452 research outputs found
Developmental changes in trak-mediated mitochondrial transport in neurons
Previous studies established that the kinesin adaptor proteins, TRAK1 and TRAK2, play an important role in mitochondrial transport in neurons. They link mitochondria to kinesin motor proteins via a TRAK acceptor protein in the mitochondrial outer membrane, the Rho GTPase, Miro. TRAKs also associate with enzyme, O-linked N-acetylglucosamine transferase (OGT), to form a quaternary, mitochondrial trafficking complex. A recent report suggested that TRAK1 preferentially controls mitochondrial transport in axons of hippocampal neurons whereas TRAK2 controls mitochondrial transport in dendrites. However, it is not clear whether the function of any of these proteins is exclusive to axons or dendrites and if their mechanisms of action are conserved between different neuronal populations and also, during maturation. Here, a comparative study was carried out into TRAK-mediated mitochondrial mobility in axons and dendrites of hippocampal and cortical neurons during maturation in vitro using a shRNA gene knockdown approach. It was found that in mature hippocampal and cortical neurons, TRAK1 predominantly mediates axonal mitochondrial transport whereas dendritic transport is mediated via TRAK2. In young, maturing neurons, TRAK1 and TRAK2 contribute similarly in mitochondrial transport in both axons and dendrites in both neuronal types. These findings demonstrate maturation regulation of mitochondrial transport which is conserved between at least two distinct neuronal subtypes
Spin Hall effect due to intersubband-induced spin-orbit interaction in symmetric quantum wells
We investigate the intrinsic spin Hall effect in two-dimensional electron
gases in quantum wells with two subbands, where a new intersubband-induced
spin-orbit coupling is operative. The bulk spin Hall conductivity
is calculated in the ballistic limit within the standard Kubo
formalism in the presence of a magnetic field and is found to remain finite
in the B=0 limit, as long as only the lowest subband is occupied. Our
calculated exhibits a nonmonotonic behavior and can change its
sign as the Fermi energy (the carrier areal density ) is varied between
the subband edges. We determine the magnitude of for realistic
InSb quantum wells by performing a self-consistent calculation of the
intersubband-induced spin-orbit coupling.Comment: 7 pages, 3 figure
Persistent Skyrmion Lattice of Noninteracting Electrons with Spin-Orbit Coupling
A persistent spin helix (PSH) is a robust helical spin-density pattern
arising in disordered 2D electron gases with Rashba and Dresselhaus
spin-orbit (SO) tuned couplings, i.e., . Here we
investigate the emergence of a Persistent Skyrmion Lattice (PSL) resulting from
the coherent superposition of PSHs along orthogonal directions -- crossed PSHs
-- in wells with two occupied subbands . For realistic GaAs wells we
show that the Rashba and Dresselhaus couplings can be
simultaneously tuned to equal strengths but opposite signs, e.g., and . In this regime and away from band
anticrossings, our {\it non-interacting} electron gas sustains a topologically
non-trivial skyrmion-lattice spin-density excitation, which inherits the
robustness against spin-independent disorder and interactions from its
underlying crossed PSHs. We find that the spin relaxation rate due to the
interband SO coupling is comparable to that of the cubic Dresselhaus term as a
mechanism of the PSL decay. Near anticrossings, the interband-induced spin
mixing leads to unusual spin textures along the energy contours beyond those of
the Rahsba-Dresselhaus bands. Our PSL opens up the unique possibility of
observing topological phenomena, e.g., topological and skyrmion Hall effects,
in ordinary GaAs wells with non-interacting electrons.Comment: 5 pages, 2 figures; changed the presentation and added supplemental
material (17 pages, 1 figure
Optimal geometry of lateral GaAs and Si/SiGe quantum dots for electrical control of spin qubits
