Time-dependent behavior of fine-grained model material in resonant column experiments

Cyclic shear experiments with saturated and dry fine-grained corundum powder, i.e. -Al₂O₃ particles, have been conducted in a resonant column device. After an increase of total pressure the shear stiffness showed a slight decrease and a subsequent increase with time. The equivalent viscous damping ratio followed an opposite trend. The increase of shear stiffness with time did not stop after the end of primary consolidation, which cannot be explained with the slight reduction of void ratio during secondary consolidation. Stiffening of grain contacts through different dissolution-precipitation mechanisms and creep at particle contacts can explain the increase of shear stiffness with time, which has also been observed in natural soils by other researchers. Smaller rates of stiffness increase of dry samples support the idea of dissolution-precipitation mechanisms in the pore water. Higher rates for samples with smaller particles show an effect of surface-to-volume ratio.The study described in this paper was sponsored by the German Research Council (DFG), Research Group FOR 371-2. The support is gratefully appreciated.We would like to thank Professor Gudehus for many interesting discussions and valuable advice.We thank the Institute of Mechanical Process Engineering and Mechanics and the Laboratory for Electron Microscopy, University of Karlsruhe, for providing the electron micrographs and the Institute for Ceramics in Mechanical Engineering for the grain size distribution.     

Impressions of groups as a function of the stimulus values of their individual members.

Beginning with a model of social perception in which the perceiver is assumed to operate according to the conventional canons of statistical inference, it was hypothesized that trait judgments of groups of individuals represented by facial photographs would match the mean values of these photographs judged individually and that confidence and the amount of information required before a judgment is reported will vary inversely with the variance in the set of photographs comprising the group, and directly with the significance of the judgment for the judge. Using different procedures and measures of the dependent variables, 2 experiments were performed which agreed in supporting the hypotheses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Traffic sense--which factors influence the skill to predict the development of traffic scenes?

A study was conducted to evaluate the skill to predict the development of traffic situations. A stop-controlled intersection was filmed over several days, and 12 scenes with varying traffic complexity were selected. In half of the scenes, the traffic rules were violated, in half of the scenes, the rules were observed. A total of 36 participants were asked to watch the scenes and predict how the scene would most likely develop in the 2s after the film was paused. Additionally, the participants rated how certain they were about their prediction, and how complex and dangerous they assessed the scenes to be. With the method used here, experienced drivers were not found to make more correct predictions of situational development, and no difference in skill to predict could be found between genders. Nevertheless, more experienced drivers were more certain in their judgements and evaluated the situations on average as less complex and dangerous than did less experienced drivers. Scenes in which the traffic rules were violated were more difficult to predict correctly. The scenes in which the participants predicted violations were rated as more complex and dangerous. It is concluded that the low-cost method used here is more useful for examining which scenes are generally easy or difficult to predict and how they are experienced subjectively than to investigate differences in performance for different driver categories.     

A comparison of headway and time to collision as safety indicators

The two safety indicators "headway" and "time to collision (TTC)" are discussed and compared with respect to their usefulness in determining the safety of different traffic situations, like different locations in a junction. Over a 6-day-period traffic flow measures were taken in a four-way junction with stop signs on the minor road. It was found that for vehicles in a car following situation headway and TTC are independent of each other. The percentage of small headways is relatively constant across different locations in the junction, while the percentage of small TTC values varies between different locations. It is recommended to use headway for enforcement purposes, because small headways generate potentially dangerous situations. TTC, on the other hand, should be used when a certain traffic environment is to be evaluated in terms of safety, because it indicates the actual occurrences of dangerous situations.     

Identification of significant pressures and impacts upon receiving waters.

This study gives a review on the process of identification of significant pressures and impacts, which is an important part of river basin planning and in particular for implementing the EU Water Framework Directive (WFD) (2000/60/EC). The questions: what is a "significant pressure" in terms of the WFD? which sources and driving forces have to be regarded? which data can be used? which pressure on a water body is significant? and which implications and requirements result from the identification process?--should be considered. The European Commission requires reporting from all Member States about the status of the water bodies within a river basin district and about the risk of failing the environmental objectives by the end of 2004. Therefore, a number of prevailing projects across Europe aim to develop a guideline on a common understanding of the most effective approach towards the identification of significant anthropogenic pressures, and the analysis of potential impacts including the identification of appropriate tools and models. In such a guideline suitable and intelligent criteria have to be developed in order to enable a uniform assessment of the anthropogenic pressures within a river basin district.