This study discusses the scope of application of the Doppler backscattering(DBS)diagnostic for the tokamak with reactor technologies(TRT)project.This involved numerical modeling of the three-dimensional(3D)beam trajec...This study discusses the scope of application of the Doppler backscattering(DBS)diagnostic for the tokamak with reactor technologies(TRT)project.This involved numerical modeling of the three-dimensional(3D)beam trajectories.Calculations were performed to investigate the propagation of microwaves in the V(40–75 GHz)and W(75–110 GHz)frequency ranges with O-mode polarization for the density profile of the base TRT scenario.Our analysis showed that the DBS system antenna on the TRT would need to be tilted in both the poloidal and toroidal directions in order to meet the condition Kperp/Kpar<10%..For the DBS system located in the equatorial plane it was shown that a wide range of poloidal and toroidal angles is available for the successful implementation of the diagnostic to study the core,pedestal and scrape-off layer(SOL)regions.The DBS system located at 35 cm above the equatorial plane would be more limited in measurements only covering the SOL and pedestal regions.A shift of the cut-offs in the toroidal direction highlighted the need for 3D analysis of the DBS data.展开更多
A polarized bidirectional reflectance distribution function(pBRDF)matrix is developed from two-scale roughness theory with the aim of providing more accurate simulations of microwave emissions and scattering required ...A polarized bidirectional reflectance distribution function(pBRDF)matrix is developed from two-scale roughness theory with the aim of providing more accurate simulations of microwave emissions and scattering required for ocean-atmosphere coupled radiative transfer models.The potential of the pBRDF matrix is explored for simu-lating the ocean backscatter at Ku-band.The effects of ocean wave spectra including the modified Durden and Vesecky(DV2),Elfouhaily,and Kudryavtsev spectra on the pBRDF matrix backscatter simulations are investi-gated.Additionally,the differences in backscattering normalized radar cross-section(NRCS)simulations between the Ku-band geophysical model function and pBRDF matrix are analyzed.The results show that the pBRDF matrix can reasonably reproduce the spatial distribution of ocean surface backscattering energy,but the distribution pat-tern and numerical values are influenced by ocean wave spectra.The DV2 spectrum is the best one for the pBRDF matrix to simulate horizontally polarized NRCSs,with the exception of scenarios where the incidence angle is below 35°,the wind speed is less than 10 m s^(−1),and in the cross-wind direction.Also,the DV2 spectrum effec-tively characterizes the wind speed and relative azimuth angle dependence for vertically polarized NRCSs.The Elfouhaily spectrum is suitable for simulating vertically polarized NRCSs under conditions of low wind speed(be-low 5 m s^(−1))and incidence angles under 40°.The Kudryavtsev spectrum excels in simulating vertically polarized NRCSs at high incidence angles(>40°)and horizontally polarized NRCSs at low incidence angles(<35°).展开更多
The relates cross sections of Non-Rutherford backscattering of lie ions from N atoms at the energy range of 2-5MeV were measured.Several resonance energies and corresponding resonance widths are tabled.For analysis of...The relates cross sections of Non-Rutherford backscattering of lie ions from N atoms at the energy range of 2-5MeV were measured.Several resonance energies and corresponding resonance widths are tabled.For analysis of N in high Z substrate,the results of both experiment and computer simulation were given in this report.展开更多
The high-alloyed wrought superalloy GH4975 tends to form coarse MC carbides and eutectic(γ+γ′)phases,which adversely affect the cogging and homogenization process.To provide theoretical guidance for control of MC c...The high-alloyed wrought superalloy GH4975 tends to form coarse MC carbides and eutectic(γ+γ′)phases,which adversely affect the cogging and homogenization process.To provide theoretical guidance for control of MC carbides and eutectic(γ+γ′)formation,differential thermal analysis(DTA)was utilized to investigate the effect of cooing rate(10-90℃·min^(-1))on solidification behavior and micro-segregation of GH4975 alloy.According to the thermodynamic calculation and distribution characteristics of precipitates,the MC carbides can act as nucleation sites forγdendrites,but the nucleation ofγdendrites becomes less dependent on the MC carbide primers at higher cooling rates.As theγdendrites grow,the elements including Ti and Nb gradually accumulate in the residual liquid and leads to the formation of more MC carbides near the interdendritic region.Finally,the solidification is terminated with the formation of eutectic(γ+γ′).With an increase in cooling rate,the liquidus temperature rises,but the solidus temperature decreases,and thus the solidification range is obviously enlarged.The dendritic structure is significantly refined by the increase of cooling rate.The secondary dendrite arm spacing,λ_(2),as a function of cooling rate,T,can be expressed asλ_(2)=216.78T^(-0.42).Moreover,the increasing cooling rate weakens the back diffusion of Al,Ti,and Nb,increases the undercooling,and limits the growth of precipitates.Consequently,the sizes of MC carbides,eutectic(γ+γ′),and primaryγ′significantly decrease,but the area fraction of eutectic(γ+γ′)linerly increases as the cooling rate rises.Thus moderate cooling rate(such as 30℃·min^(-1))should be selected during the solidification process of GH4975 alloy.展开更多
Based on the effective medium approximation theory of composites, the whitecap-covered sea surface is treated as a medium layer of dense seawater droplets and air. Two electromagnetic scattering models of randomly rou...Based on the effective medium approximation theory of composites, the whitecap-covered sea surface is treated as a medium layer of dense seawater droplets and air. Two electromagnetic scattering models of randomly rough surface are applied to the investigation of microwave backscattering of breaking waves driven by strong wind. The shapes of seawater droplets are considered by calculating the effective dielectric constant of the whitecap layer. The responses of seawater droplets shapes, such as sphere and ellipsoid, to the backscattering coefficient are discussed. Numerical results of the models are in good agreement with the experimental measurements of horizontally and vertically polarized backscattering at microwave frequency 13.9GHz and different incidence angles.展开更多
