Index maps in the K-theory of graph algebras

Let $C^*(E)$ be the graph $C^*$-algebra associated to a graph E and let J be a gauge invariant ideal in $C^*(E)$. We compute the cyclic six-term exact sequence in $K$-theory of the associated extension in terms of the adjacency matrix associated to $E$. The ordered six-term exact sequence is a complete stable isomorphism invariant for several classes of graph $C^*$-algebras, for instance those containing a unique proper nontrivial ideal. Further, in many other cases, infinite collections of such sequences comprise complete invariants. Our results allow for explicit computation of the invariant, giving an exact sequence in terms of kernels and cokernels of matrices determined by the vertex matrix of $E$

Electronic structure of single-crystalline Sr(Fe1−x_{1-x}Cox_x)2_2As2_2 probed by x-ray absorption spectroscopy: Evidence for isovalent substitution of Fe2+^{2+} by Co2+^{2+}

The substitutional dependence of valence and spin-state configurations of Sr(Fe$_{1-x}$Co$_x$)$_2$As$_2$ ($x =$ 0, 0.05, 0.11, 0.17, and 0.38) is investigated with near-edge x-ray absorption fine structure at the $L_{2,3}$ edges of Fe, Co, and As. The present data provide direct spectroscopic evidence for an effectively isovalent substitution of Fe$^{2+}$ by Co$^{2+}$, which is in contrast to the widely assumed Co-induced electron-doping effect. Moreover, the data reveal that not only does the Fe valency remain completely unaffected across the entire doping range, but so do the Co and As valencies as well. The data underline a prominent role of the hybridization between (Fe,Co) 3$d_{xy}$, $d_{xz}$, $d_{yz}$ orbitals and As $4s/4p$ states for the band structure in $A$(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and suggest that the covalency of the (Fe,Co)-As bond is a key parameter for the interplay between magnetism and superconductivity

Improved Dynamic Predictions from Joint Models of Longitudinal and Survival Data with Time-Varying Effects using P-splines

In the field of cardio-thoracic surgery, valve function is monitored over time after surgery. The motivation for our research comes from a study which includes patients who received a human tissue valve in the aortic position. These patients are followed prospectively over time by standardized echocardiographic assessment of valve function. Loss of follow-up could be caused by valve intervention or the death of the patient. One of the main characteristics of the human valve is that its durability is limited. Therefore, it is of interest to obtain a prognostic model in order for the physicians to scan trends in valve function over time and plan their next intervention, accounting for the characteristics of the data. Several authors have focused on deriving predictions under the standard joint modeling of longitudinal and survival data framework that assumes a constant effect for the coefficient that links the longitudinal and survival outcomes. However, in our case this may be a restrictive assumption. Since the valve degenerates, the association between the biomarker with survival may change over time. To improve dynamic predictions we propose a Bayesian joint model that allows a time-varying coefficient to link the longitudinal and the survival processes, using P-splines. We evaluate the performance of the model in terms of discrimination and calibration, while accounting for censoring

Disordered Topological Insulators via C∗C^*-Algebras

The theory of almost commuting matrices can be used to quantify topological obstructions to the existence of localized Wannier functions with time-reversal symmetry in systems with time-reversal symmetry and strong spin-orbit coupling. We present a numerical procedure that calculates a Z_2 invariant using these techniques, and apply it to a model of HgTe. This numerical procedure allows us to access sizes significantly larger than procedures based on studying twisted boundary conditions. Our numerical results indicate the existence of a metallic phase in the presence of scattering between up and down spin components, while there is a sharp transition when the system decouples into two copies of the quantum Hall effect. In addition to the Z_2 invariant calculation in the case when up and down components are coupled, we also present a simple method of evaluating the integer invariant in the quantum Hall case where they are decoupled.Comment: Added detail regarding the mapping of almost commuting unitary matrices to almost commuting Hermitian matrices that form an approximate representation of the sphere. 6 pages, 6 figure

On a counterexample to a conjecture by Blackadar

Blackadar conjectured that if we have a split short-exact sequence 0 -> I -> A -> A/I -> 0 where I is semiprojective and A/I is isomorphic to the complex numbers, then A must be semiprojective. Eilers and Katsura have found a counterexample to this conjecture. Presumably Blackadar asked that the extension be split to make it more likely that semiprojectivity of I would imply semiprojectivity of A. But oddly enough, in all the counterexamples of Eilers and Katsura the quotient map from A to A/I is split. We will show how to modify their examples to find a non-semiprojective C*-algebra B with a semiprojective ideal J such that B/J is the complex numbers and the quotient map does not split.Comment: 6 page

Copepod (Crustacea) distribution in the freshwater and hyposaline lakes of the Pantanal of Nhecolandia (Mato Grosso do Sul, Brazil).

Eighteen freshwater and hyposaline lakes of the Nhecolândia floodplain were sampled in two periods, April/03 (beginning of dry period) and March/04 (end of wet period). Dezoito lagoas de água doce e de água hiposalina do Pantanal da Nhecolândia foram amostrados em dois períodos, abril/03 (início da seca) e março/04(fim da cheia)

Personen, die nicht am Erwerbsleben teilnehmen - Analyse sozioökonomischer Merkmale unter besonderer Berücksichtigung des Haushaltskontextes und Bestimmung des Arbeitskräftepotenzials : Endbericht

Für die Fachkräftesicherung stellen bisher nicht am Arbeitsmarkt aktive Personen (sog. Nichterwerbspersonen) ein wichtiges Potenzial dar. Die vorliegende Studie untersucht die Eigenschaften dieser Personengruppe und schätzt auf dieser Grundlage ihr Aktivierungspotenzial ein. Betrachtet werden Aspekte wie sozio-demographische Merkmale von Nichterwerbspersonen, Übergänge in und aus Nichterwerbstätigkeit, Faktoren, die einen Austritt aus Nichterwerbstätigkeit fördern oder hemmen sowie Erwerbspläne von Nichterwerbspersonen. Mit Hilfe von Clusteranalysen werden Typen von Nichterwerbstätigen identifiziert, die die Grundlage für die Abschätzung von Wahrscheinlichkeiten zur Aktivierung bilden. Abschließend werden Aktivierungsmaßnahmen diskutiert