Starting from the extended nonlinear Schrodinger equation in which the self-steepening effect is included, the evolution and the splitting processes of continuous optical wave whose amplitude is perturbed into time re...Starting from the extended nonlinear Schrodinger equation in which the self-steepening effect is included, the evolution and the splitting processes of continuous optical wave whose amplitude is perturbed into time related ultra-short optical pulse trains in an optical fibre are numerically simulated by adopting the split-step Fourier algorithm. The results show that the self-steepening effect can cause the characteristic of the pulse trains to vary with time, which is different from the self-steepening-free case where the generated pulse trains consist of single pulses which are identical in width, intensity, and interval, namely when pulses move a certain distance, they turn into the pulse trains within a certain time range. Moreover, each single pulse may split into several sub-pulses. And as time goes on, the number of the sub-pulses will decrease gradually and the pulse width and the pulse intensity will change too. With the increase of the self-steepening parameter, the distance needed to generate time-dependent pulse trains will shorten. In addition, for a large self-steepening parameter and at the distance where more sub-pulses appear, the corresponding frequency spectra of pulse trains are also wider.展开更多
Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent ...Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent control of the spatial profile for each pulse limit their advancement.We present a pulse manipulation technique for producing spectrally separated GHz burst pulses from a single ultrashort pulse,where each pulse is spatially shapable.We demonstrated the production of pulse trains at intervals of 0.1 to 3 ns in the 800-and 400-nm wavelength bands and applied them to ultrafast single-shot transmission spectroscopic imaging(4 Gfps)of laser ablation dynamics with two-color sequentially timed all-optical mapping photography.Furthermore,we demonstrated the production of pulse trains containing a shifted or dual-peak pulse as examples of individual spatial shaping of GHz burst pulses.Our proposed technique brings unprecedented spatiotemporal manipulation of GHz burst pulses,which can be useful for a wide range of laser applications.展开更多
This paper presents a method to estimate beam pointing of phased array radar by the pulse amplitude train, which is significant in radar electronic reconnaissance and electronic support measure. Firstly, the antenna p...This paper presents a method to estimate beam pointing of phased array radar by the pulse amplitude train, which is significant in radar electronic reconnaissance and electronic support measure. Firstly, the antenna patterns modeling of the phased array system is exploited to build the radar sweeping model and the signal propagation model. Secondly, the relationship between the variation of the radiated power and the antenna beam pointing angles in the given airspace is analyzed. Based on the above two points, the sample with obvious amplitude characteristics of the pulse amplitude train can be screened out after detecting the train peaks. Finally, the sample is matched to the subsequent pulse amplitude train based on the Hausdorff distance. The proposed methods have less prior knowledge and higher efficiency and are easier to process. By cross correlating the sample of the pulse amplitude train with the sample data of the antenna follow-up radiation, the probability of detection of the beam pointing direction becomes larger in case that the subsequent antenna beam returns to the specific position.展开更多
Strategically designing the electrocatalytic system and cleverly inducing strain is an effective approach to balance the cost and activity of Pt-based electrocatalysts for industrial-scale hydrogen production.Herein,w...Strategically designing the electrocatalytic system and cleverly inducing strain is an effective approach to balance the cost and activity of Pt-based electrocatalysts for industrial-scale hydrogen production.Herein,we present a unipolar pulsed electrodeposition(UPED) strategy to induce strain in the Ni lattice by introducing trace amounts of Pt single atoms(SAs)(0.22 wt%).The overpotential decreased by 183 mV at 10 mA cm^(-2) in 1.0 M KOH after introducing trace amounts of Pt_(SAs).The industrial electrolyzer,assembled with Pt_(SAs)Ni cathode and a commercial NiFeO_(x) anode,requires a cell voltage of 1.90 V to attain 1 A cm^(-2) of current density and remains stable for 280 h,demonstrating significant potential for practical applications.Spherical aberration corrected scanning transmission electron microscopy(AC-STEM),X-ray absorption(XAS),and geometric phase analysis(GPA) indicate that the introduction of trace amounts of Pt SAs induces tensile strain in the Ni lattice,thereby altering the local electronic structure and coordination environment around cubic Ni for enhancing the water decomposition kinetics and fundamentally changing the reaction pathway.The doping-strain strategy showcases conformational relationships that could offer new ideas to construct efficient hydrogen evolution reaction(HER) electrocatalysts for industrial hydrogen production in the future.展开更多