The ionospheric oblique backscattering sounding system can not only be used to detect the state of the ionosphere and the condition of high frequency channel in real time, but also be used for over-the-horizon soundin...The ionospheric oblique backscattering sounding system can not only be used to detect the state of the ionosphere and the condition of high frequency channel in real time, but also be used for over-the-horizon sounding. Therefore, it has a very high military and civil value. For the characteristics of ionospheric oblique backscattering sounding, such as long sounding distance, wake echo, strong background noise, slow moving target, etc., a hardware platform of ionospheric oblique backscattering sounding system is designed. This platform adopts the technology of software radio and is designed as a new kind of general purpose, modularized, software-based ionosonde that is based on the VXI （Versa module eurocard eXtensions for Instrumentation） bus. This hardware platform has been successfully used in actual ionospheric oblique backscattering sounding, and the experimental results demonstrate that this system can satisfy the requirements.展开更多
The routine operational sigma0 regrouping method is proposed for a HY-2 A scatterometer（HSCAT） that maps time-ordered sigma0 s and related parameters into a subtrack aligned grid of wind vector cells（WVCs）. The re...The routine operational sigma0 regrouping method is proposed for a HY-2 A scatterometer（HSCAT） that maps time-ordered sigma0 s and related parameters into a subtrack aligned grid of wind vector cells（WVCs）. The regrouping method consists of two critical steps： ground grid generation and sigma0 resampling. The HSCAT uses subtrack swath coordinates, in which the nadir track of the satellite represents the center and the designated positions are specified in terms of a pair of along-track and cross-track coordinates. To calculate the subtrack coordinates for each sigma0, a ＂triangle marking＂ resampling method is developed. Three points, including the point of intersection, the center of a pulse footprint, and the origin of the subtrack coordinate system, form a right triangle; the length of the two right-angled sides is used to represent the cross-track and the along-track coordinates in the subtrack coordinate system. In addition, a nadir point interpolation correction is used to ensure the operation of the regrouping algorithm when the nadir point positional information is missing. To illustrate the ability of the proposed regrouping algorithm, the distribution of the WVC positions and wind vector retrieval results are analyzed, which show that the proposed regrouping algorithm meets the requirements for high-quality sea surface wind field retrieval.展开更多
The backscattering signal, which arises from the pulsed laser traveling through water, has limited the lidar system sensitivity and underwater target contrast. The transmitted optical carrier is modulated to be ultras...The backscattering signal, which arises from the pulsed laser traveling through water, has limited the lidar system sensitivity and underwater target contrast. The transmitted optical carrier is modulated to be ultrashort pulsed laser and it is effective to suppress the backscattering to adopt the coherent detection technology by identifying the modulation envelope. A nonstationary light field is formed in seawater by the ultrashort pulsed laser. The inherent relationship between the nonstationary light field formed by modulated lidar and the stationary light field formed by conventional lidar was discussed and the backscattering light model of the stationary light field for the ultrashort pulsed laser was proposed. The backscattering signal in modulated lidar system was processed and analyzed in the frequency domain on the basis of the model.展开更多
This study presents an investigation of the scattering and backscattering properties of the particulates in three Chinese inland lakes(the Taihu Lake, the Chaohu Lake and the Dianchi Lake) based on in situ measurement...This study presents an investigation of the scattering and backscattering properties of the particulates in three Chinese inland lakes(the Taihu Lake, the Chaohu Lake and the Dianchi Lake) based on in situ measurements taken at 119 sites. We modeled the particulate scattering spectra using a wavelength-dependent power-law function, finding that the power-law exponents in the Taihu Lake and the Chaohu Lake differ from those in the Dianchi Lake but are similar to the values in the U.S. coastal waters. In contrast to the open ocean, the backscattering properties in the three lakes can not be determined only from chlorophyll-a concentration. The backscattering ratio spectra exhibit a wavelength dependence feature in all three lakes, generally decreasing with the increasing wavelength. Analysis results of the correlations between the backscattering ratio and the individual water quality parameters clearly show that there are distinctive relations among the three lakes, attributed primarily to different compositions of optically active materials in the three lakes. Analysis of the mass-specific scattering and backscattering coefficients shows that the coefficients at wavelength 532 nm in the Taihu Lake and Chaohu Lake are similar, but they are apparently different from those in the Dianchi Lake. Lastly, Model I multiple linear regressions were adopted to partition the mass-specific cross-sections for scattering and backscattering into organic and inorganic cross-sections to further interpret the scattering and backscattering properties. The relative contribution of organic and inorganic particulates to scattering and backscattering is clearly different among the three lakes. The scattering and backscattering properties of the particulates in the three inland lakes vary significantly based on our collected data. The results indicated that the existing semi-analytical water quality retrieval models of the Taihu Lake can not be applied perfectly to the Chaohu Lake and the Dianchi Lake.展开更多
