Distinguishing close chirp-rates of different linear frequency modulation （LFM） signals under concentrated and complicated signal environment was studied. Firstly, detection and parameter estimation of multi-compone...Distinguishing close chirp-rates of different linear frequency modulation （LFM） signals under concentrated and complicated signal environment was studied. Firstly, detection and parameter estimation of multi-component LFM signal were used by discrete fast fractional Fourier transform （FrFT）. Then the expression of chirp-rate resolution in fractional Fourier domain （FrFD） was deduced from discrete normalize time-frequency distribution, when multi-component LFM signal had only one center frequency. Furthermore, the detail influence of the sampling time, sampling frequency and chirp-rate upon the resolution was analyzed by partial differential equation. Simulation results and analysis indicate that increasing the sampling time can enhance the resolution, but the influence of the sampling frequency can he omitted. What＇s more, in multi-component LFM signal, the chirp-rate resolution of FrFT is no less than a minimal value, and it mainly dependent on the biggest value of chirp-rates, with which it has an approximately positive exponential relationship.展开更多
A novel algorithm for the direction of arrival (DOA) estimation based on the fractional Fourier transform (FRFT) is proposed. Firstly, using the properties of FRFT and mask processing, Multi-component LFM sig-nals are...A novel algorithm for the direction of arrival (DOA) estimation based on the fractional Fourier transform (FRFT) is proposed. Firstly, using the properties of FRFT and mask processing, Multi-component LFM sig-nals are filtered and demodulated into a number of stationary single frequency signals. Then the one-dimensional (1-D) direction estimation of LFM signals can be achieved by combining with the tradi-tional spectrum search method in the fractional Fourier (FRF) domain. As for the multi-component LFM signals, there is no cross-term interference, the mean square error (MSE) and Cramer-Rao bound (CRB) are also analyzed which perfects the method theoretically, simulation results are provided to show the validity of our method. The proposed algorithm is also extended to the uniform circular array (UCA), which realizes the two-dimensional (2-D) estimation. Using the characteristics of time-frequency rotation and demodulation of FRFT, the observed LFM signals are demodulated into a series of single frequency ones;secondly, operate the beam-space mapping to the single frequency signals in FRF domain, which UCA in array space is changed into the virtual uniform circular array (ULA) in mode space;finally, the DOA estimation can be realized by the traditional spectral estimation method. Compared with other method, the complex time-frequency cluster and the parameter matching computation are avoided;meanwhile enhances the esti-mation precision by a certain extent. The proposed algorithm can also be used in the multi-path and Doppler frequency shift complex channel, which expands its application scope. In a word, a demodulated DOA esti-mation algorithm is proposed and is applied to 1-D and 2-D angle estimation by dint of ULA and UCA re-spectively. The detailed theoretical analysis and adequate simulations are given to support our proposed al-gorithm, which enriches the theory of the FRFT.展开更多
In the realm of nonlinear integrable systems,the presence of decompositions facilitates the establishment of linear superposition solutions and the derivation of novel coupled systems exhibiting nonlinear integrabilit...In the realm of nonlinear integrable systems,the presence of decompositions facilitates the establishment of linear superposition solutions and the derivation of novel coupled systems exhibiting nonlinear integrability.By focusing on single-component decompositions within the potential BKP hierarchy,it has been observed that specific linear superpositions of decomposition solutions remain consistent with the underlying equations.Moreover,through the implementation of multi-component decompositions within the potential BKP hierarchy,successful endeavors have been undertaken to formulate linear superposition solutions and novel coupled Kd V-type systems that resist decoupling via alterations in dependent variables.展开更多
