High frequency non-gyrokinetic turbulence at tokamak edge parameter

First of a kind 6D-Vlasov computer simulations of high frequency ion Bernstein wave turbulence for parameters relevant to the tokamak edge show transport comparable to sub-Larmor-frequency gyrokinetic turbulence. The customary restriction of magnetized plasma turbulence studies to the gyrokinetic approximation may not be based on physics but only a practical constraint due to computational cost

Probing non-Gaussianities on Large Scales in WMAP5 and WMAP7 Data using Surrogates

Probing Gaussianity represents one of the key questions in modern cosmology, because it allows to discriminate between different models of inflation. We test for large-scale non-Gaussianities in the cosmic microwave background (CMB) in a model-independent way. To this end, so-called first and second order surrogates are generated by first shuffling the Fourier phases belonging to the scales not of interest and then shuffling the remaining phases for the length scales under study. Using scaling indices as test statistics we find highly significant signatures for both non-Gaussianities and asymmetries on large scales for the WMAP data of the CMB. We find remarkably similar results when analyzing different ILC-maps based on the WMAP five and seven year data. Such features being independent from the map-making procedure would disfavor the fundamental principle of isotropy as well as canonical single-field slow-roll inflation - unless there is some undiscovered systematic error in the collection or reduction of the CMB data or yet unknown foreground contributions.Comment: 4 pages, 3 figures, to appear in the Proceedings of Moriond Cosmology 201

Why Don’t You Use It? Assessing the Determinants of Enterprise Social Software Usage: A Conceptual Model Integrating Innovation Diffusion and Social Capital Theories

Social software has recently attracted the attention of organizations. Nowadays organizational social software applications are often bundled within enterprise social software platforms (ESSPs). Given the popularity of social software in the private realm (e.g., Facebook), organizations expect their employees to use the ESSPs in the same frequency right after rollout. However, employees do not always meet this expectation, leading to internal social software platforms that starve for attention. While there is some research investigating users’ motives to adopt social software in the private realm, empirical research on social software adoption in an enterprise setting is still scarce. As a step towards closing this research gap, we collected a rich set of qualitative data aiming at investigating the determinants of employees’ ESSP usage. Based on theory and the collected qualitative data, this paper proposes a conceptual ESSP adoption model combining the theoretical perspectives of innovation diffusion theory and social capital theory

Surrogates with random Fourier Phases

The method of surrogates is widely used in the field of nonlinear data analysis for testing for weak nonlinearities. The two most commonly used algorithms for generating surrogates are the amplitude adjusted Fourier transform (AAFT) and the iterated amplitude adjusted Fourier transfom (IAAFT) algorithm. Both the AAFT and IAAFT algorithm conserve the amplitude distribution in real space and reproduce the power spectrum (PS) of the original data set very accurately. The basic assumption in both algorithms is that higher-order correlations can be wiped out using a Fourier phase randomization procedure. In both cases, however, the randomness of the Fourier phases is only imposed before the (first) Fourier back tranformation. Until now, it has not been studied how the subsequent remapping and iteration steps may affect the randomness of the phases. Using the Lorenz system as an example, we show that both algorithms may create surrogate realizations containing Fourier phase correlations. We present two new iterative surrogate data generating methods being able to control the randomization of Fourier phases at every iteration step. The resulting surrogate realizations which are truly linear by construction display all properties needed for surrogate data.Comment: To appear in: "Topics on Chaotic Systems: Selected Papers from Chaos 2008 International Conference", World Scientifi

Measuring the Impact of Organizational Social Web Site Usage on Work Performance: A Multilevel Model

This paper describes the development of a multilevel model for investigating the impact of organizational social web site (SWS) usage on individual and team performance. Despite the SWS focus on collective phenomena – such as crowd sourcing and collective intelligence – previous research on SWS usage in general does not investigate it as a multilevel phenomenon. Our paper addresses this gap by drawing on existing guidelines for multilevel theorizing. We thus propose that SWS usage impacts individual and team performance through its improved collaboration capabilities. Organizational learning and social capital theories serve as the theoretical foundation. Ultimately, we present a multilevel model as the foundation for future empirical research on SWS usage’s impact on individual and team performance. Our research’s contribution lies in the theoretical derivation of a multilevel model

Characterization and crystallization of biphenyl synthase I from Sorbus aucuparia

