Rotational Bose-Einstein condensates can exhibit quantized vortices as topological excitations.In this study,the ground and excited states of the rotational Bose-Einstein condensates are systematically studied by calc...Rotational Bose-Einstein condensates can exhibit quantized vortices as topological excitations.In this study,the ground and excited states of the rotational Bose-Einstein condensates are systematically studied by calculating the stationary points of the Gross-Pitaevskii energy functional.Various excited states and their connections at different rotational frequencies are revealed in solution landscapes constructed with the constrained high-index saddle dynamics method.Four excitation mechanisms are identified:vortex addition,rearrangement,merging,and splitting.We demonstrate changes in the ground state with increasing rotational frequencies and decipher the evolution of the stability of ground states.展开更多
Metasurfaces are optically thin metamaterials that promise complete control of the wavefront of light but are primarily used to control only the phase of light.Here,we present an approach,simple in concept and in prac...Metasurfaces are optically thin metamaterials that promise complete control of the wavefront of light but are primarily used to control only the phase of light.Here,we present an approach,simple in concept and in practice,that uses meta-atoms with a varying degree of form birefringence and rotation angles to create high-efficiency dielectric metasurfaces that control both the optical amplitude and phase at one or two frequencies.This opens up applications in computer-generated holography,allowing faithful reproduction of both the phase and amplitude of a target holographic scene without the iterative algorithms required in phase-only holography.We demonstrate all-dielectric metasurface holograms with independent and complete control of the amplitude and phase at up to two optical frequencies simultaneously to generate two-and three-dimensional holographic objects.We show that phaseamplitude metasurfaces enable a few features not attainable in phase-only holography;these include creating artifactfree two-dimensional holographic images,encoding phase and amplitude profiles separately at the object plane,encoding intensity profiles at the metasurface and object planes separately,and controlling the surface textures of three-dimensional holographic objects.展开更多
Reconstruction of experimental axisymmetric equilibria is an important part of toka-mak data analysis.Fourier expansion is applied to reconstruct the vessel current distribution inEFIT code.Benchmarking and testing ca...Reconstruction of experimental axisymmetric equilibria is an important part of toka-mak data analysis.Fourier expansion is applied to reconstruct the vessel current distribution inEFIT code.Benchmarking and testing calculations are performed to evaluate and validate thisalgorithm.Two cases for circular and non-circular plasma discharges are presented.Fourier ex-pansion used to fit the eddy current is a robust method and the real time EFIT can be introducedto the plasma control system in the coming campaign.展开更多
Deep learning(DL)is one of the fastest-growing topics in materials data science,with rapidly emerging applications spanning atomistic,image-based,spectral,and textual data modalities.DL allows analysis of unstructured...Deep learning(DL)is one of the fastest-growing topics in materials data science,with rapidly emerging applications spanning atomistic,image-based,spectral,and textual data modalities.DL allows analysis of unstructured data and automated identification of features.The recent development of large materials databases has fueled the application of DL methods in atomistic prediction in particular.In contrast,advances in image and spectral data have largely leveraged synthetic data enabled by high-quality forward models as well as by generative unsupervised DL methods.In this article,we present a high-level overview of deep learning methods followed by a detailed discussion of recent developments of deep learning in atomistic simulation,materials imaging,spectral analysis,and natural language processing.For each modality we discuss applications involving both theoretical and experimental data,typical modeling approaches with their strengths and limitations,and relevant publicly available software and datasets.We conclude the review with a discussion of recent cross-cutting work related to uncertainty quantification in this field and a brief perspective on limitations,challenges,and potential growth areas for DL methods in materials science.展开更多
Mesoscale simulations of gravity waves in the upper troposphere and lower stratosphere over North America and North Atlantic Ocean in January 2003 are compared with satellite radiance measurements from the Advanced Mi...Mesoscale simulations of gravity waves in the upper troposphere and lower stratosphere over North America and North Atlantic Ocean in January 2003 are compared with satellite radiance measurements from the Advanced Microwave Sounding Unit-A (AMSU-A). Four regions of strong gravity wave (GW) activities are found in the model simulations and the AMSU-A observations: the northwestern Atlantic, the U.S. Rockies, the Appalachians, and Greenland. GWs over the northwestern Atlantic Ocean are associated with the midlatitude baroclinic jet-front system, while the other three regions are apparently related to high topography. Model simulations are further used to analyze momentum fluxes in the zonal and meridional directions. It is found that strong westward momentum fluxes are prevalent over these regions over the whole period. Despite qualitative agreement between model simulations and satellite measurements, sensitivity experiments demonstrate that the simulated GWs are sensitive to the model spin-up time.展开更多
