Vortex formation in a stirred Bose-Einstein condensate

Using a focused laser beam we stir a Bose-Einstein condensate of 87Rb confined in a magnetic trap and observe the formation of a vortex for a stirring frequency exceeding a critical value. At larger rotation frequencies we produce states of the condensate for which up to four vortices are simultaneously present. We have also measured the lifetime of the single vortex state after turning off the stirring laser beam.Comment: 4 pages, 3 figure

An Atom Faucet

We have constructed and modeled a simple and efficient source of slow atoms. From a background vapour loaded magneto-optical trap, a thin laser beam extracts a continuous jet of cold rubidium atoms. In this setup, the extraction column that is typical to leaking MOT systems is created without any optical parts placed inside the vacuum chamber. For detailed analysis, we present a simple 3D numerical simulation of the atomic motion in the presence of multiple saturating laser fields combined with an inhomogeneous magnetic field. At a pressure of $P_{\rm Rb87}=1 \times 10^{-8}$ mbar, the moderate laser power of 10 mW per beam generates a jet of flux $\Phi =1.3\times 10^8$ atoms/s with a mean velocity of 14 m/s and a divergence of $<20$ mrad.Comment: Submitted to EPJD. 1 TeX file (EPJ format), 7 picture

Mixture of ultracold lithium and cesium atoms in an optical dipole trap

We present the first simultaneous trapping of two different ultracold atomic species in a conservative trap. Lithium and cesium atoms are stored in an optical dipole trap formed by the focus of a CO$_2$ laser. Techniques for loading both species of atoms are discussed and observations of elastic and inelastic collisions between the two species are presented. A model for sympathetic cooling of two species with strongly different mass in the presence of slow evaporation is developed. From the observed Cs-induced evaporation of Li atoms we estimate a cross section for cold elastic Li-Cs collisions.Comment: 10 pages 9 figures, submitted to Appl. Phys. B; v2: Corrected evaporation formulas and some postscript problem

Vortex lattices in a stirred Bose-Einstein condensate

We stir with a focused laser beam a Bose-Einstein condensate of $^{87}$Rb atoms confined in a magnetic trap. We observe the formation of a single vortex for a stirring frequency exceeding a critical value. At larger rotation frequencies we produce states of the condensate for which up to eleven vortices are simultaneously present. We present measurements of the decay of a vortex array once the stirring laser beam is removed

Kupferminimierungsstrategien im ökologischen Kartoffelanbau – Projekt “ÖKO-SIMPHYT“: Erste Erfahrungen aus dem norddeutschen Freiland

In the research project „ÖKO-SIMPHYT“ different strategies are tested to reduce the copper application for Phytophthora infestans in organic potato cultivation. Within the first two years of our research a reduction of the total amount of copper per hectare could be accomplished when applying the new developed forecast system ÖKO-SIMPHYT. With this decision support system a reduction of copper up to 46% was possible, when the infection pressure was relatively low. These first results have now to be proven under high infection pressure conditions. Experiments were carried out in the greenhouse to test the rain stability of copper and contacting agents. It could be proved that precipitation of 30 mm is able to reduce the degree of a copper treatment by up to 25%

An absolutely calibrated survey of polarized emission from the northern sky at 1.4 GHz

A new polarization survey of the northern sky at 1.41 GHz is presented. The observations were carried out using the 25.6m telescope at the Dominion Radio Astrophysical Observatory in Canada, with an angular resolution of 36 arcmin. The data are corrected for ground radiation to obtain Stokes U and Q maps on a well-established intensity scale tied to absolute determinations of zero levels, containing emission structures of large angular extent, with an rms noise of 12 mK. Survey observations were carried out by drift scanning the sky between -29 degr and +90 degr declination. The fully sampled drift scans, observed in steps of 0.25 degr to 2.5 degr in declination, result in a northern sky coverage of 41.7% of full Nyquist sampling. The survey surpasses by a factor of 200 the coverage, and by a factor of 5 the sensitivity, of the Leiden/Dwingeloo polarization survey (Spoelstra 1972) that was until now the most complete large-scale survey. The temperature scale is tied to the Effelsberg scale. Absolute zero-temperature levels are taken from the Leiden/Dwingeloo survey after rescaling those data by the factor of 0.94. The paper describes the observations, data processing, and calibration steps. The data are publicly available at http://www.mpifr-bonn.mpg.de/div/konti/26msurvey or http://www.drao.nrc.ca/26msurvey.Comment: 18 pages, 11 figures, accepted for publication in Astronomy and Astrophysic

Thermal expansion, heat capacity and magnetostriction of RAl3_3 (R = Tm, Yb, Lu) single crystals

We present thermal expansion and longitudinal magnetostriction data for cubic RAl3 (R = Tm, Yb, Lu) single crystals. The thermal expansion coefficient for YbAl3 is consistent with an intermediate valence of the Yb ion, whereas the data for TmAl3 show crystal electric field contributions and have strong magnetic field dependencies. de Haas-van Alphen-like oscillations were observed in the magnetostriction data of YbAl3 and LuAl3, several new extreme orbits were measured and their effective masses were estimated. Zero and 140 kOe specific heat data taken on both LuAl3 and TmAl3 for T < 200 K allow for the determination of a CEF splitting scheme for TmAl3

Comparison of metal-based nanoparticles and nanowires: Solubility, reactivity, bioavailability and cellular toxicity

While the toxicity of metal-based nanoparticles (NP) has been investigated in an increasing number of studies, little is known about metal-based fibrous materials, so-called nanowires (NWs). Within the present study, the physico-chemical properties of particulate and fibrous nanomaterials based on Cu, CuO, Ni, and Ag as well as TiO$_{2}$ and CeO$_{2}$ NP were characterized and compared with respect to abiotic metal ion release in different physiologically relevant media as well as acellular reactivity. While none of the materials was soluble at neutral pH in artificial alveolar fluid (AAF), Cu, CuO, and Ni-based materials displayed distinct dissolution under the acidic conditions found in artificial lysosomal fluids (ALF and PSF). Subsequently, four different cell lines were applied to compare cytotoxicity as well as intracellular metal ion release in the cytoplasm and nucleus. Both cytotoxicity and bioavailability reflected the acellular dissolution rates in physiological lysosomal media (pH 4.5); only Ag-based materials showed no or very low acellular solubility, but pronounced intracellular bioavailability and cytotoxicity, leading to particularly high concentrations in the nucleus. In conclusion, in spite of some quantitative differences, the intracellular bioavailability as well as toxicity is mostly driven by the respective metal and is less modulated by the shape of the respective NP or NW