Associative-algebraic approach to logarithmic conformal field theories

We set up a strategy for studying large families of logarithmic conformal field theories by using the enlarged symmetries and non--semi-simple associative algebras appearing in their lattice regularizations (as discussed in a companion paper). Here we work out in detail two examples of theories derived as the continuum limit of XXZ spin-1/2 chains, which are related to spin chains with supersymmetry algebras gl($n|n$) and gl($n+1|n$), respectively, with open (or free) boundary conditions in all cases. These theories can also be viewed as vertex models, or as loop models. Their continuum limits are boundary conformal field theories (CFTs) with central charge $c=-2$ and $c=0$ respectively, and in the loop interpretation they describe dense polymers and the boundaries of critical percolation clusters, respectively. We also discuss the case of dilute (critical) polymers as another boundary CFT with $c=0$. Within the supersymmetric formulations, these boundary CFTs describe the fixed points of certain nonlinear sigma models that have a supercoset space as the target manifold, and of Landau-Ginzburg field theories. The submodule structures of indecomposable representations of the Virasoro algebra appearing in the boundary CFT, representing local fields, are derived from the lattice. A central result is the derivation of the fusion rules for these fields

Edge states and conformal boundary conditions in super spin chains and super sigma models

The sigma models on projective superspaces CP^{N+M-1|N} with topological angle theta=pi mod 2pi flow to non-unitary, logarithmic conformal field theories in the low-energy limit. In this paper, we determine the exact spectrum of these theories for all open boundary conditions preserving the full global symmetry of the model, generalizing recent work on the particular case M=0 [C. Candu et al, JHEP02(2010)015]. In the sigma model setting, these boundary conditions are associated with complex line bundles, and are labelled by an integer, related with the exact value of theta. Our approach relies on a spin chain regularization, where the boundary conditions now correspond to the introduction of additional edge states. The exact values of the exponents then follow from a lengthy algebraic analysis, a reformulation of the spin chain in terms of crossing and non-crossing loops (represented as a certain subalgebra of the Brauer algebra), and earlier results on the so-called one- and two-boundary Temperley Lieb algebras (also known as blob algebras). A remarkable result is that the exponents, in general, turn out to be irrational. The case M=1 has direct applications to the spin quantum Hall effect, which will be discussed in a sequel.Comment: 50 pages, 18 figure

Fourier factorization with complex polarization bases in the plane-wave expansion method applied to two-dimensional photonic crystals

We demonstrate an enhancement of the plane wave expansion method treating two-dimensional photonic crystals by applying Fourier factorization with generally elliptic polarization bases. By studying three examples of periodically arranged cylindrical elements, we compare our approach to the classical Ho method in which the permittivity function is simply expanded without changing coordinates, and to the normal vector method using a normal-tangential polarization transform. The compared calculations clearly show that our approach yields the best convergence properties owing to the complete continuity of our distribution of polarization bases. The presented methodology enables us to study more general systems such as periodic elements with an arbitrary cross-section or devices such as photonic crystal waveguides

The Large-scale Bipolar Wind in the Galactic Center

During a 9-month campaign (1996--1997), the Midcourse Space Experiment (MSX) satellite mapped the Galactic Plane at mid-infrared wavelengths (4.3--21.3um). Here we report evidence for a spectacular limb- brightened, bipolar structure at the Galactic Center extending more than a degree (170 pc at 8.0 kpc) on either side of the plane. The 8.3um emission shows a tight correlation with the 3, 6 and 11 cm continuum structure over the same scales. Dense gas and dust are being entrained in a large-scale bipolar wind powered by a central starburst. The inferred energy injection at the source is ~10^54/kappa erg for which \kappa is the covering fraction of the dusty shell (kappa <= 0.1). There is observational evidence for a galactic wind on much larger scales, presumably from the same central source which produced the bipolar shell seen by MSX. Sofue has argued that the North Polar Spur -- a thermal x-ray/radio loop which extends from the Galactic Plane to b = +80 deg -- was powered by a nuclear explosion (1-30 x 10^55 erg) roughly 15 Myr ago. We demonstrate that an open-ended bipolar wind (~10^55 erg), when viewed in near-field projection, provides the most natural explanation for the observed loop structure. The ROSAT 1.5 keV diffuse x-ray map over the inner 45 deg provides compelling evidence for this interpretation. Since the faint bipolar emission would be very difficult to detect beyond the Galaxy, the phenomenon of large-scale galactic winds may be far more common than has been observed to date.Comment: 24 pages, 6 figures, aastex. High resolution figures are available at ftp://www.aao.gov.au/pub/local/jbh/astro-ph/GC/. Astrophysical Journal, accepte

State of green infrastructure in the GCR

July 2013This State of Green Infrastructure report is both an assessment of the set of natural and manmade landscape features in the Gauteng City-Region (GCR) and an interrogation into how the services provided by these assets are perceived, understood and valued. Inspiration is drawn from the conceptual and planning framework of ‘green infrastructure’, through which ecological systems, green spaces and other landscape features are regarded as providing services to society in the same way as those offered by traditional ‘hard’ infrastructure.written by Alexis Schäffler et al. for GCR

Total mismatch in diffusion negative patients in the WAKE-UP trial

No abstract available

Tau-Mediated Nuclear Depletion and Cytoplasmic Accumulation of SFPQ in Alzheimer's and Pick's Disease

Tau dysfunction characterizes neurodegenerative diseases such as Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD). Here, we performed an unbiased SAGE (serial analysis of gene expression) of differentially expressed mRNAs in the amygdala of transgenic pR5 mice that express human tau carrying the P301L mutation previously identified in familial cases of FTLD. SAGE identified 29 deregulated transcripts including Sfpq that encodes a nuclear factor implicated in the splicing and regulation of gene expression. To assess the relevance for human disease we analyzed brains from AD, Pick's disease (PiD, a form of FTLD), and control cases. Strikingly, in AD and PiD, both dementias with a tau pathology, affected brain areas showed a virtually complete nuclear depletion of SFPQ in both neurons and astrocytes, along with cytoplasmic accumulation. Accordingly, neurons harboring either AD tangles or Pick bodies were also depleted of SFPQ. Immunoblot analysis of human entorhinal cortex samples revealed reduced SFPQ levels with advanced Braak stages suggesting that the SFPQ pathology may progress together with the tau pathology in AD. To determine a causal role for tau, we stably expressed both wild-type and P301L human tau in human SH-SY5Y neuroblastoma cells, an established cell culture model of tau pathology. The cells were differentiated by two independent methods, mitomycin C-mediated cell cycle arrest or neuronal differentiation with retinoic acid. Confocal microscopy revealed that SFPQ was confined to nuclei in non-transfected wild-type cells, whereas in wild-type and P301L tau over-expressing cells, irrespective of the differentiation method, it formed aggregates in the cytoplasm, suggesting that pathogenic tau drives SFPQ pathology in post-mitotic cells. Our findings add SFPQ to a growing list of transcription factors with an altered nucleo-cytoplasmic distribution under neurodegenerative conditions