Rotational Dependence Research Articles

Lattice and polarizability mediated spin activity in EuTiO3

EuTiO3 is shown to exhibit novel strong spin–charge–lattice coupling deep in the paramagnetic phase. Its existence is evidenced by an, until now, unknown response of the paramagnetic susceptibility at temperatures exceeding the structural phase transition temperature TS = 282 K. The ‘extra’ features in the susceptibility follow the rotational soft zone boundary mode temperature dependence above and below TS. The theoretical modeling consistently reproduces this behavior and provides reasoning for the stabilization of the soft optic mode other than quantum fluctuations.

Simultaneous Evaluation of Multiple Rotationally Excited States of H3+, H3O+, and CH5+ Using Diffusion Monte Carlo

An extension to diffusion Monte Carlo (DMC) is proposed for simultaneous evaluation of multiple rotationally excited states of fluxional molecules. The method employs an expansion of the rotational dependence of the wave function in terms of the eigenstates of the symmetric top Hamiltonian. Within this DMC approach, each walker has a separate rotational state vector for each rotational state of interest. The values of the coefficients in the expansion of the rotational state vector associated with each walker, as well as the locations of the walkers, evolve in imaginary time under the action of a propagator based on the imaginary-time time-dependent Schrödinger equation. The approach is first applied to H3(+), H2D(+), and H3O(+) for which the calculated energies can be compared to benchmark values. For low to moderate values of J the DMC results are found to be accurate to within the evaluated statistical uncertainty. The rotational dependence of the vibrational part of the wave function is also investigated, and significant rotation–vibration interaction is observed. Based on the successful application of this approach to H3(+), H2D(+), and H3O(+), the method was applied to calculations of the rotational energies and wave functions for CH5(+) with v = 0 and J ≤ 10. Based on these calculations, the rotational energy progression is shown to be consistent with that for a nearly spherical top molecule, and little evidence of rotation–vibration interaction is found in the vibrational wave function.

Magnetic field induced nutation of exciton-polariton polarization in (Cd,Zn)Te crystals

We study the polarization dynamics of exciton-polaritons propagating in sub-mm thick (Cd,Zn)Te bulk crystals using polarimetric time-of-flight techniques. The application of a magnetic field in Faraday geometry leads to synchronous temporal oscillations of all Stokes parameters of an initially linearly or circularly polarized, spectrally broad optical pulse of 150 fs duration propagating through the crystal. Strong dispersion for photon energies close to the exciton resonance leads to stretching of the optical pulse to a duration of 200$-$300 ps and enhancement of magneto-optical effects such as the Faraday rotation and the non-reciprocal birefringence. The oscillation frequency of the exciton-polariton polarization increases with magnetic field $B$, reaching 10 GHz at $B\sim 5$T. Surprisingly, the relative contributions of Faraday rotation and non-reciprocal birefringence undergo strong changes with photon energy, which is attributed to a non-trivial spectral dependence of Faraday rotation in the vicinity of the exciton resonance. This leads to polarization nutation of the transmitted optical pulse in the time domain. The results are well explained by a model that accounts for Faraday rotation and magneto-spatial dispersion in zinc-blende crystals. We evaluate the exciton $g$-factor $|g_{\rm exc}|=0.2$ and the magneto-spatial constant $V= 5 \times 10^{-12}$ eVcm$\textup{T}^{-1}$.

Tables of radiative transition probabilities for the main diatomic molecular systems of OH, CH, CH+, CO and CO+ occurring in CO–H2 syngas-type plasma

This paper focuses on the calculation of the radiative transition probabilities for the main diatomic molecules contributing to the discrete radiation of CO–H2 syngas plasma. We propose extensive tables of rovibrational transition probabilities for the main electronic systems of OH, CH, CH+, CO and CO+. The rotational dependence of the nuclear wave-functions was included in our calculations to take into account the coupling between the rotational and vibrational motions. References are also given to data for O2, C2 and H2 molecules already published in the literature. The calculations were performed using the Rydberg–Klein–Rees (RKR) inversion procedure for the reconstruction of the potential-energy curves and an improved Numerov-type method was used to obtain the rovibrational wave-functions by solving the radial Schrödinger equation. We rigorously selected the most up-to-date equilibrium spectroscopic constants for the RKR procedure and the most accurate electronic transition moment functions (ETMF) available in the literature. The results obtained with this procedure were systematically validated by comparison with available experimental observations.

