Many animals mimic the behavior or the appearance of venomous snakes.When humans or other potential predators place their hand near the nest of tits belonging to the family Paridae(and a few other species),the incubat...Many animals mimic the behavior or the appearance of venomous snakes.When humans or other potential predators place their hand near the nest of tits belonging to the family Paridae(and a few other species),the incubating female performs a hissing display that mimics the inhalation hiss of a viper or another snake.They hiss vigorously while lunging their head forward and shaking their wings and tail,repeating this behavior several times.The structure of the hiss in tits is similar to that of the inhalation hiss of a snake,providing evidence of significant convergence of the mimic toward the model.The behavior of individual females is repeatable among tri als.Individuals that flew away from their nest box only performed the hissing display on 6%of later trials,when present at their box,whereas individuals that did not fly away hissed on 28% of occasions,consistent with great tits Parus major either cautiously flying away or staying put on their nest while actively defending it.Individuals that flew away produced fewer chicks than individuals that stayed and hissed.The hissing display was more common when snakes were more abundant:1)When breeding late during the season;2)when breeding at sites with more snakes;and 3)when breeding in subtropical and tropical China with a higher abundance of snakes than in Denmark with a lower abundance.The frequency of nest predation was higher in sites with no snakes,and the frequency of predation increased with decreasing frequency of hissing display.These findings are consistent with expectations for frequency-dependent selection acting on snake mimicry.展开更多
某商用车在开发阶段,路试发现乘客舱听到明显"嘶嘶声",初步判断是增压器的Hiss噪声向外辐射导致。对LMS Test Lab采集的车内噪声信号进行分析,确定此异响产生的原因是增压器Hiss噪声通过取气口辐射的。通过LMS Virtual Lab对...某商用车在开发阶段,路试发现乘客舱听到明显"嘶嘶声",初步判断是增压器的Hiss噪声向外辐射导致。对LMS Test Lab采集的车内噪声信号进行分析,确定此异响产生的原因是增压器Hiss噪声通过取气口辐射的。通过LMS Virtual Lab对消声器进行优化,调整原有宽频消声器的消声频率来优化进气系统,最终解决了Hiss噪声问题。展开更多
基于AAC比特流,提出了一种压缩域音频Hiss噪声抑制方法。该方法的输入为含噪音频的AAC比特流,输出为增强音频的AAC比特流。首先,利用修正的绝对中值标准差(MMAD,modified median absolute deviation)估计Hiss噪声,其次,利用修正的离散...基于AAC比特流,提出了一种压缩域音频Hiss噪声抑制方法。该方法的输入为含噪音频的AAC比特流,输出为增强音频的AAC比特流。首先,利用修正的绝对中值标准差(MMAD,modified median absolute deviation)估计Hiss噪声,其次,利用修正的离散傅里叶变换(MDFT,modified discrete Fourier transform)计算听觉掩蔽阈值参数,最后,根据参数软阈值方法得到增强的AAC比特流,并用于AAC解码器得到最终的增强音频信号。主观和客观测试结果表明,所提出的方法能有效去除AAC解码音频信号中的Hiss噪声,其性能明显优于现有的几种Hiss噪声消除方法。展开更多
Using wave measurements from the EMFISIS instrument onboard Van Allen Probes,we investigate statistically the spatial distributions of the intensity of plasmaspheric hiss waves.To reproduce these empirical results,we ...Using wave measurements from the EMFISIS instrument onboard Van Allen Probes,we investigate statistically the spatial distributions of the intensity of plasmaspheric hiss waves.To reproduce these empirical results,we establish a fitting model that is a thirdorder polynomial function of L-shell,magnetic local time(MLT),magnetic latitude(MLAT),and AE*.Quantitative comparisons indicate that the model’s fitting functions can reflect favorably the major empirical features of the global distribution of hiss wave intensity,including substorm dependence and the MLT asymmetry.Our results therefore provide a useful analytic model that can be readily employed in future simulations of global radiation belt electron dynamics under the impact of plasmaspheric hiss waves in geospace.展开更多
We present a study on the second-order resonant interaction between the ring current protons with Whistler-mode waves propagating near the quasi electrostatic limit following the previous second-order resonant theory....We present a study on the second-order resonant interaction between the ring current protons with Whistler-mode waves propagating near the quasi electrostatic limit following the previous second-order resonant theory. The diffusion coefficients are proportional to the electric field amplitude E, much greater than those for the regular first-order resonance, which are proportional to the electric field amplitudes square E^2. Numerical calculations for the pitch angle scattering are performed for typical energies of protons Ek = 50 keV and 100 keV at locations L = 2 and L = 3.5. The timescale for the loss process of protons by the Whistler waves is found to approach one hour, comparable to that by the EMIC waves, suggesting that Whistler waves may also contribute significantly to the ring current decay under appropriate conditions.展开更多
