A stochastic model of turbulent mixing with chemical reaction: Nitric oxide formulation in a plug-flow burner

A stochastic model of turbulent mixing was developed for a reactor in which mixing is represented by n-body fluid particle interactions. The model was used to justify the assumption (made in previous investigations of the role of turbulent mixing on burner generated thermal nitric oxide and carbon monoxide emissions) that for a simple plug flow reactor, composition nonuniformities can be described by a Gaussian distribution function in the local fuel:air equivalence ratio. Recent extensions of this stochastic model to include the combined effects of turbulent mixing and secondary air entrainment on thermal generation of nitric oxide in gas turbine combustors are discussed. Finally, rate limited upper and lower bounds of the nitric oxide produced by thermal fixation of molecular nitrogen and oxidation of organically bound fuel nitrogen are estimated on the basis of the stochastic model for a plug flow burner; these are compared with experimental measurements obtained using a laboratory burner operated over a wide range of test conditions; good agreement is obtained

Soot oxidation rates in gas turbine engines

A basis is proposed for extrapolating soot oxidation rate measurements obtained in laboratory flames to the more extreme operating conditions of gas turbine combustion chambers. The proposal is based on the observation that, within probable experimental uncertainty, the limited soot oxidation measurements correlate with the more extensive measurements of the surface oxidation rates of macroscopic samples of pyrographite. The soot oxidation rates thus determined for the conditions of a typical gas turbine combustion chamber are considerably lower than estimates which were based on simple extrapolations of the flame data

Shock-tube measurements of carbon to oxygen atom ratios for incipient soot formation with C2H2, C2H4 and C2H6 fuels

The critical atomic carbon to oxygen ratios, Phi sub C, for incipient soot formation in shock heated acetylene, ethylene, ethane/oxygen/ argon mixtures was measured over the temperature range 2000 K to 2500 K for reactant partial pressures between 0.1 and 0.4 atoms. Absorption of light from a He-Ne laser at 6328A was was used to detect soot. It was observed that the values of Phi sub C for all three fuels increased uniformly with temperature such that at the highest temperatures Phi sub C was considerably greater than unity, i.e. greater than the value of about unity at which solid carbon should have been precipitated on a thermochemical equilibrium basis. Observations were made over periods extending up to about one millisecond, which was well in excess of the time required for the major heat release of the combustion reactions. The relevance of these experimental findings to the problem of soot formation in gas turbine combustion chambers is discussed

The Ultrastructure of Dentine from Rat Incisors Following Exposure to Sodium Fluoride and Potassium Pyroantimonate Staining

Weanling rats were given a single intra-peritoneal injection of sodium fluoride and control animals normal saline for four consecutive days. The fluoride produced a consistent response in the mineralizing dentine of the incisors in which a hypermineralized band was succeeded by a hypomineralized band. Potassium pyroantimonate staining for calcium ions showed that following injection of fluoride, in contrast to the controls, there were large amounts of calcium pyroantimonate in the pre-dentine and throughout the odontoblasts. This suggests that fluoride temporarily affects the membrane enzyme systems which maintain calcium concentration gradients between the odontoblasts and the matrix. The resultant influx of calcium is probably associated with the hypermineralization of the dentine matrix in which more hydroxyapatite crystallites are deposited. Upon recovery of the odontoblasts the matrix is relatively depleted of calcium resulting in matrix hypomineralization

Formation and Structure of Dentine in the Rat Incisor After Chronic Exposure to Sodium Fluoride

Weanling rats were chronically exposed to sodium fluoride by feeding them for eight weeks with a standard powdered diet incorporating sodium fluoride at 0.025% , 0.05% and 0.1% by weight. After eight weeks blood was removed by cardiac puncture and the levels of plasma calcium and phosphate determined. The incisor teeth were removed and their structure examined in the scanning electron microscope (SEM) using backscattered electron imaging to determine the relative concentration and distribution of the mineral phase in the dentine. There was no significant alteration to the normal serum calcium and phosphate levels. Small scattered interglobular spaces were seen in the incisor dentine of rats consuming the 0.025% sodium fluoride diet. The principle feature with the 0.05% diet were marked striations in the circumpulpal dentine but with the 0.1% diet there was severe disruption of dentine structure with continuous bands of interglobular spaces. These spaces were larger labially than lingually reflecting differences in the size and shape of calcospherites. The distribution of interglobular dentine would suggest that its formation takes time to establish

Shock-tube measurements of the vibration- vibration energy exchange probability for the CO-N2 system

Measuring vibration-vibration energy exchange probability in nitrogen-carbon dioxide-argon mixtures in shock tube

Vibrational relaxation measurements of carbon monoxide in a shock-tube expansion wave

Infrared measurement on vibrational relaxation rate of carbon monoxide in argon shock tube wav

Adolescent Health Services: Missing Opportunities

Examines the status of adolescents' health and health services, including critical needs, promising models, and components for improving disease prevention and health promotion. Recommends better primary care, coordinated policy, and expanded coverage

X-Ray Microanalysis of Growth Cartilage After Rapid Freezing, Low Temperature Freeze Drying and Embedding in Resin

This paper reviews the work undertaken on the X-ray microanalysis of growth cartilage particularly in relation to matrix calcification. Attention is focused on the methodology available to accurately localize and retain the elements of interest. A method is described which involves rapid freezing, low temperature freeze drying in a custom built device, and embedding in Spurr resin. The results show that little tissue damage occurs and that elements of physiological interest are accurately localized at the sub-cellular level. Where damage occurs to chondrocytes as a result of freezing, however, dense intra mitochondrial granules are seen suggesting a phase transformation takes place resulting in the precipitation of calcium phosphate. Further improvements may be made in retaining the more labile elements such as K by using resins which polymerize at low temperature