394 research outputs found
A forward view on reliable computers for flight control
The requirements for fault-tolerant computers for flight control of commercial aircraft are examined; it is concluded that the reliability requirements far exceed those typically quoted for space missions. Examination of circuit technology and alternative computer architectures indicates that the desired reliability can be achieved with several different computer structures, though there are obvious advantages to those that are more economic, more reliable, and, very importantly, more certifiable as to fault tolerance. Progress in this field is expected to bring about better computer systems that are more rigorously designed and analyzed even though computational requirements are expected to increase significantly
Technique for experimental determination of radiation interchange factors in solar wavelengths
Process obtains solar heating data which support analytical design. Process yields quantitative information on local solar exposure of models which are geometrically and reflectively similar to prototypes under study. Models are tested in a shirtsleeve environment
Magnetic Monopoles as Agents of Chiral Symmetry Breaking in U(1) Lattice Gauge Theory
We present results suggesting that magnetic monopoles can account for chiral
symmetry breaking in abelian gauge theory. Full U(1) configurations from a
lattice simulation are factorized into magnetic monopole and photon
contributions. The expectation is computed using the monopole
configurations and compared to results for the full U(1) configurations. It is
shown that excellent agreement between the two values of is
obtained if the effect of photons, which "dress" the composite operator
psibarpsi, is included. This can be estimated independently by measurements of
the physical fermion mass in the photon background.Comment: 14 pages REVTeX, including 5 figure
Fermi surface of an important nano-sized metastable phase: AlLi
Nanoscale particles embedded in a metallic matrix are of considerable
interest as a route towards identifying and tailoring material properties. We
present a detailed investigation of the electronic structure, and in particular
the Fermi surface, of a nanoscale phase ( AlLi) that has so far been
inaccessible with conventional techniques, despite playing a key role in
determining the favorable material properties of the alloy (Al\nobreakdash-9
at. %\nobreakdash-Li). The ordered precipitates only form within the
stabilizing Al matrix and do not exist in the bulk; here, we take advantage of
the strong positron affinity of Li to directly probe the Fermi surface of
AlLi. Through comparison with band structure calculations, we demonstrate
that the positron uniquely probes these precipitates, and present a 'tuned'
Fermi surface for this elusive phase
Design of a fault tolerant airborne digital computer. Volume 1: Architecture
This volume is concerned with the architecture of a fault tolerant digital computer for an advanced commercial aircraft. All of the computations of the aircraft, including those presently carried out by analogue techniques, are to be carried out in this digital computer. Among the important qualities of the computer are the following: (1) The capacity is to be matched to the aircraft environment. (2) The reliability is to be selectively matched to the criticality and deadline requirements of each of the computations. (3) The system is to be readily expandable. contractible, and (4) The design is to appropriate to post 1975 technology. Three candidate architectures are discussed and assessed in terms of the above qualities. Of the three candidates, a newly conceived architecture, Software Implemented Fault Tolerance (SIFT), provides the best match to the above qualities. In addition SIFT is particularly simple and believable. The other candidates, Bus Checker System (BUCS), also newly conceived in this project, and the Hopkins multiprocessor are potentially more efficient than SIFT in the use of redundancy, but otherwise are not as attractive
Monopoles contra vortices in SU(2) lattice gauge theory?
We show that the scenario of vortex induced confinement of center--projected
SU(2) lattice gauge theory is not necessarily in conflict with the findings in
the positive plaquette model.Comment: 3 pages, LaTeX, comment to be published in Phys. Rev.
Monopoles at Finite Volume and Temperature in SU(2) Lattice Gauge Theory
We resolve a discrepancy between the SU(2) spacial string tension at finite
temperature, and the value obtained by monopoles in the maximum Abelian gauge.
Previous work had incorrectly omitted a term due to Dirac sheets. When this
term is included, the monopole and full SU(2) determinations of the spacial
string tension agree to within the statistical errors of the monopole
calculation.Comment: 8 pages, Latex files: msum.tex,msum.aux packaged with uufile
Large Loops of Magnetic Current and Confinement in Four Dimensional Lattice Gauge Theory
We calculate the heavy quark potential from the magnetic current due to
monopoles in four dimensional lattice gauge theory. The magnetic current
is found from link angle configurations using the DeGrand-Toussaint
identification method. The link angle configurations are generated in a cosine
action simulation on a lattice. The magnetic current is resolved into
large loops which wrap around the lattice and simple loops which do not.
Wrapping loops are found only in the confined phase. It is shown that the long
range part of the heavy quark potential, in particular the string tension, can
be calculated solely from the large, wrapping loops of magnetic current.Comment: 15 pages (Latex file plus 3 postscript files appended), Univeristy of
Illinois Preprint ILL-(TH)-93-\#1
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