Higher-order nonlinear Schrodinger equation with the Hirota constraint conditions is considered, and an analytic solution, which can describe the modulational instability process, is presented. Based on the solution, ...Higher-order nonlinear Schrodinger equation with the Hirota constraint conditions is considered, and an analytic solution, which can describe the modulational instability process, is presented. Based on the solution, a new pulse train without continuous wave （CW） background is generated in quadratures and the propagation of the pulse train is discussed in detail by simulating numerically. The results show that, unlike the propagation of the picosecond pulse train, under the effects of the higher-order terms, the pulse train cannot propagate along the fibre when the energy is very high; however, for some medium energy the pulse train can stably propagate. We also investigate the stability of the pulse train against violation of the Hirota conditions, and the results show that the pulse train can still propagate stably when the Hirota conditions are broken.展开更多
The HfO2-based ferroelectric field effect transistors(FeFET)have been widely studied for their ability in breaking the Boltzmann limit and the potential to be applied to low-power circuits.This article systematically ...The HfO2-based ferroelectric field effect transistors(FeFET)have been widely studied for their ability in breaking the Boltzmann limit and the potential to be applied to low-power circuits.This article systematically investigates the transient response of negative capacitance(NC)fin field-effect transistors(FinFETs)through two kinds of self-built test schemes.By comparing the results with those of conventional FinFETs,we experimentally demonstrate that the on-current of the NC FinFET is not degraded in the MHz frequency domain.Further test results in the higher frequency domain show that the on-state current of the prepared NC FinFET increases with the decreasing gate pulse width at pulse widths below 100 ns and is consistently greater(about 80%with NC NMOS)than the on-state current of the conventional transistor,indicating the great potential of the NC FET for future high-frequency applications.展开更多
We utilized a set of fused silica thin plates to broaden the spectrum of 1kHz,30 fs Ti:sapphire amplified laser pulses to an octave.Following the compression by chirped mirror pairs,the generated few-cycle pulses were...We utilized a set of fused silica thin plates to broaden the spectrum of 1kHz,30 fs Ti:sapphire amplified laser pulses to an octave.Following the compression by chirped mirror pairs,the generated few-cycle pulses were focused onto an argon filled gas cell.We detected high order harmonics corresponding to a train of 209 as pulses,characterized by the reconstruction of attosecond beating by interference of two-photon transition(RABITT)technique.Compared with the conventional attosecond pulse trains,the broad harmonics in such pulse trains cover more energy range,so it is more efficient in studying some typical cases,such as resonances,with frequency resolved RABITT.As the solid thin plates can support high power supercontinuum generation,it is feasible to tailor the spectrum to have different central wavelength and spectral width,which will make the RABITT source work in different applications.展开更多
The Henon map forms one of the most-studied two-dimensional discrete-time dynamical systems that exhibits chaotic behavior.The Henon map takes a point(Xn,Yn)in the plane and maps it to a new point(Xn+1,Yn+1).In this p...The Henon map forms one of the most-studied two-dimensional discrete-time dynamical systems that exhibits chaotic behavior.The Henon map takes a point(Xn,Yn)in the plane and maps it to a new point(Xn+1,Yn+1).In this paper,a chaotic pulse generator based on the chaotic Henon map is proposed.It consists of a Henon map function subcircuit to realize the Henon map and another subcircuit to perform the iterative operation.The Henon map subcircuit comprises operational amplifiers,multipliers,delay elements and resistors,whereas,the iterative subcircuit is implemented with a simple design that comprises of an edge forming circuit followed by a monostable multivibrator and a voltage controlled switch without the use of any clock control.The proposed design can be used to realize the Henon map and also to generate a chaotic pulse train,with a controllable time interval and pulse position.The proposed circuit is implemented and simulated using Multisim 13.0 and MATLAB R2019b.The chaotic nature of the generated pulse train and also the time interval between the consecutive pulses is verified by the calculation of its Lyapunov exponents.展开更多
