The benefits of combined electric and acoustic stimulation ͑EAS͒ in terms of speech recognition in noise are well established; however the underlying factors responsible for this benefit are not clear. The present study tests the hypothesis that having access to acoustic information in the low frequencies makes it easier for listeners to glimpse the target. Normal-hearing listeners were presented with vocoded speech alone ͑V͒, low-pass ͑LP͒ filtered speech alone, combined vocoded and LP speech ͑LP+ V͒ and with vocoded stimuli constructed so that the low-frequency envelopes were easier to glimpse. Target speech was mixed with two types of maskers ͑steady-state noise and competing talker͒ at −5 to 5 dB signal-to-noise ratios. Results indicated no advantage of LP+ V in steady noise, but a significant advantage over V in the competing talker background, an outcome consistent with the notion that it is easier for listeners to glimpse the target in fluctuating maskers. A significant improvement in performance was noted with the modified glimpsed stimuli over the original vocoded stimuli. These findings taken together suggest that a significant factor contributing to the EAS advantage is the enhanced ability to glimpse the target.
Research on detonation process is of great significance for the control optimization of pulse detonation engine. Based on absorption spectrum technology, the filling process of fresh fuel and oxidant during detonation is researched. As one of the most important products, H 2 O is selected as the target of detonation diagnosis. Fiber distributed detonation test system is designed to enable the detonation diagnosis under adverse conditions in detonation process. The test system is verified to be reliable. Laser signals at different working frequency (5Hz, 10Hz and 20Hz) are detected. Change of relative laser intensity in one detonation circle is analyzed. The duration of filling process is inferred from the change of laser intensity, which is about 100~110ms. The peak of absorption spectrum is used to present the concentration of H 2 O during the filling process of fresh fuel and oxidant. Absorption spectrum is calculated, and the change of absorption peak is analyzed. Duration of filling process calculated with absorption peak consisted with the result inferred from the change of relative laser intensity. The pulse detonation engine worked normally and obtained the maximum thrust at 10Hz under experiment conditions. The results are verified through H 2 O gas concentration monitoring during detonation.
Underwater pulse detonation gas jets generated by a detonation tube are experimentally investigated in this study utilizing detonations in explosive gas mixtures to generate pulsating bubbles under water. Three stoichiometric gaseous fuels (methane, hydrogen, and acetylene) are detonated with oxygen under the same filling conditions. Digital particle image velocimetry and wavelet transform techniques are introduced to analyze bubble dynamics and pressure field characteristics by means of which the velocity field of the bubble interface and the time–frequency distributions of the pressure response under water are elucidated, respectively. Motions of the bubble interface, which can now be clearly seen with the oscillations, are indicated in high-speed photographic images. Three main frequency components and their duration are identified: reverberations of water tank, pulsations of the detonation gas bubble, and fluctuations of free water surface. Experimental results show that the reverberation concentrating in high frequencies is due to the detonation wave (DW) and reflected shock waves in the water tank; the pulsations are related to the bubble oscillating periods, which are stronger as the detonation pressure increases; and fluctuation occurs in both the bubble oscillating and floating stages. To explain the directional growth of the detonation gas bubble, an experiment of pulse detonation gas jet in air is conducted where the sudden release of detonation products behind the DW and the subsequent impulsive detonation gas jet are qualitatively presented. Results presented in this paper give in-depth analysis of pulse detonation gas jets and provide a new way to generate pulsating bubbles under water.
The forward reflection of detonation waves on the solid wall will lead to a high pressure rise. The research systematically introduced the theoretical, numerical, and experimental exploration on the shock propagation characteristics of detonation waves forward impacting on a solid wall in the present work. The one-dimensional shock theory was carried out to solve the pressure rise ratio in this process. The exact solution and its variation law of a positive increase with filling pressure were expressed. One-dimensional simulations based on the space-time conservation element and solution element method were utilized to reveal the pressure decrease and velocity increase laws for the reflected shock wave. The blockage, oscillation, and attenuation phenomena of detonation waves and reflected shock waves under the effect of the tube–wall reflection were demonstrated in two-dimensional works. Experimental results from the detonation tube pressure test system showed a larger amplitude and duration of the reflected shock wave than the detonation wave. Pressure evolution and the formation of pressure plateaus were consistent with the simulation results. In addition, the time required for the pressure plateaus to decay to 0.5 times the Chapman-Jouget (C–J) detonation pressure is relatively constant under different filling conditions.
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