A COMBINED REFRACTION-DIFFRACTION-DISSIPATION MODEL OF WAVE PROPAGATION

A numerical model based on the mild-slope equation of water wave propagation over complicated bathymetry,taking into account the combined effects of refraction,diffraction and dissipation due to wavebreaking is presented.Wave breaking is simulated by modifying the wave height probability density func-tion and the wave energy dissipation mechanism is parameterized according to that of the hydraulic jumpformulation.Solutions of the wave height,phase function,and the wave direction at every grid point areobtained by finite difference approximation of the governing equations,using Gauss-Seidel Iterative Method(GSIM)row by row.Its computational convenience allows it to be applied to large coast regions tostudy the wave transformation problem.Several case studies have been made and the results compare verywell with the experiment data and other model solutions.The capability and utility of the model forreal coast areas are illustrated by application to a shallow bay of northeast Australia.     

Temperature dependence of the cation distribution in nickel aluminate (NiAl2O4) spinel: a powder XRD study

NiAl₂O₄ is a largely inverse spinel, which in detail shows increasing randomisation with temperature of Ni and Al between the octahedral and tetrahedral cation sites of the spinel structure. We have used powder XRD to determine this cation distribution in various samples of NiAl₂O₄ quenched after annealing between 700 and 1400° C. The inversion parameter (x) can be measured with a precision of ± 0.004 (one standard deviation), and a comparison of different methods of synthesis, X-ray diffraction and refinement techniques, suggests a probable accuracy of better than 0.01. The results are supported by some preliminary single crystal refinements on flux-grown samples.Below 800° C the rate of cation ordering becomes very slow, and, despite reaching an apparently steady state, it is doubtful if our samples attained complete internal equilibrium. Above 1250° C the cation redistribution becomes so fast that the quenching method becomes unreliable. Between 800 and 1250° C inclusive, the degree of inversion changes smoothly from 0.87 at 800° C to 0.79 at 1250° C, and is accompanied by linear changes in u, the oxygen parameter, from 0.2555 to 0.2563 (±0.0002), and a₀, the lattice parameter, from 8.0462 to 8.0522 Å (±0.0002 Å).     

Planetary nebulae in the Galaxy

It is shown that the planetary nebulae can be divided into three types according to the values of the mass of shell and a central star. The criteria are given using which one can determine the mass type of the nebula. The distance scale of each mass-type planetary nebulae is given. The distribution of planetary nebulae in the Galaxy, their formation rate, scale-height and other physical and kinematic characteristics are investigated. A catalogue of planetary nebulae emitting in the radio range is given.     

Mineralogical, chemical, and crystallographic properties of supergene jarosite-group minerals from the Xitieshan Pb-Zn sulfide deposit, northern Tibetan Plateau, China

Supergene jarosite-group minerals are widespread in weathering profiles overlying Pb-Zn sulfide ores at Xitieshan, northern Tibetan Plateau, China. They consist predominantly of K-deficient natrojarosite, with lesser amounts of K-rich natrojarosite and plumbojarosite. Electron microprobe (EMP) analyses, scanning electron microcopy (SEM) investigation, and X-ray mapping reveal that the jarosite-group minerals are characterized by spectacular oscillatory zoning composed of alternating growth bands of K-deficient and K-bearing natrojarosite (K₂O >1 wt.%). Plumbojarosite, whenever present, occurs as an overgrowth in the outermost bands, and its composition can be best represented by K_0.29Na_0.19Pb_0.31Fe_2.66Al_0.22(SO₄)_1.65(PO₄)_0.31(AsO₄)_0.04(OH)_7.37. The substitution of monovalent for divalent cations at the A site of plumbojarosite is charge balanced by the substitution of five-valent for six-valent anions in XO₄ at the X site. Thermogravimetric analysis (TGA) of representative samples reveal mass losses of 11.46 wt.% at 446.6 °C and 21.42 wt.% at 683.4 °C due to dehydroxylation and desulfidation, respectively. TGA data also indicate that the natrojarosite structure collapses at 446.6 °C, resulting in the formation of NaFe(SO₄)₂ and minor hematite. The decomposition products of NaFe(SO₄)₂ are hematite and Na₂SO₄. Powder X-ray diffraction (XRD) analyses show that the jarosite-group minerals have mean unit-cell parameters of a?=?7.315 Å and c?=?016.598 Å. XRD and EMP data support the view that substitutions of Na for K in the A site and full Fe occupancy in the B site can considerably decrease the unit-cell parameter c, but only slightly increase a. The results from this study suggest that the observed oscillatory zoning of jarosite-group minerals at Xitieshan resulted mainly from substitutions of K for Na at the A site and P for S at the X site.     

