By using non-equilibrium Green's function method, we investigate the thermoelectric properties of the molecular junctions based on acene-linked graphene nanoribbons. In this paper, effects of the length of the acene molecule, the contact position between the acene molecule and graphene nanoribbon electrodes on the thermoelectric parameters is mainly considered. It is found that the phonon contribution is dominant in the thermal conductance corresponding to the maximum of the thermoelectric figure of merit (ZTmax). As the length of the acene molecules increases, the phonon thermal conductance decreases monotonically, and eventually becomes almost independent of the acene molecules’ length. When the acene molecules are in contact with the middle (upper) part of the left (right) electrode of graphene nanoribbons, the corresponding ZTmax is highest. However, when the acene molecules are in contact with the middle (middle) part of the left (right) electrode of graphene nanoribbons, the corresponding ZTmax is lowest. When the temperature increases, ZTmax has an monotonously increasing tendency, regardless of the contact position. With the increase of the length of the acene molecules, the chemical potential corresponding to ZTmax becomes closer to the intrinsic Fermi level. The above findings may provide the valuable reference for the future design of thermoelectric devices based on the acene molecular junctions.
{"title":"A study on the thermoelectric properties of acene molecular junctions","authors":"Xie Zhong-Xiang, 周五星, Yu Xia, Jia Pin-Zhen, Chen Xue-Kun, Deng Yuan-Xiang, Zhang Yong, Zhou Wu-Xing","doi":"10.7498/aps.72.20230354","DOIUrl":"https://doi.org/10.7498/aps.72.20230354","url":null,"abstract":"By using non-equilibrium Green's function method, we investigate the thermoelectric properties of the molecular junctions based on acene-linked graphene nanoribbons. In this paper, effects of the length of the acene molecule, the contact position between the acene molecule and graphene nanoribbon electrodes on the thermoelectric parameters is mainly considered. It is found that the phonon contribution is dominant in the thermal conductance corresponding to the maximum of the thermoelectric figure of merit (ZTmax). As the length of the acene molecules increases, the phonon thermal conductance decreases monotonically, and eventually becomes almost independent of the acene molecules’ length. When the acene molecules are in contact with the middle (upper) part of the left (right) electrode of graphene nanoribbons, the corresponding ZTmax is highest. However, when the acene molecules are in contact with the middle (middle) part of the left (right) electrode of graphene nanoribbons, the corresponding ZTmax is lowest. When the temperature increases, ZTmax has an monotonously increasing tendency, regardless of the contact position. With the increase of the length of the acene molecules, the chemical potential corresponding to ZTmax becomes closer to the intrinsic Fermi level. The above findings may provide the valuable reference for the future design of thermoelectric devices based on the acene molecular junctions.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83967127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In quantum mechanics, the Hermitian Hamiltonian is generally used to describe the ideal closed quantum system, but in reality, the physical system is closely related to the environment, and the open quantum system coupled to the environment can be described by the equivalent non-Hermitian Hamiltonian to a certain extent. Among them, the dissipation intensity is closely related to the dynamic properties of non-Hermitian quantum systems. Therefore, it is of great practical significance to study how dissipation affects particle loss. In this paper, the dynamic law related to dissipation intensity in one-dimensional non-Hermitian systems under open boundary conditions is studied, and it is found that dissipation can induce the recurrence of edge burst. After the time-dependent evolution of the particles in the one-dimensional non-Hermitian dissipative lattice system with open boundary conditions, there is an edge burst in the system, that is, there is a large probability of particle loss at the edge, and the edge burst disappears after increasing the intensity of intracellular transition. It is found that if the dissipation intensity is increased or decreased, the edge burst will reappear. This kind of reappearance is different from the original edge burst, which is mainly manifested in the loss probability distribution of particles from the edge distribution to the volume distribution, which is due to the different probability of particle motion direction in the two cases. Under the re-induced edge burst, the particles move from the initial position to the left and right directions, and the left side rebounds after reaching the boundary, forming a more obvious loss probability at the edge and gradually decreasing to the body area. In the original edge burst, the probability of particles only moving to the left is larger, and the 'trapped' is completely dissipated at the edge, forming a distribution with an independent loss peak at the edge, the movement to the left is due to due to the non-Hermitian skin effect. The deeper reason for different movement directions is related to the defect of non-Hermitian system far from parity-time symmetry breaking. Under the parameter near the parity-time symmetry breaking defect, the loss probability of the particle is unilateral distribution, and the loss probability of the particle moving to both sides is bilateral distribution when it is far away. This is the description of the dissipation-induced edge burst recurrence phenomenon and its characteristics. In addition, this paper also studies the influence of impurity barrier on the probability distribution of particle loss in non-Hermitian dynamics. The results show that placing a small barrier on the non-dissipative A-site can obviously hinder the particle motion, and when the barrier increases to a certain height, its influence on the particle motion tends to be unchanged. And the barrier at the dissipative B lattice has little effect on the dynamics.
