The basic concept of synchrotron radiation beamlines for vacuum ultraviolet and X-ray experiments has been introduced to beginning users and designers of beamlines. The beamline defined here is composed of a front end...The basic concept of synchrotron radiation beamlines for vacuum ultraviolet and X-ray experiments has been introduced to beginning users and designers of beamlines. The beamline defined here is composed of a front end, pre-mirrors, and a monochromator with refocusing mirrors, which are connected by beam pipes, providing monochromatic light for the experiments. Firstly, time characteristics of the synchrotron radiation are briefly reviewed. Secondly, the basic technology is introduced as the fundamental knowledge required to both users and designers. The topics are photoabsorption by air and solids, front ends and beam pipes, mirrors, monochromators, and filters. Thirdly, the design consideration is described mainly for the designers. The topics are design principle, principle of ray tracing, optical machinery and control, and vacuum. Fourthly, polarization control is considered. The topics are polarizers, polarization diagnosis of beamline, and circularly-polarized light generation. Finally, a brief summary is given introducing some references for further knowledge of the users and the designers.展开更多
The effect of rapid thermal annealing （RTA） ambient on denuded zone and oxygen precipitates in Czochralski （CZ） silicon wafers is studied in this paper. N2 and a N2/NH3 mixture are used as RTA ambient. It is demon...The effect of rapid thermal annealing （RTA） ambient on denuded zone and oxygen precipitates in Czochralski （CZ） silicon wafers is studied in this paper. N2 and a N2/NH3 mixture are used as RTA ambient. It is demonstrated that a high density of oxygen precipitates and thin denuded zone are obtained in N2/NH3 ambient,while a relatively lower density of oxygen precipitates and thicker denuded zone are observed in N2 ambient. As the RTA duration times increased, the oxygen precipitate density increased and the denuded zone depth decreased. X-ray photoelectron spectroscopy （XPS） data and atomic force microscope （AFM） results show that there RTA process,which can explain the different effect of RTA was a surface nitriding reaction during the N2/NH3 ambient ambient.展开更多
In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures...In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures with flexible base(S1),combined base(S2),and semi-rigid base(S3)were selected to perform field strain tests under static and dynamic load using the fiber Bragg grating optical sensing technology.The changing characteristics of the strain field along the horizontal and depth directions of pavements were analyzed.The results indicate that the most unfavorable asphalt pavement layers were the upper-middle surface layer and the lower base layer.In addition,the most unfavorable loading positions on the surface layer and the base layer were the center of wheel load and the gap center between two wheels,respectively.The most unfavorable layer of the surface layers gradually moved from the lower layer to the upper layer with the increase of base layer modulus.The power function relationships between structural layer strain and vehicle speed were revealed.The semi-rigid base asphalt pavement was the most durable pavement type,since its strain value was lower compared to those of the other structures.展开更多
The LCLS-II （linac coherent light source II） will build on the success of the world＇s most powerful X-ray laser： the LCLS （linac coherent light source）. It will add two new X-ray laser beams and room for additio...The LCLS-II （linac coherent light source II） will build on the success of the world＇s most powerful X-ray laser： the LCLS （linac coherent light source）. It will add two new X-ray laser beams and room for additional new instruments, thus greatly increasing the number of experiments carried out each year. Multiple operation modes are proposed to accommodate a variety of user requirements. There are a large number of variables and objectives in the design. For each operation mode, MOGA （multi-objective genetic algorithm） is applied to optimize the machine parameters in order to minimize the jitters, energy spread, collective effects and emittance.展开更多
In the three-dimensional(3D) contour measurement,the phase shift profilometry(PSP) method is the most widely used one.However,the measurement speed of PSP is very low because of the multiple projections.In order to im...In the three-dimensional(3D) contour measurement,the phase shift profilometry(PSP) method is the most widely used one.However,the measurement speed of PSP is very low because of the multiple projections.In order to improve the measurement speed,color grating stripes are used for measurement in this paper.During the measurement,only one color sinusoidal fringe is projected on the measured object.Therefore,the measurement speed is greatly improved.Since there is coupling or interference phenomenon between the adjacent color grating stripes,a color correction method is used to improve the measurement results.A method for correcting nonlinear error of measurement system is proposed in this paper,and the sinusoidal property of acquired image after correction is better than that before correction.Experimental results show that with these correction methods,the measurement errors can be reduced.Therefore,it can support a good foundation for the high-precision 3D reconstruction.展开更多
