16,087 research outputs found
The dominant X-ray wind in massive star binaries
We investigate which shocked wind is responsible for the majority of the
X-ray emission in colliding wind binaries, an issue where there is some
confusion in the literature, and which we show is more complicated than has
been assumed. We find that where both winds rapidly cool (typically close
binaries), the ratio of the wind speeds is often more important than the
momentum ratio, because it controls the energy flux ratio, and the faster wind
is generally the dominant emitter. When both winds are largely adiabatic
(typically long-period binaries), the slower and denser wind will cool faster
and the stronger wind generally dominates the X-ray luminosity.Comment: 4 pages, 1 figure, accepted by A&A Letter
Power-Off Tests of the Northrop N9M-2 Tailless Airplane in the 40- by 80-foot Wind Tunnel
No abstract availabl
Probing the wind-wind collision in Gamma Velorum with high-resolution Chandra X-ray spectroscopy: evidence for sudden radiative braking and non-equilibrium ionization
We present a new analysis of an archived Chandra HETGS X-ray spectrum of the
WR+O colliding wind binary Gamma Velorum. The spectrum is dominated by emission
lines from astrophysically abundant elements: Ne, Mg, Si, S and Fe. From a
combination of broad-band spectral analysis and an analysis of line flux ratios
we infer a wide range of temperatures in the X-ray emitting plasma (~4-40 MK).
As in the previously published analysis, we find the X-ray emission lines are
essentially unshifted, with a mean FWHM of 1240 +/- 30 km/s. Calculations of
line profiles based on hydrodynamical simulations of the wind-wind collision
predict lines that are blueshifted by a few hundred km/s. The lack of any
observed shift in the lines may be evidence of a large shock-cone opening
half-angle (> 85 degrees), and we suggest this may be evidence of sudden
radiative braking. From the R and G ratios measured from He-like
forbidden-intercombination-resonance triplets we find evidence that the Mg XI
emission originates from hotter gas closer to the O star than the Si XIII
emission, which suggests that non-equilibrium ionization may be present.Comment: 22 pages, 14 figures. Accepted for publication in MNRA
Strange Hadron Spectroscopy with a Secondary KL Beam at GlueX
We propose to create a secondary beam of neutral kaons in Hall D at Jefferson
Lab to be used with the GlueX experimental setup for strange hadron
spectroscopy. A flux on the order of 3 x 10^4 KL/s will allow a broad range of
measurements to be made by improving the statistics of previous data obtained
on hydrogen targets by three orders of magnitude. Use of a deuteron target will
provide first measurements on the neutron which is {\it terra incognita}.
The experiment will measure both differential cross sections and
self-analyzed polarizations of the produced {\Lambda}, {\Sigma}, {\Xi}, and
{\Omega} hyperons using the GlueX detector at the Jefferson Lab Hall D. The
measurements will span c.m. cos{\theta} from -0.95 to 0.95 in the c.m. range
above W = 1490 MeV and up to 3500 MeV. These new GlueX data will greatly
constrain partial-wave analyses and reduce model-dependent uncertainties in the
extraction of strange resonance properties (including pole positions), and
provide a new benchmark for comparisons with QCD-inspired models and lattice
QCD calculations.
