A new polarization measurement algorithm by using the sum and difference beam differential property of mono-pulse radar is given.Based on the generation mechanism differences between the target scattering and multi-fa...A new polarization measurement algorithm by using the sum and difference beam differential property of mono-pulse radar is given.Based on the generation mechanism differences between the target scattering and multi-false-target jamming,the signal models of real targets and digital deceptive false target jamming for sum and delta channel are presented.The polarization discrimination parameters are designed,and the discrimination method and its performance are discussed.This novel method does not need the accurate estimation of the absolute value of full target polarization scattering matrix,but only requires the relative estimation of the orthogonal polarized component of the targets.Without the need to add additional polarization channels,the proposed method is more suitable for engineering realization.The simulation experiment verifies that the correctly identifying probability can be better than 90%.展开更多
In the present study,we aimed to investigate the in vitro antioxidant activity of the ethanol extract and its polar extracts from Ephedra saxatilis Royle ex Florin in Xizang.The chemical constituents were first screen...In the present study,we aimed to investigate the in vitro antioxidant activity of the ethanol extract and its polar extracts from Ephedra saxatilis Royle ex Florin in Xizang.The chemical constituents were first screened by the preliminary phytochemical methods.The contents of total polyphenols and total flavonoids were identified by the Folin-Ciocalteu method and colorimetric method of the aluminum chloride method,respectively.Furthermore,their antioxidant activities were investigated by the DPPH method,ABTS method,hydroxyl radical scavenging,and reduction powder method.The preliminary phytochemical screening showed that the polyphenols,glycosides,flavonoids,and saponins existed in ethanol extract,and the chemical composition in different polar extracts varied,among which the contents of polyphenols and flavonoids were highest in the ethyl acetate part,followed by the dichloromethane part,exhibiting best antioxidant capacity.Both the ethyl acetate and dichloromethane parts from Ephedra saxatilis Royle ex Florin exhibited better antioxidant activities than BHT,which was associated with the high contents of polyphenols and flavonoids.展开更多
At seasonal and intraseasonal time scales, polar motions are mainly excited by angular momentum fluctuations due to mass redistributions and relative motions in the atmosphere, oceans, and continental water, snow, and...At seasonal and intraseasonal time scales, polar motions are mainly excited by angular momentum fluctuations due to mass redistributions and relative motions in the atmosphere, oceans, and continental water, snow, and ice, which are usually provided by various global atmospheric, oceanic, and hydrological models（some with meteorological observations assimilated; e.g., NCEP, ECCO, ECMWF, OMCT and LSDM etc.）. Unfortunately, these model outputs are far from perfect and have notable discrepancies with respect to polar motion observations, due to non-uniform distributions of meteorological observatories,as well as theoretical approximations and non-global mass conservation in these models. In this study,the LDC（Least Difference Combination） method is adopted to obtain some improved atmospheric,oceanic, and hydrological/crospheric angular momentum（AAM, OAM and HAM/CAM, respectively）functions and excitation functions（termed as the LDCgsm solutions）. Various GRACE（Gravity Recovery and Climate Experiment） and SLR（Satellite Laser Ranging） geopotential data are adopted to correct the non-global mass conservation problem, while polar motion data are used as general constraints. The LDCgsm solutions can reveal not only periodic fluctuations but also secular trends in AAM, OAM and HAM/CAM, and are in better agreement with polar motion observations, reducing the unexplained excitation to the level of about 5.5 mas（standard derivation value; about 1/5-1/4 of those corresponding to the original model outputs）.展开更多
