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Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010 cm−1 (∼10–20 kcal mol−1) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2νOH) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products. [ABSTRACT FROM AUTHOR]

We report the two-photon absorption laser-induced fluorescence rotational spectrum of the CO B 1Σ+ ← X 1Σ+ Hopfield–Birge system (v′ = 0, v″ = 0) Q-branch in an ∼4850 K, atmospheric pressure plasma torch plume at thermal equilibrium in both the quenching-dominated (low laser intensity) and photoionization-dominated (high laser intensity) regimes. We provide a detailed analysis of the photophysics in these two regimes using a rate equation approach and propose modeling considerations for them as well. In the experimental spectra, distinct rotational transitions up to J″ = 83 are observed, allowing analysis over a very large range of rotational states. Evidence of predissociation is observed for J′ ≥ 64 and is likely due to the interaction with the D′1Σ+ electronic state, which has been proposed in the literature but never observed in the v′ = 0 state. The line positions of higher rotational states show disagreement with line positions calculated from molecular constants in the available literature, suggesting the need for modifications to the constants, which are reported here. A shift in the B 1Σ+ ← X 1Σ+ absorption spectrum toward higher two-photon energy as a result of the second-order Stark shift was observed in the photoionization-dominated spectrum, and the second-order Stark shift cross section was estimated to be 7 ± 3 × 10−18 cm2. The mean photoionization cross section of the excited upper state was inferred by comparing the line broadening of the two spectra and was estimated to be 11 ± 7 × 10−18 cm2. In addition, weak J′-dependent variations of the photoionization cross section were observed and are reported here. [ABSTRACT FROM AUTHOR]

The contribution of atomic nitrogen is fairly possible in plasma-assisted catalytic synthesis of ammonia since it has high adsorption probabilities on solid surfaces. On the other hand, recently, the contribution of vibrational excited molecular nitrogen to ammonia synthesis has been discussed. In this work, we compared the fluxes of atomic nitrogen and vibrational excited molecular nitrogen with the rate of plasma-assisted ammonia synthesis. We employed an atmospheric-pressure nitrogen plasma jet, and the spatial afterglow of the plasma jet and a hydrogen flow irradiated the surface of a ruthenium catalyst. The fluxes of atomic nitrogen and vibrational excited molecular nitrogen were measured by two-photon absorption laser-induced fluorescence spectroscopy and laser Raman scattering, respectively. The synthesis rate of ammonia had a positive correlation with the flux of vibrational excited molecular nitrogen, while the variation of the synthesis rate with the gas flow rate was opposite to the flux of atomic nitrogen. The experimental results indicate the contribution of vibrational excited molecular nitrogen to the synthesis of ammonia using the atmospheric-pressure plasma, where the flux of vibrational excited molecular nitrogen is more than four orders of magnitude higher than that of atomic nitrogen. [ABSTRACT FROM AUTHOR]

This study was focused on the photochemistry of OAlOH and three possible pathways, which were studied with high-level multireference configuration interaction ab initio calculations. We computed cuts of the six-dimensional potential energy surfaces for the ground, the lowest singlet and triplet excited states, and probed the photodissociation mechanisms and the stabilities. The OAlOH electronic spectrum, with an energy reaching 7.15 eV, contained four prominent peaks. Photodissociation to AlO, OH, and AlOH constituted a plausible mechanism within the deep-UV range (λ = 250.4 nm). Our data indicated the photostability of OAlOH in the near-UV‒Vis region, so detection with laser-induced fluorescence is possible. Fluorescence and phosphorescence may occur upon excitation at 363.5 nm. The roles of OAlOH in the photochemical reactions of Al-bearing molecules in the upper atmosphere and VY Canis Majoris are discussed. [ABSTRACT FROM AUTHOR]

An IR–vacuum ultraviolet (VUV) ion-dip spectroscopy method is utilized to examine the IR spectrum of acetaldehyde oxide (CH3CHOO) in the overtone CH stretch (2νCH) spectral region. IR activation creates a depletion of the ground state population that reduces the VUV photoionization signal on the parent mass channel. IR activation of the more stable and populated syn-CH3CHOO conformer results in rapid unimolecular decay to OH + vinoxy products and makes the most significant contribution to the observed spectrum. The resultant IR–VUV ion-dip spectrum of CH3CHOO is similar to that obtained previously for syn-CH3CHOO using IR action spectroscopy with UV laser-induced fluorescence detection of OH products. The prominent IR features at 5984 and 6081 cm−1 are also observed using UV + VUV photoionization of OH products. Complementary theoretical calculations utilizing a general implementation of second-order vibrational perturbation theory provide new insights on the vibrational transitions that give rise to the experimental spectrum in the overtone CH stretch region. The introduction of physically motivated small shifts of the harmonic frequencies yields remarkably improved agreement between experiment and theory in the overtone CH stretch region. The prominent features are assigned as highly mixed states with contributions from two quanta of CH stretch and/or a combination of CH stretch with an overtone in mode 4. The generality of this approach is demonstrated by applying it to three different levels of electronic structure theory/basis sets, all of which provide spectra that are virtually indistinguishable despite showing large deviations prior to introducing the shifts to the harmonic frequencies. [ABSTRACT FROM AUTHOR]

A femtosecond laser induced photofragmentation fluorescence (fs-LIPF) scheme for the sensitive detection and imaging of water vapor is presented. Two photons of 244.3 nm excite water to the D ̃ state and produce hydroxyl radicals in the fluorescing A ̃ state. Two more photons promote electrons from the D ̃ state to a neutral Rydberg state of the (1b2)−1 ionic core through a 2 + 2 doubly resonant process. The resulting high-lying Rydberg state undergoes neutral dissociation, and the energetic hydrogen fragments are detected from their Balmer series fluorescence. These channels (in the low-pressure limit) have detection sensitivities around 1012 molecules per cubic centimeters, orders of magnitude more sensitive than laser-induced fluorescence based approaches, allowing for sensitive non-invasive detection and imaging of water density for many important processes. [ABSTRACT FROM AUTHOR]

