99,963 research outputs found
Joshua Davis: Author of Spare Parts
No full textCitation: K-State First (2016). Joshua Davis: Author of Spare Parts [Flier]. Manhattan, Kansas: K-State First.Flyer advertising Joshua Davis's author talk at Kansas State University
Measuring stellar differential rotation with asteroseismology
No full textThe variation of rotation with latitude is poorly known on stars other than the Sun. Several indirect techniques, photometric and spectroscopic, have been used to search for departure from rigid rotation for sufficiently fast rotators. Here we investigate the possibility of measuring stellar differential rotation for solar-type stars through asteroseismology. Rotationally split frequencies of global oscillation provide information about rotation at different latitudes depending on the azimuthal order, m, of the mode of pulsation. We present a method to estimate differential rotation based on the realization that the m = ±1 and m = ±2 components of quadrupole oscillations can be observed simultaneously in asteroseismology. Rotational frequency splittings can be inverted to provide an estimate of the difference in stellar angular velocity between the equator and 45° latitude. The precision of the method, assessed through Monte Carlo simulations, depends on the value of the mean rotation and on the inclination angle between the rotation axis and the line of sight
Steven Johnson Author Talk Poster
No full textK-State Book NetworkA poster advertising an author talk by Steven Johnson at Kansas State University on September 3, 2014. Steven Johnson's book "The Ghost Map" was the 2014-2015 common book
Modeling Stellar Ca ii H and K Emission Variations. I. Effect of Inclination on the S-index
No full textThe emission in the near-ultraviolet Ca ii H and K lines is modulated by stellar magnetic activity. Although this emission, quantified via the S-index, has been serving as a prime proxy of stellar magnetic activity for several decades, many aspects of the complex relation between stellar magnetism and Ca ii H and K emission are still unclear. The amount of measured Ca ii H and K emission is suspected to be affected not only by the stellar intrinsic properties but also by the inclination angle of the stellar rotation axis. Until now, such an inclination effect on the S-index has remained largely unexplored. To fill this gap, we develop a physics-based model to calculate S-index, focusing on the Sun. Using the distributions of solar magnetic features derived from observations together with Ca ii H and K spectra synthesized in non-local thermodynamic equilibrium, we validate our model by successfully reconstructing the observed variations of the solar S-index over four activity cycles. Further, using the distribution of magnetic features over the visible solar disk obtained from surface flux transport simulations, we obtain S-index time series dating back to 1700 and investigate the effect of inclination on S-index variability on both the magnetic activity cycle and the rotational timescales. We find that when going from an equatorial to a pole-on view, the amplitude of S-index variations decreases weakly on the activity cycle timescale and strongly on the rotational timescale (by about 22% and 81%, respectively, for a cycle of intermediate strength). The absolute value of the S-index depends only weakly on the inclination. We provide analytical expressions that model such dependencies
Correction of atmospheric stray light in restored slit spectra
No full textContext. A long-standing issue in solar ground-based observations has been the contamination of data due to stray light, which is particularly relevant in inversions of spectropolarimetric data.
Aims. We aim to build on a statistical method of correcting stray-light contamination due to residual high-order aberrations and apply it to ground-based slit spectra.
Methods. The observations were obtained at the Swedish Solar Telescope, and restored using the multi-frame blind deconvolution restoration procedure. Using the statistical properties of seeing, we created artificially degraded synthetic images generated from magneto-hydrodynamic simulations. We then compared the synthetic data with the observations to derive estimates of the amount of the residual stray light in the observations. In the final step, the slit spectra were deconvolved with a stray-light point spread function to remove the residual stray light from the observations.
Results. The RMS granulation contrasts of the deconvolved spectra were found to increase to approximately 12.5%, from 9%. Spectral lines, on average, were found to become deeper in the granules and shallower in the inter-granular lanes, indicating systematic changes to gradients in temperature. The deconvolution was also found to increase the redshifts and blueshifts of spectral lines, suggesting that the velocities of granulation in the solar photosphere are higher than had previously been observed
Wplyw rodzaju solanki i czasu solenia na biodostepnosc skladnikow mineralnych serow dojrzewajacych
No full textThe bioavailabilities of potassium, sodium and calcium from two types of cheeses, Jeziorański and Tilsit, salted in a 20% NaCl solution or NaCl/KCl, 1:1, solution for a standard salting time (SST) or 25% of SST, were studied. The bioavailability was determined by the classical balance method based on the element intake and its excretion with faeces and urine using growing Wistar rats. The ability to assimilate the mineral elements was expressed by apparent absorption (A) and retention (R) coefficients. The type of brine did not affect significantly the intakes of sodium (25% SST) and calcium (100% SST) by rats fed the cheeses. The intake of potassium from both types of cheeses was significantly dependent on the type of brine. The salting time of Jeziorański cheese significantly influenced the intakes of sodium, potassium and calcium independent of the type of brine. The type of brine and time of salting significantly affected the apparent absorption and retention of minerals for the diets selected for statistical analysis.Badaniom poddano próby serów dojrzewających: jeziorańskiego i tylżyckiego, wyprodukowane w Zakładach Mleczarskich w Iławie i Biskupcu. Sery solono w 20% roztworach NaCl oraz w mieszaninie NaCl i KCl (1:1). Stosowano ponadto różny czas solenia wynoszący 25% i 100% czasu normatywnego. Biodostępność sodu, potasu i wapnia określano metodą bilansową na rosnących szczurach szczepu Wistar w oparciu o spożycie danego pierwiastka i jego wydalanie z kalem i moczem. Przyswajalność badanych składników mineralnych wyrażano wskaźnikami absorpcji (A) i retencji (R) pozornej. Wykazano, że rodzaj stosowanej solanki nie miał istotnego wpływu na spożycie Na (25%) i Ca (100% czasu normatywnego) przez szczury żywione badanymi serami (tab.1). Stwierdzono, że wielkość spożycia potasu dla obu gatunków serów zależała istotnie od rodzaju solanki (tab. 1). Zanotowano istotny wpływ czasu nasolenia sera jeziorańskiego na spożycie Na, K i Ca niezależnie od rodzaju solanki (tab. 1). Rodzaj solanki i czas solenia serów wpływał istotnie na absorpcję i retencję pozorną badanych składników mineralnych z wybranych do analizy statystycznej diet doświadczalnych (tab. 2)
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