• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 104
  • 82
  • 43
  • 21
  • 6
  • 6
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 307
  • 68
  • 54
  • 45
  • 43
  • 41
  • 37
  • 36
  • 34
  • 32
  • 32
  • 30
  • 29
  • 29
  • 26
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
161

Dissociabilidade das funções de inibição da expansão celular e de alcalinização do peptídeo AtRALF1 e identificação dos aminoácidos determinantes da atividade de alcalinização / The dissociability of the root growth inhibition and extracellular alkalinization activities of the AtRALF1 peptide and the identification of the essential amino acids for the alkalinization activity

Paulo Henrique de Oliveira Ceciliato 22 May 2015 (has links)
RALFs são peptídeos hormonais de aproximadamente 5kD que regulam negativamente o alongamento celular. Dentre suas atividades biológicas, a alcalinização do meio extracelular e a inibição do alongamento celular são tidas como associadas, pois a acidificação do meio extracelular é necessária para a expansão celular. A atividade de alcalinização e a de inibição do crescimento são medidas em dois ensaios distintos: o ensaio de alcalinização do meio extracelular de células em suspensão e o ensaio do crescimento de raiz primária de plantas jovens. Buscando-se fazer ambas as avaliações da inibição da expansão celular e da alcalinização em um único modelo de estudo, tomou-se como medida da expansão celular o volume das células decantadas (VCD). Quando o tampão MES ou o pré-tratamento com \"Fusicoccin\" foi utilizado para se atenuar o efeito de alcalinização do AtRALF1, verificou-se que o efeito de inibição do alongamento celular não sofreu alteração. Em arabidopsis são encontrados nove peptídeos RALF, que apresentam alta similaridade com o RALF original de tabaco. Com exceção do AtRALF4, todos são capazes de alcalinizar o meio extracelular e inibir raízes. A comparação da estrutura primária do AtRALF4 com os demais RALFs mostra que poucos resíduos são distintos entre eles, sugerindo que estes possam ser os determinantes das atividades de inibição e alcalinização. A alteração de um destes resíduos, AtRALF4(N92A), é capaz de restaurar a capacidade do AtRALF4 de inibir as raízes sem, no entanto, recuperar a atividade de alcalinização. Quando três outros resíduos exclusivos do AtRALF4 foram substituídos pelos seus correspondentes do AtRALF1, observa-se uma restauração parcial da alcalinização, desta vez, sem alterar a capacidade de inibir as raízes. Recentemente, foi mostrado pelo nosso grupo que o peptídeo AtRALF1 induz a expressão de genes relacionados ao rearranjo da parede celular. Quando verificado por PCR quantitativa, contatou-se que somente os peptídeos mutantes que apresentam atividade de inibição do crescimento são capazes de promover uma indução semelhante. Ainda, utilizando gel indicador de pH, verificou-se que plantas transgênicas super-expressando AtRALF1 (35S:AtRALF1) acidificam o meio durante seu crescimento de maneira semelhante a plantas selvagens. O peptídeo de defesa AtPEP1, a exemplo dos peptídeos RALF, também promove a alcalinização do meio extracelular. A utilização de drogas para reproduzir ou atenuar o efeito de alcalinização promovido por este peptídeo sugere que a expressão dos genes responsivos a AtPEP1 também não está relacionada à alteração na atividade das próton-ATPases. Finalmente, quando mutantes para ambos os receptores de AtPEPs foram utilizados (atpepr1/r2) em gel indicador de pH, verificou-se que estes alcalinizam o pH da rizosfera na presença do peptídeo. Nossos dados somados sugerem uma dissociação das atividades biológicas de alcalinização do meio extracelular e de inibição da expansão celular. A alteração na atividade das próton-ATPases pode não ser apenas uma mensagem secundária do efeito biológico, mas sim outra fonte de informação independente e ainda pouco explorada como tal. / RALFs are 5kD peptide hormones that negatively regulates cell expansion. Among the biological activities of the RALF peptide, the extracellular alkalinization and cellular expansion inhibition were previously suggested to be associated, once the extracellular acidification is required to cell expansion. Usually, the alkalinization and cell expansion inhibition activities are evaluated in two different assays, the cell suspension medium alkalinization and the plantlet root growth inhibition. We manage to set an assay in which both cell expansion inhibition and extracellular alkalinization activities could be evaluated. Using the package suspension cell volume through decantation as a value of cell expansion, we evaluated the relation between alkalinization and cell expansion inhibition in different conditions. When the MES buffer or the pre-treatment with Fusicoccin was used to arrest the AtRALF1 extracellular alkalinization, the package cell volume inhibition activity was not affected. There are 9 RALF peptides encoded in arabidopsis plants that are closely related with the first isoform isolated from tobacco. With exception of the AtRALF4, all those isoforms are able to alkalinize the extracellular medium and arrest root growth. Comparing the AtRALF4 with other eight isoforms, we verified that are few different amino acids between them, suggesting that those amino acids could be essential for the biological activities. The rescue of one of those amino acids, AtRALF4(N92A), was able to regain the root growth inhibition activity of the AtRALF4 peptide, although the extracellular alkalinization activity was not restored. When three other AtRALF4 amino acids were substituted by their AtRALF1 correspondent, there is a partial rescue of the extracellular alkalinization activity, but no alterations in the root growth inhibition. We had recently shown that the AtRALF1 peptide induces the expression of genes related to cell wall rearrangement. The quantitative PCR analyses demonstrates that only the mutant peptides that are able to arrest root growth are also able to induce the gene expression. When submitted to a pH indicator, it was verified that AtRALF1 overexpressing plants acidifies it during its growth, as much as wild type plants.The defense peptide AtPEP1, similarly of AtRALF1, also triggers extracellular alkalinization. The use of proton-pump chemical modulators to simulate or arrests AtPEP1 extracellular alkalinization activity suggests that the gene expression of the AtPEP1-responsive genes is not related to changes in plasma membrane proton pump activity. Finally, when double mutants for both the AtPEP1 receptors (atpepr1/r2) were submitted to a pH gel indicator, it was seen that they alkalinize the rhizosphere pH in the presence of the AtPEP1 peptide. Our data suggests that the extracellular alkalinization and arrest of cell expansion activities are dissociated. The proton pump modulation activity may not be only a secondary messenger, but another source of information independent and yet to be explored.
162

