Light Intensity Fluctuations Research Articles

Improved temperature stability of a fiber Sagnac-like detection system for atomic magnetometers.

A novel fiber Sagnac-like detection system has unique competitive advantages for detecting atomic spin precession in atomic magnetometers. Unfortunately, its operating stability is severely limited by temperature fluctuations. In this paper, we describe a new approach to improve the temperature stability by using the ratio signal as the output instead of the conventional fundamental component. This method can effectively counteract the temperature-caused fluctuations in both light intensity and scale factor of photodetector. For a temperature range from 20°C to 40°C, a relative fluctuation of the ratio output signal of 0.97% was achieved, which was 17.4 times better than the fundamental component output. Moreover, no additional equipment and complex compensation algorithms are required during this process. It is a generic method that can also be applied to improve the stability of other detection schemes used in atomic magnetometers.

Photoprotective Acclimation of the Arabidopsis thaliana Leaf Proteome to Fluctuating Light.

Plants are subjected to strong fluctuations in light intensity in their natural growth environment, caused both by unpredictable changes due to weather conditions and movement of clouds and upper canopy leaves and predictable changes during day-night cycle. The mechanisms of long-term acclimation to fluctuating light (FL) are still not well understood. Here, we used quantitative mass spectrometry to investigate long-term acclimation of low light-grown Arabidopsis thaliana to a FL condition that induces mild photooxidative stress. On the third day of exposure to FL, young and mature leaves were harvested in the morning and at the end of day for proteome analysis using a stable isotope labeling approach. We identified 2,313 proteins, out of which 559 proteins exhibited significant changes in abundance in at least one of the four experimental groups (morning-young, morning-mature, end-of-day-young, end-of-day-mature). A core set of 49 proteins showed significant responses to FL in three or four experimental groups, which included enhanced accumulation of proteins involved in photoprotection, cyclic electron flow around photosystem I, photorespiration, and glycolysis, while specific glutathione transferases and proteins involved in translation and chlorophyll biosynthesis were reduced in abundance. In addition, we observed pathway- and protein-specific changes predominantly at the end of day, whereas few changes were observed exclusively in the morning. Comparison of the proteome data with the matching transcript data revealed gene- and protein-specific responses, with several chloroplast-localized proteins decreasing in abundance despite increased gene expression under FL. Together, our data shows moderate but widespread alterations of protein abundance during acclimation to FL and suggests an important role of post-transcriptional regulation of protein abundance.

An atypical short-chain dehydrogenase-reductase functions in the relaxation of photoprotective qH in Arabidopsis.

Photosynthetic organisms experience wide fluctuations in light intensity and regulate light harvesting accordingly to prevent damage from excess energy. The antenna quenching component qH is a sustained form of energy dissipation that protects the photosynthetic apparatus under stress conditions. This photoprotective mechanism requires the plastid lipocalin LCNP and is prevented by SUPPRESSOR OF QUENCHING1 (SOQ1) under non-stress conditions. However, the molecular mechanism of qH relaxation has yet to be resolved. Here, we isolated and characterized RELAXATION OF QH1 (ROQH1), an atypical short-chain dehydrogenase-reductase that functions as a qH-relaxation factor in Arabidopsis. The ROQH1 gene belongs to the GreenCut2 inventory specific to photosynthetic organisms, and the ROQH1 protein localizes to the chloroplast stroma lamellae membrane. After a cold and high-light treatment, qH does not relax in roqh1 mutants and qH does not occur in leaves overexpressing ROQH1. When the soq1 and roqh1 mutations are combined, qH can neither be prevented nor relaxed and soq1 roqh1 displays constitutive qH and light-limited growth. We propose that LCNP and ROQH1 perform dosage-dependent, antagonistic functions to protect the photosynthetic apparatus and maintain light-harvesting efficiency in plants.

PRELIMINARY STUDY OF COAL MINING RECLAMATION USING FOREST PLANTS IN BARITO EAST DISTRICT, CENTRAL KALIMANTAN PROVINCE

The problem of post-mining coal management through the reclamation of former mining land has become a national issue in Indonesia. One important thing is how to do land reclamation and restore the preservation of the natural environment. Reclamation characteristics are open space, high light intensity, high temperature and extreme fluctuation, low pH and degradation of the number of species both flora, fauna and soil microorganisms. Such characteristics cause not all types of plants can live on the land. Theoretically, the results of the suitability of forest plant cultivation land are specifically eucalyptus plants (Melaleuca leucadendra) and Sengon (Paraserianthes falcataria). This is necessary and important to be studied regarding the limiting factors and management efforts in the former coal mining land. This can provide information and thought contributions to maximize the reclamation activities of former coal mining using plants, which have a high enough sale value, are environmentally sound and sustainable while taking into account local wisdom.

