Bosonization of the two-dimensional electron gas in the lowest Landau level

We develop a bosonization scheme for the collective dynamics of a spinless two-dimensional electron gas (2DEG) in the lowest Landau level. The system is treated as a continuous elastic medium, and quantum commutation relations are imposed between orthogonal components of the elastic displacement field. This theory provides a unified description of bulk and edge excitations of compressible and incompressible phases, and explains the results of recent tunneling experiments at the edge of the 2DEG.Comment: 4 pages, includes 1 figur

Experimental study of the microwave emission from electrons in air

We searched for the emission of microwave radiation in the Ku band generated by a 95 keV electron beam in air. We unequivocally detected the radiation, and measured its yield and angular dependence. Both the emitted power and its angular pattern are well described by a model, where microwave photons are generated via bremsstrahlung in the free-electron atomic-nucleus collisions, during the slowdown of the electrons. As a consequence, the radiation is not isotropic but peaked in the forward direction. The emission yield scales proportionally with the number of electrons. This contrasts a previous claim that the yield scales with the number squared, due to coherence. With a Monte Carlo simulation we extrapolate our results to the Ultra High Energy Cosmic Ray energy range.Comment: 5 pages, 4 figures. Accepted for publication in Phys.Rev.

The role of language, social cognition, and social skill in the functional social outcomes of young adolescents with and without a history of SLI

Social skill and language are known to relate, not least in the example of those with specific language impairment (SLI). However, most of the research examining this trend has been conducted on young primary school age children and the nature of the relationships is unclear. Furthermore, little is known about which young people in general have social difficulties and whether language, social cognition, and social skills are directly associated at this age. In this study, a large cohort made up of young people with a history of SLI (N = 134) and a typically developing (TD) group (N = 124) of the same age were followed up in their final year of compulsory schooling (aged 16). Language, social cognition, social skills, and functional social outcomes (friendships and levels of social activity) were assessed using tasks and questionnaires. Modest associations were found between social cognition, language, and social behaviours, the strongest being between language and social cognition. Regression analyses showed that as a combined group, the adolescents' functional social outcomes were most associated with expressive language, social skill, and social cognitive ability. However, the patterns differed when the groups were analysed separately, with social cognition playing more of a role for those with SLI. These findings suggest that poor language may play a complex role in adolescents' social development

Adiabatic evolution on a spatial-photonic Ising machine

Combinatorial optimization problems are crucial for widespread applications but remain difficult to solve on a large scale with conventional hardware. Novel optical platforms, known as coherent or photonic Ising machines, are attracting considerable attention as accelerators on optimization tasks formulable as Ising models. Annealing is a well-known technique based on adiabatic evolution for finding optimal solutions in classical and quantum systems made by atoms, electrons, or photons. Although various Ising machines employ annealing in some form, adiabatic computing on optical settings has been only partially investigated. Here, we realize the adiabatic evolution of frustrated Ising models with 100 spins programmed by spatial light modulation. We use holographic and optical control to change the spin couplings adiabatically, and exploit experimental noise to explore the energy landscape. Annealing enhances the convergence to the Ising ground state and allows to find the problem solution with probability close to unity. Our results demonstrate a photonic scheme for combinatorial optimization in analogy with adiabatic quantum algorithms and enforced by optical vector-matrix multiplications and scalable photonic technology.Comment: 9 pages, 4 figure

Large-scale photonic Ising machine by spatial light modulation

Quantum and classical physics can be used for mathematical computations that are hard to tackle by conventional electronics. Very recently, optical Ising machines have been demonstrated for computing the minima of spin Hamiltonians, paving the way to new ultra-fast hardware for machine learning. However, the proposed systems are either tricky to scale or involve a limited number of spins. We design and experimentally demonstrate a large-scale optical Ising machine based on a simple setup with a spatial light modulator. By encoding the spin variables in a binary phase modulation of the field, we show that light propagation can be tailored to minimize an Ising Hamiltonian with spin couplings set by input amplitude modulation and a feedback scheme. We realize configurations with thousands of spins that settle in the ground state in a low-temperature ferromagnetic-like phase with all-to-all and tunable pairwise interactions. Our results open the route to classical and quantum photonic Ising machines that exploit light spatial degrees of freedom for parallel processing of a vast number of spins with programmable couplings.Comment: https://journals.aps.org/prl/accepted/7007eYb7N091546c41ad4108828a97d5f92006df

Virtual reality in the service of user participation in architecture

The issue of user participation in the processes of building and urban design is enjoying renewed attention following its relative neglect over the last 20 years due, in large measure, to significant advances in emerging information technologies, particularly multimedia, virtual reality and internet technologies. This paper re-established the theoretical framework for participatory design evolved in the late sixties and early seventies as part of the movement towards a more explicit design methodology and attempts an explanation of why the concept failed to gain commitment from the architectural and urban design professionals. The paper then gives an account of two significant developments in the evolution of the application of information technologies with which the authors have been engaged. These are: i. a responsive and interactive interface to wholly immersive and realistic virtual reality representations of proposed buildings and urban neighbourhoods. ii. an intuitive and platform-independent VR modelling environment allowing collaborative evolution of the scheme from within the virtual world. The impact of these IT developments is demonstrated in the context of the design of a leisure facility for a community of users with physical impairment

Narrative in adolescent specific language impairment (SLI): a comparison with peers across two different narrative genres

Background: Narrative may provide a useful way in which to assess the language ability of adolescents with specific language impairment and may be more ecologically valid than standardized tests. However, the language of this age group is seldom studied and, furthermore, the effect of narrative genre has not been explored in detail. Methods & Procedures: A total of 99 typically developing adolescents and 19 peers with specific language impairment were given two different types of narrative task: a story-telling condition and a conversational condition. Four areas of narrative (productivity, syntactic complexity, syntactic errors and performance) were assessed. Outcomes & Results: The group with specific language impairment was poorer on most aspects of narrative confirming recent research that specific language impairment is a long-term disorder. A number of measures also showed interactions between group and genre, with story-telling proving to be a disproportionately more difficult task for the specific language impairment group. Error analysis also suggested that the specific language impairment group was making qualitatively different errors to the typically developing group, even within a genre. Conclusions: Adolescents with specific language impairment are not only poorer at both types of narrative than peers, but also show different patterns of competence and error, and require more support from the narrative-partner. Clinical Implications: Assessments of adolescents are less frequent than at younger ages. This is partly because of the sparsity of tests available in this age range. Qualitative analysis of narrative might prove a useful alternative. The findings suggest that in every-day conversation, young people with specific language impairment manage their difficulties more discreetly and this might make them harder to identify in a mainstream setting

On the generation and the nonlinear dynamics of X-waves of the Schroedinger equation

The generation of finite energy packets of X-waves is analysed in normally dispersive cubic media by using an X-wave expansion. The 3D nonlinear Schroedinger model is reduced to a 1D equation with anomalous dispersion. Pulse splitting and beam replenishment as observed in experiments with water and Kerr media are explained in terms of a higher order breathing soliton. The results presented also hold in periodic media and Bose-condensed gases.Comment: 18 pages, 6 figures, corrected version to be published in Physical Review