Search results for " NOISE"
showing 10 items of 659 documents
Type I optical parametric oscillators above threshold are perfect squeezers for empty gauss-hermite modes at any pumping level
2007
A type I optical parametric oscillator pumped by a Gaussian beam above threshold and tuned to its first transverse mode family is shown to yield a perfectly squeezed, empty Gauss-Hermite mode at any pumping level.
Quantum noise properties of cavity solitons
2006
General method for studying quantum fluctuations of dissipative structures formed in nonlinear optical cavities is presented. Application to cavity soliton supported by degenerate optical parametric oscillator is presented. Squeezing and intensity fluctuations spectra are discussed.
Dynamics of a quantum particle interacting with a thermal bath and subject to an oscillating asymmetric bistable potential
2012
Exploiting the approach of the Feynman-Vernon influence functional [1] within the framework of the discrete variable representation (DVR) [2], we consider a quantum particle described by the Caldeira-Leggett model [3]. The particle, “moving” in an asymmetric bistable potential and subject to a periodical driving, interacts with a thermal bath of harmonic oscillators. In this conditions we study the dynamics of the particle by analyzing the time evolution of the populations in the DVR. Specifically we focalize on the position eigenstate located in the shallower well, i.e. metastable state, finding a non-monotonic behaviour of the corresponding population as a function of the frequency. Moreo…
Dynamics of a Driven Dissipative Quantum System
2013
We investigate the dynamics of a driven multilevel system, consisting of a particle in an asymmetric bistable potential, strongly interacting with a thermal bath according to the Caldeira-Leggett model. The populations in the discrete (position) variable representation (DVR), are obtained as solution of a Markovian approximated master equation, which is derived from a discretized path integral approach based on the Feynman-Vernon influence functional. By varying the environmental parameters (temperature and coupling strength) as well as the driving frequency and amplitude, we study the transient dynamics and stationary configuration of the system. In particular, we analyze the population of…
Transient Dynamics of a Driven Quantum Bistable System
2013
We study the transient dynamics and the asymptotic behaviour of a multilevel system in the strong dissipation regime. The system is modeled as a periodically driven quantum particle in an asymmetric double well potential, interacting with the bosonic heat bath of the Caldeira-Leggett model. The analytical approach used is non- perturbative in the particle-bath coupling and is based on a space-discretized path integral expression for the particle’s reduced density matrix. By a suitable approximation on the Feynman-Vernon influence functional a Markov-approximated master equation is obtained for the populations in the Discrete Variable Representation (DVR).
Quenching of bandgaps by flow noise.
2009
We report an experimental study of acoustic effects produced by wind impinging on noise barriers based on two‐dimensional sonic crystals with square symmetry. We found that the attenuation strength of sonic‐crystal‐bandgaps decreases for increasing values of low speed. A quenching of the acoustic bandgap appears at a certain speed value that depends of the barrier filling ratio. For increasing values of low speed, the data indicate that the barrier becomes in a sound source because of its interaction with the wind. We conclude that flow noise has paramount importance in designing acoustic barriers based on sonic crystals. [Work supported by Spanish AECI.]
The modulation transfer function and signal-to-noise ratio of different digital filters: a technical approach.
2011
The aim of this study was to illustrate the influence of digital filters on the signal-to-noise ratio (SNR) and modulation transfer function (MTF) of digital images. The article will address image pre-processing that may be beneficial for the production of clinically useful digital radiographs with lower radiation dose.Three filters, an arithmetic mean filter, a median filter and a Gaussian filter (standard deviation (SD) = 0.4), with kernel sizes of 3 × 3 pixels and 5 × 5 pixels were tested. Synthetic images with exactly increasing amounts of Gaussian noise were created to gather linear regression of SNR before and after application of digital filters. Artificial stripe patterns with defin…
Mechanically stable metal layers for ohmic and blocking contacts on CdZnTe detectors by electroless deposition
2015
CdZnTe detectors are commonly exploited for the detection of gamma rays. However, obtaining mechanical stable, low noise contacts on CdZnTe is still an issue. In particular, ohmic contacts would be preferable for high flux applications. In this work, we show that it is possible to obtain mechanical stable gold contacts by electroless deposition in methanol solution. Moreover, we show that electroless deposited nickel contacts are also mechanical stable and are good candidates for the realization of ohmic contacts on high resistivity CdZnTe crystals.
Risonanza stocastica non dinamica in una popolazione di Nezara Viridula (L.)
2009
In questo lavoro viene studiato l’effetto del rumore sul comportamento, durante il periodo di accoppiamento, di individui di Nezara viridula (L.). Analizzando la risposta di insetti maschi a segnali sotto soglia, prodotti da individui di sesso femminile, si osserva, in presenza di una sorgente esterna di rumore bianco Gaussiano, un’attivazione “comportamentale”, con un andamento non monotono in funzione dell’intensit`a di rumore, chiara indicazione della presenza di risonanza stocastica non dinamica. Lo studio `e ripetuto utilizzando una sorgente di rumore colorato. Infine, i risultati sperimentali vengono riprodotti attraverso un modello a soglia “morbida”, in cui la funzione di cross-corr…
Assessment of the Reliability of the SPAC Method in Urban Areas
2015
We have carried out several long-term measures of seismic noise with triangular arrays of broad-band seismic sensors, to investigate the reliability of the SPAC method in urban areas. We investigate the stationary and anisotropy of the microtremor wave field. We have found that the anisotropy of the microtremor wave field can be evaluated analyzing the HVNSR as function the azimuth. Furthermore, we showed as strong anisotropies in the microtremors are often observable in particular at high frequencies (> 1 Hz). We have verified as microtremors can be difficult to considered as ergodic processes, and for this reason time averaging, also even over a long periods of time, cannot replace an app…