Multi-component transition group metal borides(MMB_(2))have become a research hotspot due to their new composition design concepts and superior properties compared with conventional ceramics.Most of the current method...Multi-component transition group metal borides(MMB_(2))have become a research hotspot due to their new composition design concepts and superior properties compared with conventional ceramics.Most of the current methods,however,are complicated and time-consuming,the mass production remains a chal-lenge.Herein,we proposed a new high-efficiency strategy for synthesis of MMB_(2)using molten aluminum as the medium for the first time.The prepared Al-containing multi-component borides(TiZrHfNbTa)B_(2)microcrystals had a homogeneous composition with a hexagonal AlB_(2)structure and ultra-high hardness value of∼35.3 GPa,which was much higher than data reported in the literature and the rule of mix-ture estimations.Furthermore,combined with the First-principles calculation results,we found that the Poisson’s ratio(v)values exhibit a clearly ascending trend from 0.17 at VEC=3.5 to 0.18 at VEC=3.4,then to 0.201 at VEC=3.2 with the increasing of Al content.This indicates that the intrinsic toughness of multi-component boride microcrystals is obviously enhanced by the trace-doped Al elements.Besides,the fabricated Al-containing multi-component boride microcrystals have superior oxidation activation en-ergy and structural stability.The enhanced oxidation resistance is mainly attributed to the formation of a protective Al2 O3 oxide layer and the lattice distortion,both of which lead to sluggish diffusion of O_(2).These findings propose a new unexplored avenue for the fabrication of MMB_(2)materials with supe-rior comprehensive performance including ultra-hardness and intrinsically improved thermo-mechanical properties.展开更多
A convenient photocatalytic multi-component reaction of alkenes,quinoxalin-2(1H)-ones,and diazo compounds has been developed in the presence of water.A number of ester-containing quinoxalin-2(1H)-ones could be efficie...A convenient photocatalytic multi-component reaction of alkenes,quinoxalin-2(1H)-ones,and diazo compounds has been developed in the presence of water.A number of ester-containing quinoxalin-2(1H)-ones could be efficiently obtained in moderate to good yields at room temperature.This metal-free visiblelight-driven tandem reaction was conducted through proton-coupled electron transfer(PCET)process using water as the hydrogen donor and 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene(4CzIPN)as the photocatalyst.展开更多
Wearable,flexible devices have garnered widespread attention in the realm of human motion and life activity detection.Currently,the development of simple,green,and easily scalable methods for fabricating strain sensor...Wearable,flexible devices have garnered widespread attention in the realm of human motion and life activity detection.Currently,the development of simple,green,and easily scalable methods for fabricating strain sensors still presents significant challenges.In this study,we successfully modified the surface of reduced graphene oxide(rGO)with SnCuNiIn multi-component alloy nanoparticles(MCA NPs),with an average size of 13.29 nm,utilizing a green and facile microwave heating approach.Leveraging the SnCuNiIn MCA NPs/rGO powder,we formulated a conductive ink based on water and ethylene glycol,which,when screen-printed,yielded conductive patterns with a minimum resistivity of 4.366 mΩ·cm.Strain sensors produced using this ink demonstrate exceptional performance,demonstrating favorable resistance change rates during a single bending process that meets practical application requirements,and enduring 5000 bending cycles with a resistance change of less than 5%.These sensors exhibited a high gauge factor(GF_(max)=52.7)and outstanding cycling stability.Lastly,strain sensors are employed to monitor human normal life activities and motion states,showcasing significant potential for application in wearable electronic products.展开更多
The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper stud...The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop.These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.展开更多
针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计...针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计方法。在一定多普勒频移范围内,以最小化未转发信号自模糊函数旁瓣能量以及未转发信号与转发信号互模糊函数能量建立优化模型,并设计一种基于KKT(Karush-Kuhn-Tucker)最优性条件的迭代算法对模型求解。仿真实验表明,相比于遗传算法和单一调制的LFM和DPC信号,基于KKT最优性条件的交替迭代优化算法优化的LFM-DPC波形集有更好的抗间歇采样转发干扰性能。展开更多
A multi-component system has the long fixed maintenance time, so the opportunistic maintenance policy is adopted to put preventive replacement and corrective replacement together, so that the long fixed maintenance ti...A multi-component system has the long fixed maintenance time, so the opportunistic maintenance policy is adopted to put preventive replacement and corrective replacement together, so that the long fixed maintenance time can be shared by more than one component, and the system availability can be improved. Then, the generation characteristics of the random failure time are researched based on the replacement maintenance and the minima[ maintenance. Furthermore, by choosing the opportunistic replacement ages of each component as opti- mized variables, a simulation algorithm based on an opportunistic maintenance policy is designed to maximize the total availability. Finally, the simulation result shows the validity of the algorithm by an example.展开更多
