Effect of high pressure on the electrical properties of amorphous arsenic

The room temperature resistivity of bulk amorphous arsenic subjected to increasing pressure, decreases continuously over about seven orders of magnitude, the material remaining amorphous until, at a pressure of 40 kBar, a sharp irreversible transition occurs involving a further five decades fall in resistivity, the material then crystallizing to the semi-metallic rhombohedral form. Conclusive evidence for variable-range hopping in vitreous arsenic is reported here for the first time. It is observed in samples which have been released from pressures less than 40 kBar; a value of approximately 6 x 10¹⁷ eV^-1 cm^-3 is deduced for the density at the Fermi level of pressure-induced defect states responsible for this behaviour.     

Interleaving multi-agent systems and social networks for organized adaptation

Ad hoc networks can be formed from arbitrary collections of sensors, mobile routers, or business processes. These networks are open systems, in the sense that the network nodes share a common language but do not necessarily share a common goal or common knowledge, and there is no centralised controller or global data repository. Such systems have numerous advantages in terms of enabling autonomous, heterogeneous components to achieve individual goals without central direction and with only partial knowledge. However, operational problems stem from potential conflicts over resource allocation, miscommunication, and sub-ideal operation, and the general need of embedded systems to change behaviour according to changes in the environment. To address these problems, we propose to converge aspects of norm-governed specification from distributed multi-agent systems, opinion formation from social networks, and voting procedures from computational social choice. In particular, we develop a prototype system which interleaves gossiping, expressed preferences (voting) and norms, to configure rules and assign roles. This is another demonstration of the use of socially-inspired mechanisms for regulation of decentralised systems and a key step towards the realization of organized adaptation for open multi-agent systems.     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

In vitro biocompatibility of electrospun and solvent-cast chitosan substrata towards Schwann, osteoblast, keratinocyte and fibroblast cells

Chitosan or poly(N-acetyl-d-glucosamine-co-d-glucosamine) with a degree of deacetylation of about 85% was fabricated into nanofibrous membranes by electrospinning from 7% w/v chitosan solution in 70:30 v/v trifluoroacetic acid/dichloromethane solvent system. The obtained fibers were smooth without the presence of beads. The diameters of the individual fiber segments were 126 ± 20 nm. The potential for use of the electrospun chitosan nanofibrous membranes as substrates for cell/tissue culture was evaluated with four different cell types, i.e., Schwann cells, osteoblast-like cells, keratinocytes and fibroblasts, in terms of the attachment and the proliferation of the cells as well as the morphology of the seeded and the cultured cells. The results were compared with the corresponding solvent-cast films. Both types of the chitosan substrates supported the attachment and, at the same time, promoted the largest increase in the viability of the cultured keratinocytes. The viability of Schwann cells cultured on these substrates increased marginally well, but the attachment of the cells on the surfaces was relatively poor. Finally, both types of the chitosan substrates showed cytostatic property towards both osteoblast-like cells and fibroblasts, despite the convincingly good attachment of osteoblast-like cells on the surfaces.     

Palladium/hydrogen catalyzed alcoholysis of benzylsilanes

Certain benzylsilanes are converted to methoxy or ethoxysilanes and toluene when treated with methanol or ethanol in the presence of hydrogen and catalytic amounts of palladium on charcoal. The reaction is promoted by a Si-phenyl substituent and probably by a S_NSi displacement mechanism.