2,700 research outputs found
Optical-Model Description of Time-Reversal Violation
A time-reversal-violating spin-correlation coefficient in the total cross
section for polarized neutrons incident on a tensor rank-2 polarized target is
calculated by assuming a time-reversal-noninvariant, parity-conserving
``five-fold" interaction in the neutron-nucleus optical potential. Results are
presented for the system for neutron incident energies
covering the range 1--20 MeV. From existing experimental bounds, a strength of
keV is deduced for the real and imaginary parts of the five-fold
term, which implies an upper bound of order on the relative -odd
strength when compared to the central real optical potential.Comment: 11 pages (Revtex
On the validity of the Wigner-Seitz approximation in neutron star crust
The inner crust of neutron stars formed of nuclear clusters immersed in a
neutron sea has been widely studied in the framework of the Wigner-Seitz
approximation since the seminal work of Negele and Vautherin. In this article,
the validity of this approximation is discussed in the framework of the band
theory of solids. For a typical cell of Zr, present in the external
layers of the inner crust, it is shown that the ground state properties of the
neutron gas are rather well reproduced by the Wigner-Seitz approximation, while
its dynamical properties depend on the energy scale of the process of interest
or on the temperature. It is concluded that the Wigner-Seitz approximation is
well suited for describing the inner crust of young neutron stars and the
collapsing core of massive stars during supernovae explosions. However the band
theory is required for low temperature fluid dynamics.Comment: 7 pages, with figures - PTH, version
Two European Cornus L. feeding leafmining moths, Antispila petryi Martini, 1899, sp. rev. and A. treitschkiella (Fischer von Röslerstamm, 1843) (Lepidoptera, Heliozelidae): an unjustified synonymy and overlooked range expansion
Antispila treitschkiella (Fischer von Röslerstamm, 1843) and A. petryi Martini, 1899, sp. rev. were regarded as synonymous since 1978, but are shown to be two clearly separated species with different hostplants, life histories, DNA barcodes and morphology. Antispila treitschkiella feeds on Cornus mas L., is bivoltine, and has, by following its ornamentally planted host, greatly expanded its range in north-western Europe. In contrast A. petryi feeds on the widespread native C. sanguinea L., is univoltine, and is one of only two Antispila species previously resident in the British Isles, the Netherlands and northern Europe. Consequently, the increase in abundance of A. treitschkiella in the Netherlands since the early 1990s and in Great Britain in recent years must be regarded as part of a recent expansion into north-western Europe, whereas the native A. petryi is hardly expanding and less abundant. In Britain, detailed surveys of parks and living collections confirmed the monophagy of these two species. A search of British herbarium samples provided no evidence for an earlier date of establishment. Information on recognition of all stages, including DNA barcodes, and distribution is provided, and these two species are compared with the third European Cornus L. leafminer, A. metallella (Denis & Schiffermüller, 1775)
Optimized fabrication of high quality La0.67Sr0.33MnO3 thin films considering all essential characteristics
In this article, an overview of the fabrication and properties of high
quality La0.67Sr0.33MnO3 (LSMO) thin films is given. A high quality LSMO film
combines a smooth surface morphology with a large magnetization and a small
residual resistivity, while avoiding precipitates and surface segregation. In
literature, typically only a few of these issues are adressed. We therefore
present a thorough characterization of our films, which were grown by pulsed
laser deposition. The films were characterized with reflection high energy
electron diffraction, atomic force microscopy, x-ray diffraction, magnetization
and transport measurements, x-ray photoelectron spectroscopy and scanning
transmission electron microscopy. The films have a saturation magnetization of
4.0 {\mu}B/Mn, a Curie temperature of 350 K and a residual resistivity of 60
{\mu}{\Omega}cm. These results indicate that high quality films, combining both
large magnetization and small residual resistivity, were realized. A comparison
between different samples presented in literature shows that focussing on a
single property is insufficient for the optimization of the deposition process.