随着雷达和通信系统对频谱资源需求日益增长,加之现代战争对雷达生存能力提出的严峻挑战,研究了频谱共存下基于正交频分复用-线性调频波形(Orthogonal Frequency Division Multiplexing-Linear Frequency Modulation,OFDM-LFM)的机载组...随着雷达和通信系统对频谱资源需求日益增长,加之现代战争对雷达生存能力提出的严峻挑战,研究了频谱共存下基于正交频分复用-线性调频波形(Orthogonal Frequency Division Multiplexing-Linear Frequency Modulation,OFDM-LFM)的机载组网雷达射频隐身波形优化算法。采用信干噪比(Signal to Interference Plus Noise Ratio,SINR)作为机载组网雷达探测性能表征指标。以满足雷达探测性能以及不干扰通信频谱为约束条件,以最小化机载组网雷达总辐射能量为优化目标,构建频谱共存下机载组网雷达射频隐身波形优化模型。在此基础上,针对上述非线性、凸优化模型,采用序列二次规划(Sequential Quadratic Programming,SQP)算法进行求解。构建基于OFDM-LFM的射频隐身波形多径回波模型,分析所设计射频隐身波形的探测性能和抗多径效应性能。仿真结果表明,所提算法能够有效降低机载组网雷达的总辐射能量,进而提升射频隐身性能;此外,基于OFDM-LFM的射频隐身波形具有良好的探测性能和抗多径效应性能。展开更多
This review focuses on the recent research progress in the multi-component assembly of luminescent rare earth hybrid materials, which is based on the luminescent rare earth compounds and two or more other building uni...This review focuses on the recent research progress in the multi-component assembly of luminescent rare earth hybrid materials, which is based on the luminescent rare earth compounds and two or more other building units, including the other photoactive species. It covers the multi-component luminescent rare earth hybrids which was assembled with different(a) organic-inorganic polymeric units,(b)nanoporous units,(c) nanoparticle composites or(d) other developing special units. Finally, future challenges and opportunities in this field are discussed. Herein it mainly focuses on the work of Yan's group in recent years.展开更多
A general scheme for generating a multi-component integrable equation hierarchy is proposed. A simple 3M- dimensional loop algebra ~X is produced. By taking advantage of ~X a new isospectral problem is established and...A general scheme for generating a multi-component integrable equation hierarchy is proposed. A simple 3M- dimensional loop algebra ~X is produced. By taking advantage of ~X a new isospectral problem is established and then by making use of the Tu scheme the multi-component Dirac equation hierarchy is obtained. Finally, an expanding loop algebra ~FM of the loop algebra ~X is presented. Based on the ~FM, the multi-component integrable coupling system of the multi-component Dirac equation hierarchy is investigated. The method in this paper can be applied to other nonlinear evolution equation hierarchies.展开更多
Seismic AVO analysis now is one of the major criteria for recognizing potential hydrocarbon reservoirs. Volume scattering information that carries information of stratigraphic structure, lithology, and pore fluid is m...Seismic AVO analysis now is one of the major criteria for recognizing potential hydrocarbon reservoirs. Volume scattering information that carries information of stratigraphic structure, lithology, and pore fluid is more useful for seismic exploration. However, traditional AVO analysis is based on the Zoeppritz equation, which only contains single-interface information. Quantitative interpretation of the thin bed thickness is essential to thin bed structure interpretation, reservoir description, and lateral reservoir prediction. The reflectance spectrum equation based on the elastic wave propagation matrix in the frequency domain derived in this paper shows that both interfaces and intervals have an effect on amplitude. The equation includes information about both single interfaces and volume scattering. Since the reflectance spectrum equation is a continuous function of thin bed thickness and frequency, it is convenient to analyze the effects of a single frequency and bed thickness on the reflectance spectrum. Bed thickness is analyzable until the bed thickness is vanishingly small. These characteristics can＇t be achieved by Fourier transform. The propagation of seismic waves is complex and various wave modes exist simultaneously. The reflectance spectrum includes various propagating wave modes and multiples and is better for simulating multi-component thin bed AVO responses than the ray tracing method.展开更多