Rotationally resolved Fourier-transform spectra of laser-induced fluorescence A 1 Σ u + ∼ b 3 Π u → X 1 Σ g + of K2 molecules were recorded and analyzed, yielding 4053 term values of the spin–orbit (SO) coupled A ∼ b complex of the 39K2 isotopologue with ∼0.01 cm−1 accuracy. Their compilation with 1739 term values from previously published sources allowed them to cover the energy range [9955, 17 436] cm−1 from the bottom of the lower-lying b3Πu state up to the vicinity of the atomic asymptote 4 s 2 S 1 2 + 4 p 2 P 1 2 , with a rotational quantum number J ∈ [0, 149]. The experimental data were processed by a direct 6 × 6 coupled-channel (CC) deperturbation treatment, which accounted explicitly for both SO and electronic-rotational interactions between all six e-symmetry states: A 1 Σ u + ( 0 u + ), b3Πu( 0 u + , 1 u , 2 u ), c3Σu(1u), and B1Πu(1u). The initial parameters of the global deperturbation model have been estimated in the framework of ab initio electronic structure calculations applying multi-reference configuration-interaction and coupled-clusters methods. The interatomic potentials analytically defined for A and b states, as well as SO-splitting of the triplet b state and A ∼ b SO-coupling functions, have been particularly refined to fit the 5792 term values of the 39K2 isotopologue, whereas the rest parameters were fixed on their ab initio values. The resulting mass-invariant parameters of the 6 × 6 CC model reproduced the overall rovibronic term energies of the A ∼ b complex of 39K2 with accuracy, which is well within the experimental errors. The quality of the deperturbation analysis was independently confirmed by comparison with the present obtained 705 and 14 term values of respective 39K41K and 41K2 isotopologues, as well as by agreement between measured and predicted relative intensity distributions in long A ∼ b → X(vX) band progressions. This deperturbation analysis provided the refined dissociation energy Tdis = 17 474.569(5) cm−1 and the long-range coefficient C 3 Σ = 5.501(4) × 105 cm−1 Å3 relevant to the non-relativistic atomic limit 4s + 4p. The derived Tdis yielded the accurate well depth De = 4450.910(5) cm−1 for the ground X 1 Σ g + state, whereas the new C 3 Σ value yielded the improved estimates for atomic K(4 p 2 P 1 2 ; 3 2 ) radiative lifetimes, τ 1 2 = 26.67(3) and τ 3 2 = 26.32(3) ns. [ABSTRACT FROM AUTHOR]

GaCH2, a free radical thought to play a role in the chemical vapor deposition of gallium-containing thin films and semiconductors, has been spectroscopically detected for the first time. The radical was produced in a pulsed discharge jet using a precursor mixture of trimethylgallium vapor in high pressure argon and studied by laser-induced fluorescence and wavelength resolved emission techniques. Partially rotationally resolved spectra of the hydrogenated and deuterated species were obtained, and they exhibit the nuclear statistical weight variations and subband structure expected for a 2A2–2B1 electronic transition. The measured spectroscopic quantities have been compared to our own ab initio calculations of the ground and excited state properties. The electronic spectrum of gallium methylene is similar to the corresponding spectrum of the aluminum methylene radical, which we reported in 2022. [ABSTRACT FROM AUTHOR]

A π-type hydrogen bonding between the OH group and the π electron is a crucial factor for the conformational preference of the molecular structure with a flexible group. However, the information on the effect of the substituent on the OH/π interaction is insufficient. The laser-induced fluorescence (LIF) excitation, the dispersed fluorescence (DF), the IR–UV hole-burning, and the IR dip spectra of jet-cooled 2-(4-methoxyphenyl)ethanol were measured for the first time. Almost all bands observed in the spectral region of 35 550–36 500 cm−1 in the LIF excitation spectrum were successfully assigned with the DF and the IR–UV hole-burning spectra coupled with the quantum chemical calculation at M06-2x/6-311G and MP2/6-311G levels. Five conformers were found in the LIF excitation spectrum. The most stable conformer was Ggπ, and the second most stable conformer was Ggπ′ (the trans rotamer of the methoxy group for Ggπ). Ggπ and Ggπ′ had the OH group directed toward the π electron system of the benzene ring. The OH stretching frequency of Ggπ/Ggπ′ of MPE in the IR dip spectra was red-shifted against that of Ggπ of phenylethanol, indicating that the introduction of the methoxy group would enhance the intramolecular OH/π interaction. In addition, the torsional vibration between the benzene ring and the side chain (−CH2CH2OH) (mode 63) was observed in the DF spectra of the Ggπ–00 and Ggπ′–00 band excitation, but their intensities were rather different, resulting from the different orientation of the OH group for each conformer toward the π electron system. The methoxy group would increase the negative charge on the benzene ring and would enhance the intramolecular OH/π interaction through the electrostatic interaction. [ABSTRACT FROM AUTHOR]

Gas–liquid two-phase stratified flow exists in many industrial processes. Although the flow pattern is simple, the interfacial shear prediction of stratified flow is still the focus of the study. The calculation of the shear stress at the gas–liquid interface is closely related to the measurement of the void fraction and pressure drop of the stratified flow. In this study, a new method for the calculation of interfacial shear stress of gas–liquid two-phase stratified flow is proposed. Differential pressure measurement and planar laser-induced fluorescence technology are combined to obtain important parameters for stratified flow under low-speed flow conditions (Ql = 0.10–0.25 m3/h, Qg = 0.35–1.00 m3/h). The interfacial shear stress is successfully calculated using macroparameters. The uncertainty associated with the calculated parameters using the proposed method is 2.67%, and this study verifies the accuracy of the linear relationship. The method provides a new way to obtain the interfacial shear stress of gas–liquid stratified flow. [ABSTRACT FROM AUTHOR]

We have analyzed the effects of the spreads in experimental parameters on the reliability of speeds and angular distributions extracted from a generic surface-scattering experiment based on planar laser-induced fluorescence detection. The numerical model assumes a pulsed beam of projectile molecules is directed at a surface. The spatial distribution of the scattered products is detected by imaging the laser-induced fluorescence excited by a thin, pulsed sheet of laser light. Monte Carlo sampling is used to select from realistic distributions of the experimental parameters. The key parameter is found to be the molecular-beam diameter, expressed as a ratio to the measurement distance from the point of impact. Measured angular distributions are negligibly distorted when this ratio is <∼10%. Measured most-probable speeds are more tolerant, being undistorted when it is <∼20%. In contrast, the spread of speeds or of corresponding arrival times in the incident molecular beam has only very minor systematic effects. The thickness of the laser sheet is also unimportant within realistic practical limits. These conclusions are broadly applicable to experiments of this general type. In addition, we have analyzed the specific set of parameters designed to match the experiments on OH scattering from a liquid perfluoropolyether (PFPE) surface in the Paper I [Roman et al., J. Chem. Phys. 158, 244704 (2023)]. This reveals that the detailed form of the molecular-beam profile is important, particularly on apparent angular distributions, for geometric reasons that we explain. Empirical factors have been derived to correct for these effects. [ABSTRACT FROM AUTHOR]

Inelastic collisions of OH with an inert liquid perfluoropolyether (PFPE) surface have been studied experimentally. A pulsed molecular beam of OH with a kinetic energy distribution peaking at 35 kJ mol−1 was directed at a continually refreshed PFPE surface. OH molecules were detected state-selectively with spatial and temporal resolution by pulsed, planar laser-induced fluorescence. The scattered speed distributions were confirmed to be strongly superthermal, regardless of the incidence angle (0° or 45°). Angular scattering distributions were measured for the first time; their reliability was confirmed through extensive Monte Carlo simulations of experimental averaging effects, described in Paper II [A. G. Knight et al., J. Chem. Phys. 158, 244705 (2023)]. The distributions depend markedly on the incidence angle and are correlated with scattered OH speed, consistent with predominantly impulsive scattering. For 45° incidence, the angular distributions are distinctly asymmetric to the specular side but peak at sub-specular angles. This, along with the breadth of the distributions, is incompatible with scattering from a surface that is flat on a molecular scale. New molecular dynamics simulations corroborate the roughness of the PFPE surface. A subtle but unexpected systematic dependence of the angular distribution on the OH rotational state was found, which may be dynamical in origin. The OH angular distributions are similar to those for kinematically similar Ne scattering from PFPE and hence not strongly perturbed by OH being a linear rotor. The results here are broadly compatible with prior predictions from independent quasiclassical trajectory simulations of OH scattering from a model-fluorinated self-assembled monolayer surface. [ABSTRACT FROM AUTHOR]

