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The present study aims to assess the physiological and biochemical changes in the mung plants (Vigna radiata L) due to the impact of copper oxide nanoparticles using laser-induced fluorescence, ultraviolet-visible and confocal micro-Raman spectroscopy. The mung seedlings were treated with copper oxide nanoparticles with concentrations of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6 and 1.8 mM. The growth parameters of the mung seedlings show considerable decreases at higher concentrations of nanoparticles. The laser-induced fluorescence measurements showed a decrease in photosynthetic activity as indicated by the increase in the intensity ratio (I685/I732) with the nanoparticle concentration. Further, the ultraviolet-visible measurements show a decrease in the plant pigments chlorophyll a, chlorophyll b and carotenoids with the concentration of nanoparticles. Except for 0.2 mM, the Raman spectral signatures obtained from the leaves of mung-treated copper oxide nanoparticles reveal that the cell wall component proteins, lignin, pectin, carbohydrates, aliphatics and carotenoids declined with the treatment of nanoparticles. The decreasing intensity of carotenoids from the Raman measurements and the decreasing chlorophyll and carotenoid content in laser-induced fluorescence and ultraviolet-visible measurements suggest that copper oxide nanoparticles are toxic to mung plants. The spectroscopic techniques along with discriminatory and data processing approaches such as principal component analysis (PCA) are demonstrated to provide noninvasive, nondestructive, sensitive, rapid and effective screening of plants under various stresses. [ABSTRACT FROM AUTHOR]

This study proposes a model for the measurement of microscale liquid film thickness distribution using fluorescence signals. The interfacial conditions between the tool and the workpiece in mechanical machining are important for understanding these phenomena and mechanisms. In this study, indentation tests with transparent tools were used to observe interfaces; however, it was challenging to obtain the signal from a thin fluorescent liquid film on smooth and steeply inclined surfaces. Therefore, fluorescence-based measurement, such as laser-induced fluorescence, was employed. To measure the absolute thickness of the thin fluorescent film, calibration of the measurement system is necessary. Therefore, a theoretical model was proposed considering the multiple reflections of excitation light and fluorescence at the inclined surface between the indenter and workpiece. By measuring the profile of the surface topography of the indented workpiece and comparing the results with those measured by a surface profiler, the validity of the proposed calibration method and the performance of this measurement system were demonstrated. The measured surface profiles, including scratches of 2–4 µm, were in good agreement, demonstrating the validity of the proposed method. Highlights: Development of a model for measurement of liquid film thickness distribution at a steep, smooth indentation interface. Confirmation of the linearity between the fluorescence intensity and thickness, excitation intensity, and coefficient characterized by reflectance. Consistency of the measured film thickness distribution with the workpiece surface profile. [ABSTRACT FROM AUTHOR]

Sensor-based sorting devices commonly used in plastic recycling plants, mainly working in the near infrared range (NIR), are unable to identify black plastics, due to their low spectral reflectance. The aim of this work was to investigate the potentialities offered by laser-induced fluorescence (LIF) technique (spectral range 270–750 nm) for the identification of black polymers inside a plastic waste stream, thus allowing the possibility to build efficient sorting strategies to be applied in recycling plants. Representative samples of black plastics collected among the most utilized in household packaging were selected, constituted by four different types of polymers, i.e., expanded polystyrene (EPS), polystyrene (PS), polypropylene (PP) and high-density polyethylene (HDPE). The acquired LIF spectra were processed using multivariate approaches in order to optimize polymer classification. The developed hierarchical—partial least square-discriminant analysis (Hi-PLS-DA) classification model, showed excellent performances, confirmed by the values of sensitivity and specificity values in prediction, being equal to 1. The correctness of classification obtained by LIF was confirmed by the application of Fourier Transform Infrared spectroscopy (FTIR) on the same samples. The achieved results demonstrated the potential of LIF technique combined with a machine learning approach as sorting/quality control tool of black polymers in recycling plants. [ABSTRACT FROM AUTHOR]

In this study, laser-induced fluorescence is used to investigate the homogenization in stirred vessels equipped with single- and two-stage stirrers. The acquired local mixing times across the reactor cross-section are plotted as mixing time distribution (MTD) and then compared with the previously measured flow fields of the identical systems. With the help of a novel evaluation method, the mixing times are characterized with a normal distribution fit. With mean value and standard deviation as determined parameters, the mixing results of different installation heights and stirrer combinations are quantitatively evaluated and lead to clear recommendations for installations that enable efficient mixing. [ABSTRACT FROM AUTHOR]

