4,731 research outputs found
The Power of Jets: New Clues from Radio Circular Polarization and X-rays
Jets are ubiquitous in accreting black holes. Often ignored, they may be a
major contributor to the emitted spectral energy distribution for sub-Eddington
black holes. For example, recent observations of radio-to-X-ray correlations
and broad band spectra of X-ray binaries in the low/hard state can be explained
by a significant synchrotron contribution from jets also to their IR-to-X-ray
spectrum as proposed by Markoff, Falcke, Fender 2001. This model can also
explain state-transitions from low/hard to high/soft states. Relativistic
beaming of the jet X-ray emission could lead to the appearance of seemingly
Super-Eddington X-rays sources in other galaxies. We show that a simple
population synthesis model of X-ray binaries with relativistic beaming can well
explain the currently found distribution of off-nucleus X-ray point sources in
nearby galaxies. Specifically we suggest that the so-called ultra-luminous
X-ray sources (ULXs, also IXOs) could well be relativistically beamed
microblazars. The same model that can be used to explain X-ray binaries also
fits Low-Luminosity AGN (LLAGN) and especially Sgr A* in the Galactic Center.
The recent detection of significant circular polarization in AGN radio cores,
ranging from bright quasars down to low-luminosity AGN like M81*, Sgr A* and
even X-ray binaries, now places additional new constraints on the matter
contents of such jets. The emerging picture are powerful jets with a mix of hot
and cold matter, a net magnetic flux, and a stable magnetic north pole.Comment: to appear in: ``Lighthouses of the Universe'', Springer Verlag, ESO
Astrophysics Symposia, Eds: R.Sunyaev, M.Gilfanov, E.Churazov, LaTex, 8
pages, 5 figures, also available at
http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#lighthouse
Dusty Disks Around Central Stars of Planetary Nebulae
Only a few percent of cool, old white dwarfs (WDs) have infrared excesses
interpreted as originating in small hot disks due to the infall and destruction
of single asteroids that come within the star's Roche limit. Infrared excesses
at 24 micron were also found to derive from the immediate vicinity of younger,
hot WDs, most of which are still central stars of planetary nebulae (CSPN). The
incidence of CSPN with this excess is 18%. The Helix CSPN, with a 24 micron
excess, has been suggested to have a disk formed from collisions of Kuiper
belt-like objects (KBOs). In this paper, we have analyzed an additional sample
of CSPN to look for similar infrared excesses. These CSPN are all members of
the PG 1159 class and were chosen because their immediate progenitors are known
to often have dusty environments consistent with large dusty disks. We find
that, overall, PG 1159 stars do not present such disks more often than other
CSPN, although the statistics (5 objects) are poor. We then consider the entire
sample of CSPN with infrared excesses, and compare it to the infrared
properties of old WDs, as well as cooler post-AGB stars. We conclude with the
suggestion that the infrared properties of CSPN more plausibly derive from
AGB-formed disks rather than disks formed via the collision of KBOs, although
the latter scenario cannot be ruled out. We finally remark that there seems to
be an association between CSPN with a 24 micron excess and confirmed or
possible binarity of the central star.Comment: 11 pages, 5 figures, AJ, in pres
Parametric Study on the Effect of Partial Charge on Water Infiltration Behavior in MFI Zeolites
This work analyzes the infiltration behavior of water into sub-nanometer MFI zeolite pores using molecular dynamics simulations. Infiltration simulations are run for a range of partial charge values on the zeolite atoms. Infiltration behavior is compared to partial charges to verify dependence and determine critical charge above which infiltration becomes severely inhibited even at high pressures. Attraction energy is calculated and correlated to the observed infiltration behavior. The critical partial charge of Si~1.8 occurs when the waterzeolite interaction energy becomes stronger than water-water attraction due to which water molecules get stuck and infiltration is significantly reduced. Topics: Wate
Proteolytic regulation of calcium channels - avoiding controversy
The publication of papers containing data obtained with suboptimal rigor in the experimental design and choice of key reagents, such as antibodies, can result in a lack of reproducibility and generate controversy that can both needlessly divert resources and, in some cases, damage public perception of the scientific enterprise. This exemplary paper by Buonarati et al. (2018)1 shows how a previously published, potentially important paper on calcium channel regulation falls short of the necessary mark, and aims to resolve the resulting controversy
Denuder tube preconcentration and detection of gaseous ammonia using a coated quartz piezoelectric crystal
Fast spin exchange between two distant quantum dots
The Heisenberg exchange interaction between neighboring quantum dots allows
precise voltage control over spin dynamics, due to the ability to precisely
control the overlap of orbital wavefunctions by gate electrodes. This allows
the study of fundamental electronic phenomena and finds applications in quantum
information processing. Although spin-based quantum circuits based on
short-range exchange interactions are possible, the development of scalable,
longer-range coupling schemes constitutes a critical challenge within the
spin-qubit community. Approaches based on capacitative coupling and
cavity-mediated interactions effectively couple spin qubits to the charge
degree of freedom, making them susceptible to electrically-induced decoherence.
The alternative is to extend the range of the Heisenberg exchange interaction
by means of a quantum mediator. Here, we show that a multielectron quantum dot
with 50-100 electrons serves as an excellent mediator, preserving speed and
coherence of the resulting spin-spin coupling while providing several
functionalities that are of practical importance. These include speed (mediated
two-qubit rates up to several gigahertz), distance (of order of a micrometer),
voltage control, possibility of sweet spot operation (reducing susceptibility
to charge noise), and reversal of the interaction sign (useful for dynamical
decoupling from noise).Comment: 6 pages including 4 figures, plus 8 supplementary pages including 5
supplementary figure
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