4,878 research outputs found
XAFS spectroscopy. I. Extracting the fine structure from the absorption spectra
Three independent techniques are used to separate fine structure from the
absorption spectra, the background function in which is approximated by (i)
smoothing spline. We propose a new reliable criterion for determination of
smoothing parameter and the method for raising of stability with respect to
k_min variation; (ii) interpolation spline with the varied knots; (iii) the
line obtained from bayesian smoothing. This methods considers various prior
information and includes a natural way to determine the errors of XAFS
extraction. Particular attention has been given to the estimation of
uncertainties in XAFS data. Experimental noise is shown to be essentially
smaller than the errors of the background approximation, and it is the latter
that determines the variances of structural parameters in subsequent fitting.Comment: 16 pages, 7 figures, for freeware XAFS analysis program, see
http://www.crosswinds.net/~klmn/viper.htm
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PDE Face: A Novel 3D Face Model
YesWe introduce a novel approach to face models, which
exploits the use of Partial Differential Equations (PDE) to
generate the 3D face. This addresses some common
problems of existing face models. The PDE face benefits
from seamless merging of surface patches by using only a
relatively small number of parameters based on boundary
curves. The PDE face also provides users with a great
degree of freedom to individualise the 3D face by
adjusting a set of facial boundary curves. Furthermore, we
introduce a uv-mesh texture mapping method. By
associating the texels of the texture map with the vertices
of the uv mesh in the PDE face, the new texture mapping
method eliminates the 3D-to-2D association routine in
texture mapping. Any specific PDE face can be textured
without the need for the facial expression in the texture
map to match exactly that of the 3D face model
Approximation of CNC part program within a given tolerance band
Freeform surfaces are widely used in various fields of engineering design such as automotive, aerospace and mold and die industries. With the geometric model designed by freeform surfaces in the CAD system, the tool path will be next constructed and sampled by the CAM system according to the predefined chordal deviation. The sequentially sampled short linear blocks are stored in the file called the part program, which is later interpreted by the CNC system to control the machine tool and mill the workpiece.
In order to deliver the desired motion smoothly and rapidly, the short linear blocks in the part program will be approximated with smooth spline curves within a specified tolerance band. With spline curves, which consist of longer polynomial pieces, the attainable feed rate of the machine tool can be greatly enhanced. In addition, with minimization of curvature variation, velocity and acceleration jumps in the relevant machine axes and undesired mechanical oscillation of the machine can be reduced significantly. This allows higher traversing speeds and reduces the vibration of the machine, thus improves the surface quality
Functional Regression
Functional data analysis (FDA) involves the analysis of data whose ideal
units of observation are functions defined on some continuous domain, and the
observed data consist of a sample of functions taken from some population,
sampled on a discrete grid. Ramsay and Silverman's 1997 textbook sparked the
development of this field, which has accelerated in the past 10 years to become
one of the fastest growing areas of statistics, fueled by the growing number of
applications yielding this type of data. One unique characteristic of FDA is
the need to combine information both across and within functions, which Ramsay
and Silverman called replication and regularization, respectively. This article
will focus on functional regression, the area of FDA that has received the most
attention in applications and methodological development. First will be an
introduction to basis functions, key building blocks for regularization in
functional regression methods, followed by an overview of functional regression
methods, split into three types: [1] functional predictor regression
(scalar-on-function), [2] functional response regression (function-on-scalar)
and [3] function-on-function regression. For each, the role of replication and
regularization will be discussed and the methodological development described
in a roughly chronological manner, at times deviating from the historical
timeline to group together similar methods. The primary focus is on modeling
and methodology, highlighting the modeling structures that have been developed
and the various regularization approaches employed. At the end is a brief
discussion describing potential areas of future development in this field
Doctor of Philosophy
dissertationWhile boundary representations, such as nonuniform rational B-spline (NURBS) surfaces, have traditionally well served the needs of the modeling community, they have not seen widespread adoption among the wider engineering discipline. There is a common perception that NURBS are slow to evaluate and complex to implement. Whereas computer-aided design commonly deals with surfaces, the engineering community must deal with materials that have thickness. Traditional visualization techniques have avoided NURBS, and there has been little cross-talk between the rich spline approximation community and the larger engineering field. Recently there has been a strong desire to marry the modeling and analysis phases of the iterative design cycle, be it in car design, turbulent flow simulation around an airfoil, or lighting design. Research has demonstrated that employing a single representation throughout the cycle has key advantages. Furthermore, novel manufacturing techniques employing heterogeneous materials require the introduction of volumetric modeling representations. There is little question that fields such as scientific visualization and mechanical engineering could benefit from the powerful approximation properties of splines. In this dissertation, we remove several hurdles to the application of NURBS to problems in engineering and demonstrate how their unique properties can be leveraged to solve problems of interest
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