The conventional digital core models are usually small in size and have difficulty in representing the complex structures of heterogeneous rocks;Therefore,the parameters of simulated rock physics are difficult to be r...The conventional digital core models are usually small in size and have difficulty in representing the complex structures of heterogeneous rocks;Therefore,the parameters of simulated rock physics are difficult to be referenced.In this study,we propose a feasible simulation method for obtaining multi-scale and multi-component digital cores based on three types of sandstone samples.In the proposed method,the plug and subplug samples are scanned via micro-computed tomography at different resolutions.Furthermore,the images are precisely registered using the proposed hybrid image registration method.In case of high-resolution images,the traditional segmentation method is used to segment the cores into pores and minerals.Subsequently,we established the relations between the gray values and the porosity/mineral content in case of the low-resolution images based on the registered domains and the relation curves were applied to the segmentation of the low-resolution images.The core images constitute the multi-scale and multi-component digital core models after segmentation.Further,the elastic properties of the three samples were simulated at both fine and coarse scales based on the multi-scale and multi-component digital core models,and four component models were considered.The results show that the multi-scale and multi-component digital core models can overcome the representative limits of the conventional digital core models and accurately characterize pores and minerals at different scales.The numerical results of the elastic modulus are more representative at large scales,and considerably reliable results can be obtained by appropriately considering the minerals.展开更多
The influence of melt superheating treatment on the solid/liquid （S/L） interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteri...The influence of melt superheating treatment on the solid/liquid （S/L） interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity （R） but also to the melt superheating temperature （Ts） when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.展开更多
基金Sponsored by the National Natural Science Foundation of China (60232010 ,60572094)the National Science Foundation of China for Distin-guished Young Scholars (60625104)
文摘Distinguishing close chirp-rates of different linear frequency modulation （LFM） signals under concentrated and complicated signal environment was studied. Firstly, detection and parameter estimation of multi-component LFM signal were used by discrete fast fractional Fourier transform （FrFT）. Then the expression of chirp-rate resolution in fractional Fourier domain （FrFD） was deduced from discrete normalize time-frequency distribution, when multi-component LFM signal had only one center frequency. Furthermore, the detail influence of the sampling time, sampling frequency and chirp-rate upon the resolution was analyzed by partial differential equation. Simulation results and analysis indicate that increasing the sampling time can enhance the resolution, but the influence of the sampling frequency can he omitted. What＇s more, in multi-component LFM signal, the chirp-rate resolution of FrFT is no less than a minimal value, and it mainly dependent on the biggest value of chirp-rates, with which it has an approximately positive exponential relationship.
文摘A novel algorithm for the direction of arrival (DOA) estimation based on the fractional Fourier transform (FRFT) is proposed. Firstly, using the properties of FRFT and mask processing, Multi-component LFM sig-nals are filtered and demodulated into a number of stationary single frequency signals. Then the one-dimensional (1-D) direction estimation of LFM signals can be achieved by combining with the tradi-tional spectrum search method in the fractional Fourier (FRF) domain. As for the multi-component LFM signals, there is no cross-term interference, the mean square error (MSE) and Cramer-Rao bound (CRB) are also analyzed which perfects the method theoretically, simulation results are provided to show the validity of our method. The proposed algorithm is also extended to the uniform circular array (UCA), which realizes the two-dimensional (2-D) estimation. Using the characteristics of time-frequency rotation and demodulation of FRFT, the observed LFM signals are demodulated into a series of single frequency ones;secondly, operate the beam-space mapping to the single frequency signals in FRF domain, which UCA in array space is changed into the virtual uniform circular array (ULA) in mode space;finally, the DOA estimation can be realized by the traditional spectral estimation method. Compared with other method, the complex time-frequency cluster and the parameter matching computation are avoided;meanwhile enhances the esti-mation precision by a certain extent. The proposed algorithm can also be used in the multi-path and Doppler frequency shift complex channel, which expands its application scope. In a word, a demodulated DOA esti-mation algorithm is proposed and is applied to 1-D and 2-D angle estimation by dint of ULA and UCA re-spectively. The detailed theoretical analysis and adequate simulations are given to support our proposed al-gorithm, which enriches the theory of the FRFT.
