898 research outputs found

    Approximating the inspiral of test bodies into Kerr black holes

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    We present a new approximate method for constructing gravitational radiation driven inspirals of test-bodies orbiting Kerr black holes. Such orbits can be fully described by a semi-latus rectum pp, an eccentricity ee, and an inclination angle ι\iota; or, by an energy EE, an angular momentum component LzL_z, and a third constant QQ. Our scheme uses expressions that are exact (within an adiabatic approximation) for the rates of change (p˙\dot{p}, e˙\dot{e}, ι˙\dot{\iota}) as linear combinations of the fluxes (E˙\dot{E}, Lz˙\dot{L_z}, Q˙\dot{Q}), but uses quadrupole-order formulae for these fluxes. This scheme thus encodes the exact orbital dynamics, augmenting it with approximate radiation reaction. Comparing inspiral trajectories, we find that this approximation agrees well with numerical results for the special cases of eccentric equatorial and circular inclined orbits, far more accurate than corresponding weak-field formulae for (p˙\dot{p}, e˙\dot{e}, ι˙\dot{\iota}). We use this technique to study the inspiral of a test-body in inclined, eccentric Kerr orbits. Our results should be useful tools for constructing approximate waveforms that can be used to study data analysis problems for the future LISA gravitational-wave observatory, in lieu of waveforms from more rigorous techniques that are currently under development.Comment: 15 pages, 5 figures, submitted to PR

    Who gets the Carrot and Who gets the Stick? Evidence of Gender Disparities in Executive Remuneration

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    This paper offers a new explanation of the gender pay gap in leadership positions by examining the relationship between managerial bonuses and company performance. Drawing on findings of gender studies, agency theory, and the leadership literature, we argue that the gender pay gap is a context-specific phenomenon which results partly from the fact that company performance has a moderating impact on pay inequalities. Employing a matched sample of 192 female and male executive directors of UK listed firms we corroborate the existence of the gender pay disparities in corporate boardrooms. In line with our theoretical predictions, we find that bonuses awarded to men are not only larger than those allocated to women, but also that managerial compensation of male executive directors is much more performance-sensitive than that of female executives. The contribution of attributional and expectancy-related dynamics to these patterns is highlighted in line with previous work on gender stereotypes and implicit leadership theories such as the romance of leadership. Gender differences in risk-taking and confidence are also considered as potential explanations for the observed pay disparities. The implications of organizations’ indifference to women’s performance are examined in relation to issues surrounding the recognition and retention of female talent.executive compensation;gender pay gap;gender stereotypes;implicit leadership theories;corporate performance;romance of leadership

    Evolution of circular, non-equatorial orbits of Kerr black holes due to gravitational-wave emission: II. Inspiral trajectories and gravitational waveforms

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    The inspiral of a ``small'' (μ∼1−100M⊙\mu \sim 1-100 M_\odot) compact body into a ``large'' (M∼105−7M⊙M \sim 10^{5-7} M_\odot) black hole is a key source of gravitational radiation for the space-based gravitational-wave observatory LISA. The waves from such inspirals will probe the extreme strong-field nature of the Kerr metric. In this paper, I investigate the properties of a restricted family of such inspirals (the inspiral of circular, inclined orbits) with an eye toward understanding observable properties of the gravitational waves that they generate. Using results previously presented to calculate the effects of radiation reaction, I assemble the inspiral trajectories (assuming that radiation reacts adiabatically, so that over short timescales the trajectory is approximately geodesic) and calculate the wave generated as the compact body spirals in. I do this analysis for several black hole spins, sampling a range that should be indicative of what spins we will encounter in nature. The spin has a very strong impact on the waveform. In particular, when the hole rotates very rapidly, tidal coupling between the inspiraling body and the event horizon has a very strong influence on the inspiral time scale, which in turn has a big impact on the gravitational wave phasing. The gravitational waves themselves are very usefully described as ``multi-voice chirps'': the wave is a sum of ``voices'', each corresponding to a different harmonic of the fundamental orbital frequencies. Each voice has a rather simple phase evolution. Searching for extreme mass ratio inspirals voice-by-voice may be more effective than searching for the summed waveform all at once.Comment: 15 pages, 11 figures, accepted for publication in PRD. This version incorporates referee's comments, and is much less verbos

    The place attachment of visitors to Ningaloo Marine Park, north-western Australia

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    Place attachment has been the subject of a rich, growing body of research in natural resource management, with a particular emphasis on visitors to national parks and forests. Understanding how such attachments are formed as well as their strength has been of central interest. Most of this work has been terrestrially based, with little attention to marine settings. The question of whether the same predominant elements of place attachment – physical environment, activities, social ties and emotional connection – apply to marine national parks remains to be answered. Ningaloo Marine Park in north-western Australia provided the focus for this study. Place attachment is of great interest in this Marine Park because the results of a recent visitor survey showed that 55% of respondents had visited previously and of this, 44% stayed at the same location, suggesting strong place attachment. Photo-elicitation, where photographs are taken by visitors and provide the basis for a subsequent interview, was used to explore this phenomenon. A total of 30 visitors agreed to participate, with up to eight photographs taken by each. Fieldwork was undertaken in July 2009 with preliminary results suggesting that place attachment at the Marine Park has the same four elements as those found in terrestrial-based studies. There were, however, distinct marine components for each element. For the physical environment, coastal vistas were enjoyed because of the feelings of remoteness and isolation they promoted as well as their majestic beauty. Activities centred on those that were uniquely marine, such as snorkelling, diving and fishing. Social ties were evidenced in the bonding of visitors with others who shared similar marine-based past-times such as boating. Regarding emotional connection, families enjoyed being able to visit a location where everybody was happy because all members were able to do their own activities and have a pleasurable experience. Participants were also asked about place-specific behaviours. Place-protective behaviours were obvious from the responses provided and included picking up rubbish and telling others if they were doing the ‘wrong’ thing. Place protection was also evident in the responses regarding perceptions of management. The dominant response related to increasing the presence of management to enforce rules and regulations, particularly for fishing

