887 research outputs found
Artesunate reduces but does not prevent posttreatment transmission of Plasmodium falciparum to Anopheles gambiae.
Combination therapy that includes artemisinin derivatives cures most falciparum malaria infections. Lowering transmission by reducing gametocyte infectivity would be an additional benefit. To examine the effect of such therapy on transmission, Gambian children with Plasmodium falciparum malaria were treated with standard regimens of chloroquine or pyrimethamine-sulfadoxine alone or in combination with 1 or 3 doses of artesunate. The infectivity to mosquitoes of gametocytes in peripheral blood was determined 4 or 7 days after treatment. Infection of mosquitoes was observed in all treatment groups and was positively associated with gametocyte density. The probability of transmission was lowest in those who received pyrimethamine-sulfadoxine and 3 doses of artesunate, and it was 8-fold higher in the group that received pyrimethamine-sulfadoxine alone. Artesunate reduced posttreatment infectivity dramatically but did not abolish it completely. The study raises questions about any policy to use pyrimethamine-sulfadoxine alone as the first-line treatment for malaria
Broad Feshbach resonance in the 6Li-40K mixture
We study the widths of interspecies Feshbach resonances in a mixture of the
fermionic quantum gases 6Li and 40K. We develop a model to calculate the width
and position of all available Feshbach resonances for a system. Using the model
we select the optimal resonance to study the 6Li/40K mixture. Experimentally,
we obtain the asymmetric Fano lineshape of the interspecies elastic cross
section by measuring the distillation rate of 6Li atoms from a potassium-rich
6Li/40K mixture as a function of magnetic field. This provides us with the
first experimental determination of the width of a resonance in this mixture,
Delta B=1.5(5) G. Our results offer good perspectives for the observation of
universal crossover physics using this mass-imbalanced fermionic mixture.Comment: 4 pages, 2 figure
Adiabatically changing the phase-space density of a trapped Bose gas
We show that the degeneracy parameter of a trapped Bose gas can be changed
adiabatically in a reversible way, both in the Boltzmann regime and in the
degenerate Bose regime. We have performed measurements on spin-polarized atomic
hydrogen in the Boltzmann regime demonstrating reversible changes of the
degeneracy parameter (phase-space density) by more than a factor of two. This
result is in perfect agreement with theory. By extending our theoretical
analysis to the quantum degenerate regime we predict that, starting close
enough to the Bose-Einstein phase transition, one can cross the transition by
an adiabatic change of the trap shape.Comment: 4 pages, 3 figures, Latex, submitted to PR
Towards a guided atom interferometer based on a superconducting atom chip
We evaluate the realization of a novel geometry of a guided atom
interferometer based on a high temperature superconducting microstructure. The
interferometer type structure is obtained with a guiding potential realized by
two current carrying superconducting wires in combination with a closed
superconducting loop sustaining a persistent current. We present the layout and
realization of our superconducting atom chip. By employing simulations we
discuss the critical parameters of the interferometer guide in particular near
the splitting regions of the matter waves. Based on measurements of the
relevant chip properties we discuss the application of a compact and reliable
on-chip atom interferometer.Comment: 14 pages, 7 figures, accepted for New Journal of Physic
Continuous loading of a non-dissipative atom trap
We study theoretically a scheme in which particles from an incident beam are
trapped in a potential well when colliding with particles already present in
the well. The balance between the arrival of new particles and the evaporation
of particles from the trapped cloud leads to a steady-state that we
characterize in terms of particle number and temperature. For a cigar shaped
potential, different longitudinal and transverse evaporation thresholds can be
chosen. We show that a resonance occur when the transverse evaporation
threshold coincides with the energy of the incident particles. It leads to a
dramatic increase in phase space density with respect to the incident beam.Comment: 7 pages, 2 figure
Evanescent-wave trapping and evaporative cooling of an atomic gas near two-dimensionality
A dense gas of cesium atoms at the crossover to two-dimensionality is
prepared in a highly anisotropic surface trap that is realized with two
evanescent light waves. Temperatures as low as 100nK are reached with 20.000
atoms at a phase-space density close to 0.1. The lowest quantum state in the
tightly confined direction is populated by more than 60%. The system offers
intriguing prospects for future experiments on degenerate quantum gases in two
dimensions
A high-flux 2D MOT source for cold lithium atoms
We demonstrate a novel 2D MOT beam source for cold 6Li atoms. The source is
side-loaded from an oven operated at temperatures in the range 600<T<700 K. The
performance is analyzed by loading the atoms into a 3D MOT located 220 mm
downstream from the source. The maximum recapture rate of ~10^9 /s is obtained
for T=700 K and results in a total of up to 10^10 trapped atoms. The recaptured
fraction is estimated to be 30(10)% and limited by beam divergence. The
most-probable velocity in the beam (alpha_z) is varied from 18 to 70 m/s by
increasing the intensity of a push beam. The source is quite monochromatic with
a full-width at half maximum velocity spread of 11 m/s at alpha_z=36 m/s,
demonstrating that side-loading completely eliminates beam contamination by hot
vapor from the oven. We identify depletion of the low-velocity tail of the oven
flux as the limiting loss mechanism. Our approach is suitable for other atomic
species.Comment: 13 pages,9 figures, submitted to Phys.Rev.
Does adding risk-trends to survival models improve in-hospital mortality predictions? A cohort study
<p>Abstract</p> <p>Background</p> <p>Clinicians informally assess changes in patients' status over time to prognosticate their outcomes. The incorporation of trends in patient status into regression models could improve their ability to predict outcomes. In this study, we used a unique approach to measure trends in patient hospital death risk and determined whether the incorporation of these trend measures into a survival model improved the accuracy of its risk predictions.</p> <p>Methods</p> <p>We included all adult inpatient hospitalizations between 1 April 2004 and 31 March 2009 at our institution. We used the daily mortality risk scores from an existing time-dependent survival model to create five trend indicators: absolute and relative percent change in the risk score from the previous day; absolute and relative percent change in the risk score from the start of the trend; and number of days with a trend in the risk score. In the derivation set, we determined which trend indicators were associated with time to death in hospital, independent of the existing covariates. In the validation set, we compared the predictive performance of the existing model with and without the trend indicators.</p> <p>Results</p> <p>Three trend indicators were independently associated with time to hospital mortality: the absolute change in the risk score from the previous day; the absolute change in the risk score from the start of the trend; and the number of consecutive days with a trend in the risk score. However, adding these trend indicators to the existing model resulted in only small improvements in model discrimination and calibration.</p> <p>Conclusions</p> <p>We produced several indicators of trend in patient risk that were significantly associated with time to hospital death independent of the model used to create them. In other survival models, our approach of incorporating risk trends could be explored to improve their performance without the collection of additional data.</p
Influence of nearly resonant light on the scattering length in low-temperature atomic gases
We develop the idea of manipulating the scattering length in
low-temperature atomic gases by using nearly resonant light. As found, if the
incident light is close to resonance with one of the bound levels of
electronically excited molecule, then virtual radiative transitions of a pair
of interacting atoms to this level can significantly change the value and even
reverse the sign of . The decay of the gas due to photon recoil, resulting
from the scattering of light by single atoms, and due to photoassociation can
be minimized by selecting the frequency detuning and the Rabi frequency. Our
calculations show the feasibility of optical manipulations of trapped Bose
condensates through a light-induced change in the mean field interaction
between atoms, which is illustrated for Li.Comment: 12 pages, 1 Postscript figur
- …