197 research outputs found
Jets from Sub-Parsec to Kiloparsec Scales: A Physical Connection
The Chandra discovery of bright X-ray emission from kpc-scale jets allows
insight into the physical parameters of the jet flow at large scale. At the
opposite extreme, extensive studies of the inner relativistic jets in Blazars
with multiwavelength observations, yield comparable information on sub-parsec
scales. In the framework of simple radiation models for the emission regions we
compare the physical parameters of jets on these two very different scales in
the only two well studied Blazars for which large-scale emission has been
resolved by Chandra. Notably, we find that the relativistic Doppler factors and
powers derived independently at the two scales are consistent, suggesting that
the jet does not suffer severe deceleration or dissipation. Moreover the
internal equipartition pressures in the inner jet and in the external X-ray
bright knots scale inversely with the jet cross section as expected in the
simple picture of a freely expanding jet in equipartition.Comment: 4 figures, accepted by Ap
Uncertainty estimates and L_2 bounds for the Kuramoto-Sivashinsky equation
We consider the Kuramoto-Sivashinsky (KS) equation in one spatial dimension
with periodic boundary conditions. We apply a Lyapunov function argument
similar to the one first introduced by Nicolaenko, Scheurer, and Temam, and
later improved by Collet, Eckmann, Epstein and Stubbe, and Goodman, to prove
that ||u||_2 < C L^1.5. This result is slightly weaker than that recently
announced by Giacomelli and Otto, but applies in the presence of an additional
linear destabilizing term. We further show that for a large class of Lyapunov
functions \phi the exponent 1.5 is the best possible from this line of
argument. Further, this result together with a result of Molinet gives an
improved estimate for L_2 boundedness of the Kuramoto-Sivashinsky equation in
thin rectangular domains in two spatial dimensions.Comment: 17 pages, 1 figure; typos corrected, references added; figure
modifie
(How) is formulaic language universal? Insights from Korean, German and English
The existence of common expressions, also referred to as formulaic language or phraseological units, has been evidenced in a very large number of languages. However, the extent to which languages feature such formulaic material, how formulaicity may be understood across typologically different languages and whether indeed there is a concept of formulaic language that applies across languages, are questions that have been less commonly discussed. Using a novel data set consisting of topically matched corpora in three typologically different languages (Korean, German and English), this study proposes an empirically founded universal concept for formulaic language and discusses what the shape of this concept suggests for the theoretical understanding of formulaic language going forward. In particular, it is argued that the nexus of the concept of formulaic language cannot be fixed at any particular structural level (such as the phrase or the level of polylexicality) and incorporates elements specified at varying levels of abstraction (or schematicity). This means that a cross-linguistic concept of formulaic language fits in well with a constructionist view of linguistic structure
A survey of extended radio jets with Chandra and HST
We present the results from an X-ray and optical survey of a sample of 17
radio jets in AGN performed with Chandra and HST. The sample was selected from
the radio and is unbiased toward detection at shorter wavelengths, but
preferentially it includes beamed sources. We find that X-ray emission is
common on kpc-scales, with over half radio jets exhibiting at least one X-ray
knot on the Chandra images. The distributions of the radio-to-X-ray and
radio-to-optical spectral indices for the detected jets are similar to the
limits for the non-detections,suggesting all bright radio jets have X-ray
counterparts which will be visible in longer observations. Comparing the radio
and X-ray morphologies shows that the majority of the X-ray jets have
structures that closely map the radio. Analysis of the SED of the jet knots
suggest the knots in which the X-ray and radio morphologies track each other
produce X-rays by IC scattering of the Cosmic Microwave Background. The
remaining knots produce X-rays by the synchrotron process. Spectral changes are
detected along the jets, with the ratio of the X-ray-to-radio and
optical-to-radio flux densities decreasing from the inner to the outer regions.
This suggests the presence of an additional contribution to the X-ray flux in
the jet's inner part, either from synchrotron or IC of the stellar light.
