3,058 research outputs found
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Hydrocarbon ratios during PEM-WEST A: A model perspective
A useful application of the hydrocarbon measurements collected during the Pacific Exploratory Mission (PEM-West A) is as markers or indices of atmospheric processing. Traditionally, ratios of particular hydrocarbons have been interpreted as photochemical indices, since much of the effect due to atmospheric transport is assumed to cancel by using ratios. However, an ever increasing body of observatonial and theoretical evidence suggests that turbulent mixing associated with atmospheric transport influences certain hydrocarbon ratios significantly. In this study a three-dimensional mesoscale photochemical model is used to study the interaction of photochemistry and atmospheric mixing on select hydrocarbons. In terms of correlations and functional relationships between various alkanes the model results and PEM-West A hydrocarbon observations share many similar characteristics as well as explainable differences. When the three-dimensional model is applied to inert tracers, hydrocarbon ratios and other relationships exactly follow those expected by simple dilution with model-imposed "background air," and the three-dimensional results for reactive hydrocarbons are quite consistent with a combined influence of photochemistry and simple dilution. Analogous to these model results, relationships between various hydrocarbons collected during the PEM-West A experiment appear to be consistent with this simplified picture of photochemistry and dilution affecting individual air masses. When hydrocarbons are chosen that have negligeble contributions to clean background air, unambiguous determinations of the relative contributions to photochemistry and dilution can be estimated from the hydrocarbon samples. Both the three-dimensional model results and the observations imply an average characteristic lifetime for dilution with background air roughly equivalent to the photochemical lifetime of butane for the western Pacific lower troposphere. Moreover, the dominance of OH as the primary photochemical oxidant downwind of anthropogenic source regions can be inferred from correlations between the highly reactive alkane ratios. By incorporating back-trajectory information within the three-dimensional model analysis, a correspondence between time and a particular hydrocarbon or hydrocarbon ratio can be determined, and the influence of atmospheric mixing or photochemistry can be quantified. Results of the three-dimensional model study are compared and applied to the PEM-West A hydrocarbon dataset, yielding a practical methodology for determining average OH concentrations and atmospheric mixing rates from the hydrocarbon measurements. Aircraft data taken below 2 km during wall flights east of Japan imply a diurnal average OH concentration of ∼3 × 106 cm-3. The characteristic time for dilution with background air is estimated to be ∼2.5 days for the two study areas examined in this work. Copyright 1996 by the American Geophysical Union
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Evidence of convection as a major source of condensation nuclei in the northern midlatitude upper troposphere
The Rich Structure of Gauss-Bonnet Holographic Superconductors
We study fully backreacting, Gauss-Bonnet (GB) holographic superconductors in
5 bulk spacetime dimensions. We explore the system's dependence on the scalar
mass for both positive and negative GB coupling, . We find that when
the mass approaches the Breitenlohner-Freedman (BF) bound and
the effect of backreaction is to increase the
critical temperature, , of the system: the opposite of its effect in the
rest of parameter space. We also find that reducing below zero
increases and that the effect of backreaction is diminished. We study the
zero temperature limit, proving that this system does not permit regular
solutions for a non-trivial, tachyonic scalar field and constrain possible
solutions for fields with positive masses. We investigate singular, zero
temperature solutions in the Einstein limit but find them to be incompatible
with the concept of GB gravity being a perturbative expansion of Einstein
gravity. We study the conductivity of the system, finding that the inclusion of
backreaction hinders the development of poles in the conductivity that are
associated with quasi-normal modes approaching the real axis from elsewhere in
the complex plane.Comment: 26 pages, 11 figures, V3, Added discussion of non-tachyonic scalars,
alterations to figures and tex
Analytic study of Gauss-Bonnet holographic superconductors in Born-Infeld electrodynamics
Using Sturm-Liouville (SL) eigenvalue problem, we investigate several
properties of holographic s-wave superconductors in Gauss-Bonnet gravity with
Born-Infeld electrodynamics in the probe limit. Our analytic scheme has been
found to be in good agreement with the numerical results. From our analysis it
is quite evident that the scalar hair formation at low temperatures is indeed
affected by both the Gauss-Bonnet as well as the Born-Infeld coupling
