PbZr_(0.2)Ti_(0.8)O_(3)(PZT)gate insulator with the thickness of 30 nm is grown by pulsed laser deposition(PLD)in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors(MIS-HEMTs).The ferroelectric...PbZr_(0.2)Ti_(0.8)O_(3)(PZT)gate insulator with the thickness of 30 nm is grown by pulsed laser deposition(PLD)in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors(MIS-HEMTs).The ferroelectric effect of PZT AlGaN/GaN MIS-HEMT is demonstrated.The polarization charge in PZT varies with different gate voltages.The equivalent polarization charge model(EPCM)is proposed for calculating the polarization charge and the concentration of two-dimensional electron gas(2DEG).The threshold voltage(V_(th))and output current density(I_(DS))can also be obtained by the EPCM.The theoretical values are in good agreement with the experimental results and the model can provide a guide for the design of the PZT MIS-HEMT.The polarization charges of PZT can be modulated by different gate-voltage stresses and the V_(th)has a regulation range of 4.0 V.The polarization charge changes after the stress of gate voltage for several seconds.When the gate voltage is stable or changes at high frequency,the output characteristics and the current collapse of the device remain stable.展开更多
Equivalent source layer （ESL） imaging is an important kind of high-resolution electro- encephalogram （EEG） imaging. It consists of two categories： equivalent dipole layer （EDL） and equivalent charge layer （ECL...Equivalent source layer （ESL） imaging is an important kind of high-resolution electro- encephalogram （EEG） imaging. It consists of two categories： equivalent dipole layer （EDL） and equivalent charge layer （ECL）. Both of them are assumed to be located on or near the cortical surface and have been proposed as high-resolution imaging modalities or as intermediate steps to estimate the epicortical potential. Here, EDL and ECL based on a realistic head model are presented, both simulations and real data experiment are done to compare these two models. The results show that ECL can provide higher spatial resolution about source location than EDL does.展开更多
Munitions contain casings that consume explosive energy.The blast load(e.g.,peak overpressure and maximum impulse)intensity generated by ammunition explosion will be lower than that generated by a bare charge with equ...Munitions contain casings that consume explosive energy.The blast load(e.g.,peak overpressure and maximum impulse)intensity generated by ammunition explosion will be lower than that generated by a bare charge with equal mass.To evaluate the blast load of a cased charge under different conditions,the equivalent bare mass needs to be calculated.However,the accuracy of existing correlations strongly depends on the empirical determination of relevant controlling parameters and lacks theoretical clarification.In this paper,new correlations are proposed based on a more rigorous theoretical derivation,considering both the mechanical behaviors of the casing’s material and the change of the polytropic exponent during the expansion process of the explosion products.The controlling parameters are attributed to the rupture radius ratio and the polytropic exponent of detonation products expansion to casing rupture state.The reasonability is validated by both comprehensive numerical simulations with dynamic mechanical constitutive model and theoretical derivations.The results calculated by the new correlation show better agreement with the experimental results than those calculated by previous correlations,and the results difference is explained in more consistency with the thermos-physical properties of the charge and mechanical behaviors of casing material.Furthermore,the correlation of the cased-to-bare impulse ratio is also theoretically improved,providing a more accurate theoretical basis for both the equivalent bare mass and impulse evaluation for a cased charge.展开更多
Most of the existing studies on tunnel blast wave are based on spherical or grouped charges,however,conventional weapons are mostly cylindrical rather than spherical.In order to analyze the impact of cylindrical charg...Most of the existing studies on tunnel blast wave are based on spherical or grouped charges,however,conventional weapons are mostly cylindrical rather than spherical.In order to analyze the impact of cylindrical charges on the tunnel blast wave loads and to develop a quantitative calculation method,this study carried out experimental and numerical research.Initially,external explosion experiments were conducted using both 35 kg spherical charges and cylindrical charges with aspect ratio of 4.8 at two different