Premixed turbulent flame front structure investigation by Rayleigh scattering in the thin reaction zone regime

Premixed turbulent flames of methane–air and propane–air stabilized on a bunsen type burner were studied using planar Rayleigh scattering and particle image velocimetry. The fuel–air equivalence ratio range was from lean 0.6 to stoichiometric for methane flames, and from 0.7 to stoichiometric for propane flames. The non-dimensional turbulence rms velocity, u′/S_L, covered a range from 3 to 24, corresponding to conditions of corrugated flamelets and thin reaction zones regimes. Flame front thickness increased slightly with increasing non-dimensional turbulence rms velocity in both methane and propane flames, although the flame thickening was more prominent in propane flames. The probability density function of curvature showed a Gaussian-like distribution at all turbulence intensities in both methane and propane flames, at all sections of the flame.The value of the term Dκ, the product of molecular diffusivity evaluated at reaction zone conditions and the flame front curvature, has been shown to be smaller than the magnitude of the laminar burning velocity. This finding questions the validity of extending the level set formulation, developed for corrugated flames region, into the thin reaction zone regime by increasing the local flame propagation by adding the term Dκ to laminar burning velocity.     

Physical and chemical analysis of plasma-treated cotton fabric subjected to wrinkle-resistant finishing

Cotton fabrics were treated with oxygen plasma gas and/or wrinkle-resistant finishing agent with polycarboxylic acid. The results of wicking rate, contact angle and wettability tests revealed that the atmospheric plasma treatment significantly improved hydrophilicity of cotton fiber. Such improvement greatly enhances the effectiveness of post-finishing processes. The study showed that chemical composition of cotton fabric surface changed after plasma and wrinkle-resistant treatment. Chemical composition of surface of treated cotton specimens was evaluated with different characterization methods, namely, FTIR-ATR and EDX. The experimental results are thoroughly discussed.     

An automated system for simultaneous thermal analysis and mass spectrometry. Part II. Combination with gas chromatography/mass spectrometry

Our system for simultaneous thermal analysis and mass spectrometry (TA/MS) which consists of a Mettler thermoanalyzer model TA-1 coupled with a Hewlett-Packard 5992 quadrupole mass spectrometer has been extended to include gas chromatography/mass spectrometry (GC/MS) capability. The separation power of GC offers tremendous advantage for analyzing complex gaseous mixtures resulting from thermal analysis. The combination of real-time MS and subsequent GC/MS eliminates artifacts commonly associated with trapping and hence, permits accurate and efficient interpretation of the nature of the volatiles.     

Synergistic effect of flame retardants and graphitic carbon nitride on flame retardancy of polylactide composites

In order to improve the flame retardant of polylactide (PLA), the synergistic effect of graphitic carbon nitride (g‐C₃N₄) with commercial‐available flame retardants melamine pyrophosphate (MPP) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was investigated. The PLA composites containing 5 wt% g‐C₃N₄ and 10 wt% DOPO had a highest limited oxygen index (LOI) value of 29.5% and reached the V‐0 rating of UL‐94 test. The cone calorimeter tests exhibited that DOPO had a better synergistic effect with g‐C₃N₄ than MPP to improve flame retardancy of PLA. The peak heat release rate (pHRR) and total heat release (THR) of PLA composites containing 10 wt% DOPO could be reduced by 25.2% and 23.6%, respectively, as compared with those of pure PLA. The presence of rich phosphorus element and aromatic groups in DOPO contributed to obtain continuous compact char layer and increase the graphitization level of char residues, thereby, resulting in improving the flame retardancy of PLA together with g‐C₃N₄. In addition, the incorporation of DOPO can serve as a plasticizer to reduce the complex viscosity, improving the processability of PLA composites.     

Time-resolved resonance Raman observation of the 2-fluorenylnitrenium ion reaction with guanosine to form a C8 intermediate

Time-resolved resonance Raman spectroscopy was used to directly observe the reaction of the 2-fluorenylnitrenium ion with guanosine to produce a C8 intermediate species. Comparison of the Raman spectra with results of density functional theory calculations indicates the C8 intermediate forms two C=N conjugated bonds in ring 1 of the guanosine moiety.     

