Gamma-ray Burst Spectrum Influenced by the Doppler Effect of Fireballs

The formula of the Doppler effect of fireballs, which shows how the observational flux from fireballs would be expected, is presented. It shows, when the expansion speed is very large, a weak radiation at X-ray bands would be significantly enhanced to detectable levels and shifted to much higher bands to become a gamma-ray source; at the same time, the peak of the spectrum would shift to a much higher energy band as well.

Buoyancy-Induced Flow Through a Narrow Chamber Containing an Internal Heat Source: Comparison of Experimental Measurements and Numerical Simulations

Natural convection ventilation of a rectangular chamber containing a heated rectangular body has been investigated both experimentally and computationally. The heated square blockage within the partial enclosure was adjacent to the adiabatic lower surface of the chamber and the three exposed surfaces of the block were such as to give a constant heat flux. The air inlet and outlet were located at the bottom and top of the chamber vertical walls respectively, and were of equal area. Velocity measurements were performed using laser Doppler anemometry (LDA) with a one-component He–Ne laser connected to a burst spectrum analyser (BSA). Detailed velocity profiles were measured at the inlet, outlet and at several locations inside the chamber. Temperatures of the heated air at the outlet were measured with a chromel–alumel (type K) bare wire thermocouple probe. Three-dimensional laminar and turbulent (k–e model) numerical simulations were obtained by solving the governing equations using the computational fluid dynamics (CFD) code PHOENICS. Comparisons of experimental and computational results showed very good agreement in most of the flow field.

Frequency Discrimination Ability and Stop-Consonant Identification in Normally Hearing and Hearing-Impaired Subjects

Identification of place of articulation in the synthesized syllables/bi/,/di/, and /gi/ was examined in three groups of listeners: (a) normal hearers, (b) subjects with high-frequency sensorineural hearing loss, and (c) normally hearing subjects listening in noise. Stimuli with an appropriate second formant (F2) transition (moving-F2 stimuli) were compared with stimuli in which F2 was constant (straight-F2 stimuli) to examine the importance of the F2 transition in stop-consonant perception. For straight-F2 stimuli, burst spectrum and F2 frequency were appropriate for the syllable involved. Syllable duration also was a variable, with formant durations of 10, 19, 28, and 44 ms employed. All subjects' identification performance improved as stimulus duration increased. The groups were equivalent in terms of their identification of /di/ and /gi/ syllables, whereas the hearing-impaired and noise-masked normal listeners showed impaired performance for/bi/, particularly for the straight-F2 version. No difference in performance among groups was seen for /di/ and /gi/ stimuli for moving-F2 and straight-F2 versions. Second-formant frequency discrimination measures suggested that subjects' discrimination abilities were not acute enough to take advantage of the formant transition in the /di/and /gi/stimuli.