Alternatively, in a pure IC/CMB scenario, the plasma decelerates as it flows
from the inner to the outer regions. Finally, the X-ray spectral indices for
the brightest knots are flat, indicating that the bulk of the luminosity of the
jets is emitted at GeV energies, and raising the interesting possibility of
future detections with GLAST.Comment: 26 pages, 6 ps figures, 6 jpeg figures (1 replaced); accepted for
publication in Ap
X-Ray and Optical Emission from Radio Hot Spots of Powerful Quasars
In a survey with Chandra and HST of a sample of 17 radio sources with bright radio jets (16 powerful FR II and one nearby FR I), we detected X-ray and optical emission from a number of radio hot spots and lobes. Six hot spots on the near sides of powerful FR II galaxies (as determined from the jet asymmetry) were detected at X-rays, while none were detected on the far side, suggesting that high-energy emission from hot spots is anisotropic. In the nearby FR I galaxy 0836+299 (the only FR I in our sample) both hot spots are detected in X-rays, in agreement with the symmetric radio morphology. In the latter case the spectral energy distributions (SEDs) of both hot spots can be modeled from radio to X-rays with synchrotron emission from a single power-law energy distribution of electrons with Lorentz factors up to ~2 × 107. For the six hot spots of powerful FR II galaxies the X-ray flux lies above the extrapolation from the radio-to-optical continuum. Modeling the SEDs with a one-zone synchrotron self-Compton model, we find that equipartition is strongly violated, with the particle energy density dominating over the magnetic field one by 1-2 orders of magnitude. We discuss alternatives to this simple model, concluding that a viable alternative is that the X-ray emission is produced in the still-relativistic (Doppler factor δ = 3-6) terminal part of the jet by inverse Compton (IC) scattering on the CMB or synchrotron photons emitted by plasma flowing with a small velocity. X-ray emission from some of the lobes is detected on the side opposite to the jet, suggesting the possible relevance of back-scattered central radiation in providing seed photons for the IC process
ENHANCED INTERLEUKIN-1 ACTIVITY IN PLASMA OF PATIENTS WITH ACUTE DECOMPENSATED HEART FAILURE
Hsp70 in mitochondrial biogenesis
The family of hsp70 (70 kilodalton heat shock protein) molecular chaperones plays an essential and diverse role in cellular physiology, Hsp70 proteins appear to elicit their effects by interacting with polypeptides that present domains which exhibit non-native conformations at distinct stages during their life in the cell. In this paper we review work pertaining to the functions of hsp70 proteins in chaperoning mitochondrial protein biogenesis. Hsp70 proteins function in protein synthesis, protein translocation across mitochondrial membranes, protein folding and finally the delivery of misfolded proteins to proteolytic enzymes in the mitochondrial matrix
XMM-Newton spectroscopy of an X-ray selected sample of RL AGNs
This paper presents the X-ray spectroscopy of an X-ray selected sample of 25
radio-loud (RL) AGNs extracted from the XBSS sample. The main goal is to study
the origin of the X-ray spectral differences usually observed between
radio-loud and radio-quiet (RQ) AGNs. To this end, a comparison sample of 53 RQ
AGNs has been also extracted from the same XBSS sample and studied together
with the sample of RL AGNs. We have focused the analysis on the distribution of
the X-ray spectral indices of the power-law component that models the large
majority of the spectra in both samples. We find that the mean X-ray energy
spectral index is very similar in the 2 samples and close to alpha_X~1.
However, the intrinsic distribution of the spectral indices is significantly
broader in the sample of RL AGNs. In order to investigate the origin of this
difference, we have divided the RL AGNs into blazars and ``non-blazars'', on
the basis of the available optical and radio information. We find strong
evidence that the broad distribution observed in the RL AGN sample is mainly
due to the presence of the blazars. Furthermore, within the blazar class we
have found a link between the X-ray spectral index and the value of the
radio-to-X-ray spectral index suggesting that the observed X-ray emission is
directly connected to the emission of the relativistic jet. This trend is not
observed among the ``non-blazars'' RL AGNs. This favours the hypothesis that,
in these latter sources, the X-ray emission is not significantly influenced by
the jet emission and it has probably an origin similar to the RQ AGNs. Overall,
the results presented here indicate that the observed distribution of the X-ray
spectral indices in a given sample of RL AGNs is strongly dependent on the
amount of relativistic beaming present in the selected sources.Comment: 18 pages, 10 figures, accepted for publication in A&
AGILE detection of extreme gamma-ray activity from the blazar PKS 1510-089 during March 2009. Multifrequency analysis
We report on the extreme gamma-ray activity from the FSRQ PKS 1510-089
observed by AGILE in March 2009. In the same period a radio-to-optical
monitoring of the source was provided by the GASP-WEBT and REM. Moreover,
several Swift ToO observations were triggered, adding important information on
the source behaviour from optical/UV to hard X-rays. We paid particular
attention to the calibration of the Swift/UVOT data to make it suitable to the
blazars spectra. Simultaneous observations from radio to gamma rays allowed us
to study in detail the correlation among the emission variability at different
frequencies and to investigate the mechanisms at work. In the period 9-30 March
2009, AGILE detected an average gamma-ray flux of (311+/-21)x10^-8 ph cm^-2
s^-1 for E>100 MeV, and a peak level of (702+/-131)x10^-8 ph cm^-2 s^-1 on
daily integration. The gamma-ray activity occurred during a period of
increasing activity from near-IR to UV, with a flaring episode detected on
26-27 March 2009, suggesting that a single mechanism is responsible for the
flux enhancement observed from near-IR to UV. By contrast, Swift/XRT
observations seem to show no clear correlation of the X-ray fluxes with the
optical and gamma-ray ones. However, the X-ray observations show a harder
photon index (1.3-1.6) with respect to most FSRQs and a hint of
harder-when-brighter behaviour, indicating the possible presence of a second
emission component at soft X-ray energies. Moreover, the broad band spectrum
from radio-to-UV confirmed the evidence of thermal features in the optical/UV
spectrum of PKS 1510-089 also during high gamma-ray state. On the other hand,
during 25-26 March 2009 a flat spectrum in the optical/UV energy band was
observed, suggesting an important contribution of the synchrotron emission in
this part of the spectrum during the brightest gamma-ray flare, therefore a
significant shift of the synchrotron peak.Comment: 13 pages, 7 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysic
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