775 research outputs found
A new atmospheric aerosol phase equilibrium model (UHAERO): organic systems
In atmospheric aerosols, water and volatile inorganic and organic species are distributed between the gas and aerosol phases in accordance with thermodynamic equilibrium. Within an atmospheric particle, liquid and solid phases can exist at equilibrium. Models exist for computation of phase equilibria for inorganic/water mixtures typical of atmospheric aerosols; when organic species are present, the phase equilibrium problem is complicated by organic/water interactions as well as the potentially large number of organic species. We present here an extension of the UHAERO inorganic thermodynamic model (Amundson et al., 2006c) to organic/water systems. Phase diagrams for a number of model organic/water systems characteristic of both primary and secondary organic aerosols are computed. Also calculated are inorganic/organic/water phase diagrams that show the effect of organics on inorganic deliquescence behavior. The effect of the choice of activity coefficient model for organics on the computed phase equilibria is explored
A new inorganic atmospheric aerosol phase equilibrium model (UHAERO)
A variety of thermodynamic models have been developed to predict inorganic gas-aerosol equilibrium. To achieve computational efficiency a number of the models rely on a priori specification of the phases present in certain relative humidity regimes. Presented here is a new computational model, named UHAERO, that is both efficient and rigorously computes phase behavior without any a priori specification. The computational implementation is based on minimization of the Gibbs free energy using a primal-dual method, coupled to a Newton iteration. The mathematical details of the solution are given elsewhere. The model computes deliquescence behavior without any a priori specification of the relative humidities of deliquescence. Also included in the model is a formulation based on classical theory of nucleation kinetics that predicts crystallization behavior. Detailed phase diagrams of the sulfate/nitrate/ammonium/water system are presented as a function of relative humidity at 298.15 K over the complete space of composition
A computationally efficient inorganic atmospheric aerosol phase equilibrium model (UHAERO)
A variety of thermodynamic models have been developed to predict inorganic gas-aerosol equilibrium. To achieve computational efficiency a number of the models rely on a priori specification of the phases present in certain relative humidity regimes. Presented here is a new computational model, named UHAERO, that is both efficient and rigorously computes phase behavior without any a priori specification. The computational implementation is based on minimization of the Gibbs free energy using a primal-dual method, coupled to a Newton iteration. The mathematical details of the solution are given elsewhere. The model also computes deliquescence and crystallization behavior without any a priori specification of the relative humidities of deliquescence or crystallization. Detailed phase diagrams of the sulfate/nitrate/ammonium/water system are presented as a function of relative humidity at 298.15 K over the complete space of composition
Radiative Neutralino Decay in Supersymmetric Models
The radiative decay Z2-> Z1 gamma proceeds at the one-loop level in the MSSM.
It can be the dominant decay mode for the second lightest neutralino Z2 in
certain regions of parameter space of supersymmetric models, where either a
dynamical and/or kinematic enhancement of the branching fraction occurs. We
perform an updated numerical study of this decay mode in both the minimal
supergravity model (mSUGRA) and in the more general MSSM framework. In mSUGRA,
the largest rates are found in the ``focus point'' region, where the mu
parameter becomes small, and the lightest neutralinos become higgsino-like; in
this case, radiative branching fraction can reach the 1% level. Our MSSM
analysis includes a scan over independent positive and negative gaugino masses.
We show branching fractions can reach the 10-100% level even for large values
of the parameter tan(beta). These regions of parameter space are realized in
supergravity models with non-universal gaugino masses. Measurement of the
radiative neutralino branching fraction may help pin down underlying parameters
of the fundamental supersymmetric model.Comment: 19 page JHEP file with 8 PS figures; previous version contained
figure misplacemen
A phase equilibrium model for atmospheric aerosols containing inorganic electrolytes and organic compounds (UHAERO), with application to dicarboxylic acids
Computation of phase and chemical equilibria of water-organic-inorganic mixtures is of significant interest in atmospheric aerosol modeling. A new version of the phase partitioning model, named UHAERO, is presented here, which allows one to compute the phase behavior for atmospheric aerosols containing inorganic electrolytes and organic compounds. The computational implementation of the model is based on standard minimization of the Gibbs free energy using a primal-dual method, coupled to a Newton iteration. Water uptake and deliquescence properties of mixtures of aqueous solutions of salts and dicarboxylic acids, including oxalic, malonic, succinic, glutaric, maleic, malic, or methyl succinic acids, are based on a hybrid thermodynamic approach for the modeling of activity coefficients (Clegg and Seinfeld, 2006a, 2006b). UHAERO currently considers ammonium salts and the neutralization of dicarboxylic acids and sulfuric acid. Phase diagrams for sulfate/ammonium/water/dicarboxylic acid systems are presented as a function of relative humidity at 298.15 K over the complete space of compositions
Testing a glacial erosion rule using hang heights of hanging valleys, Jasper National Park, Alberta, Canada
Acknowledgments. The glaciology group at the University of Alaska Fairbanks provided constructive feedback. Comments from R. S.
