42,591 research outputs found
Technology advancement of the static feed water electrolysis process
Some results are presented of a research and development program to continue the development of a method to generate oxygen for crew metabolic consumption during extended manned space flights. The concept being pursued is that of static feed water electrolysis. Specific major results of the work included: (1) completion of a 30-day electrode test using a Life Systems, Inc.-developed high performance catalyst. During startup the cell voltages were as low as 1.38 V at current densities of 108 mA/sq cm (100 ASF) and temperatures of 355 K (180 F). At the end of 30 days of testing the cell voltages were still only 1.42 V at 108 mA/sq cm, (2) determination that the Static Feed Water Electrolysis Module does not release an aerosol of the cell electrolyte into the product gas streams after a break-in period of 24 hours following a new electrolyte charge, and (3) completion of a detailed design analysis of an electrochemical Oxygen Generation Subsystem at a three-man level (4.19 kg/day (9.24 lb/day) of oxygen)
One- and Two-Nucleon Structure form Green's Function Theory
We review some applications of self-consistent Green's function theory to
studies of one- and two-nucleon structure in finite nuclei.
Large-scale microscopic calculations that employ realistic nuclear forces are
now possible. Effects of long-range correlations are seen to play a dominant
role in determining the quenching of absolute spectroscopic factors. They also
enhance considerably (e,e'pn) cross sections in superparallel kinematics, in
agreement with observations.Comment: Proceedings of the International Symposium on "Forefronts of
Researches in Exotic Nuclear Structures" (Niigata2010)
Static feed water electrolysis module
An advanced static feed water electrolysis module (SFWEM) and associated instrumentation for generating breathable O2 was developed. The system also generates a H2 byproduct for use in an air revitalization system for O2 recovery from metabolic CO2. Special attention was given to: (1) eliminating water feed compartment degassing, (2) eliminating need for zero gravity condenser/separators, (3) increasing current density capability, and (4) providing a self contained module so that operation is independent of laboratory instrumentation and complicated startup/shutdown procedures
Advanced combined iodine dispenser and detector
A total weight of 1.23 kg (2.7 lb), a total volume of 1213 cu m (74 cu in), and an average power consumption of 5.5W was achieved in the advanced combined iodine dispenser/detector by integrating the detector with the iodine source, arranging all iodinator components within a compact package and lowering the parasitic power to the detector and electronics circuits. These achievements surpassed the design goals of 1.36 kg (3.0 lb), 1671 cu m (102 cu in) and 8W. The reliability and maintainability were improved by reducing the detector lamp power, using an interchangeable lamp concept, making the electronic circuit boards easily accessible, providing redundant water seals and improving the accessibility to the iodine accumulator for refilling. The system was designed to iodinate (to 5 ppm iodine) the fuel cell water generated during 27 seven-day orbiter missions (equivalent to 18,500 kg (40,700 lb) of water) before the unit must be recharged with iodine crystals
Six-man, self-contained carbon dioxide concentrator subsystem for Space Station Prototype (SSP) application
A six man, self contained, electrochemical carbon dioxide concentrating subsystem for space station prototype use was successfully designed, fabricated, and tested. A test program was successfully completed which covered shakedown testing, design verification testing, and acceptance testing
Theory of STM junctions for \pi-conjugated molecules on thin insulating films
A microscopic theory of the transport in a scanning tunnelling microscope
(STM) set-up is introduced for \pi-conjugated molecules on insulating films,
based on the density matrix formalism. A key role is played in the theory by
the energy dependent tunnelling rates which account for the coupling of the
molecule to the tip and to the substrate. In particular, we analyze how the
geometrical differences between the localized tip and extended substrate are
encoded in the tunnelling rate and influence the transport characteristics.
Finally, using benzene as an example of a planar, rotationally symmetric
molecule, we calculate the STM current voltage characteristics and current maps
and analyze them in terms of few relevant angular momentum channels.Comment: 19 pages, 12 figures, minor changes to conform to published versio
First-principles study of the energetics of charge and cation mixing in U_{1-x} Ce_x O_2
The formalism of electronic density-functional-theory, with Hubbard-U
corrections (DFT+U), is employed in a computational study of the energetics of
U_{1-x} Ce_x O_2 mixtures. The computational approach makes use of a procedure
which facilitates convergence of the calculations to multiple self-consistent
DFT+U solutions for a given cation arrangement, corresponding to different
charge states for the U and Ce ions in several prototypical cation
arrangements. Results indicate a significant dependence of the structural and
energetic properties on the nature of both charge and cation ordering. With the
effective Hubbard-U parameters that reproduce well the measured
oxidation-reduction energies for urania and ceria, we find that charge transfer
between U(IV) and Ce(IV) ions, leading to the formation of U(V) and Ce(III),
gives rise to an increase in the mixing energy in the range of 4-14 kJ/mol of
formula unit, depending on the nature of the cation ordering. The results
suggest that although charge transfer between uranium and cerium ions is
disfavored energetically, it is likely to be entropically stabilized at the
high temperatures relevant to the processing and service of urania-based solid
solutions.Comment: 8 pages, 6 figure
Numerical Study of a Field Theory for Directed Percolation
A numerical method is devised for study of stochastic partial differential
equations describing directed percolation, the contact process, and other
models with a continuous transition to an absorbing state. Owing to the
heightened sensitivity to fluctuationsattending multiplicative noise in the
vicinity of an absorbing state, a useful method requires discretization of the
field variable as well as of space and time. When applied to the field theory
for directed percolation in 1+1 dimensions, the method yields critical
exponents which compare well against accepted values.Comment: 18 pages, LaTeX, 6 figures available upon request LC-CM-94-00
Efficient kinetic experiments in continuous flow microreactors
Flow chemistry is an enabling technology that can offer an automated and robust approach for the generation of reaction kinetics data. Recent studies have taken advantage of transient flows to quickly generate concentration profiles with various online analytical tools. In this work, we demonstrate an improved method where temperature and flow are transient throughout the reaction. It was observed that only two orthogonal temperature ramp experiments under the same transient flow condition were sufficient to characterize a Paal-Knorr (one step bimolecular) reaction within our chosen reaction space. This method further shortens the time and decreases the materials needed to collect sufficient kinetic data and provides a framework with which more complex kinetic studies could be performed
The Successful Operation of Hole-type Gaseous Detectors at Cryogenic Temperatures
We have demonstrated that hole-type gaseous detectors, GEMs and capillary
plates, can operate up to 77 K. For example, a single capillary plate can
operate at gains of above 10E3 in the entire temperature interval between 300
until 77 K. The same capillary plate combined with CsI photocathodes could
operate perfectly well at gains (depending on gas mixtures) of 100-1000.
Obtained results may open new fields of applications for capillary plates as
detectors of UV light and charge particles at cryogenic temperatures: noble
liquid TPCs, WIMP detectors or LXe scintillating calorimeters and cryogenic
PETs.Comment: Presented at the IEEE Nuclear Science Symposium, Roma, 200
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