23 research outputs found
Anharmonicities of giant dipole excitations
The role of anharmonic effects on the excitation of the double giant dipole
resonance is investigated in a simple macroscopic model.Perturbation theory is
used to find energies and wave functions of the anharmonic ascillator.The cross
sections for the electromagnetic excitation of the one- and two-phonon giant
dipole resonances in energetic heavy-ion collisions are then evaluated through
a semiclassical coupled-channel calculation.It is argued that the variations of
the strength of the anharmonic potential should be combined with appropriate
changes in the oscillator frequency,in order to keep the giant dipole resonance
energy consistent with the experimental value.When this is taken into
account,the effects of anharmonicities on the double giant dipole resonance
excitation probabilities are small and cannot account for the well-known
discrepancy between theory and experiment
Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV
The mass distributions of baryon resonances populated in near-central
collisions of Au on Au and Ni on Ni are deduced by defolding the spectra
of charged pions by a method which does not depend on a specific resonance
shape. In addition the mass distributions of resonances are obtained from the
invariant masses of pairs. With both methods the deduced mass
distributions are shifted by an average value of -60 MeV/c relative to the
mass distribution of the free resonance, the distributions
descent almost exponentially towards mass values of 2000 MeV/c^2. The observed
differences between and pairs indicate a contribution
of isospin resonances. The attempt to consistently describe the
deduced mass distributions and the reconstructed kinetic energy spectra of the
resonances leads to new insights about the freeze out conditions, i.e. to
rather low temperatures and large expansion velocities.Comment: 30 pages, 13 figures, Latex using documentstyle[12pt,a4,epsfig], to
appear in Eur. Phys. J.
Charged pions from Ni on Ni collisions between 1 and 2 AGeV
Charged pions from Ni + Ni reactions at 1.05, 1.45 and 1.93 AGeV are measured with the FOPI detector. The mean multiplicities per mean number of participants increase with beam energy, in accordance with earlier studies of the Ar + KCl and La + La systems. The pion kinetic energy spectra have concave shape and are fitted by the superposition of two Boltzmann distributions with different temperatures. These apparent temperatures depend only weakly on bombarding energy. The pion angular distributions show a forward/backward enhancement at all energies, but not the enhancement which was observed in case of the Au + Au system. These features also determine the rapidity distributions which are therefore in disagreement with the hypothesis of one thermal source. The importance of the Coulomb interaction and of the pion rescattering by spectator matter in producing these phenomena is discussed
Central Collisions of Au on Au at 150, 250 and 400 A MeV
Collisions of Au on Au at incident energies of 150, 250 and 400 A MeV were
studied with the FOPI-facility at GSI Darmstadt. Nuclear charge (Z < 16) and
velocity of the products were detected with full azimuthal acceptance at
laboratory angles of 1-30 degrees. Isotope separated light charged particles
were measured with movable multiple telescopes in an angular range of 6-90
degrees. Central collisions representing about 1 % of the reaction cross
section were selected by requiring high total transverse energy, but vanishing
sideflow. The velocity space distributions and yields of the emitted fragments
are reported. The data are analysed in terms of a thermal model including
radial flow. A comparison with predictions of the Quantum Molecular Model is
presented.Comment: LateX text 62 pages, plus six Postscript files with a total of 34
figures, accepted by Nucl.Phys.
Double-#gamma# decay of the electromagnetically excited double giant dipole resonance in "2"0"8Pb
In this work the electromagnetic excitation of high lying collective states has been studied in relativistic heavy ion collisions. The interaction in peripheral collisions is dominated by the exchange of high energy virtual photons. Heavy systems near 1 A GeV produce a virtual photon field that is highly luminous and of sufficiently short duration to enable the multiple excitation of Giant Resonances with high probability. In particular, the double excitation of the Giant Dipole Resonance (GDR) has been studied in this work by measuring the photons emitted in peripheral reactions with the system 1 A GeV "2"0"9Bi on "2"0"8Pb with the Two Arm Photon Spectrometer (TAPS) at SIS/GSI in Darmstadt, Germany. (orig.)SIGLEAvailable from TIB Hannover: RA 3692(93-20) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Inhibition of Cdc25A Suppresses Hepato-Renal Cystogenesis in Rodent Models of Polycystic Kidney and Liver Disease
BACKGROUND & AIMS:
In polycystic kidney (PKD) and liver (PLD) diseases, the normally non-proliferative hepato-renal epithelia acquire a proliferative, cystic phenotype, which is linked to overexpression of Cdc25A and cell cycle deregulation. We investigated the effects of Cdc25A inhibition in mice and rats, via genetic and pharmacological approaches.
METHODS:
Cdc25A(+/-) mice (which have reduced levels of Cdc25A) were cross-bred with Pkhd1(del2/del2) mice (which have increased levels of Cdc25A and develop hepatic cysts). Cdc25A expression was analyzed in livers of control and PCK rats, control and Pkd2(ws25/-) mice, healthy individuals, and patients with PLD. We examined effects of pharmacologic inhibition of Cdc25A with Vitamin K3 (VK3) on the cell cycle, proliferation, and cyst expansion in vitro; hepato-renal cystogenesis in PCK rats and Pkd2(ws25/-) mice; and expression of Cdc25A and the cell cycle proteins regulated by Cdc25A. We also examined effects of the Cdc25A inhibitor PM-20 on hepato-renal cystogenesis in Pkd2(ws25/-) mice.
RESULTS:
Liver weights and hepatic and fibrotic areas were decreased by 32%-52% in Cdc25A(+/-):Pkhd1(del2/del2) mice, compared to Pkhd1(del2/del2) mice.VK3 altered the cell cycle and reduced proliferation of cultured cholangiocytes by 32%-83% and decreased growth of cultured cysts by 23%-67%. In PCK rats and Pkd2(ws25/-) mice, VK3 reduced liver and kidney weights and hepato-renal cystic and fibrotic areas by 18%-34%. PM-20 decreased hepato-renal cystogenesis in Pkd2(ws25/-) mice by 15%.
CONCLUSIONS:
Cdc25A inhibitors block cell cycle progression and proliferation, reduce liver and kidney weights and cyst growth in animal models of PKD and PLD, and might be developed as therapeutics for these diseases
Determination of N* amplitudes from associated strangeness production in p+p collisions
We present the first determination of the energy-dependent amplitudes of Nâ resonances extracted from their decay in KÎ pairs in p+pâpK+Î reactions. A combined Partial Wave Analysis of seven data samples with exclusively reconstructed p+pâpK+Î events measured by the COSY-TOF, DISTO, FOPI and HADES Collaborations in fixed target experiments at kinetic energies between 2.14 to 3.5 GeV is used to determine the amplitude of the resonant and non-resonant contributions into the associated strangeness final state. The contribution of seven Nâ resonances with masses between 1650 MeV/c2 and 1900 MeV/c2 for an excess energy between 0 and 600 MeV has been considered. The ÎŁâp cusp and final state interactions for the pâÎ channel are also included as coherent contributions in the PWA. The Nâ contribution is found to be dominant with respect to the phase space emission of the pKÎ+ final state at all energies demonstrating the important role played by both Nâ and interference effects in hadronâhadron collisions. Keywords: Partial wave analysis, Resonance, Hadrons, Strangeness, Scattering length, Hyperonânucleon interactio