Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms

We study elastic collisions in an optically trapped spin mixture of fermionic lithium atoms in the presence of magnetic fields up to 1.5kG by measuring evaporative loss. Our experiments confirm the expected magnetic tunability of the scattering length by showing the main features of elastic scattering according to recent calculations. We measure the zero crossing of the scattering length that is associated with a predicted Feshbach resonance at 530(3)G. Beyond the resonance we observe the expected large cross section in the triplet scattering regime

Influence of a magnetic field on the viscosity of a dilute gas consisting of linear molecules.

The viscomagnetic effect for two linear molecules, N2 and CO2, has been calculated in the dilute-gas limit directly from the most accurate ab initio intermolecular potential energy surfaces presently available. The calculations were performed by means of the classical trajectory method in the temperature range from 70 K to 3000 K for N2 and 100 K to 2000 K for CO2, and agreement with the available experimental data is exceptionally good. Above room temperature, where no experimental data are available, the calculations provide the first quantitative information on the magnitude and the behavior of the viscomagnetic effect for these gases. In the presence of a magnetic field, the viscosities of nitrogen and carbon dioxide decrease by at most 0.3% and 0.7%, respectively. The results demonstrate that the viscomagnetic effect is dominated by the contribution of the jj¯ polarization at all temperatures, which shows that the alignment of the rotational axes of the molecules in the presence of a magnetic field is primarily responsible for the viscomagnetic effect

Feshbach resonances in the 6Li-40K Fermi-Fermi mixture: Elastic versus inelastic interactions

We present a detailed theoretical and experimental study of Feshbach resonances in the 6Li-40K mixture. Particular attention is given to the inelastic scattering properties, which have not been considered before. As an important example, we thoroughly investigate both elastic and inelastic scattering properties of a resonance that occurs near 155 G. Our theoretical predictions based on a coupled channels calculation are found in excellent agreement with the experimental results. We also present theoretical results on the molecular state that underlies the 155G resonance, in particular concerning its lifetime against spontaneous dissociation. We then present a survey of resonances in the system, fully characterizing the corresponding elastic and inelastic scattering properties. This provides the essential information to identify optimum resonances for applications relying on interaction control in this Fermi-Fermi mixture.Comment: Submitted to EPJD, EuroQUAM special issues "Cold Quantum Matter - Achievements and Prospects", v2 with updated calibration of magnetic field (+4mG correction) and updated figures 4 and

Pure Gas of Optically Trapped Molecules Created from Fermionic Atoms

We report on the production of a pure sample of up to 3x10^5 optically trapped molecules from a Fermi gas of 6Li atoms. The dimers are formed by three-body recombination near a Feshbach resonance. For purification a Stern-Gerlach selection technique is used that efficiently removes all trapped atoms from the atom-molecule mixture. The behavior of the purified molecular sample shows a striking dependence on the applied magnetic field. For very weakly bound molecules near the Feshbach resonance, the gas exhibits a remarkable stability with respect to collisional decay.Comment: 4 pages, 5 figure

Exploring an ultracold Fermi-Fermi mixture: Interspecies Feshbach resonances and scattering properties of 6Li and 40K

We report on the observation of Feshbach resonances in an ultracold mixture of two fermionic species, 6Li and 40K. The experimental data are interpreted using a simple asymptotic bound state model and full coupled channels calculations. This unambiguously assigns the observed resonances in terms of various s- and p-wave molecular states and fully characterizes the ground-state scattering properties in any combination of spin states.Comment: 4 pages, 4 figures, 1 tabl

Ultra-cold Polarized Fermi Gases

Recent experiments with ultra-cold atoms have demonstrated the possibility of realizing experimentally fermionic superfluids with imbalanced spin populations. We discuss how these developments have shed a new light on a half- century old open problem in condensed matter physics, and raised new interrogations of their own.Comment: 27 pages; 8 figures; Published in Report in Rep. Prog. Phys. 73 112401 (2010

Atención primaria. Diagnóstico precoz de hipocausias

La hipoacusia neurosensorial severa o profunda es un importante handicap o discapacidad que afecta del 1 a 3‰ de los recién nacidos vivos y del 2 al 4 % de los neonatos egresados de las UTI neonatales. El pronóstico para el intelecto, condición psico-emocional, lenguaje y desarrollo del habla, es mejor cuando el diagnóstico es efectuado tempranamente y la intervención comienza antes de los 6 meses de vida. La edad habitual del diagnóstico de hipoacusia es entre los 18 y los 30 meses, o aún más tarde, en casos de pérdida auditiva leve a moderada, cuando no hay implementados programas de screening auditivos. El screening auditivo universal efectuado a los RN, puede darle al niño discapacitado por sordera, la mejor oportunidad para un óptimo cuidado y desarrollo. El criterio “universal” es necesario, porque cuando el tamizaje es restringido al grupo de neonatos de alto riesgo auditivo, no son diagnosticados entre el 30 y el 50% de los RN con pérdida auditiv

Justice: a key consideration in health policy and systems research ethics

Health policy and systems research (HPSR) is increasingly being funded and conducted worldwide. There are currently no specific guidelines or criteria for the ethical review and conduct of HPSR. Academic debates on HPSR ethics in the scholarly literature can inform the development of guidelines. Yet there is a deficiency of academic bioethics work relating to justice in HPSR. This gap is especially problematic for a field like HPSR, which can entail studies that intervene in ways affecting the social and health system delivery structures of society. In this paper, we call for interpreting the principle of justice in a more expansive way in developing and reviewing HPSR studies (relative to biomedical research). The principle requires advancing health equity and social justice at population or systems levels. Drawing on the rich justice literature from political philosophy and public health ethics, we propose a set of essential justice considerations to uphold this principle. These considerations are relevant for research funders, researchers, research ethics committees, policymakers, community organisations and others who are active in the HPSR field