Nonlinear Dynamics of a Bose-Einstein Condensate in a Magnetic Waveguide

We have studied the internal and external dynamics of a Bose-Einstein condensate in an anharmonic magnetic waveguide. An oscillating condensate experiences a strong coupling between the center of mass motion and the internal collective modes. Due to the anharmonicity of the magnetic potential, not only the center of mass motion shows harmonic frequency generation, but also the internal dynamics exhibit nonlinear frequency mixing. We describe the data with a theoretical model to high accuracy. For strong excitations we test the experimental data for indications of a chaotic behavior.Comment: 4 pages, 4 figure

Perspectives of Ultra Cold Atoms Trapped in Magnetic Micro Potentials

Recent work on magnetic micro traps for ultracold atoms is briefly reviewed. The basic principles of operation are described together with the loading methods and some of the realized trap geometries. Experiments are discussed that study the interaction between atoms and the surface of micro traps as well as the dynamics of ultracold gases in wave guides are discussed. The results allow for an outlook towards future directions of research

18F-labelled triazolyl-linked argininamides targeting the neuropeptide Y Y1R for PET Imaging of mammary carcinoma

NeuropeptideYY(1) receptors (Y1R) have been found to be overexpressed in a number of different tumours, such as breast, ovarian or renal cell cancer. In mammary carcinoma the highY(1)R density together with its high incidence of 85% in primary human breast cancers and 100% in breast cancer derived lymph node metastases attracted special attention. Therefore, the aim of this study was the development of radioligandsforY(1)R imaging by positron emission tomography (PET) with a special emphasis on imaging agents with reduced lipophilicity to provide a PET ligand with improved biodistribution in comparison with previously published tracers targeting theY(1)R. Three new radioligands based on BIBP3226, bearing an F-18-fluoroethoxy linker (12), an F-18-PEG-linker (13) or an F-18-fluoroglycosyl moiety (11) were radiosynthesised in high radioactivity yields. The new radioligands displayedY(1)R affinities of 2.8 nM (12), 29 nM (13) and 208 nM (11) and were characterised in vitro regarding binding to human breast cancer MCF-7-Y1 cells and slices of tumour xenografts. In vivo, small animal PET studies were conducted in nude mice bearing MCF-7-Y1 tumours. The binding to tumours, solid tumour slices and tumour cells correlated well with theY(1)R affinities. Although 12 and 13 showed displaceable and specific binding toY(1)R in vitro and in vivo, the radioligands still need to be optimised to achieve higher tumour-to-background ratios forY(1)R imaging by PET.Yet the present study is another step towards an optimized PET radioligand for imaging ofY(1)R in vivo

Determinação dos níveis de pressão sonora em estações da Trensurb, durante a chegada e partida dos trens

É importante monitorar os níveis de pressão sonora em estações de trem, devido ao desconforto acústico, causado em seus usuários. A origem da sensação é o ruído provocado pelos trens. Neste estudo, utiliza-se a infraestrutura da Empresa de Trens Urbanos (Trensurb), localizada no município de Porto Alegre e região metropolitana, no estado do Rio Grande do Sul (RS), Brasil. Os níveis sonoros equivalentes na escala A (LAeq) são medidos em duas estações, durante a chegada, partida dos trens e ruído de fundo. O limite máximo encontra-se estabelecido em norma: 85 dB(A). Gráficos de LAeq são elaborados por espectro de frequências dos três fenômenos citados, para se identificar as faixas significativas. Comparando-se as estações, conclui-se que o ruído de fundo é menor na estação isolada. Os níveis sonoros equivalentes são mais elevados na estação aberta, durante a chegada e partida.It is important to monitor the sound pressure levels at train stations, due to acoustic discomfort, caused on their users. The origin of the sensation is the noise caused by the trains. In this study, it is used the infrastructure of the Urban Trains Company (Trensurb), located in the city of Porto Alegre and its metropolitan region, in the state of Rio Grande do Sul (RS), Brazil. The equivalent sound levels on the A scale (LAeq) are measured at two train stations during arrival, departure and background noise. The maximum limit is established in standard: 85 dB(A). LAeq graphs are plotted by frequency spectrum of the three mentioned phenomena to identify significant ranges. Comparing the stations, it is concluded that the background noise is lower in the isolated station. Equivalent sound levels are higher at the open station during arrival and departure