{"title":"Dissipation-Induced Recurrence of Non-Hermitian Edge Burst","authors":"Ren Cui-Cui, Yin Xiang-Guo","doi":"10.7498/aps.72.20230338","DOIUrl":"https://doi.org/10.7498/aps.72.20230338","url":null,"abstract":"In quantum mechanics, the Hermitian Hamiltonian is generally used to describe the ideal closed quantum system, but in reality, the physical system is closely related to the environment, and the open quantum system coupled to the environment can be described by the equivalent non-Hermitian Hamiltonian to a certain extent. Among them, the dissipation intensity is closely related to the dynamic properties of non-Hermitian quantum systems. Therefore, it is of great practical significance to study how dissipation affects particle loss. In this paper, the dynamic law related to dissipation intensity in one-dimensional non-Hermitian systems under open boundary conditions is studied, and it is found that dissipation can induce the recurrence of edge burst. After the time-dependent evolution of the particles in the one-dimensional non-Hermitian dissipative lattice system with open boundary conditions, there is an edge burst in the system, that is, there is a large probability of particle loss at the edge, and the edge burst disappears after increasing the intensity of intracellular transition. It is found that if the dissipation intensity is increased or decreased, the edge burst will reappear. This kind of reappearance is different from the original edge burst, which is mainly manifested in the loss probability distribution of particles from the edge distribution to the volume distribution, which is due to the different probability of particle motion direction in the two cases. Under the re-induced edge burst, the particles move from the initial position to the left and right directions, and the left side rebounds after reaching the boundary, forming a more obvious loss probability at the edge and gradually decreasing to the body area. In the original edge burst, the probability of particles only moving to the left is larger, and the 'trapped' is completely dissipated at the edge, forming a distribution with an independent loss peak at the edge, the movement to the left is due to due to the non-Hermitian skin effect. The deeper reason for different movement directions is related to the defect of non-Hermitian system far from parity-time symmetry breaking. Under the parameter near the parity-time symmetry breaking defect, the loss probability of the particle is unilateral distribution, and the loss probability of the particle moving to both sides is bilateral distribution when it is far away. This is the description of the dissipation-induced edge burst recurrence phenomenon and its characteristics. In addition, this paper also studies the influence of impurity barrier on the probability distribution of particle loss in non-Hermitian dynamics. The results show that placing a small barrier on the non-dissipative A-site can obviously hinder the particle motion, and when the barrier increases to a certain height, its influence on the particle motion tends to be unchanged. And the barrier at the dissipative B lattice has little effect on the dynamics.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90132965","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In a quantum system with spin, spin-orbit coupling is manifested by linking the spin angular momentum of a particle with its orbital angular momentum, which leads to many exotic phenomena. The experimental realization of synthetic spin-orbit coupling effects in ultra-cold atomic systems provides a completely new platform for exploring quantum simulations. In a spinor Bose-Einstein condensate, the spin-orbit coupling can change the properties of the system significantly, which offers a great opportunity to investigate the influence of spin-orbit coupling to the quantum state at the macroscopic level. As typical states of macroscopic quantum effects, solitons in spin-orbit coupled Bose-Einstein condensates can be manipulated by spin-orbit coupling directly, this makes the study on spin-orbit coupled Bose-Einstein condensates become one of the hottest topics in the research of ultracold atomic physics in recent years. This paper investigates exact vector soliton solutions of the Gross-Pitaevskii equation for the one-dimensional spin-orbit coupled binary Bose-Einstein condensates, which has four parameters μ,δ,α and β, where μ denotes the strength of the spin-orbit coupling, δ is the detuning parameter,α and β are the parameters of the self-and cross-interaction, respectively. For the case β=α, by a direct ansatz, two kinds of stripe solitons, namely, the oscillating dark-dark solitons are obtained; meanwhile, a transformation is presented such that from the solutions of the integrable Manakov system, one can get soliton solutions for the spin-orbit coupled Gross-Pitaevskii equation. For the case β=3α, a bright-W type soliton for α>0 and a kink-antikink type soliton for α<0 are presented. It is found that the relation between μ and δ can affect the states of the solitons. Based on these solutions, the corresponding dynamics and the impact of the spin-orbit coupling effects on the quantum magnetization and spin-polarized domains are discussed. Our results show that spin-orbit coupling can result in rich kinds of soliton states in the two-component Bose gases, including the stripe solitons as well as the classical non-stripe solitons, and various kinds of multi-solitons. Furthermore, spin-orbit coupling has remarkable influence on the behaviors of quantum magnetization. In the experiments of Bose-Einstein condensates, there have been many different methods to observe the soliton states of the population distribution, the magnetic solitons, and the spin domains, so our results provide some possible options for the related experiments.
