scholarly journals Time Course of Photosynthetic Response to Changes in Incident Light Energy

1979 ◽  
Vol 63 (6) ◽  
pp. 1033-1038 ◽  
Author(s):  
Louis J. Gross ◽  
Brian F. Chabot
Keyword(s):  
Time Course ◽  
Incident Light ◽  
Light Energy ◽  
Photosynthetic Response

scholarly journals Intrinsic optical and passive electrical properties of cut frog twitch fibers.

1987 ◽  
Vol 89 (1) ◽  
pp. 1-40 ◽  
Author(s):  
M Irving ◽  
J Maylie ◽  
N L Sizto ◽  
W K Chandler
Keyword(s):  
Time Course ◽  
Internal State ◽  
Incident Light ◽  
Operation Mode ◽  
Optical Measurements ◽  
Fiber Axis ◽  
Simple Method ◽  
General Physiology ◽  
Linearly Polarized ◽  
The Individual

This article describes a new apparatus for making simultaneous optical measurements on single muscle fibers at three different wavelengths and two planes of linear polarization. There are two modes of operation: mode 1 measures the individual absorbances of light linearly polarized along and perpendicular to the fiber axis, and mode 2 measures retardation (or birefringence) and the average of the two absorbance components. Although some intact frog twitch fibers were studied, most experiments used cut fibers (Hille, B., and D. T. Campbell. 1976. Journal of General Physiology. 67:265-293) mounted in a double-Vaseline-gap chamber (Kovacs, L., E. Rios, and M. F. Schneider. 1983. Journal of Physiology. 343:161-196). The end-pool segments were usually exposed for 2 min to 0.01% saponin. This procedure, used in subsequent experiments to make the external membranes in the end pools permeable to Ca indicators (Maylie, J., M. Irving, N. L. Sizto, G. Boyarsky, and W. K. Chandler. 1987. Journal of General Physiology. 89:145-176; Maylie, J., M. Irving, N. L. Sizto, and W. K. Chandler. 1987. Journal of General Physiology. 89:41-143), was routinely employed so that all our cut fiber results would be comparable. A simple method, which does not require microelectrodes, allowed continual estimation of a fiber's membrane (rm) and internal longitudinal (ri) resistances as well as the external resistance (re) under the Vaseline seals. The values of rm and ri obtained from cut fibers with this method agree reasonably well with values obtained from intact fibers using microelectrode techniques. Optical measurements were made on resting and action potential-stimulated fibers. The intrinsic fiber absorbance, defined operationally as log10 of the ratio of incident light to transmitted light intensity, was similar in intact and cut preparations, as were the changes that accompanied stimulation. On the other hand, the resting birefringence and the peak of the active change in cut fibers were, respectively, only 0.8 and 0.7 times the corresponding values in intact fibers. Both the amplitude and the half-width of the active retardation signal increased considerably during the time course of cut fiber experiments; a twofold increase in 2 h was not unusual. Such changes are probably due to a progressive alteration in the internal state of the cut fibers.

Hydrogen Generation for 500 hours by Photoelectrolysis of Water using GaN

2012 ◽  
Vol 1446 ◽  
Author(s):  
W. Ohara ◽  
D. Uchida ◽  
T. Hayashi ◽  
M. Deura ◽  
K. Ohkawa
Keyword(s):  
Conversion Efficiency ◽  
Electric Charge ◽  
Hydrogen Generation ◽  
Incident Light ◽  
Hydrogen Gas ◽  
Light Energy ◽  
Chemical Energy ◽  
Incident Photon

ABSTRACTWe confirmed that GaN photocatalyst with NiO cocatalyst (GaN-NiO) continuously produced hydrogen from water for 500 hours without any extra bias. The GaN-NiO photocatalyst was hardly etched and 184-mL hydrogen gas was produced from the electric charge of 1612 coulombs, the Faradic efficiency of which was 89.2%. The conversion efficiency from incident light energy to hydrogen chemical energy was 0.98% in average for 500 h. The incident photon-to-current conversion efficiency (IPCE) was 50% at 300 nm and 35% at 350 nm after the experiment, which was much higher than those of other semiconductor-based photocatalysts.

