ZrN-based composites were synthesized from zirconia via aluminothermic reduction and nitridation proces with Al powders and Mg O as the reductant and sintering aids,respectively. ZrN-based composites are promising for...ZrN-based composites were synthesized from zirconia via aluminothermic reduction and nitridation proces with Al powders and Mg O as the reductant and sintering aids,respectively. ZrN-based composites are promising for application in the refractory materials or other high temperature industry fields. The effects of extra Al powder on physical properties,phase transformation and microstructures were investigated. Products with differen phase composition and morphologies were obtained with different Al powders additions. The products were composed of Zr N,ZrO2,MgAl2O4,and Zr Al3O3N by aluminothermal reduction and nitridation of zirconia with 0% extra Al powders addition. The diffraction peaks o Zr N were the strongest while peaks of ZrO2vanished with 6% extra Al addition. The thermodynamic calculation indicated that introducing Mg O into the system could promote the reaction process.展开更多
For the detection of underwater target echo under strong interferences,the modulation feature of direct echo signal and reverberation spectrum are characterized by the signal spectral irregularity feature,and the rela...For the detection of underwater target echo under strong interferences,the modulation feature of direct echo signal and reverberation spectrum are characterized by the signal spectral irregularity feature,and the relationship between signal spectral irregularity and target physical properties is theoretically formed.A novel method of broadband underwater target echo detection under reverberation based on the signal spectral irregularity characteristics is proposed.The proposed method has the capability of discriminating between the direct target echo signal from reverberation.Simulation results of complex underwater target broadband acoustic scattering show that the echo can be detected even with the signal to reverberation ratio(SRR)below-10 dB by the proposed method based on the spectral irregularity(SI)feature.The corresponding sea experimental results also show that echo can be detected when the SRR is below 0 dB.The effectiveness and correctness of the proposed method are verified both in simulated data and in real data in sea experiment.展开更多
This paper presents a method to estimate the depth of deep-sea target by matching the time delay and amplitude structure of echo multipath highlight clusters.The echo structure is the convolution of two-way channel tr...This paper presents a method to estimate the depth of deep-sea target by matching the time delay and amplitude structure of echo multipath highlight clusters.The echo structure is the convolution of two-way channel transfer function as well as the acoustic scattering function of the target,which shows the characteristics of deep-sea highlight clusters when the target is close to the sea surface or near the sea bottom.The time delay and amplitude structure of highlight clusters are related to the target depth,which can be used to estimate the target depth.A method of matching estimation of target depth on range-depth grid using nonlinear programming cost function is established.The mismatch effects of inter-cluster time delay interval deviation and sea water sound velocity profile deviation on matching estimation are simulated and analyzed.The results of a winter experiment in the South China Sea illustrate that when the water depth is 1 km and distance is 5–8 km,the echo of target is 40 m underwater,there are three highlight clusters with a time interval of about 0.3 s,with the error range of target depth matching estimation being 0–65 m.展开更多
文摘ZrN-based composites were synthesized from zirconia via aluminothermic reduction and nitridation proces with Al powders and Mg O as the reductant and sintering aids,respectively. ZrN-based composites are promising for application in the refractory materials or other high temperature industry fields. The effects of extra Al powder on physical properties,phase transformation and microstructures were investigated. Products with differen phase composition and morphologies were obtained with different Al powders additions. The products were composed of Zr N,ZrO2,MgAl2O4,and Zr Al3O3N by aluminothermal reduction and nitridation of zirconia with 0% extra Al powders addition. The diffraction peaks o Zr N were the strongest while peaks of ZrO2vanished with 6% extra Al addition. The thermodynamic calculation indicated that introducing Mg O into the system could promote the reaction process.
基金The 13th Five-Year Plan for Advanced Research Program(No.41416030301)
文摘For the detection of underwater target echo under strong interferences,the modulation feature of direct echo signal and reverberation spectrum are characterized by the signal spectral irregularity feature,and the relationship between signal spectral irregularity and target physical properties is theoretically formed.A novel method of broadband underwater target echo detection under reverberation based on the signal spectral irregularity characteristics is proposed.The proposed method has the capability of discriminating between the direct target echo signal from reverberation.Simulation results of complex underwater target broadband acoustic scattering show that the echo can be detected even with the signal to reverberation ratio(SRR)below-10 dB by the proposed method based on the spectral irregularity(SI)feature.The corresponding sea experimental results also show that echo can be detected when the SRR is below 0 dB.The effectiveness and correctness of the proposed method are verified both in simulated data and in real data in sea experiment.
文摘This paper presents a method to estimate the depth of deep-sea target by matching the time delay and amplitude structure of echo multipath highlight clusters.The echo structure is the convolution of two-way channel transfer function as well as the acoustic scattering function of the target,which shows the characteristics of deep-sea highlight clusters when the target is close to the sea surface or near the sea bottom.The time delay and amplitude structure of highlight clusters are related to the target depth,which can be used to estimate the target depth.A method of matching estimation of target depth on range-depth grid using nonlinear programming cost function is established.The mismatch effects of inter-cluster time delay interval deviation and sea water sound velocity profile deviation on matching estimation are simulated and analyzed.The results of a winter experiment in the South China Sea illustrate that when the water depth is 1 km and distance is 5–8 km,the echo of target is 40 m underwater,there are three highlight clusters with a time interval of about 0.3 s,with the error range of target depth matching estimation being 0–65 m.