{"title":"Soliton Solutions of the Spin-Orbit Coupled Binary Bose-Einstein Condensate System","authors":"Li Xin-Yue, Qi Juan-Juan, Zhao Dun, Liu Wu-ming","doi":"10.7498/aps.72.20222319","DOIUrl":"https://doi.org/10.7498/aps.72.20222319","url":null,"abstract":"In a quantum system with spin, spin-orbit coupling is manifested by linking the spin angular momentum of a particle with its orbital angular momentum, which leads to many exotic phenomena. The experimental realization of synthetic spin-orbit coupling effects in ultra-cold atomic systems provides a completely new platform for exploring quantum simulations. In a spinor Bose-Einstein condensate, the spin-orbit coupling can change the properties of the system significantly, which offers a great opportunity to investigate the influence of spin-orbit coupling to the quantum state at the macroscopic level. As typical states of macroscopic quantum effects, solitons in spin-orbit coupled Bose-Einstein condensates can be manipulated by spin-orbit coupling directly, this makes the study on spin-orbit coupled Bose-Einstein condensates become one of the hottest topics in the research of ultracold atomic physics in recent years. This paper investigates exact vector soliton solutions of the Gross-Pitaevskii equation for the one-dimensional spin-orbit coupled binary Bose-Einstein condensates, which has four parameters μ,δ,α and β, where μ denotes the strength of the spin-orbit coupling, δ is the detuning parameter,α and β are the parameters of the self-and cross-interaction, respectively. For the case β=α, by a direct ansatz, two kinds of stripe solitons, namely, the oscillating dark-dark solitons are obtained; meanwhile, a transformation is presented such that from the solutions of the integrable Manakov system, one can get soliton solutions for the spin-orbit coupled Gross-Pitaevskii equation. For the case β=3α, a bright-W type soliton for α>0 and a kink-antikink type soliton for α<0 are presented. It is found that the relation between μ and δ can affect the states of the solitons. Based on these solutions, the corresponding dynamics and the impact of the spin-orbit coupling effects on the quantum magnetization and spin-polarized domains are discussed. Our results show that spin-orbit coupling can result in rich kinds of soliton states in the two-component Bose gases, including the stripe solitons as well as the classical non-stripe solitons, and various kinds of multi-solitons. Furthermore, spin-orbit coupling has remarkable influence on the behaviors of quantum magnetization. In the experiments of Bose-Einstein condensates, there have been many different methods to observe the soliton states of the population distribution, the magnetic solitons, and the spin domains, so our results provide some possible options for the related experiments.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90188703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Liu Yun, Wang Wen-Hai, He De-Jing, Zhou Yong-Zhuang, Shen Yong, Zou Hong-Xin
The first space optical clock (SOC) in the world developed in China, which is composed by five subsystems, including an optical unit, a physics unit, an electronic control unit, a space optical frequency comb, and an ultrastable laser, has been successfully launched with the Mengtian space laboratory into the China Space Station (CSS). Compact and stable lasers are key elements for the operation of the SOC. The optical unit consists of 5 lasers at 461 nm, 679 nm, 689 nm, 707nm, and 813 nm. With a synchronous-tuning-like scheme, high quality external cavity diode lasers (ECDL) have been developed as the seeds. The linewidth of the lasers is suppressed to the order of 100 kHz, and the mode-hop-free tuning range reaches 20 GHz, which meet the requirements of the SOC. With careful mechanical and thermal design, the stability of the lasers against vibration and temperature fluctuation has been sufficiently promoted to confront the challenge of rocket launching. While the power from the ECDL is sufficient for 679 nm and 707 nm repump lasers, additional injection lock is utilized for the 461 nm and 689 nm lasers to amplify the power of the seeds to more than 600 mW, so that efficient first and second stage Doppler cooling can be achieved. To generate an optical lattice with deep enough potential well, over 800 mW 813 nm lasers is required. Therefore, a semiconductor tapered amplifier is adopted to amplify the seed to more than 2 W, so as to cope with various losses of the coupling optics. The wavelength and output power of the 5 lasers are monitored and feedback-controlled by the electronic control unit. All the modules are designed and manufactured as orbital replaceable units, which can be easily replaced by astronauts in case failure occurs. Now the lasers are all turned on and operates normally in CSS. More data of the SOC will be obtained in the near future. At present stage, according to our evaluation, the continuous operation time of the SOC is limited by the injection locked lasers, which are relatively vulnerable to mode hopping. Hopefully this problem can be solved by improving the laser diode manufacturing technology, or developing fiber lasers with compact frequency conversion modules.
