Three-band Hubbard model for Na2_2IrO3_3: Topological insulator, zigzag antiferromagnet, and Kitaev-Heisenberg material

Na$_2$IrO$_3$ was one of the first materials proposed to feature the Kane-Mele type topological insulator phase. Contemporaneously it was claimed that the very same material is in a Mott insulating phase which is described by the Kitaev-Heisenberg (KH) model. First experiments indeed revealed Mott insulating behavior in conjunction with antiferromagnetic long-range order. Further refined experiments established antiferromagnetic order of zigzag type which is not captured by the KH model. Since then several extensions and modifications of the KH model were proposed in order to describe the experimental findings. Here we suggest that adding charge fluctuations to the KH model represents an alternative explanation of zigzag antiferromagnetism. Moreover, a phenomenological three-band Hubbard model unifies all the pieces of the puzzle: topological insulator physics for weak and KH model for strong electron-electron interactions as well as a zigzag antiferromagnet at intermediate interaction strength.Comment: 5 pages, 3 figures; v2 (as published): added discussion about kinetic energy scale C; more realistic values of C shift the zigzag AFM phase to larger values of

Quantifying alternative splicing from paired-end RNA-sequencing data

RNA-sequencing has revolutionized biomedical research and, in particular, our ability to study gene alternative splicing. The problem has important implications for human health, as alternative splicing may be involved in malfunctions at the cellular level and multiple diseases. However, the high-dimensional nature of the data and the existence of experimental biases pose serious data analysis challenges. We find that the standard data summaries used to study alternative splicing are severely limited, as they ignore a substantial amount of valuable information. Current data analysis methods are based on such summaries and are hence suboptimal. Further, they have limited flexibility in accounting for technical biases. We propose novel data summaries and a Bayesian modeling framework that overcome these limitations and determine biases in a nonparametric, highly flexible manner. These summaries adapt naturally to the rapid improvements in sequencing technology. We provide efficient point estimates and uncertainty assessments. The approach allows to study alternative splicing patterns for individual samples and can also be the basis for downstream analyses. We found a severalfold improvement in estimation mean square error compared popular approaches in simulations, and substantially higher consistency between replicates in experimental data. Our findings indicate the need for adjusting the routine summarization and analysis of alternative splicing RNA-seq studies. We provide a software implementation in the R package casper.Comment: Published in at http://dx.doi.org/10.1214/13-AOAS687 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org). With correction

Characterisation of ScN and ScGaN alloys grown by Molecular Beam Epitaxy

The wurtzite III-nitrides AlN, GaN and InN are currently widely used in optoelectronic applications such as light-emitting diodes and this success is owed in large part to the possibility of band gap engineering by alloying between the constituent nitrides. Unfortunately, the restricted material properties currently limit the performance of such devices, and efficiencies of emitters in the green and ultraviolet spectral regions remain low. These challenges have motivated the search for alloying additions offering greater degrees of freedom for tuning the material properties. ScN is of particular interest in this regard, and ScGaN alloys have been predicted to remain stable in the wurtzite structure with direct band gaps for Sc contents of up to 27%. Of further interest is the predicted deviation from wurtzite symmetry towards a non-polar structure at higher Sc contents, which could lead to additional device functionalities such as ferroelectric switching. However, experimental data regarding the properties of ScGaN alloys are very limited, and further investigations of the growth are required if these materials are to be integrated into the existing III-nitride technology. This thesis is an in-depth characterisation of ScN and dilute ScGaN films grown by molecular beam epitaxy (MBE), with special emphasis on the microstructure, surface topography and local bonding environment of Sc in these materials. The results are based on a broad range of characterisation techniques including transmission electron microscopy, scanning probe microscopy, high-resolution X-ray diffraction and X-ray absorption spectroscopy (XAS). The effects of varying growth conditions on the properties of ScN and ScGaN films are discussed, including observed growth rates and defect densities. The introduction of Sc into the GaN system was found to decrease growth rates due to the likely presence of a ‘floating layer’, as has also been observed for other transition metal doped nitrides. Microstructural investigations found that at low Sc contents the formation of I1-type basal-plane stacking faults is promoted, while at higher contents lamellar inclusions of the cubic phase of up to 4 stacking repeats were observed. The local flattening of the wurtzite unit cell around substitutional Sc atoms was directly observed by XAS measurements, confirming theoretical predictions and giving confidence that related predictions for higher Sc content films are also correct

First report of an entomopathogenic nematode from continental Portugal

In continental Portugal no information is available concerning the occurrence of entomopathogenic nematodes. During a survey in several different habitats from the southern regions of the country, several isolates where identified as Steinernema feltiae. This represents the first report of an entomopathogenic nematode genus for continental Portugal

Verbesserung der Qualität von historischen Filmen

Historische Filme stellen einen wichtigen Baustein für die Erhaltung des kulturellen Erbes dar. Durch eine Digitalisierung können diese für die Zukunft erhalten werden, ohne dass Filme durch Materialermüdung der Filmrollen bzw. Bänder Schaden nehmen. Viele der historischen Aufnahmen sind durch Abspielen oder Lagerung bereits deutlich beschädigt. In diesem Bericht werden Algorithmen zur Erkennung und Behebung solcher Fehler in historischen Schwarzweißfilmen vorgestellt. Dabei handelt es sich um die Erkennung und Beseitigung von horizontalen Störlinien, um die Helligkeits- und Kontrastkorrektur sowohl bei starken Helligkeitsschwankungen als auch bei überdunkelten oder überhellten Sequenzen, sowie um die Entfernung von Verwackelungen bei Kameraeinstellungen

Der Wert von Versorgungssicherheit mit Strom: Evidenz für deutsche Haushalte

Dieser Artikel untersucht auf Basis einer Befragung von mehr als 5.000 Haushaltsvorständen, wie viel sie für Versorgungssicherheit mit Strom zu zahlen bereit sind. Alternativ zur Zahlungsbereitschaft (willingness to pay, WTP) wird auch nach der Bereitschaft gefragt, gegen eine Entschädigungszahlung auf ein gewisses Maß an Versorgungssicherheit zu verzichten (willingness to accept, WTA). In Übereinstimmung mit zahlreichen empirischen Studien finden wir mittlere WTA-Werte, die deutlich über den mittleren WTP-Werten für die Vermeidung eines unangekündigten, vierstündigen Stromausfalls liegen. Den Grund für diese Diskrepanz sehen wir darin, dass die bekundeten Entschädigungsforderungen für den Verzicht auf Versorgungssicherheit tendenziell über dem tatsächlichen Wert liegen, der der Versorgungssicherheit mit Strom beigemessen wird, wohingegen die dafür bekundete Zahlungsbereitschaft tendenziell untertrieben wird