Laser-induced Fluorescence Data Research Articles

Fluid dynamics and mixing in a novel intermittently rotating bioreactor for CAR-T cell therapy: Spin-down from incomplete spin-up

This work explores the fluid flow and mixing within a new type of intermittently rotating bioreactor used for the automated manufacturing of CAR-T cell therapy products; CAR-T is a novel cell-based gene therapy which offers a single-dose cure for several forms of advanced blood cancer. The rotating cylinder bioreactor has a free surface and a liquid height to radius ratio of 0.5. Agitation is achieved via intermittent rotation of the entire vessel around its central vertical axis. No comprehensive engineering characterisation of the fluid dynamics in a bioprocessing context exists to date for this type of bioreactor. The present study examines the fluid dynamics and mixing during spin-down to rest following incomplete spin-up (i.e. the starting state of the fluid is not solid body rotation). Novel Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) data is presented, shedding light on the different transient flow regions inside the intermittently rotating bioreactor, and on the impact spin-up time has on the mixing efficiency of the subsequent spin-down stage. The results presented can be used to inform the design of a custom intermittent agitation pattern for any resembling cylinder bioreactors, the adoption of which could lead to higher yields and reduced costs for the cell expansion step of the manufacturing process.

Xenon tracers for cost effective laser induced fluorescence of alternative propellant Hall thrusters

One of the limiting factors to developing plasma thrusters on alternative propellants is the cost associated with changing the diagnostic tools, which are often propellant-dependent. For laser induced fluorescence (LIF), which is typically used for ion velocity distribution measurements to determine ion trajectories and potential profiles, either new lasers need to be bought, which are tuned to the wavelength of the new element’s excitation level, or a costly tunable laser is required. A method to use existing LIF setups designed for xenon on any propellant has been demonstrated on a Hall thruster operating on krypton. In the demonstration test, a small amount of xenon (0.01%–4%) was mixed with the main krypton propellant for use as a diagnostic tracer, and xenon ion velocities were measured while also monitoring changes in the mean discharge current and oscillations. High signal-to-noise ratios in LIF data acquired along the channel centerline were obtained with tracer gas fractions ≤1% that negligibly affected the thruster operation. These results and comparison of the emission spectra of xenon and other common propellants suggest that the tracer LIF method should be broadly applicable to LIF measurements in Hall thrusters operating on alternative propellants.

Fluid flow and mixing in a novel intermittently rotating bioreactor for CAR-T cell therapy manufacturing

This work explores the mixing and fluid dynamics in a novel bioreactor currently used for the automated manufacturing of CAR-T cell therapy, which offers a single-dose cure for several forms of advanced blood cancer. The cylindrical bioreactor has a low aspect ratio and a free surface. Agitation is achieved by intermittent rotation of the entire vessel around its central axis. No engineering characterisation has been conducted to date for this system in a bioprocessing context. The study examines the fluid dynamics problems of spin-up from rest and spin-down to rest. Novel Particle Image Velocimetry and Planar Laser-Induced Fluorescence data is presented alongside reflective flakes results, shedding light on the different transient flow regions inside the intermittently rotating bioreactor, and determining the timescales of macro- and micromixing. The results presented can be used to design a custom rotation pattern of the bioreactor for improved mixing performance during the cell expansion step.

