If a metalens integrates the circular polarization(CP)conversion function,the focusing lens together with circular-polariz-ing lens(CPL)in traditional cameras may be replaced by a metalens.However,in terahertz(THz)ban...If a metalens integrates the circular polarization(CP)conversion function,the focusing lens together with circular-polariz-ing lens(CPL)in traditional cameras may be replaced by a metalens.However,in terahertz(THz)band,the reported metalenses still do not obtain the perfect and strict single-handed CP,because they were constructed via Pancharatnam-Berry phase so that CP conversion contained both left-handed CP(LCP)and right-handed CP(RCP)components.In this paper,a silicon based THz metalens is constructed using dynamic phase to obtain single-handed CP conversion.Also,we can rotate the whole metalens at a certain angle to control the conversion of multi-polarization states,which can simply manipulate the focusing for incident linear polarization(LP)THz wave in three polarization conversion states,in-cluding LP without conversion,LCP and RCP.Moreover,the polarization conversion behavior is reversible,that is,the THz metalens can convert not only the LP into arbitrary single-handed CP,but also the LCP and RCP into two perpen-dicular LP,respectively.The metalens is expected to be used in advanced THz camera,as a great candidate for tradi-tional CPL and focusing lens group,and also shows potential application in polarization imaging with discriminating LCP and RCP.展开更多
The mesoscale eddy is a typical mesoscale oceanic phenomenon that transfers ocean energy. The detection and extraction of mesoscale eddies is an important aspect of physical oceanography, and automatic mesoscale eddy ...The mesoscale eddy is a typical mesoscale oceanic phenomenon that transfers ocean energy. The detection and extraction of mesoscale eddies is an important aspect of physical oceanography, and automatic mesoscale eddy detection algorithms are the most fundamental tools for detecting and analyzing mesoscale eddies. The main data used in mesoscale eddy detection are sea level anomaly(SLA) data merged by multi-satellite altimeters' data.These data objectively describe the state of the sea surface height. The mesoscale eddy can be represented by a local equivalent region surrounded by an SLA closed contour, and the detection process requires the extraction of a stable closed contour structure from SLA maps. In consideration of the characteristics of mesoscale eddy detection based on SLA data, this paper proposes a new automatic mesoscale eddy detection algorithm based on clustering. The mesoscale eddy structure can be extracted by separating and filtering SLA data sets to separate a mesoscale eddy region and non-eddy region and then establishing relationships among eddy regions and mapping them on SLA maps. This paper overcomes the problem of the sensitivity of parameter setting that affects the traditional detection algorithm and does not require a sensitivity test. The proposed algorithm is thus more adaptable. An eddy discrimination mechanism is added to the algorithm to ensure the stability of the detected eddy structure and to improve the detection accuracy. On this basis, the paper selects the Northwest Pacific Ocean and the South China Sea to carry out a mesoscale eddy detection experiment. Experimental results show that the proposed algorithm is more efficient than the traditional algorithm and the results of the algorithm remain stable. The proposed algorithm detects not only stable single-core eddies but also stable multi-core eddy structures.展开更多
The ridgetail white prawn Exopalaemon carinicauda is a euryhaline shrimp species in the estuarine and coastal areas of China.In this study,survival rates,transcription levels of two prophenoloxidase system-related gen...The ridgetail white prawn Exopalaemon carinicauda is a euryhaline shrimp species in the estuarine and coastal areas of China.In this study,survival rates,transcription levels of two prophenoloxidase system-related genes(Ec LGBP and Ecpro PO)and PO activity were determined quantitatively in juvenile and adult E.carinicauda under different salinity levels.The results showed that E.carinicauda juveniles could survive in a wider range of salinity conditions than adults.For juvenile E.carinicauda,the expression levels of Ec LGBP and Ec Pro PO were upregulated in low salinities and showed no significant difference at 20–40,while PO activities in low salinities were higher compared to those in high salinities.For adult E.carinicauda,the expression profiles of Ec LGBP and Ecpro PO had a different trend of up-regulation in salinity stress treatments and no obvious difference was observed in the gene expression levels and PO activity between 30 and 40.The salinity tolerance range of immunity for juvenile and adult E.carinicauda is 20–40 and 30–40,respectively.展开更多
In order to improve the registration accuracy of brain magnetic resonance images(MRI),some deep learning registration methods use segmentation images for training model.How-ever,the segmentation values are constant fo...In order to improve the registration accuracy of brain magnetic resonance images(MRI),some deep learning registration methods use segmentation images for training model.How-ever,the segmentation values are constant for each label,which leads to the gradient variation con-centrating on the boundary.Thus,the dense deformation field(DDF)is gathered on the boundary and there even appears folding phenomenon.In order to fully leverage the label information,the morphological opening and closing information maps are introduced to enlarge the non-zero gradi-ent regions and improve the accuracy of DDF estimation.The opening information maps supervise the registration model to focus on smaller,narrow brain regions.The closing information maps supervise the registration model to pay more attention to the complex boundary region.Then,opening and closing morphology networks(OC_Net)are designed to automatically generate open-ing and closing information maps to realize the end-to-end training process.Finally,a new registra-tion architecture,VM_(seg+oc),is proposed by combining OC_Net and VoxelMorph.Experimental results show that the registration accuracy of VM_(seg+oc) is significantly improved on LPBA40 and OASIS1 datasets.Especially,VM_(seg+oc) can well improve registration accuracy in smaller brain regions and narrow regions.展开更多