In this framework we present a new method for measurement of the UWB impulse train based on the parallel sampling of the cascaded identical RC filters. We show that the amplitudes and time locations of p sequential im...In this framework we present a new method for measurement of the UWB impulse train based on the parallel sampling of the cascaded identical RC filters. We show that the amplitudes and time locations of p sequential impulses can be reconstructed from simultaneous measurement of the outputs from 2p cascaded identical RC filters. The parallel sampling scheme has a wide range of applications including the detection of the ultra wideband (UWB) impulses. Due to identical analog RC filters and buffer amplifiers, the parallel sampling scheme is flexible to implement in VLSI applications.展开更多
Amplifying the attosecond pulse by the chirp pulse amplification method is impossible. Furthermore, the intensity of attosecond pulse is low in the interaction of laser pulse and underdense plasma. This motivates us t...Amplifying the attosecond pulse by the chirp pulse amplification method is impossible. Furthermore, the intensity of attosecond pulse is low in the interaction of laser pulse and underdense plasma. This motivates us to propose using a multi-color pulse to produce the high intense attosecond pulse. In the present study, the relativistic interaction of a three-color linearly-polarized laser-pulse with highly overdense plasma is studied. We show that the combination of ω1, ω2 and ω3 frequencies decreases the instance full width at half maximum reflected attosecond pulse train from the overdense plasma surface. Moreover, we show that the three-color pulse increases the intensity of generated harmonics, which is explained by the relativistic oscillating mirror model. The obtained results demonstrate that if the three-color laser pulse interacts with overdense plasma, it will enhance two orders of magnitude of intensity of ultra short attosecond pulses in comparison with monochromatic pulse.展开更多
目的·探究“行为干预研究单位孤独症网络家长培训”[the Research Units in Behavioral Intervention(RUBI)Autism Network Parent Training,RUBI-PT]方案的中国本土化改编并对其适应性进行调查。方法·按照文化改编的4个步骤...目的·探究“行为干预研究单位孤独症网络家长培训”[the Research Units in Behavioral Intervention(RUBI)Autism Network Parent Training,RUBI-PT]方案的中国本土化改编并对其适应性进行调查。方法·按照文化改编的4个步骤对RUBI-PT方案进行改编,包括信息收集、初步改编设计、初步改编测试、进一步调整。信息收集阶段邀请了6位儿科专家和2位心理治疗师进行6次焦点小组访谈,并根据专家意见从语言、治疗形式、治疗设置等方面对RUBI-PT方案进行初步改编;初步改编测试阶段招募了16位孤独症谱系障碍(autism spectrum disorder,ASD)患儿的家长,分2批参加线上RUBI-PT,结束后收集项目反馈问卷并行适应性调查分析,最后根据测试结果进行方案的进一步调整。结果·RUBI-PT的初步改编方案由个体培训调整为团体培训,包含8次核心技能课程,采用线上会议形式实施。初步测试结果显示,家长对于上课进度、上课过程、课后作业完成情况、作业点评情况的满意度分别为90%、80%、100%和100%;课程难度方面,第7次课(功能性沟通训练)和第8次课(教授技能)的难度最大。依据上述调查结果和专家小组意见完成进一步调整,最终形成本土化RUBI-PT的改编方案。结论·经过改编和适应性调查,形成了适用于中国ASD儿童家庭的家长行为训练策略即RUBI-PT。展开更多
Thermal characteristics of tightly-contacted copper-gold double-layer thin film target under ablation of femtosec- ond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation s...Thermal characteristics of tightly-contacted copper-gold double-layer thin film target under ablation of femtosec- ond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation shows that electron heat flux varies significantly on the boundary of copper-gold film with different maximal electron temperature of 1.15 x 103 K at 5 ps after ablating laser pulse in gold and copper films, which can reach a balance around 12.6 ps and 8.2 ps for a single and double pulse ablation, respectively, and in the meantime, the lattice temperature difference crossing the gold-copper interface is only about 0.04×103 K at the same time scale. It is also found that electron-lattice heat relaxation time increases linearly with laser fluence in both single and double pulse ablation, and a sudden change of the relaxation time appears after the laser energy density exceeds the ablation threshold.展开更多
Partial Transmit Sequences (PTS) is an efficient scheme for Peak-to-Average Power Ratio (PAPR) reduction in Orthogonal Frequency Division Multiplexing (OFDM) system. It does not bring any signal distortion. However, i...Partial Transmit Sequences (PTS) is an efficient scheme for Peak-to-Average Power Ratio (PAPR) reduction in Orthogonal Frequency Division Multiplexing (OFDM) system. It does not bring any signal distortion. However, its remarkable drawback is the high computational complexity. In order to reduce the computational complexity, currently many PTS methods have been proposed but with the cost of the loss of PAPR performance of the system. In this paper, we introduce an improved PTS optimization method with superimposed training. Simulation results show that, compared with conventional PTS, improved PTS scheme can achieve better PAPR performance while be implemented with lower computation complexity of the system.展开更多
基金supported by Key Program of Natural Science Foundation of Educational Commission of Sichuan Province, China (GrantNo 2006A124)the Fundamental Application Research Project of the Department of Science and Technology of Sichuan Province,China (Grant No 05JY029-084)the Foundation of Science and Technology Development of Chengdu University of Information Technology, China (Grant No KYTZ20060604)
