Ultrasonic polar scans: numerical simulation on generally anisotropic media

Ultrasonic polar scans are based on the recording of the reflected or transmitted amplitude of sound, impinging a fiber reinforced composite from every possible angle of incidence. The mechanical anisotropy of such materials makes the reflection coefficient direction dependent, whence an ultrasonic polar scan forms a fingerprint of the investigated material. Such scans have already proved to be very valuable in the characterization of composites. Simulations have been performed for single layered and multi-layered systems, for pulsed and harmonic waves. Fiber reinforced composites are mostly orthotropic. The current report presents simulations not only on orthotropic materials but on materials of any kind of anisotropy. These extended numerical simulations are not only valuable in the characterization of highly sophisticated composites, but may also be used to characterize thin slices of crystals and even layered crystals.     

Stability of Nonlinear Subdivision and Multiscale Transforms

Extending upon the work of Cohen, Dyn, and Matei (Appl. Comput. Harmon. Anal. 15:89–116, 2003) and of Amat and Liandrat (Appl. Comput. Harmon. Anal. 18:198–206, 2005), we present a new general sufficient condition for the Lipschitz stability of nonlinear subdivision schemes and multiscale transforms in the univariate case. It covers the special cases (weighted essentially nonoscillatory scheme, piecewise polynomial harmonic transform) considered so far but also implies the stability in some new cases (median interpolating transform, power-p schemes, etc.). Although the investigation concentrates on multiscale transforms $\bigl\{v^0,d^1,\ldots,d^J\bigr\}\longmapsto v^J,\quad J\ge1,$ in ? _∞(?) given by a stationary recursion of the form $v^{j}=Sv^{j-1}+d^{j},\quad j\ge1,$ involving a nonlinear subdivision operator S acting on ? _∞(?), the approach is extendable to other nonlinear multiscale transforms and norms, as well.     

Reactive species generated during wet chemical etching of silicon in HF/HNO3 mixtures

The role of intermediate species generated during wet chemical etching of silicon in a HF-rich HF/HNO3 mixture was studied by spectroscopic and analytical methods at 1 degrees C. The intermediate N2O3 was identified by its cobalt blue color and the characteristic features in its UV-vis and Raman spectra. Furthermore, a complex N(III) species (3NO+.NO3-) denoted as [N4O6(2+)] is observed in these solutions. The time-dependent decay of the N(III) intermediates, mainly by their oxidation at the liquid-air interface, serves as a precondition for the study of the etch rate as function of the intermediate concentration measured by Raman spectroscopy. From a linear relationship between etch rate and [N4O6(2+)] concentration, NO+ is considered to be a reactive species in the rate-limiting step. This step is attributed to the oxidation of permanent existing Si-H bonds at the silicon surface by the reactive NO+ species. N2O3 serves as a reservoir for the generation of NO+ leading to a complete coverage of the silicon surface with reactive species at high intermediate concentrations. As long as this condition is valid (plateau region), the etch rate is constant and yields a smooth silicon surface upon completion of the etching. If the N2O3 concentration is insufficient to ensure a coverage of the Si surface by NO+, the etch rate decreases linearly with the N2O3 concentration and results in a roughening of the etched silicon surface (slope region).     

Surface processes during growth of InAs/GaAs quantum dot structures monitored by reflectance anisotropy spectroscopy

The time resolved reflectance anisotropy spectroscopy (RAS) measurement at 4.2 eV was used for the optimization of technological parameters for Stranski–Krastanow quantum dot (QD) formation. TMIn dosage and waiting time following InAs deposition during which QD formation takes place were optimized.RAS measurement helps us to study the MOVPE surface processes such as QD formation, dissolution of In from InAs QDs during the growth of GaAs capping layer or recovery of epitaxial surface from As deficiency, when As partial pressure is increased. We have shown, that the recovery of epitaxial surface from As deficiency is rather a slow process of the order of tens of seconds.We have for the first time observed in situ the mechanism of In atoms migration from QDs during GaAs capping layer growth. First the GaAs layer is formed and then the In migration from QDs follows. These two processes do not start at the same time, the In dissolution is delayed. Conclusions extracted from RAS measurement are in agreement with photoluminescence results.     

In situ growth of interdigitated electrodes made of polypyrrole for active fiber composites

Active fiber composites are electromechanical actuators based on piezo-ceramic fibers, which are embedded in a polymer matrix. The fibers are electrically contacted through so-called interdigitated electrodes (IDEs). State-of-the-art metallic IDEs only contact the fibers at two small sections of their circumference at the top and bottom of the composite ply, respectively. This paper presents an original technique to manufacture IDEs made of a conducting polymer (polypyrrole/p-toluene sulfonic acid), where the polymer electrodes contact the fibers around their whole circumference. The necessary process steps are discussed, namely design of the master electrodes and electrochemical polymer growth with and without fibers. Processing issues are discussed and solutions are suggested. Copyright © 2007 John Wiley & Sons, Ltd.     

Die Bestimmung des Phosgens

Ohne Zusammenfassung     

Optimal ATRP‐Made Soluble Polymer Supports for Phosphoramidite Chemistry

Soluble polystyrene supports with optimal molecular structures for iterative phosphoramidite chemistry were prepared by atom‐transfer radical polymerization (ATRP) and subsequent chain‐end modification steps. The controlled radical polymerization of styrene was first performed in the presence of an 9‐fluorenylmethoxycarbonyl (Fmoc)‐protected amino‐functional ATRP initiator. Soluble supports of different molecular weight were prepared. Size‐exclusion chromatography and NMR analysis indicated formation of well‐defined polymers with controlled chain lengths and narrow dispersity. After synthesis, the bromo ω end group of the ATRP polymer was removed by dehalogenation in the presence of tributyltin hydride, and the Fmoc protecting group of the α moiety was subsequently cleaved with piperidine. The resulting α‐primary amine was afterwards treated with a linker containing a carboxyl group, a cleavable ester site, and a dimethoxytrityl‐protected hydroxyl group to afford ideal soluble supports for phosphoramidite chemistry. NMR analysis indicated that these chain‐end modifications were quantitative. The supports were tested for the synthesis of a non‐natural sequence‐defined oligophosphates. High‐resolution ESI‐MS analysis of the cleaved oligomers indicated formation of uniform species, and thus confirmed the efficiency of the ATRP‐made soluble polymer supports. In addition, the synthesis of a thymidine‐loaded soluble support was achieved.     

Interaction of a bounded ultrasonic beam with a thin inclusion inside a plate

A theoretical study of the reflection of a two-dimensional Gaussian ultrasonic beam, incident at a Lamb angle of a plate containing a thin rectangular inclusion at an arbitrary position, is presented on the basis radiation mode theory. The inclusion is parallel to the plate surface and its thickness is assumed to be much smaller than the ultrasonic wavelength. It is shown that the amplitude and phase of the reflected beam profile can be used for accurate inclusion characterization. However, this only holds for certain internal positions of the inclusion and for material combinations that do not strongly perturb the excitation of Lamb waves in the plate. When these conditions are satisfied, it is possible to define the Lamb waves and the associated experimental conditions for which good estimates can be obtained of the position of the beginning point of the inclusion as well as of the length and the thickness of the inclusion.