Harmful algal blooms (HABs), caused by the overgrowth of certain phytoplankton species, have negative effects on marine environments and coastal fisheries. In addition to cell-counting methods using phytoplankton nets...Harmful algal blooms (HABs), caused by the overgrowth of certain phytoplankton species, have negative effects on marine environments and coastal fisheries. In addition to cell-counting methods using phytoplankton nets, a hydroacoustic technique based on acoustic backscattering has been proposed for the detection of phytoplankton blooms. However, little is known of the acoustic properties of HAB species. In this study, as essential data to support this technique, we measured the acoustic properties of two HAB species, Akashiwo sanguinea and Alexandrium affine, which occur in the South Sea off the coast of Korea. Due to the small size of the target, we used ultrasound for the measurements. Experiments were conducted under laboratory and field conditions. In the laboratory experiment, the acoustic signal received from each species was directly proportional to the cell abundance. We derived a relationship between the cell abundance and acoustic signal received for each species. The measured signals were compared to predictions of a fluid sphere scattering model. When A. sanguinea blooms appeared at an abundance greater than 3 500 cells/mL, the acoustic signals varied with cell abundance, showing a good correlation. These results confirm that acoustic measurements can be used to detect HAB species.展开更多
The purpose of this paper is to study about the interrelationship between the backscattering intensity of PALSAR data and the laboratory measurement of dielectric constant and soil moisture. The characterization of th...The purpose of this paper is to study about the interrelationship between the backscattering intensity of PALSAR data and the laboratory measurement of dielectric constant and soil moisture. The characterization of the dielectric constant of arid soils in the 0.3 - 3 GHz frequency range, particularly focused in L-band was analyzed in varied soil moisture content and soil textures. The interrelationship between the relative dielectric constant with soil textures and backscattering of PALSAR data was also analyzed and statistical model was computed. In this study, after collecting the soil samples in the field from top soil (0 - 10 cm) in a homogeneous area then, the dielectric constant was measured using a dielectric probe tool kit. For investigated of the characteristics and behaviors of the dielectric constant and relationship with backscattering a variety of moisture content from 0% to 40% and soil fraction conditions was tested in laboratory condition. All data were analyzed by integrating it with other geophysical data in GIS, such as land cover and soil texture. Thus, the regression model computed between measured soil moisture and backscattering coefficient of PALSR data which were extracted as same point of each soil sample pixel. Finally, after completing the preprocessing, such as removing the speckle noise by averaging, the model was applied to the PALSAR data for retrieving the soil moisture map in arid region of Iran. The analysis of dielectric constant properties result has shown the soil texture after the moisture content has the largest effected on dielectric constant. In addition, the PALSAR data in dual polarization are also able to derive the soil moisture using statistical method. The dielectric constant and backscattering shown have the exponential relationship and the HV polarization mode is more sensitive than the HH mode to soil moisture and overestimated the soil moisture as well. The validation of result has shown the 4.2 Vol-% RMSE of soil moisture. It means that the backscattering analysis should consider about other factors such a surface roughness and mix pixel of vegetation effective.展开更多
In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment laye...In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment layer with finite thickness. On the basis of calculating acoustic field in the water, the sediment layer, and the basement, four kinds of scattering mechanisms are taken into account, including roughness scattering from the water-sediment interface, volume scattering from the sediment layer, roughness scattering from the sediment-basement interface,and volume scattering from the basement. Then a backscattering model for a stratified seafloor applying to low frequency（0.1-10 kHz） is established. The simulation results show that the roughness scattering from the sediment-basement interface and the volume scattering from the basement are more prominent at relative low frequency（below 1.0 kHz）. While with the increase of the frequency, the contribution of them to total bottom scattering gradually becomes weak. And the results ultimately approach to the predictions of the high-frequency（10-100 kHz） bottom scattering model. When the sound speed and attenuation of the shear wave in the basement gradually decrease, the prediction of the model tends to that of the full fluid model, which validates the backscattering model for the stratified seafloor in another aspect.展开更多
The extraction of the weakly excited anti-symmetric Lamb wave from a submerged thin spherical shell backscattering is very difficult if the carrier frequency of the incident short tone burst is not at its frequency of...The extraction of the weakly excited anti-symmetric Lamb wave from a submerged thin spherical shell backscattering is very difficult if the carrier frequency of the incident short tone burst is not at its frequency of greatest enhancement. Based on a single channel iterative time reversal technique, a method for isolating the subsonic anti-symmetric Lamb wave is proposed in this paper. The approach does not depend on the form function of a thin shell and any other priori knowledge, and it is also robust in the presence of some stochastic noise. Both theoretical and numerical results show that the subsonic anti-symmetric Lamb wave can be identified, even when the carrier frequency of the incident short tone burst is away from the frequency of greatest enhancement. The phenomenon may also be observed even in the case that the subsonic anti-symmetric Lamb wave is submerged in the noise, other than the case with the Signal to Noise Ratio being less than 10 d B, when the amplitude of the noise is comparable with the specular wave. In this paper, each iteration process contains a traditional transmission and time reversal transmission steps. The two steps can automatically compensate the time delay of the subsonic anti-symmetric Lamb wave relative to the specular wave and within-mode dispersion in the forward wave propagation.展开更多
