Circular and linear magnetic birefringences in xenon at λ=1064\lambda = 1064 nm

The circular and linear magnetic birefringences corresponding to the Faraday and the Cotton-Mouton effects, respectively, have been measured in xenon at $\lambda = 1064$ nm. The experimental setup is based on time dependent magnetic fields and a high finesse Fabry-Perot cavity. Our value of the Faraday effect is the first measurement at this wavelength. It is compared to theoretical predictions. Our uncertainty of a few percent yields an agreement at better than 1$\sigma$ with the computational estimate when relativistic effects are taken into account. Concerning the Cotton-Mouton effect, our measurement, the second ever published at $\lambda = 1064$ nm, agrees at better than $1\sigma$ with theoretical predictions. We also compare our error budget with those established for other experimental published values

Investigation of heat treatment parameters effect on the microstructure and on the mechanical properties of a powder metallurgy nickel-base superalloy

International audienceThe relationships between heat treatment parameters and microstructure, and between microstructure and mechanical properties were investigated in the SMO43 disc P/M superalloy. Various heat treatments were applied to this superalloy to determine the effect of the solution temperature on the grain size, and of the cooling path and aging temperature on the ' precipitates distribution. Microstructural features were characterised through the careful study of ' precipitation. Fatigue crack growth tests with dwell time were performed at high temperature for comparison of the mechanical properties of some selected microstructures

Food distribution influences social organization and population growth in a small rodent

This is the postprint version of the article. The published article can be located at the publisher's websiteIn polygynous mammals, the spatial clumping and predictability of food should influence spacing behavior of females whose reproductive success depends to a great extent on food availability, which would in turn affect male spacing behavior. Changes in the social and mating systems can then influence individual fitness and population dynamics. To test these hypotheses, we manipulated food distribution and predictability in enclosed populations of bank voles (Myodes glareolus) and monitored spacing behavior, survival, and reproduction of adult females and males over 3 months. Food was either spread out (dispersed treatment), spatially clumped and highly predictable (clumped treatment) or spatially clumped but less predictable (variable treatment). We found that females in the clumped treatment were more aggregated and had more overlapping home ranges compared with females in the dispersed and variable treatments. Male spacing behavior followed the same patterns. Despite different social organizations between treatments, no differences in home range size and mating systems were found in females and males. In addition, we found that females in the clumped food treatment had a higher probability of successfully producing weaned offspring, likely due to lower infanticide rates. This led to higher population growth compared with the other 2 treatments. These results suggest a tight relationship between the spatiotemporal distribution of food, social organization, and population dynamics.2014-04-3

Mediating male-male interactions: the role of the UV-blue crest coloration in blue tits

This is the postprint version of the article. The published article can be located here: http://link.springer.com/article/10.1007/s00265-010-0995-z?nullBadges of status, usually color patches, are hypothesised to serve as important signals within natural populations by communicating individual’s fighting ability or aggressiveness before an interaction ever takes place. These signals, which may evolve via sexual and/or social selection, mediate intra-specific competition by influencing the outcome or escalation of contests between individuals. The last 10 years saw the rise of interest in the role of Ultraviolet (UV)-based coloration in intra-sexual communication. However, the rare experimental studies that tested this hypothesis found opposite results, which may originate from the different methodological procedures used to assess badge of status theory. We present here the results of an experiment testing whether male blue tits (Cyanistes caeruleus) respond differently to unfamiliar conspecifics presenting contrasted UV crest coloration. In an aviary, we simultaneously presented two caged blue tits with enhanced (UV+) or reduced (UV-) crest coloration to a focal bird. We found that focal males acted more aggressively towards the UV- males than UV+ males. In addition, focal males fed more often close to males that were similar in brightness or duller than themselves. We conclude that, in blue tits, UV-blue crest coloration affects both social and aggressive responses towards unfamiliar individuals, and thus it has some properties of a badge of status

New views on how population-intrinsic and community-extrinsic processes interact during the vole population cycles

Based on evidence from a series of recent studies linking behaviour to demography in experimental vole populations we propose how intrinsic and extrinsic factors interact through the various phases of the multi-annual population cycles of voles and lemmings. We hypothesise that population growth in the increase phase of the cycle is enhanced by a high degree of space sharing (sociality) among reproductive females who share resource patches, especially during winter. These social females enjoy a high reproductive output due to good resource conditions, and facilitation provided by communal thermoregulation, breeding and defence of weanlings towards infanticidal conspecifics. We hypothesise on the other hand that the crash phase is initiated and enhanced by predation of adult males that leads to a series of cascading events involving infanticidal behaviour by immigrant males, increased mortality of adult social females, and inversely density-dependent and/or disturbance-induced dispersal. These events further enhance predation-induced mortality and thus a negative feed-back loop to the rate of the crash. In this framework we may explain how extrinsic factors such as predation and winter resource distribution contribute to transitions between docile and aggressive behaviours, and how this transition is spatially synchronised by inversely density-dependent dispersal that may act to mediate a rapidly spreading wave throughout the population. We propose that innate differences among rodent species in their propensities for different social organizations also determine their propensity for exhibiting multi-annual cycles as well as other cycle-related phenomena such as shape of the population cycles and spatial synchrony. We provide a set of testable predictions for further empirical evaluation

Concurrent effects of age class and food distribution on immigration success and population dynamics in a small mammal

1. During the settlement stage of dispersal, the outcome of conflicts between residents and immigrants should depend on the social organization of resident populations as well as on individual traits of immigrants, such as their age class, body mass and/or behaviour. 2. We have previously shown that spatial distribution of food influences the social organization of female bank voles (Myodes glareolus). Here, we aimed to determine the relative impact of food distribution and immigrant age class on the success and demographic consequences of female bank vole immigration. We manipulated the spatial distribution of food within populations having either clumped or dispersed food. After a pre-experimental period, we released either adult immigrants or juvenile immigrants, for which we scored sociability and aggressiveness prior to introduction. 3. We found that immigrant females survived less well and moved more between populations than resident females, which suggest settlement costs. However, settled juvenile immigrants had a higher probability to reproduce than field-born juveniles. 4. Food distribution had little effects on the settlement success of immigrant females. Survival and settlement probabilities of immigrants were influenced by adult female density in opposite ways for adult and juvenile immigrants, suggesting a strong adult–adult competition. Moreover, females of higher body mass at release had a lower probability to survive, and the breeding probability of settled immigrants increased with their aggressiveness and decreased with their sociability. 5. Prior to the introduction of immigrants, resident females were more aggregated in the clumped food treatment than in the dispersed food treatment, but immigration reversed this relationship. In addition, differences in growth trajectories were seen during the breeding season, with populations reaching higher densities when adult immigrants were introduced in a plot with dispersed food, or when juvenile immigrants were introduced in a plot with clumped food. 6. These results indicate the relative importance of intrinsic and extrinsic factors on immigration success and demographic consequences of dispersal and are of relevance to conservation actions, such as reinforcement of small populations

Food distribution influences social organization and population growth in a small rodent

This is the postprint version of the article. The published article can be located at the publisher's websiteIn polygynous mammals, the spatial clumping and predictability of food should influence spacing behavior of females whose reproductive success depends to a great extent on food availability, which would in turn affect male spacing behavior. Changes in the social and mating systems can then influence individual fitness and population dynamics. To test these hypotheses, we manipulated food distribution and predictability in enclosed populations of bank voles (Myodes glareolus) and monitored spacing behavior, survival, and reproduction of adult females and males over 3 months. Food was either spread out (dispersed treatment), spatially clumped and highly predictable (clumped treatment) or spatially clumped but less predictable (variable treatment). We found that females in the clumped treatment were more aggregated and had more overlapping home ranges compared with females in the dispersed and variable treatments. Male spacing behavior followed the same patterns. Despite different social organizations between treatments, no differences in home range size and mating systems were found in females and males. In addition, we found that females in the clumped food treatment had a higher probability of successfully producing weaned offspring, likely due to lower infanticide rates. This led to higher population growth compared with the other 2 treatments. These results suggest a tight relationship between the spatiotemporal distribution of food, social organization, and population dynamics.2014-04-3

Rapid collaborative knowledge building via Twitter after significant geohazard events

International audienc

SN Zwicky: uncovering a population of gravitational lens galaxies with magnified "standard candles"

We report the discovery of a very rare phenomenon, a multiply-imaged gravitationally lensed Type Ia supernova (SNe Ia), "SN Zwicky", a.k.a. SN 2022qmx, magnified nearly twenty-five times by a foreground galaxy. The system was identified as intrinsically bright thanks to the "standard candle" nature of SNe Ia. Observations with high-spatial resolution instruments resolved a system with four nearly simultaneous images, with an Einstein radius of only $\theta_E =0.167"$, corresponding to a lens mass of $8\cdot 10^9$ solar masses within a physical size below $0.8$ kiloparsecs. A smooth lens model fails to reproduce the image flux ratios, suggesting significant additional magnification from compact objects. Given the small image splitting and a relatively faint deflecting galaxy, the lensing system would not have been found through the angular separation technique generally used in large imaging surveys