1,324 research outputs found
Outbursts from IGR J17473-2721
We have investigated the outbursts of IGR J17473-2721. We analyzed all
available observations carried out by RXTE on IGR J17473-2721 during its later
outburst and as well all the available SWIFT/BAT data. The flux of the latter
outburst rose in ~ one month and then kept roughly constant for the following ~
two months. During this time period, the source was in a low/hard state. The
source moved to a high/soft state within the following three days, accompanied
by the occurrence of an additional outburst at soft X-rays and the end of the
preceding outburst in hard X-rays. During the decay of this soft outburst, the
source went back to a low/hard state within 6 days, with a luminosity 4 times
lower than the first transition. This shows a full cycle of the hysteresis in
transition between the hard and the soft states. The fact that the flux
remained roughly constant for ~ two months at times prior to the spectral
transition to a high/soft state might be regarded as the result of balancing
the evaporation of the inner disk and the inward accretion flow, in a model in
which the state transition is determined by the mass flow rate. Such a balance
might be broken via an additional mass flow accreting onto the inner disk,
which lightens the extra soft outburst and causes the state transition.
However, the possibility of an origin of the emission from the jet during this
time period cannot be excluded. The spectral analysis suggests an inclined XRB
system for IGR J17473-2721. Such a long-lived preceding low/hard state makes
IGR J17473-2721 resemble the behavior of outbursts seen in black hole X-ray
binaries like GX 339-4.Comment: A&A in pres
Nonlinear projective filtering in a data stream
We introduce a modified algorithm to perform nonlinear filtering of a time
series by locally linear phase space projections. Unlike previous
implementations, the algorithm can be used not only for a posteriori processing
but includes the possibility to perform real time filtering in a data stream.
The data base that represents the phase space structure generated by the data
is updated dynamically. This also allows filtering of non-stationary signals
and dynamic parameter adjustment. We discuss exemplary applications, including
the real time extraction of the fetal electrocardiogram from abdominal
recordings.Comment: 8 page
The hard to soft spectral transition in LMXBs - affected by recondensation of gas into an inner disk
Soft and hard spectral states of X-ray transient sources reflect two modes of
accretion, accretion via a geometrically thin, optically thick disk or an
advection-dominated accretion flow (ADAF). The luminosity at transition between
these two states seems to vary from source to source, or even for the same
source during different outbursts, as observed for GX 339-4. We investigate how
the existence of an inner weak disk in the hard state affects the transition
luminosity. We evaluate the structure of the corona above an outer truncated
disk and the resulting disk evaporation rate for different irradiation. In some
cases, recent observations of X-ray transients indicate the presence of an
inner cool disk during the hard state. Such a disk can remain during quiescence
after the last outburst as long as the luminosity does not drop to very low
values (10^-4 to 10^-3 of the Eddington luminosity). Consequently, as part of
the matter accretes via the inner disk, the hard irradiation is reduced. The
hard irradiation is further reduced, occulted and partly reflected by the inner
disk. This leads to a hard-soft transition at a lower luminosity if an inner
disk exists below the ADAF. This seems to be supported by observations for GX
339-4.Comment: 9 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Two-temperature coronal flow above a thin disk
We extended the disk corona model (Meyer & Meyer-Hofmeister 1994; Meyer, Liu,
& Meyer-Hofmeister 2000a) to the inner region of galactic nuclei by including
different temperatures in ions and electrons as well as Compton cooling. We
found that the mass evaporation rate and hence the fraction of accretion energy
released in the corona depend strongly on the rate of incoming mass flow from
outer edge of the disk, a larger rate leading to more Compton cooling, less
efficient evaporation and a weaker corona. We also found a strong dependence on
the viscosity, higher viscosity leading to an enhanced mass flow in the corona
and therefore more evaporation of gas from the disk below. If we take accretion
rates in units of the Eddington rate our results become independent on the mass
of the central black hole. The model predicts weaker contributions to the hard
X-rays for objects with higher accretion rate like narrow-line Seyfert 1
galaxies (NLS1s), in agreement with observations. For luminous active galactic
nuclei (AGN) strong Compton cooling in the innermost corona is so efficient
that a large amount of additional heating is required to maintain the corona
above the thin disk.Comment: 17 pages, 6 figures. ApJ accepte
Locality and Accessibility in Wh-Questions
