Variation Of Light Intensity Research Articles

Leaf structural adaptations in vascular epiphytes from the Atlantic rainforest along phorophyte vertical stratification

Epiphytes are constantly exposed to light, water and nutrient stress, and thereby they frequently show anatomical adaptations in response to their habit. We aimed to investigate the variation in foliar anatomical traits of epiphytes along vertical stratification. We hypothesized that different species from varied groups would show a variation in foliar anatomical traits that would reflect the variation in microclimatic variables found across phorophyte strata. To address our hypothesis, we studied 23 vascular epiphyte species from different groups (ferns, magnoliids, monocots, and eudicots), occurring on ten phorophytes from a trail at an Atlantic Rainforest fragment in southeastern Brazil. We measured six microclimatic parameters at different phorophyte heights: light intensity, temperature, relative air humidity, altitude, evaporation rate, and wind speed. We then collected expanded-leaf samples for quantitative and descriptive anatomical evaluation, seeking to detect possible correlations between structural traits and microclimatic variations. We found that overall the analyzed species showed pronounced xeromorphic characters in response to epiphytic habit, such as thick outer periclinal wall of pavement cells, lignified epidermis, multiseriate epidermis, stomata below the level of pavement cells, water-storing tissues, and parenchymatous cells with wall thickenings, among others. In most epiphytes, we also found a trend for thicker mesophyll in plants exposed to higher light intensity along different phorophyte strata. The ecophysiological significance of these adaptations is discussed in detail. Our hypothesis was accepted, since we found that species from different groups showed a variation in foliar characters that reflected the variation found in microclimatic parameters along phorophyte strata. Some anatomical traits, e.g. thick mesophyll, were influenced by height differences along phorophytes and by the consequent variation in light intensity along vertical stratification, while other traits were directly related either to the epiphytic habit, especially to the water and nutrient deficits imposed by it, or to the taxonomic group, as seen in ferns.

Modeling and Numerical Studies of Three‐Dimensional Conically Shaped Microwells Using Non‐Uniform Photolithography

AbstractConical microwells have found a wide range of applications such as in cancer diagnostics, cell spheroid formation, and three‐dimensional oncology models. Numerous microengineered fabrication techniques have been developed for the formation of such conically shaped microwells. Among many, non‐uniform photolithography (NUPL) in a PDMS microfluidic channel with a glass substrate, can be used to create polymeric microwells with tapered‐bottom and parabolic curvatures. Here, the parabolic well formation of microwells is numerically investigated using NUPL to better understand its key mechanisms. Temporal and spatial free‐radical diffusion are incorporated into the modeling of photopolymerization. In addition, the 3D‐shape tuning ability of NUPL is modeled for the synthesis of microwells through a variation of UV light intensity induced by the presence of opaque materials. The model and simulation results predict the time‐evolution of microwell formation with parabolic well features. The effects of the conical shape‐tuning parameters are numerically determined, i.e., the aspect ratio of the well diameter to channel height and the non‐uniformity of UV light intensity on the microwell depth and parabolic curvature. Numerical work provides meaningful insights into NUPL to optimize and design polymeric microwells with shape features tuned to their application.

Beyond irradiance: Visual signals influencing mammalian circadian function.

Daily changes in ambient illumination act as important time of day cues which are pivotal for aligning internal circadian clocks to external time. Melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs), generally considered specialized for encoding light intensity (irradiance), are critical to this photoentrainment process. However, ipRGCs also convey information from conventional photoreceptor cells, the rods and cones. Here we review data from animal studies identifying the nature and roles of rod and cone signaling to the suprachiasmatic nucleus (SCN) circadian clock including evidence that visual features other than irradiance (color, spatiotemporal variations in light intensity) may influence photoentrainment or other SCN-dependent functions. Finally we consider the extent to which these findings from animal studies might similarly apply to human circadian function.

