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 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

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

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

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

Decay constants, semi-leptonic and non-leptonic decays in a Bethe-Salpeter Model

We evaluate the decay constants for the B and $D$ mesons and the form factors for the semileptonic decays of the B meson to $D$ and $D^*$ mesons in a Bethe-Salpeter model. From data we extract $V_{cb}=0.039 \pm 0.002$ from ${\bar B} \to D^* l {\bar{\nu}}$ and $V_{cb}=0.037 \pm 0.004$ from ${\bar B} \to D l {\bar{\nu}}$ decays. The form factors are then used to obtain non-leptonic decay partial widths for $B\to D \pi (K)$ and $B \to D D (D_s)$ in the factorization approximation.Comment: 15 Pages, 3 Postscript figures (available also from [email protected]

Reduced disease severity following therapeutic treatment with angiotensin 1-7 in a mouse model of multiple sclerosis

Multiple Sclerosis (MS) is a chronic disease of the central nervous system (CNS) characterized by autoimmune and neurodegenerative pathologies for which there is no cure and no defined etiology. Although several, modestly effective, disease modifying drugs are available to treat MS, there are presently no treatments that offer neuroprotection and prevent clinical progression. Therapies are needed that control immune homeostasis, prevent disease progression, and stimulate regeneration in the CNS. Components of the renin-angiotensin-system (RAS) have recently been identified as chemical mediators in the CNS and in neurological disease. Here we show the beneficial effect of therapeutic treatment with the Mas receptor agonist and metabolite of the protective arm of RAS, angiotensin 1-7 (A(1-7)), in the experimental autoimmune encephalomyelitis (EAE) animal model of MS. Therapeutic treatment with A(1-7) caused a dose-dependent reduction both in clinical disease severity and progression, and was dependent on Mas receptor activation. Further analysis of the most optimal dose of A(1-7) treatment revealed that the reductions in clinical disease course were associated with decreased immune infiltration and demyelination, axonal loss and oxidative stress in the spinal cord. In addition A(1-7) treatment was also associated with increases in circulating alternatively activated monocytes/macrophages.Department of Defense, USC Clinical and Translational Science Institute, National Multiple Sclerosis Society12 month embargo; available online 25 February 2019.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [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

Dispersive Approach to Semileptonic Form-Factors in Heavy-to-Light Meson Decays

We study the semileptonic decays of heavy mesons into light pseudoscalars by making use of dispersion relations. Constraints from heavy quark symmetry, chiral symmetry and perturbative QCD are implemented into a dispersive model for the form-factors. Large deviations from $B^*$-pole dominance are observed in $B\to\pi\ell\nu$. We discuss the model prediction for this mode and its possible impact on the extraction of $|V_{ub}|$.Comment: 30 pages, including 5 Postcript figure

Mechanism of Radiation-Induced Bystander Effects: A Unifying Model

The radiation-induced bystander effect represents a paradigm shift in our understanding of the radiobiological effects of ionizing radiation, in that extranuclear and extracellular events may also contribute to the final biological consequences of exposure to low doses of radiation. Although radiation-induced bystander effects have been well documented in a variety of biological systems, the mechanism is not known. It is likely that multiple pathways are involved in the bystander phenomenon, and different cell types respond differently to bystander signalling. Using cDNA microarrays, a number of cellular signalling genes, including cyclooxygenase-2 (COX-2), have been shown to be causally linked to the bystander phenomenon. The observation that inhibition of the phosphorylation of extracellular signal-related kinase (ERK) suppressed the bystander response further confirmed the important role of the mitogen-activated protein kinase (MAPK) signalling cascade in the bystander process. Furthermore, cells deficient in mitochondrial DNA showed a significantly reduced response to bystander signalling, suggesting a functional role of mitochondria in the signalling process. Inhibitors of nitric oxide (NO) synthase (NOS) and mitochondrial calcium uptake provided evidence that NO and calcium signalling are part of the signalling cascade. The bystander observations imply that the relevant target for various radiobiological endpoints is larger than an individual cell. A better understanding of the cellular and molecular mechanisms of the bystander phenomenon, together with evidence of their occurrence in-vivo, will allow us to formulate a more accurate model for assessing the health effects of low doses of ionizing radiation