442 research outputs found
Factorizing numbers with classical interference: several implementations in optics
Truncated Fourier, Gauss, Kummer and exponential sums can be used to
factorize numbers: for a factor these sums equal unity in absolute value,
whereas they nearly vanish for any other number. We show how this factorization
algorithm can emerge from superpositions of classical light waves and we
present a number of simple implementations in optics
Dispersion force for materials relevant for micro and nanodevices fabrication
The dispersion (van der Waals and Casimir) force between two semi-spaces are
calculated using the Lifshitz theory for different materials relevant for micro
and nanodevices fabrication, namely, gold, silicon, gallium arsenide, diamond
and two types of diamond-like carbon (DLC), silicon carbide, silicon nitride
and silicon dioxide. The calculations were performed using recent experimental
optical data available in the literature, usually ranging from the far infrared
up to the extreme ultraviolet bands of the electromagnetic spectrum. The
results are presented in the form of a correction factor to the Casimir force
predicted between perfect conductors, for the separation between the
semi-spaces varying from 1 nanometre up to 1 micrometre. The relative
importance of the contributions to the dispersion force of the optical
properties in different spectral ranges is analyzed. The role of the
temperature for semiconductors and insulators is also addressed. The results
are meant to be useful for the estimation of the impact of the Casimir and van
der Waals forces on the operational parameters of micro and nanodevices
Lamb Shift of 3P and 4P states and the determination of
The fine structure interval of P states in hydrogenlike systems can be
determined theoretically with high precision, because the energy levels of P
states are only slightly influenced by the structure of the nucleus. Therefore
a measurement of the fine structure may serve as an excellent test of QED in
bound systems or alternatively as a means of determining the fine structure
constant with very high precision. In this paper an improved analytic
calculation of higher-order binding corrections to the one-loop self energy of
3P and 4P states in hydrogen-like systems with low nuclear charge number is
presented. A comparison of the analytic results to the extrapolated numerical
data for high ions serves as an independent test of the analytic
evaluation. New theoretical values for the Lamb shift of the P states and for
the fine structure splittings are given.Comment: 33 pages, LaTeX, 4 tables, 4 figure
Time evolution of non-Hermitian Hamiltonian systems
We provide time-evolution operators, gauge transformations and a perturbative
treatment for non-Hermitian Hamiltonian systems, which are explicitly
time-dependent. We determine various new equivalence pairs for Hermitian and
non-Hermitian Hamiltonians, which are therefore pseudo-Hermitian and in
addition in some cases also invariant under PT-symmetry. In particular, for the
harmonic oscillator perturbed by a cubic non-Hermitian term, we evaluate
explicitly various transition amplitudes, for the situation when these systems
are exposed to a monochromatic linearly polarized electric field.Comment: 25 pages Latex, 1 eps figure, references adde
Action Recognition with a Bio--Inspired Feedforward Motion Processing Model: The Richness of Center-Surround Interactions
International audienceHere we show that reproducing the functional properties of MT cells with various center--surround interactions enriches motion representation and improves the action recognition performance. To do so, we propose a simplified bio--inspired model of the motion pathway in primates: It is a feedforward model restricted to V1-MT cortical layers, cortical cells cover the visual space with a foveated structure, and more importantly, we reproduce some of the richness of center-surround interactions of MT cells. Interestingly, as observed in neurophysiology, our MT cells not only behave like simple velocity detectors, but also respond to several kinds of motion contrasts. Results show that this diversity of motion representation at the MT level is a major advantage for an action recognition task. Defining motion maps as our feature vectors, we used a standard classification method on the Weizmann database: We obtained an average recognition rate of 98.9%, which is superior to the recent results by Jhuang et al. (2007). These promising results encourage us to further develop bio--inspired models incorporating other brain mechanisms and cortical layers in order to deal with more complex videos
A multistep process for the dispersal of a Y chromosomal lineage in the Mediterranean area
Tn this work we focus on a microsatellite-defined Y-chromosomal lineage (network 1.2) identified by us and reported in previous studies, whose geographic distribution and antiquity appear to be compatible with the Neolithic spread of farmers. Here, we set network 1.2 in the Y-chromosomal phylogenetic tree, date it with respect to other lineages associated with the same movements by other authors, examine its diversity by means of tri- and tetranucleotide loci and discuss the implications hi reconstructing the spread of this group of chromosomes in the Mediterranean area. Our results define a tripartite phylogeny wit-bin HG 9 (Rosser et al. 2000) with the deepest branching defined by alleles T (Haplogroup Eu 10) or G (Haplogroup Eu9) at M172 (Semino et al. 2000), and a subsequent branching within Eu9 defined by network 1.2. Population distributions of HG 9 and network 1.2 show that their occurrence in the surveyed area is not due to the spread of people from a single parental population but, rather, to a process punctuated by at least two phases. Our data identify the wide area of the Balkans, Aegean and Anatolia as the possible homeland harbouring the largest variation within network 1.2. The use of recently proposed tests based on the stepwise mutation model suggests that its spread was associated to a population expansion, xvith a high rate of male gene flow in the Turkish Greek area
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