Variation Of Light Intensity Research Articles

Modulation of the rod outer segment aerobic metabolism diminishes the production of radicals due to light absorption.

Oxidative stress is a primary risk factor for both inflammatory and degenerative retinopathies. Our previous data on blue light-irradiated retinas demonstrated an oxidative stress higher in the rod outer segment (OS) than in the inner limb, leading to impairment of the rod OS extra-mitochondrial aerobic metabolism. Here the oxidative metabolism and Reactive Oxygen Intermediates (ROI) production was evaluated in purified bovine rod OS in function of exposure to different illumination conditions. A dose response was observed to varying light intensities and duration in terms of both ROI production and ATP synthesis. Pretreatment with resveratrol, inhibitor of F1Fo-ATP synthase, or metformin, inhibitor of the respiratory complex I, significantly diminished the ROI production. Metformin also diminished the rod OS Complex I activity and reduced the maximal OS response to light in ATP production. Data show for the first time the relationship existing in the rod OS between its -aerobic- metabolism, light absorption, and ROI production. A beneficial effect was exerted by metformin and resveratrol, in modulating the ROI production in the illuminated rod OS, suggestive of their beneficial action also in vivo. Data shed new light on preventative interventions for cone loss secondary to rod damage due to oxidative stress.

Developing an analytical solution for photo-sensitive hydrogel bilayers

In this article, a new conceptual design of light-sensitive switches made of a soft bilayer is introduced. The bilayer structure consists of a photothermal-sensitive hydrogel strip attached to another neutral incompressible elastomeric layer. The bilayer is assumed to be initially flat under a uniform light irradiation. Decreasing the light intensity causes the bilayer to bend due to the inhomogeneous swelling of hydrogel layer and results in the switch actuation. To enlighten the actuation mechanism and investigate the influence of various parameters on the switch’s photomechanical response, an analytical method is developed to study the bilayer deformation due to the light-intensity variation under plane-strain condition. Additionally, the finite element analysis of the bilayer is conducted, implementing the relevant constitutive model into a finite element code. The deformation and stress inside the layers are studied both analytically and numerically for several cases. The numerical results verify the accuracy of the presented analytical method in this work. The influence of various material and geometrical parameters including each layer’s modulus, the thickness ratio of the layers, and the aspect ratio of the bilayer is investigated. The analytical method is found to be useful for proper design of the light-sensitive hydrogel-based switches.

Differential coordination of stomatal conductance, mesophyll conductance, and leaf hydraulic conductance in response to changing light across species.

Stomatal conductance (gs ) and mesophyll conductance (gm ) represent major constraints to photosynthetic rate (A), and these traits are expected to coordinate with leaf hydraulic conductance (Kleaf ) across species, under both steady-state and dynamic conditions. However, empirical information about their coordination is scarce. In this study, Kleaf , gas exchange, stomatal kinetics, and leaf anatomy in 10 species including ferns, gymnosperms, and angiosperms were investigated to elucidate the correlation of H2 O and CO2 diffusion inside leaves under varying light conditions. Gas exchange, Kleaf , and anatomical traits varied widely across species. Under light-saturated conditions, the A, gs , gm , and Kleaf were strongly correlated across species. However, the response patterns of A, gs , gm , and Kleaf to varying light intensities were highly species dependent. Moreover, stomatal opening upon light exposure of dark-adapted leaves in the studied ferns and gymnosperms was generally faster than in the angiosperms; however, stomatal closing in light-adapted leaves after darkening was faster in angiosperms. The present results show that there is a large variability in the coordination of leaf hydraulic and gas exchange parameters across terrestrial plant species, as well as in their responses to changing light.

Field Performance versus Standard Test Condition Efficiency of Tandem Solar Cells and the Singular Case of Perovskites/Silicon Devices.

Multijunction cells may offer a cost-effective route to boost the efficiency of industrial photovoltaics. For any technology to be deployed in the field, its performance under actual operating conditions is extremely important. In this perspective, we evaluate the impact of spectrum, light intensity, and module temperature variations on the efficiency of tandem devices with crystalline silicon bottom cells with a particular focus on perovskite top cells. We consider devices with different efficiencies and calculate their energy yields using field data from Denver. We find that annual losses due to differences between operating conditions and standard test conditions are similar for single-junction and four-terminal tandem devices. The additional loss for the two-terminal tandem configuration caused by current mismatch reduces its performance ratio by only 1.7% when an optimal top cell bandgap is used. Additionally, the unusual bandgap temperature dependence of perovskites is shown to have a positive, compensating effect on current mismatch.

