2,073 research outputs found
Endocytosis of the ASGP receptor H1 is reduced by mutation of tyrosine-5 but still occurs via coated pits
The clustering of plasma membrane receptors in clathrin-coated pits depends on determinants within their cytoplasmic domains. In several cases, individual tyrosine residues were shown to be necessary for rapid internalization. We have mutated the single tyrosine at position 5 in the cytoplasmic domain of the major subunit H1 of the asialoglycoprotein receptor to alanine. Expressed in fibroblasts cells, the mutant protein was accumulated in the plasma membrane, and its rate of internalization was reduced by a factor of four. The residual rate of endocytosis, however, was still significantly higher than that of resident plasma membrane proteins. Upon acidification of the cytoplasm, which specifically inhibits the formation of clathrin-coated vesicles but not uptake of the fluid phase marker Lucifer yellow, residual endocytosis was blocked. By immunoelectron microscopy mutant H1 could be directly demonstrated in coated pits. The fraction of wild-type and mutant H1 present in coated pits as determined by immunogold localization correlated well with the respective rates of internalization. Thus, mutation of tyrosine-5 only partially inactivates recognition of H1 for incorporation into coated pits
Spin Effects in a Quantum Ring
Recent experiments are reviewed that explore the spin states of a ring-shaped
many-electron quantum dot. Coulomb-blockade spectroscopy is used to access the
spin degree of freedom. The Zeeman effect observed for states with successive
electron number allows to select possible sequences of spin ground states of
the ring. Spin-paired orbital levels can be identified by probing their
response to magnetic fields normal to the plane of the ring and electric fields
caused by suitable gate voltages. This narrows down the choice of ground-state
spin sequences. A gate-controlled singlet--triplet transition is identified and
the size of the exchange interaction matrix element is determined.Comment: 13 pages, 3 figures, Proceedings of the QD2004 conference in Banf
Issues in economics: what is the cost of deflation?
A steady decline in the core rate of inflation over the past few years has prompted the question: What are the economic consequences when the inflation rate drops below zero?Deflation (Finance)
Transmission Phase Through Two Quantum Dots Embedded in a Four-Terminal Quantum Ring
We use the Aharonov-Bohm effect in a four-terminal ring based on a Ga[Al]As
heterostructure for the measurement of the relative transmission phase. In each
of the two interfering paths we induce a quantum dot. The number of electrons
in the two dots can be controlled independently. The transmission phase is
measured as electrons are added to or taken away from the individual quantum
dots.Comment: 3 pages, 4 figure
Microwave shielding of transparent and conducting single-walled carbon nanotube films
The authors measured the transport properties of single-walled carbon
nanotube (SWCNT) films in the microwave frequency range from 10 MHz to 30 GHz
by using the Corbino reflection technique from temperatures of 20-400 K. Based
on the real and imaginary parts of the microwave conductivity, they calculated
the shielding effectiveness for various film thicknesses. Shielding
effectiveness of 43 dB at 10 MHz and 28 dB at 10 GHz are found for films with
90% optical transmittance, which suggests that SWCNT films are promising as a
type of transparent microwave shielding material. By combining their data with
those from the literature, the conductivity of SWCNT films was established in a
broad frequency range from dc to visible.Comment: 4 pages, 4 figure
Kondo Effect in a Many-Electron Quantum Ring
The Kondo effect is investigated in a many-electron quantum ring as a
function of magnetic field. For fields applied perpendicular to the plane of
the ring a modulation of the Kondo effect with the Aharonov-Bohm period is
observed. This effect is discussed in terms of the energy spectrum of the ring
and the parametrically changing tunnel coupling. In addition, we use gate
voltages to modify the ground-state spin of the ring. The observed splitting of
the Kondo-related zero-bias anomaly in this configuration is tuned with an
in-plane magnetic field.Comment: 4 pages, 4 figure
Singlet-Triplet Transition Tuned by Asymmetric Gate Voltages in a Quantum Ring
Wavefunction and interaction effects in the addition spectrum of a Coulomb
blockaded many electron quantum ring are investigated as a function of
asymmetrically applied gate voltages and magnetic field. Hartree and exchange
contributions to the interaction are quantitatively evaluated at a crossing
between states extended around the ring and states which are more localized in
one arm of the ring. A gate tunable singlet-triplet transition of the two
uppermost levels of this many electron ring is identified at zero magnetic
field.Comment: 4 page
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