De Sitter Holography with a Finite Number of States

We investigate the possibility that, in a combined theory of quantum mechanics and gravity, de Sitter space is described by finitely many states. The notion of observer complementarity, which states that each observer has complete but complementary information, implies that, for a single observer, the complete Hilbert space describes one side of the horizon. Observer complementarity is implemented by identifying antipodal states with outgoing states. The de Sitter group acts on S-matrix elements. Despite the fact that the de Sitter group has no nontrivial finite-dimensional unitary representations, we show that it is possible to construct an S-matrix that is finite-dimensional, unitary, and de Sitter-invariant. We present a class of examples that realize this idea holographically in terms of spinor fields on the boundary sphere. The finite dimensionality is due to Fermi statistics and an `exclusion principle' that truncates the orthonormal basis in which the spinor fields can be expanded.Comment: 23 pages, 1 eps figure, LaTe

Very hard states in neutron star low-mass X-ray binaries

We report on unusually very hard spectral states in three confirmed neutron-star low-mass X-ray binaries (1RXS J180408.9-342058, EXO 1745-248, and IGR J18245-2452) at a luminosity between ~ 10^{36-37} erg s^{-1}. When fitting the Swift X-ray spectra (0.5 - 10 keV) in those states with an absorbed power-law model, we found photon indices of \Gamma ~ 1, significantly lower than the \Gamma = 1.5 - 2.0 typically seen when such systems are in their so called hard state. For individual sources very hard spectra were already previously identified but here we show for the first time that likely our sources were in a distinct spectral state (i.e., different from the hard state) when they exhibited such very hard spectra. It is unclear how such very hard spectra can be formed; if the emission mechanism is similar to that operating in their hard states (i.e., up-scattering of soft photons due to hot electrons) then the electrons should have higher temperatures or a higher optical depth in the very hard state compared to those observed in the hard state. By using our obtained \Gamma as a tracer for the spectral evolution with luminosity, we have compared our results with those obtained by Wijnands et al. (2015). We confirm their general results in that also our sample of sources follow the same track as the other neutron star systems, although we do not find that the accreting millisecond pulsars are systematically harder than the non-pulsating systems.Comment: Accepted for publication in MNRA

Towards measurable resilience: A novel framework tool for the assessment of resilience levels in slums

This paper investigates the need for a generic technique to be applied in the assessment of resilience-related projects in slums – particularly for localised infrastructure at a community level – and proposes a novel framework tool for this purpose. The paper outlines the development of the framework tool, as well as its pilot testing on the Kenya Slum Upgrading Programme in Kibera, Nairobi. The evaluation demonstrates an improvement in asset base, capacities and external resources for the community post intervention. The lack of land tenure was identified to be a key weakness and factor which impacted resilience of the local residents

Scattering of positrons and electrons by alkali atoms

Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV

Effective temperature for black holes

The physical interpretation of black hole's quasinormal modes is fundamental for realizing unitary quantum gravity theory as black holes are considered theoretical laboratories for testing models of such an ultimate theory and their quasinormal modes are natural candidates for an interpretation in terms of quantum levels. The spectrum of black hole's quasinormal modes can be re-analysed by introducing a black hole's effective temperature which takes into account the fact that, as shown by Parikh and Wilczek, the radiation spectrum cannot be strictly thermal. This issue changes in a fundamental way the physical understanding of such a spectrum and enables a re-examination of various results in the literature which realizes important modifies on quantum physics of black holes. In particular, the formula of the horizon's area quantization and the number of quanta of area result modified becoming functions of the quantum "overtone" number n. Consequently, the famous formula of Bekenstein-Hawking entropy, its sub-leading corrections and the number of microstates are also modified. Black hole's entropy results a function of the quantum overtone number too. We emphasize that this is the first time that black hole's entropy is directly connected with a quantum number. Previous results in the literature are re-obtained in the limit n \to \infty.Comment: 10 pages,accepted for publication in Journal of High Energy Physics. Comments are welcom

Expressive aphasia in a patient with recent dual-chamber cardioverter-defibrillator implantation: A preventable complication

Transvenous pacemaker and/or defibrillator lead placement into the left heart chambers is rarely done. Approximately a third of such cases reported in the literature presented with signs of thromboembolism, mostly neurological deficits. We describe a patient who presented with a cerebrovascular accident three months after inadvertent and unrecognized lead placement into the left atrium and ventricle through a sinus venosus atrial septal defect. Implant techniques to avoid this complication are discussed. (Cardiol J 2011; 18, 2: 197-199

Thermonuclear Ti-42(p, gamma)V-43 rate in type-I x-ray bursts

The thermonuclear rate of the Ti-42(p, gamma)V-43 reaction has been reevaluated based on a recent precise proton separation energy measurement of S-p(V-43) = 83 +/- 43 keV. The astrophysical impact of our new rates has been investigated through one-zone postprocessing type-I x-ray burst calculations. It shows that the new experimental value of S-p significantly affects the yields of species for A approximate to 40-45. As well, the precision of the recent experimental S-p value constrains these yields to better than a factor of 3.Peer reviewedFinal Accepted Versio