Effect of light on N<sub>2</sub> fixation and net nitrogen release of <i>Trichodesmium</i> in a field study

Abstract. Dinitrogen fixation (NF) by marine cyanobacteria is an important pathway to replenish the oceanic bioavailable nitrogen inventory. Light is the key to modulating NF; however, field studies investigating the light response curve (NF-I curve) of NF rate and the effect of light on diazotroph-derived nitrogen (DDN) net release are relatively sparse in the literature, hampering prediction using models. A dissolution method was applied using uncontaminated 15N2 gas to examine how the light changes may influence the NF intensity and DDN net release in the oligotrophic ocean. Experiments were conducted at stations with diazotrophs dominated by filamentous cyanobacterium Trichodesmium spp. in the western Pacific and the South China Sea. The effect of light on carbon fixation (CF) was measured in parallel using the 13C tracer method specifically for a station characterized by Trichodesmium bloom. Both NF-I and CF-I curves showed a Ik (light saturation coefficient) range of 193 to 315 µE m−2 s−1, with light saturation at around 400 µE m−2 s−1. The proportion of DDN net release ranged from ∼ 6 to ∼ 50 %, suggesting an increasing trend as the light intensity decreased. At the Trichodesmium bloom station, we found that the CF ∕ NF ratio was light-dependent and the ratio started to increase as light was lower than the carbon compensation point of 200 µE m−2 s−1. Under low-light stress, Trichodesmium physiologically preferred to allocate more energy for CF to alleviate the intensive carbon consumption by respiration; thus, there is a metabolism tradeoff between CF and NF pathways. Results showed that short-term (< 24 h) light change modulates the physiological state, which subsequently determined the C ∕ N metabolism and DDN net release by Trichodesmium. Reallocation of energy associated with the variation in light intensity would be helpful for prediction of the global biogeochemical cycle of N by models involving Trichodesmium blooms.

Method to mix tea with honey and use of transient light attenuation as an indicator of homogeneity

We built a magnetic stirrer to mix tea and honey and developed a method to determine the homogeneity of the mixture based on the variation of light intensity of a laser beam with time due to its scattering by the mixture. The addressed problem was that of mixing tea and honey as fast as possible with a power limitation of one single 1.5 V battery, following the statement of Problem 15 of the 9th International Physicists’ Tournament. The influence of temperature and honey concentration on the total time of mixing was studied through the performance of several experiments reported here. In the best configuration of parameters, the total mixture occurs in less than 2 s, while in the worst configuration, the time necessary reaches 10 s. Results validate the magnetic stirrer as a proper device for mixing tea with honey and light attenuation as an excellent physical property for investigating the homogeneity of the mixture of the honey in tea. Supplementary investigations were made exploring the influence of adding sugar and or a slice of lemon to the tea.

Remote monitoring of dynamic canopy photosynthesis with high time resolution light-induced fluorescence transients.

Understanding the net photosynthesis of plant canopies requires quantifying photosynthesis in challenging environments, principally due to the variable light intensities and qualities generated by sunlight interactions with clouds and surrounding foliage. The dynamics of sunflecks and rates of change in light intensity at the beginning and end of sustained light (SL) events makes photosynthetic measurements difficult, especially when dealing with less accessible parts of plant foliage. High time resolved photosynthetic monitoring from pulse amplitude modulated (PAM) fluorometers has limited applicability due to the invasive nature of frequently applied saturating flashes. An alternative approach used here provides remote (<5 m), high time resolution (10 s), PAM equivalent but minimally invasive measurements of photosynthetic parameters. We assessed the efficacy of the QA flash protocol from the Light-Induced Fluorescence Transient (LIFT) technique for monitoring photosynthesis in mature outer canopy leaves of potted Persea americana Mill. cv. Haas (Avocado) trees in a semi-controlled environment and outdoors. Initially we established that LIFT measurements were leaf angle independent between ±40° from perpendicular and moreover, that estimates of 685 nm reflectance (R685) from leaves of similar chlorophyll content provide a species dependent, but reasonable proxy for incident light intensity. Photosynthetic responses during brief light events (≤10 min), and the initial stages of SL events, showed similar declines in the quantum yield of photosystem II (ΦII) with large transient increases in 'constitutive loss processes' (ΦNO) prior to dissipation of excitation by non-photochemical quenching (ΦNPQ). Our results demonstrate the capacity of LIFT to monitor photosynthesis at a distance during highly dynamic light conditions that potentially may improve models of canopy photosynthesis and estimates of plant productivity. For example, generalized additive modelling performed on the 85 dynamic light events monitored identified negative relationships between light event length and ∆ΦII and ∆electron transport rate using either ∆photosynthetically active radiation or ∆R685 as indicators of leaf irradiance.

