323 research outputs found
Statistics of soliton-bearing systems with additive noise
We present a consistent method to calculate the probability distribution of
soliton parameters in systems with additive noise. Even though a weak noise is
considered, we are interested in probabilities of large fluctuations (generally
non-Gaussian) which are beyond perturbation theory. Our method is a further
development of the instanton formalism (method of optimal fluctuation) based on
a saddle-point approximation in the path integral. We first solve a fundamental
problem of soliton statistics governing by noisy Nonlinear Schr\"odinger
Equation (NSE). We then apply our method to optical soliton transmission
systems using signal control elements (filters, amplitude and phase
modulators).Comment: 4 pages. Submitted to PR
Nonclassical correlations in damped quantum solitons
Using cumulant expansion in Gaussian approximation, the internal quantum
statistics of damped soliton-like pulses in Kerr media are studied numerically,
considering both narrow and finite bandwidth spectral pulse components. It is
shown that the sub-Poissonian statistics can be enhanced, under certain
circumstances, by absorption, which damps out some destructive interferences.
Further, it is shown that both the photon-number correlation and the
correlation of the photon-number variance between different pulse components
can be highly nonclassical even for an absorbing fiber. Optimum frequency
windows are determined in order to realize strong nonclassical behavior, which
offers novel possibilities of using solitons in optical fibers as a source of
nonclassically correlated light beams.Comment: 15 pages, 11 PS figures (color
Statistics of polarization dependent loss in an installed long-haul WDM system.
We have made continual, multiple-day measurements of the polarization dependent loss of multiple C-band channels in an installed 1800 km terrestrial link. The PDLs of individual channels varied on the time-scale of hours, while the temporal variations of the PDLs of adjacent channels often tracked. The probability densities of the field measurements of PDL were not Maxwellian and instead were truncated, consistent with the limited number of elements in the link having appreciable PDL. A new model for the statistics of PDL in systems with few PDL elements is proposed, where a lower bound of the distribution exists if there is a dominant PDL element. The probability distributions from measurement and theory show good agreement
On the trail of medieval wolves: ancient DNA, CT-based analyses and palaeopathology of a 1000-year-old wolf cranium from the Po Valley (northern Italy)
The Middle Ages represented a crucial period for the evolutionary history of wolves (Canis lupus), marked by both significant ecosystem changes, especially through the degradation of wooded landscapes and heavy persecution, that drove this species to a dramatic demographic decline. In Europe, informative and well-documented wolf remains from the Medieval Ages are exceptionally rare and are mostly represented by teeth and postcranial elements. In this study, we describe a well-preserved wolf cranium dated to ca. 967â1157 AD from the Po Valley (northern Italy). The specimen was analysed through a multidisciplinary approach including CT-based, ancient DNA, and palaeopathological analyses. Morphological and genetic data supported the assignment of this sample to Canis lupus species. CT-based analyses indicated a typical wolf-like morphology falling into the extant variability of the medium-sized subspecies C. lupus italicus, whereas palaeopathological analyses indicated a severe periodontitis. Phylogenetic analyses showed that the Po valley wolf had a unique and never described mtDNA control region haplotype, testifying variability in the ancient Italian wolf, which has now been lost. This study provides the first comprehensive description of a wolf from the Middle Ages, adding useful information for a deeper knowledge about population dynamics, variability, and diseases of this species
Theory of quantum fluctuations of optical dissipative structures and its application to the squeezing properties of bright cavity solitons
We present a method for the study of quantum fluctuations of dissipative
structures forming in nonlinear optical cavities, which we illustrate in the
case of a degenerate, type I optical parametric oscillator. The method consists
in (i) taking into account explicitly, through a collective variable
description, the drift of the dissipative structure caused by the quantum
noise, and (ii) expanding the remaining -internal- fluctuations in the
biorthonormal basis associated to the linear operator governing the evolution
of fluctuations in the linearized Langevin equations. We obtain general
expressions for the squeezing and intensity fluctuations spectra. Then we
theoretically study the squeezing properties of a special dissipative
structure, namely, the bright cavity soliton. After reviewing our previous
result that in the linear approximation there is a perfectly squeezed mode
irrespectively of the values of the system parameters, we consider squeezing at
the bifurcation points, and the squeezing detection with a plane--wave local
oscillator field, taking also into account the effect of the detector size on
the level of detectable squeezing.Comment: 10 figure
The Gordon-Haus effect for modified NLS solitons
Random jitter in the soliton arrival time (the Gordon-Haus effect) is
analyzed for solitons being solutions of the integrable modified nonlinear
Schroedinger equation. It is shown that the mean square fluctuation of the
soliton position depends on the soliton parameters which can be properly
adjusted to suppress the Gordon-Haus jitter.Comment: LaTeX, 7 pages, 3 figures, to be published in Europhys. Let
Statistics of noise-driven coupled nonlinear oscillators:applications to systems with Kerr nonlinearity
We present exact analytical results for the statistics of nonlinear coupled oscillators under the influence of additive white noise. We suggest a perturbative approach for analysing the statistics of such systems under the action of a deterministic perturbation, based on the exact expressions for probability density functions for noise-driven oscillators. Using our perturbation technique we show that our results can be applied to studying the optical signal propagation in noisy fibres at (nearly) zero dispersion as well as to weakly nonlinear lattice models with additive noise. The approach proposed can account for a wide spectrum of physically meaningful perturbations and is applicable to the case of large noise strength
The Italian research project ROAD-NGN âOptical frequency/wavelength division multiple access techniques for next generation networks'
The paper describes the activities of the Italian national research project ROAD-NGN âOptical frequency/wavelength division multiple access techniques for next generation networksâ; the project aims to investigate and experiment new technological solutions to facilitate the migration of access systems from copper to optical fibre, and to help the integration with broadband wireless architectures, with particular interest for the backhauling of the fourth generation (4G) Long Term Evolution (LTE) networks. The approaches, based on the orthogonal frequency division multiplexing (OFDM) and wavelength division multiplexing (WDM) techniques, can enable the unbundling of the local loop (ULL) and are upgradable toward very ultra wideband systems
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Use of radioactive tracers for selection of rare earth precipitants and ignition temperatures
Variations have been found in the specific activity of ignited radioactive-labeled rare earth oxide samples. The variations appear to depend on the precipitating agents and temperatures. Using various precipitating agents and different ignition temperatures, samples of /sup 88/Y-, /sup 168/Tm-, and /sup 173/ /sup 174/Lu-labeled oxides were produced from stock solutions. Observed specific activities were compared to the known specific activities of the starting solutions. At 800/sup 0/C ignition temperatures, errors of 6% to 7% can be obtained for yttrium precipitated with 8-hydroxyquinoline or ammonia. Thulium and lutetium quinolates and cupferrates ignited at 800/sup 0/C are in error by 3 to 5%. Results show that temperatures in excess of 1000/sup 0/C are required for complete ignition of rare earth quinolates, cupferrates, hydroxides, and chlorides
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