Vertical transport and photochemistry in the terrestrial mesosphere and lower thermosphere (50–120 km)

The coupled effects of kinetics, solar cycle flux variations and vertical transport on the distribution of long-lived hydrogen-carbon-oxygen compounds in the terrestrial mesosphere and lower thermosphere are studied using a one-dimensional aeronomy model. The calculations account for the important chemical reactions and use rocket measurements of the solar flux at solar minimum and maximum. Photodissociation rates appropriate for the mesosphere are determined with a spherical shell atmosphere formalism; detailed corrections for the O_2 Schumann-Runge bands and the temperature dependence of the CO_2 cross sections are used. Then an eddy diffusion profile is derived which gives agreement with the Aladdin 74 mass spectral measurements of atomic O, O_2, CO_2, and Ar in the lower thermosphere and observations of the O_3 minimum at ∼80 km. The 115 GHz CO radio emission line computed for the CO mixing ratio profile predicted with the new eddy diffusion profile compares well with recent observations of W. J. Wilson. Differences between the calculated CO mixing ratio profile and previous theoretical and observational determinations are discussed. Our derived eddy diffusion profile has a sudden decrease at 92 km which is necessary to produce the atomic O peak at 98 km that appears in the Aladdin 74 measurements. This stagnant region apparently is a recurrent or persistent feature of the upper atmosphere since an atomic O peak around 98 km has been seen by different techniques in different seasons over several years. Slow eddy diffusion in the lower thermosphere through the homopause was also the conclusion of earlier Ar/N_2 rocket measurements studies. The analytic approach of this paper could be used in the future to monitor variations in middle atmosphere dynamics, if regularly conducted simultaneous observations of various groups of species were available

Laser Applications to Chemical and Environmental Analysis: Introduction to the Feature Issue

This issue of Applied Optics features 16 papers describing chemical and environmental measurements made possible by lasers. Many of these contributions were presented at the Optical Society of America Topical Meeting on Laser Applications to Chemical and Environmental Analysis, held in Orlando, Florida, 9–11 March 1998.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86759/1/Sick33.pd

Exit plane H2O concentration measurements correlated with OH PLIF near-injector mixing measurements for scramjet flows

Mixing and combusting high enthalpy flows, similar to those encountered in scramjet engines, were investigated using a shock tunnel to produce the flow in conjunction with non-intrusive optical diagnostics which monitored the performance of two injector configurations. The shock tunnel is configured to produce Mach 3 flow and stagnation enthalpies corresponding to flight equivalent Mach numbers between 7 and 11. A pulsed hydrogen injection capability and interchangeable injector blocks provide a means of examining high speed, high enthalpy reacting flows. Planar laser induced fluorescence (PLIF) of OH molecules in the near injector region produced images which show the combusting and mixing zones for the reacting flow. Line-of-sight exit plane measurement of water concentration and temperature were used to provide a unique method of monitoring exit plane products. These results demonstrated that a velocity matched axial injection system produced a fuel jet that lifted off the floor of the duct. Mixing was observed to increase for this system as a velocity mismatch was introduced. Comparison of exit plane water concentrations for a wall jet injection system and a velocity matched injection system indicated similar mixing performance but an accurate pressure measurement is necessary to further validate the result. In addition, exit plane measurements indicated an approximate steady-state condition was achieved during the 1 to 2 ms test times

Physicochemical Properties and Catalytic Behavior of the Molecular Sieve SSZ-70

SSZ-70 is synthesized using 1,3-bis(isobutyl)imidazolium, 1,3-bis(cyclohexyl)imidazolium, and 1,3-bis(cycloheptyl)imidazolium structure directing agents (SDAs), and the solids obtained are characterized by powder X-ray diffraction (XRD), ^(29)Si magic angle spinning nuclear magnetic resonance (MAS NMR), electron microscopy, nitrogen and hydrocarbon adsorption, and thermogravimetric analyses. The physicochemical properties of SSZ-70 show that it is a new molecular sieve that has similarities to MWW-type materials. The catalytic behavior of SSZ-70 is evaluated through the use of the constraint index (CI) test. Distinct differences in the reactivity between Al-SSZ-70 and SSZ-25 (MWW) are observed and are the consequences of the structural differences between these two molecular sieves

Comparative Field Study Of Crassostrea gigas (Thunberg, 1793) And Crassostrea virginica (Gmelin, 1791) In Relation To Salinity In Virginia

To evaluate and compare the performance of triploid juvenile C. gigas (mean shell height = 19.2 mm) and triploid juvenile Crassostrea virginica (mean shell height = 31.7 mm), 600 oysters of each species were deployed for 1 year in floating mesh cages at three replicate sites within low, medium, and high salinity regimes (respectively,25%) in the Chesapeake Bay and the Atlantic Coast of Virginia. The comparative performance of the two oyster species varied with salinity. At low salinity sites, cumulative mortality of C. virginica (10%) was significantly (P \u3c .05) lower than that of C. gigas (63%), and over-all mean growth rate of C. virginica (2.9 mm mo(-1)) was significantly (P \u3c .05) higher than that of C. gigas (1.6 mm mo(-1)). At medium salinity sites, survival and growth rate of C. virginica and C. gigas were nor significantly (P \u3e .05) different. Both species experienced moderately high cumulative mortality at the medium salinity sites-35% for C. virginica and 53% for C. gigas-but considerable variation among sires was observed. Ar high salinity sites, mean cumulative mortality was similarly low

Test and Analysis of Buckling-Critical Stiffened Metallic Launch Vehicle Cylinders

A summary of a NASA design analysis and test program on the buckling of large-scale, integrally-stiffened metallic cylinders is presented. The test article designs were developed based on proposed NASA launch vehicle cylinder designs and span a significant portion of the design space. Various loading conditions were applied to the cylinders and include different combinations of axial compression, bending, and internal pressure loads that simulate typical launch vehicle loading scenarios. The data gathered from this test program is being used to develop and validate new analysis-based knockdown factors and design guidelines for these stiffened metallic cylinders. In this paper, the test article designs and fabrication methods are described along with the test facilities and instrumentation. Selected test and finite element analysis results are presented and compared and are used to illustrate the typical response characteristics of the stiffened metallic cylinders considered. Overall, good qualitative agreement is found, however, several discrepancies in the results were identified across several of the tests. The discrepancies were investigated thoroughly and can be attributed to variations in the as-built skin and stiffener geometry, variations in the measured geometric imperfection, and modeling assumptions associated with the boundary conditions, and loading imperfections. Based on these findings, several refinements were made to the finite element models which significantly improved the correlation between the test and analysis results. These modeling refinements are described and the updated analysis results are presented

Flow quality studies of the NASA Lewis Research Center Icing Research Tunnel diffuser

The purpose was to document the airflow characteristics in the diffuser of the NASA Lewis Research Center Icing Research Tunnel and to determine the effects of vortex generators on the flow quality in the diffuser. The results were used to determine how to improve the flow in this portion of the tunnel so that it can be more effectively used as an icing test section and such that overall tunnel efficiency can be improved. The demand for tunnel test time and the desire to test models that are too large for the test section were two of the drivers behind this diffuser study. For all vortex generator configurations tested, the flow quality was improved