5,392 research outputs found
Optimization as a design strategy. Considerations based on building simulation-assisted experiments about problem decomposition
In this article the most fundamental decomposition-based optimization method
- block coordinate search, based on the sequential decomposition of problems in
subproblems - and building performance simulation programs are used to reason
about a building design process at micro-urban scale and strategies are defined
to make the search more efficient. Cyclic overlapping block coordinate search
is here considered in its double nature of optimization method and surrogate
model (and metaphore) of a sequential design process. Heuristic indicators apt
to support the design of search structures suited to that method are developed
from building-simulation-assisted computational experiments, aimed to choose
the form and position of a small building in a plot. Those indicators link the
sharing of structure between subspaces ("commonality") to recursive
recombination, measured as freshness of the search wake and novelty of the
search moves. The aim of these indicators is to measure the relative
effectiveness of decomposition-based design moves and create efficient block
searches. Implications of a possible use of these indicators in genetic
algorithms are also highlighted.Comment: 48 pages. 12 figures, 3 table
GRASS: Generative Recursive Autoencoders for Shape Structures
We introduce a novel neural network architecture for encoding and synthesis
of 3D shapes, particularly their structures. Our key insight is that 3D shapes
are effectively characterized by their hierarchical organization of parts,
which reflects fundamental intra-shape relationships such as adjacency and
symmetry. We develop a recursive neural net (RvNN) based autoencoder to map a
flat, unlabeled, arbitrary part layout to a compact code. The code effectively
captures hierarchical structures of man-made 3D objects of varying structural
complexities despite being fixed-dimensional: an associated decoder maps a code
back to a full hierarchy. The learned bidirectional mapping is further tuned
using an adversarial setup to yield a generative model of plausible structures,
from which novel structures can be sampled. Finally, our structure synthesis
framework is augmented by a second trained module that produces fine-grained
part geometry, conditioned on global and local structural context, leading to a
full generative pipeline for 3D shapes. We demonstrate that without
supervision, our network learns meaningful structural hierarchies adhering to
perceptual grouping principles, produces compact codes which enable
applications such as shape classification and partial matching, and supports
shape synthesis and interpolation with significant variations in topology and
geometry.Comment: Corresponding author: Kai Xu ([email protected]
Generación procedural de variaciones en modelos 3D
El problema de partida de este proyecto es el de trasladar al mundo virtual la variabilidad que presentan los objetos del mundo real. Esta variabilidad juega un papel fundamental en la creación de escenas realistas, especialmente en aquellas que incluyen múltiples instancias de un mismo objeto (un bosque, un rebaño, una muchedumbre...). Sin embargo, tratar de capturar esta diversidad de forma manual es un proceso costoso tanto en tiempo de desarrollo como en espacio de memoria.
Este proyecto busca solventar estos dos inconvenientes mediante el uso de técnicas procedurales. Concretamente, se ha desarrollado un sistema capaz de generar variaciones de un modelo 3D de forma automática. Como generalizar el sistema a todo tipo de modelos excede las posibilidades de este proyecto, se ha decidido centrar el trabajo en la generación de variaciones de caballos. Estas variaciones afectan tanto a la textura como a la forma del modelo utilizado.
El sistema ha sido implementado en dos entornos diferentes. La primera implementación utiliza WebGL para llevar las funcionalidades del sistema a aplicaciones de gráficos 3D en la web. La segunda está integrada en Unity, un motor gráfico multiplataforma orientado al desarrollo de videojuegos
21-cm cosmology
Imaging the Universe during the first hundreds of millions of years remains
one of the exciting challenges facing modern cosmology. Observations of the
redshifted 21 cm line of atomic hydrogen offer the potential of opening a new
window into this epoch. This would transform our understanding of the formation
of the first stars and galaxies and of the thermal history of the Universe. A
new generation of radio telescopes is being constructed for this purpose with
the first results starting to trickle in. In this review, we detail the physics
that governs the 21 cm signal and describe what might be learnt from upcoming
observations. We also generalize our discussion to intensity mapping of other
atomic and molecular lines.Comment: 64 pages, 20 figures, submitted to Reports on Progress in Physics,
comments welcom
Delayed neutrino-driven supernova explosions aided by the standing accretion-shock instability
We present results of 2D hydrodynamic simulations of stellar core collapse,
which confirm that the neutrino-heating mechanism remains viable for the
explosion of a wider mass range of supernova progenitors with iron cores. We
used an energy-dependent treatment of the neutrino transport based on the
"ray-by-ray plus" approximation, in which the number, energy, and momentum
equations are closed with a variable Eddington factor obtained by iteratively
solving a model Boltzmann equation. We focus on the evolution of a 15 Msun
progenitor and show that shock revival and the explosion are initiated at about
600 ms post bounce, powered by neutrino energy deposition. Similar to previous
findings for an 11.2 Msun star, but significantly later, the onset of the
explosion is fostered by the standing accretion shock instability (SASI). This
instability exhibits highest growth rates for the dipole and quadrupole modes,
which lead to large-amplitude bipolar shock oscillations and push the shock to
larger radii, thus increasing the time accreted matter is exposed to neutrino
heating in the gain layer. Therefore also convective overturn behind the shock
is strengthened. A "soft" nuclear equation of state that causes a rapid
contraction and a smaller radius of the forming neutron star and thus a fast
release of gravitational binding energy, seems to be more favorable for an
explosion. Rotation has the opposite effect because it leads to a more extended
and cooler neutron star and thus lower neutrino luminosities and mean energies
and overall less neutrino heating. Neutron star g-mode oscillations and the
acoustic mechanism play no important role in our simulations. (abridged)Comment: 46 pages, 20 figures, 59 eps files; submitted to ApJ; significantly
extended and revised version to account for referee comments; high-resolution
images can be obtained upon reques
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