scholarly journals Quantification of leaf-scale light energy allocation and photoprotection processes in a Mediterranean pine forest under extensive seasonal drought

2019 ◽  
Vol 39 (10) ◽  
pp. 1767-1782 ◽  
Author(s):  
Kadmiel Maseyk ◽  
Tongbao Lin ◽  
Amnon Cochavi ◽  
Amnon Schwartz ◽  
Dan Yakir
Keyword(s):  
Soil Water ◽  
Carbon Fixation ◽  
Pinus Halepensis ◽  
Electron Flow ◽  
Incident Light ◽  
Light Energy ◽  
Absolute Amount ◽  
Summer Drought ◽  
Low Carbon ◽  
Psii Efficiency

Abstract Photoprotection strategies in a Pinus halepensis Mill. forest at the dry timberline that shows sustained photosynthetic activity during 6–7 month summer drought were characterized and quantified under field conditions. Measurements of chlorophyll fluorescence, leaf-level gas exchange and pigment concentrations were made in both control and summer-irrigated plots, providing the opportunity to separate the effects of atmospheric from soil water stress on the photoprotection responses. The proportion of light energy incident on the leaf surface ultimately being used for carbon assimilation was 18% under stress-free conditions (irrigated, winter), declining to 4% under maximal stress (control, summer). Allocation of absorbed light energy to photochemistry decreased from 25 to 15% (control) and from 50% to 30% (irrigated) between winter and summer, highlighting the important role of pigment-mediated energy dissipation processes. Photorespiration or other non-assimilatory electron flow accounted for 15–20% and ~10% of incident light energy during periods of high and low carbon fixation, respectively, representing a proportional increase in photochemical energy going to photorespiration in summer but a decrease in the absolute amount of photorespiratory CO2 loss. Resilience of the leaf photochemical apparatus was expressed in the complete recovery of photosystem II (PSII) efficiency (ΦPSII) and relaxation of the xanthophyll de-epoxidation state on the diurnal cycle throughout the year, and no seasonal decrease in pre-dawn maximal PSII efficiency (Fv/Fm). The response of CO2 assimilation and photoprotection strategies to stomatal conductance and leaf water potential appeared independent of whether stress was due to atmospheric or soil water deficits across seasons and treatments. The range of protection characteristics identified provides insights into the relatively high carbon economy under these dry conditions, conditions that are predicted for extended areas in the Mediterranean and other regions due to global climate change.

scholarly journals Dependence of Relational Colour Constancy on the Extraction of a Transient Signal

Perception ◽  
1996 ◽  
Vol 25 (2) ◽  
pp. 221-228 ◽  
Author(s):  
Karina J Linnell ◽  
David H Foster
Keyword(s):  
Computer Simulations ◽  
Spectral Reflectance ◽  
Time Course ◽  
Incident Light ◽  
Transient Signal ◽  
Colour Constancy ◽  
Rapid Changes ◽  
Reflectance Change ◽  
The Individual ◽  
Over Time

Human observers can correctly attribute changes in the appearance of a scene either to changes in the incident light or to changes in the spectral-reflectance properties of the scene. This ability was assessed as a function of the time course of illuminant and spectral-reflectance changes. Observers were presented with computer simulations of Mondrian patterns of 49 randomly selected Munsell papers. On each trial a Mondrian pattern was presented for 1 s; the pattern then changed either instantaneously or gradually into another Mondrian pattern, also presented for 1 s, which was related to the first either by an illuminant change or by an illuminant change accompanied by additional changes in the spectral-reflectance functions of the individual papers. Illuminant and spectral-reflectance changes were applied linearly in time (with respect to CIE coordinates) over intervals ranging from 0 to 7 s. Observers indicated whether there was a spectral-reflectance change. They were able to make reliable discriminations between illuminant and spectral-reflectance changes both when the changes were applied instantaneously and when they were applied gradually over time, but performance worsened progressively as the duration of the changes increased, that is, as their rate decreased. It is suggested that discrimination in this task depends on the extraction of a low-level transient signal which is generated in response to rapid changes in scene appearance and which is progressively attenuated as changes occur more and more gradually.

