7,961 research outputs found
The Impact of Delhi's CNG Program on Air Quality
This paper estimates the impact on Delhi’s air quality of a number of policy measures recently implemented in the city to curb air pollution using monthly time-series data from 1990 to 2005. The best known of these measures is the court-mandated conversion of all commercial passenger vehicles—buses, three-wheelers, and taxis—to compressed natural gas (CNG). Broadly, the results point to the success of a number of policies implemented in Delhi but also to a number of areas of growing concern. For example, the results suggest that the conversion of buses from diesel to CNG has helped to reduce PM10, CO, and SO2 concentrations in the city and has not, contrary to conventional wisdom, led to the recent increase in NO2. At the same time, however, the conversion of three-wheelers from petrol to CNG has not had the same benefit, possibly because of poor technology. Another policy measure that appears to have had a positive impact on air quality is the reduction in the sulfur content of diesel and petrol. This has led to a decrease in SO2 levels and, because of conversion of SO2 to sulfates (a fine particle), a decrease in PM10 concentrations. Some of these gains from fuel switching and fuel-quality improvements are, however, being negated by the increase in the proportion of diesel-fueled cars, which is leading to an increase in PM10 and NO2 levels, and by the sheer increase in the number of vehicles.air pollution, compressed natural gas, low-sulfur diesel, diesel-fueled cars, Delhi
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Examining the association of changes in minimum wage with health across race/ethnicity and gender in the United States.
BackgroundThe minimum wage creates both winners (through wage increases) and-potentially-losers (through job losses). Research on the health effects of minimum wage policies has been sparse, particularly across gender and among racial/ethnic minorities. We test the impact of minimum wage increases on health outcomes, health behaviors and access to healthcare across gender and race/ethnicity.MethodsUsing 1993-2014 data from the Behavioral Risk Factor Surveillance System, variables for access to healthcare (insurance coverage, missed care due to cost), health behavior (exercise, fruit, vegetable and alcohol consumption) and health outcomes (self-reported fair/poor health, hypertension, poor physical health days, poor mental health days, unhealthy days) were regressed on the product of the ratio of the 1-year lagged minimum wage to the state median wage and the national median wage, using Linear Probability Models and Poisson Regression Models for dichotomous and count outcomes, respectively. Regressions (total population, gender-stratified, race/ethnicity stratified (white, black, Latino), gender/race/ethnicity stratified and total population with interaction terms for race/ethnicity/gender) controlled for state-level ecologic variables, individual-level demographics and fixed-effects (state and year). Results were adjusted for complex survey design and Bonferroni corrections were applied to p-values such that the level of statistical significance for a given outcome category was 0.05 divided by the number of outcomes in that category.ResultsMinimum wage increases were positively associated with access to care among white men, black women and Latino women but negatively associated with access to care among white women and black men. With respect to dietary quality, minimum wage increases were associated with improvements, mixed results and negative impacts among white, Latino and black men, respectively. With respect to health outcomes, minimum wage increases were associated with positive, negative and mixed impacts among white women, white men and Latino men, respectively.ConclusionsWhile there is enthusiasm for minimum wage increases in the public health community, such increases may have to be paired with deliberate strategies to protect workers that might be vulnerable to economic dislocation. Such strategies may include more robust unemployment insurance or increased access to job training for displaced workers
On the perturbative corrections around D-string instantons
We study -threshold corrections in an eight dimensional S-dual
pair of string theories, as a prototype of dual string vacua with sixteen
supercharges. We show that the orbifold CFT description of D-string instantons
gives rise to a perturbative expansion similar to the one appearing on the
fundamental string side. By an explicit calculation, using the Nambu-Goto
action in the static gauge, we show that the first subleading term agrees
precisely on the two sides. We then give a general argument to show that the
agreement extends to all orders.Comment: 12 page
AdS/CFT correspondence and D1/D5 systems in theories with 16 supercharges
We discuss spectra of supergravities, arising in the near horizon
