The influence of the inhomogeneous tissue layer on the generation of acoustic vortices （AV） is studied theoretically and experimentally based on the phase screen model. By considering the time-shift of a random phas...The influence of the inhomogeneous tissue layer on the generation of acoustic vortices （AV） is studied theoretically and experimentally based on the phase screen model. By considering the time-shift of a random phase screen, the formula of acoustic pressure for the AV beam generated by a circular array of eight planar piston sources is derived. With the actual correlation length of the abdominal wall, numerical simulations before and after the insertion of the inhomogeneous tissue layer are conducted, and also demonstrated by experimental measurements. It is proved that, when the thickness variation of the phase screen is less than one wavelength, no significant influence on the generation of AVs can be produced. The variations of vortex nodes and antinodes in terms of the location, shape, and size of AVs are not obvious. Although the circular pressure distribution might be deformed by the phase interference with a larger thickness variation, AVs can still be generated around the center axis with perfect phase spirals in a reduced effective radius. The favorable results provide the feasibility of AV generation inside the human body and suggest the application potential of AVs in object manipulation for biomedical engineering.展开更多
Gaussian models without intermittency are extensively used in estimating the effect of turbulence,but italso brings some puzzles,for example the observed pulse shape that disagrees with the result of the standard theo...Gaussian models without intermittency are extensively used in estimating the effect of turbulence,but italso brings some puzzles,for example the observed pulse shape that disagrees with the result of the standard theoryof interstellar scintillations.Indeed the property of intermittency is inherent in turbulence,i.e.,all the quantities thatcharacterize it suffer from strong fluctuations.So it is necessary to consider turbulent intermittency in many applications.In this paper we propose a non-Gaussian phase screen,which obeys log-Poisson statistics,and also offers the correspondingpoint spread function(PSF).These results describe that intermittency leads to the more extent and different directionaldistribution of PSF.Theoretical analysis is made under the hypothesis of the phase difference satisfying log-Poissonstatistics,and the average point spread function,which accord qualitatively with the result of the above generated phasescreen,is derived.展开更多
The Fresnel approximation in phase screen model is discussed and the coherencefunction is derived for k】】k.The application condition for Rino’s results is obtained,and it is|▽R<sub>△N<sub>e</sub>...The Fresnel approximation in phase screen model is discussed and the coherencefunction is derived for k】】k.The application condition for Rino’s results is obtained,and it is|▽R<sub>△N<sub>e</sub></sub>|/R<sub>△n<sub>e</sub></sub>【【1.展开更多
An x-ray scintillator screen with a special structure, functioning as detector and analyser grating, was proposed for collecting the interferogram of differential phase contrast imaging without absorption grating and ...An x-ray scintillator screen with a special structure, functioning as detector and analyser grating, was proposed for collecting the interferogram of differential phase contrast imaging without absorption grating and difficulty of fabrication by a state of the art technique. On the basis of phase grating diffraction, a detecting model of the scintillator screen was built for analysing the phase and absorption information of objects. According to the analysis, a new method of phase retrievals based on two-images and the optimal structure of screen were presented.展开更多
The purpose of this study is to improve the surface properties of austenitic stainless steel using the double-folded electrode screen plasma nitriding (SPN) process. In general, the S-phase is well-known for its excel...The purpose of this study is to improve the surface properties of austenitic stainless steel using the double-folded electrode screen plasma nitriding (SPN) process. In general, the S-phase is well-known for its excellent properties such as improved hardness and wear resistance along with sustained corrosion resistance. The concentrated nitrogen via SPN process was injected to form S-phase with time at 713 K. This study was carried out under the conditions of 44 at% of nitrogen injection, which was higher than 25 at% known as the condition of no precipitation of S-phase formed by the SPN process, and 20 K higher than the maximum temperature without precipitation phase. The hardness analysis of stainless steel sample treated by the SPN process at 713 K showed a much higher value than the typical nitriding hardness at a depth of lower nitrogen than the maximum nitrogen concentration. The SPN 20 hr treated specimen showed the average value of 2339 HV while 40 hr showed the average value of 2215 HV. The result is attributed to the concentrated nitrogen formed in the SPN process reacting with the alloying elements contained in the base material to form fine precipitates, thus producing a synergy effect of the extreme hardening effect;that is, the movement of precipitates and dislocations due to the GP-zone (Guinier-Preston zone).展开更多
针对自由空间光通信(Free Space Optical Communication,FSO)中传统激光定位算法,如质心法、圆拟合法、Hough法等存在定位精度较差、时间较长的问题,提出了一种最大弦长算法,以提高大气湍流信道中激光中心定位效率和FSO链路性能。算法...针对自由空间光通信(Free Space Optical Communication,FSO)中传统激光定位算法,如质心法、圆拟合法、Hough法等存在定位精度较差、时间较长的问题,提出了一种最大弦长算法,以提高大气湍流信道中激光中心定位效率和FSO链路性能。算法首先对图像边缘检测后的边缘像素点进行去干扰处理,而后遍历所有边缘像素点,计算它们之间的距离,并对距离最远的每两像素点的中点累加计数,最后选出累计次数最多的中点作为中心,从而实现对激光中心的精确定位。通过与传统激光定位算法的仿真对比表明:最大弦长定位算法能有效降低激光中心的偏移量,提高定位精度,同时本算法能缩短检测过程的计算时间,提高定位效率,且在相同面积的激光中心掩膜内,本文算法包含的总像素强度更大,综合定位效果更好。展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61575095,11374155,and 11674173)
文摘The influence of the inhomogeneous tissue layer on the generation of acoustic vortices （AV） is studied theoretically and experimentally based on the phase screen model. By considering the time-shift of a random phase screen, the formula of acoustic pressure for the AV beam generated by a circular array of eight planar piston sources is derived. With the actual correlation length of the abdominal wall, numerical simulations before and after the insertion of the inhomogeneous tissue layer are conducted, and also demonstrated by experimental measurements. It is proved that, when the thickness variation of the phase screen is less than one wavelength, no significant influence on the generation of AVs can be produced. The variations of vortex nodes and antinodes in terms of the location, shape, and size of AVs are not obvious. Although the circular pressure distribution might be deformed by the phase interference with a larger thickness variation, AVs can still be generated around the center axis with perfect phase spirals in a reduced effective radius. The favorable results provide the feasibility of AV generation inside the human body and suggest the application potential of AVs in object manipulation for biomedical engineering.
