Search results for "frequencie"
showing 10 items of 34 documents
Imaging the Local Density of States of Optical Corrals
2002
International audience; This paper reports the experimental observation, at optical frequencies, of the electromagnetic local density of states established by nanostructures corresponding to the recently introduced concept of optical corral [G. Colas des Francs et al., Phys. Rev. Lett. 86, 4950 (2001)]. The images obtained by a scanning near-field optical microscope under specific operational conditions are found in agreement with the theoretical maps of the optical local density of states. A clear functionality of detection by the scanning near-field optical microscope is thereby identified since the theoretical maps are computed without including any specific tip model.
Polarization modulation instability in a Manakov fiber system
2015
International audience; The Manakov model is the simplest multicomponent model of nonlinear wave theory: It describes elementary stable soliton propagation and multisoliton solutions, and it applies to nonlinear optics, hydrodynamics, and Bose-Einstein condensates. It is also of fundamental interest as an asymptotic model in the context of the widely used wavelength-division-multiplexed optical fiber transmission systems. However, although its physical relevance was confirmed by the experimental observation of Manakov (vector) solitons in a planar waveguide in 1996, there have in fact been no quantitative experiments confirming its validity for nonlinear dynamics other than soliton formatio…
Multiple four-wave mixing-induced modulational instability in highly birefringent fibers.
2001
Theoretical and experimental results are presented that illustrate efficient generation of new optical frequencies by means of induced modulational instability in birefringent fibers for an initially highly phase-mismatched process. Modulational instability is assisted by multiple four-wave mixing interactions. This technique relaxes the strict spectral limitations imposed by the phase-matching conditions on the signal used for frequency conversion by means of modulational instability.
Collisional broadening and shifting parameters of the RamanQbranch ofH2perturbed byN2determined from speed-dependent line profiles at high temperatur…
1996
The broadening and shifting of the {ital Q} branch of H{sub 2} diluted in N{sub 2} are studied at temperatures between 300 and 1200 K. (i) In order to account for the observed anomalies (asymmetric profiles and nonlinearity of the linewidth versus perturber concentration), the results are interpreted using a speed-dependent model in its general form. This model introduces the speed dependence of the shift and the broadening. In contrast with the previous H{sub 2}{endash}rare-gas studies, the high-temperature measurements prove the necessity to include speed-dependent broadening that was ignored in the previous studies. (ii) Concomitantly, we report as well pure H{sub 2} results including Ra…
Optical frequency combs for space applications
2016
Optical frequency comb-based high resolution laser spectroscopy has been demonstrated in space under micro-gravity on two sounding rocket based experiments. The comb has been used to simultaneously measure two different atomic transitions.
Density functional theory (DFT) prediction of structural and spectroscopic parameters of cytosine using harmonic and anharmonic approximations
2015
The applicability of popular and efficient B3LYP hybrid density functional and medium-size Pople-type basis set in combination with computationally expensive anharmonic model to obtain more accurate theoretical structure, vibrational frequencies and GIAO NMR parameters of cytosine was tested. We report on prediction of cytosine equilibrium (R e ) and rovibrationally averaged (R v ) structures and vibrational frequencies in the gas phase and DMSO solution using density functional theory combined with 6-311++G** basis set. The harmonic and anharmonic vibrational frequencies (using second-order vibrational perturbation theory, VPT2) were critically discussed. In comparison with initial harmoni…
The mass load effect on the resonant acoustic frequencies of colloidal semiconductor nanoplatelets
2016
Resonant acoustic modes of ultrathin CdS and CdSe colloidal nanoplatelets (NPLs) with varying thicknesses were probed using low frequency Raman scattering. The spectra are dominated by an intense band ascribed to the thickness breathing mode of the 2D nanostructures. The measured Raman frequencies show strong deviations with respect to the values expected for simple bare plates, all the more so as the thickness is reduced. The deviation is shown to arise from the additional mass of the organic ligands that are bound to the free surfaces of the nanoplatelets. The calculated eigen frequencies of vibrating platelets weighed down by the mass of the organic ligands are in very good agreement wit…
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…
Frequency format facilitates reasoning in simple numerical tasks.
2005
This study examined whether it is easier to reason in terms of frequencies or with percentages for simple numerical tasks. Research on probabilistic reasoning has shown that humans can draw correct inferences when problems are presented in terms of natural frequencies but not when in percentages. Whether the same effect can be observed in other numerically simple tasks which are not probabilistic was studied with 40 undergraduate students who volunteered for the experiment (13 men, 27 women; M age of 23 yr.). In a simple numerical task involving frequencies or percentages ( N = 20), their performance showed representation in frequencies facilitates the task.
A large view of CYP21 locus among Sicilians and other Populations: identification of a novel CYP21A2 variant in Sicily.
2011
Background. Several mutations in CYP21 locus cause 21-Hydroxylase Deficiency (21-OHD). The most common mutations are widespread among the different geographic areas and their frequencies have been also reported to differ among certain populations. Aim. To obtain a large view on the frequencies of the most common mutations in the CYP21 locus, in Sicily, in Mediterranean and in other major geographic areas in the worldwide. Subjects and Methods. 308 unrelated CYP21A2 alleles leading 21-OHD in Sicily were genetically typed and compared with other series previously reported in Sicily and in surrounding regions. An analysis of the frequencies of the different geographic areas was also carried ou…