Bipolar disorder is characterised by recurrent and alternating episodes of mania/hypomania and depression.Current breakthroughs in functional MRI techniques have uncovered the functional neuroanatomy of bipolar disord...Bipolar disorder is characterised by recurrent and alternating episodes of mania/hypomania and depression.Current breakthroughs in functional MRI techniques have uncovered the functional neuroanatomy of bipolar disorder.However,the pathophysiology underlying mood instability,mood switching and the development of extreme mood states is less well understood.This reviewpresents a comprehensive overviewof current evidence from functional MRI studies from the perspective of mood states.We first summarise the disrupted brain activation patterns and functional connectivity that have been reported in bipolar disorder,irrespective of the mood state.We next focus on research that solely included patients in a single mood state for a better understanding of the pathophysiology of bipolar disorder and research comparing patients with different mood states to dissect mood state-related effects.Finally,we briefly summarise current theoretical models and conclude this review by proposing potential avenues for future research.A comprehensive understanding of the pathophysiology with consideration of mood states could not only deepen our understanding of how acute mood episodes develop at a neurophysiological level but could also facilitate the identification of biological targets for personalised treatment and the development of new interventions for bipolar disorder.展开更多
Metasurfaces that can realize the polarization manipulation of electromagnetic waves on the sub-wavelength scale have become an emerging research field.Here,a novel strategy of combining the metasurface and Fresnel zo...Metasurfaces that can realize the polarization manipulation of electromagnetic waves on the sub-wavelength scale have become an emerging research field.Here,a novel strategy of combining the metasurface and Fresnel zone plate to form a metasurface zone plate is proposed to realize the conversion from nearly arbitrary polarizations to a fixed polarization.Specifically,when one polarized wave is incident on adjacent ring zones constructed by different types of meta-atoms,the transmitted waves generated by odd-numbered and even-numbered ring zones converge at the same focus and superimpose to generate a fixed polarized wave.As function demonstrations,we have designed two types of metasurface zone plates:one is a focused linear polarizer,and the other can convert nearly arbitrary polarized waves into focused circularly polarized waves.The simulated and measured results are consistent with theoretical expectations,suggesting that the proposed concept is flexible and feasible.Our work provides an alternative platform for polarization manipulation and may vigorously promote the development of polarization photonic devices.展开更多
In the whole research process of electromagnetic wave,the research of terahertz wave belongs to a blank for a long time,which is the least known and least developed by far.But now,people are trying to make up the blan...In the whole research process of electromagnetic wave,the research of terahertz wave belongs to a blank for a long time,which is the least known and least developed by far.But now,people are trying to make up the blank and develop terahertz better and better.The charm of terahertz wave originates from its multiple attributes,including electromagnetic field attribute,photon attribute and thermal attribute,which also attracts the attention of researchers in different fields and different countries,and also terahertz technology have been rated as one of the top ten technologies to change the future world by the United States.The multiple attributes of terahertz make it have broad application prospects in military and civil fields,such as medical imaging,astronomical observation,6G communication,environmental monitoring and material analysis.It is no exaggeration to say that mastering terahertz technology means mastering the future.However,it is because of the multiple attributes of terahertz that the terahertz wave is difficult to be mastered.Although terahertz has been applied in some fields,controlling terahertz(such as generation and detection)is still an important issue.Nowadays,a variety of terahertz generation and detection technologies have been developed and continuously improved.In this paper,the main terahertz generation and detection technologies(including already practical and developing)are reviewed in terms of scientific and engineering principles,in order to provide a systematic and up-to-date reference for researchers in terahertz field.展开更多
Rockburst is a phenomenon in which free surfaces are formed during excavation,which subsequently causes the sudden release of energy in the construction of mines and tunnels.Light rockburst only peels off rock slices ...Rockburst is a phenomenon in which free surfaces are formed during excavation,which subsequently causes the sudden release of energy in the construction of mines and tunnels.Light rockburst only peels off rock slices without ejection,while severe rockburst causes casualties and property loss.The frequency and degree of rockburst damage increases with the excavation depth.Moreover,rockburst is the leading engineering geological hazard in the excavation process,and thus the prediction of its intensity grade is of great significance to the development of geotechnical engineering.Therefore,the prediction of rockburst intensity grade is one problem that needs to be solved urgently.By comprehensively considering the occurrence mechanism of rockburst,this paper selects the stress index(σθ/σc),brittleness index(σ_(c)/σ_(t)),and rock elastic energy index(Wet)as the rockburst evaluation indexes through the Spearman coefficient method.This overcomes the low accuracy problem of a single evaluation index prediction method.Following this,the BGD-MSR-DNN rockburst intensity grade prediction model based on batch gradient descent and a multi-scale residual deep neural network is proposed.The batch gradient descent(BGD)module is used to replace the gradient descent algorithm,which effectively improves the efficiency of the network and reduces the model training time.Moreover,the multi-scale residual(MSR)module solves the problem of network degradation when there are too many hidden layers of the deep neural network(DNN),thus improving the model prediction accuracy.The experimental results reveal the BGDMSR-DNN model accuracy to reach 97.1%,outperforming other comparable models.Finally,actual projects such as Qinling Tunnel and Daxiangling Tunnel,reached an accuracy of 100%.The model can be applied in mines and tunnel engineering to realize the accurate and rapid prediction of rockburst intensity grade.展开更多
This article studies distributed pose(orientation and position)estimation of leader–follower multi-agent systems over𝜅-layer graphs in 2-D plane.Only the leaders have access to their orientations and position...This article studies distributed pose(orientation and position)estimation of leader–follower multi-agent systems over𝜅-layer graphs in 2-D plane.Only the leaders have access to their orientations and positions,while the followers can measure the relative bearings or(angular and linear)velocities in their unknown local coordinate frames.For the orientation estimation,the local relative bearings are used to obtain the relative orientations among the agents,based on which a distributed orientation estimation algorithm is proposed for each follower to estimate its orientation.For the position estimation,the local relative bearings are used to obtain the position constraints among the agents,and a distributed position estimation algorithm is proposed for each follower to estimate its position by solving its position constraints.Both the orientation and position estimation errors converge to zero asymptotically.A simulation example is given to verify the theoretical results.展开更多
