A single-degenerate model for the progenitor of the Type Ia supernova 2002ic

Supernova 2002ic was an atypical Type Ia supernova (SN Ia) with evidence for substantial amounts of hydrogen associated with the system. Contrary to previous claims, we show that its unusual properties can be understood within the framework of one of the most favoured progenitor models, the so-called supersoft channel. This requires that the donor star was initially relatively massive  (∼3 M_⊙)  and that the system experienced a delayed dynamical instability, leading to a large amount of mass-loss from the system in the last few 10⁴ yr before the explosion. This can produce the inferred hydrogen-rich circumstellar environment, most likely with a disc-like geometry. However, in order for this model to be feasible, it requires a larger accretion efficiency on to the white dwarf than is assumed in present parametrizations. If this is confirmed, it would most likely increase estimates for the frequency of the single-degenerate channel. Based on population synthesis simulations we estimate that not more than 1 in 100 SNe Ia should belong to this subgroup of SNe Ia.     

Comparison of binding abilities of fulvic and humic acids extracted from recent marine sediments with UO2

Potentiometric titrations were used to measure conditional stability constants of UO₂²⁺-fulvic acid and UO₂²⁺-humic acid complexes. Both 2:1 and 1:1 COO^-:UO₂²⁺ binding were observed. With decreasing metal concentration (2.5·10⁻⁴-6.25·10⁻⁵ M) increasing amounts of UO₂²⁺ were in the form of 1:1 humate complexes and 2:1 fulvate complexes. Despite the high nitrogen content and the low acidic OH group content, the successive stability constant values were similar to those determined for divalent cations associated with fulvic and humic compounds isolated from soils. Stability constant values increase simultaneously with increasing ionization of the humic (or fulvic) acid polyelectrolytes and with decreasing metal concentration.     

Multivariate analysis of Kenya's urban system

The study analyzes the structure, spatial interaction, and dimension of the post-colonial urban systems of Kenya using component factor analysis and based on selected socio-cultural, economic, and demographic variables. The study identified seven major dimensions of variation accounting for 72.0%. The analysis of the urban spatial variation is compared and intertwined with studies done in other countries to find out the regional variation of the loadings. Finally, a seven-order characteristics of Kenya urban systems is suggested, based on the study. The accurate knowledge of these salient characteristics of Kenya urban sub-systems is important before any viable spatial planning should be implemented.     

Using landforms of Saudi Arabia for scenic and recreational purposes (With special reference to the Riyadh area)

The landform of Saudi Arabia in general and the Riyadh area in particular have their own potentiality for scenic and recreational purposes. The higher lands or features which have well cemented material in some areas of Riyadh have been recommended for scenic use, while lower lands like wide natural lakes, sand dunes and others can be mostly used for recreational purposes. Such features and purposes found here may be extrapolated into other similar areas within Saudi Arabia and may be compared with other areas elsewhere in the world.     

A LAYER-STRIPPING TECHNIQUE FOR THE SUPPRESSION OF WATER-BOTTOM MULTIPLE REFLECTIONS*

A new method to suppress water-bottom multiples (water-bottom reverberations) uses the fact that in the domain of intercept time and ray parameter (τ–p domain) the water-bottom reverberations are strictly periodical for a horizontal flat sea bottom. Using this property a comb filter can be designed. The window of the filter should be approximately equal to the duration of a source pulse. The algorithm finds the maximum of the periodical energy throughout the τ–p domain and then designs the comb filter which eliminates the water bottom reverberations from each trace in the τ– p domain. This process can be repeated for higher order reverberations. Finally the τ–p domain with attenuated multiples is transformed back to the conventional x -- t space. The method is illustrated on a variety of synthetic data and on a set of real marine CMP data acquired in the North Sea near the Norwegian shore.     

Two new methods for solving large scale least squares in geodetic surveying computations

This paper considers the solution of linear least squares problems arising in space geodesy, with a special application to multi-station adjustment by a short arc method based on Doppler observations. We recall briefly the widely used second-order regression algorithm due to Brown for reducing the normal equations system. Then we propose two algorithms which avoid the use of the normal equations. The first one is a direct method that applies orthogonal transformations to the observation matrix directly, in order to reduce it to upper triangular form. The solution is then obtained by backsubstitution. The second method is iterative and uses a preconditioned conjugate gradient technique. A comparison of the three procedures is provided on data of the second European Doppler Observation Campaign (EDOC-2).     

Fabrics and sequences of submarine carbonate cements in Holocene Bermuda cup reefs

A variety of precipitative synsedimentary CaCO₃ cements lines or fills cavities and surrounds sediment particles within Recent algal cup reefs which dot the rim of the Bermuda platform. These include aragonite needle, spherulitic, and lath cements as well as calcite micrite, palisade, scale, and blocky cements, listed according to respective relative abundances. No distribution pattern of cements is apparent; various combinations of three or four cements are found in almost every sample or thin section. From the occurrence of various cements, factors determining composition and fabric are deduced:

1. Morphology, composition, and coating of the substrate.
2. Direct or indirect influence of organisms such as algae, pelecypods, or crustaceans.
3. Micro-environment, specifically size and permeability, rate of sea-water circulation through the micro-environment, substrates and organisms within the microenvironment.

Various sequences of two or three precipitative cements result from changes in microenvironment; the only cause of such change recognized is the entrance of endolithic algae into partly cemented cavities. This study provides some insight into the origin of submarine cements and a basis for comparative interpretation of cements in fossil marine environments, especially fossil reefs.