Simultaneous nitric oxide (NO) laser-induced fluorescence (LIF), atomic oxygen (O) two-photon LIF (TPLIF), and molecular oxygen (O 2) LIF were demonstrated using a single broadband femtosecond (fs) laser in methane- and hydrogen-fueled flames. An amplified Ti:Sapphire laser with ∼80-fs pulse duration was used to pump an optical parametric amplifier (OPA) to generate 226.1-nm pulses having 2.3 nm (∼450 cm−1) bandwidth to excite all three species simultaneously. The specific excitation transitions are NO A-X (0,0) system, O 3 p 3 P ← ← 2 p 3 P two-photon transition, and O 2 B 3 Σ u − − X 3 Σ g − Schumann-Runge system. Detailed emission characterization was performed using a 1D imaging spectrometer to identify suitable emission bands for interference-free detection of each species. A simultaneous detection system consisting of a visible and a UV camera provided the optimal detection of all three species. Imaging studies revealed high concentrations of NO, O, and O 2 at the edge of the flame cone of Bunsen flames because NO and O are produced at the hot flame front. O 2 LIF signal was present only at the flame front because of the strong temperature dependence of the O 2 Schumann-Runge system. Direct imaging of O TPLIF enabled single-shot as well as high-fidelity shot-averaged line images in stable laminar flames. Equivalence ratio scans in the CH 4 /air Hencken flames showed good agreements for O and O 2 with Cantera equilibrium predictions performed using GRI-Mech 3.0. Although the NO measurements deviated from the equilibrium calculations on the fuel-rich side, it agreed well with previously reported NO LIF measurements in a similar flame. This discrepancy is likely due to Prompt NO, which was not considered in the simulation. NO LIF measurements as a function of height-above-the-burner in the H 2 /air Hencken flames agreed well with calculated NO mole fractions using the UNICORN flame code. The present study lays the foundation for single-laser imaging of three critical flame species in NO formation pathways in combustion systems. [ABSTRACT FROM AUTHOR]

It is well-known that the presence of geometry heterogeneity in porous media enhances solute mass mixing due to fluid velocity heterogeneity. However, laboratory measurements are still sparse on characterization of the role of high-permeability inclusions on solute transport, in particularly concerning fractured porous media. In this study, the transport of solutes is quantified after a pulse-like injection of soluble fluorescent dye into a 3D-printed fractured porous medium with distinct high-permeability (H-k) inclusions. The solute concentration and the pore-scale fluid velocity are determined using laser-induced fluorescence and particle image velocimetry techniques. The migration of solute is delineated with its breakthrough curve (BC), temporal and spatial moments, and mixing metrics (including the scalar dissipation rate, the volumetric dilution index, and the flux-related dilution index) in different regions of the medium. With the same H-k inclusions, compared to a H-k matrix, the low-permeability (L-k) matrix displays a higher peak in its BC, less solute mass retention, a higher peak solute velocity, a smaller peak dispersion coefficient, a lower mixing rate, and a smaller pore volume being occupied by the solute. The flux-related dilution index clearly captures the striated solute plume tails following the streamlines along dead-end fractures and along the interface between the H-k and L-k matrices. We propose a normalization of the scalar dissipation rate and the volumetric dilution index with respect to the maximum regional total solute mass, which offers a generalized examination of solute mixing for an open region with a varying total solute mass. Our study presents insights into the interplay between the geometric features of the fractured porous medium and the solute transport behaviors at the pore scale. [ABSTRACT FROM AUTHOR]

Gas–liquid intermittent flow commonly occurs in industrial processes such as oil well production, pipeline transportation, and nuclear reactor cooling. Investigation of Taylor bubble behavior in the intermittent flow is essential for safe operation and heat and mass transfer efficiency enhancement. Since the gas–liquid interface contains fluctuations, it is difficult to obtain high-resolution bubble surface with traditional measurement methods. In this article, a novel laser-induced fluorescence (LIF) based 3-D reconstruction and volume measurement method for Taylor bubble is developed. First, LIF technique is improved to not only detect the bubble section contour, but also measure the bubble velocity. In addition, to increase the axial spatial resolution of bubble section contour sequence, a volumetric image interpolation algorithm suitable for bubble morphology is developed. And the marching cubes algorithm is further introduced to reconstruct the Taylor bubble surface to achieve fine 3-D visualization. More importantly, the Monte Carlo method is combined with the reconstruction results to realize the volume measurement of irregularly shaped Taylor bubbles. Finally, the relationship between length and volume is established based on the measurement results, through which the volume of Taylor bubbles can be predicted by the easy-to-measure bubble length. The experimental results conclude that the reported volume measurement method for Taylor bubble is valid with high precision, and the numerical simulation data are also used to verify the effectiveness of the bubble volume prediction model. [ABSTRACT FROM AUTHOR]

The stagnant plate influence on spatial distributions of polycyclic aromatic hydrocarbons (PAHs), soot and hydroxyl radical (OH) in the surrogate fuel (80% n-heptane and 20% toluene in volume) partially premixed flame on a McKenna burner were originally investigated in terms of different plate heights above the burner (H p) and plate temperatures (T p). Both PAHs and OH distributions were qualitatively measured by laser-induced fluorescence (LIF) and soot volume fraction field was quantitatively measured by two-color laser-induced incandescence (2C-LII). It is found that the LIF intensity of 2&3-ring aromatics (A2&A3) and 4-ring aromatics (A4) and soot volume fraction firstly increase and then reduce when the H p is set from 35 to 10 mm. The variation tendency transition happens between H p = 20 and 25 mm. In contrary, OH-LIF intensity gradually decreases as the H p decreases. On the other hand, the T p has an opposite effect on the A2&A3-LIF, A4-LIF and soot volume fraction variation tendency at two H p. At H p = 15 mm, A2&A3-LIF, A4-LIF and soot volume fraction increase as the T p increases. However, A2&A3-LIF, A4-LIF and soot volume fraction decrease with the rise of the T p at H p = 35 mm. Interestingly, OH-LIF intensity always increases as the T p rises at any H p. Therefore, it can be concluded that the PAHs-LIF intensity and soot volume fraction depend on the H p and T p , and the maximums of them would be reached at the specific H p and T p. While both the H p and T p have a monotonic effect on the OH-LIF intensity. [ABSTRACT FROM AUTHOR]