{"title":"Research progress on the laser system of the cold atomic clock in China Space Station","authors":"Liu Yun, Wang Wen-Hai, He De-Jing, Zhou Yong-Zhuang, Shen Yong, Zou Hong-Xin","doi":"10.7498/aps.72.20230412","DOIUrl":"https://doi.org/10.7498/aps.72.20230412","url":null,"abstract":"The first space optical clock (SOC) in the world developed in China, which is composed by five subsystems, including an optical unit, a physics unit, an electronic control unit, a space optical frequency comb, and an ultrastable laser, has been successfully launched with the Mengtian space laboratory into the China Space Station (CSS). Compact and stable lasers are key elements for the operation of the SOC. The optical unit consists of 5 lasers at 461 nm, 679 nm, 689 nm, 707nm, and 813 nm. With a synchronous-tuning-like scheme, high quality external cavity diode lasers (ECDL) have been developed as the seeds. The linewidth of the lasers is suppressed to the order of 100 kHz, and the mode-hop-free tuning range reaches 20 GHz, which meet the requirements of the SOC. With careful mechanical and thermal design, the stability of the lasers against vibration and temperature fluctuation has been sufficiently promoted to confront the challenge of rocket launching. While the power from the ECDL is sufficient for 679 nm and 707 nm repump lasers, additional injection lock is utilized for the 461 nm and 689 nm lasers to amplify the power of the seeds to more than 600 mW, so that efficient first and second stage Doppler cooling can be achieved. To generate an optical lattice with deep enough potential well, over 800 mW 813 nm lasers is required. Therefore, a semiconductor tapered amplifier is adopted to amplify the seed to more than 2 W, so as to cope with various losses of the coupling optics. The wavelength and output power of the 5 lasers are monitored and feedback-controlled by the electronic control unit. All the modules are designed and manufactured as orbital replaceable units, which can be easily replaced by astronauts in case failure occurs. Now the lasers are all turned on and operates normally in CSS. More data of the SOC will be obtained in the near future. At present stage, according to our evaluation, the continuous operation time of the SOC is limited by the injection locked lasers, which are relatively vulnerable to mode hopping. Hopefully this problem can be solved by improving the laser diode manufacturing technology, or developing fiber lasers with compact frequency conversion modules.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90245015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shu-Peng Sun, Yongzhi Cheng, Hui Luo, Fu Chen, Xiangcheng Li
In this paper, a compact broadband bandpass filter with wide out-of-band rejection characteristics based on halberd-shaped spoof surface plasmon polariton (SSPP) is proposed. The filtering structure is achieved by etching a periodic halberd-shaped groove at the bottom of the substrate and a microstrip-to-slot line transition with a crescent-shaped patch at the top. Compared with the traditional dumbbell-shaped SSPP, the halberd-shaped SSPP has good slow-wave property, and the designed bandpass filter based on halberd-shaped SSPP can achieve a more compact size. The upper cutoff frequency and lower cutoff frequency of the passband can be adjusted by regulating the SSPP structure and the transition structure from microstrip-to-slot line, respectively. The simulation results show that the center frequency of broadband bandpass filter is 2.85 GHz, with the relative bandwidth of 130%, and the return loss in the passband is better than –10 dB, and the extreme strong out-of-band rejection of –40 dB from 5.6 GHz to 20 GHz. The size of the broadband bandpass filter is compact, only 1.08λg×0.39λg, where λg is the wavelength at the center frequency. In order to verify the effectiveness of the wideband bandpass filter, the traditional printed circuit board technology is used to fabricate the wideband bandpass filter. The measurement results are in good agreement with the simulation results, verifying the feasibility of the design. The proposed broadband bandpass filter shows promising prospects for developing SSPP functional devices and circuits at microwave frequencies.
{"title":"Compact broadband bandpass filter with wide stopband based on halberd-shaped spoof surface plasmon polariton","authors":"Shu-Peng Sun, Yongzhi Cheng, Hui Luo, Fu Chen, Xiangcheng Li","doi":"10.7498/aps.72.20222291","DOIUrl":"https://doi.org/10.7498/aps.72.20222291","url":null,"abstract":"In this paper, a compact broadband bandpass filter with wide out-of-band rejection characteristics based on halberd-shaped spoof surface plasmon polariton (SSPP) is proposed. The filtering structure is achieved by etching a periodic halberd-shaped groove at the bottom of the substrate and a microstrip-to-slot line transition with a crescent-shaped patch at the top. Compared with the traditional dumbbell-shaped SSPP, the halberd-shaped SSPP has good slow-wave property, and the designed bandpass filter based on halberd-shaped SSPP can achieve a more compact size. The upper cutoff frequency and lower cutoff frequency of the passband can be adjusted by regulating the SSPP structure and the transition structure from microstrip-to-slot line, respectively. The simulation results show that the center frequency of broadband bandpass filter is 2.85 GHz, with the relative bandwidth of 130%, and the return loss in the passband is better than –10 dB, and the extreme strong out-of-band rejection of –40 dB from 5.6 GHz to 20 GHz. The size of the broadband bandpass filter is compact, only 1.08λg×0.39λg, where λg is the wavelength at the center frequency. In order to verify the effectiveness of the wideband bandpass filter, the traditional printed circuit board technology is used to fabricate the wideband bandpass filter. The measurement results are in good agreement with the simulation results, verifying the feasibility of the design. The proposed broadband bandpass filter shows promising prospects for developing SSPP functional devices and circuits at microwave frequencies.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90347562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Large-size conductive targets or coated targets are difficult issues in computational electromagnetics. In general, such targets can be classified as multi-scale problems. Multi-scale problems usually consume a large number of computational resources. Researchers are devoted to seeking fast methods for these problems. When the skin depth is less than the size of a conductive target, the tangential components of the electric and magnetic fields over the surface of the target can be correlated by the surface impedance Ẑ. Ẑ is usually a complex function of the frequency, and it can be used to formulate an impedance boundary condition (IBC) to describe iterative equations in time domain methods to avoid the volumetric discretization of the target to improve computational efficiency. This condition is commonly known as the surface impedance boundary condition (SIBC). Similarly, for a conductor with thickness on the order or less than the skin depth, it also has high resource requirements if the target is straightforward volumetric discretization. The transmission impedance boundary condition (TIBC) can be applied to replace a coated object to reduce resource requirements. Thus, volumetric discretization is not required. There are few studies on the IBC scheme in the DGTD method. P. Li discussed the IBC scheme in DGTD, which involves complex matrix operations in the processing of IBC. In the DGTD method, numerical flux is used to transmit data between neighboring elements, and the key to the IBC scheme in DGTD is how to handle numerical flux. We hope to propose a DGTD method with a simple form and matrix-free IBC scheme. The key in dealing with IBC in DGTD is numerical flux. Unlike the literature, the impedance ẐR is not approximated by rational functions in our study. A specfic function ẐR obtained after the derivation in this paper is approximated by rational functions in the Laplace domain using the vector-fitting (VF) method, and its time-domain iteration scheme is given. This approach avoids matrix operations. The TIBC and SIBC processing schemes are given in section 4. The proposed method's advantage is that the upwind flux's standard coefficients are retained, and the complex frequency-time conversion problem is implemented by the vector-fitting method. The one-dimensional and three-dimensional examples also show the accuracy and effectiveness of our work in this paper.