A three-dimensional heat flux model for deep-penetrating electron beam welding(EBW)is established to mathematically describe the physical heat generation process during interaction between electrons and the dynamic mo...A three-dimensional heat flux model for deep-penetrating electron beam welding(EBW)is established to mathematically describe the physical heat generation process during interaction between electrons and the dynamic molten pool free surface.Monte Carlo method is used to determine the electron-target interaction,and random distribution of initial electrons,progressive trajectory tracing and electron backscattering models are used to describe the spatial distribution of electrons absorption.The model is verified in preset keyholes and applied in the simulation on electron beam welding process,and the calculated bead shape shows a good consistency with experimental results.展开更多
BACKGROUND： Liver steatosis affects 20%-30% of adults.Because of the increasing gap between graft supplies and demands, livers with steatosis are frequently used in liver transplantation. But severely steatotic liver...BACKGROUND： Liver steatosis affects 20%-30% of adults.Because of the increasing gap between graft supplies and demands, livers with steatosis are frequently used in liver transplantation. But severely steatotic liver grafts are associated with a high risk of intraoperative and postoperative complications. Accurate assessment of fat content of donor livers and monitoring of the extent of steatosis in recipients are required for liver transplantation. The present study aimed to determine the correlation between liver echogenicity and fat content, and to evaluate the use of an ultrasonic integrated backscatter system（IBS） in the assessment of changes in fat content after liver transplantation.METHODS： Seventy-nine consecutive patients receiving liver grafts from living donors were evaluated in our center. Of these recipients, 67 survived for more than two years and were included in this study. Each liver graft was evaluated with IBS and ultrasound before operation and the fat content was estimated. The fat content of the grafts in the recipients was again assessed with ultrasound at 18 months after surgery.RESULTS： A correlation was detected between each graft＇s IBS value and its fat content（P=0.001）. The IBS value in fatty grafts with various degrees of steatosis was significantly decreased in 3（P=0.02）, 12, 15 and 18（P=0.001） months after orthotopic liver transplantation. The IBS value returned to normal in all patients in 18 months after liver transplantation.CONCLUSIONS： Decreased fat content in steatotic grafts can be observed in all recipients. Ultrasonic IBS is useful in determining the steatotic degree of grafts in donors as well as in monitoring the grafts after liver transplantation.展开更多
In this study,we present a new method for the indirect integration of beam charges in external beam proton-induced X-ray emission and proton-induced c-ray emission(PIXE–PIGE) analysis.We recorded proton spectra backs...In this study,we present a new method for the indirect integration of beam charges in external beam proton-induced X-ray emission and proton-induced c-ray emission(PIXE–PIGE) analysis.We recorded proton spectra backscattered by a Kapton film extraction window in different sample situations and under different beam currents.We also simulated backscattering spectra using the simulation of backscattering spectra program(SIMNRA).We determined that in a specific geometrical arrangement,different sample situations did not significantly affect factor C_Q(the ratio between integral backscattering proton counts and integral beam charges).We also studied the reproducibility and beam current dependence of factor C_Q.The statistic factor of C_Q was28.95 ± 0.6 kilo counts/l C,with a relative standard deviation of 2.0 %.Significantly,in external beam PIXE–PIGE analysis,we were able to calculate beam charge integration from the integral backscattering proton counts in an energy region.展开更多
The MeV proton non- Rutherford elastic backscattering (PEBS) has been used to measure a variety of low Z element- containing samples including thick SiC film, N implanted stainless steel, thin films interface (Ag on C...The MeV proton non- Rutherford elastic backscattering (PEBS) has been used to measure a variety of low Z element- containing samples including thick SiC film, N implanted stainless steel, thin films interface (Ag on Cu) and very deep (4μ m) SOI structure by high energy oxygen implantation. It is demonstrated that by using the significant enhancement of cross sections for low Z elements and selecting the proper energy region of the excitation curves both the sensitivities for detecting low Z elements and the accessible depth of the PEBS technique are remarkablely improved over the ordinary RBS method. The disadvantages of the PEBS as compared with RBS as well as high energy He elastic backscattering (HeEBS) are also discussed.展开更多
A method of obtaining bottom backscattering strength by employing an omnidirectional projector and omnidirectional hydrophone is proposed. The backscattering strength is extracted from monostatic backscattering data. ...A method of obtaining bottom backscattering strength by employing an omnidirectional projector and omnidirectional hydrophone is proposed. The backscattering strength is extracted from monostatic backscattering data. The method was adopted in an experiment conducted in the South Yellow Sea of China. The seafloor surface was relatively smooth and covered by a small quantity of shell fragments, as observed through a digital camera system. Sampling data showed that the main component of the sediment at this experimental site was fine sand. In this paper, we detail the calculation method. Preliminary results of backscattering strength as a function of grazing angle(20?–70?) in the frequency range of 6–24 kHz are presented. The measured backscattering strength increased with the grazing angle and changed more rapidly at large grazing angles(60?–70?). A comparison of the data at different frequencies reveals that the measured backscattering strength substantially rises with the increase of acoustic frequency. A fitting curve of Lambert's law against the measured data shows that the backscattering strength deviates from Lambert's law at large grazing angles.展开更多
