264,946 research outputs found
Spin-depedent transmission of holes through periodically modulated diluted magnetic semiconductor waveguides
We study spin transport of holes through stubless or stubbed waveguides
modulated periodically by diluted magnetic semiconductor (DMS) sections of
width b1 . Injected holes of up (down) spin feel a periodically modulated
barrier (well) potential in the DMS sections and have different transmission
(T) coefficients. T oscillates with b1 for spin-down and decreases fast for
spin-up holes while the relative polarization Pr depends nearly periodically on
the stub height. Using asymmetric stubs leads to a nearly square-wave pattern
in T and to wide plateaus in Pr . T oscillates with the length between the DMS
sections. With two DMS sections per unit, T shows periodically wide gaps for
spin-down holes when a DMS width is varied. The results can be used to create
efficient spin filters.Comment: 5figure
Spin-dependent transmission in waveguides with periodically modulated strength of the spin-orbit interaction
The electron transmission is evaluated through waveguides, in which the
strength of the spin-orbit interaction(SOI) is varied periodically,
using the transfer-matrix technique. It is shown that exhibits a {\it
spin-transistor} action, as a function of or of the length of one of
the two subunits of the unit cell, provided only one mode is allowed to
propagate in the waveguide. A similar but not periodic behavior occurs as a
function of the incident electron energy. A transparent formula for through
one unit is obtained and helps explain its periodic behavior. The structure
considered is a good candidate for the establishment of a realistic spin
transistor
Polarized Curvature Radiation in Pulsar Magnetosphere
The propagation of polarized emission in pulsar magnetosphere is investigated
in this paper. The polarized waves are generated through curvature radiation
from the relativistic particles streaming along curved magnetic field lines and
co-rotating with the pulsar magnetosphere. Within the 1/{\deg} emission cone,
the waves can be divided into two natural wave mode components, the ordinary
(O) mode and the extraord nary (X) mode, with comparable intensities. Both
components propagate separately in magnetosphere, and are aligned within the
cone by adiabatic walking. The refraction of O-mode makes the two components
separated and incoherent. The detectable emission at a given height and a given
rotation phase consists of incoherent X-mode and O-mode components coming from
discrete emission regions. For four particle-density models in the form of
uniformity, cone, core and patches, we calculate the intensities for each mode
numerically within the entire pulsar beam. If the co-rotation of relativistic
particles with magnetosphere is not considered, the intensity distributions for
the X-mode and O-mode components are quite similar within the pulsar beam,
which causes serious depolarization. However, if the co-rotation of
relativistic particles is considered, the intensity distributions of the two
modes are very different, and the net polarization of out-coming emission
should be significant. Our numerical results are compared with observations,
and can naturally explain the orthogonal polarization modes of some pulsars.
Strong linear polarizations of some parts of pulsar profile can be reproduced
by curvature radiation and subsequent propagation effect.Comment: 12 pages, 9 figures, Accepted for publication in MNRA
Ballistic spin transport through electronic stub tuners: spin precession, selection, and square-wave transmission
Ballistic spin transport is studied through electronic tuners with double
stubs attached to them. The spins precess due to the spin-orbit interaction.
Injected polarized spins can exit the structure polarized in the opposite
direction. A nearly square-wave spin transmission, with values 1 and 0, can be
obtained using a periodic system of symmetric stubs and changing their length
or width. The gaps in the transmission can be widened using asymmetric stubs.
An additional modulation is obtained upon combining stub structures with
different values of the spin-orbit strength.Comment: 3 pages, 4 figure
Architectural implications for context adaptive smart spaces
Buildings and spaces are complex entities containing complex social structures and interactions. A smart space is a composite of the users that inhabit it, the IT infrastructure that supports it, and the sensors and appliances that service it. Rather than separating the IT from the buildings and from the appliances that inhabit them and treating them as separate systems, pervasive computing combines them and allows them to interact. We outline a reactive context architecture that supports this vision of integrated smart spaces and explore some implications for building large-scale pervasive systems
On the amplification of magnetic fields in cosmic filaments and galaxy clusters
The amplification of primordial magnetic fields via a small-scale turbulent
dynamo during structure formation might be able to explain the observed
magnetic fields in galaxy clusters. The magnetisation of more tenuous
large-scale structures such as cosmic filaments is more uncertain, as it is
challenging for numerical simulations to achieve the required dynamical range.
In this work, we present magneto-hydrodynamical cosmological simulations on
large uniform grids to study the amplification of primordial seed fields in the
intracluster medium (ICM) and in the warm-hot-intergalactic medium (WHIM). In
the ICM, we confirm that turbulence caused by structure formation can produce a
significant dynamo amplification, even if the amplification is smaller than
what is reported in other papers. In the WHIM inside filaments, we do not
observe significant dynamo amplification, even though we achieve Reynolds
numbers of . The maximal amplification for large
filaments is of the order of for the magnetic energy, corresponding
to a typical field of a few starting from a primordial weak field
of G (comoving). In order to start a small-scale dynamo, we found
that a minimum of resolution elements across the virial radius of
galaxy clusters was necessary. In filaments we could not find a minimum
resolution to set off a dynamo. This stems from the inefficiency of supersonic
motions in the WHIM in triggering solenoidal modes and small-scale twisting of
magnetic field structures. Magnetic fields this small will make it hard to
detect filaments in radio observations.Comment: MNRAS accepted, in press. 18 pages, 18 Figures. New version to match
with the one published in MNRAS. Updated publication list and footnote added
to the title as obituary notic
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