The June 2012 transit of Venus. Framework for interpretation of observations

Ground based observers have on 5/6th June 2012 the last opportunity of the century to watch the passage of Venus across the solar disk from Earth. Venus transits have traditionally provided unique insight into the Venus atmosphere through the refraction halo that appears at the planet outer terminator near ingress/egress. Much more recently, Venus transits have attracted renewed interest because the technique of transits is being successfully applied to the characterization of extrasolar planet atmospheres. The current work investigates theoretically the interaction of sunlight and the Venus atmosphere through the full range of transit phases, as observed from Earth and from a remote distance. Our model predictions quantify the relevant atmospheric phenomena, thereby assisting the observers of the event in the interpretation of measurements and the extrapolation to the exoplanet case. Our approach relies on the numerical integration of the radiative transfer equation, and includes refraction, multiple scattering, atmospheric extinction and solar limb darkening, as well as an up to date description of the Venus atmosphere. We produce synthetic images of the planet terminator during ingress/egress that demonstrate the evolving shape, brightness and chromaticity of the halo. Guidelines are offered for the investigation of the planet upper haze from vertically-unresolved photometric measurements. In this respect, the comparison with measurements from the 2004 transit appears encouraging. We also show integrated lightcurves of the Venus/Sun system at various phases during transit and calculate the respective Venus-Sun integrated transmission spectra. The comparison of the model predictions to those for a Venus-like planet free of haze and clouds (and therefore a closer terrestrial analogue) complements the discussion and sets the conclusions into a broader perspective.Comment: 14 pages; 14 figures; Submitted on 02/06/2012; A&A, accepted for publication on 30/08/201

A critical analysis of the hydrino model

Recently, spectroscopic and calorimetric observations of hydrogen plasmas and chemical reactions with them have been interpreted as evidence for the existence of electronic states of the hydrogen atom with a binding energy of more than 13.6 eV. The theoretical basis for such states, that have been dubbed hydrinos, is investigated. We discuss both, the novel deterministic model of the hydrogen atom, in which the existence of hydrinos was predicted, and standard quantum mechanics. Severe inconsistencies in the deterministic model are pointed out and the incompatibility of hydrino states with quantum mechanics is reviewed.Comment: 9 page

The role of regulatory mechanisms for control of plant diseases and food security — case studies from potato production in Britain

Being aware of the potentially devastating impacts of plant diseases on food security, governments have designed and employ plant health legislation to prevent or inhibit the worst impacts. The development of such policies in Britain, and latterly in Europe, can be closely linked to disease events that have occurred in the potato sector. We analyse early and current examples of policies governing potato diseases in Britain to identify the decision processes leading to the implementation of such phytosanitary policies and how they have evolved over time and in response to different disease threats. Reasons for developing and implementing phytosanitary policies include the desire to prevent pathogens being introduced (entering and establishing in a new area), the protection of export markets, and the lack of effective control measures. Circumstances in which regulatory policies would not be appropriate could include situations where a disease is already widely distributed, unacceptable costs, lack of exclusion measures, or difficulties of disease diagnosis. We conclude that in general, government policies have worked well in protecting British potato growing over the last one hundred years, despite of the failures of some of the policies discussed here. They have also contributed much to the development of plant health policies for other crops. Voluntary grower initiatives are a new mechanism complementing existing formal policies with an additional level of security that allows individual growers to take on additional responsibility rather than relying entirely on government legislation

Decay rate and other properties of the positronium negative ion

A new method for detecting the positronium minus ion is described, and the possibility of a long positronium mean free path in a solid is discussed

An investigation into the effect of thickness of titanium dioxide and gold-silver nanoparticle titanium dioxide composite thin-films on photocatalytic activity and photo-induced oxygen production in a sacrificial system

Thin films of titanium dioxide and titanium dioxide with incorporated gold and silver nanoparticles were deposited onto glass microscope slides, steel and titanium foil coupons by two sol–gel dip-coating methods. The film's photocatalytic activity and ability to evolve oxygen in a sacrificial solution were assessed. It was found that photocatalytic activity increased with film thickness (from 50 to 500 nm thick samples) for the photocatalytic degradation of methylene blue in solution and resazurin redox dye in an intelligent ink dye deposited on the surface. Contrastingly, an optimum film thickness of [similar]200 nm for both composite and pure films of titanium dioxide was found for water oxidation, using persulfate (S2O82−) as a sacrificial electron acceptor. The nanoparticle composite films showed significantly higher activity in oxygen evolution studies compared with plain TiO2 films

Strongly Enhanced Hole-Phonon Coupling in the Metallic State of the Dilute Two-Dimensional Hole Gas

We have studied the temperature dependent phonon emission rate $P$($T$) of a strongly interacting ($r_s\geq$22) dilute 2D GaAs hole system using a standard carrier heating technique. In the still poorly understood metallic state, we observe that $P$($T$) changes from $P$($T$)$\sim T^5$ to $P$($T$)$\sim T^7$ above 100mK, indicating a crossover from screened piezoelectric(PZ) coupling to screened deformation potential(DP) coupling for hole-phonon scattering. Quantitative comparison with theory shows that the long range PZ coupling between holes and phonons has the expected magnitude; however, in the metallic state, the short range DP coupling between holes and phonons is {\it almost twenty times stronger} than expected from theory. The density dependence of $P$($T$) shows that it is {\it easier} to cool low density 2D holes in GaAs than higher density 2D hole systems.Comment: To appear in Phys. Rev. Let