14,428 research outputs found
Lightweight orthotic braces
Leg brace is constructed of fiber-reinforced polymer material. Composite material is stiffer, stronger, and lighter than most metals
Non-detection of the OH Meinel system in comet P/Swift-Tuttle
We report a search for emissions from the OH Meinel system in high-resolution near-infrared spectra of comet P/Swift-Tuttle. Because of the large cometary heliocentric velocity and high resolution of the spectrograph, the cometary lines should be well separated from the bright OH sky lines. Contrary to the findings of Tozzi et al. (1994) - who report seeing cometary OH at intensities comparable to the sky emissions in their low-resolution spectra - we find no OH in these spectra with an upper limit of 5% the value of the night sky lines. The non-detection of these cometary lines is consistent with theoretical calculations of expected emission strengths from prompt and fluorescent emission from cometary OH
A high-Resolution Catalog of Cometary Emission Lines
Using high-resolution spectra obtained with the Hamilton echelle spectrograph at Lick Observatory, we have constructed a catalog of emission lines observed in comets Swift-Tuttle and Brorsen-Metcalf. The spectra cover the range between 3800 Å and 9900 Å with a spectral resolution of λ/Δλ~42000. In the spectra, we catalog 2997 emission lines of which we identify 2438. We find cometary lines due to H, O, C_2, CN, NH_2, C_3, H_2O^+, CH, and CH^+. We list 559 unidentified lines compiled from the two spectra and comment on possibilities for their origins
Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546
[Abridged] We present the first simultaneous radio, X-ray, ultraviolet, and
optical spectroscopic observations of the M8.5 dwarf TVLM513-46546, with a
duration of 9 hours. These observations are part of a program to study the
origin of magnetic activity in ultracool dwarfs, and its impact on
chromospheric and coronal emission. Here we detect steady quiescent radio
emission superposed with multiple short-duration, highly polarized flares;
there is no evidence for periodic bursts previously reported for this object,
indicating their transient nature. We also detect soft X-ray emission, with
L_X/L_bol~10^-4.9, the faintest to date for any object later than M5, and a
possible weak X-ray flare. TVLM513-46546 continues the trend of severe
violation of the radio/X-ray correlation in ultracool dwarfs, by nearly 4
orders of magnitude. From the optical spectroscopy we find that the Balmer line
luminosity exceeds the X-ray luminosity by a factor of a few, suggesting that,
unlike in early M dwarfs, chromospheric heating may not be due to coronal X-ray
emission. More importantly, we detect a sinusoidal H-alpha light curve with a
period of 2 hr, matching the rotation period of TVLM513-46546. This is the
first known example of such Balmer line behavior, which points to a co-rotating
chromospheric hot spot or an extended magnetic structure, with a covering
fraction of about 50%. This feature may be transitory based on the apparent
decline in light curve peak during the four observed maxima. From the radio
data we infer a large scale steady magnetic field of ~100 G, in good agreement
with the value required for confinement of the X-ray emitting plasma. The radio
flares, on the other hand, are produced in a component of the field with a
strength of ~3 kG and a likely multi-polar configuration.Comment: 13 pages, 4 figure
Accretion-powered Stellar Winds as a Solution to the Stellar Angular Momentum Problem
We compare the angular momentum extracted by a wind from a pre-main-sequence
star to the torques arising from the interaction between the star and its
Keplerian accretion disk. We find that the wind alone can counteract the
spin-up torque from mass accretion, solving the mystery of why accreting
pre-main-sequence stars are observed to spin at less than 10% of break-up
speed, provided that the mass outflow rate in the stellar winds is ~10% of the
accretion rate. We suggest that such massive winds will be driven by some
fraction of the accretion power. For observationally constrained
typical parameters of classical T-Tauri stars, needs to be between a
few and a few tens of percent. In this scenario, efficient braking of the star
will terminate simultaneously with accretion, as is usually assumed to explain
the rotation velocities of stars in young clusters.Comment: Accepted by ApJ Letter
Frequency distribution of conception dates in a white-tailed deer herd
Conception dates of white-tailed deer, Odocoi/eus virginia1111s (Zinunennann, 1780) were estimated for the breeding periods of 1974 - 76 and 1984 using fall and winter- spring fetal data. Conception dates estimated from data collected in the fall were biased. This bias resulted in an earlier mean conception date than that based on information which included data from later breeding females. Mean breeding dates differed significantly between female age classes due to delayed conception in fawns which also resulted in a skewed frequency distribution of conception dates. The frequency distribution of conception dates was leptokurtotic, suggesting that the distribution is constrnincd in time by some factor(s). Conception date estimates did not differ by habitat type but were influenced significantly by period of data collection. Mean breeding date for deer on Lhe Savannah River Site, corrected for age class sampling bias, is 20 November± 27 days (adults plus fawns) and 13 November± 15 days (only adults)
Frequency distribution of conception dates in a white-tailed deer herd
Conception dates of white-tailed deer, Odocoi/eus virginia1111s (Zinunennann, 1780) were estimated for the breeding periods of 1974 - 76 and 1984 using fall and winter- spring fetal data. Conception dates estimated from data collected in the fall were biased. This bias resulted in an earlier mean conception date than that based on information which included data from later breeding females. Mean breeding dates differed significantly between female age classes due to delayed conception in fawns which also resulted in a skewed frequency distribution of conception dates. The frequency distribution of conception dates was leptokurtotic, suggesting that the distribution is constrnincd in time by some factor(s). Conception date estimates did not differ by habitat type but were influenced significantly by period of data collection. Mean breeding date for deer on Lhe Savannah River Site, corrected for age class sampling bias, is 20 November± 27 days (adults plus fawns) and 13 November± 15 days (only adults)
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