Light Intensity Fluctuations Research Articles

Self-referenced plasmonic biosensor with gold grating on thin gold film

Surface plasmon resonance sensors based on grating coupling exhibiting two resonant wavelengths are less observed because usually thick metal films are used. In this paper, we propose gold gratings on a gold film with two narrow reflection dips. One is sensitive to the refractive index (RI) of the cover media with a sensitivity of 720 nm/RIU. However, the other is sensitive to the RI of the substrate, and hence, it can be used as a reference dip. This self-referenced sensor significantly reduces the error contributions of the light intensity fluctuations and temperature variation. Moreover, the electric field is stronger with less decay length than that of gold gratings without gold film. Therefore, gold gratings with a gold film are more suitable to be a biosensor. Besides, we also investigate the structure parameters (the thickness of the gold film, the thickness and width of gold gratings, and the RI of the substrate) on the reflection spectra.

Resolving diurnal dynamics of the chloroplastic glutathione redox state in Arabidopsis reveals its photosynthetically derived oxidation.

Plants are subjected to fluctuations in light intensity, and this might cause unbalanced photosynthetic electron fluxes and overproduction of reactive oxygen species (ROS). Electrons needed for ROS detoxification are drawn, at least partially, from the cellular glutathione (GSH) pool via the ascorbate-glutathione cycle. Here, we explore the dynamics of the chloroplastic glutathione redox potential (chl-EGSH) using high-temporal-resolution monitoring of Arabidopsis (Arabidopsis thaliana) lines expressing the reduction-oxidation sensitive green fluorescent protein 2 (roGFP2) in chloroplasts. This was carried out over several days under dynamic environmental conditions and in correlation with PSII operating efficiency. Peaks in chl-EGSH oxidation during dark-to-light and light-to-dark transitions were observed. Increasing light intensities triggered a binary oxidation response, with a threshold around the light saturating point, suggesting two regulated oxidative states of the chl-EGSH. These patterns were not affected in npq1 plants, which are impaired in non-photochemical quenching. Oscillations between the two oxidation states were observed under fluctuating light in WT and npq1 plants, but not in pgr5 plants, suggesting a role for PSI photoinhibition in regulating the chl-EGSH dynamics. Remarkably, pgr5 plants showed an increase in chl-EGSH oxidation during the nights following light stresses, linking daytime photoinhibition and nighttime GSH metabolism. This work provides a systematic view of the dynamics of the in vivo chloroplastic glutathione redox state during varying light conditions.

A methane telemetry sensor based on near-infrared laser absorption spectroscopy

In order to detect methane leakage accurately and prompt, a methane telemetry sensor is demonstrated based on near infrared absorption spectroscopy and optimized wavelength modulation technology. The distributed feedback diode laser is applied as the light source to cover the selected absorption line of 6046 cm−1 to reduce the interference of CO2 and H2O. The waveform generator and the digital quadrature lock-in amplifier are constructed by the FPGA to produce driving signals and extract WMS-1f and 2f signals. And the “2f/1f” method is adopted to eliminate the environment influence such as light intensity fluctuations and improve the signal-to-noise ratio. This methane sensor has the characteristics of fast response and strong resistance to environmental interference and has great application prospect.

Parameter estimation of Gamma–Gamma fading channel in free space optical communication

Free-space optical communication links experience atmospheric turbulent light intensity fluctuation fading, which requires accurate channel parameter estimation to ensure stable communication. In this paper, the maximum likelihood (ML) method is proposed to estimate composite Gamma–Gamma fading channel parameters. The ML estimation expression based on the expectation maximization (EM) to compute unknown parameters is derived. Newton–Raphson (N–R) and generalized moment method (GMM) are used to compare EM algorithm with the estimation performance. We used the Cramer–Rao Bound (CRB) to evaluate these estimation algorithms. Each estimator’s performance is compared using simulation data as well as experimental measurements under different meteorological conditions. It is found that the proposed technique has better estimation performance for fading parameters of atmospheric turbulence channel.

