Continuous Time Random Walks in periodic systems: fluid limit and fractional differential equations on the circle

In this article, the continuous time random walk on the circle is studied. We derive the corresponding generalized master equation and discuss the effects of topology, especially important when Levy flights are allowed. Then, we work out the fluid limit equation, formulated in terms of the periodic version of the fractional Riemann-Liouville operators, for which we provide explicit expressions. Finally, we compute the propagator in some simple cases. The analysis presented herein should be relevant when investigating anomalous transport phenomena in systems with periodic dimensions.Comment: 14 pages, 1 figure. References added. Published versio

Pseudochaotic poloidal transport in the laminar regime of the resistive ballooning instabilities

In toroidal geometry, and prior to the establishment of a fully developed turbulent state, the so-called topological instability of the pressure-gradient-driven turbulence is observed. In this intermediate state, a narrow spectral band of modes dominates the dynamics, giving rise to the formation of iso-surfaces of electric potential with a complicated topology. Since E x B advection of tracer particles takes place along these iso-surfaces, their topological complexity affects the characteristic features of radial and poloidal transport dramatically. In particular, they both become strongly non-diffusive and non-Gaussian. Since radial transport determines the system confinement properties and poloidal transport controls the equilibration dynamics (on any magnetic surface), the development of non-diffusive models in both directions is thus of physical interest. In previous work, a fractional model to describe radial transport was constructed by the authors. In this contribution, recent results on periodic fractional models are exploited for the construction of an effective model of poloidal transport. Numerical computations using a three-dimensional reduced magnetohydrodynamic set of equations are compared with analytical solutions of the fractional periodic model. It is shown that the aforementioned analytical solutions accurately describe poloidal transport, which turns out to be superdiffusive with index $\alpha=1$.Comment: 17 pages, 6 figures. Accepted for publication in Phys. Plasma

Study of radial heat transport in W7-X using the transfer entropy

Autor colectivo: W7-X TeamIn this work, we analyze data obtained using the electron cyclotron emission radiometer at the Wendelstein 7-X stellarator using a relatively new technique: the transfer entropy. Thus, we detect the propagation of information and find that it occurs in a stepwise fashion: we observe both 'trapping zones' and radial 'jumps', when the information is apparently skipping over intermediate positions. Using scans of the rotational transform, we observe that the 'trapping zones' appear to be associated with rational surfaces. Power scan experiments show that these 'jumps' increase in importance when power is increased, thus enhancing the effective diffusivity. The observations are interpreted in terms of a resistive magneto-hydrodynamic model, which displays behavior similar to the experimental results. The 'trapping zones' are explained in terms of zonal flows associated with rational surfaces, while the 'jumps' are ascribed to mode coupling effects, i.e. the transmission of turbulent energy via the magnetic field

Community-level respiration of prokaryotic microbes may rise with global warming

Understanding how the metabolic rates of prokaryotes respond to temperature is fun-damental to our understanding of how ecosystem functioning will be altered by climatechange, as these micro-organisms are major contributors to global carbon efflux. Ecologicalmetabolic theory suggests that species living at higher temperatures evolve higher growthrates than those in cooler niches due to thermodynamic constraints. Here, using a globalprokaryotic dataset, we find that maximal growth rate at thermal optimum increases withtemperature for mesophiles (temperature optima.45◦C), but not thermophiles (&45◦C).Furthermore, short-term (within-day) thermal responses of prokaryotic metabolic rates aretypically more sensitive to warming than those of eukaryotes. Because climatic warmingwill mostly impact ecosystems in the mesophilic temperature range, we conclude that asmicrobial communities adapt to higher temperatures, their metabolic rates and therefore,biomass-specific CO2production, will inevitably rise. Using a mathematical model, weillustrate the potential global impacts of these findings

Dithering transitions in resistive pressure-gradient-driven turbulence

A self-consistent model of the L to H transition has been derived from coupled nonlinear envelope equations for the fluctuation level, and radial electric field shear, E{prime}{sub r}. This model is based on general properties of the coupling between turbulence and averaged sheared flows. To extract these generic properties several turbulence models have been investigated. Here, some of the results obtained with the resistive pressure-gradient-driven turbulence are presented with special emphasis on the structure of the Reynolds stress and the existence of limit cycle solutions

Role of carbon allocation efficiency in the temperature dependence of autotroph growth rate

To predict how plant growth rate will respond to temperature requires understanding how temperature drives the underlying metabolic rates. Although past studies have considered the temperature dependences of photosynthesis and respiration rates underlying growth, they have largely overlooked the temperature dependence of carbon allocation efficiency. By combining a mathematical model that links exponential growth rate of a population of photosynthetic cells to photosynthesis, respiration, and carbon allocation; to an experiment on a freshwater alga; and to a database covering a wide range of taxa, we show that allocation efficiency is crucial for predicting how growth rates will respond to temperature change across aquatic and terrestrial autotrophs, at both short and long (evolutionary) timescales

Diagnostic accuracy of first-trimester combined screening for early-onset and preterm pre-eclampsia at 8-10 compared with 11-13 weeks' gestation

