781 research outputs found
Metal-poor dwarf galaxies in the SIGRID galaxy sample. I. HII region observations and chemical abundances
In this paper we present the results of observations of seventeen HII regions
in thirteen galaxies from the SIGRID sample of isolated gas rich irregular
dwarf galaxies. The spectra of all but one of the galaxies exhibit the auroral
[OIII] 4363A line, from which we calculate the electron temperature, Te, and
gas-phase oxygen abundance. Five of the objects are blue compact dwarf (BCD)
galaxies, of which four have not previously been analysed spectroscopically. We
include one unusual galaxy which exhibits no evidence of the [NII]
{\lambda}{\lambda} 6548,6584A lines, suggesting a particularly low metallicity
(< Zsolar/30). We compare the electron temperature based abundances with those
derived using eight of the new strong line diagnostics presented by Dopita et
al. (2013). Using a method derived from first principles for calculating total
oxygen abundance, we show that the discrepancy between the Te-based and strong
line gas-phase abundances have now been reduced to within ~0.07 dex. The
chemical abundances are consistent with what is expected from the
luminosity-metallicity relation. We derive estimates of the electron densities
and find them to be between ~5 and ~100 cm-3. We find no evidence for a
nitrogen plateau for objects in this sample with metallicities 0.5 > Zsolar >
0.15.Comment: 46 pages, 15 figures, 6 tables, 1 appendix. Accepted for publication
in the Astrophysical Journa
Ionospheric ion temperature forecasting in multiples of 27 days
he ionospheric variability found at auroral locations is usually assumed to be unpredictable. The magnetosphere, which drives this ionospheric variability via storms and substorms, is at best only qualitatively describable. In this study we demonstrate that over a 3 year period, ionospheric variability observed from Poker Flat, Alaska, has, in fact, a high degree of long-term predictability. The observations used in this study are (a) the solar wind high speed stream velocity measured by the NASA Advanced Composition Explorer satellite, used to define the corotating interaction region (CIR), and (b) the ion temperature at 300 km altitude measured by the National Science Foundation Poker Flat Incoherent Scatter Radar over Poker Flat, Alaska. After determining a seasonal and diurnal climatology for the ion temperature, we show that the residual ion temperature heating events occur synchronously with CIR-geospace interactions. Furthermore, we demonstrate examples of ion temperature forecasting at 27, 54, and 81 days. A rudimentary operational forecasting scenario is described for forecasting recurrence 27 days ahead for the CIR-generated geomagnetic storms. These forecasts apply specifically to satellite tracking operations (thermospheric drag) and emergency HF-radio communications (ionospheric modifications) in the polar regions. The forecast is based on present-day solar and solar wind observations that can be used to uniquely identify the coronal hole and its CIR. From this CIR epoch, a 27 day forecast is then made
Turning rebellion into money? Social entrepreneurship as the strategic performance of systems change
Detecting periodicity in experimental data using linear modeling techniques
Fourier spectral estimates and, to a lesser extent, the autocorrelation
function are the primary tools to detect periodicities in experimental data in
the physical and biological sciences. We propose a new method which is more
reliable than traditional techniques, and is able to make clear identification
of periodic behavior when traditional techniques do not. This technique is
based on an information theoretic reduction of linear (autoregressive) models
so that only the essential features of an autoregressive model are retained.
These models we call reduced autoregressive models (RARM). The essential
features of reduced autoregressive models include any periodicity present in
the data. We provide theoretical and numerical evidence from both experimental
and artificial data, to demonstrate that this technique will reliably detect
periodicities if and only if they are present in the data. There are strong
information theoretic arguments to support the statement that RARM detects
periodicities if they are present. Surrogate data techniques are used to ensure
the converse. Furthermore, our calculations demonstrate that RARM is more
robust, more accurate, and more sensitive, than traditional spectral
techniques.Comment: 10 pages (revtex) and 6 figures. To appear in Phys Rev E. Modified
styl
Achievement of combined goals of low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol with three different statins: Results from VOYAGER
AbstractBackgroundGuidelines suggest that the combination of low-density lipoprotein cholesterol (LDL-C) and non-high-density lipoprotein cholesterol (non-HDL-C) is the most clinically relevant goal for lipid-lowering treatments.MethodsData from VOYAGER, an individual patient data meta-analysis including 32,258 patients from 37 clinical trials, was used to determine the percentage of patients reaching combined goals of LDL-C and non-HDL-C following treatment with simvastatin, atorvastatin, or rosuvastatin. Paired comparisons were made between each dose of rosuvastatin and the same or higher doses of simvastatin and atorvastatin.ResultsEach dose of rosuvastatin brought significantly more patients to the combined goal of LDL-C < 100 mg/dL and non-HDL-C < 130 mg/dL than the same or double dose of atorvastatin; atorvastatin 80 mg was significantly superior to rosuvastatin 10 mg (all p < 0.001). Each dose of rosuvastatin helped significantly more patients reach the combined goal than any dose of simvastatin (all p < 0.001), except for rosuvastatin 10 mg versus simvastatin 80 mg (non-significant). Also, each dose of rosuvastatin helped significantly more patients to reach the combined goal of LDL-C < 70 mg/dL and non-HDL-C < 100 mg/dL than the same or double dose of atorvastatin (all p < 0.001). Every dose of rosuvastatin was significantly superior to all doses of simvastatin (all p ≤ 0.020), except for rosuvastatin 10 mg versus simvastatin 40 mg and 80 mg (non-significant).ConclusionsPhysicians' choice of statin and dose is important in helping patients achieve the combined LDL-C and non-HDL-C goals recommended in established guidelines
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