230 research outputs found
Almost Isometric Mesh Parameterization through Abstract Domains
In this paper, we propose a robust, automatic technique to build a global hi-quality parameterization of a two-manifold triangular mesh. An adaptively chosen 2D domain of the parameterization is built as part of the process. The produced parameterization exhibits very low isometric distortion, because it is globally optimized to preserve both areas and angles. The domain is a collection of equilateral triangular 2D regions enriched with explicit adjacency relationships (it is abstract in the sense that no 3D embedding is necessary). It is tailored to minimize isometric distortion, resulting in excellent parameterization qualities, even when meshes with complex shape and topology are mapped into domains composed of a small number of large continuous regions. Moreover, this domain is, in turn, remapped into a collection of 2D square regions, unlocking many advantages found in quad-based domains (e. g., ease of packing). The technique is tested on a variety of cases, including challenging ones, and compares very favorably with known approaches. An open-source implementation is made available
Non-linear Matter Spectra in Coupled Quintessence
We consider cosmologies in which a dark-energy scalar field interacts with
cold dark matter. The growth of perturbations is followed beyond the linear
level by means of the time-renormalization-group method, which is extended to
describe a multi-component matter sector. Even in the absence of the extra
interaction, a scale-dependent bias is generated as a consequence of the
different initial conditions for baryons and dark matter after decoupling. The
effect is enhanced significantly by the extra coupling and can be at the 2-3
percent level in the range of scales of baryonic acoustic oscillations. We
compare our results with N-body simulations, finding very good agreement.Comment: 20 pages, 6 figures, typo correcte
Structurally optimized shells.
Shells, i.e., objects made of a thin layer of material following a surface,
are among the most common structures in use. They are highly efficient, in
terms of material required to maintain strength, but also prone to deformation
and failure. We introduce an efficient method for reinforcing shells, that is,
adding material to the shell to increase its resilience to external loads. Our
goal is to produce a reinforcement structure of minimal weight. It has been
demonstrated that optimal reinforcement structures may be qualitatively
different, depending on external loads and surface shape. In some cases, it
naturally consists of discrete protruding ribs; in other cases, a smooth shell
thickness variation allows to save more material.
Most previously proposed solutions, starting from classical Michell trusses,
are not able to handle a full range of shells (e.g., are restricted to
self-supporting structures) or are unable to reproduce this range of behaviors,
resulting in suboptimal structures.
We propose a new method that works for any input surface with any load
configurations, taking into account both in-plane (tensile/compression) and
out-of-plane (bending) forces. By using a more precise volume model, we are
capable of producing optimized structures with the full range of qualitative
behaviors. Our method includes new algorithms for determining the layout of
reinforcement structure elements, and an efficient algorithm to optimize their
shape, minimizing a non-linear non-convex functional at a fraction of the cost
and with better optimality compared to standard solvers.
We demonstrate the optimization results for a variety of shapes, and the
improvements it yields in the strength of 3D-printed objects
Dark Energy and Dark Matter in Galaxy Halos
We consider the possibility that the dark matter is coupled through its mass
to a scalar field associated with the dark energy of the Universe. In order for
such a field to play a role at the present cosmological distances, it must be
effectively massless at galactic length scales. We discuss the effects of the
field on the distribution of dark matter in galaxy halos. We show that the
profile of the distribution outside the galaxy core remains largely unaffected
and the approximately flat rotation curves persist. The dispersion of the dark
matter velocity is enhanced by a potentially large factor relative to the case
of zero coupling between dark energy and dark matter. The counting rates in
terrestrial dark matter detectors are similarly enhanced. Existing bounds on
the properties of dark matter candidates can be extended to the coupled case,
by taking into account the enhancement factor.Comment: 7 pages, 1 figure, references added and discussion expande
State of the Art on Stylized Fabrication
© 2018 The Authors Computer Graphics Forum © 2018 The Eurographics Association and John Wiley & Sons Ltd. Digital fabrication devices are powerful tools for creating tangible reproductions of 3D digital models. Most available printing technologies aim at producing an accurate copy of a tridimensional shape. However, fabrication technologies can also be used to create a stylistic representation of a digital shape. We refer to this class of methods as ‘stylized fabrication methods’. These methods abstract geometric and physical features of a given shape to create an unconventional representation, to produce an optical illusion or to devise a particular interaction with the fabricated model. In this state-of-the-art report, we classify and overview this broad and emerging class of approaches and also propose possible directions for future research