Dye Regeneration Kinetics of C343-Sensitized Nickel Oxide Investigated by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) feedback mode has been used to investigate kinetics of dye regeneration in DSSC. Organic dye C343 and CW1 are used as sensitizers for nickel oxide (NiO) photoelectrochemical cells. The influence of film thickness on dye regeneration kinetics in the films for NiO/C343 for six different films was investigated. SECM was used to analyze effective rate constant, keff and reduction rate kred, absorption cross section, Φhv for the dye regeneration process. The data reveal a significant variation of keff and kred with a variation of light intensity, sample thickness and dye difference. This research found remarkable dependence of the dye regeneration kinetic parameters on illumination flux, dye types and film thickness of electrode.

An Improved Approach to the Performance of Remote Photoplethysmography

Heart rate is an important metric for determining physical and mental health. In recent years, remote photoplethysmography (rPPG) has been widely used in characterizing physiological signals in human subjects. Currently, research on non-contact detection of heart rate mainly focuses on the capture and separation of spectral signals from video imagery. However, this method is very sensitive to the movement of the test subject and light intensity variation, and this results in motion artifacts which presents challenges in extracting accurate physiological signals such as heart rate. In this paper, an improved method for rPPG signal preprocessing is proposed. Based on the well known red green blue (RGB) color space, we segmented skin tone in different color spaces and extracted rPPG signals, after which we use a skin segmentation training model based on the luminance component, the blue-difference chroma components, and red-difference chroma components (YCbCr), as well as hue saturation intensity (HSI) color models. In the experimental verification section, we compare the robustness of the signal on different color spaces. In summary, we are experimentally verifying a better image pre-processing method based on real-time rPPG, which results in more precise measurements through the comparative analysis of skin segmentation and signal quality.

Evidence for reversible light-dependent transitions in the photosynthetic pigments of diatoms.

Marine diatoms contribute to oxygenic photosynthesis and carbon fixation and handle large changes under variable light intensity on a regular basis. The unique light-harvesting apparatus of diatoms are the fucoxanthin-chlorophyll a/c-binding proteins (FCPs). Here, we show the enhancement of chlorophyll a/c (Chl a/c), fucoxanthin (Fx), and diadinoxanthin (Dd) marker bands in the Raman spectra of the centric diatom T. pseudonana, which allows distinction of the pigment content in the cells grown under low- (LL) and high-light (HL) intensity at room temperature. Reversible LL-HL dependent conformations of Chl c, characteristic of two conformations of the porphyrin macrocycle, and the presence of five- and six-coordinated Chl a/c with weak axial ligands are observed in the Raman data. Under HL the energy transfer from Chl c to Chl a is reduced and that from the red-shifted Fxs is minimal. Therefore, Chl c and the blue-shifted Fxs are the only contributors to the energy transfer pathways under HL and the blue- to red-shifted Fxs energy transfer pathway characteristic of the LL is inactive. The results indicate that T. pseudonana can redirect its function from light harvesting to energy-quenching state, and reversibly to light-harvesting upon subsequent illumination to LL by reproducing the red-shifted Fxs and decrease the number of Dds. The LL to HL reversible transitions are accompanied by structural modifications of Chl a/c and the lack of the red-shifted Fxs.

Modeling and Sustainability Assessment of Outdoor Chlorella vulgaris Cultivation in South Korea for Renewable Bioplastic Feedstock Production

UTEX 2714 (Chlorella vulgaris) is cultivated outdoors in vertical bubble columns contained within a greenhouse to serve as a renewable blending bioplastic feedstock (BPFS). This application has potential advantages over traditional biofuels due to a simpler downstream process and higher marketability of the bioplastic product (> 1200 USD/ton). To assess sustainability for further scale-up and predict growth for varying seasonal conditions, mathematical modeling of growth kinetics was performed. Pilot plant data for parameter estimations were provided by the Pangyo LNG power plant complex. For early June 2021 during which the data was collected, algae productivity was 0.13 kg/m3/day, with the unit cost of production and specific carbon footprint being 2768 USD/ton and 1.33 ton CO2-eq/ton, respectively. Monthly average productivity dipped to 0.061 kg/m3/day in February and peaked at 0.16 kg/m3/day in early August. Seasonal variations in temperature and light intensity significantly influenced the economic viability and greenhouse gas emission reducibility of the BPFS process, which highlights the need to improve the accuracy of the growth prediction model and expand the risk assessment scope for guiding future R&D.

