Inflaton Particles in Reheating

In many theories of reheating starting from the classical spatially homogeneous inflaton field, its accompanying inhomogeneous part (which arises from primordial quantum fluctuations) is treated as a first order perturbation. We examine some consequences of treating it non-perturbatively in a model where a first order treatment is invalid. In particular we consider effects on the long-wavelength curvature parameter relevant to the cosmic microwave background fluctuations.Comment: 14 pages, 4 figures;code corrected,figures and some conclusions change

Homework in English language teaching – Hong Kong primary English language teachers’ beliefs and practices

Homework is an important practice commonly expected of teachers in schools worldwide. However, teachers’ homework practices are not well understood. This study develops our understanding of English language homework as experienced by primary school English language teachers in Hong Kong, specifically teachers’ homework practices, beliefs regarding homework’s utility as a teaching and learning tool, and sociocultural and contextual influences on these practices and beliefs. A two-stage mixed-method research design was employed which generated qualitative and quantitative data. In the first stage, 279 English language primary school teachers working in aided or government primary schools in Hong Kong were surveyed. The second stage involved in-depth interviews with 11 teachers and the collection of homework samples. Homework was found to be a universal practice of all the participants. They assigned various kinds of homework for various purposes while devoting a significant amount of time to homework-related activities. Participants strongly believed in the benefits of homework as a teaching and learning tool. They provided characteristics of homework practices and activities, which they believe to be effective. However, they did not always see their current homework practices as effective. Such practices were often standardised within a school, with teachers teaching the same grade being required to give the same homework as their colleagues. The data suggests, this standardisation of practices appears to be due to sociocultural and contextual influences, including school policies, parents’ expectations and cultural norms. This standardisation can limit teachers’ ability to develop homework practices that meet the needs of their learners. By developing a conceptual framework, this study adds to the growing understanding of the pedagogical practice of homework within the Hong Kong context

An Exact Calculation of the Energy Density of Cosmological Gravitational Waves

In this paper we calculate the Bogoliubov coefficients and the energy density of the stochastic gravitational wave background for a universe that undergoes inflation followed by radiation domination and matter domination, using a formalism that gives the Bogoliubov coefficients as continous functions of time. By making a reasonable assumption for the equation of state during reheating, we obtain in a natural way the expected high frequency cutoff in the spectral energy density.Comment: 12 pages+5 figures, uuencoded file,DF/IST-2.9

Do risk, time and prosocial preferences predict risky sexual behaviour of youths in a low-income, high-risk setting?

Young people in sub-Saharan Africa are particularly at high risk of sexually transmitted infections. Little is known about their preferences and even less about their association with risky sexual behaviour. We conducted incentivized economic experiments to measure risk, time and prosocial preferences in Zimbabwe. Preferences measured at baseline predict biomarker and self-reported measures of risky sexual behaviour gathered 12 months later. We find robust evidence that individuals more altruistic at baseline are more likely to be Herpes Simplex Virus Type-2 (HSV-2) positive 12 months later. Analysis by sex shows this association is driven by our sample of women. Having more sexual partners is associated with greater risk tolerance amongst men and greater impatience amongst women. Results highlight heterogeneity in the association between preferences and risky sexual behaviour

Polarisation Independent Liquid Crystal Lenses and Contact Lenses using Embossed Reactive Mesogens

Liquid crystal lenses have promise in optical systems owing to their tunability combined with low electrical power, cost, and weight. A good example of such a system is switchable contact lenses for the correction of age‐related presbyopia. Sufficiently large phase modulation can be done using nematic liquid crystals in a meniscus lens configuration. However, the birefringent materials are inherently polarisation dependent, usually requiring orthogonal polarisations to be focussed separately. A novel method is presented for producing polarisation independent lenses based on reactive mesogens. Results are presented for a 2‐level and 3‐level diffractive Fresnel lenses, and the promise of the technique for use in refractive lenses such as contact lenses is discussed

Polarisation Independent Liquid Crystal Lenses using Embossed Reactive Mesogens

Liquid crystal lenses have promise in optical systems owing to their tunability combined with low electrical power, cost and weight. A good example of such a system is switchable contact lenses for the correction of age‐related presbyopia. Large phase modulation can be done using nematic liquid crystals. However, the birefringent materials are inherently polarisation dependent, usually requiring orthogonal polarisations to be focused separately. A novel method is presented for producing polarisation independent lenses based on reactive mesogens

Non-diffractive mechanisms in the ϕ\phi meson photoproduction on nucleons

We examine the non-diffractive mechanisms in the $\phi$ meson photoproduction from threshold up to a few GeV using an effective Lagrangian in a constituent quark model. The new data from CLAS at large angles can be consistently accounted for in terms of {\it s}- and {\it u}-channel processes. Isotopic effects arising from the reactions $\gamma p\to \phi p$ and $\gamma n\to \phi n$, are investigated by comparing the cross sections and polarized beam asymmetries. Our result highlights an experimental means of studying non-diffractive mechanisms in $\phi$ meson photoproduction.Comment: 4 eps figures, version accepted by Phys. Lett.