11,173 research outputs found
The demand for urban transport: An application of discrete choice model for Cadiz
The study of the demand for transport has among others applications, the valuation of travel time saving that is a very important question in cost-benefit analysis, and to adopt transport policy tools. Since McFadden developed a discrete choice model for travel demand, it has usually been the application of this model to study the individual behaviour when he has to choice among transport modes. Citizens of big cities have to face traffic congestion; pollution, wasted time in travels and fuel, noise, stress and accidents are the costs imposed by congestion to society, elements that reduce the quality of life in cities. Public transport is a real alternative to private transport that is socially less expensive, for this reason this paper tries to forecast travel demand for public transport in Cadiz when travelling have to choice between public or private transport, using a discrete choice model. The results of this analysis (travel demand, value of time, elasticities) can be used to design transport policies that could reduce congestion.
Paving streets for the poor: Experimental analysis of infrastructure effects
This is the final version. Available from MIT Press via the DOI in this recordWe provide the first experimental estimation of the effects of the supply of publicly financed urban infrastructure on property values. Using random allocation of first-time street asphalting of residential streets located in peripheral neighborhoods in Mexico, we show that within two years of the intervention, households are able to transform their increased property wealth into significantly larger rates of vehicle ownership, household appliances, and home improvements. Increased consumption is made possible by both credit use and less saving. A cost-benefit analysis indicates that the valuation of street asphalting as capitalized into property values is about as large as construction costs.Princeton UniversityPrinceton Woodrow Wilson ScholarsPrinceton Industrial Relations SectionPrinceton Research Program in Development StudiesRobert Wood Johnson Scholars in Health Policy Research ProgramBerkeley EconomicsUniversitat d’AlacantLincoln Institute of Land PolicySpanish Ministry of Science and Innovatio
Non-Abelian Chern-Simons-Higgs vortices with a quartic potential
We have constructed numerically non-Abelian vortices in an SU(2)
Chern-Simons-Higgs theory with a quartic Higgs potential. We have analyzed
these solutions in detail by means of improved numerical codes and found some
unexpected features we did not find when a sixth-order Higgs potential was
used. The generic non-Abelian solutions have been generated by using their
corresponding Abelian counterparts as initial guess. Typically, the energy of
the non-Abelian solutions is lower than that of the corresponding Abelian one
(except in certain regions of the parameter space). Regarding the angular
momentum, the Abelian solutions possess the maximal value, although there exist
non-Abelian solutions which reach that maximal value too. In order to classify
the solutions it is useful to consider the non-Abelian solutions with
asymptotically vanishing component of the gauge potential, which may be
labelled by an integer number . For vortex number and above, we have
found uniqueness violation: two different non-Abelian solutions with all the
global charges equal. Finally, we have investigated the limit of infinity Higgs
self-coupling parameter and found a piecewise Regge-like relation between the
energy and the angular momentum.Comment: 9 pages, 13 figure
Estudio comparativo de equipos fijos de pedestal y su aplicación en la detección del tráfico incontrolado de material radiactivo en aeropuertos
En este trabajo se analiza la respuesta de tres equipos comerciales, diseñados para detectar el tráfico ilícito o el desplazamiento involuntario de material radiactivo en aeropuertos cuando es transportado por los pasajeros. Se han comparado tres instrumentos fijos de pedestal: el equipo APM de Bicron, el equipo GR-606 de Exploranium y el equipo FHT-1372 de Thermo Eberline. En esta evaluación inicial, realizada en el Laboratorio de Ingeniería Nuclear de la Escuela de Caminos, Canales y Puertos, se observó que el equipo FHT-1372 presentó una respuesta de detección más rápida, sensible y permitió la medida de tasa de dosis total y tasa de dosis artificial. Este equipo fue instalado en la salida de la aduana de pasajeros del aeropuerto internacional de Barajas durante un periodo operativo de 108 días en el año 2002 y pasaron un total de 1.339.931 personas. Este periodo se dividió en 5 sesiones para poder establecer los niveles de investigación adecuados para detectar una posible incidencia de material radiactivo, que finalmente se fijaron en 110 nSv/h para la tasa de dosis total y 25 nSv/h para la tasa de dosis artificial. Durante dicho periodo se detectaron 39 posibles incidencias por encima del límite de investigación establecido para las diferentes sesiones, 5 de ellas con un valor 10 veces superior al fondo ambiental de la sala donde se instaló el equipo (alrededor de 90 nSv/h) y ninguna superó el nivel de 100 μSv/h a 1 m de distancia que la Organización Internacional de la Energía Atómica (OIEA) establece como límite para el transporte lícito de material radiactivo