The isoelectronic molecules UN and UO+ are known to have Ω = 3.5 and Ω = 4.5 ground states, respectively (where Ω is the unsigned projection of the electronic angular momentum along the internuclear axis). A ligand field theory model has been proposed to account for the difference [Matthew and Morse, J. Chem. Phys. 138, 184303 (2013)]. The ground state of UO+ arises from the U3+(5f3(4I4.5))O2− configuration. Owing to the higher nominal charge of the N3− ligand, the U3+ ion in UN is stabilized by promoting one of the 5f electrons to the more polarizable 7s orbital, reducing the repulsive interaction with the ligand and rendering U3+(5f27s(4H3.5))N3− the lowest energy configuration. In the present work, we have advanced the characterization of the UN ground state through studies of two electronic transitions, [18.35]4.5-X(1)3.5 and [18.63]4.5-X(1)3.5, using sub-Doppler laser excitation techniques with fluorescence detection. Spectra were recorded under field-free conditions and in the presence of static electric or magnetic fields. The ground state electric dipole moment [μ = 4.30(2) D] and magnetic ge-factor [2.160(9)] were determined from these data. These values were both consistent with the 5f27s configurational assignment. Dispersed fluorescence measurements were used to determine vibrational constants for the ground and first electronically excited states. Electric dipole moments and magnetic ge-factors are also reported for the higher-energy electronically excited states. [ABSTRACT FROM AUTHOR]

The formation and transportation of short-lived species on/within the plasma-liquid interfacial layer plays a crucial role in various applications because of their high chemical reactivity. However, the experimental detection and quantification of these short-lived species, such as ˙OH radicals, at the gas–liquid interface still pose formidable challenges. This study confronts this challenge by employing incident microscopic laser-induced fluorescence (mLIF) method to capture the OH-LIF signals on the interfacial layer at different time moments of the post-discharge phase under high spatial resolution. The temporal evolution of ˙OH density is subsequently quantified by fitting the OH-LIF decay behavior to a reaction-dissolution model. Results reveal that increasing the pulse width serves better to enhance ˙OH generation on liquid surface, reaching a density of 1.25 × 1016 cm−3. Furthermore, the cathode-solution interface demonstrates significantly enhanced ˙OH production compared to the anode-solution interface. These results underscore the efficacy of incident mLIF in quantitatively probing short-lived ˙OH-radical production at the interfacial layer in pulsed-driven plasma-solution interactions, with potential applicability to other reactive species. [ABSTRACT FROM AUTHOR]

Mine water inrush disaster can quickly cause significant economic losses and casualties because of its strong concealing and rapid burst speed. Quickly identifying the source of mine water inrush is of great practical significance. Compared with the traditional hydrochemical analysis method, the laser-induced fluorescence (LIF) technology has fast reaction speed, high sensitivity, and strong stability, which makes up for the shortcomings of the traditional method. As an integrated algorithm, random forest (RF) has the advantage of high accuracy. A combination of LIF technology and RF algorithm is proposed to identify mine water inrush source rapidly. The experimental samples were collected from a coal mine in Hainan City, Anhui Province, and a total of 525 sets of water samples to be tested for experiments by mixing goaf water and sandstone water into A-G7 species according to different proportions. Moving average smoothing (MA), Savitzky-Golay Smoothing (SG), First derivative (FD), and Second derivative (SD) methods are used to preprocess the original spectral data to reduce the noise and interference information existing in the original spectral data. By comparison, the Moving average smoothing (MA) method has high classification accuracy and is the final method for noise reduction. Then, the RF algorithm is used to delete the less critical spectrum after noise reduction and select the characteristic wavelength with the minimum classification error of 0. Finally, SVM, PCA-SVM, MA-SVM, MA-PCA-SVM, and MA-RF algorithm recognition models were established, respectively. Comparing the prediction accuracy of the test set, the accuracy of the MA-RF algorithm in the five groups of models reached 100%, which can quickly and accurately predict mine water inrush. [ABSTRACT FROM AUTHOR]

An experiment was carried out using a scale model of a tall building, with the goal of investigating the role of individual buildings in the dispersion of air pollution. Pollutant dispersion around an isolated building with a height-to-length aspect ratio of 1.4 is investigated using simultaneous particle image velocimetry and planar laser induced fluorescence. Dye is released from a ground-level point source five building heights upstream of the tall building. It was found that in this case the scalar plume was dispersed laterally strongly by the building, but only slightly vertically. It is hypothesized that this is due to 94% of the plume impinging below the stagnation point on the front of the building and being drawn into the horseshoe vortex. We expect this fraction would be lower in a case in which the building is in an array of smaller buildings, and that this would lead to more vertical dispersion. [ABSTRACT FROM AUTHOR]

Chlorophyll has long been used as a natural indicator of plant health and photosynthetic efficiency. Laser-induced fluorescence (LIF) is an emerging technique for understanding broad spectrum organic processes and has more recently been used to monitor chlorophyll response in plants. Previous work has focused on developing a LIF technique for imaging moss mats to identify metal contamination with the current focus shifting toward application to moss fronds and aiding sample collection for chemical analysis. Two laser systems (CoCoBi a Nd:YGa pulsed laser system and Chl-SL with two blue continuous semiconductor diodes) were used to collect images of moss fronds exposed to increasing levels of Cu (1, 10, and 100 nmol/cm2) using a CMOS camera. The best methods for the preprocessing of images were conducted before the analysis of fluorescence signatures were compared to a control. The Chl-SL system performed better than the CoCoBi, with dynamic time warping (DTW) proving the most effective for image analysis. Manual thresholding to remove lower decimal code values improved the data distributions and proved whether using one or two fronds in an image was more advantageous. A higher DTW difference from the control correlated to lower chlorophyll a/b ratios and a higher metal content, indicating that LIF, with the aid of image processing, can be an effective technique for identifying Cu contamination shortly after an event. [ABSTRACT FROM AUTHOR]

Cool red giant stars exhibit absorption bands of calcium monochloride (CaCl) in the optical region. In this work, the bands of CaCl corresponding to the A2Π − X2Σ+ transition with v ′ ≤ 4 and v ″ ≤ 4, and B2Σ+ − X2Σ+ transition with v ′ ≤ 2 and v ″ ≤ 2 are rotationally analyzed with PGOPHER, a multipurpose program for simulating and fitting molecular spectra. All bands were analyzed using high-resolution absorption spectra collected at the National Solar Observatory in 1985, calibrated with atomic lines from a high-resolution emission spectrum obtained in a separate hollow cathode experiment. The results are compared with previous laser-induced fluorescence measurements. Overall, the accuracy of spectroscopic constants for the A2Π and B2Σ+ states is improved. Scaled transition dipole moment calculations were used to obtain line strengths. Line lists are provided with Einstein A coefficients and oscillator strengths, which can be used to determine CaCl stellar abundances. Additionally, isotope splittings allowed us to estimate band origins for the 40Ca37Cl isotopologue based on band-head positions. [ABSTRACT FROM AUTHOR]

