9,958 research outputs found
Implementation of an algorithm for cylindrical object identification using range data
One of the problems in 3-D object identification and localization is addressed. In robotic and navigation applications the vision system must be able to distinguish cylindrical or spherical objects as well as those of other geometric shapes. An algorithm was developed to identify cylindrical objects in an image when range data is used. The algorithm incorporates the Hough transform for line detection using edge points which emerge from a Sobel mask. Slices of the data are examined to locate arcs of circles using the normal equations of an over-determined linear system. Current efforts are devoted to testing the computer implementation of the algorithm. Refinements are expected to continue in order to accommodate cylinders in various positions. A technique is sought which is robust in the presence of noise and partial occlusions
Local Compressibility Measurements of Correlated States in Suspended Bilayer Graphene
Bilayer graphene has attracted considerable interest due to the important
role played by many-body effects, particularly at low energies. Here we report
local compressibility measurements of a suspended graphene bilayer. We find
that the energy gaps at filling factors v = 4 do not vanish at low fields, but
instead merge into an incompressible region near the charge neutrality point at
zero electric and magnetic field. These results indicate the existence of a
zero-field ordered state and are consistent with the formation of either an
anomalous quantum Hall state or a nematic phase with broken rotational
symmetry. At higher fields, we measure the intrinsic energy gaps of
broken-symmetry states at v = 0, 1 and 2, and find that they scale linearly
with magnetic field, yet another manifestation of the strong Coulomb
interactions in bilayer graphene.Comment: 9 pages, including 4 figures and supplementary material
First Order Calculation of the Inclusive Cross Section pp to ZZ by Graviton Exchange in Large Extra Dimensions
We calculate the inclusive cross section of double Z-boson production within
large extra dimensions at the Large Hadron Collider (LHC). Using perturbatively
quantized gravity in the ADD model we perform a first order calculation of the
graviton mediated contribution to the pp to ZZ cross section. At low energies
(e.g. Tevatron) this additional contribution is very small, making it virtually
unobservable, for a fundamental mass scale above 2500 GeV. At LHC energies
however, the calculation indicates that the ZZ-production rate within the ADD
model should differ significantly from the Standard Model if the new
fundamental mass scale would be below 15000 GeV. A comparison with the observed
production rate at the LHC might therefore provide direct hints on the number
and structure of the extra dimensions.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
Quantum Secrecy in Thermal States
We propose to perform quantum key distribution using quantum correlations
occurring within thermal states produced by low power sources such as LED's.
These correlations are exploited through the Hanbury Brown and Twiss effect. We
build an optical central broadcast protocol using a superluminescent diode
which allows switching between laser and thermal regimes, enabling us to
provide experimental key rates in both regimes. We provide a theoretical
analysis and show that quantum secrecy is possible, even in high noise
situations.Comment: This version includes revisions prompted by referees comments, and
some other small editorial comment
Positive noise cross-correlations in superconducting hybrids: Roles of interfaces and interactions
Shot noise cross-correlations in normal metal-superconductor-normal metal
structures are discussed at arbitrary interface transparencies using both the
scattering approach of Blonder, Tinkham and Klapwik and a microscopic Green's
function approach. Surprisingly, negative crossed conductance in such set-ups
[R. Melin and D. Feinberg, Phys. Rev. B 70, 174509 (2004)] does not preclude
the possibility of positive noise cross-correlations for almost transparent
contacts. We conclude with a phenomenological discussion of interactions in the
one dimensional leads connected to the superconductor, which induce sign
changes in the noise cross-correlations.Comment: 15 pages, 9 figure
Perceived Visual Direction near an Occluder
When an opaque object occludes a more distant object, the two eyes often see different parts of the
distant object. Hering s laws of visual direction make an interesting prediction for this situation: the
part seen by both eyes should be seen in a different direction than the part seen by one eye. We
examined whether this prediction holds by asking observers to align a vertical monocular line
segment with a nearby vertical binocular segment. We found it necessary to correct the alignment
data for vergence errors, which were measured in a control experiment, and for monocular spatial
distortions, which were also measured in a control experiment. Settings were reasonably consistent
with Hering's laws when the monocular and binocular targets were separated by 30 arcmin or more.
Observers aligned the targets as if they were viewing them from one eye only when they were
separated by 2 arcmin; this behavior is consistent with an observation reported by Erkelens and
colleagues. The same behavior was observed when the segments were horizontal and when no
visible occluder was present. Perceived visual direction when the two eyes see different parts of a
distant target is assigned in a fashion that minimizes, but does not eliminate, distortions of the shape
of the occluded object
Is vertical disparity used to determine azimuth?
AbstractThe azimuth of a stimulus relative to the head can be determined from an extra-retinal, eye-position signal plus an estimate of the retinal eccentricity of the image. Alternatively, azimuth could be determined from retinal-image information alone. Specifically, stimulus azimuth could be estimated from two derivatives of vertical disparity: vertical size ratio (which varies with azimuth), and the horizontal gradient of vertical size ratio (a measure of distance). Here we examine the determinants of perceived azimuth in viewing conditions that, theoretically, should favor the use of vertical disparity. We find no evidence that vertical disparity is used. Perceived azimuth was determined completely by felt eye position and the retinal eccentricity of the image
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