Detection of small cancer biomarkers with low molecular weight and a low concentration range has always been challenging yet urgent in many clinical applications such as diagnosing early-stage cancer,monitoring treatm...Detection of small cancer biomarkers with low molecular weight and a low concentration range has always been challenging yet urgent in many clinical applications such as diagnosing early-stage cancer,monitoring treatment and detecting relapse.Here,a highly enhanced plasmonic biosensor that can overcome this challenge is developed using atomically thin two-dimensional phase change nanomaterial.By precisely engineering the configuration with atomically thin materials,the phase singularity has been successfully achieved with a significantly enhanced lateral position shift effect.Based on our knowledge,it is the first experimental demonstration of a lateral position signal change>340μm at a sensing interface from all optical techniques.With this enhanced plasmonic effect,the detection limit has been experimentally demonstrated to be 10^(-15) mol L^(−1) for TNF-α cancer marker,which has been found in various human diseases including inflammatory diseases and different kinds of cancer.The as-reported novel integration of atomically thin Ge_(2)Sb_(2)Te_(5) with plasmonic substrate, which results in a phase singularity and thus a giant lateral position shift, enables the detection of cancer markers with low molecular weight at femtomolar level. These results will definitely hold promising potential in biomedical application and clinical diagnostics.展开更多
We prove a theorem concerning the approximation of generalized bandlimited multivariate functions by deep ReLU networks for which the curse of the dimensionality is overcome.Our theorem is based on a result by Maurey ...We prove a theorem concerning the approximation of generalized bandlimited multivariate functions by deep ReLU networks for which the curse of the dimensionality is overcome.Our theorem is based on a result by Maurey and on the ability of deep ReLU networks to approximate Chebyshev polynomials and analytic functions efficiently.展开更多
The Earth’s natural pulse electromagnetic field data consists typically of an underlying variation tendency of intensity and irregularities.The change tendency may be related to the occurrence of earthquake disasters...The Earth’s natural pulse electromagnetic field data consists typically of an underlying variation tendency of intensity and irregularities.The change tendency may be related to the occurrence of earthquake disasters.Forecasting of the underlying intensity trend plays an important role in the analysis of data and disaster monitoring.Combining chaos theory and the radial basis function neural network,this paper proposes a forecasting model of the chaotic radial basis function neural network to conduct underlying intensity trend forecasting by the Earth’s natural pulse electromagnetic field signal.The main strategy of this forecasting model is to obtain parameters as the basis for optimizing the radial basis function neural network and to forecast the reconstructed Earth’s natural pulse electromagnetic field data.In verification experiments,we employ the 3 and 6 days’data of two channels as training samples to forecast the 14 and 21-day Earth’s natural pulse electromagnetic field data respectively.According to the forecasting results and absolute error results,the chaotic radial basis function forecasting model can fit the fluctuation trend of the actual signal strength,effectively reduce the forecasting error compared with the traditional radial basis function model.Hence,this network may be useful for studying the characteristics of the Earth’s natural pulse electromagnetic field signal before a strong earthquake and we hope it can contribute to the electromagnetic anomaly monitoring before the earthquake.展开更多
Guangdong Province in Southeast China is noted for its numerous geothermal resources due to tectonic episodes,mainly occurred during the Cretaceous.The surface heat flow and geothermal gradient are the most direct way...Guangdong Province in Southeast China is noted for its numerous geothermal resources due to tectonic episodes,mainly occurred during the Cretaceous.The surface heat flow and geothermal gradient are the most direct ways to understand the temperature of the Earth.However,geothermal resources are poorly utilized in Guangdong Province due to limited numbers of boreholes and surficial hydrothermal fluids.To improve the understanding of underground temperature distribution in Guangdong Province,we have applied power-density spectral analysis to aeromagnetic anomaly data to calculate the depth of the Curie isothermal surface.Upward continuation is applied and tested to the magnetic data.The calculated Curie isotherm is between 18.5 km and 25 km below surface.The fluctuation in the depth range reflects lateral thermal perturbations in the Guangdong crust.In particular,the eastern,northern,western and coastline areas of the province have a relatively shallow Curie isotherm.By comparing the surface heat flow,geothermal gradient,distribution of Mesozoic granite-volcanic rocks,and natural hot springs,we conclude that during Mesozoic,magmatism exerted great influence on the deep thermal state of Guangdong Province.A shallow Curie isotherm surface,as well as numerous natural hot springs and high heat flow,show clear signatures of shallow heat sources.展开更多
There have been many theoretical studies and numerical investigations of nonlocal diffusion(ND)problems in recent years.In this paper,we propose and analyze a new discontinuous Galerkin method for solving one-dimensio...There have been many theoretical studies and numerical investigations of nonlocal diffusion(ND)problems in recent years.In this paper,we propose and analyze a new discontinuous Galerkin method for solving one-dimensional steady-state and time-dependent ND problems,based on a formulation that directly penalizes the jumps across the element interfaces in the nonlocal sense.We show that the proposed discontinuous Galerkin scheme is stable and convergent.Moreover,the local limit of such DG scheme recovers classical DG scheme for the corresponding local diff usion problem,which is a distinct feature of the new formulation and assures the asymptotic compatibility of the discretization.Numerical tests are also presented to demonstrate the eff ectiveness and the robustness of the proposed method.展开更多
