K0-Sigma+ Photoproduction with SAPHIR

Preliminary results of the analysis of the reaction p(gamma,K0)Sigma+ are presented. We show the first measurement of the differential cross section and much improved data for the total cross section than previous data. The data are compared with model predictions from different isobar and quark models that give a good description of p(gamma,K+)Lambda and p(gamma,K+)Sigma0 data in the same energy range. Results of ChPT describe the data adequately at threshold while isobar models that include hadronic form factors reproduce the data at intermediate energies.Comment: 4 pages, Latex2e, 4 postscript figures. Talk given at the International Conference on Hypernuclear and Strange Particle Physics (HYP97), Brookhaven National Laboratory, USA, October 13-18, 1997. To be published in Nucl. Phys. A. Revised version due to changes in experimental dat

Photoproduction of pions and properties of baryon resonances from a Bonn-Gatchina partial wave analysis

Masses, widths and photocouplings of baryon resonances are determined in a coupled-channel partial wave analysis of a large variety of data. The Bonn-Gatchina partial wave formalism is extended to include a decomposition of t- and u-exchange amplitudes into individual partial waves. The multipole transition amplitudes for $\gamma p\to p\pi^0$ and $\gamma p\to n\pi^+$ are given and compared to results from other analyses.Comment: 18 pages, 14 figure

P-wave excited baryons from pion- and photo-induced hyperon production

We report evidence for $N(1710)P_{11}$, $N(1875)P_{11}$, $N(1900)P_{13}$, $\Delta(1600)P_{33}$, $\Delta(1910)P_{31}$, and $\Delta(1920)P_{33}$, and find indications that $N(1900)P_{13}$ might have a companion state at 1970\,MeV. The controversial $\Delta(1750)P_{31}$ is not seen. The evidence is derived from a study of data on pion- and photo-induced hyperon production, but other data are included as well. Most of the resonances reported here were found in the Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were challenged recently by the Data Analysis Center at GWU. Our analysis is constrained by the energy independent $\pi N$ scattering amplitudes from either KH84 or GWU. The two $\pi N$ amplitudes from KH84 or GWU, respectively, lead to slightly different $\pi N$ branching ratios of contributing resonances but the debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde

Properties of baryon resonances from a multichannel partial wave analysis

Properties of nucleon and $\Delta$ resonances are derived from a multichannel partial wave analysis. The statistical significance of pion and photo-induced inelastic reactions off protons are studied in a multichannel partial-wave analysis.Comment: 12 pages, 8 Table

Nucleon resonances in the fourth resonance region

Nucleon and $\Delta$ resonances in the fourth resonance region are studied in a multichannel partial-wave analysis which includes nearly all available data on pion- and photo-induced reactions off protons. In the high-mass range, above 1850\,MeV, several alternative solutions yield a good description of the data. For these solutions, masses, widths, pole residues and photo-couplings are given. In particular, we find evidence for nucleon resonances with spin-parities $J^P=1/2^+...7/2^+$. For one set of solutions, there are four resonances forming naturally a spin-quartet of resonances with orbital angular momentum L=2 and spin S=3/2 coupling to $J=1/2,...,7/2$. Just below 1.9\,GeV we find a spin doublet of resonances with $J^P=1/2^-$ and $3/2^-$. Since a spin partner with $J^P=5/2^-$ is missing at this mass, the two resonances form a spin doublet which must have a symmetric orbital-angular-momentum wave function with L=1. For another set of solutions, the four positive-parity resonances are accompanied by mass-degenerate negative-parity partners -- as suggested by the conjecture of chiral symmetry restoration. The possibility of a $J^P=1/2^+, 3/2^+$ spin doublet at 1900\,MeV belonging to a 20-plet is discussed.Comment: 16 page

Quasi-free photoproduction of eta-mesons off the deuteron

Precise data for quasi-free photoproduction of $\eta$ mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for incident photon energies up to 2.5 GeV. The $\eta$-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to $\eta$-production off the free proton. No significant effects beyond the folding of the free cross section with the momentum distribution of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of the $\eta$-nucleon pairs reconstructed from the final state four-momenta of the particles. The total cross section for quasi-free $\eta$-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1 GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant mass spectrum of the $\eta$-neutron pairs. Position and width of the peak in the invariant mass spectrum are $W\approx 1665$ MeV and FWHM $\Gamma\approx 25$ MeV. The data are compared to the results of different models.Comment: accepted for publication in Eur. Phys. J.

Affinitaetsmatrix zur Manipulation ligandengesteuerter Ionenkanaele als in-vitro-Modell fuer Teilfunktionen des menschlichen Zentralnervensystems. Teilprojekt A: PCR-Klonierung ionotroper Glutamatrezeptoren und deren heterologe Expression im kleinskaligen Massstab; Screening nach neuen Wirksubstanzen. B: Heterologe Expression von Glutamatrezeptoren im grossskaligen Massstab, Reinigung und Rekonstitution. C: Elektrochemische Charakterisierung membrangebundener Kanalproteine in Lipidmembranen in Form einer Affinitaetsmatrix. D: Selbstorganisation und Funktionssteuerung der Affinitaetsmatrix mittels nanotechnologischer Methoden

Available from TIB Hannover: F01B446 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

The cyclochlorotine mycotoxin is produced by the nonribosomal peptride syn,thetase CctN in Talaromyces islandicus (“Penicillium islandicum”)

Talaromyces islandicus ('Penicillium islandicum') is a widespread foodborne mold that produces numerous secondary metabolites, among them potent mycotoxins belonging to different chemical classes. A notable metabolite is the hepatotoxic and carcinogenic pentapeptide cyclochlorotine that contains the unusual amino acids β-phenylalanine, 2-aminobutyrate and 3,4-dichloroproline. Although the chemical structure has been known for over five decades, nothing is known about the biosynthetic pathway of cyclochlorotine. Bioinformatic analysis of the recently sequenced genome of T. islandicus identified a wealth of gene clusters potentially coding for the synthesis of secondary metabolites. Here, we show by RNA interference-mediated gene silencing that a nonribosomal peptide synthetase, CctN, is responsible for the synthesis of cyclochlorotine. Moreover, we identified novel cyclochlorotine chemical variants, whose production also depended on cctN expression. Surprisingly, the halogenase required for cyclochlorotine biosynthesis is not encoded in the cct cluster. Nonetheless, our findings enabled us to propose a detailed model for cyclochlorotine biosynthesis. In addition, comparative genomics revealed that cct-like clusters are present in all of the sequenced Talaromyces strains indicating a high prevalence of cyclochlorotine production ability.</p