2,015 research outputs found
Revealing the fastest component of the DG Tau outflow through X-rays
Some T Tauri stars show a peculiar X-ray spectrum that can be modelled by two
components with different absorbing column densities. We seek to explain the
soft X-ray component in DG Tau, the best studied of these sources, with an
outflow model, taking observations at other wavelengths into consideration. We
constrain the outflow properties through spectral fitting and employ simple
semi-analytical formulae to describe properties of a shock wave that heats up
the X-ray emitting region. The X-ray emission is consistent with its arising
from the fastest and innermost component of the optically detected outflow.
Only a small fraction of the total mass loss is required for this X-ray
emitting component. Our favoured model requires shock velocities between 400
and 500 km/s. For a density >10^5 /cm^3 all dimensions of the shock cooling
zone are only a few AU, so even in optical observations this cannot be
resolved. This X-ray emission mechanism in outflows may also operate in other,
less absorbed T Tauri stars, in addition to corona and accretion spots.Comment: 7, pages, 4 figures, accepted by A&
Suzaku Confirms NGC~3660 is an Unabsorbed Seyfert 2
An enigmatic group of objects, unabsorbed Seyfert 2s may have intrinsically
weak broad line regions, obscuration in the line of sight to the BLR but not to
the X-ray corona, or so much obscuration that the X-ray continuum is completely
suppressed and the observed spectrum is actually scattered into the line of
sight from nearby material. NGC 3660 has been shown to have weak broad
optical/near infrared lines, no obscuration in the soft X-ray band, and no
indication of "changing look" behavior. The only previous hard X-ray detection
of this source by Beppo-SAX seemed to indicate that the source might harbor a
heavily obscured nucleus. However, our analysis of a long-look Suzaku
observation of this source shows that this is not the case, and that this
source has a typical power law X-ray continuum with normal reflection and no
obscuration. We conclude that NGC 3660 is confirmed to have no unidentified
obscuration and that the anomolously high Beppo-SAX measurement must be due to
source confusion or similar, being inconsistent with our Suzaku measurements as
well as non-detections from Swift-BAT and RXTE.Comment: Accepted to PAS
Applications of TRIZ and Axiomatic Design: A Comparison to Deduce Best Practices in Industry☆
Abstract In the first decade of 2000s, several contributions have illustrated methods combining TRIZ and Axiomatic Design (AD). The strength of the connection was found in the complementary objectives AD and TRIZ pursue. AD is supposed to analyze the problem and structure it in the most convenient way, while TRIZ should solve the minimum number of design conflicts that are intrinsically present in a case study. Nevertheless, despite the promising match between AD and TRIZ, no conjoint application strategy has emerged as a reference, neither in academia, nor in industry. Conversely, the quantity has dropped of scientific papers contextually making reference to both methodologies. Some studies attempt to remark the methodological problems concerning the combination of AD and TRIZ. In a different perspective, the authors performed an application-oriented study, in order to point out the industrial domains for which the methodologies result the most suitable. The survey highlights that TRIZ is mostly employed for mass-market products, while AD is basically used to develop systems that industrial organizations make use of. The authors discuss the consequences of these findings, inferring how design can benefit from TRIZ and AD heuristics and the practical cases in which they are likely to be combined successfully
Evidence that MEK1 positively promotes interhomologue double-strand break repair
During meiosis there is an imperative to create sufficient crossovers for homologue segregation. This can be achieved during repair of programmed DNA double-strand breaks (DSBs), which are biased towards using a homologue rather than sister chromatid as a repair template. Various proteins contribute to this bias, one of which is a meiosis specific kinase Mek1. It has been proposed that Mek1 establishes the bias by creating a barrier to sister chromatid repair, as distinct from enforcing strand invasion with the homologue. We looked for evidence that Mek1 positively stimulates strand invasion of the homologue. This was done by analysing repair of DSBs induced by the VMA1- derived endonuclease (VDE) and flanked by directly repeated sequences that can be used for intrachromatid single-strand annealing (SSA). SSA competes with interhomologue strand inva- sion significantly more successfully when Mek1 function is lost. We suggest the increase in intrachromosomal SSA reflects an opportunistic default repair pathway due to loss of a MEK1 stimulated bias for strand invasion of the homologous chromosome. Making use of an inhibitor sensitive mek1-as1 allele, we found that Mek1 function influences the repair pathway throughout the first 4-5 h of meiosis. Perhaps reflecting a particular need to create bias for successful interhomologue events before chromosome pairing is complete. © The Author(s) 2010. Published by Oxford University Pres
Suzaku Observations of the Circinus galaxy
We report Suzaku observations of the active, Compton-thick Circinus galaxy.
