824 research outputs found
What makes a host profitable? Parasites balance host nutritive resources against immunity
Numerous host qualities can modulate parasite fitness, and among these, host nutritive resources and immunity are of prime importance. Indeed, parasite fitness increases with the amount of nutritive resources extracted from the host body and decreases with host immune response. To maximize fitness, parasites have therefore to balance these two host components. Yet, because host nutritive resources and immunity both increase with host body condition, it is unclear whether parasites perform better on hosts in prime, intermediate, or poor condition. We investigated blood meal size and survival of the ectoparasitic louse fly Crataerina melbae in relation to body condition and cutaneous immune response of their Alpine swift (Apus melba) nestling hosts. Louse flies took a smaller blood meal and lived a shorter period of time when feeding on nestlings that were experimentally food deprived or had their cutaneous immune response boosted with methionine. Consistent with these results, louse fly survival was the highest when feeding on nonexperimental nestlings in intermediate body condition. Our findings emphasize that although hosts in poor condition had a reduced immunocompetence, parasites may have avoided them because individuals in poor condition did not provide adequate resources. These findings highlight the fact that giving host immunocompetence primary consideration can result in a biased appraisal of host-parasite interactions
Controlling the cold collision shift in high precision atomic interferometry
We present here a new method based on a transfer of population by adiabatic
passage that allows to prepare cold atomic samples with a well defined ratio of
atomic density and atom number. This method is used to perform a measurement of
the cold collision frequency shift in a laser cooled cesium clock at the
percent level, which makes the evaluation of the cesium fountains accuracy at
the level realistic. With an improved set-up, the adiabatic passage
would allow measurements of atom number-dependent phase shifts at the
level in high precision experiments.Comment: 4 pages, 3 figures, 2 table
Effects of Common Origin and Common Rearing Environment on Variance in Ectoparasite Load and Phenotype of Nestling Alpine Swifts
Knowledge of the quantitative genetics of resistance to parasitism is key to appraise host evolutionary responses to parasite selection. Here, we studied effects of common origin (i.e. genetic and pre-hatching parental effects) and common rearing environment (i.e. post-hatching parental effects and other environment effects) on variance in ectoparasite load in nestling Alpine swifts (Apusmelba). This colonial bird is intensely parasitized by blood sucking louse-flies that impair nestling development and survival. By cross-fostering half of the hatchlings between pairs of nests, we show strong significant effect of common rearing environment on variance (90.7% in 2002 and 90.9% in 2003) in the number of louse-flies per nestling and no significant effect of common origin on variance in the number of louse-flies per nestling. In contrast, significant effects of common origin were found for all the nestling morphological traits (i.e. body mass, wing length, tail length, fork length and sternum length) under investigation. Hence, our study suggests that genetic and pre-hatching parental effects play little role in the distribution of parasites among nestling Alpine swifts, and thus that nestlings have only limited scope for evolutionary responses against parasites. Our results highlight the need to take into consideration environmental factors, including the evolution of post-hatching parental effects such as nest sanitation, in our understanding of host-parasite relationship
Catch-up growth strategies differ between body structures: interactions between age and structure-specific growth in wild nestling Alpine swifts
1. Little is known on the occurrence and magnitude of faster than normal (catch-up) growth in response to periods of undernutrition in the wild, and the extent to which different body structures compensate and over what timescales is poorly understood.
2. We investigated catch-up growth in nestling Alpine Swifts, Apus melba, by comparing nestling growth trajectories in response to a naturally occurring 1-week period of inclement weather and undernutrition with growth of nestlings reared in a good year.
3. In response to undernutrition, nestlings exhibited a hierarchy of tissues preservation and compensation, with body mass being restored quickly after the end of the period of undernutrition, acceleration of skeletal growth occurring later in development, and compensation in wing length occurring mostly due to a prolongation of growth and delayed fledging.
4. The effect of undernutrition and subsequent catch-up growth was age-dependent, with older nestlings being more resilient to undernutrition, and in turn having less need to compensate later in the development.
5. This shows that young in a free-living bird population can compensate in body mass and body size for a naturally occurring period of undernutrition, and that the timing and extent of compensation varies with age and between body structures
Progress in Atomic Fountains at LNE-SYRTE
We give an overview of the work done with the Laboratoire National de
M\'etrologie et d'Essais-Syst\`emes de R\'ef\'erence Temps-Espace (LNE-SYRTE)
fountain ensemble during the last five years. After a description of the clock
ensemble, comprising three fountains, FO1, FO2, and FOM, and the newest
developments, we review recent studies of several systematic frequency shifts.
