Progress in thermal-mechantical effects induced by laser

对激光辐照诱导的热与力学问题研究进展进行了综述,包括材料在高温、高升温速率下的本构关系,典型薄板和柱壳等结构在激光辐照下的热力破坏效应,多层材料体系的激光破坏行为等几个方面,并着重介绍了包含相变与烧蚀过程的激光破坏分析模型与机制研究,激光辐照效应的流-热-固耦合数值模拟方法,以及短脉冲激光引起的冲击与破坏机理等方面的研究新进展.     

激光辐照下有界圆厚板的热弹性弯曲响应分析

考虑板弯曲运动的旋转惯性效应和剪切变形效应，建立了轴对称热能沉积作用下，边界固支或简支圆厚板的热弹性弯曲运动控制方程。利用数学变换和摄动法，导出了各种温度－力学边界条件下板的热弹性弯曲挠度及截面广义转角的解析公式。给出了在空间Ｇａｕｓｓ型分布激光束辐照下，板整体弯曲响应的代表性数值计算结果，直观显示了板弯曲挠度的时空变化规律。     

关于激光捷联惯性导航系统姿态算法的分析

圆锥误差和量化误差是激光捷联惯性导航系统姿态解算误差的两个最主要的误差源.从分析圆锥误差产生的机理出发,分别分析了以角度和角速度为计算参数的圆锥误差补偿算法,并对量化误差对圆锥误差补偿算法的影响进行了研究.通过理论分析和数字仿真,得出在实际工程应用中,采用角速度为输入信息的激光捷联惯性导航系统姿态算法应该在考虑量化误差的情况下,采用以角速度为计算参数的圆锥误差补偿算法.     

Boundary layer effect on thermal NO decomposition behind incident shock waves

The thermal decomposition of nitric oxide (diluted in Argon) has been measured behind incident shock waves by means of IR diode laser absorption spectroscopy. In two independent runs the diode laser was tuned to the=0 =1² _3/2 R(18.5)-rotational vibrational transition and the=1 =2² _3/2 R(20.5)-rotational vibrational transition of nitric oxide, respectively. These two transitions originating from the vibrational ground state (=0) and the first excited vibrational state (=1) were selected in order to probe the homogeneity along the absorption path. The measured NO decomposition could satisfactorily be described by a chemical reaction mechanism after taking into account boundary layer corrections according to the theory of Mirels. The study forms a further proof of Mirels' theory including his prediction of the laminar-turbulent transition. It also shows, that the inhomogeneities from the boundary layer do not affect the IR linear absorption markedly.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Encapsulation and release of biomolecules from Ca-P/PHBV nanocomposite microspheres and three-dimensional scaffolds fabricated by selective laser sintering

This study focused on the fabrication of calcium phosphate (Ca-P)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposite scaffolds loaded with biomolecules using the selective laser sintering (SLS) technique and their evaluation. Ca-P/PHBV nanocomposite microspheres loaded with bovine serum albumin (BSA) as the model protein were fabricated using the double emulsion solvent evaporation method. The encapsulation efficiency of BSA in PHBV polymer microspheres and Ca-P/PHBV nanocomposite microspheres were 18.06 ± 0.86% and 24.51 ± 0.60%, respectively. The BSA loaded Ca-P/PHBV nanocomposite microspheres were successfully produced into three-dimensional porous scaffolds with good dimensional accuracy using the SLS technique. The nanocomposite microspheres served as protective carriers and maintained the bioactivity of BSA during SLS. The effects of SLS parameters such as laser power and scan spacing on the encapsulation efficiency of BSA in the scaffolds and in vitro BSA release were studied. An initial burst release was observed, which was followed by a slow release of BSA. After 28-day release, The PHBV matrix was slightly degraded after 28-day in vitro release study. It was shown that nanocomposite scaffolds with controlled architecture obtained via SLS could be incorporated with biomolecules, enhancing them with more functions for bone tissue engineering application or making them suitable for localized delivery of therapeutics.     

Formation of artificial micro‐pits on Al alloy with the photon rupture method and the localized corrosion behavior of the formed pits

An in situ artificial micro‐pit fabrication method with an area selective electrochemical measurement technique was applied to investigate the effect of the geometry of artificially formed pits on their localized corrosion behavior in anodized 1000 series aluminum. This technique enables the fabrication of artificial micro‐pits with different aspect ratios (pit depth/pit diameter) in solutions. The aspect ratios of the fabricated artificial micro‐pits in this experiment could be varied from 0.13 to 1.83 by controlling the irradiation time of the focused pulsed YAG laser beam. By applying a constant potential to the final laser‐beam‐irradiated spot in chloride environments, localized dissolution occurred only at the laser beam irradiated area, because the anodic oxide film acted as an insulator. The corrosion current and charge increase with increasing aspect ratio at any applied potential. Copyright © 2010 John Wiley & Sons, Ltd.     

