18 research outputs found
Dynamic structure selection and instabilities of driven Josephson lattice in high-temperature superconductors
We investigate the dynamics of the Josephson vortex lattice in layered
high-T superconductors at high magnetic fields. Starting from coupled
equations for superconducting phases and magnetic field we derive equations for
the relative displacements [phase shifts] between the planar Josephson arrays
in the layers. These equations reveal two families of steady-state solutions:
lattices with constant phase shifts between neighboring layers, starting from
zero for a rectangular configuration to for a triangular configuration,
and double-periodic lattices. We find that the excess Josephson current is
resonantly enhanced when the Josephson frequency matches the frequency of the
plasma mode at the wave vector selected by the lattice structure. The regular
lattices exhibit several kinds of instabilities. We find stability regions of
the moving lattice in the plane lattice structure - Josephson frequency. A
specific lattice structure at given velocity is selected uniquely by boundary
conditions, which are determined by the reflection properties of
electromagnetic waves generated by the moving lattice. With increase of
velocity the moving configuration experiences several qualitative
transformations. At small velocities the regular lattice is stable and the
phase shift between neighboring layers smoothly decreases with increase of
velocity, starting from for a static lattice. At the critical velocity
the lattice becomes unstable. At even higher velocity a regular lattice is
restored again with the phase shift smaller than . With increase of
velocity, the structure evolves towards a rectangular configuration.Comment: 28 pages, 12 figures, submitted to Phys. Rev.
Oncogenic Signaling Pathways in The Cancer Genome Atlas
Genetic alterations in signaling pathways that control cell-cycle progression, apoptosis, and cell growth are common hallmarks of cancer, but the extent, mechanisms, and co-occurrence of alterations in these pathways differ between individual tumors and tumor types. Using mutations, copy-number changes, mRNA expression, gene fusions and DNA methylation in 9,125 tumors profiled by The Cancer Genome Atlas (TCGA), we analyzed the mechanisms and patterns of somatic alterations in ten canonical pathways: cell cycle, Hippo, Myc, Notch, Nrf2, PI-3-Kinase/Akt, RTK-RAS, TGFb signaling, p53 and beta-catenin/Wnt. We charted the detailed landscape of pathway alterations in 33 cancer types, stratified into 64 subtypes, and identified patterns of co-occurrence and mutual exclusivity. Eighty-nine percent of tumors had at least one driver alteration in these one alteration potentially targetable by currently available drugs. Thirty percent of tumors had multiple targetable alterations, indicating opportunities for combination therapy
Parametric global optimisation for bilevel programming
Abstract We propose a global optimisation approach for the solution of various classes of bilevel programming problems (BLPP) based on recently developed parametric programming algorithms. We first describe how we can recast and solve the inner (follower’s) problem of the bilevel formulation as a multi-parametric programming problem, with parameters being the (unknown) variables of the outer (leader’s) problem. By inserting the obtained rational reaction sets in the upper level problem the overall problem is transformed into a set of independent quadratic, linear or mixed integer linear programming problems, which can be solved to global optimality. In particular, we solve bilevel quadratic and bilevel mixed integer linear problems, with or without right-hand-side uncertainty. A number of examples are presented to illustrate the steps and details of the proposed global optimisation strategy