Exploration in the Two-Photon Absorption Effect of Silicon Based Films

2010 ◽  
Vol 663-665 ◽  
pp. 348-351
Author(s):  
Ming Yang ◽  
Juan Li ◽  
Ying Yao ◽  
Chun Jian Yin ◽  
Chun Ya Wu ◽  
...  
Keyword(s):  
Incident Light ◽  
Light Energy ◽  
Photon Absorption ◽  
Absorption Effect ◽  
Linear Absorption ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Si Films ◽  
Silicon Based ◽  
Better Than

In this work, the crystallization of different silicon based thin films as the precursor of crystallization was investigated by femto-second laser with 800 nm wavelength. The linear absorption coefficient of a-Si films at that wavelength is quit lower than the other structures of Si-based thin film, which has no related with the incident light energy. However, we found that the crystallization of a-Si films was better than μc-Si films as the precursor. We use Z-scan techniques to prove that the two-photon absorption effect would be responsible for the crystallization. And unlike the linear absorption, the two-photon absorption effect is correlated with the incident light energy, as well as the micro-structure of the silicon based film. At the end of the paper, the crystallization by laser with wavelength longer than the absorption limit was discussed.

scholarly journals Radiative energy budgets of phototrophic surface-associated microbial communities and their photosynthetic efficiency under diffuse and collimated light

2017 ◽  
Author(s):  
Mads Lichtenberg ◽  
Kasper Elgetti Brodersen ◽  
Michael Kühl
Keyword(s):  
Energy Conservation ◽  
Photosynthetic Efficiency ◽  
Heat Dissipation ◽  
Incident Light ◽  
Energy Conversion Efficiency ◽  
Light Energy ◽  
Radiative Energy ◽  
Energy Budgets ◽  
Gross Photosynthesis ◽  
Light Regimes

AbstractWe investigated the radiative energy budgets of a heterogeneous photosynthetic coral reef sediment and a compact uniform cyanobacterial biofilm on top of coastal sediment. By combining electrochemical, thermocouple and fiber-optic microsensor measurements of O2, temperature and light, we could calculate the proportion of the absorbed light energy that was either dissipated as heat or conserved by photosynthesis. We show, across a range of different incident light regimes, that such radiative energy budgets are highly dominated by heat dissipation constituting up to 99.5% of the absorbed light energy. Highest photosynthetic energy conservation efficiency was found in the coral sediment under light-limiting conditions and amounted to ~13% of the absorbed light energy. Additionally, the effect of light directionality, i.e., diffuse or collimated light, on energy conversion efficiency was tested on the two surface-associated systems. The effects of light directionality on the radiative energy budgets of these phototrophic communities were not unanimous but, resulted in local spatial differences in heat-transfer, gross photosynthesis and light distribution. The light acclimation index, Ekwas >2 times higher in the coral sediment compared to the biofilm and changed the pattern of photosynthetic energy conservation under light-limiting conditions. At moderate to high incident 45 irradiances, the photosynthetic conservation of absorbed energy was highest in collimated light; a tendency that changed in the biofilm under sub-saturating incident irradiances, where higher photosynthetic efficiencies were observed under diffuse light. Our results suggest that the optical properties and the structural organization of phytoelements are important traits affecting the photosynthetic efficiency of biofilms and sediments.

A Model of the Effect of Interspecies Competition for Light on Dry-Matter Production

1984 ◽  
Vol 11 (4) ◽  
pp. 277 ◽  
Author(s):  
GM Rimmington
Keyword(s):  
Dry Matter ◽  
Incident Light ◽  
Light Energy ◽  
Dry Matter Production ◽  
Interspecies Competition ◽  
Area Index ◽  
Unit Leaf ◽  
Matter Production ◽  
Absorption Of Light ◽  
Competition For Light

A model of the effect of interspecies competition for light on the daily dry-matter production of competing species is developed. It describes the absorption of light by the component species, accounting for their different optical properties. Absorption equations are formulated from the principle of conservation of light energy within a unit-leaf-area-index of canopy, and the integral of absorbed light energy is then used to calculate the rate of dry-matter production of each component species. This model proved useful for the analysis of data from experiments in which New Zealand white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) were grown in mixtures. Application of the model enabled the proportion of incident light energy absorbed by each component to be estimated and unambiguous differentiation between the amount of light energy absorbed and the efficiency of use of the absorbed light energy.

