共查询到19条相似文献,搜索用时 93 毫秒
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在Fokker_P1anck方程的基础上,对超短脉冲激光烧蚀熔融硅的机理进行分析研究,建立了雪崩电离、多光子吸收电离导致的熔融硅烧蚀机理的数学模型.其计算得出的激光能量密度和临界烧蚀阀值与实验结果很好的吻合,定量解释了超短脉冲激光对熔融硅烧蚀损伤微观过程的影响. 相似文献
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采用多波长(1064nm、532nm、248nm)脉冲激光在去离子水中对责金属Au、Ag片表面进行激光烧蚀(PLA).利用TEM、AFM、SEM对烧蚀金属片表层及产物(微/纳米尺度的金属颗粒)进行观察分析,认为在液相水环境中,整个烧蚀过程主要可分为激光诱导相沸腾爆炸和等离子体羽辉混合体膨胀2个过程.在这2个过程中分别产生得到具有微米尺度的球状金属颗粒和纳米尺度的金属颗粒.同时,具有纳米尺度金属Au/Ag颗粒经过强激光光子"二次"修饰改性过程,形成具有形状统一、分散性和稳定性较好的金属纳米胶体体系,这些胶体中金属纳米颗粒作为探针,在表面增强拉曼散射(SERS)光谱学方面有很好的应用价值. 相似文献
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本文主要介绍了纳米颗粒的短脉冲激光制备及其在非线性光学领域的应用。短脉冲激光制备纳米颗粒具有纯度高、操作简单和适用性广等优点,所制备的非线性纳米颗粒尺寸分布均匀,粒度小且可调控,在非线性光学材料中有着独特的地位。为了更深入地对此进行研究,本文介绍了纳米颗粒的光学非线性和激光的特点和原理。在此基础上,通过阐述短脉冲激光与物质相互作用的机理,说明了激光制备纳米颗粒所具有的优点,详细分析了制备条件对合成纳米颗粒的影响,并结合激光制备不同的纳米颗粒,介绍当前激光制备各类纳米颗粒的研究现状。激光制备纳米颗粒是一种操作简便、适用性广,且对环境友好的方法。
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飞秒激光烧蚀材料表面产生纳米波纹结构的实验 总被引:2,自引:1,他引:1
利用飞秒脉冲激光烧蚀可以获得远小于激光中心波长(775nm)量级的周期条纹.通过多脉冲飞秒激光烧蚀Ni、Al、Cu、Ti和Si等材料表面的实验,得到材料表面产生光栅的周期均小于飞秒激光中心波长;采用对比实验,改变入射光的偏振特性,发现波纹周期方向随入射光偏振方向的改变而改变;不改变激光偏振态、脉冲能量为4.2J/cm^2时,沿波纹周期走向,发现平台移动速度为0.1mm/s时,可获得清晰的551nm的金属周期结构;最后应用上述实验结果,在铜片表面制备了长为几十微米、周期为551nm的微纳光栅结构。 相似文献
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现行规范采用阻尼修正系数(DMF)调整阻尼比不同于5%时的弹性位移反应谱,然而未考虑到近断层脉冲型地震动的影响。本文选取了代表性前方向性脉冲记录,研究了矩震级、场地类别和距离对脉冲周期的影响,同时指出脉冲周期与相应伪速度谱峰值周期之间具有较好的线性相关性,然后以周期与脉冲周期比和阻尼比为双变量,采用Levenberg–Marquardt算法进行非线性回归分析,提出了能够较为准确反映数据点分布规律的DMF模型。结果表明,随着脉冲周期的减小,DMF峰值对应的周期越小,而在中长周期范围DMF越趋近于1.0;与现行规范相比,模型MDF强烈依赖于脉冲周期、结构振动周期和阻尼比,且当三者位于不同取值范围时,规范DMF过低或过高 相似文献
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在结构动力响应的分析中,阻尼模型的选取对得到的分析结果具有相当的制约性,因此,结构的阻尼值机理及阻尼参数的识别研究一直倍受关注。由于结构实际阻尼机理的复杂性,目前常用的粘滞阻尼模型具有一定的局限性。首先介绍一种更一般的非粘滞阻尼模型,该模型的阻尼力与质点速度的时间历程相关;通过拉普拉斯变换对具有该阻尼的系统进行复模态分析,推导得到了结构阻尼系数的识别方法。对算例的数值仿真表明,该方法能有效地识别这种非粘滞阻尼模型的阻尼系数;当阻尼的非粘滞性不强时,其得出的结果与已有方法对粘滞阻尼参数识别的结果一致。 相似文献
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Wanbing LuXingkuo Li Xinzhan WangLiping Wu Li HanGuangsheng Fu Wei Yu 《Materials Science and Engineering: B》2011,176(11):835-839
Hydrogenated nanoamorphous Si (na-Si:H) films have been fabricated by reactive pulsed laser ablation technique with hydrogen as reactive gas. It is found that the hydrogen pressure has a great effect on both the structure and photoluminescence (PL) properties of the films. Increasing the hydrogen pressure leads to a structural transition of the films from amphorous Si to na-Si:H, and the PL center wavelength of the na-Si:H films is varied with the hydrogen pressure. The PL decay times of the na-Si:H films are in the nanosecond scale and are shorter on the high energy side of their PL spectrum. The results demonstrate that the na-Si:H films are promising candidates for visible, tunable and high-performance light-emitting devices. 相似文献
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In this paper the second-order differential equation with time-dependent damping coefficientx + cos (2t) x + x = 0,will be studied. In particular the coexistence of periodic solutions corresponding with the vanishing of domains of instability is investigated. The coexistence of -periodic solutions occurs for 4n
2 where n is integer. This implies that the instability area which is emanating from =4n
2 in the – stability diagram disappears. In applications, this equation can be considered as a model equation for the study of rain-wind-induced vibrations of a special oscillator.on leave as a PhD reseacher at Delft University of Technology, The Netherlands 相似文献
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根据《高层建筑混凝土结构技术规程》和《建筑抗震设计规范》对高位转换结构体系的框支层的层间位移和结构等效侧向刚度的限制要求,采用等效侧向刚度计算方法,将高位耗能减震结构分解成框撑剪结构和纯剪力结构,结合振型分解反应谱理论和线性粘滞阻尼减震结构等效阻尼比计算方法,推导出了高位转换粘滞阻尼减震结构合理阻尼系数的计算公式。最后,通过算例分析得出,采用上述方法计算高位转换粘滞阻尼减震结构粘滞阻尼系数是可行的,该方法计算公式简单实用,可用于高位转换粘滞阻尼减震结构的初步设计。 相似文献
