208,168 research outputs found
Fermion Production in Strong Magnetic Field and its Astrophysical Implications
We calculate the effective potential of a strong magnetic field induced by
fermions with anomalous magnetic moments which couple to the electromagnetic
field in the form of the Pauli interaction. For a uniform magnetic field, we
find the explicit form of the effective potential. It is found that the
non-vanishing imaginary part develops for a magnetic field stronger than a
critical field and has a quartic form which is quite different from the
exponential form of the Schwinger process. We also consider a linear magnetic
field configuration as an example of inhomogeneous magnetic fields. We find
that the imaginary part of the effective potential is nonzero even below the
critical field and shows an exponentially decreasing behavior with respect to
the inverse of the magnetic field gradient, which is the non-perturbative
characteristics analogous to the Schwinger process. These results imply the
instability of the strong magnetic field to produce fermion pairs as a purely
magnetic effect. The possible applications to the astrophysical phenomena with
strong magnetic field are also discussed.Comment: 13 pages, 3 figure
Novel in-gap spin state in Zn-doped La_1.85Sr_0.15CuO_4
Low-energy spin excitations of La1.85Sr0.15Cu1-yZnyO4 were studied by neutron
scattering. In y=0.004, the incommensurate magnetic peaks show a well defined
``spin gap'' below Tc. The magnetic signals at omega=3 meV decrease below Tc=27
K for y=0.008, also suggesting the gap opening. At lower temperatures, however,
the signal increases again, implying a novel in-gap spin state. In y=0.017, the
spin gap vanishes and elastic magnetic peaks appear. These results clarify that
doped Zn impurities induce the novel in-gap state, which becomes larger and
more static with increasing Zn.Comment: 4 pages, 4 figure
BGRID: A block-structured grid generation code for wing sections
The operation of the BGRID computer program is described for generating block-structured grids. Examples are provided to illustrate the code input and output. The application of a fully implicit AF (approximation factorization)-based computer code, called TWINGB (Transonic WING), for solving the 3D transonic full potential equation in conservation form on block-structured grids is also discussed
Self-dual Maxwell Chern-Simons Solitons In 1+1 Dimensions
We study the domain wall soliton solutions in the relativistic self-dual
Maxwell Chern-Simons model in 1+1 dimensions obtained by the dimensional
reduction of the 2+1 model. Both topological and nontopological self-dual
solutions are found in this case. A la BPS dyons here the Bogomol'ny bound on
the energy is expressed in terms of two conserved quantities. We discuss the
underlying supersymmetry. Nonrelativistic limit of this model is also
considered and static, nonrelativistic self-dual soliton solutions are
obtained.Comment: 18 pages RevTex, 2 figures included, to appear in Phys. Rev.
Charge-Density-Wave Ordering in the Metal-Insulator Transition Compound PrRu4P12
X-ray and electron diffraction measurements on the metal-insulator (M-I)
transition compound PrRuP have revealed the emergence of a periodic
ordering of charge density around the Pr atoms. It is found that the ordering
is associated with the onset of a low temperature insulator phase. These
conclusions are supported by the facts that the space group of the crystal
structure transforms from Im to Pm below the M-I transition
temperature and also that the temperature dependence of the superlattice peaks
in the insulator phase follows the squared BCS function. The M-I transition
could be originated from the perfect nesting of the Fermi surface and/or the
instability of the electrons.Comment: 4 pages, 5 figures, Phys. Rev. B (2004) (in press
Direct relation between the low-energy spin excitations and superconductivity of overdoped high- superconductors
The dynamic spin susceptibility, , has been measured over the
energy range of meV for overdoped
LaSrCuO. Incommensurate (IC) spin excitations are observed
at 8 K for all superconducting samples for with
peaking at meV. The IC peaks at 6 meV become smaller in
intensity with increasing and, finally, become unobservable for a sample
with which has no bulk superconductivity. The maximum
decreases linearly with (onset) in the overdoped region, implying a direct
cooperative relation between the spin fluctuations and the superconductivity.Comment: 4 pages, 4 figure
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