Eine Anwendung der K-Theorie in der Theorie der H-Räume

Ohne Zusammenfassung     

Study of “uncorrelated” radiation damage inNi 111In

With 1.5 MeV deuterons lattice defects have been introduced into diffused sources of¹¹¹In in Ni. Defect structure and annealing behavior were found in all respects comparable to previous work in Groningen using ion-implantation. The results suggest that the defect structure in Ni and other fcc metals is not strongly dependent on the manner in which the defects are introduced.Research supported in part by the National Science Foundation.     

Direct observation of the oxygen isotope effect on the in-plane magnetic field penetration depth in optimally doped YBa2Cu3O7-delta

We report the first direct observation of the oxygen-isotope ((16)O/(18)O) effect on the in-plane penetration depth lambda(ab) in a nearly optimally doped YBa(2)Cu(3)O(7-delta) film using the novel low-energy muon-spin rotation technique. Spin-polarized low-energy muons are implanted in the film at a known depth z beneath the surface and process in the local magnetic field B(z). This feature allows us to measure directly the profile B(z) of the magnetic field inside the superconducting film in the Meissner state and to make a straightforward determination of lambda(ab). A substantial isotope shift Delta lambda(ab)/lambda(ab)=2.8(1.0)% at 4 K is observed, implying that the in-plane effective supercarrier mass m*(ab) is oxygen-isotope dependent with Delta m*(ab)/m*(ab)=5.5(2.0)%. These results are in good agreement with magnetization measurements on powder samples.     

Thin Film, Near-Surface and Multi-Layer Investigations by Low-Energy μ +SR

At the Paul Scherrer Institute (PSI, Villigen, Switzerland) the beam of low-energy positive polarised muons (LE-μ ⁺) with tunable energy between 0.5 and 30 keV allows the extension of the muon-spin-rotation technique (μSR) to studies on thin films and multi-layers (LE-μ ⁺SR). The range of these muons in solids covers the near-surface region up to implantation depths of about 300 nm. As a sensitive local magnetic probe with a complementary observational time window to other techniques LE-μ ⁺SR offers the unique possibility to gain new insights in these nano-scale objects. After outlining the current status of the LE-μ ⁺ beam line we demonstrate the potential of this new technique by presenting the results of recent experiments: i) the direct observation of non-local effects in a superconducting Pb film, ii) the oxygen isotope effect on the in-plane penetration depth in optimally doped , and iii) the first observation of the conduction electron spin polarisation in the Ag spacer of a Fe/Ag/Fe tri-layer.     

Definition and measurement of the normalized electrical impedance of lossy piezoelectric resonators for ultrasonic transducers

Relevant equivalent circuit parameters and values of material constants of a piezoelectric resonator can be determined from measurements of its electrical input impedance as a function of frequency. The complex electrical impedance curves and the associated critical frequencies are the basis of this characterization by the piezoelectric resonance method. In this paper, the previously introduced concept of normalized electrical impedance of the lossy resonator, extended to include piezoelectric losses, is applied to the analysis of the effects of different types of intrinsic losses on peak values, bandwidths and characteristic frequencies. The resulting impedance patterns depend solely on the electromechanical coupling coefficient and the loss tangents, providing a useful tool for the analysis of low-Q resonators. The normalized impedance is experimentally evaluated from the basic data provided by an HP 4194A impedance analyser by means of specifically developed ASP programs.     

On the isomorphism of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) random copolymers

The defect Gibbs energy of hydroxyvalerate comonomer inclusions into the crystals made up by random copolymers of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) (PHB/HV) is calculated by means of the thermodynamic integration approach. The result obtained for a single inclusion is in excellent agreement with those obtained by fitting experimental melting temperature and cocrystal composition data. Lattice model calculations that cover the whole range of copolymer composition were carried out based on calculations of double inclusion, which revealed a decrease of the average defect Gibbs energy in adjacent defects. On decomposing the Gibbs energy, it is found that the configurational entropy contributes the dominant part of the defect Gibbs energy.     

Heterospirocyclic N‐(2H‐Azirin‐3‐yl)‐L‐prolinates: New Dipeptide Synthons

The synthesis of methyl N‐(1‐aza‐6‐oxaspiro[2.5]oct‐1‐en‐2‐yl)‐L ‐prolinate ( 1e ) has been performed by consecutive treatment of methyl N‐[(tetrahydro‐2H‐pyran‐4‐yl)thiocarbonyl]‐L ‐prolinate ( 5 ) with COCl₂, 1,4‐diazabicyclo[2.2.2]octane (DABCO), and NaN₃ (Scheme 1). As the first example of a novel class of dipeptide synthons, 1e has been shown to undergo the expected reactions with carboxylic acids and thioacids (Scheme 2). The successful preparation of the nonapeptide 16 , which is an analogue of the C‐terminal nonapeptide of the antibiotic Trichovirin I 1B, proved that 1e can be used in peptide synthesis as a dipeptide building block (Scheme 3). The structure of 7 has been established by X‐ray crystal‐structure analysis (Figs. 1 and 2).     

Paul J. Flory

Paul J. Flory was a pioneer in the development of a quantitative understanding of polymer science and a leader in placing it among the major scientific disciplines. Through his energy, skill and genius, and by the judicious interplay of experiment and theory, he demonstrated that polymers are not the complicated, intractable systems they were thought to be earlier, but are treatable in a rigorous and straight-forward manner. From his first scientific paper on polymers in 1936 to his last contributions, published posthumously, in 1986, Paul Flory was involved in shaping a consistent view of polymer science. A unique ability, to perceive the dominant cause in a complex effect and to formulate the action of this most important element of a situation in a simple and straightforward model, made his contributions so helpful and relevant that still today his models are often chosen over later, more refined, more accurate ones – Flory's models and concepts are of penetrating insight and a simplicity that allows all polymer scientists to understand and use them. Flory was involved in a very broad range of topics: among other topics, he laid the foundation of the understanding of polymerization reactions, illuminated the thermodynamics and hydrodynamics of polymer solutions and through this the nature of the polymer-solvent interactions and the θ-state, formulated important models of rubber elasticity, and investigated with excellent success polymeric crystals and liquid crystals. A contribution of great importance was the development of the rotational isomeric state method to the treatment of macromolecules of arbitrary size and structure and for many properties. His achievement was recognized by numerous awards, honorary degrees, and the Nobel Prize in 1974. Paul J. Flory, born on June 19, 1910, died on September 8, 1985.