Optimising photosynthesis for environmental fitness.

Optimisation of photosynthesis for environmental fitness is one of the most important approaches to increase productivity and acclimate plants to unfavourable environmental conditions. In this paper, the pathways of optimisation of photosynthesis are considered using novel tools both at the level of an individual plant and plant communities. Fast acclimation of photosynthetic apparatus to the environmental stresses and fluctuations of light intensity and light quality plays an important role in supporting effective photosynthesis. The bioengineered photosynthetic systems responsible for energy dissipation (non-photochemical quenching) and stomatal functioning, as well as some enzymes of CO2 fixation system alongside with introduction of effective mechanisms found in algae or cyanobacteria into chloroplasts, can be used for conservation of effective photosynthesis during such fluctuations. The conversion of some C3 crops grown in hot and arid climates into C4 plants may be a goal for the future. Special focus has been directed towards the detailed description of the photosynthetic optimisation under stress conditions taking into account the specifics of the most common stress factors.

Statistical Modeling of the Impact of Underwater Bubbles on an Optical Wireless Channel

In underwater wireless optical communications (UWOC), the random obstruction of light propagation by air bubbles can cause fluctuations in the incoming light intensity of a receiver. In this paper, we propose a statistical model for determining the received power by a receiver in the presence of air bubbles. First, based on real experiments of the behavior of air bubbles underwater, we propose statistical models for the generation, size, and horizontal distribution of each air bubble. Second, we mathematically derive the obstruction caused by the shadow of each bubble as it passes over the beam area. We then compute the combined obstruction of all generated air bubbles to determine the total obstructed power, which is a random variable due to the randomness of bubble behavior. Next, we find the first and second moments of the total obstructed power to model the statistical distribution of the obstructed received power by using the method of moments, which shows that the Weibull distribution suitably matches the simulation data. We also estimate the shape and scale parameters by using two derived moments. Furthermore, we also construct a statistical model of the received power with complete blockage in the presence of air bubbles and we derive the distribution of the composite channel model combining the proposed bubble-obstruction model with a Gamma-Gamma turbulence model. Finally, we obtain and verify the analytic forms of the average bit error rate and the capacity of UWOC systems under this newly proposed composite channel model.

Optimization for Scenedesmus obliquus Cultivation: the Effects of Temperature, Light Intensity and pH on Growth and Biochemical Composition

Microalgae have been explored as potential host species for biofuel production. Environmental factors affect algal growth and cellular composition. The effects of several key environmental factors, such as temperature, light, and pH of the medium on the growth and biochemical composition of Scenedesmus obliquus were investigated in this study. The highest growth rate of microalgae was observed at an optimal temperature of 25℃, 150 μmol/(m2·s) light intensity, and pH 10.0. The biochemical composition analysis revealed that the carbohydrate content decreased at lower (20℃) or higher temperature (35℃), whereas the protein and lipid contents increase at these temperatures. The fluctuation of light intensity significantly affected the contents of protein, carbohydrate, and lipid. The protein levels varied greatly when the pH of the medium was below 7.0. The carbohydrate and lipid contents significantly increased at pH above 7.0.

Simulation of a nonphotochemical quenching in plant leaf under different light intensities

An analysis of photosynthetic response on action of stressors is an important problem, which can be solved by experimental and theoretical methods, including mathematical modeling of photosynthetic processes. The aim of our work was elaboration of a mathematical model, which simulated development of a nonphotochemical quenching under different light conditions. We analyzed two variants of the model: the first variant included a light-induced activation of the electron transport chain; in contrast, the second variant did not describe this activation. Both variants of the model described interactions between transitions from open reaction centers to closed ones (and vice versa) and development of the nonphotochemical quenching. Investigation of both variants of the model showed well qualitative and quantitative accordance between simulated and experimental changes in coefficient of the nophotochemical quenching which were analyzed under different light regimes: (i) the stepped increase of the light intensity without dark intervals between steps, (ii) periodical illuminations by different light intensities with constant durations which were separated by constant dark intervals, and (iii) periodical illuminations by the constant light intensity with different durations which were separated by different dark intervals. Thus, the model can be used for theoretical prediction of stress changes in photosynthesis under fluctuations in light intensity and search of optimal regimes of plant illumination.

