Book review: Sexuality and social justice in Africa: rethinking homophobia and forging resistance

"Sexuality and Social Justice in Africa: Rethinking Homophobia and Forging Resistance." Marc Epprecht. Zed Books. July 2013. --- The persecution of people in Africa on the basis of their homosexual orientation has recently received considerable coverage in the media. However, much of the analysis thus far has been highly critical of African leadership and culture without considering local nuances, historical factors and external influences that are contributing to the problem. In this book, based on pioneering research on the history of homosexualities and engagement with current LGBTI activism, Marc Epprecht aims to provide a sympathetic overview of the issues at play. Clearly written and richly annotated, the book will prove to be a useful guide for academics, social workers, and activists, writes Jia Hui Lee

Macroscopic quantum coherence in antiferromagnetic molecular magnets

The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and preexponential factor for the ground-state tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80, 169 (1998)), but also have great influnence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.Comment: 6 pages, 1 figur

Superradiantly stable non-extremal Reissner-Nordstrom black holes

The superradiant stability is investigated for non-extremal Reissner-Nordstrom black hole. We use an algebraic method to demonstrate that all non-extremal Reissner-Nordstrom black holes are superradiantly stable against a charged massive scalar perturbation. This improves the results obtained before for non-extremal Reissner-Nordstrom black holes

Effects of arbitrarily directed field on spin phase oscillations in biaxial molecular magnets

Quantum phase interference and spin-parity effects are studied in biaxial molecular magnets in a magnetic field at an arbitrarily directed angle. The calculations of the ground-state tunnel splitting are performed on the basis of the instanton technique in the spin-coherent-state path-integral representation, and complemented by exactly numerical diagonalization. Both the Wentzel-Kramers-Brillouin exponent and the preexponential factor are obtained for the entire region of the direction of the field. Our results show that the tunnel splitting oscillates with the field for the small field angle, while for the large field angle the oscillation is completely suppressed. This distinct angular dependence, together with the dependence of the tunnel splitting on the field strengh, provide an independent test for spin-parity effects in biaxial molecular magnets. The analytical results for the molecular Fe$_{8}$ magnet, are found to be in good areement with the numerical simulations, which suggests that even the molecular magnet with total spin S=10 is large enough to be treated as a giant spin system.Comment: 19 pages, 5 figure

Low energy exciton states in a nanoscopic semiconducting ring

We consider an effective mass model for an electron-hole pair in a simplified confinement potential, which is applicable to both a nanoscopic self-assembled semiconducting InAs ring and a quantum dot. The linear optical susceptibility, proportional to the absorption intensity of near-infrared transmission, is calculated as a function of the ring radius $$. Compared with the properties of the quantum dot corresponding to the model with a very small radius $R_0$, our results are in qualitative agreement with the recent experimental measurements by Pettersson {\it et al}.Comment: 4 pages, 4 figures, revised and accepted by Phys. Rev.