16,472 research outputs found
Microscopic Restoration of Proton-Neutron Mixed Symmetry in Weakly Collective Nuclei
Starting from the microscopic low-momentum nucleon-nucleon interaction V{low
k}, we present the first systematic shell model study of magnetic moments and
magnetic dipole transition strengths of the basic low-energy one-quadrupole
phonon excitations in nearly-spherical nuclei. Studying in particular the
even-even N=52 isotones from 92Zr to 100Cd, we find the predicted evolution of
the predominantly proton-neutron non-symmetric state reveals a restoration of
collective proton-neutron mixed-symmetry structure near mid-shell. This
provides the first explanation for the existence of pronounced collective
mixed-symmetry structures in weakly-collective nuclei.Comment: 5 Pages, 3 figure
Arthritis Is Developed in Borrelia-Primed And -Infected Mice Deficient of Interleukin-17
Interleukin-17 (IL-17) has been shown to participate in the development of Lyme arthritis in experimental mice. For example, neutralization of IL-17 with antibodies inhibits induction of arthritis in Borrelia-primed and -infected C57BL/6 wild-type mice. We hypothesized that mice lacking IL-17 would fail to develop Borrelia-induced arthritis. IL-17-deficient and wild-type C57BL/6 mice were primed with heat-inactivated Borrelia and then infected with viable spirochetes 3 weeks later. No swelling or major histopathological changes of the hind paws were detected in IL-17-deficient or wild-type mice that were primed with Borrelia or infected with viable spirochetes. By contrast, IL-17-deficient and wild-type mice that were primed and subsequently infected with heterologous Borrelia developed severe swelling and histopathological changes of the hind paws. In addition, Borrelia-primed and -infected IL-17-deficient mice exhibited elevated gamma-interferon (IFN-γ) levels in sera and increased frequencies of IFN-γ-expressing lymphocytes in popliteal lymph nodes compared to Borrelia-primed and -infected wild-type mice. These results demonstrate that IL-17 is not required for development of severe pathology in response to infection with Borrelia burgdorferi, but may contribute to disease through an interaction with IFN-γ
Suppression of core polarization in halo nuclei
We present a microscopic study of halo nuclei, starting from the Paris and
Bonn potentials and employing a two-frequency shell model approach. It is found
that the core-polarization effect is dramatically suppressed in such nuclei.
Consequently the effective interaction for halo nucleons is almost entirely
given by the bare G-matrix alone, which presently can be evaluated with a high
degree of accuracy. The experimental pairing energies between the two halo
neutrons in He and Li nuclei are satisfactorily reproduced by our
calculation. It is suggested that the fundamental nucleon-nucleon interaction
can be probed in a clearer and more direct way in halo nuclei than in ordinary
nuclei.Comment: 11 pages, RevTex, 2 postscript figures; major revisions, matches
version to appear in Phys. Rev. Letter
Low momentum nucleon-nucleon potential and shell model effective interactions
A low momentum nucleon-nucleon (NN) potential V-low-k is derived from meson
exhange potentials by integrating out the model dependent high momentum modes
of V_NN. The smooth and approximately unique V-low-k is used as input for shell
model calculations instead of the usual Brueckner G matrix. Such an approach
eliminates the nuclear mass dependence of the input interaction one finds in
the G matrix approach, allowing the same input interaction to be used in
different nuclear regions. Shell model calculations of 18O, 134Te and 135I
using the same input V-low-k have been performed. For cut-off momentum Lambda
in the vicinity of 2 fm-1, our calculated low-lying spectra for these nuclei
are in good agreement with experiments, and are weakly dependent on Lambda.Comment: 5 pages, 5 figure
Low-momentum ring diagrams of neutron matter at and near the unitary limit
We study neutron matter at and near the unitary limit using a low-momentum
ring diagram approach. By slightly tuning the meson-exchange CD-Bonn potential,
neutron-neutron potentials with various scattering lengths such as
and are constructed. Such potentials are renormalized
with rigorous procedures to give the corresponding -equivalent
low-momentum potentials , with which the low-momentum
particle-particle hole-hole ring diagrams are summed up to all orders, giving
the ground state energy of neutron matter for various scattering lengths.
