Cross Sections of Excitation of 3F-Levels of Nickel Atom by Electron Impact

The excitation of ³ F-levels of the nickel atom during collisions with slow electrons is investigated by the method of extended crossing beams using optical spectroscopy. Forty excitation cross sections are measured at the electron energy of 50 eV and seven optical excitation functions. The obtained data are used to calculate the total excitation cross sections of the levels e ³ F, f³ F, g ³ F, h ³ F, and i ³ F. The levels of the state 3d ⁸4s(⁴ F)5sf³ Fare excited most effectively.     

Cross Sections of Excitation of Resonance Transitions of EuI by Electron Impact

The excitation of resonance transitions of a europium atom by electron impact is investigated using the method of extended crossing beams. Comparison of the obtained results with data of previous investigations shows that the form of the optical excitation functions is in good agreement with the experimental data but differs considerably from the theoretical ones. The absolute values of cross sections at the electron energy of 100 eV are close to predicted values and exceed the data of the previous experiment by two orders of magnitude.     

Excitation of 6S0, 6P0, and 6D0Levels of Niobium Atom by Electron Impact

The excitation of odd sextet levels of the niobium atom in collisions with slow electrons is investigated experimentally. The measured values of the excitation cross sections of the spectral lines of NbI are used to determine the excitation cross sections of energy levels. The available reference data on the branching factors are used for more complete inclusion of branching. The obtained values of excitation cross sections of the levels of the niobium atom are compared with the theoretical values.     

Two-Photon Fluorescence Excitation Cross Sections of Biomolecular Probes from 690 to 960 nm

We report on two-photon fluorescence excitation (TPE) action cross sections for five widely used molecular fluorophores. Measurements were performed by use of ultrashort (~100-fs) Ti:sapphire pulsed excitation over the range 690-960 nm. TPE spectra were obtained by comparison with a fluorescein calibration standard. Large cross sections were found for the cyanine reagent Cy 3 (~140 GM) and for Rhodamine 6G (~150 GM), both at 700 nm [1 GM = 10(-50) (cm(4) s)/photon]. Several fluorophores show interesting and desirable blue shifts with respect to twice the one-photon absorption wavelength. Fluorophore fluorescence intensities showed no significant departure (?4%) from quadratic illumination power dependence, indicating genuine two-photon processes. Implications of these measurements for two-photon laser-scanning microscopy are discussed.     

Building Structures Atom by Atom via Electron Beam Manipulation

Building materials from the atom up is the pinnacle of materials fabrication. Until recently the only platform that offered single‐atom manipulation was scanning tunneling microscopy. Here controlled manipulation and assembly of a few atom structures are demonstrated by bringing together single atoms using a scanning transmission electron microscope. An atomically focused electron beam is used to introduce Si substitutional defects and defect clusters in graphene with spatial control of a few nanometers and enable controlled motion of Si atoms. The Si substitutional defects are then further manipulated to form dimers, trimers, and more complex structures. The dynamics of a beam‐induced atomic‐scale chemical process is captured in a time‐series of images at atomic resolution. These studies suggest that control of the e‐beam‐induced local processes offers the next step toward atom‐by‐atom nanofabrication, providing an enabling tool for the study of atomic‐scale chemistry in 2D materials and fabrication of predefined structures and defects with atomic specificity.     

Excitation of PtI Transitions Terminating on Singlet Levels

The method of extended crossing beams is used to investigate the excitation of platinum atom transitions terminating on singlet levels. Thirty eight excitation cross sections are measured at the electron energy of 30 eV; nine optical excitation functions are recorded in the electron energy range from zero to 200 eV. Also measured are eight excitation cross sections of transitions which have even upper levels. Possible excitation channels are discussed, which define the absolute values of cross sections and the form of optical excitation functions.__________Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 4, 2005, pp. 510–515.Original Russian Text Copyright © 2005 by Yu. M. Smirnov.     

加载路径对变径管内高压成形影响的模拟研究

基于Dynaform有限元模拟软件,在获得合适总轴向进给量以及最大内压力的基础上,重点探讨了轴向进给路径以及内压力加载路径对变径管内高压成形的影响。结果表明：按照前段进给速度大于后段进给速度的双线性轴向进给方式进给能得到一条最优的轴向进给路径;梯形内压加载方式的成形结果要明显优于线性内压加载方式,且当内压区间为40～60MPa时,梯形内压加载方式的成形结果达到最优化。     

Electron-Impact Total Ionization Cross Sections of Hydrocarbon Ions

The Binary-Encounter-Bethe (BEB) model for electron-impact total ionization cross sections has been applied to CH2+, CH3+, CH4+, C2H2+, C2H4+, C2H6+ and H₃O⁺. The cross sections for the hydrocarbon ions are needed for modeling cool plasmas in fusion devices. No experimental data are available for direct comparison. Molecular constants to generate total ionization cross sections at arbitrary incident electron energies using the BEB formula are presented. A recent experimental result on the ionization of H₃O⁺ is found to be almost 1/20 of the present theory at the cross section peak.     

Electron-Impact Total Ionization Cross Sections of Molecular Ions

The Binary-Encounter-Bethe (BEB) model for electron-impact total ionization cross sections of neutral molecules has been modified for molecular positive ions. The total ionization cross sections for H2+, N2+, CD⁺, and CO⁺ from the modified BEB formula are compared to available experimental data. The theory is in good agreement with experimental data on H2+, N2+, and CD⁺, but the experimental data by Belic et al. on N2+, and CO⁺ are lower than the theory. The large difference between the theory and experiment on CO⁺ is a strong indication of the dominance of the dissociative ionization channel, CO⁺→C⁺+O⁺, which was not included in the experiment.     

