2,451 research outputs found
Density Distribution of a Bose-Einstein Condensate of Photons in a Dye-Filled Microcavity
The achievement of Bose-Einstein condensation of photons (phBEC) in a
dye-filled microcavity has led to a renewed interest in the density
distribution of the ideal Bose gas in a two-dimensional harmonic oscillator. We
present measurements of the radial profile of photons inside the microcavity
below and above the critical point for phBEC with a good signal-to-noise ratio.
We obtain a good agreement with theoretical profiles obtained using exact
summation of eigenstates.Comment: 5 pages, 4 figure
Density Distribution of a Bose-Einstein Condensate of Photons in a Dye-Filled Microcavity
The achievement of Bose-Einstein condensation of photons (phBEC) in a
dye-filled microcavity has led to a renewed interest in the density
distribution of the ideal Bose gas in a two-dimensional harmonic oscillator. We
present measurements of the radial profile of photons inside the microcavity
below and above the critical point for phBEC with a good signal-to-noise ratio.
We obtain a good agreement with theoretical profiles obtained using exact
summation of eigenstates.Comment: 5 pages, 4 figure
Utilisation de la mesure thermique du flux de sève pour l'évaluation de la transpiration d'un palmier dattier
International audienceL'amélioration de la gestion de l'eau en système oasien constitue l'un des principaux défis pour la préservation de son agrosystème. Des approches complémentaires doivent être mises en oeuvre pour y contribuer par la prise en compte du comportement des agriculteurs mais aussi par la compréhension du système biophysique. En particulier, la quantification des différents termes du bilan hydrique, et notamment celui de la transpiration du palmier dattier, a été relativement peu étudiée jusqu'à présent. Le terme de consommation hydrique du palmier est un indicateur indispensable en regard des contraintes de gestion de l'eau et du bilan hydrique global. Cette problématique a été abordée au sein de l'oasis de Fatnassa Nord à Kébili (33°,8 N ; 8°,7 E) dans un contexte caractérisé à la fois par de faibles fréquences de tour d'eau et une salinité plutôt élevée. L'agrosystème bi-étagée palmier/fourrage du système oasien de cette région nécessite de bien cerner la composante palmier de la strate fourrage. Une technique de mesure thermique du flux de sève a donc été mise en oeuvre pour évaluer la transpiration spécifique du palmier dattier au sein d'une parcelle dont les termes du bilan hydriques sont bien mesurés en continu. L'avantage de cette méthode est qu'elle permet aussi une mesure continue et qu'elle intègre, grâce au suivi simultané de quatre arbres, une certaine hétérogénéité du système palmier à la fois due au système radiculaire et au développement de la canopée, tous deux liés au stipe, voie unique de passage de la sève entre ces deux compartiments de l'arbre. Dans cet article, les principaux résultats des mesures réalisées depuis plus d'un an sont analysés et présentent une bonne cohérence avec la dynamique nycthémérale de la nappe superficielle donnée par un suivi piézométrique fin. Les flux de transpiration cumulés sur la journée ont varié globalement de 0.5 à 3,5 mm/j avec une moyenne de l'ordre de 2 mm/jour reflétant une consommation hydrique modeste en regard de la demande climatique. Les valeurs montrent également que ces flux journaliers, malgré leur variation inter-arbres importantes, varient en lien étroit avec le cycle des apports d'eau par irrigation. Le palmier étant malgré sa résistance aux conditions climatiques, dont en particulier une demande forte, une espèce qui régule ses pertes par régulation stomatique
Ethical difficulties in clinical practice : experiences of European doctors
Background: Ethics support services are growing in Europe to help doctors in dealing with ethical difficulties.
Currently, insufficient attention has been focused on the experiences of doctors who have faced ethical
difficulties in these countries to provide an evidence base for the development of these services.
Methods: A survey instrument was adapted to explore the types of ethical dilemma faced by European
doctors, how they ranked the difficulty of these dilemmas, their satisfaction with the resolution of a recent
ethically difficult case and the types of help they would consider useful. The questionnaire was translated and
given to general internists in Norway, Switzerland, Italy and the UK.