Avaliação do método do balanço da camada limite para a estimativa de fluxos turbulentos noturnos / Evaluation of the boundary layer budget method for nocturnal turbulent flux estimates

Conti, Tatiana de 27 October 2006 (has links)
This work is about to verify the performance of the boundary layer budgeting method as alternative for measuring the surface turbulent fluxes in conditions that allow the validation of the measurements with data taken from a tower equipped with sensors, which were processed through the eddy correlation method. A research is made on the knowledge generated to the present, which reveals the limitations of the eddy correlation method and the promises of the boundary layer budgeting in relation to measuring the surface turbulent fluxes. This work describes its theoretical underpinnings, regarding the energy budget in the atmosphere and the role of turbulence in the transport phenomena and in energy exchanges. These concepts are interpreted physically and described in the form of ruling equations and hypotheses used for the analysis of the behavior of such phenomena. The eddy correlation is described as a method that directly measures the sensible heat and latent heat fluxes in function of the data picked up by the sensors. The boundary layer budgeting method, by its turn, is described from the general formulation of scalar accumulation, on which are taken the hypotheses of elimination of the horizontal advection and of any sources or drains in the atmosphere. The context of the measuring work is described in the following, from the presentation of the project, its places, and its campaigns and to the day and times in which the measurements took place. The instruments used for data acquisition are also described, as well as the processing systematics of the raw data. The obtained results reveal significant differences in the sensible heat flux estimates, which increase with the progress of the night and smaller differences in the latent heat flux, which remain constant in the time. / Este trabalho trata de verificar o desempenho do método de balanço da camada limite como alternativa para a medição dos fluxos turbulentos superficiais em condições que permitem a validação das medidas com dados tomados a partir de uma torre equipada com sensores, os quais foram processados com o método de correlação de vórtices. É feita uma pesquisa do conhecimento gerado até o presente, que revela as limitações da sistemática de medição por correlação de vórtices e as promessas do método de balanço em relação à medição dos fluxos turbulentos. É descrita neste trabalho a fundamentação teórica necessária, a respeito do balanço energético na atmosfera e do papel da turbulência nos fenômenos de transporte e de troca de energia. Tais conceitos são interpretados fisicamente e descritos na forma de equações governantes e hipóteses utilizadas para a análise do comportamento de tais fenômenos. A correlação de vórtices é descrita como um método que mede diretamente os fluxos de calor sensível e de calor latente em função dos dados recolhidos pelos sensores. O método de balanço da camada limite, por sua vez é descrito a partir da formulação geral de acumulação de escalares, sobre a qual são tomadas as hipóteses de eliminação da advecção horizontal e de quaisquer fontes ou sumidouros na atmosfera. O contexto das medições é descrito a seguir, a partir da apresentação do projeto, dos locais, das campanhas e do dia e dos horários em que as medições foram realizadas. A instrumentação utilizada para a aquisição dos dados é também descrita, assim como a sistemática de processamento dos dados brutos. Os resultados obtidos revelam diferenças significativas na estimativa do fluxo de calor sensível, que aumentam com o avanço da noite e diferenças menores no fluxo de calor latente, que permanecem praticamente constantes no tempo.
163