Coping with 'Dark Sides of the Sun' through Photoreceptor Signaling.

Plants grow in constantly changing environments, including highly variable light intensities. Sunlight provides the energy that drives photosynthesis and is thus of the utmost importance for plant growth and the generation of oxygen, which the majority of life on Earth depends on. However, exposure to either insufficient or excess levels of light can have detrimental effects and cause light stress. Whereas exposure to insufficient light limits photosynthetic activity, resulting in 'energy starvation', exposure to excess light can damage the photosynthetic apparatus. Furthermore, strong sunlight is associated with high levels of potentially damaging UV-B radiation. Different classes of photoreceptors play important roles in coping with the negative aspects of sunlight, for which specific mechanisms are emerging that are reviewed here.

A triangle mesh-based corner detection algorithm for catadioptric images

ABSTRACTAs with conventional images corner detection is an important aspect of many computer vision problems involving catadioptric images. However, classical image processing algorithms are no longer appropriate for catadioptric images due to nonuniform resolution and distortions of catadioptric images. In this paper, we propose a novel approach to corner detection for catadioptric images based on triangle mesh. First, we transform catadioptric images to spherical images by combining an improved projection model for central catadioptric cameras with triangle mesh for a unit sphere. Spherical images yield a spatially uniform resolution domain for processing catadioptric images. Then, based on the topology of a triangle mesh, variations of light intensity with respect to directions for each image patch are measured to detect corners. The proposed algorithm addresses problems of catadioptric image processing caused by non-uniform resolution and distortions of these images. Experimental results showed that comparing to widely used methods, the triangle mesh-based corner detection algorithm can achieve higher repeatability rate relative to different imaging condition changes.

Photosome membranes merge and organize tending towards rhombohedral symmetry when light is emitted.

Polynoid worm elytra emit light when mechanically or electrically stimulated. Specialized cells, the photocytes, contain light emitting machineries, the photosomes. Successive stimulations induce light intensity variations and show a coupling within and between photosomes. Here, we describe, using electron tomography of cryo-substituted elytra and freeze-fracturing, the structural transition associated to light emission: undulating tubules come closer, organize and their number forming photosomes increases. Two repeating undulating tubules in opposite phase compose the photosome. Undulations are located on three hexagonal layers that regularly repeat and are equally displaced, in x y and z. The tubule membranes within layers merge giving rise to rings that tend to obey to quasi-rhombohedral symmetry. Merging may result either from close-association, hemifusion (one leaflet fusion) or from fusion (two leaflets fusion). Although the resolution of tomograms is not sufficient to distinguish these three cases, freeze-fracturing shows that hemifusion is a frequent process that leads to an reversible anastomosed membrane complex favoring communications, appearing as a major coupling factor of photosome light emission.

The Impacts of Fluctuating Light on Crop Performance.

Rapidly changing light conditions can reduce carbon gain and productivity in field crops because photosynthetic responses to light fluctuations are not instantaneous. Plant responses to fluctuating light occur across levels of organizational complexity from entire canopies to the biochemistry of a single reaction and across orders of magnitude of time. Although light availability and variation at the top of the canopy are largely dependent on the solar angle and degree of cloudiness, lower crop canopies rely more heavily on light in the form of sunflecks, the quantity of which depends mostly on canopy structure but also may be affected by wind. The ability of leaf photosynthesis to respond rapidly to these variations in light intensity is restricted by the relatively slow opening/closing of stomata, activation/deactivation of C3 cycle enzymes, and up-regulation/down-regulation of photoprotective processes. The metabolic complexity of C4 photosynthesis creates the apparently contradictory possibilities that C4 photosynthesis may be both more and less resilient than C3 to dynamic light regimes, depending on the frequency at which these light fluctuations occur. We review the current understanding of the underlying mechanisms of these limitations to photosynthesis in fluctuating light that have shown promise in improving the response times of photosynthesis-related processes to changes in light intensity.