基金This study was supported by the National Natural Science Foundation of China(Nos.31772453 and 31970427 to W.L.)。
文摘Many animals mimic the behavior or the appearance of venomous snakes.When humans or other potential predators place their hand near the nest of tits belonging to the family Paridae(and a few other species),the incubating female performs a hissing display that mimics the inhalation hiss of a viper or another snake.They hiss vigorously while lunging their head forward and shaking their wings and tail,repeating this behavior several times.The structure of the hiss in tits is similar to that of the inhalation hiss of a snake,providing evidence of significant convergence of the mimic toward the model.The behavior of individual females is repeatable among tri als.Individuals that flew away from their nest box only performed the hissing display on 6%of later trials,when present at their box,whereas individuals that did not fly away hissed on 28% of occasions,consistent with great tits Parus major either cautiously flying away or staying put on their nest while actively defending it.Individuals that flew away produced fewer chicks than individuals that stayed and hissed.The hissing display was more common when snakes were more abundant:1)When breeding late during the season;2)when breeding at sites with more snakes;and 3)when breeding in subtropical and tropical China with a higher abundance of snakes than in Denmark with a lower abundance.The frequency of nest predation was higher in sites with no snakes,and the frequency of predation increased with decreasing frequency of hissing display.These findings are consistent with expectations for frequency-dependent selection acting on snake mimicry.
文摘某商用车在开发阶段,路试发现乘客舱听到明显"嘶嘶声",初步判断是增压器的Hiss噪声向外辐射导致。对LMS Test Lab采集的车内噪声信号进行分析,确定此异响产生的原因是增压器Hiss噪声通过取气口辐射的。通过LMS Virtual Lab对消声器进行优化,调整原有宽频消声器的消声频率来优化进气系统,最终解决了Hiss噪声问题。
基金supported by the B-type Strategic Priority Program of the Chinese Academy of Sciences (Grant No. XDB41000000)the NSFC grants 41674163, 41974186, 41704162, 41904144, and 41904143+1 种基金the pre-research projects on Civil Aerospace Technologies No. D020308, D020104 and D020303funded by China National Space Administration。
文摘Using wave measurements from the EMFISIS instrument onboard Van Allen Probes,we investigate statistically the spatial distributions of the intensity of plasmaspheric hiss waves.To reproduce these empirical results,we establish a fitting model that is a thirdorder polynomial function of L-shell,magnetic local time(MLT),magnetic latitude(MLAT),and AE*.Quantitative comparisons indicate that the model’s fitting functions can reflect favorably the major empirical features of the global distribution of hiss wave intensity,including substorm dependence and the MLT asymmetry.Our results therefore provide a useful analytic model that can be readily employed in future simulations of global radiation belt electron dynamics under the impact of plasmaspheric hiss waves in geospace.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40774078, 40404012, 40474064 and 40674076, and the Visiting Scholar Foundation of State Key Laboratory for Space Weather, Chinese Academy Sciences.
文摘We present a study on the second-order resonant interaction between the ring current protons with Whistler-mode waves propagating near the quasi electrostatic limit following the previous second-order resonant theory. The diffusion coefficients are proportional to the electric field amplitude E, much greater than those for the regular first-order resonance, which are proportional to the electric field amplitudes square E^2. Numerical calculations for the pitch angle scattering are performed for typical energies of protons Ek = 50 keV and 100 keV at locations L = 2 and L = 3.5. The timescale for the loss process of protons by the Whistler waves is found to approach one hour, comparable to that by the EMIC waves, suggesting that Whistler waves may also contribute significantly to the ring current decay under appropriate conditions.