INFLUÊNCIA DA TURBULÊNCIA INTERMITENTE NA ESTIMATIVA DOS FLUXOS DE CO2 NOTURNOS / INTERMITTENT TURBULENCE INFLUENCE ON NOCTURNAL CO2 FLUX ESTIMATES

Santos, Diego Jatobá dos 05 September 2012 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nocturnal turbulent flux data are analysed, initially for two experimental sites in Brazil, and later for a large variety of biomes. In such case, a wide dataset, originated from more than a hundred flux stations scattered over Europe and the Americas is used. Emphasis is given to important aspects associated to the occurrence of intermittent turbulence and its implications for CO2 nocturnal flux estimates. Intermittency factors (IF) for CO2 and sensible heat fluxes are determined for the set of stations. In most cases, there was agreement between the results for CO2 and sensible heat, specially for those stations that were less intermittent, on average. A larger number of stations showed low IF for CO2 than for sensible heat fluxes. CO2 flux intermittency was significantly larger over higher canopies than over savannas or crops, while the same difference is smaller for the sensible heat flux. An investigation on the CO2 flux dependence on the temporal variability of the turbulence intensity is carried on . The main purpose of such an anlysis is identifying whether ther is CO2 storage during low turbulence periods and if such accumulated CO2 affects the fluxes in subsequent periods. In the vast majority of the stations, the classical pattern of NEE decreasing as u* tends to zero is observed. The hypothesis of the present study is that such NEE decrease under calm situations does not necessarily imply on flux lost by the eddy covariance technique, but that it may have not been properly captured by the CO2 storage term, being later measured in subsequent turbulent situations. Therefore, the present study has as the main goal identifying a potential problem in the correcting procedure commonly applied for low turbulent periods. Specifically, it is important to analyse whether the periods whose data are being replaced are not suceeded by others for which there is flux excess, characterizing, therefore, an excessive correction. Results indicate that there is a large quantity os stations for which the fluxes are independent on turbulence intensity variability, with evidences that the observed reduction during calm periods is compensated when it gets turbulent. In such cases, it is possible that corrections commonly used for calm conditions are, indeed, excessive. . / Dados de fluxos turbulentos noturnos são analisados, primeiramente, para dois sítios experimentais no Brasil e uma posterior expansão dessas análises é realizada para uma grande variedade de biomas, utilizando para tanto, um conjunto amplo de dados originados de mais de uma centena de estações de fluxos, espalhadas nas Américas e na Europa. A ênfase é dada aos aspectos importantes associados à ocorrência de turbulência intermitente e suas implicações para as estimativas de fluxos turbulentos noturnos de CO2. Fatores de intermitência (FI) dos fluxos de CO2 e de calor sensível são definidos e quantificados para o conjunto de estações. Na maioria dos casos, houve concordância entre os comportamentos obtidos para o fluxo de CO2 e de calor sensível, especialmente nas estações que na média apresentaram condições pouco intermitentes. Um número maior de estações apresentaram valores reduzidos de FI para fluxo de CO2 do que para o de calor sensível. A intermitência dos fluxos de CO2 se mostrou significativamente maior sobre estações de maior altura do dossel (florestas) do que sobre estações de savana ou agrícolas, enquanto que a mesma diferença é muito mais reduzida para os fluxos de calor sensível. Uma investigação da dependência dos fluxos de CO2 em relação à variabilidade temporal de turbulência ao longo da noite foi realizada. O propósito principal da análise é identificar se há acúmulo de CO2 em períodos pouco turbulentos e se este CO2 acumulado afeta os fluxos em períodos subsequentes. Na imensa maioria das estações, se observou um padrão clássico de NEE diminuindo conforme u* tende a zero. É hipótese do presente trabalho que o decréscimo de NEE em situações calmas não necessariamente indica fluxo não contabilizado pelo método da covariância dos vórtices, mas que este pode não ter sido propriamente capturado pelo termo de armazenamento, sendo posteriormente capturado pelo sensor em situações turbulentas subsequentes. Desta forma, o presente estudo tem como precípuo intento, contribuir no sentido de identificar um potencial problema na utilização das técnicas de correção de dados utilizadas para os períodos com pequena intensidade turbulenta. Especificamente, é importante analisar se os períodos que estão tendo seus dados substituídos não são sucedidos por outros em que houve excesso de fluxo, caracterizando, desta forma, uma correção excessiva. Os resultados indicam que há uma grande quantidade de estações para as quais os fluxos são independentes da variabilidade da intensidade turbulenta, havendo indicações que a redução observada em períodos calmos seja compensada em intervalos turbulentos. Nesses casos, é possível que correções comumente usadas para a correção de fluxos em condições calmas sejam excessivas.
164

