Low Irradiance Levels Research Articles

Melanopsin and Rod–Cone Photoreceptors Play Different Roles in Mediating Pupillary Light Responses during Exposure to Continuous Light in Humans

In mammals, the pupillary light reflex is mediated by intrinsically photosensitive melanopsin-containing retinal ganglion cells that also receive input from rod-cone photoreceptors. To assess the relative contribution of melanopsin and rod-cone photoreceptors to the pupillary light reflex in humans, we compared pupillary light responses in normally sighted individuals (n = 24) with a blind individual lacking rod-cone function. Here, we show that visual photoreceptors are required for normal pupillary responses to continuous light exposure at low irradiance levels, and for sustained pupillary constriction during exposure to light in the long-wavelength portion of the visual spectrum. In the absence of rod-cone function, pupillomotor responses are slow and sustained, and cannot track intermittent light stimuli, suggesting that rods/cones are required for encoding fast modulations in light intensity. In sighted individuals, pupillary constriction decreased monotonically for at least 30 min during exposure to continuous low-irradiance light, indicating that steady-state pupillary responses are an order of magnitude slower than previously reported. Exposure to low-irradiance intermittent green light (543 nm; 0.1-4 Hz) for 30 min, which was given to activate cone photoreceptors repeatedly, elicited sustained pupillary constriction responses that were more than twice as great compared with exposure to continuous green light. Our findings demonstrate nonredundant roles for rod-cone photoreceptors and melanopsin in mediating pupillary responses to continuous light. Moreover, our results suggest that it might be possible to enhance nonvisual light responses to low-irradiance exposures by using intermittent light to activate cone photoreceptors repeatedly in humans.

Comparison of Curve Correction Procedures for Current–Voltage Characteristics of Photovoltaic Devices

It is useful to understand the effect of irradiance, temperature, and spectral irradiance on the photovoltaic cell and module performance, to estimate their current–voltage curves under various climate conditions for power rating and energy rating. In this paper, we present the accuracy of the three methods described at the IEC 60891 and investigate the applicability of these methods. Procedure 3 showed good agreements between the calculations and experiments within ±1%. We have also demonstrated that the accuracies of procedures 1 and 2 depend on the device structure. Although both methods can introduce larger deviations at lower irradiance level, these deviations are not negligible for energy yield prediction.

Comparison of Curve Correction Procedures for Current–Voltage Characteristics of Photovoltaic Devices

It is useful to understand the effect of irradiance, temperature, and spectral irradiance on the photovoltaic cell and module performance, to estimate their current–voltage curves under various climate conditions for power rating and energy rating. In this paper, we present the accuracy of the three methods described at the IEC 60891 and investigate the applicability of these methods. Procedure 3 showed good agreements between the calculations and experiments within ±1%. We have also demonstrated that the accuracies of procedures 1 and 2 depend on the device structure. Although both methods can introduce larger deviations at lower irradiance level, these deviations are not negligible for energy yield prediction.

NAA and STS effects on potted bougainvillea: Early flower death allows delayed bract abscission

The effects of silver thiosulfate (STS) and naphthalene acetic acid (NAA) (0.45% NAA+1.2% NAA-amide at 500mgL−1) on flowering bud development, anthesis duration, bract longevity, and bract photosynthetic rate were studied in Bougainvillea spectabilis ‘Killie Campbell’ plants, under interior conditions. The relationships between bract longevity and the above parameters were also investigated.NAA induced longer bract longevity, shorter flower anthesis duration, and lower percentage of flowers reaching anthesis. STS alone increased duration of flower anthesis but did not affect completely developed bract abscission, as compared to the water treatment. Depending on the experiment, adding STS to NAA delayed or had no effect on bract abscission. Longer bract longevity was related to shorter flower anthesis and lower percentage of flowers reaching anthesis. Manual removal of flowers from the bract+flower unit increased bract longevity. Despite the low level of irradiance, bracts photosynthesized and plants treated with NAA (alone or with STS) had lower bract photosynthetic rates. Bract photosynthetic activity, although with relevant rates (similar to leaves and most probably capable of covering respiration expenditure) did not seem important as an energy source for bract longevity since bracts that lasted longer had lower photosynthetic rates. In the water control, percentage of flowers reaching anthesis positively correlated with bract photosynthetic rates.In potted bougainvillea under low light conditions, flower senescence and bract abscission are under different types of control. In addition to the classical effect of auxin reducing ethylene production, and/or sensitivity of the abscission zone to ethylene, NAA delays bougainvillea bract abscission via early interruption of flower development.