With the stat-of-the-art laser technique, the quality of electron beam generated from LPA （laser-plasma accelerator） is now becoming much better. The natural merits of electron beam from LPA, e.g., high peak current...With the stat-of-the-art laser technique, the quality of electron beam generated from LPA （laser-plasma accelerator） is now becoming much better. The natural merits of electron beam from LPA, e.g., high peak current, ultra-low emittance and ultra-short bunch length, etc., pave the way to the novel light sources, especially in the realm of developing much more compact x-ray light sources, e.g., table-top XFEL （x-ray free-electron laser）. However, the radiation power is limited by the rather larger energy spread than conventional radio-frequency electron LINAC （linear accelerator）. Luckily, much more power could be extracted by using the undulator with transverse gradient when energy spread effect could be compensated. In this paper, we introduce a novel soit x-ray light source driven by LPA together with TGU （transverse gradient undulator） technique, meanwhile we present a simple idea on how to achieve much higher rep-rate （e.g., -100 kHz） FELs （free-electron lasers） boosted by TGU based on storage rings.展开更多
Fragmentation of CO in a linearly polarized femtosecond laser field within the intensity order of 10^14 W.cm^-2 at 820nm is investigated experimentally by using velocity mapping technique. According to the observed ki...Fragmentation of CO in a linearly polarized femtosecond laser field within the intensity order of 10^14 W.cm^-2 at 820nm is investigated experimentally by using velocity mapping technique. According to the observed kinetic energy and angular distributions of different charged fragment ions, fragmentation channels of CO are proposed. The angular distributions provide helpful information for assigning the dissociation channels.展开更多
The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three g...The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three general expressions governing the nonlinear optic behavior, based on the photon number conservation, are obtained by considering the partially stripped plasma as a nonlinear optic medium. The numerical result shows that the presence of the bound electrons in partially stripped plasma can significantly change the propagating property of the intense laser pulse.展开更多
A Mixed Line Rate(MLR)optical network is a good candidate for a core backbone network because of its ability to provide diverse line rates to effectively accommodate traffic demands with heterogeneous bandwidth requir...A Mixed Line Rate(MLR)optical network is a good candidate for a core backbone network because of its ability to provide diverse line rates to effectively accommodate traffic demands with heterogeneous bandwidth requirements.Because of the deleterious effects of physical impairments,there is a maximum transmission reach for optical signals before they have to be regenerated.Being expensive devices,regenerators are expected to be sparsely located and used in such a network,called a translucent optical network.In this paper,we consider the Grooming,Routing,and Wavelength Assignment(GRWA)problem so that the Quality of Transmission(QoT)for connections is satisfied,and the network-level performance metric of blocking probability is minimized.Cross-layer heuristics to effectively allocate the sparse regenerators in MLR networks are developed,and extensive simulation results are presented to demonstrate their effectiveness.展开更多
To a multibeam echo sounder system (MBES), under water sound refraction plays an important role in depth measure- ment accuracy, and errors in sound velocity profile lead to inaccuracies in the measured depth (especia...To a multibeam echo sounder system (MBES), under water sound refraction plays an important role in depth measure- ment accuracy, and errors in sound velocity profile lead to inaccuracies in the measured depth (especially for outer beams). A method is developed to estimate the sound velocity profile based on the depth measured by vertical beam. Using this depth and other pa- rameters, such as t (sound pulse propagation time), θ (beam inclination angle), etc. We can estimate a simple sound velocity profile with which the depth error has been reduced. This method has been tested with a real dataset acquired in the East China Sea.展开更多
Most of the materials used in engineered cementitious composite are fine in size to achieve ductile nature.Stone slurry powder(SSP)is an inert material obtained from stone industries as by-product which may cause haza...Most of the materials used in engineered cementitious composite are fine in size to achieve ductile nature.Stone slurry powder(SSP)is an inert material obtained from stone industries as by-product which may cause hazardous impact on environment.In this research work,partial replacement of silica sand(SS)and fine sand(FS)by SSP with different contents(25%and 50%each)for making engineered cementitious composite has been explored.The performance was evaluated on the basis of strength,tensile strain,mid span deflection capacity,ultra-sonic pulse velocity and microstructure.Mechanical strength was found to be increased at 25%SSP in both replacements;whereas,strength decreased slightly at 50%replacement.Tensile strain,mid span deflection and quality of concrete were enhanced with increase in SSP content.Using SSP formed denser cementitious composite can help to save the natural resources and contribute in making green cementitious composite.展开更多
