3,874 research outputs found
Dynamics of thin-film spin-flip transistors with perpendicular source-drain magnetizations
A "spin-flip transistor" is a lateral spin valve consisting of ferromagnetic
source drain contacts to a thin-film normal-metal island with an electrically
floating ferromagnetic base contact on top. We analyze the
\emph{dc}-current-driven magnetization dynamics of spin-flip transistors in
which the source-drain contacts are magnetized perpendicularly to the device
plane by magnetoelectronic circuit theory and the macrospin
Landau-Lifshitz-Gilbert equation. Spin flip scattering and spin pumping effects
are taken into account. We find a steady-state rotation of the base
magnetization at GHz frequencies that is tuneable by the source-drain bias. We
discuss the advantages of the lateral structure for high-frequency generation
and actuation of nanomechanical systems over recently proposed nanopillar
structures.Comment: Accepted by Phys.Rev.B as regular articl
DNS of bifurcations in an air-filled rotating baroclinic annulus
Three-dimensional Direct Numerical Simulation (DNS) on the nonlinear dynamics
and a route to chaos in a rotating fluid subjected to lateral heating is
presented here and discussed in the context of laboratory experiments in the
baroclinic annulus. Following two previous preliminary studies by Maubert and
Randriamampianina, the fluid used is air rather than a liquid as used in all
other previous work. This study investigated a bifurcation sequence from the
axisymmetric flow to a number of complex flows. The transition sequence, on
increase of the rotation rate, from the axisymmetric solution via a steady,
fully-developed baroclinic wave to chaotic flow followed a variant of the
classical quasi-periodic bifurcation route, starting with a subcritical Hopf
and associated saddle-node bifurcation. This was followed by a sequence of two
supercritical Hopf-type bifurcations, first to an amplitude vacillation, then
to a three-frequency quasi-periodic modulated amplitude vacillation (MAV), and
finally to a chaotic MAV\@. In the context of the baroclinic annulus this
sequence is unusual as the vacillation is usually found on decrease of the
rotation rate from the steady wave flow. Further transitions of a steady wave
with a higher wave number pointed to the possibility that a barotropic
instability of the side wall boundary layers and the subsequent breakdown of
these barotropic vortices may play a role in the transition to structural
vacillation and, ultimately, geostrophic turbulence.Comment: 31 page
In vivo stability of ester- and ether-linked phospholipid-containing liposomes as measured by perturbed angular correlation spectroscopy
To evaluate liposome formulations for use as intracellular sustained-release drug depots, we have compared the uptake and degradation in rat liver and spleen of liposomes of various compositions, containing as their bulk phospholipid an ether-linked phospholipid or one of several ester-linked phospholipids, by perturbed angular correlation spectroscopy. Multilamellar and small unilamellar vesicles (MLVs and SUVs), composed of egg phosphatidylcholine, sphingomyelin, distearoyl phosphatidylcholine (DSPC), dipalmitoyl phosphatidylcholine (DPPC) or its analog dihexadecylglycerophosphorylcholine (DHPC), and cholesterol plus phosphatidylserine, and containing (111)In complexed to nitrilotriacetic acid, were injected intravenously in rats. Recovery of (111)In-labeled liposomes in blood, liver, and spleen was assessed at specific time points after injection and the percentage of liposomes still intact in liver and spleen was determined by measurement of the time-integrated angular perturbation factor ([G22(∞)] of the (111)In label. We found that MLVs but not SUVs, having DHPC as their bulk phospholipid, showed an increased resistance against lysosomal degradation as compared to other phospholipid-containing liposomes. The use of diacyl phospholipids with a high gel/liquid-crystalline phase-transition temperature, such as DPPC and DSPC, also retarded degradation of MLV, but not of SUV in the dose range tested, while the rate of uptake of these liposomes by the liver was lower
Direct Numerical Simulation of structural vacillation in the transition to geostrophic turbulence
The onset of small-scale fluctuations around a steady convection pattern in a
rotating baroclinic annulus filled with air is investigated using Direct
Numerical Simulation. In previous laboratory experiments of baroclinic waves,
such fluctuations have been associated with a flow regime termed Structural
Vacillation which is regarded as the first step in the transition to
fully-developed geostrophic turbulence.Comment: 6 page
Structure of the cell envelope of Halobacterium halobium
The structure of the isolated cell envelope of Halobacterium halobium is studied by X-ray diffraction, electron microscopy, and biochemical analysis. The envelope consists of the cell membrane and two layers of protein outside. The outer layer of protein shows a regular arrangement of the protein or glycoprotein particles and is therefore identified as the cell wall. Just outside the cell membrane is a 20 A-thick layer of protein. It is a third structure in the envelope, the function of which may be distinct from that of the cell membrane and the cell wall. This inner layer of protein is separated from the outer protein layer by a 65 Å-wide space which has an electron density very close to that of the suspending medium, and which can be etched after freeze-fracture. The space is tentatively identified as the periplasmic space. At NaCl concentrations below 2.0 M, both protein layers of the envelope disintegrate. Gel filtration and analytical ultracentrifugation of the soluble components from the two protein layers reveal two major bands of protein with apparent mol wt of ~16,000 and 21,000. At the same time, the cell membrane stays essentially intact as long as the Mg++ concentration is kept at ≥ 20 mM. The cell membrane breaks into small fragments when treated with 0.1 M NaCl and EDTA, or with distilled water, and some soluble proteins, including flavins and cytochromes, are released. The cell membrane apparently has an asymmetric core of the lipid bilayer
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