The baroclinic circulation in Hudson strait

Abstract

The baroclinic circulation in the mouth of Hudson Strait is modelled using general results for nearly geostrophic flow along an indented coastline. A simple T‐junction model is first discussed, followed by a somewhat more faithful idealization that includes the sharp northern tip of Labrador, the southwest tip of Baffin Island and part of Ungava Bay. The results show that the mouth of Hudson Strait does not present a significant obstacle to baroclinic flow in and out of it. We thus conclude that the observed recirculation must be due to other effects.     

Magnetic and nuclear structure and thermal expansion of orthorhombic and monoclinic polymorphs of CoGeO3 pyroxene

CoGeO₃ was synthesized at 1,273 and 1,448 K using ceramic sintering techniques in the monoclinic and orthorhombic modification, respectively. The two compounds were analysed by magnetic susceptibility measurements and neutron diffraction in order to study magnetic ordering and spin structures at low temperature. The monoclinic form of CoGeO₃ has C2/c symmetry and orders magnetically below 36 K with a small negative paramagnetic Curie temperature θ _P = −4.6 (2) K. The magnetic structure can be described with k = (1, 0, 0) in the magnetic space group C2′/c′ having a ferromagnetic spin arrangement within the chains of M1 sites, but a dominating antiferromagnetic coupling between the chains. At the M1 sites the magnetic spins are aligned within the a–c plane forming an angle of 120° with the +a-axis and they are not parallel to the spins at M2. Here spins are also ferromagnetically coupled within, but antiferromagnetically coupled between the M1/M2 site bands. The orthorhombic phase of CoGeO₃ displays Pbca symmetry and transforms to an antiferromagnetically ordered state [θ _P = −18.6(2) K] below 33 K. The magnetic spin structure can be described with k = (0, 0, 0) in space group Pbca′ and it is similar to the one of the C2/c phase except that it is non-collinear in nature, i.e. there are components of the magnetic moment along all three crystallographic axes. Small magneto-elastic coupling is observed in the orthorhombic phase.     

Asteroid Models from the Pan-STARRS Photometry

We present simulations on the asteroid photometric data that will be provided by the Pan-STARRS (Panoramic Survey Telescope and Rapid Response System). The simulations were performed using realistic shape and light-scattering models, random orientation of spin axes, and rotation periods in the range 2–24 h. We show that physical models of asteroids can be reconstructed from this data with some limitations (possible multiple pole solutions). We emphasize the potential of sparse photometric data to produce models of a large number of asteroids within the next decade and we outline further tests with fast and slow rotators, tumblers, and binary asteroids.     

CATCHMENT-WIDE ANALYSIS OF THE SEDIMENT REGIME WITH RESPECT TO RESERVOIR SEDIMENTATION

1 INTRODUCTIONIn Anstria reservoirs are frequentiy multi-purpose schemes, being used for power generation, floodprotechon and for wate suPPly downstream. These reservoirs have some adVerse imPaCts on theenvironment around the reservoir and also on the dOwnstream pat:. in rivers with mean annual discharge above 30 m3ls about 36 % of the total length of l884 lQn isimpounded, and only 35% remains as free flowing sections (Muhar, l992),. flooding has been, and continues to be, a serious pr…     

Finite-difference modelling of magnetotelluric fields in two-dimensional anisotropic media

An algorithm for the numerical modelling of magnetotelluric fields in 2-D generally anisotropic block structures is presented. Electrical properties of the individual homogeneous blocks are described by an arbitrary symmetric and positive-definite conductivity tensor. The problem leads to a coupled system of partial differential equations for the strike-parallel components of the electromagnetic field. E _x, and H _x These equations are numerically approximated by the finite-difference (FD) method, making use of the integro-interpolation approach. As the magnetic component H _x, is constant in the non-conductive air, only equations for the electric mode are approximated within the air layer. The system of linear difference equations, resulting from the FD approximation, can be arranged in such a way that its matrix is symmetric and band-limited, and can be solved, for not too large models, by Gaussian elimination. The algorithm is applied to model situations which demonstrate some non-trivial phenomena caused by electrical anisotropy. In particular, the effect of 2-D anisotropy on the relation between magnetotelluric impedances and induction arrows is studied in detail.     

Area-preserving Poincaré mappings of the unit disk

The best way to investigate the long-time behaviour of dynamical systems is to introduce an appropriate Poincaré mapping P and study its iterates.Two cases of physical interest arise: Conservative and dissipative systems. While the latter has been considered by a great many authors, much less is known for the first one (according to Liouville's theorem, here the mapping leaves a certain measure in phase space invariant). In this paper, we concentrate our attention on compact phase spaces (or, rather, surfaces of section). This assumption is mathematically useful and physically reasonable.We consider the simplest possible (2-dimensional) systems whehre the phase space is the compact unit disk D in ². A family of simple area-preserving mappings from D onto itselves will be given and discussed in detail.It is shown that general characteristics of the dynamics are quite similar to those of e.g. the Hénon-Heiles system, while other features, as the structure of invariant curves, are different.     

A photometric investigation of the asteroid (89) Julia

New photometric data of the light curve of the minor planet (89) Julia were obtained on nine nights during the 1972 opposition using the 60cm telescope at OHP. A synodic period of 11^h23^m14^s ± 7^s and an amplitude of 0.25mag were derived from the measurements. The light curve is rather unsymmetric and no plausible explanation for this has been offered so far. The measurements have been carried out in instrumental V′; the data obtained in B′ and U′ supplement all conclusions from V′ data concerning the rotation of Julia.