Results: Survey respondents (n = 656, response rate 43%) ranged in age from 28 to 82 years, and averaged
25 years in practice. Only a minority (17.6%) reported having access to ethics consultation in individual
cases. The ethical difficulties most often reported as being encountered were uncertain or impaired decisionmaking
capacity (94.8%), disagreement among caregivers (81.2%) and limitation of treatment at the end of
life (79.3%). The frequency of most ethical difficulties varied among countries, as did the type of issue
considered most difficult. The types of help most often identified as potentially useful were professional
reassurance about the decision being correct (47.5%), someone capable of providing specific advice
(41.1%), help in weighing outcomes (36%) and clarification of the issues (35.9%). Few of the types of help
expected to be useful varied among countries.
Conclusion: Cultural differences may indeed influence how doctors perceive ethical difficulties. The type of
help needed, however, did not vary markedly. The general structure of ethics support services would not have
to be radically altered to suit cultural variations among the surveyed countries
No planet for HD 166435
The G0V star HD166435 has been observed by the fiber-fed spectrograph ELODIE
as one of the targets in the large extra-solar planet survey that we are
conducting at the Observatory of Haute-Provence. We detected coherent,
low-amplitude, radial-velocity variations with a period of 3.7987days,
suggesting a possible close-in planetary companion. Subsequently, we initiated
a series of high-precision photometric observations to search for possible
planetary transits and an additional series of CaII H and K observations to
measure the level of surface magnetic activity and to look for possible
rotational modulation. Surprisingly, we found the star to be photometrically
variable and magnetically active. A detailed study of the phase stability of
the radial-velocity signal revealed that the radial-velocity variability
remains coherent only for durations of about 30days. Analysis of the time
variation of the spectroscopic line profiles using line bisectors revealed a
correlation between radial velocity and line-bisector orientation. All of these
observations, along with a one-quarter cycle phase shift between the
photometric and the radial-velocity variationss, are well explained by the
presence of dark photospheric spots on HD166435. We conclude that the
radial-velocity variations are not due to gravitational interaction with an
orbiting planet but, instead, originate from line-profile changes stemming from
star spots on the surface of the star. The quasi-coherence of the
radial-velocity signal over more than two years, which allowed a fair fit with
a binary model, makes the stability of this star unusual among other active
stars. It suggests a stable magnetic field orientation where spots are always
generated at about the same location on the surface of the star.Comment: 9 pages, 8 figures, Accepted for publication in A&
Tuning of observer-based estimators: theory and application to the on-line estimation of kinetic parameters
This paper deals with the tuning of observer-based estimators. Initially, these algorithms were designed for estimating on-line kinetic parameters, like specific growth rates, in bioprocesses, and have proved to be very successful in practical applications. Here a systematic tuning approach that allows a decoupled estimation of each parameter and the assignment of the estimator dynamics independently of the process dynamics is proposed. The presented approach is illustrated on an animal cell culture example in numerical simulation and with real-life data
CI-Orbitrap : An Analytical Instrument To Study Atmospheric Reactive Organic Species
While acknowledged as key components in the formation of new particles in the atmosphere, the accurate characterization of gaseous (highly) oxygenated organic compounds remains challenging and requires analytical developments. Earlier studies have successfully used the nitrate ion (NO3) based chemical ionization (CI) coupled to atmospheric pressure interface time-of-flight mass spectrometry (CI-APi-TOF) for monitoring these compounds. Despite many breakthroughs in recent years, the CI-APi-TOF has many limitations, preventing for instance the unambiguous ion identification of overlapping peaks. To tackle this analytical challenge, we developed a CI interface coupled to an ultrahigh-resolution Orbitrap mass spectrometer (CI-Orbitrap). We show that the CI-Orbitrap has similar sensitivity and selectivity as the CI-APi-TOF, but with over an order of magnitude higher mass resolving power (up to 140 000). Equally importantly, the CI-Orbitrap allows tandem mass spectrometry, providing the possibility for structural elucidation of the highly oxygenated organic molecules (HOM). As a proof of concept, we characterized HOM formed during the ozonolysis of two biogenic compounds (alpha-pinene and limonene), under different environmental conditions in a flow reactor. The CI-Orbitrap exhibited high sensitivity to both HOM and radical species, while easily separating ions of different elemental composition in cases where the more common TOF applications would not have been able to distinguish all ions. Our tandem mass spectrometry analyses revealed distinct fingerprint spectra for all the studied HOM. Overall, the CI-Orbitrap is an extremely promising instrument, and it provides a much-needed extension to ongoing research on HOM, with potential to impact also many other fields within atmospheric chemistry.Peer reviewe
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