Doppeltangenten einer Curven ter Ordnung

Ohne Zusammenfassung     

Salvinicins A and B, new neoclerodane diterpenes from Salvia divinorum

[reaction: see text] Two new neoclerodane diterpenes, salvinicins A (4) and B (5), were isolated from the dried leaves of Salvia divinorum. The structures of these compounds were elucidated by spectroscopic techniques, including (1)H and (13)C NMR, NOESY, HMQC, and HMBC. The absolute stereochemistry of these compounds was assigned on the basis of single-crystal X-ray crystallographic analysis of salvinicin A (4) and a 3,4-dichlorobenzoate derivative of salvinorin B.     

First observation of the doubly charmed baryon Xi(+)(cc)

We observe a signal for the doubly charmed baryon Xi(+)(cc) in the charged decay mode Xi(+)(cc)-->Lambda(+)(c)K-pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1+/-0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is 3519+/-1 MeV/c(2). The Gaussian mass width of this state is 3 MeV/c(2), consistent with resolution; its lifetime is less than 33 fs at 90% confidence.     

Comment on “On the Anomalon Interpretation of 40Ar + Cu Collisions at 0.9 and 1.8 AGeV”

A recent article interpreted the experiment by Dersch et al. on the formation of ²⁴Na in ⁴⁰Ar + Cu interactions in a very simple manner. The results from emulsion experiments performed with 3.6 AGeV ²²Ne were adapted for the interpretation of the experiments with 1.8 AGeV ⁴⁰Ar. The model used the same mean value for the energy of minimum ionizing protons and pions at all angles. It is argued that a more complex approach is needed for a satisfactory interpretation.     

X-ray induced fluorescence and thermoluminescence of silver atoms in solid rare gases

Two differently heat treated samples of Fe-0.8 wt% Cu and a sample of pure iron, subjected to a fast fission fluence of 0.5×10¹⁹ neutrons/cm² have been investigated by means of measurements of the peak height of the 2 -angular correlation distribution as a function of annealing temperature up to 750 °C. The results can be explained by assuming irradiation enhanced precipitation of small Cu-clusters in a supersaturated solid solution. These particles exhibit on their surfaces vacancy-like defects having the ability to trap positrons. A correlation has been observed between peak height and microhardness behaviour suggesting that both radiation induced hardening and embrittlement are due mainly to enhanced precipitation.     

Investigation of the unusual behavior of projectile fragments using nuclear chemistry techniques

In recent years the question of the unusual behavior of projectile fragments formed in the interaction of relativistic heavy ions with copper nuclei was studied using nuclear chemistry techniques. As targets we used various copper disk arrangements. It is not the intention of this conference contribution to give a complete account of the entire procedure and its results. However, we want to present a few more recent experimental findings, some of them even in a preliminary form. We want to stimulate the discussion about the entire problem which might be part of the so-called anomalon phenomenon, as observed in the field of relativistic heavy ion interactions with a few other techniques such as nuclear emulsions or bubble chambers.     

Photocrosslinkable Liquid Crystal Main‐Chain Polymers: Thin Films and Electrospinning

For mechanical actuators, a response to external stimuli is required. Main‐chain liquid crystal elastomers (MCLCEs) show high response to changes in temperature especially in the vicinity of a phase transition. Most of these crosslinked materials were synthesized in a one‐step reaction which leads to a macroscopically aligned elastomer. Up to now only macroscopic samples have been prepared. We are presenting a new approach which allows us to prepare thin films as well as aligned fibers. First a liquid crystalline main‐chain polymer with a photoactive moiety was synthesized, which was oriented by a mechanical field and photocrosslinked. The thin films show exceptional mechanical properties such as large temperature‐dependent changes in length and a nonlinear stress–strain relation. To obtain fibers, we used the electrospinning process from solution with in situ UV curing. We obtained crosslinked fibers with a uniform alignment of the nematic director.

     

Electrospun nanofibers: Internal structure and intrinsic orientation

Electrospinning gives rise to polymer nanofibers. The spinning process is characterized by strong deformations of the polymer material taking place during the spinning process and a very rapid structure formation process happening within milliseconds. We were interested in the influence of the peculiar spinning process on the structures of nanofibers. For this purpose, we analyzed the internal structures of nanofibers spun from polyamide‐6 and polylactide with an average diameter of about 50 nm. The fibers were partially crystalline, with degrees of crystallinity not significantly smaller than those found for less rapidly quenched and much thicker melt‐extruded fibers. The annealing of polyamide fibers at elevated temperatures resulted in a transformation from the disordered γ modification to the more highly ordered α modification, and this again was in close agreement with the response of melt‐extruded fibers. The orientation of the crystals along the fiber axis was strongly inhomogeneous: it was, on average, very weak, yet it could be quite pronounced locally. Small elongations of approximately 10% resulted in well‐developed homogeneous crystal orientations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 545–553, 2003