9,719 research outputs found
The fate of NOx emissions due to nocturnal oxidation at high latitudes: 1-D simulations and sensitivity experiments
The fate of nitrogen oxide pollution during high-latitude winter is controlled by reactions of dinitrogen pentoxide (N2O5) and is highly affected by the competition between heterogeneous atmospheric reactions and deposition to the snowpack. MISTRA (MIcrophysical STRAtus), a 1-D photochemical model, simulated an urban pollution plume from Fairbanks, Alaska to investigate this competition of N2O5 reactions and explore sensitivity to model parameters. It was found that dry deposition of N2O5 made up a significant fraction of N2O5 loss near the snowpack, but reactions on aerosol particles dominated loss of N2O5 over the integrated atmospheric column. Sensitivity experiments found the fate of NOx emissions were most sensitive to NO emission flux, photolysis rates, and ambient temperature. The results indicate a strong sensitivity to urban area density, season and clouds, and temperature, implying a strong sensitivity of the results to urban planning and climate change. Results suggest that secondary formation of particulate (PM2.5) nitrate in the Fairbanks downtown area does not contribute significant mass to the total PM2.5 concentration, but appreciable amounts are formed downwind of downtown due to nocturnal NOx oxidation and subsequent reaction with ammonia on aerosol particles
Fractal Cosmology in an Open Universe
The clustering of galaxies is well characterized by fractal properties, with
the presence of an eventual cross-over to homogeneity still a matter of
considerable debate. In this letter we discuss the cosmological implications of
a fractal distribution of matter, with a possible cross-over to homogeneity at
an undetermined scale R_{homo}. Contrary to what is generally assumed, we show
that, even when R_{homo} -> \infty, this possibility can be treated
consistently within the framework of the expanding universe solutions of
Friedmann. The fractal is a perturbation to an open cosmology in which the
leading homogeneous component is the cosmic background radiation (CBR). This
cosmology, inspired by the observed galaxy distributions, provides a simple
explanation for the recent data which indicate the absence of deceleration in
the expansion (q_o \approx 0). Correspondingly the `age problem' is also
resolved. Further we show that the model can be extended back from the
curvature dominated arbitrarily deep into the radiation dominated era, and we
discuss qualitatively the modifications to the physics of the anisotropy of the
CBR, nucleosynthesis and structure formation.Comment: 7 pages, no figures, to appear in Europhysics Letter
Measuring the Effects of Childbearing on Labor Market Outcomes
Decisions about childbearing and market work are significantly interrelated. Although there are many estimates of the effects of fertility on labor supply, few of them have adequately addressed the problems of simultaneity inherent in these choices. In our research we use exogenous variations in fertility due to twin births to measure the impact of an unplanned child on labor supply and earnings. We contrast these results to those for closely-spaced births (one year or less). We consider effects for married and unmarried mothers separately, and for married fathers. We discuss the implications of these measurements for estimating the magnitude of the rise in female labor supply and earnings as birthrates decline.fertility, labor supply, earnings
A study of logarithmic corrections and universal amplitude ratios in the two-dimensional 4-state Potts model
Monte Carlo (MC) and series expansion (SE) data for the energy, specific
heat, magnetization and susceptibility of the two-dimensional 4-state Potts
model in the vicinity of the critical point are analysed. The role of
logarithmic corrections is discussed and an approach is proposed in order to
account numerically for these corrections in the determination of critical
amplitudes. Accurate estimates of universal amplitude ratios ,
, and are given, which arouse
new questions with respect to previous works
A statistical mechanical description of metastable states and hysteresis in the 3D soft-spin random-field model at T=0
We present a formalism for computing the complexity of metastable states and
the zero-temperature magnetic hysteresis loop in the soft-spin random-field
model in finite dimensions. The complexity is obtained as the Legendre
transform of the free-energy associated to a certain action in replica space
and the hysteresis loop above the critical disorder is defined as the curve in
the field-magnetization plane where the complexity vanishes; the nonequilibrium
magnetization is therefore obtained without having to follow the dynamical
evolution. We use approximations borrowed from condensed-matter theory and
based on assumptions on the structure of the direct correlation functions (or
proper vertices), such as a local approximation for the self-energies, to
calculate the hysteresis loop in three dimensions, the correlation functions
along the loop, and the second moment of the avalanche-size distribution.Comment: 28 pages, 12 figure
Electroweak Baryogenesis with dimension-6 Higgs interactions
We present the computation of the baryon asymmetry in the SM amplified by
dimension-6 Higgs interactions using the WKB approximation. Analyzing the
one-loop potential it turns out that the phase transition is strongly first
order in a wide range of the parameters. It is ensured not to wash out the net
baryon number gained previously even for Higgs masses up to at least 170 GeV.
In addition dimension-6 operators induce new sources of CP violation. Novel
source terms which enhance the generated baryon asymmetry emerge in the
transport equations. This model predicts a baryon to entropy ratio close to the
observed value for a large part of the parameter space.Comment: 10 pages, 4 figures, Talk given at the 8th International Moscow
School of Physic
Discrete Matter, Far Fields, and Dark Matter
We show that in cosmology the gravitational action of the far away matter has
quite relevant effects, if retardation of the forces and discreteness of matter
(with its spatial correlation) are taken into account. The expansion rate is
found to be determined by the density of the far away matter, i.e., by the
density of matter at remote times. This leads to the introduction of an
effective density, which has to be five times larger than the present one, if
the present expansion rate is to be accounted for. The force per unit mass on a
test particle is found to be of the order of 0.2cH_0. The corresponding
contribution to the virial of the forces for a cluster of galaxies is also
discussed, and it is shown that it fits the observations if a decorrelation
property of the forces at two separated points is assumed. So it appears that
the gravitational effects of the far away matter may have the same order of
magnitude as the corresponding local effects of dark matter.Comment: 16 pages, 1 figure. LaTex documen
Dynamic heterogeneities in critical coarsening: Exact results for correlation and response fluctuations in finite-sized spherical models
We study dynamic heterogeneities in the out-of-equilibrium coarsening
dynamics of the spherical ferromagnet after a quench from infinite temperature
to its critical point. A standard way of probing such heterogeneities is by
monitoring the fluctuations of correlation and susceptibility, coarse-grained
over mesoscopic regions. We discuss how to define fluctuating coarse-grained
correlations (C) and susceptibilities (Chi) in models where no quenched
disorder is present. Our focus for the spherical model is on coarse-graining
over the whole volume of spins, which requires accounting for N^{-1/2}
non-Gaussian fluctuations of the spin. The latter are treated as a perturbation
about the leading order Gaussian statistics. We obtain exact results for these
quantities, which enable us to characterise the joint distribution of C and Chi
fluctuations. We find that this distribution is qualitatively different, even
for equilibrium above criticality, from the spin-glass scenario where C and Chi
fluctuations are linked in a manner akin to the fluctuation-dissipation
relation between the average C and Chi. Our results show that coarsening at
criticality is clearly heterogeneous for d>4 and suggest that, as in other
glassy systems, there is a well-defined timescale on which fluctuations across
thermal histories are largest. Surprisingly, however, neither this timescale
nor the amplitude of the heterogeneities increase with the age of the system,
as would be expected from the growing correlation length. For d<4, the strength
of the fluctuations varies on a timescale proportional to the age of the
system; the corresponding amplitude also grows with age, but does not scale
with the correlation volume as might have been expected naively.Comment: 39 pages, 9 figures, version for publication in J. Stat. Mech.
Shortened by cutting all technical details in section 6, with minor
corrections elsewher
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