Ondes internes du lac du Bourget: analyse des observations par des modèles linéaires

Deux campagnes de mesures effectuées sur le lac du Bourget en période de faible stratification (avril et décembre 1994) ont mis en évidence des oscillations de la thermocline de période comprise entre deux et trois jours. Ces oscillations atteignent 40 m d'amplitude pour une profondeur maximale de 145 m. Elles ont probablement un impact sur les processus biologiques et physico-chimiques qui gouvernent l'évolution de la qualité des eaux du lac.L'analyse des données brutes des températures révèle une corrélation étroite entre la génération des ondes internes et les événements de vents importants. Il apparaît en particulier que seuls les vents violents (< 8 m/s) affectent la stratification thermique de manière significative.Deux approches sont utilisées pour caractériser ces ondes :- une approche par traitement du signal qui donne accès aux périodes d'oscillations prédominantes ainsi qu'à la répartition de l'énergie dans la colonne d'eau en fonction de la fréquence.- une approche par modélisation mathématique au cours de laquelle les résultats obtenus par tjjois techniques distinctes utilisant plusieurs degrés de représentation de la bathymétrie du lac sont comparés. Ces modèles permettent de calculer les périodes d'oscillations ainsi que les déplacements de l'interface de densité et les vitesses dans chaque couche. A partir des valeurs des amplitudes d'oscillation obtenues expérimentalement, des vitesses maximales de l'ordre de 7 cm/s dans l'épîlîmnion et 3 cm/s dans l'hypolimnion ont pu être estimées pour les deux épisodes considérés.On montre que les modèles mathématiques et l'analyse spectrale corroborent les observations.There is a great concern about the understanding of water mass movements in lakes as they play a crucial role in the way nutrients and pollutants are trans-ported. This work brings new insights to the study of internal waves as it compares field data to various mathematical approaches. During the months of April and December 1994, a thermistor chain was deployed in Lake Bourget, France (length 18 km, width 3 km, maximum depth 145 m) to record temperature every 10 min, over nine unevenly spaced depths, from 10 to 51m. The time series of measurements provide a detailed picture of the characteristics and dynamics of internal waves. Records are discussed in view of the wind data observed at a meteorological station located at the south-end of the lake. According to the intensity of the wind forcing, the thermal structure is altered in different ways. When the winds are weak, the thermo-cline tilts and sets up a hydrostatic pressure gradient which balances the wind stress (TURNER, 1973). When the wind stops, the density interface oscillates until buoyancy is strong enough to balance the baroclinic pressure field. Strong winds, however, enhance large amplitude nonlinear waves which may break (Kelvin-Helmoltz instabilities), and therefore give rise to vertical mixing in the hypolimnion. During the recording periods wind stress in general is low, but occasional bursts of energy generate internal waves (fig. 2 and 3). In this paper, we focus on linear internal waves as records display a dominant response of the first longitudinal mode. The internal seiche continues to oscillate with decreasing amplitude after the wind has ceased. Two approaches have been implemented in order to characterize the internal waves. One consiste of signal treatment through spectral analysis and the second one involves mathematical modeling.Spectral analysis discloses responses of the first mode with periods of about 80h and 40h, respectively, for the April and December fleld survey (fig. 4 and 5). Further analysis of the April spectra shows that winds generate highly non-linear waves with high energy levels in a large band located in the first 30m. This band results from the mergence of two peaks of high energy at 80 and 40h respectively which probably correspond to the fundamental and second harmonie of a nonlinear wave. Then, as the wind stops, internal seiche of the first mode develops in the layer located between 30 and 50m indicating a deepening of the thermocline.Those fluctuations and their energy spectra are compared with the prédictions of three methods which are based on linear théories and consequently are not valid when the magnitude of oscillations is too high. The full phenomenon of wind-forced motion in a lake is not treated here. However, the analysis of postforcing phase is undertaken to charaterize free internai waves. One method is the Merian formula, which considers the lake as a two-layer system of constant properties and assumes the lake as a rectangular box. Another is a modified version of the Defant procédure (MORTIMER, 1979) which again assumes two layers but solves the momentum and mass équations with a varying cross section. The third method is the two layered variable depth model (TVDM) deve-loped by Schwab (HORN et aL, 1986), fitted to the basin topography and inclu-ding the free surface displacement It is expressed here through a one dimensional version directed along the main axis of the lake (i.e. the lateral variations of depth are not considered).The models display pattems of thermocline displacements (illustrated in fig. 7 and 8) which, in periodicity, are closely similar to those observed. Moreover, they give estimates of the maximum velocity induced by the seiche. Values of the order of 7 cm/s and 3 cm/s are found in the epilimnion and hypolimnion respectively. Finally, the influence exerted by the morphometry on the wave shape and associated field velocity is emphasized. In particular, the difference in the maximum speed calculated in the hypolimnion probably stems from the lateral contraction of the lake (and thus increasing speed) near Aix-les-Bains which is not taken into account in the TVD Model. The validity of the models implemented here is thrown back into question when the magnitude of the oscillations is sufficiently high to steepen the thermocline and in this particular case, a nonlinear theory (Korteweg-de Vries Equation) would be appropriate.The importance of a better knowledge of internal seiches goes beyond the field of physics. Through their influence on mixing and dispersal, those motions profoundly affect the chemical and biological economies of many lakes. Internal waves are responsible for periodic vertical displacement of the resuspended biomass, and consequently for variation in the light intensity to which algal cells are exposed. Furthermore, associated bottom currents can enhance dissolution and remobilization of nutrients by transporting the products of bacterial decomposition away from the sediment-water interface into the water column