Infrared (IR) planar laser-induced fluorescence (LIF/PLIF) exploits the vibrational level transitions of small gas molecules to achieve spatially-resolved spectroscopic information of the species for combustion and flow-field studies. While typical LIF utilizes electronic excitations with ultraviolet or visible lasers, IR LIF presents an alternative for molecules that are not readily accessible with a conventional UV/visible excitation-collection system. In view of the complexities rooting from longer vibrational level lifetimes and more densely-spaced energy levels, a comprehensive vibrational energy transfer model is developed for state-to-state population evolution and transition process characterization, and a typical CO 2 /CO/H 2 O/O 2 /N 2 system relevant to combustion gas mixture is studied by considering a total of 265 energy states and 85,036 transition pathways. The resultant fluorescence signal is thereby studied, with quantitative dependence on local temperature, pressure, gas composition, as well as excitation laser parameters including wavelength, power level and linewidth. Further optimization of collection scheme can be achieved by considering the time-histories and major transition pathways pertaining species evolution on different energy levels. The study develops general modelling and methodology for characterizing the temporal and spectral behavior of a vibrationally-excited molecular system, and demonstrates the potential for quantitative, spatially-resolved diagnostics using IR LIF/PLIF. [ABSTRACT FROM AUTHOR]

The distribution and dissipation of neutral atoms are crucial for understanding the dielectric recovery process after interrupting direct current (DC) vacuum arcs. This article aims to investigate the dissipation of copper atoms after a forced extinction of the vacuum arc experimentally, adopting the plane laser-induced fluorescence method. The change in the 2-D distribution of copper atoms with time is presented. The results show that the magnetic fields, the axial magnetic field (AMF), and the transverse magnetic field (TMF) have a limited effect on the initial density of copper atoms. For both the AMF and the TMF, the copper atom densities at current zero (CZ) vary in the range (6– $8) \times 10^{17}\,\,\text{m}^{-3}$ when 3-kA vacuum arcs are forced to 0 in 0.2 ms. Contrary to the TMF case, in the AMF case, the evaporation on the anode after the CZ results in long-existing atoms near it. Consequently, the atom density of the TMF decays faster than that of the AMF, which indicates that a vacuum interrupter with the TMF contacts has a better performance when interrupting a DC load. The difference between the two magnetic fields originates from the arc control patterns. Namely, the AMF tends to keep vacuum arcs in a stable mode, which is unfavorable for a DC interruption; on the contrary, the TMF drives the vacuum arcs to move at high velocities resulting in faster dissipation of copper atoms after the CZ. In addition, the composition proportion of CuCr contacts has a limited effect on the diffusion of copper atoms when a low-vacuum arc is interrupted. [ABSTRACT FROM AUTHOR]

As an important part of environmental water quality monitoring, efficient bacterial detection has attracted widespread attention. Among them, LIF (laser-induced fluorescence) technology has the characteristics of high efficiency and sensitivity for bacterial detection. To simplify the experimental process of bacterial detection, fluorescence emission spectra of E. coli (Escherichia coli) and its deactivated controls, K. pneumoniae (Klebsiella pneumoniae) and S. aureus (Staphylococcus aureus), were analyzed with fluorescence excitation by a 266 nm laser. By analyzing the results, it was found that the dominant fluorescence peaks of bacterial solutions at 335~350 nm were contributed by tryptophan, and the subfluorescence peaks at 515.9 nm were contributed by flavin; besides, K. pneumoniae and S. aureus had their own fluoresces characteristics, such as tyrosine contributing to sub-fluorescence peaks at 300 nm. The three species of bacteria can be differentiated with whole fluorescence spectrum by statistically analysis (p < 0.05), for various concentrations of aromatic amino acids and flavin in different bacteria. The experimental results also proved that the inactivation operation did not alter the spectral properties of E. coli. The indexes of fluorescence intensity and FIR (fluorescence intensity ratio, I335~350/I515.9) can be used to retrieve the bacteria concentration as well as for bacteria differentiation using the index of slopes. The detection limit of bacteria is less than ~105 cell/mL using laser induced fluorescence methods in the paper. The study demonstrated the rapid detection capability of the LIF bacterial detection system and its great potential for rapid quantitative analysis of bacteria. This may bring new insight into the detection of common bacteria in water in situ.