Bimodal UV photoacoustic and fluorescence sensor for breath analysis

Breath analysis using spectroscopy techniques is coming up as one of the non-invasive methods for disease diagnosis. Among several spectroscopic methods, photoacoustic spectroscopy (PAS) and laser-induced fluorescence (LIF) are used to obtain information on sample's absorption and emission characteristics, respectively. In the present work, we present breath analysis results using a bimodal sensor using 266 nm UV laser, which can be used for both PAS and LIF measurements of volatile organic compounds (VOCs). The system is optimized using standard VOC samples to show limits of detection of the order of ppb-s. Preliminary breath analysis has been carried out for breath samples from Asthma patients and healthy volunteers. Principal component analysis has shown that the two sets of PAS and LIF data of Asthma and normal breath samples are discriminated from each other as distinct clusters enabling clear discrimination. Match/no match study using M-distance and spectral residual gives a sensitivity of 90 % and specificity of 96 % for PAS, and 85 % sensitivity and 86 % specificity for LIF, using optimized M-distance cutoff values. The receiver operating curve (ROC) and the area under the curve (AUC)-ROC shows that the method is quite suitable for applying bimodal spectroscopy for breath analysis. A comparison of the breath study of the same volunteers has been carried out using an E-nose to confirm the validity of UV laser-based PAS-LIF bimodal sensor.

A fully functional palmtop microchip electrophoresis analyzer with laser-induced fluorescence detection

Microchip electrophoresis (MCE) is an ideal tool for rapid on-site analysis of multiple components, therefore the demand for portable MCE devices is increasing. In this work, a fully functional palmtop MCE analyzer was built, integrating units of sample injection, laser-induced fluorescence (LIF) detection, high-voltage (HV), imaging and data acquisition. Frames were fabricated with 3D printing to encapsulate miniaturized components selected with balanced consideration on size, cost and performance. The LIF unit contains a laser diode as the excitation light source, a collimating lens used in the commercial laser diode as the focusing lens and an avalanche photodiode (APD) for the laser distance meter as the photoelectric converter. The sample injection was achieved by negative pressure induced pinching. The total cost of the device is approximately $600 with a size of 89 × 98 × 98 mm3 and a weight of 350 g. It can be powered by a laptop or a mobile power bank. The limit of detection (LOD) measured under a typical MCE condition for sodium fluorescein could be 110 pM. The applicability of the device was demonstrated with the detection of rhodamines and DNA fragments.

Olive oil classification with Laser-induced fluorescence (LIF) spectra using 1-dimensional convolutional neural network and dual convolution structure model

Laser-induced fluorescence (LIF) spectroscopy is widely used for the analysis and classification of olive oil. This paper proposes the classification of LIF data using a specific 1-dimensional convolutional neural network (1D-CNN) model, which does not require pre-processing steps such as normalisation or denoising and can be flexibly applied to massive data. However, by adding a dual convolution structure (Dual-conv) to the model, the features of the 1-dimensional spectra are more scattered within one convolution-pooling process; thus, the classification effects are improved. The models were validated through an olive oil classification experiment which contained a total of 72,000 sets of LIF spectra data, and the classification accuracy rate reached ∼99.69%. Additionally, a common classification approach, the support vector machine (SVM), was utilised for the comparison of the results. The results show that the neural networks perform better than the SVM. The Dual-conv model structure has a faster convergence speed and higher evaluation parameters than those of the 1D-CNN in the same period of iterations, without increasing the data dimension.

The Relationship between the Strength Characteristics of Cerebral Aneurysm Walls with Their Status and Laser-Induced Fluorescence Data.

Background: Cerebral aneurysms (CA) are a widespread vascular disease affecting 50 per 1000 population. The study of the influence of histological, morphological and hemodynamic factors on the status of the aneurysm has been the subject of many works. However, an accurate and generally accepted relationship has not yet been identified. Methods: In our work, the results of mechanical and spectroscopic measurements are considered. Total investigated 14 patients and 36 their samples of CA tissue. Results: The excitation–emission matrix of each specimen was evaluated, after which the strength characteristics of the samples were investigated. Conclusions: It has been shown that there is a statistically significant difference in the size of the peaks of two components, which characterizes the status of the aneurysms. In addition, a linear regression model has been built that describes the correlation of the magnitude of the ultimate strain and stress with the magnitude of the peaks of one of the components. The results of this study will serve as a basis for the non-invasive determination of the strength characteristics of the cerebral tissue aneurysms and determination of their status.