Pancreatic cancer intrinsic PI3Kα activity accelerates metastasis and rewires macrophage component.

Pancreatic ductal adenocarcinoma (PDAC) patients frequently suffer from undetected micro-metastatic disease. This clinical situation would greatly benefit from additional investigation. Therefore, we set out to identify key signalling events that drive metastatic evolution from the pancreas. We searched for a gene signature that discriminate localised PDAC from confirmed metastatic PDAC and devised a preclinical protocol using circulating cell-free DNA (cfDNA) as an early biomarker of micro-metastatic disease to validate the identification of key signalling events. An unbiased approach identified, amongst actionable markers of disease progression, the PI3K pathway and a distinctive PI3Kα activation signature as predictive of PDAC aggressiveness and prognosis. Pharmacological or tumour-restricted genetic PI3Kα-selective inhibition prevented macro-metastatic evolution by hindering tumoural cell migratory behaviour independently of genetic alterations. We found that PI3Kα inhibition altered the quantity and the species composition of the produced lipid second messenger PIP3 , with a selective decrease of C36:2 PI-3,4,5-P3 . Tumoural PI3Kα inactivation prevented the accumulation of pro-tumoural CD206-positive macrophages in the tumour-adjacent tissue. Tumour cell-intrinsic PI3Kα promotes pro-metastatic features that could be pharmacologically targeted to delay macro-metastatic evolution

Is the Penman-Monteith model adapted to predict crop transpiration under greenhouse conditions? Application to a New Guinea Impatiens crop

International audienceReducing water consumption in greenhouses is one of the main concerns for growers. This implies better knowledge of the transpiration process in order to adapt water inputs to plant needs. Several simple models have been developed to estimate transpiration. The Penman-Monteith (PM) model and the Direct Method (DM) model are two of the most widespread transpiration models. Yet the PM model was primarily developed for crops grown in open field conditions; its validity in the case of sheltered crops is only seldom questioned. Moreover, the PM model is rarely compared to the DM model, although this could be a simple way to quantify its performance. The aim of the study is thus, first, to analyse the ability of the classical PM model to assess the transpiration rate inside a greenhouse with a New Guinea Impatiens crop in order to identify which modifications should be introduced to improve its efficiency. Comparison of the PM model with measurements reveals severe discrepancies. A detailed assessment of the assumptions underlying the PM model revealed that the location of the climatic parameters used to implement the model is a key factor that affects the results. The present study demonstrates that the temperature and humidity considered in the PM model should be taken inside the crop and not above the crop, leading to a so-called PM-Like (PML) model. Results show that the PM-Like and the DM models, in a one-layer configuration, give similar results and are in agreement with actual measurements. The capacity of the PM-Like and the DM models to investigate the vertical distribution of the transpiration inside the crop is also discussed. After dividing the canopy into two layers, the PML and DM models were applied and validated against experimental data. Even if such a procedure does not really improve the quality of the results compared to the one-layer models, it provides innovative information on the vertical distribution of the transpiration, which could have applications in CFD modelling

Analysis of the time evolution of the intercepted radiation inside a crop using CFD