{"title":"A simple DGTD method with the impedance boundary condition","authors":"Yang Qian, Wei Bing, Li Linqian, Deng Haochuan","doi":"10.7498/aps.72.20222104","DOIUrl":"https://doi.org/10.7498/aps.72.20222104","url":null,"abstract":"Large-size conductive targets or coated targets are difficult issues in computational electromagnetics. In general, such targets can be classified as multi-scale problems. Multi-scale problems usually consume a large number of computational resources. Researchers are devoted to seeking fast methods for these problems. When the skin depth is less than the size of a conductive target, the tangential components of the electric and magnetic fields over the surface of the target can be correlated by the surface impedance Ẑ. Ẑ is usually a complex function of the frequency, and it can be used to formulate an impedance boundary condition (IBC) to describe iterative equations in time domain methods to avoid the volumetric discretization of the target to improve computational efficiency. This condition is commonly known as the surface impedance boundary condition (SIBC). Similarly, for a conductor with thickness on the order or less than the skin depth, it also has high resource requirements if the target is straightforward volumetric discretization. The transmission impedance boundary condition (TIBC) can be applied to replace a coated object to reduce resource requirements. Thus, volumetric discretization is not required. There are few studies on the IBC scheme in the DGTD method. P. Li discussed the IBC scheme in DGTD, which involves complex matrix operations in the processing of IBC. In the DGTD method, numerical flux is used to transmit data between neighboring elements, and the key to the IBC scheme in DGTD is how to handle numerical flux. We hope to propose a DGTD method with a simple form and matrix-free IBC scheme. The key in dealing with IBC in DGTD is numerical flux. Unlike the literature, the impedance ẐR is not approximated by rational functions in our study. A specfic function ẐR obtained after the derivation in this paper is approximated by rational functions in the Laplace domain using the vector-fitting (VF) method, and its time-domain iteration scheme is given. This approach avoids matrix operations. The TIBC and SIBC processing schemes are given in section 4. The proposed method's advantage is that the upwind flux's standard coefficients are retained, and the complex frequency-time conversion problem is implemented by the vector-fitting method. The one-dimensional and three-dimensional examples also show the accuracy and effectiveness of our work in this paper.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88862481","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
ZEWEI LUO, GE WU, ZHI CHEN, CHINAN DANG, RONG WAN, Tao Yang, ZHENGFEI ZHUANG, AND TONGSHENG CHEN
The Structured Illumination (SI)-based Super Resolution Fluorescence Resonance Energy Transfer (SR-FRET) imaging technique, known as SISR-FRET, enables the investigation of molecular structures and functions in cellular organelles by resolving sub-diffraction FRET signals within living cells. FRET microscopy offers unique advantages for quantitatively detecting dynamic interactions and spatial distribution of biomolecules within living cells. The spatial resolution of conventional FRET microscopy is limited by the diffraction limit, and it can only capture the average behavior of these events within the resolution limits of conventional fluorescence microscopy. SISR-FRET performs sequential linear reconstruction of the three-channel SIM images followed by FRET quantitative analysis using a common localization mask-based filtering approach. This two-step process ensures the fidelity of the reconstructed SR-FRET signals while effectively removing false-positive FRET signals caused by SIM artifacts. However, the slow imaging speed resulting from the switching of excitation-emission channels in SISR-FRET imaging limits its application in fast imaging scenarios. To address this issue, this study proposes a dual-channel structured illumination super-resolution quantitative FRET imaging system and method. By incorporating a FRET dual-channel imaging and registration module into the imaging pathway, spatial switching and channel multiplexing of the SISR-FRET excitation-emission channels are achieved. Combining the image reconstruction algorithm with channel sub-pixel registration correction, the dual-channel SISR-FRET technique enhances the temporal resolution by 3.5 times while preserving the quantitative super-resolution FRET analysis. Experimental results were obtained using a multi-color SIM system to perform super-resolution imaging of living cells expressing mitochondria outer membrane FRET standard plasmids. These experiments validate the improved spatial and temporal resolution of dual-channel SISR-FRET and the fidelity of FRET quantification analysis. In summary, this research presents a novel dual-channel structured illumination super-resolution FRET imaging system and methodology. It overcomes the limitations of slow imaging speed in SISR-FRET by enabling spatial switching and channel multiplexing of excitation-emission channels. The proposed technique enhances the temporal resolution while maintaining quantitative analysis of super-resolution FRET. Experimental validation demonstrates the increased spatial and temporal resolution of dual-channel SISR-FRET and the accuracy of FRET quantification analysis. This advancement contributes to the study of molecular structures and functions in cellular organelles, providing valuable insights into the intricate mechanisms of living cells.