Multidirectional edge detection based on gradient ghost imaging

Gradient ghost imaging (GGI) is a new imaging method that can directly obtain the edge information of an unknown object from the correlation of light intensity fluctuations. However, this technique faces the problems of poor directionality and continuity. In this paper, we propose a multidirectional gradient ghost imaging scheme (MGGI), where Kirsch operator with 8-directional masks is first used to generate structured illuminations, and then a fast algorithm based on the connection of the 8 masks is applied in the sampling process. Compared with GGI based on Sobel operator, both simulation and experimental results demonstrate that the proposed method has the advantages of imaging quality and edge continuity even in a noisy environment. Furthermore, the MGGI does not increase the imaging time and thus promotes the practical development of ghost imaging.

CFD analysis of a luminescent solar concentrator-based photomicroreactor (LSC-PM) with feedforward control applied to the synthesis of chemicals under fluctuating light intensity

The luminescent solar concentrator-based photomicroreactor (LSC-PM) is a novel technology applied to the synthesis of chemicals coupling the advantages of sunlight modulation/concentration and microflow chemistry. In this work, a virtual model of this device, based on computational fluid dynamics (CFD), was implemented. The CFD model was developed considering a kinetic law that takes into account the effect of light intensity on the reaction performance for the [4+2] cycloaddition of 9,10-diphenylanthracene, used as benchmark. Then, a feedforward control algorithm was implemented and the system's performance under different functional dependences of light intensity through time was investigated, being able to maintain the conversion at the desired level despite the power fluctuations. Thus, the CFD model was independently validated considering the control framework associated to the experimental data. Finally, the effect of varying some geometrical features of the photomicroreactor was investigated, highlighting the capability of using a computational model for engineering purposes (design and optimization). Therefore, this work represents a contribution toward a fully predictable model for the investigation of the performance and for the design and optimization of LSC-PMs in a variety of chemical processes.

Low drift nuclear spin gyroscope with probe light intensity error suppression**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFB0501600 and 2017YFB0503100) and the National Natural Science Foundation of China (Grant Nos. 61773043, 61673041, and 61721091).

A nuclear spin gyroscope based on an alkali-metal–noble-gas co-magnetometer operated in spin-exchange relaxation-free (SERF) regime is a promising atomic rotation sensor for its ultra-high fundamental sensitivity. However, the fluctuation of probe light intensity is one of the main technical error sources that limits the bias stability of the gyroscope. Here we propose a novel method to suppress the bias error induced by probe light intensity fluctuations. This method is based on the inherent magnetic field response characteristics of the gyroscope. By the application of a bias magnetic field, the gyroscope can be tuned to a working point where the output signal is insensitive to probe light intensity variation, referred to herein as ‘zero point’, thus the bias error induced by intensity fluctuations can be completely suppressed. The superiority of the method was verified on a K–Rb–21Ne co-magnetometer, and a bias stability of approximately 0.01 °/h was obtained. In addition, the method proposed here can remove the requirement of the closed-loop control of probe light intensity, thereby facilitating miniaturization of the gyroscope volume and improvement of reliability.

Scintillation of laser beams carrying orbital angular momentum propagating in a near-maritime environment

Laser beams carrying orbital angular momentum (OAM) were propagated in a near-maritime environment along an 890 meter link across the Severn River at the United States Naval Academy. The OAM beams were generated using green light ( λ=532nm) and etched spiral phase plates with different topological charges. The light intensity fluctuations of Gaussian and beams carrying OAM with topological charges of 1, 6, and 8 were measured and the scintillation indices of each beam were compared. Additionally, atmospheric turbulence was measured using a co-aligned scintillometer along the 890 meter propagation path. During testing, a wide range of atmospheric conditions occurred and the refractive index structure parameter measurements ranged from 5×10−14 down to 5×10−15 m −2∕3. Our measurements of transmitted voltage in the radial intensity across the maritime link, and calculated scintillation index, for the Gaussian beam and laser beams carrying OAM indicate a weak reduction in scintillation index for increasing topological charge. To reduce the measurement uncertainty and improve upon statistical significance of our findings, additional testing is needed.

