Weak-coupling superconductivity in a strongly correlated iron pnictide

Iron-based superconductors have been found to exhibit an intimate interplay of orbital, spin, and lattice degrees of freedom, dramatically affecting their low-energy electronic properties, including superconductivity. Albeit the precise pairing mechanism remains unidentified, several candidate interactions have been suggested to mediate the superconducting pairing, both in the orbital and in the spin channel. Here, we employ optical spectroscopy (OS), angle-resolved photoemission spectroscopy (ARPES), ab initio band-structure, and Eliashberg calculations to show that nearly optimally doped NaFe$_{0.978}$Co$_{0.022}$As exhibits some of the strongest orbitally selective electronic correlations in the family of iron pnictides. Unexpectedly, we find that the mass enhancement of itinerant charge carriers in the strongly correlated band is dramatically reduced near the $\Gamma$ point and attribute this effect to orbital mixing induced by pronounced spin-orbit coupling. Embracing the true band structure allows us to describe all low-energy electronic properties obtained in our experiments with remarkable consistency and demonstrate that superconductivity in this material is rather weak and mediated by spin fluctuations.Comment: Open access article available online at http://www.nature.com/articles/srep1862

Complex financial networks and systemic risk: a review

In this paper we review recent advances in financial economics in relation to the measurement of systemic risk. We start by reviewing studies that apply traditional measures of risk to financial institutions. However, the main focus of the review is on studies that use network analysis paying special attention to those that apply complex analysis techniques. Applications of these techniques for the analysis and pricing of systemic risk has already provided significant benefits at least at the conceptual level but it also looks very promising from a practical point of view

Co-constructing cultural ecosystem services and wellbeing through a place-based approach

Reductive practices in fisheries management have tended to focus on ecological and economic dimensions that have rendered the social and cultural importance of fishing largely invisible, at least in the context of governance and policy making. This chapter builds on 5 years’ research in the English Channel and Southern North Sea in which the authors adopted a sense of place perspective as a framework for understanding the social and cultural value of small-scale fisheries. Through a number of case studies, the chapter describes how small-scale fisheries result in a series of ‘transformations’ as the marine environment is translated into cultural ecosystem services in coastal settings giving rise to socio-cultural value. This perspective is further developed by considering the value of the social wellbeing ‘lens’ to broaden the sense of place / cultural ecosystem services framework. In pursuing ‘values’ through sense of place, cultural ecosystem services and social wellbeing we discuss how the dualistic treatment of nature and society is problematic. We conclude that a relational co-constructionist approach, although challenging, offers a way of making visible an array of social and cultural values that emerge from the activity of small-scale fisheries

Memory load modulates spiking activity in prefrontal cortex

While short-term memory is an essential requirement for behavior, knowledge about its neural code remains limited. In particular, how the brain organizes maintenance of multiple items at the same time has received little attention in this context. We trained two macaque monkeys to perform well in a memory task with load 1 and then, without further training had them memorize one to four visual sample stimuli presented sequentially over a period of 900 ms. Behavioral performance was above chance for all load conditions from the first session on. After a 3 second delay, the monkeys had to decide whether a newly presented test stimulus was part of the memorized set or not. During all subsequent sessions in which the monkey performed with load > 1, we recorded multi-unit activity and LFPs in prefrontal cortex using up to 16 micro-tetrodes. We performed spike sorting with a new algorithm (bayes optimal template matching) and analyzed rate modulations across task time: preliminary results show the firing rate of most sorted single units is significantly modulated during stimulus presentations and delay, compared to the level of baseline activity. Separating units from the compound tetrode multi-unit signal provides additional information: many multi-units exhibit no significant (Friedman test, p<0.05) rate modulation for different memory loads, while we find multiple load-selective single units after sorting the respective spikes. Most selective sorted units modulate their firing rate during the first second of the delay period. For the majority of these units, the rate during this period is increased compared to the baseline activity. Later in the delay period, the selective units exhibit no preference towards an increase in firing rate. These results suggest an active memory encoding phase shortly after the stimulus presentation. We are now starting to assess single trial classification performance and include analyses of LFP oscillations and correlations between units

Structure solution of DNA-binding proteins and complexes with ARCIM- BOLDO libraries

