Spin tunnelling in mesoscopic systems

We study spin tunnelling in molecular magnets as an instance of a mesoscopic phenomenon, with special emphasis on the molecule Fe8. We show that the tunnel splitting between various pairs of Zeeman levels in this molecule oscillates as a function of applied magnetic field, vanishing completely at special points in the space of magnetic fields, known as diabolical points. This phenomena is explained in terms of two approaches, one based on spin-coherent-state path integrals, and the other on a generalization of the phase integral (or WKB) method to difference equations. Explicit formulas for the diabolical points are obtained for a model Hamiltonian.Comment: 13 pages, 5 figures, uses Pramana style files; conference proceedings articl

PAREJA [Material gráfico]

ADQUIRIDA POR EL COLECCIONISTA EN LAS PALMAS G.C.FOTO DE SEÑORA SENTDA EN SILLA CON CABALLERO DE PIE A SU LADOCopia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201

Effects of carbon black and graphene nano-platelet fillers on the mechanical properties of syntactic foam

Mechanical properties of an epoxy based syntactic foams are discussed in this study. Basic syntactic foam, composed of 30% of hollow glass spheres by volume, was modified with a 1% volume fraction addition of graphene nano-platelets (GnP), treated GnPs and carbon black (CB). In treated GnPs the hollow glass spheres and the GnPs were treated with 1-Pyrenecarboxaldehyde in xylene. The flexural, tensile, compressive and Izod properties of the five different combinations of these syntactic foams, both reinforced and not reinforced, were measured and compared with the pristine epoxy. The tests show that the reinforced foams had a higher modulus in all cases. The maximum tensile load decreased with the addition of the GnPs, while it increased when CBs were used. Scanning electron micrographs were used to evaluate the dispersion of the filler in the epoxy matrix and the interaction between matrix and fillers

Determination of the strain status of GaAs/AlAs quantum wires and quantum dots

We have investigated periodic arrays of 150 and 175 nm wide GaAs-AlAs quantum wires and quantum dots, fabricated by electron beam lithography and SiCI4/O2 reactive ion etching, by means of reciprocal space mapping using triple axis x-ray diffractometry (TAD). The reciprocal space maps reveal that after the fabrication process the lattice constant along the growth direction slightly increases for the wires and even more so for the dots