Interest, Instructional Strategies, and the Creation of Group Space

Research on small-group work and on whole class discussions has shown specific benefits for student learning. At the same time, research on interest stresses the generation of situational interest when particular learning conditions are met. This qualitative study explores whether the type of instructional strategy (small group vs. whole class discussion) influences triggering of situational interest about theoretical and practice-oriented pedagogical topics among preservice science teachers (N = 44). Triggering of interest was identified by participation rate, degree of comfort during interactions, and quality of arguments. Results show that whole class discussions of theoretical topics shifted towards practical teaching issues, while small groups sustained the theoretical nature of a topic. Both interaction patterns imply triggering of situational interest. But the small group interaction patterns indicate the collective construction of a “triple problem-solving space”, in which content, social/relational, and interest were balanced from the start; the whole class discussions needed first to renegotiate the content

Observation of Ising-like critical fluctuations in frustrated Josephson junction arrays with modulated coupling energies

We report the results of ac sheet conductance measurements performed on fully frustrated square arrays of Josephson junctions whose coupling energy is periodically modulated in one of the principal lattice directions. Such systems are predicted to exhibit two distinct transitions: a low-temperature Ising-like transition triggered by the proliferation of domain walls and a high-temperature transition driven by the vortex unbinding mechanism of the Beresinskii-Kosterlitz-Thouless (BKT) theory. Both the superfluid and dissipative components of the conductance are found to exhibit features which unambiguously demonstrate the existence of a double transition whose properties are consistent with the Ising-BKT scenario.Comment: To be published in Physica C (Proceedings of the 2nd European Conference in School Format 'Vortex Matter in Superconductors'

Sputtered W–N diffusion barriers

The thermal stability of reactively sputtered tungsten–nitrogen alloy thin films is investigated for the application as diffusion barriers in silicon contact metallizations. The composition of W–N barriers is varied over a wide range including pure W. Aluminum, gold, and silver are used as low resistivity overlayers. Metallurgical interactions at temperatures ranging from 500 to 900 °C are studied. Incorporating nitrogen into tungsten advantageously stabilizes all three systems. The overall failure takes place rapidly above critical temperatures that depend on both the metal overlayer and the microstructure of the barrier. In some cases, W–N alloys can effectively prevent interdiffusion at temperatures as high as 800 °C for 30 min

Sidedness of reconstituted calcium channels from muscle transverse tubules as determined by D600 and D890 blockade

The verapamil-type calcium antagonist, D600, and its charged quaternary derivative, D890, were used to assess the sidedness of blockade in single calcium channels reconstituted from purified transverse tubules of skeletal muscle. Spontaneous single channel openings were induced with the agonist Bay-K8644 and recordings were made in a two-chamber planar bilayer setup so that drugs could be delivered to either side of the channel. Micromolar drug addition resulted in a greater than 10-fold decrease in probability of open channel events (po) without a significant change in single channel currents. Changes in po occurred in parallel with changes in mean open time and both parameters could be titrated with a similar IC50. At pH 7.2, cis or trans D600 blocked with an IC50 of 5 microM but for D890 the IC50 was cis 3 microM and trans greater than 75 microM (cis is the intracellular-equivalent side as defined by the voltage-dependent activation). The asymmetry of D890 blockade indicates that the drug can readily gain access to the blocking site from the aqueous phase adjacent to the inner but not extracellular end of the channel

Moisture and Seasonality Shifts Recorded in Holocene and Pleistocene Speleothems From Southeastern Arabia

The source and seasonality of rainfall in southern Arabia during the early- to mid-Holocene and preceding humid periods are controversial because fossil lacustrine sediments provide solely indirect information on the amount of rainfall. Hydrogen and oxygen isotope measurements on fluid inclusion water trapped in Holocene and Pleistocene stalagmites from Hoti Cave in Northern Oman are direct indicators of the isotopic composition of paleoprecipitation. Isotope values of fluid inclusions formed during peak interglacial periods plot along monsoonal water lines and are indicative of a southern monsoonal moisture source. The last monsoon-dominated period lasting from ∼10,100 to 6,300 years before present was terminated within a few decades in southeastern Arabia. The subsequent reduction in rainfall amount and change from predominantly summer to predominantly winter rainfall had a profound impact on human communities living in this area and triggered migration from inland to coastal areas where resources were more abundant

Phase-coherence threshold and vortex-glass state in diluted Josephson-junction arrays in a magnetic field

We study numerically the interplay of phase coherence and vortex-glass state in two-dimensional Josephson-junction arrays with average rational values of flux quantum per plaquette $f$ and random dilution of junctions. For $f=1/2$, we find evidence of a phase coherence threshold value $x_s$, below the percolation concentration of diluted junctions $x_p$, where the superconducting transition vanishes. For $x_s < x < x_p$ the array behaves as a zero-temperature vortex glass with nonzero linear resistance at finite temperatures. The zero-temperature critical currents are insensitive to variations in $f$ in the vortex glass region while they are strongly $f$ dependent in the phase coherent region.Comment: 6 pages, 4 figures, to appear in Phys. Rev.