The generation of optical vortices from nonlinear photonic crystals(NPCs)with spatially modulated second-order nonlinearity offers a promising approach to extend the working wavelength and topological charge of vortex...The generation of optical vortices from nonlinear photonic crystals(NPCs)with spatially modulated second-order nonlinearity offers a promising approach to extend the working wavelength and topological charge of vortex beams for various applications.In this work,the second harmonic(SH)optical vortex beams generated from nonlinear fork gratings under Gaussian beam illumination are numerically investigated.The far-field intensity and phase distributions,as well as the orbital angular momentum(OAM)spectra of the SH beams,are analyzed for different structural topological charges and diffraction orders.Results reveal that higher-order diffraction and larger structural topological charges lead to angular interference patterns and non-uniform intensity distributions,deviating from the standard vortex profile.To optimize the SH vortex quality,the effects of the fundamental wave beam waist,crystal thickness,and grating duty cycle are explored.It is shown that increasing the beam waist can effectively suppress diffraction order interference and improve the beam’s quality.This study provides theoretical guidance for enhancing the performance of nonlinear optical devices based on NPCs.展开更多
Conventional approaches for obtaining the second and third harmonics typically employ several nonlinear crystals to generate them,which is restricted in application due to the complexity of the optical path and the bu...Conventional approaches for obtaining the second and third harmonics typically employ several nonlinear crystals to generate them,which is restricted in application due to the complexity of the optical path and the bulkiness of the device.In this work,we present a comprehensive theoretical and numerical investigation of the simultaneous generation and competition between the second harmonic waves(SHW)and the third harmonic waves(THW)in a single nonlinear crystal.Through analyzing both small-signal and large-signal regimes,we reveal the complex coupling mechanisms between SHW and THW generation processes.Using periodically poled lithium niobate as an example,we demonstrate that the relative conversion efficiencies between SHW and THW can be freely adjusted by controlling the input fundamental wave power.This work provides new insights for designing efficient frequency converters capable of generating both SHW and THW outputs with controllable intensity ratios.展开更多
Second harmonic generation(SHG),a fundamental and widely-studied phenomenon in nonlinear optics,has attracted significant attention for its ability to convert fundamental frequencies into their second harmonics.While ...Second harmonic generation(SHG),a fundamental and widely-studied phenomenon in nonlinear optics,has attracted significant attention for its ability to convert fundamental frequencies into their second harmonics.While the dominant SHG research has been focused on the optical and infrared regimes,its investigation in the microwave range presents challenges due to the requirements of materials with higher nonlinear coefficients and high-power microwave sources.Here,we provide an overview of methods together with underlying mechanisms for SHG in microwave frequencies,and discuss prospects and insights into the future developments of SHG-based technologies.The discussions on both numerical analyses and experimental studies will offer guidance for further SHG research and communication advancements in microwave regime.展开更多
Collagen characterization is crucial for disease diagnostics,prevention,and understanding,with growing focus on quantitative analysis at tissue and fibril levels.Numerous models have been developed to quantify structu...Collagen characterization is crucial for disease diagnostics,prevention,and understanding,with growing focus on quantitative analysis at tissue and fibril levels.Numerous models have been developed to quantify structural changes in collagen linked to various pathologies.However,many approaches remain limited to conceptual descriptions or rely on custom software,often requiring programming skills,which re-stricts their clinical application and potential impact.We introduce CollagenFitJ,a plugin for the open-source software platform ImageJ/FIJI,which represents a widely used microscopy image analysis tool.CollagenFitJ makes use of the cylindrical symmetry model for collagen to enable facile quantitative assessment of polarization-resolved second harmonic generation microscopy image stacks.The plugin’s main outputs are collagen structure-related maps(e.g.,orientation and anisotropy of collagen fibrils within the focal volume),which can be accompanied by distribution and randomness maps for a series of structure-related parameters.We describe and validate the use of CollagenFitJ on images acquired on rat-tail tendons,collagen capsules surrounding human thyroid nodules,and mouse colon tumors,using both scanning and widefield second harmonic generation microscopy datasets.The plugin was designed to be user-friendly,requiring little to no experience in image processing and coding to facilitate access for life scientists,medical staff,and microscopy practitioners with limited coding skills or time availability required for coding.展开更多
Designing novel two-dimensional structures and precisely modulating their second harmonic generation(SHG)attributes are key to advancing nonlinear photonic technologies.In this work,through first-principles calculatio...Designing novel two-dimensional structures and precisely modulating their second harmonic generation(SHG)attributes are key to advancing nonlinear photonic technologies.In this work,through first-principles calculations,we propose a novel tetrahedral phase of transition metal dichalcogenides(TMDs)and validate its structural feasibility in a family of compounds,i.e.,ZX_(2)(Z=Ti,Zr,Hf;X=S,Se,Te).Cohesive energy and phonon dispersion calculations further demonstrate that eight of nine possible ZX_(2)monolayers are dynamically stable.All the ZX_(2)monolayers exhibit pronounced out-of-plane SHG with nonlinear susceptibility components reaching the order of 10^(2)pm/V.Strain engineering imposes a profound influence on the SHG response of ZX_(2)monolayers by reducing symmetry and modifying nonlinear susceptibility components.The redshift and significant enhancement of the prominent peak in SHG spectra are also revealed due to strain-induced charge redistribution and band gap reduction.Intriguingly,strain-driven nonlinear optical switching effects are realized in the ZX_(2)monolayers,with a reversible switching of SHG component ordering under tensile and compressive strain.In such a case,the anisotropic SHG pattern transforms from fourfold to twofold symmetry under the strain.Our work demonstrates the efficacy of strain engineering in precisely enhancing SHG,paving the way for the integration of novel TMD structures into tunable and flexible nonlinear optical devices.展开更多
