Dreybrodt, Wolfgang
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Dreybrodt, Wolfgang
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Dreybrodt, Wolfgang
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%20Resonanz-Ramanbande:%20Der%20Nachweis%20f%C3%BCr%20taxonomische%20Konformationssubzust%C3%A4nde%20in%20der%20proximalen%20Bindung,equals&spc.page=1){kind=link}
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Item type:Publication, Lösungskinetik von Gips und AnhydritThe dissolution kinetics of gypsum and anhydrite have been measured under various conditions. For gypsum an almost linear rate equation R=k:sub:s1:/sub:(1-c/c:sub:eq:/sub:):sup:n:sub:1:/sub::/sup: is valid, where R is the surface rate, n:sub:1:/sub: :img:=approx.gif:/img: 1 is the kinetics order, c is the total calcium concentration at the surface, and c:sub:eq:/sub: the equilibrium concentration with respect to gypsum. For the determination of the entire dissolution kinetics a batch set-up was used. This batch experiment reveals a dissolution rate equation R=k:sub:s1:/sub:(1-c/c:sub:eq:/sub:):sup:n:sub:1:/sub::/sup: which switch close to equilibrium to a nonlinear rate equation R=k:sub:s2:/sub:(1-c/c:sub:eq:/sub:):sup:n:sub:2:/sub::/sup: with n:sub:2:/sub: :img:=approx.gif:/img: 4.5. The experimentally observed dissolution rates from the batch experiment could be fitted by only minor variations with a mixed kinetics model. The rotating disk experiment on anhydrite reveals a surface controlled rate equation. For anhydrite the observed experimentally dissolution rates by a batch experiment are described by R=k:sub:s:/sub:(1-c/c:sub:eq:/sub:}):sup:n:/sup:, where k:sub:s:/sub: is the surface rate constant and n :img:=approx.gif:/img: 4.2 is the kinetic order. Furthermore, a method for the determination of the rate equation parameters was developed. Experimentally observed dissolution rates of minerals in aqueous solution are determined by surface reaction rates, mass transport by molecular diffusion through a diffusion boundarylayer (DBL) and the morphology of the mineral´s surface. By solving the transport equation in the presence of a diffusion boundary layer for surfaces containing open pores their contribution to the observed dissolution rates can be quantified. Furthermore, dissolution rates are calculated for fractal surfaces. A general solution is given.doctoral thesis354 201 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Evolution of Karst Aquifers in Natural and Man Made Environments: A modeling approach(2003-04-23); ; ; The evolution of karst aquifers under various hydrological and chemical boundary conditions is studied.The influence of flow from a prominent fracture into a 2D network of fissures is compared to the evolution of a fracture isolated from this net. The modeling domain is a limestone block dissected by fissures. A prominent fracture extends along its center. Under constant head conditions between the left and the right hand side of the domain it looses flow into the network and aggressive solution from the input enhances dissolution. Breakthrough times are reduced. An isolated one-dimensional fracture with an additional single point of outflow from it is also investigated.The evolution of a karst aquifer below dam sites is studied. The modeling domain is a 2D, 1 m wide vertical section of soluble rock (gypsum and limestone), perpendicular to the dam. The chemical composition of the inflowing water is equal at all input points. A large zone of increasing permeability is created below the structure. The dependence of breakthrough times on different parameters is investigated.The effect of chemical boundary conditions on the karstification is studied. The model domain is a limestone block with two input points. The hydrological boundaries are equal for all simulated scenarios. The chemical composition of the inflowing water at both inputs is varied. Mixing corrosion is the reason for zones of increased permeability deep inside the aquifer. Two types of evolution are observed: Breakthrough type (BT) for low values of the input Ca concentration, and mixing corrosion (MC) type for values close to the equilibrium concentration. The BT - is characterized by enlarged pathways connecting an inflow point with the outflow boundary. For high Ca concentrations, MC is dominating. There is no considerably widened connection between the inflow points and the out flow boundary, but an enlarged channel along the mixing zone is observed. Also the timescale is considerably longer.doctoral thesis291 149 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Experimentelle Bestimmung der Lösungskinetik synthetischen Calciumcarbonats und natürlicher Kalkgesteine(2004-07-09); ; ; Within the scope of this work dissolution rates of synthetic calcite and natural limestone (freshly and etched surface) were measured under different boundary conditions. Experiments were conducted with the objective to determine the influence of initial pCO2, temperature, dissolved foreign ions and material on the dissolution kinetics of calcium carbonate. A dataset emerged, which can be implemented into models of karst evolution accounting for different chemical boundary conditions. The batch experiment using the free drift method was chosen for measuring dissolution rates in closed system conditions with respect to CO2. The dissolution kinetics of the studied materials react differently to the presence of foreign ions in solution. Sulfate, phosphate and magnesium inhibit the dissolution rates of synthetic Baker Calcite. The resulting dissolution kinetics resembles that of natural limestone in pure H2O-CO2-solutions. In contrast to this sulfate has no influence on the dissolution rates of Jura Limestone, whereas magnesium and phosphate do inhibit the dissolution. The different dissolution kinetics can be attributed to the various lithologies. For the first time mixing corrosion in freshwater and freshwater-saltwater mixtures was reproduced in the laboratory. Under these boundary conditions the linear kinetics of Baker Calcite and nonlinear of natural limestone could be confirmed. Model calculations on the evolution of karst systems were conducted for two different chemical boundary conditions (pCO2i = 0.001 atm, 0.05 atm; 10°C) using the kinetic parameters of Jura Limestone in one- and two-dimensional models.doctoral thesis256 241 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Die Fe:sup:2:/sup::img:=plus.gif:/img:-His(F8) Resonanz-Ramanbande: Der Nachweis für taxonomische Konformationssubzustände in der proximalen Bindung(2002-01-07); ; The band shape of the Raman line attributed to the Fe:sup:2:/sup::img:=plus.gif:/img:-N:sub::img:=epsilon.gif:/img::/sub:(His-F8) stretching mode in heme proteins contains significant information of the Fe-His proximal linkage. In the case of myoglobin Raman lines at the low and the high frequency wing of this profile obscure its true band shape. Measurements with different pH-values, different solvents and different polarizations showed that these lines are not caused by the Fe-His-linkage.:br:In order to separate these accompanying lines from the Fe-His-band the isotopic shift has been used by substituting the natural iron-isotope :sup:56:/sup:Fe of the heme with the :sup:54:/sup:Fe-isotope.This enables us to isolate the true line shape. Detailed analysis reveals that the band is composed of five distinct lines attributable to taxonomic conformational substates of the Fe-His linkage. The temperature dependence of the band is caused by intensity variations of these five different sublines. The fits reveal a glass transition temperature of T:sub:f:/sub:=155±15K with a relatively broad transition region of :img:=delta1.gif:/img:T :img:=approx.gif:/img:80K for myoglobin. The enthalpic differences between conformational substates yield values between 0.7kJ/mol and 1.5kJ/mol for myoglobin. Our data show, that the :img:=nue.gif:/img:(Fe-His) vibrational mode is governed by at least one coordinate which determines its frequency. This may be the tilt angle :img:=Theta.gif:/img:, or the displacement :img:=delta.gif:/img: of the central iron, or a combination of both. The sublines are therefore interpreted as resulting from different conformational substates of the Fe:sup:2:/sup::img:=plus.gif:/img:-N:sub::img:=epsilon.gif:/img::/sub:(His-F8) complex with respect to these comformational coordinates.doctoral thesis199 82