Quasi-bound states in the continuum (QBIC),with exceptionally high-Q factors and the local field enhancement effect,have found potential applications in matter sensing.Introducing the QBIC mechanism into terahertz(THz...Quasi-bound states in the continuum (QBIC),with exceptionally high-Q factors and the local field enhancement effect,have found potential applications in matter sensing.Introducing the QBIC mechanism into terahertz(THz) metasurfaces can significantly enhance the interaction between incident THz waves and matter,providing a feasible platform for the detection of biochemical substances.Currently,most experimental studies on terahertz QBIC metasurfaces utilize metallic structures.By contrast,research on terahertz all-dielectric QBIC metasurfaces generally remains at the simulation stage due to the high fabrication process requirements,and transitioning to the experimental stage still poses many challenges.In this paper,a hollow-structured all-silicon metasurface supporting THz QBIC is proposed.The resonance of THz QBIC is excited via a simple hollow structure and observed in experiment.Simulations and experimental results demonstrated that the designed THz QBIC metasurface can achieve sensing of Auramine O.Notably,it is the first study,to our knowledge,to employ a metasurface to sense Auramine O.Additionally,the sensing performance maintains good stability under different humidity and temperature conditions.This study provides new references and insights for the design and implementation of THz QBIC,and also opens a new pathway for the detection of Auramine O.展开更多
Chiral metasurfaces have different electromagnetic responses with circularly polarized lights,showing as circular dichroism and optical activity.Here,a novel kind of all-silicon chiral metasurface is proposed by intro...Chiral metasurfaces have different electromagnetic responses with circularly polarized lights,showing as circular dichroism and optical activity.Here,a novel kind of all-silicon chiral metasurface is proposed by introducing destructive interference between achiral meta-atoms.The maximum value of circular dichroism spectra can reach 0.49.By adding an antireflective layer at the side of the silicon substrate,the maximum circular dichroism reaches 0.54.What is more,the bandwidth of circular dichroism greater than 0.4 reaches 0.15 THz.Two samples are fabricated to verify the feasibility of this scheme,and the experimental results are in good agreement with the simulations.In addition,the proposed scheme can also be used to generate various interesting functions,such as beam control and vortex generator.This flexible and efficient implementation solution of chiral metasurface can bring new ideas to the development of chiral devices in the future.展开更多
Phase-modulated metasurfaces that can implement the independent manipulation of co-and cross-polarized output waves under circularly polarized[CP]incidence have been proposed.With this,we introduce one particular meta...Phase-modulated metasurfaces that can implement the independent manipulation of co-and cross-polarized output waves under circularly polarized[CP]incidence have been proposed.With this,we introduce one particular metasurface composed of meta-atoms with a phase difference of 2π/3 to generate specific elliptically polarized waves under various polarized incidences.Furthermore,a metasurface composed of these above meta-atoms and the meta-atoms with a phase difference of π/3 arranged in a certain rule can realize polarization conversion function between linearly polarized and CP states.The designs shed new light on multifarious optical devices and may further promote the development of metasurface polarization optics.展开更多
Chiral metasurfaces based on asymmetric meta-atoms have achieved artificial circular dichroism(CD),spin-dependent wavefront control,near-field imaging,and other spin-related electromagnetic control.In this paper,we pr...Chiral metasurfaces based on asymmetric meta-atoms have achieved artificial circular dichroism(CD),spin-dependent wavefront control,near-field imaging,and other spin-related electromagnetic control.In this paper,we propose and experimentally verify a scheme for achieving high-efficiency chiral response similar to CD of terahertz(THz)wave via phase manipulation.By introducing the geometric phase and dynamic phase in an all-silicon metasurface,the spin-decoupled terahertz transmission is obtained.The giant circular dichroism-like effect in the transmission spectrum is observed by using a random phase distribution for one of the circular polarization components.More importantly,the effect can be adjusted when we change the area of the metasurface illuminated by an incident terahertz beam.In addition,we also demonstrate the spin-dependent arbitrary wavefront control of the transmitted terahertz wave,in which one of the circularly polarized components is scattered,while the other forms a focused vortex beam.Simulated and experimental results show that this method provides a new idea for spin selective control of THz waves.展开更多
Terahertz absorbers based on doped silicon have achieved broadband and high-efficiency absorption due to their high concentration of carriers.However,their tunable performance is obviously insufficient.Here,we propose...Terahertz absorbers based on doped silicon have achieved broadband and high-efficiency absorption due to their high concentration of carriers.However,their tunable performance is obviously insufficient.Here,we propose a new scheme for active terahertz absorption based on undoped silicon with a metamaterial antireflection layer,which realizes both strong absorption and ultrahigh modulation depth.Benefiting from the weak absorption and high transmission of undoped silicon for 1064-nm continuous wave,uniformly distributed carriers across the entire thickness of the absorber are excited,and efficient free carrier absorption of the terahertz wave is obtained.We use only a 500-μm thick absorber and achieve absorption greater than 90%in the range of 0.58 to 1.92 THz,with a peak value of 99%.More important,the absorber can be switched between two working states of nonabsorption and high-efficiency absorption by changing the pump power,which means the modulation depth reaches 100%.This simple and high-performance implementation scheme provides a new idea for the design of terahertz tunable absorbers.展开更多