Photocuring of di-acrylate

Photocuring of multi-functional acrylate films for applications in large scale prints and 3D objects is a radical polymerization process under seriously changing conditions of liquid monomer to solid polymer network. Although a model is available describing this process and experimental data have been obtained for photocuring of hexanediol diacrylate (HDDA), measurements with widely varying light intensity to estimate the kinetic parameters in the model were still lacking. We have carried out such measurements with the aim of generating a proper set of parameters for the model, which then may be used for process optimization. We present results of the curing of thin HDDA films (10 μm) with initiator Irgacure 819, bis(acylphosphine oxide) under irradiation intensity varying in a range of 2–1350 W.m−2. Average conversion of vinyl groups in the films was registered by Fourier Transformed Infrared (FTIR) in transmission mode. A remarkable insensitivity of end conversion (range 78–85%) to light intensity was observed, but conversion rate varied strongly (0.1–6 s−1). Despite the large difference in irradiation and associated macroradical concentration level, a surprising similarity in the shapes of the conversion rate was observed.

Small Curvature Sensor Based on Butterfly-Shaped Mach–Zehnder Interferometer

A novel and small curvature sensor based on the butterfly-shaped Mach–Zehnder interferometer is proposed and experimentally demonstrated. The sensing element is a tapered hollow-core fiber sandwiched between two single-mode fibers. The fusion-collapsed region around the first fusion interface excites the high-order modes, and the butterfly-shaped structure couples the high-order modes back into the core and interferes with the fundamental mode in the second fusion-collapsed interface. Simulation of the butterfly-shaped structure is carried out by the beam propagation method to determine an optimized size of sensing element. The experimental results show that the light intensity variation of the interference spectrum is almost linearly proportional to the change of curvature, and the curvature sensitivity and resolution of the proposed sensor can be up to −10.9041 dB/m−1 and 0.000917 m−1, respectively, in the range from 0.387 to 1.285 m−1. The proposed curvature sensor is compact in size, high sensitive, and inexpensive. The excellent electromagnetic interference resistance and fabrication simplicity make the device an attractive candidate for curvature measurement in harsh environments.

Sintering strategies for inkjet printed metallic traces in 3D printed electronics

Emerging from 2D printed electronics, 3D printed electronics promise a break-through in additive manufacturing and prototyping of electronics. However, transferring the know-how from 2D flexible electronics to 3D parts with complex structures (e.g. internal vias and external interconnects) might not be a straightforward approach. As an example, the variation of light intensity with respect to the distance and angle of incidence casts doubt on the efficiency of the intense pulsed laser (IPL) as a robust sintering method for metallic traces in 3D printed bulk structures, whereas IPL is currently by far the most prevailing sintering technique for 2D printed flexible electronics. Sintering of metallic traces in 3D printed parts can be executed either as a sequential layer-by-layer printing and processing step (LP) or as a bulk post-processing step (BP). In the current study, a survey on the most common sintering strategies for inkjet printed silver nanoparticles was conducted, while the compatibility to 3D printed structures was brought into the focal point. To discover the capabilities and limitations of six sintering methods (i. e. IPL, ohmic curing, thermal heating, laser, atmospheric plasma and microwave sintering) for 3D printed electronics, a comparative study utilizing the same materials and diagnostic methods was pursued. The results revealed that for 3D functional parts, some of the sintering techniques can be considered as complementary methods for each other, whereas a few showed readily the potential to be adapted in 3D printed electronics production.

