870 research outputs found
High resolution, low temperature photoabsorption cross-section of C2H2 with application to Saturn's atmosphere
New laboratory observations of the VUV absorption cross-section of C2H2, obtained under physical conditions approximating stratospheres of the giant planets, were combined with IUE observations of the albedo of Saturn, for which improved data reduction techniques have been used, to produce new models for that atmosphere. When the effects of C2H2 absorption are accounted for, additional absorption by other molecules is required. The best-fitting model also includes absorption by PH3, H2O, C2H6 and CH4. A small residual disagreement near 1600 A suggests that an additional trace species may be required to complete the model
Comparative plasma catecholamine and hemodynamic responses to handgrip, cold pressor and supine bicycle exercise testing in normal subjects
Serial hemodynamic and plasma catecholamine responses were compared among 10 healthy men (27 ± 3 years) ( ± 1 standard deviation) during symptom-limited handgrip (33% maximal voluntary contraction for 4.4 ± 1.8 minutes), cold pressor testing (6 minutes) and symptom-limited supine bicycle exercise (22 ± 5 minutes). Plasma catecholamine concentrations were measured by radioenzymatic assays; ejection fraction and changes in cardiac volumes were assessed by equilibrium radionuclide angiography. During maximal supine exercise, plasma norepinephrine and epinephrine concentrations increased three to six times more than during either symptom-limited handgrip or cold pressor testing. Additionally, increases in heart rate, systolic blood pressure, rate-pressure product, stroke volume, ejection fraction and cardiac output were significantly greater during bicycle exercise than during the other two tests. A decrease in ejection fraction of 0.05 units or more was common in young normal subjects during the first 2 minutes of cold pressor testing (6 of 10 subjects) or at symptom-limited handgrip (3 of 10), but never occurred during maximal supine bicycle exercise.The magnitude of hemodynamic changes with maximal supine bicycle exercise was greater, more consistent and associated with much higher sympathetic nervous system activation, making this a potentially more useful diagnostic stress than either handgrip exercise or cold pressor testing
Discovery of the Transiting Planet Kepler-5B
We present 44 days of high duty cycle, ultra precise photometry of the 13th magnitude star Kepler-5 (KIC 8191672, T(eff) = 6300 K, log g = 4.1), which exhibits periodic transits with a depth of 0.7%. Detailed modeling of the transit is consistent with a planetary companion with an orbital period of 3.548460 +/- 0.000032 days and a radius of 1.431(-0.052)(+0.041) R(J). Follow-up radial velocity measurements with the Keck HIRES spectrograph on nine separate nights demonstrate that the planet is more than twice as massive as Jupiter with a mass of 2.114(-0.059)(+0.056) M(J) and a mean density of 0.894 +/- 0.079 g cm(-3).NASA's Science Mission DirectorateAstronom
Perceived parental control, restructuring ability, and leisure motivation: A cross-cultural comparison
Leisure is viewedworldwide as an important developmental context for adolescents. As leisure research and programs are shared across nations,
it is crucial to examine the cultural equivalence of leisure-related constructs
and how they are related. Grounded in self-determination theory,
this study explored the influence of perceived parental control
and leisure restructuring ability on leisure motivation (amotivation and
autonomous motivation) using samples of eighth grade adolescents in
the United States and South Africa. Results of multiple-group structural
equation modeling showed that the measurement model of the constructs
was equivalent across the two samples, but the determinants of
leisure motivation differed between the two samples. The findings provide
implications for future cross-cultural research in leisure and offer
insights on design and adaptation of leisure-based intervention and
education programs in different cultural contexts.IS
WFI J2026-4536 and WFI J2033-4723: Two New Quadruple Gravitational Lenses
We report the discovery of two new gravitationally lensed quasars, WFI
J2026-4536 and WFI J2033-4723, at respective source redshifts of z=2.23 and
z=1.66. Both systems are quadruply imaged and have similar PG1115-like image