geometry of D1/D5 systems in orbifolds/orientifolds of type IIB theory with 16
supercharges. These include models studied in a recent paper (hep-th/0012118),
where the group action involves also a shift along a transversal circle, as
well as IIB/, which is dual to IIB on . After appropriate
assignements of the orbifold group eigenvalues and degrees to the supergravity
single particle spectrum, we compute the supergravity elliptic genus and find
agreement, in the expected regime of validity, with the elliptic genus obtained
using U-duality map from (4,4) CFTs of U-dual backgrounds. Since this U-duality
involves the exchange of KK momentum and D1 charge , it allows us to
test the (4,4) CFTs in the and regimes by two different
supergravity duals.Comment: 28 pages, no figure
Are Coronae of Magnetically Active Stars Heated by Flares? III. Analytical Distribution of Superimposed Flares
(abridged) We study the hypothesis that observed X-ray/extreme ultraviolet
emission from coronae of magnetically active stars is entirely (or to a large
part) due to the superposition of flares, using an analytic approach to
determine the amplitude distribution of flares in light curves. The
flare-heating hypothesis is motivated by time series that show continuous
variability suggesting the presence of a large number of superimposed flares
with similar rise and decay time scales. We rigorously relate the amplitude
distribution of stellar flares to the observed histograms of binned counts and
photon waiting times, under the assumption that the flares occur at random and
have similar shapes. Applying these results to EUVE/DS observations of the
flaring star AD Leo, we find that the flare amplitude distribution can be
represented by a truncated power law with a power law index of 2.3 +/- 0.1. Our
analytical results agree with existing Monte Carlo results of Kashyap et al.
(2002) and Guedel et al. (2003). The method is applicable to a wide range of
further stochastically bursting astrophysical sources such as cataclysmic
variables, Gamma Ray Burst substructures, X-ray binaries, and spatially
resolved observations of solar flares.Comment: accepted for publication in Ap
Kaluza-Klein States versus Winding States: Can Both Be Above the String Scale?
When closed strings propagate in extra compactified dimensions, a rich
spectrum of Kaluza-Klein states and winding states emerges. Since the masses of
Kaluza-Klein states and winding states play a reciprocal role, it is often
believed that either the lightest Kaluza-Klein states or the lightest winding
states must be at or below the string scale. In this paper, we demonstrate that
this conclusion is no longer true for compactifications with non-trivial shape
moduli. Specifically, we demonstrate that toroidal compactifications exist for
which all Kaluza-Klein states as well as all winding states are heavier than
the string scale. This observation could have important phenomenological
implications for theories with reduced string scales, suggesting that it is
possible to cross the string scale without detecting any states associated with
spacetime compactification.Comment: 8 pages, LaTeX, no figure
Noncommutative Geometry and Spacetime Gauge Symmetries of String Theory
We illustrate the various ways in which the algebraic framework of
noncommutative geometry naturally captures the short-distance spacetime
properties of string theory. We describe the noncommutative spacetime
constructed from a vertex operator algebra and show that its algebraic
properties bear a striking resemblence to some structures appearing in M
Theory, such as the noncommutative torus. We classify the inner automorphisms
of the space and show how they naturally imply the conventional duality
symmetries of the quantum geometry of spacetime. We examine the problem of
constructing a universal gauge group which overlies all of the dynamical
symmetries of the string spacetime. We also describe some aspects of toroidal
compactifications with a light-like coordinate and show how certain generalized
Kac-Moody symmetries, such as the Monster sporadic group, arise as gauge
symmetries of the resulting spacetime and of superstring theories.Comment: 17 pages LaTeX; Invited paper to appear in the special issue of the
Journal of Chaos, Solitons and Fractals on "Superstrings, M, F, S, ...
Theory" (M.S. El Naschie and C. Castro, editors
Comment on the Generation Number in Orbifold Compactifications
There has been some confusion concerning the number of -forms in
orbifold compactifications of the heterotic string in numerous publications. In
this note we point out the relevance of the underlying torus lattice on this
number. We answer the question when different lattices mimic the same physics
and when this is not the case. As a byproduct we classify all symmetric
-orbifolds with world sheet supersymmetry obtaining also some new
ones.Comment: 28 pages, 9 figures not included, available in postscript at reques
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