Thirty years ago,Coullet et al.proposed that a special optical field exists in laser cavities bearing some analogy with the superfluid vortex.Since then,optical vortices have been widely studied,inspired by the hydrod...Thirty years ago,Coullet et al.proposed that a special optical field exists in laser cavities bearing some analogy with the superfluid vortex.Since then,optical vortices have been widely studied,inspired by the hydrodynamics sharing similar mathematics.Akin to a fluid vortex with a central flow singularity,an optical vortex beam has a phase singularity with a certain topological charge,giving rise to a hollow intensity distribution.Such a beam with helical phase fronts and orbital angular momentum reveals a subtle connection between macroscopic physical optics and microscopic quantum optics.These amazing properties provide a new understanding of a wide range of optical and physical phenomena,including twisting photons,spin–orbital interactions,Bose-Einstein condensates,etc.,while the associated technologies for manipulating optical vortices have become increasingly tunable and flexible.Hitherto,owing to these salient properties and optical manipulation technologies,tunable vortex beams have engendered tremendous advanced applications such as optical tweezers,high-order quantum entanglement,and nonlinear optics.This article reviews the recent progress in tunable vortex technologies along with their advanced applications.展开更多
In this paper,we propose enhancements to Beetle Antennae search(BAS)algorithm,called BAS-ADAIVL to smoothen the convergence behavior and avoid trapping in localminima for a highly noin-convex objective function.We ach...In this paper,we propose enhancements to Beetle Antennae search(BAS)algorithm,called BAS-ADAIVL to smoothen the convergence behavior and avoid trapping in localminima for a highly noin-convex objective function.We achieve this by adaptively adjusting the step-size in each iteration using the adaptive moment estimation(ADAM)update rule.The proposed algorithm also increases the convergence rate in a narrow valley.A key feature of the ADAM update rule is the ability to adjust the step-size for each dimension separately instead of using the same step-size.Since ADAM is traditionally used with gradient-based optimization algorithms,therefore we first propose a gradient estimation model without the need to differentiate the objective function.Resultantly,it demonstrates excellent performance and fast convergence rate in searching for the optimum of noin-convex functions.The efficiency of the proposed algorithm was tested on three different benchmark problems,including the training of a high-dimensional neural network.The performance is compared with particle swarm optimizer(PSO)and the original BAS algorithm.展开更多
In situ strain photoluminescence （PL） and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition （CVD）-grown...In situ strain photoluminescence （PL） and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition （CVD）-grown monolayer tungsten disulphide （WS2） under uniaxial tensile strain. Observable broadening and appearance of an extra small feature at the longer-wavelength side shoulder of the PL peak occur under 2.5% strain, which could indicate the direct-indirect bandgap transition and is further confirmed by our density-functional-theory calculations. As the strain increases further, the spectral weight of the indirect transition gradually increases. Over the entire strain range, with the increase of the strain, the light emissions corresponding to each optical transition, such as the direct bandgap transition （K-K） and indirect bandgap transition （F-K, ≥2.5%）, exhibit a monotonous linear redshift. In addition, the binding energy of the indirect transition is found to be larger than that of the direct transition, and the slight lowering of the trion dissociation energy with increasing strain is observed. The strain was used to modulate not only the electronic band structure but also the lattice vibrations. The softening and splitting of the in-plane E＇ mode is observed under uniaxial tensile strain, and polarization-dependent Raman spectroscopy confirms the observed zigzag-oriented edge of WS2 grown by CVD in previous studies. These findings enrich our understanding of the strained states of monolayer transition-metal dichalcogenide （TMD） materials and lay a foundation for developing applications exploiting their strain-dependent optical properties, including the strain detection and light-emission modulation of such emerging two-dimensional TMDs.展开更多
As the fifth-generation(5G)mobile communication network may not meet the requirements of emerging technologies and applications,including ubiquitous coverage,industrial internet of things(IIoT),ubiquitous artificial i...As the fifth-generation(5G)mobile communication network may not meet the requirements of emerging technologies and applications,including ubiquitous coverage,industrial internet of things(IIoT),ubiquitous artificial intelligence(AI),digital twins(DT),etc.,this paper aims to explore a novel space-air-ground integrated network(SAGIN)architecture to support these new requirements for the sixth-generation(6G)mobile communication network in a flexible,low-latency and efficient manner.Specifically,we first review the evolution of the mobile communication network,followed by the application and technology requirements of 6G.Then the current 5G non-terrestrial network(NTN)architecture in supporting the new requirements is deeply analyzed.After that,we proposes a new flexible,low-latency and flat SAGIN architecture,and presents corresponding use cases.Finally,the future research directions are discussed.展开更多
A new method based on principal component analysis (PCA) and support vector machines (SVMs) is proposed for fault diagnosis of mine hoists. PCA is used to extract the principal features associated with the gearbox. Th...A new method based on principal component analysis (PCA) and support vector machines (SVMs) is proposed for fault diagnosis of mine hoists. PCA is used to extract the principal features associated with the gearbox. Then, with the irrelevant gearbox variables removed, the remaining gearbox, the hydraulic system and the wire rope parameters were used as input to a multi-class SVM. The SVM is first trained by using the one class-based multi-class optimization algorithm and it is then applied to fault identification. Comparison of various methods showed the PCA-SVM method successfully removed redundancy to solve the dimensionality curse. These results show that the algorithm using the RBF kernel function for the SVM had the best classification properties.展开更多
