29,020 research outputs found
Caddoan Ceremonial Sites of the Caddoan Cultural Area of Arkansas, Louisiana, Oklahoma, and Texas: Draft Caddo National Landmark Nomination
Since 1997, we have been working on the development of a National Historic Landmark (NHL) cover nomination for Caddoan ceremonial sites - earthen mounds in the Caddoan cultural area of southwestern Arkansas, northwestern Louisiana, eastern Oklahoma, and northeastern Texas. Such a nomination establishes the historic context within which all similar cultural properties can be evaluated for significance according to the NHL criteria, as it establishes the research and other criteria by which a cultural property may be identified as a significant archeological resource
Characterizing Multi-planet Systems with Classical Secular Theory
Classical secular theory can be a powerful tool to describe the qualitative
character of multi-planet systems and offer insight into their histories. The
eigenmodes of the secular behavior, rather than current orbital elements, can
help identify tidal effects, early planet-planet scattering, and dynamical
coupling among the planets, for systems in which mean-motion resonances do not
play a role. Although tidal damping can result in aligned major axes after all
but one eigenmode have damped away, such alignment may simply be fortuitous. An
example of this is 55 Cancri (orbital solution of Fischer et al., 2008) where
multiple eigenmodes remain undamped. Various solutions for 55 Cancri are
compared, showing differing dynamical groupings, with implications for the
coupling of eccentricities and for the partitioning of damping among the
planets. Solutions for orbits that include expectations of past tidal evolution
with observational data, must take into account which eigenmodes should be
damped, rather than expecting particular eccentricities to be near zero.
Classical secular theory is only accurate for low eccentricity values, but
comparison with other results suggests that it can yield useful qualitative
descriptions of behavior even for moderately large eccentricity values, and may
have advantages for revealing underlying physical processes and, as large
numbers of new systems are discovered, for triage to identify where more
comprehensive dynamical studies should have priority.Comment: Published in Celestial Mechanics and Dynamical Astronomy, 25 pages,
10 figure
Analysis of the total 12C(α,γ)16O cross section based on available angular distributions and other primary data
Because a knowledge of the 12C/16O ratio is crucial to the understanding of the later evolution of massive stars, new R- and K-matrix fits have been completed using the available angular distribution data from radiative α capture and elastic α scattering on 12C. Estimates of the total 12C(α,γ)16O rate at stellar energies are reported. In contrast with previous work, the analyses generally involve R- and K-matrix fits directly to the primary data, i.e., the energy- and angle-dependent differential yields, with all relevant partial waves fitted simultaneously (referred to here as surface fits). It is shown that, while the E1 part of the reaction is well constrained by a recent experiment on the β-delayed α-particle decay of 16N, only upper limits can be placed on the E2 ground state cross section factor which we take conservatively as SE2(300)<140 keV b. Simulations were then carried out to explore what kind of new data could lead to better restrictions on SE2(300). We find that improved elastic scattering data may be the best short-term candidate for such restrictions while significantly improving S(300) with new radiative capture data may require a longer-term effort. Theoretical models and estimates from α-transfer reactions for the E2 part of 12C(α,γ)16O are then discussed for comparison with the R- and K-matrix fits of the present work
Tidal Heating of Extra-Solar Planets
Extra-solar planets close to their host stars have likely undergone
significant tidal evolution since the time of their formation. Tides probably
dominated their orbital evolution once the dust and gas had cleared away, and
as the orbits evolved there was substantial tidal heating within the planets.
The tidal heating history of each planet may have contributed significantly to
the thermal budget that governed the planet's physical properties, including
its radius, which in many cases may be measured by observing transit events.
Typically, tidal heating increases as a planet moves inward toward its star and
then decreases as its orbit circularizes. Here we compute the plausible heating
histories for several planets with measured radii, using the same tidal
parameters for the star and planet that had been shown to reconcile the
eccentricity distribution of close-in planets with other extra-solar planets.
Several planets are discussed, including for example HD 209458 b, which may
have undergone substantial tidal heating during the past billion years, perhaps
enough to explain its large measured radius. Our models also show that GJ 876 d
may have experienced tremendous heating and is probably not a solid, rocky
planet. Theoretical models should include the role of tidal heating, which is
large, but time-varying.Comment: Accepted for publication to Ap
On the interpretation of the long-term cyclic period variations in RR Lyrae stars
Many RR Lyrae stars show long-term variations of their pulsation period, some
of them in a cyclic way. Such behaviour can be attributed to the light-travel
time effect (LTTE) caused by an unseen companion. Solutions of the LTTE often
suggest very eccentric orbits and minimal mass of the companion on the order of
several solar masses, thus, in the black hole range. We discuss the possibility
of the occurrence of the RR Lyr-black hole pairs and on the case of Z CVn
demonstrate that the LTTE hypothesis can be false in some of the binary
candidates.Comment: 5 pages, 2 figures, published in the proceedings of "The RR Lyrae
2017 Conference", Niepolomice, Poland, 17-21 September 201
Evidence of Pentaquark States from K+ N Scattering Data?
