SummaryMagnetic resonance imaging was employed to study the dependence of clot lysing patterns on two different modes of transport of urokinase into whole blood clots. In one group of clots (nonperfused clots, n1 = 10), access of urokinase to the fibrin network was possible by diffusion only, whereas in the other group (perfused clots, n2 = 10) bulk flow of plasma containing urokinase was instituted through occlusive clots by a pressure difference of 3 .7 kPa (37 cm H2O) across 3 cm long clots with a diameter of 4 mm. It was determined separately that this pressure difference resulted in a volume flow rate of 5.05 ± 2.4 × 10−2 ml/min through occlusive clots. Perfused clots diminished in size significantly in comparison to nonperfused ones already after 20 min (p <0.005). Linear regression analysis of two-dimensional clot sizes measured by MRI showed that the rate of lysis was more than 50-times faster in the perfused group in comparison to the nonperfused group. It was concluded that penetration of the thrombolytic agent into clots by perfusion is much more effective than by diffusion. Our results might have some implications for understanding the differences in lysis of arterial and venous thrombi.

Investigative Science Learning Environment (ISLE) is a learning system, developed based on the history and philosophy of physics and observations of the work of scientists constructing new knowledge. It engages students in learning physics through processes that physicists use in their work. The processes form the so-called ISLE cycle-a logical progression of different steps from observation to testing. Research in this thesis investigates whether the physicists do indeed use the elements of ISLE while solving problems and also follow the logic of the ISLE cycle. We approached this issue with an experimental problem that was sufficiently novel to the experts so that they could employ the reasoning that they commonly use in their work. This research project is a comparison of four different case studies. Three case studies were conducted with pairs of expert scientists and one was conducted with students, who were videotaped while solving the same problem from geometrical optics. With the help of different graphical representations of the problem solving processes of the subjects we showed that not only scientists, but also students follow the transitions of the steps present in the ISLE cycle, although the experts were considerably stronger than the students. In addition, we observed that the students' problem solving approach in time became more similar to the one of scientists. It is possible that the logic of the ISLE cycle does not only come from the practice of scientists, but is a natural, inner way to approach this type of problems which easily transfers to solving similar problems.

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The surface-to-volume ratio is an important quantity in thermal physics. For example it governs the behaviour of heating or cooling of physical objects as a function of size like, e.g. cubes or spheres made of different material. The starting point in our paper is the simple physics problem of how cheese cubes of different sizes behave if heated either in a conventional oven or in a microwave oven. The outcome of these experiments depends on a balance between heating and cooling with the surface-to-volume ratio (S/V) as the key parameter. The role of (S/V) becomes most obvious in studying cooling curves of differently sized objects like cubes or spheres, alone. Besides problems in thermal physics, the surface-to-volume ratio has many important applications in biochemistry, chemistry and biology. It allows us to draw general conclusions concerning the thermal and mechanical properties of different-sized animals, in particular their metabolism. Hence, this topic offers rich contexts for interdisciplinary teaching. An example presented in this paper starts in physics while studying thermal properties of cheese cubes and ends up in biology by discussing the differences in food intake of animals from small mice to huge elephants. M This article features online multimedia enhancements