Research on two-dimensional(2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since ...Research on two-dimensional(2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since the mechanical exfoliation of graphene in 2004. Starting from graphene, 2D materials now have become a big family with numerous members and diverse categories. The unique structural features and physicochemical properties of 2D materials make them one class of the most appealing candidates for a wide range of potential applications. In particular, we have seen some major breakthroughs made in the field of 2D materials in last five years not only in developing novel synthetic methods and exploring new structures/properties but also in identifying innovative applications and pushing forward commercialisation. In this review, we provide a critical summary on the recent progress made in the field of 2D materials with a particular focus on last five years. After a brief backgroundintroduction, we first discuss the major synthetic methods for 2D materials, including the mechanical exfoliation, liquid exfoliation, vapor phase deposition, and wet-chemical synthesis as well as phase engineering of 2D materials belonging to the field of phase engineering of nanomaterials(PEN). We then introduce the superconducting/optical/magnetic properties and chirality of 2D materials along with newly emerging magic angle 2D superlattices. Following that, the promising applications of 2D materials in electronics, optoelectronics, catalysis, energy storage, solar cells, biomedicine, sensors, environments, etc. are described sequentially. Thereafter, we present the theoretic calculations and simulations of 2D materials. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future outlooks in this rapidly developing field.展开更多
Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects...Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects, etc.Herein, we summarize recent advantages in graphene preparation, sensor construction, and sensing properties of various graphene-based gas/vapor sensors, such as NH_3, NO_2, H_2, CO, SO_2, H_2S, as well as vapor of volatile organic compounds.The detection mechanisms pertaining to various gases are also discussed. In conclusion part, some existing problems which may hinder the sensor applications are presented. Several possible methods to solve these problems are proposed, for example, conceived solutions, hybrid nanostructures, multiple sensor arrays, and new recognition algorithm.展开更多
AltBOC(15,10) is the baseline of COMPASS B2 signal modulation.It is a BOC-like signal having different PN codes in the lower and the upper main split lobes,which allow one signal service per lobe.The two lobes can be ...AltBOC(15,10) is the baseline of COMPASS B2 signal modulation.It is a BOC-like signal having different PN codes in the lower and the upper main split lobes,which allow one signal service per lobe.The two lobes can be received and processed separately like two BPSK(10) signals,or coherently processed to achieve better performance.Interoperability among COMPASS B2,Galileo E5 and GPS L5 is also achievable using AltBOC modulation.However,Galileo's 4-code AltBOC has drawbacks such as low efficiency and great receiver complexity.This paper presents a new modulation type named TD-AltBOC (Time Division AltBOC).The signal generation scheme and receiving method are presented,and are compared with AltBOC in the areas of power spectrum,ranging accuracy,anti-multipath performance,anti-interference performance,processing flexibility and complexity.Analysis results show TD-AltBOC has similar spectrum characteristics,interoperability,flexibility and anti-interference performance with AltBOC.When the frontend bandwidth is more than 50 MHz,TD-AltBOC can achieve better ranging accuracy and anti-multipath performance.It also has such advantages as high efficiency and low receiver complexity.TD-AltBOC could be a good solution to COMPASS B2 navigation signal.展开更多
In this paper we present the enhanced X-ray Timing and Polarimetry mission—eXTP. eXTP is a space science mission designed to study fundamental physics under extreme conditions of density, gravity and magnetism. The m...In this paper we present the enhanced X-ray Timing and Polarimetry mission—eXTP. eXTP is a space science mission designed to study fundamental physics under extreme conditions of density, gravity and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring effects of QED, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, eXTP will be a very powerful observatory for astrophysics that will provide observations of unprecedented quality on a variety of galactic and extragalactic objects. In particular, its wide field monitoring capabilities will be highly instrumental to detect the electro-magnetic counterparts of gravitational wave sources.The paper provides a detailed description of:(1) the technological and technical aspects, and the expected performance of the instruments of the scientific payload;(2) the elements and functions of the mission, from the spacecraft to the ground segment.展开更多
The quickly increasing data transfer load requires an urgent revolution in current optical communication. Orbital angular momentum(OAM) multiplexing is a potential candidate with its ability to considerably enhance th...The quickly increasing data transfer load requires an urgent revolution in current optical communication. Orbital angular momentum(OAM) multiplexing is a potential candidate with its ability to considerably enhance the capacity of communication. However, the lack of a compact, efficient, and integrated OAM(de)multiplexer prevents it from being widely applied. By attaching vortex gratings onto the facets of a few-mode fiber, we demonstrate an integrated fiber-based OAM(de)multiplexer. A vortex grating fabricated on the fiber facet enables the direct multiplexing of OAM states at one port and the demultiplexing of OAM states at the other port. The measured bit error rate of the carrier signal after propagating through a 5-km few-mode fiber confirms the validity and effectiveness of the proposed approach. The scheme offers advantages in future high-capacity OAM communication based on optical fiber.展开更多
