The BSSN formulation is a partially constrained evolution system

Relativistic simulations in 3+1 dimensions typically monitor the Hamiltonian and momentum constraints during evolution, with significant violations of these constraints indicating the presence of instabilities. In this paper we rewrite the momentum constraints as first-order evolution equations, and show that the popular BSSN formulation of the Einstein equations explicitly uses the momentum constraints as evolution equations. We conjecture that this feature is a key reason for the relative success of the BSSN formulation in numerical relativity.Comment: 8 pages, minor grammatical correction

Gravitational waves and stalled satellites from massive galaxy mergers at z <= 1

We present a model for merger-driven evolution of the mass function for massive galaxies and their central supermassive black holes at late times. We discuss the current observational evidence in favor of merger-driven massive galaxy evolution during this epoch, and demonstrate that the observed evolution of the mass function can be reproduced by evolving an initial mass function under the assumption of negligible star formation. We calculate the stochastic gravitational wave signal from the resulting black-hole binary mergers in the low redshift universe (z <= 1) implied by this model, and find that this population has a signal-to-noise ratio as much as ~5x larger than previous estimates for pulsar timing arrays, with an expectation value for the characteristic strain h_c (f=1 yr^{-1}) = 4.1 x 10^{-15} that may already be in tension with observational constraints, and a {2-sigma, 3-sigma} lower limit within this model of h_c (f=1 yr^{-1}) = {1.1 x 10^{-15}, 6.8 x 10^{-16}}. The strength of this signal is sufficient to make it detectable with high probability under conservative assumptions within the next several years, if the principle assumption of merger-driven galaxy evolution since z = 1 holds true. For cases where a galaxy merger fails to lead to a black hole merger, we estimate the probability for a given number of satellite unmerged black holes to remain within a massive host galaxy, and interpret the result in light of ULX observations. In particular, we find that the brightest cluster galaxies should have 1-2 such sources with luminosities above 10^{39} erg/s, which is consistent with the statistics of observed ULXs.Comment: 11 pages, 5 figures, submitted to ApJ, v2 includes the referee's requested change

Meningiomas occurring during long-term survival after treatment for childhood cancer

Childhood cancer is rare but improvements in treatment over the past five decades have resulted in a cohort of more than 30,000 long-term survivors of childhood cancer in the UK with more added annually. These long-term survivors are at risk of late effects of cancer treatment which replace original tumour recurrence as the leading cause of premature death. Second neoplasms are a particular risk and in the central nervous system meningiomas occur increasingly with increased radiation dose to central nervous system tissue and length of time after exposure, resulting in a 500-fold increase above that expected in the normal population by 40 years of follow up. This multidisciplinary author group and others met to discuss the issue. Our pooled information, and consensus that screening should only follow symptoms, was published online by the Royal College of Radiologists in 2013. We outline here the current knowledge and management of these neoplasms secondary to childhood cancer treatment

Die menslike liggaam as fisiologiese eenheid*

Die menslike liggaam is ’n fisiologiese eenheid wat uit ongeveer 12 miljard sub-eenhede, die lewende selle saamgestel is. Elke individuele sel kan beskou word as ’n lewende eenheid, om dat elkeen m eeste of al die fisiologiese lewenskenm erke van die geheel soos prikkelbaarheid, geleidingsvermoë, energietransformering en voortplanting vertoon. Die eenheid van die lewende sel kom tot stand om dat talryke biochemiese en biofisiese prosesse van molekules en selorganelle en boueenhede van die sel noukeurig beheer word. Die funksies van die selle word in die weefsels en organe só gekoordineer dat ’n volgende vlak van eenheid m et wyer omvang tot stand kom. Die afsonderlike funksies van die weefsels en organe word op hul beurt w eer gekottrdineer en geïntegreer in die groter geheel van die eenheid van die liggaam, waarbinne die voortbestaan en optimale funksionering van elkeen van die lewende onderdele verseker word. Terwyl elke sel dus die voordeel van die instandhouding van die geheel as eenheid geniet, dra d it op sy beurt weer aktief by om die voortbestaan en doeltreffende funksionering van die geheel moontlik te maak

Eccles se mistisisme en kuhlendeck se boeddhisme as moontlike grondslag vir fisiologie

The discussion ranging around the issues of human worth, uniqueness, the typically human, spirituality and human freedom also includes the subject of Physiology. The sense and the meaning of physiological knowledge, foundations for ethical norms and religious functions of man are of cardinal importance for the subject philosophy of Physiology

