Magnetoswitching of current oscillations in diluted magnetic semiconductor nanostructures

Strongly nonlinear transport through Diluted Magnetic Semiconductor multiquantum wells occurs due to the interplay between confinement, Coulomb and exchange interaction. Nonlinear effects include the appearance of spin polarized stationary states and self-sustained current oscillations as possible stable states of the nanostructure, depending on its configuration and control parameters such as voltage bias and level splitting due to an external magnetic field. Oscillatory regions grow in size with well number and level splitting. A systematic analysis of the charge and spin response to voltage and magnetic field switching of II-VI Diluted Magnetic Semiconductor multiquantum wells is carried out. The description of stationary and time-periodic spin polarized states, the transitions between them and the responses to voltage or magnetic field switching have great importance due to the potential implementation of spintronic devices based on these nanostructures.Comment: 14 pages, 4 figures, Revtex, to appear in PR

Adaptive sampling in context-aware systems: a machine learning approach

As computing systems become ever more pervasive, there is an increasing need for them to understand and adapt to the state of the environment around them: that is, their context. This understanding comes with considerable reliance on a range of sensors. However, portable devices are also very constrained in terms of power, and hence the amount of sensing must be minimised. In this paper, we present a machine learning architecture for context awareness which is designed to balance the sampling rates (and hence energy consumption) of individual sensors with the significance of the input from that sensor. This significance is based on predictions of the likely next context. The architecture is implemented using a selected range of user contexts from a collected data set. Simulation results show reliable context identification results. The proposed architecture is shown to significantly reduce the energy requirements of the sensors with minimal loss of accuracy in context identification

The stability of food intake between adolescence and adulthood: a 21-year follow-up

Studies of the diet of adolescents in the UK demonstrate that dietary habits known to be detrimental to health in adulthood are evident at an early age. For example, Gregory et al (2000) found 4-18 year olds in the UK to have a frequent consumption of fatty and sugary foods and low consumption of fruit and vegetables. Concerns have therefore been expressed regarding the diet of children and adolescents and the continuation of these dietary habits into adulthood (HEA, 1995; Gaziano, 1998). This study aimed to investigate the extent to which these concerns may be justified by determining the stability of food intake of a group of adolescents followed up 21 years later in adulthood. The investigation involved 202 individuals from whom dietary data were collected in 1979-80 (mean age 11.6 years) (Hackett et al. 1984) and again in 2000-1 (mean age 32.5 years). Dietary data were collected at both time-points using two 3 d estimated food diaries followed by an interview to determine portion sizes using the method considered most appropriate at the time, i.e. calibrated food models in 1979-80 and a photographic food atlas (Nelson et al. 1997) in 2000-1. Foods consumed were allocated to one, or a combination of, the five food groups of the ‘Balance of Good Health’ food selection guide (HEA, 1994) according to Gatenby et al. (1995). The weight of food eaten from each of the five food groups was calculated (percentage of total weight of food consumed) and Pearson correlation coefficients generated to provide an estimate of the stability of food intake. The HEA guide advises that a balanced diet should consist of around 33% fruit and vegetables, 33% bread, other cereals and potatoes, 8% foods containing fat and/or sugar, 12% meat, fish and alternatives and 15% milk and dairy products (Gatenby et al. 1995). A shift in the group’s food intake towards the recommendations had occurred with age, most notably with a decrease in foods containing fat and/or sugar and an increase in fruit and vegetables. Nevertheless, at both ages, intakes of foods containing fat and/or sugar, meat, fish and alternatives were higher, and fruit, vegetables, bread, other cereals and potatoes lower than currently recommended. In addition, although there was significant evidence of tracking of relative intake of bread, cereals and potatoes (P<0.01), fruit and vegetables (P<0.01), and meat, fish and alternatives (P=0.02) between 11.6 and 32.5 years, the correlations were not strong. In conclusion, food intake patterns had changed considerably from early adolescence through to adulthood in a direction more in line with the current recommendations. The predictive value of an adolescent’s food intake of their intake in adulthood was found to be significant, but not strong. Further investigations will consider the extent to which this is influenced by factors such as social class, gender and educational level, as well as assessing tracking in terms of relative nutrient intakes

Deep ROSAT Surveys & the contribution of AGNs to the soft X-ray background

The ROSAT Deep Surveys in the Lockman Hole have revealed that AGNs are the main contributors (~75%) to the soft X-ray background in the 1–2 keV band. Using new optical/infrared and radio observations we have obtained a nearly complete identification (93%) of the 91 X-ray sources down to a limiting flux of 1.2·10^(–15) erg cm^(–2) s^(–1) in the 0.5–2.0 keV band. We present the optical colors and the emission line properties of our AGNs in comparison with other X-ray selected AGN samples. Furthermore we discuss the fraction of red AGNs found in the ROSAT Deep Surveys. From the ROSAT Deep Surveys we see no evidence for a new class of X-ray bright galaxies, which significantly contributes to the soft X-ray background

Anomalous hydrodynamics and "normal" fluids in rapidly rotating BECs

In rapidly rotating bose systems we show that there is a region of anomalous hydrodynamics whilst the system is still condensed, which coincides with the mean field quantum Hall regime. An immediate consequence is the absence of a normal fluid in any conventional sense. However, even the superfluid hydrodynamics is not described by conventional Bernoulli and continuity equations. We show there are kinematic constraints which connect spatial variations of density and phase, that the positions of vortices are not the simplest description of the dynamics of such a fluid (despite their utility in describing the instantaneous state of the condensate) and that the most compact description allows solution of some illuminating examples of motion. We demonstrate, inter alia, a very simple relation between vortices and surface waves. We show the surface waves can form a "normal fluid" which absorbs energy and angular momentum from vortex motion in the trap. The time scale of this process is sensitive to the initial configuration of the vortices, which can lead to long-lived vortex patches - perhaps related to those observed at JILA.Comment: 4 pages; 1 sentence and references modifie

Electron orbital valves made of multiply connected armchair carbon nanotubes with mirror-reflection symmetry: tight-binding study

Using the tight-binding method and the Landauer-B\"{u}ttiker conductance formalism, we demonstrate that a multiply connected armchair carbon nanotube with a mirror-reflection symmetry can sustain an electron current of the $\pi$-bonding orbital while suppress that of the $\pi$-antibonding orbital over a certain energy range. Accordingly, the system behaves like an electron orbital valve and may be used as a scanning tunneling microscope to probe pairing symmetry in d-wave superconductors or even orbital ordering in solids which is believed to occur in some transition-metal oxides.Comment: 4 figures, 12 page

Cosmic homogeneity demonstrated with luminous red galaxies

We test the homogeneity of the Universe at $z\sim 0.3$ with the Luminous Red Galaxy (LRG) spectroscopic sample of the Sloan Digital Sky Survey. First, the mean number $N(R)$ of LRGs within completely surveyed LRG-centered spheres of comoving radius $R$ is shown to be proportional to $R^3$ at radii greater than $R\sim 70 h^{-1} \mathrm{Mpc}$. The test has the virtue that it does not rely on the assumption that the LRG sample has a finite mean density; its results show, however, that there \emph{is} such a mean density. Secondly, the survey sky area is divided into 10 disjoint solid angular regions and the fractional rms density variations of the LRG sample in the redshift range $0.2<z<0.35$ among these ($\sim 2\times10^7 h^{-3} \mathrm{Mpc^3}$) regions is found to be 7 percent of the mean density. This variance is consistent with typical biased \lcdm models and puts very strong constraints on the quality of SDSS photometric calibration.Comment: submitted to Ap