The demanding objectives for the future sixth generation(6G)of wireless communication networks have spurred recent research efforts on novel materials and radio-frequency front-end architectures for wireless connectiv...The demanding objectives for the future sixth generation(6G)of wireless communication networks have spurred recent research efforts on novel materials and radio-frequency front-end architectures for wireless connectivity,as well as revolutionary communication and computing paradigms.Among the pioneering candidate technologies for 6G belong the reconfigurable intelligent surfaces(RISs),which are artificial planar structures with integrated electronic circuits that can be programmed to manipulate the incoming electromagnetic field in a wide variety of functionalities.Incorporating RISs in wireless networks have been recently advocated as a revolutionary means to transform any wireless signal propagation environment to a dynamically programmable one,intended for various networking objectives,such as coverage extension and capacity boosting,spatiotemporal focusing with benefits in energy efficiency and secrecy,and low electromagnetic field exposure.Motivated by the recent increasing interests in the field of RISs and the consequent pioneering concept of the RIS-enabled smart wireless environments,in this paper,we overview and taxonomize the latest advances in RIS hardware architectures as well as the most recent developments in the modeling of RIS unit elements and RIS-empowered wireless signal propagation.We also present a thorough overview of the channel estimation approaches for RIS-empowered communications systems,which constitute a prerequisite step for the optimized incorporation of RISs in future wireless networks.Finally,we discuss the relevance of the RIS technology in the latest wireless communication standards,and highlight the current and future standardization activities for the RIS technology and the consequent RIS-empowered wireless networking approaches.展开更多
Metasurfaces have found broad applicability in free-space optics,while its potential to tailor guided waves remains barely explored.By synergizing the Jones matrix model with generalized Snell’s law under the phase-m...Metasurfaces have found broad applicability in free-space optics,while its potential to tailor guided waves remains barely explored.By synergizing the Jones matrix model with generalized Snell’s law under the phase-matching condition,we propose a universal design strategy for versatile on-chip mode-selective coupling with polarization sensitivity,multiple working wavelengths,and high efficiency concurrently.The coupling direction,operation frequency,and excited mode type can be designed at will for arbitrary incident polarizations,outperforming previous technology that only works for specific polarizations and lacks versatile mode controllability.Here,using silicon-nanoantenna-patterned silicon-nitride photonic waveguides,we numerically demonstrate a set of chip-scale optical couplers around 1.55μm,including mode-selective directional couplers with high coupling efficiency over 57%and directivity about 23 d B.Polarization and wavelength demultiplexer scenarios are also proposed with 67%maximum efficiency and an extinction ratio of 20 d B.Moreover,a chip-integrated twisted light generator,coupling free-space linear polarization into an optical vortex carrying 1 h orbital angular momentum(OAM),is also reported to validate the mode-control flexibility.This comprehensive method may motivate compact wavelength/polarization(de)multiplexers,multifunctional mode converters,on-chip OAM generators for photonic integrated circuits,and high-speed optical telecommunications.展开更多
Due to their superior hydrophilicity and conductivity,ultra-high volumetric capacitance,and rich surface-chemistry properties,MXenes exhibit unique and excellent performance in catalysis,energy storage,electromagnetic...Due to their superior hydrophilicity and conductivity,ultra-high volumetric capacitance,and rich surface-chemistry properties,MXenes exhibit unique and excellent performance in catalysis,energy storage,electromagnetic shielding,and life sciences.Since they are derived from ceramics(MAX phase)through etching,one of the challenges in MXenes preparation is the inevitable exposure of metal atoms on their surface and embedding of anions and cations.Because the as-obtained MXenes are always in a thermodynamically metastable state,they tend to react with trace oxygen or oxygen-containing groups to form metal oxides or degrade,leading to sharply declined activity and impaired performance.Therefore,improving the stability of MXenesbased materials is of practical significance in relevant applications.Unfortunately,there lacks a comprehensive review in the literature on relevant topics.To help promote the wide applications of MXenes,we review from the following aspects:(i)insights into the factors affecting the stability of MXenes-based materials,including oxidation of MXenes flakes,stability of MXenes colloidal solutions,and swelling and degradation of MXenes thin-film,(ii)strategies for enhancing the stability of MXenes-based materials by optimizing MAX phase synthesis and modifying the MXenes preparation,and(iii)techniques for further increasing the stability of freshly prepared MXenes-based materials via controlling the storage conditions,and forming shielding on the surface and/or edge of MXenes flakes.Finally,some outlooks are proposed on the future developments and challenges of highly active and stable MXenes.We aim to provide guidance for the design,preparation,and applications of MXenes-based materials with excellent stability and activity.展开更多
The Firefly Algorithm(FA)is a highly efficient population-based optimization technique developed by mimicking the flashing behavior of fireflies when mating.This article proposes a method based on Differential Evoluti...The Firefly Algorithm(FA)is a highly efficient population-based optimization technique developed by mimicking the flashing behavior of fireflies when mating.This article proposes a method based on Differential Evolution(DE)/current-to-best/1 for enhancing the FA's movement process.The proposed modification increases the global search ability and the convergence rates while maintaining a balance between exploration and exploitation by deploying the global best solution.However,employing the best solution can lead to premature algorithm convergence,but this study handles this issue using a loop adjacent to the algorithm's main loop.Additionally,the suggested algorithm’s sensitivity to the alpha parameter is reduced compared to the original FA.The GbFA surpasses both the original and five-version of enhanced FAs in finding the optimal solution to 30 CEC2014 real parameter benchmark problems with all selected alpha values.Additionally,the CEC 2017 benchmark functions and the eight engineering optimization challenges are also utilized to evaluate GbFA’s efficacy and robustness on real-world problems against several enhanced algorithms.In all cases,GbFA provides the optimal result compared to other methods.Note that the source code of the GbFA algorithm is publicly available at https://www.optim-app.com/projects/gbfa.展开更多
