785 research outputs found
The pleiotropic deubiquitinase Ubp3 confers aneuploidy tolerance
Aneuploidy-or an unbalanced karyotype in which whole chromosomes are gained or lost-causes reduced fitness at both the cellular and organismal levels but is also a hallmark of human cancers. Aneuploidy causes a variety of cellular stresses, including genomic instability, proteotoxic and oxidative stresses, and impaired protein trafficking. The deubiquitinase Ubp3, which was identified by a genome-wide screen for gene deletions that impair the fitness of aneuploid yeast, is a key regulator of aneuploid cell homeostasis. We show that deletion of UBP3 exacerbates both karyotype-specific phenotypes and global stresses of aneuploid cells, including oxidative and proteotoxic stress. Indeed, Ubp3 is essential for proper proteasome function in euploid cells, and deletion of this deubiquitinase leads to further proteasome-mediated proteotoxicity in aneuploid yeast. Notably, the importance of UBP3 in aneuploid cells is conserved. Depletion of the human homolog of UBP3, USP10, is detrimental to the fitness of human cells upon chromosome missegregation, and this fitness defect is accompanied by autophagy inhibition. We thus used a genome-wide screen in yeast to identify a guardian of aneuploid cell fitness conserved across species. We propose that interfering with Ubp3/USP10 function could be a productive avenue in the development of novel cancer therapeutics
Phase Transitions in Isolated Vortex Chains
In very anisotropic layered superconductors (e.g. BiSrCaCuO)
a tilted magnetic field can penetrate as two co-existing lattices of vortices
parallel and perpendicular to the layers. At low out-of-plane fields the
perpendicular vortices form a set of isolated vortex chains, which have
recently been observed in detail with scanning Hall-probe measurements. We
present calculations that show a very delicate stability of this isolated-chain
state. As the vortex density increases along the chain there is a first-order
transition to a buckled chain, and then the chain will expel vortices in a
continuous transition to a composite-chain state. At low densities there is an
instability towards clustering, due to a long-range attraction between the
vortices on the chain, and at very low densities it becomes energetically
favorable to form a tilted chain, which may explain the sudden disappearance of
vortices along the chains seen in recent experiments.Comment: 9 pages, 10 figure
The Value of Inherited Deficiencies of Human Carbonic Anhydrase Isozymes in Understanding Their Cellular Roles a
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73265/1/j.1749-6632.1984.tb12346.x.pd
Evaporation of the pancake-vortex lattice in weakly-coupled layered superconductors
We calculate the melting line of the pancake-vortex system in a layered
superconductor, interpolating between two-dimensional (2D) melting at high
fields and the zero-field limit of single-stack evaporation. Long-range
interactions between pancake vortices in different layers permit a mean-field
approach, the ``substrate model'', where each 2D crystal fluctuates in a
substrate potential due to the vortices in other layers. We find the thermal
stability limit of the 3D solid, and compare the free energy to a 2D liquid to
determine the first-order melting transition and its jump in entropy.Comment: 4 pages, RevTeX, two postscript figures incorporated using eps
Vortex Collisions: Crossing or Recombination?
We investigate the collision of two vortex lines moving with viscous dynamics
and driven towards each other by an applied current. Using London theory in the
approach phase we observe a non-trivial vortex conformation producing
anti-parallel segments; their attractive interaction triggers a violent
collision. The collision region is analyzed using the time-dependent
Ginzburg-Landau equation. While we find vortices will always recombine through
exchange of segments, a crossing channel appears naturally through a double
collision process.Comment: 4 pages, 3 figure
Vortices in a Thin Film Superconductor with a Spherical Geometry
We report results from Monte Carlo simulations of a thin film superconductor
in a spherical geometry within the lowest Landau level approximation. We
observe the absence of a phase transition to a low temperature vortex solid
phase with these boundary conditions; the system remains in the vortex liquid
phase for all accessible temperatures. The correlation lengths are measured for
phase coherence and density modulation. Both lengths display identical
temperature dependences, with an asymptotic scaling form consistent with a
continuous zero temperature transition. This contrasts with the first order
freezing transition which is seen in the alternative quasi-periodic boundary
conditions. The high temperature perturbation theory and the ground states of
the spherical system suggest that the thermodynamic limit of the spherical
geometry is the same as that on the flat plane. We discuss the advantages and
drawbacks of simulations with different geometries, and compare with current
experimental conclusions. The effect of having a large scale inhomogeneity in
the applied field is also considered.Comment: This replacment contains substantial revisions: the new article is
twice as long with new and different results on the thermodynamic limit on
the sphere plus a full discussion on the alternative boundary conditions used
in simulations in the LLL approximation. 19 pages, 12 encapsulated PostScript
figures, 1 JPEG figure, uses RevTeX (with epsf
Josephson vortices and solitons inside pancake vortex lattice in layered superconductors
In very anisotropic layered superconductors a tilted magnetic field generates
crossing vortex lattices of pancake and Josephson vortices (JVs). We study the
properties of an isolated JV in the lattice of pancake vortices. JV induces
deformations in the pancake vortex crystal, which, in turn, substantially
modify the JV structure. The phase field of the JV is composed of two types of
phase deformations: the regular phase and vortex phase. The phase deformations
with smaller stiffness dominate. The contribution from the vortex phase
smoothly takes over with increasing magnetic field. We find that the structure
of the cores experiences a smooth yet qualitative evolution with decrease of
the anisotropy. At large anisotropies pancakes have only small deformations
with respect to position of the ideal crystal while at smaller anisotropies the
pancake stacks in the central row smoothly transfer between the neighboring
lattice positions forming a solitonlike structure. We also find that even at
high anisotropies pancake vortices strongly pin JVs and strongly increase their
viscous friction.Comment: 22 pages, 11 figures, to appear in Phys. Rev.
Topological Defects in the Abrikosov Lattice of Vortices in Type-II Superconductors
The free energy costs for various defects within an Abrikosov lattice of
vortices are calculated using the lowest Landau level approximation (LLL).
Defect solutions with boundary conditions for lines to meet at a point
(crossing defect) and for lines to twist around each other (braid defect) are
sought for 2, 3, 6, and 12 lines. Many results have been unexpected, including
the nonexistence of a stable two- or three-line braid. This, and the high
energy cost found for a six-line braid lead us to propose that the equilibrium
vortex state is not entangled below the irreversibility line of the high-
superconductors or in a large part of the vortex-liquid phase above this line.
Also, the solution for an infinite straight screw dislocation is found, and
used to give a limiting form for the free energy cost of very large braids.
This depends on the area enclosed by the braid as well as its perimeter length.Comment: 30 pages, 17 Encapsulated PostScript figures, uses Revtex (with epsf
Abrupt Change of Josephson Plasma Frequency at the Phase Boundary of the Bragg Glass in Bi_2Sr_2CaCu_2O_{8+\delta}
We report the first detailed and quantitative study of the Josephson coupling
energy in the vortex liquid, Bragg glass and vortex glass phases of
Bi_2Sr_2CaCu_2O_{8+\delta} by the Josephson plasma resonance. The measurements
revealed distinct features in the T- and H-dependencies of the plasma frequency
for each of these three vortex phases. When going across either
the Bragg-to-vortex glass or the Bragg-to-liquid transition line,
shows a dramatic change. We provide a quantitative discussion on the properties
of these phase transitions, including the first order nature of the
Bragg-to-vortex glass transition.Comment: 5pages, 4figure
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