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

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 ${\cal F}^4$-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 $AdS_3$ 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/$\Omega I_4$, which is dual to IIB on $K3$. 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 $P$ and D1 charge $N$, it allows us to test the (4,4) CFTs in the $P < N/4$ and $N < P/4$ 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 $(1,1)$-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 $Z_N$-orbifolds with $(2,2)$ world sheet supersymmetry obtaining also some new ones.Comment: 28 pages, 9 figures not included, available in postscript at reques