基金sponsored by the National Natural Science Foundations of China under Grant Nos.12301315,12235007,11975131the Zhejiang Provincial Natural Science Foundation of China under Grant No.LQ20A010009。
文摘In the realm of nonlinear integrable systems,the presence of decompositions facilitates the establishment of linear superposition solutions and the derivation of novel coupled systems exhibiting nonlinear integrability.By focusing on single-component decompositions within the potential BKP hierarchy,it has been observed that specific linear superpositions of decomposition solutions remain consistent with the underlying equations.Moreover,through the implementation of multi-component decompositions within the potential BKP hierarchy,successful endeavors have been undertaken to formulate linear superposition solutions and novel coupled Kd V-type systems that resist decoupling via alterations in dependent variables.
基金financially supported by the National Natural Science Foundation of China(Nos.52271033 and 52071179)the Key program of National Natural Science Foundation of China(No.51931003)+2 种基金Natural Science Foundation of Jiangsu Province,China(No.BK20221493)Jiangsu Province Leading Edge Technology Basic Research Major Project(No.BK20222014)Foundation of“Qinglan Project”for Colleges and Universities in Jiangsu Province.
文摘Multi-component transition group metal borides(MMB_(2))have become a research hotspot due to their new composition design concepts and superior properties compared with conventional ceramics.Most of the current methods,however,are complicated and time-consuming,the mass production remains a chal-lenge.Herein,we proposed a new high-efficiency strategy for synthesis of MMB_(2)using molten aluminum as the medium for the first time.The prepared Al-containing multi-component borides(TiZrHfNbTa)B_(2)microcrystals had a homogeneous composition with a hexagonal AlB_(2)structure and ultra-high hardness value of∼35.3 GPa,which was much higher than data reported in the literature and the rule of mix-ture estimations.Furthermore,combined with the First-principles calculation results,we found that the Poisson’s ratio(v)values exhibit a clearly ascending trend from 0.17 at VEC=3.5 to 0.18 at VEC=3.4,then to 0.201 at VEC=3.2 with the increasing of Al content.This indicates that the intrinsic toughness of multi-component boride microcrystals is obviously enhanced by the trace-doped Al elements.Besides,the fabricated Al-containing multi-component boride microcrystals have superior oxidation activation en-ergy and structural stability.The enhanced oxidation resistance is mainly attributed to the formation of a protective Al2 O3 oxide layer and the lattice distortion,both of which lead to sluggish diffusion of O_(2).These findings propose a new unexplored avenue for the fabrication of MMB_(2)materials with supe-rior comprehensive performance including ultra-hardness and intrinsically improved thermo-mechanical properties.
基金supported by Sichuan Science and Technology Program(No.2023NSFSC0101)the 2024 Provincial platform project of Chengdu Normal University(No.GNFZ202404)+1 种基金Natural Science Foundation of Shandong Province(No.ZR2021MB065)National Natural Science Foundation of China(No.22101237)。
文摘A convenient photocatalytic multi-component reaction of alkenes,quinoxalin-2(1H)-ones,and diazo compounds has been developed in the presence of water.A number of ester-containing quinoxalin-2(1H)-ones could be efficiently obtained in moderate to good yields at room temperature.This metal-free visiblelight-driven tandem reaction was conducted through proton-coupled electron transfer(PCET)process using water as the hydrogen donor and 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene(4CzIPN)as the photocatalyst.
