Sparrow criterion of resolution is used for assessment of the resolution of two object points of apodized optical systems under incoherent illumination of light. Semicircular arrays of circular aperture with discrete ...Sparrow criterion of resolution is used for assessment of the resolution of two object points of apodized optical systems under incoherent illumination of light. Semicircular arrays of circular aperture with discrete asymmetric apodization have suppressed side-lobes and a narrower central peak in the image plane termed as PSF good side on alternatively the right and left of the strong spectral point facilitates to detect the presence of weak spectral point in the vicinity of bright spectral point. The results of investigations on optimum discrete pupil function with semicircular arrays on the intensity distributions in the composite image of two object points with widely varying in their intensities under various degree of coherence of illumination have been studied. Sparrow resolution limits and the dip in central intensity as function of degree of coherence of the illumination (γ), intensity ratio (α), degree of asymmetric apodization (b) and number of discrete elements in semicircular array (n). The efficiency of aperture functions is discussed in terms of these parameters. Pupil function capabilities in redistribution of energy in composite image of two object points in close vicinity have been verified for different considerations. Current study has found an improvement in two-point resolution characteristics compared to their unapodized counter part. Fourier analytical properties of an optical system are presented for evaluation of this practical problem.展开更多
We propose a high-contrast coronagraph for direct imaging of young Jupiter-like planets orbiting nearby bright stars. The coronagraph employs a step- transmission filter in which the intensity is apodized with a finit...We propose a high-contrast coronagraph for direct imaging of young Jupiter-like planets orbiting nearby bright stars. The coronagraph employs a step- transmission filter in which the intensity is apodized with a finite number of steps with identical transmission in each step. It should be installed on a large ground-based telescope equipped with a state-of-the-art adaptive optics system. In this case, contrast ratios around 10-6 should be accessible within 0.1 arcsec of the central star. In recent progress, a coronagraph with a circular apodizing filter has been developed, which can be used for a ground-based telescope with a central obstruction and spider structure. It is shown that ground-based direct imaging of Jupiter-like planets is promising with current technology.展开更多
Noninvasive diagnosis of bone density and mechanical properties using non-radiation imaging modality is an emerging area with promising in early prediction of osteopenia and treatment effectiveness in the clinic and f...Noninvasive diagnosis of bone density and mechanical properties using non-radiation imaging modality is an emerging area with promising in early prediction of osteopenia and treatment effectiveness in the clinic and functional disuse,i.e.,long-term bedrest and space mission.Advances in quantitative ultrasound have shown advantages in measuring both bone density and mechanical strength,non-radiation,imaging capability,and easy to use.The challenge that remained is the poor penetration of ultrasound signals passing through trabecular and cortical bones and acoustic energy scattering.A new scanning confocal ultrasound technology is developed in this lab to detect the alteration of bone to provide diagnostic results in bone density and structure properties.A software-controlled flexible ultrasound system with 2-D dual array transducer is developed and proposed for the purpose of noninvasive bone density diagnosis and assessment of bone loss.Transmitting(Tx)transducer elements are divided into sub-blocks to excite the ultrasound signals in sequence to decrease the system complexity while maintaining beam pattern properties by the signal processing procedure at receiving(Rx)side.Apodization is also applied to reduce acoustic side lobes and to make the resolution in the ultrasound field of view(FOV)more uniform.This study may provide basic understanding of modulated confocal ultrasound beam forming for tissue characterization,such as trabecular bone structual and strength properties.展开更多
文摘Sparrow criterion of resolution is used for assessment of the resolution of two object points of apodized optical systems under incoherent illumination of light. Semicircular arrays of circular aperture with discrete asymmetric apodization have suppressed side-lobes and a narrower central peak in the image plane termed as PSF good side on alternatively the right and left of the strong spectral point facilitates to detect the presence of weak spectral point in the vicinity of bright spectral point. The results of investigations on optimum discrete pupil function with semicircular arrays on the intensity distributions in the composite image of two object points with widely varying in their intensities under various degree of coherence of illumination have been studied. Sparrow resolution limits and the dip in central intensity as function of degree of coherence of the illumination (γ), intensity ratio (α), degree of asymmetric apodization (b) and number of discrete elements in semicircular array (n). The efficiency of aperture functions is discussed in terms of these parameters. Pupil function capabilities in redistribution of energy in composite image of two object points in close vicinity have been verified for different considerations. Current study has found an improvement in two-point resolution characteristics compared to their unapodized counter part. Fourier analytical properties of an optical system are presented for evaluation of this practical problem.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant No. 10873024)
文摘We propose a high-contrast coronagraph for direct imaging of young Jupiter-like planets orbiting nearby bright stars. The coronagraph employs a step- transmission filter in which the intensity is apodized with a finite number of steps with identical transmission in each step. It should be installed on a large ground-based telescope equipped with a state-of-the-art adaptive optics system. In this case, contrast ratios around 10-6 should be accessible within 0.1 arcsec of the central star. In recent progress, a coronagraph with a circular apodizing filter has been developed, which can be used for a ground-based telescope with a central obstruction and spider structure. It is shown that ground-based direct imaging of Jupiter-like planets is promising with current technology.
基金This work is kindly supported by the National Institute of Health(R01 AR52379 and R01 AR61821)the National Space Biomedical Research Institute through a NASA contract NCC 9-58.
文摘Noninvasive diagnosis of bone density and mechanical properties using non-radiation imaging modality is an emerging area with promising in early prediction of osteopenia and treatment effectiveness in the clinic and functional disuse,i.e.,long-term bedrest and space mission.Advances in quantitative ultrasound have shown advantages in measuring both bone density and mechanical strength,non-radiation,imaging capability,and easy to use.The challenge that remained is the poor penetration of ultrasound signals passing through trabecular and cortical bones and acoustic energy scattering.A new scanning confocal ultrasound technology is developed in this lab to detect the alteration of bone to provide diagnostic results in bone density and structure properties.A software-controlled flexible ultrasound system with 2-D dual array transducer is developed and proposed for the purpose of noninvasive bone density diagnosis and assessment of bone loss.Transmitting(Tx)transducer elements are divided into sub-blocks to excite the ultrasound signals in sequence to decrease the system complexity while maintaining beam pattern properties by the signal processing procedure at receiving(Rx)side.Apodization is also applied to reduce acoustic side lobes and to make the resolution in the ultrasound field of view(FOV)more uniform.This study may provide basic understanding of modulated confocal ultrasound beam forming for tissue characterization,such as trabecular bone structual and strength properties.
