9,097 research outputs found
Simulated CII observations for SPICA/SAFARI
We investigate the case of CII 158 micron observations for SPICA/SAFARI using
a three-dimensional magnetohydrodynamical (MHD) simulation of the diffuse
interstellar medium (ISM) and the Meudon PDR code. The MHD simulation consists
of two converging flows of warm gas (10,000 K) within a cubic box 50 pc in
length. The interplay of thermal instability, magnetic field and self-gravity
leads to the formation of cold, dense clumps within a warm, turbulent
interclump medium. We sample several clumps along a line of sight through the
simulated cube and use them as input density profiles in the Meudon PDR code.
This allows us to derive intensity predictions for the CII 158 micron line and
provide time estimates for the mapping of a given sky area.Comment: 4 pages, 5 figures, to appear in the proceedings of the workshop "The
Space Infrared Telescope for Cosmology & Astrophysics: Revealing the Origins
of Planets and Galaxies" (July 2009, Oxford, United Kingdom
Time and force required for attendants boarding wheelchair users onto aircraft
Ensuring equal opportunity to all transport modes, including air travel, allows disabled people the same freedom of travel available to the rest of the population. However, boarding of wheelchair users onto airplanes is physically demanding for attendant airline or airport personal whom assist and time consuming and costly for airlines. This paper presents a comparison between two methods of boarding wheelchair users, measuring the forces required and the duration taken. Participants were asked to act as attendants and to board weighted wheelchairs onto simulated aircraft vestibules using two different manoeuvre methods (âgoing forwardsâ and âgoing backwardsâ), with two different loadings (âlightâ and âheavyâ) in two different access scenarios (âlevel accessâ and âsloped accessâ) between the jet-way/scissor-lift and the aircraft. The results reveal that the âgoing backwardsâ technique is a slightly faster manoeuvre method but no difference in the forces required exist between the two methods. The weight of the wheelchair affected the forces required to complete the boarding and exceeded health and safety guidelines for attendants. Reducing the height of the step between the aircraft and the jet-way or scissor-lift is recommended. Relevance to Industry: The research highlights the juxtaposition between the need to board wheelchair users and the excessive force required by the attendants propelling the wheelchair
Near-field interaction between domain walls in adjacent Permalloy nanowires
The magnetostatic interaction between two oppositely charged transverse
domain walls (DWs)in adjacent Permalloy nanowires is experimentally
demonstrated. The dependence of the pinning strength on wire separation is
investigated for distances between 13 and 125 nm, and depinning fields up to 93
Oe are measured. The results can be described fully by considering the
interaction between the full complex distribution of magnetic charge within
rigid, isolated DWs. This suggests the DW internal structure is not appreciably
disturbed by the pinning potential, and that they remain rigid although the
pinning strength is significant. This work demonstrates the possibility of
non-contact DW trapping without DW perturbation and full continuous flexibility
of the pinning potential type and strength. The consequence of the interaction
on DW based data storage schemes is evaluated.Comment: 4 pages, 4 figures, 1 page supplimentary material (supporting.ps
Observation of magnetic fragmentation in spin ice
Fractionalised excitations that emerge from a many body system have revealed
rich physics and concepts, from composite fermions in two-dimensional electron
systems, revealed through the fractional quantum Hall effect, to spinons in
antiferromagnetic chains and, more recently, fractionalisation of Dirac
electrons in graphene and magnetic monopoles in spin ice. Even more surprising
is the fragmentation of the degrees of freedom themselves, leading to
coexisting and a priori independent ground states. This puzzling phenomenon was
recently put forward in the context of spin ice, in which the magnetic moment
field can fragment, resulting in a dual ground state consisting of a
fluctuating spin liquid, a so-called Coulomb phase, on top of a magnetic
monopole crystal. Here we show, by means of neutron scattering measurements,
that such fragmentation occurs in the spin ice candidate NdZrO. We
observe the spectacular coexistence of an antiferromagnetic order induced by
the monopole crystallisation and a fluctuating state with ferromagnetic
correlations. Experimentally, this fragmentation manifests itself via the
superposition of magnetic Bragg peaks, characteristic of the ordered phase, and
a pinch point pattern, characteristic of the Coulomb phase. These results
highlight the relevance of the fragmentation concept to describe the physics of
systems that are simultaneously ordered and fluctuating.Comment: accepted in Nature Physic
Coupling and induced depinning of magnetic domain walls in adjacent spin valve nanotracks
The magnetostatic interaction between magnetic domain walls (DWs) in adjacent
nanotracks has been shown to produce strong inter-DW coupling and mutual
pinning. In this paper, we have used electrical measurements of adjacent
spin-valve nanotracks to follow the positions of interacting DWs. We show that
the magnetostatic interaction between DWs causes not only mutual pinning, as
observed till now, but that a travelling DW can also induce the depinning of
DWs in near-by tracks. These effects may have great implications for some
proposed high density magnetic devices (e.g. racetrack memory, DW logic
circuits, or DW-based MRAM).Comment: The following article has been accepted by the Journal of Applied
Physic
Anisotropic interactions opposing magnetocrystalline anisotropy in SrNiIrO
We report our investigation of the electronic and magnetic excitations of
SrNiIrO by resonant inelastic x-ray scattering at the Ir L edge.
