Énergie de rayonnement | EPFL Graph Search

vignette| La lumière visible, telle que celle qui provient du soleil, transporte de l'énergie rayonnante, qui est utilisée pour la production d'énergie solaire. En physique, et en particulier dans le domaine de la radiométrie, l'énergie de rayonnement, ou énergie rayonnante, est l'énergie des rayonnements électromagnétique et gravitationnel. En tant qu'énergie, son unité SI est le joule (J). La quantité d'énergie rayonnante peut être calculée en intégrant le flux (ou la puissance) rayonnant au cours du temps. Le symbole Qe désigne souvent l'énergie rayonnante dans la littérature (avec « e » pour « énergétique », afin d'éviter toute confusion avec les grandeurs photométriques). Dans les branches de la physique autres que la radiométrie, l'énergie électromagnétique est désignée par E ou W. Le terme « énergie rayonnante » est utilisé en particulier lorsqu'un rayonnement électromagnétique est émis par une source du milieu environnant. Ce rayonnement peut être visible ou invisible pour l'œi

Diel quenching of Southern Ocean phytoplankton fluorescence is related to iron limitation

Nina Schuback

Evaluation of photosynthetic competency in time and space is critical for better estimates and models of oceanic primary productivity. This is especially true for areas where the lack of iron (Fe) limits phytoplankton productivity, such as the Southern Ocean. Assessment of photosynthetic competency on large scales remains challenging, but phytoplankton chlorophyll a fluorescence (ChlF) is a signal that holds promise in this respect as it is affected by, and consequently provides information about, the photosynthetic efficiency of the organism. A second process affecting the ChlF signal is heat dissipation of absorbed light energy, referred to as non-photochemical quenching (NPQ). NPQ is triggered when excess energy is absorbed, i.e. when more light is absorbed than can be used directly for photosynthetic carbon fixation. The effect of NPQ on the ChlF signal complicates its interpretation in terms of photosynthetic efficiency, and therefore most approaches relating ChlF parameters to photosynthetic efficiency seek to minimize the influence of NPQ by working under conditions of sub-saturating irradiance. Here, we propose that NPQ itself holds potential as an easily acquired optical signal indicative of phytoplankton physiological state with respect to Fe limitation. We present data from a research voyage to the Subantarctic Zone south of Australia. Incubation experiments confirmed that resident phytoplankton were Fe-limited, as the maximum quantum yield of primary photochemistry, F-v/F-m, measured with a fast repetition rate fluorometer (FRRf), increased significantly with Fe addition. The NPQ "capacity" of the phytoplankton also showed sensitivity to Fe addition, decreasing with increased Fe availability, confirming previous work. The fortuitous presence of a remnant warm-core eddy in the vicinity of the study area allowed comparison of fluorescence behaviour between two distinct water masses, with the colder water showing significantly lower F-v/F-m than the warmer eddy waters, suggesting a difference in Fe limitation status between the two water masses. Again, NPQ capacity measured with the FRRf mirrored the behaviour observed in F-v/F-m, decreasing as F-v/F-m increased in the warmer water mass. We also analysed the diel quenching of underway fluorescence measured with a standard fluorometer, such as is frequently used to monitor ambient chlorophyll a concentrations, and found a significant difference in behaviour between the two water masses. This difference was quantified by defining an NPQ parameter akin to the Stern-Volmer parameterization of NPQ, exploiting the fluorescence quenching induced by diel fluctuations in incident irradiance. We propose that monitoring of this novel NPQ parameter may enable assessment of phytoplankton physiological status (related to Fe availability) based on measurements made with standard fluorometers, as ubiquitously used on moorings, ships, floats and gliders.

2020

Complementary Metasurfaces for Guiding Electromagnetic Wave

Mohammad Sajjad Mirmoosa

Metasurfaces can be employed for designing waveguides that confine the electromagnetic energy while they are open structures. In this communication, we introduce a new type of such waveguides, formed by two penetrable metasurfaces having complementary isotropic surface impedances. We theoretically study the guided modes supported by the proposed structure and discuss the corresponding dispersion properties. We show the results for different scenarios in which the surface impedances possess nonresonant or resonant characteristics, and the distance between the two metasurfaces changes from large values to the extreme limit of zero. We also derive and describe the general condition for existence of two modes with orthogonal polarizations having the same phase velocity. In the particular case in which the metasurfaces are complementary and the distance between them is not small, we indicate that such phenomenon occurs within a broad frequency range. This property can be promising for applications in leaky-wave antennas and field focusing.

2021

Application of bench-scale biocalorimetry to photoautotrophic cultures

Urs von Stockar

Bench-scale biocalorimetry (>=1 L) allows for the detn. of the metabolic heat flow during bioprocesses under complete control of all process conditions for extended periods of time. It can be combined with a no. of online and off-line measurement techniques. This combination can significantly improve insight into the metab. of microorganisms and the optimization of bioprocesses. In this study it is demonstrated that bench-scale biocalorimetry can also be applied to phototrophic microorganisms. The green microalga Chlorella vulgaris CCAP 211/11B was cultivated in a Mettler-Toledo RC1 calorimeter adapted for high-sensitivity biol. calorimetry (BioRC1). Heat prodn. was monitored in 1.5 L batch cultures. In the linear phase of growth, inhibitors of photosynthetic electron transport (DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and DBMIB, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone), were used to stop photosynthesis and to monitor the resulting increase in the energy dissipating heat flux. This resulted in a calcd. storage of light energy as chem. energy, i.e. biomass, of 141 +- 12.2 mW L-1 (+-S.D.). In addn., it was demonstrated that calorimetric detn. of the total amt. of light energy absorbed within the reactor was accurate by comparing two different calorimetric techniques. Using both the value of the total light input and the quantity stored as chem. energy, the photosynthetic efficiency could be calcd. as 10.5% in this example. [on SciFinder (R)]

2005

Diel quenching of Southern Ocean phytoplankton fluorescence is related to iron limitation

Nina Schuback

2020