Motivated by the recent experimental evidence of the exotic B = S = +1
baryonic state Theta(1540), we examine the older existing data on K+ N elastic
scattering through the time delay method. We find positive peaks in time delay
around 1.545 and 1.6 GeV in the D03 and P01 partial waves of K+ N scattering
respectively, in agreement with experiments. We also find an indication of the
J=3/2 Theta* spin-orbit partner to the Theta, in the P03 partial wave at 1.6
GeV. We discuss the pros and contras of these findings in support of the
interpretation of these peaks as possible exotics.Comment: 10 pages, 4 figure
Self Piercing Riveting for Metal-Polymer Joints
Self-Piercing Riveting (SPR) is a sheet metal joining technique based on the insertion of a rivet into two or more sheets, with no preparatory hole. This process has gained wide diffusion in the automotive industry, due to the increasing use of materials alternative to steel, that are difficult or impossible to join with traditional techniques. In particular, polymeric materials are becoming increasingly used, due to their favorable weight/strength ratio. This paper reports the results of experimental investigations, aimed at identifying the variables affecting the mechanical characteristics of mixed metal-plastic joints. A statistic model for the optimization of the geometrical parameters has been computed. The paper demonstrates that self-piercing riveting appears competitive for metal/polymer junction. The results analyzed in light of statistical techniques show that some geometrical parameters affect joint performance more than others and can therefore be used as independent variables for joint performance optimizatio
Dissociation cross sections of ground-state and excited charmonia with light mesons in the quark model
We present numerical results for the dissociation cross sections of
ground-state, orbitally- and radially-excited charmonia in collisions with
light mesons. Our results are derived using the nonrelativistic quark model, so
all parameters are determined by fits to the experimental meson spectrum.
Examples of dissociation into both exclusive and inclusive final states are
considered. The dissociation cross sections of several C=(+) charmonia may be
of considerable importance for the study of heavy ion collisions, since these
states are expected to be produced more copiously than the J/psi. The relative
importance of the productions of ground-state and orbitally-excited charmed
mesons in a pion-charmonium collision is demonstrated through the -dependent charmonium dissociation cross sections.Comment: 9 pages, 8 figure
A cautionary tale of interpreting O-C diagrams: period instability in a classical RR Lyr Star Z CVn mimicking as a distant companion
We present a comprehensive study of Z CVn, an RR Lyrae star that shows
long-term cyclic variations of its pulsation period. A possible explanation
suggested from the shape of the O-C diagram is the light travel-time effect,
which we thoroughly examine. We used original photometric and spectroscopic
measurements and investigated the period evolution using available maximum
times spanning more than one century. If the binary hypothesis is valid, Z CVn
orbits around a black hole with minimal mass of
on a very wide ( years) and eccentric orbit (). We
discuss the probability of a formation of a black hole-RR Lyrae pair and,
although we found it possible, there is no observational evidence of the black
hole in the direction to Z CVn. However, the main objection against the binary
hypothesis is the comparison of the systemic radial velocity curve model and
spectroscopic observations that clearly show that Z CVn cannot be bound in such
a binary. Therefore, the variations of pulsation period are likely intrinsic to
the star. This finding represents a discovery/confirmation of a new type of
cyclic period changes in RR Lyrae stars. By the analysis of our photometric
data, we found that the Blazhko modulation with period of 22.931 d is strongly
dominant in amplitude. The strength of the phase modulation varies and is
currently almost undetectable. We also estimated photometric physical
parameters of Z CVn and investigated their variations during the Blazhko cycle
using the Inverse Baade-Wesselink method.Comment: 15 pages, 8 tables, 9 figures, accepted for publication in MNRA
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Optimization of the Spectral Line Inversion Code
The Very Fast Inversion of the Stokes Vector (VFISV) is a Milne-Eddington
spectral line inversion code used to determine the magnetic and thermodynamic
parameters of the solar photosphere from observations of the Stokes vector in
the 6173 A Fe I line by the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory (SDO). We report on the modifications made to the
original VFISV inversion code in order to optimize its operation within the HMI
data pipeline and provide the smoothest solution in active regions. The changes
either sped up the computation or reduced the frequency with which the
algorithm failed to converge to a satisfactory solution. Additionally, coding
bugs which were detected and fixed in the original VFISV release, are reported
here.Comment: Accepted for publication in Solar Physic
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