Electron diffraction and microscopy of single-wall carbon nanotube bundles produced by different methods

The atomic structure of single-wall carbon nanotube bundles produced by three different techniques (laser ablation, electric arc discharge and catalytic chemical vapor deposition (CCVD)) has been characterized by electron diffraction and microscopy. Information on the helicity and the lattice packing has been obtained. Concerning the helicity, small bundles produced by CCVD exhibit only one or two tube helicities within a single bundle. The diffraction patterns of laser-ablation produced bundles also present well-defined but more diversified chiralities within a single bundle. By contrast the data acquired on bundles formed by arc discharge show a more diffuse pattern, characteristic of a random chirality dispersion within a single bundle. Concerning the lattice packing, informations are obtained via a detailed study of the equatorial line of the diffraction pattern for bundles produced by the three techniques. This electron diffraction study is completed by high-resolution electron microscopy. Received 8 August 2001 and Received in final form 14 March 2002     

New Receiving Mode of Extinction for Determining Particle Size and Density without Convex Lens

In this article a new receiving mode for scattering light by particle is theoretically discussed. Using this receiving mode the convex lens can be omitted during determining the extinction of particle. Therefore the extinction coefficient of sphere particles is redefined by extrapolating the conventional one. In terms of the calculation results of light scattering the definition of near-field extinction coefficient of a swarm particle is depicted. Through the error analysis it is proved that the error coming from the new definition of extinction coefficient is acceptable for engineering application. In addition, a technique for determining the particle size and density is presented in this article and the advantage using this receiving mode is described.     

Reliability of calculating the cepstral peak without linear regression analysis

Measures of cepstral peak prominence, using the smoothing algorithm and linear regression analysis software developed by Hillenbrand, have been shown to be reliable predictors of dysphonia in voice samples.(1-4) Recently, the Computerized Speech Laboratory [(CSL) Kay Elemetrics, Pinebrook, New Jersey] has introduced cepstral analysis as a component of that software package. The cepstral peak, in this instance, is calculated by the voice clinician analyzing the phonatory sample by subtracting the value of the peak from the apparent baseline signal. This study compares the ability of cepstral peak values calculated from the CSL software to predict dysphonia reliably with that of the values produced by the smoothing algorithm and linear regression analysis of Hillenbrand. The results of this study show that linear regression analysis is an important step in calculating the cepstral peak prominence, thus limiting the usefulness of software programs that do not employ this step.     

The efficient solution of electromagnetic scattering for inhomogeneous media

We consider an electromagnetic scattering problem for inhomogeneous media. In particular, we focus on the numerical computation of the electromagnetic scattered wave generated by the interaction of an electromagnetic plane wave and an inhomogeneity in the corresponding propagation medium. This problem is studied in the VV polarization case, where some special symmetry requirements for the incident wave and for the inhomogeneity are assumed. This problem is reformulated as a Fredholm integral equation of second kind, which is discretized by a linear system having a special form. This allows to compute efficiently an approximate solution of the scattering problem by using iterative techniques for linear systems. Some numerical examples are reported.     

Exclusive charge exchange reaction pD↦n(pp) within the Bethe-Salpeter formalism

The exclusive charge exchange reaction pD↦n(pp) at intermediate and high energies is studied within the Bethe-Salpeter formalism. The final-state interaction in the detected pp pair at nearly zero excitation energy is described by the ¹ S ₀ component of the Bethe-Salpeter amplitude. Results of numerical calculations of polarization observables and differential cross-section persuade that, as in the non-relativistic case, this reaction i) can be utilized as a “relativistic deuteron polarimeter” and ii) delivers further information about the elementary nucleon-nucleon charge exchange amplitude. Received: 26 November 2002 / Accepted: 30 January 2003 / Published online: 29 April 2003     

Determination of Soot Particle Size in a Premixed Flame: a Static and Dynamic Light Scattering Study

In this contribution we report upon our static and dynamic light scattering experiments to characterize soot particles in flames. We studied sooting laminar premixed flame with acetylene as fuel mixed with air as oxidizer. The air equivalence ratio of the combustion was larger than one. We used a Kaskan type burner with circular geometry and a stabilizing flow of nitrogen around the flame. We focused on the determination of the size of the soot particles in the center of the flame as a function of height above burner. In addition we investigated the influence of the mixing ratio of the gases on the size of the particles. Our results show that static light scattering is better suited than dynamic light scattering for a fast and reliable characterization of soot particles in flames. The latter needs detailed a priori information about the flame to allow the unique determination of sizes from the diffusion measurements. The soot particles grow monotonously with height above burner and with decreasing air equivalence ratio. The aggregates have a fractal dimension lower than two.     

Neutron dosimetry at low and high fluences with CR-39

In the Laboratory of Nuclear Microanalysis, we have developed two techniques for neutron dosimetry; the first for low fluence, the second for high fluence. These two techniques use a Solid State Nuclear Track Detector (SSNTD): the CR-39. The low fluence technique is based on the measurement of etched tracks resulting from a neutron-proton conversion. A Monte Carlo code performs a simulation of the (n,p) collision in the detector, and a numerical computer code of latent track etching allows the evaluation of the etched track parameters. The object of this is to obtain characteristics of a neutron fluence from the measured etched track parameters. When there is a high fluence and high doses, CR-39 is unsuited for optical microscopy analysis. This is because of track overlapping which makes it impossible to carry out counting and exploitation. We have therefore developed a new method permitting the reading of samples based on the measurement of the angular distribution of coherent light (He---Ne laser) transmitted through the irradiated etched SSNTD. We present these two techniques and our initial results.     

基于POT方法的商业银行操作风险极端值估计

对于商业银行而言,操作风险已经成为与市场风险和信用风险同样重要的风险。本文利用极值理论超越样本的估计能力,采用极值理论中对数据要求量较少,可以进行单步预测的超阈值(POT)方法对我国商业银行操作损失极端值分布进行估计,以均值超额函数图和拟合直线的交点确定阈值,估计出给定置信水平之下操作风险损失的分位数,从而使得国内商业银行操作风险监管资本的计算成为可能。     

The effect of evanescent wave modes on scattering and near-trapping

The effect of evanescent modes on the scattering and near-trappingof small-amplitude waves over axisymmetric topography is investigated.A two-stage numerical implementation, which facilitates an examinationof the resonant frequencies associated with near-trapping, isdeveloped. This is achieved in the latter stage of the procedureby dealing with the progressing and decaying waves separately. Numerical results are given for a selection of bed shapes, andit is found that the evanescent waves can have a significanteffect on scattering. Numerical evidence is found that, forthe selection of bed profiles considered, no new resonant frequenciesare introduced by the inclusion of the decaying wave components,but that the inclusion of these decaying waves does improveprevious approximations to resonant frequencies.     

Ternäre intermetallische Phasen des Lithiums mit Elementen der 4. Neben- und 5. Hauptgruppe mit statistischer Metallverteilung im „Kationen”︁-Teilgitter

Ternary Intermetallic Phases of Lithium, Transition Metals of the 4^th Group and Elements of the 5^th Maingroup with Statistical Metal Distribution in the ?Cation”?-Substructure The results of X-ray investigations and neutron diffraction on new and in some cases already known [1, 2] ternary intermetallic phases of Lithium with transition metals of the 4^th group (b) and those of the 5^th main group (X = P, As, Sb, Bi) will be reported. They crystallize in a partly ?filled”? antifluorite type structure with a statistical Li/B-distribution in the tetrahedral sites. The structures are obviously stabilized by small amounts of enclosed d-elements.