Effects of Annealing on the Properties of Gamma-Irradiated Sago Starch

The increase in health and safety concerns regarding chemical modification in recent years has caused a growing research interest in the modification of starch by physical techniques. There has been a growing trend toward using a combination of treatments in starch modification in producing desirable functional properties to widen the application of a specific starch. In this study, a novel combination of gamma irradiation and annealing (ANN) was used to modify sago starch (Metroxylon sagu). The starch was subjected to gamma irradiation (5, 10, 25, 50 kGy) prior to ANN at 5 °C (T_o-5) and 10 °C (T_o-10) below the gelatinization temperature. Determination of amylose content, pH, carboxyl content, FTIR (Fourier Transform Infrared) intensity ratio (R_1047/1022), swelling power and solubility, thermal behavior, pasting properties, and morphology were carried out. Annealing irradiated starch at T_o-5 promoted more crystalline perfection as compared to T_o-10, particularly when combined with 25 and 50 kGy, whereby a synergistic effect was observed. Dual-modified sago starch exhibited lower swelling power, improved gel firmness, and thermal stability with an intact granular structure. Results suggested the potential of gamma irradiation and annealing to induce some novel characteristics in sago starch for extended applications.     

Non-revisiting genetic algorithm with adaptive mutation using constant memory

The continuous non-revisiting genetic algorithm (cNrGA) uses the entire search history and parameter-less adaptive mutation to significantly enhance search performance. Storing the entire search history is natural and costs little when the number of fitness evaluations is small or moderate. However, if the number of evaluations required is substantial, some memory management is desirable. In this paper, we propose two pruning mechanisms to keep the memory used constant. They are least recently used pruning and random pruning. The basic idea is to prune a unit of memory when the memory threshold is reached and some new search information is required to be stored, thus keeping the overall memory used constant. Meanwhile, both pruning strategies naturally form parameter-less adaptive mutation operators. A study is carried out to evaluate the impact on performance caused by loss of search history information. Experimental results show that (1) both strategies can maintain the performance of cNrGA, up to the empirical limit when 90 % of the search history is not recorded, (2) cNrGA and its variants with constant memory outperform the real-coded genetic algorithm and the standard particle swarm optimization. By pre-extracting all the current prune-able history information and storing them into a list, namely, to-prune-list, the overhead of both pruning strategies becomes small. This suggests that cNrGA can be extended to use in situations when the number of fitness evaluations is much larger than before with no significant effect on statistical performance. This widens the applicability of cNrGA to include more practical problems that require larger number of fitness evaluations before converging to the global optima.     

Stimulated emission cross sections and temperature-dependent spectral shifts of neutral nitrogen-vacancy centers in diamonds

The neutral nitrogen-vacancy (NV⁰) defects in diamond are photostable color centers, suitable for a wide range of applications in science and engineering. However, the photophysical properties of the centers have not yet been fully characterized. This work measured the stimulated emission cross sections of NV⁰ in a single-crystal diamond by two-photon excitation of its matrix at 344 nm. From the measured photoluminescence spectrum and the fluorescence lifetime of 20 ± 1 ns, we determined a peak stimulated emission cross section of 1.43 ± 0.07 × 10⁻¹⁷ cm² at 650 nm for the NV⁰ centers. In addition, we have also examined the thermal shifts of the zero-phonon line of NV⁰ centers in nanoscale diamonds (~100 nm in diameter) over the temperature range of 30–120°C. A temperature measurement sensitivity of 0.2 K·Hz^−1/2 was achieved, which is about two-fold better than that of NV⁻, despite that the fluorescence intensity of NV⁰ is about six-fold lower than that of NV⁻ in the same nanoparticles. The result is attributed to the smaller electron–phonon coupling strength of the neutral center, compared with its negatively charged counterpart.     

A Supported Palladium on Gallium-based Liquid Metal Catalyst for Enhanced Oxygen Reduction Reaction

Developing high-performance catalysts for oxygen reduction reaction to replace costly platinum-based materials is of great importance but still confronted with challenges. Herein, a kind of supported palladium liquid metal catalyst, which is prepared by galvanic replacement, surpasses commercial Pt/C and Pd/C in oxygen reduction catalysis with a higher half-wave potential of 0.92 V, mass activity of 1.85 A/mg_Pd at 0.90 V, and superior durability. The liquid metal support can both optimize the electronic structures of Pd sites and guarantee the dispersion of Pd atoms, which explains the enhanced activity and durability, respectively. This work opens an avenue for rational design of catalysts.