基金financially supported by Heilongjiang Provincial Natural Science Foundation of China(No.YQ2022E024)the National Natural Science Foundation of China(No.52375327)。
文摘Wearable,flexible devices have garnered widespread attention in the realm of human motion and life activity detection.Currently,the development of simple,green,and easily scalable methods for fabricating strain sensors still presents significant challenges.In this study,we successfully modified the surface of reduced graphene oxide(rGO)with SnCuNiIn multi-component alloy nanoparticles(MCA NPs),with an average size of 13.29 nm,utilizing a green and facile microwave heating approach.Leveraging the SnCuNiIn MCA NPs/rGO powder,we formulated a conductive ink based on water and ethylene glycol,which,when screen-printed,yielded conductive patterns with a minimum resistivity of 4.366 mΩ·cm.Strain sensors produced using this ink demonstrate exceptional performance,demonstrating favorable resistance change rates during a single bending process that meets practical application requirements,and enduring 5000 bending cycles with a resistance change of less than 5%.These sensors exhibited a high gauge factor(GF_(max)=52.7)and outstanding cycling stability.Lastly,strain sensors are employed to monitor human normal life activities and motion states,showcasing significant potential for application in wearable electronic products.
基金funded by the National Natural Science Foundation of China(No.51806236,No.51806239)the Fundamental Research Funds for the Central Universities(No.2015XKMS059)+1 种基金Shaanxi Postdoctoral Fund Project(No.2018BSHEDZZ56)Foundation of Key Laboratory of Thermo-Fluid Science and Engineering(Xi'an Jiaotong University),Ministry of Education(No.KLTFSE2017KF01)。
文摘The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop.These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.
文摘针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计方法。在一定多普勒频移范围内,以最小化未转发信号自模糊函数旁瓣能量以及未转发信号与转发信号互模糊函数能量建立优化模型,并设计一种基于KKT(Karush-Kuhn-Tucker)最优性条件的迭代算法对模型求解。仿真实验表明,相比于遗传算法和单一调制的LFM和DPC信号,基于KKT最优性条件的交替迭代优化算法优化的LFM-DPC波形集有更好的抗间歇采样转发干扰性能。
文摘A multi-component system has the long fixed maintenance time, so the opportunistic maintenance policy is adopted to put preventive replacement and corrective replacement together, so that the long fixed maintenance time can be shared by more than one component, and the system availability can be improved. Then, the generation characteristics of the random failure time are researched based on the replacement maintenance and the minima[ maintenance. Furthermore, by choosing the opportunistic replacement ages of each component as opti- mized variables, a simulation algorithm based on an opportunistic maintenance policy is designed to maximize the total availability. Finally, the simulation result shows the validity of the algorithm by an example.
文摘随着雷达和通信系统对频谱资源需求日益增长,加之现代战争对雷达生存能力提出的严峻挑战,研究了频谱共存下基于正交频分复用-线性调频波形(Orthogonal Frequency Division Multiplexing-Linear Frequency Modulation,OFDM-LFM)的机载组网雷达射频隐身波形优化算法。采用信干噪比(Signal to Interference Plus Noise Ratio,SINR)作为机载组网雷达探测性能表征指标。以满足雷达探测性能以及不干扰通信频谱为约束条件,以最小化机载组网雷达总辐射能量为优化目标,构建频谱共存下机载组网雷达射频隐身波形优化模型。在此基础上,针对上述非线性、凸优化模型,采用序列二次规划(Sequential Quadratic Programming,SQP)算法进行求解。构建基于OFDM-LFM的射频隐身波形多径回波模型,分析所设计射频隐身波形的探测性能和抗多径效应性能。仿真结果表明,所提算法能够有效降低机载组网雷达的总辐射能量,进而提升射频隐身性能;此外,基于OFDM-LFM的射频隐身波形具有良好的探测性能和抗多径效应性能。
基金Project supported by the National Natural Science Foundation of China(21571142)the Developing Science Fund of Tongji University,the Natural Science Foundation of Zhejiang Province(LQ14B010001)the Natural Science Foundation of Ningbo,China(2016A610105)
文摘This review focuses on the recent research progress in the multi-component assembly of luminescent rare earth hybrid materials, which is based on the luminescent rare earth compounds and two or more other building units, including the other photoactive species. It covers the multi-component luminescent rare earth hybrids which was assembled with different(a) organic-inorganic polymeric units,(b)nanoporous units,(c) nanoparticle composites or(d) other developing special units. Finally, future challenges and opportunities in this field are discussed. Herein it mainly focuses on the work of Yan's group in recent years.