{"title":"Dual-channel structured illumination super-resolution quantitative FRET imaging","authors":"ZEWEI LUO, GE WU, ZHI CHEN, CHINAN DANG, RONG WAN, Tao Yang, ZHENGFEI ZHUANG, AND TONGSHENG CHEN","doi":"10.7498/aps.72.20230853","DOIUrl":"https://doi.org/10.7498/aps.72.20230853","url":null,"abstract":"The Structured Illumination (SI)-based Super Resolution Fluorescence Resonance Energy Transfer (SR-FRET) imaging technique, known as SISR-FRET, enables the investigation of molecular structures and functions in cellular organelles by resolving sub-diffraction FRET signals within living cells. FRET microscopy offers unique advantages for quantitatively detecting dynamic interactions and spatial distribution of biomolecules within living cells. The spatial resolution of conventional FRET microscopy is limited by the diffraction limit, and it can only capture the average behavior of these events within the resolution limits of conventional fluorescence microscopy. SISR-FRET performs sequential linear reconstruction of the three-channel SIM images followed by FRET quantitative analysis using a common localization mask-based filtering approach. This two-step process ensures the fidelity of the reconstructed SR-FRET signals while effectively removing false-positive FRET signals caused by SIM artifacts. However, the slow imaging speed resulting from the switching of excitation-emission channels in SISR-FRET imaging limits its application in fast imaging scenarios. To address this issue, this study proposes a dual-channel structured illumination super-resolution quantitative FRET imaging system and method. By incorporating a FRET dual-channel imaging and registration module into the imaging pathway, spatial switching and channel multiplexing of the SISR-FRET excitation-emission channels are achieved. Combining the image reconstruction algorithm with channel sub-pixel registration correction, the dual-channel SISR-FRET technique enhances the temporal resolution by 3.5 times while preserving the quantitative super-resolution FRET analysis. Experimental results were obtained using a multi-color SIM system to perform super-resolution imaging of living cells expressing mitochondria outer membrane FRET standard plasmids. These experiments validate the improved spatial and temporal resolution of dual-channel SISR-FRET and the fidelity of FRET quantification analysis. In summary, this research presents a novel dual-channel structured illumination super-resolution FRET imaging system and methodology. It overcomes the limitations of slow imaging speed in SISR-FRET by enabling spatial switching and channel multiplexing of excitation-emission channels. The proposed technique enhances the temporal resolution while maintaining quantitative analysis of super-resolution FRET. Experimental validation demonstrates the increased spatial and temporal resolution of dual-channel SISR-FRET and the accuracy of FRET quantification analysis. This advancement contributes to the study of molecular structures and functions in cellular organelles, providing valuable insights into the intricate mechanisms of living cells.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88924264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The problem of sharing quantum correlations is an interesting problem in the study of quantum information theory. Silva et al. proposed the study of sharing quantum nonlocality at first. They studied the fundamental limits on nonlocality, asking whether a single pair of entangled qubits could generate a long sequence of nonlocal correlations. At the same time, the sequential scenario was also introduced first, in which Alice and Bob each have half of a pair of entangled qubit states. The first Bob measures his half and then passes his part to a second Bob who measures again and so on. Obviously, even partial preservation of entanglement in a shared state in spite of a few sequences of local operations performed by the sharing parties can be important for information processing schemes in which entanglement is utilized as a resource. Thus, the problem of sharing quantum entanglement has also been extensively investigated. Recently, C. Srivastava et al. proved that there exist a class of T-states whose entanglement can be shared by arbitrarily many independent observers in[Phys. Rev. A 2022 105 062413]. Here, we want to find whether there are other entangled states that can be shared entanglement arbitrarily many times. In this paper, we consider the problem of sharing quantum entanglement when the initial shared state is a two-qubit entangled Werner state. The goal is to maximize the number of Bobs that can share entanglement with a single Alice. By suitably choosing the entanglement witness operator and the unsharp measurement settings by the Bobs, we prove that there exist two-qubit entangled initial shared Werner states whose entanglement can be detected by arbitrarily many sequential observers Bobs with a single Alice. Then, we also consider the special case of the Werner state, that is, the maximally entangled state as the initial shared state. In this case, its entanglement can also be witnessed arbitrarily many times, and the number of Bobs increases with the decrease of parameter.
