292 research outputs found
Mass measurements of very neutron-deficient Mo and Tc isotopes and their impact on rp process nucleosynthesis
The masses of ten proton-rich nuclides, including the N=Z+1 nuclides 85-Mo
and 87-Tc, were measured with the Penning trap mass spectrometer SHIPTRAP.
Compared to the Atomic Mass Evaluation 2003 a systematic shift of the mass
surface by up to 1.6 MeV is observed causing significant abundance changes of
the ashes of astrophysical X-ray bursts. Surprisingly low alpha-separation
energies for neutron-deficient Mo and Tc are found, making the formation of a
ZrNb cycle in the rp process possible. Such a cycle would impose an upper
temperature limit for the synthesis of elements beyond Nb in the rp process.Comment: Link to online abstract:
http://link.aps.org/doi/10.1103/PhysRevLett.106.12250
HITRAP: A facility at GSI for highly charged ions
An overview and status report of the new trapping facility for highly charged
ions at the Gesellschaft fuer Schwerionenforschung is presented. The
construction of this facility started in 2005 and is expected to be completed
in 2008. Once operational, highly charged ions will be loaded from the
experimental storage ring ESR into the HITRAP facility, where they are
decelerated and cooled. The kinetic energy of the initially fast ions is
reduced by more than fourteen orders of magnitude and their thermal energy is
cooled to cryogenic temperatures. The cold ions are then delivered to a broad
range of atomic physics experiments.Comment: 8 pages, 11 figure
Direct mass measurements beyond the proton drip-line
First on-line mass measurements were performed at the SHIPTRAP Penning trap
mass spectrometer. The masses of 18 neutron-deficient isotopes in the
terbium-to-thulium region produced in fusion-evaporation reactions were
determined with relative uncertainties of about , nine of them
for the first time. Four nuclides (Ho and Tm) were
found to be proton-unbound. The implication of the results on the location of
the proton drip-line is discussed by analyzing the one-proton separation
energies
Present and Future Experiments with Stored Exotic Nuclei at Relativistic Energies
Recent progress is presented from experiments on masses and lifetimes of bare
and few-electron exotic nuclei at GSI.Comment: Proceedings of International Conference on "Frontiers in Nuclear
Structure, Astrophysics and Reactions", Kos, Greece, September 12-17, 200
Efficiency of Organelle Capture by Microtubules as a Function of Centrosome Nucleation Capacity: General Theory and the Special Case of Polyspermia
Transport of organelles along microtubules is essential for the cell metabolism and morphogenesis. The presented analysis derives the probability that an organelle of a given size comes in contact with the microtubule aster. The question is asked how this measure of functionality of the microtubule aster is controlled by the centrosome. A quantitative model is developed to address this question. It is shown that for the given set of cellular parameters, such as size and total tubulin content, a centrosome nucleation capacity exists that maximizes the probability of the organelle capture. The developed general model is then applied to the capture of the female pronucleus by microtubules assembled on the sperm centrosome, following physiologically polyspermic fertilization. This application highlights an unintuitive reflection of nonlinearity of the nucleated polymerization of the cellular pool of tubulin. The prediction that the sperm centrosome should lower its nucleation capacity in the face of the competition from the other sperm is a stark illustration of the new optimality principle. Overall, the model calls attention to the capabilities of the centrosomal pathway of regulation of the transport-related functionality of the microtubule cytoskeleton. It establishes a quantitative and conceptual framework that can guide experiment design and interpretation
Spin sensitive bleaching and monopolar spin orientation in quantum wells
Spin sensitive bleaching of the absorption of far-infrared radiation has been
observed in -type GaAs/AlGaAs quantum well structures. The absorption of
circularly polarized radiation saturates at lower intensities than that of
linearly polarized light due to monopolar spin orientation in the first heavy
hole subband. Spin relaxation times of holes in -type material in the range
of tens of ps were derived from the intensity dependence of the absorption.Comment: Figures have been updated due to technical printing problems
(Postscript mismatch
Continuous dielectric permittivity II: An Iterative Method for Calculating the Polar Component of the Molecular Solvation Gibbs Energy Under a Smooth Change in the Dielectric Permittivity of a Solution
An iterative method for calculating the polar component of the solvation
Gibbs energy under a smooth change in dielectric permittivity, both between a
substrate and a solvent and in a solvent is formulated on the basis of a
previously developed model. The method is developed in the approximation of the
local relationship D = \eps (r) E between the displacement vectors D and the
electric field intensity E.Comment: 36 pages,3 Figures, in English and in Russia
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