19 research outputs found
Magnetotransport near a quantum critical point in a simple metal
We use geometric considerations to study transport properties, such as the
conductivity and Hall coefficient, near the onset of a nesting-driven spin
density wave in a simple metal. In particular, motivated by recent experiments
on vanadium-doped chromium, we study the variation of transport coefficients
with the onset of magnetism within a mean-field treatment of a model that
contains nearly nested electron and hole Fermi surfaces. We show that most
transport coefficients display a leading dependence that is linear in the
energy gap. The coefficient of the linear term, though, can be small. In
particular, we find that the Hall conductivity is essentially
unchanged, due to electron-hole compensation, as the system goes through the
quantum critical point. This conclusion extends a similar observation we made
earlier for the case of completely flat Fermi surfaces to the immediate
vicinity of the quantum critical point where nesting is present but not
perfect.Comment: 11 pages revtex, 4 figure
Efficient Synthesis of Tyrosine-Derived Marine Sponge Metabolites via Acylation of Amines with a Coumarin
Condensation of N-acetylglycine with aldehyde 15 in acetic anhydride gave acetamido coumarin 16. Hydrolysis to the enol coumarin 17 and reaction with hydroxylamine gave the oximino coumarin 18. Reaction of the oximino coumarin 18 with a range of nucleophiles gave the phenolic oximes in excellent yield. The rates of acylation of histamine with the oximino coumarin 18 and methyl ester 9 were compared. Oxidative spirocyclization of three representative phenolic oximes with polymer-supported (diacetoxyiodo) benzene gave the spiroisoxazolines
DAMPING BY UNCOUPLED PARTICULATE COMPOSITES
Large damping can be achieved by suitable design of a
composite material which contains a significant volume fraction of freely
vibrating particles in internal cavities of its matrix.An approximate analysis
of the damping behavior of such a materiel is presented. It is shown that the
damping varies linearly with amplitude, inversely with the first power of the
distance of motion and with the second power of (1-k), where k is the
coefficient fo restitution
2-Phenyl-3-(5,6,7,7a-tetrahydro-1H,3H-pyrrolo[1,2-c]oxazol-3-ylidene)-1-propene-1,1-dicarbonitrile and 4-(4-Methoxyphenyl)-2,6-bis(methylthio)pyridine-3-carbonitrile
The reaction of 3-aryl-2-cyano-5,5-bis(methylthio)penta-2,4-dienenitrile, (1), with (L)-(-)-2-hydroxymethylpyrrolidine, (2), gave two types of product, the normal substitution product, (3), and a pyridine derivative, (4). The structures of two representative examples, 2-phenyl-3-(5,6,7,7a-tetrahydro1H,3H-pyrrolo[1,2-c]oxazol-3-ylidene)-1-propene-1,1-dicarbonitrile, (3a), as its hemibenzene solvate, C17H14N3O.0.5C6H6, and 4-(4-methoxyphenyl)-2,6-bis(methylthio)pyridine-3-carbonitrile, (4b), C15H14N2OS2, have been unambiguously established by X-ray crystallographic analysis. The molecular packing of (4b) involves loosly held dimers with S1...S1\u27 distances of 3.424 (1) Å