19,252 research outputs found
Evolutionary Algorithms for Reinforcement Learning
There are two distinct approaches to solving reinforcement learning problems,
namely, searching in value function space and searching in policy space.
Temporal difference methods and evolutionary algorithms are well-known examples
of these approaches. Kaelbling, Littman and Moore recently provided an
informative survey of temporal difference methods. This article focuses on the
application of evolutionary algorithms to the reinforcement learning problem,
emphasizing alternative policy representations, credit assignment methods, and
problem-specific genetic operators. Strengths and weaknesses of the
evolutionary approach to reinforcement learning are presented, along with a
survey of representative applications
The design of linear multivariable control systems using modern control theory /with applications to coupled core reactor control/
Linear multivariable control system design using modern control theory, and application to coupled core reactor contro
Constraints and contributors in advancing Black women academic researchers at a university in South Africa
This article draws from a project that was conducted at a South African university to investigate the advancement of Black women academic researchers. A qualitative research method was used to obtain rich data from Black women academics. Thematic analysis was used to analyse the data. Findings from the study suggest that the constraints in advancing Black women academics were: research was not a priority; problems with work-life balance; research challenges; a male-dominated environment; time constraints; lack of support; and funding. The contributors in advancing Black women academic researchers were perseverance, collaboration, co-supervision, motivation, mentorship and support, including institutional support. There ought to be a deeper inquiry into how best to ensure the advancement of Black women academics at universities in South Africa
Analysis of severe atmospheric disturbances from airline flight records
Advanced methods were developed to determine time varying winds and turbulence from digital flight data recorders carried aboard modern airliners. Analysis of several cases involving severe clear air turbulence encounters at cruise altitudes has shown that the aircraft encountered vortex arrays generated by destabilized wind shear layers above mountains or thunderstorms. A model was developed to identify the strength, size, and spacing of vortex arrays. This model is used to study the effects of severe wind hazards on operational safety for different types of aircraft. The study demonstrates that small remotely piloted vehicles and executive aircraft exhibit more violent behavior than do large airliners during encounters with high-altitude vortices. Analysis of digital flight data from the accident at Dallas/Ft. Worth in 1985 indicates that the aircraft encountered a microburst with rapidly changing winds embedded in a strong outflow near the ground. A multiple-vortex-ring model was developed to represent the microburst wind pattern. This model can be used in flight simulators to better understand the control problems in severe microburst encounters
Critical research and advanced technology (CRT) support project
A critical technology base for utility and industrial gas turbines by planning the use of coal-derived fuels was studied. Development tasks were included in the following areas: (1) Combustion - investigate the combustion of coal-derived fuels and methods to minimize the conversion of fuel-bound nitrogen to NOx; (2) materials - understand and minimize hot corrosion; (3) system studies - integrate and focus the technological efforts. A literature survey of coal-derived fuels was completed and a NOx emissions model was developed. Flametube tests of a two-stage (rich-lean) combustor defined optimum equivalence ratios for minimizing NOx emissions. Sector combustor tests demonstrated variable air control to optimize equivalence ratios over a wide load range and steam cooling of the primary zone liner. The catalytic combustion of coal-derived fuels was demonstrated. The combustion of coal-derived gases is very promising. A hot-corrosion life prediction model was formulated and verified with laboratory testing of doped fuels. Fuel additives to control sulfur corrosion were studied. The intermittent application of barium proved effective. Advanced thermal barrier coatings were developed and tested. Coating failure modes were identified and new material formulations and fabrication parameters were specified. System studies in support of the thermal barrier coating development were accomplished
Magnetic nanostructures by adaptive twinning in strained epitaxial films
We exploit the intrinsic structural instability of the Fe70Pd30 magnetic
shape memory alloy to obtain functional epitaxial films exhibiting a
self-organized nanostructure. We demonstrate that coherent epitaxial straining
by 54% is possible. The combination of thin film experiments and large-scale
first-principles calculations enables us to establish a lattice relaxation
mechanism, which is not expected for stable materials. We identify a low twin
boundary energy compared to a high elastic energy as key prerequisite for the
adaptive nanotwinning. Our approach is versatile as it allows to control both,
nanostructure and intrinsic properties for ferromagnetic, ferroelastic and
ferroelectric materials.Comment: Final version. Supplementary information available on request or at
the publisher's websit
Topics concerning state variable feedback in automatic control systems. Part 1 - Specification. Part 2 - Sensitivity. Part 3 - Intentional nonlinearities. Part 4 - Unavailable states
Specifications, sensitivity, intentional nonlinearities, and unavailable states concerned with state variable feedback in automatic control system
Ionization of hydrogen and hydrogenic ions by antiprotons
Presented here is a description of the ionization of hydrogen and hydrogenic
ions by antiproton-impact, based on very large scale numerical solutions of the
time-dependent Schr\"odinger equation in three spatial dimensions and on
analysis of the topology of the electronic eigenenergy surfaces in the plane of
complex internuclear distance. Comparison is made with other theories and very
recent measurements.Comment: RevTex document, 11 pages, 4 Postscript figures are available from
the authors, in press Phys. Rev. Let
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