The heterostructures incorporated with two or more distinctive two-dimensional(2D)materials have attracted great attention be-cause they could give rise to enhanced prop-erty in comparison with their individual counte...The heterostructures incorporated with two or more distinctive two-dimensional(2D)materials have attracted great attention be-cause they could give rise to enhanced prop-erty in comparison with their individual counterparts.Here,a water-assisted two-step rapid physical vapor deposition(rPVD)method was explored and used to synthesize Bi_(2)Te_(3)-Sb_(2)Te_(3)lateral het-erostructures(LHS)successfully.The Bi_(2)Te_(3)-Sb_(2)Te_(3)LHS is in nearly uniform size,and grows along three particular orientations with the intersection angles of 120°.Inter-estingly,we found that the water molecules play a significant role in determining the growth orientation,namely whether it will grow along the vertical or lateral direction in 2D structure.Hence,a growth mechanism of LHS based on the water-assisted two-step rPVD was present,which can be used as a general strategy and extended to the growth of other 2D heterostruc-tures or homostructures,such as SnS-SnSe LHS and SnS-SnS lateral homostructures.Fur-thermore,the second-harmonic generation intensity of the Bi_(2)Te_(3)-Sb_(2)Te_(3)LHS is much stronger than that of the Bi_(2)Te_(3)/Sb_(2)Te_(3)vertical heterostructures(VHS).This work opens a new approach for the synthesis of water-assisted lateral 2D heterostructures or homostruc-tures and offers a new method to enhance the second-harmonic generation properties of topo-logical insulating materials.展开更多
Silicon nitride photonics has emerged as a promising integrated optical platform due to its broad transparency window,low optical loss,and mature fabrication technology.However,the inherent centrosymmetric crystal str...Silicon nitride photonics has emerged as a promising integrated optical platform due to its broad transparency window,low optical loss,and mature fabrication technology.However,the inherent centrosymmetric crystal structure of silicon nitride fundamentally restricts its applications in second-order nonlinear optical processes.Monolayer transition metal dichalcogenides,particularly tungsten disulfide(WS_(2)),exhibit strong second-order nonlinear responses,making them ideal candidates for nonlinear photonic applications.Herein,we demonstrate a heterogeneously integrated platform combining silicon nitride waveguides with chemical vapor deposition(CVD)-grown monolayer WS_(2),enabling second harmonic generation.A specially designed silica cladding featuring gentle-slope profile on silicon nitride strip waveguides facilitates the integration of centimeter-scale WS_(2)film with photonic circuits.This approach provides a robust solution for incorporating second-order nonlinearity into silicon nitride photonic systems.The demonstrated platform holds significant potential for advancing quantum networks,visible-light lasers,and integrated optical modulation/detection systems.展开更多
In this theoretical study,we investigate the generation of second harmonics(SH)during the interaction of a laser beam with a metallic nanoparticle(MNP)trimer.Utilizing a classical electrodynamics framework,we explore ...In this theoretical study,we investigate the generation of second harmonics(SH)during the interaction of a laser beam with a metallic nanoparticle(MNP)trimer.Utilizing a classical electrodynamics framework,we explore the nonlinear interactions between the laser beam fields and nanoparticles(NPs),accounting for dipole-dipole interactions among the particles.Analytical expressions are derived to quantify the impact of these interactions on SH radiation power for two distinct polarizations of the laser beam.Our findings indicate that when the laser electric field is aligned parallel to the trimer's symmetry axis,there is a significant enhancement in SH radiation power compared to a single non-interacting NP,accompanied by a red-shift in the plasmon resonance peak.Conversely,when the laser electric field is perpendicular to the trimer axis,the SH radiation power from each NP decreases,and the plasmon resonance peak experiences a blue-shift.Additionally,we examine the influence of particle size and interparticle separation on SH generation.These results provide valuable insights into the role of interparticle interactions in enhancing nonlinear optical processes in NP assemblies,with potential implications for the design of nanophotonic devices.展开更多
The quantum metric manifested as the Riemannian metric in the parameter space of Bloch bands,characterizes the topology and geometry of quantum states.The second harmonic generation(SHG),as one of the fundamental nonl...The quantum metric manifested as the Riemannian metric in the parameter space of Bloch bands,characterizes the topology and geometry of quantum states.The second harmonic generation(SHG),as one of the fundamental nonlinear optical responses that links geometry of optical transitions to physical observables,despite being widely studied in various materials,its relation to quantum metric,especially in the dynamical regime,stays obscure.展开更多
In this paper,we develop a new and effective multiple scale and strongly directional method for identifying and suppressing ground roll based on the second generation curvelet transform.Making the best use of the curv...In this paper,we develop a new and effective multiple scale and strongly directional method for identifying and suppressing ground roll based on the second generation curvelet transform.Making the best use of the curvelet transform＇s strong local directional characteristics,seismic frequency bands are transformed into scale data with and without noise.Since surface waves and primary reflected waves have less overlap in the curvelet domain,we can effectively identify and separate noise.Applying this method to prestack seismic data can successfully remove surface waves and,at the same time,protect the reflected events well,particularly in the low-frequency band.This indicates that the method described in this paper is an effective and amplitude-preserving method.展开更多