Structured laser illumination planar imaging (SLIPI)-based techniques have been employed during the past decade for addressing multiple light scattering issues in spray imaging. In this article, SLIPI droplet sizing based on the intensity ratio of laser-induced fluorescence (LIF) over Mie scattering (SLIPI-LIF/Mie) and SLIPI-Scan for extinction-coefficient (µe) mapping are applied simultaneously. In addition, phase Doppler anemometry (PDA) and numerical calculations based on the Lorenz–Mie theory are also employed in order to extract the droplets Sauter mean diameter (SMD), the droplets number density (N), and the liquid volume fraction (LVF) in a steady asymmetric hollow cone water spray. The SLIPI-LIF/Mie ratio is converted to droplets SMD by means of a calibration procedure based on PDA measurements. The droplet SMD for the investigated spray varies from 20 µm to 60 µm, the N values range from 5 to 60 droplets per mm3, and the LVF varies between 0.05 × 10−4 and 5.5 × 10−4 within the probed region of the spray. To generate a series of two-dimensional images at different planes, the spray scanning procedure is operated in a "bread slicing" manner by moving the spray perpendicularly to the light sheet axis. From the resulting series of images, the procedure described here shows the possibility of obtaining three-dimensional reconstructions of each scalar quantity, allowing a more complete characterization of droplet clouds forming the spray region. [ABSTRACT FROM AUTHOR]

We demonstrated recently that NO concentration measurements are feasible even in the core of largely non-sooting diesel-like jets by combined laser-induced fluorescence (LIF) and spontaneous Raman scattering (SRS). However, the question arises whether previous findings hold also for other diesel-like jets. The current study focuses on fuel effects. In the previous NO measurements, n-heptane was used. It is replaced by pure di-n-butylether (DNBE) and a tailor-made blend of 50% DNBE and 50% n-octanol. These fuels are promising biofuel candidates and lead to an interesting variation of mixing during combustion (MDC). The determination of NO concentrations turns out to be generally feasible with the blend on the jet centerline in the quasi-steady phase of the injection event. The corresponding uncertainty is about ± 28 %. By contrast, some of the NO-LIF measurements in sooting DNBE jets are discarded, primarily due to increased light attenuation. For the remaining NO concentrations with DNBE the corresponding uncertainty is about ± 40 %. For the blend, results indicate that NO formation is very similar to the one in the n-heptane jets. Thus, the net effect of changed volatility and oxygenation is seemingly weak. By contrast, quasi-steady centerline NO concentrations are apparently significantly affected by MDC for pure DNBE. Relatively high NO concentrations are observed in this case, although products of highly fuel-rich fluid parcels are also present there. This study indicates the importance of MDC in such jets. [ABSTRACT FROM AUTHOR]

The cascading process analysis in the D2Δ 5/2 state of copper monoxide molecule. • Ten unreported vibronic bands are presented. • The molecular constants of excited states for 63CuO and 65CuO are obtained. • Cascading processes are found and analyzed in all observed excited states. The electronic spectrum of the copper monoxide molecule (CuO) was investigated in the range of 430–550 nm using laser induced fluorescence spectroscopy and single vibronic level emission spectra. The CuO molecule was produced by a supersonic jet-cooled discharge assisted laser ablation of Cu target. Twenty two vibronic bands were observed and assigned to the electronic transition progressions from the ground state X2П i to excited states C2П 3/2 , C2П 1/2 , D2Δ 5/2 , E2Δ 5/2 , F2П 3/2 , G2Σ−, H2П 3/2 , and I2П 3/2 , of which ten bands were recorded firstly. The molecular constants of the excited electronic states for 63CuO and 65CuO isotopologues were obtained by a rotational analysis of the spectra. Cascading processes in the electronic excited states were found combining the time-resolved single vibronic level emission spectroscopy. The time-dependent radiative decay curves corresponding to different decay processes were recorded and analyzed. [ABSTRACT FROM AUTHOR]

• Totally 63 bands were resolved in 18,900 – 23,500 cm-1 region, and two electronic transitions were newly identified. • (0, 1), (0, 0), (1, 0), (2, 0), and (2, 1) bands of [21.5]0+ – X0+ and (0, 0) of [23.3]1 – X0+ transitions observed and analyzed. • The lifetimes of most observed vibronic bands were measured. The laser-induced fluorescence (LIF) excitation spectra of WO molecule have been recorded in the energy range of 18,900–23,500 cm−1 using laser ablation of tungsten target and reaction with free jet expansion of oxygen. Totally 63 vibronic transition bands were observed, and 60 bands were grouped into 10 electronic transition progressions, where 8 electronic transition progressions have the X0+ state as the lower state, as well as 2 progressions have the X1 state as the lower state. The electronic transition systems [21.5]0+–X0+ and [23.3]1–X0+ were newly identified by LIF spectroscopy. The molecular constants, including rotational constant, vibrational frequency, vibrational anharmonic constant, in the electronic excited states were obtained through rotational analysis of the spectra. In addition, the fluorescence lifetimes of the vibronic states were measured under the collision-free condition by exponentially fitting the fluorescence decay. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence (LIF) is a well-established technique for monitoring chemical processes and for the standoff detection of biological substances because of its simple technical implementation and high sensitivity. Frequently, standoff LIF spectra from large molecules and bio-agents are only slightly structured and a gain of deeper information, such as classification, let alone identification, might become challenging. Improving the LIF technology by recording spectral and additionally time-resolved fluorescence emission, a significant gain of information can be achieved. This work presents results from a LIF based detection system and an analysis of the influence of time-resolved data on the classification accuracy. A multi-wavelength sub-nanosecond laser source is used to acquire spectral and time-resolved data from a standoff distance of 3.5 m. The data set contains data from seven different bacterial species and six types of oil. Classification is performed with a decision tree algorithm separately for spectral data, time-resolved data and the combination of both. The first findings show a valuable contribution of time-resolved fluorescence data to the classification of the investigated chemical and biological agents to their species level. Temporal and spectral data have been proven as partly complementary. The classification accuracy is increased from 86% for spectral data only to more than 92%.