We combine the newly constructed Galerkin difference basis with the energy-based discontinuous Galerkin method for wave equations in second-order form.The approximation properties of the resulting method are excellent...We combine the newly constructed Galerkin difference basis with the energy-based discontinuous Galerkin method for wave equations in second-order form.The approximation properties of the resulting method are excellent and the allowable time steps are large compared to traditional discontinuous Galerkin methods.The one drawback of the combined approach is the cost of inversion of the local mass matrix.We demonstrate that for constant coefficient problems on Cartesian meshes this bottleneck can be removed by the use of a modified Galerkin difference basis.For variable coefficients or non-Cartesian meshes this technique is not possible and we instead use the preconditioned conjugate gradient method to iteratively invert the mass matrices.With a careful choice of preconditioner we can demonstrate optimal complexity,albeit with a larger constant.展开更多
We develop a thin-film microstructural model that represents structural markers(i.e.,triple junctions in the two-dimensional projections of the structure of films with columnar grains)in terms of a stochastic,marked p...We develop a thin-film microstructural model that represents structural markers(i.e.,triple junctions in the two-dimensional projections of the structure of films with columnar grains)in terms of a stochastic,marked point process and the microstructure itself in terms of a grain-boundary network.The advantage of this representation is that it is conveniently applicable to the characterization of microstructures obtained from crystal orientation mapping,leading to a picture of an ensemble of interacting triple junctions,while providing results that inform grain-growth models with experimental data.More specifically,calculated quantities such as pair,partial pair and mark correlation functions,along with the microstructural mutual information(entropy),highlight effective triple junction interactions that dictate microstructural evolution.To validate this approach,we characterize microstructures from Al thin films via crystal orientation mapping and formulate an approach,akin to classical density functional theory,to describe grain growth that embodies triple-junction interactions.展开更多
Metasurfaces offer a unique platform to precisely control optical wavefronts and enable the realization of flat lenses,or metalenses,which have the potential to substantially reduce the size and complexity of imaging ...Metasurfaces offer a unique platform to precisely control optical wavefronts and enable the realization of flat lenses,or metalenses,which have the potential to substantially reduce the size and complexity of imaging systems and to realize new imaging modalities.However,it is a major challenge to create achromatic metalenses that produce a single focal length over a broad wavelength range because of the difficulty in simultaneously engineering phase profiles at distinct wavelengths on a single metasurface.For practical applications,there is a further challenge to create broadband achromatic metalenses that work in the transmission mode for incident light waves with any arbitrary polarization state.We developed a design methodology and created libraries of meta-units—building blocks of metasurfaces—with complex cross-sectional geometries to provide diverse phase dispersions(phase as a function of wavelength),which is crucial for creating broadband achromatic metalenses.We elucidated the fundamental limitations of achromatic metalens performance by deriving mathematical equations that govern the tradeoffs between phase dispersion and achievable lens parameters,including the lens diameter,numerical aperture(NA),and bandwidth of achromatic operation.We experimentally demonstrated several dielectric achromatic metalenses reaching the fundamental limitations.These metalenses work in the transmission mode with polarization-independent focusing efficiencies up to 50%and continuously provide a near-constant focal length over λ=1200–1650 nm.These unprecedented properties represent a major advance compared to the state of the art and a major step toward practical implementations of metalenses.展开更多
Broadband high reflectance in nature is often the result of randomly,three-dimensionally structured materials.This study explores unique optical properties associated with one-dimensional nanostructures discovered in ...Broadband high reflectance in nature is often the result of randomly,three-dimensionally structured materials.This study explores unique optical properties associated with one-dimensional nanostructures discovered in silk cocoon fibers of the comet moth,Argema mittrei.The fibers are populated with a high density of air voids randomly distributed across the fiber cross-section but are invariant along the fiber.These filamentary air voids strongly scatter light in the solar spectrum.A single silk fiber measuring~50μm thick can reflect 66%of incoming solar radiation,and this,together with the fibers’high emissivity of 0.88 in the mid-infrared range,allows the cocoon to act as an efficient radiative-cooling device.Drawing inspiration from these natural radiative-cooling fibers,biomimetic nanostructured fibers based on both regenerated silk fibroin and polyvinylidene difluoride are fabricated through wet spinning.Optical characterization shows that these fibers exhibit exceptional optical properties for radiative-cooling applications:nanostructured regenerated silk fibers provide a solar reflectivity of 0.73 and a thermal emissivity of 0.90,and nanostructured polyvinylidene difluoride fibers provide a solar reflectivity of 0.93 and a thermal emissivity of 0.91.The filamentary air voids lead to highly directional scattering,giving the fibers a highly reflective sheen,but more interestingly,they enable guided optical modes to propagate along the fibers through transverse Anderson localization.This discovery opens up the possibility of using wild silkmoth fibers as a biocompatible and bioresorbable material for optical signal and image transport.展开更多
