Elastic properties and mechanical relaxation behaviors of PVDF (poly (vinylidene fluoride)) at temperatures between −20 and 100 °C and at 2 MHz ultrasonic frequency

The elastic properties of PVDF have been investigated as a function of temperature. The propagation velocity and absorption of longitudinal and transverse ultrasonic waves have been measured at a constant frequency of 2 MHz and temperatures between –20 and 100 °C. Hence, the temperature dependences of storage and loss elastic constants have been obtained for temperatures between –20 and 100 °C. It has been seen that the relaxation behavior is affected from the form of mechanical disturbance. For the longitudinal mode, only one relaxation peak at 42 °C, but for transverse mode three relaxation peaks at 28 °C, 60 °C, and 94 °C have been observed. The results have been compared with the literature values obtained previously for PVDF. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2862–2873, 2005     

c轴垂直取向FePt薄膜的磁和磁光性能研究

采用直流磁控溅射的方法在氧化镁(100)单晶基板上生长了一系列c轴垂直取向的FePt薄膜，通过改变沉积时的基板温度，薄膜从Fe，Pt原子无序排列的面心立方结构逐渐变化到有序排列的L1₀相面心四方结构.在此基础上，系统研究了FePt薄膜的化学有序度对磁和磁光性能的影响.随着有序度的增加，FePt薄膜的磁晶各向异性能，以及沿垂直方向的矫顽力、剩磁比均增加，在基板温度高于530 ℃时制备的薄膜中的磁晶各向异性能超过1 J/cm³.同时，还观察到有序FePt合金薄膜的磁光克尔光谱(克尔转角的大小和极值所对应的跃迁光子能量)随化学有序度的显著变化. 关键词： FePt薄膜 化学有序度参数 磁光克尔光谱     

Study on two-cell stimulated Brillouin scattering system with mixture medium

In this paper,a method of choosing mixture medium in two-cell stimulated Brillouinscattering(SBS)system to improve the system performance is proposed.The Brillouin frequency shift(BFS)of mixture medium varies with the mixing ratio andthus the difference of the BFS between the two cells can be eliminated.The two-cellSBS system with acetone(C3H6O)in its generator cell and mixture liquid ofCCl4/C2Cl4 in its amplifier cell is investigated.The C3H6O has a high optical breakdown threshold and the mixture liquid of CCl4/C2Cl4 has a small absorption coeffi-cient and the same BFS as that of C3H6O when the volume fraction of CCl4 is 4%.Compared with two-cell SBS system with the same liquid(C2Cl4)or different liquid(C3H6O and C2Cl4)in generator and amplifier cell,the SBS system with mixture liq-uid(CCl4/C2Cl4)in amplifier cell and C3H6O in generator cell improves thepower-load,energy reflectivity(ER),phase conjugation(PC)fidelity and ER stabil-ity.     

级联介质的空间排布对光场特性的影响

基于菲涅尔衍射原理，应用傅里叶变换方法，从理论上推导了高斯光束经级联非线性介质传输后任意位置处光场分布的解析表达式,研究了光场峰值强度、峰值出现的位置以及光束的束宽和调制因子等参量在级联介质中的变化规律。结果表明：随着非线性效应的增强，光场峰值强度逐渐增大，峰值距离逐渐缩短，光束束宽不断减小而调制因子逐渐增大。在介质排布中要尽量错开光束峰值位置，采用均匀排布方案虽然可以降低元件受损的风险，但还需对介质均匀配置的间距进行有效优化。     

Kerr介质中压缩真空场与耦合双原子依赖强度耦合系统的光子统计性质

研究了存在Kerr介质时依赖强度耦合单模压缩真空场与耦合双原子非共振相互作用系统中光子的统计性质,运用数值方法讨论了系统参数对光子统计性质的影响.结果表明:Kerr介质、失谐量、原子间相互作用、光场初始压缩因子和原子的初始状态对光子的统计性质有较大的影响.     

Collision of optical solitons with Kerr law nonlinearity

The intra-channel collision of optical solitons, with Kerr law nonlinearity, is studied by the aid of quasi-particle theory. The perturbation terms considered in this paper are all of Hamiltonian type. It is shown that the soliton–soliton interaction can be suppressed in the presence of these perturbations, namely, the self-steepening, the third-order dispersion, the fourth-order dispersion and the frequency separation between the soliton carrier and the gain-center frequency. The prediction of quasi-particle theory are fully confirmed by direct numerical simulations.     

Holographic recording media based on oligomers and co-oligomers with organic dye additives

We have created holographic recording media based on films of carbazolyl-, fluorenyl-, naphthyl-, and anthracenyl-containing oligomers and co-oligomers in which an intraionic organic dye is used as the sensitizer. We have established that the photoconductivity of the films and the photosensitivity of the recording media are higher in the case of co-oligomers with different donor moieties. We conclude that in the films of co-oligomers with different donor moieties in the “end” groups of the polymer chain, there is reduced probability of formation of excimers, which are centers for capturing photogenerated charge carriers, and therefore the photoconductivity of the film increases. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 132–135, January–February, 2007.     

The effect of turbulence-radiation interaction on radiative entropy generation and heat transfer

The analysis under the second law of thermodynamics is the gateway for optimisation in thermal equipments and systems. Through entropy minimisation techniques it is possible to increase the efficiency and overall performance of all kinds of thermal systems. Radiation, being the dominant mechanism of heat transfer in high-temperature systems, plays a determinant role in entropy generation within such equipments. Turbulence is also known to be a major player in the phenomenon of entropy generation. Therefore, turbulence-radiation interaction is expected to have a determinant effect on entropy generation. However, this is a subject that has not been dealt with so far, at least to the extent of the authors’ knowledge. The present work attempts to fill that void, by studying the effect of turbulence-radiation interaction on entropy generation. All calculations are approached in such a way as to make them totally compatible with standard engineering methods for radiative heat transfer, namely the discrete ordinates method. It was found that turbulence-radiation interaction does not significantly change the spatial pattern of entropy generation, or heat transfer, but does change significantly their magnitude, in a way approximately proportional to the square of the intensity of turbulence.     

Numerical solution of radiative and conductive heat transfer in concentric spherical and cylindrical media

A new technique is presented to improve the performance of the discrete ordinates method when solving the coupled conduction-radiation problems in spherical and cylindrical media. In this approach the angular derivative term of the discretized one-dimensional radiative transfer equation is derived from an expansion of the radiative intensity on the basis of Chebyshev polynomials. The set of resulting differential equations, obtained by the application of the S_N method, is numerically solved using the boundary value problem with the finite difference algorithm. Results are presented for the different independent parameters. Numerical results obtained using the Chebyshev transform method compare well with the benchmark approximate solutions. Moreover, the new technique can easily be applied to higher-order S_N calculations.     

Verification of numerical simulation method for entropy generation of radiation heat transfer in semitransparent medium

The numerical simulation method of radiative entropy generation in participating media presented by Caldas and Semiao [Entropy generation through radiative transfer in participating media: analysis and numerical computation. JQSRT 2005;96:423-37] is extended to analyze the radiative entropy generation in the enclosures filled with semitransparent media. A discrete ordinates method is used to solve radiative transfer equation and radiative entropy generation. Two different examples are employed to verify the numerical simulation method of radiative entropy generation in the enclosure. Numerical results of dimensionless radiative entropy generation of enclosure are identical to that of entire thermodynamics analysis for the enclosure system. This numerical simulation method can be used in the entropy generation analysis of high-temperature systems such as boilers and furnaces, in which radiation is the dominant mode of heat transfer.