Phase diagrams of a p-Wave superconductor inside a mesoscopic disc-shaped sample

We study the finite-size and boundary effects on a time-reversal-symmetry breaking p-wave superconducting state in a mesoscopic disc geometry using Ginzburg-Landau theory. We show that, for a large parameter range, the system exhibits multiple phase transitions. The superconducting transition from the normal state can also be reentrant as a function of external magnetic field.Comment: Revised version published in Physical Review

Location – Positioning Tregs to the right place at the right time

After a fruitless pursuit for suppressor cells spanning 1970s to mid-80s, the identification of CD4+CD25+ T cellsas a specific T-cell lineage with immune regulatory function in the 1990s has revived the theory of active immune tolerance and uncovered a brand-new avenue for immunologic research. Tregs have been shown to play a crucial role both in health and diseases. Whilst tremendous advance has been made in our understanding of the expanding varieties of effector mechanisms exploited by Tregs, the migration phenotypes as well as the anatomic sites where Tregs exert immune regulation are scarcely investigated. Migration of Tregs to either the lymph nodes or peripheral tissues has been shown to be exclusively indispensable in Treg-mediated immune regulation in a variety of experimental models with specific gene-targeted mice. The once seemingly paradoxical findings are partly reconciled by later discovery of various Treg subsets with distinct migration/homing property as well as the inflammatory stage when Tregs come into play along an immune reaction. In our recent study, we investigated the migration characteristics of Treg cells by using the endothelial cell-based shear-stress flow assay that resembles the intravascular blood flow system. We found that both FoxP3-expressing Tregs and anergic T cells generated by blockage of costimulation factors, CD80 and CD86, exhibited a significantly decreased adhesion to endothelial cells as compared to antigen-activated effector T cells (66~88 % reduction). The less migration phenotype hinted inefficient tissue trafficking of the Tregs and suggested the lymph nodes as the anatomic site where Tregs optimally exerted immune regulation. To this speculation, an essential role of Treg lymph node positioning in exerting immune suppression was demonstrated by the inability of adoptively transferred Tregs to prevent footpad inflammation after blockage of lymph node entry of these Tregs by CCR7 or CD62L Ab. Therapeutic modality targeting leukocyte migration has been a mainstay alternative for immunologic diseases. Important messages have arisen for treatments of this kind and Treg-based cell therapy that whilst inflammatory response can be harnessed by modulating the migration property of leukocytes, the relationship between Treg migration phenotypes and their immune regulatory function should always be taken into consideration

Persistent currents in a graphene ring with armchair edges

A graphene nano-ribbon with armchair edges is known to have no edge state. However, if the nano-ribbon is in the quantum spin Hall (QSH) state, then there must be helical edge states. By folding a graphene ribbon to a ring and threading it by a magnetic flux, we study the persistent charge and spin currents in the tight-binding limit. It is found that, for a broad ribbon, the edge spin current approaches a finite value independent of the radius of the ring. For a narrow ribbon, inter-edge coupling between the edge states could open the Dirac gap and reduce the overall persistent currents. Furthermore, by enhancing the Rashba coupling, we find that the persistent spin current gradually reduces to zero at a critical value, beyond which the graphene is no longer a QSH insulator