1,925 research outputs found
Influence of carbonate microfabrics on the failure strength of claystones
No full textClaystones are currently being investigated as a potential host rock for radioactive waste disposal. The relevant parameters are hydraulic conductivity, swelling and shrinkage, water uptake, rheological, and mechanical behavior. Much attention is paid to the Opalinus Clay (OPA) in Switzerland and the Callovo-Oxfordian Clay (COX) in France. One of the scientific challenges is to develop numerical models to predict the mechanical behavior of claystones under repository-like conditions. Recent studies have demonstrated the influence of carbonates on selected mechanical parameters (e.g. failure strength). In this study we show that OPA and COX behave differently with respect to their failure strength. The failure strength of OPA decreases with increasing carbonate content, whereas it increases with increasing carbonate content in case of the COX. The different behavior is caused by microstructural variations. Results of carbonate microfabric investigations verify that OPA mainly contains coarse-grained shell fragments, while COX shows a more homogeneous distribution of fine-grained, mainly non-biogenic carbonates. In conclusion, not only the carbonate content but in addition their grain size distribution, their shape and the spatial distribution control the mechanical behavior of both clays. (C) 2009 Elsevier B.V. All rights reserved
Abrasivity by bentonite dispersions
No full textBentonites are used for various industrial applications. Their physicochemical properties depend on the mineralogical and chemical composition, the type of smectite, the grain size distribution, the cation exchange capacity (CEC), the dominant interlayer cation (Na(+), Ca(2+), Mg(2+)), and the layer charge density. All these parameters can be measured with acceptable precision. Nevertheless, the performance of a bentonite in a given application is often unpredictable. An additional relevant parameter is the "microfabric" describing the arrangement of minerals and/or the intergrowth of the minerals with glass. The microfabric is supposed to affect different bentonite properties such as swelling capacity and rheology. The present study focuses on the influence of different microfabrics on the abrasivity by bentonite dispersions. The abrasivity of bentonite dispersions mainly depended on two factors: 1) on the amount of hard and sharp accessory minerals and volcanic glass and 2) the grain size distribution, which was produced by different grinding techniques. The abrasivity increased with decreasing grain size, which was caused by breaking the hard components (minerals and glass) leading to an increased number of sharp edges. In addition, there was evidence for a subordinate influence of the type of exchangeable cations. This influence is explained by the different relative arrangements of smectite particles towards the surfaces of hard and sharp minerals. Na(+) exchanged glass rich samples showed higher abrasion values than the Ca(2+) exchanged samples. (C) 2009 Elsevier B.V. All rights reserved
The N2-BET specific surface area of bentonites
No full textThe specific surface areas (SSA(N2BET)) of 36 different bentonites had larger values for Ca(2+)/Mg(2+) bentonites than for Na(+) bentonites. This trend could not be explained by the different d(001) values nor by the different microstructures. The investigation of Cu-triene-exchanged smectites, which on drying at 105 degrees C still had a d(001) value accounting for approximately 13A, proved that the SSA(N2BET) of low-charged smectites increased more than that of high-charged smectites. This could be explained by: (i) more space between the permanent charge sites in the case of low-charged smectites and (ii) the fact that the layers of Cu-triene smectites do not collapse at 105 degrees C. In contrast the SSA(N2BET) of Ca(2+)-exchanged bentonites could not be related to the layer charge density (LCD) as in the case of the Cu-triene-exchanged bentonites which is probably due to the varying number of collapsed layers. In conclusion, the SSA(N2BET) of bentonites which is known to be largely variable is probably determined by microporosity resulting from the quasi-crystalline overlap region and accessible areas of the interlayer. The number of layers per stack and the microstructure are supposed to play a subordinate role. The larger SSA(N2BET) of Ca/Mg bentonites compared to Na bentonites probably can be explained by the larger space between the charges in the case of the presence of divalent cations
Ask questions, get sales : close the deak and create long-term relationships / Stephan Schiffman.
No full textIncludes index.v, 168 pages ;In Ask Questions, Get Sales, the author and sales guru Stephan Schiffman helps readers boost their careers to the gold-medal level by teaching them how to strengthen their questioning skills during the sales process. The premise is simple yet effective: In order to be successful, salespeople need to change their mindset from "need-orientated" to "do-orientated". The message of the book centers around six core "do" questions: What do you do? How do you do it? When and where do you do it? Why do you do it that way? Who do you do it with? How can we help you do it better? With this indispensable guide in their briefcase, salespeople will have information at the ready to score big sales over the short term and the long term
Weathering of Fruchtschiefer building stones: mineral dissolution or rock disaggregation?
