Weak Light Conditions Research Articles

Shadow-free single-pixel imaging

Single-pixel imaging is an innovative imaging scheme and receives increasing attention in recent years, for it is applicable for imaging at non-visible wavelengths and imaging under weak light conditions. However, as in conventional imaging, shadows would likely occur in single-pixel imaging and sometimes bring negative effects in practical uses. In this paper, the principle of shadows occurrence in single-pixel imaging is analyzed, following which a technique for shadows removal is proposed. In the proposed technique, several single-pixel detectors are used to detect the backscattered light at different locations so that the shadows in the reconstructed images corresponding to each detector shadows are complementary. Shadow-free reconstruction can be derived by fusing the shadow-complementary images using maximum selection rule. To deal with the problem of intensity mismatch in image fusion, we put forward a simple calibration. As experimentally demonstrated, the technique is able to reconstruct monochromatic and full-color shadow-free images.

Effects of acidified seawater on calcification, photosynthetic efficiencies and the recovery processes from strong light exposure in the coral Stylophora pistillata

The aim of this study was to investigate whether coral photosynthetic efficiencies and recovery processes are affected by CO2-driven ocean acidification in symbiont photosynthesis and coral calcification. We investigated the effects of five CO2 partial pressure (pCO2) levels in adjusted seawater ranging from 300 μatm (pre-industrial) to 800 μatm (near-future) and strong and weak light intensity on maximum photosynthetic efficiency and calcification of a branching coral, Stylophora pistillata, as this species has often been used in rearing experiments to investigate the effects of acidified seawater on calcification and photosynthetic algae of corals. We found that, the photosynthetic efficiencies and recovery patterns under different light conditions did not differ among pCO2 treatments. Furthermore, calcification of S. pistillata was not affected by acidified seawater under weak or strong light conditions. Our results indicate that the photosynthetic efficiency and calcification of S. pistillata are insensitive to changes in ocean acidity.

Omnidirectional Harvesting of Weak Light Using a Graphene Quantum Dot-Modified Organic/Silicon Hybrid Device.

Despite great improvements in traditional inorganic photodetectors and photovoltaics, more progress is needed in the detection/collection of light at low-level conditions. Traditional photodetectors tend to suffer from high noise when operated at room temperature; therefore, these devices require additional cooling systems to detect weak or dim light. Conventional solar cells also face the challenge of poor light-harvesting capabilities in hazy or cloudy weather. The real world features such varying levels of light, which makes it important to develop strategies that allow optical devices to function when conditions are less than optimal. In this work, we report an organic/inorganic hybrid device that consists of graphene quantum dot-modified poly(3,4-ethylenedioxythiophene) polystyrenesulfonate spin-coated on Si for the detection/harvest of weak light. The hybrid configuration provides the device with high responsivity and detectability, omnidirectional light trapping, and fast operation speed. To demonstrate the potential of this hybrid device in real world applications, we measured near-infrared light scattered through human tissue to demonstrate noninvasive oximetric photodetection as well as characterized the device's photovoltaic properties in outdoor (i.e., weather-dependent) and indoor weak light conditions. This organic/inorganic device configuration demonstrates a promising strategy for developing future high-performance low-light compatible photodetectors and photovoltaics.

Color Scheme Adaptation to Enhance User Experience on Smartphone Displays Leveraging Ambient Light

With the rapid development of information technology, mobile devices have exhibited increasing popularity in recent years. To support the anytime-anywhere service model of mobile devices, one important problem related to the screen display arises when using these devices (e.g., smartphone and tablet) under various lighting conditions. On one hand, it is hard for users to see the display clearly under strong lighting conditions (e.g., sunlight). On the other hand, the screen appears dazzling under weak lighting conditions. This problem related to the mobile device display can significantly degrade user experience and undermine the successful deployment of the anytime-anywhere mobile service model. Existing solutions mainly focus on the automatic adjustment of brightness level under different light conditions. We show that merely utilizing brightness level to solve the display problem is not enough to maintain the user experience under both strong and weak lighting scenarios through experimenting with over 200 volunteers. In this work, we take a different approach by investigating automatic color scheme adjustment to improve user experience. We find that Readability, Comfort level, and Similarity are major factors that contribute to user experience. In recognizing these problems, we propose a system, ColorVert, which utilizes the DKL color space to adaptively transform color schemes by sensing ambient light to improve user experience under various lighting scenarios. Our experimental evaluation with over 200 precipitants and various mobile devices demonstrates that ColorVert is more effective in both maintaining as well as improving user experience compared with the existing automatic brightness adjustment system.