Times Cited: 0;International Symposium on New Technologies for Environment Control, Energy-Saving and Crop Production in Greenhouse and Plant Factory - Greensys 2013, Jeju, Korea Republic, 22-27 September 2013.International audienceAssessing the distribution of short wavelength radiation inside a greenhouse crop is of prime interest as absorbed radiation is one of the main factors governing the energy and water vapour transfers at plant level. The aim of this paper is to analyse the distribution of solar radiation inside an ornamental crop and to improve the crop submodel implemented in CFD tools. In this prospect, a glasshouse compartment was equipped with a set of five silicon solar cells equally distributed vertically inside a New Guinea Impatiens potted crop. Fitting the data with the exponential Beer's law made it possible the determination of the corresponding extinction coefficient. A CFD model was then used to predict the solar radiation distribution inside the canopy all day long. Contrary to the commonly adopted technique which consists in describing the vertical exponential decay of the radiation from the knowledge of the incident solar radiation, the model solves the radiative transfer equation with the Discrete Ordinates model. The model requires the definition of the absorption coefficient which is inferred from the measured extinction coefficient. The model was first validated comparing the vertical distribution of solar radiation to the measured one at midday. It showed its ability to predict the exponential decay of the shortwave radiation and evidenced the variation of the diurnal vertical extinction coefficient all day long. Dividing the crop into five horizontal layers, the model was then applied to assess the evolution and proportion of the absorbed radiation in each layer. It was shown that the relative proportion of radiation absorbed in the upper layer varied all day long, reaching its minimum at midday

Numerical Simulation of the Airflow and Temperature Distribution in a Closed Empty Venlo Glasshouse under Hot and Arid Climate

International audienceThe thermal behavior of the inside air of a closed Venlo glasshouse without plants was analysed under semi-arid climate conditions. The aim of the study was to investigate to what extent the characteristics of the greenhouse design and outside climatic conditions influence airflow and temperature patterns inside the greenhouse. For the purpose of the present work, a CFD modeling approach was combined with field surveys. The study focuses on the effects of (i) the thermal inertia of the soil, (ii) the movement of the interior air, and (iii) the distribution of the temperature inside the greenhouse. Two contrasted days were considered: a windy overcast day and clear day. From the results, it is concluded that when the greenhouse is fully closed with bare soil, the heat absorbed and stored by the ground during daytime represents a significant heat source which enhances buoyancy forces, the main driving forces of the movement of the air, especially during the night. The temperature of the roof was relatively low and the air temperature distribution inside the greenhouse disclosed a vertical gradient from the roof towards the ground surface due to the movement of the air above the surface of the ground absorbing thermal energy (solar energy). Maximum air velocities inside the greenhouse were observed near the ground surface, while they reached their minimum values in the middle of the greenhouse. Similar results were obtained for the windy overcast day and for the clear day

w Night Time CFD Simulations of the Distributed Climate inside a Glasshouse

International audienceThe aim of this study is to implement an unsteady 2D CFD model to predict the time-evolution of greenhouse temperature and humidity distributions all night long in winter, taking account of both radiative transfers and crop interactions with the inside climate. Beyond the classical conservation equations, specific radiative- and crop-submodels were activated. The latter takes account of both the heat and transpiration fluxes induced by the plants and their associated mechanical resistances which depend on the transfers from the plant to the air. Simulations were performed for a clear night on the basis of data collected in winter 2011 inside a 100 m(2) Venlo glasshouse with Impatiens New Guinea crop grown on shelves. The boundary conditions were modified at each time step. Numerical results were validated against data recorded inside the greenhouse: roof temperature, inside air temperature, transpiration flux and air humidity. They highlight the influence of the dynamic boundary conditions on the evolution of the microclimate inside the greenhouse. This study demonstrates the ability of the CFD code to simulate the greenhouse climate evolution with realism. It also suggests a potential exploitation for designing the heating devices in order to optimize the inside climate and energy consumption for various outside conditions

Stomatal resistance of New Guinea Impatiens pot plants. Part 2: Model extension for water restriction and application to irrigation scheduling

International audienceIn greenhouses, reducing water consumption by increasing water efficiency is of high interest. To reach this goal, predictive models of soil-plant-atmosphere water transfer could be helpful. However, such models have been mainly developed for open field conditions, and very few models exist for greenhouse plants grown in pots. Moreover, most of these models were implemented under well-watered conditions, but very few are available under water restriction. The aim of this study is to develop an integrated soil-plant-atmosphere water balance model applied to potted plants grown in greenhouses, to predict plant transpiration under different restrictive irrigation regimes. Implementing such a model requires an accurate estimation of stomatal resistance Rs under water restriction conditions. Rs is then used in the Penman-Monteith model to evaluate transpiration. To establish the model parameters, an experiment was conducted for sixteen weeks inside a greenhouse with ornamental plants (New Guinea Impatiens) grown in containers on shelves. Well-watered and water restriction conditions were applied. The peat matric potential, radiation, temperature and humidity were continuously recorded, while Rs was measured and transpiration was assessed every half-hour from 8:00 am to 8:00 pm 10, 11, 12, 14, and 16 weeks after planting. The resulting model was first validated against experimental measurements during the twelfth week of the experiment. It displayed good correlations for both the instantaneous data and integrated total transpiration. Different scenarios of irrigation reduction (frequency x volume) were tested and the results indicated real potential for water use reduction. Indeed, by reducing water application by 50% and by applying one irrigation per day, transpiration was not affecte