Temperature-dependent magnetic susceptibility behaviour of spinelloid and spinel solid solutions in the systems Fe2SiO4–Fe3O4 and (Fe,Mg)2SiO4–Fe3O4     

A. Kontny  A. B. Woodl  M. Koch 《Physics and Chemistry of Minerals》2004,31(1):28-40

The magnetic behaviour and Curie temperatures (T _C ) of spinelloids and spinels in the Fe₃O₄–Fe₂SiO₄ and Fe₃O₄–(Mg,Fe)₂SiO₄ systems have been determined from magnetic susceptibility (k) measurements in the temperature range –192 to 700 °C. Spinelloid II is ferrimagnetic at room temperature and the k measurements display a characteristic asymmetric hump before reaching a T _C at 190 °C. Spinelloid V from the Mg-free system is paramagnetic at room temperature and hysteresis loops at various low temperatures indicate a ferri- to superparamagnetic transition before reaching the T _{C .} The T _C shows a non-linear variation with composition between –50 and –183 °C with decreasing magnetite component (X _Fe3O₄). The substitution of Mg in spinelloid V further decreases T _C . Spinelloid III is paramagnetic over nearly the total temperature range. Ferrimagnetic models for spinelloid II and spinelloid V are proposed. The T _C of Fe₃O₄–Fe₂SiO₄ spinel solid solutions gradually decrease with increasing Si content. Spinel is ferrimagnetic at least to a composition of X _Fe3O₄=0.20, constraining a ferrimagnetic to antiferromagnetic transition to occur at a composition of X _Fe3O₄<0.20. A contribution of the studied ferrimagnetic phases for crustal anomalies on the Earth can be excluded because they lose their magnetization at relatively low temperatures. However, their relevance for magnetic anomalies on other planets (Mars?), where these high-pressure Fe-rich minerals could survive their exhumation or were formed by impacts, has to be considered.  相似文献   

Fractal generation of surface area of porous media   总被引：2，自引：0，他引：2  

Hongbing Sun  Manfred Koch 《Stochastic Environmental Research and Risk Assessment (SERRA)》1998,12(2):83-96

Many natural porous geological rock formations, as well as engineered porous structures, have fractal properties, i.e., they are self-similar over several length scales. While there have been many experimental and theoretical studies on how to quantify a fractal porous medium and on how to determine its fractal dimension, the numerical generation of a fractal pore structure with predefined statistical and scaling properties is somewhat scarcer. In the present paper a new numerical method for generating a three-dimensional porous medium with any desired probability density function (PDF) and autocorrelation function (ACF) is presented. The well-known Turning Bands Method (TBM) is modified to generate three-dimensional synthetic isotropic and anisotropic porous media with a Gaussian PDF and exponential-decay ACF. Porous media with other PDF's and ACF's are constructed with a nonlinear, iterative PDF and ACF transformation, whereby the arbitrary PDF is converted to an equivalent Gaussian PDF which is then simulated with the classical TBM. Employing a new method for the estimation of the surface area for a given porosity, the fractal dimensions of the surface area of the synthetic porous media generated in this way are then measured by classical fractal perimeter/area relationships. Different 3D porous media are simulated by varying the porosity and the correlation structure of the random field. The performance of the simulations is evaluated by checking the ensemble statistics, the mean, variance and ACF of the simulated random field. For a porous medium with Gaussian PDF, an average fractal dimension of approximately 2.76 is obtained which is in the range of values of actually measured fractal dimensions of molecular surfaces. For a porous medium with a non-Gaussian quadratic PDF the calculated fractal dimension appears to be consistently higher and averages 2.82. The results also show that the fractal dimension is neither strongly dependent of the porosity nor of the degree of anisotropy assumed.  相似文献   

Isotopic composition of Late Mesozoic basic and ultrabasic rocks from the Andes (23–32°S) – implications for the Andean mantle     

Friedrich Lucassen  Monica Escayola  Rolf L. Romer  José Viramonte  Kerstin Koch  Gerhard Franz 《Contributions to Mineralogy and Petrology》2002,143(3):336-349

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The use of teleseismic P-wave complexity for seismic event screening – results determined from GRF and GERESS array data     

