error in the values of line tension,
nucleation barrier and characteristics of the critical cluster. It is found
that in 2D, the classical nucleation theory (CNT) fails to provide a reliable
estimate of the free energy barrier. It underestimates the barrier by as much
as 70% at the saturation-ratio S=1.1 (defined as S=P/PC, where PC is the
coexistence pressure at reduced temperature ). Interestingly,
CNT has been found to overestimate the nucleation free energy barrier in three
dimensional (3D)systems near the triple point. In fact, the agreement with CNT
is worse in 2D than in 3D. Moreover, the existing theoretical estimate of the
line tension overestimates the value significantly.Comment: 24 pages, 8 figure
Dark Energy Constraints from Galaxy Cluster Peculiar Velocities
Future multifrequency microwave background experiments with arcminute
resolution and micro-Kelvin temperature sensitivity will be able to detect the
kinetic Sunyaev-Zeldovich (kSZ) effect, providing a way to measure radial
peculiar velocities of massive galaxy clusters. We show that cluster peculiar
velocities have the potential to constrain several dark energy parameters. We
compare three velocity statistics (the distribution of radial velocities, the
mean pairwise streaming velocity, and the velocity correlation function) and
analyze the relative merits of these statistics in constraining dark energy
parameters. Of the three statistics, mean pairwise streaming velocity provides
constraints that are least sensitive to velocity errors: the constraints on
parameters degrades only by a factor of two when the random error is increased
from 100 to 500 km/s. We also compare cluster velocities with other dark energy
probes proposed in the Dark Energy Task Force report. For cluster velocity
measurements with realistic priors, the eventual constraints on the dark energy
density, the dark energy equation of state and its evolution are comparable to
constraints from supernovae measurements, and better than cluster counts and
baryon acoustic oscillations; adding velocity to other dark energy probes
improves constraints on the figure of merit by more than a factor of two. For
upcoming Sunyaev-Zeldovich galaxy cluster surveys, even velocity measurements
with errors as large as 1000 km/s will substantially improve the cosmological
constraints compared to using the cluster number density alone.Comment: 25 pages, 10 figures. Results and conclusions unchanged. Minor
changes to match the accepted version in Physical Review
Transport and bistable kinetics of a Brownian particle in a nonequilibrium environment
A system reservoir model, where the associated reservoir is modulated by an
external colored random force, is proposed to study the transport of an
overdamped Brownian particle in a periodic potential. We then derive the
analytical expression for the average velocity, mobility, and diffusion rate.
The bistable kinetics and escape rate from a metastable state in the overdamped
region are studied consequently. By numerical simulation we then demonstrate
that our analytical escape rate is in good agreement with that of numerical
result.Comment: 10 pages, 2 figures, RevTex4, minor correction
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Geometry Processing for SLS/HIP
SLS/HIP is a new net shape manufacturing method that combines
the strengths of direct selective laser sintering and hot isostatic pressing.
Direct selective laser sintering is a rapid manufacturing technique that can
produce high density metal parts of complex geornetry with an integral,
gas iinpenneable skin. These parts can then be directly post-processed by
containerless HIP. Sophisticated processing of the part geometry is
required to facilitate the desired results from SLS/HIP. This paper presents
geometry processing algorithms being developed for in-situ canning of
SLS/HIP components. This research is funded by DARPA IONR contract
NO00 14-95-C-0 139 titled "Low Cost Metal Processing Using SLS/HIP".Mechanical Engineerin
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