112 research outputs found
Observation of the skin-depth effect on the Casimir force between metallic surfaces
We have performed comparative measurements of the Casimir force between a
metallic plate and a transparent sphere coated with metallic films of different
thicknesses. We have observed that, if the thickness of the coating is less
than the skin-depth of the electromagnetic modes that mostly contribute to the
interaction, the force is significantly smaller than that measured with a thick
bulk-like film. Our results provide the first direct evidence of the skin-depth
effect on the Casimir force between metallic surfaces.Comment: submitted for publication on Dec. 10, 2004. 3 figure
New Challenges and Directions in Casimir Force Experiments
This article is divided in three sections. In the first section we briefly
review some high precision experiments on the Casimir force, underlying an
important aspect of the analysis of the data. In the second section we discuss
our recent results in the measurement of the Casimir force using non-trivial
materials. In the third section we present some original ideas for experiments
on new phenomena related to the Casimir effects.Comment: 6 pages, invited contribution to the 6th Workshop on Quantum Field
Theory under the Influence of External Conditions (QFEXT03), Norman,
Oklahoma, September 15-19, 200
Force sensor for chameleon and Casimir force experiments with parallel-plate configuration
The search for non-Newtonian forces has been pursued following many different
paths. Recently it was suggested that hypothetical chameleon interactions,
which might explain the mechanisms behind dark energy, could be detected in a
high-precision force measurement. In such an experiment, interactions between
parallel plates kept at constant separation could be measured as a function of
the pressure of an ambient gas, thereby identifying chameleon interactions by
their unique inverse dependence on the local mass density. During the past
years we have been developing a new kind of setup complying with the high
requirements of the proposed experiment. In this article we present the first
and most important part of this setup -- the force sensor. We discuss its
design, fabrication, and characterization. From the results of the latter we
derive limits on chameleon interaction parameters that could be set by the
forthcoming experiment. Finally, we describe the opportunity to use the same
setup to measure Casimir forces at large surface separations with unprecedented
accuracy, thereby potentially giving unambiguous answers to long standing open
questions
Structure-stiffness relation of live mouse brain tissue determined by depth-controlled indentation mapping
The mechanical properties of brain tissue play a pivotal role in
neurodevelopment and neurological disorders. Yet, at present, there is no
consensus on how the different structural parts of the tissue contribute to its
stiffness variations. Here, we have gathered depth-controlled indentation
viscoelasticity maps of the hippocampus of isolated horizontal live mouse brain
sections. Our results confirm the highly viscoelestic nature of the material
and clearly show that the mechanical properties correlate with the different
morphological layers of the samples investigated. Interestingly, the relative
cell nuclei area seems to negatively correlate with the stiffness observed
Computation and visualization of Casimir forces in arbitrary geometries: non-monotonic lateral forces and failure of proximity-force approximations
We present a method of computing Casimir forces for arbitrary geometries,
with any desired accuracy, that can directly exploit the efficiency of standard
numerical-electromagnetism techniques. Using the simplest possible
finite-difference implementation of this approach, we obtain both agreement
with past results for cylinder-plate geometries, and also present results for
new geometries. In particular, we examine a piston-like problem involving two
dielectric and metallic squares sliding between two metallic walls, in two and
three dimensions, respectively, and demonstrate non-additive and non-monotonic
changes in the force due to these lateral walls.Comment: Accepted for publication in Physical Review Letters. (Expected
publication: Vol. 99 (8) 2007
On the torque on birefringent plates induced by quantum fluctuations
We present detailed numerical calculations of the mechanical torque induced
by quantum fluctuations on two parallel birefringent plates with in plane
optical anisotropy, separated by either vacuum or a liquid (ethanol). The
torque is found to vary as , where represents the angle
between the two optical axes, and its magnitude rapidly increases with
decreasing plate separation . For a 40 m diameter disk, made out of
either quartz or calcite, kept parallel to a Barium Titanate plate at nm, the maximum torque (at ) is of the order of
Nm. We propose an experiment to observe this torque
when the Barium Titanate plate is immersed in ethanol and the other
birefringent disk is placed on top of it. In this case the retarded van der
Waals (or Casimir-Lifshitz) force between the two birefringent slabs is
repulsive. The disk would float parallel to the plate at a distance where its
net weight is counterbalanced by the retarded van der Waals repulsion, free to
rotate in response to very small driving torques.Comment: 7 figures, submitted to Phys. Rev.
Virtual photons in imaginary time: Computing exact Casimir forces via standard numerical-electromagnetism techniques
We describe a numerical method to compute Casimir forces in arbitrary
geometries, for arbitrary dielectric and metallic materials, with arbitrary
accuracy (given sufficient computational resources). Our approach, based on
well-established integration of the mean stress tensor evaluated via the
fluctuation-dissipation theorem, is designed to directly exploit fast methods
developed for classical computational electromagnetism, since it only involves
repeated evaluation of the Green's function for imaginary frequencies
(equivalently, real frequencies in imaginary time). We develop the approach by
systematically examining various formulations of Casimir forces from the
previous decades and evaluating them according to their suitability for
numerical computation. We illustrate our approach with a simple
finite-difference frequency-domain implementation, test it for known geometries
such as a cylinder and a plate, and apply it to new geometries. In particular,
we show that a piston-like geometry of two squares sliding between metal walls,
in both two and three dimensions with both perfect and realistic metallic
materials, exhibits a surprising non-monotonic ``lateral'' force from the
walls.Comment: Published in Physical Review A, vol. 76, page 032106 (2007
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