Time dependent transport phenomena

The aim of this review is to give a pedagogical introduction to our recently proposed ab initio theory of quantum transport.Comment: 28 pages, 18 figure

Parent and teacher attitudes to pharmacological management of medically diagnosed attention deficit primary school children

The purpose of this study was to compare the attitudes of parents and teachers to the use of pharmacological management or intervention for the child with ADHD in the classroom. Particular focus was placed on differences in attitude toward the use of stimulants, for the management of emotional/behavioural, cognitive/academic, social and classroom organizational behaviours of children with ADHD. Thirty female Western Australian primary school teachers and 90 female parents participated in the present investigation. Participants included: (a) parents of non-medicated children with ADHD, (b) parents of medicated children with ADHD, (c) teachers in regular primary schools, and (d) parents of non-affected children. These participants were given an attitude questionnaire to determine their attitudes towards the use of stimulant medications with children who have ADHD. Teachers held significantly less positive attitudes toward the pharmacological management of children with ADHD, than did the parents surveyed. Parents of medicated children with ADHD were significantly more positive in their attitudes towards pharmacological management, than were parents of non-medicated children with ADHD. Parents of medically diagnosed children with ADHD, collectively held significantly more positive attitudes toward pharmacological management for these children, than parents of non-affected children. Findings are discussed in relation to previous research, which suggests that differences in attitudes may be related to a respondent\u27s current knowledge and experiences with pharmacological management for children who have ADHD. Practical implications for parental support and education of teachers are outlined

An exact Coulomb cutoff technique for supercell calculations

We present a new reciprocal space analytical method to cutoff the long range interactions in supercell calculations for systems that are infinite and periodic in 1 or 2 dimensions, extending previous works for finite systems. The proposed cutoffs are functions in Fourier space, that are used as a multiplicative factor to screen the bare Coulomb interaction. The functions are analytic everywhere but in a sub-domain of the Fourier space that depends on the periodic dimensionality. We show that the divergences that lead to the non-analytical behaviour can be exactly cancelled when both the ionic and the Hartree potential are properly screened. This technique is exact, fast, and very easy to implement in already existing supercell codes. To illustrate the performance of the new scheme, we apply it to the case of the Coulomb interaction in systems with reduced periodicity (as one-dimensional chains and layers). For those test cases we address the impact of the cutoff in different relevant quantities for ground and excited state properties, namely: the convergence of the ground state properties, the static polarisability of the system, the quasiparticle corrections in the GW scheme and in the binding energy of the excitonic states in the Bethe-Salpeter equation. The results are very promising.Comment: Submitted to Physical Review B on Dec 23rd 200

Bound excitons in time-dependent density-functional-theory: optical and energy-loss spectra

A robust and efficient frequency dependent and non-local exchange-correlation $f_{xc}(r,r';\omega)$ is derived by imposing time-dependent density-functional theory (TDDFT) to reproduce the many-body diagrammatic expansion of the Bethe-Salpeter polarization function. As an illustration, we compute the optical spectra of LiF, \sio and diamond and the finite momentum transfer energy-loss spectrum of LiF. The TDDFT results reproduce extremely well the excitonic effects embodied in the Bethe-Salpeter approach, both for strongly bound and resonant excitons. We provide a working expression for $f_{xc}$ that is fast to evaluate and easy to implement.Comment: 4 pages, 2 figures. To appear in Phys. Rev. Let

Micro-eukaryotic diversity in hypolithons from Miers Valley, Antarctica

The discovery of extensive and complex hypolithic communities in both cold and hot deserts has raised many questions regarding their ecology, biodiversity and relevance in terms of regional productivity. However, most hypolithic research has focused on the bacterial elements of the community. This study represents the first investigation of micro-eukaryotic communities in all three hypolith types. Here we show that Antarctic hypoliths support extensive populations of novel uncharacterized bryophyta, fungi and protists and suggest that well known producer-decomposer-predator interactions may create the necessary conditions for hypolithic productivity in Antarctic deserts

Power Spectra in a Zero-Range Process on a Ring: Total Occupation Number in a Segment

We study the dynamics of density fluctuations in the steady state of a non-equilibrium system, the Zero-Range Process on a ring lattice. Measuring the time series of the total number of particles in a \emph{segment} of the lattice, we find remarkable structures in the associated power spectra, namely, two distinct components of damped-oscillations. The essential origin of both components is shown in a simple pedagogical model. Using a more sophisticated theory, with an effective drift-diffusion equation governing the stochastic evolution of the local particle density, we provide reasonably good fits to the simulation results. The effects of altering various parameters are explored in detail. Avenues for improving this theory and deeper understanding of the role of particle interactions are indicated.Comment: 21 pages, 15 figure