In May of 2007,the second generation selected （SS） and control （SC） groups of pearl oyster Pinctada martensii were established by selecting 10% breeders with the largest and mean shell length,respectively,from the...In May of 2007,the second generation selected （SS） and control （SC） groups of pearl oyster Pinctada martensii were established by selecting 10% breeders with the largest and mean shell length,respectively,from the first generation selected group.Growth performance of the SS and SC groups were compared on the basis of measurement data at Days 8,18,60,95,195 and 365.On Day 365,100 individuals （60.0–75.0 mm at shell length） were sampled from each group and then subjected to the experiment where physiological parameters such as filtrate rate,oxygen consumption and ammonia excretion were measured at 15,20,25 and 30°C.The results show that the SS group had significantly larger mean shell length and shell height than the SC group at Days 8,18,60,95,195 and 365 （P 0.05）.The genetic gains at different ages varied from 6.0% to 17.0% for shell length and 5.7% to 14.6% for shell height,respectively.At 15,20,25 and 30 ° C,the SS groups had significantly larger filtrate rate than the SC group （P 0.05）.At 15 and 25 °C,the differences in oxygen consumption rate between the SS and SC groups were not significant （P 0.05）.At 20 and 30 °C,however,the oxygen consumption rate of the SS group was significantly larger than the SC group （P 0.05）.At 15,20,25 and 30 °C,there were no significant differences in ammonia excretion rate between the SS and SC groups （P 0.05）.The present results indicate that there existed considerable genetic variability in the base population and a further selection could be likely fruitful.Mass selection for faster growth might produce animals that had higher intake of metabolizable energy by virtue of faster filtrating behavior.展开更多
A new time-domain analysis method that uses second generation wavelettransform (SGWT) for weak fault feature extraction is proposed. To extract incipient fault feature,a biorthogonal wavelet with the characteristics o...A new time-domain analysis method that uses second generation wavelettransform (SGWT) for weak fault feature extraction is proposed. To extract incipient fault feature,a biorthogonal wavelet with the characteristics of impact is constructed by using SGWT. Processingdetail signal of SGWT with a sliding window devised on the basis of rotating operation cycle, andextracting modulus maximum from each window, fault features in time-domain are highlighted. To makefurther analysis on the reason of the fault, wavelet package transform based on SGWT is used toprocess vibration data again. Calculating the energy of each frequency-band, the energy distributionfeatures of the signal are attained. Then taking account of the fault features and the energydistribution, the reason of the fault is worked out. An early impact-rub fault caused by axismisalignment and rotor imbalance is successfully detected by using this method in an oil refinery.展开更多
Over the last years, stem cell therapy has emerged asan inspiring alternative to restore cardiac function after myocardial infarction. A large body of evidence has been obtained in this field but there is no conclusiv...Over the last years, stem cell therapy has emerged asan inspiring alternative to restore cardiac function after myocardial infarction. A large body of evidence has been obtained in this field but there is no conclusive data on the efficacy of these treatments. Preclinical studies and early reports in humans have been encouraging and have fostered a rapid clinical translation, but positive results have not been uniformly observed and when present, they have been modest. Several types of stem cells, manufacturing methods and delivery routes have been tested in different clinical settings but direct comparison between them is challenging and hinders further research. Despite enormous achievements, major barriers have been found and many fundamental issues remain to be resolved. A better knowledge of the molecular mechanisms implicated in cardiac development and myocardial regeneration is critically needed to overcome some of these hurdles. Genetic and pharmacological priming together with the discovery of new sources of cells have led to a "second generation" of cell products that holds an encouraging promise in cardiovascular regenerative medicine. In this report, we review recent advances in this field focusing on the new types of stem cells that are currently being tested in human beings and on the novel strategies employed to boost cell performance in order to improve cardiac function and outcomes after myocardial infarction.展开更多
The presence of cracks in the rotor is one of the most dangerous and critical defects for rotating machinery.Defect of fatigue cracks may lead to long out-of-service periods,heavy damages of machines and severe econom...The presence of cracks in the rotor is one of the most dangerous and critical defects for rotating machinery.Defect of fatigue cracks may lead to long out-of-service periods,heavy damages of machines and severe economic consequences.With the method of finite element,vibration behavior of cracked rotors and crack detection was received considerable attention in the academic and engineering field.Various researchers studied the response of a cracked rotor and most of them are focused on the crack detection based on vibration behavior of cracked rotors.But it is often difficult to identify the crack parameters quantitatively.Second generation wavelets(SGW)finite element has good ability in modal analysis for singularity problems like a cracked rotor.Based on the fact that the feature of SGW could be designed depending on applications,a multiresolution finite element method is presented.The new model of SGW beam element is constructed.The first three natural frequencies of the rotor with different crack location and size were solved with SGW beam elements,and the database for crack diagnosis is obtained.The first three metrical natural frequencies are employed as inputs of the database and the intersection of the three frequencies contour lines predicted the normalized crack location and size.With the Bently RK4 rotor test rig,rotors with different crack location and size are tested and diagnosed.The experimental results denote the cracks quantitative identification method has higher identification precision.With SGW finite element method,a novel method is presented that has higher precision and faster computing speed to identify the crack location and size.展开更多
In order to extract the fault feature frequency of weak bearing signals,we put forward a local mean decomposition(LMD)method combining with the second generation wavelet transform.After performing the second generatio...In order to extract the fault feature frequency of weak bearing signals,we put forward a local mean decomposition(LMD)method combining with the second generation wavelet transform.After performing the second generation wavelet denoising,the spline-based LMD is used to decompose the high-frequency detail signals of the second generation wavelet signals into a number of production functions(PFs).Power spectrum analysis is applied to the PFs to detect bearing fault information and identify the fault patterns.Application in inner and outer race fault diagnosis of rolling bearing shows that the method can extract the vibration features of rolling bearing fault.This method is suitable for extracting the fault characteristics of the weak fault signals in strong noise.展开更多
