3,606 research outputs found
Jet-torus connection in radio galaxies: Relativistic hydrodynamics and synthetic emission
High-resolution Very-Long-Baseline Interferometry observations of active
galactic nuclei have revealed asymmetric structures in the jets of radio
galaxies. These asymmetric structures may be due to internal asymmetries in the
jet, could be induced by the different conditions in the surrounding ambient
medium including the obscuring torus, or a combination of the two. In this
paper we investigate the influence of the ambient medium (including the
obscuring torus) on the observed properties of jets from radio galaxies. We
performed special-relativistic hydrodynamic (RHD) simulations of over-pressured
and pressure-matched jets using the special-relativistic hydrodynamics code
\texttt{Ratpenat}, which is based on a second-order accurate finite-volume
method and an approximate Riemann solver. Using a newly developed emission code
to compute the electromagnetic emission, we have investigated the influence of
different ambient medium and torus configurations on the jet structure and
subsequently computed the non-thermal emission produced by the jet and the
thermal absorption due to the torus. To better compare the emission simulations
with observations we produced synthetic radio maps, taking into account the
properties of the observatory. The detailed analysis of our simulations shows
that the observed asymmetries can be produced by the interaction of the jet
with the ambient medium and by the absorption properties of the obscuring
torus.Comment: 14 pages, 17 figures, submitted to A&
Effects of noise on hysteresis and resonance width in graphene and nanotubes resonators
We investigate the role that noise plays in the hysteretic dynamics of a
suspended nanotube or a graphene sheet subject to an oscillating force. We find
that not only the size but also the position of the hysteresis region in these
systems can be controlled by noise. We also find that nano-resonators act as
noise rectifiers: by increasing the noise in the setup, the resonance width of
the characteristic peak in these systems is reduced and, as a result, the
quality factor is increased.Comment: 15 pages, 6 figures. Sent to PRB (in revision
Rigidity of compact Riemannian spin Manifolds with Boundary
In this article, we prove new rigidity results for compact Riemannian spin
manifolds with boundary whose scalar curvature is bounded from below by a
non-positive constant. In particular, we obtain generalizations of a result of
Hang-Wang \cite{hangwang1} based on a conjecture of Schroeder and Strake
\cite{schroeder}.Comment: English version of "G\'eom\'etrie spinorielle extrins\`eque et
rigidit\'es", Corollary 6 in Section 3 added, to appear in Letters Math. Phy
Performance and entrepreneurial orientation in small firms : the moderating effects of strategy, structure, human resource policies and information systems.
Parallax and Kinematics of PSR B0919+06 from VLBA Astrometry and Interstellar Scintillometry
Results are presented from a long-term astrometry program on PSR B0919+06
using the NRAO Very Long Baseline Array. With ten observations (seven epochs)
between 1994--2000, we measure a proper motion of 18.35 +/- 0.06 mas/yr in RA,
86.56 +/- 0.12 mas/yr in Dec, and a parallax of 0.83 +/- 0.13 mas (68%
confidence intervals). This yields a pulsar distance of 1.21 +/- 0.19 kpc,
making PSR B0919+06 the farthest pulsar for which a trigonometric parallax has
been obtained, and the implied pulsar transverse speed is 505 +/- 80 km/s.
Combining the distance estimate with interstellar scintillation data spanning
20 years, we infer the existence of a patchy or clumpy scattering screen along
the line of sight in addition to the distributed electron density predicted by
models for the Galaxy, and constrain the location of this scattering region to
within about 250 parsecs of the Sun. Comparison with the lines of sight towards
other pulsars in the same quadrant of the Galaxy permits refinement of our
knowledge of the local interstellar matter in this direction.Comment: 12 pages, includes 4 figures and 3 tables, uses AASTeX 5 (included);
ApJ submitte
Colorimetric detection of caspase 3 activity and reactive oxygen derivatives: Potential early indicators of thermal stress in corals
© 2016 Mickael Ros et al. There is an urgent need to develop and implement rapid assessments of coral health to allow effective adaptive management in response to coastal development and global change. There is now increasing evidence that activation of caspase-dependent apoptosis plays a key role during coral bleaching and subsequent mortality. In this study, a "clinical" approach was used to assess coral health by measuring the activity of caspase 3 using a commercial kit. This method was first applied while inducing thermal bleaching in two coral species, Acropora millepora and Pocillopora damicornis. The latter species was then chosen to undergo further studies combining the detection of oxidative stress-related compounds (catalase activity and glutathione concentrations) as well as caspase activity during both stress and recovery phases. Zooxanthellae photosystem II (PSII) efficiency and cell density were measured in parallel to assess symbiont health. Our results demonstrate that the increased caspase 3 activity in the coral host could be detected before observing any significant decrease in the photochemical efficiency of PSII in the algal symbionts and/or their expulsion from the host. This study highlights the potential of host caspase 3 and reactive oxygen species scavenging activities as early indicators of stress in individual coral colonies
Toddlers may be getting enough iron in long day-care services after all
Background: Previous research has suggested that toddlers are not provided with adequate dietary iron in long-day care (LDC) services. However, the iron bioavailability provided is unknown. The present study aimed to investigate the amount and bioavailability of iron provided to toddlers aged 2–3 years at LDC services. Methods: A cross-sectional audit was conducted using a 2-day weighed food record of 30 LDC services. Iron provision (not child intake) in LDC services across Perth, Australia was compared with the estimated average requirements (EAR) and LDC services provision guidelines (50% of EAR = 2 mg/day based on a 14% bioavailability factor). Bioavailability was estimated per mealtime using haem and non-haem iron, ascorbic acid, animal protein, calcium, soy, eggs and phytates using two pre-existing algorithms (by A. P. Rickard and colleagues and H. Hallberg and H. Hulten). Results: Median iron supplied (2.52 mg/day, interquartile range [IQR] = 2.43–3.17) was above the 50% of EAR of 2.0 mg/day (p \u3c 0.001). Median bioavailable iron was 0.6 mg/day (IQR = 0.54–0.8) using the method of Rickard et al. and 0.51 mg/day (IQR = 0.43, 0.76 using that of Hallberg and Hulthen). The top three foods contributing to iron provision were bread, breakfast cereals and beef. Conclusions: Our results suggest that LDC services in Perth are meeting the minimum recommendation of provision of 50% of the iron EAR, and also that toddlers are provided with sufficient bioavailable iron. Future strategies should focus on promoting food combinations to maintain the iron bioavailability in meals currently served at LDC services
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