A New Approach to the Modeling of the Pressure Dependency of the Strength of Rocks

Based on the hypothesis that shearing stresses and normal tensile stresses both play a decisive role in fracturing and brittle failure of rock material, a novel strength criterion was developed in one of the earlier works of the author. In the criterion, a certain parameter ν′ occurs which depends on the structure of the material. Originally, the parameter was treated as a constant, which resulted in a linear form of the strength function ^F σ ₁ = f(σ ₃), where σ ₃ = σ ₂. Although the linear strength criterion is sometimes found to be applicable to various particular rock materials, it is not, in general, of a universal character. Analysis of the triaxial test results for 75 different sandstones revealed that parameter ν′ usually increases in an exponential or linear manner as confining pressure increases, and only in isolated cases does it seem to be independent of the confining pressure. For these three types of function ν′ = f(p) appropriate strength criteria ^F σ ₁ = f(σ ₃) are given in the present paper. These criteria were used to fit all of the collected empirical data sets. In general, a very good fit to the data was obtained.     

Groundwater flow rate and contaminant migration in fissure-karstic aquifer of Opole Triassic system southwest Poland

 This paper presents hydrogeological problems occurring during municipal water exploitation and mine dewatering. These activities result in groundwater quantity and quality changes in the fissure-karstic aquifer. Increase of nitrate concentration up to 12 mg NNO₃/l due to intensive fertilizer use, and high tritium concentration, show water system impact up to 100 m depth. Intensive water exploitation produces large cones of depression with over 40-m water-level depletion in the Opole region. Flow rates of major components and isotopes have been verified by chemical migration history. Some aspects of the protection policy of this type of aquifer are also discussed. Received: 7 March 1997 · Accepted: 17 November 1998     

Flotation of synthetic zinc carbonate using potassium ethylxanthate

An attempt at flotation of fine grains of zinc carbonate using potassium ethylxanthate as the collector and sulphydryl and copper ions as the activators has been undertaken. Results of the flotation tests have been interpreted in terms of the adsorption of activating agents as well as the grain size effect.     

Validation of Galileo orbits using SLR with a focus on satellites launched into incorrect orbital planes

The space segment of the European Global Navigation Satellite System (GNSS) Galileo consists of In-Orbit Validation (IOV) and Full Operational Capability (FOC) spacecraft. The first pair of FOC satellites was launched into an incorrect, highly eccentric orbital plane with a lower than nominal inclination angle. All Galileo satellites are equipped with satellite laser ranging (SLR) retroreflectors which allow, for example, for the assessment of the orbit quality or for the SLR–GNSS co-location in space. The number of SLR observations to Galileo satellites has been continuously increasing thanks to a series of intensive campaigns devoted to SLR tracking of GNSS satellites initiated by the International Laser Ranging Service. This paper assesses systematic effects and quality of Galileo orbits using SLR data with a main focus on Galileo satellites launched into incorrect orbits. We compare the SLR observations with respect to microwave-based Galileo orbits generated by the Center for Orbit Determination in Europe (CODE) in the framework of the International GNSS Service Multi-GNSS Experiment for the period 2014.0–2016.5. We analyze the SLR signature effect, which is characterized by the dependency of SLR residuals with respect to various incidence angles of laser beams for stations equipped with single-photon and multi-photon detectors. Surprisingly, the CODE orbit quality of satellites in the incorrect orbital planes is not worse than that of nominal FOC and IOV orbits. The RMS of SLR residuals is even lower by 5.0 and 1.5 mm for satellites in the incorrect orbital planes than for FOC and IOV satellites, respectively. The mean SLR offsets equal \(-44.9, -35.0\), and \(-22.4\) mm for IOV, FOC, and satellites in the incorrect orbital plane. Finally, we found that the empirical orbit models, which were originally designed for precise orbit determination of GNSS satellites in circular orbits, provide fully appropriate results also for highly eccentric orbits with variable linear and angular velocities.     