The influences of phase and group velocity matching on cumulative second harmonic generation of Lamb waves are investigated in numerical perspective. Finite element simulations of nonlinear Lamb wave propagation are p...The influences of phase and group velocity matching on cumulative second harmonic generation of Lamb waves are investigated in numerical perspective. Finite element simulations of nonlinear Lamb wave propagation are performed for Lamb wave mode pairs with exact and approximate phase velocity matching, with and without group velocity matching, respectively. The evolution of time-domain second harmonic Lamb waves is analyzed with the propagation distance. The amplitudes of primary and second harmonic waves are calculated to characterize the acoustic nonlinearity. The results verify that phase velocity matching is necessary for generation of the cumulative second harmonic Lamb wave in numerical perspective, while group velocity matching is demonstrated to not be a necessary condition.展开更多
To preserve the sharp features and details of the synthetic aperture radar （SAR） image effectively when despeckling, a despeckling algorithm with edge detection in nonsubsampled second generation bandelet transform ...To preserve the sharp features and details of the synthetic aperture radar （SAR） image effectively when despeckling, a despeckling algorithm with edge detection in nonsubsampled second generation bandelet transform （NSBT） domain is proposed. First, the Canny operator is utilized to detect and remove edges from the SAR image. Then the NSBT which has an optimal approximation to the edges of images and a hard thresholding rule are used to approximate the details while despeckling the edge-removed image. Finally, the removed edges are added to the reconstructed image. As the edges axe detected and protected, and the NSBT is used, the proposed algorithm reaches the state-of-the-art effect which realizes both despeckling and preserving edges and details simultaneously. Experimental results show that both the subjective visual effect and the mainly objective performance indexes of the proposed algorithm outperform that of both Bayesian wavelet shrinkage with edge detection and Bayesian least square-Gaussian scale mixture （BLS-GSM）.展开更多
Mass selection for fast growth was conducted in three Pacific oyster (Crassostrea gigas) stocks from China, Japan and Korea using previously established lines (CS1, JS1, and KS1). To determine whether continuous progr...Mass selection for fast growth was conducted in three Pacific oyster (Crassostrea gigas) stocks from China, Japan and Korea using previously established lines (CS1, JS1, and KS1). To determine whether continuous progress can be achieved by selection for growth, the progeny of three second-generation Pacific oyster lines was selected for shell height and evaluated via a 400-day farming experiment. When harvested at the end of the experiment, the selected crosses of CS2, JS2, and KS2 lines grew by 9.2%, 10.2% and 9.6% larger than the control crosses, respectively. During grow-out stage, the genetic gain of three selected lines was (10.2 ± 1.4)%, (10.4 ± 0.3)%, and (8.4 ± 1.6)%, respectively; and the corresponding realized heritability was 0.457 ± 0.143, 0.312 ± 0.071 and 0.332 ± 0.009, respectively. These results indicated that the selection for fast growth achieved steady progress in the second generation of oyster. Our work provides supportive evidence for the continuity of the Pacific oyster selective breeding program.展开更多
The chemical preparation, crystal structure and infrared spectroscopic characterization of the triaqua（4-amino-6-methoxypyrimidine） cuprate（II） sulfate, [Cu（C5H7N3）（H2O）3]SO4, is reported. The compound crystal...The chemical preparation, crystal structure and infrared spectroscopic characterization of the triaqua（4-amino-6-methoxypyrimidine） cuprate（II） sulfate, [Cu（C5H7N3）（H2O）3]SO4, is reported. The compound crystallizes in the noncentrosymmetric orthorhombic space group P212121 with lattice parameters a = 7.9025（3）, b = 11.1189（4）, c = 12.9720（4） , V = 1139.81（7） ~3 and Z = 4. The Cu（II） cation is fivecoordinated, in an early half-way between square pyramidal and trigonal bipyramidal fashion, by two nitrogen atoms of the 4-amino-6-methoxypyrimidine ligand and three water oxygen atoms. In the atomic arrangement, the organic ligands and the 5-connected Cu centers are linked with each other to give a 1-D corrugated hybrid chain running along the b-axis direction. The chains are interconnected by the SO4^（2-） anions via O–H...O, O–H...S, C–H...O and N–H...O hydrogen bonds to form layers spreading parallel to the（011） plane. The vibrational absorption bands were identified by infrared spectroscopy. Quantitative measurements of the second harmonic generation（SHG） of a powdered sample at 1064 nm were performed and a relative efficiency of 5.2 times the KDP standard was observed. Magnetic properties were also defined to characterize the complex. Magnetic measurements revealed that this material had a onedimensional antiferromagnetic character. The magnetic parameters were g = 2.11 and 2J/k B = -36 K.展开更多
The emergence of two dimensional(2D)materials has opened new possibilities for exhibiting second harmonic genera-tion(SHG)at the nanoscale,due to their remarkable optical response related to stable excitons at room te...The emergence of two dimensional(2D)materials has opened new possibilities for exhibiting second harmonic genera-tion(SHG)at the nanoscale,due to their remarkable optical response related to stable excitons at room temperature.However,the ultimate atomic-scale interaction length with light makes the SHG of Transition Metal Dichalcogenides(TM-Ds)monolayers naturally weak.Here,we propose coupling a monolayer of TMDs with a photonic grating slab that works with doubly resonant bound states in the continuum(BIC).The BIC slabs are designed to exhibit a pair of BICs,reson-ant with both the fundamental wave(FW)and the second harmonic wave(SHW).Firstly,the spatial mode matching can be fulfilled by tilting FW's incident angle.We theoretically demonstrate that this strategy leads to more than four orders of magnitude enhancement of SHG efficiency than a sole monolayer of TMDs,under a pump light intensity of 0.1 GW/cm^(2).Moreover,we demonstrate that patterning the TMDs monolayer can further enhance the spatial overlap coefficient,which leads to an extra three orders of magnitude enhancement of SHG efficiency.These results demonstrate remarkable pos-sibilities for enhancing SHG with nonlinear 2D materials,opening many opportunities for chip-based light sources,nano-lasers,imaging,and biochemical sensing.展开更多
基金supported by the National Nat-ural Science Foundation of China(Nos.12192251,12174185,92163216,and 62288101).