parameters. We also compute the critical exponent associated with the
condensation near the critical temperature. The value of the critical exponent
thus obtained indeed suggests a universal mean field behavior.Comment: 9 pages, Latex, minor modifications, To appear in JHE
Analytic study of properties of holographic p-wave superconductors
In this paper, we analytically investigate the properties of p-wave
holographic superconductors in -Schwarzschild background by two
approaches, one based on the Sturm-Liouville eigenvalue problem and the other
based on the matching of the solutions to the field equations near the horizon
and near the asymptotic region. The relation between the critical
temperature and the charge density has been obtained and the dependence of the
expectation value of the condensation operator on the temperature has been
found. Our results are in very good agreement with the existing numerical
results. The critical exponent of the condensation also comes out to be 1/2
which is the universal value in the mean field theory.Comment: Latex, To appear in JHE
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Model study of tropospheric trace species distributions during PEM-West A
A three-dimensional mesoscale transport/photochemical model is used to study the transport and photochemical transformation of trace species over eastern Asia and western Pacific for the period from September 20 to October 6, 1991, of the Pacific Exploratory Mission-West A experiment. The influence of emissions from the continental boundary layer that was evident in the observed trace species distributions in the lower troposphere over the ocean is well simulated by the model. In the upper troposphere, species such as O3, NOy (total reactive nitrogen species), and SO2 which have a significant source in the stratosphere are also simulated well in the model, suggesting that the upper tropospheric abundances of these species are strongly influenced by stratospheric fluxes and upper tropospheric sources. In the case of SO2 the stratospheric flux is identified to be mostly from the Mount Pinatubo eruption. Concentrations in the upper troposphere for species such as CO and hydrocarbons, which are emitted in the continental boundary layer and have a sink in the troposphere, are significantly underestimated by the model. Two factors have been identified to contribute significantly to the underestimate: one is emissions upwind of the model domain (eastern Asia and western Pacific); the other is that vertical transport is underestimated in the model. Model results are also grouped by back trajectories to study the contrast between compositions of marine and continental air masses. The model-calculated altitude profiles of trace species in continental and marine air masses are found to be qualitatively consistent with observations. However, the difference in the median values of trace species between continental air and marine air is about twice as large for the observed values as for model results. This suggests that the model underestimates the outflow fluxes of trace species from the Asian continent and the Pacific rim countries to the ocean. Observed altitude profiles for species like CO and hydrocarbons show a negative gradient in continental air and a positive gradient in marine air. A mechanism which may be responsible for the altitude gradients is proposed
Holographic Superconductors with Power-Maxwell field
With the Sturm-Liouville analytical and numerical methods, we investigate the
behaviors of the holographic superconductors by introducing a complex charged
scalar field coupled with a Power-Maxwell field in the background of
-dimensional Schwarzschild AdS black hole. We note that the Power-Maxwell
field takes the special asymptotical solution near boundary which is different
from all known cases. We find that the larger power parameter for the
Power-Maxwell field makes it harder for the scalar hair to be condensated. We
also find that, for different , the critical exponent of the system is still
1/2, which seems to be an universal property for various nonlinear
electrodynamics if the scalar field takes the form of this paper.Comment: 14 pages, 1 figure, and 2 table
Analytical study on holographic superconductors in external magnetic field
We investigate the holographic superconductors immersed in an external
magnetic field by using the analytical approach. We obtain the spatially
dependent condensate solutions in the presence of the magnetism and find
analytically that the upper critical magnetic field satisfies the relation
given in the Ginzburg-Landau theory. We observe analytically the reminiscent of
the Meissner effect where the magnetic field expels the condensate. Extending
to the D-dimensional Gauss-Bonnet AdS black holes, we examine the influence
given by the Gauss-Bonnet coupling on the condensation. Different from the
positive coupling, we find that the negative Gauss-Bonnet coupling enhances the
condensation when the external magnetism is not strong enough.Comment: revised version, to appear in JHE
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