10,679 research outputs found
Radial Velocity Studies of Close Binary Stars. XI
Radial-velocity measurements and sine-curve fits to the orbital radial
velocity variations are presented for ten close binary systems: DU Boo, ET Boo,
TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi and AG Vir. By this
contribution, the DDO program has reached the point of 100 published radial
velocity orbits. The radial velocities have been determined using an improved
fitting technique which uses rotational profiles to approximate individual
peaks in broadening functions.
Three systems, ET Boo, VW LMi and TV UMi, were found to be quadruple while AG
Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual
binary with years, was previously known to be a multiple
system, but we show that the second component is actually a close,
non-eclipsing binary. The new observations enabled us to determine the
spectroscopic orbits of the companion, non-eclipsing pairs in ET Boo and VW
LMi. The particularly interesting case is VW LMi, where the period of the
mutual revolution of the two spectroscopic binaries is only 355 days.
While most of the studied eclipsing pairs are contact binaries, ET Boo is
composed of two double-lined detached binaries and HL Dra is single-lined
detached or semi-detached system. Five systems of this group were observed
spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary),
V566 Oph, AG Vir, but our new data are of much higher quality than the previous
studies.Comment: Accepted by AJ, August 2006, 10 figures, 3 table
Incremental generalized homogeneity, observer design and semiglobal stabilization
The notion of incremental generalized homogeneity is introduced, giving new results on semiglobal stabilization by output
feedback and observer design and putting into a unifying framework the stabilization design for triangular (feedback/
feedforward) and homogeneous systems. A state feedback controller and an asymptotic state observer are designed separately by
dominating the generalized homogeneity degree of the nonlinearities with the degree of the linear approximation of the system
and an output feedback controller is obtained according to a certainty-equivalence principle
Classification of flag-transitive Steiner quadruple systems
A Steiner quadruple system of order v is a 3-(v,4,1) design, and will be
denoted SQS(v). Using the classification of finite 2-transitive permutation
groups all SQS(v) with a flag-transitive automorphism group are completely
classified, thus solving the "still open and longstanding problem of
classifying all flag-transitive 3-(v,k,1) designs" for the smallest value of k.
Moreover, a generalization of a result of H. Lueneburg (1965, Math. Z. 89,
82-90) is achieved.Comment: 11 page
Constructing Optimal Authentication Codes with Perfect Multi-fold Secrecy
We establish a construction of optimal authentication codes achieving perfect
multi-fold secrecy by means of combinatorial designs. This continues the
author's work (ISIT 2009) and answers an open question posed therein. As an
application, we present the first infinite class of optimal codes that provide
two-fold security against spoofing attacks and at the same time perfect two-
fold secrecy.Comment: 4 pages (double-column); to appear in Proc. 2010 International Zurich
Seminar on Communications (IZS 2010, Zurich
Magnetism and unusual Cu valency in quadruple perovskites
We study a selection of Cu-containing magnetic quadruple perovskites
(CaCuTiO, LaCuFeO, and
YCuCoO) by ab initio calculations, and show that Cu is in an
effective divalent Cu(II)-like state or a trivalent Cu(III) state depending on
the choice of octahedral cation. Based on the electronic structure, we also
discuss the role of Mott and Zhang-Rice physics in this materials class.Comment: 5 pages, 4 figure
Coding Theory and Algebraic Combinatorics
This chapter introduces and elaborates on the fruitful interplay of coding
theory and algebraic combinatorics, with most of the focus on the interaction
of codes with combinatorial designs, finite geometries, simple groups, sphere
packings, kissing numbers, lattices, and association schemes. In particular,
special interest is devoted to the relationship between codes and combinatorial
designs. We describe and recapitulate important results in the development of
the state of the art. In addition, we give illustrative examples and
constructions, and highlight recent advances. Finally, we provide a collection
of significant open problems and challenges concerning future research.Comment: 33 pages; handbook chapter, to appear in: "Selected Topics in
Information and Coding Theory", ed. by I. Woungang et al., World Scientific,
Singapore, 201
The High-Order-Multiplicity of Unusually Wide M-dwarf Binaries: Eleven New Triple and Quadruple Systems
M-dwarfs in extremely wide binary systems are very rare, and may thus have
different formation processes from those found as single stars or close
binaries in the field. In this paper we search for close companions to a new
sample of 36 extremely wide M-dwarf binaries, covering a spectral type range of
M1 to M5 and a separation range of 600 - 6500 AU. We discover 10 new triple
systems and one new quadruple system. We carefully account for selection
effects including proper motion, magnitude limits, the detection of close
binaries in the SDSS, and other sample biases. The bias-corrected total
high-order-multiple fraction is 45% (+18%/-16%) and the bias-corrected
incidence of quadruple systems is < 5%, both statistically compatible with that
found for the more common close M-dwarf multiple systems. Almost all the
detected companions have similar masses to their primaries, although two very
low mass companions, including a candidate brown dwarf, are found at relatively
large separations. We find that the close-binary separation distribution is
strongly peaked towards < 30AU separations. There is marginally significant
evidence for a change in high-order M-dwarf multiplicity with binding energy
and total mass. We also find 2-sigma evidence of an unexpected increased
high-order-multiple fraction for the widest targets in our survey, with a
high-order-multiple fraction of 21% (+17%/-7%) for systems with separations up
to 2000AU, compared to 77% (+9%/-22%) for systems with separations > 4000AU.
These results suggest that the very widest M-dwarf binary systems need higher
masses to form or to survive.Comment: 11 pages, 14 figures, accepted for publication in Ap
Conway groupoids, regular two-graphs and supersimple designs
A design is said to be supersimple
if distinct lines intersect in at most two points. From such a design, one can
construct a certain subset of Sym called a "Conway groupoid". The
construction generalizes Conway's construction of the groupoid . It
turns out that several infinite families of groupoids arise in this way, some
associated with 3-transposition groups, which have two additional properties.
Firstly the set of collinear point-triples forms a regular two-graph, and
secondly the symmetric difference of two intersecting lines is again a line. In
this paper, we show each of these properties corresponds to a group-theoretic
property on the groupoid and we classify the Conway groupoids and the
supersimple designs for which both of these two additional properties hold.Comment: 17 page
An electrostatically defined serial triple quantum dot charged with few electrons
A serial triple quantum dot (TQD) electrostatically defined in a GaAs/AlGaAs
heterostructure is characterized by using a nearby quantum point contact as
charge detector. Ground state stability diagrams demonstrate control in the
regime of few electrons charging the TQD. An electrostatic model is developed
to determine the ground state charge configurations of the TQD. Numerical
calculations are compared with experimental results. In addition, the tunneling
conductance through all three quantum dots in series is studied. Quantum
cellular automata processes are identified, which are where charge
reconfiguration between two dots occurs in response to the addition of an
electron in the third dot.Comment: 12 pages, 9 figure
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