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N. Donato F. NeriG. Neri M. LatinoF. Barreca S. SpadaroI. Pisagatti G. Currò 《Thin solid films》2011,520(3):922-926
A simple and effective solution route for synthesizing colloidal indium oxide (In2O3) nanocrystallites, i.e. laser ablation in liquid (LAL), is reported. The morphology and chemical structure of the as-prepared samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). The results showed the formation of In2O3 nanoparticles with a bimodal distribution, consisting mainly of particles of small diameters (2-5 nm). Sensor devices prepared by spraying directly the LAL colloidal solutions on interdigitated alumina substrates exhibited good sensing properties for the detection of CO at very low concentrations. 相似文献
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Schuffenhauer C Parkinson BA Jin-Phillipp NY Joly-Pottuz L Martin JM Popovitz-Biro R Tenne R 《Small (Weinheim an der Bergstrasse, Germany)》2005,1(11):1100-1109
Motivated by the discovery of the C(60) molecule (buckminsterfullerene), the search for inorganic counterparts of this closed-cage nanostructure started in 1992 with the discovery of nested fullerene-like nanoparticles of WS(2). Inorganic fullerene-like (IF) materials have since been found in numerous two-dimensional compounds and are available in a variety of shapes that offer major applications such as in lubricants and nanocomposites. Various synthetic methodologies have been employed to achieve the right conditions for the constricted or templated growth needed for the occurrence of this new phase. In this study, IF-TaS(2) is produced from a volatile chloride precursor in the gas phase and in small yield by room temperature laser ablation both in argon and in liquid CS(2). For the gas-phase reaction, a high yield of IF nanoparticles was obtained between 400 and 600 degrees C with a low concentration of the precursor gas. The average size and the yield of the IF-TaS(2) nanoparticles decrease with temperature. Above 600 degrees C, IF nanoparticles were found in low yields and at sizes below 20 nm. The stability of the IF nanoparticles produced by the gas-phase reaction is discussed in the light of two existing theoretical models. Laser ablation in argon leads to IF nanoparticles filled with clusters of TaS(2). Agglomeration of the nanoparticles can be avoided by laser ablation in liquid CS(2). 相似文献
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A general method to analyze the ablation temperature for different materials (in particular in the human cornea and poly-methyl-methacrylate (PMMA)) is provided. The model is comprehensive and provides directly laser beam characteristics and ablative spot properties. The model further provides a method to convert the temperature rise during ablation observed in PMMA to equivalent temperature rises in the cornea. The proposed model can be used for calibration, verification and validation purposes of laser systems used for ablation processes at relatively low cost and would directly improve the quality of results. 相似文献
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R.A. Ganeev A.S. Zakirov G.S. BoltaevR.I. Tugushev T. UsmanovP.K. Khabibullaev T.W. KangA.A. Saidov 《Optical Materials》2011,33(3):419-423
The structural, optical, and nonlinear optical properties of the manganese nanoparticles prepared by laser ablation in various liquids were investigated using the 532 and 1064 nm, 50 ps laser pulses. The TEM and spectral measurements showed temporal dynamics of size distribution of Mn nanoparticles in solutions. The nonlinear absorption (β = 2 × 10−10 and 4 × 10−11 cm W−1) and positive nonlinear refraction (γ = 8 × 10−15 and 2 × 10−14 cm2 W−1) of picosecond radiation were observed in the Mn colloidal suspensions using the 1064 and 532 nm radiation, respectively 相似文献