Fabrication and electron transport properties of epitaxial films of electron-doped 12CaO·7Al2O3 and 12SrO·7Al2O3

Epitaxial growth and electron doping of 12CaO·7Al₂O₃ (C12A7) and 12SrO·7Al₂O₃ (S12A7) are reported. The C12A7 films were prepared on Y₃Al₅O₁₂ (YAG) single-crystal substrates by pulsed laser deposition at room temperature and subsequent thermal crystallization. X-ray diffraction patterns revealed the films were grown epitaxially with the orientation relationship of (001)[100] C12A7 || (001)[100] YAG. For S12A7, pseudo-homoepitaxial growth was attained on the C12A7 epitaxial layer. Upon electron doping, metallic conduction was achieved in the C12A7 film and the S12A7/C12A7 double-layered films. Analyses of optical absorption spectra for the S12A7/C12A7 films provided the densities of free electrons in each layer separately. Hall measurements exhibited larger electron mobility in the S12A7/C12A7 film than those in C12A7 and S12A7 films, suggesting free electrons may be accumulated at the S12A7/C12A7 interface due presumably to a discontinuity of the cage conduction bands.     

Multiply ionization of diethyl ether clusters by 532 nm nanosecond laser: The influence of laser intensity and the electron energy distribution

The formation mechanism for multiply charged ions (C^q+ and O^q+ (q = 2–4)) were investigated using a dual polarity time-of-flight mass spectrometer when diethyl ether clusters interacted with nanosecond laser pulse. The signal intensity of multiply charged ions and electron energy was measured experimentally. It was shown that the intensity of multiply charged ions increased about 50 times when laser intensity increased from 7.6 × 10⁹ to 7.0 × 10¹⁰ W/cm², then saturated as laser intensity increased further. It is interesting that the evolution of the mean value of electron energy was same to that of multiply charged ions. The theoretical calculation showed the ionization potential of atomic ions could be significantly decreased due to the effect of Coulomb screening especially at low laser intensity. It indicated that the electron ionization combined with Coulomb screening effect could explain the production of multiply charged ions in nanosecond laser field.     

Stabilization of the Charge‐Separated States of Covalently Linked Zinc Porphyrin–Triphenylamine–[60]Fullerene

Spectroscopic, redox, computational, and electron transfer reactions of the covalently linked zinc porphyrin–triphenylamine–fulleropyrrolidine system are investigated in solvents of varying polarity. An appreciable interaction between triphenylamine and the porphyrin π system is revealed by steady‐state absorption and emission, redox, and computational studies. Free‐energy calculations suggest that the light‐induced processes via the singlet‐excited porphyrin are exothermic in benzonitrile, dichlorobenzene, toluene, and benzene. The occurrence of fast and efficient charge‐separation processes (≈10¹² s^?1) via the singlet‐excited porphyrin is confirmed by femtosecond transient absorption measurements in solvents with dielectric constants ranging from 25.2 (benzonitrile) to 2.2 (benzene). The rates of the charge separation processes are much less solvent‐dependent, which suggests that the charge‐separation processes occur at the top region of the Marcus parabola. The lifetimes of the singlet radical‐ion pair (70–3000 ps at room temperature) decrease substantially in more polar solvents, which suggests that the charge‐recombination process is occurring in the Marcus inverted region. Interestingly, by utilizing the nanosecond transient absorption spectral technique we can obtain clear evidence about the existence of triplet radical‐ion pairs with relatively long lifetimes of 0.71 μs (in benzonitrile) and 2.2 μs (in o‐dichlorobenzene), but not in toluene and benzene due to energetic considerations. From the point of view of mechanistic information, the synthesized zinc porphyrin–triphenylamine–fulleropyrrolidine system has the advantage that both the lifetimes of the singlet and triplet radical‐ion pair can be determined.     

Stockage de l’hydrogène dans les nanotubes de carbone à paroi unique : nouvelle méthode de préparation par excitation laser

A new mode for hydrogen adsorption and storage in single-wall carbon nanotubes is used, on the basis of laser excitation. Remember that this method has been useful to obtain, in the case of the fullerene C₆₀, many complex C₆₀-atoms or C₆₀-molecules, where atoms or molecular particles are trapped inside the C₆₀-molecules. We think this method might be important to store many hydrogen molecules inside carbon nanotubes.