Langley Research Center

About: Langley Research Center is a facility organization based out in Hampton, Virginia, United States. It is known for research contribution in the topics: Mach number & Wind tunnel. The organization has 15945 authors who have published 37602 publications receiving 821623 citations. The organization is also known as: NASA Langley & NASA Langley Research Center.

AC and DC percolative conductivity of single wall carbon nanotube polymer composites

Abstract: The equations needed to correctly interpret both AC and DC conductivity results of single wall carbon nanotube (SWNT) polymer composites and the scaling of these results onto a single master curve are presented. Brief discussions on the fac- tors that determine the critical volume fraction (/c) and the percolation exponent (t) are also given. The results for a series of SWNT-polyimide composites are presented and the parameters obtained from fitting these results are discussed. The critical vol- ume fraction for electrical percolation of the present composite was about 0.0005. Results obtained from previous work on SWNT (MWNT)-polymer composites and other percolation systems and the modeling (interpretation) of these results are also discussed and compared. V C 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3273-3287, 2005

Implications for atmospheric dynamics derived from global observations of gravity wave momentum flux in stratosphere and mesosphere

Abstract: [1] In this work absolute values of gravity wave (GW) momentum flux are derived from global temperature measurements by the satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Momentum fluxes in the stratosphere are derived for both instruments and for SABER in the whole mesosphere. The large-scale atmospheric background state is removed by a two-dimensional Fourier decomposition in longitude and time, covering even planetary-scale waves with periods as short as 1–2 days. Therefore, it is possible to provide global distributions of GW momentum flux from observations for the first time in the mesosphere. Seasonal as well as longer-term variations of the global momentum flux distribution are discussed. GWs likely contribute significantly to the equatorward tilt of the polar night jet and to the poleward tilt of the summertime mesospheric jet. Our results suggest that GWs can undergo large latitudinal shifts while propagating upward. In particular, GWs generated by deep convection in the subtropical monsoon regions probably contribute significantly to the mesospheric summertime wind reversal at mid- and high latitudes. Variations in the GW longitudinal distribution caused by those convectively generated GWs are still observed in the mesosphere and could be important for the generation of the quasi two-day wave. Indications for quasi-biennial oscillation (QBO) induced variations of GW momentum flux are found in the subtropics. Also variations at time scales of about one 11-year solar cycle are observed and might indicate a negative correlation between solar flux and GW momentum flux.

A Climatology of Surface Radiation Budget Derived from Satellite Data

Abstract: Climatological averages of surface radiation budget parameters, namely, the shortwave and longwave surface radiative fluxes, have been derived for each month of the year on a global scale. These climatological averages were derived from an 8-yr (96 month) time series of monthly average fluxes. The monthly averages were computed using fast radiation parameterizations and satellite data from the International Satellite Cloud Climatology Project and the Earth Radiation Budget Experiment. Results are presented as time series of hemispheric and global averages and as geographical distributions and time–latitude cross sections of climatological averages. The spatial/temporal variabilities of the results were found to be clearly related to the corresponding variabilities of meteorological and other inputs to the parameterizations. Numerous comparisons of the present results were made with available surface measurements for the purpose of validation. In most cases, the differences were found to be within...