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1. Journal of Biomedical Optics

Author

Adriana C, Salazar Coariti, Maurice S, Fabien, Johnny, Guzman, Jeffrey A, McGuire, Raffaella, De Vita, and Kimani C, Toussaint

Subjects
Paper, collagen, Biomaterials, Microscopy, fluid mechanics, Biomedical Engineering, vector fields, waviness, Atomic and Molecular Physics, and Optics, Extracellular Matrix, Skin, second-harmonic generation, Electronic, Optical and Magnetic Materials
Abstract

Significance: The spatial organization of collagen fibers has been used as a biomarker for assessing injury and disease progression. However, quantifying this organization for complex structures is challenging. Aim: To quantify and classify complex collagen fiber organizations. Approach: Using quantitative second-harmonic generation (SHG) microscopy, we show that collagen-fiber orientation can be viewed as pseudovector fields. Subsequently, we analyze them using fluid mechanic metrics, such as energy U, enstrophy E, and tortuosity tau. Results: We show that metrics used in fluid mechanics for analyzing fluid flow can be adapted to analyze complex collagen fiber organization. As examples, we consider SHG images of collagenous tissue for straight, wavy, and circular fiber structures. Conclusions: The results of this study show the utility of the chosen metrics to distinguish diverse and complex collagen organizations. We find that the distribution of values for E and U increases with collagen fiber disorganization, where they divide between low and high values corresponding to uniformly aligned fibers and disorganized collagen fibers, respectively. We also confirm that the values of tau cluster around 1 when the fibers are straight, and the range increases up to 1.5 when wavier fibers are present. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Published version

Published
2022

2. Generation of streamwise vortices in a slice knife model: Can streaks be generated at the slice exit?

Author

Hsu, Tsun-Ya and Wei, Timothy

Subjects
PARTICLE image velocimetry, VECTOR analysis, VECTOR fields, PAPERMAKING machinery, PAPERMAKING equipment, PAPER, PAPERMAKING, PAPER industry
Abstract

Digital particle image velocimetry (DPIV) was used to study the question of how headboxes generate machine-direction streaks. Experiments were conducted in a water tunnel with slice geometries and conditions similar to those of headboxes. An initially steady flow past a channel was terminated by a partial blockage to represent the slice knife. DPIV vector fields showed turbulent streamwise vortices being generated and an unsteady cross-direction vortex forming in the corner of the channel that resembled the top nozzle wall and knife. The size and spacing of the streamwise vortices correspond closely to MD streak spacings found in paper. Not surprisingly, headbox manufacturers indicate that paper streaks can be reduced when headboxes are designed without slice knives. Application: The slice knife can generate streaks by producing streamwise vortices in flow entering the wire section of a paper machine. Modern headbox designers are eliminating the slice knife. [ABSTRACT FROM AUTHOR]

Published
2004