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排序方式: 共有1141条查询结果,搜索用时 15 毫秒
41.
V. Z. Kasimov O. V. Ushakova Yu. P. Khomenko 《Journal of Applied Mechanics and Technical Physics》2003,44(5):612-619
An improved procedure for modeling the operation of a light-gas gun is proposed. The motion of working bodies in both the firing chamber and the light-gas chamber is studied within the framework of the mechanics of heterogeneous media. The problem of barrel heating taking into account its melting and removal of thermal ablation products into the medium inside the bore is solved in a coupled formulation. Heat and mass transfer and friction on the barrel surface are calculated using empirical dependences. The deformable piston is considered compressible and elastoviscoplastic. Allowance is made for the presence of a clearance between the lateral surface of the piston and the barrel bore walls and the associated gas flow between the firing and the light-gas chamber. Calculation results are given. 相似文献
42.
Teeth retain different elements at particular stages of life. Hence, the exposure over a selected time span may be characterized by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). A Nd:YAG laser with emission at 266?nm was coupled to a quadrupole ICP-MS for the quantitative study of historical human teeth for Sr and Ba, elements of anthropological significance. A calibration approach incorporating the experimentally derived k coefficient is reported. The coefficients were established based on the mean concentrations of the analytes determined by pneumatic nebulization ICP-MS using acid-digested calcium phosphate standards and the intensities recorded during laser ablation of corresponding standards as pellets. The k values were 0.54?±?0.05 (µg?g?1)?1 and 4.49?±?1.09 (µg?g?1)?1 for Sr and Ba, respectively. This calibration approach provided local quantitative data and demonstrated statistically significant differences in Sr concentrations in enamel and dentine. 相似文献
43.
J.S. Becker R.C. Dietrich A. Matusch D. Pozebon V.L. Dressler 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used for quantitative imaging of toxic and essential elements in thin sections (thickness of 30 or 40 μm) of tobacco plant tissues. Two-dimensional images of Mg, Fe, Mn, Zn, Cu, Cd, Rh, Pt and Pb in leaves, shoots and roots of tobacco were produced. Sections of the plant tissues (fixed onto glass slides) were scanned by a focused beam of a Nd:YAG laser in a laser ablation chamber. The ablated material was transported with argon as carrier gas to the ICP ion source at a quadrupole ICP-MS instrument. Ion intensities of the investigated elements were measured together with 13C+, 33S+ and 34S+ within the entire plant tissue section. Matrix matching standards (prepared using powder of dried tobacco leaves) were used to constitute calibration curves, whereas the regression coefficient of the attained calibration curves was typically 0.99. The variability of LA-ICP-MS process, sample heterogeneity and water content in the sample were corrected by using 13C+ as internal standard. Quantitative imaging of the selected elements revealed their inhomogeneous distribution in leaves, shoots and roots. 相似文献
44.
J.S. Cowpe J.S. Astin R.D. Pilkington A.E. Hill 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
Laser-Induced Breakdown Spectroscopy of silicon was performed using a nanosecond pulsed frequency doubled Nd:YAG (532 nm) laser. The temporal evolution of the laser ablation plumes in air at atmospheric pressure and at an ambient pressure of ∼ 10− 5 mbar is presented. Electron densities were determined from the Stark broadening of the Si (I) 288.16 nm emission line. Electron densities in the range of 6.91 × 1017 to 1.29 × 1019 cm− 3 at atmospheric pressure and 1.68 × 1017 to 3.02 × 1019 cm− 3 under vacuum were observed. Electron excitation temperatures were obtained from the line to continuum ratios and yielded temperatures in the range 7600–18,200 K at atmospheric pressure, and 8020–18,200 K under vacuum. The plasma morphology is also characterized with respect to time in both pressure regimes. 相似文献
45.
