658 research outputs found
Low-level processing for real-time image analysis
A system that detects object outlines in television images in real time is described. A high-speed pipeline processor transforms the raw image into an edge map and a microprocessor, which is integrated into the system, clusters the edges, and represents them as chain codes. Image statistics, useful for higher level tasks such as pattern recognition, are computed by the microprocessor. Peak intensity and peak gradient values are extracted within a programmable window and are used for iris and focus control. The algorithms implemented in hardware and the pipeline processor architecture are described. The strategy for partitioning functions in the pipeline was chosen to make the implementation modular. The microprocessor interface allows flexible and adaptive control of the feature extraction process. The software algorithms for clustering edge segments, creating chain codes, and computing image statistics are also discussed. A strategy for real time image analysis that uses this system is given
Computing the distribution of the maximum in balls-and-boxes problems, with application to clusters of disease cases
We present a rapid method for the exact calculation of the cumulative
distribution function of the maximum of multinomially distributed random
variables. The method runs in time , where is the desired maximum
and is the number of variables. We apply the method to the analysis of two
situations where an apparent clustering of cases of a disease in some locality
has raised the possibility that the disease might be communicable, and this
possibility has been discussed in the recent literature. We conclude that one
of these clusters may be explained on purely random grounds, whereas the other
may not
Computing region moments from boundary representations
The class of all possible formulas for computing arbitrary moments of a region from the region's boundary is derived. The selection of a particular formula depends on the choice of an independent parameter. Several choices of this parameter are explored for region boundaries approximated by polygons. The parameter choice that minimizes computation time for boundaries represented by chain code is derived. Algorithms are presented for computing arbitrary moments for a region from a polygonal approximation of its boundary and for computing low order moments from chain encoded boundaries
Transformation design and nonlinear Hamiltonians
We study a class of nonlinear Hamiltonians, with applications in quantum
optics. The interaction terms of these Hamiltonians are generated by taking a
linear combination of powers of a simple `beam splitter' Hamiltonian. The
entanglement properties of the eigenstates are studied. Finally, we show how to
use this class of Hamiltonians to perform special tasks such as conditional
state swapping, which can be used to generate optical cat states and to sort
photons.Comment: Accepted for publication in Journal of Modern Optic
First Evidence for Wollemi Pine-type Pollen (Dilwynites: Araucariaceae) in South America
We report the first fossil pollen from South America of the lineage that includes the recently discovered, extremely rare Australian Wollemi Pine, Wollemia nobilis (Araucariaceae). The grains are from the late Paleocene to early middle Eocene Ligorio Márquez Formation of Santa Cruz, Patagonia, Argentina, and are assigned to Dilwynites, the fossil pollen type that closely resembles the pollen of modern Wollemia and some species of its Australasian sister genus, Agathis. Dilwynites was formerly known only from Australia, New Zealand, and East Antarctica. The Patagonian Dilwynites occurs with several taxa of Podocarpaceae and a diverse range of cryptogams and angiosperms, but not Nothofagus. The fossils greatly extend the known geographic range of Dilwynites and provide important new evidence for the Antarctic region as an early Paleogene portal for biotic interchange between Australasia and South America.Facultad de Ciencias Naturales y Muse
Propagation on networks: an exact alternative perspective
By generating the specifics of a network structure only when needed
(on-the-fly), we derive a simple stochastic process that exactly models the
time evolution of susceptible-infectious dynamics on finite-size networks. The
small number of dynamical variables of this birth-death Markov process greatly
simplifies analytical calculations. We show how a dual analytical description,
treating large scale epidemics with a Gaussian approximations and small
outbreaks with a branching process, provides an accurate approximation of the
distribution even for rather small networks. The approach also offers important
computational advantages and generalizes to a vast class of systems.Comment: 8 pages, 4 figure
Optimization in task--completion networks
We discuss the collective behavior of a network of individuals that receive,
process and forward to each other tasks. Given costs they store those tasks in
buffers, choosing optimally the frequency at which to check and process the
buffer. The individual optimizing strategy of each node determines the
aggregate behavior of the network. We find that, under general assumptions, the
whole system exhibits coexistence of equilibria and hysteresis.Comment: 18 pages, 3 figures, submitted to JSTA
Carbon Isotope Compositions of Terrestrial C3 Plants as Indicators of (Paleo)Ecology and (Paleo)Climate
A broad compilation of modern carbon isotope compositions in all C3 plant types shows a monotonic increase in δ13C with decreasing mean annual precipitation (MAP) that differs from previous models. Corrections for temperature, altitude, or latitude are smaller than previously estimated. As corrected for altitude, latitude, and the δ13C of atmospheric CO2, these data permit refined interpretation of MAP, paleodiet, and paleoecology of ecosystems dominated by C3 plants, either prior to 7–8 million years ago (Ma), or more recently at mid- to high latitudes. Twenty-nine published paleontological studies suggest preservational or scientific bias toward dry ecosystems, although wet ecosystems are also represented. Unambiguous isotopic evidence for C4 plants is lacking prior to 7–8 Ma, and hominid ecosystems at 4.4 Ma show no isotopic evidence for dense forests. Consideration of global plant biomass indicates that average δ13C of C3 plants is commonly overestimated by approximately 2‰
Eigenvalue density of Wilson loops in 2D SU(N) YM
In 1981 Durhuus and Olesen (DO) showed that at infinite N the eigenvalue
density of a Wilson loop matrix W associated with a simple loop in
two-dimensional Euclidean SU(N) Yang-Mills theory undergoes a phase transition
at a critical size. The averages of det(z-W), 1/det(z-W), and det(1+uW)/(1-vW)
at finite N lead to three different smoothed out expressions, all tending to
the DO singular result at infinite N. These smooth extensions are obtained and
compared to each other.Comment: 35 pages, 8 figure
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