Mathematical Modeling of Photosynthesis and Analysis of Plant Productivity

Photosynthesis is the basis of the plant production process, which makes it extremely relevant to develop methods for evaluating and predicting it under various environmental conditions. The complexity of photosynthetic processes and the presence of numerous feedbacks in it make it important to develop complex approaches to its analysis, including mathematical modeling. This review analyzes mathematical models of photosynthetic processes at various levels (from processes in thylakoid membranes up to the level of the whole plant and ecosystem) and assesses potential ways to use them to study plant productivity. First of all, models describing the functioning of photosynthetic reaction centers (including primary charge separation, fluorescence, heat dissipation, etc.) are noted; they are widely used for interpreting experimental data in the analysis of photosynthetic processes in plants. The next group of models focuses on the description of electron transport by a photosynthetic electron transport chain or its parts (in particular, photosystem II). Such models can be used both for analyzing experimental data and for predicting damage to the photosynthetic apparatus under conditions of rapid changes in environmental conditions (for example, fluctuations in light intensity). Models that take into account the dark stage of photosynthesis rely on the idea of limiting stages for CO2 fixation or on detailed descriptions of Calvin–Benson cycle reactions. Models of this group can already be directly used to describe the production process. More complex models, in addition to describing photosynthesis, can also take into account the propagation of light and CO2 fluxes in the leaf and the interaction of photosynthesis with other physiological processes; this makes it possible to use such models to predict plant productivity under different conditions or under modifications of the photosynthetic apparatus. The review also analyzes “supra-organismal” photosynthetic models, which are based on fairly simple descriptions of photosynthetic processes and can be used to analyze productivity at the level of vegetation cover, natural or artificial ecosystems. In general, numerous mathematical models of photosynthesis at various levels are aimed at solving a wide range of research and practical problems. In particular, they can be potentially used to assess violations of crop productivity in unstable growing conditions or to optimize it in stable protected ground conditions. A promising direction for the development of photosynthetic modeling is the integration of individual models of various levels into a single photosynthesis modeling environment.

Some aspects of fluctuations dynamics of particles in dusty plasma

Dusty plasmas are formed when micrometre particles of solid matter are introduced into glow discharge plasma. In the present research work, we investigated the fluctuation dynamics of the particles using the dynamic light scattering (DLS) technique and particle tracking with high-speed imaging technique. The DLS technique gives light intensity fluctuation which is analysed by fractal tools namely wavelet scalogram to give the Hurst parameter, “H” being associated with the fractional Brownian motion. The structural phases of particles are analysed using the pair correlation function. Particle trajectory analysis determines the transport characteristics of the charged dust particles. The scaling behaviour of the mean squared displacement (MSD) is investigated for different pressures. Results from both the DLS and MSD analysis are discussed regarding different transport mechanisms based on the fractional Brownian motion as the transport model. This study also highlighted the use of fractal analysis as a powerful tool for investigating fluctuation dynamics in dusty plasmas.

Enhanced two-photon excited fluorescence by ultrafast intensity fluctuations from an optical parametric generator

We evaluate the enhancement of two-photon excited fluorescence from fluorescent dye by ultrafast intensity fluctuations of light generated by a nanosecond optical parametric generator (OPG). By modifying the well-established techniques for measuring the second-order coherence on ultrashort timescale, we observed the enhancement of the fluorescence from Rhodamine B dye by a factor of two due to the bunching effect of light. A nanosecond OPG can be built at a much lower cost than the ultrashort pulse used in two-photon excitation microscopes. Therefore, our work paves the way toward a low-cost and efficient nonlinear microscope.

