Testing Born-Infeld electrodynamics in waveguides

Waveguides can be employed to test non-linear effects in electrodynamics. We solve Born-Infeld equations for TE waves in a rectangular waveguide. We show that the energy velocity acquires a dependence on the amplitude, and harmonic components appear as a consequence of the non-linear behavior.Comment: 3 pages. To appear in PR

Plasmonic nanoparticle enhanced photocurrent in GaN/InGaN/GaN quantum well solar cells

We demonstrate enhanced external quantum efficiency and current-voltage characteristics due to scattering by 100 nm silver nanoparticles in a single 2.5 nm thick InGaN quantum well photovoltaic device. Nanoparticle arrays were fabricated on the surface of the device using an anodic alumina template masking process. The Ag nanoparticles increase light scattering, light trapping, and carrier collection in the III-N semiconductor layers leading to enhancement of the external quantum efficiency by up to 54%. Additionally, the short-circuit current in cells with 200 nm p-GaN emitter regions is increased by 6% under AM 1.5 illumination. AFORS-Het simulation software results were used to predict cell performance and optimize emitter layer thickness

Immigration and house prices under various labour market structures in England and Wales

This article estimates the impact of immigration on local house prices under various local economic structures in England and Wales. Typically, for the nation, newly arriving immigrants add to the overall housing demand; this would in general push up house prices when facing an upward sloping supply curve. However, sorting and native outmigration response to immigration may change the dynamics and impact at the “local” level, depressing house prices through income change. We use data on England and Wales to investigate the local house price effect of immigration when taking into account the local economic structure of the areas, particularly with respect to employment density and average socioeconomic profile of workers. We found that in high density of employment areas but with majority of the occupations in low skill sets, there is a negative house price effect led by immigrant inflows, and this might be due to a type of tenure “downgrade” in the area as immigrants increase the rate of free renting and squatting. Free renters are less likely to participate in the housing market themselves and an increase in the rate of this form of tenure could also reduce their mobility further, hence lead to lower level of housing stock turnover and transaction related renovation; as a result, both housing quality and house price fall. The evidence is in addition to the native flight argument typically found in the literature to explain house price depreciation led by immigration

Tunneling and delocalization in hydrogen bonded systems: a study in position and momentum space

Novel experimental and computational studies have uncovered the proton momentum distribution in hydrogen bonded systems. In this work, we utilize recently developed open path integral Car-Parrinello molecular dynamics methodology in order to study the momentum distribution in phases of high pressure ice. Some of these phases exhibit symmetric hydrogen bonds and quantum tunneling. We find that the symmetric hydrogen bonded phase possesses a narrowed momentum distribution as compared with a covalently bonded phase, in agreement with recent experimental findings. The signatures of tunneling that we observe are a narrowed distribution in the low-to-intermediate momentum region, with a tail that extends to match the result of the covalently bonded state. The transition to tunneling behavior shows similarity to features observed in recent experiments performed on confined water. We corroborate our ice simulations with a study of a particle in a model one-dimensional double well potential that mimics some of the effects observed in bulk simulations. The temperature dependence of the momentum distribution in the one-dimensional model allows for the differentiation between ground state and mixed state tunneling effects.Comment: 14 pages, 13 figure

The quantum algebra of superspace

We present the complete set of $N=1$, $D=4$ quantum algebras associated to massive superparticles. We obtain the explicit solution of these algebras realized in terms of unconstrained operators acting on the Hilbert space of superfields. These solutions are expressed using the chiral, anti-chiral and tensorial projectors which define the three irreducible representations of the supersymmetry on the superfields. In each case the space-time variables are non-commuting and their commutators are proportional to the internal angular momentum of the representation. The quantum algebra associated to the chiral or the anti-chiral projector is the one obtained by the quantization of the Casalbuoni-Brink-Schwarz (superspin 0) massive superparticle. We present a new superparticle action for the (superspin 1/2) case and show that their wave functions are the ones associated to the irreducible tensor multiplet.Comment: 20 pages;changes in the nomenclatur

