665 research outputs found
Spin and charge transport in U-shaped one-dimensional channels with spin-orbit couplings
A general form of the Hamiltonian for electrons confined to a curved
one-dimensional (1D) channel with spin-orbit coupling (SOC) linear in momentum
is rederived and is applied to a U-shaped channel. Discretizing the derived
continuous 1D Hamiltonian to a tight-binding version, the Landauer-Keldysh
formalism (LKF) for nonequilibrium transport can be applied. Spin transport
through the U-channel based on the LKF is compared with previous quantum
mechanical approaches. The role of a curvature-induced geometric potential
which was previously neglected in the literature of the ring issue is also
revisited. Transport regimes between nonadiabatic, corresponding to weak SOC or
sharp turn, and adiabatic, corresponding to strong SOC or smooth turn, is
discussed. Based on the LKF, interesting charge and spin transport properties
are further revealed. For the charge transport, the interplay between the
Rashba and the linear Dresselhaus (001) SOCs leads to an additional modulation
to the local charge density in the half-ring part of the U-channel, which is
shown to originate from the angle-dependent spin-orbit potential. For the spin
transport, theoretically predicted eigenstates of the Rashba rings, Dresselhaus
rings, and the persistent spin-helix state are numerically tested by the
present quantum transport calculation.Comment: 16 pages, 7 figure
A Note on the Gauge Equivalence between the Manin-Radul and Laberge-Mathieu Super KdV Hierarchies
The gauge equivalence between the Manin-Radul and Laberge-Mathieu super KdV
hierarchies is revisited. Apart from the Inami-Kanno transformation, we show
that there is another gauge transformation which also possess the canonical
property. We explore the relationship of these two gauge transformations from
the Kupershmidt-Wilson theorem viewpoint and, as a by-product, obtain the
Darboux-Backlund transformation for the Manin-Radul super KdV hierarchy. The
geometrical intepretation of these transformations is also briefly discussed.Comment: 8 pages, revtex, 1 figur
Two-step membrane binding by the bacterial SRP receptor enable efficient and accurate Co-translational protein targeting
The signal recognition particle (SRP) delivers ~30% of the proteome to the eukaryotic endoplasmic reticulum, or the bacterial plasma membrane. The precise mechanism by which the bacterial SRP receptor, FtsY, interacts with and is regulated at the target membrane remain unclear. Here, quantitative analysis of FtsY-lipid interactions at single-molecule resolution revealed a two-step mechanism in which FtsY initially contacts membrane via a Dynamic mode, followed by an SRP-induced conformational transition to a Stable mode that activates FtsY for downstream steps. Importantly, mutational analyses revealed extensive auto-inhibitory mechanisms that prevent free FtsY from engaging membrane in the Stable mode; an engineered FtsY pre-organized into the Stable mode led to indiscriminate targeting in vitro and disrupted FtsY function in vivo. Our results show that the two-step lipid-binding mechanism uncouples the membrane association of FtsY from its conformational activation, thus optimizing the balance between the efficiency and fidelity of co-translational protein targeting
Suspension of the fiber mode-cleaner launcher and measurement of the high extinction-ratio (10^{-9}) ellipsometer for the Q & A experiment
The Q & A experiment, first proposed and started in 1994, provides a feasible
way of exploring the quantum vacuum through the detection of vacuum
birefringence effect generated by QED loop diagram and the detection of the
polarization rotation effect generated by photon-interacting (pseudo-)scalar
particles. Three main parts of the experiment are: (1) Optics System (including
associated Electronic System) based on a suspended 3.5-m high finesse
Fabry-Perot cavity, (2) Ellipsometer using ultra-high extinction-ratio
polarizer and analyzer, and (3) Magnetic Field Modulation System for generating
the birefringence and the polarization rotation effect. In 2002, the Q & A
experiment achieved the Phase I sensitivity goal. During Phase II, we set (i)
to improve the control system of the cavity mirrors for suppressing the
relative motion noise, (ii) to enhance the birefringence signal by setting-up a
60-cm long 2.3 T transverse permanent magnet rotatable to 10 rev/s, (iii) to
reduce geometrical noise by inserting a polarization-maintaining optical fiber
(PM fiber) as a mode cleaner, and (iv) to use ultra-high extinction-ratio
(10^{-9}) polarizer and analyzer for ellipsometry. Here we report on (iii) &
(iv); specifically, we present the properties of the PM-fiber mode-cleaner, the
transfer function of its suspension system, and the result of our measurement
of high extinction-ratio polarizer and analyzer.Comment: 8 pages, 6 figures, presented in the 6th Edoardo Amaldi Conference on
Gravitational Waves, Okinawa, Japan, June 2005, and accepted by "Journal of
Physics: Conference Series". Modifications from version 2 were made based on
the referees' comments on figures. Ref. [31] were update
Formation of Compact Myelin Is Required for Maturation of the Axonal Cytoskeleton