The advancement of contemporary X-ray imaging heavily depends on discovering scintillators that possess high sensitivity,robust stability,low toxicity,and a uniform size distribution.Despite significant progress in th...The advancement of contemporary X-ray imaging heavily depends on discovering scintillators that possess high sensitivity,robust stability,low toxicity,and a uniform size distribution.Despite significant progress in this field,the discovery of a material that satisfies all of these criteria remains a challenge.In this study,we report the synthesis of monodisperse copper(Ⅰ)-iodide cluster microcubes as a new class of X-ray scintillators.The as-prepared microcubes exhibit remarkable sensitivity to X-rays and exceptional stability under moisture and X-ray exposure.The uniform size distribution and high scintillation performance of the copper(Ⅰ)-iodide cluster microcubes make them suitable for the fabrication of large-area,flexible scintillating films for X-ray imaging applications in both static and dynamic settings.展开更多
Potassium-ion batteries(PIBs)are appealing alternatives to conventional lithium-ion batteries(LIBs)because of their wide potential window,fast ionic conductivity in the electrolyte,and reduced cost.However,PIBs suffer...Potassium-ion batteries(PIBs)are appealing alternatives to conventional lithium-ion batteries(LIBs)because of their wide potential window,fast ionic conductivity in the electrolyte,and reduced cost.However,PIBs suffer from sluggish K+reaction kinetics in electrode materials,large volume expansion of electroactive materials,and the unstable solid electrolyte interphase.Various strategies,especially in terms of electrode design,have been proposed to address these issues.In this review,the recent progress on advanced anode materials of PIBs is systematically discussed,ranging from the design principles,and nanoscale fabrication and engineering to the structure-performance relationship.Finally,the remaining limitations,potential solutions,and possible research directions for the development of PIBs towards practical applications are presented.This review will provide new insights into the lab development and real-world applications of PIBs.展开更多
Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our pre...Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our previous work [Acta Phys. Sin. 61 174301 （2012）], an analytical model to predict the sound absorption from vibrational relaxation in a gas medium is proposed. In this paper, we develop the model to decouple the V-V coupled energy to each vibrationaltranslational deexcitation path, and analyze how the multimode relaxations form the peaks of sound absorption spectra in gas mixtures. We prove that a multimode relaxation is the sum of its decoupled single-relaxation processes, and only the decoupled process with a significant isochoric-molar-heat can be observed as an absorption peak. The decoupling model clarifies the essential processes behind the peaks in spectra arising from the multimode relaxations in multi-component gas mixtures. The simulation validates the proposed decoupling model.展开更多
The paper proposes an on-line signature verification algorithm, through which test sample and template signatures can be optimizedly matched, based on evolutionary computation （EC）. Firstly, the similarity of signat...The paper proposes an on-line signature verification algorithm, through which test sample and template signatures can be optimizedly matched, based on evolutionary computation （EC）. Firstly, the similarity of signature curve segment is defined, and shift and scale transforms are also introduced due to the randoness of on-line signature. Secondly, this paper puts forward signature verification matching algorithm after establishment of the mathematical model. Thirdly, the concrete realization of the algorithm based on EC is discussed as well. In addition, the influence of shift and scale on the matching result is fully considered in the algorithm. Finally, a computation example is given, and the matching results between the test sample curve and the template signature curve are analyzed in detail, The preliminary experiments reveal that the type of signature verification problem can be solved by EC.展开更多
基金funded by The National Key Research and Development Program of China(Grant No.2017YFB1104500)Natural Science Foundation of Beijing Municipality(4172030)+3 种基金Beijing Young Talents Support Project(2017000020124G044)Leading talents of Guangdong province program(00201505)National Natural Science Foundation of China(U1701661,91750205,61975133,11604218,61975087)Natural Science Foundation of Guangdong Province(2016A030312010,2017A030313351).
文摘Thirty years ago,Coullet et al.proposed that a special optical field exists in laser cavities bearing some analogy with the superfluid vortex.Since then,optical vortices have been widely studied,inspired by the hydrodynamics sharing similar mathematics.Akin to a fluid vortex with a central flow singularity,an optical vortex beam has a phase singularity with a certain topological charge,giving rise to a hollow intensity distribution.Such a beam with helical phase fronts and orbital angular momentum reveals a subtle connection between macroscopic physical optics and microscopic quantum optics.These amazing properties provide a new understanding of a wide range of optical and physical phenomena,including twisting photons,spin–orbital interactions,Bose-Einstein condensates,etc.,while the associated technologies for manipulating optical vortices have become increasingly tunable and flexible.Hitherto,owing to these salient properties and optical manipulation technologies,tunable vortex beams have engendered tremendous advanced applications such as optical tweezers,high-order quantum entanglement,and nonlinear optics.This article reviews the recent progress in tunable vortex technologies along with their advanced applications.
基金Supported by State Key Program of National Natural Science Foundation of China （60834001） and National Natural Science Foundation of China （60774022）.Acknowledgement Authors would like to thank NSFC organizers and participants who shared their ideas and works with us during the NSFC workshop on data-based control, decision making, scheduling, and fault diagnosis. In particular, authors would like to thank Chai Tian-You, Sun You-Xian, Wang Hong, Yan Hong-Sheng, and Gao Fu-Rong for discussing the concept on design model shown in Fig. 12, the concept on temporal multi-scale shown in Fig. 8, the concept on fault diagnosis shown in Fig. 14, the concept on dynamic scheduling shown in Fig. 15, and the concept on interval model shown in Fig. 16, respectively.
