Application of SSNTDs for study of boron distribution in alloys

A study of boron behavior and its distribution in boron doped iron-, nickel- and aluminum-base alloys subjected to various treatment conditions has been performed. For this purpose a technique based on the detection of ¹⁰B(n,)⁷Li reaction products with track etch detectors has been applied. High boron enrichment of grain boundaries of both iron base and ingot nickel base alloys has been observed. After hot and then cold rolling of the latter specimens boron rearrangement along with the proper deformation of the structure took place. Striation of boron in a hot rolled aluminum alloy along the rolling direction has been observed.     

A three‐dimensional vortex particle‐in‐cell method for vortex motions in the vicinity of a wall

A new vortex particle‐in‐cell method for the simulation of three‐dimensional unsteady incompressible viscous flow is presented. The projection of the vortex strengths onto the mesh is based on volume interpolation. The convection of vorticity is treated as a Lagrangian move operation but one where the velocity of each particle is interpolated from an Eulerian mesh solution of velocity–Poisson equations. The change in vorticity due to diffusion is also computed on the Eulerian mesh and projected back to the particles. Where diffusive fluxes cause vorticity to enter a cell not already containing any particles new particles are created. The surface vorticity and the cancellation of tangential velocity at the plate are related by the Neumann conditions. The basic framework for implementation of the procedure is also introduced where the solution update comprises a sequence of two fractional steps. The method is applied to a problem where an unsteady boundary layer develops under the impact of a vortex ring and comparison is made with the experimental and numerical literature. Copyright © 2001 John Wiley & Sons, Ltd.     

Scattering states of charged particles in the ℤ2 gauge theoriesgauge theories

Scattering states of charged particles in a massive Euclidean lattice gauge model are constructed.Partially supported by CNPq     

Strong lateral electron coupling of pb nanowires on stepped si(111): angle-resolved photoemission studies

We employ angle-resolved photoemission to characterize the electronic band structure of the Pb "nanowire" array self-assembled on a stepped Si(111) surface. Despite the highly oriented nanowires observed in scanning tunneling microscopy images, we find essentially two-dimensional Fermi contours modulated one dimensionally perpendicular to the wires. This strong two-dimensional and quasi-one-dimensional nature of the band structure explains the stability and anisotropy of the metallic phase down to 4 K as reported recently. A simple tight-binding model with each Si nanoterrace covered by a densely packed Pb overlayer successfully reproduces this modulated band structure and quantifies the electron coupling within the "nanostripes" and the step-edge potential.     

Development of an integrated optical system for warpage and hermeticity test of microdisplay

We have developed an integrated optical system to measure the warpage of a microdisplay product at post-packaging die-attach temperature and to test its hermeticity after manufacturing. This system is constructed based on the principle of Twyman/Green (T/G) interferometry and Newton interferometry. T/G interferometry is used to characterize warpage of the microdisplay's base-plate, while Newton interferometry is used to characterize the gap variance between face-plate and base-plate of the microdisplay. With these measurements, deformation and shape of the microdisplay can be comprehensively determined during its manufacturing process, which is critical for its quality test and reliability evaluation. Delicate mechanical system was designed to facilitate the optics integration and alignment. To evaluate the performance of the optical system itself, warpage of a sample was re-measured with Tailor–Hobson profilometer whose resolution is 10 nm, the results from these two testing systems agree well with each other. Some application examples of the integrated testing system were presented to verify its work efficiency.     

Passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering

We demonstrate passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering (SBS). Four off-axis beams are combined in a long multimode optical fiber using a novel all-optical mount. The combined beam has the high spatial coherence properties of the LP(01) mode owing to the beam cleanup properties of SBS. The threshold for SBS when off-axis pumps are used is shown to be a factor of 13 times higher than for on-axis pump beams. We propose this method would improve the brightness of an array of fiber amplifiers.     

Confidence intervals and ellipsoids for estimable functions and estimable vectors in models with orthogonal block structure

Sub-models of mixed linear models are considered. The independence of these sub-models leads to sufficient statistics for the parameters relevant for their densities. Using pivot variables, confidence regions are obtained as well hypothesis testing for variance components, estimable functions, and estimable vectors. In addition, to compare the estimators and the models, we present the histograms with the empirical joint densities for positive and negative parts of the estimators. The figures, for the two-dimensional charts, contain the corresponding UMVUE and are all unimodal with the UMVUE near the mode. The nearness of the estimators and the modes validates the presented methodology and allows the safe use of induced densities. A numerical example applied to real data is presented.     

Stability of low Reynolds number flow with viscous heating

Summary The stability of fully developed plane Couette flow and pipe flow with viscous heating is studied at low Reynolds number for a Newtonian liquid with a temperature-dependent viscosity. The solution is obtained by a direct integration method of the eigenfunction equations, with eigenvalues located in the complex plane by means of the argument principle of complex variable theory. An instability will occur in plane Couette flow, but outside the parameter range which will be encountered in practice. There is no comparable instability in pipe flow. It can be concluded that a thermal mechanism does not cause the low Reynolds number instabilities observed in polymer processing operations.

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Zusammenfassung Für eine newtonsche Flüssigkeit mit temperaturabhängiger Viskosität wird die Stabilität der voll entwickelten ebenen Couette-Strömung und Rohrströmung bei niedrigen Reynolds-Zahlen untersucht. Die Lösung wird durch direkte Integration der Eigenwert-Gleichungen gewonnen, wobei das Argument-Prinzip der Funktionentheorie auf die in der komplexen Ebene gelegenen Eigenwerte angewandt wird. In der ebenen Couette-Strömung wird eine Instabilität gefunden, jedoch außerhalb des in der Praxis realisierten Parameter-Bereichs. In der Rohrströmung gibt es dagegen keine vergleichbare Instabilität. Man kommt zu dem Schluß, daß thermische Mechanismen nicht für die in Polymer-Verarbeitungsprozessen beobachteten bei niedrigen Reynolds-Zahlen auftretenden Instabilitäten verantwortlich gemacht werden können.

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With 6 figures and 1 table     

Regioselective Acceptorless Dehydrogenative Coupling of N‐Heterocycles toward Functionalized Quinolines,Phenanthrolines, and Indoles

A new strategy has been developed for the oxidant‐ and base‐free dehydrogenative coupling of N‐heterocycles at mild conditions. Under the action of an iridium catalyst, N‐heterocycles undergo multiple sp³ C? H activation steps, generating a nucleophilic enamine that reacts in situ with various electrophiles to give highly functionalized products. The dehydrogenative coupling can be cascaded with Friedel–Crafts addition, resulting in a double functionalization of the N‐heterocycles.