Vibrational and Rotational Spectroscopy of 13CD3OD

We have used Fourier Transform spectral data on the C-O stretching mode of ¹³CD₃OD in order to perform a vibro-rotational analysis for this molecule. We have estimated a few molecular parameters of the ground and C-O stretching vibrational modes. Based on these parameters, and by using the Kwan-Dennison model, we propose assignments for a number of far-infrared laser transitions of ¹³CD₃OD.     

EPR,ENDOR and optical spectroscopy of Yb3+ ion in KZnF3 single crystals

The paramagnetic center of tetragonal symmetry formed by the Yb³⁺ ion in the KZnF₃ crystal has been studied using methods of EPR, ENDOR and optical spectroscopy. The location of the impurity ion and the structural model of the complex differing from the model of the Yb³⁺ center in KMgF₃ have been established. The empirical scheme of the energy levels of the Yb³⁺ ion has been found. The parameters of its interaction with the crystal electrostatic field and the hyperfine interaction with ligands of the nearest environment have been determined. The parameters of the crystal field were used for the analysis of the distortions of the crystal lattice in the vicinity of Yb³⁺. The parameters of the transferred hyperfine interaction have been calculated for the distances between Yb³⁺ and F⁻ ions of the nearest environment obtained taking into account the found distortions. They are in good agreement with the experimental values.     

Measurements of the 3ν 3 band of 14N15N16O and 15N14N16O using continuous-wave cavity ring-down spectroscopy

The absorption spectra of the 3ν₃ band of nitrous oxide isotopologues, ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O, have been measured using diode laser cavity ring-down spectroscopy in 6400–6463 and 6465–6532 cm^-1, respectively. Spectroscopic parameters and the rotational line intensities of the bands have been determined. We have applied this spectroscopic technique to the measurements of the absolute isotope ratio of those isotopologues using the absolute line intensities. PACS 32.10.Bi; 33.20.Vq; 33.70.-w; 42.55.Px; 42.62.Fi     

A subgrid model for clustering of high-inertia particles in large-eddy simulations of turbulence

Clustering (or preferential concentration) of inertial particles suspended in a homogeneous, isotropic turbulent flow is strongly influenced by the smallest scales of the turbulence. In particle-laden large-eddy simulations (LES) of turbulence, these small scales are not captured by the grid and hence their effect on particle motion needs to be modelled. In this paper, we use a subgrid model based on kinematic simulations of turbulence (Kinematic Simulation based SubGrid Model or KSSGM), for the first time in the context of predicting the clustering and the relative velocity statistics of inertial particles. This initial study focuses on the special case of inertial particles in the absence of gravitational settling. We show that the KSSGM gives excellent predictions for clustering in a priori tests for inertial particles with St ≥ 2.0, where St is the Stokes number, defined as the ratio of the particle response time to the Kolmogorov time-scale. To the best of our knowledge, the KSSGM represents the first model that has been shown to capture the effect of the subgrid scales on inertial particle clustering for St ≥ 2.0. We also show that the mean inward radial relative velocity between inertial particles (?w_r?^(?), which enters into the formula for the collision kernel) is accurately predicted by the KSSGM for all St. We explain why the model captures clustering at higher St?but not for lower St?, and provide new insights into the key statistical parameters of turbulence that a subgrid model would have to describe, in order to accurately predict clustering of low-St?particles in an LES.     

Phase transitions in the SrHfO3 perovskite measured with 111In/111Cd PAC

The temperature dependence of the hyperfine parameters in SrHfO₃ powder samples has been investigated by means of Perturbed Angular Correlation spectroscopy using implanted ¹¹¹In probes. Three quadrupole interactions have been established, with the largest fraction showing a pronounced dynamic interaction. We assign this fraction to ¹¹¹In / ¹¹¹Cd probe atoms on substitutional Hf sites. The temperature dependence of the dynamic interaction has been associated to the Pnma↔Imma phase transition at ∼700 K. We discuss the results in relation to those obtained for ¹⁸¹Hf / ¹¹¹Ta-probes in AHfO₃ (A=Ba, Sr, Ca) and for ¹¹¹In / ¹¹¹Cd-probes in PbZrO₃ and BaTiO₃. This revised version was published online in August 2006 with corrections to the Cover Date.     