At the limit of , our calculated ratio of to that of
the non-interacting case is found remarkably close to a constant of 0.44 over a
wide range of Fermi-momenta. This result reveals an universality that is well
consistent with the recent experimental and Monte-Carlo computational study on
low-density cold Fermi gas at the unitary limit. The overall behavior of this
ratio obtained with various scattering lengths is presented and discussed.
Ring-diagram results obtained with and those with -matrix
interactions are compared.Comment: 9 pages, 7 figure
Low Momentum Nucleon-Nucleon Interactions and Shell-Model Calculations
In the last few years, the low-momentum nucleon-nucleon (NN) interaction
V-low-k derived from free-space NN potentials has been successfully used in
shell-model calculations. V-low-k is a smooth potential which preserves the
deuteron binding energy as well as the half-on-shell T-matrix of the original
NN potential up to a momentum cutoff Lambda. In this paper we put to the test a
new low-momentum NN potential derived from chiral perturbation theory at
next-to-next-to-next-to-leading order with a sharp low-momentum cutoff at 2.1
fm-1. Shell-model calculations for the oxygen isotopes using effective
hamiltonians derived from both types of low-momentum potential are performed.
We find that the two potentials show the same perturbative behavior and yield
very similar results.Comment: 8 pages, 8 figures, to be published in Physical Review
Violation of the Ikeda sum rule and the self-consistency in the renormalized quasiparticle random phase approximation and the nuclear double-beta decay
The effect of the inclusion of ground state correlations into the QRPA
equation of motion for the two-neutrino double beta () decay
is carefully analyzed. The resulting model, called renormalized QRPA (RQRPA),
does not collapse near the physical value of the nuclear force strength in the
particle-particle channel, as happens with the ordinary QRPA. Still, the
transition amplitude is only slightly less sensitive on
this parameter in the RQRPA than that in the plain QRPA. It is argued that this
fact reveals once more that the characteristic behaviour of the
transition amplitude within the QRPA is not an artifact of
the model, but a consequence of the partial restoration of the spin-isospin
symmetry. It is shown that the price paid for bypassing the collapse in
the RQRPA is the violation of the Ikeda sum rule.Comment: 16 pages, latex, 3 postscript figure
Interaction between graphene and SiO2 surface
With first-principles DFT calculations, the interaction between graphene and
SiO2 surface has been analyzed by constructing the different configurations
based on {\alpha}-quartz and cristobalite structures. The single layer graphene
can stay stably on SiO2 surface is explained based on the general consideration
of configuration structures of SiO2 surface. It is also found that the oxygen
defect in SiO2 surface can shift the Fermi level of graphene down which opens
out the mechanism of hole-doping effect of graphene absorbed on SiO2 surface
observed in experiments.Comment: 17 pages, 7 figure
Application of a failure driven test profile in random testing
Random testing techniques have been extensively used in reliability assessment, as well as in debug testing. When used to assess software reliability, random testing selects test cases based on an operational profile; while in the context of debug testing, random testing often uses a uniform distribution. However, generally neither an operational profile nor a uniform distribution is chosen from the perspective of maximizing the effectiveness of failure detection. Adaptive random testing has been proposed to enhance the failure detection capability of random testing by evenly spreading test cases over the whole input domain. In this paper, we propose a new test profile, which is different from both the uniform distribution, and operational profiles. The aim of the new test profile is to maximize the effectiveness of failure detection. We integrate this new test profile with some existing adaptive random testing algorithms, and develop a family of new random testing algorithms. These new algorithms not only distribute test cases more evenly, but also have better failure detection capabilities than the corresponding original adaptive random testing algorithms. As a consequence, they perform better than the pure random testing
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