Concerning a new productive synthesis of A-nor-testerone and its 6-dehydro derivatives as well as 7-beta-methyl-A-nor-testosterone

A novel synthetic approach to 2-oxo-Δ³-A-nor-steroids is described. The photochemical ring contraction of epoxyketones, cf. 4 → 5 , serves as the key step of this procedure, which gives notably higher yields than the previously published syntheses (e.g., overall yield 6 → 10 40%).     

Bemerkungen zum Satz über die Separabilität der Fréchet-Montel-Räume

Ohne Zusammenfassung     

Direct observation of self-trapped vibrational states in alpha-helices

Femtosecond infrared pump-probe spectroscopy of the N-H mode of a stable alpha-helix reveals two excited-state absorption bands, which disappear upon unfolding of the helix. A quantitative comparison with polaron theory shows that these two bands reflect two types of two-vibron bound states connected to the trapping of two vibrons at the same site and at nearest neighbor sites, respectively. The latter states originate from an acoustic phonon in the helix, which correlates adjacent sites.     

Quantum interference of ultrastable twin optical beams

We report the first measurement of the quantum phase-difference noise of an ultrastable nondegenerate optical parametric oscillator that emits twin beams classically phase locked at exact frequency degeneracy. The measurement illustrates the property of a lossless balanced beam splitter to convert number-difference squeezing into phase-difference squeezing, and thus provides indirect evidence for Heisenberg-limited interferometry using twin beams. This experiment is a generalization of the Hong-Ou-Mandel interference effect for continuous variables and constitutes a milestone towards continuous-variable entanglement of bright, ultrastable nondegenerate beams.     

Stepped chutes: Pre-aeration and spray reduction

Stepped chutes are a standard element in hydraulic engineering. Among others, two basic problems have not yet been addressed so far. These include the direct spray reduction on stepped chutes for relatively small discharges by an improved step edge geometry, and the cavitation damage up to the point of self-aeration for relatively large discharges. This research adds to these two items by systematic observations on a stepped chute of definite slope and step size. The test data were analyzed resulting in preliminary recommendations for an improved performance of stepped chutes. It was concluded that the present knowledge applies also for stepped chutes extended with an aerator as proposed herein. The latter may be easily added to existing designs, of which the design discharge is increased.     

Alternating vorticity bands in a solution of wormlike micelles

We report on structural characterization of vorticity bands formed in a wormlike micellar solution by Rheo--small-angle neutron scattering and video imaging experiments. Below a critical shear stress tau{c} in Newtonian and shear-thinning regime, only a minor flow alignment of the micelles is observed. Above tau{c}, in the shear-thickening regime, alternating transparent and turbid bands are formed. Triggered small-angle neutron scattering shows different anisotropic patterns in both bands indicating strongly aligned structures. By high-speed video imaging, we show that such an alignment of micelles does not correspond to a phase of lower viscosity.     

Interface, Surface Tension and Reentrant Pinning Transition in the 2D Ising Model

We develop a new way to look at the high-temperature representation of the Ising model up to the critical temperature and obtain a number of interesting consequences. In the two-dimensional case, it is possible to use these tools to prove results on phase-separation lines in the whole phase-coexistence regime, by way of a duality transformation. We illustrate the power of these techniques by studying an Ising model with a boundary magnetic field, in which a reentrant pinning transition takes place; more precisely we show that the typical configurations of the model can be described, at the macroscopic level, by interfaces which are solutions of the corresponding thermodynamic variational problem; this variational problem is solved explicitly. There exist values of the boundary magnetic field and temperatures 0<T ₁<T ₂<T _c such that the interface is not pinned for T<T ₁ or T>T ₂, but is pinned for T ₁<T<T ₂; we can also find values of the boundary magnetic field and temperatures 0<T ₁<T ₂<T ₃<T _c such that for T<T ₁ or T ₂<T<T ₃ the interface is pinned, while for T ₁<T<T ₂ or T>T ₃ it is not pinned. An important property of the surface tension which is used in this paper is the sharp triangle inequality about which we report some new results. The techniques used in this work are robust and can be used in a variety of different situations. Received: 28 January 1998 / Accepted: 22 December 1998     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

Measurement of the viscoelastic properties of bituminous materials using an oscillating needle technique

An embedded oscillating needle is used to measure the dynamic viscoelastic properties of a stiff bituminous material. A Micro-Fourier Rheometer was used to cause the embedded needle to undergo pseudorandom small amplitude oscillations in the axial direction with measurement of the instantaneous resistance force. The phase and magnitude of the force signal are used to calculate the storage and loss moduli. A theoretical framework for this technique is developed from the Mindlin solution coupled with slender body theory, and the correspondence principle of linear viscoelasticity. Experiments are performed on neat bitumen binders as well as mixtures of glass spheres in bitumen; the results show that the presence of the glass spheres dramatically increases the viscoelastic response functions. The results agree reasonably well with those obtained using the parallel plate squeezing mode. Received: 31 March 1999 Accepted: 14 July 1999