Photonic devices rarely provide both elaborate spatial control and sharp spectral control over an incoming wavefront.In optical metasurfaces,for example,the localized modes of individual meta-units govern the wavefron...Photonic devices rarely provide both elaborate spatial control and sharp spectral control over an incoming wavefront.In optical metasurfaces,for example,the localized modes of individual meta-units govern the wavefront shape over a broad bandwidth,while nonlocal lattice modes extended over many unit cells support high quality-factor resonances.Here,we experimentally demonstrate nonlocal dielectric metasurfaces in the near-infrared that offer both spatial and spectral control of light,realizing metalenses focusing light exclusively over a narrowband resonance while leaving off-resonant frequencies unaffected.Our devices attain this functionality by supporting a quasi-bound state in the continuum encoded with a spatially varying geometric phase.We leverage this capability to experimentally realize a versatile platform for multispectral wavefront shaping where a stack of metasurfaces,each supporting multiple independently controlled quasi-bound states in the continuum,molds the optical wavefront distinctively at multiple wavelengths and yet stay transparent over the rest of the spectrum.Such a platform is scalable to the visible for applications in augmented reality and transparent displays.展开更多
Nucleation is one of the most common physical phenomena in physical,chemical,biological and materials sciences.Owing to the complex multiscale nature of various nucleation events and the difficulties in their direct e...Nucleation is one of the most common physical phenomena in physical,chemical,biological and materials sciences.Owing to the complex multiscale nature of various nucleation events and the difficulties in their direct experimental observation,development of effective computational methods and modeling approaches has become very important and is bringing new light to the study of this challenging subject.Our discussions in this manuscript provide a sampler of some newly developed numerical algorithms that are widely applicable to many nucleation and phase transformation problems.We first describe some recent progress on the design of efficient numerical methods for computing saddle points and minimum energy paths,and then illustrate their applications to the study of nucleation events associated with several different physical systems.展开更多
The recent advancement in lithium-niobite-on-insulator(LNOI)technology is opening up new opportunities in optoelectronics,as devices with better performance,lower power consumption and a smaller footprint can be reali...The recent advancement in lithium-niobite-on-insulator(LNOI)technology is opening up new opportunities in optoelectronics,as devices with better performance,lower power consumption and a smaller footprint can be realised due to the high optical confinement in the structures.The LNOI platform offers both largeχ(2)andχ(3)nonlinearities along with the power of dispersion engineering,enabling brand new nonlinear photonic devices and applications for the next generation of integrated photonic circuits.However,Raman scattering and its interaction with other nonlinear processes have not been extensively studied in dispersion-engineered LNOI nanodevices.In this work,we characterise the Raman radiation spectra in a monolithic lithium niobate(LN)microresonator via selective excitation of Raman-active phonon modes.The dominant mode for the Raman oscillation is observed in the backward direction for a continuous-wave pump threshold power of 20mW with a high differential quantum efficiency of 46%.We explore the effects of Raman scattering on Kerr optical frequency comb generation.We achieve mode-locked states in an X-cut LNOI chip through sufficient suppression of the Raman effect via cavity geometry control.Our analysis of the Raman effect provides guidance for the development of future chip-based photonic devices on the LNOI platform.展开更多
基金L.Z.is supported by the National Key Research and Development Program of China 2021YFF1200500 and the National Natural Science Foundation of China(No.12225102,T2321001,12050002,and 12288101)J.Y.is supported by the National Research Foundation,Singapore(Project No.NRF-NRFF13-2021-0005)+1 种基金Q.D.is supported by the National Science Foundation(DMS-2012562 and DMS-1937254)Y.C.is supported by the National Natural Science Foundation of China(No.12171041)。
文摘Rotational Bose-Einstein condensates can exhibit quantized vortices as topological excitations.In this study,the ground and excited states of the rotational Bose-Einstein condensates are systematically studied by calculating the stationary points of the Gross-Pitaevskii energy functional.Various excited states and their connections at different rotational frequencies are revealed in solution landscapes constructed with the constrained high-index saddle dynamics method.Four excitation mechanisms are identified:vortex addition,rearrangement,merging,and splitting.We demonstrate changes in the ground state with increasing rotational frequencies and decipher the evolution of the stability of ground states.
基金supported by the Defense Advanced Research Projects Agency(grant no.D15AP00111 and HR0011-17-2-0017)the National Science Foundation(grant no.ECCS-1307948 and QII-TAQS-1936359)+2 种基金the Air Force Office of Scientific Research(grant no.FA9550-14-1-0389 and FA9550-16-1-0322)support from the NSF IGERT program(grant no.DGE-1069240)supported by the US Department of Energy,Office of Basic Energy Sciences(contract no.DESC0012704).
