Browsing by Author "Zhang, Hongbo"

Now showing 1 - 5 of 5
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    Automatic elimination of phase aberrations in digital holography based on Gaussian 1o-criterion and histogram segmentation
    Chen, Zhenkai; Zhou, Wenjing; Duan, Lian; Zhang, Hongbo; Zheng, Huadong; Xia, Xinxing; Yu, Yingjie; Poon, Ting-chung (Optica Publishing Group, 2023-04)
    We propose a numerical and automatic quadratic phase aberration elimination method in digital holography for phase-contrast imaging. A histogram segmentation method based on Gaussian 1 sigma-criterion is used to obtain the accurate coefficients of quadratic aberrations using the weighted least-squares algorithm. This method needs no manual intervention for specimen-free zone or prior parameters of optical components. We also propose a maximum-minimum-average -standard deviation (MMASD) metric to quantitatively evaluate the effectiveness of quadratic aberration elimination. Simulation and experimental results are demonstrated to verify the efficacy of our proposed method over the traditional least-squares algorithm.
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    Encryption of 3D Point Cloud Object with Deformed Fringe
    Yang, Xin; Zhang, Hongbo (Hindawi, 2016-02-15)
    A 3D point cloud object encryption method was proposed with this study. With the method, a mapping relationship between 3D coordinates was formulated and coordinate was transformed to deformed fringe by a phase coding method. The deformed fringe and gray image were used for encryption and decryption with simulated off-axis digital Fresnel hologram. Results indicated that the proposed method is able to accurately decrypt the coordinates and gray image of the 3D object. The method is also robust against occlusion attacks.
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    Genus-Wide Characterization of Bumblebee Genomes Provides Insights into Their Evolution and Variation in Ecological and Behavioral Traits
    Sun, Cheng; Huang, Jiaxing; Wang, Yun; Zhao, Xiaomeng; Su, Long; Thomas, Gregg W. C.; Zhao, Mengya; Zhang, Xingtan; Jungreis, Irwin; Kellis, Manolis; Vicario, Saverio; Sharakhov, Igor V.; Bondarenko, Semen M.; Hasselmann, Martin; Kim, Chang N.; Paten, Benedict; Penso-Dolfin, Luca; Wang, Li; Chang, Yuxiao; Gao, Qiang; Ma, Ling; Ma, Lina; Zhang, Zhang; Zhang, Hongbo; Zhang, Huahao; Ruzzante, Livio; Robertson, Hugh M.; Zhu, Yihui; Liu, Yanjie; Yang, Huipeng; Ding, Lele; Wang, Quangui; Ma, Dongna; Xu, Weilin; Liang, Cheng; Itgen, Michael W.; Mee, Lauren; Cao, Gang; Zhang, Ze; Sadd, Ben M.; Hahn, Matthew W.; Schaack, Sarah; Barribeau, Seth M.; Williams, Paul H.; Waterhouse, Robert M.; Mueller, Rachel Lockridge (Oxford University Press, 2021-02-01)
    Bumblebees are a diverse group of globally important pollinators in natural ecosystems and for agricultural food production. With both eusocial and solitary life-cycle phases, and some social parasite species, they are especially interesting models to understand social evolution, behavior, and ecology. Reports of many species in decline point to pathogen transmission, habitat loss, pesticide usage, and global climate change, as interconnected causes. These threats to bumblebee diversity make our reliance on a handful of well-studied species for agricultural pollination particularly precarious. To broadly sample bumblebee genomic and phenotypic diversity, we de novo sequenced and assembled the genomes of 17 species, representing all 15 subgenera, producing the first genus-wide quantification of genetic and genomic variation potentially underlying key ecological and behavioral traits. The species phylogeny resolves subgenera relationships, whereas incomplete lineage sorting likely drives high levels of gene tree discordance. Five chromosome-level assemblies show a stable 18-chromosome karyotype, with major rearrangements creating 25 chromosomes in social parasites. Differential transposable element activity drives changes in genome sizes, with putative domestications of repetitive sequences influencing gene coding and regulatory potential. Dynamically evolving gene families and signatures of positive selection point to genus-wide variation in processes linked to foraging, diet and metabolism, immunity and detoxification, as well as adaptations for life at high altitudes. Our study reveals how bumblebee genes and genomes have evolved across the Bombus phylogeny and identifies variations potentially linked to key ecological and behavioral traits of these important pollinators.
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    Study of Image Classification Accuracy with Fourier Ptychography
    Zhang, Hongbo; Zhang, Yaping; Wang, Lin; Hu, Zhijuan; Zhou, Wenjing; Tsang, Peter W. M.; Cao, Deng; Poon, Ting-Chung (MDPI, 2021-05-14)
    In this research, the accuracy of image classification with Fourier Ptychography Microscopy (FPM) has been systematically investigated. Multiple linear regression shows a strong linear relationship between the results of image classification accuracy and image visual appearance quality based on PSNR and SSIM with multiple training datasets including MINST, Fashion MNIST, Cifar, Caltech 101, and customized training datasets. It is, therefore, feasible to predict the image classification accuracy only based on PSNR and SSIM. It is also found that the image classification accuracy of FPM reconstructed with higher resolution images is significantly different from using the lower resolution images under the lower numerical aperture (NA) condition. The difference is yet less pronounced under the higher NA condition.
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    Use of Statistical Mechanics Methods to Assess the Effects of Localized muscle fatigue on Stability during Upright Stance
    Zhang, Hongbo (Virginia Tech, 2007-12-11)
    Human postural control is a complex process, but that is critical to understand in order to reduce the prevalence of occupational falls. Localized muscle fatigue (LMF), altered sensory input, and inter-individual differences (e.g. age and gender) have been shown to influence postural control, and numerous methods have been developed in order to quantify such effects. Recently, methods based on statistical mechanics have become popular, and when applied to center of pressure (COP) data, appear to provide new information regarding the postural control system. This study addresses in particular the stabilogram diffusion and Hurst exponent methods. An existing dataset was employed, in which sway during quiet stance was measured under different visual and surface compliance conditions, among both genders and different age groups, as well as before and after induction of localized muscle fatigue at the ankle, knee, torso, and shoulder. The stabilogram diffusion method determines both short-term and long-term diffusion coefficients, which correspond to open- and closed-loop control of posture, respectively. To do so, a "critical point" (or critical time interval) needs to be determined to distinguish between the two diffusion regions. Several limitations are inherent in existing methods to determine this critical point. To address this, a new algorithm was developed, based on a wavelet transform of COP data. The new algorithm is able to detect local maxima over specified frequency bands within COP data; therefore it can identify postural control mechanisms correspondent to those frequency bands. Results showed that older adults had smaller critical time intervals, and indicating that sway control of older adults was essentially different from young adults. Diffusion coefficients show that among young adults, torso LMF significantly compromised sway stability. In contrast, older adults appeared more resistance to LMF. Similar to earlier work, vision was found to play a crucial role in maintaining sway stability, and that stability was worse under eyes-closed (EC) than eyes-opened (EO) conditions. It was also found that the short-term Hurst exponent was not successful at detecting the effects of LMF on sway stability, likely because of a small sample size. The new critical point identification algorithm was verified to have better sensitivity and reliability than the traditional approach. The new algorithm can be used in future work to aid in the assessment of postural control and the mechanisms underlying this control.