146 research outputs found
Renormalized spin coefficients in the accumulated orbital phase for unequal mass black hole binaries
We analyze galactic black hole mergers and their emitted gravitational waves.
Such mergers have typically unequal masses with mass ratio of the order 1/10.
The emitted gravitational waves carry the inprint of spins and mass quadrupoles
of the binary components. Among these contributions, we consider here the
quasi-precessional evolution of the spins. A method of taking into account
these third post-Newtonian (3PN) effects by renormalizing (redefining) the 1.5
PN and 2PN accurate spin contributions to the accumulated orbital phase is
developed.Comment: 10 pages, to appear in Class. Quantum Grav. GWDAW13 Proceedings
Special Issue, v2: no typos conjectur
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Binding energy referencing for XPS in Alkali metal-based battery materials research (II): Application to complex composite electrodes
X-ray photoelectron spectroscopy (XPS) is a key method for studying (electro-)chemical changes in metal-ion battery electrode materials. In a recent publication, we pointed out a conflict in binding energy (BE) scale referencing at alkali metal samples, which is manifested in systematic deviations of the BEs up to several eV due to a specific interaction between the highly reactive alkali metal in contact with non-conducting surrounding species. The consequences of this phenomenon for XPS data interpretation are discussed in the present manuscript. Investigations of phenomena at surface-electrolyte interphase regions for a wide range of materials for both lithium and sodium-based applications are explained, ranging from oxide-based cathode materials via alloys and carbon-based anodes including appropriate reference chemicals. Depending on material class and alkaline content, specific solutions are proposed for choosing the correct reference BE to accurately define the BE scale. In conclusion, the different approaches for the use of reference elements, such as aliphatic carbon, implanted noble gas or surface metals, partially lack practicability and can lead to misinterpretation for application in battery materials. Thus, this manuscript provides exemplary alternative solutions
The spin-flip phenomenon in supermassive black hole binary mergers
Massive merging black holes will be the primary sources of powerful
gravitational waves at low frequency, and will permit to test general
relativity with candidate galaxies close to a binary black hole merger. In this
paper we identify the typical mass ratio of the two black holes but then show
that the distance when gravitational radiation becomes the dominant dissipative
effect (over dynamical friction) does not depend on the mass ratio. However the
dynamical evolution in the gravitational wave emission regime does. For the
typical range of mass ratios the final stage of the merger is preceded by a
rapid precession and a subsequent spin-flip of the main black hole. This
already occurs in the inspiral phase, therefore can be described analytically
by post-Newtonian techniques. We then identify the radio galaxies with a
super-disk as those in which the rapidly precessing jet produces effectively a
powerful wind, entraining the environmental gas to produce the appearance of a
thick disk. These specific galaxies are thus candidates for a merger of two
black holes to happen in the astronomically near future.Comment: v3: 36 pages, 1 figure; discussion on the validity of the model and
estimates for the angular value of the spin-flip added to Section 5; v4:
minor changes, 2 new references, published versio
Binary black holes and tori in AGN II. Can stellar winds constitute a dusty torus?
We determine the properties of the stellar torus that we showed in a previous
paper to result as a product of two merging black holes. If the surrounding
stellar cluster is as massive as the binary black hole, the torque acting on
the stars ejects a fraction which extracts all the binary's angular momentum on
scales of ~10^7 yr, and a geometrically thick torus remains. In the present
article we show that a certain fraction of the stars has winds, shaped into
elongated tails by the central radiation pressure, which are optically thick
for line of sights aligned with them. These stars are sufficiently numerous to
achieve a covering factor of 1, so that the complete torus is optically thick.
