2,493 research outputs found
Rank-Based Analysis of Linear Models Using R
It is well-known that Wilcoxon procedures out perform least squares procedures when the data deviate from normality and/or contain outliers. These procedures can be generalized by introducing weights; yielding so-called weighted Wilcoxon (WW) techniques. In this paper we demonstrate how WW-estimates can be calculated using an L1 regression routine. More importantly, we present a collection of functions that can be used to implement a robust analysis of a linear model based on WW-estimates. For instance, estimation, tests of linear hypotheses, residual analyses, and diagnostics to detect differences in fits for various weighting schemes are discussed. We analyze a regression model, designed experiment, and autoregressive time series model for the sake of illustration. We have chosen to implement the suite of functions using the R statistical software package. Because R is freely available and runs on multiple platforms, WW-estimation and associated inference is now universally accessible.
Vertex-Unfoldings of Simplicial Polyhedra
We present two algorithms for unfolding the surface of any polyhedron, all of
whose faces are triangles, to a nonoverlapping, connected planar layout. The
surface is cut only along polyhedron edges. The layout is connected, but it may
have a disconnected interior: the triangles are connected at vertices, but not
necessarily joined along edges.Comment: 10 pages; 7 figures; 8 reference
Laser-CVD silicon carbide fibers as non woven preforms in fiber-reinforced SiC-SiC composites
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The Thousand Asteroid Light Curve Survey
We present the results of our Thousand Asteroid Light Curve Survey (TALCS)
conducted with the Canada-France-Hawaii Telescope in September 2006. Our
untargeted survey detected 828 Main Belt asteroids to a limiting magnitude of
g'~22.5 corresponding to a diameter range of 0.4 km <= D <= 10 km. Of these,
278 objects had photometry of sufficient quality to perform rotation period
fits. We debiased the observations and light curve fitting process to determine
the true distribution of rotation periods and light curve amplitudes of Main
Belt asteroids. We confirm a previously reported excess in the fraction of fast
rotators but find a much larger excess of slow rotating asteroids (~15% of our
sample). A few percent of objects in the TALCS size range have large light
curve amplitudes of ~1 mag. Fits to the debiased distribution of light curve
amplitudes indicate that the distribution of triaxial ellipsoid asteroid shapes
is proportional to the square of the axis-ratio, (b/a)^2, and may be bi-modal.
Finally, we find six objects with rotation periods that may be less than 2
hours with diameters between 400 m and 1.5 km, well above the break-up limit
for a gravitationally-bound aggregate. Our debiased data indicate that this
population represents <4% of the Main Belt in the 1-10 km size range.Comment: Accepted to Icarus. Full tables to appear there in electronic format,
or contact autho
Enhancing the Control Objectives for Information and Related Technologies (COBIT 5) Framework for Sustainable IT Governance
Rank-Based Analysis of Linear Models Using R
It is well-known that Wilcoxon procedures out perform least squares procedures when the data deviate from normality and/or contain outliers. These procedures can be generalized by introducing weights; yielding so-called weighted Wilcoxon (WW) techniques. In this paper we demonstrate how WW-estimates can be calculated using an L1 regression routine. More importantly, we present a collection of functions that can be used to implement a robust analysis of a linear model based on WW-estimates. For instance, estimation, tests of linear hypotheses, residual analyses, and diagnostics to detect differences in fits for various weighting schemes are discussed. We analyze a regression model, designed experiment, and autoregressive time series model for the sake of illustration. We have chosen to implement the suite of functions using the R statistical software package. Because R is freely available and runs on multiple platforms, WW-estimation and associated inference is now universally accessible
Goal Programming Techniques to Support End User Decision Making
End users are frequently challenged with decision making where the goals, objectives, and priorities of management and entire functional areas are in conflict or defy standard quantifiable assessment (i.e., return on investment, payback period, etc.). In addition, objectives, priorities, and resources are constantly changing as corporate politics, staff turnover, or market conditions drive a firm in new directions. End users require, therefore, a straightforward capability of displaying resource or other constraints and the relative priorities of initiatives and projects in such a way that the manager can strive towards several objectives simultaneously. This paper discusses a well-established modeling technique, Goal Programming and shows how this once involved analysis technique has been simplified with the advent of powerful desktop hardware and software. GP models can now be developed on personal computers and used by managers and senior staff to simulate, in a matter of a few minutes, any scenario, which represents the relative priorities of initiatives and projects within defined resource or other constraints
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