3D CFD simulation of a gaseous fuel injection in a hydrogen-fueled internal combustion engine

Nowadays, one of the hottest topic in the automotive engineering community is the reduction of fossil fuels. Hydrogen is an alternative energy source that is already providing clean, renewable, and efficient power being used in fuel cells. Despite being developed since a few decades, fuel cells are affected by several hurdles, the most impacting one being their cost per unit power. While waiting for their cost reduction and mass-market penetration, hydrogen-fueled internal combustion engines (H2ICEs) can be a rapidly applicable solution to reduce pollution caused by the combustion of fossil fuels. Such engines benefit from the advanced technology of modern internal combustion engines (ICEs) and the advantages related to hydrogen combustion, although some modifications are needed for conventional liquid-fueled engines to run on hydrogen. The gaseous injection of hydrogen directly into the combustion chamber is a challenge both for the designers and for the injection system suppliers. To reduce uncertainties, time, and development cost, computational fluid dynamics (CFD) tools appear extremely useful, since they can accurately predict mixture formation and combustion before the expensive production/testing phase. The high-pressure gaseous injection which takes place in Direct-Injected H2ICEs promotes a super-sonic flow with very high gradients in the zone between the bulk of the injected hydrogen and the flow already inside the combustion chamber. To develop a methodology for an accurate simulation of these phenomena, the SoPHy Engine of the Engine Combustion Network group (ECN) is used and presented. This engine is fed through a single nozzle H2-injector; planar laser-induced fluorescence (PLIF) data are available for comparison with the CFD outcomes.

Injection of a heavy fluid into a light fluid in a closed-end pipe

We report experimental results on the injection of a heavy fluid into a light one in a closed-end pipe, inclined at intermediate angles. The injection of the heavy fluid is made using an inner duct with a smaller diameter than that of the pipe in which the light fluid is placed. The fluids used are miscible and Newtonian, and they have the same viscosity. Our observation shows that, during the removal/replacement of the light fluid by the heavy fluid, at least four distinct flow stages can be identified: (i) initial buoyant jet of the heavy fluid, (ii) development of a mixing region, (iii) slumping flow of the heavy fluid, and (iv) heavy fluid front reaching the pipe end and returning toward the mixing region. Using high-speed camera images along with the ultrasound Doppler velocimetry and laser induced fluorescence data, the flow characteristics in these flow stages are quantified, and they are described in detail vs the dimensionless groups that govern the flow dynamics, namely, the Froude number (Fr), the Reynolds number (Re), the Archimedes number (Ar), and the pipe inclination angle (β). While our findings are of fundamental importance, they can also be used to provide a fluid mechanics understanding of the dump bailing method in the plug and abandonment (P&A) of oil and gas wells.

Mass-independent dunham analysis of the [7.7] Y2Σ+ – X2Πi and [16.3] A2Σ− – X2Πi transitions of copper monoxide, CuO

