2,537 research outputs found
Comparing the Risk Attitudes of U.S. and German Farmers
Risk and Uncertainty,
Time-stepping approach for solving upper-bound problems: Application to two-dimensional Rayleigh-Benard convection
An alternative computational procedure for numerically solving a class of variational problems arising from rigorous upper-bound analysis of forced-dissipative infinite-dimensional nonlinear dynamical systems, including the Navier-Stokes and Oberbeck-Boussinesq equations, is analyzed and applied to Rayleigh-Benard convection. A proof that the only steady state to which this numerical algorithm can converge is the required global optimal of the relevant variational problem is given for three canonical flow configurations. In contrast with most other numerical schemes for computing the optimal bounds on transported quantities (e.g., heat or momentum) within the "background field" variational framework, which employ variants of Newton's method and hence require very accurate initial iterates, the new computational method is easy to implement and, crucially, does not require numerical continuation. The algorithm is used to determine the optimal background-method bound on the heat transport enhancement factor, i.e., the Nusselt number (Nu), as a function of the Rayleigh number (Ra), Prandtl number (Pr), and domain aspect ratio L in two-dimensional Rayleigh-Benard convection between stress-free isothermal boundaries (Rayleigh's original 1916 model of convection). The result of the computation is significant because analyses, laboratory experiments, and numerical simulations have suggested a range of exponents alpha and beta in the presumed Nu similar to (PrRa beta)-Ra-alpha scaling relation. The computations clearly show that for Ra <= 10(10) at fixed L = 2 root 2, Nu <= 0.106Pr(0)Ra(5/12), which indicates that molecular transport cannot generally be neglected in the "ultimate" high-Ra regime.NSF DMS-0928098 DMS-1515161 DMS-0927587 PHY-1205219Simons FoundationNSFONRInstitute for Computational Engineering and Sciences (ICES
Spectroscopic survey of faint planetary-nebula nuclei. I. Six new "O VI" central stars
We report initial results from an ongoing spectroscopic survey of central
stars of faint planetary nebulae (PNe), obtained with the Low-Resolution
Spectrograph on the Hobby-Eberly Telescope. The six PN nuclei (PNNi) discussed
here all have strong emission at the O VI 3811-3834 A doublet, indicative of
very high temperatures. Five of them--the nuclei of Ou 2, Kn 61, Kn 15, Abell
72, and Kn 130--belong to the hydrogen-deficient PG 1159 class, showing a
strong absorption feature of He II and C IV at 4650-4690 A. Based on
exploratory comparisons with synthetic model-atmosphere spectra, and the
presence of Ne VIII emission lines, we estimate them to have effective
temperatures of order 170,000 K. The central star of Kn 15 has a
Wolf-Rayet-like spectrum, with strong and broad emission lines of He II, C IV,
N V, and O V-VI. We classify it [WO2], but we note that the N V 4604-4620 A
emission doublet is extremely strong, indicating a relatively high nitrogen
abundance. Several of the emission lines in Kn 15 vary in equivalent width by
factors as large as 1.5 among our four observations from 2019 to 2022, implying
significant variations in the stellar mass-loss rate. We encourage
spectroscopic monitoring. Follow-up high-time-resolution photometry of these
stars would be of interest, given the large fraction of pulsating variables
seen among PG 1159 and [WO] PNNi.Comment: Accepted by MNRA
Cross-sectional associations between variations in ankle shape by statistical shape modeling, injury history, and race : the Johnston County Osteoarthritis Project
Rheumatology Research Foundation Medical Student Preceptorship Award (Lateef/Nelson), NIAMS K23 AR061406 (Nelson); NIH/NIAMS P60AR064166 and U01DP003206 (Jordan/Renner), NIH/NIAMS R01AR067743 (Golightly). The funders had no role in study design; collection, analysis, or interpretation of data; writing the manuscript or the decision to submit for publication.Peer reviewedPublisher PD
Law, Business Strategy, And Social Change In The Global Environment
In this article, we examine the dynamic relationship between law, economics, and sustainability. Increased legal regulation is not a sufficient condition for the mitigation of economic and social crises. Corporations are not legally required to respect global social and human rights under international law. In addition, select legal regulations increase social harm through the preservation of corporate financial interests. Laws that attempt to protect social rights at the expense of corporate interests can provoke hostile reactions from the business community. However, recent trends and examples from within the pharmaceutical and information industries suggest a new era of global corporate citizenship where socially responsible organizations achieve profit through pursuing ethical goals
The NASA-UC Eta-Earth Program: III. A Super-Earth orbiting HD 97658 and a Neptune-mass planet orbiting Gl 785
We report the discovery of planets orbiting two bright, nearby early K dwarf
stars, HD 97658 and Gl 785. These planets were detected by Keplerian modelling
of radial velocities measured with Keck-HIRES for the NASA-UC Eta-Earth Survey.
HD 97658 b is a close-in super-Earth with minimum mass Msini = 8.2 +/- 1.2
M_Earth, orbital period P = 9.494 +/- 0.005 d, and an orbit that is consistent
with circular. Gl 785 b is a Neptune-mass planet with Msini = 21.6 +/- 2.0
M_Earth, P = 74.39 +/- 0.12 d, and orbital eccentricity 0.30 +/- 0.09.
Photometric observations with the T12 0.8 m automatic photometric telescope at
Fairborn Observatory show that HD 97658 is photometrically constant at the
radial velocity period to 0.09 mmag, supporting the existence of the planet.Comment: Submitted to ApJ, 7 pages, 6 figures, 5 table
The NASA-UC Eta-Earth Program: II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses
We report the discovery of HD 156668b, an extrasolar planet with a minimum
mass of M_P sin i = 4.15 M_Earth. This planet was discovered through Keplerian
modeling of precise radial velocities from Keck-HIRES and is the second
super-Earth to emerge from the NASA-UC Eta-Earth Survey. The best-fit orbit is
consistent with circular and has a period of P = 4.6455 d. The Doppler
semi-amplitude of this planet, K = 1.89 m/s, is among the lowest ever detected,
on par with the detection of GJ 581e using HARPS. A longer period (P ~ 2.3 yr),
low-amplitude signal of unknown origin was also detected in the radial
velocities and was filtered out of the data while fitting the short-period
planet. Additional data are required to determine if the long-period signal is
due to a second planet, stellar activity, or another source. Photometric
observations using the Automated Photometric Telescopes at Fairborn Observatory
show that HD 156668 (an old, quiet K3 dwarf) is photometrically constant over
the radial velocity period to 0.1 mmag, supporting the existence of the planet.
No transits were detected down to a photometric limit of ~3 mmag, ruling out
transiting planets dominated by extremely bloated atmospheres, but not
precluding a transiting solid/liquid planet with a modest atmosphere.Comment: This planet was announced at the 2010 AAS meeting in Wash. DC; 12
pages, 8 figures, 3 tables, submitted to Ap
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