文摘Metasurfaces are optically thin metamaterials that promise complete control of the wavefront of light but are primarily used to control only the phase of light.Here,we present an approach,simple in concept and in practice,that uses meta-atoms with a varying degree of form birefringence and rotation angles to create high-efficiency dielectric metasurfaces that control both the optical amplitude and phase at one or two frequencies.This opens up applications in computer-generated holography,allowing faithful reproduction of both the phase and amplitude of a target holographic scene without the iterative algorithms required in phase-only holography.We demonstrate all-dielectric metasurface holograms with independent and complete control of the amplitude and phase at up to two optical frequencies simultaneously to generate two-and three-dimensional holographic objects.We show that phaseamplitude metasurfaces enable a few features not attainable in phase-only holography;these include creating artifactfree two-dimensional holographic images,encoding phase and amplitude profiles separately at the object plane,encoding intensity profiles at the metasurface and object planes separately,and controlling the surface textures of three-dimensional holographic objects.
基金supported by National Natural Science Foundation of China (No. 10725523)
文摘Reconstruction of experimental axisymmetric equilibria is an important part of toka-mak data analysis.Fourier expansion is applied to reconstruct the vessel current distribution inEFIT code.Benchmarking and testing calculations are performed to evaluate and validate thisalgorithm.Two cases for circular and non-circular plasma discharges are presented.Fourier ex-pansion used to fit the eddy current is a robust method and the real time EFIT can be introducedto the plasma control system in the coming campaign.
基金Contributions from K.C.were supported by the financial assistance award 70NANB19H117 from the U.S.Department of CommerceNational Institute of Standards and Technology+5 种基金E.A.H.and R.C.(CMU)were supported by the National Science Foundation under grant CMMI-1826218the Air Force D3OM2S Center of Excellence under agreement FA8650-19-2-5209A.J.,C.C.,and S.P.O.were supported by the Materials Project,funded by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division under contract no,DE-AC02-05-CH11231Materials Project program KC23MP.S.J.L.B.was supported by the U.S.National Science Foundation through grant DMREF-1922234A.A.and A.C.were supported by NIST award 70NANB19H005NSF award CMMI-2053929.
文摘Deep learning(DL)is one of the fastest-growing topics in materials data science,with rapidly emerging applications spanning atomistic,image-based,spectral,and textual data modalities.DL allows analysis of unstructured data and automated identification of features.The recent development of large materials databases has fueled the application of DL methods in atomistic prediction in particular.In contrast,advances in image and spectral data have largely leveraged synthetic data enabled by high-quality forward models as well as by generative unsupervised DL methods.In this article,we present a high-level overview of deep learning methods followed by a detailed discussion of recent developments of deep learning in atomistic simulation,materials imaging,spectral analysis,and natural language processing.For each modality we discuss applications involving both theoretical and experimental data,typical modeling approaches with their strengths and limitations,and relevant publicly available software and datasets.We conclude the review with a discussion of recent cross-cutting work related to uncertainty quantification in this field and a brief perspective on limitations,challenges,and potential growth areas for DL methods in materials science.
基金Supported by the United States NSF Grants ATM-0618662 and ATM-0904635
文摘Mesoscale simulations of gravity waves in the upper troposphere and lower stratosphere over North America and North Atlantic Ocean in January 2003 are compared with satellite radiance measurements from the Advanced Microwave Sounding Unit-A (AMSU-A). Four regions of strong gravity wave (GW) activities are found in the model simulations and the AMSU-A observations: the northwestern Atlantic, the U.S. Rockies, the Appalachians, and Greenland. GWs over the northwestern Atlantic Ocean are associated with the midlatitude baroclinic jet-front system, while the other three regions are apparently related to high topography. Model simulations are further used to analyze momentum fluxes in the zonal and meridional directions. It is found that strong westward momentum fluxes are prevalent over these regions over the whole period. Despite qualitative agreement between model simulations and satellite measurements, sensitivity experiments demonstrate that the simulated GWs are sensitive to the model spin-up time.
基金We thank Shiyue Liu from School of Life Sciences in The Chinese University of Hong Kong for helpful discussions.This work is supported under the PROCORE-France/Hong Kong Joint Research Scheme(F-CUHK402/19)the Research Grants Council,Hong Kong Special Administration Region(AoE/P-02/12,14210517,14207419,N_CUHK407/16)the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No.798916.Y.Wang is supported under the Hong Kong PhD Fellowship Scheme.
