Lines in the sand: Social representations of substance use boundaries in life narratives

This study identifies social representations in interviews about alcohol and substance use in the discourse of 129 young adults, who were interviewed for 2.5 to 3.5 hr each for their life histories and use or nonuse of alcoholic beverages and drugs. Respondents spontaneously delineated their substance use boundaries, creating a continuum of behaviors with boundary points separating acceptable from unacceptable behaviors. They used signaling expressions to indicate go and stop signs and movement along the substance use continuum and reported negotiating substance use boundaries both internally and with peers. A ubiquitous narrative element was the cautionary tale, in which a negative exemplar goes too far with alcohol and/or drugs, providing an example of the possible negative outcomes of transgressing boundaries. In general, the narratives revealed complex relationships to alcohol and other drugs that may be useful in refining messages for more effective communication in prevention and intervention programs

Electron-magnon coupling and nonlinear tunneling transport in magnetic nanoparticles

We present a theory of single-electron tunneling transport through a ferromagnetic nanoparticle in which particle-hole excitations are coupled to spin collective modes. The model employed to describe the interaction between quasiparticles and collective excitations captures the salient features of a recent microscopic study. Our analysis of nonlinear quantum transport in the regime of weak coupling to the external electrodes is based on a rate-equation formalism for the nonequilibrium occupation probability of the nanoparticle many-body states. For strong electron-boson coupling, we find that the tunneling conductance as a function of bias voltage is characterized by a large and dense set of resonances. Their magnetic field dependence in the large-field regime is linear, with slopes of the same sign. Both features are in agreement with recent tunneling experiments.Comment: 4 pages, 2 figure

Efficient computation of the Shapley value for game-theoretic network centrality

The Shapley value—probably the most important normative payoff division scheme in coalitional games—has recently been advocated as a useful measure of centrality in networks. However, although this approach has a variety of real-world applications (including social and organisational networks, biological networks and communication networks), its computational properties have not been widely studied. To date, the only practicable approach to compute Shapley value-based centrality has been via Monte Carlo simulations which are computationally expensive and not guaranteed to give an exact answer. Against this background, this paper presents the first study of the computational aspects of the Shapley value for network centralities. Specifically, we develop exact analytical formulae for Shapley value-based centrality in both weighted and unweighted networks and develop efficient (polynomial time) and exact algorithms based on them. We empirically evaluate these algorithms on two real-life examples (an infrastructure network representing the topology of the Western States Power Grid and a collaboration network from the field of astrophysics) and demonstrate that they deliver significant speedups over the Monte Carlo approach. Fo

General method for extracting the quantum efficiency of dispersive qubit readout in circuit QED

We present and demonstrate a general three-step method for extracting the quantum efficiency of dispersive qubit readout in circuit QED. We use active depletion of post-measurement photons and optimal integration weight functions on two quadratures to maximize the signal-to-noise ratio of the non-steady-state homodyne measurement. We derive analytically and demonstrate experimentally that the method robustly extracts the quantum efficiency for arbitrary readout conditions in the linear regime. We use the proven method to optimally bias a Josephson traveling-wave parametric amplifier and to quantify different noise contributions in the readout amplification chain.Comment: 10 pages, 6 figure

Mass and density of B-type asteroid (702) Alauda

Observations with the adaptive optics system on the Very Large Telescope reveal that outer main belt asteroid (702) Alauda has a small satellite with primary to secondary diameter ratio of $\sim$56. The secondary revolves around the primary in 4.9143 $\pm$ 0.007 days at a distance of 1227 $\pm$ 24 km, yielding a total system mass of (6.057 $\pm$ 0.36) $\times$ 10$^{18}$ kg. Combined with an IRAS size measurement, our data yield a bulk density for this B-type asteroid of 1570 $\pm$ 500 kg~m$^{-3}$.Comment: In press, ApJ 2011. 6 pages, 4 figure

Carbon Deficiency in Externally-Polluted White Dwarfs: Evidence for Accretion of Asteroids

Existing determinations show that n(C)/n(Fe) is more than a factor of 10 below solar in the atmospheres of three white dwarfs that appear to be externally-polluted. These results are not easily explained if the stars have accreted interstellar matter, and we re-interpret these measurements as evidence that these stars have accreted asteroids of a chrondritic composition.Comment: 23 pages, 6 figures, accepted for Ap