The Measurement of Neutron Cross Sections for Contrast-Enhancing Penetrant Fluids

Abstract

The purpose of this experiment was to evaluate penetrant fluids of high neutron cross section. These fluids are useful in neutron radiographic investigations for contrast enhancement. Saturated solutions of the gadolinium salts and one chelate were formed by using one of several solvents, and the resulting fluid's macroscopic neutron cross sections were measured experimentally.

The results of this experiment provided a quantitative measure of the mean and standard deviation of the macroscopic neutron cross section for the penetrant fluids. In addition, a confidence interval was generated for each fluid. The measured neutron cross section for a control fluid was in close agreement with published values.     

Mutiple Ionization of Rare Gases by Electron Impact

Electron impact studies of multiple ionization processes in helium, neon, argon, and xenon appear to support theoretical conclusions that the threshold probability for n-fold ionization is proportional to the nth power of the electron energy in excess of the threshold energy. The probability law applies, for the cases studied, over a considerable energy range that, for all but He²⁺, includes the possible onset of more than one mode of ionization. The presence of a Boltzmann spread in the energy of the electron beam or specific focusing effects due to ion source geometry are found to affect only the foot of the probability curve. By the use of certain assumptions, an estimate is also made of the departure from a ³P ionization probability curve resulting from onset of ionization to the ¹D and ¹S states.     

Experimental Cross Sections of Erbium-Doped Silica Fibers Pumped at 1480 nm

Absorption and stimulated emission coefficients for a pump power at 1480 nm are determined experimentally for three types of erbium-doped silica fiber. Starting from these coefficients and using previous gain measurements, we calculate absorption and stimulated emission cross sections of the erbium laser transition. The results obtained are in good agreement with the ones that appear in the literature.     

复杂变截面梁的轴向自由振动分析的近似方法

介绍了带有附加影响的变截面梁轴向自由振动问题的求解方法－模态摄动法，这一方法在由等截面均匀梁低阶主模态函数组成的模态子空间中，将复杂梁的变系数微分方程的求解化为线性代数方程组的求解，从而简化了计算过程，通过与其它方法的比较，说明了本文方法的优越性。     

Electron-Impact Total Ionization Cross Sections of CH and C2H2

Electron-impact total ionization cross sections for the CH radical and C₂H₂ (acetylene) have been calculated using the Binary-Encounter-Bethe (BEB) model. The BEB model combines the Mott cross section and the asymptotic form of the Bethe theory, and has been shown to generate reliable ionization cross sections for a large variety of molecules. The BEB cross sections for CH and C₂H₂ are in good agreement with the available experimental data from ionization thresholds to hundreds of eV in incident energies.     

Excitation of Resonance Transitions of Neodymium Atom in Ultraviolet in e–Nd Collisions

The excitation of resonance transitions of neodymium atoms in ultraviolet is investigated using the method of extended crossing beams. The majority of the measured cross sections lie in the range from 10^–17 to 10^–18 cm². Thirty-one optical excitation functions are registered upon variation of the electron energy from the excitation threshold to 200 eV. For 39 transitions, a classification within the framework of the known system of terms is suggested.     

Electron Addition and Excitation Spectra of Individual Single-wall Carbon Nanotubes

We present mK-temperature non-linear current-voltagecharacteristics of an individual single-wall carbon nanotubeas a function of magnetic field. The measurements show Coulombblockade and resonant tunneling through single molecularlevels. Correlations between the addition spectrum and theexcitation spectrum are observed. The magnetic fielddependence of the addition and excitation spectra isdiscussed.     

Electron-Impact Cross Sections for Ground State to np Excitations of Sodium and Potassium

Cross sections for electron impact excitation of atoms are important for modeling of low temperature plasmas and gases. While there are many experimental and theoretical results for excitation to the first excited states, little information is available for excitation to higher states. We present here calculations of excitations from the ground state to the np levels of sodium (n = 3 through 11) and potassium (n = 4 through 12). We also present a calculation for a transition from the excited sodium level 3p to 3d to show the generality of the method. Scaling formulas developed earlier by Kim [Phys. Rev. A 64, 032713 (2001)] for plane-wave Born cross sections are used. These formulas have been shown to be remarkably accurate yet simple to use. We have used a core polarization potential in a Dirac-Fock wave function code to calculate target atom wave functions and a matching form of the dipole transition operator to calculate oscillator strengths and Born cross sections. The scaled Born results here for excitation to the first excited levels are in very good agreement with experimental and other theoretical data, and the results for excitation to the next few levels are in satisfactory agreement with the limited data available. The present results for excitation to the higher levels are believed to be the only data available.     

基于圆环和等强度截面的纤维缠绕环形容器设计与分析

复合材料环形压力容器以其特有的结构形状得到了日益广泛的应用.目前关于纤维缠绕环形容器的研究主要局限于测地线缠绕圆环截面容器.由于环形容器的结构效率取决于它的管截面形状,所以使用圆环截面的环形容器无法实现等强度结构.本文提出了分别使用圆环截面和等强度截面的环形压力容器设计方法,并对二者进行了比较.基于最小应变能准则,得到了缠绕层铺设角和环壳内力间的最优化关系.根据网格理论,考虑截面缠绕层的厚度变化,导出了圆环容器缠绕的最优线型.引入应力比,分析了环壳上纤维的应力分布.描述了等强度经线曲线的一般形状,分析了轴向截荷对等强度曲线形状的影响.计算结果表明当轴向载荷达到一定数值时,等强度曲线能够实现闭合形成环形容器.进一步计算和比较了两种截面形状的环形压力容器在不同相对弯曲半径下的结构质量.研究表明,使用等强度截面设计的环形容器比使用圆环截面的环形容器要轻的多.通过等强度截面设计,环形压力容器的结构性能得到了明显的提高.