10,805 research outputs found
The line parameters and ratios as the physical probe of the line emitting regions in AGN
Here we discuss the physical conditions in the emission line regions (ELR) of
active galactic nuclei (AGN), with the special emphasize on the unresolved
problems, e.g. the stratification of the Broad Line Region (BLR) or the failure
of the photoionization to explain the strong observed optical Fe II emission.
We use here different line fluxes in order to probe the properties of the ELR,
such as the hydrogen Balmer lines (Ha to He), the helium lines from two
subsequent ionization levels (He II 4686 and He I 5876) and the strongest Fe II
lines in the wavelength interval 4400-5400 \AA. We found that the hydrogen
Balmer and helium lines can be used for the estimates of the physical
parameters of the BLR, and we show that the Fe II emission is mostly emitted
from an intermediate line region (ILR), that is located further away from the
central continuum source than the BLR.Comment: 8 pages, 9 figures, 2 tables, New Astronomy Reviews (Proceeding of
7th SCSLSA), in pres
Observational Effects of Strong Gravity in Vicinity of Supermassive Black Holes
Here we discuss the effects of strong gravity that can be observed in
electromagnetic spectra of active galactic nuclei (AGN). According to the
unification model of an AGN, there is a supermassive black hole () in its center, surrounded by an accretion disk that radiates in the
X-ray band. Accretion disks could have different forms, dimensions, and
emission, depending on the type of central black hole (BH), whether it is
rotating (Kerr metric) or nonrotating (Schwarzschild metric). We modeled the
emission of an accretion disk around supermassive BH using numerical
simulations based on a ray-tracing method in the Kerr metric. A broad emission
line Fe K at 6.4 keV with asymmetric profile (narrow bright blue peak
and a wide faint red wing) has been observed in a number of type 1 AGN. The
effects of strong gravitational field are investigated by comparison between
the modeled and observed iron K line profiles. The results of our
modeling show that the parameters of the Fe K line emitting region have
significant influence on the line profile and thus, allow us to determine the
space-time geometry (metric) in vicinity of the central BH of AGN, and also can
give us information about the plasma conditions in these regions.Comment: 5 pages, 3 figures. Accepted for publication in Fortschr. Phys.
(proceedings of the BW2007 WORKSHOP "III Southeastern European Workshop
Challenges Beyond the Standard Model"
Conductance Fluctuations Near the Two-Dimensional Metal-Insulator Transition
Measurements of conductance on short, wide, high-mobility Si-MOSFETs
reveal both a two-dimensional metal-insulator transition (MIT) at moderate
temperatures (1 4~K) and mesoscopic fluctuations of the conductance at
low temperatures ( 1~K). Both were studied as a function of chemical
potential (carrier concentration ) controlled by gate voltage () and
magnetic field near the MIT. Fourier analysis of the low temperature
fluctuations reveals several fluctuation scales in that vary
non-monotonically near the MIT. At higher temperatures, is similar
to large FETs and exhibits a MIT. All of the observations support the
suggestion that the MIT is driven by Coulomb interactions among the carriers.Comment: 4 pages, LaTeX, physica.sty (slightly modified prabib.sty), Submitted
to the 1997 Conference on Electronic Properties of Two-Dimensional System
Evaluating conjunction disambiguation on English-to-German and French-to-German WMT 2019 translation hypotheses
We present a test set for evaluating an MT system’s capability to translate ambiguous conjunctions depending on the sentence structure. We concentrate on the English conjunction ”but” and its French equivalent ”mais” which can be translated into two different German conjunctions. We evaluate all English-to-German and French-to-German submissions to the WMT 2019 shared translation task. The evaluation is done mainly automatically, with additional fast manual inspection of unclear cases. All systems almost perfectly recognise the ta-get conjunction ”aber”, whereas accuracies fo rthe other target conjunction ”sondern” range from 78% to 97%, and the errors are mostly caused by replacing it with the alternative cojjunction ”aber”. The best performing system for both language pairs is a multilingual Transformer TartuNLP system trained on all WMT2019 language pairs which use the Latin script, indicating that the multilingual approach is beneficial for conjunction disambiguation. As for other system features, such as using synthetic back-translated data, context-aware, hybrid, etc., no particular (dis)advantages can be observed. Qualitative manual inspection of translation hypotheses shown that highly ranked systems generally produce translations with high adequacy and fluency, meaning that these systems are not only capable of capturing the right conjunction whereas the rest of the translation hypothesis is poor. On the other hand, the low ranked systems generally exhibit lower fluency and poor adequacy