A mode-locked thulium-doped fiber laser(TDFL) based on nonlinear polarization rotation(NPR) with different net anomalous dispersion is demonstrated. When the cavity dispersion is-1.425 ps^2, the noise-like(NL) pulse w...A mode-locked thulium-doped fiber laser(TDFL) based on nonlinear polarization rotation(NPR) with different net anomalous dispersion is demonstrated. When the cavity dispersion is-1.425 ps^2, the noise-like(NL) pulse with coherence spike width of 406 fs and pulse energy of 12.342 nJ is generated at a center wavelength of 2003.2 nm with 3 dB spectral bandwidth of 23.20 nm. In the experimental period of 400 min, the 3 dB spectral bandwidth variation, the output power fluctuation, and the central wavelength shift are less than 0.06 nm, 0.04 d B, and0.4 nm, respectively, indicating that the NPR-based TDFL operating in the NL regime holds good long-term stability.展开更多
Low Earth Orbit (LEO) satellite communications (SATCOM) are important for wireless networks and offer better global wireless access services than higher altitude SATCOM options. SATCOM performance is affected by the n...Low Earth Orbit (LEO) satellite communications (SATCOM) are important for wireless networks and offer better global wireless access services than higher altitude SATCOM options. SATCOM performance is affected by the number of antennas, which is usually constrained by the satellite space. In this paper, the application of dual-polarized technology is considered to assist LEO SATCOM. Compared with single-polarized antennas, dual-polarized antennas utilize two different polarization orientations to transmit and receive data. This can improve the quality of service (QoS) performance, as it allows for twice the amount of data to be transmitted over the same time–frequency resources. Specifically, we characterize the dual-polarized channel in massive multiple-input multiple-output (MIMO) LEO SATCOM and investigate the precoding design for enhancing the system performance. In particular, a precoding optimization problem is formulated, which aims to jointly optimize the system throughput and the QoS performance. We divide the problem into two stages and develop novel algorithms for each stage to obtain the precoding vectors. The numerical results demonstrate that the dual-polarized technology can improve the system throughput, and the proposed algorithm leads to a higher percentage of users achieving their QoS requirements compared to conventional approaches.展开更多
基金supported by the National Natural Science Foundation of China (6073600660802078)the Hunan Provincial Innovation Foundation for Postgraduate (CX2009B010)
文摘A new polarization measurement algorithm by using the sum and difference beam differential property of mono-pulse radar is given.Based on the generation mechanism differences between the target scattering and multi-false-target jamming,the signal models of real targets and digital deceptive false target jamming for sum and delta channel are presented.The polarization discrimination parameters are designed,and the discrimination method and its performance are discussed.This novel method does not need the accurate estimation of the absolute value of full target polarization scattering matrix,but only requires the relative estimation of the orthogonal polarized component of the targets.Without the need to add additional polarization channels,the proposed method is more suitable for engineering realization.The simulation experiment verifies that the correctly identifying probability can be better than 90%.
基金The National Natural Science Foundation of China(Gr ant No.82260823)the co-construction and Innovation Fund for Tibet Economic and Social Development and Plateau Scientific Re search(Grant No.1zj2021014)the 2020 Tibetan Medicine Doctoral Program of Tibet Medical University(Grant No.BSDJS-20-12)
文摘In the present study,we aimed to investigate the in vitro antioxidant activity of the ethanol extract and its polar extracts from Ephedra saxatilis Royle ex Florin in Xizang.The chemical constituents were first screened by the preliminary phytochemical methods.The contents of total polyphenols and total flavonoids were identified by the Folin-Ciocalteu method and colorimetric method of the aluminum chloride method,respectively.Furthermore,their antioxidant activities were investigated by the DPPH method,ABTS method,hydroxyl radical scavenging,and reduction powder method.The preliminary phytochemical screening showed that the polyphenols,glycosides,flavonoids,and saponins existed in ethanol extract,and the chemical composition in different polar extracts varied,among which the contents of polyphenols and flavonoids were highest in the ethyl acetate part,followed by the dichloromethane part,exhibiting best antioxidant capacity.Both the ethyl acetate and dichloromethane parts from Ephedra saxatilis Royle ex Florin exhibited better antioxidant activities than BHT,which was associated with the high contents of polyphenols and flavonoids.
