Search results for "VIBRATION"
showing 10 items of 823 documents
Random vibration of linear and nonlinear structural systems with singular matrices: A frequency domain approach
2017
Abstract A frequency domain methodology is developed for stochastic response determination of multi-degree-of-freedom (MDOF) linear and nonlinear structural systems with singular matrices. This system modeling can arise when a greater than the minimum number of coordinates/DOFs is utilized, and can be advantageous, for instance, in cases of complex multibody systems where the explicit formulation of the equations of motion can be a nontrivial task. In such cases, the introduction of additional/redundant DOFs can facilitate the formulation of the equations of motion in a less labor intensive manner. Specifically, relying on the generalized matrix inverse theory, a Moore-Penrose (M-P) based f…
A passive stabilization solution for camera embedded onboard small planes
2014
Embedded camera is becoming democratized in personal uses like sport. Thus the need for a stabilized video leads to a development of dedicated stabilized systems. However, in professional uses like video protection, stabilization solutions are not yet common. Moreover such a system needs to fit application specific requirements in term of size, weight, amplitude and frequency response.
Characterization of the dynamic behaviour of flax fibre reinforced composites using vibration measurements
2017
International audience; Experimental and numerical methods to identify the linear viscoelastic properties of flax fibre reinforced epoxy (FFRE) composite are presented in this study. The method relies on the evolution of storage modulus and loss factor as observed through the frequency response. Free-free symmetrically guided beams were excited on the dynamic range of 10 Hz to 4 kHz with a swept sine excitation focused around their first modes. A fractional derivative Zener model has been identified to predict the complex moduli. A modified ply constitutive law has been then implemented in a classical laminates theory calculation (CLT) routine.
Determination of dynamic properties of flax fibres reinforced laminate using vibration measurements
2017
International audience; Experimental and numerical methods to identify the linear viscoelastic properties of flax fibre reinforced polymer (FFRP) composite are presented in this study. The method relies on the evolution of storage modulus and loss factor as observed through the frequency response. Free-free symmetrically guided beams were excited in the dynamic range of 10 Hz to 4 kHz with a swept sine excitation focused around their first modes. A fractional derivative Zener model has been identified to predict the complex moduli. A modified ply constitutive law has been then implemented in a classical laminates theory calculation (CLT) routine. Overall, the Zener model fitted the experime…
Stimulated Raman-Spectroscopy of the Q-Branch of Nitrogen at High Pressure - Collisional Narrowing and Shifting in the 150-6800 Bar Range at Room Tem…
1992
0026-8976; The Raman Q branch of N2 has been recorded at room temperature in the pressure range 150-6800 bar, which corresponds to densities from 135 to 800 amagat. In this domain, the Raman Q branch profile is mainly determined by the well-known collisional narrowing. The experimental data have been obtained by means of a high resolution stimulated Raman spectrometer. The linewidth and line shift of the band have been accurately measured as functions of the density, and their density dependences have been fitted by polynomials. The minimum of the linewidth and the maximum of the red shift have been clearly observed at respectively 735.8 and 532.3 amagat. The lineshape was found to be Loren…
GUI Implementation of VCDtools, A Program to Analyze Computed Vibrational Circular Dichroism Spectra
2020
As computing power increases, vibrational circular dichroism (VCD) calculations on molecules of larger sizes and complexities become possible. At the same time, the spectra resulting from these computations become increasingly more cumbersome to analyze. Here, we describe the GUI implementation into the Amsterdam Density Functional (ADF) software package of VCDtools, a toolbox that provides a user-friendly means to analyze VCD spectra. Key features are the use of the generalized coupled oscillator analysis methods, as well as an easy visualization of the atomic electric and magnetic transition dipole moments which together provide detailed insight in the origin of the VCD intensity. Using s…
UV laser induced photolysis of glycolic acid isolated in argon matrices
2021
The photochemistry of matrix-isolated glycolic acid, induced by UV light, was studied by FTIR spectroscopy and B3LYPD3/6-311++G(3df,3pd) calculations. Several decomposition pathways were found to take place upon 212 nm and 226 nm wavelengths irradiation. A number of complexes formed between photoproducts were identified, among them those of formaldehyde with water, carbon monoxide and carbon dioxide as well as the H2O-CO complexes. The structure and spectroscopic assignment of the photoproducts were made comparing the experimental results with the theoretical predictions and available literature data. The observed formation of different complexes indicates various pathways for their formati…
Large-scale ab initio modelling of defects in perovskites: Fe impurity in SrTiO3
2002
Abstract Using the unrestricted Hartree–Fock method and supercells containing up to 160 atoms, we calculated the energy level positions in the gap and atomic geometry for the Fe4+ impurity substituting for a host Ti atom in SrTiO3. In agreement with experiment, the high-spin (S=2) state is much lower in energy than the zero-spin state. The energy level positions strongly depend on the asymmetric displacement mode of the six nearest O ions which is a combination of the Jahn–Teller and breathing modes. A considerable covalent bonding between the Fe ion and the four nearest O ions takes place.
Femtosecond time resolved coherent anti-Stokes Raman spectroscopy: Experiment and modelization of speed memory effects on H2-N2 mixtures in the colli…
2005
194317; With the aim of temperature diagnostic, femtosecond time-resolved CARS (coherent anti-Stokes Raman spectroscopy) is applied to probe H2 in H2-N2 mixtures. In a first part, a Lorentzian profile is used to model the femtosecond CARS response. A difference between the experimental broadening and the expected one is observed in the collision regime. The observed broadening increases strongly in an inhomogeneous way with respect to the perturber concentration. This is of considerable importance for temperature measurements. In a second part, we show that in the collision regime, this inhomogeneous broadening is due to the speed dependence of the collisional parameters and the memory effe…
Membrane Structure of Aquaporin Observed with Combined Experimental and Theoretical Sum Frequency Generation Spectroscopy
2021
High-resolution structural information on membrane proteins is essential for understanding cell biology and for the structure-based design of new medical drugs and drug delivery strategies. X-ray diffraction (XRD) can provide angstrom-level information about the structure of membrane proteins, yet for XRD experiments, proteins are removed from their native membrane environment, chemically stabilized, and crystallized, all of which can compromise the conformation. Here, we describe how a combination of surface-sensitive vibrational spectroscopy and molecular dynamics simulations can account for the native membrane environment. We observe the structure of a glycerol facilitator channel (GlpF)…