19,398 research outputs found
Stripes in thin ferromagnetic films with out-of-plane anisotropy
We examine the T=0 phase diagram of a thin ferromagnetic film with a strong
out-of-plane anisotropy in the vicinity of the reorientation phase transition
(with Co on Pt as an example). The phase diagram in the anisotropy-applied
field plane is universal in the limit where the film thickness is the shortest
length scale. It contains uniform fully magnetized and canted phases, as well
as periodically nonuniform states: a weakly modulated spin-density wave and
strongly modulated stripes. We determine the boundaries of metastability of
these phases and point out the existence of a critical point at which the
difference between the SDW and stripes vanishes. Out-of-plane magnetization
curves exhibit a variety of hysteresis loops caused by the coexistence of one
or more phases. Additionally, we study the effect of a system edge on the
orientation of stripes. We compare our results with recent experiments.Comment: added references and clarified derivations in response to referee
comment
Diffuse radio emission in MACS J0025.41222: the effect of a major merger on bulk separation of ICM components
Mergers of galaxy clusters are among the most energetic events in the
Universe. These events have significant impact on the intra-cluster medium,
depositing vast amounts of energy - often in the form of shocks - as well as
heavily influencing the properties of the constituent galaxy population. Many
clusters have been shown to host large-scale diffuse radio emission, known
variously as radio haloes and relics. These sources arise as a result of
electron (re-)acceleration in cluster-scale magnetic fields, although the
processes by which this occurs are still poorly understood. We present new,
deep radio observations of the high-redshift galaxy cluster MACS
J0025.41222, taken with the GMRT at 325 MHz, as well as new analysis of all
archival X-ray observations. We aim to investigate the potential of
diffuse radio emission and categorise the radio population of this cluster,
which has only been covered previously by shallow radio surveys. We produce
low-resolution maps of MACS J0025.41222 through a combination of uv-tapering
and subtracting the compact source population. Radial surface brightness and
mass profiles are derived from the data. We also derive a 2D map of
the ICM temperature. For the first time, two sources of diffuse radio emission
are detected in MACS J0025.41222, on linear scales of several hundred kpc.
Given the redshift of the cluster and the assumed cosmology, these sources
appear to be consistent with established trends in power scaling relations for
radio relics. The X-ray temperature map presents evidence of an asymmetric
temperature profile and tentative identification of a temperature jump
associated with one relic. We classify the pair of diffuse radio sources in
this cluster as a pair of radio relics, given their consistency with scaling
relations, location toward the cluster outskirts, and the available X-ray data.Comment: 20 pages, 15 figures, accepted for publication in A&
Dynamics of domain walls in magnetic nanostrips
We express dynamics of domain walls in ferromagnetic nanowires in terms of
collective coordinates generalizing Thiele's steady-state results. For weak
external perturbations the dynamics is dominated by a few soft modes. The
general approach is illustrated on the example of a vortex wall relevant to
recent experiments with flat nanowires. A two-mode approximation gives a
quantitatively accurate description of both the steady viscous motion of the
wall in weak magnetic fields and its oscillatory behavior in moderately high
fields above the Walker breakdown.Comment: 4 pages, update to published versio
Ballistic transport in induced one-dimensional hole systems
We have fabricated and studied a ballistic one-dimensional p-type quantum
wire using an undoped AlGaAs/GaAs heterostructure. The absence of modulation
doping eliminates remote ionized impurity scattering and allows high mobilities
to be achieved over a wide range of hole densities, and in particular, at very
low densities where carrier-carrier interactions are strongest. The device
exhibits clear quantized conductance plateaus with highly stable gate
characteristics. These devices provide opportunities for studying spin-orbit
coupling and interaction effects in mesoscopic hole systems in the strong
interaction regime where rs > 10.Comment: 6 pages, 4 figures (accepted to Applied Physics Letters
Electric Dipole Moments and Polarizability in the Quark-Diquark Model of the Neutron
For a bound state internal wave function respecting parity symmetry, it can
be rigorously argued that the mean electric dipole moment must be strictly
zero. Thus, both the neutron, viewed as a bound state of three quarks, and the
water molecule, viewed as a bound state of ten electrons two protons and an
oxygen nucleus, both have zero mean electric dipole moments. Yet, the water
molecule is said to have a nonzero dipole moment strength with
. The neutron may also be said to have
an electric dipole moment strength with .
The neutron analysis can be made experimentally consistent, if one employs a
quark-diquark model of neutron structure.Comment: four pages, two figure
Beam steering for circular switched parasitic arrays using a combinational approach
In this paper we present a method of electronic beam steering for circular switched parasitic array (SPA) antennas. In circular SPA antennas, one achieves azimuth beam steering by open-circuiting and short-circuiting different parasitic elements, usually with only one parasitic element open-circuited at a time. For the SPA antenna with few parasitic elements, this results in low azimuth beam steering resolution. In the proposed method, we iterate through different combinations of parasitic elements and the possible switch states of the lumped impedance loads connected to the parasitic elements. Our method aims to increase the azimuth beam steering resolution of the circular SPA antennas. The method is verified using a combination of simulation (using both MATLAB and WIPL-D) and a SPA antenna prototype implementation. The MATLAB code uses the induced EMF method, while the WIPL-D uses the Methods of Moment (MoM) for solving the antenna impedances. The three sets of results (simulations and measurement) match very well at 2.4 GHz. The results indicate the availability of more options (different loading configurations) for electronic beam switching that can be adopted to improve the beam steering resolution of circular SPA antennas
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