Microwave-assisted non-aqueous route to deposit well-dispersed ZnO nanocrystals on reduced graphene oxide sheets with improved photoactivity for the decolorization of dyes under visible light

A new strategy is discussed for deposition of monodisperse ZnO nanocrystals on the surface of reduced graphene oxide (rGO) sheets to form rGO/ZnO nanohybrids via a microwave-assisted route in a non-aqueous media. This is a facile and rapid process, which only requires a proration of zinc salt and rGO sheets react in diethylene glycol (DEG) under a low level of microwave irradiation (300W) for 10min. The as-prepared nanohybrids demonstrate well-dispersed ZnO nanocrystals loading and powerful photocatalytic activity for the decolorization of self-photosensitized dyes (rhodamine-B and methylene blue) under visible-light illumination. Here, DEG does not only help to enhance dispersion of rGO sheets, but also play an important role of controlling the growth of ZnO. Furthermore, the average size and loading amount of ZnO nanocrystals can be conveniently varied or controlled by the concentration of zinc precursor. The result uncovers that the loading of ZnO nanocrystals in the as-prepared nanohybrids is crucial to obtain an optimal synergistic effect between ZnO and rGO sheets in the mediated photocatalysis process for the photosensitized dyes decolorization. Accordingly, the optimum matching for the best photocatalytic activity is investigated thoroughly and a reasonable mechanism is also proposed.

High variability and low irradiance of phototherapy devices in Dutch NICUs

ObjectiveTo evaluate phototherapy practices by measuring the irradiance levels of phototherapy (PT) devices.DesignProspective study.SettingTertiary neonatal intensive care units.PatientsNone.InterventionsIrradiance levels of PT devices used in the 10 Dutch Neonatal Intensive Care...

Photosynthetic characteristics and physiological plasticity of an Aphanizomenon flos-aquae (Cyanobacteria, Nostocaceae) winter bloom in a deep oligo-mesotrophic lake (Lake Stechlin, Germany)

In winter of 2009/2010, Aphanizomenonflos-aquae bloomed in the ice and snow covered oligo-mesotrophic Lake Stechlin, Germany. The photosynthesis of the natural population was measured at eight temperatures in the range of 2–35°C, at nine different irradiance levels in the range of 0–1,320 μmol m−2 s−1 PAR at each applied temperature. The photoadaptation parameter (Ik) and the maximum photosynthetic rate (Pmax) correlated positively with the temperature between 2 and 30°C, and there was a remarkable drop in both parameters at 35°C. The low Ik at low temperatures enabled the active photosynthesis of overwintering populations at low irradiance levels under ice and snow cover. The optimum of the photosynthesis was above 20°C at irradiances above 150 μmol m−2 s−1. At lower irradiance levels (7.5–30 μmol m−2 s−1), the photosynthesis was the most intensive in the temperature range of 2–5°C. The interaction between light and temperature allowed the proliferation of A. flos-aquae in Lake Stechlin resulting in winter water bloom in this oligo-mesotrophic lake. The applied 2°C is the lowest experimental temperature ever in the photosynthesis/growth studies of A. flos-aquae, and the results of the P–I and P–T measurements provide novel information about the tolerance and physiological plasticity of this species.

Facile One-Step Microwave-Assisted Route towards Ni Nanospheres/Reduced Graphene Oxide Hybrids for Non-Enzymatic Glucose Sensing

In this work, a facile one-step microwave-assisted method for deposition of monodisperse Ni nanospheres on reduced graphene oxide (rGO) sheets to form Ni-rGO nanohybrids is discussed. In the presence of hydrazine monohydrate, Ni nanospheres are grown onto rGO sheets using nickel precursor and GO as starting materials in ethylene glycol (EG) solution under a low level of microwave irradiation (300 W) for 20 min, during which GO is also reduced to rGO. The as-prepared nanohybrids exhibit well-dispersed Ni nanosphere (about 80 nm in diameter) loadings and effective reduction of graphene oxide. The resulting Ni-rGO nanohybrids-modified glassy carbon electrode (GCE) shows significantly improved electrochemical performance in nonenzymatic amperometric glucose detection. In addition, interference from the oxidation of common interfering species under physiological conditions, such as ascorbic acid (AA) and uric acid (UA), is effectively avoided.

