RESUMO
We report the results of new differential force measurements between a test mass and rotating source masses of gold and silicon to search for forces beyond Newtonian gravity at short separations. The technique employed subtracts the otherwise dominant Casimir force at the outset and, when combined with a lock-in amplification technique, leads to a significant improvement (up to a factor of 10^{3}) over existing limits on the strength (relative to gravity) of a putative force in the 40-8000 nm interaction range.
RESUMO
The analysis of all Casimir force experiments using a sphere-plate geometry requires the use of the proximity-force approximation (PFA) to relate the Casimir force between a sphere and a flat plate to the Casimir energy between two parallel plates. Because it has been difficult to assess the PFA's range of applicability theoretically, we have conducted an experimental search for corrections to the PFA by measuring the Casimir force and force gradient between a gold-coated plate and five gold-coated spheres with different radii using a microelectromechanical torsion oscillator. For separations z<300 nm, we find that the magnitude of the fractional deviation from the PFA in the force gradient measurement is, at the 95% confidence level, less than 0.4z/R, where R is the radius of the sphere.
RESUMO
Recently, Brevik [Phys. Rev. E, 71, 056101 (2005)] adduced arguments against the traditional approach to the thermal Casimir force between real metals and in favor of one of the alternative approaches. The latter assume zero contribution from the transverse electric mode at zero frequency in qualitative disagreement with unity as given by the thermal quantum field theory for ideal metals. Those authors claim that their approach is consistent with experiments as well as with thermodynamics. We demonstrate that these conclusions are incorrect. We show specifically that their results are contradicted by four recent experiments and also violate the third law of thermodynamics (the Nernst heat theorem).
RESUMO
The first precise measurement of the Casimir force between dissimilar metals is reported. The attractive force, between a Cu layer evaporated on a microelectromechanical torsional oscillator and an Au layer deposited on an Al2O3 sphere, was measured dynamically with a noise level of 6 fN/sqrt[Hz]. Measurements were performed for separations in the 0.2-2 micro m range. The results agree to better than 1% in the 0.2-0.5 micro m range with a theoretical model that takes into account the finite conductivity and roughness of the two metals. The observed discrepancies, which are much larger than the experimental precision, can be attributed to a lack of a complete characterization of the optical properties of the specific samples used in the experiment.
RESUMO
It is the fiberoptic endoscope and its related hardware that distinguish endoscopic sinus surgery from previous techniques. Lens angles of 0, 25, and 70 degrees, comprising a representative telescope set, accommodate virtually any endoscopic sinus procedure, diagnostic or therapeutic, with unsurpassed visualization. Each telescope may be fitted with an optional suction-irrigation adaptor, a highly controversial accessory among endoscopic surgeons. The clinical situation often dictates the optimal combination of equipment, anesthesia, and technique; surgeon's preference is equally influential. Mastery of conventional operative techniques combined with thorough endoscopic skills is essential for consistent, effective, and safe surgical performance.