To compare the ability of first-trimester combined screening for pre-eclampsia (PE) to predict early-onset and preterm PE when pregnancy-associated plasma protein-A (PAPP-A) and placental growth factor (PlGF) were assessed before vs after 11 weeks' gestation. This was a secondary analysis of a prospective cohort study of singleton pregnancies undergoing routine first-trimester screening conducted at Vall d'Hebron University Hospital, Barcelona, Spain, between October 2015 and September 2017. Demographic characteristics, obstetric history, maternal history and biophysical markers (mean uterine artery pulsatility index and mean arterial blood pressure (MAP)) were recorded at the first-trimester scan (at 11 + 0 to 13 + 6 weeks' gestation). Maternal serum concentrations of PAPP-A and PlGF were assessed from the routine first-trimester blood test (at 8 + 0 to 13 + 6 weeks). Women were classified into two groups depending on whether serum biomarkers were assessed at 8 + 0 to 10 + 6 weeks or at 11 + 0 to 13 + 6 weeks. Probability scores for early-onset and preterm PE were calculated by using two different algorithms: the multivariate Gaussian-distribution model and The Fetal Medicine Foundation (FMF) competing-risks model. Receiver-operating-characteristics (ROC) curves were produced and detection rates at fixed 5% and 10% false-positive rates were computed to compare the performance of these algorithms when PAPP-A and PlGF were assessed before vs after 11 weeks. Of the 2641 women included, serum biomarkers were assessed before 11 weeks in 1675 (63.4%) and at or after 11 weeks in 966 (36.6%). Of these, 90 (3.4%) women developed PE, including 11 (0.4%) cases of early-onset PE and 30 (1.1%) of preterm PE. Five (45.5%) cases of early-onset and 16 (53.3%) of preterm PE were identified in the group in which serum biomarkers were assessed at 8 + 0 to 10 + 6 weeks and six (54.5%) cases of early-onset and 14 (46.7%) of preterm PE in the group in which serum biomarkers were assessed at 11 + 0 to 13 + 6 weeks. In the prediction of early-onset and preterm PE using the Gaussian algorithm, no differences were observed between the areas under the ROC curves (AUCs) when PAPP-A and PlGF were measured before or after 11 weeks. In the prediction of early-onset and preterm PE using the FMF algorithm, no differences were observed between AUCs for any of the combinations used for risk calculation when the serum biomarkers were obtained before vs after 11 weeks, except for the combination of PAPP-A and MAP, which showed a greater AUC for the prediction of early-onset PE when PAPP-A was measured at or after 11 weeks. The prediction of early-onset and preterm PE is similar when serum biomarkers are measured before or after 11 weeks. This allows the use of a two-step approach for PE risk assessment that permits immediate risk calculation at the time of the first-trimester scan. © 2020 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology

Burden of respiratory disease attributable to secondhand smoke exposure at home in children in Spain (2015)

This study aimed to estimate the number of incident cases and hospital admissions attributable to secondhand smoke (SHS) exposure at home for asthma, otitis media (OM), and lower respiratory infections (LRI) in children in Spain. The burden of respiratory disease caused by SHS exposure was estimated in terms of incident cases and hospitalized cases for asthma, OM, and LRI. Estimates were calculated using the population attributable fraction. The age-specific (0-1 year, 0-4 years, 5-11 years, and 0-11 years) prevalence of SHS exposure in children was estimated through a telephone survey performed in a representative sample of Spanish households with children in 2016. The risk estimates for all diseases were selected from international meta-analyses. The number of hospitalized cases was obtained for each disease from the Hospital Minimum Data Set provided by the Ministry of Health of Spain. Incident cases were obtained from the Global Health Data Exchange. In 2015, SHS exposure caused an estimated total of 136,403 incident cases of the following respiratory diseases: 9058 (8.5%) cases of asthma, 120,248 (8.5%) of OM, and 7097 (13.5%) of LRI in children aged 0-14 years old in Spain. Likewise, SHS exposure caused a total of 3028 hospitalized cases, with 379 (8.5%) for asthma and 167 (8.5%) for OM in children 0-11 years old, and 2482 (11.6%) for LRI in children <2 years old. The high burden of respiratory disease attributed to SHS exposure supports the need to improve protection of children against SHS exposure by extending smoke-free regulations to homes and cars

Quantifying particle size and turbulent scale dependence of dust uplift in the Sahara using aircraft measurements

The first size-resolved airborne measurements of dust fluxes and the first dust flux measurements from the central Sahara are presented and compared with a parameterization by Kok (2011a). High-frequency measurements of dust size distribution were obtained from 0.16 to 300 µm diameter, and eddy covariance fluxes were derived. This is more than an order of magnitude larger size range than previous flux estimates. Links to surface emission are provided by analysis of particle drift velocities. Number flux is described by a −2 power law between 1 and 144 µm diameter, significantly larger than the 12 µm upper limit suggested by Kok (2011a). For small particles, the deviation from a power law varies with terrain type and the large size cutoff is correlated with atmospheric vertical turbulent kinetic energy, suggesting control by vertical transport rather than emission processes. The measured mass flux mode is in the range 30–100 µm. The turbulent scales important for dust flux are from 0.1 km to 1–10 km. The upper scale increases during the morning as boundary layer depth and eddy size increase. All locations where large dust fluxes were measured had large topographical variations. These features are often linked with highly erodible surface features, such as wadis or dunes. We also hypothesize that upslope flow and flow separation over such features enhance the dust flux by transporting large particles out of the saltation layer. The tendency to locate surface flux measurements in open, flat terrain means these favored dust sources have been neglected in previous studies