Manganoan garnet rocks associated with the Broken Hill Pb–Zn–Ag orebody, Australia

Summary The Palaeoproterozoic Broken Hill Pb–Zn–Ag stratiform orebody is intimately associated with manganoan garnet-bearing rocks. On stratigraphic and chemical grounds it is argued that garnet-rich metasediments below, equivalent to and above massive sulphide were hydrothermal precipitates. Other manganoan garnet rocks formed during pre-metamorphic hydrothermal alteration, syn-metamorphic dehydration and reaction of manganese with prograde pelitic rocks, reaction between cataclastic manganese-bearing sulphide rocks injected along axial planes, shears and faults and pelitic wall rocks and reaction between dolerite dykes and sulphide rocks.     

The Cone-in-Cone Structure and Its Origin

Morphostructural investigation of carbonate cone-in-cone formations allows to conclude that they belong to self-organizing (dissipative, according to I. Prigogine's terminology) systems of the geological past formed in a thermogradient field at the expense of energy of heat and mass transfer (Prigogine and Stengers, 1984). First, the fluid-convective metasomatic hypothesis unites and reconciles the most well-known hypotheses that previously seemed to be incompatible and transforms them to rather consistent particular cases of a more intricate multistage geological phenomenon. Second, it helps to identify the morphologically and genetically analogous noncarbonate structures that mimic biogenic ones. The probable indicative role of cone-in-cone structure in the mapping of fluid-conducting systems is a consequence of the proposed hypothesis.     

Modeling Lake Ladoga Zoobenthos and Studying Its Role in Phosphorus Exchange at the Water–Bed Interface

A zoobenthos submodel is included in an ecosystem model. The new model is used to assess the role of zoobenthos in the phosphorus exchange at the water–bed interface, in particular, the phosphorus cycle in the water body ecosystem is described more accurately. The calculated zoobenthos distribution over the bed of a lake can be used in modeling the lake ichthyocenoses.     

A canonical theory for short GPS baselines. Part II: the ambiguity precision and correlation

The present contribution is the second of four parts. It considers the precision and correlation of the least-squares estimators of the carrier phase ambiguities. It is shown how the precision and correlation of the double-differenced ambiguities as well as of the widelane ambiguities are effected by the observation weights, by the number of satellites tracked, by the number of observation epochs used, and by the change over time of the relative receiver-satellite geometry. Also the ability of the widelane transformation to decorrelate and to improve the precision is investigated. Received: 16 July 1996 / Accepted: 14 November 1996     

Detection of Local Inhomogeneities by Means of Cross-borehole Seismic Tomography

—This numerical study is devoted to distortions of local anomalies which are revealed by 2-D and 3-D cross-borehole seismic tomography based on first arrival travel times. The fact that prolonged subvertical anomalies may disappear in the final velocity model is well known. But distortions are also inherent to images of local inhomogeneities. These distortions are accompanied with false anomalies of the opposite sign located just above and below true ones. I offer a semi-empirical explanation of their existence, proving that they are an inherent consequence of observation geometry incompleteness. To improve the quality of the model obtained with cross-borehole tomography, a 3-D acquisition geometry may be used when additional boreholes are positioned around the target object. Results of 3-D tomographic experiments however may be considerably distorted for another reason nonaccounted bending of seismic rays.¶To generate the travel times, a ray-tracing procedure making use of the graph theory was applied. Tomographic inversion was performed by an algorithm based on the assumption of the unknown function smoothness.     

Doppler radar spectral width broadening due to beamwidth and wind shear

The spectral width observed by Doppler radars can be due to several effects including the atmospheric turbulence within the radar sample volume plus effects associated with the background flow and the radar geometry and configuration. This study re-examines simple models for the effects due to finite beam-width and vertical shear of the horizontal wind. Analytic solutions of 1- and 2-dimensional models are presented. Comparisons of the simple 2-dimensional model with numerical integrations of a 3-dimensional model with a symmetrical Gaussian beam show that the 2-dimensional model is usually adequate. The solution of the 2-dimensional model gives a formula that can be applied easily to large data sets. Analysis of the analytic solutions of the 2-dimensional model for off-vertical beams reveals a term that has not been included in mathematical formulas for spectral broadening in the past. This term arises from the simultaneous effects of the changing geometry due to curvature within a finite beamwidth and the vertical wind shear. The magnitude of this effect can be comparable to that of the well-known effects of beam-broadening and wind shear, and since it can have either algebraic sign, it can significantly reduce (or increase) the expected spectral broadening, although under typical conditions it is smaller than the beam-broadening effect. The predictions of this simple model are found to be consistent with observations from the VHP radar at White Sands Missile Range, NM.     

Karst database development in Minnesota: design and data assembly

The Karst Feature Database (KFD) of Minnesota is a relational GIS-based Database Management System (DBMS). Previous karst feature datasets used inconsistent attributes to describe karst features in different areas of Minnesota. Existing metadata were modified and standardized to represent a comprehensive metadata for all the karst features in Minnesota. Microsoft Access 2000 and ArcView 3.2 were used to develop this working database. Existing county and sub-county karst feature datasets have been assembled into the KFD, which is capable of visualizing and analyzing the entire data set. By November 17 2002, 11,682 karst features were stored in the KFD of Minnesota. Data tables are stored in a Microsoft Access 2000 DBMS and linked to corresponding ArcView applications. The current KFD of Minnesota has been moved from a Windows NT server to a Windows 2000 Citrix server accessible to researchers and planners through networked interfaces.     

The Influence of a Uniform Magnetic Field of Arbitrary Strength on Turbulence

The spectral tensor of turbulent motion in an infinite conductive incompressible medium is given in the case of a uniform magnetic field of any strenght affecting a homogeneous turbulence. With the help of BOCHNER 's theorem we make sure that the trace u_i(x, t) u_i(x, t) is non-negative. The presence of a weak magnetic field causes a damping of the turbulence, in some cases a strengthening. For strong magnetic fields the norms of the velocity vectors parallel and perpendicular to B approach one and the same value. Compared with the correlation length measured perpendicular to the magnetic field the correlation length measured along the magnetic field increases. Furthermore, our formulas have allowed to calculate the dependence of the α-effect on the magnetic field.     

Helligkeitsschätzungen von 12 quasistellaren Objekten auf photographischen Himmelsaufnahmen

Twelve QSO's have been investigated for variability on plates of the “Sonneberger Himmelsüberwachung”. Besides for 3 C 273 and Ton 616 no variability exceeding the mean error (±0.08 mag for m < 17.0) was found. TON 616 shows variability of 0,4 mag on time scales from hours (1964 Apr. 15) to one year.     

The radio luminosity function and the luminosity diameter function of extragalactic radio sources

On the basis of a radio index-surface brightness diagram recently published, the luminosity function and the luminosity diameter function are obtained. The uncertainties due to the incompleteness of the sample are of the same order as the statistical uncertainties. The luminosity function differs considerably from a simple power law and supports the distinction of two populations. The density of the weak population (P<10³⁵ W Hz⁻¹ ster⁻¹ at 1400 MHz) follows nearly a power law in P and increases towards small diameters at least down to I kpc. The density of the strong population (the high luminosity and small diameter part of which is occupied by the quasars) has a maximum between 10²⁵ and 10²⁸ W Hz⁻¹ ster⁻¹ and around 100 kpc. A strong evolution effect is clearly present and is in a good agreement with the models obtained from the log N-log S counts.