The problems of laser-induced fluorescence (LIF) measurements in a partially saturated regime with spatially dependent laser intensity in the sample (caused by absorption) are analyzed. The obtained equations are tested by means of LIF of free tellurium atoms in a plasma of an atmospheric pressure dielectric barrier discharge (DBD) by comparing fluorescence and absorption measurements. The results show a high reliability of LIF measurements. [ABSTRACT FROM AUTHOR]

A 3D model is established to discuss the influence of combustion reaction on jet characteristics. Based on this, combustion behaviors of supersonic jet for single‐flow postcombustion oxygen lance with various secondary nozzle parameters (diameter, inclination angle, and number) are analyzed. The results indicate that after activating combustion reaction, the jet velocity, dynamic pressure, density, and temperature of primary jet at H = 1.45 m are 1.27, 1.15, 0.56, and 1.97 times than those of without considering the combustion, respectively. Enlarging secondary nozzle diameter is helpful to extend the flame core lengths of primary and secondary jets (the axial distance from lance tip to isotherm of 1773 K) as well as the combustion region. With the increase of secondary nozzle angle, the two flame core lengths both decrease, while the combustion zone increases. Increasing the number of secondary nozzles, the flame core length of primary jet increases while that of the secondary jet decreases, and the combustion region first increases and then decreases. As for the influences of the above parameters on flame core lengths of primary and secondary jets as well as the combustion region, the number is the greatest, followed by the inner diameter, and the inclination angle is the smallest. [ABSTRACT FROM AUTHOR]

The current work investigates the effects of oblique Lorentz force and Navier's slip boundary condition on unsteady hybrid nanoliquid flow with three different base liquids (H2O, CH3OH and H2O–EG) across a nonlinearly elongating surface set in a porous medium. This research considers the effects of viscous–Ohmic dissipation, nonlinearly variable thermal radiation, internal heat source, the Soret effect, first-order chemical reaction and thermal and solutal jump conditions at the boundary. Proper thermo-physical relationships for the hybrid nanoliquid have been established. Rosseland's estimate for an optically thick regime is used when calculating the heat flow owing to radiation. The dimensional governing equations are translated into nondimensional forms using appropriate similarity transformations. The velocity, energy and concentration fields are numerically solved using a shooting strategy based on the secant iteration and the Runge–Kutta–Fehlberg method. The physical implications of several essential parameters on the hybrid nanoliquid velocity, temperature and concentration are investigated using graphical and tabular representations of numerical data. Furthermore, the multiple (quadratic) regression analysis reveals that physical parameters strongly influence the local skin friction coefficient, Sherwood and Nusselt numbers. For continuously growing values of the unsteadiness parameter, the velocity, thermal and concentration scattering declined everywhere within the boundary layer region. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence (LIF) Doppler spectroscopy using an optical vortex beam with an asymmetric intensity distribution, referred to as aOVLIF, is proposed as a new method to measure plasma flow velocity. LIF spectra were calculated numerically using typical laboratory low-temperature plasma parameters, and it was revealed that an ion flow across the beam produces a frequency shift of the spectra. This method also has the capability of temperature measurements. The propagation effects of asymmetric optical vortex beams are discussed assuming an actual experiment, and it is found that the sensitivity to the transverse flow velocity is approximately unchanged. The aOVLIF method, which exploits the inhomogeneous phase structure of optical vortices, can be applied to the determination of three-dimensional velocity vectors and promises to enhance the usefulness of conventional LIF spectroscopy using plane waves. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3), hydrogen (H 2) and methane (CH 4) as zero- or low-carbon fuels are considered as highly promising alternative fuels. Turbulent non-premixed jet combustion is a prospective way in practical combustion devices for ammonia, hydrogen and methane, but the relevant experimental researches are rare, while such information is critical for the development and validation of numerical models. In this paper, the laser diagnostic studies are carried out in a constant volume combustion chamber to investigate the characteristics of the 50%NH 3 +50%H 2 blend jet with or without ignition in comparison to H 2 , CH 4 and NH 3 jets. Firstly, the morphological developments and concentration distributions of the four gas jets without ignition are compared. Then, the OH or NO distributions in the non-premixed gas jet flames are clarified by the planar laser-induced fluorescence techniques. The generation and consumption processes of OH and NO are elucidated by the one-dimensional simulation. The results show that the four jets exhibit a similar morphological development with the nearly same jet angles, except for a little slower tip penetration of 50%NH 3 +50%H 2 blend. The equivalence ratio of the 50%NH 3 +50%H 2 blend and NH 3 jets along the jet axis are lower than those in the CH 4 and H 2 jets due to the difference in the flow rate and stoichiometric number. The H 2 jet exhibits the highest combustion intensity, featuring faster flame propagation, the shortest lift-off length and an apparently higher OH radical intensity, while the NH 3 jet fails to develop a stable flame. The mixture in the 50%NH 3 +50%H 2 blend jet is too lean, resulting in a weaker combustion intensity than the H 2 and CH 4 jets. However, the NO intensity in the 50%NH 3 +50%H 2 jet flame is remarkably stronger than those of the H 2 and CH 4 jet, due to the much higher amount of fuel-type NO converted from NH 3 than that of thermal NO. A self-reducing (SR) zone can be observed where OH is produced and then consumed in the 50%NH 3 +50%H 2 blend, H 2 and CH 4 jet flames. However, the NO SR zone is only observable in the 50%NH 3 +50%H 2 blend jet flames, probably owing to the consumption by the NH 2 and NH radicals. • The laser diagnostic was used to obtained the OH and NO distributions. • The 50%NH 3 +50%H 2 , H 2 , CH 4 and NH 3 jets exhibit a similar morphologic development. • The equivalence ratios of the 50%NH 3 +50%H 2 blend and NH 3 jets are the lowest. • The fuel-type NO makes the strongest NO intensity in 50%NH 3 +50%H 2 blend flames. • For the first time a self-reducing zone was observed for the OH and NO. [ABSTRACT FROM AUTHOR]

This study explores the stabilization of non-premixed NH 3 /CH 4 flames using gradient magnetic fields, overcoming challenges like low flame speed and instability inherent in ammonia—a carbon-free fuel and efficient hydrogen carrier. The action of the magnetic field modified the flame flow field, resulting in the suppression of emissions. By applying magnetic fields, the blending ratio of ammonia in the diffusion flame was elevated, resulting in an increase of 69% in the limit concentration to a near-pure level of 0.914. Measurements with Particle Image Velocimetry and schlieren system, alongside computational fluid dynamics, reveal how gradient magnetic fields mitigate flame detachment, lift-off, and blowout by altering flame root stabilization mechanisms. Specifically, gradient magnetic fields reduce localized flow velocity at the flame root and improve mass transfer. This indicates that gradient magnetic fields can significantly enhance the stability of NH 3 /CH 4 flames, suggesting a promising route toward cleaner energy production and environmental sustainability. [Display omitted] • Achieves near-pure ammonia combustion in diffusion flames by imposing gradient magnetic fields. • Identified critical impact of magnetic fields on flame structure and reactant species distribution. • Investigates gradient magnetic field effects on flame root dynamics, offering new stabilization insights. • Integrates PIV, schlieren photography, and simulations to detail magnetic fields' role in sustaining ammonia flames. [ABSTRACT FROM AUTHOR]