文摘In this paper,we propose enhancements to Beetle Antennae search(BAS)algorithm,called BAS-ADAIVL to smoothen the convergence behavior and avoid trapping in localminima for a highly noin-convex objective function.We achieve this by adaptively adjusting the step-size in each iteration using the adaptive moment estimation(ADAM)update rule.The proposed algorithm also increases the convergence rate in a narrow valley.A key feature of the ADAM update rule is the ability to adjust the step-size for each dimension separately instead of using the same step-size.Since ADAM is traditionally used with gradient-based optimization algorithms,therefore we first propose a gradient estimation model without the need to differentiate the objective function.Resultantly,it demonstrates excellent performance and fast convergence rate in searching for the optimum of noin-convex functions.The efficiency of the proposed algorithm was tested on three different benchmark problems,including the training of a high-dimensional neural network.The performance is compared with particle swarm optimizer(PSO)and the original BAS algorithm.
基金This work is supported by the Singapore National Research Foundation NRF RF Award No. NRFRF2010- 07, MOE Tier 2 MOE2012-T2-2-049, A＇Star SERC PSF grant No. 1321202101, and MOE Tier 1 MOE2013- T1-2-235. W. Huang acknowledges the support of the National Basic Research Program of China （973 Program） （No. 2015CB932200）, the National Natural Science Foundation of China （NSFC） （Grant Nos. 21144004, 20974046, 21101095, 21003076, 20774043, 51173081, 50428303, 61136003, and 50428303）, the Ministry of Education of China （No. IRT1148）, the NSF of Jiangsu Province （Grant Nos. SBK201122680, 11KJB510017, BK2008053, 11KJB510017, BK2009025, 10KJB510013, and BZ2010043）, and NUPT （Nos. NY210030 and NY211022）. J. R Wang is grateful for the NSFC （No. 11474164）, NSF of Jiangsu province （No. BK20131413）, and the Jiangsu Specially-Appointed Professor program. Y. L. Wang thanks Luqing Wang, Dr. Xiaolong Zou, and Dr. Alex Kutana for the constructive discussion.
文摘In situ strain photoluminescence （PL） and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition （CVD）-grown monolayer tungsten disulphide （WS2） under uniaxial tensile strain. Observable broadening and appearance of an extra small feature at the longer-wavelength side shoulder of the PL peak occur under 2.5% strain, which could indicate the direct-indirect bandgap transition and is further confirmed by our density-functional-theory calculations. As the strain increases further, the spectral weight of the indirect transition gradually increases. Over the entire strain range, with the increase of the strain, the light emissions corresponding to each optical transition, such as the direct bandgap transition （K-K） and indirect bandgap transition （F-K, ≥2.5%）, exhibit a monotonous linear redshift. In addition, the binding energy of the indirect transition is found to be larger than that of the direct transition, and the slight lowering of the trion dissociation energy with increasing strain is observed. The strain was used to modulate not only the electronic band structure but also the lattice vibrations. The softening and splitting of the in-plane E＇ mode is observed under uniaxial tensile strain, and polarization-dependent Raman spectroscopy confirms the observed zigzag-oriented edge of WS2 grown by CVD in previous studies. These findings enrich our understanding of the strained states of monolayer transition-metal dichalcogenide （TMD） materials and lay a foundation for developing applications exploiting their strain-dependent optical properties, including the strain detection and light-emission modulation of such emerging two-dimensional TMDs.
基金supported in part by the National Key Research and Development Program under grant number 2020YFB1806800the Beijing Natural Science Foundation under grant number L212003the National Natural Science Foundation of China(NSFC)under grant numbers 62171010 and 61827901.
文摘As the fifth-generation(5G)mobile communication network may not meet the requirements of emerging technologies and applications,including ubiquitous coverage,industrial internet of things(IIoT),ubiquitous artificial intelligence(AI),digital twins(DT),etc.,this paper aims to explore a novel space-air-ground integrated network(SAGIN)architecture to support these new requirements for the sixth-generation(6G)mobile communication network in a flexible,low-latency and efficient manner.Specifically,we first review the evolution of the mobile communication network,followed by the application and technology requirements of 6G.Then the current 5G non-terrestrial network(NTN)architecture in supporting the new requirements is deeply analyzed.After that,we proposes a new flexible,low-latency and flat SAGIN architecture,and presents corresponding use cases.Finally,the future research directions are discussed.
基金Project 06KJD470182 supported by the Jiangsu Educational Natural Science Foundation of china
文摘A new method based on principal component analysis (PCA) and support vector machines (SVMs) is proposed for fault diagnosis of mine hoists. PCA is used to extract the principal features associated with the gearbox. Then, with the irrelevant gearbox variables removed, the remaining gearbox, the hydraulic system and the wire rope parameters were used as input to a multi-class SVM. The SVM is first trained by using the one class-based multi-class optimization algorithm and it is then applied to fault identification. Comparison of various methods showed the PCA-SVM method successfully removed redundancy to solve the dimensionality curse. These results show that the algorithm using the RBF kernel function for the SVM had the best classification properties.