Although traditional roles ascribed to myelinating glial cells are structural and supportive, the importance of compact myelin for proper functioning of the nervous system can be inferred from mutations in myelin proteins and neuropathologies associated with loss of myelin. Myelinating Schwann cells are known to affect local properties of peripheral axons (de Waegh et al., 1992), but little is known about effects of oligodendrocytes on CNS axons. The shiverer mutant mouse has a deletion in the myelin basic protein gene that eliminates compact myelin in the CNS. In shiverer mice, both local axonal features like phosphorylation of cytoskeletal proteins and neuronal perikaryon functions like cytoskeletal gene expression are altered. This leads to changes in the organization and composition of the axonal cytoskeleton in shiverer unmyelinated axons relative to age-matched wild-type myelinated fibers, although connectivity and patterns of neuronal activity are comparable. Remarkably, transgenic shiverer mice with thin myelin sheaths display an intermediate phenotype indicating that CNS neurons are sensitive to myelin sheath thickness. These results indicate that formation of a normal compact myelin sheath is required for normal maturation of the neuronal cytoskeleton in large CNS neurons
Cold Nuclear Matter In Holographic QCD
We study the Sakai-Sugimoto model of holographic QCD at zero temperature and
finite chemical potential. We find that as the baryon chemical potential is
increased above a critical value, there is a phase transition to a nuclear
matter phase characterized by a condensate of instantons on the probe D-branes
in the string theory dual. As a result of electrostatic interactions between
the instantons, this condensate expands towards the UV when the chemical
potential is increased, giving a holographic version of the expansion of the
Fermi surface. We argue based on properties of instantons that the nuclear
matter phase is necessarily inhomogeneous to arbitrarily high density. This
suggests an explanation of the "chiral density wave" instability of the quark
Fermi surface in large N_c QCD at asymptotically large chemical potential. We
study properties of the nuclear matter phase as a function of chemical
potential beyond the transition and argue in particular that the model can be
used to make a semi-quantitative prediction of the binding energy per nucleon
for nuclear matter in ordinary QCD.Comment: 31 pages, LaTeX, 1 figure, v2: some formulae corrected, qualitative
results unchange
Formation of Compact Myelin Is Required for Maturation of the Axonal Cytoskeleton
Although traditional roles ascribed to myelinating glial cells are structural and supportive, the importance of compact myelin for proper functioning of the nervous system can be inferred from mutations in myelin proteins and neuropathologies associated with loss of myelin. Myelinating Schwann cells are known to affect local properties of peripheral axons (de Waegh et al., 1992), but little is known about effects of oligodendrocytes on CNS axons. The shiverer mutant mouse has a deletion in the myelin basic protein gene that eliminates compact myelin in the CNS. In shiverer mice, both local axonal features like phosphorylation of cytoskeletal proteins and neuronal perikaryon functions like cytoskeletal gene expression are altered. This leads to changes in the organization and composition of the axonal cytoskeleton in shiverer unmyelinated axons relative to age-matched wild-type myelinated fibers, although connectivity and patterns of neuronal activity are comparable. Remarkably, transgenic shiverer mice with thin myelin sheaths display an intermediate phenotype indicating that CNS neurons are sensitive to myelin sheath thickness. These results indicate that formation of a normal compact myelin sheath is required for normal maturation of the neuronal cytoskeleton in large CNS neurons
On the B\"acklund Transformation for the Moyal Korteweg-de Vries Hierarchy
We study the B\"acklund symmetry for the Moyal Korteweg-de Vries (KdV)
hierarchy based on the Kuperschmidt-Wilson Theorem associated with second
Gelfand-Dickey structure with respect to the Moyal bracket, which generalizes
the result of Adler for the ordinary KdV.Comment: 9 pages, Revte
Conformal Covariantization of Moyal-Lax Operators
A covariant approach to the conformal property associated with Moyal-Lax
operators is given. By identifying the conformal covariance with the second
Gelfand-Dickey flow, we covariantize Moyal-Lax operators to construct the
primary fields of one-parameter deformation of classical -algebras.Comment: 13 pages, Revtex, no figures, v.2: typos corrected, references added
and conclusion modifie
Kernel Formula Approach to the Universal Whitham Hierarchy
We derive the dispersionless Hirota equations of the universal Whitham
hierarchy from the kernel formula approach proposed by Carroll and Kodama.
Besides, we also verify the associativity equations in this hierarchy from the
dispersionless Hirota equations and give a realization of the associative
algebra with structure constants expressed in terms of the residue formulas.Comment: 18 page
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