Estimativa dos fluxos de energia superficiais utilizando o modelo de superfície noah modificado para culturas alagadas / Surface energy fluxes estimates using noah land surface model modified for flooding crops

Timm, Andréa Ucker 12 August 2011 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The following study quantifies the seasonal and annual distribution of energy balance components (sensible heat fluxes, latent, soil, and net radiation) in this flooded irrigated rice ecosystem in Southern Brazil for three different periods (Fallow 1: 22 July 2003 to 24 November 2003; Rice: 25 November 2003 to 04 April 2004 and Fallow 2: 05 April 2004 to 21 July 2004). In addition, it has been applied the Noah Land Surface Model with the objective of estimating the surface energy fluxes. An important challenge is to implement a new version of Noah Land Surface Model applied to flooded agricultural land called Noah-Paddy. The stabilization of the models has been performed using the atmospheric forcing data obtained from South American Land Data Assimilation System (SALDAS) for the period 22 July 2000 to 21 July 2003. The models were simulated using the observed atmospheric forcing from a micrometeorological tower installed on a flooded irrigated rice paddies located in the city of Paraíso do Sul - RS. The initial conditions were obtained from the last time step of the spin-up experiment performed with atmospheric forcing data of SALDAS. The models results were compared with experimental data for surface energy fluxes. From the simulated results generated by the Noah Land Surface Model, it seems that when the rice crop is flooded, the model does not satisfactorily represents the experimental data. However, using the Noah-Paddy model the components of surface energy balance are more realistic for the system surface-water-atmosphere. The most important contribution performed in this research was to describe the diffent physical processes originated by the presence of a body of water between the soil surface and the atmosphere. This physical system occorr always in flooded agricultural crops in wich the rice paddies field are predominant. / No presente trabalho, quantifica-se a distribuição sazonal e anual das componentes do balanço de energia (fluxos de calor sensível, latente, do solo e saldo de radiação) em um ecossistema de arroz irrigado por inundação localizado no Sul do Brasil para três períodos distintos ao longo do ano (Pousio 1: 22Jul2003 a 24Nov2003; Arroz: 25Nov2003 a 04Abr2004 e Pousio 2: 05Abr2004 a 21Jul2004). Além disso, é utilizado o Modelo de Superfície Noah (Noah LSM) com o objetivo de estimar os fluxos de energia superficiais. Um dos desafios mais importantes é a implementação de uma nova versão do Noah LSM aplicado para áreas agrícolas alagáveis chamado Noah-Paddy. A estabilização dos modelos foi realizada utilizando dados de forçantes atmosféricas do South American Land Data Assimilation System (SALDAS) para o período de 22Jul2000 a 21Jul2003. Os modelos foram executados usando dados de forçantes atmosféricas observados obtidos a partir da torre micrometeorológica instalada sobre uma cultura de arroz irrigado por inundação localizada em Paraíso do Sul - RS. As condições iniciais foram obtidas a partir do último passo de tempo do experimento spin-up realizado com os dados de forçantes atmosféricas do SALDAS. O desempenho dos modelos estudados foi comparado com dados experimentais de fluxos de energia superficiais. A partir dos resultados obtidos pela simulação do Noah LSM verifica-se que, quando a cultura do arroz está irrigada, o modelo não representa satisfatoriamente os dados experimentais. Porém, utilizando o Noah-Paddy as trocas de energia superficiais são representadas de forma mais realísticas para o sistema superfície-água-atmosfera. A contribuição mais importante realizada neste trabalho foi a descrição dos diferentes processos físicos originados pela presença de uma massa de água entre a superfície do solo e a atmosfera. Esse sistema físico ocorre sempre em culturas agrícolas alagadas nas quais as plantações de arroz são predominantes.
