4,297 research outputs found
Optical polarization angle and VLBI jet direction in the binary black hole model of OJ287
We study the variation of the optical polarization angle in the blazar OJ287
and compare it with the precessing binary black hole model with a 'live'
accretion disk. First, a model of the variation of the jet direction is
calculated, and the main parameters of the model are fixed by the long term
optical brightness evolution. Then this model is compared with the variation of
the parsec scale radio jet position angle in the sky. Finally, the variation of
the polarization angle is calculated using the same model, but using a magnetic
field configuration which is at a constant angle relative to the optical jet.
It is found that the model fits the data reasonably well if the field is almost
parallel to the jet axis. This may imply a steady magnetic field geometry, such
as a large-scale helical field.Comment: to appear in Monthly Notices of Royal Astronomical Societ
Testing black hole no-hair theorem with OJ287
We examine the ability to test the black hole no-hair theorem at the 10%
level in this decade using the binary black hole in OJ287. In the test we
constrain the value of the dimensionless parameter q that relates the scaled
quadrupole moment and spin of the primary black hole: q2 = -q 2 . At the
present we can say that q = 1 \pm 0.3 (one), in agreement with General
Relativity and the no-hair theorems. We demonstrate that this result can be
improved if more observational data is found in historical plate archives for
the 1959 and 1971 outbursts. We also show that the predicted 2015 and 2019
outbursts will be crucial in improving the accuracy of the test. Space-based
photometry is required in 2019 July due the proximity of OJ287 to the Sun at
the time of the outburst. The best situation would be to carry out the
photometry far from the Earth, from quite a different vantage point, in order
to avoid the influence of the nearby Sun. We have considered in particular the
STEREO space mission which would be ideal if it has a continuation in 2019 or
LORRI on board the New Horizons mission to Pluto.Comment: 14 pages, 14 figure
Uses of Economic Rhetoric â Told by Designers, Represented by Economic Press
The design discipline is constantly moving and reshaping itself. As the practices are often new and still evolving, the professionals in the field need to position their own activities to the context in which they are practiced (Valtonen, 2007). In the case of industrial design, the practice is conducted and increasingly discussed in the realm of the economic world. When issues such as global competitiveness or companiesâ competitive advantages are discussed, design is often seen as a mean to improve business. This is the case especially where(onko tĂ€mĂ€ where ok?) competing on merely price or technological advantage becomes increasingly difficult. This paper shows how the designers present industrial design as an economically viable action and how the economic press represents industrial design in the context of economy.
Keywords:
Economic Rhetoric; Industrial Design; Interviews; Media; Rhetorical Analysis</p
A helical jet model for OJ287
Context. OJ287 is a quasar with a quasi-periodic optical light curve, with
the periodicity observed for over 120 years. This has lead to a binary black
hole model as a common explanation of the quasar. The radio jet of OJ287 has
been observed for a shorter time of about 30 years. It has a complicated
structure that varies dramatically in a few years time scale. Aims. Here we
propose that this structure arises from a helical jet being observed from a
small and varying viewing angle. The viewing angle variation is taken to be in
tune with the binary orbital motion. Methods. We calculate the effect of the
secondary black hole on the inner edge of the accretion disk of the primary
using particle simulations. We presume that the axis of the helix is
perpendicular to the disk. We then follow the jet motion on its helical path
and project the jet to the sky plane. This projection is compared with
observations both at mm waves and cm waves. Results. We find that this model
reproduces the observations well if the changes in the axis of the conical
helix propagate outwards with a relativistic speed of about 0.85c. In
particular, this model explains at the same time the long-term optical
brightness variations as varying Doppler beaming in a component close to the
core, i.e. at parsec scale in real linear distance, while the mm and cm radio
jet observations are explained as being due to jet wobble at much larger (100
parsec scale) distances from the core.Comment: 5 pages, 7 figures, to be published in Astronomy & Astrophysic
Foundations of multiple black hole evolutions
We present techniques for long-term, stable, and accurate evolutions of
multiple-black-hole spacetimes using the `moving puncture' approach with
fourth- and eighth-order finite difference stencils. We use these techniques to
explore configurations of three black holes in a hierarchical system consisting
of a third black hole approaching a quasi-circular black-hole binary, and find
that, depending on the size of the binary, the resulting encounter may lead to
a prompt merger of all three black holes, production of a highly elliptical
binary (with the third black hole remaining unbound), or disruption of the
binary (leading to three free black holes). We also analyze the classical
Burrau three-body problem using full numerical evolutions. In both cases, we
find behaviors distinctly different from Newtonian predictions, which has
important implications for N-body black-hole simulations. For our simulations
we use analytic approximate data. We find that the eighth-order stencils
significantly reduce the numerical errors for our choice of grid sizes, and
that the approximate initial data produces the expected waveforms (after a
rescaling of the puncture masses) for black-hole binaries with modest initial
separations.Comment: Revtex 4, 13 pages, 15 figure
Measuring the spin of the primary black hole in OJ287
The compact binary system in OJ287 is modelled to contain a spinning primary
black hole with an accretion disk and a non-spinning secondary black hole.
