Search results for " vibration"
showing 10 items of 296 documents
Raman study of crystals
1997
In this work we present a polarized Raman study of single crystals for several values of the concentration made using different scattering geometries. The Raman spectra, composed of broad bands, have been fitted in accordance with a symmetry analysis which allowed us to assign the vibrational modes, and determine their frequencies and damping constants. The results are compatible with an average hexagonal symmetry for the solid solutions with x in the range . In each of the spectra we found two bands at about 590 and , probably associated with the existence of structures in the solid solutions.
A closed-form solution for natural frequencies of thin-walled cylinders with clamped edges
2016
Abstract This paper presents an approximate closed-form solution for the free-vibration problem of thin-walled clamped–clamped cylinders. The used indefinite equations of motion are classic. They derive from Reissner׳s version of Love׳s theory, properly modified with Donnell׳s assumptions, but an innovative approach has been used to find the equations of natural frequencies, based on a solving technique similar to Rayleigh׳s method, on the Hamilton׳s principle and on a proper constructions of the eigenfuctions. Thanks to the used approach, given the geometric and mechanical characteristics of the cylinder, the model provides the natural frequencies via a sequence of explicit algebraic equat…
Risk exposure to vibration and noise in the use of tracklaying tractors
2014
Human exposure to mechanical vibration may represent a significant risk factor for exposed workers in the agricultural sector, with particular reference to the operators driving tractors. Also noise in agriculture is one of the risk factors to be taken into account for the evaluation of workers health and safety. In particular, one of the major sources of discomfort for the workers operating a tractor is the noise to which they are subjected during work. In Italy, Law Decree 81/2008 has defined the obligations of vibration and noise assessment and risk management.The aim of this study is to evaluate the risk of exposure to whole-body vibration for the operator driving a tracklaying tractor …
Analytical solution for the transient response of symmetric magnetoelectric laminated beams
2010
In this paper an analytical solution is presented for the forced vibration problem of magnetoelectric symmetric laminated beams. In deriving the mathematical model the Timoshenko’s beam theory is used and the electric and magnetic fields are assumed to be quasi-static. The model is written for a magnetoelectric sensing device by applying proper magnetoelectric boundary conditions on the beam top and bottom surfaces. The model highlights that the magneto-electro-mechanical couplings affect the bending stiffness and that the magnetoelectric inputs can be treated as equivalent bending moments. Forced vibration analyses are presented to assess the reliability of the solution.
A FEM piezoelectric beam model for damping circuit analysis
2013
A finite element, developed for straight generally layered smart beam, is used to investigate vibration damping capability of circuit elements. First, the electric state is analytically condensed to kinematical quantities and the mechanical model is then written for shear deformable Timoshenko’s beam including the effects of electro-elastic couplings stacking sequence. The contributions of the external electric loads on both the equivalent stiffness properties and the equivalent mechanical boundary conditions are also taken into account. The finite element is formulated by using Hermite shape functions, which depend on parameters representative of the staking sequence through the equivalent…
"Expanded" local mode approach and isotopic effect in polyatomic molecules
2014
In this thesis, on the base of the "expanded", local mode approach and general isotopic substitution theory we obtain sets of simple analytical relations between spectroscopic parameters (harmonic frequencies, anharmonic coefficients, ro-vibrational parameters, different kinds of Fermi and Coriolis-type interaction parameters) of the CH2D2, CH3D and CHD3 molecules. All of them are expressed as simple functions of spectroscopic parameters of the mother CH4 molecule. Test calculations with the isotopic relations show that even without including prior informations about the isotopic species, numerical results of calculations are in a good agreement both with experimental data and results of ab…
Determining Key Local Vibrations in the Relaxation of Molecular Spin Qubits and Single-Molecule Magnets.
2017
To design molecular spin qubits and nanomagnets operating at high temperatures, there is an urgent need to understand the relationship between vibrations and spin relaxation processes. Herein we develop a simple first-principles methodology to determine the modulation that vibrations exert on spin energy levels. This methodology is applied to [Cu(mnt)2]2– (mnt2– = 1,2-dicyanoethylene-1,2-dithiolate), a highly coherent complex. By theoretically identifying the most relevant vibrational modes, we are able to offer general strategies to chemically design more resilient magnetic molecules, where the energy of the spin states is not coupled to vibrations.
MgO/Ag(100): confined vibrational modes in the limit of ultrathin films
2003
The vibrational modes of clean MgO films are investigated vs film thickness by means of high-resolution electron energy-loss spectroscopy. For thin films (20\char21{}30 monolayers) we observe, in accord with the literature, the Fuchs-Kliewer phonon at $677{\mathrm{cm}}^{\ensuremath{-}1}$ and the Wallis mode at $524{\mathrm{cm}}^{\ensuremath{-}1}.$ For ultrathin films standing wave optical phonons confined in the overlayer are present, whose frequencies depend strongly on film thickness. Comparison with theoretical calculations for MgO slabs on a perfect conductor shows that the experimental frequencies are lower than expected, indicating the presence of compressive stress. At and below one-…
Signatures of noise-enhanced stability in metastable state
2005
The lifetime of a metastable state in the transient dynamics of an overdamped Brownian particle is analyzed, both in terms of the mean first passage time and by means of the mean growth rate coefficient. Both quantities feature non monotonic behaviors as a function of the noise intensity, and are independent signatures of the noise enhanced stability effect. They can therefore be alternatively used to evaluate and estimate the presence of this phenomenon, which characterizes metastability in nonlinear physical systems.
Molecular materials with conducting and magnetic properties based on ET and [ M(tdas)2]x-dithiolenes
2004
Two hybrid molecular materials showing a combination of magnetic and conducting properties, the charge-transfer (ET) 2 [Fe(tdas) 2 ] (1) and (ET)Ni(tdas) 2 (2), (ET=bis(ethylenedithio) tetrathiafulvalene; M=Fe, Ni; tdas=l,2,5-thiadiazole-3,4-dithiolate) salts, are characterized by vibrational (IR and Raman) and UV-VIS-NIR spectroscopies. These studies have proved to be effective and diagnostic tools in identifying the oxidation state (partial or integer) and the packing pattern (dimers or segregated stacks) of the ET donor only, since no v(C=C) group vibration sensitive to the charge of M(tdas) 2 complexes has been observed. This is ascribed to the extensive electron-delocalization inside t…