THE ANTICORRELATED NATURE OF THE PRIMARY AND SECONDARY ECLIPSE TIMING VARIATIONS FOR THEKEPLERCONTACT BINARIES

We report on a study of eclipse timing variations in contact binary systems, using long-cadence lightcurves in the Kepler archive. As a first step, 'observed minus calculated' (O-C) curves were produced for both the primary and secondary eclipses of some 2000 Kepler binaries. We find ~390 short-period binaries with O-C curves that exhibit (i) random-walk like variations or quasi-periodicities, with typical amplitudes of +/- 200-300 seconds, and (ii) anticorrelations between the primary and secondary eclipse timing variations. We present a detailed analysis and results for 32 of these binaries with orbital periods in the range of 0.35 +/- 0.05 days. The anticorrelations observed in their O-C curves cannot be explained by a model involving mass transfer, which among other things requires implausibly high rates of ~0.01 M_sun per year. We show that the anticorrelated behavior, the amplitude of the O-C delays, and the overall random-walk like behavior can be explained by the presence of a starspot that is continuously visible around the orbit and slowly changes its longitude on timescales of weeks to months. The quasi-periods of ~50-200 days observed in the O-C curves suggest values for k, the coefficient of the latitude dependence of the stellar differential rotation, of ~0.003-0.013.

Vortex dynamics in cubic-quintic Bose-Einstein condensates

We study vortex dynamics in a trapped Bose-Einstein condensate with tunable two- and three-body interactions. The dynamics is governed by two-dimensional cubic-quintic Gross-Pitaevskii equation. A time-dependent variational method has been used to obtain critical rotational frequency and surface mode frequency analytically and are compared with numerical simulation results. An imaginary time propagation method and Crank-Nicolson scheme for discretization have been used for numerical simulation. The numerically calculated average value of the angular momentum per particle shows very clearly its dynamical relation with the time development of the vortex formation. The rotational frequency dependence of the variation of average value of the angular momentum per particle with time shows that vortices form much faster in time for higher rotational frequency. Similarly, the vortex forms much faster in time with an increase of the strength of the repulsive three-body interaction. The simulation of the vortex lattice formation in the condensate shows that the presence of the three-body interactions does not alter the vortex lattice pattern but it helps in the shape deformations of the condensate thereby leading to vortex lattice formation. Likewise, the three-body interactions enable the vortex lattice formation in Bose-Einstein condensates even with attractive two-body interactions and in purely quintic BEC.

Vibrational dependence of an intermolecular potential for H2O–He system

The intermolecular interaction potential, taken as the sum of pair potentials which, in turn, were modeled by the Lennard–Jones potential has been determined by means of nonlinear least squares fitting its parameters to the experimental data on the lines broadening (γ) and shift (δ) coefficients. The data on γ and δ for nine vibration bands ν1, ν3, 2ν2, ν1+ν2, ν2+ν3, 2ν1, ν1+ν3, 2ν2+ν3 and ν1+ν2+ν3 have been obtained from the analysis of the H2O–He absorption spectra, recorded from 3000 to 9000cm−1 with help of IFS 125HR Fourier spectrometer at room temperature, spectral resolution of 0.01cm−1 and in wide pressure range of He. Additionally we use literature data for rotational band (∼180GHz) and ν2 band (1850–2140cm−1). The vibrational and rotational dependence of the potential parameters as well as the temperature dependence of the calculated lines broadening coefficients have been demonstrated.

Effect of molecular-orbital rotations on ground-state energies in the parametric two-electron reduced density matrix method

Different sets of molecular orbitals and the rotations connecting them are of great significance in molecular electronic structure. Most electron correlation methods depend on a reference wave function that separates the orbitals into occupied and unoccupied spaces. Energies and properties from these methods depend upon rotations between the spaces. Some electronic structure methods, such as modified coupled electron pair approximations and the recently developed parametric two-electron reduced density matrix (2-RDM) methods [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], also depend upon rotations between occupied orbitals and rotations between unoccupied orbitals. In this paper, we explore the sensitivity of the ground-state energies from the parametric 2-RDM method to rotations within the occupied space and within the unoccupied space. We discuss the theoretical origin of the rotational dependence and provide computational examples at both equilibrium and non-equilibrium geometries. We also study the effect of these rotations on the size extensivity of the parametric 2-RDM method. Computations show that the orbital rotations have a small effect upon the parametric 2-RDM energies in comparison to the energy differences observed between methodologies such as coupled cluster and parametric 2-RDM. Furthermore, while the 2-RDM method is rigorously size extensive in a local molecular orbital basis set, calculations reveal negligible deviations in nonlocal molecular orbital basis sets such as those from canonical Hartree-Fock calculations.

