276 research outputs found
The Effect of Vincristine Sulphate on the Axoplasmic Flow of Proteins in Cultured Sympathetic Neurons
The effect of vincristine sulphate on the axoplasmic flow of labelled proteins in neurites of chick embryo sympathetic neurons growing in tissue culture was studied by autoradiography. In control neurons most of the 3H-proteins synthesized during a 90-min pulse with a 3H-amino acid were localized in cell bodies. There was a diminishing gradient of labelled proteins in the neurites which was highest in portions adjacent to the cell bodies and lowest at the periphery. During a physiological chase there was a gradual increase in the amount of label in the neurites, so that after a 15-h chase even the most peripheral portions were well labelled. This indicates that a portion of the labelled proteins synthesized in the cell bodies are transported peripherally into the neurites.
The centrifugal movement of labelled proteins in neurites was markedly decreased when cells were grown in medium containing 10 µg/ml vincristine sulphate. After a 15-h chase in the presence of drug only a small amount of label was in the peripheral portion of the neurites. Treatment with vincristine did not decrease the rate of amino acid incorporation or alter the rate of protein turnover during the course of the experiment. Thus an explanation of the results based on an altered rate of total cell protein synthesis or degradation is unlikely.
The capacity of sympathetic neurons to take up and concentrate exogenous [3H]norepinephrine in their neurites was only slightly reduced by vincristine. This indicates that at least some cellular activities requiring metabolic energy are relatively unaffected by the interruption in axoplasmic flow caused by vincristine and that the mechanism by which vincristine interferes with axoplasmic flow does not involve general cellular toxicity.
The major morphological differences between control and vincristine-treated neurons were the absence of microtubules and the presence of crystal-like structures within the cells. The relationship between the effect of vincristine on the axoplasmic flow of proteins and the arrangement of the microtubule system is discussed
Dissipative phase-fluctuations in superconducting wires capacitively coupled to diffusive metals
We study the screening of the Coulomb interaction in a quasi one-dimensional
superconductor given by the presence of either a one- or a two-dimensional
non-interacting electron gas. To that end, we derive an effective low-energy
phase-only action, which amounts to treating the Coulomb and superconducting
correlations in the random-phase approximation. We concentrate on the study of
dissipation effects in the superconductor, induced by the effect of Coulomb
coupling to the diffusive density-modes in the metal, and study its
consequences on the static and dynamic conductivity. Our results point towards
the importance of the dimensionality of the screening metal in the behavior of
the superconducting plasma mode of the wire at low energies. In absence of
topological defects, and when the screening is given by a one-dimensional
electron gas, the superconducting plasma mode is completely damped in the limit
, and consequently superconductivity is lost in the wire. In contrast,
we recover a Drude-response in the conductivity when the screening is provided
by a two-dimensional electron gas.Comment: 16 pages, 8 figures, 1 table, 2 appendice
Kinetic-inductance-limited reset time of superconducting nanowire photon counters
We investigate the recovery of superconducting NbN-nanowire photon counters
after detection of an optical pulse at a wavelength of 1550 nm, and present a
model that quantitatively accounts for our observations. The reset time is
found to be limited by the large kinetic inductance of these nanowires, which
forces a tradeoff between counting rate and either detection efficiency or
active area. Devices of usable size and high detection efficiency are found to
have reset times orders of magnitude longer than their intrinsic photoresponse
time.Comment: Submitted to Applied Physics Letter
Resistivity scaling and critical dynamics of fully frustrated Josephson-junction arrays with on-site dissipation
We study the scaling behavior and critical dynamics of the resistive
transition in Josephson-junction arrays, at f=1/2 flux quantum per plaquette,
by numerical simulation of an on-site dissipation model for the dynamics. The
results are compared with recent simulations using the
resistively-shunted-junction model. For both models, we find that the
resistivity scaling and critical dynamics of the phases are well described by
the same critical temperature as for the chiral (vortex-lattice) transition,
with a power-law divergent correlation length. The behavior is consistent with
the single transition scenario, where phase and chiral variables order at the
same temperature, but with different dynamic exponents z for phase coherence
and chiral order.Comment: 17 pages, 13 figures, to appear in Phys. Rev.
