Reductive alkylation of beta-alkoxy aziridines: new route to substituted allylic amines

[reaction: see text] A new route to substituted cyclic allylic amines via the reductive alkylation of beta-alkoxy aziridines using excess alkyllithium reagents is described.     

Towards the Discrimination of Carboxylates by Hydrogen‐Bond Donor Anion Receptors

The binding constants (log K_ass) of small synthetic receptor molecules based on indolocarbazole, carbazole, indole, urea and some others, as well as their combinations were measured for small carboxylate anions of different basicity, hydrophilicity and steric demands, that is, trimethylacetate, acetate, benzoate and lactate, in 0.5 % H₂O/[D₆]DMSO by using the relative NMR‐based measurement method. As a result, four separate binding affinity scales (ladders) including thirty‐eight receptors were obtained with the scales anchored to indolocarbazole. The results indicate that the binding strength is largely, but not fully, determined by the strength of the primary hydrogen‐bonding interaction. The latter in turn is largely determined by the basicity of the anion. The higher is the basicity of the anion the stronger in general is the binding, leading to the approximate order of increasing binding strength, lactate<benzoate<acetate≤trimethylacetate, which holds with all investigated receptors. Nevertheless, there are a number of occasions when the binding order changes with changing of the carboxylate anion, sometimes quite substantially. Principal component analysis (PCA) reveals that this is primarily connected to preferential binding of trimethylacetate, supposedly caused by an additional hydrophobic/solvophobic interaction. These findings enable making better predictions, which receptor framework or cavity is best suited for carboxylate anions in receptor design.     

Rheological characteristics of sewage sludge: A granuloviscous material

Problems have been experienced in the screw conveying of a centrifuge dewatered sewage sludge, at about 66% by weight water content. The rheology of the sludge was therefore tested in a viscometer in which the normal stress between the platens could be controlled. Rough platens were used to measure internal shear strengths while smooth steel platens were used to study wall slip.The sludge displayed a number of the characteristics of a granuloviscous material. It was found to possess high initial shear strength, but rapidly softened with shear to lower steady-state strengths. The initial shear strength increased with increasing normal stress, indicating that the sludge was frictional. The initial strength was lower against the smooth platen.The steady-state shear strengths were both rate and stress dependent using the rough platen, and this internal shear strength could be described by a frictional pseudoplastic equation. Using the smooth platen the material was nearly rate independent, and was best described by a Coulomb friction equation. At the higher rates the wall shear strengths were lower than the internal shear strengths.The strengths (both initial and steady-state) were characterised by a high degree of variability from sample to sample, and also showed marked hysteresis with the rough platen. They did not show any consistent variation with moisture content.In terms of screw conveying, the major conclusion is that smooth walls to the flights of the screw and barrel of the conveyor are desirable.     

Exponentially closed fields and the conjecture on intersections with tori

We give an axiomatization of the class ECF of exponentially closed fields, which includes the pseudo-exponential fields previously introduced by the second author, and show that it is superstable over its interpretation of arithmetic. Furthermore, ECF is exactly the elementary class of the pseudo-exponential fields if and only if the Diophantine conjecture CIT on atypical intersections of tori with subvarieties is true.     

Electron sources utilizing thin CsBr coatings

We present experimental results obtained in solid Cu targets coated with ～18 nm thick CsBr films operating in a reflection mode. The results indicate a factor of 50X increase in quantum efficiency relative to uncoated Cu samples. The CsBr/Cu samples are very robust allowing brief exposures to air without a substantial decrease in quantum efficiency and lifetime. The results are very encouraging from the point of view of reliable high efficiency electron sources for lithography or other applications including free electron lasers.     

Millimeter-Wave Profiled Corrugated Horns for the Quad Cosmic Background Polarization Experiment

In this paper we report on the design and validation process for the profiled corrugated horn antennas, which feed the bolometer array of a cosmology experiment known as QUaD located at the South Pole. This is a cosmic background radiation polarization project, which demands precise knowledge and control of the optical coupling to the signal in order to map the feeble E- and B-polarization mode structure. The system will operate in two millimeter wavelength bands at 100 and 150 GHz. The imaging horn array collects the incoming signal via on-axis front-end optics and a Cassegrain telescope, with a cold stop in front of the array to terminate side-lobe structure at an edge taper of –20dB. The corrugated horn design process was undertaken using in-house analytical software tools, based on modal scattering, specially developed for millimeter -wave profiled horn antennas. An important part of the instrument development was the validation of the horn design, in particular to verify low edge taper levels and the required well-defined band edges. Suitable feed horn designs were measured and were found to be in excellent agreement with theoretical predictions.     

Quantum invariants at the sixth root of unity

A general topological formula is given for theSU (2) quantum invariant of a 3-manifoldM at the sixth root of unity. It is expressed in terms of the homology, Witt invariants and signature defects of the various 2-fold covers ofM, and thus ties in with basic 4-dimensional invariants. A discussion of the range of values of these quantum invariants is included, and explicit evaluations are made for lens spaces.