487,927 research outputs found
Integration of geometric modeling and advanced finite element preprocessing
The structure to a geometry based finite element preprocessing system is presented. The key features of the system are the use of geometric operators to support all geometric calculations required for analysis model generation, and the use of a hierarchic boundary based data structure for the major data sets within the system. The approach presented can support the finite element modeling procedures used today as well as the fully automated procedures under development
A geometrical model for the Monte Carlo simulation of the TrueBeam linac
Monte Carlo (MC) simulation of linacs depends on the accurate geometrical
description of the head. The geometry of the Varian TrueBeam (TB) linac is not
available to researchers. Instead, the company distributes phase-space files
(PSFs) of the flattening-filter-free (FFF) beams tallied upstream the jaws.
Yet, MC simulations based on third party tallied PSFs are subject to
limitations. We present an experimentally-based geometry developed for the
simulation of the FFF beams of the TB linac. The upper part of the TB linac was
modeled modifying the Clinac 2100 geometry. The most important modification is
the replacement of the standard flattening filters by ad hoc thin filters which
were modeled by comparing dose measurements and simulations. The experimental
dose profiles for the 6MV and 10MV FFF beams were obtained from the Varian
Golden Data Set and from in-house measurements for radiation fields ranging
from 3X3 to 40X40 cm2. Indicators of agreement between the experimental data
and the simulation results obtained with the proposed geometrical model were
the dose differences, the root-mean-square error and the gamma index. The same
comparisons were done for dose profiles obtained from MC simulations using the
second generation of PSFs distributed by Varian for the TB linac. Results of
comparisons show a good agreement of the dose for the ansatz geometry similar
to that obtained for the simulations with the TB PSFs for all fields
considered, except for the 40X40 cm2 field where the ansatz geometry was able
to reproduce the measured dose more accurately. Our approach makes possible to:
(i) adapt the initial beam parameters to match measured dose profiles; (ii)
reduce the statistical uncertainty to arbitrarily low values; and (iii) assess
systematic uncertainties by employing different MC codes
Second Harmonic Generation from Critically Coupled Surface Phonon Polaritons
Mid-infrared nanophotonics can be realized using sub-diffractional light
localization and field enhancement with surface phonon polaritons in polar
dielectric materials. We experimentally demonstrate second harmonic generation
due to the optical field enhancement from critically coupled surface phonon
polaritons at the 6H-SiC-air interface, employing an infrared free-electron
laser for intense, tunable, and narrowband mid-infrared excitation. Critical
coupling to the surface polaritons is achieved using a prism in the Otto
geometry with adjustable width of the air gap, providing full control over the
excitation conditions along the polariton dispersion. The calculated
reflectivity and second harmonic spectra reproduce the full experimental data
set with high accuracy, allowing for a quantification of the optical field
enhancement. We also reveal the mechanism for low out-coupling efficiency of
the second harmonic light in the Otto geometry. Perspectives on surface phonon
polariton-based nonlinear sensing and nonlinear waveguide coupling are
discussed
A comparison of data collection methods for spatial analysis
This report looks at three methods for capturing the geometry of buildings and their elements to be used in the generation of energy models of those buildings. A heritage building in Salford, UK, is used as a case study, receiving each data collection method. Energy models developed based upon data collected for this building is analysed for variations in geometry and predictions of energy performance
Communication Theoretic Data Analytics
Widespread use of the Internet and social networks invokes the generation of
big data, which is proving to be useful in a number of applications. To deal
with explosively growing amounts of data, data analytics has emerged as a
critical technology related to computing, signal processing, and information
networking. In this paper, a formalism is considered in which data is modeled
as a generalized social network and communication theory and information theory
are thereby extended to data analytics. First, the creation of an equalizer to
optimize information transfer between two data variables is considered, and
financial data is used to demonstrate the advantages. Then, an information
coupling approach based on information geometry is applied for dimensionality
reduction, with a pattern recognition example to illustrate the effectiveness.
These initial trials suggest the potential of communication theoretic data
analytics for a wide range of applications.Comment: Published in IEEE Journal on Selected Areas in Communications, Jan.
201
A numerical code for a three-dimensional magnetospheric MHD equilibrium model
Two dimensional and three dimensional MHD equilibrium models were begun for Earth's magnetosphere. The original proposal was motivated by realizing that global, purely data based models of Earth's magnetosphere are inadequate for studying the underlying plasma physical principles according to which the magnetosphere evolves on the quasi-static convection time scale. Complex numerical grid generation schemes were established for a 3-D Poisson solver, and a robust Grad-Shafranov solver was coded for high beta MHD equilibria. Thus, the effects were calculated of both the magnetopause geometry and boundary conditions on the magnetotail current distribution
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