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in creator/contributor: "Evans, J.W."

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High-Contrast Imaging using Adaptive Optics for Extrasolar Planet Detection

Direct imaging of extrasolar planets is an important, but challenging, next step in planetary science. Most planets identified to date have been detected indirectly--not by emitted or reflected light but through the effect of the planet on the parent star. For example, radial velocity techniques measure the doppler shift in the spectrum of the star produced by the presence of a planet. Indirect techniques only probe about 15% of the orbital parameter space of our solar system. Direct methods wo… more

Date: August 18, 2006

Creator: Evans, J. W.

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

open access

Magnetic fields, current densities, melt velocities and current efficiencies in Hall-Heroult cells: computations and comparison with measurements

The magnetic fields, current densities, metal and electrolyte velocities, and current efficiencies within the Hall-Heroult cells used to produce aluminum have been predicted from first principles. The computation of current densities was carried out by solving Ohms law enabling the calculation of magnetic field vectors from the Biot-Savart law. The cross product of the current densities and magnetic fields then yielded the electromagnetic stirring forces acting on the molten metal and electroly… more

Date: March 1, 1979

Creator: Evans, J. W.; Zundelevich, Y.; Tarapore, E. D. & Sharma, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Scaling analysis of surface roughness in simple models for Molecular-Beam Epitaxy

There is currently interest in simple models for Molecular-Beam Epitaxy (MBE) which mimic the effect of thermal mobility by allowing incorporation of deposited atoms at kink sites with in a distance l of the deposition site. Scaling of the interface width, W, with mean film height, <h>, of the form W {approximately}<h>{beta}, is analysed. Studies for a Solid-on-Solid geometry in d=1+1 dimensions revealed a sudden transition from the T=0 K (l=0) behavior of {beta} = {1/2} to a new universality c… more

Date: January 1, 1991

Creator: Kang, H. C. & Evans, J. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Resource management plan for the Oak Ridge Reservation. Volume 27, Wildlife Management Plan

A plan for management of the wildlife resources on the US Department of Energy`s Oak Ridge Reservation is outlined in this document. Management includes wildlife population control (hunts, trapping, and removal), handling specific problems with wildlife, restoration of species, coordination with researchers on wildlife studies, preservation and management of habitats, and law enforcement. Wildlife resources are divided into five categories, each with a specific set of objectives and procedures … more

Date: June 1, 1992

Creator: Parr, P. D. & Evans, J. W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Rate Equation Theory for Island Sizes and Capture Zone Areas in Submonolayer Deposition: Realistic Treatment of Spatial Aspects of Nucleation

Extensive information on the distribution of islands formed during submonolayer deposition is provided by the joint probability distribution (JPD) for island sizes, s, and capture zone areas, A. A key ingredient determining the form of the JPD is the impact of each nucleation event on existing capture zone areas. Combining a realistic characterization of such spatial aspects of nucleation with a factorization ansatz for the JPD, we provide a concise rate equation formulation for the variation w… more

Date: December 5, 2002

Creator: Evans, J. W.; Li, M. & Bartelt, M. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A Mathematical Model for Prediction of Currents, Magnetic Fields, Melt Velocities, Melt Topography and Current Efficiency in Hall-Heroult Cells

The magnetic fields, current densities, metal and electrolyte velocities, current efficiencies and topography of the electrolyte-metal interface within the Hall-Heroult cells used to produce aluminum have been predicted from first principles. The computation of current densities was carried out by solving Ohms law enabling the calculation of magnetic field vectors from the Biot-Savart law. The cross product of the current densities and magnetic fields then yielded the electromagnetic stirring f… more

Date: October 1, 1980

Creator: Evans, J. W.; Zundelevich, Y. & Sharma, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Effect of Wavefront Error on 10^-7 Contrast Measurements

We have measured a contrast of 6.5 {center_dot} 10{sup -8} from 10-25{lambda}/D in visible light on the Extreme Adaptive Optics testbed using a shaped pupil for diffraction suppression. The testbed was designed with a minimal number of high-quality optics to ensure low wavefront error and uses a phase shifting diffraction interferometer for metrology. This level of contrast is within the regime needed for imaging young Jupiter-like planets, a primary application of high-contrast imaging. We hav… more

