A threshold model of plastic waste fragmentation: New insights into the distribution of microplastics in the ocean and its evolution over time

Plastic pollution in the aquatic environment has been assessed for many years by ocean waste collection expeditions around the globe or by river sampling. While the total amount of plastic produced worldwide is well documented, the amount of plastic found in the ocean, the distribution of particles on its surface and its evolution over time are still the subject of much debate. In this article, we propose a general fragmentation model, postulating the existence of a critical size below which particle fragmentation becomes extremely unlikely. In the frame of this model, an abundance peak appears for sizes around 1mm, in agreement with real environmental data. Using, in addition, a realistic exponential waste feed to the ocean, we discuss the relative impact of fragmentation and feed rates, and the temporal evolution of microplastics (MP) distribution. New conclusions on the temporal trend of MP pollution are drawn.Comment: 14 pages, 14 figure

Optimising reactive disease management using spatially explicit models at the landscape scale

Increasing rates of global trade and travel, as well as changing climatic patterns, have led to more frequent outbreaks of plant disease epidemics worldwide. Mathematical modelling is a key tool in predicting where and how these new threats will spread, as well as in assessing how damaging they might be. Models can also be used to inform disease management, providing a rational methodology for comparing the performance of possible control strategies against one another. For emerging epidemics, in which new pathogens or pathogen strains are actively spreading into new regions, the spatial component of spread becomes particularly important, both to make predictions and to optimise disease control. In this chapter we illustrate how the spatial spread of emerging plant diseases can be modelled at the landscape scale via spatially explicit compartmental models. Our particular focus is on the crucial role of the dispersal kernel-which parameterises the probability of pathogen spread from an infected host to susceptible hosts at any given distance-in determining outcomes of epidemics. We add disease management to our model by testing performance of a simple "one off" form of reactive disease control, in which sites within a particular distance of locations detected to contain infection are removed in a single round of disease management. We use this simplified model to show how ostensibly arcane decisions made by the modeller-most notably whether or not the underpinning disease model allows for stochasticity (i.e. randomness)-can greatly impact on disease management recommendations. Our chapter is accompanied by example code in the programming language R available via an online repository, allowing the reader to run the models we present for him/herself

The Academic Market and the Rise of Universities in Medieval and Early Modern Europe (1000-1800)

We argue that market forces shaped the geographic distribution of upper-tail human capital across Europe during the Middle Ages, and contributed to bolstering universities at the dawn of the Humanistic and Scientific Revolutions. We build a unique database of thousands of scholars from university sources covering all of Europe, construct an index of their ability, and map the academic market in the medieval and early modern periods. We show that scholars tended to concentrate in the best universities (agglomeration), that better scholars were more sensitive to the quality of the university (positive sorting) and migrated over greater distances (positive selection). Agglomeration, selection and sorting patterns testify to an integrated academic market, made possible by the use of a common language (Latin)

Are Scholars’ Wages Correlated with their Human Capital?

Throughout our project on premodern academia, we use a heuristic human capital index to measure each scholar’s quality. This index is built by combining several statistics from individual Wikipedia and Worldcat pages. The question we address here is whether this measure is correlated with the actual wages professors received. This note is a technical appendix to our paper on the academic market (De la Croix et al. 2020) but also has an interest as a stand-alone publication. There is considerable evidence that compensations for academic contractswentwell beyond paid salaries.1 They included payments from students, prebends,2 and many forms of in-kind benefits. Yet, it is interesting to examine the relationship between scholars’ human capital and existing data on monetary remunerations. Such remunerations have been used by Dittmar (2019) to show that professor salaries increased significantly relative to skilled wages after printing spread, with science professors benefiting from the largest salary increases. In the two sections below, we first review the available data on salaries, and argue that such data are imperfect proxies for the overall remuneration for academic services (i.e. a scholar’s market value). Keeping in mind such limitations, we thendocument a positive correlation between monetary income and scholars’ human capital.&nbsp

Oscillations of a liquid bridge resulting from the coalescence of two droplets

The inertial oscillations of a bridge of liquid maintained between two disks are studied under condition of negligible gravity. Both experimental and theoretical results are reported. In the experiment, the bridge is formed by the coalescence of two droplets so that its static equilibrium shape is either concave or convex depending on its length. After coalescence, the bridge performs weakly damped oscillations until it reaches its equilibrium shape. Four modes of oscillations are extracted from digital processing of images recorded by means of a high-speed camera. Their frequency and damping rate are determined and found to be independent of the initial conditions that fix the amplitudes of each mode. Concurrently, the eigen modes of oscillations of a non-cylindrical bridge have been computed by assuming inviscid flow and small amplitude oscillations. The agreement between theoretical and measured frequencies confirms that the experimental modes correspond to the eigenmodes of the linear inviscid theory. Their characteristics turn out to be significantly different from that of a cylindrical bridge. In particular, the eigenfrequencies scale as root gamma/rho R-m(3), where gamma is the surface tension, rho the liquid density, and R-m the radius at the middle of the bridge, which characterizes the shrunk/swollen character of the mean shape

Comparison of mechanical ventilatory constraints between continuous and intermittent exercises in healthy prepubescent children.

International audienceBBackground: The aim of this study was to evaluate the occurrence and severity of mechanical ventilatory constraints in healthy prepubescent children during continuous and intermittent exercise. Methods: Twelve prepubescent children (7 - 11 years old) performed 7 exercises on a treadmill: one graded test for the determination of maximal aerobic speed (MAS), three continuous exercises (CE) at 60, 70 and 80% of MAS and three intermittent exercises (IE), alternating 15s of exercise with 15s of passive recovery, at 90, 100 and 110% of MAS. During each CE and IE, tidal flow/volume loops were plotted within a maximal flow/volume loop (MFVL) measured at rest before each exercise. Expiratory flow limitation (expFL expressed in %Vt) was defined as the part of exercise tidal volume (Vt) meeting the boundary of MFVL. Breathing strategy was estimated by measuring inspiratory capacity relative to forced vital capacity and tidal volume relative to inspiratory capacity. Other breathing pattern parameters (ventilation VE, Vt, respiratory frequency f) were continuously recorded during exercise. Results: An "intensity" effect was found for during CE (p<0.001) but not during IE (p=0.08). The increase in was predominantly assumed by an increase in f for both exercise modalities. During each exercise, several children heterogeneously experienced expFL ranging between 10 - 90%Vt. For all exercises, Vt was predominantly regulated by an increase in Vt/IC with no change in IC/FVC from rest to exercise. Finally, no significant "modality" effect was found for mechanical ventilatory constraint parameters (expFL, VT/IC and IV/FVC). Discussion: We could conclude that neither of the modalities studied induced more mechanical ventilatory constraints than the other, but that exercise intensities specific to each modality might be greater sources of exacerbation for mechanical ventilatory constraints