51,004 research outputs found
Coupling bioturbation activity to metal (Fe and Mn) profiles in situ
This work was supported by a University of Aberdeen 6th century scholarship (awarded to L. T.), CEFAS Lowestoft (DP204), NERC NFSD support (08/02) and a SAMS research bursary (awarded to L. T)Peer reviewedPublisher PD
Towers of recollement and bases for diagram algebras: planar diagrams and a little beyond
The recollement approach to the representation theory of sequences of
algebras is extended to pass basis information directly through the
globalisation functor. The method is hence adapted to treat sequences that are
not necessarily towers by inclusion, such as symplectic blob algebras (diagram
algebra quotients of the type-\hati{C} Hecke algebras).
By carefully reviewing the diagram algebra construction, we find a new set of
functors interrelating module categories of ordinary blob algebras (diagram
algebra quotients of the type- Hecke algebras) at {\em different} values
of the algebra parameters. We show that these functors generalise to determine
the structure of symplectic blob algebras, and hence of certain two-boundary
Temperley-Lieb algebras arising in Statistical Mechanics.
We identify the diagram basis with a cellular basis for each symplectic blob
algebra, and prove that these algebras are quasihereditary over a field for
almost all parameter choices, and generically semisimple. (That is, we give
bases for all cell and standard modules.)Comment: 61 page
Instabilities leading to vortex lattice formation in rotating Bose-Einstein condensates
We present a comprehensive theoretical study of vortex lattice formation in
atomic Bose-Einstein condensates confined by a rotating elliptical trap. We
consider rotating solutions of the classical hydrodynamic equations, their
response to perturbations, as well as time-dependent simulations. We
discriminate three distinct, experimentally testable, regimes of instability:
{\em ripple}, {\em interbranch}, and {\em catastrophic}. Under
symmetry-breaking perturbations these instabilities lead to lattice formation
even at zero temperature. While our results are consistent with previous
theoretical and experimental results, they shed new light on lattice formation.Comment: 5 pages, 2 figure
Common bearing material has highest fatigue life at moderate temperature
AISI 52100, a high carbon chromium steel, has the longest fatigue life of eight bearing materials tested. Fatigue lives of the other materials ranged from 7 to 78 percent of the fatigue life of AISI 52100 at a temperature of 340 K (150 F)
Intumescent Coatings as Fire Retardants
Fire-retardant paint, when activated by the heat of fire, reacts to form a thick, low-density, polymeric coating or char layer. Water vapor and sulphur dioxide are released during the intumescent reaction
Magnetic Flux Expulsion in the Powerful Superbubble Explosions and the Alpha-Omega Dynamo
The possibility of the magnetic flux expulsion from the Galaxy in the
superbubble (SB) explosions, important for the Alpha-Omega dynamo, is
considered. Special emphasis is put on the investigation of the downsliding of
the matter from the top of the shell formed by the SB explosion which is able
to influence the kinematics of the shell. It is shown that either Galactic
gravity or the development of the Rayleigh-Taylor instabilities in the shell
limit the SB expansion, thus, making impossible magnetic flux expulsion. The
effect of the cosmic rays in the shell on the sliding is considered and it is
shown that it is negligible compared to Galactic gravity. Thus, the question of
possible mechanism of flux expulsion in the Alpha-Omega dynamo remains open.Comment: MNRAS, in press, 11 pages, 9 figure
Flexural fatigue of hollow rolling elements
Hollow cylindrical bars were tested in the rolling-contact fatigue tester to determine the effects of material and outside diameter to inside diameter (OD/ID) ratios of 2.0, 1.6, 1.4, and 1.2 on fatigue failure mode and subsequent failure propagation. The range of applied loads with these OD/ID ratios resulted in maximum tangential tensile stresses ranging from 165 to 655 megapascals (24,000 to 95,000 psi) at the bore surface. Flexural failures of the hollow test bars occurred when this bore stress was 490 megapascals (71,000 psi) or greater with AISI 52100 hollow bars and 338 megapascals (49,000 psi) or greater with AISI M-50 hollow bars. Good correlation was obtained in relating the failures of these hollow bars with flexural failures of drilled balls from previously published full scale bearing tests
Evaluation of ball and roller bearings restored by grinding
The restoration by grinding of those rolling element bearings which are currently being discarded at aircaft engine and transmission overhaul is considered. Three bearing types were selected from the UH-1 helicopter engine and transmission for the pilot program. Groups of each of these bearings were visually and dimensionally inspected for suitability for restoration. A total of 250 bearings were restored by grinding. Of this number, 30 bearings from each type were endurance tested to a TBO of 1600 hours. No bearing failures occurred related to the restoration by grinding process. The two bearing failures which occurred were due to defective rolling elements and were typical of those which may occur in new bearings. The restorable component yield to the three groups was in excess of 90 percent
Does the geoid drift west?
In 1970 Hide and Malin noted a correlation of about 0.8 between the geoid and the geomagnetic potential at the Earth's surface when the latter is rotated eastward in longitude by about 160 degrees and the spherical harmonic expansions of both functions are truncated at degree 4. From a century of magnetic observatory data, Hide and Malin inferred an average magnetic westward drift rate of about 0.27 degrees/year. They attributed the magnetic-gravitational correlation to a core event at about 1350 A.D. which impressed the mantle's gravity pattern at long wavelengths onto the core motion and the resulting magnetic field. The impressed pattern was then carried westward 160 degrees by the nsuing magnetic westward drift. An alternative possibility is some sort of steady physical coupling between the magnetic and gravitational fields (perhaps migration of Hide's bumps on the core-mantle interface). This model predicts that the geoid will drift west at the magnetic rate. On a rigid earth, the resulting changes in sea level would be easily observed, but they could be masked by adjustment of the mantle if it has a shell with viscosity considerably less than 10 to the 21 poise. However, steady westward drift of the geoid also predicts secular changes in g, the local acceleration of gravity, at land stations. These changes are now ruled out by recent independent high-accuracy absolute measurements of g made by several workers at various locations in the Northern Hemisphere
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