{"title":"Sharing entanglement of the Werner state by arbitrarily many independent observers","authors":"Yu Xin-Miao, Yang Shu-Yuan, He Kan","doi":"10.7498/aps.72.20222039","DOIUrl":"https://doi.org/10.7498/aps.72.20222039","url":null,"abstract":"The problem of sharing quantum correlations is an interesting problem in the study of quantum information theory. Silva et al. proposed the study of sharing quantum nonlocality at first. They studied the fundamental limits on nonlocality, asking whether a single pair of entangled qubits could generate a long sequence of nonlocal correlations. At the same time, the sequential scenario was also introduced first, in which Alice and Bob each have half of a pair of entangled qubit states. The first Bob measures his half and then passes his part to a second Bob who measures again and so on. Obviously, even partial preservation of entanglement in a shared state in spite of a few sequences of local operations performed by the sharing parties can be important for information processing schemes in which entanglement is utilized as a resource. Thus, the problem of sharing quantum entanglement has also been extensively investigated. Recently, C. Srivastava et al. proved that there exist a class of T-states whose entanglement can be shared by arbitrarily many independent observers in[Phys. Rev. A 2022 105 062413]. Here, we want to find whether there are other entangled states that can be shared entanglement arbitrarily many times. In this paper, we consider the problem of sharing quantum entanglement when the initial shared state is a two-qubit entangled Werner state. The goal is to maximize the number of Bobs that can share entanglement with a single Alice. By suitably choosing the entanglement witness operator and the unsharp measurement settings by the Bobs, we prove that there exist two-qubit entangled initial shared Werner states whose entanglement can be detected by arbitrarily many sequential observers Bobs with a single Alice. Then, we also consider the special case of the Werner state, that is, the maximally entangled state as the initial shared state. In this case, its entanglement can also be witnessed arbitrarily many times, and the number of Bobs increases with the decrease of parameter.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80719068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jing Chen-Xuan, Shi Sheng-Guo, Yang De-Sen, Zhang Jiang-Yi, Li Song
The scattering of sound waves by underwater vortex flow filed is the basic problem of sound waves propagating in complex flow fields, which has important significance in underwater target detection and sound imaging of flow field. The theoretical analysis model and numerical calculation method are established for the problem of sound scattering modulation in underwater low frequency oscillating vortex flow fields, and the generation mechanism and time frequency and space characteristics of the scattering modulation sound field are explored. Firstly, based on the wave equation of the moving medium, under the first-order approximation, the wave equation is decomposed into the flow-sound coupling term and the non flow-sound coupling term by introducing a potential function, and the flow-sound coupling term is analyzed in the frequency domain, revealing the underwater oscillating vortex flow field. Secondly, the discontinuous Galerkin numerical calculation method is used to solve the wave equation of the moving medium, and the sound propagation process in the underwater low frequency oscillating vortex flow field is numerically simulated. Under the condition of low Mach number, the effects of different incident sound frequency, the oscillation frequency of the vortex flow field and the scale of the vortex core on the time-frequency and space characteristics of the scattering modulating sound fields of vortex flow field are analyzed, and theoretical analysis model is used to explain the characteristics.The research results show that: under the condition of low Mach number, the scattering of sound wave by oscillating vortex flow field can produce a scattering modulated sound field containing the harmonic of oscillating frequency side frequency modulation. The amplitude of the scattered sound pressure changes periodically with time, and the forward scattering is much stronger than the backward scattering. The fundamental frequency scattering modulation is much stronger than the frequency doubling scattering modulation. With the increase of the frequency of the incident sound wave and the scale of the vortex core, the intensity of the scattering modulating sound field increases, and the spatial distribution of the total scattering sound field has symmetry and an obvious main lobe, the main lobe is gradually sharpened, the azimuth angle of the main lobe is close to the propagation direction of the incident wave. When the frequency ratio is much greater than 1, the vortex flow field oscillation frequency has little effect on the spatial distribution of the sound field intensity of scattering modulating sound field.