Evaluation of Power Maximization and Curtailment Control Methods for Converters in Wearable Photovoltaic Energy Harvesting Applications

As wearables become more widely adopted, powering them from ambient energy sources can improve reliability and reduce reliance on batteries. Solar photovoltaic (PV) power is a viable power source for such emerging applications. However, because wearable applications bend and move with the user&#x0027;s motion, the PV panels used in these applications experience varying light intensities over multiple PV cells that reduce power generation in traditional series-string configurations. To address the PV power reduction problem, a configuration of boost converters with parallel-connected outputs are utilized, which is effective in uneven lighting conditions. Depending on the load demand and available solar power, a converter control system should quickly transition between maximum power point tracking (MPPT) and power curtailment operation. This work evaluates MPPT (perturb &amp; observe and constant-voltage) algorithms and power curtailment (over-voltage shut-off and flexible power point tracking) methods on their effectiveness in wearable applications. Experimental results verify that the perturb &amp; observe with flexible power point tracking effectively adapts to changes in the load and light conditions while maintaining 30&#x0025; and 31&#x0025; higher output power, respectively. It also maintains the maximum component temperature below <inline-formula><tex-math notation="LaTeX">$29{}^{\circ }$</tex-math></inline-formula>C which is a safe temperature for wearable applications.

Deep Spatio-Temporal Illuminant Estimation Under Time-Varying AC Lights

Artificial lights, which are powered by alternating current (AC), are ubiquitous nowadays. The intensity of these lights fluctuates dynamically depending on the AC power. In contrast to previous color constancy methods that exploited the spatial color information, we propose a novel deep learning-based color constancy method that exploits the temporal variations exhibited by AC-powered lights. Using a high-speed camera, we capture the intensity variations of AC lights. Then, we use these variations as an important cue for illuminant learning. We propose a network composed of spatial and temporal branches to train the model with both spatial and temporal features. The spatial branch learns the conventional spatial features from a single image, whereas the temporal branch learns the temporal features of AC-induced light intensity variations in a high-speed video. The proposed method calculates the temporal correlation between the high-speed frames to extract the effective temporal features. The calculations are done at a low computational cost and the output is fed into the temporal branch to help the model concentrate on illuminant-attentive regions. By learning both spatial and temporal features, the proposed method performs remarkably under a complex illuminant environment in a real world scenario in which color constancy is difficult to investigate. The experimental results demonstrate that the proposed method produces lower angular error than the previous state-of-the-art by 30%, and works exceptionally well under various illuminants, including complex ambient light environments.

Reconstructing Clear Image for High-Speed Motion Scene With a Retina-Inspired Spike Camera

Conventional digital cameras typically accumulate all the photons within an exposure period to form a snapshot image. It requires the scene to be quite still during the imaging time, otherwise it would result in blurry image for the moving objects. Recently, a retina-inspired spike camera has been proposed and shown great potential for recording high-speed motion scenes. Instead of capturing the visual scene by a single snapshot, the spike camera records the dynamic light intensity variation continuously. Each pixel on spike camera sensor accumulates the incoming photons independently and persistently, which fires a spike and restarts the photon accumulation immediately once the dispatch threshold is reached, producing a continuous stream of spikes recorded at very high temporal resolution. To recover the dynamic scene from captured spike stream, this paper presents an image reconstruction approach for spike camera. In order to generate high-quality reconstruction, we investigate the temporal correlation along motion trajectories and exploit it via adaptive temporal filtering. In particular, we present a hierarchical motion-aligned temporal filtering scheme, combining short-term filtering with long-term filtering to take advantage of long-term temporal correlation with low model complexity. Experimental results demonstrate that the proposed scheme outperforms the existing schemes significantly, producing much better objective and subjective qualities for spike camera image reconstruction.