We find the parameters of such a patchy torus to be in the right range to
explain the observed large column densities in AGN and their temporal
variations on time scales of about a decade. Within this model the BAL quasars
can be interpreted as quasars seen at intermediate inclination angles, with the
line of sight grazing the edge of the torus. The opening angle of the torus is
wider for major mergers and thus correlates with the central luminosity. In
this picture the spin of the merged black hole is possibly dominated by the
orbital angular momentum of the binary. Thus the spin of the merged black hole
points into a new direction, and consequently the jet experiences a spin-flip
according to the spin-paradigm. This re-orientation could be an explanation for
the X-shaped radio galaxies, and the advancing of a new jet through the ambient
medium for Compact Symmetric Objects.Comment: 20 pages, 10 figures, final version, A&A accepte
Active Galactic Nuclei: Sources for ultra high energy cosmic rays?
The origin of ultra high energy cosmic rays promises to lead us to a deeper
understanding of the structure of matter. This is possible through the study of
particle collisions at center-of-mass energies in interactions far larger than
anything possible with the Large Hadron Collider, albeit at the substantial
cost of no control over the sources and interaction sites. For the extreme
energies we have to identify and understand the sources first, before trying to
use them as physics laboratories. Here we describe the current stage of this
exploration. The most promising contenders as sources are radio galaxies and
gamma ray bursts. The sky distribution of observed events yields a hint
favoring radio galaxies. Key in this quest are the intergalactic and galactic
magnetic fields, whose strength and structure are not yet fully understood.
Current data and statistics do not yet allow a final judgment. We outline how
we may progress in the near future.Comment: proceedings for "Origin, Mass, Composition and Acceleration
Mechanisms of UHECRs (CRIS 2008)" in Malfa (Salina Island - Italy) on
September 15-19, 200
FIRST `Winged' and `X'-shaped Radio Source Candidates
A small number of double-lobed radio galaxies (17 from our own census of the
literature) show an additional pair of low surface brightness `wings', thus
forming an overall `X'-shaped appearance. The origin of the wings in these
radio sources is unclear. They may be the result of back-flowing plasma from
the currently active radio lobes into an asymmetric medium surrounding the
active nucleus, which would make these ideal systems in which to study
thermal/non-thermal plasma interactions in extragalactic radio sources. Another
possibility is that the wings are the aging radio lobes left over after a
(rapid) realignment of the central supermassive black-hole/accretion disk
system due perhaps to a merger. Generally, these models are not well tested;
with the small number of known examples, previous works focused on detailed
case studies of selected sources with little attempt at a systematic study of a
large sample. Using the VLA-FIRST survey database, we are compiling a large
sample of winged and X-shaped radio sources for such studies. As a first step
toward this goal, an initial sample of 100 new candidate objects of this type
are presented in this paper. ...[abridged]Comment: (all comments same as v2 except updated external link) AJ, accepted.
36 pgs. Added low resolution figures but table 2 still incomplete. Otherwise,
unchanged from previous astro-ph version. For complete version and table 2:
http://www.slac.stanford.edu/~teddy/Preprints/xshaped.pdf.g
Detecting One-Hundred-Year Environmental Changes in Western China Using Seven-Year Repeat Photography
Due to its diverse, wondrous plants and unique topography, Western China has drawn great attention from explorers and naturalists from the Western World. Among them, Ernest Henry Wilson (1876 –1930), known as ‘Chinese’ Wilson, travelled to Western China five times from 1899 to 1918. He took more than 1,000 photos during his travels. These valuable photos illustrated the natural and social environment of Western China a century ago. Since 1997, we had collected E.H. Wilson's old pictures, and then since 2004, along the expedition route of E.H. Wilson, we took 7 years to repeat photographing 250 of these old pictures. Comparing Wilson's photos with ours, we found an obvious warming trend over the 100 years, not only in specific areas but throughout the entire Western China. Such warming trend manifested in phenology changes, community shifts and melting snow in alpine mountains. In this study, we also noted remarkable vegetation changes. Out of 62 picture pairs were related to vegetation change, 39 indicated vegetation has changed to the better condition, 17 for degraded vegetation and six for no obvious change. Also in these photos at a century interval, we found not only rapid urbanization in Western China, but also the disappearance of traditional cultures. Through such comparisons, we should not only be amazed about the significant environmental changes through time in Western China, but also consider its implications for protecting environment while meeting the economic development beyond such changes
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