Ferns, mosses and liverworts as model systems for light-mediated chloroplast movements.

Light-induced chloroplast movement is found in most plant species, including algae and land plants. In land plants with multiple small chloroplasts, under weak light conditions, the chloroplasts move towards the light and accumulate on the periclinal cell walls to efficiently perceive light for photosynthesis (the accumulation response). Under strong light conditions, chloroplasts escape from light to avoid photodamage (the avoidance response). In most plant species, blue light induces chloroplast movement, and phototropin receptor kinases are the blue light receptors. Molecular mechanisms for photoreceptors, signal transduction and chloroplast motility systems are being studied using the model plant Arabidopsis thaliana. However, to further understand the molecular mechanisms and evolutionary history of chloroplast movement in green plants, analyses using other plant systems are required. Here, we review recent works on chloroplast movement in green algae, liverwort, mosses and ferns that provide new insights on chloroplast movement.

Involvement of STH7 in light-adapted development in Arabidopsis thaliana promoted by both strigolactone and karrikin.

Strigolactones (SLs) and karrikins (KARs) regulate photomorphogenesis. GR24, a synthetic SL and KAR1, a KAR, inhibit the hypocotyl elongation of Arabidopsis thaliana in a weak light. GR24 and KAR1 up-regulate the expression of STH7, encoding a transcription factor belonging to the double B-box zinc finger subfamily. In this study, we used STH7-overexpressing (STH7ox) lines and functionally defective STH7 (STH7-SRDX) mutants to investigate roles of SLs and KARs in photomorphogenesis of Arabidopsis. Hypocotyl elongation of STH7-SRDX mutants was less sensitive to both GR24 and KAR1 treatment than that of wild-type Arabidopsis under weak light conditions. Furthermore, the chlorophyll and anthocyanin content was increased in STH7ox lines when de-etiolated with light and GR24-treated plants had enhanced anthocyanin production. GR24 and KAR1 treatment significantly increased the expression level of photosynthesis-related genes LHCB1 and rbcS. The results strongly suggest that SL and KAR induce photomorphogenesis of Arabidopsis in an STH7-dependent manner.

Synthesis of a nano-sized hybrid C3N4/TiO2 sample for enhanced and steady solar energy absorption and utilization

A sub-15 nm C3N4/TiO2 heterojunction is reported for the steady and constant photocatalytic hydrogen evolution under weak and strong incident light conditions.

The role of 24-epibrassinolide in the regulation of photosynthetic characteristics and nitrogen metabolism of tomato seedlings under a combined low temperature and weak light stress

In the present study, we aimed to investigate the effects of exogenous 24-epibrassinolide (EBR) on growth, photosynthetic characteristics, chlorophyll fluorescence imaging, and nitrogen metabolism of tomato leaves under low temperature and weak light conditions. The results showed that foliar application of EBR significantly alleviated the inhibition of plant growth, and increased the fresh and dry weights of tomato plants under a combined low temperature and weak light stress. Moreover, EBR also increased the net photosynthetic rate (Pn), light saturation point (LSP), maximal quantum yield of PSII photochemistry (Fv/Fm), actual photochemical efficiency of PSII (ФPSII), and photochemical quenching coefficient (qP), but decreased the intercellular CO2 concentration (Ci), light compensation point (LCP) and apparent quantum efficiency (AQE) under low temperature and weak light conditions. In addition, application of EBR to tomato leaves significantly enhanced the activities of nitrate reductase (NR), glutamate dehydrogenase (GDH), glutamine synthetase (GS), and glutamate synthase (GOGAT), but decreased the ammonium content and nitrite reductase (NiR) activity. We observed that EBR remarkably increased the contents of aspartic acid, threonine, serine, glycine, and phenylalanine, while decreasing the accumulation of cysteine, methionine, arginine, and proline under a combined low temperature and light stress. These results suggest that EBR could alleviate the combined stress-induced harmful effects on photosynthesis and nitrogen metabolism, thus leading to improved plant growth.

