762 research outputs found
Binary Black Holes: Spin Dynamics and Gravitational Recoil
We present a study of spinning black hole binaries focusing on the spin
dynamics of the individual black holes as well as on the gravitational recoil
acquired by the black hole produced by the merger. We consider two series of
initial spin orientations away from the binary orbital plane. In one of the
series, the spins are anti-aligned; for the second series, one of the spins
points away from the binary along the line separating the black holes. We find
a remarkable agreement between the spin dynamics predicted at 2nd
post-Newtonian order and those from numerical relativity. For each
configuration, we compute the kick of the final black hole. We use the kick
estimates from the series with anti-aligned spins to fit the parameters in the
\KKF{,} and verify that the recoil along the direction of the orbital angular
momentum is and on the orbital plane ,
with the angle between the spin directions and the orbital angular
momentum. We also find that the black hole spins can be well estimated by
evaluating the isolated horizon spin on spheres of constant coordinate radius.Comment: 15 pages, 10 figures, replaced with version accepted for publication
in PR
Supermassive recoil velocities for binary black-hole mergers with antialigned spins
Recent calculations of the recoil velocity in binary black hole mergers have
found the kick velocity to be of the order of a few hundred km/s in the case of
non-spinning binaries and about km/s in the case of spinning
configurations, and have lead to predictions of a maximum kick of up to km/s. We test these predictions and demonstrate that kick velocities of at
least km/s are possible for equal-mass binaries with anti-aligned spins
in the orbital plane. Kicks of that magnitude are likely to have significant
repercussions for models of black-hole formation, the population of
intergalactic black holes and the structure of host galaxies.Comment: Final version, published by Phys. Rev. Lett.; title changed according
to suggestion of PRL; note added after preparation of manuscrip
Consumption and cultural commodification : the case of the museum as commodity
Marketing theory has traditionally sought explanation of commodity consumption based upon psychological and economic assumptions of needs, utility and exchange value, a paradigm of understanding that is becoming increasingly problematic. An alternative perspective of commodity consumption is presented, drawing on contemporary social and cultural theory where the commodity form
constitutes a cultural and social logic; a discourse of communication which consumers use to mediate and participate in daily life. Instead of defining commodities in terms of use value and economic value, the commodity is seen in terms of a specific subject-object relation experienced in late capitalism, manifest as sign value and sign exchange. Taking the case of the museum, a context that it increasingly applying the
terminology of the market, consumer and commodity; a qualitative research project is undertaken to asses the credibility of the cultural theoretical approach. It is proposed that the museum functions as a site of commodification, presenting history and culture as a set of commodities for visitors consumption. Whilst sign value is a useful concept in explaining commodity consumption, it is suggested a clear distinction between use value, exchange value and sign value is unworkable in practice and that utility and exchange value can be most accurately represented as cultural conditions rather than economic ones. The study suggests that
consumption should be conceptualised as a constructive, active and productive process which involves the consumer in a continual exchange, use and manipulation of signs. The role of marketing is thus most appropriately thought of as a facilitative capacity rather as a provisional or directive force that mediates consumption behaviour
Gravitational recoil from spinning binary black hole mergers
The inspiral and merger of binary black holes will likely involve black holes
with both unequal masses and arbitrary spins. The gravitational radiation
emitted by these binaries will carry angular as well as linear momentum. A net
flux of emitted linear momentum implies that the black hole produced by the
merger will experience a recoil or kick. Previous studies have focused on the
recoil velocity from unequal mass, non-spinning binaries. We present results
from simulations of equal mass but spinning black hole binaries and show how a
significant gravitational recoil can also be obtained in these situations. We
consider the case of black holes with opposite spins of magnitude
aligned/anti-aligned with the orbital angular momentum, with the
dimensionless spin parameters of the individual holes. For the initial setups
under consideration, we find a recoil velocity of V = 475 \KMS a.
