In order to meet the demands for high transmission rates and high service quality in broadband wireless communication systems, orthogonal frequency division multiplexing （OFDM） has been adopted in some standards. Ho...In order to meet the demands for high transmission rates and high service quality in broadband wireless communication systems, orthogonal frequency division multiplexing （OFDM） has been adopted in some standards. However, the inter-block interference （IBI） and inter-carrier interference （ICI） in an OFDM system affect the performance. To mitigate IBI and ICI, some pre-processing approaches have been proposed based on full channel state information （CSI）, which improved the system performance. A pre-processing filter based on partial CSI at the transmitter is designed and investigated. The filter coefficient is given by the optimization processing, the symbol error rate （SER） is tested, and the computation complexity of the proposed scheme is analyzed. Computer simulation results show that the proposed pre-processing filter can effectively mitigate IBI and ICI and the performance can be improved. Compared with pre-processing approaches at the transmitter based on full CSI, the proposed scheme has high spectral efficiency, limited CSI feedback and low computation complexity.展开更多
The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces.This study conducted low-frequency di...The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces.This study conducted low-frequency disturbance dynamic uniaxial compression tests on coal specimens using a self-developed dynamic-static load coupling electro-hydraulic servo system,and studied the strength evolutions,surface deformations,acoustic emission(AE)characteristic parameters,and the failure modes of coal specimens with different static preloading levels were studied.The disturbance damage is positively correlated with the coal specimen static preload level.Specifically,the cumulative AE count rates of the initial accelerated damage stage for the coal specimens with static preloading level of 60%and 70%of the uniaxial compressive strength(UCS)were 2.66 and 3.19 times that of the 50%UCS specimens,respectively.Macroscopically,this behaviour manifested as a decrease in the compressive strength,and the mean strengths of the disturbance-damaged coal specimens with 60%and 70%of UCS static preloading decreased by 8.53%and 9.32%,respectively,compared to those of the specimens under pure static loading.The crack sources,such as the primary fissures,strongly control the dynamic response of the coal specimen.The difference between the dynamic responses of the coal specimens and that of dense rocks is significant.展开更多
Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the ...Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair technique.Damage evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]s.Quasi Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection technique.Damaged laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged hole.Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI test.The results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine laminates.Patches of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68%and 73%higher peak loads,respectively,than the respective pristine laminates.Furthermore,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.展开更多
先前的固件静态污点分析方案通过识别中间污点源来精确污点分析的起点,过滤部分情况的安全的命令劫持类危险函数调用点以精简污点分析的目标终点,减少了待分析的污点传播路径,缩短了漏洞挖掘的时间。但由于其在识别中间污点源时所用时...先前的固件静态污点分析方案通过识别中间污点源来精确污点分析的起点,过滤部分情况的安全的命令劫持类危险函数调用点以精简污点分析的目标终点,减少了待分析的污点传播路径,缩短了漏洞挖掘的时间。但由于其在识别中间污点源时所用时间过长,以及没有实现充分过滤安全的危险函数调用点,导致固件漏洞挖掘的整体时间依旧较长。为改进这一现状,提出了一种利用精确中间污点源和危险函数定位加速固件漏洞分析方案ALTSDF(Accurate Locating of intermediate Taint Sources and Dangerous Functions)。在快速精确识别中间污点源作为污点分析的起点时,收集每个函数在程序中不同调用点处使用的参数字符串构成每个函数的函数参数字符串集合,并计算此集合在前后端共享关键字集合中的占比,根据占比对所有函数进行降序排列,占比越高,则此函数越有可能是中间污点源。在过滤安全的危险函数调用点时,通过函数参数静态回溯分析参数类型,排除参数来源是常量的复杂情况的安全的命令劫持类危险函数调用点和安全的缓冲区溢出类危险函数调用点。最终缩短定位中间污点源所用时间,减少由中间污点源到危险函数调用点所构成的污点传播路径数量,进而缩短将污点分析应用于污点传播路径所需的分析时间,达到缩短漏洞挖掘时间的目的。对21个真实设备固件的嵌入式Web程序进行测试后得出,ALTSDF相比先进工具FITS,在中间污点源推断方面所用时间大幅缩短;在安全的危险函数调用点过滤方面,相比先进工具CINDY,ALTSDF使污点分析路径减少了8%,最终使漏洞挖掘时间相比SaTC结合FITS与CINDY的整合方案缩短32%。结果表明,ALTSDF可加速识别固件嵌入式Web程序中的漏洞。展开更多
基金supported by the National Natural Science Foundation of China(60902045)the National High-Tech Research and Developmeent Program of China(863 Program)(2011AA01A105)
文摘In order to meet the demands for high transmission rates and high service quality in broadband wireless communication systems, orthogonal frequency division multiplexing （OFDM） has been adopted in some standards. However, the inter-block interference （IBI） and inter-carrier interference （ICI） in an OFDM system affect the performance. To mitigate IBI and ICI, some pre-processing approaches have been proposed based on full channel state information （CSI）, which improved the system performance. A pre-processing filter based on partial CSI at the transmitter is designed and investigated. The filter coefficient is given by the optimization processing, the symbol error rate （SER） is tested, and the computation complexity of the proposed scheme is analyzed. Computer simulation results show that the proposed pre-processing filter can effectively mitigate IBI and ICI and the performance can be improved. Compared with pre-processing approaches at the transmitter based on full CSI, the proposed scheme has high spectral efficiency, limited CSI feedback and low computation complexity.