文摘Detection of small cancer biomarkers with low molecular weight and a low concentration range has always been challenging yet urgent in many clinical applications such as diagnosing early-stage cancer,monitoring treatment and detecting relapse.Here,a highly enhanced plasmonic biosensor that can overcome this challenge is developed using atomically thin two-dimensional phase change nanomaterial.By precisely engineering the configuration with atomically thin materials,the phase singularity has been successfully achieved with a significantly enhanced lateral position shift effect.Based on our knowledge,it is the first experimental demonstration of a lateral position signal change>340μm at a sensing interface from all optical techniques.With this enhanced plasmonic effect,the detection limit has been experimentally demonstrated to be 10^(-15) mol L^(−1) for TNF-α cancer marker,which has been found in various human diseases including inflammatory diseases and different kinds of cancer.The as-reported novel integration of atomically thin Ge_(2)Sb_(2)Te_(5) with plasmonic substrate, which results in a phase singularity and thus a giant lateral position shift, enables the detection of cancer markers with low molecular weight at femtomolar level. These results will definitely hold promising potential in biomedical application and clinical diagnostics.
基金The research of the second author was partially supported by US NSF under the grant award DMS-1945029The research of the third author is supported in part by US NSF DMS-1719699the NSF TRIPODS program CCF-1704833.
文摘We prove a theorem concerning the approximation of generalized bandlimited multivariate functions by deep ReLU networks for which the curse of the dimensionality is overcome.Our theorem is based on a result by Maurey and on the ability of deep ReLU networks to approximate Chebyshev polynomials and analytic functions efficiently.
基金sponsored by the National Natural Science Foundation of China(61333002)Open Research Foundation of the State Key Laboratory of Geodesy and Earth’s Dynamics(SKLGED2018-5-4-E)+5 种基金Foundation of the Hubei Key Laboratory of Advanced Control and Intelligent Automation for Complex Systems(ACIA2017002)111 projects under Grant(B17040)Open Research Project of the Hubei Key Laboratory of Intelligent Geo-Information Processing(KLIGIP-2017A02)supported by the Three Gorges Research Center for geo-hazardMinistry of Education cooperation agreements of Krasnoyarsk Science Center and Technology BureauRussian Academy of Sciences。
文摘The Earth’s natural pulse electromagnetic field data consists typically of an underlying variation tendency of intensity and irregularities.The change tendency may be related to the occurrence of earthquake disasters.Forecasting of the underlying intensity trend plays an important role in the analysis of data and disaster monitoring.Combining chaos theory and the radial basis function neural network,this paper proposes a forecasting model of the chaotic radial basis function neural network to conduct underlying intensity trend forecasting by the Earth’s natural pulse electromagnetic field signal.The main strategy of this forecasting model is to obtain parameters as the basis for optimizing the radial basis function neural network and to forecast the reconstructed Earth’s natural pulse electromagnetic field data.In verification experiments,we employ the 3 and 6 days’data of two channels as training samples to forecast the 14 and 21-day Earth’s natural pulse electromagnetic field data respectively.According to the forecasting results and absolute error results,the chaotic radial basis function forecasting model can fit the fluctuation trend of the actual signal strength,effectively reduce the forecasting error compared with the traditional radial basis function model.Hence,this network may be useful for studying the characteristics of the Earth’s natural pulse electromagnetic field signal before a strong earthquake and we hope it can contribute to the electromagnetic anomaly monitoring before the earthquake.
基金This research was supported by grant from the National Natural Science Foundation of China:Study of radioactive heat in the mantle with Geoneutrino(No.41874100).
文摘Guangdong Province in Southeast China is noted for its numerous geothermal resources due to tectonic episodes,mainly occurred during the Cretaceous.The surface heat flow and geothermal gradient are the most direct ways to understand the temperature of the Earth.However,geothermal resources are poorly utilized in Guangdong Province due to limited numbers of boreholes and surficial hydrothermal fluids.To improve the understanding of underground temperature distribution in Guangdong Province,we have applied power-density spectral analysis to aeromagnetic anomaly data to calculate the depth of the Curie isothermal surface.Upward continuation is applied and tested to the magnetic data.The calculated Curie isotherm is between 18.5 km and 25 km below surface.The fluctuation in the depth range reflects lateral thermal perturbations in the Guangdong crust.In particular,the eastern,northern,western and coastline areas of the province have a relatively shallow Curie isotherm.By comparing the surface heat flow,geothermal gradient,distribution of Mesozoic granite-volcanic rocks,and natural hot springs,we conclude that during Mesozoic,magmatism exerted great influence on the deep thermal state of Guangdong Province.A shallow Curie isotherm surface,as well as numerous natural hot springs and high heat flow,show clear signatures of shallow heat sources.
基金Q.Du’s research is partially supported by US National Science Foundation Grant DMS-1719699,US AFOSR MURI Center for Material Failure Prediction Through Peridynamics,and US Army Research Office MURI Grant W911NF-15-1-0562.L.Ju’s research is partially supported by US National Science Foundation Grant DMS-1818438.J.Lu’s research is partially supported by Postdoctoral Science Foundation of China Grant 2017M610749.X.Tian’s research is partially supported by US National Science Foundation Grant DMS-1819233.