Protein–DNA interactions play a major role in all aspects of genetic activity within an organism, such as transcription, packaging, rearrangement, replication and repair. The molecular detail of protein–DNA interactions can be best visualized through crystallography, and structures emphasizing insight into the principles of binding and base-sequence recognition are essential to understanding the subtleties of the underlying mechanisms. An increasing number of high-quality DNA-binding protein structure determinations have been witnessed despite the fact that the crystallographic particularities of nucleic acids tend to pose specific challenges to methods primarily developed for proteins. Crystallographic structure solution of protein–DNA complexes therefore remains a challenging area that is in need of optimized experimental and computational methods. The potential of the structure-solution program ARCIMBOLDO for the solution of protein–DNA complexes has therefore been assessed. The method is based on the combination of locating small, very accurate fragments using the program Phaser and density modification with the program SHELXE. Whereas for typical proteins main-chain α-helices provide the ideal, almost ubiquitous, small fragments to start searches, in the case of DNA complexes the binding motifs and DNA double helix constitute suitable search fragments. The aim of this work is to provide an effective library of search fragments as well as to determine the optimal ARCIMBOLDO strategy for the solution of this class of structures

Spike Sorting of Synchronous Spikes from Local Neuron Ensembles

Synchronous spike discharge of cortical neurons is thought to be a fingerprint of neuronal cooperativity. Because neighboring neurons are more densely connected to one another than neurons that are located further apart, near-synchronous spike discharge can be expected to be prevalent and it might provide an important basis for cortical computations. Using microelectrodes to record local groups of neurons does not allow for the reliable separation of synchronous spikes from different cells, because available spike sorting algorithms cannot correctly resolve the temporally overlapping waveforms. We show that high spike sorting performance of in vivo recordings, including overlapping spikes, can be achieved using a recently developed filter-based template matching procedure. Using tetrodes with a 3-dimensional structure, we demonstrate with simulated data and ground truth in vitro data, obtained by dual intracellular recording of two neurons located next to a tetrode, that the spike sorting of synchronous spikes can be as successful as the spike sorting of non-overlapping spikes, and that the spatial information provided by multielectrodes greatly reduces the error rates. We apply the method to tetrode recordings from the prefrontal cortex of behaving primates and we show that overlapping spikes can be identified and assigned to individual neurons to study synchronous activity in local groups of neurons

Structure of sulfamidase provides insight into the molecular pathology of mucopolysaccharidosis IIIA.

Mucopolysaccharidosis type IIIA (Sanfilippo A syndrome), a fatal childhood-onset neurodegenerative disease with mild facial, visceral and skeletal abnormalities, is caused by an inherited deficiency of the enzyme N-sulfoglucosamine sulfohydrolase (SGSH; sulfamidase). More than 100 mutations in the SGSH gene have been found to reduce or eliminate its enzymatic activity. However, the molecular understanding of the effect of these mutations has been confined by a lack of structural data for this enzyme. Here, the crystal structure of glycosylated SGSH is presented at 2 A resolution. Despite the low sequence identity between this unique N-sulfatase and the group of O-sulfatases, they share a similar overall fold and active-site architecture, including a catalytic formylglycine, a divalent metal-binding site and a sulfate-binding site. However, a highly conserved lysine in O-sulfatases is replaced in SGSH by an arginine (Arg282) that is positioned to bind the N-linked sulfate substrate. The structure also provides insight into the diverse effects of pathogenic mutations on SGSH function in mucopolysaccharidosis type IIIA and convincing evidence for the molecular consequences of many missense mutations. Further, the molecular characterization of SGSH mutations will lay the groundwork for the development of structure-based drug design for this devastating neurodegenerative disorder

Multischichten für optische Komponenten im weichen Röntgengebiet

Schmiedeskamp B, Döhring T, Heidemann B, et al. Multischichten für optische Komponenten im weichen Röntgengebiet. In: Dünnschichttechnologien 1992. Düsseldorf: VDI Verlag; 1992: 329

Preparation and microstructure analysis of Mo/Si multilayers as x-ray optical components

Kloidt A, Stock HJ, Kleineberg U, et al. Preparation and microstructure analysis of Mo/Si multilayers as x-ray optical components. In: Varga P, ed. Proceedings of Symposium on Surface Science 1993. Wien: HTU Druck; 1993: 115

Fabrication, thermal stability and reflectivity measurements of Mo/Si-multilayers as X-ray mirrors and other optical components

Kloidt A, Stock HJ, Kleineberg U, et al. Fabrication, thermal stability and reflectivity measurements of Mo/Si-multilayers as X-ray mirrors and other optical components. Spie Proc. 1992 (Soc. Phot. Opt. Instr. Eng.). 1992;1742:593