The intra- electronic transitions are analyzed using an atomic model,
including spin-orbit coupling and trigonal distortion of the IrO
octahedron, confronted to {\it ab initio} quantum chemistry calculations. The
Ir spin-orbital entanglement is quantified and its implication on the magnetic
properties, in particular in inducing highly anisotropic magnetic interactions,
is highlighted. These are included in the spin-wave model proposed to account
for the dispersionless magnetic excitation that we observe at 90 meV. By
counterbalancing the strong Ni easy-plane anisotropy that manifests
itself at high temperature, the anisotropy of the interactions finally leads to
the remarkable easy-axis magnetism reported in this material at low
temperature
Dynamo models and differential rotation in late-type rapidly rotating stars
Increasing evidence is becoming available about not only the surface
differential rotation of rapidly rotating cool stars but, in a small number of
cases, also about temporal variations, which possibly are analogous to the
solar torsional oscillations. Given the present difficulties in resolving the
precise nature of such variations, due to both the short length and poor
resolution of the available data, theoretical input is vital to help assess the
modes of behaviour that might be expected, and will facilitate interpretation
of the observations. Here we take a first step in this direction by studying
the variations in the convection zones of such stars, using a two dimensional
axisymmetric mean field dynamo model operating in a spherical shell in which
the only nonlinearity is the action of the azimuthal component of the Lorentz
force of the dynamo generated magnetic field on the stellar angular velocity.
We consider three families of models with different depths of dynamo-active
regions. For moderately supercritical dynamo numbers we find torsional
oscillations that penetrate all the way down to the bottom of the convection
zones, similar to the case of the Sun. For larger dynamo numbers we find
fragmentation in some cases and sometimes there are other dynamical modes of
behaviour, including quasi-periodicity and chaos. We find that the largest
deviations in the angular velocity distribution caused by the Lorentz force are
of the order of few percent, implying that the original assumed `background'
rotation field is not strongly distorted.Comment: Astronomy and Astrophysics, in pres
Magneto-elastic coupling and unconventional magnetic ordering in triangular multiferroic AgCrS2
The temperature evolution of the crystal and magnetic structures of
ferroelectric sulfide AgCrS2 have been investigated by means of neutron
scattering. AgCrS2 undergoes at TN = 41.6 K a first-order phase transition,
from a paramagnetic rhombohedral R3m to an antiferromagnetic monoclinic
structure with a polar Cm space group. In addition to being ferroelectric below
TN, the low temperature phase of AgCrS2 exhibits an unconventional collinear
magnetic structure that can be described as double ferromagnetic stripes
coupled antiferromagnetically, with the magnetic moment of Cr+3 oriented along
b within the anisotropic triangular plane. The magnetic couplings stabilizing
this structure are discussed using inelastic neutron scattering results.
Ferroelectricity below TN in AgCrS2 can possibly be explained in terms of
atomic displacements at the magneto-elastic induced structural distortion.
These results contrast with the behavior of the parent frustrated
antiferromagnet and spin-driven ferroelectric AgCrO2
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