754 research outputs found
The membrane-embedded segment of cytochrome b5 as studied by cross-linking with photoactivatable phospholipids
Vesicles were prepared from a 9:1 (mole/mol) mixture of dipalmitoyl phosphatidylcholine and the radioactively labeled phospholipids, 1-palmitoyl-2-ω -(m-diazirinophenoxy)undecanoyl-sn-glycero-3-phosphocholine (PC-I) or 1-palmitoyl-2-ω -(2-diazo-3,3,3-trifluropropionyloxy)lauroyl-sn- glycero-3-phosphocholine (PC-II). Rabbit liver cytochrome b5 was inserted into these vesicles spontaneously and the resulting vesicles containing the cytochrome b5 in the transferable form were photolyzed. Cytochrome b5 containing covalently cross-linked phospholipids was isolated by Sephadex LH-60 column chromatography using ethanol/formic acid as the solvent. Of the total radioactivity, 4.6% (PC-I) or 11.3% (PC-II) was linked to the protein; of the former, up to 51% was base-labile, while in the latter, 22% was base-labile. The sites of cross-linking of PC-I to the protein were investigated by fragmentation with trypsin, Staphylococcus aureas V8 protease, CNBr, and o-iodosobenzoic acid followed by Sephadex LH-60 chromatography and Edman sequencing (solid phase) of the appropriate fragments. The distribution of cross-linking was broad (Ser-104 to Met-130), showing a bell-shaped pattern with a significant peak at Ser-118. The labeling pattern is consistent with the previously proposed loop-back model for the membranous segment in the transferable form of cytochrome b5
Solutions to the ultradiscrete Toda molecule equation expressed as minimum weight flows of planar graphs
We define a function by means of the minimum weight flow on a planar graph
and prove that this function solves the ultradiscrete Toda molecule equation,
its B\"acklund transformation and the two dimensional Toda molecule equation.
The method we employ in the proof can be considered as fundamental to the
integrability of ultradiscrete soliton equations.Comment: 14 pages, 10 figures Added citations in v
Electron-beam propagation in a two-dimensional electron gas
A quantum mechanical model based on a Green's function approach has been used
to calculate the transmission probability of electrons traversing a
two-dimensional electron gas injected and detected via mode-selective quantum
point contacts. Two-dimensional scattering potentials, back-scattering, and
temperature effects were included in order to compare the calculated results
with experimentally observed interference patterns. The results yield detailed
information about the distribution, size, and the energetic height of the
scattering potentials.Comment: 7 pages, 6 figure
Contacts and Edge State Equilibration in the Fractional Quantum Hall Effect
We develop a simple kinetic equation description of edge state dynamics in
the fractional quantum Hall effect (FQHE), which allows us to examine in detail
equilibration processes between multiple edge modes. As in the integer quantum
Hall effect (IQHE), inter-mode equilibration is a prerequisite for quantization
of the Hall conductance. Two sources for such equilibration are considered:
Edge impurity scattering and equilibration by the electrical contacts. Several
specific models for electrical contacts are introduced and analyzed. For FQHE
states in which edge channels move in both directions, such as , these
models for the electrical contacts {\it do not} equilibrate the edge modes,
resulting in a non-quantized Hall conductance, even in a four-terminal
measurement. Inclusion of edge-impurity scattering, which {\it directly}
transfers charge between channels, is shown to restore the four-terminal
quantized conductance. For specific filling factors, notably and
, the equilibration length due to impurity scattering diverges in the
zero temperature limit, which should lead to a breakdown of quantization for
small samples at low temperatures. Experimental implications are discussed.Comment: 14 pages REVTeX, 6 postscript figures (uuencoded and compressed
Magnetic Quantum Dot: A Magnetic Transmission Barrier and Resonator
We study the ballistic edge-channel transport in quantum wires with a
magnetic quantum dot, which is formed by two different magnetic fields B^* and
B_0 inside and outside the dot, respectively. We find that the electron states
located near the dot and the scattering of edge channels by the dot strongly
depend on whether B^* is parallel or antiparallel to B_0. For parallel fields,
two-terminal conductance as a function of channel energy is quantized except
for resonances, while, for antiparallel fields, it is not quantized and all
channels can be completely reflected in some energy ranges. All these features
are attributed to the characteristic magnetic confinements caused by nonuniform
fields.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Magnetic Properties of 2-Dimensional Dipolar Squares: Boundary Geometry Dependence
By means of the molecular dynamics simulation on gradual cooling processes,
we investigate magnetic properties of classical spin systems only with the
magnetic dipole-dipole interaction, which we call dipolar systems. Focusing on
their finite-size effect, particularly their boundary geometry dependence, we
study two finite dipolar squares cut out from a square lattice with
and , where is an angle between the direction of the lattice axis
and that of the square boundary. Distinctly different results are obtained in
the two dipolar squares. In the square, the ``from-edge-to-interior
freezing'' of spins is observed. Its ground state has a multi-domain structure
whose domains consist of the two among infinitely (continuously) degenerated
Luttinger-Tisza (LT) ground-state orders on a bulk square lattice, i.e., the
two antiferromagnetically aligned ferromagnetic chains (af-FMC) orders directed
in parallel to the two lattice axes. In the square, on the other
hand, the freezing starts from the interior of the square, and its ground state
is nearly in a single domain with one of the two af-FMC orders. These geometry
effects are argued to originate from the anisotropic nature of the
dipole-dipole interaction which depends on the relative direction of sites in a
real space of the interacting spins.Comment: 21 pages, 13 figures, submitted to Journal of Physical Society Japa
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