Nowadays, because of its wide bandwidth and high communication capability, the optical fiber is more and more used for high data rate transmission of information in railway environments. Conventionally, only one servi...Nowadays, because of its wide bandwidth and high communication capability, the optical fiber is more and more used for high data rate transmission of information in railway environments. Conventionally, only one service is sent over the fiber at a time. However, many different services can be simultaneously conveyed in railway stations such as passenger information service, cellular phone, Wi-Fi... The objective of the work proposed in this paper is to demonstrate the potential benefits of transmitting radio signals over fiber in a railway environment. The main idea is to exploit the full capacity of the fiber by transmitting multiple services using the same fiber. Since, different services are operating in different frequency bands; we propose a new multiplexing technique called Mode Group Diversity Multiplexing （MGDM） to ensure the transmission of multiple services using the same fiber, without additional infrastructure. There are numerous advantages of the proposed technique, e.g., faster and reliable data exchange, high resolution video surveillance capability, high data rate information exchange in railway stations. We present, in this paper, the physical characteristics of optical fibers, performance of MGDM multiplexing technique, and the influence of the laser excitation conditions at the entrance of the fiber on the performances of the system.展开更多
A single-mode optical fiber with a convex chromatic dispersion profile is proposed for generating a flat supercontinuum(SC).The fiber has normal dispersion and the dispersion parameter D(λ,z) is a convex function of ...A single-mode optical fiber with a convex chromatic dispersion profile is proposed for generating a flat supercontinuum(SC).The fiber has normal dispersion and the dispersion parameter D(λ,z) is a convex function of wavelengths.It is shown from the numerical results that the chromatic dispersion,the flatness of the dispersion curve and the pump conditions have significant effect on SC generation.A flat and broad SC without strong residual pump component can be obtained when the pump wavelength is set in the vicinity of the wavelength at which the fiber has small normal group-velocity dispersion(GVD) and small dispersion slope.The fiber with a smaller normal GVD,a flatter dispersion profile and a higher nonlinear coefficient are more suitable for broad SC generation.展开更多
From the analysis and the contrast of band-limited ray tracing method based on Kirchhoff integral, it was found that the method performs many approximations in the derivation process and omits the derivative term of t...From the analysis and the contrast of band-limited ray tracing method based on Kirchhoff integral, it was found that the method performs many approximations in the derivation process and omits the derivative term of the phase factor in the Kirchhoff integral. Numerical calculations and analysis show that the omission of cor-relation terms in Kirchhoff integrals has a non-negligible effect on the calculation results, and the different terms in the Kirchhoff integral have different effects on different frequency ranges. The method can be applied to ve-locity models containing complex interfaces without changing waves and continuous media. the velocity model and can be extended to elastic waves and continuous media.展开更多
Mathematical programs with complementarity constraints(MPCC) is an important subclass of MPEC.It is a natural way to solve MPCC by constructing a suitable approximation of the primal problem.In this paper,we propose a...Mathematical programs with complementarity constraints(MPCC) is an important subclass of MPEC.It is a natural way to solve MPCC by constructing a suitable approximation of the primal problem.In this paper,we propose a new smoothing method for MPCC by using the aggregation technique.A new SQP algorithm for solving the MPCC problem is presented.At each iteration,the master direction is computed by solving a quadratic program,and the revised direction for avoiding the Maratos effect is generated by an explicit formula.As the non-degeneracy condition holds and the smoothing parameter tends to zero,the proposed SQP algorithm converges globally to an S-stationary point of the MPEC problem,its convergence rate is superlinear.Some preliminary numerical results are reported.展开更多
[Objective]The aim was to measure photosynthetic characters of SC 205, a cassava cultivar, and explore the relationships of the net photosynthetic rate （Pn） with physiological and ecological factors. [Method] The di...[Objective]The aim was to measure photosynthetic characters of SC 205, a cassava cultivar, and explore the relationships of the net photosynthetic rate （Pn） with physiological and ecological factors. [Method] The diurnal variations of photosyn-thesis in leaves of SC205 were studied by LICOR-6400 portable photosynthesis system, and the relationships of the net photosynthetic rate （Pn） with physiological and ecological factors were studied by simple correlation analysis and path analysis. [Result] The curve of diurnal variation of Pn showed single peak at 10：00 am at 24.07 μ mol CO2 m2/s, without showing midday depression; the diurnal changes of stomatal conductance （Gs）, transpiration rate （Tr）, leaf temperature （Tl）, air tempera-ture （Ta） and photosynthetic active radiation （PAR） al showed single peak curves, and there were positive relationships of Pn with Gs, Tr, Tl, Ta and PAR. The diur-nal variations of intercellular CO2 concentration （Ci）, atmospheric CO2 concentration （Ca）, relative humidity （RH） showed in a U-shape curve. There were highly signifi-cant positive correlation of Pn with Gs and PAR; the diurnal variation of Pn had highly significant negative correlations with Ci and Ca. The direct impact of physio-logical factors on Pn was as fol ows： Ci＆gt;Gs＆gt;Tl＆gt;Tr, and the direct impact of ecologi-cal factors was RH＆gt;PAR＆gt;Ca＆gt;Ta. [Conclusion] The research showed that Ci, Gs and Tr play very important roles in the changes of Pn among the physiological fac-tors, and PAR and Ca affect the changes of Pn among the ecological factors.展开更多
