Combustion in thermonuclear supernova explosions

Type Ia supernovae are associated with thermonuclear explosions of white dwarf stars. Combustion processes convert material in nuclear reactions and release the energy required to explode the stars. At the same time, they produce the radioactive species that power radiation and give rise to the formation of the observables. Therefore, the physical mechanism of the combustion processes, as reviewed here, is the key to understand these astrophysical events. Theory establishes two distinct modes of propagation for combustion fronts: subsonic deflagrations and supersonic detonations. Both are assumed to play an important role in thermonuclear supernovae. The physical nature and theoretical models of deflagrations and detonations are discussed together with numerical implementations. A particular challenge arises due to the wide range of spatial scales involved in these phenomena. Neither the combustion waves nor their interaction with fluid flow and instabilities can be directly resolved in simulations. Substantial modeling effort is required to consistently capture such effects and the corresponding techniques are discussed in detail. They form the basis of modern multidimensional hydrodynamical simulations of thermonuclear supernova explosions. The problem of deflagration-to-detonation transitions in thermonuclear supernova explosions is briefly mentioned.Comment: Author version of chapter for 'Handbook of Supernovae,' edited by A. Alsabti and P. Murdin, Springer. 24 pages, 4 figure

Optimal competitiveness for the Rectilinear Steiner Arborescence problem

We present optimal online algorithms for two related known problems involving Steiner Arborescence, improving both the lower and the upper bounds. One of them is the well studied continuous problem of the {\em Rectilinear Steiner Arborescence} ($RSA$). We improve the lower bound and the upper bound on the competitive ratio for $RSA$ from $O(\log N)$ and $\Omega(\sqrt{\log N})$ to $\Theta(\frac{\log N}{\log \log N})$, where $N$ is the number of Steiner points. This separates the competitive ratios of $RSA$ and the Symetric-$RSA$, two problems for which the bounds of Berman and Coulston is STOC 1997 were identical. The second problem is one of the Multimedia Content Distribution problems presented by Papadimitriou et al. in several papers and Charikar et al. SODA 1998. It can be viewed as the discrete counterparts (or a network counterpart) of $RSA$. For this second problem we present tight bounds also in terms of the network size, in addition to presenting tight bounds in terms of the number of Steiner points (the latter are similar to those we derived for $RSA$)

COVID-19 Post-lockdown: Perspectives, implications and strategies for disabled staff / COVID-19 Au-delà du confinement : perspectives, conséquences et stratégies pour les travailleurs handicapés

The National Association of Disabled Staff Networks (NADSN) is a super-network that connects and represents disabled staff networks at organisations across the United Kingdom. NADSN has been very concerned about the development of national policy up to this time and for moving out of the COVID-19 lockdown stage as national policy has been silent in relation to disabled staff apart from in presenting a narrow, medicalised view. We have structured this paper within a social model of disability and the sentiments expressed in the UN Convention of the Rights of People with Disabilities (CRPD) in considering the current issues and setting out our 12 recommendations. This paper discusses NADSN's observations about the lived experiences of Disabled people during COVID-19. Secondly, it moves to outline COVID-19 and the changing workplace. The paper then moves to a broad discussion concerning safe working practices and policies as we move out of lockdown and beyond

Haematological profiles of pigs raised under intensive management system in South-Eastern Nigeria

The haematological profile of pigs raised under intensive management system in South-Eastern Nigeria was studied. A total of 114 pigs were sampled comprising of 48 males and 66 females. Thirty-seven pigs were sampled in Anambra State, 46 in Enugu State and 31 in Ebonyi State with 38 being piglets and 76 adults. The blood values compared favourably with the reference values except for MCV and MCH that were slightly lower than the standard. The mean total WBC and neutrophil values were slightly higher than the standard. The PCV, Hb, MCHC and basophils were not significantly different (p>0.05) between the states. The RBC count was significantly (p.0.01) lower in Anambra State when compared with other states whereas Enugu State was significantly lower (

'A beginning and not the end’: Work after a diagnosis of dementia

YesWhile there is a growing literature on the experiences of disabled workers, this article presents an account of a work experience not frequently documented: being employed while living with dementia. It does this through the account of Elizabeth Draper, an NHS Hospital Trust manager, who received a diagnosis of dementia while employed. The article offers new ways of conceptualizing the struggles of disabled workers to continue with their project of self-becoming through work. It shows how work practices can enact violence through ‘non-recognition’ and how workers can subvert this violence to create opportunities for future development

Quasi-periodic X-ray brightness fluctuations in an accreting millisecond pulsar

The relativistic plasma flows onto neutron stars that are accreting material from stellar companions can be used to probe strong-field gravity as well as the physical conditions in the supranuclear-density interiors of neutron stars. Plasma inhomogeneities orbiting a few kilometres above the stars are observable as X-ray brightness fluctuations on the millisecond dynamical timescale of the flows. Two frequencies in the kilohertz range dominate these fluctuations: the twin kilohertz quasi-periodic oscillations (kHz QPOs). Competing models for the origins of these oscillations (based on orbital motions) all predict that they should be related to the stellar spin frequency, but tests have been difficult because the spins were not unambiguously known. Here we report the detection of kHz QPOs from a pulsar whose spin frequency is known. Our measurements establish a clear link between kHz QPOs and stellar spin, but one not predicted by any current model. A new approach to understanding kHz QPOs is now required. We suggest that a resonance between the spin and general relativistic orbital and epicyclic frequencies could provide the observed relation between QPOs and spin.Comment: Published in the 2003 July 3 issue of Natur