Video-Based Heart Rate Measurement Against Uneven Illuminations Using Multivariate Singular Spectrum Analysis

Spatially uneven illuminations are the dominant interference of video-based heart rate (HR) screening for cooperated subjects in a telehealth service. In this letter, a remote photoplethysmography (rPPG) method is introduced to stably extract pulsatile signals against uneven facial illuminations based on the multivariate singular spectrum analysis (MSSA). This method first divides the facial skins into multiple patches, where the hue channels resistant to light intensity variations are prepared from selected optimal patches. Considering the spatial correlations of heartbeats, the hue signals are then decomposed using the MSSA to reconstruct pulses. Finally, the HR is determined as the one with the highest ratio of energy around the dominant frequency from the first group of MSSA reconstructed signals. Experimental results demonstrate the effectiveness of the proposed method on the in-house BSIPL-rPPG database and the public COHFACE database, where the correlation coefficients of the estimated HRs achieve 0.95 and 0.98, respectively, outperforming those of the comparison methods.

Cyclic Photoisomerization of Azobenzene in Atomistic Simulations: Modeling the Effect of Light on Columnar Aggregates of Azo Stars.

This computational study investigates the influence of light on supramolecular aggregates of three-arm azobenzene stars. Every star contains three azobenzene (azo) moieties, each able to undergo reversible photoisomerization. In solution, the azo stars build column-shaped supramolecular aggregates. Previous experimental works report severe morphological changes of these aggregates under UV–Vis light. However, the underlying molecular mechanisms are still debated. Here we aim to elucidate how light affects the structure and stability of the columnar stacks on the molecular scale. The system is investigated using fully atomistic molecular dynamics (MD) simulations. To implement the effects of light, we first developed a stochastic model of the cyclic photoisomerization of azobenzene. This model reproduces the collective photoisomerization kinetics of the azo stars in good agreement with theory and previous experiments. We then apply light of various intensities and wavelengths on an equilibrated columnar stack of azo stars in water. The simulations indicate that the aggregate does not break into separate fragments upon light irradiation. Instead, the stack develops defects in the form of molecular shifts and reorientations and, as a result, it eventually loses its columnar shape. The mechanism and driving forces behind this order–disorder structural transition are clarified based on the simulations. In the end, we provide a new interpretation of the experimentally observed morphological changes.

On the measurement accuracy of coherent Rayleigh-based distributed sensors

The phase change of back-scattered light due to external perturbations is retrieved in coherent Rayleigh-based distributed sensors by estimating the frequency shift (FS) between the traces of different measurements. The uncertainty associated with the estimator, due to the presence of system noises, can lead to an inaccurate evaluation of the FS. Additionally, in coherent Rayleigh-based sensors, the calculation of the signal-to-noise ratio (SNR) from the jagged back-scattered intensity trace using the statistical estimators can cause an erroneous determination of the absolute value of the SNR. In this work, a method to accurately evaluate the non-uniform SNR caused by the stochastic variation of the back-scattered light intensity along the fibre is presented and validated. Furthermore, an analytical expression to evaluate the uncertainty in the FS estimation using one of the standard estimators, namely cross-correlation, is presented. A direct-detection frequency-scanned phase-sensitive optical time-domain reflectometer (φ-OTDR) is employed for the experimental verification of the expression as a function of two crucial system parameters: the SNR and the spatial resolution. The performance of various distributed sensing system configurations utilising cross-correlation for determining the FS occurring due to the external perturbations can be properly predicted hereafter with the aid of the analytical expression presented in this study.

Optimal Light Source Intensity Setting in Endoscopic Ear Surgery

Hypothesis: Higher light intensity settings do not yield improved image quality in endoscopic ear surgery. Background: Light intensity is a parameter with major impact on the quality of digital images. For ear surgery, light produces heat associated with a thermal risk to ear structures and the light source setting should be accordingly optimized. Methods: Several series of still images were acquired during live middle ear surgery, using cadaveric and plastic temporal bone models and with three-dimensional printed models. Images obtained under varying light intensities were compared with the image acquired at maximum intensity of a light emitting diode light source. We analyzed digital image brightness and noise using quantitative methods. Results: Our measurements revealed significantly decreased image brightness with light intensities set below 20% with an increase in noise at light intensities lower than 30%. Conclusion: The optimal light source setting corresponded to 30% intensity in our experimental set-up. Special attention should be given to those cases where faster image quality degradation is expected (dark or bloody scenes or larger cavities). The results were strongly dependent on the equipment used. The methods described in this study can serve as a general guide for determining the optimal light source setting in any specific set-up.