Moving through Medieval Macedonia: Late Modern Cartography, Archive Material and Hydrographic Data Used for the Regressive Modelling of Transportation Networks
The aim of this article is to illustrate how the rich data which was gathered during the
scholarly work on Macedonia, Southern Part (Tabula Imperii Byzantini, 11) as well as on Macedonia,
Northern Part (Tabula Imperii Byzantini, 16) from 2002 until 2010 can be combined with applications
deriving from Historical Geographic Information System (HGIS) in order to create a case study
on the transportation network and on the hydrography of Lake Vegoritis in the historical region
of Macedonia.
For this reason a holistic approach combining humanities and natural sciences is applied,
which comprises not only written medieval sources, which have already been evaluated in the
bibliography, but also late modern datasets. Their undisputable value lies in the fact that they
convey the state of the respective landscapes before industrialisation commenced in South-East
Europe.
In the near future the author will expand his research in order to cover eight lakes in the
southern Balkan peninsula – namely Lake Ohrid, the Great Prespa Lake, the Small Prespa Lake,
Lake Petron, Lake Vegoritis, Lake Dojran, Lake Kerkini and the vanished Lake Achianos, which lay on the Thessalonica Front (Macedonian Front) between 1915 and 1918 and on which hydrographic
data was gathered before, during and shortly after the Great War. By combining Byzantine
and Ottoman sources, travel literature, maps, archaeological evidence and hydrographic data
the author ventures to compare different water basins, to discern their impact on the transportation
networks through time and thus to reconstruct the landscapes of past times.This scholarly research was funded by the Adolf Holzhausen Legat of the Austrian Academy of Sciences
Automated text simplification as a preprocessing step for machine translation into an under-resourced language
In this work, we investigate the possibility of using fully automatic text simplification system on the English source in machine translation (MT) for improving its translation into an under-resourced language. We use the state-of-the-art automatic text simplification (ATS) system for lexically and syntactically simplifying source sentences, which are then translated with two state-of-the-art English-to-Serbian MT systems, the phrase-based MT (PBMT) and the neural MT (NMT). We explore three different scenarios for using the ATS in MT: (1) using the raw output of the ATS; (2) automatically filtering out the sentences with low grammaticality and meaning preservation scores; and (3) performing a minimal manual correction of the ATS output. Our results show improvement in fluency of the translation regardless of the chosen scenario, and difference in success of the three scenarios depending on the MT approach used (PBMT or NMT) with regards to improving translation fluency and post-editing effort
Are ambiguous conjunctions problematic for machine translation?
The translation of ambiguous words still poses challenges for machine translation.
In this work, we carry out a systematic quantitative analysis regarding the ability of different machine translation systems to disambiguate the source language conjunctions “but” and “and”. We evaluate specialised test sets focused on the translation of these two conjunctions. The test sets contain source languages that do not distinguish different variants of the given conjunction, whereas the target languages do. In total, we evaluate the conjunction “but” on 20 translation outputs, and the conjunction “and” on 10. All machine translation systems almost perfectly recognise one variant of the target conjunction, especially for the source conjunction
“but”. The other target variant, however, represents a challenge for machine translation systems, with accuracy varying from 50% to 95% for “but” and from 20% to 57% for “and”. The major error for all systems is replacing the correct target variant with the opposite one
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