176 research outputs found
FITTING A PARAMETRIC MODEL TO A CLOUD OF POINTS VIA OPTIMIZATION METHODS
Computer Aided Design (CAD) is a powerful tool for designing
parametric geometry. However, many CAD models of current
configurations are constructed in previous generations of CAD
systems, which represent the configuration simply as a collection of
surfaces instead of as a parametrized solid model. But since many
modern analysis techniques take advantage of a parametrization, one
often has to re-engineer the configuration into a parametric
model. The objective here is to generate an efficient, robust, and
accurate method for fitting parametric models to a cloud of
points. The process uses a gradient-based optimization technique,
which is applied to the whole cloud, without the need to segment or
classify the points in the cloud a priori.
First, for the points associated with any component, a variant of
the Levenberg-Marquardt gradient-based optimization method (ILM) is
used to find the set of model parameters that minimizes the
least-square errors between the model and the points. The
efficiency of the ILM algorithm is greatly improved through the use
of analytic geometric sensitivities and sparse matrix techniques.
Second, for cases in which one does not know a priori the
correspondences between points in the cloud and the geometry model\u27s
components, an efficient initialization and classification algorithm
is introduced. While this technique works well once the
configuration is close enough, it occasionally fails when the
initial parametrized configuration is too far from the cloud of
points. To circumvent this problem, the objective function is
modified, which has yielded good results for all cases tested.
This technique is applied to a series of increasingly complex
configurations. The final configuration represents a full transport
aircraft configuration, with a wing, fuselage, empennage, and
engines. Although only applied to aerospace applications, the
technique is general enough to be applicable in any domain for which
basic parametrized models are available
工业生态与节能——面向工业车间非均匀热环境营造的低碳空调系统
The problem of indoor heat supply in industrial workshops in high latitude areas in winter is complex. The energy consumption of air conditioners used in most workshops is huge. In this paper, an innovative industrial low carbon air conditioning design based on the concept of “nonuniform thermal environment” is proposed. Through orthogonal experiment and three-level evaluation, the best operating parameters and energy-saving effect of air conditioning are obtained
Dirac Fermion in Strongly-Bound Graphene Systems
It is highly desirable to integrate graphene into existing semiconductor
technology, where the combined system is thermodynamically stable yet maintain
a Dirac cone at the Fermi level. Firstprinciples calculations reveal that a
certain transition metal (TM) intercalated graphene/SiC(0001), such as the
strongly-bound graphene/intercalated-Mn/SiC, could be such a system. Different
from free-standing graphene, the hybridization between graphene and Mn/SiC
leads to the formation of a dispersive Dirac cone of primarily TM d characters.
The corresponding Dirac spectrum is still isotropic, and the transport behavior
is nearly identical to that of free-standing graphene for a bias as large as
0.6 V, except that the Fermi velocity is half that of graphene. A simple model
Hamiltonian is developed to qualitatively account for the physics of the
transfer of the Dirac cone from a dispersive system (e.g., graphene) to an
originally non-dispersive system (e.g., TM).Comment: Apr 25th, 2012 submitte
Method based on fast fourier transform for calculating conical refraction of beams with noncircular symmetry
Conical refraction of optical beams with circular symmetry is often analyzed using Belsky-Khapalyuk-Berry (BKB) theory; however, for beams with noncircular symmetry, it is difficult to obtain analytical expressions for far-field diffraction patterns. We propose a method, based on fast Fourier transform (FFT), for calculating conical refraction of beams with noncircular symmetry and verify it experimentally using a quasi-plane wave passing through a square aperture and focusing lens. Excellent agreement between theoretical and experimental results has been achieved
Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case of BaFeNiAs
The characteristics of Fe-based superconductors are manifested in their
electronic, magnetic properties, and pairing symmetry of the Cooper pair, but
the latter remain to be explored. Usually in these materials, superconductivity
coexists and competes with magnetic order, giving unconventional pairing
mechanisms. We report on the results of the bulk magnetization measurements in
the superconducting state and the low-temperature specific heat down to 0.4 K
for BaFeNiAs single crystals. The {electronic} specific
heat displays a pronounced anomaly at the superconducting transition
temperature and a small residual part {at low temperatures in the
superconducting state}. The normal-state Sommerfeld coefficient increases with
Ni doping for = 0.092, 0.096, and 0.10, which illustrates the competition
between magnetism and superconductivity. Our analysis of the temperature
dependence of the superconducting-state specific heat and the London
penetration depth provides strong evidence for a two-band -wave order
parameter. Further, the data of the London penetration depth calculated from
the lower critical field follow an exponential temperature dependence,
characteristic of a fully gapped superconductor. These observations clearly
show that the superconducting gap in the nearly optimally doped compounds is
nodeless.Comment: 11 pages, 5 figure
- …