Al2O3:V3+晶体局域结构及其自旋哈密顿参量研究

提出了解释掺杂离子局域结构畸变的配体平面移动模型，建立了此模型下晶体微观结构与自旋哈密顿参量之间的定量关系.在考虑自旋与自旋、自旋与另一电子轨道和轨道与轨道作用等微小磁相互作用的基础上，采用全组态完全对角化方法，对Al₂O₃晶体中V³⁺的局域结构和自旋哈密顿参量进行了系统的研究.结果表明，V³⁺掺入Al₂O₃晶体后，上下配体氧平面间距离增大了0.0060 nm.从而成功地解释了Al₂O₃:V³⁺晶体的自旋哈密顿参量.在此基础上，研究了三角晶场下3d²离子自旋哈密顿参量的微观起源.研究发现，自旋三重态对自旋哈密顿参量的贡献是主要的，微小磁相互作用对自旋哈密顿参量的贡献只与自旋三重态有关.     

Rotational spectra of isotopic species of silyl fluoride. Part I: Lamb-dip measurements and quantum-chemical calculations

The Lamb-dip technique has been employed for recording the rotational spectra of three isotopic species of silyl fluoride, namely ²⁸SiH₃F, ²⁹SiH₃F, and ³⁰SiH₃F, in order to improve the knowledge of their spectroscopic parameters as well as to try to resolve their hyperfine structure. High-level quantum-chemical computations using state-of-the-art coupled-cluster techniques together with core-polarized correlation-consistent basis sets have been employed to provide reliable reference values for the hyperfine parameters involved and have been used to guide the experimental investigation. Analysis of the experimental spectra allowed to improve the accuracy of the known spectroscopic parameters as well as to determine for the first time sextic and octic centrifugal-distortion constants.     

低温高压下的Na5Eu(WO4)4的发光和晶体场参数

用低温金刚石对顶砧高压显微光谱系统在20—300K低温和0—10GPa高压范围内研究了白钨矿型化学计量的基质发光晶体四钨酸铕钠Na₅Eu(WO₄)₄中Eu³⁺的发光.确定了Eu³⁺荧光谱线和能级在低温下的压力移动率.它随温度变化,表明温度和压力对Eu³⁺谱线作用不是独立无关的.按晶体场理论简化方法推导了能级的晶体场参数表达式,并按实验数据拟合出在不同低温下晶体场参数随压力的移     

Stopping powers of Al,Ti, Cu,Zr, Rh,Ag, Ta and Au for 26 MeV alpha particles and Z3 1 correction

Abstract

Stopping powers of Al, Ti, Cu, Zr, Rh, Ag, Ta and Au for 26 MeV alpha particles have been measured using a surface barrier silicon detector with an accuracy of 0.35%. The stopping powers for alpha particles divided by 4 have been compared with the stopping powers for 6.500 MeV protons of the same velocity. Experimental magnitudes of the Z ³ ₁ correction which is contained in the Bethe-Bloch stopping formula were extracted using the alpha-proton difference. Using the experimental Z ³ ₁ corrections thus obtained and the experimental Z ³ ₁ corrections of the previous paper, parameters of γ and b which appear in the theory of Ashley, Ritchie and Brandt for the Z ³ ₁ correction have been determined with exactly the same method as the previous paper as γ = 1.336 and b = 1.32. The magnitude of the Z ³ ₁ correction calculated by the theory of Ashley, Ritchie and Brandt using these parameters have been compared with those obtained by other authors.     

Elastic and inelastic scattering of 270 MeV3He particles from58Ni,90Zr,116Sn and208Pb

Differential cross-section angular distributions for the elastic scattering of 270 MeV³He particles from⁵⁸Ni,⁹⁰Zr,¹¹⁶Sn and²⁰⁸Pb have been measured. Optical model analysis of the cross-sections has yielded the optical model parameters for³He particles at 270 MeV. Angular distributions have also been measured for the inelastic excitation of the low-lying levels in the above mentioned nuclei. A collective model analysis using the distorted wave Born approximation (DWBA) of these cross-sections with the distorted waves generated by the optical model parameters determined from the elastic scattering analysis, has yielded the reduced transition probability (B(EL)) values consistent with those reported in the literature.     

