2,195 research outputs found
Evolution of level density step structures from 56,57-Fe to 96,97-Mo
Level densities have been extracted from primary gamma spectra for 56,57-Fe
and 96,97-Mo nuclei using (3-He,alpha gamma) and (3-He,3-He') reactions on
57-Fe and 97-Mo targets. The level density curves reveal step structures above
the pairing gap due to the breaking of nucleon Cooper pairs. The location of
the step structures in energy and their shapes arise from the interplay between
single-particle energies and seniority-conserving and seniority-non-conserving
interactions.Comment: 9 pages, including 5 figure
Fragmentation and systematics of the Pygmy Dipole Resonance in the stable N=82 isotones
The low-lying electric dipole (E1) strength in the semi-magic nucleus 136Xe
has been measured which finalizes the systematic survey to investigate the
so-called pygmy dipole resonance (PDR) in all stable even N=82 isotones with
the method of nuclear resonance fluorescence using real photons in the entrance
channel. In all cases, a fragmented resonance-like structure of E1 strength is
observed in the energy region 5 MeV to 8 MeV. An analysis of the fragmentation
of the strength reveals that the degree of fragmentation decreases towards the
proton-deficient isotones while the total integrated strength increases
indicating a dependence of the total strength on the neutron-to-proton ratio.
The experimental results are compared to microscopic calculations within the
quasi-particle phonon model (QPM). The calculation includes complex
configurations of up to three phonons and is able to reproduce also the
fragmentation of the E1 strength which allows to draw conclusions on the
damping of the PDR. Calculations and experimental data are in good agreement in
the degree of fragmentation and also in the integrated strength if the
sensitivity limit of the experiments is taken into account
Critical fluctuations in superconductors and the magnetic field penetration depth
The superconducting transition is studied within the one-loop renormalization
group in fixed dimension and at the critical point. A tricritical
behavior is found, and for , an attractive charged fixed
point, distinct from that of a neutral superfluid. The critical exponents of
the continuous transition are evaluated, and it is shown that the anomalous
dimension of the gauge field equals unity. This implies the proportionality of
the magnetic field penetration depth and the superconducting correlation length
below the transition. The penetration depth exponent is nonclassical. We argue
that it can not be extracted from the dual theory in a straightforward manner
since it is not renormalized by fluctuations of the dual field.Comment: 12 pages, LaTex, two figures available upon reques
Isospin Character of the Pygmy Dipole Resonance in 124Sn
The pygmy dipole resonance has been studied in the proton-magic nucleus 124Sn
with the (a,a'g) coincidence method at E=136 MeV. The comparison with results
of photon-scattering experiments reveals a splitting into two components with
different structure: one group of states which is excited in (a,a'g) as well as
in (g,g') reactions and a group of states at higher energies which is only
excited in (g,g') reactions. Calculations with the self-consistent relativistic
quasiparticle time-blocking approximation and the quasiparticle phonon model
are in qualitative agreement with the experimental results and predict a
low-lying isoscalar component dominated by neutron-skin oscillations and a
higher-lying more isovector component on the tail of the giant dipole
resonance
Reducing decoherence in optical and spin transitions in rare-earth-ion doped materials
In many important situations the dominant dephasing mechanism in cryogenic
rare-earth-ion doped systems is due to magnetic field fluctuations from spins
in the host crystal. Operating at a magnetic field where a transition has a
zero first-order-Zeeman (ZEFOZ) shift can greatly reduce this dephasing. Here
we identify the location of transitions with zero first-order Zeeman shift for
optical transitions in Pr3+:YAG and for spin transitions in Er3+:Y2SiO5. The
long coherence times that ZEFOZ would enable would make Pr3+:YAG a strong
candidate for achieving the strong coupling regime of cavity QED, and would be
an important step forward in creating long-lived telecommunications wavelength
quantum memories in Er3+:Y2SiO5. This work relies mostly on published spin
Hamiltonian parameters but Raman heterodyne spectroscopy was performed on
Pr3+:YAG to measure the parameters for the excited state.Comment: 10 pages, 5 figure
PACAP-38 Signaling in \u3ci\u3eTetrahymena thermophila\u3c/i\u3e Involves NO and cGMP
Chemorepellents are signaling molecules, which have been shown to be important for mammalian neuronal development, and are presumed to have a role in protozoan defense. Tetrahymena thermophila represent a good model system in which to study repellents because of their ease of use in biochemical, behavioral, electrophysiological, and genetic analyses. In this study, we have used Tetrahymena as a model in which to study the chemorepellent, PACAP. Using behavioral and biochemical (EIA) assays, we have found that the NO/cGMP pathway plays an important role in PACAP signaling. An increase in intracellular calcium is also critical for PACAP avoidance, which appears to be mediated through a pertussis toxin-sensitive G-protein
Dual superfluid-Bose glass critical point in two dimensions and the universal conductivity
We study the continuum version of the dual theory for a system of
two-dimensional, zero temperature, disordered bosons, interacting with short
range repulsion and at a commensurate density. The dual theory, which describes
vortices in the bosonic ground state, and has a form of 3D classical scalar
electrodynamics in random, correlated magnetic field, admits a new disordered
critical point within RG calculation at fixed dimension. The universal
conductivity and the critical exponents at the superfluid-Bose glass critical
point are calculated as series in fixed-point values of the dual coupling
constants, to the lowest non-trivial order: ,
and . The comparison with numerical results and experiments
is discussed.Comment: 8 pages, LaTex, some clarifications and references adde
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