Non-integer flux quanta for a spherical superconductor

A thin film superconductor shaped into a spherical shell at whose center lies the end of long thin solenoid in which there is an integer flux $N\Phi_0$ has been previously extensively studied numerically as a model of a two-dimensional superconductor. The emergent flux from the solenoid produces a radial B-field at the superconducting shell and $N$ vortices in the superconducting film. We study here the effects of including a second solenoid (carrying a flux $f$) which is inserted inside the first solenoid but passing right across the sphere. This Aharonov-Bohm (AB) flux does not have to be quantized to make the order parameter single valued. The Ginzburg-Landau (GL) free energy is minimized at fixed $N$ as a function of $f$ and it is found that the minimum is usually achieved when the AB flux $f$ is half a flux quantum, but depending on $N$ the minimum may be at $f=0$ or values which are not obvious rational fractions.Comment: 6 pages, RevTeX, 5 figures include

Phase Transitions in Isolated Vortex Chains

In very anisotropic layered superconductors (e.g. Bi$_2$Sr$_2$CaCu$_2$O$_x$) 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 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

A novel filtration system for point of care washing of cellular therapy products

The cell therapy industry would greatly benefit from a simple point of care solution to remove Dimethyl Sulfoxide (DMSO) from small volume thawed cell suspensions prior to injection. We have designed and validated a novel dead-end filtration device, which takes advantage of the higher density of thawed cell suspensions to remove the DMSO and protein impurities from the cell suspension without fouling the filter membrane. The filter was designed to avoid fluid circuits and minimize the surface area that is contacted by the cell suspension, thus reducing cell losses by design. The filtration process was established through optimization of the fluid flow configuration, backflush cycles and filter geometry. Overall, this novel filtration device allows for a 1 mL of thawed cryopreserved cell suspensions, containing 107 cells of a foetal lung fibroblast cell line (MRC-5), to be washed in less than 30 minutes. More than 95% of the DMSO and up to 94% of the Albumin- Fluorescein-Isothiocyanate content can be removed while the viable cell recovery is higher than 80%. We have also demonstrated that this system can be used for bone marrow-derived human mesenchymal stem cells with more than 73% cell recovery and 85% DMSO reduction. This is the first time that a dead end (normal) filtration process has been used to successfully wash high density human cell suspensions. In practice, this novel solid-liquid separation technology fills the need for small volume washing in closed processing systems for cellular therapies

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

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

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

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