Large Magnetoresistance in Co/Ni/Co Ferromagnetic Single Electron Transistors

We report on magnetotransport investigations of nano-scaled ferromagnetic Co/Ni/Co single electron transistors. As a result of reduced size, the devices exhibit single electron transistor characteristics at 4.2K. Magnetotransport measurements carried out at 1.8K reveal tunneling magnetoresistance (TMR) traces with negative coercive fields, which we interpret in terms of a switching mechanism driven by the shape anisotropy of the central wire-like Ni island. A large TMR of about 18% is observed within a finite source-drain bias regime. The TMR decreases rapidly with increasing bias, which we tentatively attribute to excitation of magnons in the central island.Comment: 12 pages (including 4 figures). Accepted for publishing on AP

Spatial and temporal resolution of carbon flux estimates for 1983?2002

International audienceWe discuss the spatial and temporal resolution of monthly carbon flux estimates for the period 1983?2002 using a fixed-lag Kalman Smoother technique with a global chemical transport model, and the GLOBALVIEW data product. The observational network has expanded substantially over this period, and we the improvement in the constraints provided flux estimates by observations for the 1990's in comparison to the 1980's. The estimated uncertainties also decrease as observational coverage expands. In this study, we use the Globalview data product for a network that changes every 5 y, rather than using a small number of continually-operating sites (fewer observational constraints) or a large number of sites, some of which may consist almost entirely of extrapolated data. We show that the discontinuities resulting from network changes reflect uncertainty due to a sparse and variable network. This uncertainty effectively limits the resolution of trends in carbon fluxes. The ability of the inversion to distinguish, or resolve, carbon fluxes at various spatial scales is examined using a diagnostic known as the resolution kernel. We find that the global partition between land and ocean fluxes is well-resolved even for the very sparse network of the 1980's, although prior information makes a significant contribution to the resolution. The ability to distinguish zonal average fluxes has improved significantly since the 1980's, especially for the tropics, where the zonal ocean and land biosphere fluxes can be distinguished. Care must be taken when interpreting zonal average fluxes, however, since the lack of air samples for some regions in a zone may result in a large influence from prior flux estimates for these regions. We show that many of the TransCom 3 source regions are distinguishable throughout the period over which estimates are produced. Examples are Boreal and Temperate North America. The resolution of fluxes from Europe and Australia has greatly improved since the 1990's. Other regions, notably Tropical South America and the Equatorial Atlantic remain practically unresolved. Comparisons of the average seasonal cycle of the estimated carbon fluxes with the seasonal cycle of the prior flux estimates reveals a large adjustment of the summertime uptake of carbon for Boreal Eurasia, and an earlier onset of springtime uptake for Temperate North America. In addition, significantly larger seasonal cycles are obtained for some ocean regions, such as the Northern Ocean, North Pacific, North Atlantic and Western Equatorial Pacific, regions that appear to be well-resolved by the inversion

Theory of tunneling spectroscopy in a Mn_12 single-electron transistor by density-functional theory methods

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-ependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance

High resolution measurements of kinetic energy release distributions of neon, argon, and krypton cluster ions using a three sector field mass spectrometer

Using a newly constructed three sector field mass spectrometer (resulting in a BE1E2 field configuration) we have measured the kinetic energy release distributions of neon, argon, and krypton cluster ions. In the present study we used the first two sectors, B and E1, constituting a high resolution mass spectrometer, to select the parent ions in terms of mass, charge, and energy, and studied the decay of those ions in the third field free region. Due to the improved mass resolution we were able to extend earlier studies carried out with a two sector field machine, where an upper size limit arose from the fact that several isotopomers contribute to a decaying parent ion beam when the cluster size exceeds a certain value. Furthermore we developed a new data analysis. It allows us to model also fragment ion peaks that are a superposition of different decay reactions and thus we can determine the average kinetic energy release for all decay reactions of a given cluster ion. In a further step we used these results to determine the binding energies of cluster ions Rg(n) (ngreater than or equal to10) by applying finite heat bath theory. The smaller sizes have not been included in this analysis, because the validity of finite heat bath theory becomes questionable below napproximate to10. The present average kinetic energy releases and binding energies are compared with other experiments and various calculations. (C) 2004 American Institute of Physics