Moment – rotation dependence under fire conditions for steel beam-to-column joint with known flexibility

Simplified methodology helpful in a reliable specification of moment - rotation dependences characterizing the steel beam-to-column joint flexibility under fully developed fire conditions is presented and discussed in detail. The shape of identified dependences changes with the temperature increase of the members connected in the considered joint. The analogous relation, known a priori and determined for examined joint being under persistent design situation, is adopted as the reference dependence specified on the basis of the classical component approach. In the presented paper the alternative calculation technique, recommended by the authors in this field, deals with the replacement of such reference relation by another one resulted from the use of Richard – Abbott formal model. Furthermore, the additional approach, taken from the standard PN-EN 1993-1-8, is examined for comparative purposes. To transform such input dependence, related to the room member temperature, into the case of fully developed fire scenario it is firstly approximated by suitable segmental curve and afterwards the relative reduction ratios referring to the steel elasticity modulus as well as to the steel yield point, the joint is made of, are taken into consideration. As a result, a number of the requested relations is obtained, differentiated dependently on the assumed member temperature.

Argon-Induced Pressure Broadening, Shifting, and Narrowing in the CN A2Π–X2Σ+ (1–0) Band

Selected isolated rotational transitions in the 1-0 band of the red A(2)Π-X (2)Σ(+) system in CN have been recorded with transient frequency modulation spectroscopy as a function of argon pressure up to 0.2 atm at room temperature. Line shapes were fit using Fourier transforms of a parametrized time correlation function, including Doppler and velocity-dependent collisional broadening, and collisional shifts. Deviations from Voigt line shapes can be equally well fit by modeling the narrowing with a speed-dependent collision model or with a velocity-changing collisional narrowing model. Pressure broadening coefficients were observed with little rotational state dependence, in the range of 0.070-0.075 cm(-1) atm(-1). In contrast, stronger and qualitatively different rotational state dependences are observed for both pressure-dependent blue shift coefficients and the narrowing parameters. No asymmetry in the pressure broadened lines was observed.

Theoretical self-broadening and self-shifting coefficients of 12C2H2 transitions in the 3ν5, (2ν4 + ν5)І and (2ν4 + ν5)ІІ bands

Using a semi-classical model based upon the Robert and Bonamy formalism, self-broadening and self-shifting coefficients of 12C2H2 have been calculated for transitions belonging to the P, Q and R branches of the 3ν5, (2ν4+ν5)І and (2ν4+ν5)ІІ cold bands near the 5μm region. The intermolecular potential used in this work includes, in addition to the overwhelming electrostatic interactions, a Tipping–Herman potential. Such a calculation leads to satisfactory agreement with measurements from literature.For the studied bands, the theoretical results reproduce the experimental rotational dependence of the self-broadening and self-shifting coefficients.The self-broadening coefficients show the predominance of the quadrupole–quadrupole contributions, especially for middle J values.

Line-mixing effect on NH3 line intensities

Line intensities belonging to nine branches of the ν2, 2ν2 and ν4 vibrational bands of ammonia have been measured between 1000 and 2000cm−1. The laboratory spectra at room temperature (T=295K) were recorded using a high-resolution Fourier transform spectrometer Bruker IFS 120 HR.More than 460 lines with J≤12 were analyzed using a non-linear least-squares multi-pressure fitting procedure. The fits were performed with and without including the line mixing effects using 11 experimental spectra recorded at different pressures of pure NH3. On average the line intensities uncertainty is estimated to be 2%. The dependence of the line intensities on the J and K quantum numbers is discussed. The effect of line mixing on the line intensities is analyzed as a function of the rotational quantum numbers, of the branches, and of the bands.On average the values of line intensities obtained in the ν4 band when taking into account line mixing have been found to be 6% smaller than those obtained using the Voigt profile.The transition dipole moments squared, determined for each line from the measured intensities, exhibit significant rotational dependencies which are mainly caused by vibration–rotation interactions. These moments are discussed as a function of vibrational and rotational states. Finally the measurements are compared with previous measurements and with values from spectroscopic databases.The whole set of line intensities and transition dipole moments are given as supplementary data for use in spectroscopic databases.

