Search for the magnetic field of the O7.5 III star xi Persei

Cyclical wind variability is an ubiquitous but as yet unexplained feature among OB stars. The O7.5 III(n)((f)) star xi Persei is the brightest representative of this class on the Northern hemisphere. As its prominent cyclical wind properties vary on a rotational time scale (2 or 4 days) the star has been already for a long time a serious magnetic candidate. As the cause of this enigmatic behavior non-radial pulsations and/or a surface magnetic field are suggested. We present a preliminary report on our attempts to detect a magnetic field in this star with high-resolution measurements obtained with the spectropolarimeter Narval at TBL, France during 2 observing runs of 5 nights in 2006 and 5 nights in 2007. Only upper limits could be obtained, even with the longest possible exposure times. If the star hosts a magnetic field, its surface strength should be less than about 300 G. This would still be enough to disturb the stellar wind significantly. From our new data it seems that the amplitude of the known non-radial pulsations has changed within less than a year, which needs further investigation.Comment: 2 pages, 6 figures, contributed poster at IAU Symposium 259 "Cosmic Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain, November 3-7, 200

The influence of negative-energy states on proton-proton bremsstrahlung

We investigate the effect of negative-energy states on proton-proton bremsstrahlung using a manifestly covariant amplitude based on a T-matrix constructed in a spectator model. We show that there is a large cancellation among the zeroth-order, single- and double-scattering diagrams involving negative-energy nucleonic currents. We thus conclude that it is essential to include all these diagrams when studying effects of negative-energy states.Comment: 12 pages revtex and 3 figure

Latent dirichlet markov allocation for sentiment analysis

In recent years probabilistic topic models have gained tremendous attention in data mining and natural language processing research areas. In the field of information retrieval for text mining, a variety of probabilistic topic models have been used to analyse content of documents. A topic model is a generative model for documents, it specifies a probabilistic procedure by which documents can be generated. All topic models share the idea that documents are mixture of topics, where a topic is a probability distribution over words. In this paper we describe Latent Dirichlet Markov Allocation Model (LDMA), a new generative probabilistic topic model, based on Latent Dirichlet Allocation (LDA) and Hidden Markov Model (HMM), which emphasizes on extracting multi-word topics from text data. LDMA is a four-level hierarchical Bayesian model where topics are associated with documents, words are associated with topics and topics in the model can be presented with single- or multi-word terms. To evaluate performance of LDMA, we report results in the field of aspect detection in sentiment analysis, comparing to the basic LDA model

The stellar populations of spiral galaxies

We have used a large sample of low-inclination spiral galaxies with radially-resolved optical and near-infrared photometry to investigate trends in star formation history with radius as a function of galaxy structural parameters. A maximum likelihood method was used to match all the available photometry of our sample to the colours predicted by stellar population synthesis models. The use of simplistic star formation histories, uncertainties in the stellar population models and regarding the importance of dust all compromise the absolute ages and metallicities derived in this work, however our conclusions are robust in a relative sense. We find that most spiral galaxies have stellar population gradients, in the sense that their inner regions are older and more metal rich than their outer regions. Our main conclusion is that the surface density of a galaxy drives its star formation history, perhaps through a local density dependence in the star formation law. The mass of a galaxy is a less important parameter; the age of a galaxy is relatively unaffected by its mass, however the metallicity of galaxies depends on both surface density and mass. This suggests that galaxy mass-dependent feedback is an important process in the chemical evolution of galaxies. In addition, there is significant cosmic scatter suggesting that mass and density may not be the only parameters affecting the star formation history of a galaxy.Comment: 25 pages; 17 figures; re-submitted to MNRAS after replying to referee's repor

A nesting conformation of the 5′-bromo-1′,3′-xylyl-18-crown-5·tert-butylammonium hexafluorophosphate complex; the correlation of the structures of crown ether complexes in the solid state and in solution

Single-crystal X-ray analysis of the 5′-bromo-1′,3′-xylyl-18-crown-5· tert-butylammonium hexafluorophosphate complex shows that the complex is of the “nesting” type in which the cation and the aryl group are on the same face of the macroring and that the macroring has a (ag+a) (ag−a) (ag+a) (ag−a)(ag+a) (ag−a) conformation

Editorial: Understanding developmental dyslexia: linking perceptual and cognitive deficits to reading processes

The problem of causation has proven particularly elusive in the case of developmental dyslexia (DD). The field has been dominated by very general hypotheses, such as the idea that DD is caused by a phonological deficit and/or an impairment of the magnocellular pathway. Results are contrasting and causal unidirectional links have not been persuasively demonstrated. Some studies in the Research Topic (RT) re-examine these general hypotheses from the critical perspective of more selective predictions. Others focus on less general deficit hypotheses and stay closer to reading by investigating specific aspects of the reading process such as orthographic learning ability or the ability to deal with multiple-stimulus displays. Studies benefit from new research paradigms as well as new information from research areas such as neuroimaging or genetics. Below, we sketch the general questions tackled by these studies

Creative industries

Creative industries are nowadays central in many policies to stimulate the economic development of cities, regions and advanced capitalist economies in general. This paper contributes to the� creative industries literature in two respects. First, we empirically explore if high shares of creative industries in regions go together with one particular aspect of regional economic development, namely firm entry rates. Drawing on Dutch trade register data over a six-year period, it is concluded that at the level of municipalities there is indeed a connection between the share of creative industries and firm entry, even after controlling for the sizes of municipalities, and no matter if creative industries are defined broadly or narrowly. Second, the paper analyses if firms in creative industries are heterogeneous in terms of business processes and their contribution to regional firm entry. Drawing on previous work four creative domains are identified: arts, media and entertainment, creative business services and, at the periphery, knowledge intensive business services. After analysing survey data of 4,746 Dutch SMEs, we find that firms across these domains are distinct in their use of the surveyed business practices: innovation, strategy and marketing, and human resources practices. Especially knowledge intensive services firms are deviant. For the connection with firm entry rates, it appears that high shares of firms in the arts and knowledge intensive business services are significantly connected with regional firm entry rates, while media and entertainment and creative business services remain insignificant. Implications for practitioners and future research are discussed. �