We discovered two percolation processes in succession in dc conductivity of bulk baker's yeast in the course of dehydration. Critical exponents characteristic for the three-dimensional network for heavily hydrated system, and two dimensions in the light hydration limit, evidenced a dramatic change of the water network dimensionality in the dehydration process.
In studying the dehydration of surface-moistened fumed silica Aerosil powders, we found a conductivity percolation transition at low hydration levels. Both the percolation exponent and the threshold are typical for correlated site-bond transitions in complex two-dimensional (2D) systems. The exponent values, 0.94-1.10, are indicative of severe heterogeneity in the conducting medium. The surface moisture at the percolation threshold takes on a universal value of 0.65 mg([H2O])/m(2)([silica]), independent of the silica grain size, and equivalent to twice the first hydration monolayer. This level is just sufficient to sustain a quasi-2D, hydrogen-bonded water network spanning the silica surface.
Over the past 25 years, the Davidson College Physics Department has developed small computer programs called Physlets. These programs were written in Java and distributed as Java applets embedded in HTML pages. Physics teachers from around the world used Physlets to author interactive computer-based curricular materials for the teaching of introductory and advanced physics courses in multiple languages. Unfortunately, the Java plugin that enabled Java applets, including our original Physlets, to run was removed from browsers in 2018, Removing applet support, though critical for security reasons, was a major setback for physics education, since there had been thousands of applet-based HTML pages developed for physics and mathematics. To address this problem, we have converted Physlets to JavaScript so that they are compatible with all devices, inducing mobile platforms. This paper describes how these JavaScript Physlets can be used to improve teaching.
Testing knowledge is an integral part of a summative assessment at schools. It can be performed in many different ways. In this study we propose assessment of physics knowledge by using a class tournament approach. Prior to a statistical analysis of the results obtained over a tournament organized in one of Polish high schools, all its specifics are discussed at length, including the types of questions assigned, as well as additional self-and peer-evaluation questionnaires, constituting an integral part of the tournament. The impact of the tournament upon student improvement is examined by confronting the results of a post-test with pre-tournament students' achievements reflected in scores earned in former, tests written by the students in experimental group and their colleagues from control group. We also present some of students' and teachers' feedback on the idea of a tournament as a tool of assessment. Both the analysis of the tournament results and the students' and teachers' opinions point to at least several benefits of our approach.
Articles you may be interested inThe bucket rheometer for shear stress-shear rate measurement of industrial suspensions J. Rheol. 51, 821 (2007); 10.1122/1.2750657 Mass-controlled capillary viscometer for a Newtonian liquid: Viscosity of water at different temperatures Rev. Sci. Instrum. 78, 035112 (2007); 10.1063/1.2716824 Transient torque method: A fast and nonintrusive technique to simultaneously determine viscosity and electrical conductivity of semiconducting and metallic melts Rev. Sci. Instrum. 75, 2810 (2004); 10.1063/1.1781380
Measurements of viscosity, velocity slip coefficients, and tangential momentum accommodation coefficients using a modified spinning rotor gaugeWe describe a new viscometer developed for liquid crystals. It has been designed for measurement of the MiJsowicz viscosity coefficient 2 ͑n ʈ v͒ in particular, but can be used for measuring 1 ͑n ʈ ٌv͒ as well. The measurement is based on observation of the damped motion of a pendulum and derivation of the viscosity coefficient from the damping constant.
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