Simultaneous detection of atmospheric HONO and NO<sub>2</sub> utilising an IBBCEAS system based on an iterative algorithm

Abstract. We present an improved incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) system based on an iterative retrieval algorithm for the simultaneous detection of atmospheric nitrous acid (HONO) and nitrogen dioxide (NO2). The conventional IBBCEAS retrieval algorithm depends on the absolute change in the light intensity, which requires high light source stability and the stable transmission of the light intensity of all optical components. The new algorithm has an iterative module to obtain the effective absorption optical path length, and the concentrations of HONO and NO2 are then determined by differential optical absorption spectroscopy (DOAS) retrieval; thus, the method is insensitive to the fluctuation in the absolute light intensity. The robustness of the system is verified by simulating the influence of the relative change in the light intensity on the spectral retrieval results. The effect of nitrogen purging in front of the cavity mirrors on shortening the actual cavity length was measured and corrected using NO2 gas samples. Allan deviation analysis was conducted to determine the system stability, and it indicated that the detection limits (2σ) of HONO and NO2 are 0.08 and 0.14 ppbv at an integration time of 60 s respectively. Furthermore, Kalman filtering was used to improve the measurement precision of the system. The measurement precision at an integration time of 3 s can be improved 4.5-fold by applying Kalman filtering, which is equivalent to the measurement precision at an integration time of 60 s without applying Kalman filtering. The atmospheric HONO and NO2 concentrations were observed by the IBBCEAS system based on an iterative algorithm and were compared with values measured by conventional IBBCEAS.

A Hybrid Flux Balance Analysis and Machine Learning Pipeline Elucidates Metabolic Adaptation in Cyanobacteria.

SummaryMachine learning has recently emerged as a promising tool for inferring multi-omic relationships in biological systems. At the same time, genome-scale metabolic models (GSMMs) can be integrated with such multi-omic data to refine phenotypic predictions. In this work, we use a multi-omic machine learning pipeline to analyze a GSMM of Synechococcus sp. PCC 7002, a cyanobacterium with large potential to produce renewable biofuels. We use regularized flux balance analysis to observe flux response between conditions across photosynthesis and energy metabolism. We then incorporate principal-component analysis, k-means clustering, and LASSO regularization to reduce dimensionality and extract key cross-omic features. Our results suggest that combining metabolic modeling with machine learning elucidates mechanisms used by cyanobacteria to cope with fluctuations in light intensity and salinity that cannot be detected using transcriptomics alone. Furthermore, GSMMs introduce critical mechanistic details that improve the performance of omic-based machine learning methods.

THE GROWTH OF LOCAL TREE SPECIES ON POST-COAL MINING AREAS IN EAST KALIMANTAN

Post-coal mining areas need rehabilitation to restore its functionality. Not all plants could grow well on bare ex-coal mining area because of the excessive light intensity and extreme temperature fluctuations. This study is aimed to determine suitable local tree species for rehabilitating mined areas. Planting was carried out in November 2012, and observations were made in November 2015. The study site was in the district of Samboja, Kutai Kartanegara, East Kalimantan Province, Indonesia. Research results revealed that seven tree species survived well in the ex-coal mining land, i.e., Vitex pinnata L., Syzygium scortechinii (Merr.) Merr. & Perry, Syzygium polyanthum (Wight) Walp., Shorea balangeran (Korth.) Burck, Macaranga motleyana (Mull.Arg.) Mull.Arg., Cleistanthus myrianthus (Hassk.) Kurz and Syzygium lineatum (DC.) Merr. & L.M. Perry. From the seven species V. pinnata, Sy. scortechinii and Sy. polyanthum performed best in both survival and growth rates. This study suggests those three species are excellent local tree species for ex-coal mining rehabilitation, not only because of their high survival rate (≥80%) and fast-growing but also they produce favourable fruits and flowers for wildlife.