基金Projects(51925402,52334005,52304094)supported by the National Natural Science Foundation of ChinaProject(20201102004)supported by the Shanxi Science and Technology Major Project,China。
文摘The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces.This study conducted low-frequency disturbance dynamic uniaxial compression tests on coal specimens using a self-developed dynamic-static load coupling electro-hydraulic servo system,and studied the strength evolutions,surface deformations,acoustic emission(AE)characteristic parameters,and the failure modes of coal specimens with different static preloading levels were studied.The disturbance damage is positively correlated with the coal specimen static preload level.Specifically,the cumulative AE count rates of the initial accelerated damage stage for the coal specimens with static preloading level of 60%and 70%of the uniaxial compressive strength(UCS)were 2.66 and 3.19 times that of the 50%UCS specimens,respectively.Macroscopically,this behaviour manifested as a decrease in the compressive strength,and the mean strengths of the disturbance-damaged coal specimens with 60%and 70%of UCS static preloading decreased by 8.53%and 9.32%,respectively,compared to those of the specimens under pure static loading.The crack sources,such as the primary fissures,strongly control the dynamic response of the coal specimen.The difference between the dynamic responses of the coal specimens and that of dense rocks is significant.
基金the financial support by the Council of Scientific&Industrial Research(CSIR)-Research Scheme,India(22/0809/2019-EMR-II)。
文摘Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair technique.Damage evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]s.Quasi Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection technique.Damaged laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged hole.Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI test.The results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine laminates.Patches of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68%and 73%higher peak loads,respectively,than the respective pristine laminates.Furthermore,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.
文摘先前的固件静态污点分析方案通过识别中间污点源来精确污点分析的起点,过滤部分情况的安全的命令劫持类危险函数调用点以精简污点分析的目标终点,减少了待分析的污点传播路径,缩短了漏洞挖掘的时间。但由于其在识别中间污点源时所用时间过长,以及没有实现充分过滤安全的危险函数调用点,导致固件漏洞挖掘的整体时间依旧较长。为改进这一现状,提出了一种利用精确中间污点源和危险函数定位加速固件漏洞分析方案ALTSDF(Accurate Locating of intermediate Taint Sources and Dangerous Functions)。在快速精确识别中间污点源作为污点分析的起点时,收集每个函数在程序中不同调用点处使用的参数字符串构成每个函数的函数参数字符串集合,并计算此集合在前后端共享关键字集合中的占比,根据占比对所有函数进行降序排列,占比越高,则此函数越有可能是中间污点源。在过滤安全的危险函数调用点时,通过函数参数静态回溯分析参数类型,排除参数来源是常量的复杂情况的安全的命令劫持类危险函数调用点和安全的缓冲区溢出类危险函数调用点。最终缩短定位中间污点源所用时间,减少由中间污点源到危险函数调用点所构成的污点传播路径数量,进而缩短将污点分析应用于污点传播路径所需的分析时间,达到缩短漏洞挖掘时间的目的。对21个真实设备固件的嵌入式Web程序进行测试后得出,ALTSDF相比先进工具FITS,在中间污点源推断方面所用时间大幅缩短;在安全的危险函数调用点过滤方面,相比先进工具CINDY,ALTSDF使污点分析路径减少了8%,最终使漏洞挖掘时间相比SaTC结合FITS与CINDY的整合方案缩短32%。结果表明,ALTSDF可加速识别固件嵌入式Web程序中的漏洞。
文摘利用线性弹簧斜向布置的几何非线性产生非线性恢复力,提出了引入非线性恢复力的水下涡激振动(VIV)发电系统.该系统通过单向轴承、齿轮齿条机构、增速箱和转子发电机,将钝体横向往复运动转变为发电机的单向旋转运动.建立了综合考虑流-固-电耦合的水下涡激振动发电系统动力学方程,利用非线性振动理论,获得了钝体非线性振动的静态平衡点分岔和不同稳态运动的区间,重点研究了PF-2SN和2PF-2SN两种静态分岔情况下钝体的非线性动力学行为,获得了不同流速下钝体振动的Poincaré映射、相图和幅频图,分析了钝体在单周期小幅运动、大幅混沌运动和准周期大幅运动等运动模式下的振动行为及运动规律,并计算了在钝体处于不同稳态运动时的发电机功率.结果表明:在PF-2SN分岔方式中,系统处于二稳态运动时的振动和发电具有明显优势,平均振幅比为2.18、发电功率最大值为24.45 W.而在2PF-2SN分岔方式中,系统处于三稳态运动时的振动和发电更具优势,平均振幅比为1.98、发电功率最大值为18.32 W.