Magnetic hyperfine structure and centrifugal distortion in quadrupole spectra of 12CH3I and 13CH3I

Quadrupole spectra of ¹²CH₃¹²⁷I and ¹³CH₃¹²⁷I in the ground vibrational state have been recorded at high resolution (1–2 KHz) using a radiofrequency-microwave double-resonance spectrometer. The magnetic structure of the quadrupole transitions has been resolved and analyzed. Spin-spin and spin-rotation interaction parameters have been determined, together with accurate values of the quadrupole coupling constants and their centrifugal corrections. Comparison with theory is made by using isotopic relations for the two species of iodomethane.     

Modelling of Tm3+-doped LiNbO3 Waveguide Lasers

In this work, CW laser operation of Tm³⁺-doped LiNbO₃ channel waveguides has been modelled. The model is based on time dependent laser rate equations coupled with the laser signal and pump photon flux equations. Steady state solutions for the population densities, pump and signal powers are obtained by using finite difference discretization of the active volume. The effects of spectroscopic parameters such as concentration dependent cross-relaxation and excess waveguide loss have been analyzed. We demonstrate good agreement with experimental data previously reported in Zn-diffused LiNbO₃:Tm³⁺ channel waveguide lasers. It is shown also that laser performance can be substantially improved by optimizing the cavity length.     

Doubly-Excited 1,3 P o States of H− Interacting with Screened Coulomb (Yukawa) Potentials

We have investigated the doubly excited 2s2p ³ P ^o and 2s3p ¹ P ^o resonance states of H⁻ embedded in a model plasma environment. Plasma effects are taken care of by using a screened Coulomb (Yukawa-type) potential. Correlated wave functions are used to represent the correlation effect between the charged particles. The density of resonance states has been calculated using the stabilization method. The calculated resonance energies and widths for various screening parameters are reported.     

Order parameters in lanthanum gallate lightly doped with manganese and paramagnetic resonance

The Cr³⁺ centers have been revealed, transitions at room temperature have been identified, and spin Hamiltonian parameters have been determined for the Cr³⁺ and Fe³⁺ triclinic centers in lanthanum gallate lightly doped with manganese. The principal axes of the fourth-rank fine-structure tensor for the Fe³⁺ triclinic centers have been established and used to determine the order parameters, i.e., the angles of rotation of oxygen octahedra of lanthanum gallate with respect to the perovskite structure. The order parameter in the rhombohedral phase has been estimated.     

Large-scale parallel simulations of turbulent combustion using combined dimension reduction and tabulation of chemistry

Simulations of turbulent reacting flows with chemistry represented using detailed kinetic model involving a large number of species and reactions are computationally expensive. Here we present a combined dimension reduction and tabulation strategy for implementing chemistry in large scale parallel Large-Eddy Simulation (LES)/Probability Density Function (PDF) computations of turbulent reacting flows. In this approach, the dimension reduction is performed using the Rate Controlled Constrained-Equilibrium (RCCE) method, and tabulation of the reduced space is performed using the In Situ Adaptive Tabulation (ISAT) algorithm. In addition, we use x2f_mpi — a Fortran library for parallel vector-valued function evaluation (used with ISAT in this context) — to efficiently redistribute the chemistry workload among the participating cores in parallel LES/PDF computations to reduce the overall wall clock time of the simulation. We test three parallel strategies for redistributing the chemistry workload, namely (a) PLP, purely local processing; (b) URAN, the uniform random distribution of chemistry computations among all cores following an early stage of PLP; and (c) P-URAN, a Partitioned URAN strategy that redistributes the workload within partitions or subsets of the cores. To demonstrate the efficiency of this combined approach, we perform parallel LES/PDF computations (on 1024 cores) of the Sandia Flame D with chemistry represented using a 38-species C₁–C₄ skeletal mechanism. We show that relative to using ISAT alone with the 38-species full representation, the combined ISAT/RCCE approach with 10 represented species (i) predicts time-averaged mean and standard deviation statistics with a normalized root-mean-square difference of less than 3% (30 K) in temperature, less than 2% (0.02 kg/m³) in density, less than 2.5% in mass fraction of major species, and less than 8% in mass fraction of minor species of interest; and (ii) reduces the simulation wall clock time by over 40% with the P-URAN strategy.     