Using Post Newtonian (PN) accurate equations that include 2.5PN accurate
non-spinning contributions, the leading order general relativistic and
classical spin-orbit terms, the orbit of the binary black hole in OJ287 is
calculated and as expected it depends on the spin of the primary black hole.
Using the orbital solution, the specific times when the orbit of the secondary
crosses the accretion disk of the primary are evaluated such that the record of
observed outbursts from 1913 up to 2007 is reproduced. The timings of the
outbursts are quite sensitive to the spin value. In order to reproduce all the
known outbursts, including a newly discovered one in 1957, the Kerr parameter
of the primary has to be . The quadrupole-moment contributions
to the equations of motion allow us to constrain the `no-hair' parameter to be
where 0.3 is the one sigma error. This supports the `black hole
no-hair theorem' within the achievable precision.
It should be possible to test the present estimate in 2015 when the next
outburst is due. The timing of the 2015 outburst is a strong function of the
spin: if the spin is 0.36 of the maximal value allowed in general relativity,
the outburst begins in early November 2015, while the same event starts in the
end of January 2016 if the spin is 0.2Comment: 12 pages, 6 figure
Iron-rich solar particle events measured by SOHO/ERNE during two solar cycles
We study the differences in the heavy ion composition of solar energetic
particle (SEP) events between solar cycles 23 and 24. We have surveyed the
SOHO/ERNE heavy ion data from the beginning of solar cycle 23 until the end of
June 2015, that is, well into the declining phase of cycle 24. We used this
long observation period to study the properties of heavy ions (from C to Fe)
and to compare the two solar cycles in this respect. We surveyed the data for
SEP events with enhancements in the Fe/C and Fe/O intensity ratios in the
energy range 5-15 MeV per nucleon, and associated the events with solar flare
and coronal mass ejections (CME) when possible. We studied the properties of
heavy ions in these events and compared the average relative abundances of
heavy ions between the two solar cycles. We found that fewer days had C and O
intensities higher than ~10
cmsrs(MeVn) during solar cycle 24 than
during cycle 23. For Fe this difference was clear even at lower intensities. We
also found that fewer days had Fe/(C+O) > 0.183 during cycle 24. We identified
86 SEP events with at least one Fe-rich day, 65 of which occurred during cycle
23 and only 21 during cycle 24. We found that impulsive events have been almost
completely absent during cycle 24. Mean abundances of heavy ions in the events
were found to be significantly lower during cycle 24 than in cycle 23. Our
results reflect the reduced solar activity in cycle 24 and indicate lower
efficiency of particle acceleration processes for both gradual and impulsive
SEP events in cycle 24.Comment: 14 pages, 9 figures and 3 tables. To be published in A&
Preventing pain on injection of propofol: A comparison between lignocaine pre-treatment and lignocaine added to propofol
Publisher's copy made available with the permission of the publisherA randomized double-blind study compared two methods of preventing the pain from injection of propofol, lignocaine pre-treatment followed by propofol and lignocaine added to propofol. One hundred patients received a 4 ml solution intravenously with a venous tourniquet for 1 minute, followed by propofol mixed with 2 ml of solution. Patients were divided into two treatment groups of 50 patients each: 4 ml 1% lignocaine pre-treatment followed by propofol and 2 ml saline, or 4 ml saline followed by propofol and 2 ml 2% lignocaine. Pain was assessed with a 100 mm visual analogue scale after induction and in recovery. The incidence of injection pain was 8% in the propofol mixed with lignocaine group, and 28% in the lignocaine pre-treatment group. This difference is statistically significant (P=0.017). For those patients who had pain, the mean pain score was 26.5 on induction for the propofol with lignocaine group (n=4), while the mean score was 44.4 for the pre-treatment group (n=13). The difference was not statistically significant (P=0.25). None of the propofol mixed with lignocaine group recalled pain, while 13 of the pre-treatment group did so. Lignocaine pre-treatment does not improve the immediate or the recalled comfort of patients during propofol induction when compared to lignocaine added to propofol. It is recommended that lignocaine should be added to propofol for induction rather than given before induction.P. Lee, W. J. Russellhttp://www.aaic.net.au/Article.asp?D=200339
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