For high quality films, all properties have to be adressed. For LSMO devices,
the thin film quality is crucial for the device performance. Therefore, this
research is important for the application of LSMO in devices.Comment: Accepted for publication in Journal of Physics D - Applied Physic
A Microscopic T-Violating Optical Potential: Implications for Neutron-Transmission Experiments
We derive a T-violating P-conserving optical potential for neutron-nucleus
scattering, starting from a uniquely determined two-body -exchange
interaction with the same symmetry. We then obtain limits on the T-violating
-nucleon coupling from neutron-transmission
experiments in Ho. The limits may soon compete with those from
measurements of atomic electric-dipole moments.Comment: 8 pages, 2 uuencoded figures in separate files (replaces version sent
earlier in the day with figures attached), in RevTeX 3, submitted to PR
Effective calculation of LEED intensities using symmetry-adapted functions
The calculation of LEED intensities in a spherical-wave representation can be substantially simplified by symmetry relations. The wave field around each atom is expanded in symmetry-adapted functions where the local point symmetry of the atomic site applies. For overlayer systems with more than one atom per unit cell symmetry-adapted functions can be used when the division of the crystal into monoatomic subplanes is replaced by division into subplanes containing all symmetrically equivalent atomic positions
Ballistic anisotropic magnetoresistance
Electronic transport in ferromagnetic ballistic conductors is predicted to
exhibit ballistic anisotropic magnetoresistance (BAMR) - a change in the
ballistic conductance with the direction of magnetization. This phenomenon
originates from the effect of the spin-orbit interaction on the electronic band
structure which leads to a change in the number of bands crossing the Fermi
energy when the magnetization direction changes. We illustrate the significance
of this phenomenon by performing ab-initio calculations of the ballistic
conductance in ferromagnetic Ni and Fe nanowires which display a sizable BAMR
when the magnetization changes direction from parallel to perpendicular to the
wire axis
Quasiperiodic waves at the onset of zero Prandtl number convection with rotation
We show the possibility of quasiperiodic waves at the onset of thermal
convection in a thin horizontal layer of slowly rotating zero-Prandtl number
Boussinesq fluid confined between stress-free conducting boundaries. Two
independent frequencies emerge due to an interaction between a stationary
instability and a self-tuned wavy instability in presence of coriolis force, if
Taylor number is raised above a critical value. Constructing a dynamical system
for the hydrodynamical problem, the competition between the interacting
instabilities is analyzed. The forward bifurcation from the conductive state is
self-tuned.Comment: 9 pages of text (LaTex), 5 figures (Jpeg format
Multibaryons as Symmetric Multiskyrmions
We study non-adiabatic corrections to multibaryon systems within the bound
state approach to the SU(3) Skyrme model. We use approximate ansatze for the
static background fields based on rational maps which have the same symmetries
of the exact solutions. To determine the explicit form of the collective
Hamiltonians and wave functions we only make use of these symmetries. Thus, the
expressions obtained are also valid in the exact case. On the other hand, the
inertia parameters and hyperfine splitting constants we calculate do depend on
the detailed form of the ansatze and are, therefore, approximate. Using these
values we compute the low lying spectra of multibaryons with B <= 9 and
strangeness 0, -1 and -B. Finally, we show that the non-adiabatic corrections
do not affect the stability of the tetralambda and heptalambda found in a
previous work.Comment: 17 pages, RevTeX, no figure
Quasiparticle transport equation with collision delay. II. Microscopic Theory
For a system of non-interacting electrons scattered by neutral impurities, we
derive a modified Boltzmann equation that includes quasiparticle and virial
corrections. We start from quasiclassical transport equation for
non-equilibrium Green's functions and apply limit of small scattering rates.
Resulting transport equation for quasiparticles has gradient corrections to
scattering integrals. These gradient corrections are rearranged into a form
characteristic for virial corrections
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