High energy ion backscattering can be used to enhance the sensitivity of oxygen analysis. At He++ ion energy of 8.8 MeV, the yield due to oxygen is about 25 times larger than that predicted by Rutherford formula. The ...High energy ion backscattering can be used to enhance the sensitivity of oxygen analysis. At He++ ion energy of 8.8 MeV, the yield due to oxygen is about 25 times larger than that predicted by Rutherford formula. The elemental stoichiometry of some bulk and thin film superconductor samples was determined. The details of the measuring method are discribed.展开更多
Annealing behavior of Er-implanted Si was studied by Rutherford backscattering (RBS) and photoluminescence (PL). RBS data show that the recrystallization process of damaged layers is accompanied by migration of Er ato...Annealing behavior of Er-implanted Si was studied by Rutherford backscattering (RBS) and photoluminescence (PL). RBS data show that the recrystallization process of damaged layers is accompanied by migration of Er atoms toward surface during annealing. After annealing the depth of the Er concentration peak corresponds to the depth of the residual damage layer. Er atoms in Si mainly occupy nonsubstitution sites. The presence of a lot of interstitial Er atoms in Si retards the recrystallization process of damaged layers. The 1.546 μm PL peak related to Er was observed at 77K.展开更多
基金financial support of the Ministry of Science and Higher Education of the Russian Federation in the framework of the state contract in the field of science(No.FSEG-2024-0005)。
文摘This study discusses the scope of application of the Doppler backscattering(DBS)diagnostic for the tokamak with reactor technologies(TRT)project.This involved numerical modeling of the three-dimensional(3D)beam trajectories.Calculations were performed to investigate the propagation of microwaves in the V(40–75 GHz)and W(75–110 GHz)frequency ranges with O-mode polarization for the density profile of the base TRT scenario.Our analysis showed that the DBS system antenna on the TRT would need to be tilted in both the poloidal and toroidal directions in order to meet the condition Kperp/Kpar<10%..For the DBS system located in the equatorial plane it was shown that a wide range of poloidal and toroidal angles is available for the successful implementation of the diagnostic to study the core,pedestal and scrape-off layer(SOL)regions.The DBS system located at 35 cm above the equatorial plane would be more limited in measurements only covering the SOL and pedestal regions.A shift of the cut-offs in the toroidal direction highlighted the need for 3D analysis of the DBS data.
基金funded by the National Key Research and Development Program[grant number 2022YFC3004200]the National Natural Science Foundation of China[grant number U2142212]the Hunan Provincial Natural Science Foundation of China[grant number 2021JC0009]。
文摘A polarized bidirectional reflectance distribution function(pBRDF)matrix is developed from two-scale roughness theory with the aim of providing more accurate simulations of microwave emissions and scattering required for ocean-atmosphere coupled radiative transfer models.The potential of the pBRDF matrix is explored for simu-lating the ocean backscatter at Ku-band.The effects of ocean wave spectra including the modified Durden and Vesecky(DV2),Elfouhaily,and Kudryavtsev spectra on the pBRDF matrix backscatter simulations are investi-gated.Additionally,the differences in backscattering normalized radar cross-section(NRCS)simulations between the Ku-band geophysical model function and pBRDF matrix are analyzed.The results show that the pBRDF matrix can reasonably reproduce the spatial distribution of ocean surface backscattering energy,but the distribution pat-tern and numerical values are influenced by ocean wave spectra.The DV2 spectrum is the best one for the pBRDF matrix to simulate horizontally polarized NRCSs,with the exception of scenarios where the incidence angle is below 35°,the wind speed is less than 10 m s^(−1),and in the cross-wind direction.Also,the DV2 spectrum effec-tively characterizes the wind speed and relative azimuth angle dependence for vertically polarized NRCSs.The Elfouhaily spectrum is suitable for simulating vertically polarized NRCSs under conditions of low wind speed(be-low 5 m s^(−1))and incidence angles under 40°.The Kudryavtsev spectrum excels in simulating vertically polarized NRCSs at high incidence angles(>40°)and horizontally polarized NRCSs at low incidence angles(<35°).
文摘The relates cross sections of Non-Rutherford backscattering of lie ions from N atoms at the energy range of 2-5MeV were measured.Several resonance energies and corresponding resonance widths are tabled.For analysis of N in high Z substrate,the results of both experiment and computer simulation were given in this report.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52474362,52174317 and 51904146)the General Project Funded by Liaoning Province Education Department(Grant No.JYTMS20230943)。
文摘The high-alloyed wrought superalloy GH4975 tends to form coarse MC carbides and eutectic(γ+γ′)phases,which adversely affect the cogging and homogenization process.To provide theoretical guidance for control of MC carbides and eutectic(γ+γ′)formation,differential thermal analysis(DTA)was utilized to investigate the effect of cooing rate(10-90℃·min^(-1))on solidification behavior and micro-segregation of GH4975 alloy.According to the thermodynamic calculation and distribution characteristics of precipitates,the MC carbides can act as nucleation sites forγdendrites,but the nucleation ofγdendrites becomes less dependent on the MC carbide primers at higher cooling rates.As theγdendrites grow,the elements including Ti and Nb gradually accumulate in the residual liquid and leads to the formation of more MC carbides near the interdendritic region.Finally,the solidification is terminated with the formation of eutectic(γ+γ′).With an increase in cooling rate,the liquidus temperature rises,but the solidus temperature decreases,and thus the solidification range is obviously enlarged.The dendritic structure is significantly refined by the increase of cooling rate.The secondary dendrite arm spacing,λ_(2),as a function of cooling rate,T,can be expressed asλ_(2)=216.78T^(-0.42).Moreover,the increasing cooling rate weakens the back diffusion of Al,Ti,and Nb,increases the undercooling,and limits the growth of precipitates.Consequently,the sizes of MC carbides,eutectic(γ+γ′),and primaryγ′significantly decrease,but the area fraction of eutectic(γ+γ′)linerly increases as the cooling rate rises.Thus moderate cooling rate(such as 30℃·min^(-1))should be selected during the solidification process of GH4975 alloy.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 40476062 and 10374026）.
