2,679 research outputs found
Reduction of Magnetic Noise in Atom Chips by Material Optimization
We discuss the contribution of the material type in metal wires to the
electromagnetic fluctuations in magnetic microtraps close to the surface of an
atom chip. We show that significant reduction of the magnetic noise can be
achieved by replacing the pure noble metal wires with their dilute alloys. The
alloy composition provides an additional degree of freedom which enables a
controlled reduction of both magnetic noise and resistivity if the atom chip is
cooled. In addition, we provide a careful re-analysis of the magnetically
induced trap loss observed by Yu-Ju Lin et al. [Phys. Rev. Lett. 92, 050404
(2004)] and find good agreement with an improved theory.Comment: 25 pages with 9 figures ep
Multi-objective shape and material optimization of composite structures including damping
A multi-objective optimal design methodology is developed for light-weight, low cost composite structures of improved dynamic performance. The design objectives include minimization of resonance amplitudes (or maximization of modal damping), weight, and material cost. The design vector includes micromechanics, laminate, and structural shape parameters. Performance constraints are imposed on static displacements, dynamic amplitudes, and natural frequencies. The effects of damping on the dynamics of composite structures are incorporated. Preliminary applications on a cantilever composite beam illustrated that only the proposed multi-objective optimization, as opposed to single objective functions, simultaneously improved all objectives. The significance of composite damping in the design of advanced composite structures was also demonstrated, indicating the design methods based on undamped dynamics may fail to improve the dynamic performance near resonances
High superconductivity in MgB by nonadiabatic pairing
The evidence for the key role of the bands in the electronic
properties of MgB points to the possibility of nonadiabatic effects in the
superconductivity of these materials. These are governed by the small value of
the Fermi energy due to the vicinity of the hole doping level to the top of the
bands. We show that the nonadiabatic theory leads to a coherent
interpretation of K and the boron isotope coefficient without invoking very large couplings and it naturally explains the
role of the disorder on . It also leads to various specific predictions
for the properties of MgB and for the material optimization of these type
of compounds.Comment: 4 revtex pages, 3 eps figures, to appear on Phys. Rev. Let
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