The electronic spectrum of the gaseous gold monoxide molecule has been investigated in the range of 16000－18500 cm−1 using laser induced fluorescence spectroscopy and single vibronic level emission spectra. Five rotationally resolved vibronic bands are observed and assigned to the transitions B2Σ− (v' = 0－4) －X2п3/2 (v'' = 0), in which the 0－0 transition is observed for the first time. The molecular constants of the excited state B2Σ− are obtained by a rotational analysis of the spectra. The spin-orbit coupling constant and the vibrational constants of the ground state X2пi are determined with the accuracy improved by one order of magnitude. The lifetimes of most observed bands are also measured for the first time. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Two newly electronic transitions of WO in 21,000–23,200 cm−1 spectral region. • (0, 0) and (1, 0) bands of the [21.2]0+–X0+ and [22.2]0+–X0+ transitions observed and analyzed. • Abnormal isotopic shifts in the vibrational levels were observed and analyzed. • The lifetimes of most observed vibronic bands were measured. Abstract The laser-induced fluorescence (LIF) excitation spectra of jet-cooled WO molecule have been investigated in the range of 21,000–23,200 cm−1, and two electronic band systems have been observed for the first time and labeled as the [21.2]0+– X 0+ and [22.2]0+– X 0+ transitions. The vibrational and rotational constants of these two excited electronic states have been derived by rotational analysis of the spectra. The tungsten isotopic structures of these two excited states are clearly resolved, and the analysis of LIF spectra reveals that the isotopic shifts are due to the strong interstate perturbations between different vibronic states. Based on the ab initio calculation results by Ram et al., the primarily attributed configuration of these two newly identified states was discussed. In addition, the lifetimes of the observed vibronic states were measured under the collision-free condition. [ABSTRACT FROM AUTHOR]

Structured laser illumination planar imaging (SLIPI)-based techniques have been employed during the past decade for addressing multiple light scattering issues in spray imaging. In this article, SLIPI droplet sizing based on the intensity ratio of laser-induced fluorescence (LIF) over Mie scattering (SLIPI-LIF/Mie) and SLIPI-Scan for extinction-coefficient (µe) mapping are applied simultaneously. In addition, phase Doppler anemometry (PDA) and numerical calculations based on the Lorenz–Mie theory are also employed in order to extract the droplets Sauter mean diameter (SMD), the droplets number density (N), and the liquid volume fraction (LVF) in a steady asymmetric hollow cone water spray. The SLIPI-LIF/Mie ratio is converted to droplets SMD by means of a calibration procedure based on PDA measurements. The droplet SMD for the investigated spray varies from 20 µm to 60 µm, the N values range from 5 to 60 droplets per mm3, and the LVF varies between 0.05 × 10−4 and 5.5 × 10−4 within the probed region of the spray. To generate a series of two-dimensional images at different planes, the spray scanning procedure is operated in a “bread slicing” manner by moving the spray perpendicularly to the light sheet axis. From the resulting series of images, the procedure described here shows the possibility of obtaining three-dimensional reconstructions of each scalar quantity, allowing a more complete characterization of droplet clouds forming the spray region.

Maintaining low NO x emissions over the operating range of diesel engines continues to be a major issue. However, quantitative measurements of nitric oxide (NO) are lacking especially in the core of diesel jets even if optical measurement techniques like laser-induced fluorescence (LIF) are used. NO may be present in the jet core due to enhanced fuel/air premixing. Close to the flame axis, severe light attenuation occurs. However, the diesel-like jets investigated in this study are largely non-sooting, so that light attenuation is reduced. n-heptane is used as diesel-surrogate fuel in the current investigations, which are performed in a combustion vessel. Quantitative NO measurements are conducted based on the knowledge of attenuation, temperature, the estimated equivalence ratio, and a calibration procedure. Attenuation turns out to be the most important factor in terms of measurement uncertainty. To avoid interfering LIF emissions by PAHs (polycyclic aromatic hydrocarbons) and O 2 , line imaging with a relatively high spectral resolution is conducted. Thereby, a higher accuracy can be achieved than by state-of-the-art planar imaging set-ups. Results show that NO initially forms throughout the jet cross-section. Quasi-steady NO concentrations measured in the jet core are compared to detailed kinetic simulations, taking the residence time of the fluid parcels in the main reaction zone into account. The residence-time “corrected” NO concentrations seemingly show a significant amount of prompt NO and are essentially consistent with simulation results for a corresponding equivalence ratio that was previously determined by Raman scattering. [ABSTRACT FROM AUTHOR]