Karl Koch  Jörg Schlittenhardt 《Journal of Seismology》2002,6(2):183-197

Seismic data recorded at the broad-band teleseismic GRF array and theshort-period regional GERESS array, which is a designated IMS primarystation, are analyzed to determine the effectiveness of teleseismic P-wave complexity for the purpose of seismic event screening within theframework of Comprehensive Nuclear-Test-Ban Treaty verification. For theGRF array, seismic waveform data from nearly 200 nuclear explosions havebeen recorded since its installation in the late 1970's, which were studiedalong with several thousand earthquakes from the last few years.Additionally, we investigated teleseismic P wave complexity for a similarnumber of earthquakes recorded at GERESS. However, owing to itsoperation starting in 1991, only a limited number of nuclear explosionseismograms are available for study.For nuclear explosions, complexity does not exceed levels of 0.3 except fora number of events from the Nevada Test Site recorded only at the GRFarray and located at a large distance where PcP may interfere with the initialP wavelet. Since all events with complexity at GRF larger than 0.3 areexclusively located on Pahute Mesa within the Nevada Test Site,near-source geology or topography must play a dominant role for theseincreased complexity values, while PcP may not contribute significantly tothe high-frequency energy measured by the complexity parameter.Although many earthquakes show complexities below this level, for morethan 25% of the earthquakes investigated the complexities determined arelarger than 0.7, thus showing distinctly larger values than nuclearexplosions. Therefore, this percentage may be screened as earthquakes fromall seismic events detected. As currently only about half of the eventsdetected by the global IMS network are screened out based on focal depthand the m _b :M _s criterion, teleseismic P-wavecomplexity may contribute significantly to the task of seismic eventscreening.  相似文献   

KEITH,L. H.: Identification and Analysis of Organic Pollutants in Water, 2. Aufl. Ann Arbor Science Publishers,Inc., 1977. 718 S.     

R. Koch 《洁净——土壤、空气、水》1979,7(5):518-518

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M. SONNEBORN (Hrsg.): Gesundheitliche Probleme der Wasserchlorung und Bewertung der dabei gebildeten halogenierten organischen Verbindungen,Wasser, Boden,Luft-Berichte,Nr. 3. Berlin,Dietrich Reimer Verlag, 1978, 141 S.     

R. Koch 《洁净——土壤、空气、水》1979,7(6):625-625

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Least squares adjustment and collocation   总被引：10，自引：1，他引：10  

K. -R. Koch 《Journal of Geodesy》1977,51(2):127-135

Summary For the estimation of parameters in linear models best linear unbiased estimates are derived in case the parameters are random variables. If their expected values are unknown, the well known formulas of least squares adjustment are obtained. If the expected values of the parameters are known, least squares collocation, prediction and filtering are derived. Hence in case of the determination of parameters, a least squares adjustment must precede a collocation because otherwise the collocation gives biased estimates. Since the collocation can be shown to be equivalent to a special case of the least squares adjustment, the variance of unit weight can be estimated for the collocation also. This estimate gives the scale factor for the covariance matrices being used in the collocation. In addition, the methods of testing hypotheses and establishing confidence intervals for the parameters of the least squares adjustment may be applied to the collocation.  相似文献   

Hygienische Probleme des Bleis unter besonderer Berücksichtigung des Umweltfaktors Wasser     

R. Koch  Ch. Mühlhausen 《洁净——土壤、空气、水》1977,5(3):231-241

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Ed.: S. Williams: Official Methods of Analysis. 14. Auflage,Arlington, Va., Publ. Assoc. Official Analytical Chemists,INC, 1984, 1141 S., US $ 151.50     

R. Koch 《洁净——土壤、空气、水》1986,14(4):446-447

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Processing of altimetry data     

Karl-Rudolf Koch 《Journal of Geodesy》1975,49(1):35-40

Summary Two methods are discussed for the processing of altimetry data. For the first method it is assumed that the altimetry data, may be analyzed independent of the orbit computation for the satellite that carries the altimeter. Because of the high accuracy of the altimetry data, which can only be fully utilized if it is also introduced into the orbit computations, the second method deals with a simultaneous processing of altimetry data, orbit tracking, and gravity anomalies for the continents. To represent the gravity field, the potential of a simple layer is chosen whose unknown density is assumed to be constant over surface elements into which the surface of the earth is divided. Depending on the accuracy and the amount of the altimetry data, the surface elements for the density values are chosen smaller or larger, so that a very flexible representation of the earth’s gravity field is obtained. Because of the amount and the resolution of the altimetry data a large number of density values have to be determined in a least squares adjustment. To facilitate the computations, buffer zones are introduced so that the large system of normal equations can be broken up into small independent subsystems. Shortened version of a paper presented to the 14 th International Congress of Surveyors in Washington, Sept. 1974.  相似文献