Mass and Heat Flow through Snowpacks

Accurate estimation of snowmelt runoff is of primary importance in streamflow prediction for water management and flood forecasting in cold regions. Lateral flow, preferential flow pathways, and distinctive wetting and drying water retention curves in porous media have proven critical to improving soil water flow models; the most sophisticated physically based snowmelt models only account for 1D matrix flow and employ a single drying water retention curve for both drying and wetting snowpacks. Thus, there is an immediate need to develop snowmelt models that represent lateral and preferential flows, as well as full capillary hysteresis to examine the potential to improve snowmelt hydrological modelling. In this dissertation, the primary objective is to improve understanding and prediction of water flow through snow by investigating the formation of preferential flow paths and the coupling of heat and mass fluxes within snow. Of particular interest is the prediction of capillary pressure at macroscale, as it is of importance for simulating preferential flow in porous media. A novel 2D numerical model is developed that enables an improved understanding of energy and water flows within deep heterogeneous snowpacks on flat and sloping terrains. The numerical model simulates vertical and lateral water flow through snow matrix and preferential flow paths, and accounts for hysteresis in capillary pressure, internal energy fluxes, melt at the surface, and internal refreezing. Implementing a water entry pressure for initially dry snow was necessary for the formation of preferential flow paths. By coupling the simulation of preferential flow with heat transfer, ice layer formation was realistically simulated when water infiltrated an initially cold snowpack. Heat convection was added to the model and coupled to the energy balance at the snow surface; the transfer of heat by topography-driven airflow affected the estimated snow surface temperature by transporting thermal energy from the warm snow-soil interface to the upper snowpack. Comparisons of the model meltwater flow predictions against snowmelt field data revealed limitations in the current theories of water flow through snow, such as the use of a capillary entry pressure in the snow water retention curve that is limited to high-density snow. This suggested further concepts that would improve the representation of capillary pressure in snow models. This improved model, which considers a dynamic capillary pressure, gave better results than models based on previous theories when simulating capillary pressure overshoot. The research demonstrates how heterogeneous flow through snow can be modelled and how this research model furthers understanding of snowmelt flow processes and potential improvements in snowmelt-derived streamflow prediction

Microbiote intestinal de Mesonauta festivus dans un écosystème fluvial contrasté : influence de l'environnement, du génotype de l'hôte et des infections parasitaires

Plusieurs facteurs modulent le microbiote intestinal des Téléostéens tels que : l'environnement, l'alimentation, l'état de santé et le génotype. Le Cichlidé drapeau (Mesonauta festivus) a des populations génétiques bien étudiées et prospère dans des rivières aux caractéristiques physico-chimiques radicalement divergentes, ce qui en fait un bon modèle pour l'étude de la contribution relative de ces facteurs sur la structure taxonomique du microbiote. Dans le premier chapitre, nous avons développé et testé des amorces de blocage d'amplification spécifiques au gène de l'ARNr 18S de M. festivus. Nos amorces de blocage ont réduit de 66 % l'abondance relative d'ADN hôte dans les échantillons et ont augmenté la détectabilité de taxons parasitaires potentiellement dangereux, démontrant le potentiel de la méthode. De plus, nous avons collecté des données sur les habitudes alimentaires de l'espèce et décrit brièvement les communautés Eucaryotes commensales de son microbiote intestinal. Dans le chapitre deux, nous avons collecté 167 M. festivus à 12 sites d'étude en Amazonie centrale. Nous avons utilisé une double approche de métabarcodage génétique des gènes de l'ARNr 16S et 18S pour caractériser la structure taxonomique du microbiote intestinal et inférer l'influence du génotype des hôtes et aux caractéristiques physico-chimiques de l'eau à chaque site. Entre autres, nos résultats soutiennent un impact plus important de l'apparentement phylogénétique entre les poissons que la similarité environnementale entre les sites d'étude sur la structuration du microbiote intestinal pour ce Cichlidé amazonien. De plus, nous avons détecté des infections par Nyctoterus sp. et lié la présence de ce parasite à une dysbiose du microbiote intestinal de l'hôte. Nous avons également détecté la présence de vers intestinaux, dont la présence avait un impact mineur sur le microbiote. Notre étude, dans un paysage fluvial hétérogène, améliore la compréhension de la relation complexe entre les poissons, leurs parasites, leur microbiote et l'environnement.A number of key factors can structure the gut microbiota of fish such as: environment, diet, health state and genotype. Mesonauta festivus, an Amazonian cichlid, is a good model organism to study the relative contribution of these factors on the community structure of fish gut microbiota. M. festivus has well-studied genetic populations and thrives in rivers with drastically divergent physicochemical characteristics. In chapter one, we developed and tested species-specific elongation arrest blocking primers to block the M. festivus, 18S rRNA SSU gene. Our elongation arrest blocking primers significantly reduced the amount of host DNA in samples by 66 %. The blocking primers increased the detectability of potentially dangerous parasitic taxa in fish gut, highlighting the potential of the method for parasitic screening. Also, we collected data on the species feeding habits and obtained data on the commensal eukaryotic communities of this species gut microbiota. In chapter two, we collected 167 M. festivus from 12 study sites in central Amazonia. We used dual 16S and 18S rRNA metabarcoding approaches to characterize the gut microbiota structure in light of the host fish genotypes (Genotyping-By-Sequencing) and an extensive characterization of environmental physico-chemical parameters. We documented occurrences of ciliates from the genus Nyctoterus sp. infecting a fish and linked its presence to a dysbiosis of the gut microbiota of the host. Moreover, we detected the presence of helminths which had a minor impact on the gut microbiota of their host. Also, our results support a higher impact of the phylogenetic relatedness between fish rather than environmental similarity between sites of study on structuring the gut microbiota for this Amazonian cichlid. Our study in a heterogeneous riverscape integrates a wide range of factors known to structure fish gut microbiota. It significantly improves understanding of the complex relationship between fish, their parasites, their microbiota, and the environment

