Search results for "VIBRATION"

Environmental effects on the natural vibrations of nanoplatelets: a high pressure study.

2017

International audience; Resonant acoustic modes from ultrathin CdS colloidal nanoplatelets (NPLs) are probed under high pressure using low frequency Raman spectroscopy. In particular we focus on the characterization of the recently evidenced mass load effect that is responsible for a significant downshift of the NPL breathing frequency due to the inert mass of organic ligands. We show that a key parameter in the observation of the mass effect is whether the surrounding medium is able to support THz acoustic wave propagation, at a frequency close to that of the inorganic vibrating core. At low pressures, surface organic molecules show a single particle-like behavior and a strong mass effect …

On the ”Expanded” Local Mode Approach and Isotopic Effect (CH2D2/CH3D/CHD3) in the Methane Molecule

2010

Earlier derived, [1] - [3], for the XY2 (C2v and XY3 (C3v molecules) ”expanded local mode model” is applied to the methane-type, XH4, molecules. On the base of using os specially obtained value of the ambiguity parameter, sin gamma , simple value of all transformation coefficients, l_{N \alpha \lambda}, were obtained for the CH4 molecule. It gave us possibility, on the one hand, 1). to derive simple relations between different spectroscopic parameters (harmonic frequencies, anharmonic parameters and vibrational tetrahedral coefficients, rotational-vibrational and rotational tetrahedral coefficients) of the CH4 molecule, and, on the other hand, 2). on the base of the genegal isotopic substit…

Vibrational Spectrum of Phosphine Molecule

2004

Vibrational interactions and resonances in XY2 molecules of C2v symmetry. Algebraic application to D2S system.

2008

On the 'expanded local mode' approach applied to the methane molecule: isotopic substitution CH2D2 <--- CH4

2011

International audience; On the basis of a compilation of the 'expanded local mode' model and the general isotopic substitution theory, sets of simple analytical relations between different spectroscopic parameters (harmonic frequencies, anharmonic coefficients, ro-vibrational coefficients, different kinds of Fermi- and Coriolis-type interaction parameters) of the CH2D2 molecule are derived. All of them are expressed as simple functions of a few initial spectroscopic parameters of the mother, CH4, molecule. Test calculations with the derived isotopic relations show that, in spite of a total absence of initial information about the CH2D2 species, the numerical results of the calculations have…

Tensorial development of the rovibronic Hamiltonian and transition moment operators for octahedral molecules

2001

Abstract We present a development of the Hamiltonian, dipole moment and polarizability operators of octahedral XY 6 molecules in a degenerate electronic state. These rovibronic operators are written with the aid of a tensorial formalism derived from the one already used in Dijon in the case of molecules in a non-degenerate electronic state. Electronic operators are defined from the group theory properties. Transition moment operators are introduced in order to consider rovibronic transitions. Spectrum simulations are made thanks to a new version of the HTDS sofware [J. Quant. Spectrosc. Radiat. Transfer 66 (2000) 16] used for the calculation of rovibrational spectra.

A la découverte des odeurs

2019

Often taken for granted, the sense of smell has seldom been discussed or understood. However, since the start of the 20th Century, studies in this area have grown exponentially and today there is a greater understanding of the olfactory system – at both structural and functional levels. Scientists now concern themselves with questions about the holistic nature of our sense of smell and are investigating the role of odors in interpersonal relations, in food intake processes, in the diagnosis of certain illnesses, and many other areas. The beginnings of this knowledge are as fascinating as they are abundant and numerous disciplines are involved: psychology, physiology, genetics, neuroscience,…

Recent developments in the acoustical properties of perforated and porous materials containing dead-end pores

2017

It was shown recently in Nevers, France, Sherbrooke, Canada and Salford, UK, that porous materials with semi-opened pores or materials with open pores bearing lateral cavities or resonators at the microscopic scale of the pores can result in peculiar sound absorption properties. Various examples of these materials can be found in engineering and in everyday life including bio-based materials. The cavities and resonators can be assimilated to dead-end pores, which are opened at one end and closed at the other. The dead-end pores are known to geophysicists. We studied them more recently in the field of engineering acoustics where the saturating fluid is air. The closed ends prevent the fluid …

Numerical vibroacoustic analysis of plates with constrained-layer damping patches

2011

International audience; A numerical vibroacoustic model that can manage multilayered plates locally covered with damping patches is presented. All the layers can have an on-axis orthotropic viscoelastic behavior. Continuity of displacements and transverse shear stresses at each interface is enforced, which permits to write the entire displacement field in function of the displacements of the-common-first layer, leading to a two-dimensional plate model. The problem is then discretized by Rayleigh-Ritz's method using a trigonometric basis that includes both sine and cosine functions in order to treat various boundary conditions. The excitation can be of mechanical kind (concentrated or distri…

Nonlinear resonances and some of their applications to information processing

2021

The study of resonance phenomena in nonlinear dynamical systems has drawn considerable attention for years. The most studied nonlinear resonance is undoubtedly the famous stochastic resonance, which consists of perturbing a nonlinear system with an appropriate amount of noise to enhance the detection of a subthreshold input signal. Since the introduction of stochastic resonance in the context of climate dynamics, it was later observed that a deterministic high frequency perturbation can replace noise leading to vibrational resonance. Even if this latter resonance was investigated in many areas of science for more than two decades now, it is still receiving attentions. It is the subject of t…