21 research outputs found
Экспериментальное исследование динамики фрикционных процессов при трении латуни Л63 с ультрамелкозернистой структурой
В работе рассматривается экспериментальное исследование динамики фрикционных процессов при трении объемных ультрамелкозернистых материалов. В качестве модельных образцов использовалась латунь Л63 с крупнокристаллической и ультрамелкозернистой структурой, сформированной методом равноканального углового прессования. В процессе сухого трения скольжения осуществлялась регистрация сигналов виброускорений и акустической эмиссии. Анализ коротких сигналов с применением преобразований Фурье позволил установить характерные параметры сигналов, полученных при трении крупнокристаллических и ультрамелкозернистых материалов
Electromagnetic Polarizabilities of Nucleons bound in Ca, O and He
Differential cross sections for elastic scattering of photons have been
measured for Ca at energies of 58 and 74 MeV and for O and He
at 61 MeV, in the angular range from 45 to 150. Evidence is obtained
that there are no significant in-medium modifications of the electromagnetic
polarizabilities except for those originating from meson exchange currents.Comment: 20 pages including 5 Figure
Compton scattering on the nucleon at intermediate energies and polarizabilities in a microscopic model
A microscopic calculation of Compton scattering on the nucleon is presented
which encompasses the lowest energies -- yielding nucleon polarizabilities --
and extends to energies of the order of 600 MeV. We have used the covariant
"Dressed K-Matrix Model" obeying the symmetry properties which are appropriate
in the different energy regimes. In particular, crossing symmetry, gauge
invariance and unitarity are satisfied. The extent of violation of analyticity
(causality) is used as an expansion parameter.Comment: 35 pages, 15 figures, using REVTeX. Modified version to be published
in Phys. Rev. C, more extensive comparison with data for Compton scattering,
all results unchange
Vector meson production and nucleon resonance analysis in a coupled-channel approach for energies m_N < sqrt(s) < 2 GeV II: photon-induced results
We present a nucleon resonance analysis by simultaneously considering all
pion- and photon-induced experimental data on the final states gamma N, pi N, 2
pi N, eta N, K Lambda, K Sigma, and omega N for energies from the nucleon mass
up to sqrt(s) = 2 GeV. In this analysis we find strong evidence for the
resonances P_{31}(1750), P_{13}(1900), P_{33}(1920), and D_{13}(1950). The
omega N production mechanism is dominated by large P_{11}(1710) and
P_{13}(1900) contributions. In this second part we present the results on the
photoproduction reactions and the electromagnetic properties of the resonances.
The inclusion of all important final states up to sqrt(s) = 2 GeV allows for
estimates on the importance of the individual states for the GDH sum rule.Comment: 41 pages, 26 figures, discussion extended, typos corrected,
references updated, to appear in Phys. Rev.
Colonoscopy quality across Europe : a report of the European Colonoscopy Quality Investigation (ECQI) Group
publishedVersionPeer reviewe
Chitinolytic activity in viable spores of encephalitozoon species
By employing 4-methylumbelliferyl-beta-D-NN',N"-triacetylchitotriose
substrate in a semi quantitative assay, chitinolytic activity in viable
spores of Encephalitozoon cuniculi and E. intestinalis was detected and
dependence on reaction time, spore concentration, concentration of
substrate and temperature were demonstrated. It was possible to block
the chitinolytic activity by chitin hydrolysate. By incubation at 80C
for 10 min or at 55C for 20 min the spores were loosing the
chitinolytic activity. Incubation of the spores in trypsin reduced the
chitinolytic activity. Cellulase activity could not be detected
Total synthesis of five thapsigargins: guaianolide natural products exhibiting sub-nanomolar SERCA inhibition.
Herein we describe the total synthesis of five guaianolide natural products: thapsigargin, thapsivillosin C, thapsivillosin F, trilobolide and nortrilobolide. Prodrug derivatives of thapsigargin have shown selective in vivo cytotoxicity against prostate tumours and the need for further investigation of this phenomenon highlights the importance of these total syntheses. The first absolute stereochemical assignment of thapsivillosin C is also delineated
Compton scattering from He-4 in the Delta(1232) resonance region
Differential cross sections for Compton scattering from He-4 have been measured at theta(lab) = 37 degrees and E(gamma) = 120-510 MeV using the tagged photon beam of MAMI and the Mainz large NaI(TI) detector. The shape of the cross section is qualitatively reproduced by a simple schematic model, which however underestimates the absolute scale. More profound calculations like the Delta-hole model also fail to describe the data quantitatively, in particular in the Delta-resonance region