Additive Manufacturing(AM)can provide customized parts that conventional techniques fail to deliver.One important parameter in AM is the quality of the parts,as a result of the material extrusion 3D printing(3D-P)proc...Additive Manufacturing(AM)can provide customized parts that conventional techniques fail to deliver.One important parameter in AM is the quality of the parts,as a result of the material extrusion 3D printing(3D-P)procedure.This can be very important in defense-related applications,where optimum performance needs to be guaranteed.The quality of the Polyetherimide 3D-P specimens was examined by considering six control parameters,namely,infill percentage,layer height,deposition angle,travel speed,nozzle,and bed temperature.The quality indicators were the root mean square(Rq)and average(Ra)roughness,porosity,and the actual to nominal dimensional deviation.The examination was performed with optical profilometry,optical microscopy,and micro-computed tomography scanning.The Taguchi design of experiments was applied,with twenty-five runs,five levels for each control parameter,on five replicas.Two additional confirmation runs were conducted,to ensure reliability.Prediction equations were constructed to express the quality indicators in terms of the control parameters.Three modeling approaches were applied to the experimental data,to compare their efficiency,i.e.,Linear Regression Model(LRM),Reduced Quadratic Regression Model,and Quadratic Regression Model(QRM).QRM was the most accurate one,still the differences were not high even considering the simpler LRM model.展开更多
在LTE移动通信系统中信道质量指示参数(Channel Quality Indicator,CQI)是自适应调制编码(AdaptiveModulation and Coding,AMC)技术的一项重要参数。由于GEO卫星信道存在较长的传输时延,为保证有效的AMC调整,对CQI进行预测是非常必要的...在LTE移动通信系统中信道质量指示参数(Channel Quality Indicator,CQI)是自适应调制编码(AdaptiveModulation and Coding,AMC)技术的一项重要参数。由于GEO卫星信道存在较长的传输时延,为保证有效的AMC调整,对CQI进行预测是非常必要的。但是大多数预测算法的可预测时长受到输入序列的相关时间限制,而含有小尺度衰落影响的信号的CQI序列的相关时间远远小于所需预测时长,对获得的CQI序列进行预测是不现实的。针对这一问题,提出了一种使用仅含有大尺度衰落的CQI数据进行预测的近似方法。将获得的CQI序列平滑后去掉小尺度衰落的影响,余下的数据可以认为是只受大尺度衰落影响,其相关时间可以大大延长。通过对GEO卫星信道信道质量进行建模分析,对使用近似方法处理前后的CQI序列数据差距以及相关时间的变化进行了数值仿真,结果表明所提出的近似方法不会导致CQI数据产生较大的偏差,且近似后的序列具有较长相关时间。在此种近似方法处理下的CQI数据相关时间能够满足预测模型的需要,从而为保证GEO卫星移动通信系统中使用AMC的可行性和可靠性提供可能。展开更多
文摘Additive Manufacturing(AM)can provide customized parts that conventional techniques fail to deliver.One important parameter in AM is the quality of the parts,as a result of the material extrusion 3D printing(3D-P)procedure.This can be very important in defense-related applications,where optimum performance needs to be guaranteed.The quality of the Polyetherimide 3D-P specimens was examined by considering six control parameters,namely,infill percentage,layer height,deposition angle,travel speed,nozzle,and bed temperature.The quality indicators were the root mean square(Rq)and average(Ra)roughness,porosity,and the actual to nominal dimensional deviation.The examination was performed with optical profilometry,optical microscopy,and micro-computed tomography scanning.The Taguchi design of experiments was applied,with twenty-five runs,five levels for each control parameter,on five replicas.Two additional confirmation runs were conducted,to ensure reliability.Prediction equations were constructed to express the quality indicators in terms of the control parameters.Three modeling approaches were applied to the experimental data,to compare their efficiency,i.e.,Linear Regression Model(LRM),Reduced Quadratic Regression Model,and Quadratic Regression Model(QRM).QRM was the most accurate one,still the differences were not high even considering the simpler LRM model.
文摘在LTE移动通信系统中信道质量指示参数(Channel Quality Indicator,CQI)是自适应调制编码(AdaptiveModulation and Coding,AMC)技术的一项重要参数。由于GEO卫星信道存在较长的传输时延,为保证有效的AMC调整,对CQI进行预测是非常必要的。但是大多数预测算法的可预测时长受到输入序列的相关时间限制,而含有小尺度衰落影响的信号的CQI序列的相关时间远远小于所需预测时长,对获得的CQI序列进行预测是不现实的。针对这一问题,提出了一种使用仅含有大尺度衰落的CQI数据进行预测的近似方法。将获得的CQI序列平滑后去掉小尺度衰落的影响,余下的数据可以认为是只受大尺度衰落影响,其相关时间可以大大延长。通过对GEO卫星信道信道质量进行建模分析,对使用近似方法处理前后的CQI序列数据差距以及相关时间的变化进行了数值仿真,结果表明所提出的近似方法不会导致CQI数据产生较大的偏差,且近似后的序列具有较长相关时间。在此种近似方法处理下的CQI数据相关时间能够满足预测模型的需要,从而为保证GEO卫星移动通信系统中使用AMC的可行性和可靠性提供可能。
