16,657 research outputs found
Comment on "Tricritical Behavior in Rupture Induced by Disorder"
In their letter, Andersen, Sornette, and Leung [Phys. Rev. Lett. 78, 2140
(1997)] describe possible behaviors for rupture in disordered media, based on
the mean field-like democratic fiber bundle model. In this model, fibers are
pulled with a force which is distributed uniformly. A fiber breaks if the
stress on it exceeds a threshold chosen from a probability distribution, and
the force is then redistributed over the intact fibers. Andersen et al. claim
the existence of a tricritical point, separating a "first-order" regime,
characterized by a sudden global failure, from a "second-order" regime,
characterized by a divergence in the breaking rate. We show that a first-order
transition is an artifact of a (large enough) discontinuity put by hand in the
disorder distribution. Thus, in generic physical cases, a first-order regime is
not present. This result is obtained from a graphical method, which, unlike
Andersen at al.'s analytical solution, enables us to distinguish the various
classes of qualitatively different behaviors of the model.Comment: 1 page, 1 figure included, revte
Design optimization of high-performance electrodynamic actuators for use in a cryogenically cooled telescope
An analysis and optimization of a mirror-actuator system for large excursion/high-frequency chopping is developed. The results of this analysis, combined with laboratory measurements of a prototype actuator operating at cryogenic temperatures, allow performance predictions to be made for a real system utilizing this technology
Thermal treatment of superconductor thin film of the BSCCO system using domestic microwave oven
In this work, we report the preparation of a superconductor thin film of the
BSCCO system using a good quality powder with nominal composition
Bi_{1.8}Pb_{0.4}Sr_2CaCu_2O_x which was thermally treated using a domestic
microwave oven (2.45 GHz, 800 W). This film was grew on a single crystal of
LaAlO_3(100) substrate and exhibited a crystalline structure with the c-axis
perpendicular to the plane of the substrate. An onset superconducting
transition temperature was measured at 80 K.Comment: 4 pages, 5 figure
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