configurations. WFI J2026-4536 has a maximum image separation of 1.4", a total
brightness of g = 16.5, and a relatively simple lensing environment, while WFI
J2033-4723 has a maximum image separation of 2.5", an estimated total
brightness of g = 17.9, and a more complicated environment of at least six
galaxies within 20". The primary lensing galaxies are detected for both systems
after PSF subtraction. Several of the broadband flux ratios for the two lenses
show a strong (0.1-0.4 mags) trend with wavelength, suggesting either
microlensing or differential extinction through the lensing galaxy. For WFI
J2026-4536, the total quasar flux has dimmed by 0.1 mag in the blue but only
half as much in the red over three months, suggestive of microlensing-induced
variations. For WFI J2033-4723, resolved spectra of some of the quasar
components reveal emission line flux ratios that agree better with the
macromodel predictions than either the broadband or continuum ratios, also
indicative of microlensing. The predicted differential time delays for WFI
J2026-4536 are short, ranging from 1-2 weeks for the long delay, but are longer
for WFI J2033-4723, ranging from 1-2 months. Both systems hold promise for
future monitoring campaigns aimed at microlensing or time delay studies.Comment: 34 pages, including 9 postscript figures. Submitted to A
The Shape and Scale of Galactic Rotation from Cepheid Kinematics
A catalog of Cepheid variables is used to probe the kinematics of the
Galactic disk. Radial velocities are measured for eight distant Cepheids toward
l = 300; these new Cepheids provide a particularly good constraint on the
distance to the Galactic center, R_0. We model the disk with both an
axisymmetric rotation curve and one with a weak elliptical component, and find
evidence for an ellipticity of 0.043 +/- 0.016 near the Sun. Using these
models, we derive R_0 = 7.66 +/- 0.32 kpc and v_circ = 237 +/- 12 km/s. The
distance to the Galactic center agrees well with recent determinations from the
distribution of RR Lyrae variables, and disfavors most models with large
ellipticities at the solar orbit.Comment: 36 pages, LaTeX, 10 figure
New Low-Mass Members of the Taurus Star-Forming Region
Briceno et al. recently used optical imaging, data from the Two-Micron
All-Sky Survey (2MASS), and follow-up spectroscopy to search for young low-mass
stars and brown dwarfs in 8 square degrees of the Taurus star-forming region.
By the end of that study, there remained candidate members of Taurus that
lacked the spectroscopic observations needed to measure spectral types and
determine membership. In this work, we have obtained spectroscopy of the 22
candidates that have A_V<=8, from which we find six new Taurus members with
spectral types of M2.75 through M9. The new M9 source has the second latest
spectral type of the known members of Taurus (~0.02 M_sun). Its spectrum
contains extremely strong emission in H_alpha (W~950 A) as well as emission in
He I 6678 A and the Ca II IR triplet. This is the least massive object known to
exhibit emission in He I and Ca II, which together with the strong H_alpha are
suggestive of intense accretion.Comment: to be published in The Astrophysical Journal, 13 pages, 6 figures,
also found at http://cfa-www.harvard.edu/sfgroup/preprints.htm
Gravitational-Wave Cosmology across 29 Decades in Frequency
Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. We derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with baryon acoustic oscillations and big bang nucleosynthesis measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiments constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows us to constrain cosmological parameters, including the inflationary spectral index nt and the tensor-to-scalar ratio r. Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, ΩGW(f)\u3c2.3×10−10. Observations of the cosmic microwave background alone limit the gravitational-wave spectral index at 95% confidence to nt≲5 for a tensor-to-scalar ratio of r=0.11. However, the combination of all the above experiments limits nt\u3c0.36. Future Advanced LIGO observations are expected to further constrain nt\u3c0.34 by 2020. When cosmic microwave background experiments detect a nonzero r, our results will imply even more stringent constraints on nt and, hence, theories of the early Universe
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