文摘The generation of optical vortices from nonlinear photonic crystals(NPCs)with spatially modulated second-order nonlinearity offers a promising approach to extend the working wavelength and topological charge of vortex beams for various applications.In this work,the second harmonic(SH)optical vortex beams generated from nonlinear fork gratings under Gaussian beam illumination are numerically investigated.The far-field intensity and phase distributions,as well as the orbital angular momentum(OAM)spectra of the SH beams,are analyzed for different structural topological charges and diffraction orders.Results reveal that higher-order diffraction and larger structural topological charges lead to angular interference patterns and non-uniform intensity distributions,deviating from the standard vortex profile.To optimize the SH vortex quality,the effects of the fundamental wave beam waist,crystal thickness,and grating duty cycle are explored.It is shown that increasing the beam waist can effectively suppress diffraction order interference and improve the beam’s quality.This study provides theoretical guidance for enhancing the performance of nonlinear optical devices based on NPCs.
基金supported by the Science and Technology Project of Guangdong Province,China(Grant No.2020B010190001)the National Natural Science Foundation of China(Grant No.12434016)+1 种基金the National Key Research and Development Program of China(Grant No.2023YFA1406900)the Fund of the National Postdoctoral Researcher Program(Grant No.GZB20240785).
文摘Conventional approaches for obtaining the second and third harmonics typically employ several nonlinear crystals to generate them,which is restricted in application due to the complexity of the optical path and the bulkiness of the device.In this work,we present a comprehensive theoretical and numerical investigation of the simultaneous generation and competition between the second harmonic waves(SHW)and the third harmonic waves(THW)in a single nonlinear crystal.Through analyzing both small-signal and large-signal regimes,we reveal the complex coupling mechanisms between SHW and THW generation processes.Using periodically poled lithium niobate as an example,we demonstrate that the relative conversion efficiencies between SHW and THW can be freely adjusted by controlling the input fundamental wave power.This work provides new insights for designing efficient frequency converters capable of generating both SHW and THW outputs with controllable intensity ratios.
基金supported by the National Natural Science Foun-dation of China(No.12274339).
文摘Second harmonic generation(SHG),a fundamental and widely-studied phenomenon in nonlinear optics,has attracted significant attention for its ability to convert fundamental frequencies into their second harmonics.While the dominant SHG research has been focused on the optical and infrared regimes,its investigation in the microwave range presents challenges due to the requirements of materials with higher nonlinear coefficients and high-power microwave sources.Here,we provide an overview of methods together with underlying mechanisms for SHG in microwave frequencies,and discuss prospects and insights into the future developments of SHG-based technologies.The discussions on both numerical analyses and experimental studies will offer guidance for further SHG research and communication advancements in microwave regime.
基金supported by the Ministry of Research,Innovation and Digitalization,CNCS-UEFISCDI[Grant Nos.RO-NO-2019-0601(MEDYCONAI),PN-III-P4-PCE-2021-0444(RESONANO)]PN-IV-P1-PCE-2023-1137+2 种基金supported in part by IN2SIGHT,European Union’s Horizon 2020(GA.no.964481)by the Research Council of Lithuania(LMTLTAgreement No.P-MIP-23-237).
文摘Collagen characterization is crucial for disease diagnostics,prevention,and understanding,with growing focus on quantitative analysis at tissue and fibril levels.Numerous models have been developed to quantify structural changes in collagen linked to various pathologies.However,many approaches remain limited to conceptual descriptions or rely on custom software,often requiring programming skills,which re-stricts their clinical application and potential impact.We introduce CollagenFitJ,a plugin for the open-source software platform ImageJ/FIJI,which represents a widely used microscopy image analysis tool.CollagenFitJ makes use of the cylindrical symmetry model for collagen to enable facile quantitative assessment of polarization-resolved second harmonic generation microscopy image stacks.The plugin’s main outputs are collagen structure-related maps(e.g.,orientation and anisotropy of collagen fibrils within the focal volume),which can be accompanied by distribution and randomness maps for a series of structure-related parameters.We describe and validate the use of CollagenFitJ on images acquired on rat-tail tendons,collagen capsules surrounding human thyroid nodules,and mouse colon tumors,using both scanning and widefield second harmonic generation microscopy datasets.The plugin was designed to be user-friendly,requiring little to no experience in image processing and coding to facilitate access for life scientists,medical staff,and microscopy practitioners with limited coding skills or time availability required for coding.
基金supported by the National Natural Science Foundation of China(Grant Nos.12304220,12174157,12074150,and 12374174)the Natural Science Foundation of Jiangsu Province(Grant No.BK20230518)+2 种基金the China Postdoctoral Science Foundation(Grant No.2023M731383)the College Student Innovation Project(Grant No.202410299946X)the Scientific Research Project of Jiangsu University(Grant No.22A397).
文摘Designing novel two-dimensional structures and precisely modulating their second harmonic generation(SHG)attributes are key to advancing nonlinear photonic technologies.In this work,through first-principles calculations,we propose a novel tetrahedral phase of transition metal dichalcogenides(TMDs)and validate its structural feasibility in a family of compounds,i.e.,ZX_(2)(Z=Ti,Zr,Hf;X=S,Se,Te).Cohesive energy and phonon dispersion calculations further demonstrate that eight of nine possible ZX_(2)monolayers are dynamically stable.All the ZX_(2)monolayers exhibit pronounced out-of-plane SHG with nonlinear susceptibility components reaching the order of 10^(2)pm/V.Strain engineering imposes a profound influence on the SHG response of ZX_(2)monolayers by reducing symmetry and modifying nonlinear susceptibility components.The redshift and significant enhancement of the prominent peak in SHG spectra are also revealed due to strain-induced charge redistribution and band gap reduction.Intriguingly,strain-driven nonlinear optical switching effects are realized in the ZX_(2)monolayers,with a reversible switching of SHG component ordering under tensile and compressive strain.In such a case,the anisotropic SHG pattern transforms from fourfold to twofold symmetry under the strain.Our work demonstrates the efficacy of strain engineering in precisely enhancing SHG,paving the way for the integration of novel TMD structures into tunable and flexible nonlinear optical devices.
