1,721,199 research outputs found
Cyclo-synchrotron emission from magnetically dominated active regions above accretion discs
No full textWe discuss the role of thermal cyclo-synchrotron emission in a magnetically dominated corona above an accretion disc in an active galaxy or a Galactic black hole candidate. The dissipation occurs in localized active regions around the central black hole. Cyclo-synchrotron radiation is found to be an important process. In the case of Galactic black hole candidates, its emission can dominate the inverse Compton scattering of the soft photon field produced in the disc by thermal electrons. We discuss observational predictions and the detectability of cyclo-synchrotron radiation both for these sources and for radio-quiet active galactic nuclei
Magnetic flares in accretion disc coronae and the spectral states of black hole candidates: the case of GX 339-4
No full textWe examine the constraints that the observations of different spectral states displayed by Galactic black hole candidates impose on the properties of magnetic flares resulting from the reconnection of flux tubes that rise from the accretion disc into a corona because of the magnetic buoyancy (Parker) instability. Using observations of one of the best-studied examples, GX339-4, we identify the geometry and physical conditions characterizing each of these states. We find that, if in the soft state flaring occurs at small scaleheights above the accretion disc, a soft thermal-like spectrum, characteristic of this state, can result from the heating and consequent reradiation of the hard X-rays produced by such flares. The hard tail can then be produced by Comptonization of the soft radiation. Conversely, the hard state may result from a phase in which flares are triggered high above the underlying accretion disc and produce X-rays via Comptonization of either internal cyclo-synchrotron radiation or soft disc photons. The spectral characteristics of the different states are naturally accounted for by the choice of geometry: when flares are triggered high above the disc the system is photon-starved, hence the hard Comptonized spectrum of the hard state. Intense flaring close to the disc greatly enhances the local soft-photon field with the result that the spectrum softens. We interpret these two states as being related to two different phases of magnetic energy dissipation. We speculate that, in the soft state. Parker instability in the disc may favour the emergence of large numbers of relatively low-magnetic-field flux tubes. In the hard state, only intense magnetic fields become buoyant and magnetic loops are able to rise and expand in the coronal atmosphere. This possibility can also qualitatively account for the observed short time-scale variability and the characteristics of the X-ray-reflected component of the hard state
Correlation filtering in financial time series
No full textWe apply a method to filter relevant information from the correlation coefficient matrix by extracting a network of relevant interactions. This method succeeds to generate networks with the same hierarchical structure of the Minimum Spanning Tree but containing a larger amount of links resulting in a richer network topology allowing loops and cliques. In Tumminello et al.,(1) we have shown that this method, applied to a financial portfolio of 100 stocks in the USA equity markets, is pretty efficient in filtering relevant information about the clustering of the system and its hierarchical structure both on the whole system and within each cluster. In particular, we have found that triangular loops and 4 element cliques have important and significant relations with the market structure and properties. Here we apply this filtering procedure to the analysis of correlation in two different kind of interest rate time serie
The kappa-generalized distribution: A new descriptive model for the size distribution of incomes
No full textStatistically validated network for analysing textual data
Full text linkThis paper presents a novel methodology, called Word Co-occurrence SVN topic
model (WCSVNtm), for document clustering and topic modeling in textual datasets.
This method represents the corpus as a bipartite network of words and documents
to rigorously assess the statistical significance of word co-occurrences within documents
and document overlap based on shared vocabulary. By employing the Leiden
community detection algorithm to the SVN, distinct communities of words can be
identified and interpreted as topics. Similarly, documents can be sorted into groups
based on their thematic similarities. We demonstrate the effectiveness of our approach
by analyzing three datasets: a set of 120 Wikipedia articles, the arXiv10 dataset, which
consists of 100,000 abstracts from scientific papers, and a sampled subset of 10,000
documents from the original arXiv10. To benchmark our results, we compare our
approach with several well-established models in the field of topic modeling and document
clustering, including the hierarchical Stochastic Block Model (hSBM), BERTopic,
and Latent Dirichlet Allocation (LDA). The results show that WCSVNtm achieves competitive
performance across all datasets, automatically selecting the number of topics
and document clusters, whereas state-of-the-art methods require prior knowledge
or additional tuning for optimization. Finally, any advancements in community detection
algorithms could further improve our method
The k-generalized distribution: A new descriptive model for the size distribution of incomes
No full textThis paper proposes the k-generalized distribution as a model for describing the distribution and dispersion of income within a population. Formulas for the shape, moments and standard tools for inequality measurement–such as the Lorenz curve and the Gini coefficient–are given. A method for parameter estimation is also discussed. The model is shown to fit extremely well the data on personal income distribution in Australia and in the United States
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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