Effects of Temperature, Light Intensity and DIF on Growth Characteristics in Platycodon grandiflorum

Bellflower (P. grandiflorum) has been an important medicinal plant since the ancient time. In the present study, we aimed to determine the effects of temperature, light intensity, and the difference between day and night temperature (DIF) on plant leaf and root morphology in P. grandiflorum. Plants were grown for five months in a Biotron room with a constant temperature (15, 20, 25, and 30°C) as well as natural light and shading condition. In the natural light, the lowest plant height (23.8 cm) was observed at 30°C compared than low-intensity light. Shading caused inhibition in the leaf length and leaf width compared than natural light condition. The number of branches decreased significantly (p≤0.05) under the low light intensity condition except for the temperature at 30°C. Root morphology was significantly affected by different levels of light intensity treatment in P. grandiflorum for. duplex. However, the highest root length (8.2 cm) and diameter (7.8 mm) was observed when the plants were grown under high light intensity. In P. grandiflorum with green petal, temperature and shading showed significant changes in plant morphology. However, the plant height under the natural light condition was in the range of 45.8~48.2 cm in the temperature range of 15~25°C. The negative DIF at 15/30°C decreased growth and development of both P. grandiflorum for. duplex and P. grandiflorum with green petals plants as reflected in the lowest plant height, leaf width, leaf length, number of branches, root length, root diameter, and root fresh weight. The present study concluded that the fluctuation of temperature and light intensity affects both leaf and root morphology, and the DIF has a significant influence on the growth and development of bellflower.

Disentangling the sites of non-photochemical quenching in vascular plants.

In nature, plants experience large fluctuations in light intensity and they need to balance the absorption and utilization of this energy accordingly. Non-photochemical quenching (NPQ) is a rapidly-switchable mechanism which protects plants from photodamage caused by high light exposure by dissipating the energy absorbed in excess as heat. It is triggered by the ΔpH across the thylakoid membrane and requires the presence of the protein PsbS and the xanthophyll zeaxanthin. However, the site and mechanism of the quencher(s) remain equivocal. Here, we constructed a mutant of Arabidopsis thaliana which lacks LHCII, the main antenna complexes of plants, to verify its contribution to NPQ. The mutant has normally stacked thylakoid membranes, displays no upregulation of other LHCs but shows a relative decrease in PSI which compensates for the decrease of the PSII antenna. The mutant exhibits a ~60% reduction in NPQ, while the remaining NPQ resembles that of the Chl b-less mutant, which lacks all PSII peripheral antenna complexes. We thus report that PsbS-dependent NPQ mainly occurs within LHCII, but there is an additional quenching site within the PSII core.

Self-corrected frequency modulation spectroscopy immune to phase random and light intensity fluctuation.

Light intensity fluctuations and phase randomness in quadrature demodulation disturb the accuracy of frequency modulation spectroscopy. The proposed self-corrected method eliminated these effects: the profile of correctly demodulated signals identified whether a demodulation was phase matched and corrected a phase-mismatched demodulated signal; we extracted the measured signal's direct current component and corrected the light intensity fluctuation. We conducted theoretical analysis and experimental verification to reduce light-intensity errors by 16.8% under different intensity conditions and obtained spectral features by phase difference corrections under the same measurement conditions. We reduced the effect of light intensity fluctuation and demodulated signals were freed from phase stability limitations.

Neural sensitization improves encoding fidelity in the primate retina

An animal’s motion through the environment can induce large and frequent fluctuations in light intensity on the retina. These fluctuations pose a major challenge to neural circuits tasked with encoding visual information, as they can cause cells to adapt and lose sensitivity. Here, we report that sensitization, a short-term plasticity mechanism, solves this difficult computational problem by maintaining neuronal sensitivity in the face of these fluctuations. The numerically dominant output pathway in the macaque monkey retina, the midget (parvocellular-projecting) pathway, undergoes sensitization under specific conditions, including simulated eye movements. Sensitization is present in the excitatory synaptic inputs from midget bipolar cells and is mediated by presynaptic disinhibition from a wide-field mechanism extending >0.5 mm along the retinal surface. Direct physiological recordings and a computational model indicate that sensitization in the midget pathway supports accurate sensory encoding and prevents a loss of responsiveness during dynamic visual processing.