Single‐molecule localization microscopy (SMLM) has revolutionized optical microscopy by exceeding the diffraction limit and revealing previously unattainable nanoscale details of cellular structures and molecular dynamics. This super‐resolution imaging capability relies on fluorophore photoswitching, which is crucial for optimizing the imaging conditions and accurately determining the fluorophore positions. To understand the general on and off photoswitching mechanisms of single dye molecules, various photoswitching reagents were evaluated. Systematic measurement of the single‐molecule‐level fluorescence on and off rates (kon and koff) in the presence of various photoswitching reagents and theoretical calculation of the structure of the photoswitching reagent‐fluorophore pair indicated that the switch‐off mechanism is mainly determined by the nucleophilicity of the photoswitching reagent, and the switch‐on mechanism is a two‐photon‐induced dissociation process, which is related to the power of the illuminating laser and bond dissociation energy of this pair. This study contributes to a broader understanding of the molecular photoswitching mechanism in SMLM imaging and provides a basis for designing improved photoswitching reagents with potential applications extending to materials science and chemistry. [ABSTRACT FROM AUTHOR]

Ytterbium‐doped lanthanum titanate glasses were prepared by levitation melting for the detailed characterization of the Yb3+${\rm Yb}^{3+}$ spectroscopic properties in the rare‐earth titanate glass host. Low‐temperature fluorescence spectroscopy reveals distinct site‐selectivity in both static and lifetime fluorescence measurements suggesting an absence of clustering as well as significant variation of local ytterbium environments. Typical site‐selectivity behavior of a shrinking Stark manifold with lower excitation energy is observed. At 77 K, both the mean emission frequency and the fluorescence lifetime initially increase as the excitation energy decreases from about 11100 to 10750 cm−1${\rm cm}^{-1}$ and then slightly decrease at lower excitation energy. Temperature‐dependent lifetime measurements between 77 and 420 K show a decreasing lifetime with increasing temperature and are well described by a two‐level thermal activation model. The temperature‐dependent fluorescence spectroscopy coupled with a room temperature white light absorption measurement allow the determination of the Stark energy levels of Yb3+${\rm Yb}^{3+}$ in lanthanum titanate glass as well as the calculation of the laser cross‐sections. [ABSTRACT FROM AUTHOR]

Groundwater contamination caused by hydrocarbons is a common issue worldwide. Determining the volume of light non-aqueous phase liquids (LNAPL) that contaminate the subsurface environment is crucial for planning effective groundwater and soil remediation strategies, as well as determining the remediation endpoint. However, accurate approaches for quantifying the LNAPL volume in subsurface environments are scarce. To address this gap, we developed and tested a novel approach to quantify the volume of oil phase filling the soil pores. Our approach involves using a high-resolution technique, the laser induced fluorescence (LIF), to identify the presence of the oil phase, which was then correlated to total petroleum hydrocarbons (TPH) quantifications. For that, first, we obtained an empirical model to estimate the TPH present in the soil using fluorescence intensity and then, we converted the fluorescence intensity data in each log to equivalent TPH values. We used the model block approach, commonly used for ore resource estimation, to compute and discretize the volume of the aquifer contaminated by LNAPL into a set of blocks using the LIF data. Each block was assigned a mean TPH mass, which we used as a proxy for the LNAPL mass in the block. By summing the LNAPL mass in all blocks, we estimated the total LNAPL volume/mass in the investigated site. Our approach provides a simple and effective way to determine the amount of LNAPL contaminating the soil and groundwater, offering a new perspective for investigating hydrocarbon-contaminated sites. [ABSTRACT FROM AUTHOR]

We theoretically investigate the photoelectron angular distribution induced in argon atoms using an XUV+IR two-color scheme, comprising a Ti:sapphire laser pulse and its 13th harmonic. The photoelectron angular distributions (PADs) are computed by directly solving the three-dimensional time-dependent Schrödinger equation (TDSE) within the single active electron approximation. Particular attention is devoted to analyzing the contributing continuum partial waves of the emitted photoelectrons to the formation of the photoelectron angular distribution. We found that the shapes of the obtained angular distributions for both harmonic and sideband peaks are consistent with the predictions of the generalized Fano rule for the absorption and emission of photons. Moreover, the structure of the energy spectrum of the ejected photoelectrons is presented and discussed where we can remark that the sideband SB + 1 peak is slightly higher than the sideband peak SB − 1 . [ABSTRACT FROM AUTHOR]

AbstractAccurate models of turbulent buoyant flows are essential for the design of the cooling circuit of nuclear reactors and passive safety systems. However, available models fail to fully capture the physics of turbulent mixing when buoyancy becomes predominant with respect to momentum. Therefore, high-fidelity experiments of well-controlled fundamental flows are needed to develop and validate more accurate models. We analyze experiments of positive and negative turbulent buoyant jets, both in uniform and stratified environments, with the aim of understanding the thermal hydraulics of turbulent mixing with variable density and providing high-fidelity data for the development and validation of turbulence models. Non-intrusive, simultaneous particle image velocimetry and laser-induced fluorescence measurements were carried out to acquire instantaneous velocity and concentration fields on a vertical section parallel to the axis of a jet in the self-similar region. The refractive index matching method was applied to measure high-resolution buoyant jets with up to 8.6% density difference. These data are free of the typical errors that characterize optical measurements of buoyancy-driven flows (e.g. natural and mixed convection) where the refractive index of the fluid is inhomogeneous throughout the measurement domain. Turbulent statistics and entrainment of buoyant jets in uniform and stratified environments are presented. These data are compared with non-buoyant jets in a uniform environment, as a reference to investigate the effects of buoyancy and stratification on turbulent mixing. The results will be used for the assessment of current turbulence models and as a basis for the development of a new model that captures turbulent mixing. [ABSTRACT FROM AUTHOR]

Digital PCR (dPCR) holds immense potential for precisely detecting nucleic acid markers essential for personalized medicine. However, its broader application is hindered by high consumable costs, complex procedures, and restricted multiplexing capabilities. To address these challenges, an all‐in‐one dPCR system is introduced that eliminates the need for microfabricated chips, offering fully automated operations and enhanced multiplexing capabilities. Using this innovative oscillation‐induced droplet generation technique, OsciDrop, this system supports a comprehensive dPCR workflow, including precise liquid handling, pipette‐based droplet printing, in situ thermocycling, multicolor fluorescence imaging, and machine learning‐driven analysis. The system's reliability is demonstrated by quantifying reference materials and evaluating HER2 copy number variation in breast cancer. Its multiplexing capability is showcased with a quadruplex dPCR assay that detects key EGFR mutations, including 19Del, L858R, and T790M in lung cancer. Moreover, the digital stepwise melting analysis (dSMA) technique is introduced, enabling high‐multiplex profiling of seven major EGFR variants spanning 35 subtypes. This innovative dPCR system presents a cost‐effective and versatile alternative, overcoming existing limitations and paving the way for transformative advances in precision diagnostics. [ABSTRACT FROM AUTHOR]