Supermassive black hole mergers producing kicks of this magnitude could result
in the ejection from the cores of dwarf galaxies of the final hole produced by
the collision.Comment: 8 pages, 8 figures, replaced with version accepted for publication in
Ap
Binary black hole merger gravitational waves and recoil in the large mass ratio limit
Spectacular breakthroughs in numerical relativity now make it possible to
compute spacetime dynamics in almost complete generality, allowing us to model
the coalescence and merger of binary black holes with essentially no
approximations. The primary limitation of these calculations is now
computational. In particular, it is difficult to model systems with large mass
ratio and large spins, since one must accurately resolve the multiple
lengthscales which play a role in such systems. Perturbation theory can play an
important role in extending the reach of computational modeling for binary
systems. In this paper, we present first results of a code which allows us to
model the gravitational waves generated by the inspiral, merger, and ringdown
of a binary system in which one member of the binary is much more massive than
the other. This allows us to accurately calibrate binary dynamics in the large
mass ratio regime. We focus in this analysis on the recoil imparted to the
merged remnant by these waves. We closely examine the "antikick", an anti-phase
cancellation of the recoil arising from the plunge and ringdown waves,
described in detail by Schnittman et al. We find that, for orbits aligned with
the black hole spin, the antikick grows as a function of spin. The total recoil
is smallest for prograde coalescence into a rapidly rotating black hole, and
largest for retrograde coalescence. Amusingly, this completely reverses the
predicted trend for kick versus spin from analyses that only include inspiral
information.Comment: 15 pages, 5 figures. Submitted to Phys. Rev.
How black holes get their kicks: Gravitational radiation recoil revisited
Gravitational waves from the coalescence of binary black holes carry away
linear momentum, causing center of mass recoil. This "radiation rocket" effect
has important implications for systems with escape speeds of order the recoil
velocity. We revisit this problem using black hole perturbation theory,
treating the binary as a test mass spiraling into a spinning hole. For extreme
mass ratios (q = m1/m2 << 1) we compute the recoil for the slow inspiral epoch
of binary coalescence very accurately; these results can be extrapolated to q ~
0.4 with modest accuracy. Although the recoil from the final plunge contributes
significantly to the final recoil, we are only able to make crude estimates of
its magnitude. We find that the recoil can easily reach ~ 100-200 km/s, but
most likely does not exceed ~ 500 km/s. Though much lower than previous
estimates, this recoil is large enough to have important astrophysical
consequences. These include the ejection of black holes from globular clusters,
dwarf galaxies, and high-redshift dark matter halos.Comment: 4 pages, 2 figures, emulateapj style; minor changes made; accepted to
ApJ Letter
Non-surgical interventions for pelvic organ prolapse in rural Nepal: a prospective monitoring and evaluation study
OBJECTIVES: Pelvic organ prolapse (POP) is a major cause of morbidity in Nepal, particularly affecting women in the rural communities. Women with POP in Nepal may suffer from symptoms for decades. At present, the Government of Nepal advocates surgical intervention but access to surgical care is inadequate. This report evaluated the feasibility of a non-surgical public health programme in rural Nepal, and describes risk factors associated with POP in this setting. DESIGN: Prospective monitoring and evaluation study of a new public health programme. SETTING: Baglung district, rural Nepal. PARTICIPANTS: Women with gynaecological symptoms of POP. MAIN OUTCOME MEASURES: Risk factors for disease progression were assessed using Fisher’s exact test, Pearson’s χ(2)-test and logistic regression analysis. RESULTS: Of the 74 women included in this analysis, 70.8% were diagnosed with stage 2 POP or greater. The majority of women did not have any further children following the onset of POP symptoms (63.5%). Duration of symptoms ranged from 2 months to 60 years, with 73.4% of women suffering for over 5 years and 28.4% suffering for over 20 years. Univariate analyses identified age at screening, age at onset of symptoms, the duration of symptoms and an associated rectocele as factors associated with increasing POP severity (p < 0.05). Kegel exercises were taught to 25 (33.8%) women with POP and ring pessaries were offered to 47 (63.5%) women with POP. CONCLUSIONS: Non-surgical interventions may provide an opportunity to address the significant burden of POP in rural Nepal
Recoil velocity at 2PN order for spinning black hole binaries
We compute the flux of linear momentum carried by gravitational waves emitted
from spinning binary black holes at 2PN order for generic orbits. In particular
we provide explicit expressions of three new types of terms, namely
next-to-leading order spin-orbit terms at 1.5 PN order, spin-orbit tail terms
at 2PN order, and spin-spin terms at 2PN order. Restricting ourselves to
quasi-circular orbits, we integrate the linear momentum flux over time to
obtain the recoil velocity as function of orbital frequency. We find that in
the so-called superkick configuration the higher-order spin corrections can
increase the recoil velocity up to about a factor 3 with respect to the
leading-order PN prediction. Furthermore, we provide expressions valid for
generic orbits, and accurate at 2PN order, for the energy and angular momentum
carried by gravitational waves emitted from spinning binary black holes.
