Quantum Yield Calculations for Strongly Absorbing Chromophores

This article demonstrates that a commonly-made assumption in quantum yield calculations may produce errors of up to 25% in extreme cases and can be corrected by a simple modification to the analysis.Comment: 3 pages, 2 figures. Accepted by Journal of Fluorescenc

Properties of Umbral Dots as Measured from the New Solar Telescope Data and MHD Simulations

We studied bright umbral dots (UDs) detected in a moderate size sunspot and compared their statistical properties to recent MHD models. The study is based on high resolution data recorded by the New Solar Telescope at the Big Bear Solar Observatory and 3D MHD simulations of sunspots. Observed UDs, living longer than 150 s, were detected and tracked in a 46 min long data set, using an automatic detection code. Total 1553 (620) UDs were detected in the photospheric (low chromospheric) data. Our main findings are: i) none of the analyzed UDs is precisely circular, ii) the diameter-intensity relationship only holds in bright umbral areas, and iii) UD velocities are inversely related to their lifetime. While nearly all photospheric UDs can be identified in the low chromospheric images, some small closely spaced UDs appear in the low chromosphere as a single cluster. Slow moving and long living UDs seem to exist in both the low chromosphere and photosphere, while fast moving and short living UDs are mainly detected in the photospheric images. Comparison to the 3D MHD simulations showed that both types of UDs display, on average, very similar statistical characteristics. However, i) the average number of observed UDs per unit area is smaller than that of the model UDs, and ii) on average, the diameter of model UDs is slightly larger than that of observed ones.Comment: Accepted by the AP

Factors that influence shelterbelt retention and removal in prairie agriculture as identified by Saskatchewan producers

Non-Peer ReviewedThe role of shelterbelts in prairie agriculture is changing. Traditionally, shelterbelts were promoted and adopted for soil stabilization and protection of farm infrastructure, equipment, and livestock from harsh weather elements; however, advances in production technology, larger scale operations, and the removal of a subsidy (distribution of free seedlings) have changed the context in which shelterbelts are currently being maintained, planted, or removed. This research identified the factors that are influencing producer’s management decisions related to retention and adoption of shelterbelts in the early 21st century in Saskatchewan, Canada. In the summer of 2013, surveys were conducted with producers from throughout the province of Saskatchewan (and several from Alberta). From the surveys, costs, benefits, and factors influencing producer’s management decisions, related to shelterbelts in the farm operations, were identified. Survey results show that 40% of the produces removed shelterbelts from their operations. Reasons for such decisions included: high labor requirements, difficulty in the operation of large equipment, and loss of land for production. Those who did not remove shelterbelts recognized their non-economic values more than those who removed them. Shelterbelts have the potential to play a major role in climate change mitigation by sequestering significant amounts of atmospheric CO2 into the soil and as biomass carbon in aboveground and belowground biomass of planted shelterbelt trees or shrubs within the agricultural landscape, both presently and in the future. As a result, understanding the context in which producers are making decisions related to this agroforestry practice will be important from a policy perspective

Properties of simulated sunspot umbral dots

Realistic 3D radiative MHD simulations reveal the magneto-convective processes underlying the formation of the photospheric fine structure of sunspots, including penumbral filaments and umbral dots. Here we provide results from a statistical analysis of simulated umbral dots and compare them with reports from high-resolution observations. A multi-level segmentation and tracking algorithm has been used to isolate the bright structures in synthetic bolometric and continuum brightness images. Areas, brightness, and lifetimes of the resulting set of umbral dots are found to be correlated: larger umbral dots tend to be brighter and live longer. The magnetic field strength and velocity structure of umbral dots on surfaces of constant optical depth in the continuum at 630 nm indicate that the strong field reduction and high velocities in the upper parts of the upflow plumes underlying umbral dots are largely hidden from spectro-polarimetric observations. The properties of the simulated umbral dots are generally consistent with the results of recent high-resolution observations. However, the observed population of small, short-lived umbral dots is not reproduced by the simulations, possibly owing to insufficient spatial resolution.Comment: Accepted for publication in A&