文摘Based on the effective medium approximation theory of composites, the whitecap-covered sea surface is treated as a medium layer of dense seawater droplets and air. Two electromagnetic scattering models of randomly rough surface are applied to the investigation of microwave backscattering of breaking waves driven by strong wind. The shapes of seawater droplets are considered by calculating the effective dielectric constant of the whitecap layer. The responses of seawater droplets shapes, such as sphere and ellipsoid, to the backscattering coefficient are discussed. Numerical results of the models are in good agreement with the experimental measurements of horizontally and vertically polarized backscattering at microwave frequency 13.9GHz and different incidence angles.
基金Supported by the National Natural Science Foundation of China (40474066)
文摘The ionospheric oblique backscattering sounding system can not only be used to detect the state of the ionosphere and the condition of high frequency channel in real time, but also be used for over-the-horizon sounding. Therefore, it has a very high military and civil value. For the characteristics of ionospheric oblique backscattering sounding, such as long sounding distance, wake echo, strong background noise, slow moving target, etc., a hardware platform of ionospheric oblique backscattering sounding system is designed. This platform adopts the technology of software radio and is designed as a new kind of general purpose, modularized, software-based ionosonde that is based on the VXI （Versa module eurocard eXtensions for Instrumentation） bus. This hardware platform has been successfully used in actual ionospheric oblique backscattering sounding, and the experimental results demonstrate that this system can satisfy the requirements.
基金The National High Technology Research and Development Program(863 Program) of China under contract No.2013BAD13B01the National Natural Science Foundation of China under contract No.41576177
文摘The routine operational sigma0 regrouping method is proposed for a HY-2 A scatterometer（HSCAT） that maps time-ordered sigma0 s and related parameters into a subtrack aligned grid of wind vector cells（WVCs）. The regrouping method consists of two critical steps： ground grid generation and sigma0 resampling. The HSCAT uses subtrack swath coordinates, in which the nadir track of the satellite represents the center and the designated positions are specified in terms of a pair of along-track and cross-track coordinates. To calculate the subtrack coordinates for each sigma0, a ＂triangle marking＂ resampling method is developed. Three points, including the point of intersection, the center of a pulse footprint, and the origin of the subtrack coordinate system, form a right triangle; the length of the two right-angled sides is used to represent the cross-track and the along-track coordinates in the subtrack coordinate system. In addition, a nadir point interpolation correction is used to ensure the operation of the regrouping algorithm when the nadir point positional information is missing. To illustrate the ability of the proposed regrouping algorithm, the distribution of the WVC positions and wind vector retrieval results are analyzed, which show that the proposed regrouping algorithm meets the requirements for high-quality sea surface wind field retrieval.
文摘The backscattering signal, which arises from the pulsed laser traveling through water, has limited the lidar system sensitivity and underwater target contrast. The transmitted optical carrier is modulated to be ultrashort pulsed laser and it is effective to suppress the backscattering to adopt the coherent detection technology by identifying the modulation envelope. A nonstationary light field is formed in seawater by the ultrashort pulsed laser. The inherent relationship between the nonstationary light field formed by modulated lidar and the stationary light field formed by conventional lidar was discussed and the backscattering light model of the stationary light field for the ultrashort pulsed laser was proposed. The backscattering signal in modulated lidar system was processed and analyzed in the frequency domain on the basis of the model.
基金Under the auspices of National Natural Science Foundation of China(No.41171269,41101378)
文摘This study presents an investigation of the scattering and backscattering properties of the particulates in three Chinese inland lakes(the Taihu Lake, the Chaohu Lake and the Dianchi Lake) based on in situ measurements taken at 119 sites. We modeled the particulate scattering spectra using a wavelength-dependent power-law function, finding that the power-law exponents in the Taihu Lake and the Chaohu Lake differ from those in the Dianchi Lake but are similar to the values in the U.S. coastal waters. In contrast to the open ocean, the backscattering properties in the three lakes can not be determined only from chlorophyll-a concentration. The backscattering ratio spectra exhibit a wavelength dependence feature in all three lakes, generally decreasing with the increasing wavelength. Analysis results of the correlations between the backscattering ratio and the individual water quality parameters clearly show that there are distinctive relations among the three lakes, attributed primarily to different compositions of optically active materials in the three lakes. Analysis of the mass-specific scattering and backscattering coefficients shows that the coefficients at wavelength 532 nm in the Taihu Lake and Chaohu Lake are similar, but they are apparently different from those in the Dianchi Lake. Lastly, Model I multiple linear regressions were adopted to partition the mass-specific cross-sections for scattering and backscattering into organic and inorganic cross-sections to further interpret the scattering and backscattering properties. The relative contribution of organic and inorganic particulates to scattering and backscattering is clearly different among the three lakes. The scattering and backscattering properties of the particulates in the three inland lakes vary significantly based on our collected data. The results indicated that the existing semi-analytical water quality retrieval models of the Taihu Lake can not be applied perfectly to the Chaohu Lake and the Dianchi Lake.