Cluster detection from surface-brightness fluctuations in SDSS data
Galaxy clusters can be detected as surface brightness enhancements in
smoothed optical surveys. This method does not require individual galaxies to
be identifiable, and enables clusters to be detected out to surprisingly high
redshifts, as recently demonstrated by the Las Campanas Distant Cluster Survey
(LCDCS). Here, we investigate redshift limits for cluster detection in the
Sloan Digital Sky Survey (SDSS). Calibrating assumptions about the surface
brightness profile, the mass-to-light ratio, and the spectral energy
distribution of galaxy clusters using available observational data, we show
that it should be possible to detect galaxy groups out to redshifts of ~0.5,
and massive galaxy clusters out to redshifts of ~1.2 in summed r'+i'+z' SDSS
data. Redshift estimates can be derived from the SDSS magnitudes of brightest
cluster members out to redshifts near unity. Over the area of sky it covers,
SDSS should find >~98% of the clusters detectable by the Planck satellite
through the thermal Sunyaev-Zel'dovich effect. The few Planck clusters not
detected in SDSS will almost all be at z>~1.2.Comment: 7 pages, submitted to Astronomy & Astrophysic
Negative ions formed in N<sub>2</sub>/CH<sub>4</sub>/Ar discharge – a simulation of Titan's atmosphere chemistry
The formation of negative ions produced in a negative point-to-plane corona discharge fed by a Ar/N2//CH4/ gas mixture has been studied using mass spectrometry. The measurements were carried out in flowing regime at ambient temperature and a reduced pressure of 460 mbar. The CN ? anion has been found to be the most dominant negative ion in the discharge and is believed to be the precursor of heavier negative ions such as C3/N ? and C5/N ? . The most likely pathway for the formation of such molecular anions is H-loss dissociative electron attachment to HCN, H3/CN and H5/CN formed in the discharge. These same anions have been detected in Titan's atmosphere and the present experiments may provide some novel insights into the chemical and physical mechanisms prevalent in Titan's atmosphere and hence assist in the interpretation of results from the Cassini Huygens space mission
Dependence on the Identification of the Scale Energy Parameter Q 2 in the Quark Distribution Functions for a DIS Production of Za
We discuss the Z-production in a DIS (Deep Inelastic Scattering) process e + p → e + Z + X using the Parton Model, within the context of the Standard Model. In contrast with deep inelastic eP-scattering (e + p → e + X), where the choice of Q2, as the transferred momentum squared, is unambiguous; whereas in the case of boson production , the transferred momentum squared, at quark level, depends on the reaction mechanism (where is the EW interaction taking place). We suggest a proposal based on kinematics of the process considered and the usual criterion for Q2 , which leads to a simple and practical prescription to calculate Z-production via ep-DIS. We also introduce different options in order o perform the convolution of the parton distribution functions (PDFs) and the scattering amplitude of he quark processes. Our aim in this work is to analyze and show how large could be the dependence of the total cross section rates on different possible prescriptions used for the identification of the scale energy parameter Q2 . We present results for the total cross section as a function of the total energy √s of the system ep, in the range 300 <√s ≤ 1300 Ge
Detection of vortex tubes in solar granulation from observations with Sunrise
We have investigated a time series of continuum intensity maps and
corresponding Dopplergrams of granulation in a very quiet solar region at the
disk center, recorded with the Imaging Magnetograph eXperiment (IMaX) on board
the balloon-borne solar observatory Sunrise. We find that granules frequently
show substructure in the form of lanes composed of a leading bright rim and a
trailing dark edge, which move together from the boundary of a granule into the
granule itself. We find strikingly similar events in synthesized intensity maps
from an ab initio numerical simulation of solar surface convection. From cross
sections through the computational domain of the simulation, we conclude that
these `granular lanes' are the visible signature of (horizontally oriented)
vortex tubes. The characteristic optical appearance of vortex tubes at the
solar surface is explained. We propose that the observed vortex tubes may
represent only the large-scale end of a hierarchy of vortex tubes existing near
the solar surface.Comment: Astrophysical Journal Letters: Sunrise Special Issue, reveived 2010
June 16; accepted 2010 August
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