64,282 research outputs found
Theory of magnetization plateaux in the Shastry-Sutherland model
Using perturbative continuous unitary transformations, we determine the
long-range interactions between triplets in the Shastry-Sutherland model, and
we show that an unexpected structure develops at low magnetization with
plateaux progressively appearing at 2/9, 1/6, 1/9 and 2/15 upon increasing the
inter-dimer coupling. A critical comparison with previous approaches is
included. Implications for the compound SrCu(BO) are also
discussed: we reproduce the magnetization profile around localized triplets
revealed by NMR, we predict the presence of a 1/6 plateau, and we suggest that
residual interactions beyond the Shastry-Sutherland model are responsible for
the other plateaux below 1/3.Comment: 5 pages, 6 figure
Navigation and guidance analysis for a Mars mission Interim study report
Error propagation program simulating earth based tracking for navigation and guidance analysis of Mars missio
The Phase Diagram of 2 flavour QCD with improved Actions
It has been proposed, that the chiral continuum limit of 2-flavour QCD with
Wilson fermions is brought about by a phase in which flavour and parity
symmetry are broken spontaneously at finite lattice spacing. At finite
temperature this phase should retract from the weak coupling limit to form 5
cusps. This scenario is studied with tree level Symanzik improved actions for
both gauge and fermion fields on lattices of size and .Comment: Talk given at Conference on Strong and Electroweak Matter (SEWM 98),
Copenhagen, Denmark, 2-5 Dec 199
Single-particle versus pair condensation of hard-core bosons with correlated hopping
We investigate the consequences of correlated hopping on the ground state
properties of hard-core bosons on a square lattice as revealed by extensive
exact diagonalizations and quantum Monte Carlo simulations. While for non
interacting hard-core bosons the effective attraction induced by the correlated
hopping leads to phase separation at low density, we show that a modest
nearest-neighbor repulsion suppresses phase separation, leading to a remarkable
low-density pairing phase with no single particle Bose-Einstein condensation
but long-range two-particle correlations, signaling a condensation of pairs. We
also explain why the unusual properties of the pairing phase are a real
challenge for standard one-worm quantum Monte Carlo simulations.Comment: 8 pages, 7 figure
Development and flight tests of a Kalman filter for navigation during terminal area and landing operations
A Kalman filter for aircraft terminal area and landing navigation was implemented and flight tested in the NASA Ames STOLAND avionics computer onboard a Twin Otter aircraft. This system combines navaid measurements from TACAN, MODILS, air data, radar altimeter sensors along with measurements from strap-down accelerometer and attitude angle sensors. The flight test results demonstrate that the Kalman filter provides improved estimates of the aircraft position and velocity as compared with estimates from the more standard complementary filter. The onboard computer implementation requirements to achieve this improved performance are discussed
FORTRAN optical lens design program
Computer program uses the principles of geometrical optics to design optical systems containing up to 100 planes, conic or polynomial aspheric surfaces, 7 object points, 6 colors, and 200 rays. This program can be used for the automatic design of optical systems or for the evaluation of existing optical systems
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