Contribution of Starlette,Stella, and AJISAI to the SLR-derived global reference frame

The contribution of Starlette, Stella, and AJISAI is currently neglected when defining the International Terrestrial Reference Frame, despite a long time series of precise SLR observations and a huge amount of available data. The inferior accuracy of the orbits of low orbiting geodetic satellites is the main reason for this neglect. The Analysis Centers of the International Laser Ranging Service (ILRS ACs) do, however, consider including low orbiting geodetic satellites for deriving the standard ILRS products based on LAGEOS and Etalon satellites, instead of the sparsely observed, and thus, virtually negligible Etalons. We process ten years of SLR observations to Starlette, Stella, AJISAI, and LAGEOS and we assess the impact of these Low Earth Orbiting (LEO) SLR satellites on the SLR-derived parameters. We study different orbit parameterizations, in particular different arc lengths and the impact of pseudo-stochastic pulses and dynamical orbit parameters on the quality of the solutions. We found that the repeatability of the East and North components of station coordinates, the quality of polar coordinates, and the scale estimates of the reference are improved when combining LAGEOS with low orbiting SLR satellites. In the multi-SLR solutions, the scale and the \(Z\) component of geocenter coordinates are less affected by deficiencies in solar radiation pressure modeling than in the LAGEOS-1/2 solutions, due to substantially reduced correlations between the \(Z\) geocenter coordinate and empirical orbit parameters. Eventually, we found that the standard values of Center-of-mass corrections (CoM) for geodetic LEO satellites are not valid for the currently operating SLR systems. The variations of station-dependent differential range biases reach 52 and 25 mm for AJISAI and Starlette/Stella, respectively, which is why estimating station-dependent range biases or using station-dependent CoM, instead of one value for all SLR stations, is strongly recommended. This clearly indicates that the ILRS effort to produce CoM corrections for each satellite, which are site-specific and depend on the system characteristics at the time of tracking, is very important and needs to be implemented in the SLR data analysis.     

Estimation of the third and fourth order central moments of measurement errors from sums of powers of least squares adjustment residuals

Summary In the paper a method of determination of estimators of the central moments of the third and fourth order on the basis of the least squares adjustment is presented. These estimators concern the moments of the observation results as well as to readjustment (better) of observation sets with application of methods that take into consideration moments of higher order (not only the variance-covariance matrix).The obtained estimators are not biased, but their effectiveness was not studied. That is why the presented theory is not completed (in the sense of the estimators properties).     

Radioisotopic evidence of perturbations of recent sedimentary record in lakes: a word of caution for climate studies

The rate of climatic change estimated from the gradient of signals recorded in lake sediments may be erroneous if post-depositional perturbations are overlooked. A smear out of a pulse signal, over a variable thickness of core section, due to physical or biological mixing, is a well known phenomena. Much less attention is paid to a possible overestimation of the rate of change when a part of record is missing due to an erosion event. In this paper we show a few examples of recent lake sediment perturbations and the resulting distortions in the time scale, as documented by short-lived radionuclides.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Chemistry of sediments from the Dobezyce Reservoir, Poland, and the environmental implications

Sediments samples of the Dobczyce Reservoir(South Poland) were taken in three successive years(2004-06) at 17 points,analyzed for 12 elements by atomic absorption spectrometry.Substantial variations in elemental composition due to hydrological and environmental reasons were found.The use of statistical and chemometric tools enabled objective and effective analysis of the data obtained,both in case of long term observations as well as in terms of interpretation of incidental changes in metal concentrations.T...     

The dynamics of rupture in porous media

This paper presents a laboratory investigation of electric resistivity parameter for samples subject to loading in automatic press of INOVA type. The procedure of automatic quasi-continuous measurements of resistivity is briefly outlined. The distribution of mini-electrodes within the sample is described. Also shown is the manner in which reliability can be improved by increasing the repetition of resistivity measurements (every 7–16 s).     

Influence of a method of evaluation of the curvature of flexible vegetation elements on vertical distributions of flow velocities

Methods of computing the deflections of flexible vegetation elements under the dynamic pressure of water were presented in the paper. Two methods, based on Euler-Bernoulli beam theory, were discussed, one designed for small deflections and the other, generalized one, also for larger deflections. The choice of the method for computations of deflections was discussed from the perspective of the computation of flow velocities above flexible vegetation. Computational results were compared with laboratory experiments and it was found that the simplified, computationally less expensive method may be used in many practical situations without deterioration of the results.