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Wood, David

Publications and source records attributed to Wood, David.

27 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

X-ray laser–induced electron dynamics observed by femtosecond diffraction from nanocrystals of Buckminsterfullerene

X-ray free-electron lasers (XFELs) deliver x-ray pulses with a coherent flux that is approximately eight orders of magnitude greater than that available from a modern third-generation synchrotron source. The power density of an XFEL pulse may be so high that it can modify the electronic properties of a sample on a femtosecond time scale. Exploration of the interaction of intense coherent x-ray pulses and matter is both of intrinsic scientific interest and of critical importance to the interpretation of experiments that probe the structures of materials using high-brightness femtosecond XFEL pulses. We report observations of the diffraction of extremely intense 32-fs nanofocused x-ray pulses by a powder sample of crystalline C 60 . We find that the diffraction pattern at the highest available incident power significantly differs from the one obtained using either third-generation synchrotron sources or XFEL sources operating at low output power and does not correspond to the diffraction pattern expected from any known phase of crystalline C 60 . We interpret these data as evidence of a long-range, coherent dynamic electronic distortion that is driven by the interaction of the periodic array of C 60 molecular targets with intense x-ray pulses of femtosecond duration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Enhanced thermal conductance of polymer composites through embedding aligned carbon nanofibers

The focus of this work is to find a more efficient method of enhancing the thermal conductance of polymer thin films. This work compares polymer thin films embedded with randomly oriented carbon nanotubes to those with vertically aligned carbon nanofibers. Thin films embedded with carbon nanofibers demonstrated a similar thermal conductance between 40–60 μm and a higher thermal conductance between 25–40 μm than films embedded with carbon nanotubes with similar volume fractions even though carbon nanotubes have a higher thermal conductivity than carbon nanofibers

36 MATERIALS SCIENCE↗
DOE OSTI2012

21st Century Computer Architecture

Because most technology and computer architecture innovations were (intentionally) invisible to higher layers, application and other software developers could reap the benefits of this progress without engaging in it. Higher performance has both made more computationally demanding applications feasible (e.g., virtual assistants, computer vision) and made less demanding applications easier to develop by enabling higher-level programming abstractions (e.g., scripting languages and reusable components). Improvements in computer system cost-effectiveness enabled value creation that could never have been imagined by the field's founders (e.g., distributed web search sufficiently inexpensive so as to be covered by advertising links). The wide benefits of computer performance growth are clear. Recently, Danowitz et al. apportioned computer performance growth roughly equally between technology and architecture, with architecture credited with ~80x improvement since 1985. As semiconductor technology approaches its "end-of-the-road" (see below), computer architecture will need to play an increasing role in enabling future ICT innovation. But instead of asking, "How can I make my chip run faster?," architects must now ask, "How can I enable the 21st century infrastructure, from sensors to clouds, adding value from performance to privacy, but without the benefit of near-perfect technology scaling?". The challenges are many, but with appropriate investment, opportunities abound. Underlying these opportunities is a common theme that future architecture innovations will require the engagement of and investments from innovators in other ICT layers.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

New Polytypoid SnO2(ZnO:Sn)m Nanowire: Characterization and Calculation of its Electronic Structure

A new SnO{sub 2}(ZnO:Sn){sub m} polytypoid nanowire has been synthesized through a two-step chemical vapor deposition (CVD) method. Cs-corrected scanning transmission electron microscopy (STEM) studies indicate the crystal structure consists of an alternating stack of a Sn-O octahedral layer and a (Sn/Zn)-O wurtzite slab. First-principles density-functional theory (DFT) calculations suggest Sn atoms in the Sn-doped ZnO slabs have both 4- and 6-fold coordination, forming an inversion boundary of polarity. The SnO{sub 2}(ZnO:Sn){sub m} nanowires may exhibit unique anisotropic electronic properties: poor conductivity along the wire axis, but metallic conductivity along the diametrical directions according to the calculations.

14 SOLAR ENERGY↗
NASA NTRS2011

Designing the Space Shuttle Propulsion System

The major elements of the Space Shuttle Main Propulsion System include two reusable solid rocket motors integrated into recoverable solid rocket boosters, an expendable external fuel and oxidizer tank, and three reusable Space Shuttle Main Engines. Both the solid rocket motors and space shuttle main engines ignite prior to liftoff, with the solid rocket boosters separating about two minutes into flight. The external tank separates after main engine shutdown and is safely expended in the ocean. The SSME's, integrated into the Space Shuttle Orbiter aft structure, are reused after post landing inspections. Both the solid rocket motors and the space shuttle main engine throttle during early ascent flight to limit aerodynamic loads on the structure. The configuration is called a stage and a half as all the propulsion elements are active during the boost phase, and the SSME's continue operation to achieve orbital velocity approximately eight and a half minutes after liftoff. Design and performance challenges were numerous, beginning with development work in the 1970 s. The solid rocket motors were large, and this technology had never been used for human space flight. The SSME s were both reusable and very high performance staged combustion cycle engines, also unique to the Space Shuttle. The multi body side mount configuration was unique and posed numerous integration and interface challenges across the elements. Operation of the system was complex and time consuming. This paper discusses a number of the system level technical challenges including development and operations.

Owen, James↗
NASA NTRS2011

Space Shuttle Propulsion Materials, Manufacturing, and Operational Challenges

Presentations in this session include: (1) External Tank (ET) Materials, Manufacturing, and Operational Challenges; (2) Space Shuttle Main Engine (SSME) Materials, Manufacturing, and Operational Challenges,(3) Reusable Solid Rocket Motor (RSRM) Materials, Manufacturing, and Operational Challenges and (4) Solid Rocket Booster (SRB) Materials, Manufacturing, and Operational Challenges.

Owen, James↗
NASA NTRS2011

Space Shuttle Propulsion System Reliability

This session includes the following sessions: (1) External Tank (ET) System Reliability and Lessons, (2) Space Shuttle Main Engine (SSME), Reliability Validated by a Million Seconds of Testing, (3) Reusable Solid Rocket Motor (RSRM) Reliability via Process Control, and (4) Solid Rocket Booster (SRB) Reliability via Acceptance and Testing.

Welzyn, Ken↗
NASA NTRS1992

Simulation and model reduction for the AFW program

The simulation methodology used in the Active Flexible Wing wind-tunnel test program is described. An overview of the aeroservoelastic modeling used in building the required batch and hot-bench simulations is presented. Successful hot-bench implementation required that the full mathematical model be significantly reduced while assuring that accuracy be maintained for all combinations of 10 inputs and 56 outputs. The reduction was accomplished by using a method based on internally balanced realizations and focussing on the linear, aeroelastic portion of the full mathematical model. The error-bound properties of the internally balanced realization significantly contribute to its utility in the model reduction process. The reduction method and the results achieved are described.

Buttrill, Carey↗