文摘There have been many theoretical studies and numerical investigations of nonlocal diffusion(ND)problems in recent years.In this paper,we propose and analyze a new discontinuous Galerkin method for solving one-dimensional steady-state and time-dependent ND problems,based on a formulation that directly penalizes the jumps across the element interfaces in the nonlocal sense.We show that the proposed discontinuous Galerkin scheme is stable and convergent.Moreover,the local limit of such DG scheme recovers classical DG scheme for the corresponding local diff usion problem,which is a distinct feature of the new formulation and assures the asymptotic compatibility of the discretization.Numerical tests are also presented to demonstrate the eff ectiveness and the robustness of the proposed method.
文摘We combine the newly constructed Galerkin difference basis with the energy-based discontinuous Galerkin method for wave equations in second-order form.The approximation properties of the resulting method are excellent and the allowable time steps are large compared to traditional discontinuous Galerkin methods.The one drawback of the combined approach is the cost of inversion of the local mass matrix.We demonstrate that for constant coefficient problems on Cartesian meshes this bottleneck can be removed by the use of a modified Galerkin difference basis.For variable coefficients or non-Cartesian meshes this technique is not possible and we instead use the preconditioned conjugate gradient method to iteratively invert the mass matrices.With a careful choice of preconditioner we can demonstrate optimal complexity,albeit with a larger constant.
基金K.B.acknowledges support from the U.S.National Science Foundation(NSF)grant DMS-1905492the DMREF program under DMS-2118206+3 种基金The work of Y.E.was partially supported by DMREF program NSF DMS-2118172JMR acknowledges support from the U.S.National Science Foundation(NSF)DMREF grant DMS-2118197C.L.acknowledges support from the U.S.National Science Foundation(NSF)DMREF grant DMS-2118181Matthew Patrick is thanked for providing the processed PED data.
文摘We develop a thin-film microstructural model that represents structural markers(i.e.,triple junctions in the two-dimensional projections of the structure of films with columnar grains)in terms of a stochastic,marked point process and the microstructure itself in terms of a grain-boundary network.The advantage of this representation is that it is conveniently applicable to the characterization of microstructures obtained from crystal orientation mapping,leading to a picture of an ensemble of interacting triple junctions,while providing results that inform grain-growth models with experimental data.More specifically,calculated quantities such as pair,partial pair and mark correlation functions,along with the microstructural mutual information(entropy),highlight effective triple junction interactions that dictate microstructural evolution.To validate this approach,we characterize microstructures from Al thin films via crystal orientation mapping and formulate an approach,akin to classical density functional theory,to describe grain growth that embodies triple-junction interactions.
基金supported by the Defense Advanced Research Projects Agency(no.D15AP00111 and no.HR0011-17-2-0017)the Air Force Office of Scientific Research(no.FA9550-14-1-0389 and no.FA9550-16-1-0322)+2 种基金the National Science Foundation(no.ECCS-1307948)support from the NSF IGERT program(no.DGE-1069240)supported by the US Department of Energy,Office of Basic Energy Sciences(contract no.DE-SC0012704)。
文摘Metasurfaces offer a unique platform to precisely control optical wavefronts and enable the realization of flat lenses,or metalenses,which have the potential to substantially reduce the size and complexity of imaging systems and to realize new imaging modalities.However,it is a major challenge to create achromatic metalenses that produce a single focal length over a broad wavelength range because of the difficulty in simultaneously engineering phase profiles at distinct wavelengths on a single metasurface.For practical applications,there is a further challenge to create broadband achromatic metalenses that work in the transmission mode for incident light waves with any arbitrary polarization state.We developed a design methodology and created libraries of meta-units—building blocks of metasurfaces—with complex cross-sectional geometries to provide diverse phase dispersions(phase as a function of wavelength),which is crucial for creating broadband achromatic metalenses.We elucidated the fundamental limitations of achromatic metalens performance by deriving mathematical equations that govern the tradeoffs between phase dispersion and achievable lens parameters,including the lens diameter,numerical aperture(NA),and bandwidth of achromatic operation.We experimentally demonstrated several dielectric achromatic metalenses reaching the fundamental limitations.These metalenses work in the transmission mode with polarization-independent focusing efficiencies up to 50%and continuously provide a near-constant focal length over λ=1200–1650 nm.These unprecedented properties represent a major advance compared to the state of the art and a major step toward practical implementations of metalenses.
基金supported by the NSF(grant no.PHY-1411445)the Air Force Office of Scientific Research(grant nos.FA9550-14-1-0389 and FA9550-16-1-0322)supported by the US Department of Energy,Office of Basic Energy Sciences,under contract no.DE-SC0012704.