基金project titled "Establishment and demonstration of red tide detection and prediction system for minimizing red tide damage" funded by the Ministry of Oceans and Fisheries, Korea (PM61410)
文摘Harmful algal blooms (HABs), caused by the overgrowth of certain phytoplankton species, have negative effects on marine environments and coastal fisheries. In addition to cell-counting methods using phytoplankton nets, a hydroacoustic technique based on acoustic backscattering has been proposed for the detection of phytoplankton blooms. However, little is known of the acoustic properties of HAB species. In this study, as essential data to support this technique, we measured the acoustic properties of two HAB species, Akashiwo sanguinea and Alexandrium affine, which occur in the South Sea off the coast of Korea. Due to the small size of the target, we used ultrasound for the measurements. Experiments were conducted under laboratory and field conditions. In the laboratory experiment, the acoustic signal received from each species was directly proportional to the cell abundance. We derived a relationship between the cell abundance and acoustic signal received for each species. The measured signals were compared to predictions of a fluid sphere scattering model. When A. sanguinea blooms appeared at an abundance greater than 3 500 cells/mL, the acoustic signals varied with cell abundance, showing a good correlation. These results confirm that acoustic measurements can be used to detect HAB species.
文摘The purpose of this paper is to study about the interrelationship between the backscattering intensity of PALSAR data and the laboratory measurement of dielectric constant and soil moisture. The characterization of the dielectric constant of arid soils in the 0.3 - 3 GHz frequency range, particularly focused in L-band was analyzed in varied soil moisture content and soil textures. The interrelationship between the relative dielectric constant with soil textures and backscattering of PALSAR data was also analyzed and statistical model was computed. In this study, after collecting the soil samples in the field from top soil (0 - 10 cm) in a homogeneous area then, the dielectric constant was measured using a dielectric probe tool kit. For investigated of the characteristics and behaviors of the dielectric constant and relationship with backscattering a variety of moisture content from 0% to 40% and soil fraction conditions was tested in laboratory condition. All data were analyzed by integrating it with other geophysical data in GIS, such as land cover and soil texture. Thus, the regression model computed between measured soil moisture and backscattering coefficient of PALSR data which were extracted as same point of each soil sample pixel. Finally, after completing the preprocessing, such as removing the speckle noise by averaging, the model was applied to the PALSAR data for retrieving the soil moisture map in arid region of Iran. The analysis of dielectric constant properties result has shown the soil texture after the moisture content has the largest effected on dielectric constant. In addition, the PALSAR data in dual polarization are also able to derive the soil moisture using statistical method. The dielectric constant and backscattering shown have the exponential relationship and the HV polarization mode is more sensitive than the HH mode to soil moisture and overestimated the soil moisture as well. The validation of result has shown the 4.2 Vol-% RMSE of soil moisture. It means that the backscattering analysis should consider about other factors such a surface roughness and mix pixel of vegetation effective.
基金The National Natural Science Foundation of China under contract Nos 41606081,41330965 and 41527809the Taishan Scholar Project Funding under contract No.tspd20161007
文摘In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment layer with finite thickness. On the basis of calculating acoustic field in the water, the sediment layer, and the basement, four kinds of scattering mechanisms are taken into account, including roughness scattering from the water-sediment interface, volume scattering from the sediment layer, roughness scattering from the sediment-basement interface,and volume scattering from the basement. Then a backscattering model for a stratified seafloor applying to low frequency（0.1-10 kHz） is established. The simulation results show that the roughness scattering from the sediment-basement interface and the volume scattering from the basement are more prominent at relative low frequency（below 1.0 kHz）. While with the increase of the frequency, the contribution of them to total bottom scattering gradually becomes weak. And the results ultimately approach to the predictions of the high-frequency（10-100 kHz） bottom scattering model. When the sound speed and attenuation of the shear wave in the basement gradually decrease, the prediction of the model tends to that of the full fluid model, which validates the backscattering model for the stratified seafloor in another aspect.
基金supported by the National Natural Science Foundation of China (46976019)the open project of the State Key Laboratory of Acoustics, Chinese Academy of Sciences (SKLA201202)
文摘The extraction of the weakly excited anti-symmetric Lamb wave from a submerged thin spherical shell backscattering is very difficult if the carrier frequency of the incident short tone burst is not at its frequency of greatest enhancement. Based on a single channel iterative time reversal technique, a method for isolating the subsonic anti-symmetric Lamb wave is proposed in this paper. The approach does not depend on the form function of a thin shell and any other priori knowledge, and it is also robust in the presence of some stochastic noise. Both theoretical and numerical results show that the subsonic anti-symmetric Lamb wave can be identified, even when the carrier frequency of the incident short tone burst is away from the frequency of greatest enhancement. The phenomenon may also be observed even in the case that the subsonic anti-symmetric Lamb wave is submerged in the noise, other than the case with the Signal to Noise Ratio being less than 10 d B, when the amplitude of the noise is comparable with the specular wave. In this paper, each iteration process contains a traditional transmission and time reversal transmission steps. The two steps can automatically compensate the time delay of the subsonic anti-symmetric Lamb wave relative to the specular wave and within-mode dispersion in the forward wave propagation.