基金supported by the Natural Science Foundation of Fujian Province of China(2022J01646)。
文摘The heterostructures incorporated with two or more distinctive two-dimensional(2D)materials have attracted great attention be-cause they could give rise to enhanced prop-erty in comparison with their individual counterparts.Here,a water-assisted two-step rapid physical vapor deposition(rPVD)method was explored and used to synthesize Bi_(2)Te_(3)-Sb_(2)Te_(3)lateral het-erostructures(LHS)successfully.The Bi_(2)Te_(3)-Sb_(2)Te_(3)LHS is in nearly uniform size,and grows along three particular orientations with the intersection angles of 120°.Inter-estingly,we found that the water molecules play a significant role in determining the growth orientation,namely whether it will grow along the vertical or lateral direction in 2D structure.Hence,a growth mechanism of LHS based on the water-assisted two-step rPVD was present,which can be used as a general strategy and extended to the growth of other 2D heterostruc-tures or homostructures,such as SnS-SnSe LHS and SnS-SnS lateral homostructures.Fur-thermore,the second-harmonic generation intensity of the Bi_(2)Te_(3)-Sb_(2)Te_(3)LHS is much stronger than that of the Bi_(2)Te_(3)/Sb_(2)Te_(3)vertical heterostructures(VHS).This work opens a new approach for the synthesis of water-assisted lateral 2D heterostructures or homostruc-tures and offers a new method to enhance the second-harmonic generation properties of topo-logical insulating materials.
基金Project supported by the National Innovative Training Program for College Students of China(Grant No.2023069)the University Research and Innovation Project of the National University of Defense Technology。
文摘Silicon nitride photonics has emerged as a promising integrated optical platform due to its broad transparency window,low optical loss,and mature fabrication technology.However,the inherent centrosymmetric crystal structure of silicon nitride fundamentally restricts its applications in second-order nonlinear optical processes.Monolayer transition metal dichalcogenides,particularly tungsten disulfide(WS_(2)),exhibit strong second-order nonlinear responses,making them ideal candidates for nonlinear photonic applications.Herein,we demonstrate a heterogeneously integrated platform combining silicon nitride waveguides with chemical vapor deposition(CVD)-grown monolayer WS_(2),enabling second harmonic generation.A specially designed silica cladding featuring gentle-slope profile on silicon nitride strip waveguides facilitates the integration of centimeter-scale WS_(2)film with photonic circuits.This approach provides a robust solution for incorporating second-order nonlinearity into silicon nitride photonic systems.The demonstrated platform holds significant potential for advancing quantum networks,visible-light lasers,and integrated optical modulation/detection systems.
文摘In this theoretical study,we investigate the generation of second harmonics(SH)during the interaction of a laser beam with a metallic nanoparticle(MNP)trimer.Utilizing a classical electrodynamics framework,we explore the nonlinear interactions between the laser beam fields and nanoparticles(NPs),accounting for dipole-dipole interactions among the particles.Analytical expressions are derived to quantify the impact of these interactions on SH radiation power for two distinct polarizations of the laser beam.Our findings indicate that when the laser electric field is aligned parallel to the trimer's symmetry axis,there is a significant enhancement in SH radiation power compared to a single non-interacting NP,accompanied by a red-shift in the plasmon resonance peak.Conversely,when the laser electric field is perpendicular to the trimer axis,the SH radiation power from each NP decreases,and the plasmon resonance peak experiences a blue-shift.Additionally,we examine the influence of particle size and interparticle separation on SH generation.These results provide valuable insights into the role of interparticle interactions in enhancing nonlinear optical processes in NP assemblies,with potential implications for the design of nanophotonic devices.
基金supported by National Natural Science Foundation of China(Grant Nos.12025407,12474246,and 12450401)the National Key Research and Development Program of China(Grant No.2021YFA1400201)the Chinese Academy of Sciences(Grant Nos.YSBR-047 and XDB33030100)。
文摘The quantum metric manifested as the Riemannian metric in the parameter space of Bloch bands,characterizes the topology and geometry of quantum states.The second harmonic generation(SHG),as one of the fundamental nonlinear optical responses that links geometry of optical transitions to physical observables,despite being widely studied in various materials,its relation to quantum metric,especially in the dynamical regime,stays obscure.
基金the Natural Science Foundation(Grant No.40739908)National Basic Research Program of China(973 Program)(Grant No.2007CB209605).
文摘In this paper,we develop a new and effective multiple scale and strongly directional method for identifying and suppressing ground roll based on the second generation curvelet transform.Making the best use of the curvelet transform＇s strong local directional characteristics,seismic frequency bands are transformed into scale data with and without noise.Since surface waves and primary reflected waves have less overlap in the curvelet domain,we can effectively identify and separate noise.Applying this method to prestack seismic data can successfully remove surface waves and,at the same time,protect the reflected events well,particularly in the low-frequency band.This indicates that the method described in this paper is an effective and amplitude-preserving method.
