13,199 research outputs found
Comparison of Monte Carlo Results for the 3D Ising Interface Tension and Interface Energy with (Extrapolated) Series Expansions
We compare Monte Carlo results for the interface tension and interface energy
of the 3-dimensional Ising model with Pad\'e and inhomogeneous differential
approximants of the low temperature series that was recently extended by Arisue
to order in . The series is expected to suffer
from the roughening singularity at . The comparison with the
Monte Carlo data shows that the Pad\'e and inhomogeneous differential
approximants fail to improve the truncated series result of the interface
tension and the interface energy in the region around the roughening
transition. The Monte Carlo data show that the specific heat displays a peak in
the smooth phase. Neither the truncated series nor the Pad\'e approximants find
this peak. We also compare Monte Carlo data for the energy of the ASOS model
with the corresponding low temperature series that we extended to order
.Comment: 22 pages, 9 figures appended as 3 PS-files, preprints
CERN-TH.7029/93, MS-TPI-93-0
Scattering Models and Basic Experiments in the Microwave Regime
The objectives of research over the next three years are: (1) to develop a randomly rough surface scattering model which is applicable over the entire frequency band; (2) to develop a computer simulation method and algorithm to simulate scattering from known randomly rough surfaces, Z(x,y); (3) to design and perform laboratory experiments to study geometric and physical target parameters of an inhomogeneous layer; (4) to develop scattering models for an inhomogeneous layer which accounts for near field interaction and multiple scattering in both the coherent and the incoherent scattering components; and (5) a comparison between theoretical models and measurements or numerical simulation
Consistent ICP for the registration of sparse and inhomogeneous point clouds
In this paper, we derive a novel iterative closest point (ICP) technique that performs point cloud alignment in a robust and consistent way. Traditional ICP techniques minimize the point-to-point distances, which are successful when point clouds contain no noise or clutter and moreover are dense and more or less uniformly sampled. In the other case, it is better to employ point-to-plane or other metrics to locally approximate the surface of the objects. However, the point-to-plane metric does not yield a symmetric solution, i.e. the estimated transformation of point cloud p to point cloud q is not necessarily equal to the inverse transformation of point cloud q to point cloud p. In order to improve ICP, we will enforce such symmetry constraints as prior knowledge and make it also robust to noise and clutter. Experimental results show that our method is indeed much more consistent and accurate in presence of noise and clutter compared to existing ICP algorithms
Review of the mathematical foundations of data fusion techniques in surface metrology
The recent proliferation of engineered surfaces, including freeform and structured surfaces, is challenging current metrology techniques. Measurement using multiple sensors has been proposed to achieve enhanced benefits, mainly in terms of spatial frequency bandwidth, which a single sensor cannot provide. When using data from different sensors, a process of data fusion is required and there is much active research in this area. In this paper, current data fusion methods and applications are reviewed, with a focus on the mathematical foundations of the subject. Common research questions in the fusion of surface metrology data are raised and potential fusion algorithms are discussed
Quantum energies with worldline numerics
We present new results for Casimir forces between rigid bodies which impose
Dirichlet boundary conditions on a fluctuating scalar field. As a universal
computational tool, we employ worldline numerics which builds on a combination
of the string-inspired worldline approach with Monte-Carlo techniques.
Worldline numerics is not only particularly powerful for inhomogeneous
background configurations such as involved Casimir geometries, it also provides
for an intuitive picture of quantum-fluctuation-induced phenomena. Results for
the Casimir geometries of a sphere above a plate and a new perpendicular-plates
configuration are presented.Comment: 8 pages, 2 figures, Submitted to the Proceedings of the Seventh
Workshop QFEXT'05 (Barcelona, September 5-9, 2005), Refs updated, version to
appear in JPhys
A computer code for forward calculation and inversion of the H/V spectral ratio under the diffuse field assumption
During a quarter of a century, the main characteristics of the
horizontal-to-vertical spectral ratio of ambient noise HVSRN have been
extensively used for site effect assessment. In spite of the uncertainties
about the optimum theoretical model to describe these observations, several
schemes for inversion of the full HVSRN curve for near surface surveying have
been developed over the last decade.
In this work, a computer code for forward calculation of H/V spectra based on
the diffuse field assumption (DFA) is presented and tested.It takes advantage
of the recently stated connection between the HVSRN and the elastodynamic
Green's function which arises from the ambient noise interferometry theory.
The algorithm allows for (1) a natural calculation of the Green's functions
imaginary parts by using suitable contour integrals in the complex wavenumber
plane, and (2) separate calculation of the contributions of Rayleigh, Love,
P-SV and SH waves as well. The stability of the algorithm at high frequencies
is preserved by means of an adaptation of the Wang's orthonormalization method
to the calculation of dispersion curves, surface-waves medium responses and
contributions of body waves.
This code has been combined with a variety of inversion methods to make up a
powerful tool for passive seismic surveying.Comment: Published in Computers & Geosciences 97, 67-7
Accelerated expansion from structure formation
We discuss the physics of backreaction-driven accelerated expansion. Using
the exact equations for the behaviour of averages in dust universes, we explain
how large-scale smoothness does not imply that the effect of inhomogeneity and
anisotropy on the expansion rate is small. We demonstrate with an analytical
toy model how gravitational collapse can lead to acceleration. We find that the
conjecture of the accelerated expansion being due to structure formation is in
agreement with the general observational picture of structures in the universe,
and more quantitative work is needed to make a detailed comparison.Comment: 44 pages, 1 figure. Expanded treatment of topics from the Gravity
Research Foundation contest essay astro-ph/0605632. v2: Added references,
clarified wordings. v3: Published version. Minor changes and corrections,
added a referenc
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