It is essential to develop a single mode operation and improve the performance of lasing in order to ensure practical applicability of microlasers and nanolasers. In this paper, two hexagonal microteeth with varied na...It is essential to develop a single mode operation and improve the performance of lasing in order to ensure practical applicability of microlasers and nanolasers. In this paper, two hexagonal microteeth with varied nanoscaled air-gaps of a ZnO microcomb are used to construct coupled whispering-gallery cavities. This is done to achieve a stable single mode lasing based on Vernier effect without requiring any complicated or sophisticated manipulation to achieve positioning with nanoscale precision. Optical gain and the corresponding ultraviolet lasing performance were improved greatly through coupling with localized surface plasmons of Pt nanoparticles. The ZnO/Pt hybrid microcavities achieved a seven-fold enhancement of intensity of single mode lasing with higher side- mode suppression ratio and lower threshold. The mechanism that led to this enhancement has been described in detail.展开更多
Polarization manipulation of electromagnetic wave or polarization multiplexed beam shaping based on metasurfaces has been reported in various frequency bands.However,it is difficult to shape the beam with multi-channe...Polarization manipulation of electromagnetic wave or polarization multiplexed beam shaping based on metasurfaces has been reported in various frequency bands.However,it is difficult to shape the beam with multi-channel polarization conversion in a single metasurface.Here,we propose a new method for terahertz wavefront shaping with multi-channel polarization conversion via all-silicon metasurface,which is based on the linear shape birefringence effect in spatially interleaved anisotropic meta-atoms.By superimposing the eigen-and non-eigen-polarization responses of the two kinds of meta-atoms,we demonstrate the possibility for high-efficiency evolution of several typical polarization states with two independent channels for linearly polarized waves.The measured polarization conversion efficiency is higher than 70%in the range of 0.9–1.3 THz,with a peak value of 89.2%at 1.1 THz.In addition,when more other polarization states are incident,combined with the integration of sub-arrays,we can get more channels for both polarization conversion and beam shaping.Simulated and experimental results verify the feasibility of this method.The proposed method provides a new idea for the design of terahertz multi-functional metadevices.展开更多
Collaborative enhancements from surface plasmons （SPs） and whispering-gallery modes （WGMs） can induce intense near-field effects with high spatial localization around the surface of a semiconducting material. One ...Collaborative enhancements from surface plasmons （SPs） and whispering-gallery modes （WGMs） can induce intense near-field effects with high spatial localization around the surface of a semiconducting material. One can construct a highly efficient hybrid microcavity using semiconducting materials through resonant coupling between SPs and WGMs. Hexagonal ZnO micro-/nanostructures, which have been employed as natural WGM microcavities for ultraviolet （UV） lasing, can be used as ideal platforms to construct such hybrid microcavities. Here, we comprehensively review the recent efforts for improving lasing performance by resonant coupling between SPs and WGMs. Traditional SPs originating from various metals as well as novel SPs originating from atomic layers such as graphene are considered. Moreover, we discuss the mechanism of light-matter interactions beyond the improvements in lasing performance.展开更多
Vortex and vector terahertz(THz)beams with inhomogeneous polarization states have become a considerable hot topic in the last decade due to their important roles in multiplexed wireless data transmission.However,the t...Vortex and vector terahertz(THz)beams with inhomogeneous polarization states have become a considerable hot topic in the last decade due to their important roles in multiplexed wireless data transmission.However,the technical instruments to form and evaluate such beams are rather limited,as they are mainly collected in the visible range.The emergence of coded metasurfaces has reinvigorated the design of functional devices with multiple degrees of freedom.Here,we demonstrate a versatile design inspired by a binary encoding approach for generating off-axis vectorial THz beams on all-silicon metasurfaces.Experimentally,simultaneous manipulation of the encoding method within the orthogonal circularly polarized(CP)channel provides strong support for developing versatility in vector THz beams,including the generation of arbitrary polarization profiles and the directional emission of multiplexed vector vortex beams(VVBs)with specified polarization states.The introduction of the latitudinal polarization control factor guarantees that continuously rotating or independently designed vector polarization profiles can be obtained on a pre-defined focal plane.Subsequently,a universal parametric theoretical model is developed to analyze the evolutionary trend of off-axis VVB in detail.Notably,the proposed monolayer vector metasurface bypasses the requirement of multiple cascaded optical elements,further inducing the advancement of ultra-thin vector THz sources,and also facilitating the generation of vector fields with tailored polarization distributions in 3D space.展开更多
Conventional metasurfaces for terahertz polarization are limited to performing lateral(in the x-y plane)polarization control of the output wave.In such cases,the polarization state remains unchanged in each output pla...Conventional metasurfaces for terahertz polarization are limited to performing lateral(in the x-y plane)polarization control of the output wave.In such cases,the polarization state remains unchanged in each output plane along the propagation path.Herein,we propose a terahertz polarization metasurface that operates longitudinally(i.e.,along the z-axis direction of propagation),which modifies the polarization state of each output plane throughout the propagation path.Our designed metasurface can control the phase delays of the left-handed and right-handed circularly polarized(LCP and RCP)components of the incident terahertz wave.This enables the LCP beam and RCP beam to converge to the z-axis through distinct paths,creating a Bessel beam.The proposed design achieved a linearly polarized terahertz wave including both LCP and RCP components with a precise phase differenceΔφat each point within a certain range along the z-axis.TheΔφvaries as the propagation distance,resulting in a rotated linearly polarized output wave along the propagation path,while the rotation angle ranges from 0 toπ.Based on the variable property of longitudinal polarization,we propose an application concept of dielectric refractive index sensing,in which an additional medium is placed in the terahertz propagation path and the unknown refractive index is determined by detecting the rotation angle of the output polarization state.Theoretically,the device might find potential applications in variable media excitation,terahertz communication,and terahertz radar ranging.展开更多
基金supported by the National Natural Science Foundation of China(Nos.61675147,61735010 and 91838301)National Key Research and Development Program of China(No.2017YFA0700202)Basic Re-search Program of Shenzhen(JCYJ20170412154447469).