文摘A three-dimensional heat flux model for deep-penetrating electron beam welding(EBW)is established to mathematically describe the physical heat generation process during interaction between electrons and the dynamic molten pool free surface.Monte Carlo method is used to determine the electron-target interaction,and random distribution of initial electrons,progressive trajectory tracing and electron backscattering models are used to describe the spatial distribution of electrons absorption.The model is verified in preset keyholes and applied in the simulation on electron beam welding process,and the calculated bead shape shows a good consistency with experimental results.
文摘BACKGROUND： Liver steatosis affects 20%-30% of adults.Because of the increasing gap between graft supplies and demands, livers with steatosis are frequently used in liver transplantation. But severely steatotic liver grafts are associated with a high risk of intraoperative and postoperative complications. Accurate assessment of fat content of donor livers and monitoring of the extent of steatosis in recipients are required for liver transplantation. The present study aimed to determine the correlation between liver echogenicity and fat content, and to evaluate the use of an ultrasonic integrated backscatter system（IBS） in the assessment of changes in fat content after liver transplantation.METHODS： Seventy-nine consecutive patients receiving liver grafts from living donors were evaluated in our center. Of these recipients, 67 survived for more than two years and were included in this study. Each liver graft was evaluated with IBS and ultrasound before operation and the fat content was estimated. The fat content of the grafts in the recipients was again assessed with ultrasound at 18 months after surgery.RESULTS： A correlation was detected between each graft＇s IBS value and its fat content（P=0.001）. The IBS value in fatty grafts with various degrees of steatosis was significantly decreased in 3（P=0.02）, 12, 15 and 18（P=0.001） months after orthotopic liver transplantation. The IBS value returned to normal in all patients in 18 months after liver transplantation.CONCLUSIONS： Decreased fat content in steatotic grafts can be observed in all recipients. Ultrasonic IBS is useful in determining the steatotic degree of grafts in donors as well as in monitoring the grafts after liver transplantation.
基金supported by the Beijing Natural Science Funds(No.1142006)
文摘In this study,we present a new method for the indirect integration of beam charges in external beam proton-induced X-ray emission and proton-induced c-ray emission(PIXE–PIGE) analysis.We recorded proton spectra backscattered by a Kapton film extraction window in different sample situations and under different beam currents.We also simulated backscattering spectra using the simulation of backscattering spectra program(SIMNRA).We determined that in a specific geometrical arrangement,different sample situations did not significantly affect factor C_Q(the ratio between integral backscattering proton counts and integral beam charges).We also studied the reproducibility and beam current dependence of factor C_Q.The statistic factor of C_Q was28.95 ± 0.6 kilo counts/l C,with a relative standard deviation of 2.0 %.Significantly,in external beam PIXE–PIGE analysis,we were able to calculate beam charge integration from the integral backscattering proton counts in an energy region.
文摘The MeV proton non- Rutherford elastic backscattering (PEBS) has been used to measure a variety of low Z element- containing samples including thick SiC film, N implanted stainless steel, thin films interface (Ag on Cu) and very deep (4μ m) SOI structure by high energy oxygen implantation. It is demonstrated that by using the significant enhancement of cross sections for low Z elements and selecting the proper energy region of the excitation curves both the sensitivities for detecting low Z elements and the accessible depth of the PEBS technique are remarkablely improved over the ordinary RBS method. The disadvantages of the PEBS as compared with RBS as well as high energy He elastic backscattering (HeEBS) are also discussed.
基金supported in part by the National Natural Science Foundation of China (Nos. 41606081, 4152 7809, and 41330965)in part by the Opening Fund of Pilot National Laboratory for Marine Science and Technology (Qingdao) (No. QNLM2016ORP0209)in part by the Taishan Scholar Project Funding (No. tspd20161007)
文摘A method of obtaining bottom backscattering strength by employing an omnidirectional projector and omnidirectional hydrophone is proposed. The backscattering strength is extracted from monostatic backscattering data. The method was adopted in an experiment conducted in the South Yellow Sea of China. The seafloor surface was relatively smooth and covered by a small quantity of shell fragments, as observed through a digital camera system. Sampling data showed that the main component of the sediment at this experimental site was fine sand. In this paper, we detail the calculation method. Preliminary results of backscattering strength as a function of grazing angle(20?–70?) in the frequency range of 6–24 kHz are presented. The measured backscattering strength increased with the grazing angle and changed more rapidly at large grazing angles(60?–70?). A comparison of the data at different frequencies reveals that the measured backscattering strength substantially rises with the increase of acoustic frequency. A fitting curve of Lambert's law against the measured data shows that the backscattering strength deviates from Lambert's law at large grazing angles.
文摘High energy ion backscattering can be used to enhance the sensitivity of oxygen analysis. At He++ ion energy of 8.8 MeV, the yield due to oxygen is about 25 times larger than that predicted by Rutherford formula. The elemental stoichiometry of some bulk and thin film superconductor samples was determined. The details of the measuring method are discribed.
文摘Annealing behavior of Er-implanted Si was studied by Rutherford backscattering (RBS) and photoluminescence (PL). RBS data show that the recrystallization process of damaged layers is accompanied by migration of Er atoms toward surface during annealing. After annealing the depth of the Er concentration peak corresponds to the depth of the residual damage layer. Er atoms in Si mainly occupy nonsubstitution sites. The presence of a lot of interstitial Er atoms in Si retards the recrystallization process of damaged layers. The 1.546 μm PL peak related to Er was observed at 77K.
