THE ROLE OF DIELECTRIC CONTINUUM MODELS IN ELECTRON TRANSFER: THEORETICAL AND COMPUTATIONAL ASPECTS.

Condensed phase physical and chemical processes generally involve interactions covering a wide range of distance scales, from short-range molecular interactions requiring orbital overlap to long-range coulombic interaction between local sites of excess charge (positive or negative monopoles). Intermediate-range distances pertain to higher-order multipolar as well as inductive and dispersion interactions. Efforts to model such condensed phase phenomena typically involve a multi-tiered strategy in which quantum mechanics is employed for full electronic structural characterization of a site of primary interest (e.g., a molecular solute or cluster), while more remote sites are treated at various classical limits (e.g., a molecular force field for discrete solvent molecules or a dielectric continuum (DC) model, if the solute is charged or has permanent multipole moments). In particular, DC models have been immensely valuable in modeling chemical reactivity and spectroscopy in media of variable polarity. Simple DC models account qualitatively for many important trends in the solvent dependence of reaction free energies, activation free energies, and optical excitation energies, and many results of semiquantitative or fully quantitative significance in comparison with experiment have been obtained, especially when detailed quantum chemical treatment of the solute is combined self consistently with DC treatment of the solvent (e.g., as in the currently popular PCM (polarized continuum model) approaches)

Percolation model for structural phase transitions in Li1−x_{1-x}Hx_xIO3_3 mixed crystals

A percolation model is proposed to explain the structural phase transitions found in Li$_{1-x}$H$_x$IO$_3$ mixed crystals as a function of the concentration parameter $x$. The percolation thresholds are obtained from Monte Carlo simulations on the specific lattices occupied by lithium atoms and hydrogen bonds. The theoretical results strongly suggest that percolating lithium vacancies and hydrogen bonds are indeed responsible for the solid solution observed in the experimental range $0.22 < x < 0.36$.Comment: 4 pages, 2 figure

Bacterially mediated removal of phosphorus and cycling of nitrate and sulfate in the waste stream of a "zero-discharge" recirculating mariculture system

Simultaneous removal of nitrogen and phosphorus by microbial biofilters has been used in a variety of water treatment systems including treatment systems in aquaculture. In this study, phosphorus, nitrate and sulfate cycling in the anaerobic loop of a zero-discharge, recirculating mariculture system was investigated using detailed geochemical measurements in the sludge layer of the digestion basin. High concentrations of nitrate and sulfate, circulating in the overlying water (~15 mM), were removed by microbial respiration in the sludge resulting in a sulfide accumulation of up to 3 mM. Modelling of the observed S and O isotopic ratios in the surface sludge suggested that, with time, major respiration processes shifted from heterotrophic nitrate and sulfate reduction to autotrophic nitrate reduction. The much higher inorganic P content of the sludge relative to the fish feces is attributed to conversion of organic P to authigenic apatite. This conclusion is supported by: (a) X-ray diffraction analyses, which pointed to an accumulation of a calcium phosphate mineral phase that was different from P phases found in the feces, (b) the calculation that the pore waters of the sludge were highly oversaturated with respect to hydroxyapatite (saturation index = 4.87) and (c) there was a decrease in phosphate (and in the Ca/Na molar ratio) in the pore waters simultaneous with an increase in ammonia showing there had to be an additional P removal process at the same time as the heterotrophic breakdown of organic matter

Emergency department utilization after hospitalization discharge for acute stroke: The COMprehensive Post-Acute Stroke Services (COMPASS) study

Each year nearly 800,000 people in the United States experience a stroke. Those that survive are at high risk for complications after hospital discharge. Providing appropriate care during the recovery from this complex condition is a challenge for patients, caregivers, and health care providers. Understanding emergency department (ED) utilization after a stroke may provide insights into long-term management of stroke, inform interventions, improve patient outcomes, and reduce medical costs. A comprehensive transitional care model for post-acute stroke care may influence the need to seek ED care for downstream events after a stroke. To date, most transitional care trials exploring post-stroke healthcare utilization were conducted outside of the U.S. health-care system. We examined data from the Comprehensive Post-Acute Stroke Services (COMPASS) study, a cluster-randomized pragmatic trial of a post-discharge transitional care model for stroke survivors and their caregivers compared with usual care

Socioeconomic status and access to care and the incidence of a heart failure diagnosis in the inpatient and outpatient settings

Purpose: Despite well-documented associations of socioeconomic status with incident heart failure (HF) hospitalization, little information exists on the relationship of socioeconomic status with HF diagnosed in the outpatient (OP) setting. Methods: We used Poisson models to examine the association of area-level indicators of educational attainment, poverty, living situation, and density of primary care physicians with incident HF diagnosed in the inpatient (IP) and OP settings among a cohort of Medicare beneficiaries (n = 109,756; 2001–2013). Results: The age-standardized rate of HF incidence was 35.8 (95% confidence interval [CI], 35.1–36.5) and 13.9 (95% CI, 13.5–14.4) cases per 1000 person-years in IP and OP settings, respectively. The incidence rate differences (IRDs) per 1000 person-years in both settings suggested greater incidence of HF in high- compared to low-poverty areas (IP IRD = 4.47 [95% CI, 3.29–5.65], OP IRD = 1.41 [95% CI, 0.61–2.22]) and in low- compared to high-education areas (IP IRD = 3.73 [95% CI, 2.63–4.82], OP IRD = 1.72 [95% CI, 0.97–2.47]). Conclusions: Our results highlight the role of area-level social determinants of health in the incidence of HF in both the IP and OP settings. These findings may have implications for HF prevention policies

The CLAS12 software framework and event reconstruction

We describe offline event reconstruction for the CEBAF Large Acceptance Spectrometer at 12 GeV (CLAS12), including an overview of the offline reconstruction framework and software tools, a description of the algorithms developed for the individual detector subsystems, and the overall approach for charged and neutral particle identification. We also present the scheme for data processing and the code management procedures

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic

Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{$6\times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^\circ$ from the position of an active galactic nucleus within 75 Mpc (using the V\'eron-Cetty and V\'eron $12^{\rm th}$ catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is $(38^{+7}_{-6})$, compared with $21$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})$. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201