Foliar anatomical and morphological variation in Nothofagus pumilio seedlings under controlled irradiance and soil moisture levels

Foliar anatomy and morphology are strongly related to physiological performance; therefore, phenotypic plasticity in leaves to variations in environmental conditions, such as irradiance and soil moisture availability, can be related to growth rate and survivorship, mainly during critical growth phases, such as establishment. The aim of this work was to analyze changes in the foliar internal anatomy (tissue proportions and cell dimensions) and external morphology (leaf length, width and area) of Nothofagus pumilio (Poepp. et Endl.) Krasser seedlings growing in a greenhouse under controlled irradiance (three levels) and soil moisture (two levels) during one growing season (measured three times), and to relate them to physiological traits. Three irradiance levels (4, 26 and 64% of the natural incident light) and two soil moisture levels (40 and 80% soil capacity) were evaluated during November, January and March. Internal foliar anatomy of seedlings was analyzed using digital photographs of histological cuttings, while leaf gross morphology was measured using digital calipers and image analysis software. Most internal anatomical variables presented significant differences under different irradiance levels during the growing season, but differences were not detected between soil moisture levels. Palisade parenchyma was the tissue most sensitive to irradiance levels, and high irradiance levels (64% natural incident light) produced greater values in most of the internal anatomical variables than lower irradiance levels (4-24% natural incident light). Complementarily, larger leaves were observed in medium and low irradiance levels, as well as under low soil moisture levels (40% soil capacity). The relationship of main results with some eco-physiological traits was discussed. Foliar internal anatomical and external morphological plasticity allows quick acclimation of seedlings to environmental changes (e.g., during harvesting). These results can be used to propose new forest practices that consider soil moisture and light availability changes to maintain high physiological performance of seedlings.

Photosynthetic Photon Flux Density, Carbon Dioxide Concentration and Temperature Influence Photosynthesis in Crotalaria Species

Crotalarias are tropical legumes grown as cover crops or as green manure to improve soil fertility. As an understory plant in plantation systems, these cover crops receive low levels of irradiance and are subjected to elevated levels of CO2 and temperatures. A greenhouse experiment was conducted to evaluate the independent short-term effects of photosynthetic photon flux density (PPFD), external carbon dioxide concentration (Ca) and temperature (T) on net photosynthesis (PN), internal CO2 (Ci), stomatal conductance (gs) and transpiration (E) in four Crotalaria species (C. breviflora, C. mucronata, C. ochroleuca, C. spectabilis). These crotalarias responded differently to changing PPFD, Ca and T. In all the Crotalaria species, increasing PPFD from 50 to 1500 � mol m -2 s -1 increased PN by 21 fold, increased gs by 2.3 fold (136%), decreased Ci by 3.9 times, and increased E by 2.1 times. Increasing the external Ca from 100 to 1000 cm 3 m -3 increased PN by 4.7 fold, decreased gs by 1.3 times, increased Ci by 28 fold, and decreased E by 1.2 times. Increasing the T from 25 to 35 °C increased PN of Crotalaria species by 11%, decreased gs by 33%, decreased Ci by 64%, and increased E by 56%. Shade management is critical to maintaining the productivity of these tropical legumes.

Enhanced Light Harvesting in Plasmonic Dye‐Sensitized Solar Cells by Using a Topologically Ordered Gold Light‐Trapping Layer

Dye-sensitized solar cells (DSSCs) are promising low-cost, high-efficiency devices with low environmental impact. One of the important methods to improve their efficiencies involves increasing the light-harvesting efficiency. Earlier work has focused on varying the morphology of the photoanode. With such a hierarchical structured photoanode in hand, we modify herein the structure of the counter electrode to enhance the optical path length through the plasmonic and reflecttion effects. With the introduced topological gold layer, the photocurrent and efficiency are increased by 16 % and 18 %, respectively, due to the increased light collection. Besides, this effect is effective at both high and low levels of solar irradiation.

