MAG Waves in Sunspots Umbrae: Slow Waves Leaking to the Corona

The linear oscillations of a stratified atmosphere embedded in a uniform vertical magnetic field are studied here. We use a simple theoretical model, formed by the superposition of two isothermal layers, representing, respectively, i) the photosphere and the chromosphere, and ii) the corona. The bottom layer behaves, for some modes, as a resonant cavity where MAG waves are semi-trapped. We find the existence of two types of modes: 1) Fast modes which are trapped below the transition layer, 2) Mixed modes which are resonant modes in the first layer and leak part of the energy to the corona. These mixed modes have been found to be damped in the horizontal direction and can explain the observed slow modes in the corona.     

Three-dimensional subsatellite motion under air drag and oblateness perturbations

The three-dimensional relative motion of a subsatellite with respect to a reference station in an elliptical orbit is studied. A general theory based on the variation of the relative elements, i.e. the instantaneous differences between the orbital parameters of the subsatellite and those of the station, is formulated in order to incorporate arbitrary perturbing forces acting on both satellites. The loss of precision inherent in the subtraction of almost identical quantities is avoided by the consistent use of difference variables. In the absence of perturbations exact analytical representations can be obtained for the relative state parameters. The influences of air drag and Earth's oblateness on the relative motion trajectories are investigated and illustrated graphically for a number of cases.     

Processing map and well log data for geological and soil surveys

Design of a system which accepts geological maps or soil maps, together with corresponding well logs and produces interpretation maps, is described. The major aim was to get a processing program that would be useful at an operational scale that avoids the use of special purpose graphics hardware. This was achieved by using segment encoding of lines and by treatment of mapped units as basic graphical units (atoms). The system operation was split into an input phase and a processed phase. Input- and file-building require some technical experience, but are a one-time affair, whereas subsequent processing requires less (graphical) resources and experience, but is of a repetitive nature. When writing processing programs, emphasis was placed on ease of adding options. Clever improvements of efficiency (e.g., disk traffic) were not deemed worthwhile or even wise. Two driving forces behind the project required the programs reported here. First was the observation that digital data can be used only if appropriate programs are readily available to produce required results without need for large investments in hardware. Second was the idea that digital tools could be most effective if they allow the end-user (customer) to interact directly with the full base of data without recourse to technical experts. The resulting system is operational and running on a VAX 11/750, coded in FORTRAN.     

Freshwater Ostracodes in Quaternary Permafrost Deposits in the Siberian Arctic

Ostracode analysis was carried out on samples from ice-rich permafrost deposits obtained on the Bykovsky Peninsula (Laptev Sea). A composite profile was investigated that covers most of a 38-m thick permafrost sequence and corresponds to the last ca. 60 kyr of the Late Quaternary. The ostracode assemblages are similar to those known from European Quaternary lake deposits during cold stages. The ostracode habitats were small, shallow, cold, oligotrophic pools located in low centred ice wedge polygons or in small thermokarst depressions. In total, 15 taxa, representing 7 genera, were identified from 65 samples. The studied section is subdivided into six ostracode zones that correspond to Late Quaternary climatic and environmental stadial-interstadial variations established by other paleoenvironmental proxies: (1) cold and dry Zyrianian stadial (58–53 kyr BP); (2) warm and dry Karginian interstadial (48–34 kyr BP); (3) transition from the Karginian interstadial to the cold and dry Sartanian stadial (34–21 kyr BP); (4) transition from the Sartanian stadial to the warm and dry Late Pleistocene period, the Allerød (21–14 kyr BP); (5) transition from the Allerød to the warm and wet Middle Holocene (14–7 kyr BP); and (6) cool and wet Late Holocene (ca. 3 kyr BP). The abundance and diversity of the ostracodes will be used as an additional bioindicator for paleoenvironmental reconstructions of the Siberian Arctic.     

HI absorption observations of two radio sources near the supernova remnant G 127.1 + 0.5

The compact source 0125 + 628 in the centre of the galactic supernova remnant G 127.1 + 0.5 has been re-observed in HI absorption using the Westerbork Synthesis Radio Telescope (WSRT). The outer arm HI absorption atV = -95km s^-1 has been confirmed. The absorption spectrum is similar to that of the nearby extragalactic source 0123 + 633. We discuss the arguments concerning an extragalactic origin of 0125 + 628 and conclude that it is most likely extragalactic and not an SS 433 type object. The National Radio Astronomy Observatory is operated by Associated Universities Inc. under contract with the National Science Foundation.     

3D seismic study of a ductile shear zone from laboratory and petrofabric data (Saint Barthélémy Massif, Northern Pyrenees, France)

In order to constrain interpretations of seismic reflection records more effectively, the seismic properties of a middle crustal section exposed in the Saint Barthélémy Massif have been determined. The massif, transected by a 200 m thick shear zone has been systematically sampled for density measurements and modal analysis has been performed in order to define the spatial variations of physical properties. Seismic velocities ( V _p, V _S, shear wave birefringence), have been measured on five representative samples to 600 MPa and 600°C simultaneously in the three structural directions (X, Y and Z). For two samples, the experimental data have been compared with calculated values, based on petrofabric analyses. The Lattice Preferred Orientation (LPO) is determined using universal stage, electron channelling microscopy and neutron diffraction goniometry. Using the experimental and calculated velocity data, we establish a lateral homogeneous anisotropic model.     

Alternate schemes in synthetic aperture sonar processing

Suboptimal processing schemes, the application of which is not widespread in synthetic aperture sonar processing, are described with reference to seafloor imaging. It is shown that their application can result in a significant increase of the azimuth resolution of the sonar system with respect to the resolution due to its physical beamwidth, without imposing unreasonable constraints on the sonar platform trajectory.     

Arsenic Speciation in Lichens and in Coarse and Fine Airborne Particulate Matter by HPLC–UV–HG–AFS

A three-step sequential extraction procedure with Milli-Q, CaCl₂ and H₃PO₄ was applied for extraction of arsenic species in lichen transplants and airborne particulate matter (fine and coarse fractions). The samples used in this work were collected in 1994–1995 near coal-fired power plants. Both transplant lichens and airborne particulate matter were submitted to the same environment simultaneously. Arsenic species identification and quantification was performed by HPLC–UV–HG–AFS. Inorganic forms of arsenic (arsenite and arsenate) were present in significant amounts in most of the samples. Only in lichens also organic forms of arsenic (monomethyl arsonic acid and dimethyl arsinic acid) were identified which may indicate biotransformation of inorganic arsenic.