文摘Starting from the extended nonlinear Schrodinger equation in which the self-steepening effect is included, the evolution and the splitting processes of continuous optical wave whose amplitude is perturbed into time related ultra-short optical pulse trains in an optical fibre are numerically simulated by adopting the split-step Fourier algorithm. The results show that the self-steepening effect can cause the characteristic of the pulse trains to vary with time, which is different from the self-steepening-free case where the generated pulse trains consist of single pulses which are identical in width, intensity, and interval, namely when pulses move a certain distance, they turn into the pulse trains within a certain time range. Moreover, each single pulse may split into several sub-pulses. And as time goes on, the number of the sub-pulses will decrease gradually and the pulse width and the pulse intensity will change too. With the increase of the self-steepening parameter, the distance needed to generate time-dependent pulse trains will shorten. In addition, for a large self-steepening parameter and at the distance where more sub-pulses appear, the corresponding frequency spectra of pulse trains are also wider.
基金supported by MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) (Grant No.JPMXS0118067246)K.S.was supported by JST ACT-X (JPMJAX22K8).Y.I.and A.I.were partly supported by JST PRESTO (JPMJPR2003 and JPMJPR1902,respectively)K.N.was partly supported by JST FOREST (JPMJFR215C).
文摘Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent control of the spatial profile for each pulse limit their advancement.We present a pulse manipulation technique for producing spectrally separated GHz burst pulses from a single ultrashort pulse,where each pulse is spatially shapable.We demonstrated the production of pulse trains at intervals of 0.1 to 3 ns in the 800-and 400-nm wavelength bands and applied them to ultrafast single-shot transmission spectroscopic imaging(4 Gfps)of laser ablation dynamics with two-color sequentially timed all-optical mapping photography.Furthermore,we demonstrated the production of pulse trains containing a shifted or dual-peak pulse as examples of individual spatial shaping of GHz burst pulses.Our proposed technique brings unprecedented spatiotemporal manipulation of GHz burst pulses,which can be useful for a wide range of laser applications.
基金supported by the National Natural Science Foundation of China(61501501)
文摘This paper presents a method to estimate beam pointing of phased array radar by the pulse amplitude train, which is significant in radar electronic reconnaissance and electronic support measure. Firstly, the antenna patterns modeling of the phased array system is exploited to build the radar sweeping model and the signal propagation model. Secondly, the relationship between the variation of the radiated power and the antenna beam pointing angles in the given airspace is analyzed. Based on the above two points, the sample with obvious amplitude characteristics of the pulse amplitude train can be screened out after detecting the train peaks. Finally, the sample is matched to the subsequent pulse amplitude train based on the Hausdorff distance. The proposed methods have less prior knowledge and higher efficiency and are easier to process. By cross correlating the sample of the pulse amplitude train with the sample data of the antenna follow-up radiation, the probability of detection of the beam pointing direction becomes larger in case that the subsequent antenna beam returns to the specific position.
基金National Natural Science Foundation of China (grants U22A20418, 22075196, and 21878204)Research Project Supported by Shanxi Scholarship Council of China (2022-050)。
文摘Strategically designing the electrocatalytic system and cleverly inducing strain is an effective approach to balance the cost and activity of Pt-based electrocatalysts for industrial-scale hydrogen production.Herein,we present a unipolar pulsed electrodeposition(UPED) strategy to induce strain in the Ni lattice by introducing trace amounts of Pt single atoms(SAs)(0.22 wt%).The overpotential decreased by 183 mV at 10 mA cm^(-2) in 1.0 M KOH after introducing trace amounts of Pt_(SAs).The industrial electrolyzer,assembled with Pt_(SAs)Ni cathode and a commercial NiFeO_(x) anode,requires a cell voltage of 1.90 V to attain 1 A cm^(-2) of current density and remains stable for 280 h,demonstrating significant potential for practical applications.Spherical aberration corrected scanning transmission electron microscopy(AC-STEM),X-ray absorption(XAS),and geometric phase analysis(GPA) indicate that the introduction of trace amounts of Pt SAs induces tensile strain in the Ni lattice,thereby altering the local electronic structure and coordination environment around cubic Ni for enhancing the water decomposition kinetics and fundamentally changing the reaction pathway.The doping-strain strategy showcases conformational relationships that could offer new ideas to construct efficient hydrogen evolution reaction(HER) electrocatalysts for industrial hydrogen production in the future.
