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A generating set direct search augmented Lagrangian algorithm for optimization with a combination of general and linear constraints

Kolda, Tamara G.

We consider the solution of nonlinear programs in the case where derivatives of the objective function and nonlinear constraints are unavailable. To solve such problems, we propose an adaptation of a method due to Conn, Gould, Sartenaer, and Toint that proceeds by approximately minimizing a succession of linearly constrained augmented Lagrangians. Our modification is to use a derivative-free generating set direct search algorithm to solve the linearly constrained subproblems. The stopping criterion proposed by Conn, Gould, Sartenaer and Toint for the approximate solution of the subproblems requires explicit knowledge of derivatives. Such information is presumed absent in the generating set search method we employ. Instead, we show that stationarity results for linearly constrained generating set search methods provide a derivative-free stopping criterion, based on a step-length control parameter, that is sufficient to preserve the convergence properties of the original augmented Lagrangian algorithm.

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TYPE SAND Report YEAR 2006
DOIOSTI

Final LDRD report human interaction with complex systems: advances in hybrid reachability and control

Oishi, Meeko M.

This document describes new advances in hybrid reachability techniques accomplished during the course of a one-year Truman Postdoctoral Fellowship. These techniques provide guarantees of safety in complex systems, which is especially important in high-risk, expensive, or safety-critical systems. My work focused on new approaches to two specific problems motivated by real-world issues in complex systems: (1) multi-objective controller synthesis, and (2) control for recovery from error. Regarding the first problem, a novel application of reachability analysis allowed controller synthesis in a single step to achieve (a) safety, (b) stability, and (c) prevent input saturation. By extending the state to include the input parameters, constraints for stability, saturation, and envelope protection are incorporated into a single reachability analysis. Regarding the second problem, a new approach to the problem of recovery provides (a) states from which recovery is possible, and (b) controllers to guide the system during a recovery maneuver from an error state to a safe state in minimal time. Results are computed in both problems on nonlinear models of single longitudinal aircraft dynamics and two-aircraft lateral collision avoidance dynamics.

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TYPE SAND Report YEAR 2006
DOIOSTI

Flute instability growth on a magnetized plasma column

Proposed for publication in Physics of Plasma.

Mehlhorn, Thomas A.

The growth of the flute-type instability for a field-aligned plasma column immersed in a uniform magnetic field is studied. Particle-in-cell simulations are compared with a semi-analytic dispersion analysis of the drift cyclotron instability in cylindrical geometry with a Gaussian density profile in the radial direction. For the parameters considered here, the dispersion analysis gives a local maximum for the peak growth rates as a function of R/r{sub i}, where R is the Gaussian characteristic radius and r{sub i} is the ion gyroradius. The electrostatic and electromagnetic particle-in-cell simulation results give azimuthal and radial mode numbers that are in reasonable agreement with the dispersion analysis. The electrostatic simulations give linear growth rates that are in good agreement with the dispersion analysis results, while the electromagnetic simulations yield growth rate trends that are similar to the dispersion analysis but that are not in quantitative agreement. These differences are ascribed to higher initial field fluctuation levels in the electromagnetic field solver. Overall, the simulations allow the examination of both the linear and nonlinear evolution of the instability in this physical system up to and beyond the point of wave energy saturation. Keywords: Microinstabilities, Magnetic confinement and equilibrium, Particle-in-cell method.

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TYPE Journal Article YEAR 2006
OSTI

Impact of sensor detection limits on protecting water distribution systems from contamination events

Journal of Water Resources Planning and Management

McKenna, Sean A.; Hart, David; Yarrington, Lane

Real-time water quality sensors are becoming commonplace in water distribution systems. However, field deployable, contaminant-specific sensors are still in the development stage. As development proceeds, the necessary operating parameters of these sensors must be determined to protect consumers from accidental and malevolent contamination events. This objective can be quantified in several different ways including minimization of: the time necessary to detect a contamination event, the population exposed to contaminated water, the extent of the contamination within the network, and others. We examine the ability of a sensor set to meet these objectives as a function of both the detection limit of the sensors and the number of sensors in the network. A moderately sized distribution network is used as an example and different sized sets of randomly placed sensors are considered. For each combination of a certain number of sensors and a detection limit, the mean values of the different objectives across multiple random sensor placements are calculated. The tradeoff between the necessary detection limit in a sensor and the number of sensors is evaluated. Results show that for the example problem examined here, a sensor detection limit of 0.01 of the average source concentration is adequate for maximum protection. Detection of events is dependent on the detection limit of the sensors, but for those events that are detected, the values of the performance measures are not a function of the sensor detection limit. The results of replacing a single sensor in a network with a sensor having a much lower detection limit show that while this replacement can improve results, the majority of the additional events detected had performance measures of relatively low consequence. © 2006 ASCE.

