Search results for "Stokes"
showing 10 items of 242 documents
Experimental and theoretical study of line mixing in methane spectra. III. The Q branch of the Raman ν1 band
2000
The shape of the ν1 Raman Q branch of CH4 perturbed by Ar and He at room temperature has been studied. Stimulated Raman spectroscopy (SRS) experiments have been made in the 2915–2918 cm−1 spectral region for total pressures from 0.4 to 70 atm and mixtures of ≈5% CH4 with He and Ar. Analysis of the spectra demonstrates that the shape of the Q branch is significantly influenced by line mixing and much narrower than what is predicted by the addition of individual line profiles. For the first time, a model is proposed for the calculation and analysis of the effects of collisions on the considered spectra. In this approach, the rotational part of the relaxation matrix is constructed, with no adj…
Collisional shifting and broadening coefficients for the rovibrational anisotropic lines of the ν1/2ν2 fermi dyad in CO2 gas studied by stimulated Ra…
1998
High-resolution stimulated Raman spectroscopy was applied to the study of collisional broadening and shifting for rovibrational anisotropic Raman lines of the Fermi dyad of molecular carbon dioxide. The O(J) lines of the ν1 band and the S(J) lines of the 2ν2 band were recorded at 295 K. The pressure-induced line shifts were obtained and compared with the overall shift of the high-density Raman Q-branch. A rotational quantum number dependence of the rovibrational line broadening coefficients was observed. The experimental line broadening coefficients were used in order to check the ability of two theoretical methods (random phase approximation and sum rule) for calculating the line broadenin…
Separation of selected peptides by capillary electroendoosmotic chromatography using 3 μm reversed-phase bonded silica and mixed-mode phases
1999
The retention behaviour and selectivity of selected basic, neutral and acidic peptides have been studied by capillary electroendoosmotic chromatography (CEC) with Hypersil C8, C18, Hypersil mixed-mode, and Spherisorb C18/SCX columns, 250 (335) mm x 100 microns, packed with 3 microns particles, and eluted with mobile phases composed of acetonitrile-triethylamine-phosphoric acid (TEAP) at pH 3.0 using a Hewlett-Packard Model HP3DCE capillary electrophoresis system. The selected peptides were desmopressin (D), two analogues (A and B) of desmopressin, oxytocin (O) and carbetocin (C). The peptides eluted either before or after the electroendoosmotic flow (EOF) marker, depending on the concentrat…
The dependence of circular dichroism in photoemission on the optical properties of Cs monolayers on Pt(111)
1997
We report on the dependence of dichroic photoemission excited by circularly polarised light on the angle of photon incidence. We measured the difference in the angle-resolved photoemission intensities from Cs 5p semi-core levels excited by photons of opposite helicity, which is known as CDAD. We found that the dependence of the measured differences on the angle of light incidence deviates strongly from the model of CDAD for free atoms, as expected. Using the Fresnel equations and a complex index of refraction, one finds that not only the third component but also the second component of the Stokes vector is responsible for the excitation process. Both Stokes components change sign if the ini…
Flow properties and hydrodynamic interactions of rigid spherical microswimmers.
2017
We analyze a minimal model for a rigid spherical microswimmer and explore the consequences of its extended surface on the interplay between its self-propulsion and flow properties. The model is the first order representation of microswimmers, such as bacteria and algae, with rigid bodies and flexible propelling appendages. The flow field of such a microswimmer at finite distances significantly differs from that of a point-force (Stokeslet) dipole. For a suspension of microswimmers, we derive the grand mobility matrix that connects the motion of an individual swimmer to the active and passive forces and torques acting on all the swimmers. Our investigation of the mobility tensors reveals tha…
The effect of geometrical parameters on the discharge capacity of meandering compound channels
2008
A number of methods and formulae has been proposed in the literature to estimate the discharge capacity of compound channels. When the main channel has a meandering pattern, a reduction in the conveyance capacity for a given stage is observed, which is due to the energy dissipations caused by the development of strong secondary currents and to the decrease of the main channel bed slope with respect to the valley bed slope. The discharges in meandering compound channels are usually assessed applying, with some adjustments, the same methods used in the straight compound channels. Specifically, the sinuosity of the main channel is frequently introduced to account for its meandering pattern, al…
Mesh-adaptive methods for viscous flow problem with rotation
2007
In this paper, new functional type a posteriori error estimates for the viscous flow problem with rotating term are presented. The estimates give guaranteed upper bounds of the energy norm of the error and provide reliable error indication. We describe the implementation of the adaptive finite element methods (AFEM) in the framework of the functional type estimates proposed. Computational properties of the estimates are investigated on series of numerical examples.
Luminescence of a self-trapped exciton in GeO2 crystal
1993
Abstract The self-trapped exciton (STE) is discovered in the GeO2 crystal. A PL band at 2.5 eV with a strong Stokes shift is excited only in the fundamental absorption range of GeO2 crystal with the quantum yield about 0.4 and the decay time constant 800 ± 5 μs at 80 K. The PL thermal quenching occurs at 200 K with the energy about 0.25 eV and the frequency factor 107. At 4.5 K the PL decay kinetics splits into two components with time constants 270 μs and 8000 μs, which can be due to a triplet state split in the zero magnetic field. The STE in GeO2 is very similar to a STE in SiO2.
Inelastic neutron and low-frequency Raman scattering in niobium-phosphate glasses: the role of spatially fluctuating elastic and elasto-optic constan…
2011
We investigate the low-frequency enhancement of vibrational excitations ('boson peak') in niobium-phosphate glasses through the combination of inelastic neutron and polarization-resolved Raman scattering. The spectra of these glasses reveal an enhancement of the vibrational density of states and of the cross section for spontaneous Raman scattering in the frequency range below 150?cm ? 1. A recent theoretical model that is based on fluctuating elastic and elasto-optic (Pockels) constants provides a unified description of the measured neutron and Raman spectra, including the depolarization ratio.
Raman Scattering in CuCl under Pressure
1999
Raman spectra of CuCl were measured under hydrostatic pressures up to 14 GPa at low temperatures (T = 5 K). The anomaly in the Raman lineshape of zincblende CuCl at frequencies near the transverse-optic (TO) mode, which consists of a broad structure with several maxima, disappears at a pressure near 3 GPa. This effect is well reproduced by a model calculation of the anharmonic coupling of the TO mode to acoustic two-phonon states (Fermi resonance). Alternative interpretations of the TO Raman anomaly in terms of local vibrational modes of Cu atoms in off-center positions are not supported by the present results. Raman spectra indicate the existence of the phase CuCl-IIa in a narrow pressure …