Non-destructive testing of tubes using a time reverse numerical simulation (TRNS) method

A method for the detection of defects in cylindrical structures and the determination of their positions and orientations is presented in this paper. The scattered field, which is generated by the interaction of excited guided waves with a defect, is evaluated with an approach named time reverse numerical simulation method (TRNS). Since the excited waves and the scattered field propagate along the sample, the time-consuming scanning of the whole tube can be eliminated. The scattered displacement field is measured in three dimensions over time with a laser vibrometer at different locations distributed equally around the circumference at a fixed axial coordinate far away from the defect. Instead of analyzing the complicated time signals directly, they are played back in time. If the recorded displacement histories of the scattered field are reversed in time and played back in an identical structure, the waves travel back the same path and interfere to a maximum at their origin. The result is an amplitude increase at the position of the defect where the scattered field was generated. Instead of playing back the recorded time signals in an experiment, this step is replaced by a numerical simulation. Only this enables the visualization and detection of the amplitude increase. As long as the simulation is of high accuracy, the position of the maximum interference corresponds exactly to the location of the defect in the experiment, although no defect is implemented in the simulation.     

Investigation into factors affecting precision in ion trap mass spectrometry using different scan directions and axial modulation potential amplitudes

Electrospray ionization mass spectra obtained from different scan directions are observed to be dependent on the axial modulation potential amplitudes used for resonant ejection and on the positive deviation caused by higher even-multipole fields present in most commercial ion traps. The axial modulation voltage influences the dissociation of ions during resonant ejection and the observed mass shifts. The higher even-multipole fields in commercial ion traps are known to influence resonant ejection from the ion trap and can cause a loss in mass resolution for peaks in reverse scan mass spectra compared with that obtained by the forward scan. However, along with the dissociation of ions during resonant ejection causing a loss in resolution, the possibility of resolving an isotopic distribution is also shown to be influenced by the mass shifts caused by the space charge. These mass shifts differ depending on the scan direction employed. A significant loss in resolution can also result from resonant ejection using non-optimal axial modulation voltages. We also present results showing the ejection of ions at betaz = 1/2 using the reverse scan mode without the axial modulation voltage. Ion ejection at betaz = 1/2 is uncommon in commercial (stretched ion traps) with the conventional analytical scan without the use of a frequency of the axial modulation voltage corresponding to this non-linear resonance.     

Specific Interaction of Coproporphyrin I with Antibodies in Water and Reverse Micelles: Dimerization of Antibodies Affects Antigen Binding Site

The antigen-antibody interaction between coproporphyrin I and anti-coproporphyrin antibodies was studied by a fluorescence method in water and a reverse micellar system: n-octane/Aerosol OT. Coproporphyrin fluorescence was quenched, and coproporphyrin emission maximum was shifted to the long-wavelength region after binding to the antibodies or Fab-fragments. The mechanism of this quenching is static, most probably, by a tryptophan residue (or maybe lysine or methionine). Apparent dynamic quenching, in this case, arises from protein backbone motion. A special kind of antibody Fab-Fab dimerization was proposed.     

Dependence Properties of Multivariate Mixture Distributions and Their Applications

Consider a multivariate mixture model where the random variables X ₁, ..., X _n given (₁, ..., _n ), are conditionally independent. Conditions are obtained under which different kinds of positive dependence hold among X _i 's. The results obtained are applied to a variety of problems including the concomitants of order statistics and of record values; and to frailty models.     

Facile fabrication and optical properties of novel Pb(OH)Cl nanotubes

Uniform Pb(OH)Cl nanotubes were synthesized for the first time through a reverse micelles system. The system was consisting of C₁₂E₉ as a surfactant, n-pentanol as a cosurfactant, hexamethylene as the continuous oil phase and lead acetate or sodium chloride solution as the dispersed aqueous phase. The obtained Pb(OH)Cl nanotubes have an average outer diameter of 60 nm, inner diameter of about 40 nm, and an length up to 3 μm as TEM picture showed. And the range of the nanotube diameter is from 50 nm to 70 nm. XRD result indicated that Pb(OH)Cl crystallized in an orthorhombic phase. Photoluminescent (PL) spectrum showed that the product emit in near ultraviolet region and visible region at 335 nm and 439 nm respectively. The experimental results show that reaction temperature have effect on the shape of Pb(OH)Cl nanotubes. A possible formation mechanism was also discussed.     

基于X射线断层成像的逆向工程中轮廓序列分割算法的原理及实现

为了实现基于X射线断层成像(CT)的逆向工程中具有参数识别的三维图像重构, 提出了一种分割轮廓序列的新算法. 首先通过一定角度的射线法来得到轮廓间的嵌套关系,然后采用扫描一次关系矩阵生成轮廓树的方法实现层内轮廓定位, 最后运用轮廓间定量、定性的属性判定来完成层间的轮廓匹配. 通过实例, 本文提供的算法可以准确、快速地分割CT零件中的轮廓序列.     

Step-economic synthesis of (±)-debromoflustramine A using indole C3 activation strategy

A concise and practical strategy to obtain C3 reverse-prenylated pyrrolidinoindoline scaffold has been executed in 28.8% overall yield. The key conjugative step involved a Booker-Milburn-Feudoloff reaction involving an NCS-mediated activation of indole, followed by coupling to C₅ dimethylallylalcohol. This linchpin step proceeded in 74% yield. The overall sequence proceeded in five steps from commercially available N-methyltryptamine with a single protection-deprotection operation and a single redox manipulation. Mechanistic insights of NCS activation, and an ensuing rearrangement of the isoprene unit were gained by rationally varying the C3 substituent.     

The influence of the structure of tetracoordinate phosphorus acid esters on the catalytic effect of the sodium dodecyl sulfate-hexanol-water ternary reverse micellar system

The catalytic effect of the sodium dodecyl sulfate-hexanol-water ternary reverse micellar system in the alkaline hydrolysis ofO-alkylO′-aryl chloromethylphosphonates as a function of the substrate structure was studied. The micellar effect is mainly determined by a change in the electronic properties of the substituents, while the hydrophobicity plays a secondary role. The kinetic data were examined in the framework of the pseudo-phase model of micellar catalysis. The rate constants of the reaction in the surface layer and the partition constants of the reactants were calculated. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1366–1370., August, 2000.     

Nondifferentiable reverse convex programs and facetial convexity cuts via a disjunctive characterization

Disjunctive Programs can often be transcribed as reverse convex constrained problems with nondifferentiable constraints and unbounded feasible regions. We consider this general class of nonconvex programs, called Reverse Convex Programs (RCP), and show that under quite general conditions, the closure of the convex hull of the feasible region is polyhedral. This development is then pursued from a more constructive standpoint, in that, for certain special reverse convex sets, we specify a finite linear disjunction whose closed convex hull coincides with that of the special reverse convex set. When interpreted in the context of convexity/intersection cuts, this provides the capability of generating any (negative edge extension) facet cut. Although this characterization is more clarifying than computationally oriented, our development shows that if certain bounds are available, then convexity/intersection cuts can be strengthened relatively inexpensively.