Recent Advances and Tendency in Fiber Bragg Grating-Based Vibration Sensor: A Review

Vibration sensing is critical to monitor and ultimately preserve the health state of engineering systems. These systems with a large structure are typically working in some harsh environments including strong magnetic fields. However, traditional electrical sensors are difficult to accurately measure the vibration under harsh environments. Besides these instinct advantages of normal fiber optic sensors (FOS) sensors such as compact size, passive sensing, resistance to electromagnetic interference, etc., fiber Bragg grating (FBG) sensors have a capability of distributed sensing based on wavelength demodulation and resistance to light intensity fluctuation and unwanted fiber bending losses. Such merits lead them to be a hot topic in FOS field and excellent candidates for vibration sensing. Three types of FBG-based vibration sensors have been classified based on the difference of vibration-strain coupling way to FBG in this survey, which are pasted FBG-based, axial property of FBG-based and transverse property of FBG-based, respectively. FBG-based vibration sensors' principles and designs have been introduced and discussed. Recent advances in the applications of FBG-based vibration sensors have been investigated. The limitations and prospects of the FBG-based vibration sensing technologies have been analyzed and discussed.

Diffuse correlation spectroscopy measurements of blood flow using 1064nm light.

.Significance: Diffuse correlation spectroscopy (DCS) is an established optical modality that enables noninvasive measurements of blood flow in deep tissue by quantifying the temporal light intensity fluctuations generated by dynamic scattering of moving red blood cells. Compared with near-infrared spectroscopy, DCS is hampered by a limited signal-to-noise ratio (SNR) due to the need to use small detection apertures to preserve speckle contrast. However, DCS is a dynamic light scattering technique and does not rely on hemoglobin contrast; thus, there are significant SNR advantages to using longer wavelengths () for the DCS measurement due to a variety of biophysical and regulatory factors.Aim: We offer a quantitative assessment of the benefits and challenges of operating DCS at 1064 nm versus the typical 765 to 850 nm wavelength through simulations and experimental demonstrations.Approach: We evaluate the photon budget, depth sensitivity, and SNR for detecting blood flow changes using numerical simulations. We discuss continuous wave (CW) and time-domain (TD) DCS hardware considerations for 1064 nm operation. We report proof-of-concept measurements in tissue-like phantoms and healthy adult volunteers.Results: DCS at 1064 nm offers higher intrinsic sensitivity to deep tissue compared with DCS measurements at the typically used wavelength range (765 to 850 nm) due to increased photon counts and a slower autocorrelation decay. These advantages are explored using simulations and are demonstrated using phantom and in vivo measurements. We show the first high-speed (cardiac pulsation-resolved), high-SNR measurements at large source–detector separation (3 cm) for CW-DCS and late temporal gates (1 ns) for TD-DCS.Conclusions: DCS at 1064 nm offers a leap forward in the ability to monitor deep tissue blood flow and could be especially useful in increasing the reliability of cerebral blood flow monitoring in adults.

Using DMSP/OLS nighttime light data and K–means method to identify urban–rural fringe of megacities

Urban–rural fringe, which form a link between urban construction areas and rural hinterland, is the most sensitive area to urbanization. Its accurate identification is of great significance for the further study of urbanization related socio–economic and eco-environmental changes in the perspective of urban–rural contrast. Previous studies of urban–rural fringe identification had problems with narrow scope of application, low efficiency of identification, and the results were greatly influenced by subjective factors. Nighttime light, as an important product of human activities, can reflect the gradient changes of urban–rural landscapes, and can be used to identify urban–rural fringes. Therefore, a K–means–based approach was developed using Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data. Taking Beijing City as an example, in this study we delineated its urban–rural fringes. Our results indicate that a ring–shaped urban–rural fringe surrounds urban central areas, with an area of 3712 km2, which is mainly located in new urban development zones. Inside the urban–rural fringe, lights fluctuated obviously, and the fluctuation index was up to 76.75. Meanwhile, the combination of nighttime light intensity and light fluctuation had better performance than that when they were considered separately in the identification of urban–rural fringes. Furthermore, the K–means algorithm based on nighttime light found more details related to urban–rural fringes when compared with the traditional mutation detection method. This study provided an approach to identifying urban–rural fringes accurately and objectively, which is conducive to the study of eco–environmental effects in the process of urbanization.

