Navstar GPS - Charting Aspects

The historical development of positioning in relation to the nautical chart is very briefly described. Present nautical charts are largely based on geodetic surveys which date from the 19th and early 20th century. This gave rise to the use of many local datums and there has been a need to provide the mariner with information to enable him to transfer his position from one chart to an adjacent one on a different datum. The sizes of discrepancies in position between various datums are given. The availability of the Global Positioning System (GPS) and the World Geodetic System 1984 (WGS 84) datum enables positioning on a single worldwide datum to become a reality. The important factors affecting the adoption of WGS 84 as the datum for nautical charts, namely data availability and the practical and political considerations, are discussed. The importance of the proper consideration of datum in relation to new developments in the use of nautical charts is also mentioned

Multi-site mean-field theory for cold bosonic atoms in optical lattices

We present a detailed derivation of a multi-site mean-field theory (MSMFT) used to describe the Mott-insulator to superfluid transition of bosonic atoms in optical lattices. The approach is based on partitioning the lattice into small clusters which are decoupled by means of a mean field approximation. This approximation invokes local superfluid order parameters defined for each of the boundary sites of the cluster. The resulting MSMFT grand potential has a non-trivial topology as a function of the various order parameters. An understanding of this topology provides two different criteria for the determination of the Mott insulator superfluid phase boundaries. We apply this formalism to $d$-dimensional hypercubic lattices in one, two and three dimensions, and demonstrate the improvement in the estimation of the phase boundaries when MSMFT is utilized for increasingly larger clusters, with the best quantitative agreement found for $d=3$. The MSMFT is then used to examine a linear dimer chain in which the on-site energies within the dimer have an energy separation of $\Delta$. This system has a complicated phase diagram within the parameter space of the model, with many distinct Mott phases separated by superfluid regions.Comment: 30 pages, 23 figures, accepted for publication in Phys. Rev.

The wallaby menace in the Kimberleys

Countless thousands of Sandy Wallabies (Macropus agilis) have long been a menace to the pastoral industry in the Kimberleys. These animals eat almost the same foods as the sheep and cattle and have substantially reduced the stock-carrying capacity of the river-frontage areas where they are found in the greatest numbers. Research into control methods was commenced in 1952 when Mr. L. A. Harrison undertook some investigations designed to ascertain the best line of approach to a poisoning campaign

Spin and Charge Texture around In-Plane Charge Centers in the CuO_2 planes

Recent experiments on La_2Cu_{1-x}Li_xO_4 show that although the doped holes remain localized near the substitutional Li impurities, magnetic order is rapidly suppressed. An examination of the spin texture around a bound hole in a CuO_2 plane shows that the formation of a skyrmion is favored in a wide range of parameters, as was previously proposed in the context of Sr doping. The spin texture may be observable by elastic diffuse neutron scattering, and may also have a considerable effect on NMR lineshapes.Comment: 4 pages, postscript file, hardcopy available upon request, to appear in PR

Satellite navigation for meteorological purposes: Inverse referencing for NOAA-N and ERS-1 imagers with a 1 km nadir pixel size

Iterative methods for inverse referencing from mean orbital elements or osculating position and velocity, accounting for all necessary orbital perturbations with respect to given nadir pixel size, are described. [Inverse referencing means that the geodetic coordinates of a point on the surface are given and the corresponding image coordinates (scan line number and pixel number) are obtained from satellite orbital elements or coordinates.] The idea is to treat a pixel like a satellite tracking station on the ground. This permits the use of existing software for the computation of satellite ephemerides and orbit determination. The time of culmination of a satellite over the pixel and the off-nadir angle at that moment have been computed. Two variants for such a computation have been tested. Numerical results for the NOAA-N meteorological satellites and ERS-1 are presented. The present state of our software for inverse referencing should fulfil ordinary requirements posed by meteorologists. For NOAA-N satellites, the accuracy achieved roughly the nadir pixel size. The main obstacle to an increase in accuracy is the low quality of the mean orbital elements usually available. For ERS-1, the accuracy may achieve a level of 100 m. A software package, containing versions of the FORTRAN 77 programs PIXPO 3, PIXPO 4 and PIXPOSC, for various data types, including US-2 line or TBUS mean elements or a state vector, is available for scientific exchange. © 1994