Where surface physics and fluid dynamics meet: rupture of an amphiphile layer by fluid flow

We investigate the fluctuating pattern created by a jet of fluid impingent upon an amphiphile-covered surface. This microscopically thin layer is initially covered with 50 $\mu$m floating particles so that the layer can be visualized. A vertical jet of water located below the surface and directed upward drives a hole in this layer. The hole is particle-free and is surrounded by the particle-laden amphiphile region. The jet ruptures the amphiphile layer creating a particle-free region that is surrounded by the particle-covered surface. The aim of the experiment is to understand the (fluctuating) shape of the ramified interface between the particle-laden and particle-free regions.Comment: published in Journal of Chemical Physic

Fragility and hysteretic creep in frictional granular jamming

The granular jamming transition is experimentally investigated in a two-dimensional system of frictional, bi-dispersed disks subject to quasi-static, uniaxial compression at zero granular temperature. Currently accepted results show the jamming transition occurs at a critical packing fraction $\phi_c$. In contrast, we observe the first compression cycle exhibits {\it fragility} - metastable configuration with simultaneous jammed and un-jammed clusters - over a small interval in packing fraction ($\phi_1 < \phi < \phi_2$). The fragile state separates the two conditions that define $\phi_c$ with an exponential rise in pressure starting at $\phi_1$ and an exponential fall in disk displacements ending at $\phi_2$. The results are explained through a percolation mechanism of stressed contacts where cluster growth exhibits strong spatial correlation with disk displacements. Measurements with several disk materials of varying elastic moduli $E$ and friction coefficients $\mu$, show friction directly controls the start of the fragile state, but indirectly controls the exponential slope. Additionally, we experimentally confirm recent predictions relating the dependence of $\phi_c$ on $\mu$. Under repetitive loading (compression), the system exhibits hysteresis in pressure, and the onset $\phi_c$ increases slowly with repetition number. This friction induced hysteretic creep is interpreted as the granular pack's evolution from a metastable to an eventual structurally stable configuration. It is shown to depend upon the quasi-static step size $\Delta \phi$ which provides the only perturbative mechanism in the experimental protocol, and the friction coefficient $\mu$ which acts to stabilize the pack.Comment: 12 pages, 10 figure

Is it possible to experimentally verify the fluctuation relation? A review of theoretical motivations and numerical evidence

The theoretical motivations to perform experimental tests of the stationary state fluctuation relation are reviewed. The difficulties involved in such tests, evidenced by numerical simulations, are also discussed.Comment: 36 pages, 4 figures. Extended version of a presentation to the discussion "Is it possible to experimentally verify the fluctuation theorem?", IHP, Paris, December 1, 2006. Comments are very welcom

Detection of Endosymbiont Candidatus Midichloria mitochondrii and Tickborne Pathogens in Humans Exposed to Tick Bites, Italy

: During 2021, we collected blood and serum samples from 135 persons exposed to tick bites in southern Italy. We serologically and molecularly screened for zoonotic tickborne pathogens and only molecularly screened for Candidatus Midichloria mitochondrii. Overall, 62 (45.9%) persons tested positive for tickborne pathogens. Coxiella burnetii was detected most frequently (27.4%), along with Rickettsia spp. (21.5%) and Borrelia spp. (10.4%). We detected Candidatus M. mitochondrii DNA in 46 (34.1%) participants who had statistically significant associations to tickborne pathogens (p<0.0001). Phylogenetic analysis of Candidatus M. mitochondrii sequences revealed 5 clades and 8 human sequence types that correlated with vertebrates, Ixodes spp. ticks, and countries in Europe. These data demonstrated a high circulation of tickborne pathogens and Candidatus M. mitochondrii DNA in persons participating in outdoor activities in southern Italy. Our study shows how coordinated surveillance among patients, clinicians, and veterinarians could inform a One Health approach for monitoring and controlling the circulation of tickborne pathogens

Discrete-time volatility forecasting with persistent leverage effect and the link with continuous-time volatility modeling

We first propose a reduced-form model in discrete time for S&P 500 volatility showing that the forecasting performance can be significantly improved by introducing a persistent leverage effect with a long-range dependence similar to that of volatility itself. We also find a strongly significant positive impact of lagged jumps on volatility, which however is absorbed more quickly. We then estimate continuous-time stochastic volatility models that are able to reproduce the statistical features captured by the discrete-time model. We show that a single-factor model driven by a fractional Brownian motion is unable to reproduce the volatility dynamics observed in the data, while a multifactor Markovian model fully replicates the persistence of both volatility and leverage effect. The impact of jumps can be associated with a common jump component in price and volatility

Life and Death of an Influential Passenger: Wolbachia and the Evolution of CI-Modifiers by Their Hosts

Wolbachia are intracellular bacteria widely distributed among arthropods and nematodes. In many insect species these bacteria induce a cytoplasmic incompatibility (CI) between sperm of infected males and eggs of uninfected females. From an evolutionary point of view, CI is puzzling: In order to induce this modification-rescue system, Wolbachia affect sperm of infected males even though Wolbachia are only transmitted maternally. Phylogenetic studies of Wolbachia and hosts show that the bacteria rarely cospeciate with their hosts, indicating that infections are lost in host species. However, the mechanisms leading to Wolbachia loss are not well understood.Using a population genetic model, we investigate the spread of host mutants that enhance or repress Wolbachia action by affecting either bacterial transmission or the level of CI. We show that host mutants that decrease CI-levels in males (e.g. by reducing Wolbachia-density during spermatogenesis) spread, even at cost to mutant males. Increase of these mutants can lead to loss of Wolbachia infections, either as a direct consequence of their increase or in a step-wise manner, and we derive analytically a threshold penetrance above which a mutation's spread leads to extinction of Wolbachia. Selection on host modifiers is sexually antagonistic in that, conversely, host mutants that enhance Wolbachia in females are favoured whereas suppressors are not.Our results indicate that Wolbachia is likely to be lost from host populations on long evolutionary time scales due to reduction of CI levels in males. This can occur either by evolution of single host modifiers with large effects or through accumulation of several modifier alleles with small effects on Wolbachia action, even at cost to mutant males and even if infected hosts do not incur fecundity costs. This possibility is consistent with recent findings and may help to explain the apparent short evolutionary persistence times of Wolbachia in many host systems