The pressure gain combustion in wave rotors has the potential to significantly enhance the performance of gas turbine engines. Wave rotor design focuses on understanding the complex behavior of rotating channels, which is challenging due to high rotational speeds. To investigate the influence of different working conditions on the unsteady process within the wave rotor combustor, a simplified 24-channel model was established to study both the unsteady flow and the wave dynamics. The calculations indicate that, for the current port position adopted and a rotor speed of 4000 rpm, backflow occurs at the inlet port for various inlet pressures. By analyzing the working sequence of the wave rotor combustor, it is found that the inlet port does not close in time when the pre-compression wave returns. This delay results in reflected expansion waves or compression waves moving within the channel, which affect a portion of the pressure gain, leading to a damped sinusoidal trend in the pressure profiles within the channel. The optimal pre-pressurization effect can be achieved at a rotor speed of 2000 rpm for the test conditions considered, and the total pressure gain achieved was 6.3%. By adding hot-jet ignition, it is found that the shock wave and flame interact at least five times in the current simulation. The shock–flame interaction can greatly accelerate the process of chemical reactions. After the fourth interaction, the shock wave achieved local coupling with the flame, forming a local high-pressure area of 4 bar, verifying the effectiveness of the wave rotor as a constant-volume supercharging device. [ABSTRACT FROM AUTHOR]

The behavior of ions in the plasma is an essential component in the process of industrial etching. We studied the motions and energy distribution of argon ions in a inductively coupled plasma (ICP) etching tool, by the method of laser induced fluorescence (LIF). The silicon wafer clamped to a chuck at the bottom of the chamber was biased with a 1 MHz 1–1.2 kV peak-to-peak sinusoidal voltage. The plasma is formed with a 2 MHz ICP coil pulsed at 10 Hz. Sheath thickness was measured at different phases of the bias waveform. The experiment also compared the ion motions with and without wafer bias, as well as different switch-on time of wafer bias. For all cases, ion energy distribution functions and the two-dimensional flow pattern were studied near the center and edge of the wafer. Significant vortex flows were observed near the wafer edge. Experiments in which the wafer was biased in the plasma afterglow resulted in a narrow distribution of ion energy close to the bias voltage at the vicinity of the wafer, and the ion incident angle on the wafer was the smallest. The results were compared to simulations using the Hybrid Plasma Equipment Model code. [ABSTRACT FROM AUTHOR]

The objective of this paper is to assess the capabilities of the Conditional Source-term Estimation (CSE) approach applied to a laboratory scaled turbulent buoyant flame without extinction. CSE is coupled with the Large Eddy Simulation (LES) solver, FireFOAM. Tabulated detailed chemistry is included. Radiation is treated using the optically thin model using four different implementations and the effect of subgrid scale (sgs) Turbulence-Radiation Interactions (TRI) is considered. Predictions of time-averaged temperatures and corresponding root mean square (rms) are compared with the experimental measurements at several locations. Further, flame shape, unconditional and conditional species mass fractions, axial velocity and mixture fraction are also examined for qualitative analysis. The predicted temperatures are in good agreement with the experimental data, except very close to the fuel inlet. The predicted temperatures increase more slowly compared to the experimental data in the first 0.09 m above the burner. The temperature rms is in reasonable agreement with experimental data with the peak being overpredicted by approximately 17%. The predicted flame height closely matches the experimental value. The temperature predictions are consistent with previously published results. Best predictions are obtained when the effect of sgs TRI is included. For this flame, the optically thin assumption is found to be valid, in agreement with previous investigations. The calculated radiative fraction is found to be close to the experimental value, but the postprocessed heat release rate is larger than the experimental finding. This first LES-CSE study provides a good foundation for further developments, for example more detailed radiation models, for more complex fire cases. [ABSTRACT FROM AUTHOR]

This paper delves into the methodology employed in examining lean premixed turbulent flame fronts extracted from Planar Laser Induced Fluorescence (PLIF) images at elevated pressures. In such flow regimes, the PLIF signal suffers from significant collisional quenching, typically resulting in image data with low signal-to-noise ratio (SNR). This poses severe difficulties for conventional flame front extraction algorithms based on intensity gradients and requires intense user intervention to yield acceptable results. In this work, we propose Convolutional Neural Network (CNN)-based Deep Learning (DL) models as an alternative to problem specific conventional methods. The pretrained DL models were fine-tuned, employing data augmentation, on a small annotated dataset including a variety of conditions between SNR ≈ 1.6 to 2.6 and subsequently evaluated. All DL models significantly outperformed the best-scoring conventional implementation both quantitatively and visually, while having similar inference times. IoU-scores and Recall values were found to be up to a factor ≈ 1.2 and ≈ 2.5 higher, respectively, with ≈ 1.15 times improved Precision. Small-scale structures were captured much better with fewer erroneous predictions, becoming particularly pronounced for the lower SNR data investigated. Moreover, by applying artificially modeled noise, it was shown that the range of image conditions in terms of SNR that can be reliably processed extends well beyond the images included in the training data, and satisfactory segmentation performances were found for SNR as low as ≈ 1.1. The presented DL-based flame front detection algorithm marks a methodology with significantly increased detection performance, while a similar computational effort for inference is achieved and the need for user-based parameter tuning is eliminated. It enables a very accurate extraction of instantaneous flame fronts in large image datasets where supervised processing is infeasible, unlocking unprecedented possibilities for the study of flame dynamics and instability mechanisms at industry-relevant conditions. [ABSTRACT FROM AUTHOR]

The process of Infrared Multiphoton Dissociation (IRMPD) was studied in a mixture of vinyl bromide/chlorodifluoromethane (VBr, C2H3Br/CF2HCl) using single and double infrared pulsed transverse excitations atmospheric CO2 laser beams. The dissociation of VBr was investigated using FTIR, and the product composition was analysed, and various dissociation routes were proposed. The study found that the VBr molecules were more heavily dissociated when exposed to the CF2HCl environment than without it. By using a time-resolved LIF, the kinetics reactions with CF2HCl were explored under pseudo-first-order conditions, and the quenching rate constant for the interaction between CF2HCl and C 2 d 3 Π g was published using the classical Stern–Volmer model. The impact of pulsed laser heating on the generation of C 2 a 3 Π u radicals was also observed. The decrease in the intensity of the C 2 (a 3 Π u) LIF signal was due to faster recombination of the C 2 a 3 Π u radicals, together with a decrease in V - V ′ energy transfer and the pressure oscillations produced by the effect of pulsed laser heating in the irradiated volume and the experimental conditions. [ABSTRACT FROM AUTHOR]

The existence of pathogenic microorganisms is a significant contributor to high morbidity rates in both developed and developing countries. Numerous human diseases have been related to Escherichia coli and Enterococcus faecalis. Fast diagnosis of these bacteria is crucial for limiting the progress of the associated diseases. The current study investigated the potential application of femtosecond laser-induced fluorescence spectroscopy (LIF) in monitoring bacteria. The INSPIRE HF100 laser system, which was pumped by a mode-locked femtosecond Ti: sapphire MAI TAI HP laser, delivered 100 femtosecond laser pulses to the samples. E. coli and E. faecalis were exposed to femtosecond laser pulses, and a spectrometer was used to monitor the fluorescence emission spectra. The measured LIF spectra of the two bacteria showed that E. coli and E. faecalis had fluorescence peaks at 502 and 512.5 nm, respectively. When the excitation wavelength varied from 350 to 400 nm, E. coli and E. faecalis fluorescence peak intensities linearly decreased. Furthermore, the LIF peaks revealed that the full width at half maximum of E. coli is 91.9 nm and that of E. faecalis is 101.3 nm. The current study findings suggest that femtosecond laser-induced fluorescence spectroscopy is a reliable, accurate, and sensitive approach for rapidly and directly identifying pathogenic bacteria. [ABSTRACT FROM AUTHOR]

