2,743 research outputs found
Remote lightning monitor system
An apparatus for monitoring, analyzing and accurately determining the value of peak current, the peak rate of change in current with respect to time and the rise time of the electrical currents generated in an electrical conductive mast that is located in the vicinity where lightning is to be monitored is described. The apparatus includes an electrical coil for sensing the change in current flowing through the mast and generating a voltage responsive. An on-site recorder and a recorder control system records the voltages produced responsive to lightning strikes and converts the voltage to digital signals for being transmitted back to the remote command station responsive to command signals. The recorder and the recorder control system are carried within an RFI proof environmental housing into which the command signals are fed by means of a fiber optic cable so as to minimize electrical interference
LINKING LAKES WITH THE LANDSCAPE: THE FATE OF TERRESTRIAL ORGANIC MATTER IN PLANKTONIC FOOD WEBS
Terminal velocities of luminous, early-type SMC stars
Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are
used to determine terminal velocities for 11 O and B-type giants and
supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV
resonance lines. Using archival data from observations with the Goddard
High-Resolution Spectrograph and the International Ultraviolet Explorer
telescope, terminal velocities are obtained for a further five B-type
supergiants. We discuss the metallicity dependence of stellar terminal
velocities, finding no evidence for a significant scaling between Galactic and
SMC metallicities for Teff < 30,000 K, consistent with the predictions of
radiation driven wind theory for supergiant stars. A comparison of the
ratio between the SMC and Galactic samples, while
consistent with the above statement, emphasizes that the uncertainties in the
distances to galactic O-stars are a serious obstacle to a detailed comparison
with theory. For the SMC sample there is considerable scatter in this ratio at
a given effective temperature, perhaps indicative of uncertainties in stellar
masses.Comment: 28 pages, 8 figures, accepted by ApJ; minor revisions prior to
acceptanc
Radiation-driven winds of hot stars. XIII. A description of NLTE line blocking and blanketing towards realistic models of expanding atmospheres
We present significant improvements of our approach in constructing detailed
atmospheric models and synthetic spectra for hot luminous stars:
1. A sophisticated and consistent description of line blocking and
blanketing. Our solution concept renders the line blocking influence on the
ionizing fluxes (mainly the EUV and UV are affected) in identical quality as
the synthetic high resolution spectra representing the observable region. Line
blanketing is properly accounted for in the energy balance.
2. A considerably improved and enhanced atomic data archive providing the
basis for a detailed multilevel NLTE treatment of the metal ions (from C to Zn)
and an adequate representation of line blocking and the radiative line
acceleration.
3. A revised inclusion of EUV and X-ray radiation produced by cooling zones
originating from shock heated matter.
This new tool not only provides an easy to use method for O-star diagnostics,
whereby physical constraints on the properties of stellar winds, stellar
parameters, and abundances can be obtained via a comparison of observed and
synthetic spectra, but also allows the astrophysically important information
about the ionizing fluxes of hot stars to be determined automatically. Results
illustrating this are discussed by means of a basic model grid calculated for
O-stars with solar metallicity. To further demonstrate the astrophysical
potential of our new method we provide a first detailed spectral diagnostic
determination of the stellar parameters, the wind parameters, and the
abundances by an exemplary application to the O9.5Ia supergiant alpha Cam.Comment: 42 Pages, 39 Figures. LaTeX documentclass aa, packages graphicx and
times. Submitted to Astronomy and Astrophysic
Knowing When to Draw the Line: Designing More Informative Ecological Experiments
Linear regression and analysis of variance (ANOVA) are two of the most widely used statistical techniques in ecology. Regression quantitatively describes the relationship between a response variable and one or more continuous independent variables, while ANOVA determines whether a response variable differs among discrete values of the independent variable(s). Designing experiments with discrete factors is straightforward because ANOVA is the only option, but what is the best way to design experiments involving continuous factors? Should ecologists prefer experiments with few treatments and many replicates analyzed with ANOVA, or experiments with many treatments and few replicates per treatment analyzed with regression? We recommend that ecologists choose regression, especially replicated regression, over ANOVA when dealing with continuous factors for two reasons: (1) regression is generally a more powerful approach than ANOVA and (2) regression provides quantitative output that can be incorporated into ecological models more effectively than ANOVA output
Trajectories of objectively measured physical activity in free-living older men.
BACKGROUND: The steep decline in physical activity (PA) among the oldest old is not well understood; there is little information about the patterns of change in PA and sedentary behaviour (SB) in older people. Longitudinal data on objectively measured PA data can give insights about how PA and SB change with age.
METHODS: Men age 70-90 yr, from a United Kingdom population-based cohort wore a GT3X accelerometer over the hip annually on up to three occasions (56%, 50%, and 51% response rates) spanning 2 yr. Multilevel models were used to estimate change in activity. Men were grouped according to achieving ≥150 min·wk of MVPA in bouts of ≥10 min (current guidelines) at two or three time points.
RESULTS: A total of 1419 ambulatory men had ≥600 min wear time on ≥3 d at ≥2 time points. At baseline, men took 4806 steps per day and spent 72.5% of their day in SB, 23.1% in light PA, and 4.1% in moderate-to-vigorous PA (MVPA). Mean change per year was -341 steps, +1.1% SB, -0.7% light PA, and -0.4% MVPA each day (all P 30 min increased from 5.1 by 0.1 per year (P = 0.02).
CONCLUSIONS: Among older adults, the steep decline in total PA occurred because of reductions in MVPA, while light PA is relatively spared and sedentary time and long sedentary bouts increase
- …