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المؤلفون: Shen, R. F., Im, M., Sugita, S., Volnova, A., Andreev, M., Gehrels, N., Urata, Y., Sahu, D. K., Sakamoto, T., Gorosabel, J., Barthelmy, S. D., Pozanenko, A., Zheng, W., Klunko, E., Breeveld, A., Beardmore, A. P., Wu, X. F., Ukwatta, T. N., Zhang, B., Nissinen, M., Akerlof, C. W., De Pasquale, M., Anto, P., Carsenty, U., Sonbas, E.
المصدر: CASI
مصطلحات موضوعية: Astrophysics
جغرافية الموضوع: Unclassified, Unlimited, Publicly available
الوصف: We present a comprehensive analysis of a bright, long duration (T(sub 90) approx. 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb and BOOTES telescopes when the GRB was still radiating in the gamma-ray band. Thanks to its long duration, nearly 200 s of observations were obtained simultaneously from optical, X-ray to gamma-ray (1 eV - 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution across 6 orders of magnitude in energy during the prompt emission phase. In particular, by fitting the time resolved prompt spectra, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard GRB synchrotron emission model in the fast cooling regime. Although the prompt optical emission is brighter than the extrapolation of the best fit X/ -ray spectra, it traces the -ray light curve shape, suggesting a relation to the prompt high energy emission. The synchrotron + synchrotron self-Compton (SSC) scenario is disfavored by the data, but the models invoking a pair of internal shocks or having two emission regions can interpret the data well. Shortly after prompt emission (approx. 1100 s), a bright (R = 14.0) optical emission hump with very steep rise ( alpha approx. 5.5) was observed which we interpret as the emission from the reverse shock. It is the first time that the rising phase of a reverse shock component has been closely observed.
وصف الملف: application/pdf
العلاقة: Document ID: 20120008684; http://hdl.handle.net/2060/20120008684Test
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المؤلفون: Pagani, C., Evans, P. A., Holland, S. T., Wu, X. F., Covino, S., Antonelli, L. A., OBrien, P. T., Osborne, J. P., Zhang, B., Liang, E. W., Marshall, Frank, Siegel, M. H., Burrows, D. N., dePasquale, M., Sakamoto, T., Fugazza, D.
المصدر: CASI
مصطلحات موضوعية: Astrophysics
جغرافية الموضوع: Unclassified, Unlimited, Publicly available
الوصف: GRB 100418A is a long Gamma-Ray Burst at redshift z=0.6235 discovered with the Swift Gamma-Ray Burst Explorer with unusual optical and X-ray light curves ' After an initial short-lived, rapid decline in X-rays, the optical and X-ray light curves observed with Swift are approximately flat or rising slightly out to at least approx.7 ks after the trigger, peak at approx.50 ks, and then follow an approximately power-law decay. Such a long optical plateau and late peaking is rarely seen in 6R8 afterglows. Observations with REM during a gap in the Swift coverage indicate a bright optical flare at approx.25 ks, The long plateau phase of the afterglow is interpreted using either a model with continuous injection of energy into the forward shock of the burst or a model in which the 'et of the burst is viewed off-axis. In both models the isotropic kinetic energy in the late afterglow after the plateau phase is >100 times the 10(exp 51) erg of the prompt isotropic gamma-ray energy release. The energy injection model is favored because the off-axis 'et model would require the intrinsic $T f801$ for the GR8 'et viewed on-axis to be very short, approx.10 ms, and the intrinsic isotropic gamma-ray energy release and the true jet energy to be much higher than the typical values of known short GRBs^ The non-detection of a 'et break up to approx.2 Ms indicates a jet half-opening angle of at least 14 degrees, and a relatively high collimation-corrected 'et energy of at least 10(exp 52) erg.
وصف الملف: application/pdf
العلاقة: Document ID: 20110005586; http://hdl.handle.net/2060/20110005586Test
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المؤلفون: Wu, T. W., Seybert, A. F., Wu, X. F.