Amorphous silicon nitride films were deposited by low-frequency plasma-enhanced chemical vapor deposition（LF-PECVD） using silane and nitrogen as precursors. Characteristics such as deposition rate, surface morpholog...Amorphous silicon nitride films were deposited by low-frequency plasma-enhanced chemical vapor deposition（LF-PECVD） using silane and nitrogen as precursors. Characteristics such as deposition rate, surface morphology, and chemical composition were measured by spectroscopic ellipsometry（SE）, atomic force mieroscope（AFM） and x-ray photoelectron spectroscopy（XPS）. It was shown that amorphous silicon nitride film could be prepared by LF-PECVD with good uniformity and even surface. The XPS result indicated that a small quantity of oxygen was involved in the sample, which was discussed in this paper.展开更多
A new type of compact terahertz (THz) radiation source using free electron laser (FEL) is discussed in this paper.The concept machine consists of an independently tunable cell thermionic RF gun (ITC-RF Gun),an acceler...A new type of compact terahertz (THz) radiation source using free electron laser (FEL) is discussed in this paper.The concept machine consists of an independently tunable cell thermionic RF gun (ITC-RF Gun),an accelerating structure with symmetry RF-incoupler and a coaxial load RF-outcoupler,an undulator combined with an optical resonance cavity of hole-coupling mode.Withoutα-magnet and other bunch compressors,the size of this machine is decreased.The conceptual design and numerical simulation are presented.展开更多
Yellow light-emitting diodes(LEDs) are widely utilized in high-quality lighting, light communication,indicator lamps, etc. Owing to their outstanding material properties and device performance, the metal halide perovs...Yellow light-emitting diodes(LEDs) are widely utilized in high-quality lighting, light communication,indicator lamps, etc. Owing to their outstanding material properties and device performance, the metal halide perovskites have demonstrated a significant potential for LED applications. However, the performance of the yellow perovskite LEDs(PeLEDs) is inferior to that of their green and red counterparts, with the maximum external quantum efficiency(EQE) limited to ~3.1%. Further, a majority of the yellow PeLEDs are fabricated using the spin-coating methods. The current study reports the development of the yellow CsPbBr_(2)I PeLEDs based on an all-vacuum deposition approach, which has been widely employed in the commercial organic LEDs(OLEDs). By controlling the co-evaporation rate of CsI and PbBr;, the growth kinetics of the perovskite layer are regulated to achieve a small grain size of~31.8 nm. Consequently, an improved radiative recombination rate(8.04 × 10^(-9)cm^(3)/s) is obtained owing to the spatial confinement effect. The PeLEDs based on the optimal perovskite film demonstrate the yellow electroluminescence(574 nm) with a maximum EQE of ~3.7% and luminance of~16,200 cd/m^(2), thus, representing one of the most efficient and bright yellow PeLEDs. Overall, this study provides a useful guideline for realizing the efficient PeLEDs based on the thermal evaporation strategy and highlights the potential of PeLED as an efficient and bright yellow light source.展开更多
The Proper Orthogonal Decomposition(POD)-based ensemble four-dimensional variational(4DVar) assimilation method(POD4DEnVar) was proposed to combine the strengths of EnKF(i.e.,the ensemble Kalman filter) and 4DVar assi...The Proper Orthogonal Decomposition(POD)-based ensemble four-dimensional variational(4DVar) assimilation method(POD4DEnVar) was proposed to combine the strengths of EnKF(i.e.,the ensemble Kalman filter) and 4DVar assimilation methods.Recently,a POD4DEnVar-based radar data assimilation scheme(PRAS) was built and its effectiveness was demonstrated.POD4 DEnVar is based on the assumption of a linear relationship between the model perturbations(MPs)and the observation perturbations(OPs);however,this assumption is likely to be destroyed by the highly non-linear forecast model or observation operator.To address this issue,using the Gauss-Newton iterative method,the nonlinear least squares enhanced POD4 DEnVar algorithm(referred to as NLS-4DVar) was proposed.Naturally,the PRAS was upgraded to form the NLS-4DVar-based radar data assimilation scheme(NRAS).To evaluate the performance of NRAS against PRAS,observing system simulation experiments(OSSEs) were conducted to assimilate reflectivity and radial velocity individually,with one,two,and three iterations.The results demonstrated that the NRAS outperformed PRAS in improving the initial condition and the forecasting of model variables and rainfall.The NRAS,with a smaller number of iterations,can yield a convergent result.In contrast to the situation when assimilating radial velocity,the advantages of NRAS over PRAS were more obvious when assimilating reflectivity.展开更多
文摘The basic concept of synchrotron radiation beamlines for vacuum ultraviolet and X-ray experiments has been introduced to beginning users and designers of beamlines. The beamline defined here is composed of a front end, pre-mirrors, and a monochromator with refocusing mirrors, which are connected by beam pipes, providing monochromatic light for the experiments. Firstly, time characteristics of the synchrotron radiation are briefly reviewed. Secondly, the basic technology is introduced as the fundamental knowledge required to both users and designers. The topics are photoabsorption by air and solids, front ends and beam pipes, mirrors, monochromators, and filters. Thirdly, the design consideration is described mainly for the designers. The topics are design principle, principle of ray tracing, optical machinery and control, and vacuum. Fourthly, polarization control is considered. The topics are polarizers, polarization diagnosis of beamline, and circularly-polarized light generation. Finally, a brief summary is given introducing some references for further knowledge of the users and the designers.
