3,223 research outputs found
Evaluation of the public health impacts of traffic congestion: a health risk assessment
Background: Traffic congestion is a significant issue in urban areas in the United States and around the world. Previous analyses have estimated the economic costs of congestion, related to fuel and time wasted, but few have quantified the public health impacts or determined how these impacts compare in magnitude to the economic costs. Moreover, the relative magnitudes of economic and public health impacts of congestion would be expected to vary significantly across urban areas, as a function of road infrastructure, population density, and atmospheric conditions influencing pollutant formation, but this variability has not been explored. Methods: In this study, we evaluate the public health impacts of ambient exposures to fine particulate matter (PM2.5) concentrations associated with a business-as-usual scenario of predicted traffic congestion. We evaluate 83 individual urban areas using traffic demand models to estimate the degree of congestion in each area from 2000 to 2030. We link traffic volume and speed data with the MOBILE6 model to characterize emissions of PM2.5 and particle precursors attributable to congestion, and we use a source-receptor matrix to evaluate the impact of these emissions on ambient PM2.5 concentrations. Marginal concentration changes are related to a concentration-response function for mortality, with a value of statistical life approach used to monetize the impacts. Results: We estimate that the monetized value of PM2.5-related mortality attributable to congestion in these 83 cities in 2000 was approximately 60 billion. In future years, the economic impacts grow (to over 13 billion in 2020 before increasing to $17 billion in 2030, given increasing population and congestion but lower emissions per vehicle. Across cities and years, the public health impacts range from more than an order of magnitude less to in excess of the economic impacts. Conclusions: Our analyses indicate that the public health impacts of congestion may be significant enough in magnitude, at least in some urban areas, to be considered in future evaluations of the benefits of policies to mitigate congestion
Influence of Spin Orbit Coupling in the Iron-Based Superconductors
We report on the influence of spin-orbit coupling (SOC) in the Fe-based
superconductors (FeSCs) via application of circularly-polarized spin and
angle-resolved photoemission spectroscopy. We combine this technique in
representative members of both the Fe-pnictides and Fe-chalcogenides with ab
initio density functional theory and tight-binding calculations to establish an
ubiquitous modification of the electronic structure in these materials imbued
by SOC. The influence of SOC is found to be concentrated on the hole pockets
where the superconducting gap is generally found to be largest. This result
contests descriptions of superconductivity in these materials in terms of pure
spin-singlet eigenstates, raising questions regarding the possible pairing
mechanisms and role of SOC therein.Comment: For supplementary information, see
http://qmlab.ubc.ca/ARPES/PUBLICATIONS/articles.htm
Scholarly Responses to ‘Students’ experiences of Open Distance Learning: A Samoan case study’
Scholarly Responses to ‘Students’ experiences of Open Distance Learning: A Samoan case study
Between-airport heterogeneity in air toxics emissions associated with individual cancer risk thresholds and population risks
Abstract Background Airports represent a complex source type of increasing importance contributing to air toxics risks. Comprehensive atmospheric dispersion models are beyond the scope of many applications, so it would be valuable to rapidly but accurately characterize the risk-relevant exposure implications of emissions at an airport. Methods In this study, we apply a high resolution atmospheric dispersion model (AERMOD) to 32 airports across the United States, focusing on benzene, 1,3-butadiene, and benzo [a]pyrene. We estimate the emission rates required at these airports to exceed a 10-6 lifetime cancer risk for the maximally exposed individual (emission thresholds) and estimate the total population risk at these emission rates. Results The emission thresholds vary by two orders of magnitude across airports, with variability predicted by proximity of populations to the airport and mixing height (R2 = 0.74–0.75 across pollutants). At these emission thresholds, the population risk within 50 km of the airport varies by two orders of magnitude across airports, driven by substantial heterogeneity in total population exposure per unit emissions that is related to population density and uncorrelated with emission thresholds. Conclusion Our findings indicate that site characteristics can be used to accurately predict maximum individual risk and total population risk at a given level of emissions, but that optimizing on one endpoint will be non-optimal for the other.</p
Giant magnetoresistance in quantum magnetic contacts
We present calculations of quantized conductance and magnetoresistance in
nanosize point contacts between two ferromagnetic metals. When conductance is
open for only one conduction electrons spin-projection, the magnitude of
magnetoresistance is limited by the rate of conduction electron spin-reversal
processes. For the case when both spin-channels contribute to the conductance
we analyze the influence of the point contact cross-section asymmetry on the
giant megnetoresistance. Recent experiments on magnetoresistance of magnetic
point contacts are discussed in the framework of the developed theory.Comment: 11 pages, TEX, 2 Figures. Journ. Magn. Magn. Mater. (2002) submitte
Diamagnetic Suppression of Component Magnetic Reconnection at the Magnetopause
We present particle-in-cell simulations of collisionless magnetic
reconnection in a system (like the magnetopause) with a large density asymmetry
