1,685 research outputs found
Efficient loading of a He* magneto-optic trap using a liquid He cooled source
We report loading large numbers (up to 3×10⁹) of metastable triplet helium atoms into a magneto-optical trap using an atomic beam derived from a liquid He (LHe) cooled dc discharge source. Moreover, we compare the effect of liquidN₂ cooling to LHe cooling the source and demonstrate that LHe cooling offers a significant increase in performance
Prolonging oxygen consumption during preservation of canine kidneys by the addition of continuous dialysis
Kidneys were preserved by continuous pulsatile perfusion and their metabolic rate monitored by O2 consumption. Experiments were carried out to determine if dialyzing the perfusate to supply metabolic substrates would aid in kidney preservation. A control group was compared against two experimental groups at 25°C. Average preservation time before fall off of oxygen consumption differed for each group: control - 8 hours, dialysis with amino acids - 6 hours, dialysis with amino acids and cofactors - 11 hours. Results indicated that, if suitable concentrations of metabolic substrates and cofactors were used, the preserved kidneys maintained higher levels of O2 consumption for longer periods of time
Paired atom laser beams created via four-wave mixing
A method to create paired atom laser beams from a metastable helium atom
laser via four-wave mixing is demonstrated. Radio frequency outcoupling is used
to extract atoms from a Bose Einstein condensate near the center of the
condensate and initiate scattering between trapped and untrapped atoms. The
unequal strengths of the interactions for different internal states allows an
energy-momentum resonance which leads to the creation of pairs of atoms
scattered from the zero-velocity condensate. The resulting scattered beams are
well separated from the main atom laser in the 2-dimensional transverse atom
laser profile. Numerical simulations of the system are in good agreement with
the observed atom laser spatial profiles, and indicate that the scattered beams
are generated by a four-wave mixing process, suggesting that the beams are
correlated.Comment: 5 pages, 3 figure
Solar-like oscillations and magnetic activity of the slow rotator EK Eri
We aim to understand the interplay between non-radial oscillations and
stellar magnetic activity and test the feasibility of doing asteroseismology of
magnetically active stars. We analyze 30 years of photometric time-series data,
3 years of HARPS radial velocity monitoring, and 3 nights of high-cadence HARPS
asteroseismic data. We construct a high-S/N HARPS spectrum that we use to
determine atmospheric parameters and chemical composition. Spectra observed at
different rotation phases are analyzed to search for signs of temperature or
abundance variations. An upper limit on the projected rotational velocity is
derived from very high-resolution CES spectra. We detect oscillations in EK Eri
with a frequency of the maximum power of nu_max = 320+/-32 muHz, and we derive
a peak amplitude per radial mode of ~0.15 m/s, which is a factor of ~3 lower
than expected. We suggest that the magnetic field may act to suppress
low-degree modes. Individual frequencies can not be extracted from the
available data. We derive accurate atmospheric parameters, refining our
previous analysis. We confirm that the main light variation is due to cool
spots, but that other contributions may need to be taken into account. We
suggest that the rotation period is twice the photometric period, i.e., P_rot =
2 P_phot = 617.6 d. We conclude from our derived parameters that v sin i < 0.40
km/s. We also link the time series of direct magnetic field measurements
available in the literature to our newly derived photometric ephemeris.Comment: 11 pages, 10 figures. Accepted by A&
The true story behind the annotation of a pathway
On 2010 we worked on the annotation of the N-Glycosylation pathway in the Reactome database. During this process, we found some unclear points and errors in other databases, and we reported and helped fix them. After we finished, we realized that the work of reporting errors to a database is basically not acknowledged by the scientific community: this is unfortunate because if only this process would be a bit more recognized and transparent, we could have better data in the databases and a more active community. Moreover, the fact that many databases tend to keep error reporting private creates great issues to the reproducibility of a work.

Another way to look at this talk is: if you dedicate 6 months of your PhD thesis to annotate carefully a set of genes, in this case a pathway I have been studying, how many errors do you expect to find in other databases, or what should you be careful at
The amplitude of solar oscillations using stellar techniques
The amplitudes of solar-like oscillations depend on the excitation and
damping, both of which are controlled by convection. Comparing observations
with theory should therefore improve our understanding of the underlying
physics. However, theoretical models invariably compute oscillation amplitudes
relative to the Sun, and it is therefore vital to have a good calibration of
the solar amplitude using stellar techniques. We have used daytime spectra of
the Sun, obtained with HARPS and UCLES, to measure the solar oscillations and
made a detailed comparison with observations using the BiSON helioseismology
instrument. We find that the mean solar amplitude measured using stellar
techniques, averaged over one full solar cycle, is 18.7 +/- 0.7 cm/s for the
strongest radial modes (l=0) and 25.2 +/- 0.9 cm/s for l=1. In addition, we use
simulations to establish an equation that estimates the uncertainty of
amplitude measurements that are made of other stars, given that the mode
lifetime is known. Finally, we also give amplitudes of solar-like oscillations
for three stars that we measured from a series of short observations with HARPS
(gamma Ser, beta Aql and alpha For), together with revised amplitudes for five
other stars for which we have previously published results (alpha Cen A, alpha
Cen B, beta Hyi, nu Ind and delta Pav).Comment: 8 pages, accepted by ApJ. Minor wording changes and added a referenc
A common rule for decision-making in animal collectives across species
A diversity of decision-making systems has been observed in animal
collectives. In some species, choices depend on the differences of the numbers
of animals that have chosen each of the available options, while in other
species on the relative differences (a behavior known as Weber's law) or follow
more complex rules. We here show that this diversity of decision systems
corresponds to a single rule of decision-making in collectives. We first
obtained a decision rule based on Bayesian estimation that uses the information
provided by the behaviors of the other individuals to improve the estimation of
the structure of the world. We then tested this rule in decision experiments
using zebrafish (Danio rerio), and in existing rich datasets of argentine ants
(Linepithema humile) and sticklebacks (Gasterosteus aculeatus), showing that a
unified model across species can quantitatively explain the diversity of
decision systems. Further, these results show that the different counting
systems used by animals, including humans, can emerge from the common principle
of using social information to make good decisions
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