Electron transport in Tradescantia leaves acclimated to high and low light: thermoluminescence, PAM-fluorometry, and EPR studies.

Using thermoluminescence, PAM-fluorometry, and electron paramagnetic resonance (EPR) for assaying electron transport processes in chloroplasts in situ, we have compared photosynthetic characteristics in Tradescantia fluminensis leaves grown under low light (LL, 50-125µmol photons m-2 s-1) or high light (HL, 875-1000µmol photons m-2 s-1) condition. We found differences in the thermoluminescence (TL) spectra of LL- and HL-acclimated leaves. The LL and HL leaves show different proportions of the Q (~ 0°C) and B (~ 25-30°C) bands in their TL spectra; the ratios of the "light sums" of the Q and B bands being SQ/SB ≈ 1/1 (LL) and SQ/SB ≈ 1/3 (HL). This suggests the existence of different redox states of electron carriers on the acceptor side of PSII in LL and HL leaves, which may be affected, in particular, by different capacities of their photo-reducible PQ pools. Enhanced content of PQ in chloroplasts of LL leaves may be the reason for an efficient performance of photosynthesis at low irradiance. Kinetic studies of slow induction of Chl a fluorescence and measurements of P700 photooxidation by EPR demonstrate that HL leaves have faster (about 2 times) response to switching on actinic light as compared to LL leaves grown at moderate irradiation. HL leaves also show higher non-photochemical quenching (NPQ) of Chl a fluorescence. These properties of HL leaves (faster response to light and generation of enhanced NPQ) reflect the flexibility of their photosynthetic apparatus, providing sustainability and rapid response to fluctuations of environmental light intensity and solar stress resistance. Analysis of time-courses of the EPR signals of [Formula: see text] induced by far-red (λmax = 707nm), exciting predominantly PSI, and white light, exciting both PSI and PSII, suggests that there is a contribution of cyclic electron flow around PSI to electron flow through PSI in HL leaves. The data obtained are discussed in terms of photosynthetic apparatus sustainability of HL and LL leaves under variable irradiation conditions.

Pairs of peaks stabilize output power

Photosynthesis A counterintuitive feature of photosynthesis is that the primary pigments involved in absorbing light—for example, chlorophyll a and b in plants—do not all absorb right at the peak of the spectrum but instead are offset from the peak and each other. Arp et al. formulated a network model that explains how using pigments with this absorption-peak pattern can mitigate internal and external fluctuations in energy transfer, minimizing noise in output power (see the Perspective by Duffy). The model accurately reproduces absorption peaks for three diverse photosynthetic systems from different spectral environments. Such a mechanism may provide an underlying robustness to biological photosynthetic processes that can be further tuned and tweaked to adapt to longer-scale fluctuations in light intensity. Science , this issue p. [1490][1]; see also p. [1427][2] [1]: /lookup/doi/10.1126/science.aba6630 [2]: /lookup/doi/10.1126/science.abc8063

The cold-induced switch in direction of chloroplast relocation occurs independently of changes in endogenous phototropin levels.

When exposed to fluctuating light intensity, chloroplasts move towards weak light (accumulation response), and away from strong light (avoidance response). In addition, cold treatment (5°C) induces the avoidance response even under weak-light conditions (cold-avoidance response). These three responses are mediated by the phototropin (phot), which is a blue-light photoreceptor and has also been reported to act as a thermosensory protein that perceives temperature variation. Our previous report indicated that cold-induced changes in phot biochemical activity initiate the cold-avoidance response. In this study, we further explored the induction mechanism of the cold-avoidance response in the liverwort Marchantia polymorpha and examined the relationship between changes in the amount of phot and the induction of the cold-avoidance response. The switch between the accumulation and avoidance responses occurs at a so-called ‘transitional’ light intensity. Our physiological experiments revealed that a cold-mediated decrease in the transitional light intensity leads to the induction of the cold-avoidance response. While artificial overexpression of phot decreased the transitional light intensity as much as cold treatment did, the amount of endogenous phot was not increased by cold treatment in wild-type M. polymorpha. Taken together, these findings show that the cold-avoidance response is initiated by a cold-mediated reduction of the transitional light intensity, independent of the amount of endogenous phot. This study provides a clue to understanding the mechanism underlying the switch in direction of chloroplast relocation in response to light and temperature.

