Enhanced Pauli blocking of light scattering in a trapped Fermi gas

Pauli blocking of spontaneous emission by a single excited-state atom has been predicted to be dramatic at low temperature when the Fermi energy $E_\mathrm{F}$ exceeds the recoil energy $E_\mathrm{R}$. The photon scattering rate of a ground-state Fermi gas can also be suppressed by occupation of the final states accessible to a recoiling atom, however suppression is diminished by scattering events near the Fermi edge. We analyze two new approaches to improve the visibility of Pauli blocking in a trapped Fermi gas. Focusing the incident light to excite preferentially the high-density region of the cloud can increase the blocking signature by 14%, and is most effective at intermediate temperature. Spontaneous Raman scattering between imbalanced internal states can be strongly suppressed at low temperature, and is completely blocked for a final-state $E_\mathrm{F} > 4 E_\mathrm{R}$ in the high imbalance limit.Comment: 12 pages, 8 figures. v4: to appear in Journal of Physics B: Atomic, Molecular, and Optical Physic

Anharmonic mixing in a magnetic trap

We have experimentally observed re-equilibration of a magnetically trapped cloud of metastable neon atoms after it was put in a non-equilibrium state. Using numerical simulations we show that anharmonic mixing, equilibration due to the collisionless dynamics of atoms in a magnetic trap, is the dominant process in this equilibration. We determine the dependence of its time on trap parameters and atom temperature. Furthermore we observe in the simulations a resonant energy exchange between the radial and axial trap dimensions at a ratio of trap frequencies \omega_r / \omega_z = 3/2. This resonance is explained by a simple oscillator model.Comment: 9 pages, 6 figure

Quantum dynamics in strong fluctuating fields

A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a two-state dissipative quantum dynamics, commonly known under the label of a spin-boson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong time-dependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. Herein, we review the general theoretical framework which is based on the method of projector operators, yielding the quantum master equations for systems that are exposed to strong external fields. This allows one to investigate on a common basis the influence of nonequilibrium fluctuations and periodic electrical fields on quantum transport processes. Most importantly, such strong fluctuating fields induce a whole variety of nonlinear and nonequilibrium phenomena. A characteristic feature of such dynamics is the absence of thermal (quantum) detailed balance.Comment: review article, Advances in Physics (2005), in pres

Heide en stuifzandbeheer in relatie tot fauna : "variatie in de ruimte, rust in de tijd" : infoblad op basis van de veldwerkplaatsen in Nationaal Park de Hoge Veluwe, 20 november en 14 december 2007

Dit informatieblad gaat over beheer en renovatie van heide en stuifzand en hoe je daarbij rekening kan houden met de bijzondere fauna. Als specifiek voorbeeld is Nationaal Park de Hoge Veluwe gekozen

Control of sulphide during anaerobic treatment of S-containing wastewaters by adding limited amounts of oxygen or nitrate

Sulphide generated during anaerobic treatment of S-containing wastewaters represents an environmental problem. Adding limited amounts of oxygen or nitrate (or nitrite) to biologically (or chemically) oxidise sulphide forms a simple process level strategy to control this problem. This short review evaluates the feasibility and limitations of this strategy on the basis of the results of bioreactor studies.Sulphide generated during anaerobic treatment of S-containing wastewaters represents an environmental problem. Adding limited amounts of oxygen or nitrate (or nitrite) to biologically (or chemically) oxidise sulphide forms a simple process level strategy to control this problem. This short review evaluates the feasibility and limitations of this strategy on the basis of the results of bioreactor studies.Spanish Ministry of Education and Science; AEA Technology Environment; Nova Energie; The Swedish Gas Centre; University of Southern Denmark

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

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The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package

The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical community. A key element of the Astropy project is the core package Astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of inter-operable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy project

Metal halide perovskite toxicity effects on Arabidopsis thaliana plants are caused by iodide ions

Highly efficient solar cells containing lead halide perovskites are expected to revolutionize sustainable energy production in the coming years. Perovskites are generally assumed to be toxic because of the lead (Pb), but experimental evidence to support this prediction is scarce. We tested the toxicity of the perovskite MAPbI3 (MA = CH3NH3) and several precursors in Arabidopsis thaliana plants. Both MAPbI3 and the precursor MAI hamper plant growth at concentrations above 5 μM. Lead-based precursors without iodide are only toxic above 500 μM. Iodine accumulation in Arabidopsis correlates with growth inhibition at much lower concentrations than lead. This reveals that perovskite toxicity at low concentrations is caused by iodide ions specifically, instead of lead. We calculate that toxicity thresholds for iodide, but not lead, are likely to be reached in soils upon perovskite leakage. This work stresses the importance to further understand and predict harmful effects of iodide-containing perovskites in the environment