703 research outputs found
Parametrization of translational surfaces
The algebraic translational surface is a typical modeling surface in computer
aided design and architecture industry. In this paper, we give a necessary and
sufficient condition for that algebraic surface having a standard parametric
representation and our proof is constructive. If the given algebraic surface is
translational, then we can compute a standard parametric representation for the
surface
A symbolic-numeric approach for parametrizing ruled surfaces
This paper presents symbolic algorithms to determine whether a given surface (implicitly or parametrically defined) is a rational ruled surface and find a proper parametrization of the ruled surface. However, in practical applications, one has to deal with numerical objects that are given approximately, probably because they proceed from an exact data that has been perturbed under some previous measuring process or manipulation. For these numerical objects, the authors adapt the symbolic algorithms presented by means of the use of numerical techniques. The authors develop numeric algorithms that allow to determine ruled surfaces "close" to an input (not necessarily ruled) surface, and the distance between the input and the output surface is computed.Ministerio de Ciencia, InnovaciĂłn y UniversidadesNational Natural Science Foundation of Chin
On the computation of singularities of parametrized ruled surfaces
Given a ruled surface V defined in the standard parametric form P(t1, t2), we present an algorithm that determines the singularities (and their multiplicities) of V from the parametrization P. More precisely, from P we construct an auxiliary parametric curve and we show how the problem can be simplified to determine the singularities of this auxiliary curve. Only one univariate resultant has to be computed and no elimination theory techniques are necessary. These results improve some previous algorithms for detecting singularities for the special case of parametric ruled surfaces.Ministerio de Ciencia, InnovaciĂłn y Universidade
The Edgeworth-Kuiper debris disk
(Abridged) The Edgeworth-Kuiper belt with its presumed dusty debris is a
natural reference for extrsolar debris disks. We employ a new algorithm to
eliminate the inclination and the distance selection effects in the known TNO
populations to derive expected parameters of the "true" EKB. Its estimated mass
is M_EKB=0.12 M_earth, which is by a factor of \sim 15 larger than the mass of
the EKB objects detected so far. About a half of the total EKB mass is in
classical and resonant objects and another half is in scattered ones. Treating
the debiased populations of EKB objects as dust parent bodies, we then
"generate" their dust disk with our collisional code. Apart from accurate
handling of collisions and direct radiation pressure, we include the
Poynting-Robertson (P-R) drag, which cannot be ignored for the EKB dust disk.
Outside the classical EKB, the radial profile of the optical depth
approximately follows tau \sim r^-2 which is roughly intermediate between the
slope predicted analytically for collision-dominated (r^-1.5) and
transport-dominated (r^-2.5) disks. The cross section-dominating grain size
still lies just above the blowout size (\sim 1...2 \microm), as it would
without the P-R transport. However, if the EKB were by one order of magnitude
less massive, the optical depth profile would fall off as tau \sim r^-3, and
the cross section-dominating grain size would shift from \sim 1...2\microm to
~100 \microm. These properties are seen if dust is assumed to be generated only
by known TNOs. If the solar system were observed from outside, the thermal
emission flux from the EKB dust would be about two orders of magnitude lower
than for solar-type stars with the brightest known infrared excesses observed
from the same distance. Herschel and other new-generation facilities should
reveal extrasolar debris disks nearly as tenuous as the EKB disk. The
Herschel/PACS instrument should be able to detect disks at a \sim 1...2M_EKB
level.Comment: 18 pages, 14 figures, accepted for publication in A&
Characterization of rational ruled surfaces
The algebraic ruled surface is a typical modeling surface in computer aided geometric design. In this paper, we present algorithms to determine whether a given implicit or parametric algebraic surface is a rational ruled surface, and in the affirmative case, to compute a standard parametric representation for the surface
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