Use of thermal imaging to determine leaf conductance along a canopy gradient in European beech (Fagus sylvatica)

Using an infrared camera, we measured the leaf temperature across different canopy positions of a 23-m-tall deciduous forest tree (Fagus sylvatica L.) including typical sun and shade leaves as well as intermediate leaf forms, which differed significantly in specific leaf area (SLA). We calculated a temperature index (I(G)) and a crop water stress index (CWSI) using the surface temperatures of wet and dry reference leaves. Additional indices were computed using air temperature plus 5 °C (I(G) + 5, CWSI + 5) as dry references. The minimum temperature of the wet leaf and the maximum temperature of the dry leaf proved to be most suitable as reference values. We correlated the temperature indices with leaf area-related conductance to water vapor (g(L)) using porometry at the leaf level and using xylem sap flow at the branch level. At the leaf and at the branch level, I(G) and CWSI were equally well suited as proxies of g(L), whereas the relationships of I(G) + 5 and CWSI + 5 with g(L) were only weak or even insignificant. At the leaf level, the correlations of I(G) and CWSI with g(L) were significant in all parts of the crown. The slopes of g(L) vs. I(G) and CWSI did not differ significantly among the crown parts; this indicates that they were not influenced by SLA or irradiance. At the branch level, close correlations (r > 0.8) were found between temperature indices and g(L) across the crown. These results demonstrate that satisfactory relationships between temperature indices and g(L) can be established in tall trees even in those canopy parts that are exposed to relatively low levels of irradiance and exhibit relatively low values of g(L).

A model for improved solar irradiation measurement at low flux

Accurate measurement of solar radiation heat flux is important in characterizing the performance of CSP plants. Thermopile type Heat Flux Sensors (HFSs) are usually used for this purpose. These sensors are typically reasonably accurate at high heat fluxes. However measurement accuracy drops significantly as the measured radiation is below 1 kW/m2, this often leads to underestimation of the actual flux. At the Masdar Institute Beam Down Solar Thermal Concentrator (BDSTC), measurement of fluxes ranging from 0 kW/m2 to more than 100 kW/m2 is required. To improve the accuracy of the sensors in the lower range around 1 kW/m2, we have performed a test under ambient (not-concentrated) sunlight. Such low irradiation levels are experienced in characterizing the concentration quality of individual heliostats. It was found during the test that the measurement at this low range is significantly affected by ambient conditions and transients in the HFS cooling water temperature. A Root Mean Square Error (RMSE) of more than 100 W/m2 was observed even though we kept the transients in water temperature to a minimum. Hence we devised a model to account for this measurement error at this flux range. Using the proposed model decreased the RMSE to less than 10 W/m2. The application of the model on existing heat flux measurement installations is facilitated by the fact that it only employs easily measurable variables. This model was checked by using a test data set and the results were in good agreement with the training data set.

Alpha-Particles and 60Co y-Rays Have Different Biological Effects on Upland Cotton (Gossypium hirsutum L.) Pollen Grains

To compared the irradiation effects by y-rays and alpha-particles on the structure and function of upland cotton pollen grains during pollination, pollen grains from Gossypium hirsutum L. cultivar “Lumian 21” were irradiated by alpha-particles (1, 10, 30, 40 and 100 Gy) and y-rays (20, 30 and 40 Gy). We looked for changes in the ultrastructure of the exine and interior walls of the pollen grains. After germinating the irradiated pollen grains in liquid medium, we looked for changes in germination rate, the number of pollen tubes in styles after pollination and F-actin distribution in the pollen tubes. Alpha-particles penetrated and etched the exine and interior walls of the pollen grains and also damaged the organelles in the pollen grains. More pollen grains were destroyed as the alpha-particles dose increased. y-rays had no effects on the exine walls of the pollen grains but had stronger effects on the interior structure of the pollen grains than those induced by alpha-particle irradiation. The pollen grain germination rate, the number of pollen tubes in the styles and the average length of the pollen tubes in pollen grains treated with y-ray irradiation were decreased and shortened with increased y-rays irradiation dose, compared with that of control. However, under alpha-particle irradiation, these features initially increased at a low level of irradiation (1 Gy) and then decreased as the dose was increased. There was evident damage to F-actin structures in pollen tubes induced by the two kinds of mutagens. The mechanisms underlying the biological effects induced by alpha-particles and y-rays were different. The function and structure of pollen tubes in pollination and fertilization may be affected by the ultrastructure of pollen grains.