A laser-induced fluorescence (LIF) was used as a complimentary detection system for time-of-flight ion mobility spectrometry (TOF-IMS). A LIF detection system is potentially faster than a conventional electrometer detector and can provide additional (to usual for IMS drift time) analytical information, namely wavelength of fluorescence maxima and fluorescence lifetime. Therefore, better discrimination ability can be expected. Additionally, the combination of IMS and LIF operates at atmospheric pressure. This allows fluorescence measurements of specified ions and ion clusters, which would not survive in a mass spectrometer. An IMS drift cell of open design with both the electrometer and LIF detectors was designed. The feasibility of IMS-LIF was demonstrated on the example of the Xanthene dye Rhodamine 6G (R6G). Electrospray was used as an ionization source. The release and desolvation of R6G ions from the electrospray with following IMS-LIF analysis were demonstrated. The effects of experimental parameters (e.g., ion gate and drift voltages, distance to ESI emitter) are demonstrated and discussed. The obtained results are promising enough to ensure the potential of LIF as a complimentary/alternative detection system for time-of-flight ion mobility spectrometry. [ABSTRACT FROM AUTHOR]

We have investigated the treatment of a mixture of fatty acid methyl esters by an RF-plasma jet with He-H2O and He-O2 gas feed. We have measured the concentration of the hydroxyl radical in the jet by laser induced fluorescence, looking for correlation with the lipid reactivity. We have detected four product families, whose yields increase with the OH exposure: volatile products, polymerization products, reduced chains, and oxidized chains. Theoretical calculations give insights on the radical attack to the lipid chain and show that none of the products can be attributed exclusively to reactions with OH. Therefore, the observed reactant conversion as function of the OH exposure must be interpreted as a qualitative relationship with the total amount of radical species present in the plasma jet. PACS: 52.80.Tn, 82.33.Xj, 31.15.E-. [ABSTRACT FROM AUTHOR]

This paper presents a study of the waves generated by a solid block landslide moving along a horizontal boundary. The landslide was controlled using a mechanical system in a series of physical experiments, and laser-induced fluorescence measurements resolved both spatial and temporal variations in the free surface elevation. During its constant-velocity motion, the landslide transferred energy into 'trapped' offshore-propagating waves within a narrow frequency band. The wave trapping is demonstrated by investigating the wave dispersion characteristics using a two-dimensional Fourier Transform. The first of the trailing waves broke at Froude numbers greater than or equal to 0.625. The parametric dependence of the largest-amplitude waves and the potential energy within the wave field are discussed. The experimental results were compared to the predictions of an incompressible Navier-Stokes solver with and without turbulence models. The numerical model under-predicted the measured wave amplitudes, although it accurately predicted the measured wave phasing. The turbulent model more accurately predicted the shapes of the trailing waves. Both experimental and numerical results confirmed that investigations into wave generation by submerged objects moving at constant velocity should also consider the initial acceleration of the object, as this affects the overall evolution of the wave field. The applicability of the horizontal-boundary results to more realistic field scenarios is discussed. [ABSTRACT FROM AUTHOR]

Formaldehyde (CH 2 O) is an important intermediate in spray combustion of diesel-like fuels. Experimentally, its spatial distribution is often assessed by means of planar Laser-Induced Fluorescence (PLIF), using a frequency-tripled Nd:YAG laser for excitation and spectrally-filtered fluorescence detection. Especially in soot-laden spray flames, however, considerable spectral interference cannot be avoided, which renders interpretation of the fluorescence distribution challenging. We introduce a more selective strategy, involving dye laser excitation and background subtraction by means of off-resonant excitation in combination with a bootstrap evaluation of sets of individual events. The latter extracts persistent features out of non-simultaneously recorded snapshots of stochastic events, thereby mitigating possible interpretation issues related to the turbulent nature of the process under study. Following this approach, recurrent patterns can be distinguished from random high-intensity events (allegedly due to turbulent fluctuations). We demonstrate our method on the Engine Combustion Network (ECN) “Spray A”-benchmark, with 15 vol-% and 21 vol-% ambient oxygen; we also present spatially well-delimited CH 2 O fluorescence distributions, and compare these to simultaneously recorded OH* chemiluminescence intensities. [ABSTRACT FROM AUTHOR]

Biological hazardous substances such as certain fungi and bacteria represent a high risk for the broad public if fallen into wrong hands. Incidents based on bio-agents are commonly considered to have unpredictable and complex consequences for first responders and people. The impact of such an event can be minimized by an early and fast detection of hazards. The presented approach is based on optical standoff detection applying laser-induced fluorescence (LIF) on bacteria. The LIF bio-detector has been designed for outdoor operation at standoff distances from 20 m up to more than 100 m. The detector acquires LIF spectral data for two different excitation wavelengths (280 and 355 nm) which can be used to classify suspicious samples. A correlation analysis and spectral classification by a decision tree is used to discriminate between the measured samples. In order to demonstrate the capabilities of the system, suspensions of the low-risk and non-pathogenic bacteria Bacillus thuringiensis, Bacillus atrophaeus, Bacillus subtilis, Brevibacillus brevis, Micrococcus luteus, Oligella urethralis, Paenibacillus polymyxa and Escherichia coli (K12) have been investigated with the system, resulting in a discrimination accuracy of about 90%. [ABSTRACT FROM AUTHOR]

This paper presents a detailed experimental study to understand the fundamental process of jet breakup during a core disruptive accident of a sodium-cooled fast reactor. The study mainly focuses on hydrodynamic interaction of jet breakup and fragmentation behavior. The experiments were carried out in an immiscible liquid-liquid system. The indices of refraction in the two liquids were matched, so that the vertical plane of jet flow was clearly visualized using laser-induced fluorescence (LIF). The jet breakup length obtained by image processing is compared with the existing correlations. The applicability of the jet breakup length correlations is discussed from the viewpoints of Weber number and film-boiling effect. When the Weber number is from 10 to 1000, and the boiling effect is small enough, it is suggested that jet breakup length is described by Epstein's correlation. Finally, the reduction of jet core diameter is investigated. It is shown, in this experiment, that the mean jet diameter reduces in the flow direction gradually, but it does not reduce linearly.