基金Supported by the National Natural Science Foundation Science Foundation of China Academy of Engineering Physics (NSAF) under Grant No.10576005the National Natural Science Foundation of China under Grant No.10647127+1 种基金the Science Foundation of Hebei Education Department under Grant No.2009135the Science Foundation of Hebei Normal University
文摘Gaussian models without intermittency are extensively used in estimating the effect of turbulence,but italso brings some puzzles,for example the observed pulse shape that disagrees with the result of the standard theoryof interstellar scintillations.Indeed the property of intermittency is inherent in turbulence,i.e.,all the quantities thatcharacterize it suffer from strong fluctuations.So it is necessary to consider turbulent intermittency in many applications.In this paper we propose a non-Gaussian phase screen,which obeys log-Poisson statistics,and also offers the correspondingpoint spread function(PSF).These results describe that intermittency leads to the more extent and different directionaldistribution of PSF.Theoretical analysis is made under the hypothesis of the phase difference satisfying log-Poissonstatistics,and the average point spread function,which accord qualitatively with the result of the above generated phasescreen,is derived.
文摘The Fresnel approximation in phase screen model is discussed and the coherencefunction is derived for k】】k.The application condition for Rino’s results is obtained,and it is|▽R<sub>△N<sub>e</sub></sub>|/R<sub>△n<sub>e</sub></sub>【【1.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60232090 and 10774102)the Science & Technology Project from Shenzhen Government of China (Grant Nos. 2008340 and 200717)
文摘An x-ray scintillator screen with a special structure, functioning as detector and analyser grating, was proposed for collecting the interferogram of differential phase contrast imaging without absorption grating and difficulty of fabrication by a state of the art technique. On the basis of phase grating diffraction, a detecting model of the scintillator screen was built for analysing the phase and absorption information of objects. According to the analysis, a new method of phase retrievals based on two-images and the optimal structure of screen were presented.
文摘The purpose of this study is to improve the surface properties of austenitic stainless steel using the double-folded electrode screen plasma nitriding (SPN) process. In general, the S-phase is well-known for its excellent properties such as improved hardness and wear resistance along with sustained corrosion resistance. The concentrated nitrogen via SPN process was injected to form S-phase with time at 713 K. This study was carried out under the conditions of 44 at% of nitrogen injection, which was higher than 25 at% known as the condition of no precipitation of S-phase formed by the SPN process, and 20 K higher than the maximum temperature without precipitation phase. The hardness analysis of stainless steel sample treated by the SPN process at 713 K showed a much higher value than the typical nitriding hardness at a depth of lower nitrogen than the maximum nitrogen concentration. The SPN 20 hr treated specimen showed the average value of 2339 HV while 40 hr showed the average value of 2215 HV. The result is attributed to the concentrated nitrogen formed in the SPN process reacting with the alloying elements contained in the base material to form fine precipitates, thus producing a synergy effect of the extreme hardening effect;that is, the movement of precipitates and dislocations due to the GP-zone (Guinier-Preston zone).
文摘针对自由空间光通信(Free Space Optical Communication,FSO)中传统激光定位算法,如质心法、圆拟合法、Hough法等存在定位精度较差、时间较长的问题,提出了一种最大弦长算法,以提高大气湍流信道中激光中心定位效率和FSO链路性能。算法首先对图像边缘检测后的边缘像素点进行去干扰处理,而后遍历所有边缘像素点,计算它们之间的距离,并对距离最远的每两像素点的中点累加计数,最后选出累计次数最多的中点作为中心,从而实现对激光中心的精确定位。通过与传统激光定位算法的仿真对比表明:最大弦长定位算法能有效降低激光中心的偏移量,提高定位精度,同时本算法能缩短检测过程的计算时间,提高定位效率,且在相同面积的激光中心掩膜内,本文算法包含的总像素强度更大,综合定位效果更好。
