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In this work, the structure of laminar premixed ethylene/air flat flames at low pressure are studied experimentally. The aim of the work is to exploit the spatial expansion of laminar 1D flames and advanced laser techniques to better understand the conditions and precursors affecting soot particles inception. Soot volume fraction ( f v ) profiles were measured using laser-induced incandescence (LII), while spatial distribution of the CH * and C 2 * radicals was measured using spatially resolved emission spectroscopy. Spatially resolved laser-induced fluorescence has been used to record emission from 2–3 rings, 3–4 rings and > 5 rings. The temperature of soot particles ( T s ) was evaluated through fitting the spectrally resolved soot luminosity, while flame gaseous temperature ( T g ) was measured using a fine thermocouple. The laminar flow velocity was modeled and used to evaluate the reaction time at each HAB. Taking advantage of the expanded flame structure at low pressure, the profiles of CH * , C 2 * , soot and temperatures, as a function of the height above the burner, were well resolved. It was found that CH * and C 2 * chemiluminescence overlap in space. The thickness of CH * layer is larger than that of C 2 * , and it peaks at slightly different location, CH * appears approximately 1 mm before C 2 * . The distance between the two peaks decreases linearly with the increase in pressure. The lowest value of the initial soot volume fraction ( f v ) was 0.19 ppb, measured at pressure 27 kPa. It was found that f v scales with the pressure following a power function of the form f v α Pr n , where n is 2.15 ± 0.7. It was observed that, in all the flames investigated, the initial soot particles first appear at a common critical inception temperature, T inception , of 1465 ± 66 K. It was found that the T inception is lower than the maximum flame temperature, T max , by ~ 45° and appeared ~ 1 mm further than the location of T max . Using the Lagrangian quantity df v /dt and f v , it was possible to reveal the soot growth rate, k SG . At pressure of 27 kPa, the value of k SG was evaluated as 20 s −1 .

Microwave-assisted laser-induced breakdown spectroscopy (MA-LIBS) was demonstrated to be an effective method for the quantitative detection of silicon in the aqua phase. Microwave radiation was transmitted into plasma using a near-field applicator device under ambient pressure and temperature conditions. Silicon detection was performed directly on the surface of a water jet. Two Si emission lines, 251.6 nm and 288.16 nm, were selected to evaluate the MA-LIBS enhancement and determine the limit of detection for silicon. The signal-to-noise ratio of the MA-LIBS spectra was investigated as a function of laser energy and microwave power. The calibration curve was established for Si quantitative analysis using 8 mJ of laser energy and 900 W of microwave power. The MA-LIBS recorded a 51-fold and 77-fold enhancement for Si I 251.6 nm and 288.16 nm, respectively. Reducing liquid splashes after laser ablation is essential to improving the quantitative analysis. Using MA-LIBS reduced the liquid splashes due to MA-LIBS using 8 mJ. The detection limit achieved was 1.25, a 16-fold improvement over traditional LIBS.

Suspension microsphere immunoassays are rapidly gaining attention in multiplex bioassays. Accurate detection of multiple analytes from a single measurement is critical in modern bioanalysis, which always requires complex encoding systems. In this study, a novel bioassay with Raman-coded antibody supports (polymer microbeads with different Raman signatures) and surface-enhanced Raman scattering (SERS)-coded nanotags (organic thiols on a gold nanoparticle surface with different SERS signatures) was developed as a model fluorescent, label-free, bead-based multiplex immunoassay system. The developed homogeneous immunoassays included two surface-functionalized monodisperse Raman-coded microbeads of polystyrene and poly(4-tert-butylstyrene) as the immune solid supports, and two epitope modified nanotags (self-assembled 4-mercaptobenzoic acid or 3-mercaptopropionic acid on gold nanoparticles) as the SERS-coded reporters. Such multiplex Raman/SERS-based microsphere immunoassays could selectively identify specific paratope–epitope interactions from one mixture sample solution under a single laser illumination, and thus hold great promise in future suspension multiplex analysis for diverse biomedical applications.

Mid-infrared laser polarization spectroscopy (IRPS) has been applied to measure the mole fraction of acetylene in rich premixed laminar C 2 H 4 /Air flat flames at equivalence ratios ( Φ ) of 1.7, 2.1, and 2.3, and under atmospheric pressure. The detection was conducted by probing the ro-vibrational P(19) transition at ~ 3.1 μm. The total collisional broadening coefficient of C 2 H 2 was approximately 0.074 cm −1  atm −1 and varied within a range of 0.5% under different flame conditions, which made the effect of linewidth not obvious in the CH 4 /air flame. The calculated mole fraction of C 2 H 2 , using the Chemkin model, at Φ  = 1.3 and 1.5 was used to calibrate the recorded IRPS signal intensities at different Height Above Burner (HAB). A single scaling factor was then used to quantify the measured C 2 H 2 at highly sooting conditions, Φ  = 1.7, 2.1, and 2.3, with a Limit of Detection (LoD) of 35 ± 5 ppm. The first observed C 2 H 2 mole fraction appeared at HAB of 3 mm and measured as 2003 ppm, 2217 ppm, and 2495 ppm, for Φ  = 1.7, 2.1, and 2.3, respectively. The mole fraction increased as the HAB increased to reach the maximum value of 2296 ppm, 2807 ppm, and 3478 ppm, for Φ  = 1.7, 2.1, and 2.3, respectively, up to HAB of 5 mm. It was observed that the C 2 H 2 mole fraction reaches a plateau region at HAB of ~ 8 mm. The production of C 2 H 2 has been observed to be subject to a critical gas temperature of 1400 ± 30 K. The critical soot inception temperature, where the first incepted soot particles are observed, is the same as the gas temperature where χ C 2 H 2 max was detected, namely at 1500 ± 30 K. These measurements and calibration procedure demonstrate a plausible technique to probe other flames and to better understand soot inception and its correlation with C 2 H 2 .