Vibrational spectra of volatile inorganic hydrides in the liquid state

The results of studies of IR and Raman spectra of volatile inorganic hydrides of Group IV–VI and Periods 3 and 4 elements in the liquid state are surveyed and analyzed. The mechanisms of intermolecular interactions in these liquids are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 629–644, April, 1999.     

Thermoelastic Behaviour of Amorphous Polymers Above and Through the Glass Transition Interval I. Polystyrene

The thermoelastic behaviour of an unfractionated polystyrene was studied in the temperature interval 353–453 K in the regimes of isobaric cooling and of isothermal quasi-adiabatic loading, respectively. The main experimental results can be summarized as follows. 1. In the temperature interval far above the glass transition temperature T_g, both the temperature and volume relaxations of the polystyrene melt after sudden pressure jumps were completely reversible and proved to be simple exponential functions of the time. Therefore, by a straightforward application of Eqs (1) and (2) to the relevant thermoelastic data obtained in a single experimental run one can arrive at the reasonable values of the specific volume, specific heat capacity, thermal diffusivity and heat conductivity of the polymer in the equilibrium melt state. 2. In the temperature interval close to T_g, both the temperature and volume relations of the supercooled polystyrene melt in compression/expansion cycles became markedly asymmetric and non-exponential. The low values of the exponent β in the fractional-exponent Eq. (5) for the volume relaxation suggest a broad spectrum of relaxation times indicating the high degree of coupling between different mechanisms of the molecular motions involved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Convergence of relaxation schemes for hyperbolic conservation laws with stiff source terms

We focus in this study on the convergence of a class of relaxation numerical schemes for hyperbolic scalar conservation laws including stiff source terms. Following Jin and Xin, we use as approximation of the scalar conservation law, a semi-linear hyperbolic system with a second stiff source term. This allows us to avoid the use of a Riemann solver in the construction of the numerical schemes. The convergence of the approximate solution toward a weak solution is established in the cases of first and second order accurate MUSCL relaxed methods.

     

全光纤波长可调谐调Q激光器

实现了全光纤波长可调谐主动调Ｑ和自调Ｑ激光脉冲输出。波长可调谐范围为５．７ｎｍ。主动调Ｑ激光脉冲的最高峰值功率可达２．６Ｗ,平均功率１ｍＷ。观察到了自调Ｑ现象,且对自调Ｑ现象给予了初步的解释。     

Electron paramagnetic resonance of Gd3+ in Eu2Zn3(NO3)12·24H2O single crystals

Electron paramagnetic resonance of Gd³⁺ in Eu₂Zn₃(NO₃)₁₂·24H₂O single crystals is studied at ≈9.45 GHz and at 298 and 77 K. Gd³⁺ substitutes for the Eu³⁺ site. In addition to the allowed fine structure lines, forbidden transitions (ΔM = ±2,±3,±4,±5) are observed. The superposition model is applied to the zero‐field splitting parameter b₂⁰. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Methods for correlating T1ρ and FID components in wideline H NMR studies of motionally heterogeneous polymer systems

We address the problem of correlating the observed FID and T_1ρ components in wideline ¹H relaxation measurements of motionally heterogeneous polymers, and show that different methods of data treatment can highlight different aspects of the correlations present. For a sample of polypropylene we find that the T_1ρ relaxation behaviour is driven by relaxation associated with the intermediate FID component, which strongly suggests a motionally inhomogeneous amorphous region in the sample.     

Triplet-triplet transfer of electronic energy upon nonequilibrium vibrational excitation of triplet molecules

The specific features of the triplet-triplet (T-T) transfer of electronic excitation energy in a gas phase upon nonequilibrium vibrational excitation of the triplet molecules of a donor were studied for an anthraquinone-diacetyl donor-acceptor pair using the time-resolved slow fluoresence of anthraquinone and sensitized phosphorescence of diacetyl. It is shown that in the gas phase, which allows regular control of the number of collisions, competition between the processes of T-T transfer and intermolecular vibrational relaxation is observed for nanosecond time resolution. The T-T transfer rate for the molecular system investigated exceeded the rate of intermolecular vibrational relaxation k_V in the triplet state T₁ of the donor. The effectiveness of the T-T transfer of energy by vibrationally excited molecules turned out to be higher than the effectiveness of transfer by thermalized ones, but even the highest of them was much less than unity. An increase in the equilibrium temperature of vapors led to a decrease in the effectiveness of transfer for both vibrationally excited and thermalized triplet molecules, thus indicating the importance of the collisional complex in the intermolecular process studied. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 474–479, July–August, 2000.     

Structure and stability of the anatase TiO2 (101) and (001) surfaces

Well-defined (101) and (001) surfaces of anatase TiO₂ were studied for the first time by secondary-electron imaging and low-energy electron diffraction. Initially, both surfaces show a crystalline structure corresponding to the bulk anatase phase, buried under an atomically thin contamination layer. After mild sputtering with 500 eV Ne⁺ ions, we have observed a surface phase transition from tetragonal anatase to face-centered cubic titanium monoxide TiO. Subsequent annealing at 900 K restores the (1×1) anatase structure at the (101) surface. On the (001) surface, however, a (1×4) reconstruction appears. The unreconstructed structure can be recovered by exposing the surface to oxygen. These observations demonstrate the stability of the anatase surfaces and illustrate the feasibility of preparing and investigating clean surfaces of this technological important form of TiO₂.     

High pressure μSR studies: rare earths and related materials

After a short introduction to μSR with respect to the study of magnetic properties, followed by a brief outline of the principle of the high pressure-low temperature μSR spectrometer installed at the Paul Scherrer Institute, we discuss some measurements on rare earth materials employing this instrument. They are concerned with: (1) The pressure dependence of the spin turning process in ferromagnetic Gd. (2) The volume dependence of the internal magnetic field in the heavy rare earth metals Gd, Dy, and Ho in their ordered magnetic states. (3) The response of the (first order) magnetic transition in the frustrated antiferromagnets of type RMn₂ (R = Y,Gd) to pressure. (4) The variation of magnetic parameters with pressure in La₂CuO₄ (powder sample), the antiferromagnetic parent compound of the high T_C superconductors of type La_2−x(Sr, Ba)_xCuO₄. In conclusion a short outlook on further developments is given. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于运动约束解过约束并联机构变形协调方程

提出利用运动约束关系来间接求解过约束并联机构变形协调方程．首先介绍了该方法的原理,接着分别针对平面和空间过约束并联机构,详述该方法的解决步骤,结果验证了该方法的正确性,从中还可看出该方法在求解复杂过约束并联机构时非常简洁,最后介绍了采用该方法解决多度过约束问题．