V. I. Nasonov 《Journal of Applied Spectroscopy》2006,73(2):234-244
Radiation scattering by particles of condensed phase in an ablation plasma plume has been experimentally studied during quasicontinuous
laser irradiation (λ = 1.06 μm, q = 0.1–9 MW/cm2, τ ∼ 1.5 msec) of duraluminum D16T, aluminum A99, and bismuth. The particle size distribution and the nature of their dispersal
during irradiation was studied in scattered light (λ = 0.69 μm) from individual particles that could be visually observed
on photographs. It was found that under the pressure developed in the plume, large particles ejected from the irradiated zone
can move backward and return to the target (D16T). The plume (Bi) becomes brighter due to ablation of particles in the path
of the laser beam. The directional scattering coefficients for scattering from the local zone on the axis of the plume, measured
during the laser pulse, were used to study the relationship between the dynamics of entry of condensed phase into the plume,
shielding of the target by the particles, and brightening of the plume under the action of the incident laser radiation.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 210–219, March–April, 2006. 相似文献
46.
Elemental mapping and quantitative analysis of Cu, Zn, and Fe in rat brain sections by laser ablation ICP-MS 总被引:1,自引:0,他引:1
This report details the application of laser ablation quadrupole ICP-MS for the (multi)elemental mapping of 100-μm-thick sections
of rat brain. The laser spot size used was 60 μm, and the laser scan speed was 120 μm s−1. The analysis was relatively rapid, allowing mapping of a whole brain thin section (≈1 cm2) in about 2 h. Furthermore, the method was amenable to multi-element data collection including the physiologically important
elements P and S and afforded sub μg g−1 detection limits for the important trace elements Cu and Zn. Calibrations were performed with pressed pellets of biological
certified reference materials, and the elemental distributions and concentrations of Cu, Zn, and Fe were determined in whole
rat brain sections. The distributions and concentration ranges for these elements were consistent with previous studies and
demonstrate the utility of this technique for rapid mapping of brain thin sections. 相似文献
47.
J. Hermann L. Mercadier E. Mothe G. Socol P. Alloncle 《Spectrochimica Acta Part B: Atomic Spectroscopy》2010
We have performed spectroscopic analysis of the plasma produced by pulsed laser ablation of brass in a low pressure argon atmosphere. The intensities of several spectral lines of copper, zinc and lead were measured for succeeding laser pulses applied to the same irradiation site. The intensities and spectral shapes of the observed transitions were compared to the spectral radiance computed for plasma in local thermal equilibrium. At a delay of 600 ns after the laser pulse, the plasma is characterized by typical values of temperature and electron density of 1.1 × 104 K and 1.2 × 1017 cm− 3, respectively, and an elemental composition equal to that of the sample. Small changes of spectral line intensities were observed with increasing number of applied laser pulses. They were attributed to the alteration of the plume expansion dynamics as a consequence of crater formation on the sample surface. The results indicate that the mass transfer from the solid to the plasma is stoichiometric. 相似文献
48.
The paper describes past and present efforts in modeling of laser-induced plasma and overviews plasma diagnostics carried out by pump-probe techniques. Besides general information on existing plasma models, the emphasis is given to models relevant to spectrochemical analysis, i.e. models of radiating plasma. Special attention is paid to collisional-radiative (CR) and collisional-dominated (CD) plasma models where radiative processes play an important role. Also, calibration-free (CF) models are considered which may endow with the possibility for standardless spectroscopic analysis. In the diagnostic part, only methods based on the use of additional diagnostic tools (auxiliary lasers, optics, and probes) are described omitting those based on plasma own radiation. A short review is provided on image-based diagnostics (shadowgraphy, schlieren, and interferometry), absorption and fluorescence, Langmuir probe, and less frequently used cavity ringdown and Thomson scattering methods. 相似文献
49.
50.
脉冲激光烧蚀金属平面铝靶产生的热原子与气相CF4碰撞反应中,在400—600nm之间观测到激发态C2分子的发光光谱,它们可归属为Swan带的d3Πg-a3Πu跃迁中Δv=2,1,0,-1,-2五个振动序列(v'≤6).光谱强度分析表明,C2激发态的振动温度达6340K左右.与激光烧蚀Al+O2反应生成AlO的实验结果以及激光烧蚀Cu+CF4的光谱比较,对比Al(2P1/2-2S1/2,3944nm)和C2的d—a跃迁(0—0)带带头(5165nm)的飞行时间轮廓,认为激发态的Al(2S1/2)原子通过
关键词:
激光烧蚀
发光光谱
C2分子 相似文献