Physicochemical and sensory properties of irradiated dry-cured ham

To determine the effect of different irradiation doses on ready-to-eat (RTE) dry-cured shoulder hams, physicochemical and sensory attributes were analyzed during 8 weeks of refrigerated storage. The results show that irradiation reduced the redness value and increased the 2-thiobarbituric acid-reactive substance (TBARS) value as well as the irradiation aroma during storage. However, ham samples irradiated with 2.5 and 5.0 kGy did not show significant changes in lightness values compared to the control sample during 8 weeks of storage. TBARS values were lower in the sample irradiated with 2.5 kGy than in the other irradiated samples. The total plate counts of the 5.0 kGy-irradiated samples were not measured after 0 weeks. Sensory panels found that the 2.5- and 5.0 kGy-irradiated samples had better overall acceptability scores than the other irradiated samples. It was concluded that treatments with lower levels of irradiation (≤5.0 kGy) can enhance the microbial safety and sensory acceptance of dry-cured shoulder hams.

Sun’s total irradiance reconstruction based on multiple solar indices

In order to uncover a possible influence on the Earth’s climate, we need a much longer time series, i.e., the total solar irradiance (TSI) which is also an interesting issue in its own right in solar physics. By comparing different solar indices associated with TSI during the period 1979 to 2009, several empirical models in the TSI are presented. We verify that the reconstruction model based on the three variables: sunspot number, sunspot area, and solar 10.7 cm radio flux, is the best one. As demonstrated by model calculations, the history of TSI was reconstructed back to 1947 based on 3-indices and to 1874 based on 2-indices, respectively. The reason that the reduced irradiance on the trough during 2006 to 2009 lasts long may be due to the about 85-year cycle of solar activity, which modulates the intensity of the 11-year cycle (Schwabe cycles), possesses a considerable potential to produce an effective reducing, and holds on a steadily lower level of irradiance.

Acclimation of winter wheat (Triticum aestivum, cv. Yangmai 13) to low levels of solar irradiance

Winter wheat is a grass species widely planted in northern and central China, where the increase of aerosols, air pollutants and population density are causing significant reduction in solar irradiance. In order to investigate the adaptation of winter wheat (Triticum aestivum L., cv. Yangmai 13) to low irradiance conditions occurring in the downstream plain of the Yangtze River (China), plants were subjected to four solar irradiance treatments (100%, 60%, 40%, and 20% of environmental incident solar irradiance). Significant increases in chlorophyll (Chl) and xanthophyll (Xan) pigments, and decreases in Chl a/b and Xan/Chl ratios were observed in plants under low light. Light-response curves showed higher net photosynthetic rates (P N) in fully irradiated plants, that also showed a higher light-compensation point. Shaded plants maintained high values of minimal fluorescence of dark-adapted state (Fo) and maximum quantum efficiency of PSII photochemistry (Fv/Fm) that assess a lower degree of photoinhibition under low light. Reduced irradiance caused decreases in effective quantum yield of PSII photochemistry (ΦPSII), electron transport rate (ETR), and nonphotochemical quenching coefficient (qN), and the promotion of excitation pressure of PSII (1 - qP). The activities of the antioxidant enzymes superoxide dismutase and peroxidase were high under reduced light whereas no light-dependent changes in catalase activity were observed. Thiobarbituric acid reactive species content and electrolyte leakage decreased under shaded plants that showed a lower photooxidative damage. The results suggest that winter wheat cv. Yangmai 13 is able to maintain a high photosynthetic efficiency under reduced solar irradiance and acclimates well to shading tolerance. The photosynthetic and antioxidant responses of winter wheat to low light levels could be important for winter wheat cultivation and productivity.