Date: October 6, 2005

Creator: Evans, J. W.; Sommargren, G.; Macintosh, B.; Severson, S. & Dillon, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Survey of protected terrestrial vertebrates on the Oak Ridge Reservation. Final report

This document is the final report on surveys of protected terrestrial vertebrates on the Oak Ridge Reservation (ORR) conducted from October 1994 through May 1996. The surveys were undertaken to gain information that could help prevent or minimize the potential impacts of projects on the ORR to species listed by the state or federal government as endangered, threatened, or in need of management; federal species of concern were also included. The results of the survey will assist in the effective… more

Date: July 1, 1996

Creator: Mitchell, J. M.; Vail, E. R.; Webb, J. W. & Evans, J. W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Characterization of an AO-OCT system

Adaptive optics (AO) and optical coherence tomography (OCT) are powerful imaging modalities that, when combined, can provide high-volumetric-resolution, images of the retina. The AO-OCT system at UC Davis has been under development for 2 years and has demonstrated the utility of this technology for microscopic, volumetric, in vivo retinal imaging [1]. The current system uses an AOptix bimorph deformable mirror (DM) for low-order, high-stroke correction [2] and a 140-actuator Boston Micromachine… more

Date: July 26, 2007

Creator: Evans, J. W.; Zawadzki, R. J.; Jones, S.; Olivier, S. & Werner, J. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Extreme Adaptive Optics Testbed: High Contrast Measurements with a MEMS Deformable Mirror

''Extreme'' adaptive optics systems are optimized for ultra-high-contrast applications, such as ground-based extrasolar planet detection. The Extreme Adaptive Optics Testbed at UC Santa Cruz is being used to investigate and develop technologies for high-contrast imaging, especially wavefront control. We use a simple optical design to minimize wavefront error and maximize the experimentally achievable contrast. A phase shifting diffraction interferometer (PSDI) measures wavefront errors with sub… more

Date: August 16, 2005

Creator: Evans, J. W.; Morzinski, K.; Reza, L.; Severson, S.; Poyneer, L.; Macintosh, B. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Extreme Adaptive Optics Testbed: Performance and Characterization of a 1024 Deformable Mirror

We have demonstrated that a microelectrical mechanical systems (MEMS) deformable mirror can be flattened to < 1 nm RMS within controllable spatial frequencies over a 9.2-mm aperture making it a viable option for high-contrast adaptive optics systems (also known as Extreme Adaptive Optics). The Extreme Adaptive Optics Testbed at UC Santa Cruz is being used to investigate and develop technologies for high-contrast imaging, especially wavefront control. A phase shifting diffraction interferomet… more

Date: October 30, 2005

Creator: Evans, J. W.; Morzinski, K.; Severson, S.; Poyneer, L.; Macintosh, B.; Dillon, D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Extreme Adaptive Optics Testbed: Results and Future Work

'Extreme' adaptive optics systems are optimized for ultra-high-contrast applications, such as ground-based extrasolar planet detection. The Extreme Adaptive Optics Testbed at UC Santa Cruz is being used to investigate and develop technologies for high-contrast imaging, especially wavefront control. A simple optical design allows us to minimize wavefront error and maximize the experimentally achievable contrast before progressing to a more complex set-up. A phase shifting diffraction interferome… more

Date: July 15, 2004

Creator: Evans, J. W.; Sommargren, G.; Poyneer, L.; Macintosh, B.; Severson, S.; Dillon, D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

eXtreme Adaptive Optics Planet Imager: Overview and status

As adaptive optics (AO) matures, it becomes possible to envision AO systems oriented towards specific important scientific goals rather than general-purpose systems. One such goal for the next decade is the direct imaging detection of extrasolar planets. An 'extreme' adaptive optics (ExAO) system optimized for extrasolar planet detection will have very high actuator counts and rapid update rates - designed for observations of bright stars - and will require exquisite internal calibration at the… more

Date: August 18, 2004

Creator: Macintosh, B. A.; Bauman, B.; Evans, J. W.; Graham, J.; Lockwood, C.; Poyneer, L. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department