Improved chlorate candle provides concentrated oxygen source

Improved chlorate candle is used as a solid, portable source of oxygen in emergency situations. It contains sodium chlorate, iron, barium peroxide, and glass mixed in powdered form. The oxygen evolves from the decomposition of the sodium chlorate when an ignition pellet is electrically initiated

Spin noise spectroscopy in GaAs

We observe the noise spectrum of electron spins in bulk GaAs by Faraday rotation noise spectroscopy. The experimental technique enables the undisturbed measurement of the electron spin dynamics in semiconductors. We measure exemplarily the electron spin relaxation time and the electron Lande g-factor in n-doped GaAs at low temperatures and find good agreement of the measured noise spectrum with an unpretentious theory based on Poisson distribution probability.Comment: 4 pages, 4 figure

Parasitic pumping currents in an interacting quantum dot

We analyze the charge and spin pumping in an interacting dot within the almost adiabatic limit. By using a non-equilibrium Green's function technique within the time-dependent slave boson approximation, we analyze the pumped current in terms of the dynamical constraints in the infinite-U regime. The results show the presence of parasitic pumping currents due to the additional phases of the constraints. The behavior of the pumped current through the quantum dot is illustrated in the spin-insensitive and in the spin-sensitive case relevant for spintronics applications

Excitation Induced Dephasing in Semiconductor Quantum Dots

A quantum kinetic theory is used to compute excitation induced dephasing in semiconductor quantum dots due to the Coulomb interaction with a continuum of states, such as a quantum well or a wetting layer. It is shown that a frequency dependent broadening together with nonlinear resonance shifts are needed for a microscopic explanation of the excitation induced dephasing in such a system, and that excitation induced dephasing for a quantum-dot excitonic resonance is different from quantum-well and bulk excitons.Comment: 6 pages, 4 figures. Extensively revised text, two figures change

Competition between Kondo screening and quantum Hall edge reconstruction

We report on a Kondo correlated quantum dot connected to two-dimensional leads where we demonstrate the renormalization of the g-factor in the pure Zeeman case i.e, for magnetic fields parallel to the plane of the quantum dot. For the same system we study the influence of orbital effects by investigating the quantum Hall regime i.e. a perpendicular magnetic field is applied. In this case an unusual behaviour of the suppression of the Kondo effect and of the split zero-bias anomaly is observed. The splitting decreases with magnetic field and shows discontinuous changes which are attributed to the intricate interplay between Kondo screening and the quantum Hall edge structure originating from electrostatic screening. This edge structure made up of compressible and incompressible stripes strongly affects the Kondo temperature of the quantum dot and thereby influences the renormalized g-factor

Physicians' preferences for information sources: a meta-analytic study.

Identification of the resources physicians use to acquire information for clinical practice and medical research is an important area of research for health sciences librarianship and medical practice. During the past twenty years several studies have addressed questions about physicians' preferences for information sources, but generalization from the results of these studies has been hampered by limited sampling, diverse methods, and varied reportorial formats. Meta-analysis provides a method for reducing these limits. Using a meta-analytic procedure, this study reviews twelve studies published between 1978 and 1992, categorizes and ranks the physicians' preferred information sources reported in each study, then aggregates and counts the frequencies of the top six preferences, as well as the associated first and second preferences, for all the study populations or their strata. The results indicate that physicians prefer to obtain information from journals and books, but also that they often consult colleagues to get answers to clinical and research questions. The implications of these findings for health sciences librarianship are briefly discussed. Originally published Bulletin of the Medical Library Association, Vol. 85, No. 3, July 199

Anomalous dephasing of bosonic excitons interacting with phonons in the vicinity of the Bose-Einstein condensation

The dephasing and relaxation kinetics of bosonic excitons interacting with a thermal bath of acoustic phonons is studied after coherent pulse excitation. The kinetics of the induced excitonic polarization is calculated within Markovian equations both for subcritical and supercritical excitation with respect to a Bose-Einstein condensation (BEC). For excited densities n below the critical density n_c, an exponential polarization decay is obtained, which is characterized by a dephasing rate G=1/T_2. This dephasing rate due to phonon scattering shows a pronounced exciton-density dependence in the vicinity of the phase transition. It is well described by the power law G (n-n_c)^2 that can be understood by linearization of the equations around the equilibrium solution. Above the critical density we get a non-exponential relaxation to the final condensate value p^0 with |p(t)|-|p^0| ~1/t that holds for all densities. Furthermore we include the full self-consistent Hartree-Fock-Bogoliubov (HFB) terms due to the exciton-exciton interaction and the kinetics of the anomalous functions F_k= . The collision terms are analyzed and an approximation is used which is consistent with the existence of BEC. The inclusion of the coherent x-x interaction does not change the dephasing laws. The anomalous function F_k exhibits a clear threshold behaviour at the critical density.Comment: European Physical Journal B (in print