STUDY OF THE EFFECT OF HYPOTHERMIC CONSERVATION ON THE INTRACELLULAR SODIUM CONCENTRATION IN THE ENDOTHELIUM OF CORNEAL TRANSPLANTS

Endothelial keratoplasty has become the treatment of choice for corneal endothelial dysfunction. Advancements in the surgical treatment of corneal endothelial diseases depend on progress in graft conservation and its related advantages in assessing the suitability of grafts for transplantation. Transport of water and ions by cornea endothelium is important for the optic properties of cornea. In this work, we study the intracellular sodium concentration in cornea endothelial cells in samples of pig cornea that underwent hypothermic conservation for 1 and 10 days and endothelial cells of human cornea grafts after 10-day conservation. The concentration of intracellular sodium in preparations of endothelial cells was assayed using fluorescent dye SodiumGreen. The fluorescent images were analyzed with the custom-made computer program CytoDynamics. An increased level of intracellular sodium was shown in the endothelium after 10-day conservation in comparison with one-day conservation (pig samples). Sodium permeability of pig endothelial cell plasma membranes significantly decreased in these samples. Assessment of intracellular sodium in human cornea endothelium showed a higher level – as was in analogues pig samples of the corneal endothelium. The assay of the intracellular sodium balance concentration established in endothelial cells after hypothermic conservation in mediums L-15 and Optisol-GS showed a significant advantage of specialized me dium Optisol-GS. The balanced intracellular concentration after 10 days of hypothermic conservation was significantly lower in cells incubated at 4 °C in Optisol-GS (L-15, 128 ± 14,  n = 15; Optisol-GS, 108 ± 14, n = 11; mM, p < 0.001). Intracellular sodium concentration could be a useful parameter for assessing cornea endothelium cell viability

Quantum Nucleation and Macroscopic Quantum Tunneling in Cold-Atom Boson-Fermion Mixtures

Kinetics of phase separation transition in boson-fermion cold atom mixtures is investigated. We identify the parameters at which the transition is governed by quantum nucleation mechanism, responsible for the formation of critical nuclei of a stable phase. We demonstrate that for low fermion-boson mass ratio the density dependence of quantum nucleation transition rate is experimentally observable. The crossover to macroscopic quantum tunneling regime is analyzed. Based on a microscopic description of interacting cold atom boson-fermion mixtures we derive an effective action for the critical droplet and obtain an asymptotic expression for the nucleation rate in the vicinity of the phase transition and near the spinodal instability of the mixed phase. We show that dissipation due to excitations in fermion subsystem play a dominant role close to the transition point.Comment: 13 pages, 5 figure

On the Puzzle of Odd-Frequency Superconductivity

Since the first theoretical proposal by Berezinskii, an odd-frequency superconductivity has encountered the fundamental problems on its thermodynamic stability and rigidity of a homogenous state accompanied by unphysical Meissner effect. Recently, Solenov {\it et al}. [Phys. Rev. B {\bf 79} (2009) 132502.] have asserted that the path-integral formulation gets rid of the difficulties leading to a stable homogenous phase with an ordinary Meissner effect. Here, we show that it is crucial to choose the appropriate saddle-point solution that minimizes the effective free energy, which was assumed {\it implicitly} in the work by Solenov and co-workers. We exhibit the path-integral framework for the odd-frequency superconductivity with general type of pairings, including an argument on the retarded functions via the analytic continuation to the real axis.Comment: 6 pages, in JPSJ forma

Quantitative Treatment of Decoherence

We outline different approaches to define and quantify decoherence. We argue that a measure based on a properly defined norm of deviation of the density matrix is appropriate for quantifying decoherence in quantum registers. For a semiconductor double quantum dot qubit, evaluation of this measure is reviewed. For a general class of decoherence processes, including those occurring in semiconductor qubits, we argue that this measure is additive: It scales linearly with the number of qubits.Comment: Revised version, 26 pages, in LaTeX, 3 EPS figure

Possible Odd-Frequency Superconductivity in Strong-Coupling Electron-Phonon Systems

A possibility of the odd-frequency pairing in the strong-coupling electron-phonon systems is discussed. Using the Holstein-Hubbard model, we demonstrate that the anomalously soft Einstein mode with the frequency $\omega_{\rm E}\ll\omega_{c}$ ($\omega_{c}$ is the order of the renormalized bandwidth) mediates the s-wave odd-frequency triplet pairing against the ordinary even-frequency singlet pairing. It is necessary for the emergence of the odd-frequency pairing that the pairing interaction is strongly retarded as well as the strong coupling, since the pairing interaction for the odd-frequency pairing is effective only in the diagonal scattering channel, $(\omega_{n},-\omega_{n})\to(\omega_{n'},-\omega_{n'})$ with $\omega_{n'}=\omega_{n}\gtrsim \omega_{\rm E}$. Namely, the odd-frequency superconductivity is realized in the opposite limit of the original BCS theory. The Ginzburg-Landau analysis in the strong-coupling region shows that the specific-heat discontinuity and the slope of the temperature dependence of the superfluid density can be quite small as compared with the BCS values, depending on the ratio of the transition temperature $T_{c}$ and $\omega_{c}$.Comment: 6 pages, 7 figures, submitted to J. Phys. Soc. Jp