文摘Research on two-dimensional(2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since the mechanical exfoliation of graphene in 2004. Starting from graphene, 2D materials now have become a big family with numerous members and diverse categories. The unique structural features and physicochemical properties of 2D materials make them one class of the most appealing candidates for a wide range of potential applications. In particular, we have seen some major breakthroughs made in the field of 2D materials in last five years not only in developing novel synthetic methods and exploring new structures/properties but also in identifying innovative applications and pushing forward commercialisation. In this review, we provide a critical summary on the recent progress made in the field of 2D materials with a particular focus on last five years. After a brief backgroundintroduction, we first discuss the major synthetic methods for 2D materials, including the mechanical exfoliation, liquid exfoliation, vapor phase deposition, and wet-chemical synthesis as well as phase engineering of 2D materials belonging to the field of phase engineering of nanomaterials(PEN). We then introduce the superconducting/optical/magnetic properties and chirality of 2D materials along with newly emerging magic angle 2D superlattices. Following that, the promising applications of 2D materials in electronics, optoelectronics, catalysis, energy storage, solar cells, biomedicine, sensors, environments, etc. are described sequentially. Thereafter, we present the theoretic calculations and simulations of 2D materials. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future outlooks in this rapidly developing field.
基金financial supports provided by the National Basic Research Program of China(2013CB932500)the National Natural Science Foundation of China(21171117 and 61574091)+3 种基金the Program for New Century Excellent Talents in University(NCET-12-0356)the Program of Shanghai Academic/Technology Research Leader(15XD1525200)Shanghai Jiao Tong University Agri-X Funding(Agri-X2015007)the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning
文摘Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects, etc.Herein, we summarize recent advantages in graphene preparation, sensor construction, and sensing properties of various graphene-based gas/vapor sensors, such as NH_3, NO_2, H_2, CO, SO_2, H_2S, as well as vapor of volatile organic compounds.The detection mechanisms pertaining to various gases are also discussed. In conclusion part, some existing problems which may hinder the sensor applications are presented. Several possible methods to solve these problems are proposed, for example, conceived solutions, hybrid nanostructures, multiple sensor arrays, and new recognition algorithm.
文摘AltBOC(15,10) is the baseline of COMPASS B2 signal modulation.It is a BOC-like signal having different PN codes in the lower and the upper main split lobes,which allow one signal service per lobe.The two lobes can be received and processed separately like two BPSK(10) signals,or coherently processed to achieve better performance.Interoperability among COMPASS B2,Galileo E5 and GPS L5 is also achievable using AltBOC modulation.However,Galileo's 4-code AltBOC has drawbacks such as low efficiency and great receiver complexity.This paper presents a new modulation type named TD-AltBOC (Time Division AltBOC).The signal generation scheme and receiving method are presented,and are compared with AltBOC in the areas of power spectrum,ranging accuracy,anti-multipath performance,anti-interference performance,processing flexibility and complexity.Analysis results show TD-AltBOC has similar spectrum characteristics,interoperability,flexibility and anti-interference performance with AltBOC.When the frontend bandwidth is more than 50 MHz,TD-AltBOC can achieve better ranging accuracy and anti-multipath performance.It also has such advantages as high efficiency and low receiver complexity.TD-AltBOC could be a good solution to COMPASS B2 navigation signal.
基金support of the Chinese Academy of Sciences through the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA15020100)support by ASI, under the dedicated eXTP agreements and agreement ASI-INAF (Grant No. 2017-14-H.O.)+3 种基金by INAF and INFN under project REDSOXsupport from the Deutsche Zentrum für Luft- und Raumfahrt, the German Aerospce Center (DLR)support of Science Centre (Grant No. 2013/10/M/ST9/00729)support from MINECO (Grant No. ESP2017-82674-R) and FEDER funds
文摘In this paper we present the enhanced X-ray Timing and Polarimetry mission—eXTP. eXTP is a space science mission designed to study fundamental physics under extreme conditions of density, gravity and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring effects of QED, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, eXTP will be a very powerful observatory for astrophysics that will provide observations of unprecedented quality on a variety of galactic and extragalactic objects. In particular, its wide field monitoring capabilities will be highly instrumental to detect the electro-magnetic counterparts of gravitational wave sources.The paper provides a detailed description of:(1) the technological and technical aspects, and the expected performance of the instruments of the scientific payload;(2) the elements and functions of the mission, from the spacecraft to the ground segment.
基金National Natural Science Foundation of China(NSFC)(U1701661,61427819,61525502,61435006,11604218,61601199,61775085,61405121)Science and Technology Innovation Commission of Shenzhen(KQCS2015032416183980,KQJSCX20160226193555889,KQTD2015071016560101,KQTD2017033011044403,ZDSYS201703031605029)+2 种基金Leading Talents of Guangdong Province(00201505)Natural Science Foundation of Guangdong Province(2016A030312010,2017A030313351)National Key Basic Research Program of China(973)(2015CB352004)
文摘The quickly increasing data transfer load requires an urgent revolution in current optical communication. Orbital angular momentum(OAM) multiplexing is a potential candidate with its ability to considerably enhance the capacity of communication. However, the lack of a compact, efficient, and integrated OAM(de)multiplexer prevents it from being widely applied. By attaching vortex gratings onto the facets of a few-mode fiber, we demonstrate an integrated fiber-based OAM(de)multiplexer. A vortex grating fabricated on the fiber facet enables the direct multiplexing of OAM states at one port and the demultiplexing of OAM states at the other port. The measured bit error rate of the carrier signal after propagating through a 5-km few-mode fiber confirms the validity and effectiveness of the proposed approach. The scheme offers advantages in future high-capacity OAM communication based on optical fiber.