The electronic spectrum of CuO has been studied extensively experimentally. In his review on the spectroscopy of the 3d transition metal oxides (Merer, 1989), Anthony Merer summarized the available experimental data for CuO, which encompassed over 20 publications. There have been 4 subsequent publications on CuO that have included: high resolution Fourier-Transform emission spectroscopy (FTS) (O’Brien et al., 1996), mm- and sub-mm microwave absorption spectroscopy (Steimle et al., 1997), moderate resolution laser induced fluorescence (LIF) spectroscopy (Jin et al., 2002), and high-resolution molecular beam LIF spectroscopy, both in the presence and absence of an external electric field (Zhuang et al., 2010). Despite this extensive study, analyses of spectra have been restricted to 63CuO, even though the natural abundance of 65Cu is significant (63Cu:65Cu is 69%:31%). Additionally, the Λ-doubling parameter for the X 2Πi state of CuO is assigned a negative sign in the FTS analysis, but is assigned a positive sign in the microwave and molecular beam LIF analyses. In this study, high resolution spectra for (0,0) and (1,1) bands of the [16.3] A2Σ− – X2Πi transition of CuO have been recorded using intracavity laser absorption spectroscopy (ILS). Features due to the (0,0) band of 65CuO were clearly identified in the spectra and included in the analysis. The CuO FTS spectrum was retrieved from the archive for the McMath-Pierce Solar Observatory at Kitt Peak, and several additional vibrational bands of the [7.7] Y2Σ+ – X2Πi transition of CuO were identified in the FTS data, including the (1,0), (0,0), and (0,1) bands of 65CuO. The ILS, FTS, microwave and molecular beam LIF data were simultaneously fit to a mass-independent Dunham type Hamiltonian using PGOPHER. In total, 13,019 observations were fit to 1 constrained and 46 floated parameters. The results of this simultaneous fit show a Cu-isotope dependent shift in electronic energy for the [7.7] Y2Σ+ – X2Πi and [16.3] A2Σ− – X2Πi transitions of CuO. The results also confirm that the sign of q in the X 2Πi ground state is negative. Potential energy curves were generated from the molecular constants obtained in the fit for the [7.7] Y2Σ+ and X 2Πi states using the RKR method. These potential energy curves are significantly different and clearly indicate the Y and X state do not form a pure-precession pair.

Helical vortex core dynamics and flame interaction in turbulent premixed swirl combustion: A combined experimental and large eddy simulation investigation

In this study, a combined experimental and Large Eddy Simulation (LES) investigation is performed to identify the vortical structures, their dynamics, and interaction with a turbulent premixed flame in a swirl-stabilized combustor. Our non-reacting flow experiment shows the existence of large scale precessing motion, commonly observed for such flows. This off-axis precessing dynamics disappears with combustion but only above a critical equivalence ratio at which the flame attaches to the swirler centerbody and vortex breakdown changes from a cone to a bubble type. For compact flames stabilized along the inner shear layer (ISL), no precessing is seen, but large scale vortices along the ISL are observed; these structures interact with the ISL-stabilized flame and contribute to its wrinkling as revealed by laser-induced fluorescence data. After validating the LES results in terms of low order statistics and point temperature measurements in relevant areas of the flow, we show that it can capture the precessing motion in the non-reacting flow and its suppression with combustion. The simulations show that the ISL vortices in the reacting case originate from a vortex core that is formed at the swirler’s centerbody. This vortex core has a conical helical shape that interacts—as it winds out—with the ISL and the flame stabilized along it. The simulated helical vortex core (HVC) exists in both reacting and non-reacting flows; in the latter, it is dominated by the off-axis motion, whereas in the reacting case, that motion is damped and only remains the cork-screw type solid body rotation of the HVC.

Implementation of Detailed Chemistry Mechanisms in Engine Simulations

The stiffness of large chemistry mechanisms has been proved to be a major hurdle toward predictive engine simulations. As a result, detailed chemistry mechanisms with a few thousand species need to be reduced based on target conditions so that they can be accommodated within the available computational resources. The computational cost of simulations typically increases super-linearly with the number of species and reactions. This work aims to bring detailed chemistry mechanisms within the realm of engine simulations by coupling the framework of unsteady flamelets and fast chemistry solvers. A previously developed tabulated flamelet model (TFM) framework for nonpremixed combustion was used in this study. The flamelet solver consists of the traditional operator-splitting scheme with variable coefficient ordinary differential equation (ODE) solver (VODE) and a numerical Jacobian for solving the chemistry. In order to use detailed mechanisms with thousands of species, a new framework with the Livermore solver for ODEs in sparse form (LSODES) chemistry solver and an analytical Jacobian was implemented in this work. Results from 1D simulations show that with the new framework, the computational cost is linearly proportional to the number of species in a given chemistry mechanism. As a result, the new framework is 2–3 orders of magnitude faster than the conventional variable coefficient ODE (VODE) solver for large chemistry mechanisms. This new framework was used to generate unsteady flamelet libraries for n-dodecane using a detailed chemistry mechanism with 2755 species and 11,173 reactions. The engine combustion network (ECN) spray A experiments, which consist of an igniting n-dodecane spray in turbulent, high-pressure engine conditions are simulated using large eddy simulations (LES) coupled with detailed mechanisms. A grid with 0.06 mm minimum cell size and 22 ×106 peak cell count was implemented. The framework is validated across a range of ambient temperatures against ignition delay and liftoff lengths (LOLs). Qualitative results from the simulations were compared against experimental OH and CH2O planar laser-induced fluorescence (PLIF) data. The models are able to capture the spatial and temporal trends in species compared to those observed in the experiments. Quantitative and qualitative comparisons between the predictions of the reduced and detailed mechanisms are presented in detail. The main goal of this study is to demonstrate that detailed reaction mechanisms (∼1000 species) can now be used in engine simulations with a linear increase in computation cost with number of species during the tabulation process and a small increase in the 3D simulation cost.

