The Nπ^{0}π^{0} decays of positive-parity N^{*} and Δ^{*} resonances at about 2 GeV are studied at ELSA by photoproduction of two neutral pions off protons. The data reveal clear evidence for several ...intermediate resonances: Δ(1232), N(1520)3/2^{-}, and N(1680)5/2^{+}, with spin parities J^{P}=3/2^{+}, 3/2^{-}, and 5/2^{+}. The partial wave analysis (within the Bonn-Gatchina approach) identifies N(1440)1/2^{+} and the N(ππ)_{S wave} (abbreviated as Nσ here) as further isobars and assigns the final states to the formation of nucleon and Δ resonances and to nonresonant contributions. We observe the known Δ(1232)π decays of Δ(1910)1/2^{+}, Δ(1920)3/2^{+}, Δ(1905)5/2^{+}, Δ(1950)7/2^{+}, and of the corresponding spin-parity series in the nucleon sector, N(1880)1/2^{+}, N(1900)3/2^{+}, N(2000)5/2^{+}, and N(1990)7/2^{+}. For the nucleon resonances, these decay modes are reported here for the first time. Further new decay modes proceed via N(1440)1/2^{+}π, N(1520)3/2^{-}π, N(1680)5/2^{+}π, and Nσ. The latter decay modes are observed in the decay of N^{*} resonances and at most weakly in Δ^{*} decays. It is argued that these decay modes provide evidence for a 3-quark nature of N^{*} resonances rather than a quark-diquark structure.
Quasifree photoproduction of eta mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The ...eta mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasifree n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta production off the neutron shows a pronounced bumplike structure at W=1.68 GeV (E{gamma} approximately 1 GeV), which is absent for the proton.
The photoproduction of omega mesons on nuclei has been investigated using the Crystal Barrel/TAPS experiment at the ELSA tagged photon facility in Bonn. The aim is to study possible in-medium ...modifications of the omega meson via the reaction gamma + A --> omega + X --> pi(0)gamma + X('). Results obtained for Nb are compared to a reference measurement on a LH2 target. While for recoiling, long-lived mesons (pi(0), eta, and eta;(')), which decay outside of the nucleus, a difference in the line shape for the two data samples is not observed, we find a significant enhancement towards lower masses for omega mesons produced on the Nb target. For momenta less than 500 MeV/c an in-medium omega meson mass of M(medium) = 722(+4)(-4)(stat)+35-5(syst) MeV/c(2) has been deduced at an estimated average nuclear density of 0.6rho(0).
Information on hadron properties in the nuclear medium has been derived from the photoproduction of omega mesons on the nuclei C, Ca, Nb, and Pb using the Crystal Barrel/TAPS detector at the ELSA ...tagged photon facility in Bonn. The dependence of the omega-meson cross section on the nuclear mass number has been compared with three different types of models: a Glauber analysis, a Boltzmann-Uehling-Uhlenbeck analysis of the Giessen theory group, and a calculation by the Valencia theory group. In all three cases, the inelastic omega width is found to be 130-150 MeV/c(2) at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the rest frame of the omega meson, this inelastic omega width corresponds to a reduction of the omega lifetime by a factor approximately 30. For the first time, the momentum dependent omegaN cross section has been extracted from the experiment and is in the range of 70 mb.
The differential cross sections and unpolarized spin-density matrix elements for the reaction γp→pω were measured using the CBELSA/TAPS experiment for initial photon energies ranging from the ...reaction threshold to 2.5 GeV. These observables were measured from the radiative decay of the ω meson, ω→π0γ. The cross sections cover the full angular range and show the full extent of the t-channel forward rise. The overall shape of the angular distributions in the differential cross sections and unpolarized spin-density matrix elements are in fair agreement with previous data. In addition, for the first time, a beam of linearly-polarized tagged photons in the energy range from 1150 MeV to 1650 MeV was used to extract polarized spin-density matrix elements.
These data were included in the Bonn–Gatchina partial wave analysis (PWA). The dominant contribution to ω photoproduction near threshold was found to be the 3/2+ partial wave, which is primarily due to the sub-threshold N(1720)3/2+ resonance. At higher energies, pomeron-exchange was found to dominate whereas π-exchange remained small. These t-channel contributions as well as further contributions from nucleon resonances were necessary to describe the entire dataset: the 1/2−, 3/2−, and 5/2+ partial waves were also found to contribute significantly.
A radiative deuteron–proton capture experiment was carried out at KVI using polarized-deuteron beams at incident energies of 55, 66.5, and 90 MeV/nucleon. Vector and tensor-analyzing powers were ...obtained for a large angular range. The results are interpreted with the help of Faddeev calculations, which are based on modern two- and three-nucleon potentials. Our data are described well by the calculations, and disagree significantly with the observed tensor anomaly at RCNP.
