Guided wave helical ultrasonic tomography of pipes

Ultrasonic guided waves have been used for a wide variety of ultrasonic inspection techniques. We describe here a new variation called helical ultrasound tomography (HUT) that uses guided ultrasonic waves along with tomographic reconstruction algorithms that have been developed by seismologists for what they call "cross borehole" tomography. In HUT, the Lamb-like guided waves travel the various helical criss-cross paths between two parallel circumferential transducer arrays instead of the planar criss-cross seismic paths between two boreholes. Although the measurement itself is fairly complicated, the output of the tomographic reconstruction is a readily interpretable map of a quantity of interest such as pipe wall thickness. In this paper we demonstrate HUT via laboratory scans on steel pipe segments into which controlled thinnings have been introduced.     

pH responsive Eu(III)-phenanthroline supramolecular conjugate: novel "off-on-off" luminescent signaling in the physiological pH range

The formation of luminescent supramolecular ternary complexes in water: delayed luminescence sensing of aromatic carboxylates using coordinated unsaturated cationic heptadenatate lanthanide ion complexes.     

A transient N-O-linked Pauson-Khand strategy for the synthesis of the deschloro carbocyclic core of the palau'amines and styloguanidines

A stereocontrolled route to the deschloro cyclopentyl core of the palau'amines and styloguanidines has been developed. This strategy makes use of the intramolecular Pauson-Khand cyclization of an enyne with a "transient N-O tether" to construct a five-membered carbocycle in a diastereoselective fashion. [reaction: see text]     

Borel Subalgebras Redux with Examples from Algebraic and Quantum Groups

Both building upon and revising previous literature, this paper formulates the general notion of a Borel subalgebra B of a quasi-hereditary algebra A. We present various general constructions of Borel subalgebras, establish a triangular factorization of A, and relate the concept to graded Kazhdan–Lusztig theories in the sense of Cline et al. (Tôhoku Math. J. 45 (1993), 511–534). Various interesting types of Borel subalgebras arise naturally in different contexts. For example, `excellent" Borel subalgebras come about by abstracting the theory of Schubert varieties. Numerous examples from algebraic groups, q-Schur algebras, and quantum groups are considered in detail.     

Negative differential resistance in nanotube devices

Carbon nanotube junctions are predicted to exhibit negative differential resistance, with very high peak-to-valley current ratios even at room temperature. We treat both nanotube p-n junctions and undoped metal-nanotube-metal junctions, calculating quantum transport through the self-consistent potential within a tight-binding approximation. The undoped junctions in particular may be suitable for device integration.     

Polymerization of α-Methylstyrene in p-Dioxane with Potassium as Initiator. III. Gel-Permeation Chromatographic Analyses of Polymers

Gel-permeation chromatographic studies on poly-α-methyl-styrene initiated with potassium and potassium-naphthalene in p-dioxane as solvent and polymerized at 5, 15, 25, and 40°C, have been carried out. Bimodal and trimodal distributions are observed in these polymers. It has been shown that these multimodal distributions do not arise because of the monofunctional and bifunctional living ends produced by the reaction of solvent dioxane with the living polymer. These, on the other hand, may be related to the presence of different ion-pairs which contribute to the reaction but to different extents. Contrary to the belief that only contact ion-pairs are responsible for propagation in p-dioxane because of its low dielectric constant, the presence of solvent-separated ion-pairs yielding reversible propagation has been speculated. The different components (D + A), B, and C, similar to the ones present in the a-methyl-styrene-potassium tetrahydrofuran system, have been found in the present study also and are attributed to the dead and a dormant polymer, solvent-separated ion-pair polymer, and that due to a contact pair, respectively. The extent of the formation of component (D + A) has been linked directly to the concentration of living ends. In reactions where naphthalene was used along with potassium for initiation purposes, a unique component yielding reversible propagation was observed. This has been attributed to the presence of polymer due to potassium-naphthalene complex which is different in character to a contact ion-pair but may resemble a solvent-separated ion-pair.     

Infrared diffuse reflectance instrumentation and standards at NIST

A spectrophotometer system for spectral characterization of materials in the infrared has been built around a bench-top Fourier transform instrument. Its capabilities include the measurement of directional-hemispherical reflectance from 1 to 18 μm. The spectral reflectance measurement is performed with an integrating sphere with an incidence angle of 8°. Both relative and absolute measurements can be made. Several methods can be used to determine the absolute value of the directional-hemispherical reflectance of samples. The primary method used is independent of the integrating sphere theory and the requisite assumptions associated with its use. The calibration of a standard reference material (SRM) is described. This SRM has a reflectance value near 0.9 over the complete calibration range 2–18 μm. As part of the calibration procedure the spatial uniformity of the sphere throughput and the bi-directional reflectance distribution function (BRDF) of the SRM material are evaluated.