A support vector regression method for efficiently determining neutral profiles from laser induced fluorescence data.

A support vector regression (SVR) method is integrated with a collisional radiative (CR) model of helicon plasmas in the Helicon-Cathode (HelCat) linear plasma device to determine Ar i profiles based on metastable-pumped Laser Induced Fluorescence (LIF) measurements. A machine learning approach to the CR model allows for an efficient exploration of the input parameter space and can inherently incorporate probe and LIF measurement errors in profile inputs to which a CR model would normally be sensitive. A training set is created for mapping CR model outputs to Ar i input profiles using radial points as SVR input features and parameters of a sigmoidal-type function as output features. This SVR method may easily be adapted to other LIF pumping schemes and may even be used in conjunction with a CR model to validate electron temperature and density plasma profiles if neutral or ion profiles are already known.

FPGA based demodulation of laser induced fluorescence in plasmas.

We present a field programmable gate array (FPGA)-based system that counts photons from laser-induced fluorescence (LIF) on a laboratory plasma. This is accomplished with FPGA-based up/down counters that demodulate the data, giving a background-subtracted LIF signal stream that is updated with a new point as each laser amplitude modulation cycle completes. We demonstrate using the FPGA to modulate a laser at 1 MHz and demodulate the resulting LIF data stream. This data stream is used to calculate an LIF-based measurement sampled at 1 MHz of a plasma ion fluctuation spectrum.

Detailed modeling of soot particle formation and comparison to optical diagnostics and size distribution measurements in premixed flames using a method of moments

Recently improved knowledge about key processes for the formation and growth of soot particles lead to very extensive soot models describing several kinetic pathways for particle nucleation and growth in detail. One of these models has been proposed by D’Anna and coworkers (D’Anna et al., 2010, Sirignano et al., 2010). In these original studies, the multivariate formulation was solved with a sectional approach, while a more recent study (Salenbauch et al., 2017) also showed the suitability of moment methods such as the Conditional Quadrature Method of Moments (CQMOM) (Yuan et al., 2011). However, being a moment method, CQMOM does not allow to directly access the soot particle size distribution (PSD). This prevents the consistent comparability of CQMOM results to soot measurements based on a scanning mobility particle sizer (SMPS). Furthermore, the comparison to laser-induced fluorescence (LIF) experiments is also limited, as the LIF signal only represents small particles and their concentration is only extractable from the simulation results if the PSD shape is known.The aim of this study is to extend the previously developed CQMOM soot model by a PSD reconstruction step applying the concept of entropy maximization. Maintaining the efficiency of the CQMOM moment inversion algorithm to close the moment equations, the model extension enables to evaluate the diameter-based PSD in a post-processing step without prescribing a specific shape as input. The updated algorithm is applied to simulate soot formation in two different burner-stabilized premixed C2H4/O2/N2 flames with a very lightly sooting (C/O = 0.67) and a heavily sooting (C/O = 0.77) character. Numerical results are compared to recently published LIF, laser-induced incandescence (LII) and SMPS measurement data. The analysis investigates the model’s capability to predict phenomena such as uni- or bimodal distribution shapes and the transition of small nanostructures to agglomerates in the two target flames both of which exhibit very different sooting behaviour.

