Evolution of Binary Black Hole Spacetimes

We describe early success in the evolution of binary black hole spacetimes with a numerical code based on a generalization of harmonic coordinates. Indications are that with sufficient resolution this scheme is capable of evolving binary systems for enough time to extract information about the orbit, merger and gravitational waves emitted during the event. As an example we show results from the evolution of a binary composed of two equal mass, non-spinning black holes, through a single plunge-orbit, merger and ring down. The resultant black hole is estimated to be a Kerr black hole with angular momentum parameter a~0.70. At present, lack of resolution far from the binary prevents an accurate estimate of the energy emitted, though a rough calculation suggests on the order of 5% of the initial rest mass of the system is radiated as gravitational waves during the final orbit and ringdown.Comment: 4 pages, 3 figure

Two-dimensional quantum black holes: Numerical methods

We present details of a new numerical code designed to study the formation and evaporation of 2-dimensional black holes within the CGHS model. We explain several elements of the scheme that are crucial to resolve the late-time behavior of the spacetime, including regularization of the field variables, compactification of the coordinates, the algebraic form of the discretized equations of motion, and the use of a modified Richardson extrapolation scheme to achieve high-order convergence. Physical interpretation of our results will be discussed in detail elsewhere

When Coping Resources Fail: The Health-Sustaining and Moderating Role of Fortitude in the Relationship Between COVID-19-Related Worries and Psychological Distress

The COVID-19 pandemic is a global public health crisis and governments worldwide have attempted to mitigate the spread of the virus by implementing a range of stringent preventative measures. However, both the pandemic and the preventative strategies enacted may undercut critical protective factors that are known to buffer the negative impact of psychological stressors. The current study aimed to characterise the mental health impact of the pandemic in South Africa by investigating the potential protective role of fortitude in the relationship between COVID-19-related worries and psychological distress, indicated by the levels of depression and hopelessness. The participants were 337 young adults who completed four self-report questionnaires: the Fortitude Questionnaire, the Beck Hopelessness Scale, the Centre for Epidemiological Depression Scale and the COVID19-Related Worries Scale. In addition to descriptive statistics, path analysis was performed to determine the direct, indirect, mediating and moderating effects of fortitude on psychological distress. In this regard, psychological distress was conceptualised as a latent variable that is defined by the two indices of depression and hopelessness. The results demonstrated unprecedented levels of hopelessness and depression among the study sample. These levels were significantly higher than those encountered in previous studies in other contexts, suggesting a possible mental health crisis in the country. Women reported higher levels of psychological distress than men. On its own, fortitude had significant direct effects on psychological distress, affirming its role as a protective factor. However, fortitude was found to have an aggravating rather than buffering effect in interaction with worries. In this regard, the relationship between COVID-19-related worries and psychological distress was stronger among those with high levels of fortitude

Black Hole Mergers and Unstable Circular Orbits

We describe recent numerical simulations of the merger of a class of equal mass, non-spinning, eccentric binary black hole systems in general relativity. We show that with appropriate fine-tuning of the initial conditions to a region of parameter space we denote the threshold of immediate merger, the binary enters a phase of close interaction in a near-circular orbit, stays there for an amount of time proportional to logarithmic distance from the threshold in parameter space, then either separates or merges to form a single Kerr black hole. To gain a better understanding of this phenomena we study an analogous problem in the evolution of equatorial geodesics about a central Kerr black hole. A similar threshold of capture exists for appropriate classes of initial conditions, and tuning to threshold the geodesics approach one of the unstable circular geodesics of the Kerr spacetime. Remarkably, with a natural mapping of the parameters of the geodesic to that of the equal mass system, the scaling exponent describing the whirl phase of each system turns out to be quite similar. Armed with this lone piece of evidence that an approximate correspondence might exist between near-threshold evolution of geodesics and generic binary mergers, we illustrate how this information can be used to estimate the cross section and energy emitted in the ultra relativistic black hole scattering problem. This could eventually be of use in providing estimates for the related problem of parton collisions at the Large Hadron Collider in extra dimension scenarios where black holes are produced.Comment: 16 pages, 12 figures; updated to coincide with journal versio

Comparisons of binary black hole merger waveforms

This a particularly exciting time for gravitational wave physics. Ground-based gravitational wave detectors are now operating at a sensitivity such that gravitational radiation may soon be directly detected, and recently several groups have independently made significant breakthroughs that have finally enabled numerical relativists to solve the Einstein field equations for coalescing black-hole binaries, a key source of gravitational radiation. The numerical relativity community is now in the position to begin providing simulated merger waveforms for use by the data analysis community, and it is therefore very important that we provide ways to validate the results produced by various numerical approaches. Here, we present a simple comparison of the waveforms produced by two very different, but equally successful approaches--the generalized harmonic gauge and the moving puncture methods. We compare waveforms of equal-mass black hole mergers with minimal or vanishing spins. The results show exceptional agreement for the final burst of radiation, with some differences attributable to small spins on the black holes in one case.Comment: Revtex 4, 5 pages. Published versio

Staphylococcus aureus bacteraemia in children: a formidable foe

Staphylococcus aureus remains one of the most common causes of bacteraemia in children. In order to evade and overcome the immune responses of its host and any antimicrobial therapies aimed at destroying it, this organism, through various mechanisms, continues to evolve. Staphylococcus aureus bacteraemia is a systemic disease; and, multiple organ involvement should be assessed and appropriately managed. This is especially important for the anaesthetist who will be administering general anaesthesia to children presenting for surgical source control.Keywords: bacteraemia, children, pneumonia, septic arthritis, staphylococcus aureu