{"title":"Study on mechanism and characteristics of sound scattering modulation by underwater low frequency oscillating vortex flow field","authors":"Jing Chen-Xuan, Shi Sheng-Guo, Yang De-Sen, Zhang Jiang-Yi, Li Song","doi":"10.7498/aps.72.20221748","DOIUrl":"https://doi.org/10.7498/aps.72.20221748","url":null,"abstract":"The scattering of sound waves by underwater vortex flow filed is the basic problem of sound waves propagating in complex flow fields, which has important significance in underwater target detection and sound imaging of flow field. The theoretical analysis model and numerical calculation method are established for the problem of sound scattering modulation in underwater low frequency oscillating vortex flow fields, and the generation mechanism and time frequency and space characteristics of the scattering modulation sound field are explored. Firstly, based on the wave equation of the moving medium, under the first-order approximation, the wave equation is decomposed into the flow-sound coupling term and the non flow-sound coupling term by introducing a potential function, and the flow-sound coupling term is analyzed in the frequency domain, revealing the underwater oscillating vortex flow field. Secondly, the discontinuous Galerkin numerical calculation method is used to solve the wave equation of the moving medium, and the sound propagation process in the underwater low frequency oscillating vortex flow field is numerically simulated. Under the condition of low Mach number, the effects of different incident sound frequency, the oscillation frequency of the vortex flow field and the scale of the vortex core on the time-frequency and space characteristics of the scattering modulating sound fields of vortex flow field are analyzed, and theoretical analysis model is used to explain the characteristics.The research results show that: under the condition of low Mach number, the scattering of sound wave by oscillating vortex flow field can produce a scattering modulated sound field containing the harmonic of oscillating frequency side frequency modulation. The amplitude of the scattered sound pressure changes periodically with time, and the forward scattering is much stronger than the backward scattering. The fundamental frequency scattering modulation is much stronger than the frequency doubling scattering modulation. With the increase of the frequency of the incident sound wave and the scale of the vortex core, the intensity of the scattering modulating sound field increases, and the spatial distribution of the total scattering sound field has symmetry and an obvious main lobe, the main lobe is gradually sharpened, the azimuth angle of the main lobe is close to the propagation direction of the incident wave. When the frequency ratio is much greater than 1, the vortex flow field oscillation frequency has little effect on the spatial distribution of the sound field intensity of scattering modulating sound field.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83785960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhang Zhen-Chi, Tang Hui-Bo, Wang Jin-Chan, Si Hua-Chong, Wang Zhi, Lan Xiang, Hu Guang-Yue
Diamagnetic cavity and flute instability generated by plasma expansion in an external magnetic field are important phenomena in space and fusion physics.We use a nanosecond laser to irradiate a carbon planar target to generate plasma, and at the same time apply a 7T transverse pulsed strong magnetic field to the plasma. The flute instability generated on the surface of the diamagnetic cavity when the plasma expands in an external magnetic field is studied experimentally. Data analysis shows that under our experimental parameters, the radius of gyration of electrons(ρe) is much smaller than the density gradient scale length of the diamagnetic cavity(Ln), while the ion's gyration radius(ρi) is much larger than Ln, indicating that the electrons are magnetized while the ions are non magnetized. The relative drift between electrons and ions provides free energy for the development of instability.The drift velocity is composed of the gravity drift velocity and the diamagnetic gradient drift velocity. The calculation shows that the gravity drift velocity is much larger than the diamagnetic gradient drift velocity in our experiment, so the instability belongs to the Large Larmor Radius Instability. By filling the target chamber with helium, we found that the background gas can significantly inhibit the development of flute instability. When the background gas pressure exceeds 50Pa (about 1% of the interface plasma density), the flute instability is almost is completely suppressed. Kinetic dispersion equations show that ion-ion collisions and electron-ion collision effects are the main factors that inhibit the development of instability. Calculations on the dispersion equation show that ion-ion collisions are the main factor that inhibits the development of instabilities.
{"title":"Influence of ambient gas to flute instability produced at the interface between laser plasma and external magnetic field","authors":"Zhang Zhen-Chi, Tang Hui-Bo, Wang Jin-Chan, Si Hua-Chong, Wang Zhi, Lan Xiang, Hu Guang-Yue","doi":"10.7498/aps.72.20231108","DOIUrl":"https://doi.org/10.7498/aps.72.20231108","url":null,"abstract":"Diamagnetic cavity and flute instability generated by plasma expansion in an external magnetic field are important phenomena in space and fusion physics.We use a nanosecond laser to irradiate a carbon planar target to generate plasma, and at the same time apply a 7T transverse pulsed strong magnetic field to the plasma. The flute instability generated on the surface of the diamagnetic cavity when the plasma expands in an external magnetic field is studied experimentally. Data analysis shows that under our experimental parameters, the radius of gyration of electrons(ρe) is much smaller than the density gradient scale length of the diamagnetic cavity(Ln), while the ion's gyration radius(ρi) is much larger than Ln, indicating that the electrons are magnetized while the ions are non magnetized. The relative drift between electrons and ions provides free energy for the development of instability.The drift velocity is composed of the gravity drift velocity and the diamagnetic gradient drift velocity. The calculation shows that the gravity drift velocity is much larger than the diamagnetic gradient drift velocity in our experiment, so the instability belongs to the Large Larmor Radius Instability. By filling the target chamber with helium, we found that the background gas can significantly inhibit the development of flute instability. When the background gas pressure exceeds 50Pa (about 1% of the interface plasma density), the flute instability is almost is completely suppressed. Kinetic dispersion equations show that ion-ion collisions and electron-ion collision effects are the main factors that inhibit the development of instability. Calculations on the dispersion equation show that ion-ion collisions are the main factor that inhibits the development of instabilities.","PeriodicalId":6995,"journal":{"name":"Acta Physica Sinica","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83440570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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