Description of optical properties of cholesteric photonic liquid crystals based on Maxwell equations and Kramers-Kronig relations

Transmission spectra and rotation of the plane of polarization of light were measured on perfect samples of cholesteric liquid crystal. We found peculiarities of the spectral dependence of rotation of the plane of polarization related to Pendell\"osung oscillations that were predicted theoretically but never observed experimentally. The experimental data are well described by expressions based on an analytical solution of the Maxwell equations. An approach based on fundamental Kramers-Kronig relations is used to describe the optical properties of the photonic crystal. It is shown that the rotatory power of cholesterics consists of two parts: one of them is related to the diffraction-induced circular dichroism whereas the other one originates from the tails of the Mauguin rotation of the plane of light polarization.

Magnetic moment of a single metal nanoparticle determined from the Faraday effect

Optical properties of a composite material made of ferromagnetic metal nanoparticles embedded in a dielectric host are studied. We constructed an effective dielectric tensor of the composite material taking into account the orientational distribution of nanoparticle magnetic moments in external magnetic field. A nonlinear dependence of the optical rotation on magnetic field resulting from the reorientation of nanoparticles is demonstrated. The theoretical findings were applied to the magneto-optical experimental data of cobalt ferromagnetic nanoparticles embedded in a dielectric liquid host. The dependence of the Faraday rotation on Co-based ferromagnetic nanoparticles was measured as a function of the external magnetic field, varying the size of nanoparticles and the wavelength of light. The proposed approach enables quantitative determination of the magnetic moment and the plasma frequency of a single nanoparticle, and from this the size of the nonmagnetic shell of magnetic nanoparticles.

Line broadening, shifting and mixing parameters of OCS perturbed by O2 in the ν3 + ν2 − ν2 and 5ν2 − ν2 bands

Molecular spectroscopic parameters are useful for the interpretation of high-resolution infrared spectra of gaseous species in the Earth’s atmosphere and those of giant planets.In this work line broadening, shifting and mixing parameters have been measured for the ν3+ν2−ν2 and 5ν2−ν2 bands of the primary isotopologue of carbonyl sulfide (16O12C32S), perturbed by O2 at room temperature. Measurements have been made using a high-resolution Fourier transform spectrometer (Bruker IFS125HR, resolution=0.004cm−1) at the LISA Laboratory in France. A total of six pressures between 5.80 and 83.2Torr of O2 perturbing gas were recorded. The measurements cover the P and R branches of the studied bands, located in the 5μm spectral region. The line broadening, shifting and mixing parameters were derived using a multi-pressure fitting method, applied to the measured shapes of the lines, including line-mixing effects.The results are compared with values calculated using a semi-classical model based on the Robert and Bonamy formalism that reproduces rather well the observed m rotational dependence of the O2 broadening coefficients.

Rotational threshold in global numerical dynamo simulations

Abstract Magnetic field observations of low-mass stars reveal an increase of magnetic activity with increasing rotation rate. The so-called activity–rotation relation is usually attributed to changes in the underlying dynamo processes generating the magnetic field. We examine the dependence of the field strength on rotation in global numerical dynamo models and interpret our results on the basis of energy considerations. In agreement with the scaling law proposed by Christensen and Aubert, the field strength in our simulations is set by the fraction of the available power used for the magnetic field generation. This is controlled by the dynamo efficiency calculated as the ratio of ohmic to total dissipation in our models. The dynamo efficiency grows strongly with increasing rotation rate at a Rossby number of 0.1 until it reaches its upper bound of 1 and becomes independent of rotation. This gain in efficiency is related to the strong rotational dependence of the mean electromotive force in this parameter regime. For multipolar models at Rossby numbers clearly larger than 0.1, on the other hand, we do not find a systematic dependence of the field strength on rotation. Whether the enhancement of the dynamo efficiency found in our dipolar models explains the observed activity–rotation relation needs to be further assessed.

Determination of Very Rapid Molecular Rotation by Using the Central Electron Paramagnetic Resonance Line

Picosecond rotational correlation times of perdeuterated tempone (PDT) are found in alkane and aromatic liquids by directly using the spectral width of the central electron paramagnetic resonance line. This is done by mathematically eliminating the nonsecular spectral density from the spectral parameter equations, thereby removing the need to assume a particular form for it. This is preferable to fitting a constant correction factor to the spectral density, because such a factor does not fit well in the low picosecond range. The electron-nuclear spin dipolar interaction between the probe and solvent is shown to be negligible for the very rapid rotation of PDT in these liquids at the temperatures of the study. The rotational correlation times obtained with the proposed method generally agree to within experimental uncertainty with those determined by using the traditional parameters. Using the middle line width offers greater precision and smoother trends. Previous work with the central line width is discussed, and past discrepancies are explained as possibly resulting from residual inhomogeneous broadening. The rotational correlation time almost forms a common curve across all of the solvents when plotted with respect to isothermal compressibility, which shows the high dependence of rotation on liquid free volume.

