Inertial stretching separation in binary droplet collisions

Binary droplet collisions exhibit a wide range of outcomes, including coalescence and stretching separation, with a transition between these two outcomes arising for high Weber numbers and impact parameters. Our experimental study elucidates the effect of viscosity on this transition, which we show exhibits inertial (viscosity-independent) behaviour over an order-of-magnitude-wide range of Ohnesorge numbers. That is, the transition is not always shifted towards higher impact parameters by increasing droplet viscosity, as it might be thought from the existing literature. Moreover, we provide compelling experimental evidence that stretching separation only arises if the length of the coalesced droplet exceeds a critical multiple of the original droplet diameters (3.35). Using this as a criterion, we provide a simple but robust model (without any arbitrarily chosen free parameters) to predict the coalescence/stretching-separation transition.

Magnetic Recording of Superconducting States

Local polarization of magnetic materials has become a well-known and widely used method for storing binary information. Numerous applications in our daily life such as credit cards, computer hard drives, and the popular magnetic drawing board toy, rely on this principle. In this work, we review the recent advances on the magnetic recording of inhomogeneous magnetic landscapes produced by superconducting films. We summarize the current compelling experimental evidence showing that magnetic recording can be applied for imprinting in a soft magnetic layer the flux trajectory taking place in a superconducting layer at cryogenic temperatures. This approach enables the ex situ observation at room temperature of the imprinted magnetic flux landscape obtained below the critical temperature of the superconducting state. The undeniable appeal of the proposed technique lies in its simplicity and the potential to improve the spatial resolution, possibly down to the scale of a few vortices.

Addition of pollen increases growth of nectar-living yeasts

ABSTRACT Nectar is frequently inhabited by a limited number of microorganisms. Nonetheless, these species can quickly attain relatively high cell densities. This is quite surprising because of the limited availability of nutrients and unbalanced Carbon/Nitrogen ratios. Because nectar yeasts commonly aggregate around pollen and pollen grains are particularly rich in proteins, it has been suggested that the presence of pollen in nectar contributes to enhanced growth of yeasts in nectar, but compelling experimental evidence is still lacking. In this study, we conducted in vitro growth experiments to investigate whether the addition of pollen to sugar water increased growth of yeasts that naturally occur in nectar and honey provisions: Metschnikowia reukaufii, Starmerella orientalis and Torulaspora delbueckii. Our results indicate that yeasts benefit from the addition of pollen to a sugar-dominated medium, but the effects depended on type of pollen used. Overall, these results demonstrate that pollen plays an important role in the population dynamics of nectar-inhabiting yeasts and supports the idea that the chemical composition and the concentration of dehisced pollen may be more important factors determining the population growth of nectar yeasts than the chemistry of the nectar itself.

Frequency dependence shapes the adaptive landscape of imperfect Batesian mimicry

Despite more than a century of biological research on the evolution and maintenance of mimetic signals, the relative frequencies of models and mimics necessary to establish and maintain Batesian mimicry in natural populations remain understudied. Here we investigate the frequency-dependent dynamics of imperfect Batesian mimicry, using predation experiments involving artificial butterfly models. We use two geographically distinct populations of Adelpha butterflies that vary in their relative frequencies of a putatively defended model ( Adelpha iphiclus ) and Batesian mimic ( Adelpha serpa ). We found that in Costa Rica, where both species share similar abundances, Batesian mimicry breaks down, and predators more readily attack artificial butterfly models of the presumed mimic, A. serpa . By contrast, in Ecuador, where A. iphiclus (model) is significantly more abundant than A. serpa (mimic), both species are equally protected from predation. Our results provide compelling experimental evidence that imperfect Batesian mimicry is frequency-dependent on the relative abundance of models and mimics in natural populations, and contribute to the growing body of evidence that complex dynamics, such as seasonality or the availability of alternative prey, influence the evolution of mimetic traits.

Fluorescence-based gene reporter plasmid to track canonical Wnt signaling in ENS inflammation

In several gut inflammatory or cancer diseases, cell-cell interactions are compromised, and an increased cytoplasmic expression of β-catenin is observed. Over the last decade, numerous studies provided compelling experimental evidence that the loss of cadherin-mediated cell adhesion can promote β-catenin release and signaling without any specific activation of the canonical Wnt pathway. In the present work, we took advantage of the ability of lipofectamine-like reagent to cause a synchronous dissociation of adherent junctions in cells isolated from the rat enteric nervous system (ENS) for obtaining an in vitro model of deregulated β-catenin signaling. Under these experimental conditions, a green fluorescent protein Wnt reporter plasmid called ΔTop_EGFP3a was successfully tested to screen β-catenin stabilization at resting and primed conditions with exogenous Wnt3a or lipopolysaccharide (LPS). ΔTop_EGFP3a provided a reliable and strong fluorescent signal that was easily measurable and at the same time highly sensitive to modulations of Wnt signaling following Wnt3a and LPS stimulation. The reporter gene was useful to demonstrate that Wnt3a exerts a protective activity in the ENS from overstimulated Wnt signaling by promoting a downregulation of the total β-catenin level. Based on this evidence, the use of ΔTop_EGFP3a reporter plasmid could represent a more reliable tool for the investigation of Wnt and cross-talking pathways in ENS inflammation.