165

Evaluation of Surface Layer Parameterizations Using In-Situ Observations

Katz, Jeremy 28 June 2016 (has links)
Appropriate calculation of surface turbulent fluxes between the atmosphere and the underlying surface is one of the major challenges in geosciences. In practice, the surface turbulent fluxes are estimated from the mean surface meteorological variables based on the bulk transfer model combined with Monnin-Obukhov Similarity (MOS) theory. Few studies have been done to examine the extent that to which this flux parameterization framework can be applied to different weather and surface conditions. A novel validation method is developed in this thesis research, which is applied to evaluate the surface flux parameterization using in-situ observations. The main findings are: (a) the theoretical prediction that uses MOS theory does not match well with those directly computed from the observations collected in the coastal region. (b) Large spread in exchange coefficients mainly occurs in the calm wind regime with strong stability. (c) Large turbulent eddies, which depend largely on the mean flow and surface conditions, tend to break the constant flux assumption in the surface layer.
166

The I2T5 : Enhancement of the Thermal Design of an Iodine Cold Gas Thruster

Pereira, Roger Michael January 2020 (has links)
The I2T5, an iodine-propelled, cold gas thruster, developed by ThrustMe, France, is the first of its kind to make it successfully to space. Due to its simple, reliable and cost-effective design, it is a suitable propulsion system for CubeSat missions with low delta-V (ΔV) requirements. To ensure that the I2T5 performs at its peak, it is crucial to maintain good thermal control of the thruster, to keep it within the operational temperature range. The first flight measurements of the I2T5 provided insight into its thermal performance. It was observed that the required temperature to sublimate the iodine propellant was not reached within the expected time frame, which led to a longer warm-up period, and a reduction in thrust. The problem arose due to an unforeseen conductive thermal contact between the tank and the thruster walls. This thesis delves deeper into this issue, and focuses on alleviating the total conductive heat loss from the tank to the satellite frame, where the I2T5 is integrated. The insulating washer-bolt configuration of the I2T5 side panels is observed to be responsible for the conductive heat transfer. A preliminary analysis is performed to obtain an initial maximum for the conductive heat flux lost to the satellite frame. A plan of action is then determined to optimise the geometry, material or configuration of the insulating washers to lower the maximum heat flux value. Following this, an experiment was conducted with a new washer-bolt configuration to determine the heat flux values. A case study is performed for the orbital environment heat fluxes that the I2T5 would receive if it were integrated to a CubeSat in sun-synchronous orbit. An overview of results shows that, for the thermal simulations, all the methods employed to reduce the conductive heat loss at the frame were effective. The experiment provided neutral results, and would need to be repeated with different experimental parameters to have a clear perspective of the heat losses. In reality, the satellite frame receives radiative fluxes in addition to conductive heat fluxes, but radiation is not considered for this thesis, and is suggested as a prospective study.
167