Biphenyle und Dibenzofurane sind die Phytoalexine der Maloideae, einer Unterfamilie der im Obst- und Gartenbau bedeutenden Rosengewächse. Die Biosynthese der Kohlenstoffgrundgerüste dieser beiden antimikrobiellen Substanzklassen aus dem Sekundärstoffwechsel wird durch die Biphenylsynthase I (BIS I), eine neue Typ III-Polyketidsynthase (PKS) katalysiert. Das Enzym bildet durch schrittweise Kondensation von einem Molekül Benzoyl-CoA mit drei Molekülen Malonyl-CoA ein lineares Tetraketidintermediat, welches durch eine anschließende intramolekulare Aldol-Kondensation sowie eine Decarboxylierung in das Endprodukt, das 3,5-Dihydroxybiphenyl überführt wird. Die bekannteste Typ III-PKS ist die ubiquitäre Chalkonsynthase (CHS), aus der durch Genduplizierung und nachfolgende Mutationen die anderen Typ III-PKS hervorgegangen sind. Auch die CHS katalysiert die sich wiederholende Kondensation eines Coenzym A-aktivierten Startersubstrates, p-Cumaroyl-CoA, mit drei Molekülen Malonyl-CoA zu einem linearen Tetraketid. Im Unterschied zur BIS I katalysiert die Chalkonsynthase den Ringschluss über eine intramolekulare Claisen-Kondensation zum 4,2?,4?,6?-Tetrahydroxychalkon, das von weiterführenden Enzymen als Vorstufe für die Synthese der verschiedenen Flavonoide genutzt wird. Die BIS I konnte in Hefeextrakt-behandelten Zellkulturen von Sorbus aucuparia detektiert und ihre cDNA kloniert werden. Ein Vergleich der Aminosäurensequenzen der BIS I und der CHS zeigte eine Homologie von ca. 60 %. BIS I wurde in Kooperation mit der Arbeitsgruppe Stubbs in Halle kristallisiert und seine Struktur ermittelt. Die Aufklärung des Reaktionsmechanismus ist in Arbeit. Die Charakterisierung und die Strukturaufklärung werden dazu beitragen, die funktionellen Unterschiede und die evolutionären Zusammenhänge der verschiedenen Typ III-PKS besser zu verstehen.Biphenyls and dibenzofurans are the phytoalexins of Maloideae, a subfamily of the horticulturally significant Rosaceae. The biosynthesis of the carbon skeletons of the two classes of antimicrobial secondary metabolites is catalyzed by a novel type III polyketide synthase (PKS), named biphenyl synthase I (BIS I). The enzyme catalyzes the iterative condensation of the preferred starter substrate benzoyl-CoA with three molecules of malonyl- CoA to give a linear tetraketide. This intermediate then undergoes an intramolecular cyclization via aldol condensation to yield 3,5-dihydroxybiphenyl. The most common type III PKS is the ubiquitous chalcone synthase (CHS) from which all type III PKSs evolved by gene duplication and subsequent mutations. Like BIS I, CHS catalyzes the iterative condensation of a coenzyme A-linked starter substrate, p-coumaroyl-CoA, with three units of malonyl-CoA to give a linear tetraketide intermediate. In contrast to BIS I, CHS catalyzes cyclization by intramolecular Claisen condensation to give 4,2?,4?,6?-tetrahydroxychalcone, which is used by downstream enzymes as a starter substrate to form the diverse flavonoids. BIS I was detected in yeast-extract-treated cell cultures from Sorbus aucuparia and its cDNA was cloned. The comparison of the amino acid sequences of BIS I and CHS showed a homology of nearly 60 %. BIS I was crystallized in cooperation with the Stubbs group in Halle and its structure was determined. Elucidation of its reaction mechanism is in progress. Characterization and structure determination contribute to the understanding of the functional differences and the evolutionary relationships between type III PKSs

Spectral variability analysis of an XMM-Newton observation of Ark 564

We present a spectral variability analysis of the X-ray emission of the Narrow Line Seyfert 1 galaxy Ark 564 using the data from a ~100 ks XMM-Newton observation. Taking advantage of the high sensitivity of this long observation and the simple spectral shape of Ark 564, we determine accurately the spectral variability patterns in the source. We use standard cross-correlation methods to investigate the correlations between the soft and hard energy band light curves. We also generated 200 energy spectra from data stretches of 500 s duration each and fitted each one of them with a power law plus a bremsstrahlung component (for the soft excess) and we investigated the correlations between the various best fit model parameter values. The ``power law plus bremsstrahlung'' model describes the spectrum well at all times. The iron line and the absorption features, which are found in the time-averaged spectrum of the source are too weak to effect the results of the time resolved spectral fits. We find that the power law and the soft excess flux are variable, on all measured time scales. The power law slope is also variable, and leads the flux variations of both the power law and the bremsstrahlung components. Our results can be explained in the framework of time-dependent Comptonization models. They are consistent with a picture where instabilities propagate through an extended X-ray source, affecting first the soft and then the hard photons producing regions. The soft excess could correspond to ionized disc reflection emission, in which case it responds fast to the primary continuum variations. The time scales are such that light travel times might additionally influence the observed variability structure

Correlated spectral and temporal changes in 3C 390.3: a new link between AGN and Galactic Black Hole Binaries?

This work presents the results from a systematic search for evidence of temporal changes (i.e., non-stationarity) associated with spectral variations in 3C 390.3, using data from a two-year intensive RXTE monitoring campaign of this broad-line radio galaxy. In order to exploit the potential information contained in a time series more efficiently, we adopt a multi-technique approach, making use of linear and non-linear techniques. All the methods show suggestive evidences for non-stationarity in the temporal properties of 3C 390.3 between 1999 and 2000, in the sense that the characteristic time-scale of variability decreases as the energy spectrum of the source softens. However, only the non-linear, "scaling index method" is able to show conclusively that the temporal characteristics of the source do vary, although the physical interpretation of this result is not clear at the moment. Our results indicate that the variability properties of 3C 390.3 may vary with time, in the same way as they do in Galactic black holes in the hard state, strengthening the analogy between the X-ray variability properties of the two types of object. This is the first time that such a behavior is detected in an AGN X-ray light curve. Further work is needed in order to investigate whether this is a common behavior in AGN, just like in the Galactic binaries, or not.Comment: 15 pages, 12 figures, accepted for publication in A&