across the current layer. In the presence of an ambient component of the
magnetic field perpendicular to the reconnection plane the gradient creates a
diamagnetic drift that advects the X-line with the electron diamagnetic
velocity. When the relative drift between the ions and electrons is of the
order the Alfven speed the large scale outflows from the X-line necessary for
fast reconnection cannot develop and the reconnection is suppressed. We discuss
how these effects vary with both the plasma beta and the shear angle of the
reconnecting field and discuss observational evidence for diamagnetic
stabilization at the magnetopause.Comment: 10 pages, 10 figures; accepted by JGR; agu2001.cls and agu.bst
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The total virtual photoabsorption cross section, deeply virtual Compton scattering and vector-meson production
Based on the two-gluon-exchange dynamical mechanism for deeply inelastic
scattering at low x ~= Q^2/W^2 <<1, we stress the intimate connection between
the total virtual photoabsorption cross section, deeply virtual Compton
scattering and vector-meson electroproduction. A simple expression for the
cross section for deeply virtual Compton scattering is derived. Parameter-free
predictions are obtained for deeply-virtual Compton forward scattering and
vector-meson forward production, once the parameters in the total virtual
photoabsorption cross section are determined in a fit to the experimental data
on deeply inelastic scattering. Our predictions are compared with the
experimental data from HERA.Comment: 31 pages Latex, 10 figures and 1 tabl
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Guiding Sustainable Development in East Port of Spain
As one of IDB’s newest corporate initiatives, the Emerging and Sustainable Cities Initiative (ESCI)ƒ is a technical assistance program that helps intermediate cities in Latin America and the Caribbean identify, prioritize, and structure projects to improve their environmental, urban, and fiscal sustainability, and improve governance. Port of Spain is one of the pilot projects of ESCI. In that context, this Columbia University’s Planning Studio in the Graduate School of Architecture, Planning and Preservation was invited as academic consultants to evaluate the socio-economic viability of some IDB’s ESCI proposals in East Port of Spain, specifically examining: 1) Institutional coordination for improved urban planning; 2) Community engagement in planning; 3) Cultural preservation planning; 4) River revitalization and the creation of a linear park; and 5) An aerial cable car project. We restructured the original five requests presented to us into assessments of three physical interventions complemented by assessments of the broader goals of improved institutional coordination and community engagement, two process-oriented focus areas that ought to support the three urban investment projects. After a semester-long study in spring 2014 and a field work conducted in East Port of Spain in March 2014, we finally offer a reframing of the conceptualization of the three physical interventions and a series of phased proposals. They synergistically support the preservation of cultural heritage, including heritage walks; a series of connected pocket parks lining and permeating the East Dry Rive; and an integrated, multi-modal transit system supported by a data gathering process; along with strategies for enhancing the broader goals of institutional coordination and community engagement. Our goal was to prioritize the residents of East Port of Spain in the development of planning initiatives. In each of the project areas, we are recommending a process rather than specific design recommendations, because we feel it is critical that the community members should be the ones that drive these interventions
The influence of location, source, and emission type in estimates of the human health benefits of reducing a ton of air pollution
The benefit per ton (/ton estimate. We employ a reduced-form air quality model to predict changes in ambient PM2.5 resulting from an array of emission control scenarios affecting 12 different combinations of sources emitting carbonaceous particles, NOx, SOx, NH3, and volatile organic compounds. We perform this modeling for each of nine urban areas and one nationwide area. Upon modeling the air quality change, we then divide the total monetized health benefits by the PM2.5 precursor emission reductions to generate /ton estimates exhibit the greatest variability across certain precursors and sources such as area source SOx, point source SOx, and mobile source NH3. Certain /ton across all locations
Ionic and electronic properties of the topological insulator BiTeSe investigated using -detected nuclear magnetic relaxation and resonance of Li
We report measurements on the high temperature ionic and low temperature
electronic properties of the 3D topological insulator BiTeSe using
ion-implanted Li -detected nuclear magnetic relaxation and
resonance. With implantation energies in the range 5-28 keV, the probes
penetrate beyond the expected range of the topological surface state, but are
still within 250 nm of the surface. At temperatures above ~150 K, spin-lattice
relaxation measurements reveal isolated Li diffusion with an
activation energy eV and attempt frequency s for atomic site-to-site hopping. At lower
temperature, we find a linear Korringa-like relaxation mechanism with a field
dependent slope and intercept, which is accompanied by an anomalous field
dependence to the resonance shift. We suggest that these may be related to a
strong contribution from orbital currents or the magnetic freezeout of charge
carriers in this heavily compensated semiconductor, but that conventional
theories are unable to account for the extent of the field dependence.
Conventional NMR of the stable host nuclei may help elucidate their origin.Comment: 17 pages, 12 figures, submitted to Phys. Rev.
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