distances from the tunnel entrance.Comparative analysis of the blast wave parameters in the tunnel revealed that the explosive equivalent of the cylindrical charges was significantly higher than that of the spherical charges.To address this,an equivalent coefficient k based on the spherical charges was proposed for the cylindrical charges.Subsequently,numerical simulations were conducted for the experimental conditions,and the numerical simulation results match the experiments well.Through numerical calculations,the reliability of the equivalent coefficient k under the experimental conditions was verified,and comparison analysis indicated that the explosion energy of cylindrical charges spreads more radially,resulting in more explosion energy entering the tunnel,which is the fundamental reason for the increase in tunnel blast wave loads.Additionally,analyzing the explosion energy ratio entering the tunnel is an effective method for calculating the equivalent coefficient k.Finally,through more than one hundred sets of numerical calculation results,the impact of the proportional distance l and the ratio of charge mass to the tunnel cross-section dimension 4 on the equivalence coefficients k was investigated.An empirical formula for the equivalence coefficient k was derived through fitting,and the accuracy of the formula was validated through literature experimental results.The research findings of this paper will provide valuable guidance for the calculation of blast wave loads in tunnel.展开更多
锂离子电池具有无记忆效应、轻量化、环保等特点,因此常作为电动交通工具、电子设备的能源来源,并适用于各种规模的能源存储。在锂离子电池管理系统中,电池的荷电状态(state of charge,SOC)是最关键的指标之一,其准确估计对于实现电池...锂离子电池具有无记忆效应、轻量化、环保等特点,因此常作为电动交通工具、电子设备的能源来源,并适用于各种规模的能源存储。在锂离子电池管理系统中,电池的荷电状态(state of charge,SOC)是最关键的指标之一,其准确估计对于实现电池系统的高效能量管理和优化控制至关重要。因此本文提出了一种基于动态噪声自适应无迹卡尔曼滤波的SOC估计方法。首先,通过间歇放电实验获取电池不同SOC下的开路电压,并进一步拟合得到电池的OCV-SOC曲线,接着采用二阶RC等效电路模型对锂离子电池建模,然后通过混合功率脉冲特性工况测试对电池模型参数进行辨识。由于实际应用中锂离子电池为非线性系统且SOC估计精度容易受到噪声的影响,本文在卡尔曼滤波算法的基础上采用无迹变换处理,加入噪声自适应过程,以实现噪声特性自适应估计,动态调整测量噪声与过程噪声,提高算法鲁棒性以及估计精度。最后选取DST与FUDS工况进行验证,结果表明在不同工况下动态噪声自适应无迹卡尔曼滤波算法的估计平均绝对误差、最大绝对误差以及均方根误差相较于自适应无迹卡尔曼滤波、无迹卡尔曼滤波算法均有降低,其平均绝对误差小于0.59%。本文提出的动态噪声自适应无迹卡尔曼滤波算法能够更准确地估计锂离子电池SOC。展开更多
针对当前等效全装药(Equivalent Full Charge,EFC)折算系数的国家军用标准预测值与实际测试结果差距较大的问题,基于热-化学烧蚀模型,研究不同工况下射击发数与EFC射击发数间的折算系数计算方法。射击一定发数后,假设身管内壁白层厚度...针对当前等效全装药(Equivalent Full Charge,EFC)折算系数的国家军用标准预测值与实际测试结果差距较大的问题,基于热-化学烧蚀模型,研究不同工况下射击发数与EFC射击发数间的折算系数计算方法。射击一定发数后,假设身管内壁白层厚度及成分随射击发数呈周期性变化,由质量扩散定律建立膛线起始部热-化学烧蚀量与火药燃气侵蚀性、内膛表面瞬态温度的关系。通过经典内弹道模型获得弹后空间火药燃气平均温度及内壁面强制对流换热系数,在考虑后效期高温燃气影响的基础上,建立身管内壁瞬态温度计算模型。以对内弹道过程有重要影响的射速、药量和药温为重点,计算不同射速、不同药号和不同药温下的身管内壁烧蚀量,并据此获得不同工况下的折算系数。研究发现,射速越快,装药质量越大,装药初始温度越高,单发射击造成的身管烧蚀越严重,其对应的EFC折算系数越大,其中强装药的EFC折算系数可达2.131。以某型155 mm火炮身管实弹射击数据为例,验证了新模型的合理性。展开更多
基金the National Natural Science Foundation of China(Grant Nos.61974111,62004150,and 61974115)the China Postdoctoral Science Foundation(Grant No.2018M643575)the Civil Aerospace Pre-Research Plan of China(Grant No.B0202).
文摘PbZr_(0.2)Ti_(0.8)O_(3)(PZT)gate insulator with the thickness of 30 nm is grown by pulsed laser deposition(PLD)in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors(MIS-HEMTs).The ferroelectric effect of PZT AlGaN/GaN MIS-HEMT is demonstrated.The polarization charge in PZT varies with different gate voltages.The equivalent polarization charge model(EPCM)is proposed for calculating the polarization charge and the concentration of two-dimensional electron gas(2DEG).The threshold voltage(V_(th))and output current density(I_(DS))can also be obtained by the EPCM.The theoretical values are in good agreement with the experimental results and the model can provide a guide for the design of the PZT MIS-HEMT.The polarization charges of PZT can be modulated by different gate-voltage stresses and the V_(th)has a regulation range of 4.0 V.The polarization charge changes after the stress of gate voltage for several seconds.When the gate voltage is stable or changes at high frequency,the output characteristics and the current collapse of the device remain stable.
文摘Equivalent source layer （ESL） imaging is an important kind of high-resolution electro- encephalogram （EEG） imaging. It consists of two categories： equivalent dipole layer （EDL） and equivalent charge layer （ECL）. Both of them are assumed to be located on or near the cortical surface and have been proposed as high-resolution imaging modalities or as intermediate steps to estimate the epicortical potential. Here, EDL and ECL based on a realistic head model are presented, both simulations and real data experiment are done to compare these two models. The results show that ECL can provide higher spatial resolution about source location than EDL does.