基金The National Key Technology R&D Program in the 11th Five Year Plan of China under contract No. 2007BAD29B01-2National Department Public Benefit Research Foundation under contract No. nyhyzx 07-048Guangdong Marine and Fishery Bureau under contract Nos A200708C01, A200908A02 and A200908A05
文摘In May of 2007,the second generation selected （SS） and control （SC） groups of pearl oyster Pinctada martensii were established by selecting 10% breeders with the largest and mean shell length,respectively,from the first generation selected group.Growth performance of the SS and SC groups were compared on the basis of measurement data at Days 8,18,60,95,195 and 365.On Day 365,100 individuals （60.0–75.0 mm at shell length） were sampled from each group and then subjected to the experiment where physiological parameters such as filtrate rate,oxygen consumption and ammonia excretion were measured at 15,20,25 and 30°C.The results show that the SS group had significantly larger mean shell length and shell height than the SC group at Days 8,18,60,95,195 and 365 （P 0.05）.The genetic gains at different ages varied from 6.0% to 17.0% for shell length and 5.7% to 14.6% for shell height,respectively.At 15,20,25 and 30 ° C,the SS groups had significantly larger filtrate rate than the SC group （P 0.05）.At 15 and 25 °C,the differences in oxygen consumption rate between the SS and SC groups were not significant （P 0.05）.At 20 and 30 °C,however,the oxygen consumption rate of the SS group was significantly larger than the SC group （P 0.05）.At 15,20,25 and 30 °C,there were no significant differences in ammonia excretion rate between the SS and SC groups （P 0.05）.The present results indicate that there existed considerable genetic variability in the base population and a further selection could be likely fruitful.Mass selection for faster growth might produce animals that had higher intake of metabolizable energy by virtue of faster filtrating behavior.
文摘A new time-domain analysis method that uses second generation wavelettransform (SGWT) for weak fault feature extraction is proposed. To extract incipient fault feature,a biorthogonal wavelet with the characteristics of impact is constructed by using SGWT. Processingdetail signal of SGWT with a sliding window devised on the basis of rotating operation cycle, andextracting modulus maximum from each window, fault features in time-domain are highlighted. To makefurther analysis on the reason of the fault, wavelet package transform based on SGWT is used toprocess vibration data again. Calculating the energy of each frequency-band, the energy distributionfeatures of the signal are attained. Then taking account of the fault features and the energydistribution, the reason of the fault is worked out. An early impact-rub fault caused by axismisalignment and rotor imbalance is successfully detected by using this method in an oil refinery.
文摘Over the last years, stem cell therapy has emerged asan inspiring alternative to restore cardiac function after myocardial infarction. A large body of evidence has been obtained in this field but there is no conclusive data on the efficacy of these treatments. Preclinical studies and early reports in humans have been encouraging and have fostered a rapid clinical translation, but positive results have not been uniformly observed and when present, they have been modest. Several types of stem cells, manufacturing methods and delivery routes have been tested in different clinical settings but direct comparison between them is challenging and hinders further research. Despite enormous achievements, major barriers have been found and many fundamental issues remain to be resolved. A better knowledge of the molecular mechanisms implicated in cardiac development and myocardial regeneration is critically needed to overcome some of these hurdles. Genetic and pharmacological priming together with the discovery of new sources of cells have led to a "second generation" of cell products that holds an encouraging promise in cardiovascular regenerative medicine. In this report, we review recent advances in this field focusing on the new types of stem cells that are currently being tested in human beings and on the novel strategies employed to boost cell performance in order to improve cardiac function and outcomes after myocardial infarction.
基金supported by National Natural Science Foundation of China(Grant No.50875195)National Hi-tech Research and Development Program(863 Program,Grant No.2009AA04Z406)Foundation for the Author of National Excellent Doctoral Dissertation of China(Grant No.2007B33)
文摘The presence of cracks in the rotor is one of the most dangerous and critical defects for rotating machinery.Defect of fatigue cracks may lead to long out-of-service periods,heavy damages of machines and severe economic consequences.With the method of finite element,vibration behavior of cracked rotors and crack detection was received considerable attention in the academic and engineering field.Various researchers studied the response of a cracked rotor and most of them are focused on the crack detection based on vibration behavior of cracked rotors.But it is often difficult to identify the crack parameters quantitatively.Second generation wavelets(SGW)finite element has good ability in modal analysis for singularity problems like a cracked rotor.Based on the fact that the feature of SGW could be designed depending on applications,a multiresolution finite element method is presented.The new model of SGW beam element is constructed.The first three natural frequencies of the rotor with different crack location and size were solved with SGW beam elements,and the database for crack diagnosis is obtained.The first three metrical natural frequencies are employed as inputs of the database and the intersection of the three frequencies contour lines predicted the normalized crack location and size.With the Bently RK4 rotor test rig,rotors with different crack location and size are tested and diagnosed.The experimental results denote the cracks quantitative identification method has higher identification precision.With SGW finite element method,a novel method is presented that has higher precision and faster computing speed to identify the crack location and size.
基金the Key Fund Project of Sichuan Provincial Department of Education(No.13CZ0012)
文摘In order to extract the fault feature frequency of weak bearing signals,we put forward a local mean decomposition(LMD)method combining with the second generation wavelet transform.After performing the second generation wavelet denoising,the spline-based LMD is used to decompose the high-frequency detail signals of the second generation wavelet signals into a number of production functions(PFs).Power spectrum analysis is applied to the PFs to detect bearing fault information and identify the fault patterns.Application in inner and outer race fault diagnosis of rolling bearing shows that the method can extract the vibration features of rolling bearing fault.This method is suitable for extracting the fault characteristics of the weak fault signals in strong noise.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51325504,11474093,11622430 and 11474361the National Key Research and Development Program of China(2016YFC0801903-02)the Fundamental Research Funds for the Central Universities
文摘The influences of phase and group velocity matching on cumulative second harmonic generation of Lamb waves are investigated in numerical perspective. Finite element simulations of nonlinear Lamb wave propagation are performed for Lamb wave mode pairs with exact and approximate phase velocity matching, with and without group velocity matching, respectively. The evolution of time-domain second harmonic Lamb waves is analyzed with the propagation distance. The amplitudes of primary and second harmonic waves are calculated to characterize the acoustic nonlinearity. The results verify that phase velocity matching is necessary for generation of the cumulative second harmonic Lamb wave in numerical perspective, while group velocity matching is demonstrated to not be a necessary condition.