Specializing to quasi-circular orbits we compute the spin-spin terms at 2PN
order in the expression for the evolution of the orbital frequency and found
agreement with Mik\'oczi, Vas\'uth and Gergely. We also verified that in the
limit of extreme mass ratio our expressions for the energy and angular momentum
fluxes match the ones of Tagoshi, Shibata, Tanaka and Sasaki obtained in the
context of black hole perturbation theory.Comment: 28 pages (PRD format), 1 figure, reference added, version published
in PRD, except that the PRD version contains a sign error: the sign of the
RHS of Eqs.(4.26) and (4.27) is wrong; it has been corrected in this
replacemen
Gravitational wave recoil in Robinson-Trautman spacetimes
We consider the gravitational recoil due to non-reflection-symmetric
gravitational wave emission in the context of axisymmetric Robinson-Trautman
spacetimes. We show that regular initial data evolve generically into a final
configuration corresponding to a Schwarzschild black-hole moving with constant
speed. For the case of (reflection-)symmetric initial configurations, the mass
of the remnant black-hole and the total energy radiated away are completely
determined by the initial data, allowing us to obtain analytical expressions
for some recent numerical results that have been appeared in the literature.
Moreover, by using the Galerkin spectral method to analyze the non-linear
regime of the Robinson-Trautman equations, we show that the recoil velocity can
be estimated with good accuracy from some asymmetry measures (namely the first
odd moments) of the initial data. The extension for the non-axisymmetric case
and the implications of our results for realistic situations involving head-on
collision of two black holes are also discussed.Comment: 9 pages, 6 figures, final version to appear in PR
Construction and testing of a low-cost device for the collection of rainfall samples destined for stable isotope analysis
Oxygen- and hydrogen-isotope ratios in rainfall provide important hydroclimatic information, yet despite a global network of rainfall isotope measurements, significant geographical gaps exist in data coverage, with only three long-term stations spanning the southern African region. Project-based, ad hoc collections of rainfall for isotope analysis can improve this coverage. However, all rainfall samples that are destined for stable isotope analysis must be collected in such a way to avoid evaporation and resultant isotope fractionation. While such rainwater collectors are available commercially, both the product and shipping are prohibitively costly. We describe the construction of a simple rainfall collector using a design from the literature and materials that are readily available in South African hardware stores. Our rainwater collector can be constructed for the much lower cost of just under ZAR820 in comparison with the cost of ZAR9300 inclusive of shipping from commercial outlets (2022 prices). Our design modifications have the added advantage of portability, with the rainwater collector housed in a bucket with a handle. The device was tested by comparing its performance, in terms of evaporative water loss and isotopic fractionation, with that of an open bottle, using tap water in both cases. Testing confirmed that the collector prevented evaporation over a one-week period, indicating that it is suitable for weekly or more frequent sampling of rainfall. Although the design described was based on materials procured in South Africa, it could easily be adapted for construction elsewhere
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