Fatty acids in beef from grain- and grass-fed cattle: the unique South African scenario

Objective: Different fatty acids elicit different responses in the human body once ingested. Although red meat is often considered to be a source of fatty acids which has a negative impact on human health, many studies have reflected variability in the quantity and quality of fatty acids found in red meat produced on different production systems in different countries. This study evaluated the fatty acid profile of beef, produced by the grass- and grain-fed production systems practised in South Africa.Design: Data are reported as a percentage of lipid per 100 g total fat to enable a comparison with international findings. Furthermore, the findings are translated into edible meat portions, taking fat trimming (often associated with red meat intake) into consideration in order to determine the contribution which the different products can make to the human diet.Subjects and setting: Three cuts of beef from cattle from four production groups were sampled and the fatty acid composition analysed for the meat and fat fractions.Results: Notable differences were found in the quantity and quality of different fatty acids in beef from the different production systems. When untrimmed, no statistically significant difference was found in the total fat between beef produced on the different production systems. Differences became more significant as trimming was performed. When trimmed of all visible fat, beef from young cattle fed according to a grain-based feeding system contained less total fat (6.96 g), and less saturated fat (2.16 g) per 100 g, than beef produced from their grass-fed counterparts (9.77 g and 3.30 g, respectively). There was a more favourable omega-6 to omega-3 fatty acid ratio, i.e. 2.0–2.5:1.0 for grassfed cattle, compared to 8–30:1 for grain-fed cattle, irrespective of the degree of trimming. The beef from the grass-fed cattle also contained a higher quantity of conjugated linoleic acid.Conclusion: A unique classification system for red meat has been implemented in South Africa and dictates the characteristics of the fresh meat that is available to consumers. The results of this study consequently indicate distinctive differences between the fatty acid profile of local red meat and that of beef produce from other countries; often used as a reference for dietary guidance.Keywords: grain fed, grass fed, cattle, fatty acids, red mea

Ninja data analysis with a detection pipeline based on the Hilbert-Huang Transform

The Ninja data analysis challenge allowed the study of the sensitivity of data analysis pipelines to binary black hole numerical relativity waveforms in simulated Gaussian noise at the design level of the LIGO observatory and the VIRGO observatory. We analyzed NINJA data with a pipeline based on the Hilbert Huang Transform, utilizing a detection stage and a characterization stage: detection is performed by triggering on excess instantaneous power, characterization is performed by displaying the kernel density enhanced (KD) time-frequency trace of the signal. Using the simulated data based on the two LIGO detectors, we were able to detect 77 signals out of 126 above SNR 5 in coincidence, with 43 missed events characterized by signal to noise ratio SNR less than 10. Characterization of the detected signals revealed the merger part of the waveform in high time and frequency resolution, free from time-frequency uncertainty. We estimated the timelag of the signals between the detectors based on the optimal overlap of the individual KD time-frequency maps, yielding estimates accurate within a fraction of a millisecond for half of the events. A coherent addition of the data sets according to the estimated timelag eventually was used in a characterization of the event.Comment: Accepted for publication in CQG, special issue NRDA proceedings 200

Reducing orbital eccentricity in binary black hole simulations

Binary black hole simulations starting from quasi-circular (i.e., zero radial velocity) initial data have orbits with small but non-zero orbital eccentricities. In this paper the quasi-equilibrium initial-data method is extended to allow non-zero radial velocities to be specified in binary black hole initial data. New low-eccentricity initial data are obtained by adjusting the orbital frequency and radial velocities to minimize the orbital eccentricity, and the resulting ($\sim 5$ orbit) evolutions are compared with those of quasi-circular initial data. Evolutions of the quasi-circular data clearly show eccentric orbits, with eccentricity that decays over time. The precise decay rate depends on the definition of eccentricity; if defined in terms of variations in the orbital frequency, the decay rate agrees well with the prediction of Peters (1964). The gravitational waveforms, which contain $\sim 8$ cycles in the dominant l=m=2 mode, are largely unaffected by the eccentricity of the quasi-circular initial data. The overlap between the dominant mode in the quasi-circular evolution and the same mode in the low-eccentricity evolution is about 0.99.Comment: 27 pages, 9 figures; various minor clarifications; accepted to the "New Frontiers" special issue of CQ

Challenges and strength of current industrial energy efficiency management practices in steam industries

Abstract: The aim of this study is to achieve greater output by examining the existing way of coordinating the determined attempts of Steam Industries in South Africa to successfully reach a sustainable industrial development by using energy source adequately in a more competent way. Furthermore into the study we look at obstacles that prevent and those that leads to maximum utilization of energy management measures and also highlights the effects of implementing cheap available energy source in South Africa. The investigation and analysis have shown that energy is not well managed in Steam Industries and that the use of energy is minimized and not fully utilized due to poor management and lack of knowledge. Another detection was that lack of government structured and strategic measures of implementing and motivating the use of energy effectively. The effective and rational use of available power by Steam Industries in South Africa is a key player in developing a sustainable industrial development. The use of energy efficiency management strategies has contributed an increase in economic and improve environmentally friendly in the industrial sector. The slow pace adoption of energy saving and cost effective management programmes are negatively impacting on the benefits to Steam Industries in South Africa. In conclusion the study finds that the economy can be boosted by implementing energy efficiency management programmes and environmentally friendly. These will also stabilize the negative impact of energy raising prices