Laser-induced fluorescence (LIF) is an active technology that is closely related to excitation wavelength (EW). This study has mainly analyzed the performance of LIF LiDAR with different EWs in distinguishing plant species. The 355-, 460-, and 556-nm lasers were utilized to excite leaf fluorescence. The fluorescence signals were measured by the LIF system built in the laboratory. Subsequently, principal component analysis combined with back-propagation neural network was used to analyze fluorescence spectra. For the three EWs, the overall identification rates of the eight plant species were 75%, 80%, and 87.5%. However, when the plant species of the same genus were taken as a category, the overall classification rates were 92.5%, 81.3%, and 86.3%. Experimental results demonstrated that, when the plant species of the same genus were regarded as a category, 355 nm was the optimal EW. However, 556 nm was superior to 355 and 460 nm in the identification of plant species of the same genus. [ABSTRACT FROM PUBLISHER]

The most meaningful spectral components in laser-induced fluorescence (LIF) spectra for several different commercial plastics have been individuated and used to automatically discriminate among different plastic materials and between plastics and complex organic materials, such as woods. Starting from LIF measurements on known samples, a number of significant wavelengths have been identified by principal component analysis (PCA). These have been used to produce intensity ratios functional to the discrimination. Threshold values for such ratios have been individuated in order to obtain an automatic recognition of plastics. The work done has been preparatory to the design and development of a multispectral imaging LIF system for fast detection of plastic debris in a post-blast scene. [ABSTRACT FROM AUTHOR]

We propose combining laser-induced breakdown spectroscopy (LIBS) with molecular laser-induced fluorescence (MLIF) with resulting plasma-borne molecules as a means of studying laser-induced plasma (LIP). Examples of this method with LIP-created Al, Si, and B monoxides are presented. Applicability of the LIBS-MLIF method for elemental and isotope analysis is demonstrated. [ABSTRACT FROM AUTHOR]

This study compares a two-phase flow through a foam-like porous structure and a Sulzer SMX TM static mixing element. Refractive index matching between two immiscible fluids and the internal structures enables optical measurements to be performed. The droplet size and position within the internal structures were observed by laser-induced fluorescence. The results show that at low flowrates, droplets follow preferred paths, whereas at higher flowrates, they are more homogeneously distributed within the structures. The droplet size distribution was found to be well represented by the Sauter mean diameter. Measuring along the axis of the two static mixers, we found that droplets disintegrate more quickly in the foam-like porous structure. As both geometries have the same porosity and hydraulic diameter, we conclude that the change in the free cross section is also an important parameter. We observed that in the geometry with large changes in the free cross section, the droplets are smaller. [ABSTRACT FROM AUTHOR]

[Display omitted] • Silvered or aluminized one-side cuvette enhances LIF analytical sensitivity. • The reflecting side should face the incident laser beam. • A sixfold increase in the chlorophyll-a fluorescence intensity was achieved. • Application of RELIF on six brands of olive oil provided 2–3-fold enhancement. • PLSR analysis of the RELIF & LIF data of olive oil showed the superiority of RELIF. The current work demonstrates a novel approach to enhancing the analytical sensitivity of the laser-induced fluorescence (LIF) technique in liquids. An increase in the fluorescence spectral band intensity of about sixfold compared to the conventional LIF has been achieved. Such betterment has been accomplished by having the fluorophore liquid in a cuvette having a reflecting mirror-like side facing the exciting incident laser beam. The silvered or aluminized reflecting side of the cuvette was tested. The pilot test of the proposed cuvette was performed using an excitation laser light of 405 nm wavelength and five mW average power on chlorophyll-a (Chl-a) samples of different concentrations. As a result, a pronounced improvement in the Chl-a fluorescence spectral band intensity is achieved. Such a novel approach, the reflection-enhanced laser-induced fluorescence (RELIF), has been used to analyze six Egyptian brands of extra virgin olive oil (EVOO). Compared to the LIF measurement results on the same EVOO, the RELIF was superior in terms of the fluorescence-spectrum intensity enhancement factor. Both Ag and Al coatings of the cuvette revealed similar results. Statistical analysis of the measured fluorescence spectra via the partial least square regression (PLSR) method for LIF and RELIF revealed a higher coefficient of determination R2 for both RELIF measurements (with silver and aluminum coating) than for LIF. The proposed novel RELIF approach can be utilized for other fluorophore liquids at higher analytical sensitivity than conventional LIF. On the other hand, the RELIF technique is straightforward, cost-effective, and does not complicate the traditional LIF setup. [ABSTRACT FROM AUTHOR]