文摘The effect of rapid thermal annealing （RTA） ambient on denuded zone and oxygen precipitates in Czochralski （CZ） silicon wafers is studied in this paper. N2 and a N2/NH3 mixture are used as RTA ambient. It is demonstrated that a high density of oxygen precipitates and thin denuded zone are obtained in N2/NH3 ambient,while a relatively lower density of oxygen precipitates and thicker denuded zone are observed in N2 ambient. As the RTA duration times increased, the oxygen precipitate density increased and the denuded zone depth decreased. X-ray photoelectron spectroscopy （XPS） data and atomic force microscope （AFM） results show that there RTA process,which can explain the different effect of RTA was a surface nitriding reaction during the N2/NH3 ambient ambient.
基金Projects(51908071,51708071)supported by National Natural Science Foundation of ChinaProject(2020JJ5975)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(18C0194)supported by the Scientific Research Project of Education Department of Hunan Province,ChinaProject(kfj190301)supported by Open Fund of Key Laboratory of Road Structure and Material of Ministry of Transport(Changsha University of Science&Technology),China。
文摘In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures with flexible base(S1),combined base(S2),and semi-rigid base(S3)were selected to perform field strain tests under static and dynamic load using the fiber Bragg grating optical sensing technology.The changing characteristics of the strain field along the horizontal and depth directions of pavements were analyzed.The results indicate that the most unfavorable asphalt pavement layers were the upper-middle surface layer and the lower base layer.In addition,the most unfavorable loading positions on the surface layer and the base layer were the center of wheel load and the gap center between two wheels,respectively.The most unfavorable layer of the surface layers gradually moved from the lower layer to the upper layer with the increase of base layer modulus.The power function relationships between structural layer strain and vehicle speed were revealed.The semi-rigid base asphalt pavement was the most durable pavement type,since its strain value was lower compared to those of the other structures.
文摘The LCLS-II （linac coherent light source II） will build on the success of the world＇s most powerful X-ray laser： the LCLS （linac coherent light source）. It will add two new X-ray laser beams and room for additional new instruments, thus greatly increasing the number of experiments carried out each year. Multiple operation modes are proposed to accommodate a variety of user requirements. There are a large number of variables and objectives in the design. For each operation mode, MOGA （multi-objective genetic algorithm） is applied to optimize the machine parameters in order to minimize the jitters, energy spread, collective effects and emittance.
基金supported by the National Natural Science Foundation of China(Nos.60808020 and 61078041)the National Science and Technology Support(No.2014BAH03F01)+1 种基金the Tianjin Research Program of Application Foundation and Advanced Technology(No.10JCYBJC07200)the Technology Program of Tianjin Municipal Education Commission(No.20130324)
文摘In the three-dimensional(3D) contour measurement,the phase shift profilometry(PSP) method is the most widely used one.However,the measurement speed of PSP is very low because of the multiple projections.In order to improve the measurement speed,color grating stripes are used for measurement in this paper.During the measurement,only one color sinusoidal fringe is projected on the measured object.Therefore,the measurement speed is greatly improved.Since there is coupling or interference phenomenon between the adjacent color grating stripes,a color correction method is used to improve the measurement results.A method for correcting nonlinear error of measurement system is proposed in this paper,and the sinusoidal property of acquired image after correction is better than that before correction.Experimental results show that with these correction methods,the measurement errors can be reduced.Therefore,it can support a good foundation for the high-precision 3D reconstruction.