基金Project supported by the National Natural Science Foundation of China （Grant No 60477026）.
文摘Higher-order nonlinear Schrodinger equation with the Hirota constraint conditions is considered, and an analytic solution, which can describe the modulational instability process, is presented. Based on the solution, a new pulse train without continuous wave （CW） background is generated in quadratures and the propagation of the pulse train is discussed in detail by simulating numerically. The results show that, unlike the propagation of the picosecond pulse train, under the effects of the higher-order terms, the pulse train cannot propagate along the fibre when the energy is very high; however, for some medium energy the pulse train can stably propagate. We also investigate the stability of the pulse train against violation of the Hirota conditions, and the results show that the pulse train can still propagate stably when the Hirota conditions are broken.
基金This project was supported in part by the Science and Technology program of Beijing Municipal Science and Technology Commission under grant Z201100006820084,in part by the National Natural Science Foundation of China(NSFC)under grants 92064003,61904194,91964202 and 61874135,in part by the Youth Innovation Promotion Association,Chinese Academy of Sciences under grants Y9YQ01R004 and Y2020037,in part by the Opening Project of Key Laboratory of Microelectronic Devices and Integrated Technology,Institute of Microelectronics,Chinese Academy of Sciences under grants E0YS01X001 and E0290X03.
文摘The HfO2-based ferroelectric field effect transistors(FeFET)have been widely studied for their ability in breaking the Boltzmann limit and the potential to be applied to low-power circuits.This article systematically investigates the transient response of negative capacitance(NC)fin field-effect transistors(FinFETs)through two kinds of self-built test schemes.By comparing the results with those of conventional FinFETs,we experimentally demonstrate that the on-current of the NC FinFET is not degraded in the MHz frequency domain.Further test results in the higher frequency domain show that the on-state current of the prepared NC FinFET increases with the decreasing gate pulse width at pulse widths below 100 ns and is consistently greater(about 80%with NC NMOS)than the on-state current of the conventional transistor,indicating the great potential of the NC FET for future high-frequency applications.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFB0405202)the Major Program of the National Natural Science Foundation of China(Grant No.61690221)+1 种基金the Key Program of the National Natural Science Foundation of China(Grant No.11434016)the National Natural Science Foundation of China(Grant Nos.11574384,11674386,and 11774277)
文摘We utilized a set of fused silica thin plates to broaden the spectrum of 1kHz,30 fs Ti:sapphire amplified laser pulses to an octave.Following the compression by chirped mirror pairs,the generated few-cycle pulses were focused onto an argon filled gas cell.We detected high order harmonics corresponding to a train of 209 as pulses,characterized by the reconstruction of attosecond beating by interference of two-photon transition(RABITT)technique.Compared with the conventional attosecond pulse trains,the broad harmonics in such pulse trains cover more energy range,so it is more efficient in studying some typical cases,such as resonances,with frequency resolved RABITT.As the solid thin plates can support high power supercontinuum generation,it is feasible to tailor the spectrum to have different central wavelength and spectral width,which will make the RABITT source work in different applications.
文摘The Henon map forms one of the most-studied two-dimensional discrete-time dynamical systems that exhibits chaotic behavior.The Henon map takes a point(Xn,Yn)in the plane and maps it to a new point(Xn+1,Yn+1).In this paper,a chaotic pulse generator based on the chaotic Henon map is proposed.It consists of a Henon map function subcircuit to realize the Henon map and another subcircuit to perform the iterative operation.The Henon map subcircuit comprises operational amplifiers,multipliers,delay elements and resistors,whereas,the iterative subcircuit is implemented with a simple design that comprises of an edge forming circuit followed by a monostable multivibrator and a voltage controlled switch without the use of any clock control.The proposed design can be used to realize the Henon map and also to generate a chaotic pulse train,with a controllable time interval and pulse position.The proposed circuit is implemented and simulated using Multisim 13.0 and MATLAB R2019b.The chaotic nature of the generated pulse train and also the time interval between the consecutive pulses is verified by the calculation of its Lyapunov exponents.