Environmental and Genetic Factors Regulating Localization of the Plant Plasma Membrane H+-ATPase

A P-type H+-ATPase is the primary transporter that converts ATP to electrochemical energy at the plasma membrane of higher plants. Its product, the proton-motive force, is composed of an electrical potential and a pH gradient. Many studies have demonstrated that this proton-motive force not only drives the secondary transporters required for nutrient uptake, but also plays a direct role in regulating cell expansion. Here, we have generated a transgenic Arabidopsis (Arabidopsis thaliana) plant expressing H+-ATPase isoform 2 (AHA2) that is translationally fused with a fluorescent protein and examined its cellular localization by live-cell microscopy. Using a 3D imaging approach with seedlings grown for various times under a variety of light intensities, we demonstrate that AHA2 localization at the plasma membrane of root cells requires light. In dim light conditions, AHA2 is found in intracellular compartments, in addition to the plasma membrane. This localization profile was age-dependent and specific to cell types found in the transition zone located between the meristem and elongation zones. The accumulation of AHA2 in intracellular compartments is consistent with reduced H+ secretion near the transition zone and the suppression of root growth. By examining AHA2 localization in a knockout mutant of a receptor protein kinase, FERONIA, we found that the intracellular accumulation of AHA2 in the transition zone is dependent on a functional FERONIA-dependent inhibitory response in root elongation. Overall, this study provides a molecular underpinning for understanding the genetic, environmental, and developmental factors influencing root growth via localization of the plasma membrane H+-ATPase.

Behavior of Electrical Properties of Synthetic Chlorophyll Pigment Solution by using the T.E-Model

Objective: Our purpose is to propose a new method for studying the electrical activity of chlorophyll pigment solution. Methods/Statistical Analysis: The technic and method employed consisted of modeling the chlorophyll as an electrical circuit, which made up of two parallel branches; where R represents the extra chlorophyll space resistance, R’ the intra chlorophyll space resistance and C the chlorophyll capacitance. Then at low frequency, measure R according to the variation of light intensity. Chlorophyll fluorescence is generally used to study chlorophyll pigment solution; but it does not directly show us the electrical activity that occurs as the proposed method. Findings: Our study has shown that electric behavior of synthetic solution of pigment depends of the solution concentration. There is a consensus between the behavior of synthetic chlorophyll and the existing behavior of natural pigments for some concentrations; for example, for 5.1 g/L and 10.2 g/L the extra-chlorophyll resistance of the synthetic pigments, just like that of the natural pigments, decreases according to the intensity of light until it reaches a certain threshold. On the other hand, for concentrations of 4.25 g/L and 2.55 g/L we observe a different electric behavior. Moreover, it is noted that for concentrations reproducing the same electric behavior as for the natural pigments, the decrease of extra chlorophyll resistance is all the more marked that the concentration is high. These results are helpful because we can directly have the electrical behavior of chlorophyll than fluorescence, where we need first to determine parameters like: primary fluorescence (F0), maximal fluorescence (Fm), variable fluorescence (Fv), the photochemical quantic yield (ΦPSII ) of the photosystem II and the assimilation quantic yield of CO2 (ΦCO2 ) before having an information about the electrical behavior of chlorophyll. Application/Improvements: This method of study can be applied in phototherapy about drugs made from chlorophyll to avoid side effects of chlorophyll solution. Keywords: Electrical Impedance, Electrical Resistance, Photosynthesis, Synthetic Chlorophyll, T.E Model

ANÁLISE DA INFLUÊNCIA LUMINOSA NOS ASPECTOS ANATÔMICOS DE FOLHAS DE&lt;i&gt; Theobroma speciosum &lt;/i&gt;WILLD EX SPRENG. (MALVACEAE)

O conhecimento anatômico de espécies do gênero Theobroma é importante para o estabelecimento e manutenção de coleções de germoplasma, tendo em vista estudos agronômicos e fitopatológicos e programas de melhoramento genético. Este estudo objetivou caracterizar a anatomia das folhas de Theobroma speciosum, registrando as diferenças estruturais observadas entre folhas de sol e folhas de sombra. Folhas de indivíduos de Theobroma speciosum foram coletadas no Parque Nacional do Juruena e em pastagens na zona rural do município de Alta Floresta – MT. Foram analisados a espessura do mesofilo foliar, dos parênquimas paliçádico e lacunoso, da nervura mediana e do feixe vascular. A análise de agrupamento foi realizada utilizando o método Hierárquico UPGMA, com base na distância euclidiana média padronizada. Foram observados tricomas glandulares do tipo claviforme e estrelados sésseis. A epiderme é unisseriada, o mesofilo é dorsiventral, entretanto os parênquimas são pouco distintos. Feixes vasculares colaterais estão dispersos no mesofilo, formando bainhas que se estendem até as epidermes. A nervura central, em secção transversal, possui formato biconvexo, com sistema vascular fechado envolto por bainha esclerenquimática. A constituição do mesofilo das folhas variou com o ambiente. Plantas expostas a pleno sol apresentam células mais alongadas no parênquima paliçádico, parênquima lacunoso com mais camadas e maior quantidade de tricomas, enquanto que as folhas de sombra apresentaram células com muitos espaços intercelulares no mesofilo. O dendrograma mostrou a formação de dois grupos distintos: o grupo I composto pelas plantas do Parque e o grupo II pelas plantas das pastagens. Tal agrupamento demonstrou alterações anatômicas significativas ocasionadas pelas variações da intensidade luminosa sobre as folhas, o que evidenciou grande capacidade adaptativa de Theobroma speciosum.

