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.

Distributed measurement of static strain in an optical fiber with multiple bragg gratings at nominally equal wavelengths.

Abstract: The Fourier transform relationship between the reflected light froma Bragg grating and the complex spatial modulation of the Bragg grating is used to produce a distributed strain sensing system A tunable external cavity diode laser along with a reference reflector in anoptical fiber are used to produce a measurement of the phase and amplitude of the reflected light from the modulated Bragg grating as a function of wavelength The system is demonstrated with 22 Bragg gratings in a single fiber on a cantilever beam and compared with foil strain gauge readings

Inferring black carbon content and specific absorption from Aerosol Robotic Network (AERONET) aerosol retrievals

Abstract: [1] Black carbon is ubiquitous in the atmosphere and is the main anthropogenic absorbing particulate. Absorption by black carbon is thought to be comparable to the cooling associated with sulfate aerosols, although present-day satellites are incapable of obtaining this measurement, and model estimates are highly uncertain. More measurements of black carbon concentration are necessary for improving and validating transport and general circulation models. The Aerosol Robotics Network (AERONET) of 180 worldwide radiometers offers an opportunity to obtain these measurements. We use the Maxwell Garnett effective medium approximation to infer the column-averaged black carbon concentration and specific absorption of AERONET retrievals at 46 locations. The yearly averaged black carbon column concentrations exhibit the expected regional dependence, with remote island locations having values about an order of magnitude lower than the continental biomass burning locations. The yearly averaged black carbon specific absorption cross section is consistent with other measured values, 9.9 m2 g−1 for 19,591 retrievals, but varies from 7.7 to 12.5 m2 g−1. We attribute this variability to the details of the size distributions and the fraction of black carbon contained in the aerosol mixture. We also used the Maxwell Garnett equations to parameterize the imaginary refractive index with respect to the black carbon volume fraction, enabling simple but accurate absorption estimates for aerosol mixtures when the black carbon fraction and size distribution is known. The black carbon concentrations that we derive from AERONET measurements correctly describe the radiance field and represent an alternative to absorption optical thickness in the link between models and AERONET measurements.

Nonlinear vibrations of beams with various boundary conditions.

Abstract: Amplitude frequency relations of nonlinear vibrations in uniform beams with various boundary conditions using perturbation method