Spectral Investigations on Ho3+ Doped Mixed Alkali Chloroborate Glasses

The optical absorption and emission spectra of two different Ho³⁺ doped mixed alkali chloroborate glasses have been studied in the ultraviolet-visible near-infrared regions. Various spectroscopic parameters like Racah (E¹, E², and E³), spin orbit (ξ_4f), and configuration interaction (α) parameters have been calculated. From the measured spectral intensities of the various absorption bands of Ho³⁺ ion, the Judd–Ofelt intensity parameters (Ω₂, Ω₄, and Ω₆) have been evaluated and covalency was studied as a function of x in the glass matrices. Using these parameters, radiative transition probabilities, radiative lifetimes, branching ratios, and integrated absorption cross-sections have been calculated and reported for certain excited states of Ho³⁺ ion. From the emission spectra, stimulated emission cross-sections are determined for the emission transitions, ⁵F₄, ⁵S₂?→?⁵I₈, and ⁵F₅?→?⁵I₈ in these two mixed alkali chloroborate glasses. An attempt has been made to throw some light on the environment of Ho³⁺ ions in these glass systems by studying the variation in various spectroscopic parameters.     

New Investigations of the AΔ-XΠ Band System in the CH Radical and a New Reduction of the Vibration-Rotation Spectrum of CH from the ATMOS Spectra

Seven bands of the A²Δ-X²Π system of the CH radical have been photographed in emission from a Geissler tube using conventional spectroscopic techniques. Under high resolution and using Th lines as standards, as well as an interferometric comparator equipped with a photoelectric scanning device, the 0-0, 1-1, 2-2, 0-1, and 1-2 bands have been rephotographed and the 3-3 and 2-3 bands, with a total number of 144 lines, have been recorded for the first time. In the previously reported (J. Mol. Spectrosc.134, 305, 1989; 147, 16, 1991) evaluation of the ATMOS spectrum of CH for determining the molecular parameters we found total interparameter correlations between some of them, due to the absence of high-J lines of the P and Q branches. With the help of the precise constants obtained from our 0-0 band measurements (12 branches with J_max = 24.5, f = 181, σ = 0.0025 cm⁻¹) of the A²Δ-X²Π transition, we have been able to remove the correlations and obtain more accurate molecular parameters for the X²Π ground state. These constants have subsequently been used to derive new exact molecular parameters for the A²Δ , ν = 1, 2, and 3 levels of CH. The Λ-doubling constants in the A²Δ state were obtained for the first time. The complex vibrational analysis has been carried out to determine the equilibrium molecular constants. Also, RKR potentials and r-centroids have been calculated for both the combining states, as well as Franck-Condon factors for the A-X system.     

Anomalous Scaling of Structure Functions and Dynamic Constraints on Turbulence Simulations

The connection between anomalous scaling of structure functions (intermittency) and numerical methods for turbulence simulations is discussed. It is argued that the computational work for direct numerical simulations (DNS) of fully developed turbulence increases as Re ⁴, and not as Re ³ expected from Kolmogorov’s theory, where Re is a large-scale Reynolds number. Various relations for the moments of acceleration and velocity derivatives are derived. An infinite set of exact constraints on dynamically consistent subgrid models for Large Eddy Simulations (LES) is derived from the Navier–Stokes equations, and some problems of principle associated with existing LES models are highlighted     

Crystal field and spectrum of Pr4+ in BaPrO3

We have measured the absorption spectrum of BaPrO₃ in the spectral range 1900–11000 cm⁻¹. All the energy levels of the 4f electronic configuration of the Pr⁴⁺ ion in a crystal have been observed for the first time. We describe the total set of electron-nuclear states and the integral intensities of the magnetic dipole transitions of the Pr⁴⁺ in BaPrO₃ in the framework of the crystal field approximation. The crystal field parameters corresponding to the real orthorhombic symmetry of BaPrO₃ are obtained with the exchange charge model.     

Entropic, LES and boundary conditions in lattice Boltzmann simulations of turbulence

Large scale (1600³-grid) entropic lattice Boltzmann (ELB) simulations are performed on the 27-bit model at sufficiently high Reynolds numbers to find intermittency corrections to the Kolmogorov k ^-5/3 inertial spectrum. Even though the transport coefficients in ELB and in the Large Eddy Simulation (LES) lattice Boltzmann schemes have very different origins, there are strong similarities in their turbulence statistics from 512³-grid simulations. A new LB moment-space boundary condition algorithm is tested on the 2D backstep problem, with excellent agreement with experimental data even up to a Reynolds number of 800.