Three-dimensional fluid motion in Faraday waves: creation of vorticity and generation of two-dimensional turbulence

We study the generation of 2D turbulence in Faraday waves by investigating the creation of spatially periodic vortices in this system. Measurements which couple a diffusing light imaging technique and particle tracking algorithms allow the simultaneous observation of the three-dimensional fluid motion and of the temporal changes in the wave field topography. Quasi-standing waves are found to coexist with a spatially extended fluid transport. More specifically, the destruction of regular patterns of oscillons coincides with the emergence of a complex fluid motion whose statistics are similar to that of two-dimensional turbulence. We reveal that a lattice of oscillons generates vorticity at the oscillon scale in the horizontal flow. The interaction of these vortices explain how 2D turbulence is fueled by almost standing waves. Remarkably, the curvature of Lagrangian trajectories reveals a "footprint" of the forcing scale vortices in fully developed turbulence. 2D Navier-Stokes turbulence should be considered a source of disorder in Faraday waves. These findings also provide a new paradigm for vorticity creation in 2D flows

Electron localisation in static and time-dependent one-dimensional model systems

Electron localization is the tendency of an electron in a many-body system to exclude other electrons from its vicinity. Using a new natural measure of localization based on the exact manyelectron wavefunction, we find that localization can vary considerably between different ground-state systems, and can also be strongly disrupted, as a function of time, when a system is driven by an applied electric field. We use our new measure to assess the well-known electron localization function (ELF), both in its approximate single-particle form (often applied within density-functional theory) and its full many-particle form. The full ELF always gives an excellent description of localization, but the approximate ELF fails in time-dependent situations, even when the exact Kohn-Sham orbitals are employed.Comment: 7 pages, 4 figure

Diffusional Relaxation in Random Sequential Deposition

The effect of diffusional relaxation on the random sequential deposition process is studied in the limit of fast deposition. Expression for the coverage as a function of time are analytically derived for both the short-time and long-time regimes. These results are tested and compared with numerical simulations.Comment: 9 pages + 2 figure

Associated reading skills in children with a history of Specific Language Impairment (SLI)

A large cohort of 200 eleven-year-old children with Specific Language Impairment (SLI) were assessed on basic reading accuracy and on reading comprehension as well as language tasks. Reading skills were examined descriptively and in relation to early language and literacy factors. Using stepwise regression analyses in which age and nonverbal IQ were controlled for, it was found that a single word reading measure taken at 7 years was unsurprisingly a strong predictor of the two different types of reading ability. However, even with this measure included, a receptive syntax task (TROG) entered when reading accuracy score was the DV. Furthermore, a test of expressive syntax/narrative and a receptive syntax task completed at 7 years entered into the model for word reading accuracy. When early reading accuracy was excluded from the analyses, early phonological skills also entered as a predictor of both reading accuracy and comprehension at 11 years. The group of children with a history of SLI were then divided into those with no literacy difficulties at 11 and those with some persisting literacy impairment. Using stepwise logistic regression, and again controlling for IQ and age, 7 years receptive syntax score (but not tests of phonology, expressive vocabulary or expressive syntax/narrative) entered as a positive predictor of membership of the ‘no literacy problems’ group regardless of whether early reading accuracy was controlled for in step one. The findings are discussed in relation to the overlap of SLI and dyslexia and the long term sequelae of language impairment

Specificity in V(D)J recombination: new lessons from biochemistry and genetics

Recent in vitro work on V(D)J recombination has helped to clarify its mechanism. The first stage of the reaction, which can be reproduced with the purified RAG1 and RAG2 proteins, is a site-specific cleavage that generates the same broken DNA species found in vivo. The cleavage reaction is closely related to known types of transpositional recombination, such as that of HIV integrase. All the site specificity of V(D)J recombination, including the 12/23 rule, is determined by the RAG proteins. The later steps largely overlap with the repair of radiation-induced DNA double-strand breaks, as indicated by the identity of several newly characterized factors involved in repair. These developments open the way for a thorough biochemical study of V(D)J recombination

Do natural enemies really make a difference? Field scale impacts of parasitoid wasps and hoverfly larvae on cereal aphid populations

Naturally occurring predators and parasitoids are known to reduce the abundance of pest invertebrates in arable crops, yet current treatment thresholds do not account for such a contribution to pest management. In the present study, we provide evidence for the presence of natural enemies correlating with a subsequent reduction in pest population growth. The abundance of cereal aphid pests and two key aphidophagous natural enemies, parasitoid wasps (Aphidiinae) and hoverfly larvae (Syrphinae), was assessed at field boundaries and interiors in southeast England. The highest rate of aphid population growth was associated with locations where no natural enemies were found. The presence of either Aphidiinae wasps or predatory Syrphinae larvae was associated with a reduction in the rate of aphid population growth, irrespective of location within the field, and overall aphid population growth was negatively correlated with increasing natural enemy abundance. The results of the present study indicate that natural enemies contribute significantly to pest control, and provide further evidence supporting the use of management strategies for promoting natural enemies in agro-ecosystems. Aphid predators and parasitoids make an important contribution to aphid pest control within cereal fields, and thresholds for insecticide application should account for this to avoid unnecessary treatments