A symbolic method to analyse patterns in plant structure whose organogenesis is driven by a multitype branching process

International audienceFormal grammars like L-systems have long been used to describe plant growth dynamics. In this article, they are used for a new purpose. The aim is to build a symbolic method derived from computer science that enables the computation of the distribution associated to the number of complex structures in plants whose organogenesis is driven by a multitype branching process. To that purpose, a new combinatorial framework is set in which plant structure is coded by a Dyck word. Moreover, the organogenesis is represented by stochastic F0L-systems. By doing so, the problem is equivalent to determining the distribution of patterns in random words generated by stochastic F0L-system. This method leads directly to numerous applications like parametric identication for plant growth model

Plants as Combinatorial Structures and Applications

International audienceIn this article, we introduce a new method allowing the computation of the distribution associated to the number of complex structures in plants deriving from GreenLab type growth model. In order to use this method, we set a new mathematical framework based on combinatorics. We show how plants can be seen as plane rooted trees and how their topology can be described by Dyck words. Moreover, we integrate plant growth in the formalism by adapting stochastic F0L-systems to the framework. This new representation enables not only the computation of the distribution associated to all types of organ but also the analysis of particular patterns thanks to a symbolic method. This approach gives new kinds of applications such as estimating the age of a plant from a set of botanical data

Effects of excitonic diffusion on stimulated emission in nanocrystalline ZnO

We present optically-pumped emission data for ZnO, showing that high excitation effects and stimulated emission / lasing are observed in nanocrystalline ZnO thin films at room temperature, although such effects are not seen in bulk material of better optical quality. A simple model of exciton density profiles is developed which explains our results and those of other authors. Inhibition of exciton diffusion in nanocrystalline samples compared to bulk significantly increases exciton densities in the former, leading, via the nonlinear dependence of emission in the exciton bands on the pump intensity, to large increases in emission and to stimulated emission

ZnO wide bandgap semiconductor nanostructures: growth, characterisation and applications

The compound ZnO, or zincite, has a long, fascinating and diverse history displaying a number of peaks and troughs in terms of the degree of research interest, numbers of publications per annum and so forth. These peaks have in some cases been associated with the discovery of a new aspect of its behaviour which is relevant to some scientific or technological focus (such as UV light emission) and the ambitions associated with these technologies. Some of these ambitions have been realized and some, to date, remain ambitions. The general public will most probably know of this material from some of its earlier applications. Zinc oxide was initially known by a variety of names, some of rather unclear origin, including “nihil album”, “flowers of zinc”, “chinese white” and “philosopher’s wool”. The usage of these terms has obviously declined since the standardization of chemical nomenclature since the early 1800’s as discussed by Kent (1958). ZnO is, or has been, used as a pigment in paints and enamel coatings (hence the name “chinese white”) and also as an ingredient in cements, glass, tires, glue, matches, white ink, reagents, photocopy paper, flame retardant, fungicides, cosmetics and dental cements and ~ 100,000 tonnes of ZnO is produced per annum as reported by Klingshirn (2007). These diverse applications rely on various properties of ZnO such as the white colour of the material, its chemical activity, UV blocking capability, heat conductivity and bioactivity. ZnO is used extensively in various pharmaceutical and cosmetic products including ointments and sunscreen preparations (including an appearance in the Hollywood movie “Jaws”, where Brody’s wife enquires if he has remembered to bring the zinc oxide sunscreen before he boards the Orca). ZnO is a material which is used in a very wide variety of applications in a diverse range of technological spaces. In addition to this already impressive technological resume, ZnO is used widely in the semiconductor industry, primarily in varistor manufacture, but also as a transparent conducting oxide, a photoconductor and a phosphor, see e.g. Klingshirn (2007), Minami (2005), Monroy et al. (2003) and Heiland et al. (1959)

Exciton-polariton behaviour in bulk and polycrystalline ZnO

We report detailed reflectance studies of the exciton–polariton structure of thin film polycrystalline ZnO and comparison with bulk crystal behaviour. Near-normal incidence reflectance spectra of these samples are fitted using a two-band dielectric response function. Our data show that the reflectance data in polycrystalline ZnO differ substantially from the bulk material, with Fabry–Perot oscillations at energies below the transverse A exciton and above the longitudinal B exciton in the films. In the strong interaction regime between these energies no evidence is seen of the normally rapid oscillations associated with the anomalous waves. We demonstrate that the strong interaction of the damped exciton with the photon leads to polaritons in this region with substantial damping such that the Fabry–Perot modes are eliminated. Good qualitative agreement is achieved between the model and data. The importance of the polariton model in understanding the reflectance data of polycrystalline material is clearly see