USING ENVIRONMENTAL LIGHT THERAPY TO IMPROVE SLEEP AND NEUROPSYCHIATRIC SYMPTOMS IN DEMENTIA

Introduction: Alzheimer’s disease and related syndromes (AD) is a disease affecting memory but also the relationship with the environment and empower people. No study has shown proven efficacy on the behavior of patients with AD. The main objective of the study was to assess the influence of environmental light therapy on sleep. Secondary objectives were the study of, anxiety by the COVI scale and behavioral disorders by the NPI scale. Material and Method: 12 residents of a nursing home with an integrated light therapy in common areas were studied., residents was equipped with a actimeter wrist or ankle for 42 days divided into three periods of 14 days with a standard lightin period 1 and 3 and light therapy on period 2. Sleep time was estimated by two algorithms. Results: Average age was 84.2 (SD 6.5).Total sleep time during period 2 was significantly increased with 55.1 minutes compared to the period 1 without significant difference between period 2 and 3. For the COVI scale there was a significant decrease of 0,7 point and the NPI scale decrease of 4.7 points significantly between period 1 and 2. For the 2 scales there were no difference between the period 2 and 3. Conclusion: The originality of this work was not to use a light intensity variation but a color light variation. We reached to show a improvement on sleep and behaviour.

Photoresponsive Smart Coloration Electrochromic Supercapacitor.

Electrochromic devices have been widely adopted in energy saving applications by taking advantage of the electrode coloration, but it is critical to develop a new electrochromic device that can undergo smart coloration and can have a wide spectrum in transmittance in response to input light intensity while also functioning as a rechargeable energy storage system. In this study, a photoresponsive electrochromic supercapacitor based on cellulose-nanofiber/Ag-nanowire/reduced-graphene-oxide/WO3 -composite electrode that is capable of undergoing "smart" reversible coloration while simultaneously functioning as a reliable energy-storage device is developed. The fabricated device exhibits a high coloration efficiency of 64.8 cm2 C-1 and electrochemical performance with specific capacitance of 406.0 F g-1 , energy/power densities of 40.6-47.8 Wh kg-1 and 6.8-16.9 kW kg-1 . The electrochromic supercapacitor exhibits excellent cycle reliability, where 75.0% and 94.1% of its coloration efficiency and electrochemical performance is retained, respectively, beyond 10 000 charge-discharge cycles. Cyclic fatigue tests show that the developed device is mechanically durable and suitable for wearable electronics applications. The smart electrochromic supercapacitor system is then integrated with a solar sensor to enable photoresponsive coloration where the transmittance changes in response to varying light intensity.

Effect of fan induced photoperiod on live performance and yield of male broiler chickens

Increasing broiler house size and ventilation capacity has resulted in increased light ingress through ventilation system components. Light ingress may alter the effective photoperiod for broiler chickens and create local increases in light intensity. This study examined live performance and processing yields in male broilers reared to 63 d of age exposed to either a constant light intensity of 2.5 lx for 18L:6D or a variable light intensity to mimic light ingress through tunnel fans. Body weight, body weight gain, and mortality were not different between treatments. Feed conversion ratio and feed consumption were significantly increased for the variable light treatment, with a difference of 0.06 g feed:g gain (P = 0.01) and 228 g/bird (P = 0.02), respectively. The data herein illustrate the need to mitigate light ingress through ventilation system components to improve live performance in broilers.