Effect of leaf rust ( Puccinia triticina) on photosynthesis and related processes of leaves in wheat crops grown at two contrasting sites and with different nitrogen levels

Leaf rust is one of the main diseases affecting wheat yield production. Considering the physiological variables that determine yield, diseases could affect radiation capture and/or radiation use efficiency. Reductions in radiation use efficiency may be mediated through effects on photosynthesis rate and related variables (i.e. dark respiration rate, stomatal conductance or photosynthesis events per se). The aim of this study was to analyze the effects of leaf rust on wheat leaves photosynthesis rate and to understand which processes determining photosynthesis are affected by this pathogen. Gas exchange measurements were taken on flag leaves with various rust severity levels in experiments carried out on two locations which included different nitrogen fertilization rates and sowing dates. Leaf rust reduced net photosynthesis rate at light saturation through reductions in gross photosynthesis (average reduction: 6.1 μmol CO 2 m −2 green area s −1) rather than through increases in dark respiration rate (average increase: 0.7 μmol CO 2 m −2 green area s −1). Changes in leaf nitrogen concentration did not modify the effects of leaf rust on net photosynthesis rate. Although net photosynthesis rate at light saturation was reduced, no effects were observed at low irradiance levels. The reduction of photosynthesis was due to effects on non-stomatal processes; indeed, important reductions of SPAD units (i.e. chlorophyll) were observed on green areas of diseased leaves. SPAD values on diseased leaves were 26.4 ± 0.98 and 27.6 ± 1.05 for N 0 and N 1 treatments, respectively; while on healthy leaves, values were 32.0 ± 0.83 and 38.6 ± 0.41, respectively.

Short-term photoacclimation effects on photoinhibition of phytoplankton in the Drake Passage (Southern Ocean)

We assessed whether short-term photoacclimation responses of natural phytoplankton populations in the Drake Passage (Southern Ocean) were affecting protection from photodamage as cells are mixed up to the surface from depth. To this end, we measured phytoplankton fluorescence characteristics and their ratio of xanthophyll cycle pigment to photosynthetic pigments within the upper mixed layer (UML) and in short-term deck incubation experiments. Phytoplankton within the UML photoacclimated by increasing their ratio of xanthophyll cycle (diadinoxanthin [dd] and diatoxanthin [dt]) pigments to chlorophyll a. The photoacclimation processes observed within the UML did, however, not influence the protection of phytoplankton from photodamage during short-term near-surface irradiance experiments. Exposure to near-surface irradiance resulted in photodamage in all experiments, regardless of the phytoplankton community composition and irradiance levels. Incubating phytoplankton for six hours at either 2% or 50% of surface irradiance prior to exposure to near-surface irradiance did not alter the photodamage characteristics. This suggests that short-term photoacclimation processes within the UML are not adequate to protect phytoplankton from photodamage when cells are mixed up to the surface from depth, and that repair of damaged photosystems is crucial for maintaining photosynthesis under fluctuating irradiance conditions, even at very low mean irradiance levels. Likely, continuously operating photoacclimation processes offset to some extent the negative effects of photodamage on photosynthetic performance, albeit with increased metabolic costs.

A comprehensive MATLAB Simulink PV system simulator with partial shading capability based on two-diode model

Abstract This paper proposes a comprehensive MATLAB Simulink simulator for photovoltaic (PV) system. The simulator utilizes a new two-diode model to represent the PV cell. This model is known to have better accuracy at low irradiance level that allows for a more accurate prediction of PV system performance during partial shading condition. To reduce computational time, only four parameters are extracted for the model. The values of R p and R s are computed by an efficient iteration method. Furthermore, all the inputs to the simulators are information available on standard PV module datasheet. The simulator supports a large array combination that can be interfaced to MPPT algorithms and power electronic converters. The accurateness of the simulator is verified by applying the model to five PV modules of different types (multi-crystalline, mono-crystalline, and thin-film) from various manufacturers. It is envisaged that the proposed work can be very useful for PV professionals who require simple, fast, and accurate PV simulator to design their systems. The developed simulator is freely available for download.