Socially shared regulation of learning in CSCL: understanding and prompting individual- and group-level shared regulatory activities

The field of computer supported collaborative learning (CSCL) is progressing instrumentally and theoretically. Nevertheless, few studies examine the effectiveness and efficiency of CSCL with respect to cognitive, motivational, emotional, and social issues, despite the fact that the role of regulatory processes is critical for the quality of students’ engagement in collaborative learning settings. We review the four earlier lines in developing support in CSCL and show how there has been a lack of work to support individuals in groups to engage in, sustain, and productively regulate their own and the group’s collaborative processes. Our aim is to discuss how our conceptual work in socially shared regulation of learning (SSRL) contributes to effective and efficient CSCL, what tools are presently available, and what the implications of research on these tools are for future tool development.     

Messung und Theorie der Wandschubspannung bei Zweiphasenströmung im Rohr

Zusammenfassung Im allgemeinen gilt es als selbstverst?ndlich, da? ein durch ein Rohr str?mendes Medium auf die Rohrwand eine Schubspannung in Richtung der Str?mung übertr?gt. Aus Versuchen und überlegungen geht jedoch hervor, da? bei Zweiphasenstr?mungen im Schwerefeld auf Grund der Vorg?nge an der Wand die Schubspannung u. U. der Hauptstromrichtung entgegengerichtet ist. Auch ergibt sich, da? die dynamisch, d. h. unter Einflu? der Reibung gemessene F?rderh?he einer Pumpe h?her als die hydrostatisch berechnete sein kann. VDI Mitteilung aus dem Institut für kalorische Apparate und K?ltetechnik der Eidgen?ssischen Technischen Hochschule Zürich Herrn Prof. Dr. phil.E. Justi zur Vollendung seines 60. Geburtstags gewidmet.     

Quasistatische zustandsänderungen und ihr Zusammenhang mit den reversiblen und irreversiblen prozessen der thermodynamik

Ohne Zusammenfassung     

Rheokinetic model to characterize the maturation process of gelatin solutions under shear flow

The characterization of maturing gelatin solutions in shear flow is required for an appropriate formulation of food products. Under static conditions, the maturation process of gelatin solutions may be described through a basic structural parameter evolving to the percolation value (gel point). Within the rheological framework, two asymptotic viscosities are well identified for the maturing process of gelatin solutions at the limit zero shear rate. One involves the initial solution viscosity that may be associated with the null structural parameter (the microstructure is not formed yet). The other is the percolation zero shear rate viscosity (assuming an infinite value when approaching the gel time) and corresponds to the maximum value of the structural parameter. Under flow, thixotropic theories combined with the knowledge of suspension rheology allow one to convert directly experimental data obtained as shear stress versus time for a given shear rate into the time evolution of the structural parameter. Consequently rheometric experimental data available places the search for a rheokinetic model of the structural parameter. Here, different expressions for this model are investigated, mainly those involving both the rates of structure breakdown and buildup, where the average cluster size is affected by the shear rate. The rate equation thus obtained may be then applied to arbitrary shear rate histories. Numerical results of the rheokinetic model proposed in this work fit well experimental rheometric data obtained in shear flow for the maturing of different gelatin solutions. Experimental data acquired in this work are presented and discussed in relation to those reported previously in the literature.     

Modeling the rheology of gelatin gels for finite deformations. Part 2. Viscoelastic solid model

The viscoelastic solid model proposed in this work can predict the rheological responses of gelatin gels for finite deformations. This rheological model considers a degree of physical cross-links at a given maturation time, which is partially attained from those links totally available when a pure elastic network is achieved. Thus, both an elastic network formed by permanent links on the average and a viscoelastic network composed of the remaining adaptive links are described at each maturation time. This model for gelatin gels considers appropriately the interplay between the networks involving: (a) viscoelastic relaxation as a consequence of an imposed mechanical history, (b) average degree of physical cross-links in the partially generated permanent network acting in the short-term mechanical response. In this context of analysis the standard viscoelastic solid is obtained asymptotically for small deformations. Also the effect of shear rate on the shear test is studied and the braking phenomenon is analysed in relation to the formation of microstructure by considering viscoelastic parameters.     

Characterization of cross-linked polyampholytic gelatin hydrogels through the rubber elasticity and thermodynamic swelling theories

A new approach is proposed to characterize polyampholytic gelatin hydrogels, cross-linked covalently with glutaraldehyde. An experimental methodology involving simple mechanical extension and compression and equilibrium swelling tests is developed to estimate relevant microstructural parameters and electrokinetic properties of this type of hydrogel, for different cross-linker to gelatin mass ratios. The polyampholytic cross-linked matrices are studied here in the framework of the rubber elasticity and thermodynamic swelling theories. The main purposes of this work are the estimations of average mesh size and toughness of the swollen hydrogels, and the determination of the feasibility of polyion complexation between cross-linked gelatin chains and bioactive macromolecules to be delivered through hydrogel biodegradation.     

Modeling the rheology of gelatin gels for finite deformations. Part 1. Elastic rheological model

The rheological behavior of gelatin gels is studied through a constitutive equation derived in the literature from the classical hyperelasticity theory by using a nonlinear strain energy density. Gelatin gels are assumed to be an elastic solid here, which at a given maturation time has a degree of physical cross-links composing a permanent elastic network. It is also studied in particular: (a) the validation of the elastic rheological model proposed here in relation to the prediction of two data sets pertaining to different experimental tests (shear and simple compression) by using fixed values of rheological parameters, (b) the increase of the stress-strain nonlinearity with increasing maturation time, at a given protein concentration, (c) the evolution of the stress-strain nonlinearity with increasing gelatin concentration. It is found that gelatin gels exhibit a strong nonlinear strain energy density, which is expressed through two shear modules related to nucleation and growing of junction zones.     

Properties of CsI(TI) — Renaissance of an old scintillation material

CsI(TI) is an interesting material for calorimeters in high energy physics. Properties of this material are reported.