文摘If a metalens integrates the circular polarization(CP)conversion function,the focusing lens together with circular-polariz-ing lens(CPL)in traditional cameras may be replaced by a metalens.However,in terahertz(THz)band,the reported metalenses still do not obtain the perfect and strict single-handed CP,because they were constructed via Pancharatnam-Berry phase so that CP conversion contained both left-handed CP(LCP)and right-handed CP(RCP)components.In this paper,a silicon based THz metalens is constructed using dynamic phase to obtain single-handed CP conversion.Also,we can rotate the whole metalens at a certain angle to control the conversion of multi-polarization states,which can simply manipulate the focusing for incident linear polarization(LP)THz wave in three polarization conversion states,in-cluding LP without conversion,LCP and RCP.Moreover,the polarization conversion behavior is reversible,that is,the THz metalens can convert not only the LP into arbitrary single-handed CP,but also the LCP and RCP into two perpen-dicular LP,respectively.The metalens is expected to be used in advanced THz camera,as a great candidate for tradi-tional CPL and focusing lens group,and also shows potential application in polarization imaging with discriminating LCP and RCP.
基金The National Key R&D Program of China under contract No.2016YFC1401800the National Natural Science Foundation of China under contract No.41576176the National Programme on Global Change and Air-Sea Interaction under contract Nos GASI-02-PAC-YGST2-04,GASI-02-IND-YGST2-04 and GASI-02-SCS-YGST2-04
文摘The mesoscale eddy is a typical mesoscale oceanic phenomenon that transfers ocean energy. The detection and extraction of mesoscale eddies is an important aspect of physical oceanography, and automatic mesoscale eddy detection algorithms are the most fundamental tools for detecting and analyzing mesoscale eddies. The main data used in mesoscale eddy detection are sea level anomaly(SLA) data merged by multi-satellite altimeters' data.These data objectively describe the state of the sea surface height. The mesoscale eddy can be represented by a local equivalent region surrounded by an SLA closed contour, and the detection process requires the extraction of a stable closed contour structure from SLA maps. In consideration of the characteristics of mesoscale eddy detection based on SLA data, this paper proposes a new automatic mesoscale eddy detection algorithm based on clustering. The mesoscale eddy structure can be extracted by separating and filtering SLA data sets to separate a mesoscale eddy region and non-eddy region and then establishing relationships among eddy regions and mapping them on SLA maps. This paper overcomes the problem of the sensitivity of parameter setting that affects the traditional detection algorithm and does not require a sensitivity test. The proposed algorithm is thus more adaptable. An eddy discrimination mechanism is added to the algorithm to ensure the stability of the detected eddy structure and to improve the detection accuracy. On this basis, the paper selects the Northwest Pacific Ocean and the South China Sea to carry out a mesoscale eddy detection experiment. Experimental results show that the proposed algorithm is more efficient than the traditional algorithm and the results of the algorithm remain stable. The proposed algorithm detects not only stable single-core eddies but also stable multi-core eddy structures.
基金The National Key R&D Program of China under contract No.2019YFD0900400the China Agriculture Research System under contract No.CARS-48+2 种基金the National Natural Science Foundation of China under contract No.31702319the Program of Shandong Leading Talent under contract No.LNJY2015002the Central Public-interest Scientific Institution Basal Research Fund,CAFS under contract No.2019ZD0603
文摘The ridgetail white prawn Exopalaemon carinicauda is a euryhaline shrimp species in the estuarine and coastal areas of China.In this study,survival rates,transcription levels of two prophenoloxidase system-related genes(Ec LGBP and Ecpro PO)and PO activity were determined quantitatively in juvenile and adult E.carinicauda under different salinity levels.The results showed that E.carinicauda juveniles could survive in a wider range of salinity conditions than adults.For juvenile E.carinicauda,the expression levels of Ec LGBP and Ec Pro PO were upregulated in low salinities and showed no significant difference at 20–40,while PO activities in low salinities were higher compared to those in high salinities.For adult E.carinicauda,the expression profiles of Ec LGBP and Ecpro PO had a different trend of up-regulation in salinity stress treatments and no obvious difference was observed in the gene expression levels and PO activity between 30 and 40.The salinity tolerance range of immunity for juvenile and adult E.carinicauda is 20–40 and 30–40,respectively.
基金supported by Shandong Provincial Natural Science Foundation(No.ZR2023MF062)the National Natural Science Foundation of China(No.61771230).
文摘In order to improve the registration accuracy of brain magnetic resonance images(MRI),some deep learning registration methods use segmentation images for training model.How-ever,the segmentation values are constant for each label,which leads to the gradient variation con-centrating on the boundary.Thus,the dense deformation field(DDF)is gathered on the boundary and there even appears folding phenomenon.In order to fully leverage the label information,the morphological opening and closing information maps are introduced to enlarge the non-zero gradi-ent regions and improve the accuracy of DDF estimation.The opening information maps supervise the registration model to focus on smaller,narrow brain regions.The closing information maps supervise the registration model to pay more attention to the complex boundary region.Then,opening and closing morphology networks(OC_Net)are designed to automatically generate open-ing and closing information maps to realize the end-to-end training process.Finally,a new registra-tion architecture,VM_(seg+oc),is proposed by combining OC_Net and VoxelMorph.Experimental results show that the registration accuracy of VM_(seg+oc) is significantly improved on LPBA40 and OASIS1 datasets.Especially,VM_(seg+oc) can well improve registration accuracy in smaller brain regions and narrow regions.
基金the National Key Technology R&D Program(2015BA/13B01)Beijing National Science Foundation(7222236)+1 种基金Capital Health Research and Development of Special Fund(2022-1-4111)National Natural Science Foundation of China(82071528,82171529,82271569,82371530).