Even in relatively configurational languages, such as English, speakers frequently have a choice between different constituent orders. Many of these word order variations have been linked to complexity (Hawkins 2005; inter alia). For example, heavy-NP shift is more likely if the shifted NP is more complex than the NP it shifts over (Wasow 1997). Other cases of word order variations, however, have not been considered in these terms. The choice between different wh-phrase orders, as in (1), has been said to be determined by (categorical) grammatical constraints, such as Superiorit
Structural investigation of K-feldspar KAlSi3O8 crystals by XRD and Raman spectroscopy: an application to petrological study of Luc Yen Pegmatites, Yen Bai Province, Vietnam
K-feldspars in pegmatites from Luc Yen gem mining area, Yen Bai province, Vietnam were studied by
X-ray fluorescence, X-ray powder diffraction and the Raman spectroscopy. Chemical analysis determined the
K-feldspars in the form of (K0:8909Na0:0388Ca0:002Pb0:0042Cs0:0024Rb0:0338)(Al0:9975Fe0:0053Ti0:0004)Si2:988O8. Both
X-ray powder diffraction and Raman spectroscopy indicated Luc Yen K-feldspars as orthoclase phase. Together
with the values of Al content of the T1 tetrahedral sites in orthoclase, it is understood that Luc Yen pegmatites
are of young ages (Cenozoic) and shallow intrusive types
Fluorescent Silicon Clusters and Nanoparticles
The fluorescence of silicon clusters is reviewed. Atomic clusters of silicon
have been at the focus of research for several decades because of the relevance
of size effects for material properties, the importance of silicon in
electronics and the potential applications in bio-medicine. To date numerous
examples of nanostructured forms of fluorescent silicon have been reported.
This article introduces the principles and underlying concepts relevant for
fluorescence of nanostructured silicon such as excitation, energy relaxation,
radiative and non-radiative decay pathways and surface passivation.
Experimental methods for the production of silicon clusters are presented. The
geometric and electronic properties are reviewed and the implications for the
ability to emit fluorescence are discussed. Free and pure silicon clusters
produced in molecular beams appear to have properties that are unfavourable for
light emission. However, when passivated or embedded in a suitable host, they
may emit fluorescence. The current available data show that both quantum
confinement and localised transitions, often at the surface, are responsible
for fluorescence. By building silicon clusters atom by atom, and by embedding
them in shells atom by atom, new insights into the microscopic origins of
fluorescence from nanoscale silicon can be expected.Comment: 5 figures, chapter in "Silicon Nanomaterials Sourcebook", editor
Klaus D. Sattler, CRC Press, August 201
Discovery of a Magnetic White Dwarf in the Symbiotic Binary Z Andromedae
We report the first result from our survey of rapid variability in symbiotic
binaries: the discovery of a persistent oscillation at P=1682.6 +- 0.6 s in the
optical emission from the prototype symbiotic, Z Andromedae. The oscillation
was detected on all 8 occasions on which the source was observed over a
timespan of nearly a year, making it the first such persistent periodic pulse
found in a symbiotic binary. The amplitude was typically 2 - 5 mmag, and it was
correlated with the optical brightness during a relatively small outburst of
the system. The most natural explanation is that the oscillation arises from
the rotation of an accreting, magnetic (B_S > 10^5 G) white dwarf. This
discovery constrains the outburst mechanisms, since the oscillation emission
region near the surface of the white dwarf was visible during the outburst.Comment: Accepted for publication in the Astrophysical Journal (6 pages,
including 4 figures), LaTe
The source ambiguity problem: Distinguishing the effects of grammar and processing on acceptability judgments
Judgments of linguistic unacceptability may theoretically arise from either grammatical deviance or significant processing difficulty. Acceptability data are thus naturally ambiguous in theories that explicitly distinguish formal and functional constraints. Here, we consider this source ambiguity problem in the context of Superiority effects: the dispreference for ordering a wh-phrase in front of a syntactically “superior” wh-phrase in multiple wh-questions, e.g., What did who buy? More specifically, we consider the acceptability contrast between such examples and so-called D-linked examples, e.g., Which toys did which parents buy? Evidence from acceptability and self-paced reading experiments demonstrates that (i) judgments and processing times for Superiority violations vary in parallel, as determined by the kind of wh-phrases they contain, (ii) judgments increase with exposure, while processing times decrease, (iii) reading times are highly predictive of acceptability judgments for the same items, and (iv) the effects of the complexity of the wh-phrases combine in both acceptability judgments and reading times. This evidence supports the conclusion that D-linking effects are likely reducible to independently motivated cognitive mechanisms whose effects emerge in a wide range of sentence contexts. This in turn suggests that Superiority effects, in general, may owe their character to differential processing difficulty
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