This includes the distributed cavity phase shift, which we evaluate for the FO1
and FOM fountains, applying the techniques of our recent work on FO2. We also
report calculations of the microwave lensing frequency shift for the three
fountains, review the status of the blackbody radiation shift, and summarize
recent experimental work to control microwave leakage and spurious phase
perturbations. We give current accuracy budgets. We also describe several
applications in time and frequency metrology: fountain comparisons,
calibrations of the international atomic time, secondary representation of the
SI second based on the 87Rb hyperfine frequency, absolute measurements of
optical frequencies, tests of the T2L2 satellite laser link, and review
fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally,
we give a summary of the tests of the PHARAO cold atom space clock performed
using the FOM transportable fountain.Comment: 19 pages, 12 figures, 5 tables, 126 reference
A Search for Variations of Fundamental Constants using Atomic Fountain Clocks
Over five years we have compared the hyperfine frequencies of 133Cs and 87Rb
atoms in their electronic ground state using several laser cooled 133Cs and
87Rb atomic fountains with an accuracy of ~10^{-15}. These measurements set a
stringent upper bound to a possible fractional time variation of the ratio
between the two frequencies : (d/dt)ln(nu_Rb/nu_Cs)=(0.2 +/- 7.0)*10^{-16}
yr^{-1} (1 sigma uncertainty). The same limit applies to a possible variation
of the quantity (mu_Rb/mu_Cs)*alpha^{-0.44}, which involves the ratio of
nuclear magnetic moments and the fine structure constant.Comment: 4 pages, 3 figures, 1 table submitted to Phys. Rev. Let
Improved tests of Local Position Invariance using 87Rb and 133Cs fountains
We report tests of local position invariance based on measurements of the
ratio of the ground state hyperfine frequencies of 133Cs and 87Rb in
laser-cooled atomic fountain clocks. Measurements extending over 14 years set a
stringent limit to a possible variation with time of this ratio: d
ln(nu_Rb/nu_Cs)/dt=(-1.39 +/- 0.91)x 10-16 yr-1. This improves by a factor of
7.7 over our previous report (H. Marion et al., Phys. Rev. Lett. 90, 150801
(2003)). Our measurements also set the first limit to a fractional variation of
the Rb/Cs ratio with gravitational potential at the level of c^2 d
ln(nu_Rb/nu_Cs)/dU=(0.11 +/- 1.04)x 10^-6, providing a new stringent
differential redshift test. The above limits equivalently apply to the
fractional variation of the quantity alpha^{-0.49}x(g_Rb/g_Cs), which involves
the fine structure constant alpha and the ratio of the nuclear g-factors of the
two alkalis. The link with variations of the light quark mass is also presented
together with a global analysis combining with other available highly accurate
clock comparisons.Comment: 5 pages, 3 figures, 3 tables, 34 reference
Interference-filter-stabilized external-cavity diode lasers
We have developed external-cavity diode lasers, where the wavelength
selection is assured by a low loss interference filter instead of the common
diffraction grating. The filter allows a linear cavity design reducing the
sensitivity of the wavelength and the external cavity feedback against
misalignment. By separating the feedback and wavelength selection functions,
both can be optimized independently leading to an increased tunability of the
laser. The design is employed for the generation of laser light at 698, 780 and
852 nm. Its characteristics make it a well suited candidate for space-born
lasers.Comment: 12 pages, 5 figure
Relativistic theory for time and frequency transfer to order c^{-3}
This paper is motivated by the current development of several space missions
(e.g. ACES on International Space Station) that will fly on Earth orbit laser
cooled atomic clocks, providing a time-keeping accuracy of the order of
5~10^{-17} in fractional frequency. We show that to such accuracy, the theory
of frequency transfer between Earth and Space must be extended from the
currently known relativistic order 1/c^2 (which has been needed in previous
space experiments such as GP-A) to the next relativistic correction of order
1/c^3. We find that the frequency transfer includes the first and second-order
Doppler contributions, the Einstein gravitational red-shift and, at the order
1/c^3, a mixture of these effects. As for the time transfer, it contains the
standard Shapiro time delay, and we present an expression also including the
first and second-order Sagnac corrections. Higher-order relativistic
corrections, at least O(1/c^4), are numerically negligible for time and
frequency transfers in these experiments, being for instance of order 10^{-20}
in fractional frequency. Particular attention is paid to the problem of the
frequency transfer in the two-way experimental configuration. In this case we
find a simple theoretical expression which extends the previous formula (Vessot
et al. 1980) to the next order 1/c^3. In the Appendix we present the detailed
proofs of all the formulas which will be needed in such experiments.Comment: 11 pages, 2 figures, to appear in Astronomy & Astrophysic
Evaluation de la mise en oeuvre du plan canicule dans le canton de Vaud en 2015
Le SSP a mis en place depuis 2009 un plan cantonal de prévention et d'intervention sanitaire en cas de canicule qui a depuis évolué et s'est affiné pour aboutir au plan canicule actuel, daté de mars 2014. Ce plan a pour objectifs principaux « de prévenir et d'atténuer les atteintes à la santé de la population dues à la chaleur accablante et d'éviter la surcharge du système sanitaire ». Ce plan décrit les procédures à suivre et le rôle des différent-e-s acteurs/actrices concerné-e-s en cas de canicule. Ces personnes sont réunies au sein d'un groupe appelé « Groupe alerte canicule » (GA) formé de représentant-e-s de divers services de l'administration cantonale et des professionnel-le-s du domaine socio-sanitaire. Si toute la population est visée par les messages de prévention et les recommandations de ce plan, les cibles principales en sont les personnes âgées de 70 ans et plus, à travers notamment le système des visites communautaires.
Le niveau « canicule persistante » de ce plan a été activé pour la première lors des deux épisodes caniculaires de l'été 2015, suite à quoi le SSP a mandaté l'IUMSP pour mener une évaluation de processus portant sur la mise en oeuvre de ce plan
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