On the Meissner Effect of the Odd-Frequency Superconductivity with Critical Spin Fluctuations: Possibility of Zero Field FFLO pairing

We investigate the influence of critical spin fluctuations on electromagnetic responses in the odd-frequency superconductivity. It is shown that the Meissner kernel of the odd-frequency superconductivity is strongly reduced by the critical spin fluctuation or the massless spin wave mode in the antiferromagnetic phase. These results imply that the superfluid density is reduced, and the London penetration depth is lengthened for the odd-frequency pairing. It is also shown that the zero field Flude-Ferrell-Larkin-Ovchinnikov pairing is spontaneously realized both for even- and odd-frequency in the case of sufficiently strong coupling with low lying spin-modes.Comment: 10 pages, 7 figure

Symmetry and Topology in Superconductors - Odd-frequency pairing and edge states -

Superconductivity is a phenomenon where the macroscopic quantum coherence appears due to the pairing of electrons. This offers a fascinating arena to study the physics of broken gauge symmetry. However, the important symmetries in superconductors are not only the gauge invariance. Especially, the symmetry properties of the pairing, i.e., the parity and spin-singlet/spin-triplet, determine the physical properties of the superconducting state. Recently it has been recognized that there is the important third symmetry of the pair amplitude, i.e., even or odd parity with respect to the frequency. The conventional uniform superconducting states correspond to the even-frequency pairing, but the recent finding is that the odd-frequency pair amplitude arises in the spatially non-uniform situation quite ubiquitously. Especially, this is the case in the Andreev bound state (ABS) appearing at the surface/interface of the sample. The other important recent development is on the nontrivial topological aspects of superconductors. As the band insulators are classified by topological indices into (i) conventional insulator, (ii) quantum Hall insulator, and (iii) topological insulator, also are the gapped superconductors. The influence of the nontrivial topology of the bulk states appears as the edge or surface of the sample. In the superconductors, this leads to the formation of zero energy ABS (ZEABS). Therefore, the ABSs of the superconductors are the place where the symmetry and topology meet each other which offer the stage of rich physics. In this review, we discuss the physics of ABS from the viewpoint of the odd-frequency pairing, the topological bulk-edge correspondence, and the interplay of these two issues. It is described how the symmetry of the pairing and topological indices determines the absence/presence of the ZEABS, its energy dispersion, and properties as the Majorana fermions.Comment: 91 pages, 38 figures, Review article, references adde

Superconducting pairing symmetry on the extended Hubbard model in the presence of the Rashba-type spin-orbit coupling

In order to study the pairing symmetry in non-centrosymmetric superconductors, we solve the linearized Eliashberg's equation on the two-dimensional extended Hubbard model in the presence of the Rashba-type spin-orbit coupling (RSOC) within the random phase approximation. In the presence of the RSOC, three types of pairing symmetries appear in the phase diagram with respect to the on-site Coulomb repulsion U and off-site one V. Each of pairing symmetries is admixture of spin-singlet and -triplet ones. On the basis of analytical study, it is found that the admixture of spin-singlet and -triplet components depends on not only the predominant pairing symmetry but also dispersion relation and pairing interaction.Comment: 11 pages, 12 figure

Aquaporin water channels in the nervous system.

The aquaporins (AQPs) are plasma membrane water-transporting proteins. AQP4 is the principal member of this protein family in the CNS, where it is expressed in astrocytes and is involved in water movement, cell migration and neuroexcitation. AQP1 is expressed in the choroid plexus, where it facilitates cerebrospinal fluid secretion, and in dorsal root ganglion neurons, where it tunes pain perception. The AQPs are potential drug targets for several neurological conditions. Astrocytoma cells strongly express AQP4, which may facilitate their infiltration into the brain, and the neuroinflammatory disease neuromyelitis optica is caused by AQP4-specific autoantibodies that produce complement-mediated astrocytic damage

RESTORATION OF CORNEA ENDOTHELIUM FUNCTION (REVIEW)

Review highlights modern findings on molecular mechanisms of dysfunction of human corneal endothelial cells causes decline of vision. When water enters the corneal stroma, it disorganizes the regular arrangement of the collagen fibrils, which reduces corneal transparency. Corneal endothelial cells are responsible for keeping the dehydration state of the stroma by pumping out fluid. However, this layer of cells can become deficient, for example following intra-corneal surgery or because of a pathology. Corneal transplantation is currently the only treatment in order to restore vision following endothelial dysfunctions. The authors survey methodological problems and prospects for correction of endothelial cells dysfunction. Human endothelial cells do not proliferate in vivo because these cells arrest in the G1 phase of the cell cycle. Modern research showed that corneal endothelium cells could proliferate in special conditions. An alternative approach is to use human stem cells as an endothelial cells source. New methods and improved technique of storage and preservation of corneal grafts, palliative methods of surgical treatment aimed at reducing the hydration of the surface layers of the cornea are considered. The review includes consideration of works for endothelial tissue engineering using cell culture technologies. Endothelial keratoplasty limited by the technical difficulty of the procedure, a shortage of available grafts, and the potential for graft failure or rejection. These limitations are driving researchers to develop new approaches, such as methods of organ cultur