We investigate the effects of the orientation of the magnetic field and the orientation of a quantum dot, with respect to crystallographic coordinates, on the quality of an electrically controlled qubit realized in a gated semiconductor quantum dot. We find that, due to the anisotropy of the spin-orbit interactions, by varying the two orientations it is possible to tune the qubit in the sense of optimizing the ratio of its couplings to phonons and to a control electric field. We find conditions under which such optimal setup can be reached by solely reorienting the magnetic field, and when a specific positioning of the dot is required. We also find that the knowledge of the relative sign of the spin-orbit interaction strengths allows to choose a robust optimal dot geometry, with the dot main axis along [110], or [110], where the qubit can be always optimized by reorienting the magnetic field
Cotunneling in the \nu = 5/2 fractional quantum Hall regime
We show that cotunneling in the 5/2 fractional quantum Hall regime allows us
to test the Moore-Read wave function, proposed for this regime, and to probe
the nature of the fractional charge carriers. We calculate the cotunneling
current for electrons that tunnel between two quantum Hall edge states via a
quantum dot and for quasiparticles with fractional charges e/4 and e/2 that
tunnel via an antidot. While electron cotunneling is strongly suppressed, the
quasiparticle tunneling shows signatures characteristic of the Moore-Read
state. For comparison, we also consider cotunneling between Laughlin states,
and find that electron transport between Moore-Read states and between Laughlin
states at filling factor 1/3 have identical voltage dependences
Probing Single-Electron Spin Decoherence in Quantum Dots using Charged Excitons
We propose to use optical detection of magnetic resonance (ODMR) to measure the decoherence time T 2 of a single-electron spin in a semiconductor quantum dot. The electron is in one of the spin 1/2 states and a circularly polarized laser can only create an optical excitation for one of the electron spin states due to Pauli blocking. An applied electron spin resonance (ESR) field leads to Rabi spin flips and thus to a modulation of the photoluminescence or, alternatively, of the photocurrent. This allows one to measure the ESR linewidth and the coherent Rabi oscillations, from which the electron spin decoherence can be determined. We study different possible schemes for such an ODMR setup, including cw or pulsed laser excitatio
On non- solutions to the Seiberg-Witten equations
We show that a previous paper of Freund describing a solution to the
Seiberg-Witten equations has a sign error rendering it a solution to a related
but different set of equations. The non- nature of Freund's solution is
discussed and clarified and we also construct a whole class of solutions to the
Seiberg-Witten equations.Comment: 8 pages, Te
There are No Unfilled Shells in Hartree-Fock Theory
Hartree-Fock theory is supposed to yield a picture of atomic shells which may
or may not be filled according to the atom's position in the periodic table. We
prove that shells are always completely filled in an exact Hartree-Fock
calculation. Our theorem generalizes to any system having a two-body
interaction that, like the Coulomb potential, is repulsive.Comment: 5 pages, VBEHLMLJPS--16/July/9
Localization of the kinesin adaptor proteins trafficking kinesin proteins 1 and 2 in primary cultures of hippocampal pyramidal and cortical neurons
Neuronal function requires regulated anterograde and retrograde trafficking of mitochondria along microtubules by using the molecular motors kinesin and dynein. Previous work has established that trafficking kinesin proteins (TRAKs),TRAK1 and TRAK2, are kinesin adaptor proteins that link mitochondria to kinesin motor proteins via an acceptor protein in the mitochondrial outer membrane, etc. the Rho GTPase Miro. Recent studies have shown that TRAK1 preferentially controls mitochondrial transport in axons of hippocampal neurons by virtue of its binding to both kinesin and dynein motor proteins, whereas TRAK2 controls mitochondrial transport in dendrites resulting from its binding to dynein. This study further investigates the subcellular localization of TRAK1 and TRAK2 in primary cultures of hippocampal and cortical neurons by using both commercial antibodies and anti-TRAK1 and anti-TRAK2 antibodies raised in our own laboratory (in-house). Whereas TRAK1 was prevalently localized in axons of hippocampal and cortical neurons, TRAK2 was more prevalent in dendrites of hippocampal neurons. In cortical neurons, TRAK2 was equally distributed between axons and dendrites. Some qualitative differences were observed between commercial and in-house-generated antibody immunostaining
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