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Qualitative Understanding (qualitative + understanding)
Selected AbstractsThe impact of groundwater,surface water interactions on the water balance of a mesoscale lowland river catchment in northeastern GermanyHYDROLOGICAL PROCESSES, Issue 2 2007Stefan Krause Abstract The glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics. A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time-variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM-ETH-I with the three-dimensional finite-difference-based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km2), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km2 catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain-dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Molecular Modeling Of The Aldose Reductase-Inhibitor Complex Based On The X-Ray Crystal Structure And Studies With Single-Site- Directed MutantsJOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 2 2000S.B. Singh Aldose reductase (AR) has been implicated in the etiology of the secondary complications of diabetes. This enzyme catalyzes the reduction of glucose to sorbitol using nicotinamide adenine dinucleotide phosphate as an essential cofactor. AR has been localized at the sites of tissue damage, and inhibitors of this enzyme prevent the development of neuropathy, nephropathy, retinopathy, and cataract formation in animal models of diabetes. The crystal structure of AR complexed with zopolrestat, a potent inhibitor of AR, has been described. (1) We have generated a model of the AR-inhibitor complex based on the reported C alpha coordinates of the protein and results of a structure-activity relationship study using four structurally distinct classes of inhibitors, recombinant human AR, and four single-site-directed mutants of this enzyme. The effects of the site-directed mutations on residues within the active site of the enzyme were evaluated by average interaction energy calculations and by calculations of carbon atom surface area changes. These values correlated well with the IC50 values for zopolrestat with the wildtype and mutant enzymes, validating the model. On the basis of the zopolrestat-binding model, we have proposed binding models for 10 other AR inhibitors. Our models have enabled us to gain a qualitative understanding of the binding domains of the enzyme and how different inhibitors impact the size and shape of the binding site. [source] Static single channel and multichannel water perfusion pressure profilometry in a bench model of a urethra,,NEUROUROLOGY AND URODYNAMICS, Issue 7 2010G.R. Hirst Abstract Aims To determine the catheter perfusion and withdrawal rate which generate the most repeatable single (SCPP) and multichannel pressure profilometry (MCPP) profiles in a bench model. Methods A bench model using a urethral substitute was developed in which SCPP and MCPP were performed using the Brown,Wickham method. One single channel and four multichannel catheters were tested using seven withdrawal rates and three perfusion rates. Repeatability was determined using spread of mean profile pressure, cross-correlation, Bland,Altman statistic, and a one-tailed Student's t -statistic. An artificial urinary sphincter (AUS) model was constructed to create a predictable intraluminal profile. MCPP data were used to generate three-dimensional (3D) images of the pressures exerted by the AUS model. Results A withdrawal rate of 0.5,mm/sec and perfusion rate 1,ml/min produced the most repeatable SCPP profiles with a spread of mean profile pressure ,7,cmH2O. For MCPP, a 10,F 6-channel catheter using a withdrawal rate of 1,mm/sec and perfusion rate of 1,ml/min produced the most similar profiles (cross-correlation,=,0.99). However, the spread of MCPP was large (spread ,44,cmH2O per channel). Nevertheless MCPP was able to consistently demonstrate areas of high pressure as predicted by the AUS model. Conclusions MCPP was not repeatable and is an unreliable measure of urethral pressure. MCPP and 3D images do demonstrate directional differences predicted from the AUS model. These may be of use for qualitative understanding and appreciation of relative relationships if not actual forces within the urethra and have application in understanding urethral function in vivo. Neurourol. Urodynam. 29:1312,1319, 2010. © 2010 Wiley-Liss, Inc. [source] Transition-State Energy and Position along the Reaction Coordinate in an Extended Activation Strain Model,CHEMPHYSCHEM, Issue 8 2007G. Theodoor de Jong Dr. Abstract We investigate palladium-induced activation of the CH, CC, CF, and CCl bonds in methane, ethane, cyclopropane, fluoromethane, and chloromethane, using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. Our purpose is to arrive at a qualitative understanding, based on accurate calculations, of the trends in activation barriers and transition state (TS) geometries (e.g. early or late along the reaction coordinate) in terms of the reactants' properties. To this end, we extend the activation strain model (in which the activation energy ,E, is decomposed into the activation strain ,E,strain of the reactants and the stabilizing TS interaction ,E,int between the reactants) from a single-point analysis of the TS to an analysis along the reaction coordinate ,, that is, ,E(,)=,Estrain(,)+,Eint(,). This extension enables us to understand qualitatively, trends in the position of the TS along , and, therefore, the values of the activation strain ,E,strain=,Estrain(,TS) and TS interaction ,E,int=,Eint(,TS) and trends therein. An interesting insight that emerges is that the much higher barrier of metal-mediated CC versus CH activation originates from steric shielding of the CC bond in ethane by CH bonds. Thus, before a favorable stabilizing interaction with the CC bond can occur, the CH bonds must be bent away, which causes the metal,substrate interaction ,Eint(,) in CC activation to lag behind. Such steric shielding is not present in the metal-mediated activation of the CH bond, which is always accessible from the hydrogen side. Other phenomena that are addressed are anion assistance, competition between direct oxidative insertion (OxIn) versus the alternative SN2 pathway, and the effect of ring strain. [source] | ||||||||||