010] uniaxial-anisotropy induced asymmetry of magnetic reversal in (Ga,Mn)As

We investigate the asymmetric magnetic rotation arising from [010] uniaxial anisotropy in (Ga,Mn)As thin films by measuring the planar Hall effect, with the Hall bars fabricated along [110] direction. Two modes, angle-scan and field-scan, are utilized to do the measurements, both of which show remarkably asymmetric rotations. This phenomenon is found to arise from the minimal [010] uniaxial anisotropy, which is commonly overshadowed by its strong cubic anisotropy counterpart. Besides, we also measure the temperature and film thickness dependence of asymmetric rotation, showing a more remarkable behavior with the increase of temperature or thickness. The direct demonstration of [010] uniaxial anisotropy by an electrical fashion provides useful information for designing electrically programmable memory and logic device on the basis of (Ga,Mn)As.

Effect of tungsten carbide in carbon Pt catalyst support on electrochemical oxygen reduction in acid solution

Tungsten carbide was synthesized by calcination of carbon cryogel with embedded tungsten in a form of metatungstate. This material was used as a support for Pt nanoparticles. XRD pattern of W-C support indicates the presence of WC, W2C, and unreacted W, as well as graphitized carbon. According to the previous TEM analysis of W-C support, it contains particles with core-shell structure, where W particle was covered with the shell of a mixture of WC and W2C. The average Pt grain size calculated from XRD pattern was about 6 nm. Cyclic voltammogram of W-C support was recorded within potential range relevant for its application as a catalyst support in fuel cells. Pair of anodic/cathodic peaks close to the negative potential limit could be ascribed to the intercalation of hydrogen within hydrous tungsten oxide, which is always present on the surface of WC in aqueous solutions. Cyclic voltammogram of Pt/W-C indicated that tungsten oxide species are present on tungsten carbide shell as well as on the surface of Pt nanoparticles. Pt surface is only partially covered by hydrous tungsten oxide. Hydrogen intercalation in hydrous tungsten oxide is enhanced in the presence of Pt nanoparticles. Also, the presence of hydrated tungsten oxide leads to the decrease of OH chemisorbed on Pt surface. Stripping of underpotentially deposited copper was used for the assessment of Pt surface area and the specific surface area of Pt was estimated to 41 m2 g-1. Electrochemical oxygen reduction reaction was examined on the synthesized Pt/W-C catalyst and compared with the results on the commercial Pt/C catalyst. It was found that the current densities at Pt/W-C are almost double as those on Pt/C. The Tafel plots for both catalysts are characterized with two Tafel slopes: -0.060 V dec-1 at low current densities, and -0.120 V dec-1 at high current densities. From the rotational dependence of the reaction rate, it was found that oxygen reduction on both Pt/W-C and Pt/C follows the first order kinetics with respect to O2 and that four electrons are transferred per O2 molecule. The results show that the presence of tungsten carbide in support material i.e. hydrous tungsten oxide on Pt surface, leads to promotion of oxygen reduction on the Pt/W-C catalyst. It was assumed that oxophilic hydrated tungsten oxide hinders OH adsorption on Pt surface, thus increasing Pt surface area available for O2 adsorption and its electrochemical reduction.

Focused Magneto-Optic Kerr Effect Spectroscopy in Ni75Fe25 and Fe Ferromagnetic Thin Films on Organic Substrates

We apply the theory of the magneto-optic Kerr effect (MOKE) for multilayer thin films to analyze the surface magnetic properties, which have been observed using focused MOKE, for Ni75Fe25 and Fe thin films evaporated on poly(ethylene naphthalate) (PEN) organic substrates. The calculation is performed for the thickness dependence and incident angle dependence of Kerr rotation and ellipticity. We have measured the thickness dependence of Kerr rotation at a wavelength of 405 nm for both Ni75Fe25 and Fe thin films on PEN organic substrates. These results are fitted using the theory by adjusting the values of magneto-optic constants Q's. These Q's are 0.01exp (-i48π/180) and 0.025exp (-i47π/180) for Ni75Fe25 and Fe thin films, respectively. These results lead to the quantitative estimation of the surface magnetic properties of thin films on organic substrates. Also, the magneto-optic constants are estimated for ferromagnetic thin films on organic substrates for the first time.