43,595 research outputs found
Effect of curvature on the backscattering from leaves
Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii
Exact zero-point interaction energy between cylinders
We calculate the exact Casimir interaction energy between two perfectly
conducting, very long, eccentric cylindrical shells using a mode summation
technique. Several limiting cases of the exact formula for the Casimir energy
corresponding to this configuration are studied both analytically and
numerically. These include concentric cylinders, cylinder-plane, and eccentric
cylinders, for small and large separations between the surfaces. For small
separations we recover the proximity approximation, while for large separations
we find a weak logarithmic decay of the Casimir interaction energy, typical of
cylindrical geometries.Comment: 20 pages, 7 figure
On the accuracy of the PFA: analogies between Casimir and electrostatic forces
We present an overview of the validity of the Proximity Force Approximation
(PFA) in the calculation of Casimir forces between perfect conductors for
different geometries, with particular emphasis for the configuration of a
cylinder in front of a plane. In all cases we compare the exact numerical
results with those of PFA, and with asymptotic expansions that include the next
to leading order corrections. We also discuss the similarities and differences
between the results for Casimir and electrostatic forces.Comment: 17 pages, 5 figures, Proceedings of the meeting "60 years of Casimir
effect", Brasilia, 200
Casimir force between surfaces close to each other
Casimir interactions (due to the massless scalar field fluctuations) of two
surfaces which are close to each other are studied.
After a brief general presentation, explicit calculations for co-axial
cylinders, co-centric spheres and co-axial cones are performed.Comment: Latex, 20 pages, added references, corrected typos, changed conten
Casimir force between eccentric cylinders
We consider the Casimir interaction between a cylinder and a hollow cylinder,
both conducting, with parallel axis and slightly different radii. The Casimir
force, which vanishes in the coaxial situation, is evaluated for both small and
large eccentricities using the proximity approximation. The cylindrical
configuration offers various experimental advantages with respect to the
parallel planes or the plane-sphere geometries, leading to favourable
conditions for the search of extra-gravitational forces in the micrometer range
and for the observation of finite temperature corrections.Comment: To be published in Europhysics Letters. 7 pages, 4 figure
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