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1. Modeling flux in tangential flow filtration using a reverse asymmetric membrane for Chinese hamster ovary cell clarification

   https://doi.org/10.1002/btpr.3115  

   Zhang, Da; Patel, Parag; Strauss, Daniel; Qian, Xianghong; Wickramasinghe, S_Ranil (January 2021, Biotechnology Progress)

   Abstract Tangential flow filtration is advantageous for bioreactor clarification as the permeate stream could be introduced directly to the subsequent product capture step. However, membrane fouling coupled with high product rejection has limited its use. Here, the performance of a reverse asymmetric hollow fiber membrane where the more open pore structure faces the feed stream and the barrier layer faces the permeate stream has been investigated. The open surface contains pores up to 40 μm in diameter while the tighter barrier layer has an average pore size of 0.4 μm. Filtration of Chinese hamster ovary cell feed streams has been investigated under conditions that could be expected in fed batch operations. The performance of the reverse asymmetric membrane is compared to that of symmetric hollow fiber membranes with nominal pore sizes of 0.2 and 0.65 μm. Laser scanning confocal microscopy was used to observe the locations of particle entrapment. The throughput of the reverse asymmetric membrane is significantly greater than the symmetric membranes. The membrane stabilizes an internal high permeability cake that acts like a depth filter. This stabilized cake can remove particulate matter that would foul the barrier layer if it faced the feed stream. An empirical model has been developed to describe the variation of flux and transmembrane pressure drop during filtration using reverse asymmetric membranes. Our results suggest that using a reverse asymmetric membrane could avoid severe flux decline associated with fouling of the barrier layer during bioreactor clarification. 

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2. Dissimilar cavitation dynamics and damage patterns produced by parallel fiber alignment to the stone surface in holmium:yttrium aluminum garnet laser lithotripsy

   https://doi.org/10.1063/5.0139741  

   Xiang, Gaoming; Li, Daiwei; Chen, Junqin; Mishra, Arpit; Sankin, Georgy; Zhao, Xuning; Tang, Yuqi; Wang, Kevin; Yao, Junjie; Zhong, Pei (March 2023, Physics of Fluids)

   Recent studies indicate that cavitation may play a vital role in laser lithotripsy. However, the underlying bubble dynamics and associated damage mechanisms are largely unknown. In this study, we use ultra-high-speed shadowgraph imaging, hydrophone measurements, three-dimensional passive cavitation mapping (3D-PCM), and phantom test to investigate the transient dynamics of vapor bubbles induced by a holmium:yttrium aluminum garnet laser and their correlation with solid damage. We vary the standoff distance ( SD) between the fiber tip and solid boundary under parallel fiber alignment and observe several distinctive features in bubble dynamics. First, long pulsed laser irradiation and solid boundary interaction create an elongated “pear-shaped” bubble that collapses asymmetrically and forms multiple jets in sequence. Second, unlike nanosecond laser-induced cavitation bubbles, jet impact on solid boundary generates negligible pressure transients and causes no direct damage. A non-circular toroidal bubble forms, particularly following the primary and secondary bubble collapses at SD = 1.0 and 3.0 mm, respectively. We observe three intensified bubble collapses with strong shock wave emissions: the intensified bubble collapse by shock wave, the ensuing reflected shock wave from the solid boundary, and self-intensified collapse of an inverted “triangle-shaped” or “horseshoe-shaped” bubble. Third, high-speed shadowgraph imaging and 3D-PCM confirm that the shock origins from the distinctive bubble collapse form either two discrete spots or a “smiling-face” shape. The spatial collapse pattern is consistent with the similar BegoStone surface damage, suggesting that the shockwave emissions during the intensified asymmetric collapse of the pear-shaped bubble are decisive for the solid damage. 

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3. Optical characterization of disordered Yb-doped silica glass Anderson localizing optical fiber

   https://doi.org/10.1364/JOSAB.444214  

   Bassett, Cody; Tuggle, Matthew; Ballato, John; Mafi, Arash (March 2022, Journal of the Optical Society of America B)

   We investigate and report the optical and laser characteristics of a ytterbium-doped transverse Anderson localizing optical fiber to develop a fundamental understanding of the light propagation, generation, and amplification processes in this novel fiber. Ultimately, the goal based on the measurements and calculations conducted herein is to design and build a random fiber laser with a highly directional beam. The measurements are based on certain observations of the laser pump propagation and amplified spontaneous emission generation in this fiber. Judicious approximations are used in the propagation equations to obtain the relevant desired parameters in simple theoretical fits to experimental observations, without resorting to speculations based on the intended construction from the fiber preform. 

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4. Laser Processing Technology for PAN Fiber Carbonization

   Xie, Jianxin; Zhang, Mei (October 2018, The Composites and Advanced Materials Expo. CAMX Conference Proceedings)

   Carbon fibers (CFs) are an important engineering material due to their superior mechanical, electrical, and thermal properties. Majority of them are produced from the thermal conversion of polyacrylonitrile (PAN)-based fibers. In order to promote the CF manufacturing speed and offer the possibility to control the microstructure of the fibers, an alternative technology for carbonization of stabilized PAN fiber are explored by laser processing technology. In this work, we investigated the relationship between the laser process and the properties of fibers. Laser irradiation introduces the structural changes in the stabilized PAN fibers. The appearance of D band and G band in Raman spectrum verifies the existence of graphite structures in the laser scanned fibers. The characteristic peaks in FTIR disappear when the high laser energy condition is engaged, which indicates diminishing of non-carbon bonds. Laser treatment also introduces an obvious shrinkage in fiber diameter. The condition of laser irradiation could influence the electrical and mechanical properties of fibers. A new approach to convert stabilized PAN fiber into carbon fiber was demonstrated. 

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5. Ultrafast laser inscription of asymmetric integrated waveguide 3  dB couplers for astronomical K-band interferometry at the CHARA array

   https://doi.org/10.1364/JOSAB.423727  

   Benoît, Aurélien; Pike, Fraser_A; Sharma, Tarun_K; MacLachlan, David_G; Dinkelaker, Aline_N; Nayak, Abani_S; Madhav, Kalaga; Roth, Martin_M; Labadie, Lucas; Pedretti, Ettore; et al (August 2021, Journal of the Optical Society of America B)

   We present the fabrication and characterization of 3 dB asymmetric directional couplers for the astronomical K-band at wavelengths between 2.0 and 2.4 µm. The couplers were fabricated in commercial Infrasil silica glass using an ultrafast laser operating at 1030 nm. After optimizing the fabrication parameters, the insertion losses of straight single-mode waveguides were measured to be $\sim <\#comment/>1.2\pm <\#comment/>0.5\mathrm{d}\mathrm{B}$across the full K-band. We investigate the development of asymmetric 3 dB directional couplers by varying the coupler interaction lengths and by varying the width of one of the waveguide cores to detune the propagation constants of the coupled modes. In this manner, we demonstrate that ultrafast laser inscription is capable of fabricating asymmetric 3 dB directional couplers for future applications in K-band stellar interferometry. Finally, we demonstrate that our couplers exhibit an interferometric fringe contrast of $><\#comment/>90\mathrm{\%<\#comment/>}$. This technology paves the path for the development of a two-telescope K-band integrated optic beam combiner for interferometry to replace the existing beam combiner (MONA) in Jouvence of the Fiber Linked Unit for Recombination (JouFLU) at the Center for High Angular Resolution Astronomy (CHARA) telescope array. 

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