Development of motivation in first-year students in Dutch senior secondary vocational education

This study examined the development in motivation for school in students in senior secondary vocational education and factors related to this development. There have been many concerns about a decline in motivation after school transitions. Little about this subject is known in relation to the transition to senior secondary vocational education. Knowledge about this is necessary, as the decline is expected to be more extensive in this type of school because the percentage of dropouts is high. For this research, 614 first-year students filled out a questionnaire four times. The results showed little average change in motivation during the first school year, although there was a decrease in students' academic delay of gratification after the transition. Associations with motivation similar to those found in studies of secondary schools were found, but only at the start of the school year, not with changes in it during the remainder of the year

Patterns of calculated basal drag on ice streams B and C, Antarctica

This is the published version.Patterns of strain rate and slope on the ice streams are unusual. They cannot be accounted for in the usual way as due to standing waves in ice flow over a basal obstruction to flow (such as a sticky spot) . The features are studied using the force-budget technique. The conventional flow law is used, together with measurements of surface strain rate and shape of the glacier, to compute basal drag. The results for Ice Stream C are as expected, in that the drag varies from site to site but is directed inland, restraining the flow. The calculated drag at the base of Ice Stream B, on the other hand, is in places such that it acts to propel the glacier forward. This result is untenable. Either the conventional flow law is not applicable to Ice Stream B or there are large spatial variations in ice stiffness, perhaps associated with foliation, or both

Force budget: I. Theory and numerical methods

This is the published version, also available here: http://dx.doi.org/10.3189/002214389793701581.A practical method is developed for calculating stresses and velocities at depth using field measurements of the geometry and surface velocity of glaciers. To do this, it is convenient to partition full stresses into lithostatic and resistive components. The horizontal gradient in vertically integrated lithostatic stress is the driving stress and it describes the horizontal action of gravity. The horizontal resistive stress gradients describe the reactions. Resistive stresses are simply related to deviatoric stresses and hence to strain-rates through a constitutive relation. A numerical scheme can be used to calculate stresses and velocities from surface velocities and slope, and from ice thickness. There is no mathematical requirement that the variations in these quantities be small

The role of lateral drag in the dynamics of Ice Stream B, Antarctica

The partitioning of resistive force between the bed and sides of Ice Stream B, Antarctica , is obtained for three large areas that have bee n measured using repeat aerial photogrammetry. Problems associated with data errors and local variations in ice strength and velocity are reduced by considering the a really ave raged budget of forces for each photo block. Results indicate that the bed under Ice Stream B must be very weak and unable to provide much res instance. Mechanical l control on this ice stream emanates almost entirely from the lateral margins

Flow laws for glacier ice: comparison of numerical predictions and field measurements

This is the published version, also available here: http://dx.doi.org/10.3189/002214390793701372.Ice flow along the 20 km long strain network up-stream of the Dye 3 bore hole in Greenland is studied in detail. By solving the force—balance equations and using selected flow laws, stresses and strain-rates are calculated throughout the section of the ice sheet. The validity of the results is evaluated by comparison with the velocity profile derived from bore-hole-tilting measurements, and with observed surface strain-rates. A number of constitutive relations are tried and most predict a velocity profile at the bore-hole site that is in good agreement with that observed, if appropriate enhancement factors are used. However, there are major discrepancies between modeled and measured surface strain-rates. Use of Nye's generalization of Glen's flow law, or an anisotropic constitutive relation, requires unrealistically large along-flow variations in the enhancement factor. Inclusion of normal stress effects can lead to much better agreement, but it is possible that other processes, such as dynamic recrystallization or primary creep, should be included in the constitutive relation of polar ice