The limits of validity of the Frequency Ratio Method: The particular case of γ Doradus stars

This work provides a general vision of the limits of validity of the Frequency Ratio Method applied to the g‐mode pulsators in asymptotic regime, the γ Doradus stars. In particular, the work is mainly focused on the role of rotation which is found one of the most important source of uncertainty of the method. The particular case of the moderately rotating γ Doradus star HD48501 is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lower Cambrian patch reefs and associated sediments: southern Labrador, Canada

The complex pattern of biological accretion, internal sedimentation, early lithification, and biological destruction, that characterizes modern reefs and many fossil reefs has been recognized in archaeocyathid-rich patch reefs of Lower Cambrian age in the Forteau Formation, southern Labrador. Patch reefs occur as isolated masses or complex associations of many discrete masses of archaeocyathid-rich limestone and skeletal lime sands, surrounded by well-bedded skeletal limestones and shales. Each reef is composed of many loafshaped mounds stacked on top of one another. The limestone of each mound comprises archaeocyathids and Renalcis or Renalcis-like structures in a matrix of argillaceous lime mud rich in sponge spicules, trilobite and salterellid skeletons. Numerous growth cavities roofed by pendant Renalcis-like organisms and Renalcis are partially to completely filled with geopetal sediment indicating that much of the matrix was deposited as internal sediment. Two stages of diagenetic alteration are recognized: (1) syn-depositional, which affected only the reefs, and (2) post-depositional, which affected both reefs and inter-reef sediments. On the sea floor reef sediments were pervasively cemented and fibrous carbonate was precipitated in intraskeletal and growth cavities. These limestones and cements as well as archaeocyathid skeletons, were subsequently bored by endolithic organisms. Later post-depositional subaerial diagenesis resulted first in dissolution of certain skeletons and precipitation of calcite cement above the water table, followed by extensive precipitation of pore-filling calcite below the water table. These carbonate reefs are similar in structure to the basal pioneer accumulations of much younger lower and middle Palaeozoic reefs. They did not develop into massive ‘ecologic’ reefs because archaeocyathids never developed the necessary large, massive, hemispherical skeletons. This occurrence indicates that reefs developed more or less coincident with, and not long after, the appearance of skeletal metazoans in the Lower Cambrian.     

Non-point source pollution in Indian agriculture: Estimation of nitrogen losses from rice crop using remote sensing and GIS

The paper presents a detailed understanding of nitrogenous fertilizer use in Indian agriculture and estimation of seasonal nitrogen loosses from rice crop in Indo-Gangetic plain region, the ‘food bowl’ of the Indian sub-continent. An integrated methodology was developed for quantification of different forms of nitrogen losses from rice crop using remote sensing derived inputs, field data of fertilizer application, collateral data of soil and rainfall and nitrogen loss coefficients derived from published nitrogen dynamics studies. The spatial patterns of nitrogen losses in autumn or ‘kharif’ and spring or ‘rabi’ season rice at 1 × 1 km grid were generated using image processing and GIS. The nitrogen losses through leaching in form of urea-N, ammonium-N (NH₄-N) and nitrate-N (NO₃-N) are dominant over ammonia volatilization loss. The study results indicate that nitrogen loss through leaching in kharif and rabi rice is of the order of 34.9% and 39.8% of the applied nitrogenous fertilizer in the Indo-Gangetic plain region. This study provides a significant insight to the role of nitrogenous fertilizer as a major non-point source pollutant from agriculture.     

Karst groundwater protection in the Kupa River catchment area and sustainable development

One of the most significant water resources in the Republic of Croatia is the catchment area of the Kupa River, located in the region bordering the Republic of Slovenia. About 88% of the total amount of water in this catchment originates in Croatia and just 12% from Slovenia; therefore, the largest part of the catchment area (about 1000 km²) is on the Croatian side of the border. It is a typical karst area of the Dinarides with aquifers characterized by a relatively rapid water exchange, high groundwater flow velocities and aquifers open to human impact from the surface. Consequently, the aquifers are highly vulnerable and at risk. Due to the availability of large quantities of high-quality spring water (about 6 m³/s), the entire area has a strategic importance within the context of any future development strategy pertaining to the western part of Croatia. The catchment area on the Croatian side was investigated using a wide range of research methods that included a classical hydrogeological approach, the detailed hydrologic calculation of water balance to the hydrogeochemical analyses and modelling. The objective was to determine protection zones and protection measures for the whole area. The difficulties are increased due to the fact that the karst catchment area is crossed by major traffic corridors, oil pipelines and a railway and that many settlements and a highly developed wood industry are present. The combination of protecting water resources with adequate prevention measures and necessary remedial activities that should satisfy the very strict requirements necessary for the protection of the karst aquifers while still allowing for present and future human activities is difficult – but not impossible – to achieve. One good example is the present highway with a closed dewatering system and waste water treatment before the water passes into the karst underground system.