Search results for " Order"
showing 10 items of 827 documents
Gravito-magnetic vacuum spacetimes: kinematic restrictions
2003
We show that there are no vacuum solutions with a purely magnetic Weyl tensor with respect to an observer submitted to kinematic restrictions involving first order differential scalars. This result generalizes previous ones for the vorticity-free and shear-free cases. We use a covariant approach which makes evident that only the Bianchi identities are used and, consequently, the results are also valid for non vacuum solutions with vanishing Cotton tensor.
Active reduction of fluctuations in fourth-order modulation instability
2012
International audience; We experimentally study the fluctuation properties of a scalar fourth-order modulation instability process obtained by pumping a photonic crystal fiber in the normal dispersion region. We observe large wavelength-dependant pulse-to-pulse fluctuations which cannot be significantly reduced by stimulating the process with a single seed. Their reduction requires two seeds slightly detuned from the maximum gain frequency in order to also stimulate the second-order modulation instability process cascaded from the fourth-order one. This concept is validated by experiments and numerical simulations.
2nu3 band of 12CF4 and its simultaneous analysis with nu3
1995
Abstract A nearly Doppler-limited spectrum of the 2ν 3 band of the 12 CF 4 molecule between 2536.0 and 2599.8 cm −1 was recorded at T = 77 K using difference-frequency laser spectroscopy. The simultaneous analysis of the ground (G.S.), ν 3 = 1, and ν 3 = 2 states was performed using an isolated band model to sixth order in the tetrahedral formalism. Fourteen hundred seventy-five transitions were assigned through J = 35 to the F 2 and E vibrational components of the ν 3 = 2 level. A total of 1864 transition frequencies were fit simultaneously (1000 2ν 3 - G.S. newly assigned transitions together with 575 ν 3 - G.S. and 289 ν 3 - ν 3 transitions already reported in the literature). The ground…
Simultaneous Analysis of the ν2 Raman and ν2 + ν6 Infrared Spectra of the SF6 Molecule
2001
High-resolution Raman spectra of the nu(2) band of SF(6) have been recorded at a temperature of 195 K (dry ice) and a pressure of 39 mbar. These spectra were analyzed using a new set of programs specially written for XY(6) molecules. These programs, called HTDS (highly spherical top data system) in reference to the set of programs called STDS (spherical top data system written for XY(4) molecules) can be freely accessible through ftp (user anonymous) at jupiter.u-bourgogne.fr or on the web at the URL http://www.u-bourgogne.fr/LPUB/shTDS.html. The study of nu(2) was made using a Hamiltonian developed through the third order. Four parameters were determined. The standard deviation obtained us…
The Intensities of Methane in the 3–5 μm Region Revisited
2001
The analysis of the linestrengths of the infrared spectrum of methane (12 and 13) in the 3-5 µm region has been revisited on the basis of new measurements from Fourier transform spectra recorded at Kitt Peak under various optical densities. A simultaneous fit of these new data with previously reported tunable difference-frequency laser data has been done. An effective transition moment model in tensorial form up to the third order of approximation within the Pentad scheme has been used. The standard deviations achieved are very close to the experimental precision: 3 and 1.5%, respectively, for the two sets of data for the (12)CH(4) molecule, representing a substantial improvement with respe…
Rotational Doppler Frequency Shift from Time‐Evolving High‐Order Pancharatnam–Berry Phase: A Metasurface Approach
2021
The Doppler frequency shift of sound or electromagnetic waves has been widely investigated in many different contexts and, nowadays, represents a formidable tool in medicine, engineering, astrophysics, and optics. Such effect is commonly described in the framework of the universal energy-momentum conservation law. In particular, the rotational Doppler effect has been recently demonstrated using light carrying orbital angular momentum. When a wave undergoes a cyclic adiabatic transformation of its Hamiltonian, it is known to acquire the so-called Pancharatnam–Berry (PB) phase. In this work, an experimental evidence of the direct connection between the high-order PB phase time evolution on th…
Control of the high harmonic generation spectra by changing the molecule-laser field relative orientation
2010
The time dependent Schrodinger equation of a homonuclear diatomic molecule in the presence of a linearly polarized laser field is numerically solved by means of a split-operator parallel code. The calculations are carried out by assuming a single active electron model with fixed nuclei; a simplified two-dimensional model of the system is used. The highly nonlinear response of the electron wave function to the laser electric field stimulates the molecule to emit electromagnetic radiation consisting of a wide plateau of odd harmonics of the laser field. It is shown that the emitted spectrum can be finely controlled by changing the angle between the laser electric field and the molecular axis;…
Event-Driven Simulation of the Dynamics of Hard Ellipsoids
2008
We introduce a novel algorithm to perform event-driven simulations of hard rigid bodies of arbitrary shape, that relies on the evaluation of the geometric distance. In the case of a monodisperse system of uniaxial hard ellipsoids,we perform molecular dynamics simulations varying the aspect-ratio X0 and the packing fraction phi. We evaluate the translational Dtrans and the rotational Drot diffusion coefficient and the associated isodiffusivity lines in the phi-X0 plane. We observe a decoupling of the translational and rotational dynamics which generates an almost perpendicular crossing of the Dtrans and Drot isodiffusivity lines. While the self intermediate scattering function exhibits stret…
Time-Independent Canonical Perturbation Theory
2001
First we consider the perturbation calculation only to first order, limiting ourselves to only one degree of freedom. Furthermore, the system is to be conservative, ∂ H∕∂ t = 0, and periodic in both the unperturbed and perturbed case. In addition to periodicity, we shall require the Hamilton–Jacobi equation to be separable for the unperturbed situation. The unperturbed problem H0(J0) which is described by the action-angle variables J0 and w0 will be assumed to be solved. Thus we have, for the unperturbed frequency: $$\displaystyle{ \nu _{0} = \frac{\partial H_{0}} {\partial J_{0}} }$$ (10.1) and $$\displaystyle{ w_{0} =\nu _{0}t +\beta _{0}\;. }$$ (10.2) Then the new Hamiltonian reads, up t…
Ethiopia as a Linguistic Area
2006
The Ethiopian linguistic area is one of the most famous linguistic areas in the world. It is characterized by phonological, grammatical, and lexical features. After summarizing the research done since 1945, this article focuses on the contradictory views concerning the validity of most of the features. For phonological and grammatical features, Ferguson (1976), which is still the most important study, is the starting point of discussion. Lexical features are dealt with only by Hayward (1991, 2000) and there has been therefore little controversy.