Biocompatibility of Alexandrium minutum in the growth and paralytic shellfish toxins production under five cultivation methods

This study evaluated the performance of an easy-cultivation device for the mass culture of Alexandrium minutum (A. minutum), a dinoflagellate that produces paralytic shellfish toxins (PSTs). Five culture conditions including three different sizes of containers (250 mL conical flask, 500 mL beaker, and 20 L jar) in two different environments (out-incubator and incubator) were compared in terms of growth and PSTs production. Compared with the incubator environment, the out-incubator environment had more fluctuations in temperature and light intensity. Results showed that the cell densities of A. minutum increased in all groups, especially in the conical flask (I, out-incubator, 6.29×106 cells/mL) and the beaker (IV, incubator, 7.28×106 cells/mL). When cultured in the 20 L jar under out-incubator condition, the algae had the lowest cell density (2.82×106 cells/mL) but the highest toxicity (93.42 ± 2.55×10−6 MU/cell). The negative correlation between average growth rate and single-cell toxicity could be explained by biocompatibility, thereby indicating that the low growth rate led to high toxicity. HPLC-FLD showed that the cellular toxicity increased due to the quantitative increase in GTX1/4, which are the more toxic derivatives. The PSTs types consistently contained GTX1/4 and GTX2/3. The differences in algae growth and toxin-production could be due to changes in bacteria (out-incubator) and CO2 (incubator) with vessel size. The effects of environmental factors on algae are strain specific. The out-incubator device can be applied for large-scale cultivation of A. minutum considering the algae density and toxin-producing ability.

A dual-gas sensor for simultaneous detection of methane and acetylene based on time-sharing scanning assisted wavelength modulation spectroscopy.

Methane (CH4) and acetylene (C2H2) are important bioscience and chemical gases. The real-time monitoring and analysis of them have important research value in industrial process control. The time-sharing scanning assisted wavelength modulation spectroscopy (WMS) technique is developed for real-time and simultaneous detection of CH4 and C2H2. This system involves two near-infrared distributed feedback (DFB) lasers and a compact multipass cavity with an effective optical path of 52.2m. The selected strong absorption lines of methane and acetylene are located at 6046.96cm-1 and 6531.7cm-1, respectively. The experiment environment is conducted at room temperature 23°C and pressure 760Torr. The sensor performance, including the minimum detection limit (MDL) and the stability, was improved by eliminating the influence of light intensity fluctuation using the WMS-2f/SAW technique. Allan deviation analysis indicates that a MDL of 0.1ppm for CH4 and 0.2ppm for C2H2 are achieved with 1-s integration time. And the instrument response time is about 44s through the continuous analysis of standard gases. This sensitive, simple, reliable, and lowcost dual-gas sensor is very suitable for applications in the field environment, chemical process, and many other gas-phase analysis areas.

Trace gas detect based on spectral analysis and harmonic ratio

A novel method of gas concentration calibration for tunable diode laser absorption spectroscopy, in which spectral analysis and harmonic signal intensity ratio measurement are combined, is proposed in this study. A harmonic signal is extracted from a transmitted light intensity by spectral analysis. The ratio of the second harmonic to the first harmonic is proportional to the gas concentration. The noise caused by electronics and environment is filtered out via frequency-domain filtering, and the harmonic ratio measurement eliminates the effects of light intensity fluctuations. The accuracy and effectiveness of the proposed method are verified by simulation and experiment. Experimental results show that the relative error of measurement is less than 3% and the correlation coefficient between measurement and calibration line is 0.9991.

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.