Absence of charge backscattering in the nonequilibrium current of normal-superconductor structures
We study the nonequilibrium transport properties of a
normal-superconductor-normal structure, focussing on the effect of adding an
impurity in the superconducting region. Current conservation requires the
superfluid velocity to be nonzero, causing a distortion of the quasiparticle
dispersion relation within the superconductor. For weakly reflecting interfaces
we find a regime of intermediate voltages in which Andreev transmission is the
only permitted mechanism for quasiparticles to enter the superconductor.
Impurities in the superconductor can only cause Andreev reflection of these
quasiparticles and thus cannot degrade the current. At higher voltages, a state
of gapless superconductivity develops which is sensitive to the presence of
impurities.Comment: Latex file, 11 pages, 2 figures available upon request
[email protected], to be published in Journal of Physics: Condensed Matte
Mouse Genome Informatics (MGI): latest news from MGD and GXD.
The Mouse Genome Informatics (MGI) database system combines multiple expertly curated community data resources into a shared knowledge management ecosystem united by common metadata annotation standards. MGI\u27s mission is to facilitate the use of the mouse as an experimental model for understanding the genetic and genomic basis of human health and disease. MGI is the authoritative source for mouse gene, allele, and strain nomenclature and is the primary source of mouse phenotype annotations, functional annotations, developmental gene expression information, and annotations of mouse models with human diseases. MGI maintains mouse anatomy and phenotype ontologies and contributes to the development of the Gene Ontology and Disease Ontology and uses these ontologies as standard terminologies for annotation. The Mouse Genome Database (MGD) and the Gene Expression Database (GXD) are MGI\u27s two major knowledgebases. Here, we highlight some of the recent changes and enhancements to MGD and GXD that have been implemented in response to changing needs of the biomedical research community and to improve the efficiency of expert curation. MGI can be accessed freely at http://www.informatics.jax.org
Mouse Genome Database (MGD): Knowledgebase for mouse-human comparative biology.
The Mouse Genome Database (MGD; http://www.informatics.jax.org) is the community model organism knowledgebase for the laboratory mouse, a widely used animal model for comparative studies of the genetic and genomic basis for human health and disease. MGD is the authoritative source for biological reference data related to mouse genes, gene functions, phenotypes and mouse models of human disease. MGD is the primary source for official gene, allele, and mouse strain nomenclature based on the guidelines set by the International Committee on Standardized Nomenclature for Mice. MGD\u27s biocuration scientists curate information from the biomedical literature and from large and small datasets contributed directly by investigators. In this report we describe significant enhancements to the content and interfaces at MGD, including (i) improvements in the Multi Genome Viewer for exploring the genomes of multiple mouse strains, (ii) inclusion of many more mouse strains and new mouse strain pages with extended query options and (iii) integration of extensive data about mouse strain variants. We also describe improvements to the efficiency of literature curation processes and the implementation of an information portal focused on mouse models and genes for the study of COVID-19
Rearrangement of the vortex lattice due to instabilities of vortex flow
With increasing applied current we show that the moving vortex lattice
changes its structure from a triangular one to a set of parallel vortex rows in
a pinning free superconductor. This effect originates from the change of the
shape of the vortex core due to non-equilibrium effects (similar to the
mechanism of vortex motion instability in the Larkin-Ovchinnikov theory). The
moving vortex creates a deficit of quasiparticles in front of its motion and an
excess of quasiparticles behind the core of the moving vortex. This results in
the appearance of a wake (region with suppressed order parameter) behind the
vortex which attracts other vortices resulting in an effective
direction-dependent interaction between vortices. When the vortex velocity
reaches the critical value quasi-phase slip lines (lines with fast vortex
motion) appear which may coexist with slowly moving vortices between such
lines. Our results are found within the framework of the time-dependent
Ginzburg-Landau equations and are strictly valid when the coherence length
is larger or comparable with the decay length of the
non-equilibrium quasiparticle distribution function. We qualitatively explain
experiments on the instability of vortex flow at low magnetic fields when the
distance between vortices . We speculate that a
similar instability of the vortex lattice should exist for even when
.Comment: 10 pages, 11 figure
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