In most literature about joint direction of arrival（DOA） and polarization estimation, the case that sources possess different power levels is seldom discussed. However, this case exists widely in practical applicati...In most literature about joint direction of arrival（DOA） and polarization estimation, the case that sources possess different power levels is seldom discussed. However, this case exists widely in practical applications, especially in passive radar systems. In this paper, we propose a joint DOA and polarization estimation method for unequal power sources based on the reconstructed noise subspace. The invariance property of noise subspace（IPNS） to power of sources has been proved an effective method to estimate DOA of unequal power sources. We develop the IPNS method for joint DOA and polarization estimation based on a dual polarized array. Moreover, we propose an improved IPNS method based on the reconstructed noise subspace, which has higher resolution probability than the IPNS method. It is theoretically proved that the IPNS to power of sources is still valid when the eigenvalues of the noise subspace are changed artificially. Simulation results show that the resolution probability of the proposed method is enhanced compared with the methods based on the IPNS and the polarimetric multiple signal classification（MUSIC） method. Meanwhile, the proposed method has approximately the same estimation accuracy as the IPNS method for the weak source.展开更多
There is mounting concern over the sustainability of global energy supplies.Among the key drivers are:(ⅰ) global warming,ocean surface acidification and air pollution,which imply the need to control and reduce anthro...There is mounting concern over the sustainability of global energy supplies.Among the key drivers are:(ⅰ) global warming,ocean surface acidification and air pollution,which imply the need to control and reduce anthropogenic emissions of greenhouse gases(especially carbon dioxide),nitrogen oxides,sulfur oxides,unburnt hydrocarbons and fine particles;(ⅱ) the low estimated reserves of oil and natural gas;(ⅲ) the need for energy security adapted to each country,such as decreasing the dependence on fossil-fuel imports(in particular,the vulnerability to volatile oil prices) from regions where there is political or economic instability;(ⅳ) the expected growth in world population with the ever-increasing aspiration for an improved standard-of-living for all.Hydrogen is being promoted world-wide as a total panacea for energy problems.As a versatile carrier for storing and transporting energy from any one of a myriad of sources to an electricity generator,it is argued that hydrogen will eventually replace(or at least greatly reduce) the reliance on fossil fuels and thereby also avoid/decrease emissions of carbon dioxide.Not unexpectedly,the building of a ’Hydrogen Economy’ presents great scientific and technological challenges in the production,delivery,storage,conversion and end-use of this energy vector.In addition,there are many policy,regulatory,economic,financial,investment,environmental and safety questions to be addressed.Notwithstanding these obstacles,it is indeed plausible that hydrogen will become increasingly deployed and will compete with traditional systems of energy storage and supply.Future roles for electrochemical power sources ——batteries,supercapacitors,photoelectrochemical cells and fuel cells ——on the pathway to universal energy sustainability in stationary,mobile-power and road transportation applications are examined.展开更多
The model of heat source(MHS) which reflects the thermal interaction between materials and laser during processing determines the accuracy of simulation results. To acquire desirable simulations results, although vari...The model of heat source(MHS) which reflects the thermal interaction between materials and laser during processing determines the accuracy of simulation results. To acquire desirable simulations results, although various modifications of heat sources in the aspect of absorption process of laser by materials have been purposed, the distribution of laser power density(DLPD) in MHS is still modeled theoretically. However, in the actual situations of laser processing, the DLPD is definitely different from the ideal models. So, it is indispensable to build MHS using actual DLPD to improve the accuracy of simulation results. Besides, an automatic modeling method will be benefit to simplify the tedious pre-processing of simulations. This paper presents a modeling method and corresponding algorithm to model heat source using measured DLPD. This algorithm automatically processes original data to get modeling parameters and provides a step MHS combining with absorption models. Simulations and experiments of heat transfer in steel plates irradiated by laser prove the mothed and the step MHS. Moreover, the investigations of laser induced thermal-crack propagation in glass highlight the signification of modeling heat source based on actual DLPD and demonstrate the enormous application of this method in the simulation of laser processing.展开更多
基金supported by the National Natural Science Foundation of China(61501142)the China Postdoctoral Science Foundation(2015M571414)+3 种基金the Fundamental Research Funds for the Central Universities(HIT.NSRIF.2016102)Shandong Provincial Natural Science Foundation(ZR2014FQ003)the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology(HIT.NSRIF 2013130HIT(WH)XBQD 201022)
文摘In most literature about joint direction of arrival（DOA） and polarization estimation, the case that sources possess different power levels is seldom discussed. However, this case exists widely in practical applications, especially in passive radar systems. In this paper, we propose a joint DOA and polarization estimation method for unequal power sources based on the reconstructed noise subspace. The invariance property of noise subspace（IPNS） to power of sources has been proved an effective method to estimate DOA of unequal power sources. We develop the IPNS method for joint DOA and polarization estimation based on a dual polarized array. Moreover, we propose an improved IPNS method based on the reconstructed noise subspace, which has higher resolution probability than the IPNS method. It is theoretically proved that the IPNS to power of sources is still valid when the eigenvalues of the noise subspace are changed artificially. Simulation results show that the resolution probability of the proposed method is enhanced compared with the methods based on the IPNS and the polarimetric multiple signal classification（MUSIC） method. Meanwhile, the proposed method has approximately the same estimation accuracy as the IPNS method for the weak source.
