The burning of a horizontal wood slab situated atop an insulating substrate was modeled using three coupled submodels for the gas-phase, wood, and substrate processes. A global analytical model was used to determine the radiative and convective heat feedback from the gas-phase combustion to the wood surface. The char-fonning wood model was a one-dimensional numerical computation of the density change as a function of position and time. The backside boundary condition of the wood was treated as conductive heat loss into a substrate material modeled by the heat conduction equation. The condensed-phase model results were tested by exposing Douglas Fir samples to an external flux in a nitrogen environment (no combustion). Heat release rate calculations are compared to experimental results for Douglas Fir samples of 0.1 m and 0.6 m diameter. Both theory and experiments show that, for the conditions studied, the heat release rate is nearly independent of the specimen diameter except for the initial peak and the affect of this peak on the first portion of the quasi-steady settling period. Model predictions also indicate that the second peak, which follows the settling period, is very sensitive to the thickness of the insulating substrate.

The fates of cranial neural crest cells are unique compared to trunk neural crest. Cranial neural crest cells form bone and cartilage and ultimately these cells make up the entire facial skeleton. Previous studies had established that exogenous retinoic acid has effects on neurogenic derivatives of cranial neural crest cells and on segmentation of the hindbrain. In the present study we investigated the role of retinoic acid on the skeletal derivatives of migrating cranial neural crest cells. We wanted to test whether low doses of locally applied retinoic acid could respecify the neural crest-derived, skeletal components of the beak in a reproducible manner. Retinoic acid-soaked beads were positioned at the presumptive mid-hindbrain junction in stage 9 chicken embryos. Two ectopic cartilage elements were induced, the first a sheet of cartilage ventral and lateral to the quadrate and the second an accessory cartilage rod branching from Meckel's cartilage. The accessory rod resembled a retroarticular process that had formed within the first branchial arch domain. In addition the quadrate was often displaced laterally and fused to the retroarticular process. The next day following bead implantation, expression domains of Hoxa2 and Hoxb1 were shifted in an anterior direction up to the mesencephalon and Msx-2 was slightly down-regulated in the hindbrain. Despite down-regulation in neural crest cells, the onset of Msx-2 expression in the facial prominences at stage 18-20 was normal. This correlates with normal distal beak morphology. Focal labeling of neural crest with DiI showed that instead of migrating in a neat group toward the second branchial arch, a cohort of labeled cells from r4 spread anteriorly toward the proximal first arch region. AP-2 expression data confirmed the uninterrupted presence of AP-2-expressing cells from the anterior mesencephalon to r4. The morphological changes can be explained by mismigration of r4 neural crest into the first arch, but at the same time maintenance of their identity. Up-regulation of the Hoxa2 gene in the first branchial arch may have encouraged r4 cells to move in the anterior direction. This combination of events leads to the first branchial arch assuming some of the characteristics of the second branchial arch.

Silica gel combined with potassium carbonate is an effective fire retardant for a wide variety of common polymers (at mass fraction of only 10% total additive) such as polypropylene, nylon, polymethylmethacrylate, poly(vinyl alcohol), cellulose, and to a lesser extent polystyrene and styrene-acrylonitrile. The peak heat release rate is reduced by up to 68% without significantly increasing the smoke or carbon monoxide levels during the combustion.

Silica gel combined with potassium carbonate is an effective fire retardant for a wide variety of common polymers (at mass fraction of only 10% total additive) such as polypropylene, nylon, polymethylmethacrylate, poly(vinyl alcohol), cellulose, and to a lesser extent polystyrene and styrene‐acrylonitrile. The peak heat release rate is reduced by up to 68% without significantly increasing the smoke or carbon monoxide levels during the combustion. © 1997 by John Wiley & Sons, Ltd.

The objective of the work is to develop and experimentally verify a model for CO 2 laser-induced ignition of nitramine-based propellants. The one-dimensional model considers heat conduction in the condensed-phase coupled to heat and mass transport with global chemical kinetics of a heterogeneous propellant in the gas-phase region. The highly nonlinear model was solved numerically. Experimentally, increases in heat ux [125 -375 W/cm 2 (193 -578 cal/s-in. 2 )] lowered the ignition delay time, but changes in pressure [1.38 -3.79 MPa (200 -550 psia)] had very little effect. This supports the assumption that cyclotrimethylenetrinitramine decomposition is primarily temperature controlled. These trends are correctly predicted by the model. Predictions of ignition delay time match the experimental data within the measurement uncertainty. Sensitivities of the numerical solution to the material properties and kinetic rate constants are addressed. Nomenclature= velocity w Ç 0 = species ux w Ç -= volumetric species production rate Y = species mass fraction y = vertical coordinate in the direction outward from the propellant surface a = thermal diffusivity b = extinction coef cient l = thermal conductivity r = density s = absorptivity of gas-solid interface Subscripts g = gas j = jth species LE = light emission m = mixture ref = reference value Presented as Paper 95-2862 at the AIAA/SAE/ASME/ASEE 31st