基金supported by the EU H2020 Industrial Leadership Project(No.101017011)the Scientific and Technological Research Council of Turkey(TUBITAK)(No.120E401).
文摘The demanding objectives for the future sixth generation(6G)of wireless communication networks have spurred recent research efforts on novel materials and radio-frequency front-end architectures for wireless connectivity,as well as revolutionary communication and computing paradigms.Among the pioneering candidate technologies for 6G belong the reconfigurable intelligent surfaces(RISs),which are artificial planar structures with integrated electronic circuits that can be programmed to manipulate the incoming electromagnetic field in a wide variety of functionalities.Incorporating RISs in wireless networks have been recently advocated as a revolutionary means to transform any wireless signal propagation environment to a dynamically programmable one,intended for various networking objectives,such as coverage extension and capacity boosting,spatiotemporal focusing with benefits in energy efficiency and secrecy,and low electromagnetic field exposure.Motivated by the recent increasing interests in the field of RISs and the consequent pioneering concept of the RIS-enabled smart wireless environments,in this paper,we overview and taxonomize the latest advances in RIS hardware architectures as well as the most recent developments in the modeling of RIS unit elements and RIS-empowered wireless signal propagation.We also present a thorough overview of the channel estimation approaches for RIS-empowered communications systems,which constitute a prerequisite step for the optimized incorporation of RISs in future wireless networks.Finally,we discuss the relevance of the RIS technology in the latest wireless communication standards,and highlight the current and future standardization activities for the RIS technology and the consequent RIS-empowered wireless networking approaches.
基金National Natural Science Foundation of China(61675114,61875103,61935013,61975133,U1701661)Natural Science Foundation of Beijing Municipality(501100004826)+1 种基金Tsinghua University Initiative Scientific Research Program(20151080709)Beijing Young Talents Support Project(2017000020124G044)。
文摘Metasurfaces have found broad applicability in free-space optics,while its potential to tailor guided waves remains barely explored.By synergizing the Jones matrix model with generalized Snell’s law under the phase-matching condition,we propose a universal design strategy for versatile on-chip mode-selective coupling with polarization sensitivity,multiple working wavelengths,and high efficiency concurrently.The coupling direction,operation frequency,and excited mode type can be designed at will for arbitrary incident polarizations,outperforming previous technology that only works for specific polarizations and lacks versatile mode controllability.Here,using silicon-nanoantenna-patterned silicon-nitride photonic waveguides,we numerically demonstrate a set of chip-scale optical couplers around 1.55μm,including mode-selective directional couplers with high coupling efficiency over 57%and directivity about 23 d B.Polarization and wavelength demultiplexer scenarios are also proposed with 67%maximum efficiency and an extinction ratio of 20 d B.Moreover,a chip-integrated twisted light generator,coupling free-space linear polarization into an optical vortex carrying 1 h orbital angular momentum(OAM),is also reported to validate the mode-control flexibility.This comprehensive method may motivate compact wavelength/polarization(de)multiplexers,multifunctional mode converters,on-chip OAM generators for photonic integrated circuits,and high-speed optical telecommunications.
基金supported by the National Natural Science Foundation of China(Nos.62004143 and 62174085)the Central Government Guided Local Science and Technology Development Special Fund Project(No.2020ZYYD033)+2 种基金the China Postdoctoral Science Foundation(No.2019M660607)the Opening Fund of Key Laboratory of Rare Mineral,Ministry of Natural Resources(No.KLRM-KF 202005)the open research fund of State Key Laboratory of Organic Electronics and Information Displays.
文摘Due to their superior hydrophilicity and conductivity,ultra-high volumetric capacitance,and rich surface-chemistry properties,MXenes exhibit unique and excellent performance in catalysis,energy storage,electromagnetic shielding,and life sciences.Since they are derived from ceramics(MAX phase)through etching,one of the challenges in MXenes preparation is the inevitable exposure of metal atoms on their surface and embedding of anions and cations.Because the as-obtained MXenes are always in a thermodynamically metastable state,they tend to react with trace oxygen or oxygen-containing groups to form metal oxides or degrade,leading to sharply declined activity and impaired performance.Therefore,improving the stability of MXenesbased materials is of practical significance in relevant applications.Unfortunately,there lacks a comprehensive review in the literature on relevant topics.To help promote the wide applications of MXenes,we review from the following aspects:(i)insights into the factors affecting the stability of MXenes-based materials,including oxidation of MXenes flakes,stability of MXenes colloidal solutions,and swelling and degradation of MXenes thin-film,(ii)strategies for enhancing the stability of MXenes-based materials by optimizing MAX phase synthesis and modifying the MXenes preparation,and(iii)techniques for further increasing the stability of freshly prepared MXenes-based materials via controlling the storage conditions,and forming shielding on the surface and/or edge of MXenes flakes.Finally,some outlooks are proposed on the future developments and challenges of highly active and stable MXenes.We aim to provide guidance for the design,preparation,and applications of MXenes-based materials with excellent stability and activity.