A detector system for a high-energy phase-contrast human computed tomography experimental device

Abstract A detector system is designed for a high-energy phase-contrast computed tomography (CT) experimental device with an X-ray tube voltage of 80 kV. The spot size of the X-ray tube is 0.4 mm*0.7 mm. The Gd2O2S scintillator detector is adopted in our design, which is characterized by a high detection efficiency and high light yield. This system contains 2304 channels and the corresponding high-density read-out electronics. Considering the influence of the large spot size of the X-ray tube source, a detector pixel size of 0.75 mm*1 mm is adopted to obtain sufficient spatial resolution. Because the light intensity fluctuation caused by the phase shift is very weak, a 20bit ADC is used to achieve sufficient efficient resolution (ER). The electronics test shows that the SNR can reach 72. Compared to a commercial detector board, the detector system has better resolution for the sample used in the phase-contrast imaging experiment.

Plastic fiber optic sensor for continuous liquid level monitoring

The study demonstrates the development of a novel low-cost plastic optical fiber (POF) based sensor for liquid level measurement. The sensor works on the principle of reduction in scattering-based optical losses (in contrast to the increase in optical losses for evanescent wave-based sensing) in a straight decladded fiber with an increase in the liquid level due to refractive index changes in the medium surrounding the fiber. A compact optical setup is developed in-house consisting of two U-bent fiber probes coupled to a single LED on one end and two photodetectors on the other ends to measure the optical intensity changes. One of the U-bent probes is decladded over the length of the fiber to act as a test probe to measure the liquid level, while the other probe acts as a reference to compensate for the light intensity fluctuations due to light source instability and ambient conditions. The difference in voltage responses of the two photodetectors gives a measure for liquid level. We have investigated the fiber optic level sensor response to rising and falling liquid levels over 55 cm in presence of aqueous liquids of different refractive index values (1.33 to 1.38) and 95% ethanol as well as DI water at various temperatures from 16 °C up to 70 °C. A level sensitivity of 1.4 and 3.3 mV/mm for water level changes was obtained for the liquid level below and above 45 cm respectively. In addition, the fiber optic level sensor shows a stable and reproducible response over several cycles of 30 min duration at different liquid levels. The results demonstrate that this fiber optic level sensor is not only easy-to-make, cost-effective and robust but also offers sensitive, stable and reproducible instantaneous level measurements.

Corner detection based on gradient ghost imaging

Gradient ghost imaging (GGI) is a new imaging method that can directly extract the edge of a target from the correlation of light intensity fluctuations. However, there are problems of poor image quality and practicability in GGI. The corner point is an important target feature and has important applications in the fields of image processing and machine vision. In this paper, we propose a corner detection scheme that combines a corner detection algorithm based on curvature scale space with a GGI system, which can directly extract corner points from the reconstruction results of ghost imaging. A simulation and experimental results show that our method can acquire precise and robust corner information of an unknown target in undersampled cases, which promotes the practical development of ghost imaging.

Near-Infrared C2H2 Detection System Based on Single Optical Path Time Division Multiplexing Differential Modulation Technique and Multi-Reflection Chamber

A time division multiplexing differential modulation technique is proposed to address the interference problem caused by the fluctuation of laser light intensity in the single optical path detection system. Simultaneously, a multi-reflection chamber is designed and manufactured to further improve the system’s precision with an optical path length of 80 m. A near-infrared C2H2 detection system was developed. The absorption peak of the acetylene (C2H2) molecule near 1520 nm was selected as the absorption line. A laser driver is developed, and a lock-in amplifier is used to extract the second harmonic (2f) signal. A good linear relationship existed between C2H2 concentration and the 2f signal, and the correlation coefficient was 0.9997. In the detection range of 10–100 ppmv, the minimum detection limit was 0.3 ppmv, and the precision was 2%. At 50 ppmv, C2H2 and continuous detection for 10 h, the data average was 50.03 ppmv, and the fluctuation was less than ±1.2%. The Allan variance method was adopted to evaluate the long-term characteristic of the system. At 1 s of integration time, the Allan deviation was 0.3 ppmv. When the integration time reached 362 s, the Allan deviation was 0.0018 ppmv, which indicates the good stability of the detection system.