基金supported by the National Natural Science Foundation of China(6067309760702062)+3 种基金the National HighTechnology Research and Development Program of China(863 Program)(2008AA01Z1252007AA12Z136)the National ResearchFoundation for the Doctoral Program of Higher Education of China(20060701007)the Program for Cheung Kong Scholarsand Innovative Research Team in University(IRT 0645).
文摘To preserve the sharp features and details of the synthetic aperture radar （SAR） image effectively when despeckling, a despeckling algorithm with edge detection in nonsubsampled second generation bandelet transform （NSBT） domain is proposed. First, the Canny operator is utilized to detect and remove edges from the SAR image. Then the NSBT which has an optimal approximation to the edges of images and a hard thresholding rule are used to approximate the details while despeckling the edge-removed image. Finally, the removed edges are added to the reconstructed image. As the edges axe detected and protected, and the NSBT is used, the proposed algorithm reaches the state-of-the-art effect which realizes both despeckling and preserving edges and details simultaneously. Experimental results show that both the subjective visual effect and the mainly objective performance indexes of the proposed algorithm outperform that of both Bayesian wavelet shrinkage with edge detection and Bayesian least square-Gaussian scale mixture （BLS-GSM）.
基金supported by the National High Technology Research and Development Program (2006AA10A409)the National Basic Research Program of China (2010CB126406)
文摘Mass selection for fast growth was conducted in three Pacific oyster (Crassostrea gigas) stocks from China, Japan and Korea using previously established lines (CS1, JS1, and KS1). To determine whether continuous progress can be achieved by selection for growth, the progeny of three second-generation Pacific oyster lines was selected for shell height and evaluated via a 400-day farming experiment. When harvested at the end of the experiment, the selected crosses of CS2, JS2, and KS2 lines grew by 9.2%, 10.2% and 9.6% larger than the control crosses, respectively. During grow-out stage, the genetic gain of three selected lines was (10.2 ± 1.4)%, (10.4 ± 0.3)%, and (8.4 ± 1.6)%, respectively; and the corresponding realized heritability was 0.457 ± 0.143, 0.312 ± 0.071 and 0.332 ± 0.009, respectively. These results indicated that the selection for fast growth achieved steady progress in the second generation of oyster. Our work provides supportive evidence for the continuity of the Pacific oyster selective breeding program.
基金support provided by the Secretary of State for Scientific Research and Technology of TunisiaThe X-ray diffractometer was funded by NSF Grant 0087210, Ohio Board of Regents Grant CAP-491 and by Youngstown State University, USA
文摘The chemical preparation, crystal structure and infrared spectroscopic characterization of the triaqua（4-amino-6-methoxypyrimidine） cuprate（II） sulfate, [Cu（C5H7N3）（H2O）3]SO4, is reported. The compound crystallizes in the noncentrosymmetric orthorhombic space group P212121 with lattice parameters a = 7.9025（3）, b = 11.1189（4）, c = 12.9720（4） , V = 1139.81（7） ~3 and Z = 4. The Cu（II） cation is fivecoordinated, in an early half-way between square pyramidal and trigonal bipyramidal fashion, by two nitrogen atoms of the 4-amino-6-methoxypyrimidine ligand and three water oxygen atoms. In the atomic arrangement, the organic ligands and the 5-connected Cu centers are linked with each other to give a 1-D corrugated hybrid chain running along the b-axis direction. The chains are interconnected by the SO4^（2-） anions via O–H...O, O–H...S, C–H...O and N–H...O hydrogen bonds to form layers spreading parallel to the（011） plane. The vibrational absorption bands were identified by infrared spectroscopy. Quantitative measurements of the second harmonic generation（SHG） of a powdered sample at 1064 nm were performed and a relative efficiency of 5.2 times the KDP standard was observed. Magnetic properties were also defined to characterize the complex. Magnetic measurements revealed that this material had a onedimensional antiferromagnetic character. The magnetic parameters were g = 2.11 and 2J/k B = -36 K.
基金financial supports from the National Natural Science Foundation of China(Grant No.11604150)Fundamental Research Funds for the Central Universities of China(Grant No.ZYGX2020J010)M.Rahmani.acknowledges support from the UK Research and Innovation Future Leaders Fellowship(MR/T040513/1)。
文摘The emergence of two dimensional(2D)materials has opened new possibilities for exhibiting second harmonic genera-tion(SHG)at the nanoscale,due to their remarkable optical response related to stable excitons at room temperature.However,the ultimate atomic-scale interaction length with light makes the SHG of Transition Metal Dichalcogenides(TM-Ds)monolayers naturally weak.Here,we propose coupling a monolayer of TMDs with a photonic grating slab that works with doubly resonant bound states in the continuum(BIC).The BIC slabs are designed to exhibit a pair of BICs,reson-ant with both the fundamental wave(FW)and the second harmonic wave(SHW).Firstly,the spatial mode matching can be fulfilled by tilting FW's incident angle.We theoretically demonstrate that this strategy leads to more than four orders of magnitude enhancement of SHG efficiency than a sole monolayer of TMDs,under a pump light intensity of 0.1 GW/cm^(2).Moreover,we demonstrate that patterning the TMDs monolayer can further enhance the spatial overlap coefficient,which leads to an extra three orders of magnitude enhancement of SHG efficiency.These results demonstrate remarkable pos-sibilities for enhancing SHG with nonlinear 2D materials,opening many opportunities for chip-based light sources,nano-lasers,imaging,and biochemical sensing.