Competition between plants of different initial seed sizes in swards of subterranean clover (Trifolium subterraneum L.) with particular reference to leaf area and the light microclimate

1958 ◽  
Vol 9 (3) ◽  
pp. 299 ◽  
Author(s):  
JN Black
Keyword(s):  
Leaf Area ◽  
Incident Light ◽  
Subterranean Clover ◽  
Trifolium Subterraneum ◽  
Light Energy ◽  
Light Extinction ◽  
Unexpected Finding ◽  
Sampling Occasion ◽  
Area Index ◽  
Initial Seed

A study was made of the development and fate of individual plants growing from contrasting seed sizes in swards of subterranean clover (var. Bacchus Marsh). Three sets of swards were grown in boxes, from large, small, and mixed (large and small) seeds respectively, all sown at the same number of plants per unit area; the swards were harvested on five occasions. Leaf area in each 2 cm layer of the sward was determined separately and measurements of the light intensity reaching each layer were obtained at each harvest. Counts of the plants on each occasion revealed a steady drop of about 30 per cent. over the whole period; in the "mixed" swards, only plants from small seed sizes died, the number of large-seeded plants remaining unchanged. The data of leaf area and numbers in each layer showed that leaf area is concentrated in a relatively shallow band at the top of the sward, the area attained by individual leaves increasing with height in the sward and with time. Leaves are not retained in the canopy at heights below that at which light extinction occurs. An unexpected finding was that, as the sward developed, the leaf area index (the ratio of leaf area to ground covered) required for the absorption of all incident light energy increases, and it is suggested that this is due to changes in leaf morphology. The importance of the position at which leaves of individual plants are held in the canopy is stressed; although at the first sampling occasion, the small-seeded plants had 25 per cent. of the leaf area of the mixed sward, they were so located as to absorb only 10 per cent. of the incident light energy; at the last sampling occasion, the values were 10 and 2 per cent. respectively. It is concluded that the disappearance of the small-seeded plants from the mixed swards was due to shading from the large-seeded plants.

scholarly journals Supra-Optimal Temperature: An Efficient Approach for Overaccumulation of Starch in the Green Alga Parachlorella kessleri

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1806
Author(s):  
Vilém Zachleder ◽  
Veronika Kselíková ◽  
Ivan N. Ivanov ◽  
Vitali Bialevich ◽  
Milada Vítová ◽  
...  
Keyword(s):  
Green Alga ◽  
Time Course ◽  
Neutral Lipids ◽  
Incident Light ◽  
Energy Reserves ◽  
Optimal Temperature ◽  
Algal Biotechnology ◽  
Cell Reproduction ◽  
Parachlorella Kessleri ◽  
Synchronized Cultures

Green algae are fast-growing microorganisms that are considered promising for the production of starch and neutral lipids, and the chlorococcal green alga Parachlorella kessleri is a favorable model, as it can produce both starch and neutral lipids. P. kessleri commonly divides into more than two daughter cells by a specific mechanism—multiple fission. Here, we used synchronized cultures of the alga to study the effects of supra-optimal temperature. Synchronized cultures were grown at optimal (30 °C) and supra-optimal (40 °C) temperatures and incident light intensities of 110 and 500 μmol photons m−2 s−1. The time course of cell reproduction (DNA replication, cellular division), growth (total RNA, protein, cell dry matter, cell size), and synthesis of energy reserves (net starch, neutral lipid) was studied. At 40 °C, cell reproduction was arrested, but growth and accumulation of energy reserves continued; this led to the production of giant cells enriched in protein, starch, and neutral lipids. Furthermore, we examined whether the increased temperature could alleviate the effects of deuterated water on Parachlorella kessleri growth and division; results show that supra-optimal temperature can be used in algal biotechnology for the production of protein, (deuterated) starch, and neutral lipids.

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