Observations were obtained with both the X-ray Imaging spectrometer (XIS) and
the Hard X-ray Detector (HXD). Below 10 keV, the nuclear spectrum is dominated
by radiation reflected from cold dense gas of high column density, while above
13 keV the radiation is directly transmitted nuclear emission seen through a
column density of $~ 4 x 10^{24} cm^-2. In the 0.2--10 keV band, the XIS
spectrum is contaminated at 5% level by the brightest off-nuclear source in
Circinus (CG X-1), but drops to 1% in the 5-10 keV and is negligible at higher
energies. We find no significant evidence for variability in the hard (>12 keV)
emission. The Circinus is marginally detected with the HXD/GSO in the 50--100
keV band at 2.5\sigma level. We model the 3-70 keV band XIS+PIN spectra with a
four components: the Compton transmitted nuclear emission, the reflected
nuclear emission, a soft power law (representing a combination of scattered
nuclear emission, extended emission and contamination by sources in the galaxy
below a few keV). The hard nuclear power-law is found to have a photon index
Gamma_h ~= 1.6, very similar to the soft power-law. The high energy cut-off is
E_C ~= 49 keV. These results agree with those from BeppoSax. An extrapolation
of this model up to the GSO band shows good agreement with the GSO spectrum and
supports our detection of the Circinus up to ~= 100keV.Comment: ApJ accepte
An extended scheme for fitting X-ray data with accretion disk spectra in the strong gravity regime
Accreting black holes are believed to emit X-rays which then mediate
information about strong gravity in the vicinity of the emission region. We
report on a set of new routines for the Xspec package for analysing X-ray
spectra of black-hole accretion disks. The new computational tool significantly
extends the capabilities of the currently available fitting procedures that
include the effects of strong gravity, and allows one to systematically explore
the constraints on more model parameters than previously possible (for example
black-hole angular momentum). Moreover, axial symmetry of the disk intrinsic
emissivity is not assumed, although it can be imposed to speed up the
computations. The new routines can be used also as a stand-alone and flexible
code with the capability of handling time-resolved spectra in the regime of
strong gravity. We have used the new code to analyse the mean X-ray spectrum
from the long XMM--Newton 2001 campaign of the Seyfert 1 galaxy MCG--6-30-15.
Consistent with previous findings, we obtained a good fit to the broad Fe K
line profile for a radial line intrinsic emissivity law in the disk which is
not a simple power law, and for near maximal value of black hole angular
momentum. However, equally good fits can be obtained also for small values of
the black hole angular momentum. The code has been developed with the aim of
allowing precise modelling of relativistic effects. Although we find that
current data cannot constrain the parameters of black-hole/accretion disk
system well, the approach allows, for a given source or situation, detailed
investigations of what features of the data future studies should be focused on
in order to achieve the goal of uniquely isolating the parameters of such
systems.Comment: Accepted for publication in ApJ S
Line Emission from an Accretion Disk around a Black hole: Effects of Disk Structure
The observed iron K-alpha fluorescence lines in Seyfert-1 galaxies provide
strong evidence for an accretion disk near a supermassive black hole as a
source of the line emission. These lines serve as powerful probes for examining
the structure of inner regions of accretion disks. Previous studies of line
emission have considered geometrically thin disks only, where the gas moves
along geodesics in the equatorial plane of a black hole. Here we extend this
work to consider effects on line profiles from finite disk thickness, radial
accretion flow and turbulence. We adopt the Novikov and Thorne (1973) solution,
and find that within this framework, turbulent broadening is the dominant new
effect. The most prominent change in the skewed, double-horned line profiles is
a substantial reduction in the maximum flux at both red and blue peaks. The
effect is most pronounced when the inclination angle is large, and when the
accretion rate is high. Thus, the effects discussed here may be important for
future detailed modeling of high quality observational data.Comment: 21 pages including 8 figures; LaTeX; ApJ format; accepted by ApJ;
short results of this paper appeared before as a conference proceedings
(astro-ph/9711214
Optical vortex generation from molecular chromophore arrays
The generation of light endowed with orbital angular momentum, frequently termed optical vortex light, is commonly achieved by passing a conventional beam through suitably constructed optical elements. This Letter shows that the necessary phase structure for vortex propagation can be directly produced through the creation of twisted light from the vacuum. The mechanism is based on optical emission from a family of chromophore nanoarrays that satisfy specific geometric and symmetry constraints. Each such array can support pairs of electronically delocalized doubly degenerate excitons whose azimuthal phase progression is responsible for the helical wave front of the emitted radiation. The exciton symmetry dictates the maximum magnitude of topological charge; detailed analysis secures the conditions necessary to deliver optical vortices of arbitrary order
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