Thermochemical Mechanism Optimization for Accurate Predictions of CH Concentrations in Premixed Flames of C1–C3 Alkane Fuels

Increasingly stringent regulations on NOx emissions are enforced by governments owing to their contribution in the formation of ozone, smog, fine aerosols, acid rains, and nutrient pollution of surface water, which affect human health and the environment. The design of high-efficiency, low-emission combustors achieving these ever-decreasing emission standards requires thermochemical mechanisms of sufficiently high accuracy. Recently, a comprehensive set of experimental data, collected through laser-based diagnostics in atmospheric, jet-wall, stagnation, premixed flames, was published for all isomers of C1–C4 alkane and alcohol fuels. The rapid formation of NO through the flame front via the prompt (Fenimore) route was shown to be strongly coupled to the maximum concentration of the methylidyne radical, [CH]peak, and the flow residence time within the CH layer. A proper description of CH formation is then a prerequisite for accurate predictions of NO concentrations in hydrocarbon–air flames. However, a comparison against the Laser-induced fluorescence (LIF) experimental data of Versailles, P., et al. (2016, “Quantitative CH Measurements in Atmospheric-Pressure, Premixed Flames of C1–C4 Alkanes,” Combust. Flame, 165, pp. 109--124) revealed that (1) modern thermochemical mechanisms are unable to accurately capture the stoichiometric dependence of [CH]peak, and (2) for a given equivalence ratio, the predictions of different mechanisms span over more than an order of magnitude. This paper presents an optimization of the specific rate of a selection of nine elementary reactions included in the San Diego combustion mechanism. A quasi-Newton algorithm is used to minimize an objective function defined as the sum of squares of the relative difference between the numerical and experimental CH–LIF data of Versailles, P., et al. (2016, “Quantitative CH Measurements in Atmospheric-Pressure, Premixed Flames of C1–C4 Alkanes,” Combust. Flame, 165, pp. 109--124), while constraining the specific rates to physically reasonable values. A mechanism properly describing CH formation for lean to rich, C1–C3 alkane–air flames is obtained. This optimized mechanism will enable accurate predictions of prompt-NO formation over a wide range of equivalence ratios and alkane fuels. Suggestions regarding which reactions require further investigations, either through experimental or theoretical assessments of the individual specific rates, are also provided.

A comparative study on the sooting tendencies of various 1-alkene fuels in counterflow diffusion flames

Alkenes are important components in transportation fuels, and are known to have increased sooting tendencies compared to analogous saturated hydrocarbons with the same carbon number. This work aims to understand the sooting tendencies of various 1-alkenes through experiments and numerical simulations for counterflow diffusion flames. Soot and PAH formation tendencies of 1-alkene fuels, including ethylene (C2H4), propene (C3H6), 1-butene (1-C4H8), 1-pentene (1-C5H10), 1-hexene (1-C6H12) and 1-octene (1-C8H16), were experimentally studied using laser induced-incandescence (LII) and laser-induced fluorescence (LIF) techniques, respectively. From the LII results, 1-C4H8 was found to be the most sooting fuel, followed by C3H6 > 1-C5H10 > 1-C6H12 > 1-C8H16 > C2H4. The LIF data with a detection wavelength of 500 nm indicated the PAH formation tendencies followed the order of 1-C4H8 > 1-C5H10 ∼1-C6H12 > C3H6 > 1-C8H16 > C2H4, which were different from the order of sooting tendencies. Numerical simulations with a comprehensive chemical kinetic model including PAH growth chemistry for the tested 1-alkene fuels were conducted to elucidate the aromatic formation pathways and rationalize the experimentally observed trends. The numerical results highlighted the importance of intermediate species with odd carbon numbers in aromatic species formation, such as propargyl, allyl, cyclopentadienyl and indenyl radicals. Their concentration differences, which could be traced back to the parent fuel molecules through rate of production analysis, rationalize the experimentally observed differences in soot and PAH formation tendencies.