文摘Bipolar disorder is characterised by recurrent and alternating episodes of mania/hypomania and depression.Current breakthroughs in functional MRI techniques have uncovered the functional neuroanatomy of bipolar disorder.However,the pathophysiology underlying mood instability,mood switching and the development of extreme mood states is less well understood.This reviewpresents a comprehensive overviewof current evidence from functional MRI studies from the perspective of mood states.We first summarise the disrupted brain activation patterns and functional connectivity that have been reported in bipolar disorder,irrespective of the mood state.We next focus on research that solely included patients in a single mood state for a better understanding of the pathophysiology of bipolar disorder and research comparing patients with different mood states to dissect mood state-related effects.Finally,we briefly summarise current theoretical models and conclude this review by proposing potential avenues for future research.A comprehensive understanding of the pathophysiology with consideration of mood states could not only deepen our understanding of how acute mood episodes develop at a neurophysiological level but could also facilitate the identification of biological targets for personalised treatment and the development of new interventions for bipolar disorder.
文摘Metasurfaces that can realize the polarization manipulation of electromagnetic waves on the sub-wavelength scale have become an emerging research field.Here,a novel strategy of combining the metasurface and Fresnel zone plate to form a metasurface zone plate is proposed to realize the conversion from nearly arbitrary polarizations to a fixed polarization.Specifically,when one polarized wave is incident on adjacent ring zones constructed by different types of meta-atoms,the transmitted waves generated by odd-numbered and even-numbered ring zones converge at the same focus and superimpose to generate a fixed polarized wave.As function demonstrations,we have designed two types of metasurface zone plates:one is a focused linear polarizer,and the other can convert nearly arbitrary polarized waves into focused circularly polarized waves.The simulated and measured results are consistent with theoretical expectations,suggesting that the proposed concept is flexible and feasible.Our work provides an alternative platform for polarization manipulation and may vigorously promote the development of polarization photonic devices.
文摘In the whole research process of electromagnetic wave,the research of terahertz wave belongs to a blank for a long time,which is the least known and least developed by far.But now,people are trying to make up the blank and develop terahertz better and better.The charm of terahertz wave originates from its multiple attributes,including electromagnetic field attribute,photon attribute and thermal attribute,which also attracts the attention of researchers in different fields and different countries,and also terahertz technology have been rated as one of the top ten technologies to change the future world by the United States.The multiple attributes of terahertz make it have broad application prospects in military and civil fields,such as medical imaging,astronomical observation,6G communication,environmental monitoring and material analysis.It is no exaggeration to say that mastering terahertz technology means mastering the future.However,it is because of the multiple attributes of terahertz that the terahertz wave is difficult to be mastered.Although terahertz has been applied in some fields,controlling terahertz(such as generation and detection)is still an important issue.Nowadays,a variety of terahertz generation and detection technologies have been developed and continuously improved.In this paper,the main terahertz generation and detection technologies(including already practical and developing)are reviewed in terms of scientific and engineering principles,in order to provide a systematic and up-to-date reference for researchers in terahertz field.
基金funded by State Key Laboratory for GeoMechanics and Deep Underground Engineering&Institute for Deep Underground Science and Engineering,Grant Number XD2021021BUCEA Post Graduate Innovation Project under Grant,Grant Number PG2023092.
文摘Rockburst is a phenomenon in which free surfaces are formed during excavation,which subsequently causes the sudden release of energy in the construction of mines and tunnels.Light rockburst only peels off rock slices without ejection,while severe rockburst causes casualties and property loss.The frequency and degree of rockburst damage increases with the excavation depth.Moreover,rockburst is the leading engineering geological hazard in the excavation process,and thus the prediction of its intensity grade is of great significance to the development of geotechnical engineering.Therefore,the prediction of rockburst intensity grade is one problem that needs to be solved urgently.By comprehensively considering the occurrence mechanism of rockburst,this paper selects the stress index(σθ/σc),brittleness index(σ_(c)/σ_(t)),and rock elastic energy index(Wet)as the rockburst evaluation indexes through the Spearman coefficient method.This overcomes the low accuracy problem of a single evaluation index prediction method.Following this,the BGD-MSR-DNN rockburst intensity grade prediction model based on batch gradient descent and a multi-scale residual deep neural network is proposed.The batch gradient descent(BGD)module is used to replace the gradient descent algorithm,which effectively improves the efficiency of the network and reduces the model training time.Moreover,the multi-scale residual(MSR)module solves the problem of network degradation when there are too many hidden layers of the deep neural network(DNN),thus improving the model prediction accuracy.The experimental results reveal the BGDMSR-DNN model accuracy to reach 97.1%,outperforming other comparable models.Finally,actual projects such as Qinling Tunnel and Daxiangling Tunnel,reached an accuracy of 100%.The model can be applied in mines and tunnel engineering to realize the accurate and rapid prediction of rockburst intensity grade.
基金supported by Nanyang Technological University,Singapore under the Wallenberg-NTU Presidential Postdoctoral Fellowship and the Natural Science Foundation in Heilongjiang Province,China(YQ2022F003).
文摘This article studies distributed pose(orientation and position)estimation of leader–follower multi-agent systems over𝜅-layer graphs in 2-D plane.Only the leaders have access to their orientations and positions,while the followers can measure the relative bearings or(angular and linear)velocities in their unknown local coordinate frames.For the orientation estimation,the local relative bearings are used to obtain the relative orientations among the agents,based on which a distributed orientation estimation algorithm is proposed for each follower to estimate its orientation.For the position estimation,the local relative bearings are used to obtain the position constraints among the agents,and a distributed position estimation algorithm is proposed for each follower to estimate its position by solving its position constraints.Both the orientation and position estimation errors converge to zero asymptotically.A simulation example is given to verify the theoretical results.