Robust optical clock transitions in trapped ions using dynamical decoupling

We present a novel method for engineering an optical clock transition that is robust agaiast external field fluctuations and is able to overcome limits resulting from field inhomogeneities. The technique is based on the application of continuous driving fields to form a pair of dressed states essentially free of all relevant shifts. Specifically, the clock transition is robust to magnetic field shifts, quadrupole and other tensor shifts, and amplitude fluctuations of the driving fields. The scheme is applicable to either a single ion or an ensemble ofions, and is relevant for several types of ions, such as 40Ca, Sr1", l38BiT and 176Lo". Taking a spherically symmetric Coulomb crystal formed by 400 40Ca+ ions as an example, we show through numerical simulations that the in homogeneous linewidth of teas of Hertz in such a crystal together with linear Zeeman shifts of order 10 MHz are reduced to form a linewidth of around 1 Hz. We estimate a two-order-of-magnitude reduction in averaging time compared tostate-of-the art single ion frequency references, assuming a probe laser fractional instability of 10~1 Furthermore, a statistical uncertainty reaching2.9 x 10"16 in 1 s is estimated for a cascaded clock scheme in which the dynamically decoupled Coulomb crystal clock stabilizes the interrogation laser for an 2/Al clock

La matière Congo

Écrit  avec un K ou un C, le Congo constitue « au cœur » de l'Afrique un lieu privilégié où un imaginaire plus ou moins mythifié s'est élaboré autour de quelques lieux ou de quelques traces. Écoulement du fleuve vers la mer, souvenir du Royaume Kongo, représentations du colon entre Stanley et de Brazza, voilà autant de motifs qui s'appuient sur un espace à géométrie variable et qui génèrent des écritures qui se réécrivent sans fin. Ce dossier est conçu comme un cheminement d'une version à l'a..

Potential of Sentinel-2 satellite images to monitor vine fields grown at a territorial scale

Aim: The aim of this short note is to provide first insights into the ability of Sentinel-2 images to monitor vine growth across a whole season. It focuses on verifying the practical temporal resolution that can be reached with Sentinel-2 images, the main stages of Mediterranean vineyard development as well as potential relevant agronomic information that can be seen on the temporal vegetation curves arising from Sentinel-2 images. Methods and results: The study was carried out in 2017 in a production vineyard located in southern France, 2 km from the Mediterranean seashore. Sentinel-2 images acquired during the whole vine growing cycle were considered, i.e. between the 3rd of March 2017 and the 10th of October 2017. The images were used to compute the classical normalized difference vegetation index (NDVI). Time series of NDVI values were analyzed on four blocks chosen for exhibiting different features, e.g. age, missing plants, weeding practices. The practical time lag between two usable images was closer to 16 days than to the 10 theoretical days (with only one satellite available at the date of the experiment), i.e. near 60% of the theoretical one. Results show that it might be possible to identify i) the main steps of vine development (e.g. budburst, growth, trimming, growth stop and senescence), ii) weed management and inter-row management practices, and iii) possible reasons for significant inter-block differences in vegetative expression (e.g. young vines that have recently been planted, low-productive blocks affected by many missing vines). Conclusions: Although this experiment was conducted at a time when Sentinel-2b was not fully operational, results showed that a sufficient number of usable images was available to monitor vine development. The availability of two Sentinel satellites (2a and 2b) in upcoming seasons should increase the number of usable images and the temporal resolution of the time series. This study also showed the limitations of the Sentinel-2 images’ resolution to provide within-block information in the case of small blocks or blocks with complex borders or both. Significance and impact of the study: This technical note demonstrated the potential of Sentinel-2 images to characterize vineyard blocks’ vigor and to monitor winegrowers’ practices at a territorial (regional) scale. The impact of management operations such as weeding and trimming, along with their incidence on canopy size, were observed on the NDVI time series. Some relevant parameters (slope, maximum values) may be derived from the NDVI time series, providing new insights into the monitoring of vineyards at a large scale. These results provided areas for further investigation, especially regarding the development of new indicators to characterize block-climate relationships

Enumeration and Decidable Properties of Automatic Sequences

We show that various aspects of k-automatic sequences -- such as having an unbordered factor of length n -- are both decidable and effectively enumerable. As a consequence it follows that many related sequences are either k-automatic or k-regular. These include many sequences previously studied in the literature, such as the recurrence function, the appearance function, and the repetitivity index. We also give some new characterizations of the class of k-regular sequences. Many results extend to other sequences defined in terms of Pisot numeration systems

WHOLE ISSUE \u3ci\u3eNebraska Bird Review\u3c/i\u3e (March 1974) 42(1)

Table of Contents 1973 Treasurer\u27s ........................................... 2 1973 Nebraska Nesting Survey ...................................... 3 1973 Christmas Count ...................................... 10 Canyon Wren in Nebraska ......................... 16 A Nebraska Swainson\u27s Thrush Nest .................................... 17 Another Black-throated Sparrow in Nebraska ................................. 18 Notes .......................................................... 1