Although Agapanthus africanus (L.) Hoffm. is one of the most popular ornamental species in both hemispheres, it has an extremely restricted wild occurrence (Cape province, South Africa). This ...contradiction between generalized ornamental application and natural distribution was the basis for the analytical approach adopted in the present work. We hypothesized that characteristic features of the cuticular waxes were adopted by this species to help it cope with severe dehydration associated with marine salinity on account of the short distance of the wild populations to the sea. A comprehensive morpho-anatomical, histological and physical-chemical analysis was performed on the epicuticular and intracuticular layers of the adaxial and abaxial surfaces of leaves of specimens of A. africanus. The adaxial epicuticular surface is hydrophilic and the abaxial epicuticular surface exhibits globally hydrophobic behavior. The main chemical compounds detected in the wax layers of both surfaces of the leaf are the short-chain monocaprylin monoglyceride (C8), and very long-chain 1-hexacosanol (C26) and 1-octacosanol (C28) alcohols. While monocaprylin is particularly abundant in the intracuticular layers, the epicuticular adaxial surface revealed the highest concentration of both alcohols. We demonstrate that the smart combination of these two classes of molecules with opposite water affinity endows the A. africanus leaf cuticle with a unique water management system combining the efficient entrapment of water in the disordered α-gel phase formed by monocaprylin and the high resistance to water transport provided by ordered domains composed of tightly packed, all-trans alkyl chains of the above pair of alcohols. The remarkable structural similarity existing between the monocaprylin α-gel and the mucilage of algae is an evidence of the terrestrialization process.
•A. africanus leaf has a unique ability to preserve water in harsh marine environments.•Histological and chemical properties of leaf cuticle allow it surviving dryness and high-irradiance.•Monocaprylin, 1-hexacosanol and 1-octacosanol contribute to efficient water preservation.•Monocaprylin ∝-gel's similarity to algae mucilage suggests terrestrialization.
.
Precise data for quasi-free photoproduction of
η
-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 2.5GeV. The
η
-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
η
-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
η
-nucleon pairs reconstructed from the final-state four-momenta of the particles. The total cross-section for quasi-free
η
-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant-mass spectrum of the
η
-neutron pairs. Position and width of the peak in the invariant-mass spectrum are
W
≈ 1665 MeV and FWHM
Γ
≈ 25 MeV. The data are compared to the results of different models.
In this study, we assessed the genetic diversity of Ascaris lumbricoides / Ascaris suum circulating in humans and pigs, exploring potential zoonotic cycles in endemic areas in Brazil. We carried out ...cross-sectional surveys in four municipalities: Santa Isabel do Rio Negro (SIRN-AM) (n = 328); Nossa Senhora de Nazaré (NSN-PI) and Teresina (TER-PI) (n = 605 and n = 297, respectively); and Cachoeiras de Macacu (CAM-RJ) (n = 543). We also studied 61 fecal samples/adult worms obtained from pigs (n = 53 in NSN-PI and n = 8 in TER-PI). A ~450 bp fragment of the Ascaris cytochrome c oxidase subunit 1 (cox1) and ~400 bp of the NADH dehydrogenase subunit 1 (nad1) were amplified and sequenced. Maximum-likelihood (ML) tree and Median-joining (MJ) haplotype network analyses were performed. We also performed scanning electron micrographs of adult specimens. Positivity rates were 93/328 (28.4%) in SIRN-AM, 6/297 (2.0%) in TER-PI, 0/605 (0%) in NSN-PI, and 6/543 (1.1%) in CAM-RJ. In NSN-PI it reached 11/53 (20.7%) in pigs. The MJ network based on cox1 locus (383 bp) revealed three main clusters, one centered around haplotypes H01/H28/H32 and the other around H07/H11. The cox1 haplotypes had a heterogeneous distribution, showing no pattern by geographic region, and high haplotype diversity. The ML trees based on cox1 and nad1 loci showed a similar topology with each other, and with the haplotype networks. Three distinct clusters were observed. Sequences of cox1 and nad1 from humans and animals were distributed throughout the tree and it was not possible to differentiate specimens of human and swine origin. Ascaris populations obtained from humans and swine in different Brazilian regions are not discriminable through the genetic markers used, which indicates the potential for zoonotic transmission and the need for better control of these infections in swine herds, mainly when created in a peridomestic environment.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ω
photoproduction off hydrogen and deuterium has been studied with the tagged photon beam of the ELSA accelerator in Bonn for photon energies up to 2.0 GeV. The
ω
meson has been identified via the
ω
...→ π
0
γ
→
γγγ
decay mode, using the combined setup of the Crystal Barrel/TAPS detector systems. Both inclusive and exclusive analyses have been carried out. Differential and total cross-sections have been derived for
ω
mesons produced off free protons and off protons and neutrons bound in deuterium. The cross-section for the production off the bound neutron is found to be a factor of ≈ 1.3 larger than the one off the bound proton in the incident beam energy region 1.2 GeV <
E
γ
< 1.6 GeV. For higher incident beam energies this factor goes down to ≈ 1.1 at 2.0 GeV. The cross-sections of this work have been used as normalization for transparency ratio measurements.
PDF
