7,291 research outputs found
Combinatorial identities for binary necklaces from exact ray-splitting trace formulae
Based on an exact trace formula for a one-dimensional ray-splitting system,
we derive novel combinatorial identities for cyclic binary sequences (P\'olya
necklaces).Comment: 15 page
Mississippi State University Research / Demonstration Module
A final report on the Mississippi State Module Planning Grant prepared by E. T. Kohler and R. C. Maxson in September of 1968
Star formation environments and the distribution of binary separations
We have carried out K-band speckle observations of a sample of 114 X-ray
selected weak-line T Tauri stars in the nearby Scorpius-Centaurus OB
association. We find that for binary T Tauri stars closely associated to the
early type stars in Upper Scorpius, the youngest subgroup of the OB
association, the peak in the distribution of binary separations is at 90 A.U.
For binary T Tauri stars located in the direction of an older subgroup, but not
closely associated to early type stars, the peak in the distribution is at 215
A.U. A Kolmogorov-Smirnov test indicates that the two binary populations do not
result from the same distibution at a significance level of 98%. Apparently,
the same physical conditions which facilitate the formation of massive stars
also facilitate the formation of closer binaries among low-mass stars, whereas
physical conditions unfavorable for the formation of massive stars lead to the
formation of wider binaries among low-mass stars. The outcome of the binary
formation process might be related to the internal turbulence and the angular
momentum of molecular cloud cores, magnetic field, the initial temperature
within a cloud, or - most likely - a combination of all of these. We conclude
that the distribution of binary separations is not a universal quantity, and
that the broad distribution of binary separations observed among main-sequence
stars can be explained by a superposition of more peaked binary distributions
resulting from various star forming environments. The overall binary frequency
among pre-main-sequence stars in individual star forming regions is not
necessarily higher than among main-sequence stars.Comment: 7 pages, Latex, 4 Postscript figures; also available at
http://spider.ipac.caltech.edu/staff/brandner/pubs/pubs.html ; accepted for
publication in ApJ Letter
Sorption, Desorption and Exchange of Cesium on Glaciofluvial Deposits
Distribution ratios and isotherms for Sorption, desorption and isotope-exchange of cesium (labelled with Cs-137) were measured on grain size fractions (<2mm) of quatemary glaciofluvial deposits. Sediment materials from two locations within Switzerland and synthetic groundwaters of different compositions were used. The investigated concentration range for cesium was 10"" — 10"' M. Cesium introduced into the system with the solid phase may influence the measurements at the lowest concentrations.
Depending on the experimental conditions, the distribution ratios vary between 3 and 30'000 ml/g. The isotherms are non-linear. Normalization of the cesium concentration in the solid with the cation-exchange capacity leads to nearly identical isotherms for all size fractions of the two geographic locations. Desorption and exchange are retarded at the higher cesium concentrations. This can be explained by structural changes in clay minerals which dominate the Sorption of cesium on this material. Variations in the composition of the groundwater influence the Sorption of cesium only sHghtly; potassium and hydrogen ions are the main competitors
Torsion Degrees of Freedom in the Regge Calculus as Dislocations on the Simplicial Lattice
Using the notion of a general conical defect, the Regge Calculus is
generalized by allowing for dislocations on the simplicial lattice in addition
to the usual disclinations. Since disclinations and dislocations correspond to
curvature and torsion singularities, respectively, the method we propose
provides a natural way of discretizing gravitational theories with torsion
degrees of freedom like the Einstein-Cartan theory. A discrete version of the
Einstein-Cartan action is given and field equations are derived, demanding
stationarity of the action with respect to the discrete variables of the
theory
A Multiplicity Census of Young Stars in Chamaeleon I
We present the results of a multiplicity survey of 126 stars spanning ~0.1-3
solar masses in the ~2-Myr-old Chamaeleon I star-forming region, based on
adaptive optics imaging with the ESO Very Large Telescope. Our observations
have revealed 30 binaries and 6 triples, of which 19 and 4, respectively, are
new discoveries. The overall multiplicity fraction we find for Cha I (~30%) is
similar to those reported for other dispersed young associations, but
significantly higher than seen in denser clusters and the field, for comparable
samples. Both the frequency and the maximum separation of Cha I binaries
decline with decreasing mass, while the mass ratios approach unity; conversely,
tighter pairs are more likely to be equal mass. We confirm that brown dwarf
companions to stars are rare, even at young ages at wide separations. Based on
follow-up spectroscopy of two low-mass substellar companion candidates, we
conclude that both are likely background stars. The overall multiplicity
fraction in Cha I is in rough agreement with numerical simulations of cloud
collapse and fragmentation, but its observed mass dependence is less steep than
predicted. The paucity of higher-order multiples, in particular, provides a
stringent constraint on the simulations, and seems to indicate a low level of
turbulence in the prestellar cores in Cha I.Comment: Accepted for publication in Ap
A double-lined spectroscopic orbit for the young star HD 34700
We report high-resolution spectroscopic observations of the young star HD
34700, which confirm it to be a double-lined spectroscopic binary. We derive an
accurate orbital solution with a period of 23.4877 +/- 0.0013 days and an
eccentricity of e = 0.2501 +/- 0.0068. The stars are found to be of similar
mass (M2/M1 = 0.987 +/- 0.014) and luminosity. We derive also the effective
temperatures (5900 K and 5800 K) and projected rotational velocities (28 km/s
and 22 km/s) of the components. These values of v sin i are much higher than
expected for main-sequence stars of similar spectral type (G0), and are not due
to tidal synchronization. We discuss also the indicators of youth available for
the object. Although there is considerable evidence that the system is young
--strong infrared excess, X-ray emission, Li I 6708 absorption (0.17 Angstroms
equivalent width), H alpha emission (0.6 Angstroms), rapid rotation-- the
precise age cannot yet be established because the distance is unknown.Comment: 17 pages, including 2 figures and 2 tables. Accepted for publication
in AJ, to appear in February 200
Forces Induced by Non-Equilibrium Fluctuations: The Soret-Casimir Effect
The notion of fluctuation-induced forces is generalized to the cases where
the fluctuations have nonequilibrium origin. It is shown that a net force is
exerted on a single flat plate that restricts scale-free fluctuations of a
scalar field in a temperature gradient. This force tends to push the object to
the colder regions, which is a manifestation of thermophoresis or the Soret
effect. In the classic two-plate geometry, it is shown that the Casimir forces
exerted on the two plates differ from each other, and thus the Newton's third
law is violated.Comment: 8 pages, 5 postscript figures, uses (old) RevTe
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