260 research outputs found
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
Dynamical Relaxation of the Dark Matter to Baryon Ratio
A scalar field interacting differently with dark matter and baryons may
explain why their ratio is of order unity today. We provide three working
examples, checking them against the observations of CMB, Large Scale Structure,
supernovae Ia, and post-newtonian tests of gravity. Such a scenario could make
life much easier for supersymmetric dark matter candidates.Comment: 7 pages, 5 .eps figures. Discussion of the approach of the field to
the fixed point added. Figures modified accordingly. Conclusions unchanged.
Version to be published on Phys Rev.
Dark Matter Relic Abundance and Scalar-Tensor Dark Energy
Scalar-tensor theories of gravity provide a consistent framework to
accommodate an ultra-light quintessence scalar field. While the equivalence
principle is respected by construction, deviations from General Relativity and
standard cosmology may show up at nucleosynthesis, CMB, and solar system tests
of gravity. After imposing all the bounds coming from these observations, we
consider the expansion rate of the universe at WIMP decoupling, showing that it
can lead to an enhancement of the dark matter relic density up to few orders of
magnitude with respect to the standard case. This effect can have an impact on
supersymmetric candidates for dark matter.Comment: 12 pages, 13 figures; V2: references added, matches published versio
Non-linear dark energy clustering
We consider a dark energy fluid with arbitrary sound speed and equation of
state and discuss the effect of its clustering on the cold dark matter
distribution at the non-linear level. We write the continuity, Euler and
Poisson equations for the system in the Newtonian approximation. Then, using
the time renormalization group method to resum perturbative corrections at all
orders, we compute the total clustering power spectrum and matter power
spectrum. At the linear level, a sound speed of dark energy different from that
of light modifies the power spectrum on observationally interesting scales,
such as those relevant for baryonic acoustic oscillations. We show that the
effect of varying the sound speed of dark energy on the non-linear corrections
to the matter power spectrum is below the per cent level, and therefore these
corrections can be well modelled by their counterpart in cosmological scenarios
with smooth dark energy. We also show that the non-linear effects on the matter
growth index can be as large as 10-15 per cent for small scales.Comment: 33 pages, 7 figures. Improved presentation. References added. Matches
published version in JCA
A Comment on the Path Integral Approach to Cosmological Perturbation Theory
It is pointed out that the exact renormalization group approach to
cosmological perturbation theory, proposed in Matarrese and Pietroni, JCAP 0706
(2007) 026, arXiv:astro-ph/0703563 and arXiv:astro-ph/0702653, constitutes a
misnomer. Rather, having instructively cast this classical problem into path
integral form, the evolution equation then derived comes about as a special
case of considering how the generating functional responds to variations of the
primordial power spectrum.Comment: 2 pages, v2: refs added, published in JCA
Volume-aware design of composite molds
© 2019 Association for Computing Machinery. We propose a novel technique for the automatic design of molds to cast highly complex shapes. The technique generates composite, two-piece molds. Each mold piece is made up of a hard plastic shell and a flexible silicone part. Thanks to the thin, soft, and smartly shaped silicone part, which is kept in place by a hard plastic shell, we can cast objects of unprecedented complexity. An innovative algorithm based on a volumetric analysis defines the layout of the internal cuts in the silicone mold part. Our approach can robustly handle thin protruding features and intertwined topologies that have caused previous methods to fail. We compare our results with state of the art techniques, and we demonstrate the casting of shapes with extremely complex geometry
On the Physical Significance of Infra-red Corrections to Inflationary Observables
Inflationary observables, like the power spectrum, computed at one- and
higher-order loop level seem to be plagued by large infra-red corrections. In
this short note, we point out that these large infra-red corrections appear
only in quantities which are not directly observable. This is in agreement with
general expectations concerning infra-red effects.Comment: 11 pages; LateX file; 5 figures. Some coefficients in Eq.(A6)
corrected; References adde
Quad Meshing
Triangle meshes have been nearly ubiquitous in computer graphics, and a large body of data structures and geometry processing algorithms based on them has been developed in the literature. At the same time, quadrilateral meshes, especially semi-regular ones, have advantages for many applications, and significant progress was made in quadrilateral mesh generation and processing during the last several years. In this State of the Art Report, we discuss the advantages and problems of techniques operating on quadrilateral meshes, including surface analysis and mesh quality, simplification, adaptive refinement, alignment with features, parametrization, and remeshing
Hard Non-commutative Loops Resummation
The non-commutative version of the euclidean theory is
considered. By using Wilsonian flow equations the ultraviolet renormalizability
can be proved to all orders in perturbation theory. On the other hand, the
infrared sector cannot be treated perturbatively and requires a resummation of
the leading divergencies in the two-point function. This is analogous to what
is done in the Hard Thermal Loops resummation of finite temperature field
theory. Next-to-leading order corrections to the self-energy are computed,
resulting in contributions in the massless case, and
in the massive one.Comment: 4 pages, 3 figures. The resummation procedure is now discussed also
at finite ultraviolet cut-off. Minor changes in abstract and references.
Final version to be published in Physical Review Letter
Boltzmann Suppression of Interacting Heavy Particles
Matsumoto and Yoshimura have recently argued that the number density of heavy
particles in a thermal bath is not necessarily Boltzmann-suppressed for T << M,
as power law corrections may emerge at higher orders in perturbation theory.
This fact might have important implications on the determination of WIMP relic
densities. On the other hand, the definition of number densities in a
interacting theory is not a straightforward procedure. It usually requires
renormalization of composite operators and operator mixing, which obscure the
physical interpretation of the computed thermal average. We propose a new
definition for the thermal average of a composite operator, which does not
require any new renormalization counterterm and is thus free from such
ambiguities. Applying this definition to the model of Matsumoto and Yoshimura
we find that it gives number densities which are Boltzmann-suppressed at any
order in perturbation theory. We discuss also heavy particles which are
unstable already at T=0, showing that power law corrections do in general
emerge in this case.Comment: 7 pages, 5 figures. New section added, with the discussion of the
case of an unstable heavy particle. Version to appear on Phys. Rev.
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