8,549 research outputs found
Polar Varieties and Efficient Real Equation Solving: The Hypersurface Case
The objective of this paper is to show how the recently proposed method by
Giusti, Heintz, Morais, Morgenstern, Pardo \cite{gihemorpar} can be applied to
a case of real polynomial equation solving. Our main result concerns the
problem of finding one representative point for each connected component of a
real bounded smooth hypersurface. The algorithm in \cite{gihemorpar} yields a
method for symbolically solving a zero-dimensional polynomial equation system
in the affine (and toric) case. Its main feature is the use of adapted data
structure: Arithmetical networks and straight-line programs. The algorithm
solves any affine zero-dimensional equation system in non-uniform sequential
time that is polynomial in the length of the input description and an
adequately defined {\em affine degree} of the equation system. Replacing the
affine degree of the equation system by a suitably defined {\em real degree} of
certain polar varieties associated to the input equation, which describes the
hypersurface under consideration, and using straight-line program codification
of the input and intermediate results, we obtain a method for the problem
introduced above that is polynomial in the input length and the real degree.Comment: Late
Structural characters of epidermal cell walls and resistance to powdery mildew of different grapevine cultivars
The analysis of 12 grapevine cultivars differing in susceptibility to powdery mildew revealed a correlation between the thickness of cuticle plus cell wall of young leaves and resistance to mildew. Neither in mature leaves or in leaves of in vitro plants or in berries such correlations could be established. Coating of the leaf surface with a polymetacrylate antitranspirant prevented sporulation in all cases, although infection structures were formed
Le Wilinwiga des Mossi (Guiera senegalensis, Lam.), ses usages thérapeutiques indigènes et son application au traitement des diarrhées cholériformes
Orbit Determination of Close Binary Systems using Lucky Imaging
We present relative positions of visual binaries observed during 2009 with
the FastCam "lucky-imaging" camera at the 1.5-m Carlos Sanchez Telescope (TCS)
at the Observatorio del Teide. We obtained 424 CCD observations (averaged in
198 mean relative positions) of 157 binaries with angular separations in the
range 0.14-15.40", with a median separation of 0.51". For a given system, each
CCD image represents the sum of the best 10-25% images from 1000-5000
short-exposure frames. Derived internal errors were 7 mas in r and 1.2^{\circ}
(9 mas) in q. When comparing to systems with very well-known orbits, we find
that the rms deviation in r residuals is 23 mas, while the rms deviation in q
residuals is 0.73 deg/r. We confirmed 18 Hipparcos binaries and we report new
companions to BVD 36 A and J 621 B. For binaries with preliminary orbital
parameters, the relative radial velocity was estimated as well. We also present
four new revised orbits computed for LDS 873, BU 627 A-BC, BU 628 and HO 197
AB. This work is the first results on visual binaries using the FastCam
lucky-imaging camera.Comment: 23 pages, 10 figures, 14 tables, accepted August 18th, 2011, to be
published in MNRA
The High Angular Resolution Multiplicity of Massive Stars
We present the results of a speckle interferometric survey of Galactic
massive stars that complements and expands upon a similar survey made over a
decade ago. The speckle observations were made with the KPNO and CTIO 4 m
telescopes and USNO speckle camera, and they are sensitive to the detection of
binaries in the angular separation regime between 0.03" and 5" with relatively
bright companions (Delta V < 3). We report on the discovery of companions to 14
OB stars. In total we resolved companions of 41 of 385 O-stars (11%), 4 of 37
Wolf-Rayet stars (11%), and 89 of 139 B-stars (64%; an enriched visual binary
sample that we selected for future orbital determinations). We made a
statistical analysis of the binary frequency among the subsample that are
listed in the Galactic O Star Catalog by compiling published data on other
visual companions detected through adaptive optics studies and/or noted in the
Washington Double Star Catalog and by collecting published information on
radial velocities and spectroscopic binaries. We find that the binary frequency
is much higher among O-stars in clusters and associations compared to the
numbers for field and runaway O-stars, consistent with predictions for the
ejection processes for runaway stars. We present a first orbit for the O-star
Delta Orionis, a linear solution of the close, apparently optical, companion of
the O-star Iota Orionis, and an improved orbit of the Be star Delta Scorpii.
Finally, we list astrometric data for another 249 resolved and 221 unresolved
targets that are lower mass stars that we observed for various other science
programs.Comment: 76 pages, 6 figures, 11 table
Formation Scenario for Wide and Close Binary Systems
Fragmentation and binary formation processes are studied using
three-dimensional resistive MHD nested grid simulations. Starting with a
Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we
calculate the cloud evolution from the molecular cloud core (n=10^4 cm^-3) to
the stellar core (n \simeq 10^22 cm^-3). We calculated 147 models with
different initial magnetic, rotational, and thermal energies, and the
amplitudes of the non-axisymmetric perturbation. In a collapsing cloud,
fragmentation is mainly controlled by the initial ratio of the rotational to
the magnetic energy, regardless of the initial thermal energy and amplitude of
the non-axisymmetric perturbation. When the clouds have large rotational
energies in relation to magnetic energies, fragmentation occurs in the
low-density evolution phase (10^12 cm^-3 < n < 10^15 cm^-3) with separations of
3-300 AU. Fragments that appeared in this phase are expected to evolve into
wide binary systems. On the other hand, fragmentation does not occur in the
low-density evolution phase, when initial clouds have large magnetic energies
in relation to the rotational energies. In these clouds, fragmentation only
occurs in the high-density evolution phase (n > 10^17 cm^-3) after the clouds
experience significant reduction of the magnetic field owing to Ohmic
dissipation in the period of 10^12 cm^-3 < n < 10^15 cm^-3. Fragments appearing
in this phase have separations of < 0.3 AU, and are expected to evolve into
close binary systems. As a result, we found two typical fragmentation epochs,
which cause different stellar separations. Although these typical separations
are disturbed in the subsequent gas accretion phase, we might be able to
observe two peaks of binary separations in extremely young stellar groups.Comment: 45 pages,12 figures, Submitted to ApJ, For high resolution figures
see
http://www2.scphys.kyoto-u.ac.jp/~machidam/protostar/proto/main-astroph.pd
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