Compressive microscopic imaging with “positive–negative” light modulation

An experiment on compressive microscopic imaging with single-pixel detector and single-arm has been performed on the basis of “positive–negative” (differential) light modulation of a digital micromirror device (DMD). A magnified image of micron-sized objects illuminated by the microscope's own incandescent lamp has been successfully acquired. The image quality is improved by one more orders of magnitude compared with that obtained by conventional single-pixel imaging scheme with normal modulation using the same sampling rate, and moreover, the system is robust against the instability of light source and may be applied to very weak light condition. Its nature and the analysis of noise sources is discussed deeply. The realization of this technique represents a big step to the practical applications of compressive microscopic imaging in the fields of biology and materials science.

Grouping by bulk resistivity of production-line mono-crystalline silicon wafers and its influence on the manufacturing of solar cells modules

Weak light performance of crystalline silicon solar module presents a clear dependence on the type of cell used, mainly wafer resistivity and shunt resistance. This paper shows that a proper wafer and cell classification can provide a further optimization opportunity. This means a well-controlled product fabrication and production line yield improvement without an additional cost. For these reasons a resistivity boron-doped Czochralski silicon (Cz–Si) wafer classification has been implemented as the first stage of a photovoltaic monocrystalline silicon solar cell production line which allows to process solar device batches with similar raw material properties. This new production stage leads to a narrower solar cell efficiency distribution and a tailored power photovoltaic module fabrication. After that, solar cell devices have been sorted by shunt resistance criterion. Their behaviors under weak light conditions have been carefully studied at cell and module levels. Finally, one and two diode models have been used to justify the obtained results.

Pathogenicity of Fusarium solani associated with a bark beetle, Scolytogenes birosimensis, to Pittosporum tobira

Pittosporum tobira seedlings were inoculated with Fusarium solani isolated from Scolytogenes birosimensis, a bark beetle that infects P. tobira. The fungus produced necrotic lesions in the phloem and a discolored zone in the sapwood. Seedlings inoculated with the fungus and grown under weak light conditions were killed within 12–30 days after inoculation. Isolates from both S. birosimensis, which has caused P. tobira decline in Aichi and Fukuoka prefectures, and from the beetle under endemic conditions in Ibaraki Prefecture were both pathogenic to P. tobira.

Responses of the Hybrid between Sphagneticola trilobata and Sphagneticola calendulacea to Low Temperature and Weak Light Characteristic in South China.

Hybridization between exotic and native species is of great interest to evolutionary biologists and ecologists because it usually shows a quick evolution of species and invasiveness. It has been reported that such hybridization frequently increases the adaptation and aggressiveness of the new hybrids. A hybrid between invasive Sphagneticola trilobata and its native congener S. calendulacea was recently found in subtropical China. S. calendulacea has a significantly higher tolerance to low temperature and weak light stress than S. trilobata, and its range includes both tropical and temperate regions. This study examined how the tolerance of the new hybrid to low temperature and weak light conditions (LTWL), expanded its geographical range. All changes of phenotype, gas exchange parameters, chlorophyll fluorescence parameters, contents of malonaldehyde (MDA) and activity of superoxide dismutase (SOD) and peroxidase (POD) indicated that hybridization slightly catalyzed the tolerance of the hybrid to LTWL condition and the responses of the hybrid were more similar with their invasive parent. The results demonstrate that the current hybrid populations may not expand their geographical distribution ranges in a short period, but the distribution of the backcrossed generations is still uncertain. The threat of the hybrid to its native parent in subtropical region should be concerned.