Combining magneto-hydrostatic constraints with Stokes profiles inversions

Inversion codes for the polarized radiative transfer equation can be used to infer the temperature $T$, line-of-sight velocity $v_{\rm los}$, and magnetic field $\rm{\bf B}$ as a function of the continuum optical-depth $\tau_{\rm c}$. However, they do not directly provide the gas pressure $P_{\rm g}$ or density $\rho$. In order to obtain these latter parameters, inversion codes rely instead on the assumption of hydrostatic equilibrium (HE) in addition to the equation of state (EOS). Unfortunately, the assumption of HE is rather unrealistic across magnetic field lines. This is because the role of the Lorentz force, among other factors, is neglected. This translates into an inaccurate conversion from optical depth $\tau_{\rm c}$ to geometrical height $z$. We aim at improving this conversion via the application of magneto-hydrostatic (MHS) equilibrium instead of HE. We develop a method to solve the momentum equation under MHS equilibrium (i.e., taking the Lorentz force into account) in three dimensions. The method is based on the solution of a Poisson-like equation. Considering the gas pressure $P_{\rm g}$ and density $\rho$ from three-dimensional magneto-hydrodynamic (MHD) simulations of sunspots as a benchmark, we compare the results from the application of HE and MHS equilibrium. We find that HE retrieves the gas pressure and density within an order of magnitude of the MHD values in only about 47 \% of the domain. This translates into an error of about $160-200$ km in the determination of the $z-\tau_{\rm c}$ conversion. On the other hand, the application of MHS equilibrium allows determination of $P_{\rm g}$ and $\rho$ within an order of magnitude in 84 \% of the domain. In this latter case, the $z-\tau_{\rm c}$ conversion is obtained with an accuracy of $30-70$ km.Comment: Accepted for publication in Astronomy \& Astrophysics. 12 pages, 10 figure

Minnestoa Sheep Research Notes

This report provides condensed summaries of research projects conducted by researches at the University of Minnesota

Sol-Gel Synthesis of Nonstoichiometric Titanium Dioxide for Photo-Oxidation of Toxic Organic Substances

Titanium dioxide (TiO2) was synthesized by sol-gel method at different values of pH = 3, 7, 8, 9, or 10. X-ray phase analysis has shown that in an acid rout, an anatase phase had crystallized, and in an alkaline rout an amorphous phase of TiO2 was achieved. After annealing for 4 hours at 350∘C, all samples were transformed into anatase phase. The particle size in the different samples varies from 7 to 50 nm depending on the pH. The diffuse reflectance spectra revealed a high value of the band gap width in the range from 2.9 to 3.4 eV and its narrowing after annealing to the range from 2.8to 3.1 eV. The specific surface area measured by BET method was changing from 80 up to 140 m2 /g. Keywords: Titanium dioxide, nanostructure, photocatalysis, band gap, specific surface are

Acoustic-gravity wave propagation characteristics in 3D radiation hydrodynamic simulations of the solar atmosphere

There has been tremendous progress in the degree of realism of three-dimensional radiation magneto-hydrodynamic simulations of the solar atmosphere in the past decades. Four of the most frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D, and MURaM. Here we test and compare the wave propagation characteristics in model runs from these four codes by measuring the dispersion relation of acoustic-gravity waves at various heights. We find considerable differences between the various models. The height dependence of wave power, in particular of high-frequency waves, varies by up to two orders of magnitude between the models, and the phase difference spectra of several models show unexpected features, including $\pm180^\circ$ phase jumps.Comment: 19 pages, 15 figure

Astrophysical Fluid Dynamics via Direct Statistical Simulation

In this paper we introduce the concept of Direct Statistical Simulation (DSS) for astrophysical flows. This technique may be appropriate for problems in astrophysical fluids where the instantaneous dynamics of the flows are of secondary importance to their statistical properties. We give examples of such problems including mixing and transport in planets, stars and disks. The method is described for a general set of evolution equations, before we consider the specific case of a spectral method optimised for problems on a spherical surface. The method is illustrated for the simplest non-trivial example of hydrodynamics and MHD on a rotating spherical surface. We then discuss possible extensions of the method both in terms of computational methods and the range of astrophysical problems that are of interest.Comment: 26 pages, 11 figures, added clarifying remarks and references, and corrected typos. This version is accepted for publication in The Astrophysical Journa

Elliptic operators in even subspaces

In the paper we consider the theory of elliptic operators acting in subspaces defined by pseudodifferential projections. This theory on closed manifolds is connected with the theory of boundary value problems for operators violating Atiyah-Bott condition. We prove an index formula for elliptic operators in subspaces defined by even projections on odd-dimensional manifolds and for boundary value problems, generalizing the classical result of Atiyah-Bott. Besides a topological contribution of Atiyah-Singer type, the index formulas contain an invariant of subspaces defined by even projections. This homotopy invariant can be expressed in terms of the eta-invariant. The results also shed new light on P.Gilkey's work on eta-invariants of even-order operators.Comment: 39 pages, 2 figure