1,721,054 research outputs found
Allevamento del suino iberico
No full textNegli ultimi anni si è sviluppata nell’opinione pubblica una sensibilità maggiore verso i problemi di tutela del benessere animale e verso la tipicità e genuinità dei prodotti. Nell’ambito di tale ottica si è avuto nel settore zootecnico un aumento dei sistemi d’allevamento alternativi a quello intensivo; un’esempio è dato dall’allevamento del Suino Iberico spagnolo, che può essere considerato, nell’ambito degli allevamenti estensivi, un’esempio unico al mondo per consistenza e volume commerciale, tale da risultare un modello per proposte di miglioramento e valorizzazione di molte realtà di allevamento di suini autoctoni italiani
A Monte-Carlo simulation of low energy photoelectron scattering in Cs2Te
No full textThe quantitative description of low kinetic energy photoelectron emission in semiconductors is still an open question. In this article a model is developed to simulate the photoexcitation and transport of low kinetic energy electrons in Cs2Te. The statistical extension of the model, by Monte Carlo trajectory calculations, gives photon energy dependent quantum yields in agreement with experimental data. This is regarded as evidence that for near threshold photoemission in Cs2Te the dominant scattering mechanism is electron-phonon, while the mean energy scattering energy loss is 5 meV and the electron mean free path is 3 nm. The spatial distribution and the time response (0.4 ps) of the photoemitted electrons are estimated
Time-frequency analysis of non-stationary signals
No full textSignals consisting of multiple frequencies and changing their amplitude while propagating in time generate in many experiments. The analysis of such signals requires special methodological approach and mathematical apparatus, which allows ascertain the main features of the signal by a signal transformation. The general method is to apply Fourier transform analysis. However, Fourier transform analysis provides actual spectra for stationary signals alone. For signals changing their characteristics over time the method of analysis that presents the signal changes in both time and frequency is required, and one of the most valid methods is wavelet transform. The present work is aimed to show the advantages of wavelet transform in comparison with FT, when signals changing their characteristics over time is necessary to investigate
Time-frequency representation of signals by wavelet transform
No full textThe aim of the data analysis is to explore the main characteristics of the signal by a signal transformation. The most commonly used way of analyzing the signals is the Fourier transform (FT). For stationary systems, where the signal properties over time do not change, the FT spectrum is easily interpreted. However, in cases where the systems change their physical properties and hence their characteristic spectrum in time, FT shows only the spectrum integrated over the acquisition time. As a consequence the modifications of the temporal signal are not directly correlated with the frequency features of the spectrum. For such non-stationary signals the method that combines the time and frequency domain analysis and hence shows the signal evolution in both time and frequency is needed. The windowed FT belongs to the family of techniques with such temporal and spectral resolution and it has been one of the first methods devised to operate in the time-frequency plane. However, windowed FT has the drawback of the fixed time-frequency resolution, because after the choice of a window function, the size of the time-frequency window is fixed. In contrary, the wavelet transform (WT) is a mathematical approach that gives the time-frequency representation of a signal with the possibility to adjust the time-frequency resolution, hence, WT may be considered as the time-frequency analysis method with an adjustable window, which is an improved alternative to the windowed FT. In the article, the advantages of WT in comparison with FT analysis are illustrated
Transient eigenmodes analysis of single-impact cantilever dynamics combining Fourier and wavelet transforms
No full textThe transient eigenmode structure of an interacting cantilever during a single impact on different surfaces evidences the excitation of higher flexural modes and low frequency oscillations. The frequency shift of the fundamental mode after the tip comes into contact with the sample surface allows calculating the tip–sample interaction stiffness and evidences the role of capillary condensation and surface wettability on the cantilever dynamics. Wavelet transforms are used to trace the origin of spectral features in the cantilever spectra and calculate force gradients of the tip–sample interaction
Wavelet cross-correlation and phase analysis of a free cantilever subjected to band excitation
Full text linkThis work introduces the concept of time-frequency map of the phase difference between the cantilever response signal and the driving signal, calculated with a wavelet cross-correlation technique. The wavelet cross-correlation quantifies the common power and the relative phase between the response of the cantilever and the exciting driver, yielding "instantaneous" information on the driver-response phase delay as a function of frequency. These concepts are introduced through the calculation of the response of a free cantilever subjected to continuous and impulsive excitation over a frequency band. © 2012 Banfi and Ferrini
Wavelet transforms to probe long- and short-range forces by thermally excited dynamic force spectroscopy
No full textThe use of wavelet transforms in thermally excited dynamic force spectroscopy allows us to gain insight into the fundamental thermodynamical properties of a cantilever's Brownian motion as well as giving a meaningful and intuitive representation of the cantilever dynamics in time and frequency caused by the interaction with long- and short-range forces. The possibility of carrying out measurements across the jump-to-contact transition without interruption, providing information on both van der Waals forces and short-range adhesion surface forces, is remarkable
Complex force dynamics in atomic force microscopy resolved by wavelet transforms
No full textThe amplitude and phase evolution of the oscillations of a cantilever after a single tip–sample impact are investigated using a cross-correlation wavelet analysis. The excitation of multiple flexural modes is evidenced and the instantaneous amplitude and phase evolution is extracted from the experimental data at all frequencies simultaneously. The instantaneous total force acting on the tip during a single impact is reconstructed. This method has general relevance for the development of an atomic force spectroscopy of single tip–sample interactions, that develop in a few oscillation cycles of the interacting cantilever eigenmodes and their harmonics
Tip-sample interactions on graphite studied in the thermal oscillation regime
No full textThermal noise is caused by random thermal excitations that result in positional fluctuations of the cantilever, thereby setting a lower limit on the force resolution of an atomic force microscope (AFM). However, thermal noise can also be utilized for measurement purposes. Here, the authors present three different approaches to exploit the information contained in the cantilever thermal motion (frequency shift, Brownian motion, and thermal mean square displacement) and some results concerning the characterization of the AFM system in the thermal driving regime. (C) 2010 American Vacuum Society
Tip-sample interactions on graphite studied using the wavelet transform
Full text linkWavelet transform analysis is applied to a thermally excited cantilever to get insights into fundamental thermodynamical properties of its motion. The shortcomings of the widely used Fourier analysis are briefly discussed to put into perspective the wavelet transform analysis, used to describe the temporal evolution of the spectral content of the thermal oscillations of a cantilever with an interacting tip. This analysis allows to retrieve the force gradients, the forces and the Hamaker constant in a measurement time of less than 40 ms
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