Solution processed flexible hybrid cell for concurrently scavenging solar and mechanical energies

Flexible device that can harvest renewable energy from environment is urgently needed nowadays. A satisfactory device should be able to harvest multi-type energies around the clock without any economic difficulties for mass production. Here we report an all solution processed flexible hybrid cell by integrating an organic solar cell and triboelectric nanogenerator into a thin film, which is capable to convert both of the solar and mechanical energies into electric power independently or simultaneously, the generated energy can be used either to charge an energy storage unit or as a primary energy source for wearable self-powered devices even in the weak light conditions. This work provides a feasible and scalable method to fabricate the hybrid energy devices within reasonable cost to overcome the environmental restrictions of the devices that the mode of harvest single energy form.

Preparation of desiccation-resistant aquatic-living Nostoc flagelliforme (Cyanophyceae) for potential ecological application.

Nostoc flagelliforme is a terrestrial edible cyanobacterium that grows in arid and semi-arid steppes. The continued over-exploitation in the last century has led to a sharp decline of this resource and a severe deterioration of the steppe ecology. Liquid-cultured N. flagelliforme serves as promising algal ‘seeds’ for resource restoration. In this study, macroscopic (or visible) aquatic-living colonies (MaACs) of N. flagelliforme were developed under weak light and high nitrogen conditions. In a 24 day shake-flask culture, MaACs were propagated by about 4.5-fold in biomass without loss of their macro-morphology; at the same time, the addition of weak UV-B treatment resulted in slightly bigger MaACs. Polyvinylpyrrolidone (PVP) k30, a water-soluble polymer, was used to generate the coating around MaACs, and after full desiccation, the coated MaACs could recover their photosynthetic physiological activity when rehydrated, with 4% PVP k30 for coating being most effective. In contrast, PVP k30-coated microscopic aquatic-living colonies of N. flagelliforme and non-coated MaACs showed no resistance to full desiccation. The macroscopic morphology or structure of MaACs should be crucial for the formation of protection by PVP k30 coating. PVP k30-coated MaACs were more approaching to actual application for resource restoration.

Low irradiance loss quantification in c-Si panels for photovoltaic systems

Performance of bulk Si based solar photovoltaic (PV) panels deteriorate in weak light conditions. This generally affects the efficiency of associated power electronic components and compounds the overall loss in the yield of a PV system. It is, therefore, imperative to carefully plan the PV sizing and quantify this inherent loss in the efficiency of PV panels. In this work, the impact of varying solar irradiation on the efficiency of crystalline Si based solar panels has been quantified through a novel mathematical formulation, which models the deterioration in performance based on actual insolation and temperature profiles. This loss phenomenon is attributed mainly to a reduction in open circuit voltage and fill factor of a panel which in turn lowers the conversion efficiency. An empirical relationship is also derived which relates the loss in energy harvested to the actual peak-sunlight hours of a region. Results indicate that this low irradiance loss has approximately a linear dependence on equivalent peak sunlight hours (EPSH). For instance, the loss of 3.8%, 4%, 4.5% for Austin, Washington and Seattle was observed for EPSH of 4.4, 4, and 3.4, respectively. Moreover, the loss variation from one year to another for a region has been approximately constant. Finally, a comparison was performed for predicted energy harvested to the measured yield and a good fit has been observed between predicted and actual values.

Recruitment to forage of bumblebees in artificial low light is less impaired in light sensitive colonies, and not only determined by external morphological parameters

Bumblebees of Bombus terrestris are essential pollinators in natural and managed ecosystems. Their foraging ability relies on the individual morphology, task allocation within the colony, and external factors, such as light intensity. The foraging activities of commercial bumblebees can sometimes be impaired, especially in the artificial and weak light intensities of greenhouses at high altitudes. Here we investigated whether the eagerness (or willingness) to forage of bumblebee colonies in different light conditions is correlated with the light sensitivity of bumblebees colonies and/or different external morphological parameters. The initial foraging capacity of bumblebee colonies correlated with their light sensitivity. However, light sensitive bumblebee colonies did not necessarily had a higher foraging activity at lower light intensities. Differences in initial foraging capacity and light sensitivity among colonies could not be explained by the external morphological parameters. In conclusion, our data illustrated that the recruitment to forage in artificial low light is less impaired in light sensitive colonies, and that not only the external morphology parameters determine the light sensitivity of bumblebees and their eagerness to forage in weak light conditions. The data obtained here create a better understanding of which criteria are able to select towards light sensitive bumblebees and their link with the foraging capacity of these bumblebees.