Surface Effects in Magnetic Microtraps

We have investigated Bose-Einstein condensates and ultra cold atoms in the vicinity of a surface of a magnetic microtrap. The atoms are prepared along copper conductors at distances to the surface between 300 um and 20 um. In this range, the lifetime decreases from 20 s to 0.7 s showing a linear dependence on the distance to the surface. The atoms manifest a weak thermal coupling to the surface, with measured heating rates remaining below 500 nK/s. In addition, we observe a periodic fragmentation of the condensate and thermal clouds when the surface is approached.Comment: 4 pages, 4 figures; v2: corrected references; v3: final versio

Short-period variability in the Class II methanol maser source G12.89+0.49 (IRAS 18089-1732)

Time series are presented for the class II methanol maser source G12.89+0.49, which has been monitored for nine years at the Hartebeesthoek Radio Astronomy Observatory. The 12.2 and 6.7 GHz methanol masers were seen to exhibit rapid, correlated variations on timescales of less than a month. Daily monitoring has revealed that the variations have a periodic component with a period of 29.5 days. The period seems to be stable over the 110 cycles spanned by the time series. There are variations from cycle to cycle, with the peak of the flare occurring anywhere within an eleven day window but the minima occur at the same phase of the cycle. Time delays of up to 5.7 days are seen between spectral features at 6.7 GHz and a delay of 1.1 day is seen between the dominant 12.2 GHz spectral feature and its 6.7 GHz counterpart.Comment: Accepted by MNRAS. 18 pages, 20 figure

Critical fields and growth rates of the Tayler instability as probed by a columnar gallium experiment

Many astrophysical phenomena (such as the slow rotation of neutron stars or the rigid rotation of the solar core) can be explained by the action of the Tayler instability of toroidal magnetic fields in the radiative zones of stars. In order to place the theory of this instability on a safe fundament it has been realized in a laboratory experiment measuring the critical field strength, the growth rates as well as the shape of the supercritical modes. A strong electrical current flows through a liquid-metal confined in a resting columnar container with an insulating outer cylinder. As the very small magnetic Prandtl number of the gallium-indium-tin alloy does not influence the critical Hartmann number of the field amplitudes, the electric currents for marginal instability can also be computed with direct numerical simulations. The results of this theoretical concept are confirmed by the experiment. Also the predicted growth rates of the order of minutes for the nonaxisymmetric perturbations are certified by the measurements. That they do not directly depend on the size of the experiment is shown as a consequence of the weakness of the applied fields and the absence of rotation.Comment: 8 pages, 5 figures, accepted by Ap

Absorption Imaging of Ultracold Atoms on Atom Chips

Imaging ultracold atomic gases close to surfaces is an important tool for the detailed analysis of experiments carried out using atom chips. We describe the critical factors that need be considered, especially when the imaging beam is purposely reflected from the surface. In particular we present methods to measure the atom-surface distance, which is a prerequisite for magnetic field imaging and studies of atom surface-interactions.Comment: 12 pages, 8 figures. v2 contains updated figures, modifications to tex

Neural networks for modeling gene-gene interactions in association studies

<p>Abstract</p> <p>Background</p> <p>Our aim is to investigate the ability of neural networks to model different two-locus disease models. We conduct a simulation study to compare neural networks with two standard methods, namely logistic regression models and multifactor dimensionality reduction. One hundred data sets are generated for each of six two-locus disease models, which are considered in a low and in a high risk scenario. Two models represent independence, one is a multiplicative model, and three models are epistatic. For each data set, six neural networks (with up to five hidden neurons) and five logistic regression models (the null model, three main effect models, and the full model) with two different codings for the genotype information are fitted. Additionally, the multifactor dimensionality reduction approach is applied.</p> <p>Results</p> <p>The results show that neural networks are more successful in modeling the structure of the underlying disease model than logistic regression models in most of the investigated situations. In our simulation study, neither logistic regression nor multifactor dimensionality reduction are able to correctly identify biological interaction.</p> <p>Conclusions</p> <p>Neural networks are a promising tool to handle complex data situations. However, further research is necessary concerning the interpretation of their parameters.</p