基金The authors would like to thank Huang, Z., and Ding, Y. from SLAC and Feng, C., Deng, H., Lan, T., Shen, L., Wang, X. and Liu, B. from SINAP for helpful discussions. The authors are grateful for the support of Major State Basic Research Development Program of China （No. 2011CB808300）, and Natural Science Foundation of China （No. 11075199）.
文摘With the stat-of-the-art laser technique, the quality of electron beam generated from LPA （laser-plasma accelerator） is now becoming much better. The natural merits of electron beam from LPA, e.g., high peak current, ultra-low emittance and ultra-short bunch length, etc., pave the way to the novel light sources, especially in the realm of developing much more compact x-ray light sources, e.g., table-top XFEL （x-ray free-electron laser）. However, the radiation power is limited by the rather larger energy spread than conventional radio-frequency electron LINAC （linear accelerator）. Luckily, much more power could be extracted by using the undulator with transverse gradient when energy spread effect could be compensated. In this paper, we introduce a novel soit x-ray light source driven by LPA together with TGU （transverse gradient undulator） technique, meanwhile we present a simple idea on how to achieve much higher rep-rate （e.g., -100 kHz） FELs （free-electron lasers） boosted by TGU based on storage rings.
基金Supported by the National Natural Science Foundation of China under Grant Nos 20633070 and 20473090.
文摘Fragmentation of CO in a linearly polarized femtosecond laser field within the intensity order of 10^14 W.cm^-2 at 820nm is investigated experimentally by using velocity mapping technique. According to the observed kinetic energy and angular distributions of different charged fragment ions, fragmentation channels of CO are proposed. The angular distributions provide helpful information for assigning the dissociation channels.
基金the National Natural Science Foundation of China under
文摘The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three general expressions governing the nonlinear optic behavior, based on the photon number conservation, are obtained by considering the partially stripped plasma as a nonlinear optic medium. The numerical result shows that the presence of the bound electrons in partially stripped plasma can significantly change the propagating property of the intense laser pulse.
基金supported in part by National Science Foundation (NSF) under Grants No. CNS-0915795 and No.CNS-0916890
文摘A Mixed Line Rate(MLR)optical network is a good candidate for a core backbone network because of its ability to provide diverse line rates to effectively accommodate traffic demands with heterogeneous bandwidth requirements.Because of the deleterious effects of physical impairments,there is a maximum transmission reach for optical signals before they have to be regenerated.Being expensive devices,regenerators are expected to be sparsely located and used in such a network,called a translucent optical network.In this paper,we consider the Grooming,Routing,and Wavelength Assignment(GRWA)problem so that the Quality of Transmission(QoT)for connections is satisfied,and the network-level performance metric of blocking probability is minimized.Cross-layer heuristics to effectively allocate the sparse regenerators in MLR networks are developed,and extensive simulation results are presented to demonstrate their effectiveness.
基金funded by the National High Technology Research and Development Program of China('863'Program)under contract Nos.2004AA616080 and 2006AA09ZI03the National Natural Science Foundation of China(Project code:40606026).
文摘To a multibeam echo sounder system (MBES), under water sound refraction plays an important role in depth measure- ment accuracy, and errors in sound velocity profile lead to inaccuracies in the measured depth (especially for outer beams). A method is developed to estimate the sound velocity profile based on the depth measured by vertical beam. Using this depth and other pa- rameters, such as t (sound pulse propagation time), θ (beam inclination angle), etc. We can estimate a simple sound velocity profile with which the depth error has been reduced. This method has been tested with a real dataset acquired in the East China Sea.
基金Project(F1-17.1/2017-18/MANF-2017-18-HAR-78129)supported by the University Grants Commission New Delhi,India。
文摘Most of the materials used in engineered cementitious composite are fine in size to achieve ductile nature.Stone slurry powder(SSP)is an inert material obtained from stone industries as by-product which may cause hazardous impact on environment.In this research work,partial replacement of silica sand(SS)and fine sand(FS)by SSP with different contents(25%and 50%each)for making engineered cementitious composite has been explored.The performance was evaluated on the basis of strength,tensile strain,mid span deflection capacity,ultra-sonic pulse velocity and microstructure.Mechanical strength was found to be increased at 25%SSP in both replacements;whereas,strength decreased slightly at 50%replacement.Tensile strain,mid span deflection and quality of concrete were enhanced with increase in SSP content.Using SSP formed denser cementitious composite can help to save the natural resources and contribute in making green cementitious composite.