文摘Munitions contain casings that consume explosive energy.The blast load(e.g.,peak overpressure and maximum impulse)intensity generated by ammunition explosion will be lower than that generated by a bare charge with equal mass.To evaluate the blast load of a cased charge under different conditions,the equivalent bare mass needs to be calculated.However,the accuracy of existing correlations strongly depends on the empirical determination of relevant controlling parameters and lacks theoretical clarification.In this paper,new correlations are proposed based on a more rigorous theoretical derivation,considering both the mechanical behaviors of the casing’s material and the change of the polytropic exponent during the expansion process of the explosion products.The controlling parameters are attributed to the rupture radius ratio and the polytropic exponent of detonation products expansion to casing rupture state.The reasonability is validated by both comprehensive numerical simulations with dynamic mechanical constitutive model and theoretical derivations.The results calculated by the new correlation show better agreement with the experimental results than those calculated by previous correlations,and the results difference is explained in more consistency with the thermos-physical properties of the charge and mechanical behaviors of casing material.Furthermore,the correlation of the cased-to-bare impulse ratio is also theoretically improved,providing a more accurate theoretical basis for both the equivalent bare mass and impulse evaluation for a cased charge.
文摘Most of the existing studies on tunnel blast wave are based on spherical or grouped charges,however,conventional weapons are mostly cylindrical rather than spherical.In order to analyze the impact of cylindrical charges on the tunnel blast wave loads and to develop a quantitative calculation method,this study carried out experimental and numerical research.Initially,external explosion experiments were conducted using both 35 kg spherical charges and cylindrical charges with aspect ratio of 4.8 at two different distances from the tunnel entrance.Comparative analysis of the blast wave parameters in the tunnel revealed that the explosive equivalent of the cylindrical charges was significantly higher than that of the spherical charges.To address this,an equivalent coefficient k based on the spherical charges was proposed for the cylindrical charges.Subsequently,numerical simulations were conducted for the experimental conditions,and the numerical simulation results match the experiments well.Through numerical calculations,the reliability of the equivalent coefficient k under the experimental conditions was verified,and comparison analysis indicated that the explosion energy of cylindrical charges spreads more radially,resulting in more explosion energy entering the tunnel,which is the fundamental reason for the increase in tunnel blast wave loads.Additionally,analyzing the explosion energy ratio entering the tunnel is an effective method for calculating the equivalent coefficient k.Finally,through more than one hundred sets of numerical calculation results,the impact of the proportional distance l and the ratio of charge mass to the tunnel cross-section dimension 4 on the equivalence coefficients k was investigated.An empirical formula for the equivalence coefficient k was derived through fitting,and the accuracy of the formula was validated through literature experimental results.The research findings of this paper will provide valuable guidance for the calculation of blast wave loads in tunnel.
文摘锂离子电池具有无记忆效应、轻量化、环保等特点,因此常作为电动交通工具、电子设备的能源来源,并适用于各种规模的能源存储。在锂离子电池管理系统中,电池的荷电状态(state of charge,SOC)是最关键的指标之一,其准确估计对于实现电池系统的高效能量管理和优化控制至关重要。因此本文提出了一种基于动态噪声自适应无迹卡尔曼滤波的SOC估计方法。首先,通过间歇放电实验获取电池不同SOC下的开路电压,并进一步拟合得到电池的OCV-SOC曲线,接着采用二阶RC等效电路模型对锂离子电池建模,然后通过混合功率脉冲特性工况测试对电池模型参数进行辨识。由于实际应用中锂离子电池为非线性系统且SOC估计精度容易受到噪声的影响,本文在卡尔曼滤波算法的基础上采用无迹变换处理,加入噪声自适应过程,以实现噪声特性自适应估计,动态调整测量噪声与过程噪声,提高算法鲁棒性以及估计精度。最后选取DST与FUDS工况进行验证,结果表明在不同工况下动态噪声自适应无迹卡尔曼滤波算法的估计平均绝对误差、最大绝对误差以及均方根误差相较于自适应无迹卡尔曼滤波、无迹卡尔曼滤波算法均有降低,其平均绝对误差小于0.59%。本文提出的动态噪声自适应无迹卡尔曼滤波算法能够更准确地估计锂离子电池SOC。
文摘针对当前等效全装药(Equivalent Full Charge,EFC)折算系数的国家军用标准预测值与实际测试结果差距较大的问题,基于热-化学烧蚀模型,研究不同工况下射击发数与EFC射击发数间的折算系数计算方法。射击一定发数后,假设身管内壁白层厚度及成分随射击发数呈周期性变化,由质量扩散定律建立膛线起始部热-化学烧蚀量与火药燃气侵蚀性、内膛表面瞬态温度的关系。通过经典内弹道模型获得弹后空间火药燃气平均温度及内壁面强制对流换热系数,在考虑后效期高温燃气影响的基础上,建立身管内壁瞬态温度计算模型。以对内弹道过程有重要影响的射速、药量和药温为重点,计算不同射速、不同药号和不同药温下的身管内壁烧蚀量,并据此获得不同工况下的折算系数。研究发现,射速越快,装药质量越大,装药初始温度越高,单发射击造成的身管烧蚀越严重,其对应的EFC折算系数越大,其中强装药的EFC折算系数可达2.131。以某型155 mm火炮身管实弹射击数据为例,验证了新模型的合理性。