While the current practice in designing brine outfalls for seawater desalination plants has provided a level of protection to the coastal environment that is deemed acceptable, additional research can be pursued to further improve the state-of-the-art understanding as well as enable the integration of beneficial features introduced by the brine outfall. The present study performed both numerical simulations and laboratory experiments to investigate the mixing and spreading of an 45º inclined dense jet in coastal regions with submerged vegetation canopies at the seabed. The numerical simulations utilized the Reynolds-Averaged Navier-Stokes (RANS) equations with the standard k-ε turbulence closure and non-interactive species transport model. The experiments were performed using the technique of Planar Laser Induced Fluorescence (PLIF) for verification. The overall results showed that the mixing of the inclined dense jet is enhanced just above the top of the submerged canopy due to the presence of stem-scale wakes and increased dispersity promoted by the spatial inhomogeneity near the canopy interface. A threshold value of 0.6 for the characteristic parameter, ϕFr, where Fr is the densimetric Froude number of jets and ϕ is the canopy density, has been observed above which the dilution coefficients reach a plateau and are no longer influenced by the canopy density. Within the canopy, however, the barrier effect prevails in the mixing process leading to constrained dilution particularly with denser canopies. In particular, the concentration at the impingement region within the canopy near the bottom is observed to increase with the increase in the general canopy density. Highlights: The effects of submerged canopy on the mixing and spreading of inclined dense jets are investigated numerically and experimentally. The presence of the canopy enhances the dilution of the inclined dense jet above canopies while increase the concentration within canopies. Quantitative influence depends on the discharge characteristics of the inclined dense jet as well as the characteristics of the canopy. [ABSTRACT FROM AUTHOR]

In this study, we explore the potential of using laser-induced photo-fragmentation of O3 by UV radiation as a quantitative diagnostic tool in non-thermal O2-mixed plasmas. We analyze the optical processes of O3 using a comprehensive kinetic model with a 226 nm laser, which is typically used in the two-photon absorption laser-induced fluorescence (TALIF) measurement of O atoms. Our model demonstrates that the fluorescence intensity from atomic O fragments produced by the same laser is directly proportional to the population of precursor O3. This makes various diagnostic purposes achievable through the proposed O3 full photo-fragmentation (FPF) TALIF spectroscopy, including calibration of TALIF signals of O atoms and quantification of both O and O3 in O2-mixed plasmas. We present detailed theoretical principles, technical requirements, and successful examples of implementation for different diagnostic aims using the proposed O3 FPF-TALIF spectroscopy. However, we also specify the limitations of the developed diagnostic methods, particularly under low E/N conditions (<30 Td), where other interferential species such as the vibrationally excited ground-state O 2 ( X 3 Σ g − , v ≠ 0) are abundantly produced. [ABSTRACT FROM AUTHOR]

We present the first experimental application of coherent Raman spectroscopy (CRS) on the ro-vibrational ν2 mode spectrum of methane (CH4). Ultrabroadband femtosecond/picosecond (fs/ps) CRS is performed in the molecular fingerprint region from 1100 to 2000 cm−1, employing fs laser-induced filamentation as the supercontinuum generation mechanism to provide the ultrabroadband excitation pulses. We introduce a time-domain model of the CH4ν2 CRS spectrum, including all five ro-vibrational branches allowed by the selection rules Δv = 1, ΔJ = 0, ±1, ±2; the model includes collisional linewidths, computed according to a modified exponential gap scaling law and validated experimentally. The use of ultrabroadband CRS for in situ monitoring of the CH4 chemistry is demonstrated in a laboratory CH4/air diffusion flame: CRS measurements in the fingerprint region, performed across the laminar flame front, allow the simultaneous detection of molecular oxygen (O2), carbon dioxide (CO2), and molecular hydrogen (H2), along with CH4. Fundamental physicochemical processes, such as H2 production via CH4 pyrolysis, are observed through the Raman spectra of these chemical species. In addition, we demonstrate ro-vibrational CH4v2 CRS thermometry, and we validate it against CO2 CRS measurements. The present technique offers an interesting diagnostics approach to in situ measurement of CH4-rich environments, e.g., in plasma reactors for CH4 pyrolysis and H2 production. [ABSTRACT FROM AUTHOR]

In response to the deficiencies of traditional power transformer fault detection techniques, such as low sensitivity and the inability for online monitoring, a novel transformer fault diagnosis model combining laser-induced fluorescence (LIF) technology with deep learning is proposed. Initially, the spectral data of transformer insulation oil is acquired using LIF technology, yielding spectral data for various fault types. Subsequently, MinMaxScaler and standard normalized variate methods are employed for denoising and preprocessing the spectral data. The preprocessed data is then subjected to dimensionality reduction using linear discriminant analysis and T-distributed stochastic neighbor embedding to ensure that the spectral data retains maximal feature information while minimizing its dimensionality. Following this, long short-term memory, bidirectional long short-term memory (BiLSTM), dung beetle optimizer-BiLSTM, convolutional neural network, and support vector machine models are constructed. The reduced-dimensional data is fed into each of the five models for training to facilitate transformer fault diagnosis. Through comparative analysis among the five models, the optimal model is selected. Experimental results indicate that the dung beetle optimization-BiLSTM model is the most suitable for transformer fault diagnosis in this experiment, underscoring its significant implications for ensuring the safety of power systems. [ABSTRACT FROM AUTHOR]

In this work, we investigated non-equilibrium plasma produced by nanosecond repetitively pulsed glow discharges applied across a lean premixed methane-air flame. The flame is stationary, axisymmetric, and laminar. The discharges are applied on the symmetry axis crossing the reactant gases, flame front, and product gases, allowing phase-locked averaged measurements and comparisons with axisymmetric numerical simulations. The thermal effect and methyl radical production are quantified in the discharge in the reactant gas region. One-dimensional, two-beam, hybrid, femtosecond-picosecond, coherent anti-Stokes Raman scattering is used to acquire spatial and temporal profiles of temperature and oxygen-to-nitrogen concentration ratio. Photo-fragmentation laser-induced fluorescence is used to acquire quantitative two-dimensional profiles of methyl radicals in the discharge providing the first quantitative imaging of methyl produced ahead of a flame by plasma-induced methane dissociation. The spatial profiles of temperature and oxygen-to-nitrogen concentration ratio are in steady state, indicating that individual discharges have an insignificant heating effect. Upper and lower bounds of the produced mole fraction of methyl radicals in the plasma are obtained due to uncertainties in the collisional quenching rates of excited state methylidyne radicals in the plasma. The discharges produce a maximum of 600–1100 ppm of methyl radicals upstream of the flame front within 25 ns. This amount is similar to the predicted methyl mole fraction for the flame without plasma and thus represents a significant chemical perturbation to the reactants upstream of the flame front. The produced methyl follows an exponential decay in the first microsecond after the discharge with a decay constant of 8 µs close to the flame, and 0.8 µs further from the flame. The decay then deviates from the exponential curve and the methyl persists for tens of microseconds. The results suggest that for the tested configuration, the thermal effect of individual discharges through fast gas heating is negligible, while active chemical species are produced in large quantities in the reactant gases, upstream of the flame front. [ABSTRACT FROM AUTHOR]