文摘The Firefly Algorithm(FA)is a highly efficient population-based optimization technique developed by mimicking the flashing behavior of fireflies when mating.This article proposes a method based on Differential Evolution(DE)/current-to-best/1 for enhancing the FA's movement process.The proposed modification increases the global search ability and the convergence rates while maintaining a balance between exploration and exploitation by deploying the global best solution.However,employing the best solution can lead to premature algorithm convergence,but this study handles this issue using a loop adjacent to the algorithm's main loop.Additionally,the suggested algorithm’s sensitivity to the alpha parameter is reduced compared to the original FA.The GbFA surpasses both the original and five-version of enhanced FAs in finding the optimal solution to 30 CEC2014 real parameter benchmark problems with all selected alpha values.Additionally,the CEC 2017 benchmark functions and the eight engineering optimization challenges are also utilized to evaluate GbFA’s efficacy and robustness on real-world problems against several enhanced algorithms.In all cases,GbFA provides the optimal result compared to other methods.Note that the source code of the GbFA algorithm is publicly available at https://www.optim-app.com/projects/gbfa.
基金This work is supported by the National Key and Program of China(grant number 2020YFA0709900)the National Natural Science Foundation of China(grant numbers 22075228 and 62134007)+1 种基金the Joint Research Funds of the Department of Science&Technology of Shaanxi Province and Northwestern Polytechnical University(grant number 2020GXLH-Z011)the Fundamental Research Funds for the Central Universities(grant numbers 0515023GH0202078 and 0515023SH0201078).
文摘The advancement of contemporary X-ray imaging heavily depends on discovering scintillators that possess high sensitivity,robust stability,low toxicity,and a uniform size distribution.Despite significant progress in this field,the discovery of a material that satisfies all of these criteria remains a challenge.In this study,we report the synthesis of monodisperse copper(Ⅰ)-iodide cluster microcubes as a new class of X-ray scintillators.The as-prepared microcubes exhibit remarkable sensitivity to X-rays and exceptional stability under moisture and X-ray exposure.The uniform size distribution and high scintillation performance of the copper(Ⅰ)-iodide cluster microcubes make them suitable for the fabrication of large-area,flexible scintillating films for X-ray imaging applications in both static and dynamic settings.
基金This project was financially supported by the National Key Research and Development Program of China(No.2017YFA0208200)the National Natural Science Foundation of China(Nos.22005003,22022505,and 21872069)+4 种基金the Fundamental Research Funds for the Central Universities(Nos.0205-14380219 and 0205-14913212)the Scientific Research Foundation of Anhui University of Technology for Talent Introduction(No.DT19100069)the Yong Scientific Research Foundation of Anhui University of Technology(No.QZ202003)the Natural Science Foundation of Jiangsu Province(No.BK20180008)the Shenzhen Fundamental Research Program of Science,Technology,and Innovation Commission of Shenzhen Municipality(No.JCYJ20180307155007589).
文摘Potassium-ion batteries(PIBs)are appealing alternatives to conventional lithium-ion batteries(LIBs)because of their wide potential window,fast ionic conductivity in the electrolyte,and reduced cost.However,PIBs suffer from sluggish K+reaction kinetics in electrode materials,large volume expansion of electroactive materials,and the unstable solid electrolyte interphase.Various strategies,especially in terms of electrode design,have been proposed to address these issues.In this review,the recent progress on advanced anode materials of PIBs is systematically discussed,ranging from the design principles,and nanoscale fabrication and engineering to the structure-performance relationship.Finally,the remaining limitations,potential solutions,and possible research directions for the development of PIBs towards practical applications are presented.This review will provide new insights into the lab development and real-world applications of PIBs.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60971009 and 61001011)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090142110019)+1 种基金the Natural Science Foundation of Hubei Province, China (Grant No. 2010CDB02701)the Fundamental Research Funds for the Central Universities, China (Grant No. 2012QN083)
文摘Decoupling the complicated vibrational-vibrational （V-V） coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our previous work [Acta Phys. Sin. 61 174301 （2012）], an analytical model to predict the sound absorption from vibrational relaxation in a gas medium is proposed. In this paper, we develop the model to decouple the V-V coupled energy to each vibrationaltranslational deexcitation path, and analyze how the multimode relaxations form the peaks of sound absorption spectra in gas mixtures. We prove that a multimode relaxation is the sum of its decoupled single-relaxation processes, and only the decoupled process with a significant isochoric-molar-heat can be observed as an absorption peak. The decoupling model clarifies the essential processes behind the peaks in spectra arising from the multimode relaxations in multi-component gas mixtures. The simulation validates the proposed decoupling model.
基金Supported by the National Natural Science Foun-dation of China (60496315)
文摘The paper proposes an on-line signature verification algorithm, through which test sample and template signatures can be optimizedly matched, based on evolutionary computation （EC）. Firstly, the similarity of signature curve segment is defined, and shift and scale transforms are also introduced due to the randoness of on-line signature. Secondly, this paper puts forward signature verification matching algorithm after establishment of the mathematical model. Thirdly, the concrete realization of the algorithm based on EC is discussed as well. In addition, the influence of shift and scale on the matching result is fully considered in the algorithm. Finally, a computation example is given, and the matching results between the test sample curve and the template signature curve are analyzed in detail, The preliminary experiments reveal that the type of signature verification problem can be solved by EC.
