Topological semimetal in a fermionic optical lattice

Optical lattices play a versatile role in advancing our understanding of correlated quantum matter. The recent implementation of orbital degrees of freedom in chequerboard and hexagonal optical lattices opens up a new thrust towards discovering novel quantum states of matter, which have no prior analogs in solid state electronic materials. Here, we demonstrate that an exotic topological semimetal emerges as a parity-protected gapless state in the orbital bands of a two-dimensional fermionic optical lattice. The new quantum state is characterized by a parabolic band-degeneracy point with Berry flux $2\pi$, in sharp contrast to the $\pi$ flux of Dirac points as in graphene. We prove that the appearance of this topological liquid is universal for all lattices with D$_4$ point group symmetry as long as orbitals with opposite parities hybridize strongly with each other and the band degeneracy is protected by odd parity. Turning on inter-particle repulsive interactions, the system undergoes a phase transition to a topological insulator whose experimental signature includes chiral gapless domain-wall modes, reminiscent of quantum Hall edge states.Comment: 6 pages, 3 figures and Supplementary Informatio

Topological Photonics

Topology is revolutionizing photonics, bringing with it new theoretical discoveries and a wealth of potential applications. This field was inspired by the discovery of topological insulators, in which interfacial electrons transport without dissipation even in the presence of impurities. Similarly, new optical mirrors of different wave-vector space topologies have been constructed to support new states of light propagating at their interfaces. These novel waveguides allow light to flow around large imperfections without back-reflection. The present review explains the underlying principles and highlights the major findings in photonic crystals, coupled resonators, metamaterials and quasicrystals.Comment: progress and review of an emerging field, 12 pages, 6 figures and 1 tabl

In Vivo Methods to Study Uptake of Nanoparticles into the Brain

Several in vivo techniques have been developed to study and measure the uptake of CNS compounds into the brain. With these techniques, various parameters can be determined after drug administration, including the blood-to-brain influx constant (Kin), the permeability-surface area (PS) product, and the brain uptake index (BUI). These techniques have been mostly used for drugs that are expected to enter the brain via transmembrane diffusion or by carrier-mediated transcytosis. Drugs that have limitations in entering the brain via such pathways have been encapsulated in nanoparticles (based on lipids or synthetic polymers) to enhance brain uptake. Nanoparticles are different from CNS compounds in size, composition and uptake mechanisms. This has led to different methods and approaches to study brain uptake in vivo. Here we discuss the techniques generally used to measure nanoparticle uptake in addition to the techniques used for CNS compounds. Techniques include visualization methods, behavioral tests, and quantitative methods

Cytoskeletal control of B cell responses to antigens.

The actin cytoskeleton is essential for cell mechanics and has increasingly been implicated in the regulation of cell signalling. In B cells, the actin cytoskeleton is extensively coupled to B cell receptor (BCR) signalling pathways, and defects of the actin cytoskeleton can either promote or suppress B cell activation. Recent insights from studies using single-cell imaging and biophysical techniques suggest that actin orchestrates BCR signalling at the plasma membrane through effects on protein diffusion and that it regulates antigen discrimination through the biomechanics of immune synapses. These mechanical functions also have a role in the adaptation of B cell subsets to specialized tasks during antibody responses

Organisationskultur. Eine Konkretisierung aus systemtheoretischer Perspektive

Kühl S. Organisationskultur. Eine Konkretisierung aus systemtheoretischer Perspektive. Managementforschung. 2018;28(1):7-35.Die Bestimmung des Verhältnisses von Informalität und Organisationskultur bereitet in der Organisationstheorie Schwierigkeiten. Das liegt daran, dass der Begriff Informalität häufig stillschweigend durch den Begriff der Organisationskultur ersetzt wurde, ohne dass dafür eine präzise, abgrenzungsscharfe Definition vorgenommen worden wäre. Unter Rückgriff auf Überlegungen von Dario Rodríguez argumentiert dieser Artikel, dass die beiden Begriffe Organisationskultur und Informalität das gleiche Phänomen bezeichnen: die nichtentschiedenen Entscheidungsprämissen einer Organisation. Dabei wird systematisch zwischen „unentscheidbaren Entscheidungsprämissen“ und „prinzipiell entscheidbaren, aber nicht entschiedenen Entscheidungsprämissen“ unterschieden. Es wird gezeigt, wie sich mit einer präzisen Bestimmung über das Konzept der Entscheidungsprämissen Ordnung in die „wilden Merkmallisten“ der Literatur sowohl über Informalität als auch Organisationskultur bringen lässt und empirische Phänomene genauer erfasst werden können