Genetics and genomics of reproductive performance in dairy and beef cattle

peer-reviewedExcellent reproductive performance in both males and females is fundamental to profitable dairy and beef production systems. In this review we undertook a meta-analysis of genetic parameters for female reproductive performance across 55 dairy studies or populations and 12 beef studies or populations as well as across 28 different studies or populations for male reproductive performance. A plethora of reproductive phenotypes exist in dairy and beef cattle and a meta-analysis of the literature suggests that most of the female reproductive traits in dairy and beef cattle tend to be lowly heritable (0.02 to 0.04). Reproductive-related phenotypes in male animals (e.g. semen quality) tend to be more heritable than female reproductive phenotypes with mean heritability estimates of between 0.05 and 0.22 for semen-related traits with the exception of scrotal circumference (0.42) and field non-return rate (0.001). The low heritability of reproductive traits, in females in particular, does not however imply that genetic selection cannot alter phenotypic performance as evidenced by the decline until recently in dairy cow reproductive performance attributable in part to aggressive selection for increased milk production. Moreover, the antagonistic genetic correlations among reproductive traits and both milk (dairy cattle) and meat (beef cattle) yield is not unity thereby implying that simultaneous genetic selection for both increased (milk and meat) yield and reproductive performance is indeed possible. The required emphasis on reproductive traits within a breeding goal to halt deterioration will vary based on the underlying assumptions and is discussed using examples for Ireland, the United Kingdom and Australia as well as quantifying the impact on genetic gain for milk production. Advancements in genomic technologies can aid in increasing the accuracy of selection for especially reproductive traits and thus genetic gain. Elucidation of the underlying genomic mechanisms for reproduction could also aid in resolving genetic antagonisms. Past breeding programmes have contributed to the deterioration in reproductive performance of dairy and beef cattle. The tools now exist, however, to reverse the genetic trends in reproductive performance underlying the observed phenotypic trends

Naive mean field approximation for image restoration

We attempt image restoration in the framework of the Baysian inference. Recently, it has been shown that under a certain criterion the MAP (Maximum A Posterior) estimate, which corresponds to the minimization of energy, can be outperformed by the MPM (Maximizer of the Posterior Marginals) estimate, which is equivalent to a finite-temperature decoding method. Since a lot of computational time is needed for the MPM estimate to calculate the thermal averages, the mean field method, which is a deterministic algorithm, is often utilized to avoid this difficulty. We present a statistical-mechanical analysis of naive mean field approximation in the framework of image restoration. We compare our theoretical results with those of computer simulation, and investigate the potential of naive mean field approximation.Comment: 9 pages, 11 figure

The collectivity of British alcohol consumption trends across different temporal processes : a quantile age‐period‐cohort analysis

Background and aims UK alcohol consumption per capita has fallen by 18% since 2004 while the alcohol‐specific death rate has risen by 6%. Inconsistent consumption trends across the population may explain this. Drawing on the theory of the collectivity of drinking cultures and age‐period‐cohort analyses, we tested whether consumption trends are consistent across lighter and heavier drinkers for three temporal processes: (i) the life course, (ii) calendar time, (iii) successive birth cohorts. Design Sex‐specific quantile age‐period‐cohort regressions using repeat cross‐sectional survey data. Setting Great Britain, 1984‐2011. Participants Adult (18+) drinkers responding to 17 waves of the General Lifestyle Survey (total N=175,986). Measurements Dependent variable: The 10th, 25th, 50th, 75th, 90th, 95th and 99th quantiles of the logged weekly alcohol consumption distribution (excluding abstainers). Independent variables: seven age groups (18‐24, 25‐34 … 65‐74, 75+), five time periods (1984‐1988 … 2002‐2006, 2008‐2011) and 16 five‐year birth cohorts (1915‐1919 … 1990‐1994). Additional control variables: ethnicity and UK country. Findings Within age, period and cohort trends, changes in consumption were not consistently in the same direction at different quantiles of the consumption distribution. When they were, the scale of change sometimes differed between quantiles. For example, consumption among women decreased by 18% (CI95: ‐32% ‐ ‐2%) but increased by 11% (CI95: 2% ‐ 21%) at the median and by 28% (CI95: 19%‐38%) at the 99th quantile, implying consumption fell among lighter drinkers and rose among heavier drinkers. This type of polarised trend also occurred between 1984‐1988 and 1996‐2000 for men and women. Age trends showed collectivity but cohort trends showed a mixture of collectivity and polarisation. Conclusions Countervailing alcohol consumption and alcohol‐related harm trends in the UK may be explained by lighter and heavier drinkers having different period and cohort trends as well as by the presence of cohort trends that mean consumption may rise in some age groups while falling in others

A comparison of the economic value for enteric methane emissions with other biological traits associated with dairy cows

This is the first study to derive the economic value of enteric methane produced by a ruminant animal. There is considerable interest globally in selecting for low methane-emitting ruminant livestock, as methane is a potent greenhouse gas. However, before enteric methane can be included in a genetic selection index for breeding, the economic value for enteric methane needs to be derived. An animal model including a partial budget was used to derive economic values for a range of production and fitness (health and fertility) traits typically used in genetic selection of dairy cows with the addition of enteric methane. This study found that enteric methane (kilograms/lactation) has an economic value of -£1.68 per kg increase in methane per lactation. The economic value for enteric methane was of similar magnitude to the traits of milk fat yield (£1.14 per unit change in milk fat) and mastitis (-£1.55 per % incidence). Based on the variation seen in the dairy cow population in the UK, genetic selection on enteric methane has potential to increase herd profit per cow and reduce emissions. Even if the economic and abatement gains associated with selecting low methane producing livestock are relatively small, reductions in enteric methane emissions appear possible if a reliable and repeatable measure becomes available for use on commercial farms