Chemical nonlinearities in relating intercontinental ozone pollution to anthropogenic emissions

Model studies typically estimate intercontinental influence on surface ozone by perturbing emissions from a source continent and diagnosing the ozone response in the receptor continent. Since the response to perturbations is non-linear due to chemistry, conclusions drawn from different studies may depend on the magnitude of the applied perturbation. We investigate this issue for intercontinental transport between North America, Europe, and Asia with sensitivity simulations in three global chemical transport models. In each region, we decrease anthropogenic emissions of NOx and nonmethane volatile organic compounds (NMVOCs) by 20% and 100%. We find strong nonlinearity in the response to NOx perturbations outside summer, reflecting transitions in the chemical regime for ozone production. In contrast, we find no significant nonlinearity to NOx perturbations in summer or to NMVOC perturbations year-round. The relative benefit of decreasing NOx vs. NMVOC from current levels to abate intercontinental pollution increases with the magnitude of emission reductions

Generating Cosmological Gaussian Random Fields

We present a generic algorithm for generating Gaussian random initial conditions for cosmological simulations on periodic rectangular lattices. We show that imposing periodic boundary conditions on the real-space correlator and choosing initial conditions by convolving a white noise random field results in a significantly smaller error than the traditional procedure of using the power spectrum. This convolution picture produces exact correlation functions out to separations of L/2, where L is the box size, which is the maximum theoretically allowed. This method also produces tophat sphere fluctuations which are exact at radii $R \le L/4$. It is equivalent to windowing the power spectrum with the simulation volume before discretizing, thus bypassing sparse sampling problems. The mean density perturbation in the volume is no longer constrained to be zero, allowing one to assemble a large simulation using a series of smaller ones. This is especially important for simulations of Lyman-$\alpha$ systems where small boxes with steep power spectra are routinely used. We also present an extension of this procedure which generates exact initial conditions for hierarchical grids at negligible cost.Comment: 12 pages incl 3 figures, accepted in ApJ Letter

Advanced materials development under NASA\u27s Hybrid Thermally Efficient Core (HyTEC) project

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Tectonics of the central Andes

Acquisition of nearly complete coverage of Thematic Mapper data for the central Andes between about 15 to 34 degrees S has stimulated a comprehensive and unprecedented study of the interaction of tectonics and climate in a young and actively developing major continental mountain belt. The current state of the synoptic mapping of key physiographic, tectonic, and climatic indicators of the dynamics of the mountain/climate system are briefly reviewed

Mental health and employment : a bounding approach using panel data

The disability employment gap is an issue of concern in most Western developed economies. This paper provides important empirical evidence on the influence of mental health on the probability of being in employment for prime age workers. We use longitudinal data and recently developed techniques, which use selection on observable characteristics to provide information on selection along unobservable factors, to estimate an unbiased effect of changes in mental health. Our results suggest that selection into mental health is almost entirely based on time-invariant characteristics, and hence fixed effects estimates are unbiased in this context. Our results indicate that transitioning into poor mental health leads to a reduction of 1.6 percentage points in the probability of employment. This is approximately 10 per cent of the raw employment gap. This effect is substantially smaller than the typical instrumental variable estimates, which dominate the literature, and often provide very specific estimates of a local average treatment effect based on an arbitrary exogenous shock. These findings should provide some reassurance to practitioners using fixed effects methods to investigate the impacts of health on work. They should also be useful to policy makers as the average effect of mental health on employment for those whose mental health changes is a highly relevant policy parameter

The McKinsey-Tarski theorem for locally compact ordered spaces

We prove that the modal logic of a crowded locally compact generalized ordered space is S4. This provides a version of the McKinsey–Tarski theorem for generalized ordered spaces. We then utilize this theorem to axiomatize the modal logic of an arbitrary locally compact generalized ordered space

Cosmic Texture from a Broken Global SU(3) Symmetry

We investigate the observable consequences of creating cosmic texture by breaking a global SU(3) symmetry, rather than the SU(2) case which is generally studied. To this end, we study the nonlinear sigma model for a totally broken SU(3) symmetry, and develop a technique for numerically solving the classical field equations. This technique is applied in a cosmological context: the energy of the collapsing SU(3) texture field is used as a gravitational source for the production of perturbations in the primordial fluids of the early universe. From these calculations, we make predictions about the appearance of the anisotropies in the cosmic microwave background radiation (CMBR) which would be present if the large scale structure of the universe was gravitationally seeded by the collapse of SU(3) textures.Comment: 28 pages, latex, 11 figures, submitted to Phys. Rev.