Response of Osmotic Regulation Substance Content and Protective Enzyme Activities to Shading in Leaves of Different Rice Genotypes

Effects of shading at the flowering and grain filling stages on osmotic regulation substance content and protective enzyme activities in the leaves of different rice genotypes (e.g., IIyou 498, Gangyou 188, Dexiang 4103, Gangyou 527 and Chuanxiang 9838) were investigated. The results showed that the malondialdehyde content of Gangyou 188 significantly increased under shading, whereas those of IIyou 498, Dexiang 4103, Gangyou 527 and Chuanxiang 9838 showed no significant differences compared to the control. The soluble sugar content significantly decreased in IIyou 498, Gangyou 188, Dexiang 4103 and Chuanxiang 9838, whereas it did not significantly increase in Gangyou 527 under the weak light conditions (shading). Moreover, the soluble protein content in the leaves of different genotypes tended to decrease under shading. Further, the protective enzyme activities in the leaves varied in different rice genotypes under the shading treatment. Based on the osmotic regulation substance content and the protective enzyme activities in the leaves of different rice genotypes, it was concluded that Gangyou 188 and Gangyou 527 had strong abilities to adapt to the low light conditions. In addition, the mechanism of damage to rice leaves in different genotypes under shading was discussed.

NIGHT IMAGE ENHANCEMENT USING FUSION TECHNIQUE

Video surveillance is used in monitoring the road traffic. However because the surveillance system is limited by many objective factors. Surveillance video may not be seen clearly. Especially under the weak light conditions, the picture quality of the night video is very poor. In this paper, we propose an enhancement method of nighttime images for surveillance camera. We apply the moving target extraction technology and illumination estimation theory and combine the nighttime image with the daytime background by the image fusion. The proposed method recoveries scene information of the night video and highlights the details. The resultant images show the vehicles of the night time but surrounding is fused from the day image taken at day. In this, it is observed that the PSNR value is 65.9 dB is very high and MSE is 0.128 which is very low as compared with earlier reported night image enhancement technique [1]. Experimental results prove that our method is effective.

Effects of Irradiance Level on the Growth and Photosynthesis of Salvia

Seedlings of Salvia coccinea, S. splendens and S. viridis were grown at 100, 50, 25 and 5% of full sunlight level to determine the influence of irradiance level on their grown and photosynthesis. For all species the shoot length and dry weight of wholeplant were decreased at 25% sunlight, but there was little defference in them between at 50 and 100% sunlight. Total leaf area tended to increase at 50% sunlight in S. splendens and S. viridis and to decrease at 25% sunlight in S.coccinea. Leaf area ratio increased with decreasing light intensity in every species, and the degree of increase was the least in S.coccinea. With decreasing light intensity, leaves became thinner and the specific leaf weight decreased for all species. Chlorophyll content and photosynthetic rate more decreased at 25% than those at 100 and 50% sunlight in S. splendens and S. viridis. There were little differences both in the chlorophyll content and photosynthesis among these light intensities in S.coccinea. This indicates that S.coccinea has higher adaptability to low irradiance than other two species. Under weak light condition the stomatal conductance increased for all species. At 5% sunlight, the plant dry weight was less than about 90% of that of 100% sunlight and photosynthetic rate almost decreased to the light compensation point.

Assessment of weak light condition in parallel four-step phase-shifting digital holography

Minimum optical energy required for four-step parallel phase-shifting digital holography (PPSDH) is evaluated numerically by using photon-counting analysis. PPSDH enables us to develop instantaneous three-dimensional (3D) measurement by single-shot measurement. In fast measurement of dynamic 3D events, detected optical power at an image sensor will be decreased. For biomedical sensing, maximum light intensity exists for preventing the damage of the tissue. In the numerical evaluation, a photon-counting approach is used for the evaluation of minimum detected energy by comparing the reconstructed images. Numerical results indicate that hundreds of photons at each pixel in the image sensor are enough for the reconstruction and total detected energy in a multiplexed hologram is about 1 pJ.