基金National Natural Science Foundation of China(12035012, 12375322, 12375323, 62205319, U2330129)Central Government Guided Local Science and Technology Development Projects of China (2023ZYD0175)Key Laboratories of Sensing and Application of Intelligent Optoelectronic System in Sichuan Provincial Universities(ZNGD2302)。
文摘Quasi-bound states in the continuum (QBIC),with exceptionally high-Q factors and the local field enhancement effect,have found potential applications in matter sensing.Introducing the QBIC mechanism into terahertz(THz) metasurfaces can significantly enhance the interaction between incident THz waves and matter,providing a feasible platform for the detection of biochemical substances.Currently,most experimental studies on terahertz QBIC metasurfaces utilize metallic structures.By contrast,research on terahertz all-dielectric QBIC metasurfaces generally remains at the simulation stage due to the high fabrication process requirements,and transitioning to the experimental stage still poses many challenges.In this paper,a hollow-structured all-silicon metasurface supporting THz QBIC is proposed.The resonance of THz QBIC is excited via a simple hollow structure and observed in experiment.Simulations and experimental results demonstrated that the designed THz QBIC metasurface can achieve sensing of Auramine O.Notably,it is the first study,to our knowledge,to employ a metasurface to sense Auramine O.Additionally,the sensing performance maintains good stability under different humidity and temperature conditions.This study provides new references and insights for the design and implementation of THz QBIC,and also opens a new pathway for the detection of Auramine O.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.61675147,61735010,and 91838301)National Key Research and Development Program of China(Grant No.2017YFA0700-202)+1 种基金Basic Research Program of Shenzhen(Grant No.JCYJ2017041215-4447469)Program for Science&Technology Innovation Talents of Henan Province(Grant No.202102310001)。
文摘Chiral metasurfaces have different electromagnetic responses with circularly polarized lights,showing as circular dichroism and optical activity.Here,a novel kind of all-silicon chiral metasurface is proposed by introducing destructive interference between achiral meta-atoms.The maximum value of circular dichroism spectra can reach 0.49.By adding an antireflective layer at the side of the silicon substrate,the maximum circular dichroism reaches 0.54.What is more,the bandwidth of circular dichroism greater than 0.4 reaches 0.15 THz.Two samples are fabricated to verify the feasibility of this scheme,and the experimental results are in good agreement with the simulations.In addition,the proposed scheme can also be used to generate various interesting functions,such as beam control and vortex generator.This flexible and efficient implementation solution of chiral metasurface can bring new ideas to the development of chiral devices in the future.
基金This work was supported by the National Natural Science Foundation of China(Nos.61675147,61735010,and 91838301)National Key Research and Development Program of China(No.2017YFA0700202).
文摘Phase-modulated metasurfaces that can implement the independent manipulation of co-and cross-polarized output waves under circularly polarized[CP]incidence have been proposed.With this,we introduce one particular metasurface composed of meta-atoms with a phase difference of 2π/3 to generate specific elliptically polarized waves under various polarized incidences.Furthermore,a metasurface composed of these above meta-atoms and the meta-atoms with a phase difference of π/3 arranged in a certain rule can realize polarization conversion function between linearly polarized and CP states.The designs shed new light on multifarious optical devices and may further promote the development of metasurface polarization optics.
基金Basic Research Program of Shenzhen(JCYJ20170412154447469)National Key Research and Development Program of China(2017YFA0700202)National Natural Science Foundation of China(61675147,61735010,91838301).
文摘Chiral metasurfaces based on asymmetric meta-atoms have achieved artificial circular dichroism(CD),spin-dependent wavefront control,near-field imaging,and other spin-related electromagnetic control.In this paper,we propose and experimentally verify a scheme for achieving high-efficiency chiral response similar to CD of terahertz(THz)wave via phase manipulation.By introducing the geometric phase and dynamic phase in an all-silicon metasurface,the spin-decoupled terahertz transmission is obtained.The giant circular dichroism-like effect in the transmission spectrum is observed by using a random phase distribution for one of the circular polarization components.More importantly,the effect can be adjusted when we change the area of the metasurface illuminated by an incident terahertz beam.In addition,we also demonstrate the spin-dependent arbitrary wavefront control of the transmitted terahertz wave,in which one of the circularly polarized components is scattered,while the other forms a focused vortex beam.Simulated and experimental results show that this method provides a new idea for spin selective control of THz waves.
基金supported by the National Natural Science Foundation of China(Grant Nos.61675147,61735010,and 91838301)National Key Research and Development Program of China(Grant No.2017YFA0700202)。
文摘Terahertz absorbers based on doped silicon have achieved broadband and high-efficiency absorption due to their high concentration of carriers.However,their tunable performance is obviously insufficient.Here,we propose a new scheme for active terahertz absorption based on undoped silicon with a metamaterial antireflection layer,which realizes both strong absorption and ultrahigh modulation depth.Benefiting from the weak absorption and high transmission of undoped silicon for 1064-nm continuous wave,uniformly distributed carriers across the entire thickness of the absorber are excited,and efficient free carrier absorption of the terahertz wave is obtained.We use only a 500-μm thick absorber and achieve absorption greater than 90%in the range of 0.58 to 1.92 THz,with a peak value of 99%.More important,the absorber can be switched between two working states of nonabsorption and high-efficiency absorption by changing the pump power,which means the modulation depth reaches 100%.This simple and high-performance implementation scheme provides a new idea for the design of terahertz tunable absorbers.
基金Acknowledgements The authors sincerely appreciate the help of Shufeng Wang and Yu Li at Peking University and Andong Xia at Institute of Chemistry Chinese Academy of Sciences for their technical support on time-resolved PL. This work was supported by the National Basic Research Program （No. 2013CB932903）, National Natural Science Foundation （Nos. 61275054, 61475035, and 11404289）, Jiangsu Province Science and Technology Support Program （No. BE2016177） and Natural Science Foundation of Zhejiang Province （No. LY17A040011）.
