12,044 research outputs found
A Dynamical Analysis of the 47 UMa Planetary System
The mass and period ratios of the two planets orbiting 47 UMa suggest a
possible kinship to the Jupiter-Saturn pair in our solar system. We explore the
current dynamical state of the 47 UMa system with numerical integrations, and
compare the results with analytic secular theory. We find that the planets in
the system are likely participating in a secular resonance in which the
difference in the longitudes of pericenter librates around zero. Alternately,
it is possible that the system is participating in the 7:3 mean motion
resonance. We show that stability considerations restrict the mutual
inclination between the two planets to 40 degrees or less, and that this result
is relatively insensitive to the total mass of the two planets. We present
hydrodynamical simulations which measure the torques exerted on the planets by
a hypothesized external protoplanetary disk. We show that planetary migration
in response to torques from the disk may have led to capture of the system into
a 7:3 mean-motion resonance, although it is unclear how the eccentricities of
the planets would have been damped after capture occured. We show that
Earth-mass planets can survive for long periods in some regions of the
habitable zone of the nominal co-planar system. A set of planetary accretion
calculations, however, shows that it is unlikely that large terrestrial planets
can form in the 47 UMa habitable zone.Comment: Accepted by the Astrophysical Journal (Original submission November
2001
Strain monitoring of tapestries: results of a three-year research project
The outcomes of an interdisciplinary research project between conservators and engineers investigating the strain experienced by different areas of a tapestry are described. Two techniques were used: full-field monitoring using digital image correlation (DIC) and point measurements using optical fibre sensors. Results showed that it is possible to quantify the global strain across a discrete area of a tapestry using DIC; optical fibre and other sensors were used to validate the DIC. Strain maps created by the DIC depict areas of high and low strain and can be overlaid on images of the tapestry, creating a useful visual tool for conservators, custodians and the general public. DIC identifies areas of high strain not obvious to the naked eye. The equipment can be used in situ in a historic house. In addition the work demonstrated the close relationship between relative humidity and strain
Symmetry Scheme for Amino Acid Codons
Group theoretical concepts are invoked in a specific model to explain how
only twenty amino acids occur in nature out of a possible sixty four. The
methods we use enable us to justify the occurrence of the recently discovered
twenty first amino acid selenocysteine, and also enables us to predict the
possible existence of two more, as yet undiscovered amino acids.Comment: 18 pages which include 4 figures & 3 table
PATENTS, R&D AND LAG EFFECTS: EVIDENCE FROM FLEXIBLE METHODS FOR COUNT PANEL DATA ON MANUFACTURING FIRMS
Hausman, Hall and Griliches (1984) and Hall, Griliches and Hausman (1986) investigated whether there was a lag in the patent-R&D relationship for the U.S. manufacturing sector using 1970Âżs data. They found that there was little evidence of anything but contemporaneous movement of patents and R&D. We reexamine this important issue employing new longitudinal patent data at the firm level for the U.S. manufacturing sector from 1982 to 1992. To address unique features of the data, we estimate various distributed lag and dynamic multiplicative panel count data models. The paper also develops a new class of count panel data models based on series expansion of the distribution of individual effects. The empirical analyses show that, although results are somewhat sensitive to different estimation methods, the contemporaneous relationship between patenting and R&D expenditures continues to be rather strong, accounting for over 60% of the total R&D elasticity. Regarding the lag structure of the patents-R&D relationship, we do find a significant lag in all empirical specifications. Moreover, the estimated lag effects are higher than have previously been found, suggesting that the contribution of R&D history to current patenting has increased from the 1970Âżs to the 1980Âżs.Innovative activity, Patents and R&D, Individual effects, count panel data methods.
Einstein Cluster Alignments Revisited
We have examined whether the major axes of rich galaxy clusters tend to point
toward their nearest neighboring cluster. We have used the data of Ulmer,
McMillan, and Kowalski, who used position angles based on X-ray morphology. We
also studied a subset of this sample with updated positions and distances from
the MX Northern Abell Cluster Survey (for rich clusters () with well
known redshifts). A Kolmogorov-Smirnov (KS) test showed no significant signal
for nonrandom angles on any scale Mpc. However, refining the
null hypothesis with the Wilcoxon rank-sum test, we found a high confidence
signal for alignment. Confidence levels increase to a high of 99.997% as only
near neighbors which are very close are considered. We conclude there is a
strong alignment signal in the data, consistent with gravitational instability
acting on Gaussian perturbations.Comment: Minor revisions. To be published in Ap
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