基金supported in parts by the National 973 Project of China(No.2013CB733301 and 2013CB733305)the National Natural Science Foundation of China(No.41474022,41210006 and 41374022)+2 种基金the R&D Special Fund for Public Welfare Industry(Surveying and Mapping,No.201512001)the Fundamental Research Funds for the Central Universities of China(No.2042016kf0146)the China Postdoctoral Science Foundation(No.2014T70737)
文摘At seasonal and intraseasonal time scales, polar motions are mainly excited by angular momentum fluctuations due to mass redistributions and relative motions in the atmosphere, oceans, and continental water, snow, and ice, which are usually provided by various global atmospheric, oceanic, and hydrological models（some with meteorological observations assimilated; e.g., NCEP, ECCO, ECMWF, OMCT and LSDM etc.）. Unfortunately, these model outputs are far from perfect and have notable discrepancies with respect to polar motion observations, due to non-uniform distributions of meteorological observatories,as well as theoretical approximations and non-global mass conservation in these models. In this study,the LDC（Least Difference Combination） method is adopted to obtain some improved atmospheric,oceanic, and hydrological/crospheric angular momentum（AAM, OAM and HAM/CAM, respectively）functions and excitation functions（termed as the LDCgsm solutions）. Various GRACE（Gravity Recovery and Climate Experiment） and SLR（Satellite Laser Ranging） geopotential data are adopted to correct the non-global mass conservation problem, while polar motion data are used as general constraints. The LDCgsm solutions can reveal not only periodic fluctuations but also secular trends in AAM, OAM and HAM/CAM, and are in better agreement with polar motion observations, reducing the unexplained excitation to the level of about 5.5 mas（standard derivation value; about 1/5-1/4 of those corresponding to the original model outputs）.
基金Fundamental Research Funds for the Central Universities(2016YJS034)
文摘A mode-locked thulium-doped fiber laser(TDFL) based on nonlinear polarization rotation(NPR) with different net anomalous dispersion is demonstrated. When the cavity dispersion is-1.425 ps^2, the noise-like(NL) pulse with coherence spike width of 406 fs and pulse energy of 12.342 nJ is generated at a center wavelength of 2003.2 nm with 3 dB spectral bandwidth of 23.20 nm. In the experimental period of 400 min, the 3 dB spectral bandwidth variation, the output power fluctuation, and the central wavelength shift are less than 0.06 nm, 0.04 d B, and0.4 nm, respectively, indicating that the NPR-based TDFL operating in the NL regime holds good long-term stability.
基金supported by the National Natural Science Foundation of China for Outstanding Young Scholars under grant 62322104the Key Technologies R&D Program of Jiangsu(Prospective and Key Technologies for Industry)under grants BE2022067 and BE2022067-5+3 种基金the Natural Science Foundation of Jiangsu Province under grant BK20231415the Natural Science Foundation on Frontier Leading Technology Basic Research Project of Jiangsu under grant BK20222001the Jiangsu Province Basic Research Project under grant BK20192002the Fundamental Research Funds for the Central Universities under grants 2242022k60007 and 2242023K5003.
文摘Low Earth Orbit (LEO) satellite communications (SATCOM) are important for wireless networks and offer better global wireless access services than higher altitude SATCOM options. SATCOM performance is affected by the number of antennas, which is usually constrained by the satellite space. In this paper, the application of dual-polarized technology is considered to assist LEO SATCOM. Compared with single-polarized antennas, dual-polarized antennas utilize two different polarization orientations to transmit and receive data. This can improve the quality of service (QoS) performance, as it allows for twice the amount of data to be transmitted over the same time–frequency resources. Specifically, we characterize the dual-polarized channel in massive multiple-input multiple-output (MIMO) LEO SATCOM and investigate the precoding design for enhancing the system performance. In particular, a precoding optimization problem is formulated, which aims to jointly optimize the system throughput and the QoS performance. We divide the problem into two stages and develop novel algorithms for each stage to obtain the precoding vectors. The numerical results demonstrate that the dual-polarized technology can improve the system throughput, and the proposed algorithm leads to a higher percentage of users achieving their QoS requirements compared to conventional approaches.
