A novel modified four path method (FPM) is presented for calculating coupling field of super-low altitude aircraft target. Based on the hybrid method PO + MEC (Physical Optics and Method of Equivalent Currents), the a...A novel modified four path method (FPM) is presented for calculating coupling field of super-low altitude aircraft target. Based on the hybrid method PO + MEC (Physical Optics and Method of Equivalent Currents), the antenna radiation pattern is introduced to consider the multipath interference from side lobe of seeker. The modified FPM is used to calculate the coupling field from super-low altitude aircraft target above different terrestrial environments. The curves of scattering coefficient are analyzed. The influences of height of target, root mean square (RMS), and incident angle on coupling field characteristics are discussed. The simulation results can be used for reference in detection for super-low altitude target and optimization for radar system.展开更多
In the contemporary pursuit of ensuring long-term lubrication for transmission units operating under harsh conditions,significant challenges remain.Researchers have investigated porous polymer materials as potential s...In the contemporary pursuit of ensuring long-term lubrication for transmission units operating under harsh conditions,significant challenges remain.Researchers have investigated porous polymer materials as potential solutions;however,achieving exceptionally low friction and wear has proven elusive.To address this issue,we developed a novel porous fluorinated polyimide(PPIF-250)characterized by superior mechanical performance,heat resistance,and higher oil content and retention than other porous polyimide(PPI)with comparable pore sizes and porosities.Extensive lubrication testing under varying conditions has demonstrated that PPIF-250 achieves remarkably low friction and wear characteristics,even under high FV(force×velocity)values,representing a significant advancement in this field.Furthermore,our findings indicate that the polarity of base oils plays a crucial role in determining the oil content and retention of PPIF-250.Specifically,the integration of polyethylene glycol 200(PEG200)with a tailored PEG-200 structure results in significantly improved oil content,retention,and long-term lubrication relative to those of other base oils.This improvement is attributed to the formation of high-load capacity boundary films within the PPIF-250 matrix,comprising oxidation processes involving carboxyl functional groups that chelate with iron or its oxides,alongside multilayer adsorption films stabilized by intermolecular hydrogen bonding and van der Waals forces.These insights will be instrumental in the development of more efficient and effective lubrication materials to meet the demands of modern technology.展开更多
The Super-Low Frequency （SLF） electromag- netic prospecting technique, adopted as a non-imaging remote sensing tool for depth sounding, is systematically proposed for subsurface geological survey. In this paper, we ...The Super-Low Frequency （SLF） electromag- netic prospecting technique, adopted as a non-imaging remote sensing tool for depth sounding, is systematically proposed for subsurface geological survey. In this paper, we propose and theoretically illustrate natural source magnetic amplitudes as SLF responses for the first step. In order to directly calculate multi-dimensional theoretical SLF responses, modeling algorithms were developed and evaluated using the finite difference method. The theore- tical results of three-dimensional （3-D） models show that the average normalized SLF magnetic amplitude responses were numerically stable and appropriate for practical interpretation. To explore the depth resolution, three-layer models were configured. The modeling results prove that the SLF technique is more sensitive to conductive objective layers than high resistive ones, with the SLF responses of conductive objective layers obviously show- ing uprising amplitudes in the low frequency range. Afterwards, we proposed an improved Frequency-Depth transformation based on Bostick inversion to realize the depth sounding by empirically adjusting two parameters. The SLF technique has already been successfully applied in geothermal exploration and coalbed methane （CBM） reservoir interpretation, which demonstrates that the proposed methodology is effective in revealing low resistive distributions. Furthermore, it siginificantly contributes to reservoir identification with electromagnetic radiation anomaly extraction. Meanwhile, the SLF inter- pretation results are in accordance with dynamic production status of CBM reservoirs, which means it could provide an economical, convenient and promising method for exploring and monitoring subsurface geo-objects.展开更多
文摘A novel modified four path method (FPM) is presented for calculating coupling field of super-low altitude aircraft target. Based on the hybrid method PO + MEC (Physical Optics and Method of Equivalent Currents), the antenna radiation pattern is introduced to consider the multipath interference from side lobe of seeker. The modified FPM is used to calculate the coupling field from super-low altitude aircraft target above different terrestrial environments. The curves of scattering coefficient are analyzed. The influences of height of target, root mean square (RMS), and incident angle on coupling field characteristics are discussed. The simulation results can be used for reference in detection for super-low altitude target and optimization for radar system.
基金financially supported by the Natural Science Foundation of Henan Province of China(Grant No.222300420124)the National Natural Science Foundation of China(Grant No.52175199)+1 种基金the Tribology Science Fund of the State Key Laboratory of Tribology in Advanced Equipment at Tsinghua University(Grant No.SKLTKF22B07)the National United Engineering Laboratory for Advanced Bearing Tribology(Grant No.202305)at Henan University of Science and Technology.
文摘In the contemporary pursuit of ensuring long-term lubrication for transmission units operating under harsh conditions,significant challenges remain.Researchers have investigated porous polymer materials as potential solutions;however,achieving exceptionally low friction and wear has proven elusive.To address this issue,we developed a novel porous fluorinated polyimide(PPIF-250)characterized by superior mechanical performance,heat resistance,and higher oil content and retention than other porous polyimide(PPI)with comparable pore sizes and porosities.Extensive lubrication testing under varying conditions has demonstrated that PPIF-250 achieves remarkably low friction and wear characteristics,even under high FV(force×velocity)values,representing a significant advancement in this field.Furthermore,our findings indicate that the polarity of base oils plays a crucial role in determining the oil content and retention of PPIF-250.Specifically,the integration of polyethylene glycol 200(PEG200)with a tailored PEG-200 structure results in significantly improved oil content,retention,and long-term lubrication relative to those of other base oils.This improvement is attributed to the formation of high-load capacity boundary films within the PPIF-250 matrix,comprising oxidation processes involving carboxyl functional groups that chelate with iron or its oxides,alongside multilayer adsorption films stabilized by intermolecular hydrogen bonding and van der Waals forces.These insights will be instrumental in the development of more efficient and effective lubrication materials to meet the demands of modern technology.
文摘The Super-Low Frequency （SLF） electromag- netic prospecting technique, adopted as a non-imaging remote sensing tool for depth sounding, is systematically proposed for subsurface geological survey. In this paper, we propose and theoretically illustrate natural source magnetic amplitudes as SLF responses for the first step. In order to directly calculate multi-dimensional theoretical SLF responses, modeling algorithms were developed and evaluated using the finite difference method. The theore- tical results of three-dimensional （3-D） models show that the average normalized SLF magnetic amplitude responses were numerically stable and appropriate for practical interpretation. To explore the depth resolution, three-layer models were configured. The modeling results prove that the SLF technique is more sensitive to conductive objective layers than high resistive ones, with the SLF responses of conductive objective layers obviously show- ing uprising amplitudes in the low frequency range. Afterwards, we proposed an improved Frequency-Depth transformation based on Bostick inversion to realize the depth sounding by empirically adjusting two parameters. The SLF technique has already been successfully applied in geothermal exploration and coalbed methane （CBM） reservoir interpretation, which demonstrates that the proposed methodology is effective in revealing low resistive distributions. Furthermore, it siginificantly contributes to reservoir identification with electromagnetic radiation anomaly extraction. Meanwhile, the SLF inter- pretation results are in accordance with dynamic production status of CBM reservoirs, which means it could provide an economical, convenient and promising method for exploring and monitoring subsurface geo-objects.
