113,437 research outputs found
SU3 isoscalar factors
A summary of the properties of the Wigner Clebsch-Gordan coefficients and
isoscalar factors for the group SU3 in the SU2U1 decomposition is
presented. The outer degeneracy problem is discussed in detail with a proof of
a conjecture (Braunschweig's) which has been the basis of previous work on the
SU3 coupling coefficients. Recursion relations obeyed by the SU3 isoscalar
factors are produced, along with an algorithm which allows numerical
determination of the factors from the recursion relations. The algorithm
produces isoscalar factors which share all the symmetry properties under
permutation of states and conjugation which are familiar from the SU2 case. The
full set of symmetry properties for the SU3 Wigner-Clebsch-Gordan coefficients
and isoscalar factors are displayed.Comment: 20 pages, LaTeX (earlier version incomplete
Monolayers of 3He on the Surface of Bulk Superfluid 4He
We have used quantum evaporation to investigate the two-dimensional fermion
system that forms at the free surface of (initially isotopically pure) 4He when
small quantities of 3He are added to it. By measuring the first-arrival times
of the evaporated atoms, we have determined that the 3He-3He potential in this
system is V_3S/k_B=(0.23+/-0.02) K nm^2 (repulsive) and estimated a value of
m_3S=(1.53+/-0.02)m_3 for the zero-coverage effective mass. We have also
observed the predicted second layer-state which becomes occupied once the first
layer-state density exceeds about 0.6 monolayers.Comment: 2 pages, 3 figures. Submitted to Proc. LT-22 (1999) to appear in
Physica
Relative Evaporation Probabilities of 3He and 4He from the Surface of Superfluid 4He
We report a preliminary experiment which demonstrates that 3He atoms in
Andreev states are evaporated by high-energy (E/k_B ~ 10.2 K) phonons in a
quantum evaporation process similar to that which occurs in pure 4He. Under
conditions of low 3He coverage, high-energy phonons appear to evaporate 3He and
4He atoms with equal probability. However, we have not managed to detect any
3He atoms that have been evaporated by rotons, and conclude that the
probability of a roton evaporating a 3He atom is less than 2% of the
probability that it evaporates a 4He atom.Comment: 2 pages, 3 figures. Submitted to Proc. LT-22 (1999) Physica
Traffic scenario generation technique for piloted simulation studies
Piloted simulation studies of cockpit traffic display concepts require the development of representative traffic scenarios. With the exception of specific aircraft interaction issues, most research questions can be addressed using traffic scenarios consisting of prerecorded aircraft movements merged together to form a desired traffic pattern. Prerecorded traffic scenarios have distinct research advantages, allowing control of traffic encounters with repeatability of scenarios between different test subjects. A technique is described for generation of prerecorded jet transport traffic scenarios suitable for use in piloted simulation studies. Individual flight profiles for the aircraft in the scenario are created interactively with a computer program designed specifically for this purpose. The profiles are then time-correlated and merged into a complete scenario. This technique was used to create traffic scenarios for the Denver, Colorado area with operations centered at Stapleton International Airport. Traffic scenarios for other areas may also be created using this technique, with appropriate modifications made to the navigation fix locations contained in the flight profile generation program
Extended plasticity in commercial-purity zinc
90% rolling-reduction of annealed commercial-purity zinc sheet
(grain size 100 - 150 μ) results in the fragmentation of the large grains
into, finally, stable micro-grains, 1 - 211 in diameter. The stability of
the micro-grains is due to the presence of soluble and insoluble impurities
which prevent recrystallization.
This micro-grain material is strain-rate sensitive, and elongations of
200% have been obtained at room temperature.
Although this as-rolled, 90% reduction zinc sheet is not super-plastic
according to the current definition, its behaviour has led to the coining of
the phase 'extended plasticity'.
Evidence of grain-boundary sliding is found on examination of the surface
by scanning electron microscopy, while the examination of thin foils and
activation energy measurements support the dynamic softening (recovery) theory;
thus, both these mechanisms must be operating, to a greater or less extent,
to confer on this material the observe mechanical behaviour.
It is finally concluded that it is dangerous to draw conclusions regarding
the mechanism of plastic deformation from surface observations alone
Simulation study of traffic-sensor noise effects on utilization of traffic situation display for self-spacing task
The effect of traffic sensor noise on the ability of a pilot to perform an intrail spacing task was determined. The tests were conducted in a fixed base cockpit simulator configured as a current generation transport aircraft, with an electronic traffic display provided in the weather radarscope location. The true positions of the traffic were perturbed in both relative range and azimuth by random errors to simulate traffic sensor noise associated with an onboard sensor. The evaluation task involved simulated instrument approaches into a terminal area while maintaining self separation on a lead aircraft. Separation performance data and pilot subjective ratings and comments were obtained. The results of the separation data indicate that displayed traffic position errors, having standard deviation values up to 0.3-n.mi. range and 8 deg azimuth, had negligible effect on the spacing performance achieved by the pilots. Speed profiles of the lead aircraft, display of the lead aircraft groundspeed, and individual pilot techniques were found to significantly affect the mean spacing performance
Low speed testing of the inlets designed for a tamden-fan V/STOL nacelle
An approximately 0.25 scale model of a tandem fan nacelle, designed for a subsonic V/STOL aircraft, was tested in a Lewis wind tunnel. Model variables included long and short aft inlet cowls and the addition of exterior strakes to the short inlet cowl. Inlet pressure recoveries and distortion were measured at pitch angles to 40 deg and at combinations of pitch and yaw to 30 deg. Airspeeds covered a range to 135 knots (69 m/sec). The short aft inlet with added strakes had the best aerodynamic performance and is considered suitable for the intended V/STOL application
Feeding Records of Aphids (Hemiptera: Aphididae) From Wisconsin
Basic to our understanding of any animal and its habitat requirements is knowing what it eats. Reported here are observations of feeding by 27 species of aphids encountered in Wisconsin over 1992-2002
Degree of Cajal-Retzius cell mislocalisation correlates with the severity of structural brain defects in mouse models of dystroglycanopathy
The secondary dystroglycanopathies are characterized by the hypoglycosylation of alpha dystroglycan, and are associated with mutations in at least 18 genes that act on the glycosylation of this cell surface receptor rather than the Dag1 gene itself. At the severe end of the disease spectrum, there are substantial structural brain defects, the most striking of which is often cobblestone lissencephaly. The aim of this study was to determine the gene‐specific aspects of the dystroglycanopathy brain phenotype through a detailed investigation of the structural brain defects present at birth in three mouse models of dystroglycanopathy—the FKRPKD, which has an 80% reduction in Fkrp transcript levels; the Pomgnt1null, which carries a deletion of exons 7–16 of the Pomgnt1 gene; and the Largemyd mouse, which carries a deletion of exons 5–7 of the Large gene. We show a rostrocaudal and mediolateral gradient in the severity of brain lesions in FKRPKD, and to a lesser extent Pomgnt1null mice. Furthermore, the mislocalization of Cajal–Retzius cells is correlated with the gradient of these lesions and the severity of the brain phenotype in these models. Overall these observations implicate gene‐specific differences in the pathogenesis of brain lesions in this group of disorders
Feeding Records of Aphids (Hemiptera: Aphididae) From Wisconsin, Supplement
Basic to our understanding of any animal and its habitat requirements is knowing what it eats. Reported here are observations of feeding by 24 species of aphids encountered in Wisconsin over 2002-2010
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