Selektivní pájení / Selective Soldering

Stoklásek, Lukáš January 2019 (has links)
This diploma thesis introduces the problematics of selective soldering. The theoretical part deals with description of soldering process and its possibilitites, use of this processes for selective soldering and the control of production. The practical part describes the methodics of measuring the amount and uniformity of flux applied on printed circuit boards, effects and stability of preheaters and dwell time if PCB in the soldering wave. The next part deals with the production test for the certain product, cleanness of the single processes, x-ray diagnostics and cross section of the boards. In the end is economic evaluation of the processes. The main object of this thesis is to suggest the optimal production process for the product.
168

Arctic Soils in a Warming Climate: Plot-scale Changes of CO2 Fluxes after Five Years of Experimental Warming.

Schröer, Cosima January 2020 (has links)
Terrestrial arctic ecosystems store large amounts of carbon (C). With global warming, this C might be released into the atmosphere as CO2 by stimulation of soil microbial degradation. At the same time, CO2 uptake in plants is enhanced, which might, in parts, offset CO2 losses. Yet, the future balance of these two contrasting feedbacks remain uncertain. This study aimed to better understand changes of input and output CO2 fluxes in an arctic tussock tundra ecosystem in response to global warming, with a special focus on the contrast between two sub-ecosystem habitats, the tussocks and the space between tussocks.  An experimental setup was used, where snow fences simulated winter warming by increasing snow depth, and open top chambers simulated summer warming. Daytime ecosystem respiration (ER), reflecting the outward CO2 flux, gross ecosystem production (GEP), reflecting the inward CO2 flux, and net ecosystem exchange (NEE), reflecting the net balance of both, were measured in the summer 2019 in the tussock and the intertussock habitat. In the tussock, both ER and GEP were as twice as high compared to the intertussock and increased with summer warming in a similar magnitude, resulting in an unchanged NEE. Fluxes in the intertussock were not altered with summer warming. Winter warming had no significant effects on ER and GEP in neither of the habitats. However, winter warming increased NEE and green biomass in the intertussock, indicating that in this habitat, plants benefit from warmer winter soil temperatures. Interaction effects of winter and summer warming underline the role of ecological processes outside the summer season, which are to date poorly understood. Contrasting responses of the two sub-ecosystem habitats highlight the challenges in predicting future C balances that are caused by small-scale spatial and temporal heterogeneity of C dynamics.
169

Etude des flux turbulents à l'interface air-mer à partir de données de la plateforme OCARINA / Analysis of Turbulent fluxes based on data from the OCARINA platform

