36,497 research outputs found
Stability and control characteristics of an air-breathing missile configuration having a forward located inlet
An investigation was made to determine the aerodynamic characteristics of an airbreathing missile configuration having a forward located inlet. Control was provided by cruciform tail surfaces. Aerodynamic data were obtained for the body-tail configuration alone and with planar or cruciform wings. At Mach numbers from 2.86 to 4.63, the model had internal flow. At Mach numbers from 1.70 to 2.86, the internal duct was closed, and an inlet fairing was installed to simulate boost conditions
Power spectral density analysis
Equations for power spectral density function, and for root mean square of power spectral density functio
Illuminance and luminance distributions of a prototype ambient illumination system for Space Station Freedom
Preliminary results of research conducted in the late 1970's indicate that perceptual qualities of an enclosure can be influenced by the distribution of illumination within the enclosure. Subjective impressions such as spaciousness, perceptual clarity, and relaxation or tenseness, among others, appear to be related to different combinations of surface luminance. A prototype indirect ambient illumination system was developed which will allow crew members to alter surface luminance distributions within an enclosed module, thus modifying perceptual cues to match crew preferences. A traditional lensed direct lighting system was compared to the prototype utilizing the full-scale mockup of Space Station Freedom developed by Marshall Space Flight Center. The direct lensed system was installed in the habitation module with the indirect prototype deployed in the U.S. laboratory module. Analysis centered on the illuminance and luminance distributions resultant from these systems and the implications of various luminaire spacing options. All test configurations were evaluated for compliance with NASA Standard 3000, Man-System Integration Standards
Experimental investigation at high subsonic speeds of the rolling-stability derivatives of a 1/22 scale model of the Republic F-105 airplane
Analysis of the excited-state absorption spectral bandshape of oligofluorenes
We present ultrafast transient absorption spectra of two oligofluorene
derivatives in dilute solution. These spectra display clear vibronic structure,
which we analyze rigorously using a time-dependent formalism of absorption to
extract the principal excited-state vibrational normal-mode frequencies that
couple to the electronic transition, the configurational displacement of the
higher-lying excited state, and the reorganization energies. We can model the
excited-state absorption spectrum using two totally symmetric vibrational modes
with frequencies 450 (dimer) or 400 cm (trimer), and 1666 cm. The
reorganization energy of the ground-state absorption is rather insensitive to
the oligomer length at 230 meV. However, that of the excited-state absorption
evolves from 58 to 166 meV between the oligofluorene dimer and trimer. Based on
previous theoretical work [Shukla et al., Phys. Rev. B \textbf{67}, 245203
(2003)], we assign the absorption spectra to a transition from the
excited state to a higher-lying state, and find that the energy of the
excited-state transition with respect to the ground-state transition energy is
in excellent agreement with the theoretical predictions for both oligomers
studied here. These results and analysis permit profound understanding of the
nature of excited-state absorption in -conjugated polymers, which are the
subject of general interest as organic semiconductors in the solid state.Comment: Resubmitted to J. Chem. Phys on 28 April 2010; 31 pages, 7 figure
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