The computer code system penelope (version 2003) performs Monte Carlo simulation of coupled electron-photon transport in arbitrary materials for a wide energy range, from a few hundred eV to about 1 GeV. Photon transport is simulated by means of the standard, detailed simulation scheme. Electron and positron histories are generated on the basis of a mixed procedure, which combines detailed simu...

We introduce an algorithm for fast topology-sensitive decimation of volume meshes. The algorithm employs a planar quadric error metric to guarantee minimum geometric error at every simplification step, while maintaining the input mesh's geometric consistency, and restraining changes to its topological genus, at low computational costs. The proposed method presents a new alternative to existing ...

We present an approach for the exact and efficient computation of a cell in an arrangement of quadric surfaces. All calculations are based on exact rational algebraic methods and provide the correct mathematical results in all, even degenerate, cases. By projection, the spatial problem is reduced to the one of computing planar arrangements of algebraic curves. We succeed in locating all event p...

Motivated by recent work of Florian Pop, we study the connections between three notions of equivalence of function fields: isomorphism, elementary equivalence, and the condition that each of a pair of fields can be embedded in the other, which we call isogeny. Some of our results are purely geometric: we give an isogeny classification of Severi-Brauer varieties and quadric surfaces. These resul...

This paper addresses a common problem in dealing with range images. We propose a novel method to fit surfaces of known types via a parameter decomposition approach. This approach is faithful and it strongly reduces the possibilities of dropping into local minima in the process of iterative optimization. Therefore, it increases the tolerance in selecting the initializations. Moreover, it reduces...

I. Introduction Rational spline is a commonly used spline function. In many cases the rational spline curves better approximating functions than the usual spline functions. It has been observed that many simple shapes including conic section and quadric surfaces can not be represented exactly by piecewise polynomials, whereas rational polynomials can exactly represent all conic sections and qua...

We show that if A is a d-dimensional abelian variety in a smooth quadric of dimension 2d then d = 1 and A is an elliptic curve of bidegree (2, 2) on a quadric. This extends a result of Van de Ven which says that A only can be embedded in P when d = 1 or 2. Mathematics Subject Classifications (1991): Primary, 14K05; secondary, 14E25, 14C99.

Say that a surface in S ⊂ R has the central plane oval property, or cpo, if • S meets some affine plane transversally along an oval, and • Every such transverse plane oval on S has central symmetry. We show that a complete, connected C surface with cpo must either be a cylinder over a central oval, or else quadric. We apply this to deduce that a complete C surface containing a transverse plane ...

greenhouse and laboratory studies were conducted to examine the allelopathic effects of water extracts of pigweed (amaranthus retroflexu l.) leaf, stem, root and flower at different growth stages on canola seed germination and seedling growth. water extracts of leaf, stem, root and flower as individually, binary, ternary and quadri mixtures at 0, 50 and 100% concentrations were made and their e...

In this paper, we propose the utilization of a kd-tree based hierarchy as an implicit object representation. Compared to an octree, the kd-tree based hierarchy is superior in terms of adaptation to the object surface. In consequence, we obtain considerably more compact implicit representations especially in case of thin object structures. We describe a new isosurface extraction algorithm for th...