Electroosmotic flow significantly impacts the resolution of separations in capillary electrophoresis and its modification is often necessary. Coating of the inner capillary surface either dynamically or permanently offers a way to alter the electroosmotic flow, potentially reducing the adsorption of analytes, in our case liposomes, to the capillary wall. At first, we measured fluorescently labeled liposomes in an uncoated capillary by capillary electrophoresis with laser-induced fluorescence detection. We used a special procedure of the electrophoretic experiment allowing us to observe the development of peak shape at the early stages of migration. We proved that the liposomes were adsorbed to the capillary wall, which led to a very quick and severe dispersion of their peak during their electromigration. For this reason, we used a commercially coated capillary with polyvinyl alcohol, where at the same separation conditions, we observed the peak of the liposome with a stable shape during the migration. However, this capillary is costly, thus four simple dynamic coating methods were tested for four polymers, namely Pluronic F-127, polyvinyl pyrrolidone K30, polyethylene glycol, and polydiallyldimethylammonium chloride. Among them, we chose a method where we flushed the capillary with a 10% solution of polyvinyl pyrrolidone K30 before the first measurement. In addition, in-house made permanent coating with linear polyacrylamide was investigated, which has led to effective suppression of the electroosmotic flow and stable liposome peak, not dispersed during its migration. Liposome separation using this coating fully confirmed that the studied liposomes are negatively charged and migrate in the anodic direction. [ABSTRACT FROM AUTHOR]

Sulfur–chlorine cycles play a role in the atmosphere of Venus. It is thought that many sulfur–chlorine bearing molecules could be present in Venus's atmosphere and play an important role in its chemical processes. The goal of this work is to provide new insight into the electronic structure and spectroscopy of the [Cl, S, S, O] molecular system. Eight isomers could be formed, but only three were found to be thermodynamically stable relative to the first dissociation limit. We spectroscopically characterized the two lowest energy stable isomers, C1–ClSSO and trans-ClSSO, using the accurate CCSD(T)-F12/aug-cc-pVTZ method. The dipole moments of the two lowest energy stable isomers are predicted to be 1.90 and 1.60 debye, respectively. The C1–ClSSO isomer is suitable for laser induced fluorescence detection since the lowest excited electronic states absorb in the visible, ∼610 nm, and near UV region, 330 nm. We mapped the evolution of the low-lying excited electronic states along the ClS, SS, and SO bond lengths to find that the production of ClS, SO, or S2O is plausible, whereas the production of ClS2 is not allowed. [ABSTRACT FROM AUTHOR]

Blending hydrogen with natural gas is useful for reducing CO 2 emissions, but this alters the flame structure, creating challenges for flame stability. Numerous researches on methane-hydrogen flame structure have been carried out based on two-dimensional combustion diagnostic techniques such as flame chemiluminescence and planar laser-induced fluorescence. In this paper, a low-cost OH* chemiluminescence imaging system consisting of 8 ultraviolet (UV) cameras is proposed to reconstruct the three-dimensional (3D) structure of methane-hydrogen flames, and validated through use of the correlation coefficient. Further experimental investigations of the low-swirl methane-hydrogen flames are performed by this computed tomography of chemiluminescence (CTC) system. The flame properties are determined to evaluate the effects of various fractions of blended hydrogen on the flame structure, including the flame center of mass, flame surface density and fractal dimension. Results showed that the flame initially has bowl-shape structure. The flame height gradually decreases and the flame cross-sectional area increases as the blended hydrogen fraction increases. Meanwhile, the bottom of the flame moves toward the nozzle outlet. Nevertheless, when the blended hydrogen fraction reaches 50%, the flame transforms into a cup-shaped flame and shows a double-layer flame structure. When the flame is bowl-shaped, the flame center of mass moves away from the nozzle center axis with increasing blended hydrogen fraction, but the fractal dimension and flame surface density are not sensitive to the blended hydrogen fraction. In contrast, when the flame is cup-shaped, the flame center of mass moves towards the nozzle center axis, and the flame surface density and fractal dimension increase significantly, indicating the increase of flame wrinkling. These results reveal that blending hydrogen leads to two distinct flame structures and characteristics in low-swirl flame, also demonstrate that the proposed 3D low-cost CTC system based on multiple UV cameras is well-suited for combustion diagnostics. • A low-cost 3D computed tomography of OH* chemiluminescence system is proposed. • Two distinct low-swirl CH 4 –H 2 flame shapes are observed and reconstructed. • The change in flame shape is accompanied by a significant change in flame wrinkling. [ABSTRACT FROM AUTHOR]

Clean-burning oxygenated and synthetic fuels derived from renewable power, so-called e-fuels, are a promising pathway to decarbonize compression–ignition engines. Polyoxymethylene dimethyl ethers (PODEs or OMEs) are one candidate of such fuels with good prospects. Their lack of carbon-to-carbon bonds and high concentration of chemically bound oxygen effectively negate the emergence of polycyclic aromatic hydrocarbons (PAHs) and even their precursors like acetylene (C2H2), enabling soot-free combustion without the soot-NOx trade-off common for diesel engines. The differences in the spray combustion process for OMEs and diesel-like reference fuels like n-dodecane and their potential implications on engine applications include discrepancies in the observed ignition delay, the stabilized flame lift-off location, and significant deviations in high-temperature flame morphology. For CFD simulations, the accurate modeling and prediction of these differences between OMEs and n-dodecane proved challenging. This study investigates the spray combustion process of an OME3 − 5 mixture and n-dodecane with advanced optical diagnostics, Reynolds-Averaged Navier–Stokes (RANS), and Large-Eddy Simulations (LESs) within a constant-volume vessel. Cool-flame and high-temperature combustion were measured simultaneously via high-speed (50 kHz) imaging with formaldehyde (CH2O) planar laser-induced fluorescence (PLIF) representing the former and line-of-sight OH* chemiluminescence the latter. Both RANS and LES simulations accurately describe the cool-flame development process with the formation of CH2O. However, CH2O consumption and the onset of high-temperature reactions, signaled by the rise of OH* levels, show significant deviations between RANS, LES, and experiments as well as between n-dodecane and OME. A focus is set on the quality of the simulated results compared to the experimentally observed spatial distribution of OH*, especially in OME fuel-rich regions. The influence of the turbulence modeling is investigated for the two distinct ambient temperatures of 900 K and 1200 K within the Engine Combustion Network Spray A setup. The capabilities and limitations of the RANS simulations are demonstrated with the initial cool-flame propagation and periodic oscillations of CH2O formation/consumption during the quasi-steady combustion period captured by the LES. [ABSTRACT FROM AUTHOR]