Coherent photon manipulation in interacting atomic ensembles

Coupling photons to Rydberg excitations in a cold atomic gas yields unprecedentedly large optical nonlinearities at the level of individual light quanta, where the formation of nearby dark-state polaritons is blocked by the strong interactions between Rydberg atoms. This blockade mechanism, however, realizes an inherently dissipative nonlinearity, which limits the performance of practical applications. In this work, we propose a new approach to strong photon interactions via a largely coherent mechanism at drastically suppressed photon losses. Rather than a polariton blockade, it is based on an interaction induced conversion between distinct types of dark-state polaritons with different propagation characteristics. We outline a specific implementation of this approach and show that it permits to turn a single photon into an effective mirror with a robust and continuously tuneable reflection phase. We describe potential applications, including a detailed discussion of achievable operational fidelities

Care Planning and Review for Looked After Children: Fifteen Years of Slow Progress?

This Critical Commentary reviews progress in research into planning and reviewing for children in care in England and Wales since the publication of two major studies in the late 1990s (roughly coinciding with the New Labour period). It briefly considers the changing context of law, regulation and guidance and the aims and objectives of the care planning and review system. It then reviews the limited research literature available, in relation to a series of key topics. Consideration is also given to guides for children and practitioners on the subject. The commentary concludes by suggesting that this is an area in which research has failed to keep pace with changes in policy and practice, and recommends a more systematic approach

New techniques for estimating household climate preferences (and the benefits and costs of climate change)

In order to make an informed decision on the optimal reduction in greenhouse gas emissions it is necessary to understand fully the damage costs of climate change. However, current modelling techniques fail to provide adequate emphasis on important components of the costs and benefits of avoided climate change. This approach risks over or underestimating true damage costs. Disregard for the amenity value that climate may hold and assumptions that restrict geographic mobility and determine the rate of social discounting may all contribute to significant error. Using spatial variations as an analogue for future climate change, this thesis finds that climate is important in determining the desirability of migration destinations and holds substantial amenity value. It also concludes that more work is required to be confident in assuming an elasticity of marginal utility equal to unity. Alternative techniques, including subjective wellbeing and hypothetical equivalence scales, are utilised to avoid having to make potentially restrictive assumptions on preferences for climate. Finally, this thesis stresses the importance of accounting for measurement error in cross-sectional survey data on household income. It seeks to inform how an econometrician can seek to implement appropriate instrumental variables to overcome this error

Extending the aridity record of the Southwest Kalahari: current problems and future perspectives

An extensive luminescence-based chronological framework has allowed the reconstruction of expansions and contractions of the Kalahari Desert over the last 50 ka. However, this chronology is largely based on near-surface pits and sediment exposures. These are the points on the landscape most prone to reactivation and resetting of the luminescence dating ‘clock’. This is proving to be a limiting feature for extending palaeoenvironmental reconstructions further back in time. One way to obviate this is to sample desert marginal areas that only become active during significant arid phases. An alternative is to find and sample deep stratigraphic exposures. The Mamatwan manganese mine at Hotazel in the SW Kalahari meets both these criteria. Luminescence dating of this site shows the upper sedimentary unit to span at least the last 60 ka with tentative age estimates from underlying cemented aeolian units dating back to the last interglacial and beyond. Results from Mamatwan are comparable to new and previously published data from linear dunes in the SW Kalahari but extend back much further. Analysis of the entire data set of luminescence ages for the SW Kalahari brings out important inferences that suggest that different aeolian forms (1) have been active over different time scales in the past, (2) have different sensitivities to environmental changes and (3) have different time scales over which they record and preserve the palaeoenvironmental record. This implies that future optically stimulated luminescence work and palaeoenvironmental reconstructions must consider both site location and its relationship to desert margins and sediment depositional styles, so that the resolution and duration of the aridity record can be optimally understood

Can You Translate Esperanto?

Esperanto is a language that was created in 1887 by Ludovic Lazarus Zamenhof, a Polish polyglot who sought to facilitate communication among the many nations of the world by creating a new language made up of bits and pieces of several existing (mostly European) languages. Though the use of Esperanto never became as widespread as Zamenhof had hoped, more than ten million people around the world speak and understand it, and thousands of books, newspapers, and magazines have been (and continue to be) published in it