Discrepancy in photosynthetic responses of the red alga Pyropia yezoensis to dehydration stresses under exposure to desiccation, high salinity, and high mannitol concentration

Macroalgae that inhabit intertidal zones are exposed to the air for several hours during low tide and must endure desiccation and high variations in temperature, light intensity, and salinity. Pyropia yezoensis (Rhodophyta, Bangiales), a typical intertidal red macroalga that is commercially cultivated in the northwestern Pacific Ocean, was investigated under different dehydration stresses of desiccation, high salinity, and high mannitol concentration. Using chlorophyll fluorescence imaging, photosynthetic activities of P. yezoensis thalli were analyzed using six parameters derived from quenching curves and rapid light curves. A distinct discrepancy was revealed in photosynthetic responses to different dehydration stresses. Dehydration caused by exposure to air resulted in rapid decreases in photosynthetic activities, which were always lower than two other stresses at the same water loss (WL) level. High salinity only reduced photosynthesis significantly at its maximum WL of 40% but maintained a relatively stable maximum quantum yield of photosystem II (PSII) (Fv/Fm). High mannitol concentration induced maximum WL of 20% for a longer time (60 min) than the other two treatments and caused no adverse influences on the six parameters at different WL except for a significant decrease in non-photochemical quenching (NPQ) at 20% WL. Illustrated by chlorophyll fluorescence images, severe spatial heterogeneities were induced by desiccation with lower values in the upper parts than the middle or basal parts of the thalli. The NPQ and rETRmax (maximum relative electron transport rate) demonstrated clear distinctions for evaluating photosynthetic responses, indicating their sensitivity and applicability. The findings of this study indicated that the natural dehydration of exposure to air results in stronger and more heterogeneous effects than those of high salinity or high mannitol concentration.

Light intensity distribution in images from rigid endoscopes used in minimal access sinus surgery.

Objectives/HypothesisTo investigate the pattern of intensity levels in images generated by the two most commonly used rigid endoscopes angulations in sinus surgery: 0° and 30°.MethodsAn enclosed light box containing an optical square grid, under endoscope illumination set just below saturation level, was used for measuring light distribution levels across test images. Endoscopes with 0° and 30° angulations were tested at 10 mm from the grid, typical for sinus surgery. The grid was set perpendicular to the axis of the shaft of the endoscope. The grayscale light intensity (GLI) levels (0 = black, 255 = white) in each of the grid squares were quantified from the digitized images.ResultsLight intensity was highly non‐uniform for both endoscopes. The brightest area of the field of view was at the center for the 0° endoscope and at about 20% of the image diameter proximally from the center for the 30° endoscope. For the 0° endoscope with a maximum value of about 230 GLI (90% of white saturation) at the center the minimum value was about 100 GLI at the periphery. The 30° endoscope with a similar maximum GLI value of 226 had a minimum of under 50 GLI at the most distant periphery, too dark for clear grid line definition.ConclusionThere are wide variations in light intensity across the image circle and much reduced illumination of the field edge. Surgeons should be aware of this fact so that accommodation can be made when surgical manipulation is performed away from the center of the endoscope field. This is especially relevant in angled cavities such as the frontal sinus recess, where the degree of angulation necessitates “edge of field” surgery.