文摘Nowadays, because of its wide bandwidth and high communication capability, the optical fiber is more and more used for high data rate transmission of information in railway environments. Conventionally, only one service is sent over the fiber at a time. However, many different services can be simultaneously conveyed in railway stations such as passenger information service, cellular phone, Wi-Fi... The objective of the work proposed in this paper is to demonstrate the potential benefits of transmitting radio signals over fiber in a railway environment. The main idea is to exploit the full capacity of the fiber by transmitting multiple services using the same fiber. Since, different services are operating in different frequency bands; we propose a new multiplexing technique called Mode Group Diversity Multiplexing （MGDM） to ensure the transmission of multiple services using the same fiber, without additional infrastructure. There are numerous advantages of the proposed technique, e.g., faster and reliable data exchange, high resolution video surveillance capability, high data rate information exchange in railway stations. We present, in this paper, the physical characteristics of optical fibers, performance of MGDM multiplexing technique, and the influence of the laser excitation conditions at the entrance of the fiber on the performances of the system.
基金National Basic Research Program of China(2003CB314906)
文摘A single-mode optical fiber with a convex chromatic dispersion profile is proposed for generating a flat supercontinuum(SC).The fiber has normal dispersion and the dispersion parameter D(λ,z) is a convex function of wavelengths.It is shown from the numerical results that the chromatic dispersion,the flatness of the dispersion curve and the pump conditions have significant effect on SC generation.A flat and broad SC without strong residual pump component can be obtained when the pump wavelength is set in the vicinity of the wavelength at which the fiber has small normal group-velocity dispersion(GVD) and small dispersion slope.The fiber with a smaller normal GVD,a flatter dispersion profile and a higher nonlinear coefficient are more suitable for broad SC generation.
基金Supported by National Natural Science Foundation of China(No.41274120)
文摘From the analysis and the contrast of band-limited ray tracing method based on Kirchhoff integral, it was found that the method performs many approximations in the derivation process and omits the derivative term of the phase factor in the Kirchhoff integral. Numerical calculations and analysis show that the omission of cor-relation terms in Kirchhoff integrals has a non-negligible effect on the calculation results, and the different terms in the Kirchhoff integral have different effects on different frequency ranges. The method can be applied to ve-locity models containing complex interfaces without changing waves and continuous media. the velocity model and can be extended to elastic waves and continuous media.
基金supported by the National Natural Science Foundation of China(No.10861005)the Natural Science Foundation of Guangxi Province (No.0728206)the Innovation Project of Guangxi Graduate Education(No. 2009105950701M29).
文摘Mathematical programs with complementarity constraints(MPCC) is an important subclass of MPEC.It is a natural way to solve MPCC by constructing a suitable approximation of the primal problem.In this paper,we propose a new smoothing method for MPCC by using the aggregation technique.A new SQP algorithm for solving the MPCC problem is presented.At each iteration,the master direction is computed by solving a quadratic program,and the revised direction for avoiding the Maratos effect is generated by an explicit formula.As the non-degeneracy condition holds and the smoothing parameter tends to zero,the proposed SQP algorithm converges globally to an S-stationary point of the MPEC problem,its convergence rate is superlinear.Some preliminary numerical results are reported.
基金Supported by the Earmarked Fund for China Agriculture Research System(CARS-12)
文摘[Objective]The aim was to measure photosynthetic characters of SC 205, a cassava cultivar, and explore the relationships of the net photosynthetic rate （Pn） with physiological and ecological factors. [Method] The diurnal variations of photosyn-thesis in leaves of SC205 were studied by LICOR-6400 portable photosynthesis system, and the relationships of the net photosynthetic rate （Pn） with physiological and ecological factors were studied by simple correlation analysis and path analysis. [Result] The curve of diurnal variation of Pn showed single peak at 10：00 am at 24.07 μ mol CO2 m2/s, without showing midday depression; the diurnal changes of stomatal conductance （Gs）, transpiration rate （Tr）, leaf temperature （Tl）, air tempera-ture （Ta） and photosynthetic active radiation （PAR） al showed single peak curves, and there were positive relationships of Pn with Gs, Tr, Tl, Ta and PAR. The diur-nal variations of intercellular CO2 concentration （Ci）, atmospheric CO2 concentration （Ca）, relative humidity （RH） showed in a U-shape curve. There were highly signifi-cant positive correlation of Pn with Gs and PAR; the diurnal variation of Pn had highly significant negative correlations with Ci and Ca. The direct impact of physio-logical factors on Pn was as fol ows： Ci＆gt;Gs＆gt;Tl＆gt;Tr, and the direct impact of ecologi-cal factors was RH＆gt;PAR＆gt;Ca＆gt;Ta. [Conclusion] The research showed that Ci, Gs and Tr play very important roles in the changes of Pn among the physiological fac-tors, and PAR and Ca affect the changes of Pn among the ecological factors.
