49,252 research outputs found
Topological correction of hypertextured implicit surfaces for ray casting
Hypertextures are a useful modelling tool in that they
can add three-dimensional detail to the surface of otherwise
smooth objects. Hypertextures can be rendered as implicit
surfaces, resulting in objects with a complex but well
defined boundary. However, representing a hypertexture as
an implicit surface often results in many small parts being
detached from the main surface, turning an object into a
disconnected set. Depending on the context, this can detract
from the realism in a scene where one usually does not
expect a solid object to have clouds of smaller objects floating around it. We present a topology correction technique, integrated in a ray casting algorithm for hypertextured implicit surfaces, that detects and removes all the surface components that have become disconnected from the main surface. Our method works with implicit surfaces that are C2 continuous and uses Morse theory to find the critical points of the surface. The method follows the separatrix lines joining the critical points to isolate disconnected components
An Efficient Linear Programming Algorithm to Generate the Densest Lattice Sphere Packings
Finding the densest sphere packing in -dimensional Euclidean space
is an outstanding fundamental problem with relevance in many
fields, including the ground states of molecular systems, colloidal crystal
structures, coding theory, discrete geometry, number theory, and biological
systems. Numerically generating the densest sphere packings becomes very
challenging in high dimensions due to an exponentially increasing number of
possible sphere contacts and sphere configurations, even for the restricted
problem of finding the densest lattice sphere packings. In this paper, we apply
the Torquato-Jiao packing algorithm, which is a method based on solving a
sequence of linear programs, to robustly reproduce the densest known lattice
sphere packings for dimensions 2 through 19. We show that the TJ algorithm is
appreciably more efficient at solving these problems than previously published
methods. Indeed, in some dimensions, the former procedure can be as much as
three orders of magnitude faster at finding the optimal solutions than earlier
ones. We also study the suboptimal local density-maxima solutions (inherent
structures or "extreme" lattices) to gain insight about the nature of the
topography of the "density" landscape.Comment: 23 pages, 3 figure
Recommended from our members
RGFGA: An efficient representation and crossover for grouping genetic algorithms
There is substantial research into genetic algorithms that are used to group large numbers of
objects into mutually exclusive subsets based upon some fitness function. However, nearly all
methods involve degeneracy to some degree.
We introduce a new representation for grouping genetic algorithms, the restricted growth function
genetic algorithm, that effectively removes all degeneracy, resulting in a more efficient search. A new crossover operator is also described that exploits a measure of similarity between chromosomes in a population. Using several synthetic datasets, we compare the performance of our representation and crossover with another well known state-of-the-art GA method, a strawman
optimisation method and a well-established statistical clustering algorithm, with encouraging results
Lattice study of the Silver Blaze phenomenon for a charged scalar phi-4 field
We analyze a complex scalar field with phi-4 interaction and a chemical
potential mu on the lattice. An exact flux representation of the partition sum
is used which avoids the complex action problem and based on a generalized worm
algorithm we can run Monte Carlo simulations at arbitrary densities. We study
thermodynamical quantities as a function of the chemical potential mu for zero-
and finite temperature. It is shown that at zero temperature thermodynamical
observables are independent of mu up to a critical value mu_c (Silver Blaze
phenomenon). In a spectroscopy calculation we cross-check that mu_c agrees with
the mass m of the scalar field. The Silver Blaze region ends in a second order
phase transition and we show that for low temperatures the second order phase
boundary persists and separates a pseudo Silver Blaze region from a condensed
phase with strong mu-dependence.Comment: Two typos in the appendix fixe
Characteristics and variability of storm tracks in the north Pacific, Bering Sea, and Alaska
The North Pacific and Bering Sea regions represent loci of cyclogenesis and storm track activity. In this paper climatological properties of extratropical storms in the North Pacific/Bering Sea are presented based upon aggregate statistics of individual storm tracks calculated by means of a feature-tracking algorithm run using NCEPâNCAR reanalysis data from 1948/49 to 2008, provided by the NOAA/Earth System Research Laboratory and the Cooperative Institute for Research in Environmental Sciences, Climate Diagnostics Center. Storm identification is based on the 850-hPa relative vorticity field (ζ) instead of the often-used mean sea level pressure; ζ is a prognostic field, a good indicator of synoptic-scale dynamics, and is directly related to the wind speed. Emphasis extends beyond winter to provide detailed consideration of all seasons.
Results show that the interseasonal variability is not as large during the spring and autumn seasons. Most of the storm variablesâgenesis, intensity, track densityâexhibited a maxima pattern that was oriented along a zonal axis. From season to season this axis underwent a northâsouth shift and, in some cases, a rotation to the northeast. This was determined to be a result of zonal heating variations and midtropospheric moisture patterns. Barotropic processes have an influence in shaping the downstream end of storm tracks and, together with the blocking influence of the coastal orography of northwest North America, result in high lysis concentrations, effectively making the Gulf of Alaska the âgraveyardâ of Pacific storms. Summer storms tended to be longest in duration. Temporal trends tended to be weak over the study area. SST did not emerge as a major cyclogenesis control in the Gulf of Alaska
- âŠ