文摘In this framework we present a new method for measurement of the UWB impulse train based on the parallel sampling of the cascaded identical RC filters. We show that the amplitudes and time locations of p sequential impulses can be reconstructed from simultaneous measurement of the outputs from 2p cascaded identical RC filters. The parallel sampling scheme has a wide range of applications including the detection of the ultra wideband (UWB) impulses. Due to identical analog RC filters and buffer amplifiers, the parallel sampling scheme is flexible to implement in VLSI applications.
文摘Amplifying the attosecond pulse by the chirp pulse amplification method is impossible. Furthermore, the intensity of attosecond pulse is low in the interaction of laser pulse and underdense plasma. This motivates us to propose using a multi-color pulse to produce the high intense attosecond pulse. In the present study, the relativistic interaction of a three-color linearly-polarized laser-pulse with highly overdense plasma is studied. We show that the combination of ω1, ω2 and ω3 frequencies decreases the instance full width at half maximum reflected attosecond pulse train from the overdense plasma surface. Moreover, we show that the three-color pulse increases the intensity of generated harmonics, which is explained by the relativistic oscillating mirror model. The obtained results demonstrate that if the three-color laser pulse interacts with overdense plasma, it will enhance two orders of magnitude of intensity of ultra short attosecond pulses in comparison with monochromatic pulse.
文摘目的·探究“行为干预研究单位孤独症网络家长培训”[the Research Units in Behavioral Intervention(RUBI)Autism Network Parent Training,RUBI-PT]方案的中国本土化改编并对其适应性进行调查。方法·按照文化改编的4个步骤对RUBI-PT方案进行改编,包括信息收集、初步改编设计、初步改编测试、进一步调整。信息收集阶段邀请了6位儿科专家和2位心理治疗师进行6次焦点小组访谈,并根据专家意见从语言、治疗形式、治疗设置等方面对RUBI-PT方案进行初步改编;初步改编测试阶段招募了16位孤独症谱系障碍(autism spectrum disorder,ASD)患儿的家长,分2批参加线上RUBI-PT,结束后收集项目反馈问卷并行适应性调查分析,最后根据测试结果进行方案的进一步调整。结果·RUBI-PT的初步改编方案由个体培训调整为团体培训,包含8次核心技能课程,采用线上会议形式实施。初步测试结果显示,家长对于上课进度、上课过程、课后作业完成情况、作业点评情况的满意度分别为90%、80%、100%和100%;课程难度方面,第7次课(功能性沟通训练)和第8次课(教授技能)的难度最大。依据上述调查结果和专家小组意见完成进一步调整,最终形成本土化RUBI-PT的改编方案。结论·经过改编和适应性调查,形成了适用于中国ASD儿童家庭的家长行为训练策略即RUBI-PT。
基金supported by the National Natural Science Foundation of China (Grant No. 60978014)the Natural Science Foundation of Jilin Province (Grant No. 20090523)the Educational Commission of Jilin Province (Grant No. [2008]297)
文摘Thermal characteristics of tightly-contacted copper-gold double-layer thin film target under ablation of femtosec- ond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation shows that electron heat flux varies significantly on the boundary of copper-gold film with different maximal electron temperature of 1.15 x 103 K at 5 ps after ablating laser pulse in gold and copper films, which can reach a balance around 12.6 ps and 8.2 ps for a single and double pulse ablation, respectively, and in the meantime, the lattice temperature difference crossing the gold-copper interface is only about 0.04×103 K at the same time scale. It is also found that electron-lattice heat relaxation time increases linearly with laser fluence in both single and double pulse ablation, and a sudden change of the relaxation time appears after the laser energy density exceeds the ablation threshold.
文摘Partial Transmit Sequences (PTS) is an efficient scheme for Peak-to-Average Power Ratio (PAPR) reduction in Orthogonal Frequency Division Multiplexing (OFDM) system. It does not bring any signal distortion. However, its remarkable drawback is the high computational complexity. In order to reduce the computational complexity, currently many PTS methods have been proposed but with the cost of the loss of PAPR performance of the system. In this paper, we introduce an improved PTS optimization method with superimposed training. Simulation results show that, compared with conventional PTS, improved PTS scheme can achieve better PAPR performance while be implemented with lower computation complexity of the system.