The proposed facility will also have an impact in the strange meson sector by
providing measurements of the final-state K{\pi} system from threshold up to 2
GeV invariant mass to establish and improve on the pole positions and widths of
all K*(K{\pi}) P-wave states as well as for the S-wave scalar meson
{\kappa}(800).Comment: 97 pages, 63 figures, Proposal for JLab PAC45, PR12-17-001; v3 missed
citation in Sec 9 (pg 22
Effect of the Coriolis Force on the Hydrodynamics of Colliding Wind Binaries
Using fully three-dimensional hydrodynamic simulations, we investigate the
effect of the Coriolis force on the hydrodynamic and observable properties of
colliding wind binary systems. To make the calculations tractable, we assume
adiabatic, constant velocity winds. The neglect of radiative driving,
gravitational deceleration, and cooling limit the application of our models to
real systems. However, these assumptions allow us to isolate the effect of the
Coriolis force, and by simplifying the calculations, allow us to use a higher
resolution (up to 640^3) and to conduct a larger survey of parameter space. We
study the dynamics of collidng winds with equal mass loss rates and velocities
emanating from equal mass stars on circular orbits, with a range of values for
the ratio of the wind to orbital velocity. We also study the dynamics of winds
from stars on elliptical orbits and with unequal strength winds. Orbital motion
of the stars sweeps the shocked wind gas into an Archimedean spiral, with
asymmetric shock strengths and therefore unequal postshock temperatures and
densities in the leading and trailing edges of the spiral. We observe the
Kelvin-Helmholtz instability at the contact surface between the shocked winds
in systems with orbital motion even when the winds are identical. The change in
shock strengths caused by orbital motion increases the volume of X-ray emitting
post-shock gas with T > 0.59 keV by 63% for a typical system as the ratio of
wind velocity to orbital velocity decreases to V_w/V_o = 2.5. This causes
increased free-free emission from systems with shorter orbital periods and an
altered time-dependence of the wind attenuation. We comment on the importance
of the effects of orbital motion on the observable properties of colliding wind
binaries.Comment: 12 pages, 17 figures, accepted for publication in Ap
The cool wake around 4C 34.16 as seen by XMM-Newton
We present XMM-Newton observations of the wake-radiogalaxy system 4C34.16,
which shows a cool and dense wake trailing behind 4C34.16's host galaxy. A
comparison with numerical simulations is enlightening, as they demonstrate that
the wake is produced mainly by ram pressure stripping during the galactic
motion though the surrounding cluster. The mass of the wake is a substantial
fraction of the mass of an elliptical galaxy's X-ray halo. This observational
fact supports a wake formation scenario similar to the one demonstrated
numerically by Acreman et al (2003): the host galaxy of 4C34.16 has fallen into
its cluster, and is currently crossing its central regions. A substantial
fraction of its X-ray halo has been stripped by ram pressure, and remains
behind to form the galaxy wake.Comment: 9 pages, 6 figures, accepted for publication in MNRA
The investigation of particle acceleration in colliding-wind massive binaries with SIMBOL-X
An increasing number of early-type (O and Wolf-Rayet) colliding wind binaries
(CWBs) is known to accelerate particles up to relativistic energies. In this
context, non-thermal emission processes such as inverse Compton (IC) scattering
are expected to produce a high energy spectrum, in addition to the strong
thermal emission from the shock-heated plasma. SIMBOL-X will be the ideal
observatory to investigate the hard X-ray spectrum (above 10 keV) of these
systems, i.e. where it is no longer dominated by the thermal emission. Such
observations are strongly needed to constrain the models aimed at understanding
the physics of particle acceleration in CWB. Such systems are important
laboratories for investigating the underlying physics of particle acceleration
at high Mach number shocks, and probe a different region of parameter space
than studies of supernova remnants.Comment: 2 pages, 2 figures, to appear in the proceedings of the workshop
"Simbol-X: the hard X-ray universe in focus", held in Bologna, Italy (14-16
May 2007
CXCR4-targeted and MMP-responsive iron oxide nanoparticles for enhanced magnetic resonance imaging
MRI offers high spatial resolution with excellent tissue penetration but it has limited sensitivity and the commonly administered contrast agents lack specificity. In this study, two sets of iron oxide nanoparticles (IONPs) were synthesized that were designed to selectively undergo copper-free click conjugation upon sensing of matrix metalloproteinase (MMP) enzymes, thereby leading to a self-assembled superparamagnetic nanocluster network with T2 signal enhancement properties. For this purpose, IONPs with bioorthogonal azide and alkyne surfaces masked by polyethylene glycol (PEG) layers tethered to CXCR4-targeted peptide ligands were synthesized and characterized. The IONPs were tested in vitro and T2 signal enhancements of around 160 % were measured when the IONPs were incubated with cells expressing MMP2/9 and CXCR4. Simultaneous systemic administration of the bioorthogonal IONPs in tumor-bearing mice demonstrated the signal-enhancing ability of these ‘smart’ self-assembling nanomaterials
Modeling urban street patterns
Urban streets patterns form planar networks whose empirical properties cannot
be accounted for by simple models such as regular grids or Voronoi
tesselations. Striking statistical regularities across different cities have
been recently empirically found, suggesting that a general and
details-independent mechanism may be in action. We propose a simple model based
on a local optimization process combined with ideas previously proposed in
studies of leaf pattern formation. The statistical properties of this model are
in good agreement with the observed empirical patterns. Our results thus
suggests that in the absence of a global design strategy, the evolution of many
different transportation networks indeed follow a simple universal mechanism.Comment: 4 pages, 5 figures, final version published in PR
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