文摘A general scheme for generating a multi-component integrable equation hierarchy is proposed. A simple 3M- dimensional loop algebra ~X is produced. By taking advantage of ~X a new isospectral problem is established and then by making use of the Tu scheme the multi-component Dirac equation hierarchy is obtained. Finally, an expanding loop algebra ~FM of the loop algebra ~X is presented. Based on the ~FM, the multi-component integrable coupling system of the multi-component Dirac equation hierarchy is investigated. The method in this paper can be applied to other nonlinear evolution equation hierarchies.
基金The research was supported by the Notion's Fifteenth Scientific and Technological Breakthrough Project: Research of Vector and Mountain Seismic Exploration (No.2001BA605A-12).
文摘Seismic AVO analysis now is one of the major criteria for recognizing potential hydrocarbon reservoirs. Volume scattering information that carries information of stratigraphic structure, lithology, and pore fluid is more useful for seismic exploration. However, traditional AVO analysis is based on the Zoeppritz equation, which only contains single-interface information. Quantitative interpretation of the thin bed thickness is essential to thin bed structure interpretation, reservoir description, and lateral reservoir prediction. The reflectance spectrum equation based on the elastic wave propagation matrix in the frequency domain derived in this paper shows that both interfaces and intervals have an effect on amplitude. The equation includes information about both single interfaces and volume scattering. Since the reflectance spectrum equation is a continuous function of thin bed thickness and frequency, it is convenient to analyze the effects of a single frequency and bed thickness on the reflectance spectrum. Bed thickness is analyzable until the bed thickness is vanishingly small. These characteristics can＇t be achieved by Fourier transform. The propagation of seismic waves is complex and various wave modes exist simultaneously. The reflectance spectrum includes various propagating wave modes and multiples and is better for simulating multi-component thin bed AVO responses than the ray tracing method.
基金supported by the National Natural Science Foundation of China Research(Nos.41574122 and 41374124)National Science and Technology major Project(No.2016ZX05006002-004)。
文摘The conventional digital core models are usually small in size and have difficulty in representing the complex structures of heterogeneous rocks;Therefore,the parameters of simulated rock physics are difficult to be referenced.In this study,we propose a feasible simulation method for obtaining multi-scale and multi-component digital cores based on three types of sandstone samples.In the proposed method,the plug and subplug samples are scanned via micro-computed tomography at different resolutions.Furthermore,the images are precisely registered using the proposed hybrid image registration method.In case of high-resolution images,the traditional segmentation method is used to segment the cores into pores and minerals.Subsequently,we established the relations between the gray values and the porosity/mineral content in case of the low-resolution images based on the registered domains and the relation curves were applied to the segmentation of the low-resolution images.The core images constitute the multi-scale and multi-component digital core models after segmentation.Further,the elastic properties of the three samples were simulated at both fine and coarse scales based on the multi-scale and multi-component digital core models,and four component models were considered.The results show that the multi-scale and multi-component digital core models can overcome the representative limits of the conventional digital core models and accurately characterize pores and minerals at different scales.The numerical results of the elastic modulus are more representative at large scales,and considerably reliable results can be obtained by appropriately considering the minerals.
基金supports from the National Natural Science Foundation of China (Grant No. 50931004)the National Basic Research Program of China (Grant Nos. 2011CB610406 and 2010CB631202)the National High Technology Research and Development Program (Grant No. 2007AA03Z552)
文摘The influence of melt superheating treatment on the solid/liquid （S/L） interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity （R） but also to the melt superheating temperature （Ts） when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.