    Molecular characterization of Cryptosporidium and Giardia in farmers and their ruminant livestock from the Coastal Savannah zone of Ghana

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    Cryptosporidium and Giardia are major causes of diarrhoea in developing countries including Ghana, however, nothing is known about the species and subtypes of Cryptosporidium and Giardia in farmers and their ruminant livestock in this country. A total of 925 faecal samples from humans (n = 95), cattle (n = 328), sheep (n = 217) and goats (n = 285), were screened for Cryptosporidium and Giardia by quantitative PCR (qPCR) at the 18S rRNA and glutamate dehydrogenase (gdh) loci respectively. Cryptosporidium positives were typed by sequence analysis of 18S and 60 kDa glycoprotein (gp60) loci amplicons. Giardia positives were typed at the triose phosphate isomerase (tpi), beta-giardin (bg) and gdh loci. The prevalence of Cryptosporidium and Giardia by qPCR was 8.4% and 10.5% in humans, 26.5% and 8.5% in cattle, 34.1% and 12.9% in sheep, and 33.3% and 12.3% in goat faecal samples, respectively. G. duodenalis assemblages A and B were detected in humans and assemblage E was detected in livestock. Cryptosporidium parvum was the only species identified in humans; C. andersoni, C. bovis, C. ryanae and C. ubiquitum were identified in cattle; C. xiaoi, C. ubiquitum and C. bovis in sheep; and C. xiaoi, C. baileyi and C. parvum in goats. This is the first molecular study of Cryptosporidium and Giardia in livestock in Ghana. The identification of zoonotic species and the identification of C. parvum subtype IIcA5G3q in livestock, which has previously been identified in children in Ghana, suggests potential zoonotic transmission. Further studies on larger numbers of human and animal samples, and on younger livestock are required to better understand the epidemiology and transmission of Cryptosporidium and Giardia in Ghana

    A survey of spinning test particle orbits in Kerr spacetime

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    We investigate the dynamics of the Papapetrou equations in Kerr spacetime. These equations provide a model for the motion of a relativistic spinning test particle orbiting a rotating (Kerr) black hole. We perform a thorough parameter space search for signs of chaotic dynamics by calculating the Lyapunov exponents for a large variety of initial conditions. We find that the Papapetrou equations admit many chaotic solutions, with the strongest chaos occurring in the case of eccentric orbits with pericenters close to the limit of stability against plunge into a maximally spinning Kerr black hole. Despite the presence of these chaotic solutions, we show that physically realistic solutions to the Papapetrou equations are not chaotic; in all cases, the chaotic solutions either do not correspond to realistic astrophysical systems, or involve a breakdown of the test-particle approximation leading to the Papapetrou equations (or both). As a result, the gravitational radiation from bodies spiraling into much more massive black holes (as detectable, for example, by LISA, the Laser Interferometer Space Antenna) should not exhibit any signs of chaos.Comment: Submitted to Phys. Rev. D. Follow-up to gr-qc/0210042. Figures are low-resolution in order to satisfy archive size constraints; a high-resolution version is available at http://www.michaelhartl.com/papers

    Towards a formalism for mapping the spacetimes of massive compact objects: Bumpy black holes and their orbits

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    Observations have established that extremely compact, massive objects are common in the universe. It is generally accepted that these objects are black holes. As observations improve, it becomes possible to test this hypothesis in ever greater detail. In particular, it is or will be possible to measure the properties of orbits deep in the strong field of a black hole candidate (using x-ray timing or with gravitational-waves) and to test whether they have the characteristics of black hole orbits in general relativity. Such measurements can be used to map the spacetime of a massive compact object, testing whether the object's multipoles satisfy the strict constraints of the black hole hypothesis. Such a test requires that we compare against objects with the ``wrong'' multipole structure. In this paper, we present tools for constructing bumpy black holes: objects that are almost black holes, but that have some multipoles with the wrong value. The spacetimes which we present are good deep into the strong field of the object -- we do not use a large r expansion, except to make contact with weak field intuition. Also, our spacetimes reduce to the black hole spacetimes of general relativity when the ``bumpiness'' is set to zero. We propose bumpy black holes as the foundation for a null experiment: if black hole candidates are the black holes of general relativity, their bumpiness should be zero. By comparing orbits in a bumpy spacetime with those of an astrophysical source, observations should be able to test this hypothesis, stringently testing whether they are the black holes of general relativity. (Abridged)Comment: 16 pages + 2 appendices + 3 figures. Submitted to PR

    Despite NAIS concerns electronic identification use by cow-calf producers is increasing

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    The proposed U.S. National Animal Identification System has generated concerns among producers relative to implementation of the system. Many of these concerns stem from the USDA’s Bovine Identification Working Group’s recommendations to use electronic Identification Plan Bovine Working Group has recommended radio frequency identification as the technology to individually identify cattle. Understanding and implementing an electronic identification system for cow-calf producers is believed to be one of the greatest challenges of implementing the National Animal Identification System
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