No full textBuilding stones manufactured from contact metamorphic slates (Fruchtschiefer slate) from Theuma (Sachsen, Germany) were investigated for mineralogical alterations as well as for changes in porosity and surface roughness due to weathering. After weathering periods of several years to decades, the originally dark gray-colored slates show pale spots of several centimeters in size at the surface of building stones. The dark-colored and light-colored sections of the slate show no differences in mineralogy. Surface weathering did not result in newly precipitated minerals. It was also found that the observed differences in color are not caused by variations in sedimentary organic carbon concentration or in sulfide/sulfate concentrations. Obtained results instead indicate that dark surface sections may show a thin cover of recent organic matter (OM), e.g., living OM, soot, dirt, etc. Microscopic investigations suggested that this cover was exfoliated at light-colored surface sections. The observed disaggregation of the upper 2 mm of the building block material results in an increase in porosity. Porosity of black (unweathered) slate is < 2 vol.%. Due to weathering, the slate's pores with diameters > 1 mu m show a significant increase in frequency compared to the original pore size distribution. Porosity of weathered rock volumes increased to approx. 8 vol.%. Discolored surface sections show a higher surface roughness (root-mean-square roughness, Rq similar to 1 mu m) compared to dark-colored slate surfaces (Rq similar to 200 nm), both data are for cleavage planes. Preferentially, the discolored surface sections are located close to the edges of cut stones. This and the alteration in porosity, pore size, and surface roughness indicate that color changes of the slate are largely influenced by rock disaggregation proceeding from the edges into the center rather than by mineral dissolution/precipitation processes.BMBF [03G0719A]; DF
Unemployment Benefits and Unemployment Rates of Low-Skilled and Elder Workers in West Germany: A Search Equilibrium Approach
No full textApproach Author & abstract Download 16 References 1 Citations Related works & more Corrections Author Listed: Launov, Andrey ([email protected]) (University of Kent) Wolff, Joachim ([email protected]) (Institute for Employment Research (IAB), Nuremberg) Klasen, Stephan ([email protected]) (University of Göttingen) Registered: Stephan Klasen Abstract In this paper we investigate whether the extension of the entitlement to unemployment benefits in the mid 80s can explain the increase in the unemployment rates of unskilled and elder workers in western Germany. To answer this question we estimate a version of the Burdett-Mortensen search equilibrium model and analyze how workers’ search behaviour responded to these reforms. We try both nonparametric and fully-parametric estimation methods and identify the cases in which the nonparametric approach cannot be applied. We find that the entitlement reforms are largely responsible for the increase of unemployment among unskilled workers
Unemployment Benefits and Unemployment Rates of Low-Skilled and Elder Workers in West Germany: A Search Equilibrium Approach
No full textApproach Author & abstract Download 16 References 1 Citations Related works & more Corrections Author Listed: Launov, Andrey ([email protected]) (University of Kent) Wolff, Joachim ([email protected]) (Institute for Employment Research (IAB), Nuremberg) Klasen, Stephan ([email protected]) (University of Göttingen) Registered: Stephan Klasen Abstract In this paper we investigate whether the extension of the entitlement to unemployment benefits in the mid 80s can explain the increase in the unemployment rates of unskilled and elder workers in western Germany. To answer this question we estimate a version of the Burdett-Mortensen search equilibrium model and analyze how workers’ search behaviour responded to these reforms. We try both nonparametric and fully-parametric estimation methods and identify the cases in which the nonparametric approach cannot be applied. We find that the entitlement reforms are largely responsible for the increase of unemployment among unskilled workers
Measuring Vulnerability to Poverty Using Long-Term Panel Data
No full textMeasuring Vulnerability to Poverty Using Long-Term Panel Data Author & abstract Download & other version 16 References 4 Citations Related works & more Corrections Author Listed: Katja Landau (Georg-August-University Göttingen) Stephan Klasen (Georg-August-University Göttingen) Walter Zucchini (Georg-August-University Göttingen) Registered: Stephan Klasen Abstract We investigate the accuracy of ex ante assessments of vulnerability to income poverty using cross-sectional data and panel data. We use long-term panel data from Germany and apply di fferent regression models, based on household covariates and previous-year equivalence income, to classify a household as vulnerable or not. Predictive performance is assessed using the Receiver Operating Characteristics (ROC), which takes account of false positive as well as true positive rates. Estimates based on cross-sectional data are much less accurate than those based on panel data, but for Germany, the accuracy of vulnerability predictions is limited even when panel data are used. In part this low accuracy is due to low poverty incidence and high mobility in and out of poverty
Measuring Vulnerability to Poverty Using Long-Term Panel Data
No full textMeasuring Vulnerability to Poverty Using Long-Term Panel Data Author & abstract Download & other version 16 References 4 Citations Related works & more Corrections Author Listed: Katja Landau (Georg-August-University Göttingen) Stephan Klasen (Georg-August-University Göttingen) Walter Zucchini (Georg-August-University Göttingen) Registered: Stephan Klasen Abstract We investigate the accuracy of ex ante assessments of vulnerability to income poverty using cross-sectional data and panel data. We use long-term panel data from Germany and apply di fferent regression models, based on household covariates and previous-year equivalence income, to classify a household as vulnerable or not. Predictive performance is assessed using the Receiver Operating Characteristics (ROC), which takes account of false positive as well as true positive rates. Estimates based on cross-sectional data are much less accurate than those based on panel data, but for Germany, the accuracy of vulnerability predictions is limited even when panel data are used. In part this low accuracy is due to low poverty incidence and high mobility in and out of poverty
Evaluation of in-store processes related to returnable packaging services offered in grocery stores - the store management perspective
No full textAuthor Stephan LehnerMasterarbeit Universität Linz 202
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