文摘There is mounting concern over the sustainability of global energy supplies.Among the key drivers are:(ⅰ) global warming,ocean surface acidification and air pollution,which imply the need to control and reduce anthropogenic emissions of greenhouse gases(especially carbon dioxide),nitrogen oxides,sulfur oxides,unburnt hydrocarbons and fine particles;(ⅱ) the low estimated reserves of oil and natural gas;(ⅲ) the need for energy security adapted to each country,such as decreasing the dependence on fossil-fuel imports(in particular,the vulnerability to volatile oil prices) from regions where there is political or economic instability;(ⅳ) the expected growth in world population with the ever-increasing aspiration for an improved standard-of-living for all.Hydrogen is being promoted world-wide as a total panacea for energy problems.As a versatile carrier for storing and transporting energy from any one of a myriad of sources to an electricity generator,it is argued that hydrogen will eventually replace(or at least greatly reduce) the reliance on fossil fuels and thereby also avoid/decrease emissions of carbon dioxide.Not unexpectedly,the building of a ’Hydrogen Economy’ presents great scientific and technological challenges in the production,delivery,storage,conversion and end-use of this energy vector.In addition,there are many policy,regulatory,economic,financial,investment,environmental and safety questions to be addressed.Notwithstanding these obstacles,it is indeed plausible that hydrogen will become increasingly deployed and will compete with traditional systems of energy storage and supply.Future roles for electrochemical power sources ——batteries,supercapacitors,photoelectrochemical cells and fuel cells ——on the pathway to universal energy sustainability in stationary,mobile-power and road transportation applications are examined.
基金Project(2021YFF0500200) supported by the National Key R&D Program of ChinaProject(52105437) supported by the National Natural Science Foundation of China+1 种基金Project(202006120184) supported by the Heilongjiang Provincial Postdoctoral Science Foundation,ChinaProject(LBH-Z20054) supported by the China Scholarship Council。
文摘The model of heat source(MHS) which reflects the thermal interaction between materials and laser during processing determines the accuracy of simulation results. To acquire desirable simulations results, although various modifications of heat sources in the aspect of absorption process of laser by materials have been purposed, the distribution of laser power density(DLPD) in MHS is still modeled theoretically. However, in the actual situations of laser processing, the DLPD is definitely different from the ideal models. So, it is indispensable to build MHS using actual DLPD to improve the accuracy of simulation results. Besides, an automatic modeling method will be benefit to simplify the tedious pre-processing of simulations. This paper presents a modeling method and corresponding algorithm to model heat source using measured DLPD. This algorithm automatically processes original data to get modeling parameters and provides a step MHS combining with absorption models. Simulations and experiments of heat transfer in steel plates irradiated by laser prove the mothed and the step MHS. Moreover, the investigations of laser induced thermal-crack propagation in glass highlight the signification of modeling heat source based on actual DLPD and demonstrate the enormous application of this method in the simulation of laser processing.