Anderson, B. Hallet, B. Hubbard, J. Tomkin, and S. Tulaczyk improved the manuscript.In most models of glacial erosion, glacier sliding velocity is hypothesized to control rates of bedrock erosion. If this hypothesis is correct, then the elevation difference between hanging and trunk valley floors, the hang height, should be dictated by the relative sliding velocities of the glaciers that occupied these valleys. By considering sliding velocity to be proportional to balance velocity and using mass continuity, hang height is expressed in terms of glacier catchment areas, slopes, and widths, which can be estimated for past glaciers from the morphology of glacial valleys. These parameters were estimated for
46 hanging valleys and their trunk valleys in three adjacent regions of Jasper National Park. The variability in valley morphology can account for 55–85% of the hang height variability if erosion rate scales with balance velocity raised to a power of 1/3. This correspondence is in spite of spatial variations in glaciation duration, snow accumulation rates, and other variables that likely affected hang heights but cannot be readily estimated and so are not included in our formulation. Thus it appears that balance velocity, and by extension, sliding velocity if the two are proportional, may be a reasonable control variable for assessing erosion rate.Ye
Radiative Leptonic Decays of Heavy Mesons
We compute the photon spectrum and the rate for the decays These photonic modes constitute a potentially large background
for the purely leptonic decays which are used to extract the heavy meson decay
constants. While the rate for D\to l\n\g is small, the radiative decay in the
meson case could be of comparable magnitude or even larger than B\to\m\n.
This would affect the determination of if the channel cannot be
identified. We obtain theoretical estimates for the photonic rates and disscuss
their possible experimental implications.Comment: 12 pages, RevTex, 3 uuencoded figures include
Decay constants, semi-leptonic and non-leptonic decays in a Bethe-Salpeter Model
We evaluate the decay constants for the B and mesons and the form factors
for the semileptonic decays of the B meson to and mesons in a
Bethe-Salpeter model. From data we extract from and from decays. The form factors are then used to obtain non-leptonic
decay partial widths for and in the
factorization approximation.Comment: 15 Pages, 3 Postscript figures (available also from [email protected]
Dynamic jamming of iceberg-choked fjords
We investigate the dynamics of ice mélange by analyzing rapid motion recorded by a time-lapse camera and terrestrial radar during several calving events that occurred at Jakobshavn Isbræ, Greenland. During calving events (1) the kinetic energy of the ice mélange is 2 orders of magnitude smaller than the total energy released during the events, (2) a jamming front propagates through the ice mélange at a rate that is an order of magnitude faster than the motion of individual icebergs, (3) the ice mélange undergoes initial compaction followed by slow relaxation and extension, and (4) motion of the ice mélange gradually decays before coming to an abrupt halt. These observations indicate that the ice mélange experiences widespread jamming during calving events and is always close to being in a jammed state during periods of terminus quiescence. We therefore suspect that local jamming influences longer timescale ice mélange dynamics and stress transmission
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Radiation-Induced Bystander Signaling Pathways in Human Fibroblasts: A Role for Interleukin-33 in the Signal Transmission
The main goal of this study is to elucidate the mechanisms of the signal transmission for radiation-induced bystander response. The NF-κB-dependent gene expression of IL8, IL6, PTGS2/COX2, TNF and IL33 in directly irradiated human skin fibroblasts produced the cytokines and prostaglandin E2 (PGE2) with autocrine/paracrine functions, which further activated signaling pathways and induced NF-κB-dependent gene expression in bystander cells. As a result, bystander cells also started expression and production of interleukin-8, interleukin-6, COX-2-generated PGE2 and interleukin-33 (IL-33) followed by autocrine/paracrine stimulation of the NF-κB and MAPK pathways. A blockage of IL-33 transmitting functions with anti-IL-33 monoclonal antibody added into the culture media decreased NF-κB activation in directly irradiated and bystander cells. On the other hand, the IGF-1-Receptor kinase regulated the PI3K–AKT pathway in both directly irradiated and bystander fibroblasts. A pronounced and prolonged increase in AKT activity after irradiation was a characteristic feature of bystander cells. AKT positively regulated IL-33 protein expression levels. Suppression of the IGF-R1–AKT–IL-33 pathway substantially increased radiation-induced or TRAIL-induced apoptosis in fibroblasts. Taken together, our results demonstrated the early activation of NF-κB-dependent gene expression first in directly irradiated and then bystander fibroblasts, the further modulation of critical proteins, including IL-33, by AKT in bystander cells and late drastic changes in cell survival and in enhanced sensitivity to TRAIL-induced apoptosis after suppression of the IGF-1R–AKT–IL-33 signaling cascade in both directly irradiated and bystander cells
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