Practical quad mesh simplification
In this paper we present an innovative approach to incremental quad mesh simplification, i.e. the task of producing a low complexity quad mesh starting from a high complexity one. The process is based on a novel set of strictly local operations which preserve quad structure. We show how good tessellation quality (e.g. in terms of vertex valencies) can be achieved by pursuing uniform length and canonical proportions of edges and diagonals. The decimation process is interleaved with smoothing in tangent space. The latter strongly contributes to identify a suitable sequence of local modification operations. The method is naturally extended to manage preservation of feature lines (e.g. creases) and varying (e.g. adaptive) tessellation densities. We also present an original Triangle-to-Quad conversion algorithm that behaves well in terms of geometrical complexity and tessellation quality, which we use to obtain the initial quad mesh from a given triangle mesh
Practical quad mesh simplification
In this paper we present an innovative approach to incremental quad mesh simplification, i.e. the task of producing a low complexity quad mesh starting from a high complexity one. The process is based on a novel set of strictly local operations which preserve quad structure. We show how good tessellation quality (e.g. in terms of vertex valencies) can be achieved by pursuing uniform length and canonical proportions of edges and diagonals. The decimation process is interleaved with smoothing in tangent space. The latter strongly contributes to identify a suitable sequence of local modification operations. The method is naturally extended to manage preservation of feature lines (e.g. creases) and varying (e.g. adaptive) tessellation densities. We also present an original Triangle-to-Quad conversion algorithm that behaves well in terms of geometrical complexity and tessellation quality, which we use to obtain the initial quad mesh from a given triangle mesh
HexBox: Interactive Box Modeling of Hexahedral Meshes
We introduce HexBox, an intuitive modeling method and interactive tool for creating and editing hexahedral meshes. Hexbox brings the major and widely validated surface modeling paradigm of surface box modeling into the world of hex meshing. The main idea is to allow the user to box-model a volumetric mesh by primarily modifying its surface through a set of topological and geometric operations. We support, in particular, local and global subdivision, various instantiations of extrusion, removal, and cloning of elements, the creation of non-conformal or conformal grids, as well as shape modifications through vertex positioning, including manual editing, automatic smoothing, or, eventually, projection on an externally-provided target surface. At the core of the efficient implementation of the method is the coherent maintenance, at all steps, of two parallel data structures: a hexahedral mesh representing the topology and geometry of the currently modeled shape, and a directed acyclic graph that connects operation nodes to the affected mesh hexahedra. Operations are realized by exploiting recent advancements in grid- based meshing, such as mixing of 3-refinement, 2-refinement, and face-refinement, and using templated topological bridges to enforce on-the-fly mesh conformity across pairs of adjacent elements. A direct manipulation user interface lets users control all operations. The effectiveness of our tool, released as open source to the community, is demonstrated by modeling several complex shapes hard to realize with competing tools and techniques
Enlarging mSUGRA parameter space by decreasing pre-BBN Hubble rate in Scalar-Tensor Cosmologies
We determine under what conditions Scalar Tensor cosmologies predict an
expansion rate which is reduced as compared to the standard General Relativity
case. We show that ST theories with a single matter sector typically predict an
enchanced Hubble rate in the past, as a consequence of the requirement of an
attractive fixed point towards General Relativity at late times. Instead, when
additional matter sectors with different conformal factors are added, the late
time convergence to General Relativity is mantained and at the same time a
reduced expansion rate in the past can be driven. For suitable choices of the
parameters which govern the scalar field evolution, a sizeable reduction (up to
about 2 orders of magnitude) of the Hubble rate prior to Big Bang
Nucleosynthesis can be obtained. We then discuss the impact of these
cosmological models on the relic abundance of dark matter is minimal
Supergravity models: we show that the cosmologically allowed regions in
parameter space are significantly enlarged, implying a change in the potential
reach of LHC on the neutralino phenomenology.Comment: 10 pages, 7 figure
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