16,352 research outputs found
Macrospin Models of Spin Transfer Dynamics
The current-induced magnetization dynamics of a spin valve are studied using
a macrospin (single domain) approximation and numerical solutions of a
generalized Landau-Lifshitz-Gilbert equation. For the purpose of quantitative
comparison with experiment [Kiselev {\it et al.} Nature {\bf 425}, 380 (2003)],
we calculate the resistance and microwave power as a function of current and
external field including the effects of anisotropies, damping, spin-transfer
torque, thermal fluctuations, spin-pumping, and incomplete absorption of
transverse spin current. While many features of experiment appear in the
simulations, there are two significant discrepancies: the current dependence of
the precession frequency and the presence/absence of a microwave quiet magnetic
phase with a distinct magnetoresistance signature. Comparison is made with
micromagnetic simulations designed to model the same experiment.Comment: 14 pages, 14 figures. Email [email protected] for a
pdf with higher quality figure
Spatio-temporal patterns in the Hantavirus infection
We present a model of the infection of Hantavirus in deer mouse, Peromyscus
maniculatus, based on biological observations of the system in the North
American Southwest. The results of the analysis shed light on relevant
observations of the biological system, such as the sporadical disappearance of
the infection, and the existence of foci or ``refugia'' that perform as
reservoirs of the virus when environmental conditions are less than optimal.Comment: 6 pages, 5 inlined figures, RevTeX 4 forma
Structure of a Complete ATP Synthase Dimer Reveals the Molecular Basis of Inner Mitochondrial Membrane Morphology
We determined the structure of a complete, dimeric F1Fo-ATP synthase from yeast Yarrowia lipolytica mitochondria by a combination of cryo-EM and X-ray crystallography. The final structure resolves 58 of the 60 dimer subunits. Horizontal helices of subunit a in Fo wrap around the c-ring rotor, and a total of six vertical helices assigned to subunits a, b, f, i, and 8 span the membrane. Subunit 8 (A6L in human) is an evolutionary derivative of the bacterial b subunit. On the lumenal membrane surface, subunit f establishes direct contact between the two monomers. Comparison with a cryo-EM map of the F1Fo monomer identifies subunits e and g at the lateral dimer interface. They do not form dimer contacts but enable dimer formation by inducing a strong membrane curvature of ∼100°. Our structure explains the structural basis of cristae formation in mitochondria, a landmark signature of eukaryotic cell morphology
The potential benefit of pre-operative assessment of amputation wound healing potential in peripheral vascular disease
Choosing the most distal amputation level that will heal is difficult in patients with peripheral vascular disease. From 1984 to 1988,965 patients underwent 1 563 amputations for lower limb peripheral vascular disease at King Edward VIII Hospital, Durban. The primary amputation revision rate was 51% with a mortality rate of 23,1%. Random pre-operative assessment of amputation wound healing potential using a transcutaneous oxygen pressure index was investigated over the 4-year period, 1987 - 1990. This was responsible for a reduction in the amputation revision rate to 8,2% in patients tested
A decomposition theorem for compact groups with application to supercompactness
We show that every compact connected group is the limit of a continuous
inverse sequence, in the category of compact groups, where each successor
bonding map is either an epimorphism with finite kernel or the projection from
a product by a simple compact Lie group. As an application, we present a proof
of an unpublished result of Charles Mills from 1978: every compact group is
supercompact.Comment: 12 page
Radio Observations of the Supernova Remnant Candidate G312.5-3.0
The radio images from the Parkes-MIT-NRAO (PMN) Southern Sky Survey at 4850
MHz have revealed a number of previously unknown radio sources. One such
source, G312.5-3.0 (PMN J1421-6415), has been observed using the
multi-frequency capabilities of the Australia Telescope Compact Array (ATCA) at
frequencies of 1380 MHz and 2378 MHz. Further observations of the source were
made using the Molonglo Observatory Synthesis Telescope (MOST) at a frequency
of 843 MHz. The source has an angular size of 18 arcmin and has a distinct
shell structure. We present the reduced multi-frequency observations of this
source and provide a brief argument for its possible identification as a
supernova remnant.Comment: 5 pages, 5 figures, Accepted for publication in MNRA
The Rehabilitation of Terminal 2 – A Case History
The Port of Portland, Oregon recently completed the rehabilitation of the downstream portion of Terminal 2. The project included the placement of more than 1 million cy of dredged hydraulic sand fill and the construction of a 1,400-ft-long pile-supported wharf. Up to 60 ft of sand fill was placed over soft, submerged sediments. The silt along the toe of the slope was removed prior to placing the fill. No shear failures or mudwaves were detected during filling. The fill induced settlements of up to 63 in., which agreed well with the predicted maximum settlement of about 60 in. Underwater sand fill slopes were placed at about 2.5H: 1V and subsequently trimmed to 2.25H: 1V. The slope was subsequently densified and steepened to 1.75H: 1V with fragmental quarry rock. After slope construction, 840 vertical, 24-in. octagonal prestressed concrete piles were driven for the wharf
Magnetization damping in a local-density approximation
The linear response of itinerant transition metal ferromagnets to transverse
magnetic fields is studied in a self-consistent adiabatic local-density
approximation. The susceptibility is calculated from a microscopic Hamiltonian,
including spin-conserving impurities, impurity induced spin-orbit interaction
and magnetic impurities using the Keldysh formalism. The Gilbert damping
constant in the Landau-Lifshitz-Gilbert equation is identified, parametrized by
an effective transverse spin dephasing rate, and is found to be inversely
proportional to the exchange splitting. Our result justify the phenomenological
treatment of transverse spin dephasing in the study of current-induced
magnetization dynamics in weak, itinerant ferromagnets by Tserkovnyak
\textit{et al.}. We show that neglect of gradient corrections in the
quasiclassical transport equations leads to incorrect results when the exchange
potential becomes of the order of the Fermi energy.Comment: 11 pages, 41 references, no figure
Heat Bath Particle Number Spectrum
We calculate the number spectrum of particles radiated during a scattering
into a heat bath using the thermal largest-time equation and the
Dyson-Schwinger equation. We show how one can systematically calculate
{d}/{d\omega} to any order using modified real time
finite-temperature diagrams. Our approach is demonstrated on a simple model
where two scalar particles scatter, within a photon-electron heat bath, into a
pair of charged particles and it is shown how to calculate the resulting
changes in the number spectra of the photons and electrons.Comment: 29 pages, LaTeX; 14 figure
Nonmonotonic Temperature-dependent Resistance in Low Density 2D Hole Gases
The low temperature longitudinal resistance-per-square Rxx(T) in ungated
GaAs/AlGaAs quantum wells of high peak hole mobility 1.7x10^6 cm^2/Vs is
metallic for 2D hole density p as low as 3.8x10^9 cm-2. The electronic
contribution to the resistance, R_{el}(T), is a nonmonotonic function of T,
exhibiting thermal activation, R_{el}(T) ~ exp{-E_a/kT}, for kT<<E_F and a
heretofore unnoted decay R_{el}(T) ~ 1/T for k_T>EF. The form of R_{el}(T) is
independent of density, indicating a fundamental relationship between the low
and high T scattering mechanisms in the metallic state
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