Total cholesterol monitoring in human plasma is one of the most important routine analysis performed in the clinical laboratory. Here we report a new capillary electrophoresis method for determination of plasma total cholesterol based on on-column enzymatic assay and laser-induced fluorescence detection. In this method, the capillary is used not only as a separation medium but also as the reaction chamber which minimizes the amount of samples and the consumption of the reagents. The whole procedure can be automated which minimizes the possible errors and saves experimental time. The analytical characteristics of the proposed method, such as linearity and repeatability of the peak area and the migration time, were evaluated. The RSD of the migration time and peak area were 1.0 and 3.5 % (intraday), and 2.2 and 2.9 % (interday), respectively. The obtained LOQ values were at the nanomolar concentration level, therefore the developed method is sufficient for determination and quantification of plasma total cholesterol. [ABSTRACT FROM AUTHOR]

The waves generated by a submarine landslide, of great concern to coastal communities, exhibit strong dependence on the landslide motion along the sea floor. A series of two-dimensional physical experiments investigate the waves generated by a solid block landslide moving along a horizontal boundary, allowing measurement of both onshore- and offshore-propagating waves using the laser-induced fluorescence technique. This technique provides high-quality free surface measurements over the entire length of the experimental flume, and hence a data set that can be used to validate numerical models for this idealised scenario. The landslide motion is provided by a mechanical system, allowing testing of a range of landslide accelerations and terminal velocities. The landslide Froude number governs the overall behaviour of the wave field. At lower Froude numbers, the waves are almost entirely generated by the landslide acceleration and deceleration, and the offshore- and onshore-propagating wave groups contain approximately equal energy. Interactions between the landslide and the offshore-propagating waves become more important as the Froude number increases. Two inviscid-irrotational models demonstrate the importance of dispersive effects for tsunamis generated by a submarine landslide, and correctly predict the behaviour of the entire wave field at low Froude numbers. The predictions in the vicinity of the landslide worsen with increasing Froude number, due to the linear free surface conditions used by the models. Lower Froude numbers appear to be more representative of previous sloping-boundary experimental geometries, although rigid block landslides still represent an idealisation of a field scenario. [ABSTRACT FROM AUTHOR]

We have investigated the laser-induced fluorescence (LIF) excitation spectra and dispersed fluorescence (DF) spectra of yttrium monosulfide (YS) in the energy range of 17 860–20 700 cm −1 . Rotational analyses indicated that almost all of the intense vibronic bands can be attributed to the new [ 19.38 ] 2 Σ + ( υ ′ ) - X 2 Σ + ( υ ″ ) transition system. The missing (1, 2), (2, 1) and (3, 3) bands are caused by their very small Franck–Condon factors, as confirmed by our calculations. The new 2 Σ + state has been suggested to arise from the electronic configuration of ( core )1 σ 2 2 σ 2 1 π 3 3 σ 2 π , featuring a charge-transfer nature. Moreover, the spin-rotation parameter γ for the newly observed 2 Σ + state has been determined to be 0.0206 cm −1 , the magnitude of which is larger than the known γ ( X 2 Σ + ) (0.001427 cm −1 ) but smaller than γ ( B 2 Σ + ) (−0.1515 cm −1 ). [ABSTRACT FROM AUTHOR]

Hydroxyl (OH) radicals generated in wire–plate pulsed corona discharge (PCD) were detected by laser-induced fluorescence (LIF). In this paper, the 2-D distribution of OH radicals and the time-resolved development of the streamers in humidified nitrogen were recorded by an intensified charge-coupled device camera. The results indicate that the OH-LIF signals could not be detected when secondary streamer was absent in PCD with low input energy. Input energy, which varies with the configuration of wire–plate reactor and applied voltage, significantly affected the spatial distribution of OH radicals. [ABSTRACT FROM PUBLISHER]

By applying down-sizing and high-pressure injection on gasoline direct injection (GDI) and dual-fuel spark ignition (DFSI) engines, the deposited fuel film caused by spray impingement would significantly increase engine soot emissions. In this study, laser-induced fluorescence (LIF) was used to initially explore the difference in deposited fuel film of gasoline surrogate fuel (GSF) and ethanol spray impingement. And, phase doppler anemometry (PDA) was used to further reveal the difference in deposited film formation mechanisms by analysing microscopic droplet characteristics quantitatively. The study could contribute novel insights to the fuel injection strategy optimisation, spray modelling research, pollution reduction and thermal efficiency improvement for GDI and DFSI engines. The results showed that 60% to 70% mass of the ethanol spray would deposit on the wall when vertical impingement, while that of GSF only is 40% to 60%. Moreover, due to ethanol's high viscosity, ethanol film is at least 39% thicker than GSF under the same injection condition. Thicker average film thickness easily results in pool fire and high soot emissions. Inclined impingement angle and high injection pressure could help reduce the deposited film mass of both fuels. Particularly, the film mass of GSF would decrease by 36% by increasing injection from 7 MPa to 15 MPa. Regarding microscopic droplet characteristics, a considerable difference can be seen for the incident droplets in different radial positions. Compared to ethanol, GSF spray droplet velocity is at least 13% higher, which would further enhance the reflection and secondary breakup. • LIF technique was used to initially explore the difference in deposited fuel film of GSF and ethanol spray impingement. • PDA technique was used to analyse microscopic droplet characteristics quantitatively • New insights were provided for fuel injection strategy optimisation and spray modelling research in GDI and DFSI engines. • New information was provided for analysing the difference between GSF and ethanol in deposited film formation mechanisms. [ABSTRACT FROM AUTHOR]