The instantaneous as well as conditionally averaged flame structure of a 78% H2-22% Ar jet diffusion flame is investigated with the Line-Raman/Rayleigh/LIPF-OH technique. Radial profiles of major species concentration, flame temperature, and OH concentration are measured along a line 10,5 mm long at two exit velocities and several axial positions. Statistical distributions of mixture fraction and one-dimensional scalar dissipation rate at different turbulence levels can be obtained to validate current model assumptions. The difference between upstream flamelets and downstream connected reaction zones can be inferred from the simultaneously measured multipoint scalar profiles in the mixture fraction space. Comparison with flamelet calculations shows that in the near field close to the nozzle region, flamelet behavior is qualitatively preserved. At positions farther downstream, the root mean square (rms) of the instantaneous mixture fraction in the mean reaction zone =st becomes smaller than the reaction zone width. Connected reaction zones are therefore a more appropriate conceptual model. Preferential molecular diffusion is found to be unimportant under strong small-scale turbulent mixing inside the jet flame, which justified the Lc=1 assumption for calculation of hydrogen diffusion flamelets at high strain rates. The probability density function of the measured one-dimensional scalar dissipation rates is lognormal at downstream positions but becomes more skewed when moving upstream. The mean scalar dissipation rate scales inversely with the streamwise distance in the axial direction, showing a rather slower decay than that in the cold flows. In addition, a local minimum of the radial scalar dissipation rate near the instantaneous reaction zone position is found at all the measuring stations and can be attributed to the thermal expansion effect and low turbulence level of the surrounding air. © 1996 Combustion Institute.

The premixed stoichiometric turbulent methane flames are investigated on a piloted Bunsen burner with a nozzle diameter of 12 mm and mean nozzle exit velocities of 65, 50, and 30 m/s. Advanced laser diagnostics of the flow field using two-component and two-point laser Doppler anenometer (LDA), as well as of the scalar fields with 2-D Rayleigh thermometry and line Raman/Rayleigh laser-induced predissociation fluorescence (LIPF)-OH techniques, are applied to obtain both the instantaneous and mean flame structure in terms of velocity, temperature, and major species concentrations, as well as turbulent kinetic energy and length scales. In terms of their location on the combustion diagram, the three flames cover the entire range of the distributed-reaction-zones regime from the borderline to the well-stirred reactor regime to the flamelet regime. Measurements were from X/D = 2.5 above the nozzle exit plane to X/D = 12.5 downstream. Thus, a complete database is established for comparison with the numerical predictions. Within the mixing layer between the unburnt gas and the pilot flame, the instantaneous temperatures are much lower than the adiabatic flame temperature due to the short residence time and heat loss to the burner. With increasing residence time the mean flame temperature increases in the axial direction. The radial mixing of the turbulence generated with the shear layers between the nozzle jet stream and surrounding pilot stream is supressed, such that the turbulence kinetic energy remains nearly constant on the centerline. From the two-dimensional (2D) temperature fields instantaneous iso-temperature contours are plotted showing broad regions where burnt and unburnt gas are partially mixed. These regions are interpreted in terms of the quench scale l(q) = (ετ(c)3)(1/2). The measured values of the flame brush thickness are proportional to the quench scale for the two high-velocity flames, whereas the low-velocity flame exhibits essential flamelet behavior. The premixed stoichiometric turbulent methane flames were studied on a piloted Bunsen burner. The instantaneous and mean flame structure of the flames were measured in terms of velocity, temperature, and major species concentrations as well as turbulent kinetic energy and length scales. The instantaneous temperatures between the unburnt gas and the pilot flame were much lower than the adiabatic flame temperature due to the short residence time. Mean flame temperature increased proportionally with residence time.

An imaging system was developed to resolve the instantaneous two-dimensional reaction zone structure in combustion media with combined Rayleigh thermometry and laser-induced saturated CH fluorescence technique. The carefully chosen excitation/detection strategy and high laser spectral intensity permit single-shot CH fluorescence imaging in premixed CH4/air flames where CH concentration is on the order of 1 ppm based on flamelet calculations. The present experimental conditions are also examined and shown to be suitable for quantitative measurements of CH radical based on the two-level model analysis. A linear relationship can be found between the measured CH signal intensity and the calculated CH concentration within a maximum 30% uncertainty range. The FWHM thickness of the CH profile in a stoichiometric laminar methane flame was shown to be less than 0.3 mm, which is the smallest ever achieved. Simultaneous image pairs of flame temperature and concentration of CH radicals from a premixed turbulent Bunsen flame at an exit velocity of 65 m/sec are obtained to demonstrate the system superiority of application on high-speed reacting flows.

An imaging system was developed to resolve the instantaneous two-dimensional reaction zone structure in combustion media with combined Rayleigh thermometry and laser-induced saturated CH fluorescence technique. The carefully chosen excitation/detection strategy and high laser spectral intensity permit single-shot CH fluorescence imaging in premixed CH4/air flames where CH concentration is on the order of 1 ppm based on flamelet calculations. The present experimental conditions are also examined and shown to be suitable for quantitative measurements of CH radical based on the two-level model analysis. A linear relationship can be found between the measured CH signal intensity and the calculated CH concentration within a maximum 30% uncertainty range. The FWHM thickness of the CH profile in a stoichiometric laminar methane flame was shown to be less than 0.3 mm, which is the smallest ever achieved. Simultaneous image pairs of flame temperature and concentration of CH radicals from a premixed turbulent Bunsen flame at an exit velocity of 65 m/sec are obtained to demonstrate the system superiority of application on high-speed reacting flows.