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TYPE Journal Article YEAR 2006
ScopusOSTI

Focused ion beam sculpting curved shape cavities in crystalline and amorphous targets

Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures

Adams, D.P.; Vasile, M.J.; Mayer, Thomas M.

This work demonstrates accurate sculpting of predetermined micron-scale, curved shapes in initially planar solids. Using a 20 keV focused Ga + ion beam, various features are sputtered including hemispheres, parabolas, and sinusoidal wave forms having dimensions from 1 to 30 μm. Ion sculpting is accomplished by varying the dose at different points within individual scans. The doses calculated per point account for the material-specific, angle-dependent sputter yield, Y(θ), the beam current, and the ion beam spatial distribution. Several target materials are sculpted using this technique. These include semiconductors that are made amorphous or disordered by the high-energy beam and metals that remain crystalline with ion exposure. For several target materials, curved feature shapes closely match desired geometries with milled depths within 5% of intended values. Deposition of sputtered material and reflection of ions from sloped surfaces are important factors in feature depth and profile evolution. Materials that are subject to severe effects of redeposition (e.g., C and Si) require additional dose in certain regions in order to achieve desired geometries. The angle-dependent sputter yields of Si, C, Au, Al, W, SiC, and Al 2O 3 are reported. This includes normal incidence values, Y(0°), and Yamamura parameters f and Σ. © 2006 American Vacuum Society.

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TYPE Journal Article YEAR 2006
ScopusOSTI

Investigation of sidewall cracking in PMMA LIGA structures

Journal of Micromechanics and Microengineering

Hunter, L.L.; Skala, Dawn M.; Levey, B.S.

During x-ray exposure in the LIGA process, the polymethylmethacrylate (PMMA) photoresist undergoes chain scission, which reduces the molecular weight of the exposed materials. Under some exposure and development conditions, sidewall cracking is observed on the PMMA sidewall, creating surface texture that is undesirable. In this research, exposed and developed PMMA sidewalls were examined for evidence of crack formation using optical profilometry. PMMA thickness, exposure dose and delay time between the end of exposure and beginning of development were varied. Our analysis of samples, with three different radiation doses and four different delay times from the end of exposure to the beginning of development, indicate that the first occurrence of cracking and the extent of cracking are affected by both the dose and the development delay time. This work includes the examination of the depth of cracks into the PMMA, distance between cracks, the width of cracks and the relationship between crack occurrence and dose profile. An empirical predictive model to correlate the delay time to the observance of sidewall cracking based on the deposited dose is presented. This information has direct implication for predicting processing conditions and logistics for LIGA fabricated parts. © 2006 IOP Publishing Ltd.

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TYPE Journal Article YEAR 2006
ScopusOSTI

Federal technology transfer requirements :a focused study of principal agencies approaches with implications for the Department of Homeland Security

Koker, Denise E.; Micheau, Jill M.

This report provides relevant information and analysis to the Department of Homeland Security (DHS) that will assist DHS in determining how to meet the requirements of federal technology transfer legislation. These legal requirements are grouped into five categories: (1) establishing an Office of Research and Technology Applications, or providing the functions thereof; (2) information management; (3) enabling agreements with non-federal partners; (4) royalty sharing; and (5) invention ownership/obligations. These five categories provide the organizing framework for this study, which benchmarks other federal agencies/laboratories engaged in technology transfer/transition Four key agencies--the Department of Health & Human Services (HHS), the U.S. Department of Agriculture (USDA), the Department of Energy (DOE), and the Department of Defense (DoD)--and several of their laboratories have been surveyed. An analysis of DHS's mission needs for commercializing R&D compared to those agencies/laboratories is presented with implications and next steps for DHS's consideration. Federal technology transfer legislation, requirements, and practices have evolved over the decades as agencies and laboratories have grown more knowledgeable and sophisticated in their efforts to conduct technology transfer and as needs and opinions in the federal sector have changed with regards to what is appropriate. The need to address requirements in a fairly thorough manner has, therefore, resulted in a lengthy paper. There are two ways to find summary information. Each chapter concludes with a summary, and there is an overall ''Summary and Next Steps'' chapter on pages 57-60. For those readers who are unable to read the entire document, we recommend referring to these pages.

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TYPE SAND Report YEAR 2006
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Results 83901–84000 of 99,299
Results 83901–84000 of 99,299