Learning object relationships which determine the outcome of actions

Peer reviewedPublisher PD

Anisotropic Colossal Magnetoresistance Effects in Fe_{1-x}Cu_xCr_2S_4

A detailed study of the electronic transport and magnetic properties of Fe$_{1-x}$Cu$_x$Cr$_2$S$_4$ ($x \leq 0.5$) on single crystals is presented. The resistivity is investigated for $2 \leq T \leq 300$ K in magnetic fields up to 14 Tesla and under hydrostatic pressure up to 16 kbar. In addition magnetization and ferromagnetic resonance (FMR) measurements were performed. FMR and magnetization data reveal a pronounced magnetic anisotropy, which develops below the Curie temperature, $T_{\mathrm{C}}$, and increases strongly towards lower temperatures. Increasing the Cu concentration reduces this effect. At temperatures below 35 K the magnetoresistance, $MR = \frac{\rho(0) - \rho(H)}{\rho(0)}$, exhibits a strong dependence on the direction of the magnetic field, probably due to an enhanced anisotropy. Applying the field along the hard axis leads to a change of sign and a strong increase of the absolute value of the magnetoresistance. On the other hand the magnetoresistance remains positive down to lower temperatures, exhibiting a smeared out maximum with the magnetic field applied along the easy axis. The results are discussed in the ionic picture using a triple-exchange model for electron hopping as well as a half-metal utilizing a band picture.Comment: some typos correcte

Stable amorphous georgeite as a precursor to a high-activity catalyst .

Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable—and hence little known and largely ignored1—georgeite. The first three of these minerals are widely used as catalyst precursors2, 3, 4 for the industrially important methanol-synthesis and low-temperature water–gas shift (LTS) reactions5, 6, 7, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase2, 3, 8, 9, 10 is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite11; with few exceptions12 it uses sodium carbonate as the carbonate source, but this also introduces sodium ions—a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide (refs 13, 14), a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts

Common ground in collaborative intelligence analysis: an empirical study

This paper reports an empirical exploration of how different configurations of collaboration technology affect peoples’ ability to construct and maintain common ground while conducting collaborative intelligence analysis work. Prior studies of collaboration technology have typically focused on simpler conversational tasks, or ones that involve physical manipulation, rather than the complex sensemaking and inference involved in intelligence work. The study explores the effects of video communication and shared visual workspace (SVW) on the negotiation of common ground by distributed teams collaborating in real time on intelligence analysis tasks. The experimental study uses a 2x2 factorial, between-subjects design involving two independent variables: presence or absence of Video and SVW. Two-member teams were randomly assigned to one of the four experimental media conditions and worked to complete several intelligence analysis tasks involving multiple, complex intelligence artefacts. Teams with access to the shared visual workspace could view their teammates’ eWhiteboards. Our results demonstrate a significant effect for the shared visual workspace: the effort of conversational grounding is reduced in the cases where SVW is available. However, there were no main effects for video and no interaction between the two variables. Also, we found that the “conversational grounding effort” required tended to decrease over the course of the tas

On the Physical Basis of Biological Signaling by Interface Pulses

Currently, biological signaling is envisaged as a combination of activation and movement, triggered by local molecular interactions and molecular diffusion, respectively. However, here, we suggest that other fundamental physical mechanisms might play an at least equally important role. We have recently shown that lipid interfaces permit the excitation and propagation of sound pulses. Here, we demonstrate that these reversible perturbations can control the activity of membrane-embedded enzymes without a requirement for molecular transport. They can thus facilitate rapid communication between distant biological entities at the speed of sound, which is here on the order of 1 m/s within the membrane. The mechanism described provides a new physical framework for biological signaling that is fundamentally different from the molecular approach that currently dominates the textbooks