System Validation Experiments for Obtaining Tracer Laser-Induced Fluorescence Data at Elevated Pressure and Temperature.

This paper presents a set of system validation experiments that can be used to qualify either static or flow experimental systems for gathering tracer photophysical data or conducting laser diagnostics at high pressure and temperature in order to establish design and operation limits and reduce uncertainty in data interpretation. Tests demonstrated here quantify the effect of tracer absorption at the test cell walls, stratification, photolysis, pyrolysis, adequacy of mixing and seeding, and reabsorption of laser light using acetone as the tracer and 282 nm excitation. Results show that acetone exhibits a 10% decrease in fluorescence signal over 36 000 shots at 127.4 mJ/cm2, and photolysis is negligible below 1000 shots collected. Meanwhile, appropriately chosen gas residence times can mitigate risks due to pyrolysis and inadequate mixing and seeding; for the current work 100 ms residence time ensured <0.5% alteration of tracer number density due to thermal destruction. Experimental results here are compared to theoretical values from the literature.

Coplanar surface barrier discharge ignited in water vapor—a selective source of OH radicals proved by (TA)LIF measurement

Coplanar dielectric barrier discharge (DBD) was ignited in pure water vapor at atmospheric pressure in order to generate highly oxidizing plasma with one specific type of reactive radicals. In order to prevent water condensation the used plasma reactor was heated to 120 C. The composition of the radical species in the discharge was studied by methods based on laser-induced fluorescence (LIF) and compared with analogous measurements realized in the same coplanar DBD ignited in air. Fast collisional processes and laser-surface interaction were taken into account during LIF data processing. It was found that coplanar DBD ignited in water vapor produces hydroxyl (OH) radicals with concentration in the order of 1020 m−3, which is higher than the value measured in discharge in humid air (40% relative humidity at 21 C). The concentration of atomic hydrogen radicals in the DBD ignited in water vapor was below the detection limit, which proves that the generation of oxidizing plasma with dominance of one specific type of reactive radicals was achieved. The temporal evolution, spatial distribution, power dependence and rotational temperature of the OH radicals was determined in the DBD ignited in both water vapor and air.

Potential of spectral ratio indices derived from hyperspectral LiDAR and laser-induced chlorophyll fluorescence spectra on estimating rice leaf nitrogen contents.

Accurate estimation of leaf nitrogen contents (LNCs) is essential for nutrition management in monitoring crop growth status. The aim of this study was to compare the potential of hyperspectral LiDAR (HSL) and laser-induced chlorophyll fluorescence (LIF) data in accurately predicting rice LNC. First of all, the intensity values of HSL at 694 and 742 nm and LIF at ~685 and ~740 nm were selected as the characteristic variables to analyze rice LNC using data collected in 2014 and 2015, respectively. Second, spectral indices derived from HSL (only) and LIF (only) were utilized to estimate LNC of rice, respectively. Third, a combined ratio indices (the ratio indices of reflectance to fluorescence and NDVI-based indices at the above four wavelengths) was developed and evaluated in estimating rice LNC. The statistical method of linking these spectral indices to rice LNC was the artificial neural network, which was to obtain the optimum performance in LNC estimation of rice. The results demonstrated that the combined ratio indices, especially the ratio of reflectance to fluorescence at ~740 nm, showed a moderate relationship with rice LNC (R2 = 0.736, 0.704, and 0.713 for the 2014 first experiment, 2014 second experiment, and 2015 experiment, respectively).