The moderating role of population succession in the adaptive responses of Synechococcus assemblages: evidence from light intensity simulation experiment

Synechococcus is one of the most abundant photoautotrophic picoplankton in the marine ecosystem. However, it is not clear how Synechococcus assemblages respond to light intensity variation in a genus group. Here, enriched Synechococcus assemblages from in situ coastal seawater were subjected to light intensity simulation experiments in a range of 9-243 &mu;mol(photon) m-2 s-1. Characteristics concerning physiology, genomics, and metatranscriptomics were analyzed. Physiologically, the fitting model predicted photosynthesis indications and pigment contents increased with different trends following the light intensity. Genomic sequencing demonstrated that both the phylogenetic and phenotypic compositions of Synechococcus assemblage exhibited population succession. Especially, the proportion of Synechococcus pigment type 2 was changed significantly. In metatranscriptomics, most genes were downregulated in the high-light intensity group, while photosynthesis-related genes were entirely upregulated. The high upregulation of photosynthesis-related genes, such as psbO, psbA, apcB, and cpcB, corresponded to the succession of Synechococcus genotype and was responsible for the physiological shift in response to light intensity.

Regulation of carbon source metabolism in mixotrophic microalgae cultivation in response to light intensity variation

Microalgae are one of the promising sources for renewable energy production, and the light intensity variation can affect the biofuel generation and carbon assimilation of mixotrophic microalgae. To reveal the response of carbon assimilation to light intensity, the effect of light intensity on the carbon source metabolism of Chlorella vulgaris under mixotrophic cultivation was investigated in this study. Moreover, the optimal carbon source composition for mixotrophic microalgae cultivation was evaluated using bicarbonate (HCO3−) and carbonate (CO32−) as inorganic carbon sources, and glucose and acetate as organic carbon sources. The optimal light intensity for Chlorella vulgaris growth was at the range of 8000–12000 lux. For the accumulation of biochemical components, low light intensity was beneficial to protein accumulation, and high light intensity was advantageous for carbohydrate and lipid accumulation. With HCO3− and glucose, the maximum lipid content reached 37.0% at a light intensity of 12000 lux. The citrate synthase activity was negatively correlated with light intensity, showing an opposite trend to biomass production. High light intensity had a positive impact on Rubisco expression, which promoted the microalgae growth and carbon fixing. The energy produced by heterotrophic metabolic activities increased at low light intensity, and the enhancement of biomass production with high light intensity was mainly caused by the improved photoreaction efficiency during the mixotrophic cultivation.

Photo tuned electron field emission from vertically aligned CH3NH3PbI3 nanorods grown in AAO template

Among the several untapped aspects of CH3NH3PbI3 i.e. Methylammonium lead iodide perovskite, electron field emission is an important one. Motivated by the scarcity of reports available in this segment, this work carries out a detail investigation of the field emission properties of vertically aligned CH3NH3PbI3 nanorods (NRs) grown within AAO (Anodic aluminum oxide) template. The emission produced considerable current density of 187 μA/cm2 with turn on field 3.4 V/μm and enhancement factor 5500. Accompanied by the simulation results of local electric field distribution, examination of incident photons impact upon emission behaviour under varying light intensities revealed enhanced electron emission under increased light intensities due to improved number of photo-excited carriers.

Computational Analysis of Alternative Photosynthetic Electron Flows Linked With Oxidative Stress.

During photosynthesis, organisms respond to their energy demand and ensure the supply of energy and redox equivalents that sustain metabolism. Hence, the photosynthetic apparatus can, and in fact should, be treated as an integrated supply-demand system. Any imbalance in the energy produced and consumed can lead to adverse reactions, such as the production of reactive oxygen species (ROS). Reaction centres of both photosystems are known sites of ROS production. Here, we investigate in particular the central role of Photosystem I (PSI) in this tightly regulated system. Using a computational approach we have expanded a previously published mechanistic model of C3 photosynthesis by including ROS producing and scavenging reactions around PSI. These include two water to water reactions mediated by Plastid terminal oxidase (PTOX) and Mehler and the ascorbate-glutathione (ASC-GSH) cycle, as a main non-enzymatic antioxidant. We have used this model to predict flux distributions through alternative electron pathways under various environmental stress conditions by systematically varying light intensity and enzymatic activity of key reactions. In particular, we studied the link between ROS formation and activation of pathways around PSI as potential scavenging mechanisms. This work shines light on the role of alternative electron pathways in photosynthetic acclimation and investigates the effect of environmental perturbations on PSI activity in the context of metabolic productivity.