20 research outputs found
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Sublimating and cracking apparatus
A furnace having a sublimating section, a cracking section oriented off axis to the sublimating section, and a valve for controlling flux between the sections. The valve includes an annular plug having at least one longitudinal slot. The plug is retractable from a fully closed position where the slot is completely covered, to a fully open position where the slot is completely exposed. The slot becomes increasingly exposed as the plug is moved from the fully closed position to the fully opened position, thereby increasing flux from the sublimating section to the cracking section.Board of Regents, University of Texas Syste
Recommended from our members
Modulation doped field effect transistor having built-in drift field
A MODFET device has highly doped source and drain regions separated by an undoped semiconductor alloy in which the mole fraction is graded between the source and the drain and with a conduction (and/or valence) band discontinuity at the heterojunction between the source and semiconductor alloy channel region of the device. Due to the graded mole fraction, the bandgap of the undoped semiconductor alloy decreases along the channel from the source to the drain and creates a built-in electric field. The higher bandgap in the source compared to that in the channel permits high energy carrier injection into the channel, with the built-in longitudinal electric field increasing carrier drift velocity and reducing transit time between the source and drain. In a preferred embodiment, the MODFET device has a vertical structure with the source and semiconductor alloy layers stacked on a drain substrate. The channel is defined by selectively etching the stacked structure with the exposed edge of the semiconductor alloy layer forming the channel. An undoped semiconductor layer and a modulation doped semiconductor layer are formed over the exposed edge with the undoped layer forming a spacer for the modulation doped layer. Carriers from the modulation doped layer spill over into the undoped channel and form a two-dimensional (or hole) electron gas. The devices can be implemented as p-channel and as n-channel devices fabricated in III-V compound and in Column IV-based semiconductor materials.Board of Regents, University of Texas Syste
Limitations on the attainable intensity of high power lasers
It is shown that even a single pair created by a super strong laser
field in vacuum would cause development of an avalanche-like QED cascade which
rapidly depletes the incoming laser pulse. This confirms the old N. Bohr
conjecture that the electric field of the critical QED strength
could never be created.Comment: 4 pages, 3 figure
High-Frequency (> 100 GHz) and High-Speed (< 10 ps) Electronic Devices
Contains an introduction, reports on four research projects and a list of publications.Defense Advanced Research Projects Agency Contract MDA972-90-C-0021National Aeronautics and Space Administration Grant NAGW-4691National Aeronautics and Space Administration Grant 959705National Science Foundation Grant AST 94-23608National Science Foundation/MRSEC Grant DMR 94-00334MIT Lincoln Laboratory Advanced Concept Program Grant BX-5464U.S. Army Research Office Grant DAAH04-95-1-0610Hertz Foundation FellowshipU.S. Army - Office of Scientific Research Grant DAAH04-94-G-016
Ionic Interactions in Biological and Physical Systems: a Variational Treatment
Chemistry is about chemical reactions. Chemistry is about electrons changing
their configurations as atoms and molecules react. Chemistry studies reactions
as if they occurred in ideal infinitely dilute solutions. But most reactions
occur in nonideal solutions. Then everything (charged) interacts with
everything else (charged) through the electric field, which is short and long
range extending to boundaries of the system. Mathematics has recently been
developed to deal with interacting systems of this sort. The variational theory
of complex fluids has spawned the theory of liquid crystals. In my view, ionic
solutions should be viewed as complex fluids. In both biology and
electrochemistry ionic solutions are mixtures highly concentrated (~10M) where
they are most important, near electrodes, nucleic acids, enzymes, and ion
channels. Calcium is always involved in biological solutions because its
concentration in a particular location is the signal that controls many
biological functions. Such interacting systems are not simple fluids, and it is
no wonder that analysis of interactions, such as the Hofmeister series, rooted
in that tradition, has not succeeded as one would hope. We present a
variational treatment of hard spheres in a frictional dielectric. The theory
automatically extends to spatially nonuniform boundary conditions and the
nonequilibrium systems and flows they produce. The theory is unavoidably
self-consistent since differential equations are derived (not assumed) from
models of (Helmholtz free) energy and dissipation of the electrolyte. The
origin of the Hofmeister series is (in my view) an inverse problem that becomes
well posed when enough data from disjoint experimental traditions are
interpreted with a self-consistent theory.Comment: As prepared for Faraday Discussion, Pavel Jungwirth Organizer, 3 - 5
September 2012, Queens College Oxford, UK on Ion Specific Hofmeister Effects.
Version 2 has significant typo corrections in eq. 1 and eq. 4, and has been
reformatted to be easier to rea
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure