Autocorrelation analysis for the unbiased determination of power-law exponents in single-quantum-dot blinking

We present an unbiased and robust analysis method for power-law blinking statistics in the photoluminescence of single nano-emitters, allowing us to extract both the bright- and dark-state power-law exponents from the emitters' intensity autocorrelation functions. As opposed to the widely-used threshold method, our technique therefore does not require discriminating the emission levels of bright and dark states in the experimental intensity timetraces. We rely on the simultaneous recording of 450 emission timetraces of single CdSe/CdS core/shell quantum dots at a frame rate of 250 Hz with single photon sensitivity. Under these conditions, our approach can determine ON and OFF power-law exponents with a precision of 3% from a comparison to numerical simulations, even for shot-noise-dominated emission signals with an average intensity below 1 photon per frame and per quantum dot. These capabilities pave the way for the unbiased, threshold-free determination of blinking power-law exponents at the micro-second timescale

No evidence for differential sociosexual behavior and space use in the color morphs of the European common wall lizard (Podarcis muralis)

Explaining the evolutionary origin and maintenance of color polymorphisms is a major challenge in evolutionary biology. Such polymorphisms are commonly thought to reflect the existence of alternative behavioral or life-history strategies under negative frequency-dependent selection. The European common wall lizardPodarcis muralisexhibits a striking ventral color polymorphism that has been intensely studied and is often assumed to reflect alternative reproductive strategies, similar to the iconic "rock-paper-scissors" system described in the North American lizardUta stansburiana. However, available studies so far have ignored central aspects in the behavioral ecology of this species that are crucial to assess the existence of alternative reproductive strategies. Here, we try to fill this gap by studying the social behavior, space use, and reproductive performance of lizards showing different color morphs, both in a free-ranging population from the eastern Pyrenees and in ten experimental mesocosm enclosures. In the natural population, we found no differences between morphs in site fidelity, space use, or male-female spatial overlap. Likewise, color morph was irrelevant to sociosexual behavior, space use, and reproductive success within experimental enclosures. Our results contradict the commonly held hypothesis thatP. muralismorphs reflect alternative behavioral strategies, and suggest that we should instead turn our attention to alternative functional explanations

Behavioural Thermoregulatory Tactics in Lacustrine Brook Charr, Salvelinus fontinalis

The need to vary body temperature to optimize physiological processes can lead to thermoregulatory behaviours, particularly in ectotherms. Despite some evidence of within-population phenotypic variation in thermal behaviour, the occurrence of alternative tactics of this behaviour is rarely explicitly considered when studying natural populations. The main objective of this study was to determine whether different thermal tactics exist among individuals of the same population. We studied the behavioural thermoregulation of 33 adult brook charr in a stratified lake using thermo-sensitive radio transmitters that measured hourly individual temperature over one month. The observed behavioural thermoregulatory patterns were consistent between years and suggest the existence of four tactics: two “warm” tactics with both crepuscular and finer periodicities, with or without a diel periodicity, and two “cool” tactics, with or without a diel periodicity. Telemetry data support the above findings by showing that the different tactics are associated with different patterns of diel horizontal movements. Taken together, our results show a clear spatio-temporal segregation of individuals displaying different tactics, suggesting a reduction of niche overlap. To our knowledge, this is the first study showing the presence of behavioural thermoregulatory tactics in a vertebrate

Eppur si muove, and yet it moves: Patchy (phoretic) swimmers

International audienceAdvances in colloidal synthesis allow for the design of particles with controlled patches. This article reviews routes towards colloidal locomotion, where energy is consumed and converted into motion, and its implementation with active patchy particles. A special emphasis is given to phoretic swimmers, where the self-propulsion originates from an interfacial phenomenon, raising experimental challenges and opening up opportunities for particles with controlled anisotropic surface chemistry and novel behaviors

Understanding Local-Field Correction Factors in the Framework of the Onsager-Bottcher Model

The determination of the appropriate local‐field factor for quantifying the response of a molecule to an external electric field is of major importance in optical spectroscopy. Although numerous studies have dealt with the evolution of the optical properties of emitters as a function of their environment, the choice of the model used to quantify local fields is still ambiguous, and sometimes even arbitrary. In this paper, we review the Onsager–Böttcher model, which introduces the polarizability of the probe molecule as the determinant parameter for the local field factor, and we establish a simple conceptual framework encompassing all commonly used models. Finally, a discussion of published experimental research illustrates the potential of the measurement of local electric fields in dense dielectric media, as well as the subtleties involved in their interpretation.Biological and Soft Matter Physic

Does using a polyethylene RM press-fit cup modify the preparation of the acetabulum and acetabular offset in primary hip arthroplasty?

International audienceIntroductionWhen performing total hip arthroplasty (THA), it is important to maintain the femoral and acetabular offsets to ensure good joint stability and to restore the function of the hip abductor muscles. In our practice, we mainly use a lateralized stem and hollow out the acetabulum to the quadrilateral plate to accommodate a press-fit polyethylene cup. However, the repercussions of this preparation method, which is driven by the cup's design, are not known. We carried out a retrospective study to assess: (1) the changes in the femoral and acetabular offset; (2) the height of the center of rotation; and (3) the repercussions on wear.HypothesisWe hypothesized there would be no significant differences between the preoperative and postoperative femoral and acetabular offsets.Patients and methodsWe reviewed 88 primary THA cases performed with the RM Pressfit™ cup that had a minimum of 5 years’ follow-up. A lateralized self-locking Muller-type cemented femoral stem was used in 92.0% of cases and a standard stem in 8.0%. Measurements were done on plain radiographs with MHP™ and Mesurim Pro™ software. The average follow-up was 6.5 years (5–8).ResultsOn average, the acetabular offset was reduced by 2.75 mm ± 5.9 mm (range: –17.5 to +10.6 mm) (P < 0.001) and the femoral offset was increased by 0.01 mm ± 5.5 mm (range: –17.8 to +11.0 mm) (P = 0.99). In terms of total offset, medialization of 2.74 mm ± 7 mm (range: –17.7 to +18.2 mm) was found (P = 0.001). The acetabular center of rotation was on average 4.77 mm ± 5.1 mm higher (P < 0.001). The mean annual wear at the more recent follow-up (min.: 5 years) was 0.068 mm (range: 0.01 to 0.25 mm) per year. The wear was not impacted by having more than 5 mm change in offset.DiscussionMeasurements of acetabular offset revealed statistically significant medialization due to the type of implant used and the surgical technique. The anatomical technique consists of positioning the cup in subchondral bone without contacting the quadrilateral plate. This preserves bone stock, which may be useful later on if the cup is revised, particularly in younger patients. Conversely, the femoral offset did not change significantly, despite the use of lateralized stems in 92.0% of cases. We measured an annual wear rate of 0.068 mm per year, which is lower than in other published studies, possibly because our patient population was older.Level of evidenceIV, retrospective study