European Multidisciplinary and Water-Column Observatory - European Research Infrastructure Consortium (EMSO ERIC): challenges and opportunities for strategic European marine sciences

EMSO (European Multidisciplinary Seafloor and water-column Observatory, www.emso-eu.org) is a large‐scale European Research Infrastructure I. It is a distributed infrastructure of strategically placed, deep‐sea seafloor and water column observatory nodes with the essential scientific objective of real‐time, longterm observation of environmental processes related to the interaction between the geosphere, biosphere, and hydrosphere. The geographic locations of the EMSO observatory nodes represent key sites in European waters, from the Arctic, through the Atlantic and Mediterranean, to the Black Sea (Figure 1), as defined through previous studies performed in FP6 and FP7 EC projects such as ESONET‐CA, ESONET‐NoE, EMSO-PP (Person et al., 2015)Peer Reviewe

Outbreak of Fatal Childhood Lead Poisoning Related to Artisanal Gold Mining in Northwestern Nigeria, 2010.

Background: In May 2010, a team of national and international organizations was assembled to investigate children's deaths due to lead poisoning in villages in northwestern Nigeria. Objectives: To determine the cause of the childhood lead poisoning outbreak, investigate risk factors for child mortality, and identify children aged <5 years in need of emergency chelation therapy for lead poisoning. Methods: We administered a cross-sectional, door-to-door questionnaire in two affected villages, collected blood from children aged 2-59 months, and soil samples from family compounds. Descriptive and bivariate analyses were performed with survey, blood-lead, and environmental data. Multivariate logistic regression techniques were used to determine risk factors for childhood mortality. Results: We surveyed 119 family compounds. One hundred eighteen of 463 (25%) children aged <5 years had died in the last year. We tested 59% (204/345) of children, aged <5 years, and all were lead poisoned (≥10 µg/dL); 97% (198/204) of children had blood-lead levels ≥45 µg/dL, the threshold for initiating chelation therapy. Gold ore was processed inside two-thirds of the family compounds surveyed. In multivariate modeling significant risk factors for death in the previous year from suspected lead poisoning included: the child's age, the mother performing ore-processing activities, community well as primary water source, and the soil-lead concentration in the compound. Conclusion: The high levels of environmental contamination, percentage of children aged <5 years with elevated blood-lead levels (97%, >45 µg/dL), and incidence of convulsions among children prior to death (82%) suggest that most of the recent childhood deaths in the two surveyed villages were caused by acute lead poisoning from gold ore-processing activities. Control measures included environmental remediation, chelation therapy, public health education, and control of mining activities

Optical properties of nanocrystalline ZnO thin films grown using pulsed laser deposition

Raman spectroscopy, x-ray diffractometry, atomic force microscopy, photoluminescence spectroscopy and reflectance spectroscopy have been used to characterize ZnO thin films grown by pulsed laser deposition as a function of the post-growth annealing temperature. Raman results show enhancement and broadening of certain Raman features which correlate with changes in the widths of the x-ray diffraction peaks for samples with varying grain size in the 50-100 nm range. These data suggest that electric fields, arising from charge trapping at grain boundaries, in conjunction with localised and surface phonon modes, are the cause of the intensity enhancement and asymmetry of the Raman features. Band-edge photoluminescence and reflectance spectra also altered considerably with increases in grain size, showing clearly observable excitonic structure in the reflectance spectra. An analysis using a deformation potential Hamiltonian demonstrates that the experimental exciton energies are not explicable solely in terms of sample strain and give additional evidence for electric fields in the samples due to charge trapping at grain boundaries. This is supported by theoretical estimates of the exciton energy perturbation due to electric fields and also by the behaviour of the green band in the samples. Detailed studies show that reflectance spectra in nanocrystalline ZnO differ substantially from bulk material. Interaction of excitons, damped by strong electric field effects, with photons leads to exciton-polaritons with substantial damping, eliminating the normal Fabry-Perot structure seen in thin films. Good qualitative agreement is achieved between the model and data and the conclusions are also in good agreement with the photoluminescence and Raman data. Finally, high intensity optical pumping data of these samples again shows a dependence on grain size. All samples show evidence of high excitation effects and the sample with the largest grain size displays random lasing at room temperature. All our results indicate the very strong influence of electric fields due to charge trapping at grain boundaries on the optical properties of nanocrystalline ZnO