Two fast X-ray transients in archival Chandra data

We present the discovery of two new X-ray transients in archival Chandra data. The first transient, XRT 110103, occurred in January 2011 and shows a sharp rise of at least three orders of magnitude in count rate in less than 10 s, a flat peak for about 20 s and decays by two orders of magnitude in the next 60 s. We find no optical or infrared counterpart to this event in preexisting survey data or in an observation taken by the SIRIUS instrument at the Infrared Survey Facility 2.1 yr after the transient, providing limiting magnitudes of J>18.1, H>17.6 and Ks>16.3. This event shows similarities to the transient previously reported in Jonker et al. which was interpreted as the possible tidal disruption of a white dwarf by an intermediate mass black hole. We discuss the possibility that these transients originate from the same type of event. If we assume these events are related a rough estimate of the rates gives 1.4*10^5 per year over the whole sky with a peak 0.3-7 keV X-ray flux greater than 2*10^-10 erg cm^-2 s^-1 . The second transient, XRT 120830, occurred in August 2012 and shows a rise of at least three orders of magnitude in count rate and a subsequent decay of around one order of magnitude all within 10 s, followed by a slower quasi-exponential decay over the remaining 30 ks of the observation. We detect a likely infrared counterpart with magnitudes J=16.70+/-0.06, H=15.92+/-0.04 and Ks=15.37+/-0.06 which shows an average proper motion of 74+/-19 milliarcsec per year compared to archival 2MASS observations. The JHKs magnitudes, proper motion and X-ray flux of XRT 120830 are consistent with a bright flare from a nearby late M or early L dwarf.Comment: Accepted for publication in MNRAS, 6 pages, 5 figure

Application of the event chain project management methodology to a mining stope

Abstract: Although South Africa possesses more than 80% of the world’s platinum reserves, its reputation for reliability in supplying platinum to global markets is under threat. This is due to the 49% decrease in output per worker (1999–2014), while the domestic costs have risen by more than 10% annually for the past 5 years. In addition, the continued decline in the commodity price by 38.3% (2012–2016) has resulted in a significant portion of the sector producing at a loss in 2015. The Chamber of Mines (now the Minerals Councilof South Africa) has suggested that solutions to improve productivity and reduce cost pressures are required. This research aims to provide operational excellence through the application of event chain project management (ECPM) to improve productivity and reduce operational costs. A case study was used to carry out research in platinum mines, with data collected using a motion-time study to measure the current efficiency of operations in each mining stope through actual activity durations. The results indicate that through the application of the event chain project management methodology, risks affecting the mining stope schedule can be managed, the efficiency of operations was improved by reducing the time spent on each activity, productivity was increased by shortening the project duration, and operational costs were reduced in the process

A Dynamical Systems Approach to Schwarzschild Null Geodesics

The null geodesics of a Schwarzschild black hole are studied from a dynamical systems perspective. Written in terms of Kerr-Schild coordinates, the null geodesic equation takes on the simple form of a particle moving under the influence of a Newtonian central force with an inverse-cubic potential. We apply a McGehee transformation to these equations, which clearly elucidates the full phase space of solutions. All the null geodesics belong to one of four families of invariant manifolds and their limiting cases, further characterized by the angular momentum L of the orbit: for |L|>|L_c|, (1) the set that flow outward from the white hole, turn around, then fall into the black hole, (2) the set that fall inward from past null infinity, turn around outside the black hole to continue to future null infinity, and for |L|<|L_c|, (3) the set that flow outward from the white hole and continue to future null infinity, (4) the set that flow inward from past null infinity and into the black hole. The critical angular momentum Lc corresponds to the unstable circular orbit at r=3M, and the homoclinic orbits associated with it. There are two additional critical points of the flow at the singularity at r=0. Though the solutions of geodesic motion and Hamiltonian flow we describe here are well known, what we believe is a novel aspect of this work is the mapping between the two equivalent descriptions, and the different insights each approach can give to the problem. For example, the McGehee picture points to a particularly interesting limiting case of the class (1) that move from the white to black hole: in the limit as L goes to infinity, as described in Schwarzschild coordinates, these geodesics begin at r=0, flow along t=constant lines, turn around at r=2M, then continue to r=0. During this motion they circle in azimuth exactly once, and complete the journey in zero affine time.Comment: 14 pages, 3 Figure

Utilising high and premium efficiency three phase motors with VFDs in a public water supply system

The increased reliability and ultimately reduced life cycle cost of high and premium efficiency three phase motors in a process control application is discussed. The reduced energy consumption of these motors is evaluated in a public water system case study under variable frequency conditions. The importance of the consideration of a combined system, which includes variable speed control, motor and load - as opposed to only replacing with high efficiency motors for energy saving purposes - is practically observed and reported on. The paper reports on the marginal improvement in energy consumption at reduced supply frequency for motor replacement only (not surprising) but a very impressive 46% saving in energy consumption by controlling pumped water at a reduced but constant delivery rate