3,032 research outputs found
Gravitational-wave detectability of equal-mass black-hole binaries with aligned spins
Binary black-hole systems with spins aligned or anti-aligned to the orbital
angular momentum provide the natural ground to start detailed studies of the
influence of strong-field spin effects on gravitational wave observations of
coalescing binaries. Furthermore, such systems may be the preferred end-state
of the inspiral of generic supermassive binary black-hole systems. In view of
this, we have computed the inspiral and merger of a large set of binary systems
of equal-mass black holes with spins parallel to the orbital angular momentum
but otherwise arbitrary. Our attention is particularly focused on the
gravitational-wave emission so as to quantify how much spin effects contribute
to the signal-to-noise ratio, to the horizon distances, and to the relative
event rates for the representative ranges in masses and detectors. As expected,
the signal-to-noise ratio increases with the projection of the total black hole
spin in the direction of the orbital momentum. We find that equal-spin binaries
with maximum spin aligned with the orbital angular momentum are more than
"three times as loud" as the corresponding binaries with anti-aligned spins,
thus corresponding to event rates up to 30 times larger. We also consider the
waveform mismatch between the different spinning configurations and find that,
within our numerical accuracy, binaries with opposite spins S_1=-S_2 cannot be
distinguished whereas binaries with spin S_1=S_2 have clearly distinct
gravitational-wave emissions. Finally, we derive a simple expression for the
energy radiated in gravitational waves and find that the binaries always have
efficiencies E_rad/M > 3.6%, which can become as large as E_rad/M = 10% for
maximally spinning binaries with spins aligned with the orbital angular
momentum.Comment: 18 pages, 11 figures, matches published versio
Dietary variability of western gorillas (Gorilla gorilla gorilla)
Spatial and temporal variability in the availability of food resources will lead to variation in a speciesâ diet, which can then influence patterns of space use, sociality, and life history characteristics. Despite such potential impacts, little information is available about dietary variability for some species with large geographical ranges. Here we quantify the diet and nutritional content of plants consumed by western lowland gorillas (Gorilla gorilla gorilla) in Loango National Park, Gabon over a 2.6 year period and make comparisons with two study sites located 800 km away. The major foods consumed by the Loango gorillas differed greatly from the other two study sites, but gorillas at all three locations spent a similar proportion of feeding time consuming herbaceous vegetation and tree leaves (~ 50%) and fruit (35%). The Loango gorillas spent approximately 10% of feeding time eating nuts, which were not consumed at the other two study sites. Gorillas at those sites spent about 5% of feeding time eating insects, which were not consumed by Loango gorillas. Even though the species composition of the diet differed among the three sites, the nutritional composition of the major food items differed very little, suggesting that western gorillas consume foods of similar nutritional values to meet their dietary needs. This study shows the flexibility of diet of a species with a wide geographic distribution, which has implications for understanding variation in life history characteristics and can be useful for conservation management plans
Deterministically Computing Reduction Numbers of Polynomial Ideals
We discuss the problem of determining reduction number of a polynomial ideal
I in n variables. We present two algorithms based on parametric computations.
The first one determines the absolute reduction number of I and requires
computation in a polynomial ring with (n-dim(I))dim(I) parameters and n-dim(I)
variables. The second one computes via a Grobner system the set of all
reduction numbers of the ideal I and thus in particular also its big reduction
number. However,it requires computations in a ring with n.dim(I) parameters and
n variables.Comment: This new version replaces the earlier version arXiv:1404.1721 and it
has been accepted for publication in the proceedings of CASC 2014, Warsaw,
Polna
On the relevance of large scale pulsed-laser deposition: Evidence of structural heterogeneities in ZnO thin films
Pulsed-laser deposition is known as a well-suited method for growing thin films of oxide compounds presenting a wide range of functional properties. A limitation of this method for industrial process is the very anisotropic expansion dynamics of the plasma plume, which induces difficulties to grow on large scale films with homogeneous thickness and composition. The specific aspect of the crystalline or orientation uniformity has not been investigated, despite its important role on oxide films properties. In this work, the crystalline parameters and the texture of zinc oxide films are studied as a function of position with respect to the central axis of the plasma plume. We demonstrate the existence of large non-uniformities in the films. The stoichiometry, the lattice parameter, and the distribution of crystallites orientations drastically depend on the position with respect to the plume axis, i.e., on the oblique incidence of the ablated species. The origin of these non-uniformities, in particular, the unexpected tilted orientation of the ZnO c-axis may be attributed to the combined effects of the oblique incidence and of the ratio between oxygen and zinc fluxes reaching the surface of the growing film
Gribov horizon and i-particles: about a toy model and the construction of physical operators
Restricting the functional integral to the Gribov region leads to a
deep modification of the behavior of Euclidean Yang-Mills theories in the
infrared region. For example, a gluon propagator of the Gribov type,
, can be viewed as a propagating pair of
unphysical modes, called here -particles, with complex masses . From this viewpoint, gluons are unphysical and one can see them as
being confined. We introduce a simple toy model describing how a suitable set
of composite operators can be constructed out of -particles whose
correlation functions exhibit only real branch cuts, with associated positive
spectral density. These composite operators can thus be called physical and are
the toy analogy of glueballs in the Gribov-Zwanziger theory.Comment: 35 pages, 10 .pdf figures. v2: version accepted for publication in
Physical Review
The impact of competition on management quality: evidence from public hospitals
We analyse the causal impact of competition on managerial quality and hospital performance. To address the endogeneity of market structure we analyse the English public hospital sector where entry and exit are controlled by the central government. Because closing hospitals in areas where the governing party is expecting a tight election race (âmarginalsâ) is rare due to the fear of electoral defeat, we can use political marginality as an instrumental variable for the number of hospitals in a geographical area. We find that higher competition results in higher management quality, measured using a new survey tool, and improved hospital performance. Adding a rival hospital increases management quality by 0.4 standard deviations and increases survival rates from emergency heart attacks by 9.7%. We confirm the robustness of our IV strategy to âhidden policiesâ that could be used in marginal districts to improve hospital management and to changes in capacity that may follow from hospital closure
Inspiral-merger-ringdown waveforms for black-hole binaries with non-precessing spins
We present the first analytical inspiral-merger-ringdown gravitational
waveforms from binary black holes (BBHs) with non-precessing spins, that is
based on a description of the late-inspiral, merger and ringdown in full
general relativity. By matching a post-Newtonian description of the inspiral to
a set of numerical-relativity simulations, we obtain a waveform family with a
conveniently small number of physical parameters. These waveforms will allow us
to detect a larger parameter space of BBH coalescence, including a considerable
fraction of precessing binaries in the comparable-mass regime, thus
significantly improving the expected detection rates.Comment: To appear in Phys. Rev. Lett. Significant new results. One figure
removed due to page limitatio
Involution and Constrained Dynamics I: The Dirac Approach
We study the theory of systems with constraints from the point of view of the
formal theory of partial differential equations. For finite-dimensional systems
we show that the Dirac algorithm completes the equations of motion to an
involutive system. We discuss the implications of this identification for field
theories and argue that the involution analysis is more general and flexible
than the Dirac approach. We also derive intrinsic expressions for the number of
degrees of freedom.Comment: 28 pages, latex, no figure
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