文摘It is essential to develop a single mode operation and improve the performance of lasing in order to ensure practical applicability of microlasers and nanolasers. In this paper, two hexagonal microteeth with varied nanoscaled air-gaps of a ZnO microcomb are used to construct coupled whispering-gallery cavities. This is done to achieve a stable single mode lasing based on Vernier effect without requiring any complicated or sophisticated manipulation to achieve positioning with nanoscale precision. Optical gain and the corresponding ultraviolet lasing performance were improved greatly through coupling with localized surface plasmons of Pt nanoparticles. The ZnO/Pt hybrid microcavities achieved a seven-fold enhancement of intensity of single mode lasing with higher side- mode suppression ratio and lower threshold. The mechanism that led to this enhancement has been described in detail.
基金National Natural Science Foundation of China(61675147,61735010,91838301)National Key Research and Development Program of China(2017YFA0700202)Basic Research Program of Shenzhen(JCYJ20170412154447469).
文摘Polarization manipulation of electromagnetic wave or polarization multiplexed beam shaping based on metasurfaces has been reported in various frequency bands.However,it is difficult to shape the beam with multi-channel polarization conversion in a single metasurface.Here,we propose a new method for terahertz wavefront shaping with multi-channel polarization conversion via all-silicon metasurface,which is based on the linear shape birefringence effect in spatially interleaved anisotropic meta-atoms.By superimposing the eigen-and non-eigen-polarization responses of the two kinds of meta-atoms,we demonstrate the possibility for high-efficiency evolution of several typical polarization states with two independent channels for linearly polarized waves.The measured polarization conversion efficiency is higher than 70%in the range of 0.9–1.3 THz,with a peak value of 89.2%at 1.1 THz.In addition,when more other polarization states are incident,combined with the integration of sub-arrays,we can get more channels for both polarization conversion and beam shaping.Simulated and experimental results verify the feasibility of this method.The proposed method provides a new idea for the design of terahertz multi-functional metadevices.
文摘Collaborative enhancements from surface plasmons （SPs） and whispering-gallery modes （WGMs） can induce intense near-field effects with high spatial localization around the surface of a semiconducting material. One can construct a highly efficient hybrid microcavity using semiconducting materials through resonant coupling between SPs and WGMs. Hexagonal ZnO micro-/nanostructures, which have been employed as natural WGM microcavities for ultraviolet （UV） lasing, can be used as ideal platforms to construct such hybrid microcavities. Here, we comprehensively review the recent efforts for improving lasing performance by resonant coupling between SPs and WGMs. Traditional SPs originating from various metals as well as novel SPs originating from atomic layers such as graphene are considered. Moreover, we discuss the mechanism of light-matter interactions beyond the improvements in lasing performance.
基金supported by the National Key Research and Development Program of China(2021YFB2800703 and 2017YFA0700202)the National Natural Science Foundation of China(61675147)Sichuan Science and Technology Program(2021ZYD0039)。
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFB2800703,and 2017YFA0700202)the National Natural Science Foundation of China(Grant Nos.61675147,61975146,62075159,62105240,and 91838301).
文摘Vortex and vector terahertz(THz)beams with inhomogeneous polarization states have become a considerable hot topic in the last decade due to their important roles in multiplexed wireless data transmission.However,the technical instruments to form and evaluate such beams are rather limited,as they are mainly collected in the visible range.The emergence of coded metasurfaces has reinvigorated the design of functional devices with multiple degrees of freedom.Here,we demonstrate a versatile design inspired by a binary encoding approach for generating off-axis vectorial THz beams on all-silicon metasurfaces.Experimentally,simultaneous manipulation of the encoding method within the orthogonal circularly polarized(CP)channel provides strong support for developing versatility in vector THz beams,including the generation of arbitrary polarization profiles and the directional emission of multiplexed vector vortex beams(VVBs)with specified polarization states.The introduction of the latitudinal polarization control factor guarantees that continuously rotating or independently designed vector polarization profiles can be obtained on a pre-defined focal plane.Subsequently,a universal parametric theoretical model is developed to analyze the evolutionary trend of off-axis VVB in detail.Notably,the proposed monolayer vector metasurface bypasses the requirement of multiple cascaded optical elements,further inducing the advancement of ultra-thin vector THz sources,and also facilitating the generation of vector fields with tailored polarization distributions in 3D space.
基金supported by National Key Research and Development Program of China(2021YFB2800703 and 2017YFA0700202).
文摘Conventional metasurfaces for terahertz polarization are limited to performing lateral(in the x-y plane)polarization control of the output wave.In such cases,the polarization state remains unchanged in each output plane along the propagation path.Herein,we propose a terahertz polarization metasurface that operates longitudinally(i.e.,along the z-axis direction of propagation),which modifies the polarization state of each output plane throughout the propagation path.Our designed metasurface can control the phase delays of the left-handed and right-handed circularly polarized(LCP and RCP)components of the incident terahertz wave.This enables the LCP beam and RCP beam to converge to the z-axis through distinct paths,creating a Bessel beam.The proposed design achieved a linearly polarized terahertz wave including both LCP and RCP components with a precise phase differenceΔφat each point within a certain range along the z-axis.TheΔφvaries as the propagation distance,resulting in a rotated linearly polarized output wave along the propagation path,while the rotation angle ranges from 0 toπ.Based on the variable property of longitudinal polarization,we propose an application concept of dielectric refractive index sensing,in which an additional medium is placed in the terahertz propagation path and the unknown refractive index is determined by detecting the rotation angle of the output polarization state.Theoretically,the device might find potential applications in variable media excitation,terahertz communication,and terahertz radar ranging.