DELAY OF GERMINATION1 (DOG1) is a primary regulator of seed dormancy. Accumulation of DOG1 in seeds leads to deep dormancy and delayed germination in Arabidopsis. B3 domain-containing transcriptional repressors HSI2/VAL1 and HSL1/VAL2 silence seed dormancy and enable the subsequent germination and seedling growth. However, the roles of HSI2 and HSL1 in regulation of DOG1 expression and seed dormancy remain elusive. Seed dormancy was analysed by measurement of maximum germination percentage of freshly harvested Arabidopsis seeds. In vivo protein-protein interaction analysis, ChIP-qPCR and EMSA were performed and suggested that HSI2 and HSL1 can form dimers to directly regulate DOG1. HSI2 and HSL1 dimers interact with RY elements at DOG1 promoter. Both B3 and PHD-like domains are required for enrichment of HSI2 and HSL1 at the DOG1 promoter. HSI2 and HSL1 recruit components of polycomb-group proteins, including CURLY LEAF (CLF) and LIKE HETERCHROMATIN PROTEIN 1 (LHP1), for consequent deposition of H3K27me3 marks, leading to repression of DOG1 expression. Our findings suggest that HSI2- and HSL1-dependent histone methylation plays critical roles in regulation of seed dormancy during seed germination and early seedling growth.

Fractal analyses have been conducted to investigate flame-front wrinkling of turbulent premixed Bunsen flames. Emphasis is placed on the geometric interpretation of measured fractal parameters and their relationship with parameters used in current combustion models. The outer cutoff scale is found to be four times the integral length scale of flame-front wrinkling defined in the Bray-Moss-Libby model. A revised Gibson length scale is derived by taking into account the curvature effect. Dependency of the revised Gibson scale on the Karlovitz number agrees better with the bulk of available data for the inner cutoff scale than the original definition. The term "self-similarity dimension" is proposed for the fractal dimension measured at finite spatial resolution to highlight the self-similarity feature of local flame fronts. The self-similarity dimension is found to increase linearly with time, and correlates well with the turbulent flame brush thickness. © 2003 Elsevier Science Inc. All rights reserved.

Fractal analyses have been conducted to investigate flame-front wrinkling of turbulent premixed Bunsen flames. Emphasis is placed on the geometric interpretation of measured fractal parameters and their relationship with parameters used in current combustion models. The outer cutoff scale is found to be four times the integral length scale of flame-front wrinkling defined in the Bray-Moss-Libby model. A revised Gibson length scale is derived by taking into account the curvature effect. Dependency of the revised Gibson scale on the Karlovitz number agrees better with the bulk of available data for the inner cutoff scale than the original definition. The term "self-similarity dimension" is proposed for the fractal dimension measured at finite spatial resolution to highlight the self-similarity feature of local flame fronts. The self-similarity dimension is found to increase linearly with time, and correlates well with the turbulent flame brush thickness. © 2003 Elsevier Science Inc. All rights reserved.

We present a distributed fiber optic sensing scheme to image 3D strain fields inside concrete blocks during laboratory-scale hydraulic fracturing. Strain fields were measured by optical fibers embedded during casting of the concrete blocks. The axial strain profile along the optical fiber was interrogated by the in-fiber Rayleigh backscattering with 1-cm spatial resolution using optical frequency domain reflectometry (OFDR). The 3D strain fields inside the cubes under various driving pressures and pumping schedules were measured and used to characterize the location, shape, and growth rate of the hydraulic fractures. The fiber optic sensor detection method presented in this paper provides scientists and engineers an unique laboratory tool to understand the hydraulic fracturing processes via internal, 3D strain measurements with the potential to ascertain mechanisms related to crack growth and its associated damage of the surrounding material as well as poromechanically-coupled mechanisms driven by fluid diffusion from the crack into the permeable matrix of concrete specimens.

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This paper presents the development, evaluation, calibration, and field application of a novel, relatively inexpensive, vision-based sensor system employing commercially available off-the-shelf devices, for enabling the autonomous data acquisition of road surface conditions. Detailed evaluations and enhancements of a variety of technical approaches and algorithms for overcoming vision-based measurement distortions induced by the motion of the monitoring platform were conducted. It is shown that the proposed multi-sensor system, by capitalizing on powerful data-fusion approaches of the type developed in this paper, can provide a robust cost-effective road surface monitoring system with sufficient accuracy to satisfy typical maintenance needs, in regard to the detection, localization, and quantification of potholes and similar qualitative deterioration features where the measurements are acquired via a vehicle moving at normal speeds on typical city streets. The proposed system is ideal to be used for crowdsourcing where several vehicles would be equipped with this cost-effective system for more frequent data collection of road surfaces. Suggestions for future research needs to enhance the capabilities of the proposed system are included.