文摘Amorphous silicon nitride films were deposited by low-frequency plasma-enhanced chemical vapor deposition（LF-PECVD） using silane and nitrogen as precursors. Characteristics such as deposition rate, surface morphology, and chemical composition were measured by spectroscopic ellipsometry（SE）, atomic force mieroscope（AFM） and x-ray photoelectron spectroscopy（XPS）. It was shown that amorphous silicon nitride film could be prepared by LF-PECVD with good uniformity and even surface. The XPS result indicated that a small quantity of oxygen was involved in the sample, which was discussed in this paper.
文摘A new type of compact terahertz (THz) radiation source using free electron laser (FEL) is discussed in this paper.The concept machine consists of an independently tunable cell thermionic RF gun (ITC-RF Gun),an accelerating structure with symmetry RF-incoupler and a coaxial load RF-outcoupler,an undulator combined with an optical resonance cavity of hole-coupling mode.Withoutα-magnet and other bunch compressors,the size of this machine is decreased.The conceptual design and numerical simulation are presented.
基金supported by the National Natural Science Foundation of China(62050039 61725401 5171101030 51761145048 62004075 62005089 and 51902113)the National Key R&D Program of China(2016YFA0204000 and 2016YFB0201204)+2 种基金the Fundamental Research Funds for the Central Universities(HUST: 2019421JYCXJJ004)the Fund for Innovative Research Groups of the Natural Science Foundation of Hubei Province(2020CFA034)the Graduates’ Innovation Fund of Huazhong University of Science and Technology(HUST)(2021yjscxcy036)。
文摘Yellow light-emitting diodes(LEDs) are widely utilized in high-quality lighting, light communication,indicator lamps, etc. Owing to their outstanding material properties and device performance, the metal halide perovskites have demonstrated a significant potential for LED applications. However, the performance of the yellow perovskite LEDs(PeLEDs) is inferior to that of their green and red counterparts, with the maximum external quantum efficiency(EQE) limited to ~3.1%. Further, a majority of the yellow PeLEDs are fabricated using the spin-coating methods. The current study reports the development of the yellow CsPbBr_(2)I PeLEDs based on an all-vacuum deposition approach, which has been widely employed in the commercial organic LEDs(OLEDs). By controlling the co-evaporation rate of CsI and PbBr;, the growth kinetics of the perovskite layer are regulated to achieve a small grain size of~31.8 nm. Consequently, an improved radiative recombination rate(8.04 × 10^(-9)cm^(3)/s) is obtained owing to the spatial confinement effect. The PeLEDs based on the optimal perovskite film demonstrate the yellow electroluminescence(574 nm) with a maximum EQE of ~3.7% and luminance of~16,200 cd/m^(2), thus, representing one of the most efficient and bright yellow PeLEDs. Overall, this study provides a useful guideline for realizing the efficient PeLEDs based on the thermal evaporation strategy and highlights the potential of PeLED as an efficient and bright yellow light source.
基金partially supported by theNational Key Research and Development Program of China(Grant No.2016YFA0600203)the High-resolution Earth Observation System Major Special Project(CHEOS)(Grant No.32-Y20A17-9001-15/17)+1 种基金the National Natural Science Foundation of China(Grant No.41575100)the Special Fund for Meteorological Scientific Research in Public Interest(Grant No.GYHY201306045)
文摘The Proper Orthogonal Decomposition(POD)-based ensemble four-dimensional variational(4DVar) assimilation method(POD4DEnVar) was proposed to combine the strengths of EnKF(i.e.,the ensemble Kalman filter) and 4DVar assimilation methods.Recently,a POD4DEnVar-based radar data assimilation scheme(PRAS) was built and its effectiveness was demonstrated.POD4 DEnVar is based on the assumption of a linear relationship between the model perturbations(MPs)and the observation perturbations(OPs);however,this assumption is likely to be destroyed by the highly non-linear forecast model or observation operator.To address this issue,using the Gauss-Newton iterative method,the nonlinear least squares enhanced POD4 DEnVar algorithm(referred to as NLS-4DVar) was proposed.Naturally,the PRAS was upgraded to form the NLS-4DVar-based radar data assimilation scheme(NRAS).To evaluate the performance of NRAS against PRAS,observing system simulation experiments(OSSEs) were conducted to assimilate reflectivity and radial velocity individually,with one,two,and three iterations.The results demonstrated that the NRAS outperformed PRAS in improving the initial condition and the forecasting of model variables and rainfall.The NRAS,with a smaller number of iterations,can yield a convergent result.In contrast to the situation when assimilating radial velocity,the advantages of NRAS over PRAS were more obvious when assimilating reflectivity.