Cambra, Rémi 04 December 2015 (has links)
Les échanges de chaleur et de quantité de mouvement à l'interface-océan atmosphère jouent un rôle majeur dans la formation et la dynamique des masses d'air et d'eau. Malgré des décennies de recherche, nous avons encore besoin d'améliorer nos connaissances sur ces échanges, et plus spécifiquement nos connaissances sur les flux turbulents, qui sont des variables clés dans les modèles météorologiques et de climat. Dans ces modèles, les processus turbulents sont des processus sous-maille, non-résolus explicitement, ainsi les flux turbulents doivent être modélisés, au travers de paramétrisations, qui sont pour la plupart réalisées à partir de la théorie des similitudes de Monin-Obukhov [1954]. Cependant, d'une part, l'utilisation d'un modèle implique que les coefficients doivent être ajustés. D'autre part, le modèle lui-même peut demander des améliorations. Malheureusement, l'obtention d'estimations de flux avec une bonne précision est un gros défi, à cause des effets intrusifs de la plate-forme sur la mesure, de la précision limité des instruments et des capacités d'échantillonnages propres de chaque instrument.Notre étude porte sur l'estimation des flux turbulents en mer à partir de mesures réalisées avec la nouvelle plate-forme OCARINA (trimaran autonome) lors des campagnes STRASSE 2012 et AMOP 2014. Nous analysons les caractéristiques de la turbulence dans la couche limite de surface, nous estimons les flux turbulents par différentes méthodes, et nous comparons les valeurs des flux en fonction des conditions environnementales, en prenant en compte l'état de mer. / Exchanges of heat and momentum at the air-sea interface play a major role in the formation and the dynamics of water and air masses. In spite of decades of research, we still need to improve our knowledge of these exchanges, and more specifically our knowledge of turbulent fluxes, which are key variables in meteorological and climate models. In these models, sub-grid turbulent processes, thus turbulent fluxes also have to be modeled, which is mostly done with the Monin-Obukhov (1954, MOS hereafter) similarity theory. However, on the one hand, the use of a model implies that coefficients have to be adjusted. On the other hand, the model itself may require improvements. Unfortunately, obtaining flux estimates that have a good accuracy is a challenging effort, because of the intrusive effect of the platform, the limited accuracy the instruments, and because the instruments have their own sampling volume.Our study focuses on the estimation of turbulent fluxes at sea from measurements made with the new OCARINA platform (autonomous trimaran) during two campaigns : STRASSE 2012 and AMOP 2014. We analyze the characteristics of turbulence in the surface boundary layer, we estimate the turbulent fluxes by different methods, and compare the values of fluxes depending on environmental conditions, taking into account the sea state.
170

Energy and water balance in a deciduous forest in southern Ontario

Khader, Reham 10 1900 (has links)
<p><h1>This study discusses energy and water balance in an 80-year-old deciduous Carolinian forest in the Great Lakes region in southern Ontario, Canada. The eddy covariance technique and associated meteorological and soil variables were used to make a year-round measurements of energy and water vapour fluxes from January-December,2012. This site is part of the Turkey Point Flux Station and global Fluxnet. The linear relationship between daily turbulent (sensible heat (H), latent heat (LE)) and radiative fluxes (net radiation (Rn),soil heat (G) and canopy heat storage ( S)) has a the slope of 0.75 (intercept of -15.8 Wm<sup>-2</sup>, and a correlation coefficient, r<sup>2</sup> of 0.93) indicating a 25% deficiency in energy balance closure. The mean value of canopy albedo was 0.16 during the growing season. Maximum daily evapotranspiration (E) rate was 3.8 mm day<sup>-1</sup> in June, when growing is at its peak in the region. Total annual E was 400 mm, which accounted for 42% of the total annual precipitation of 950 mm. The water storage in upper soil column (1.0 m depth) was approximately 100 mm, indicating that about 450 mm of water was lost from the forest as runoff. Apart from radiation, vapour pressure deficit (D) was the dominant control on E. Maximum value of bulk surface conductance (Gs) was about 18.5 mm s<sup>-1</sup>. Gs linearly decreased in response to increase in D. The minimum Gs values were recorded when D was maximum, i.e. 3 to 3.5 kPa. Gs also showed high sensitivity to the volumetric soil water content (ϴ), during dry periods, for example the drought event in 2012. In the growing season, the typical value of Priestley-Taylor α ranged between 0.8 to 1.2 with a maximum of 1.8, indicating a wet deciduous forest. However, the LE/Rn relationship showed a linear increase with increasing D with a low (0.26) slope, indicating a conservative response of forest E to atmospheric demand. This study provides insight into energy partitioning, the water balance and their controls in this Carolinian deciduous forest. A better understanding of evapotranspiration processes and their controls in these forests would help to better quantify water availability at local and regional scales and to evaluate the impacts of future climate change on water resources in the region.</h1></p> / Master of Science (MSc)

Page generated in 0.0375 seconds