文摘Broadband high reflectance in nature is often the result of randomly,three-dimensionally structured materials.This study explores unique optical properties associated with one-dimensional nanostructures discovered in silk cocoon fibers of the comet moth,Argema mittrei.The fibers are populated with a high density of air voids randomly distributed across the fiber cross-section but are invariant along the fiber.These filamentary air voids strongly scatter light in the solar spectrum.A single silk fiber measuring~50μm thick can reflect 66%of incoming solar radiation,and this,together with the fibers’high emissivity of 0.88 in the mid-infrared range,allows the cocoon to act as an efficient radiative-cooling device.Drawing inspiration from these natural radiative-cooling fibers,biomimetic nanostructured fibers based on both regenerated silk fibroin and polyvinylidene difluoride are fabricated through wet spinning.Optical characterization shows that these fibers exhibit exceptional optical properties for radiative-cooling applications:nanostructured regenerated silk fibers provide a solar reflectivity of 0.73 and a thermal emissivity of 0.90,and nanostructured polyvinylidene difluoride fibers provide a solar reflectivity of 0.93 and a thermal emissivity of 0.91.The filamentary air voids lead to highly directional scattering,giving the fibers a highly reflective sheen,but more interestingly,they enable guided optical modes to propagate along the fibers through transverse Anderson localization.This discovery opens up the possibility of using wild silkmoth fibers as a biocompatible and bioresorbable material for optical signal and image transport.
基金supported by the Nationall Science Foundation(grant no.QI-TAQ5-1936359 and no.ECCS-2004685)and the Air Force fice of Scientifc Research(grant no.FA9550-14-1-0389 and no,FA9550-16-03221.S.C.M.acknowledges support from the NSF Graduate Research Fellowship Program(grant no.DGE-1644869).ACO.acknowledges support from the NSF IGERT program(grant no.DGE-1069240).Device fabrication was carried out at the Columbia Nano lnitiative dleanoom,and at the Advanced Science Research Center NanoFabrication Facility at the Gradute Center of the City University of New York.
文摘Photonic devices rarely provide both elaborate spatial control and sharp spectral control over an incoming wavefront.In optical metasurfaces,for example,the localized modes of individual meta-units govern the wavefront shape over a broad bandwidth,while nonlocal lattice modes extended over many unit cells support high quality-factor resonances.Here,we experimentally demonstrate nonlocal dielectric metasurfaces in the near-infrared that offer both spatial and spectral control of light,realizing metalenses focusing light exclusively over a narrowband resonance while leaving off-resonant frequencies unaffected.Our devices attain this functionality by supporting a quasi-bound state in the continuum encoded with a spatially varying geometric phase.We leverage this capability to experimentally realize a versatile platform for multispectral wavefront shaping where a stack of metasurfaces,each supporting multiple independently controlled quasi-bound states in the continuum,molds the optical wavefront distinctively at multiple wavelengths and yet stay transparent over the rest of the spectrum.Such a platform is scalable to the visible for applications in augmented reality and transparent displays.
基金supported by China NSFC No.11421110001 and 91430217supported by AcRF Tier-1 grant R-146-000-216-112+1 种基金the auspices of the U.S.Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344supported in part by NSF-DMS1318586.
文摘Nucleation is one of the most common physical phenomena in physical,chemical,biological and materials sciences.Owing to the complex multiscale nature of various nucleation events and the difficulties in their direct experimental observation,development of effective computational methods and modeling approaches has become very important and is bringing new light to the study of this challenging subject.Our discussions in this manuscript provide a sampler of some newly developed numerical algorithms that are widely applicable to many nucleation and phase transformation problems.We first describe some recent progress on the design of efficient numerical methods for computing saddle points and minimum energy paths,and then illustrate their applications to the study of nucleation events associated with several different physical systems.
基金supported by the National Science Foundation under NSF ECCS award No.1541959supported by the National Science Foundation(NSF)(ECCS-1740296 E2CDA)+1 种基金Defense Advanced Research Projects Agency(DARPA)(W31P4Q-15-1-0013)Air Force Office of Scientific Research(AFOSR)(FA9550-15-1-0303).
文摘The recent advancement in lithium-niobite-on-insulator(LNOI)technology is opening up new opportunities in optoelectronics,as devices with better performance,lower power consumption and a smaller footprint can be realised due to the high optical confinement in the structures.The LNOI platform offers both largeχ(2)andχ(3)nonlinearities along with the power of dispersion engineering,enabling brand new nonlinear photonic devices and applications for the next generation of integrated photonic circuits.However,Raman scattering and its interaction with other nonlinear processes have not been extensively studied in dispersion-engineered LNOI nanodevices.In this work,we characterise the Raman radiation spectra in a monolithic lithium niobate(LN)microresonator via selective excitation of Raman-active phonon modes.The dominant mode for the Raman oscillation is observed in the backward direction for a continuous-wave pump threshold power of 20mW with a high differential quantum efficiency of 46%.We explore the effects of Raman scattering on Kerr optical frequency comb generation.We achieve mode-locked states in an X-cut LNOI chip through sufficient suppression of the Raman effect via cavity geometry control.Our analysis of the Raman effect provides guidance for the development of future chip-based photonic devices on the LNOI platform.