المصدر: CASI
مصطلحات موضوعية: MECHANICAL ENGINEERING
جغرافية الموضوع: Unclassified, Unlimited, Publicly available
الوصف: This research report is presented in three parts. In the first part, acoustical analyses were performed on modes of vibration of the housing of a transmission of a gear test rig developed by NASA. The modes of vibration of the transmission housing were measured using experimental modal analysis. The boundary element method (BEM) was used to calculate the sound pressure and sound intensity on the surface of the housing and the radiation efficiency of each mode. The radiation efficiency of each of the transmission housing modes was then compared to theoretical results for a finite baffled plate. In the second part, analytical and experimental validation of methods to predict structural vibration and radiated noise are presented. A rectangular box excited by a mechanical shaker was used as a vibrating structure. Combined finite element method (FEM) and boundary element method (BEM) models of the apparatus were used to predict the noise level radiated from the box. The FEM was used to predict the vibration, while the BEM was used to predict the sound intensity and total radiated sound power using surface vibration as the input data. Vibration predicted by the FEM model was validated by experimental modal analysis; noise predicted by the BEM was validated by measurements of sound intensity. Three types of results are presented for the total radiated sound power: sound power predicted by the BEM model using vibration data measured on the surface of the box; sound power predicted by the FEM/BEM model; and sound power measured by an acoustic intensity scan. In the third part, the structure used in part two was modified. A rib was attached to the top plate of the structure. The FEM and BEM were then used to predict structural vibration and radiated noise respectively. The predicted vibration and radiated noise were then validated through experimentation.
وصف الملف: application/pdf
العلاقة: Document ID: 19940025049; Accession ID: 94N29552; http://hdl.handle.net/2060/19940025049Test
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المؤلفون: Seybert, A. F., Oswald, Fred B., Wu, X. F.
المصدر: CASI
مصطلحات موضوعية: MECHANICAL ENGINEERING
جغرافية الموضوع: Unclassified, Unlimited, Publicly available
الوصف: Analytical and experimental validation of methods to predict structural vibration and radiated noise are presented. A rectangular box excited by a mechanical shaker was used as a vibrating structure. Combined finite element method (FEM) and boundary element method (BEM) models of the apparatus were used to predict the noise radiated from the box. The FEM was used to predict the vibration, and the surface vibration was used as input to the BEM to predict the sound intensity and sound power. Vibration predicted by the FEM model was validated by experimental modal analysis. Noise predicted by the BEM was validated by sound intensity measurements. Three types of results are presented for the total radiated sound power: (1) sound power predicted by the BEM modeling using vibration data measured on the surface of the box; (2) sound power predicted by the FEM/BEM model; and (3) sound power measured by a sound intensity scan. The sound power predicted from the BEM model using measured vibration data yields an excellent prediction of radiated noise. The sound power predicted by the combined FEM/BEM model also gives a good prediction of radiated noise except for a shift of the natural frequencies that are due to limitations in the FEM model.
وصف الملف: application/pdf
العلاقة: Document ID: 19920020454; Accession ID: 92N29697; http://hdl.handle.net/2060/19920020454Test
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المؤلفون: Seybert, A. F., Oswald, Fred B., Wu, X. F., Wu, T. W.
المصدر: CASI
مصطلحات موضوعية: MECHANICAL ENGINEERING
جغرافية الموضوع: Unclassified, Unlimited, Publicly available
الوصف: The modal and acoustical analysis of the NASA gear-noise rig is described. Experimental modal analysis techniques were used to determine the modes of vibration of the transmission housing. The resulting modal data were then used in a boundary element method (BEM) analysis to calculate the sound pressure and sound intensity on the surface of the housing as well as the radiation efficiency of each mode. The radiation efficiencies of the transmission housing modes are compared with theoretical results for finite, baffled plates. A method that uses the measured mode shapes and the BEM to predict the effect of simple structural changes on the sound radiation efficiency of the modes of vibration is also described.
وصف الملف: application/pdf
العلاقة: Document ID: 19910016097; Accession ID: 91N25411; http://hdl.handle.net/2060/19910016097Test
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المؤلفون: Seybert, A. F., Wu, T. W., Wu, X. F., Oswald, Fred B.
المصدر: Other Sources
جغرافية الموضوع: Unclassified, Unlimited, Publicly available
الوقت: 71
الوصف: The modal and acoustical analysis of the NASA gear-noise rig is described. Experimental modal analysis techniques were used to determine the modes of vibration of the transmission housing. The resulting modal data were then used in a boundary element method (BEM) analysis to calculate the sound pressure and sound intensity on the surface of the housing as well as the radiation efficiency of each mode. The radiation efficiencies of the transmission housing modes are compared with theoretical results for finite, baffled plates. A method that uses the measured mode shapes and the BEM to predict the effect of simple structural changes on the sound radiation efficiency of the modes of vibration is also described.
العلاقة: http://ntrs.nasa.gov/search.jsp?R=19930045423Test; Accession ID: 93A29420
