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1. Controlling Porosity of 3D Bioprinted Scaffold: A Process Parameter-Based Approach

   Quigley, C.; Clark, S.; & Habib, M. A. (May 2023, Proceedings of the IISE Annual Conference & Expo 2023)

   Babski-Reeves, K; Eksioglu, B; Hampton, D. (Ed.)

   Extrusion-based 3D bioprinting is a promising method for repairing patient-specific tissues and organs due to its inherent capacity to release biocompatible materials containing living cells in a preset area. The filament geometry and width mostly determine the scaffold architecture. Extrusion pressure, print speed, print distance, nozzle diameter, and material viscosity are just a few of the process variables that can be carefully chosen to affect the filament shape and width, ultimately verifying the user-defined scaffold porosity. To maintain defined filament width variation for various hydrogels within an acceptable range and to confirm the overall geometric fidelity of the scaffold, in this paper, filament width for a set of biomaterial compositions was determined using an image processing technique and an analytical relationship, including various process parameters, was developed. 

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2. Systemic Control of 3D Bioprinting Process Parameters to Achieve Defined Scaffold Porosity

   https://doi.org/10.1115/msec2023-104235  

   Quigley, Connor; Tuladhar, Slesha; Adhikari, Samrat; Habib, MD Ahasan (June 2023, Proceedings of the ASME 2023 18th International Manufacturing Science and Engineering Conference (MSEC2023))

   Abstract Due to its inbuilt ability to release biocompatible materials encapsulating living cells in a predefined location, 3D bioprinting is a promising technique for regenerating patient-specific tissues and organs. Among various 3D bioprinting techniques, extrusion-based 3D bio-printing ensures a higher percentage of cell release, ensuring suitable external and internal scaffold architectures. Scaffold architecture is mainly defined by filament geometry and width. A systematic selection of a set of process parameters, such as nozzle diameter, print speed, print distance, extrusion pressure, and material viscosity, can control the filament geometry and width, eventually confirming the user-defined scaffold porosity. For example, carefully selecting two sets of process parameters can result in a similar filament width. However, the lack of availability of sufficient analytical relations between printing process parameters and filament width creates a barrier to achieving defined scaffold architectures with available resources. In this paper, filament width was determined using an image processing technique and an analytical relationship was developed, including various process parameters to maintain defined filament width variation for different hydrogels within an acceptable range to confirm the overall geometric fidelity of the scaffold. Proposed analytical relations can help achieve defined scaffold architectures with available resources. 

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3. Velocities of an Erupting Filament

   https://doi.org/10.3847/1538-4357/ac3a04  

   Shuo, W; Jenkins, M; Muglach, K; Pillet, V; Beck, C; Long, M; Choudhary, D; McAteer, J (February 2022, The Astrophysical Journal)

   Abstract Solar filaments exist as stable structures for extended periods of time before many of them form the core of a coronal mass ejection (CME). We examine the properties of an erupting filament on 2017 May 29–30 with high-resolution He i 10830 Å and H α spectra from the Dunn Solar Telescope, full-disk Dopplergrams of He i 10830 Å from the Chromospheric Telescope, and EUV and coronograph data from SDO and STEREO. Pre-eruption line-of-sight velocities from an inversion of He i with the HAZEL code exhibit coherent patches of 5 Mm extent that indicate counter-streaming and/or buoyant behavior. During the eruption, individual, aligned threads appear in the He i velocity maps. The distribution of velocities evolves from Gaussian to strongly asymmetric. The maximal optical depth of He i 10830 Å decreased from τ = 1.75 to 0.25, the temperature increased by 13 kK, and the average speed and width of the filament increased from 0 to 25 km s −1 and 10 to 20 Mm, respectively. All data sources agree that the filament rose with an exponential acceleration reaching 7.4 m s −2 that increased to a final velocity of 430 km s −1 at 22:24 UT; a CME was associated with this filament eruption. The properties during the eruption favor a kink/torus instability, which requires the existence of a flux rope. We conclude that full-disk chromospheric Dopplergrams can be used to trace the initial phase of on-disk filament eruptions in real time, which might potentially be useful for modeling the source of any subsequent CMEs. 

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4. Nanoparticle growth by particle-phase chemistry

   https://doi.org/10.5194/acp-18-1895-2018  

   Apsokardu, Michael J.; Johnston, Murray V. (January 2018, Atmospheric Chemistry and Physics)

   The ability of particle-phase chemistry to alter the molecular composition and enhance the growth rate of nanoparticles in the 2–100 nm diameter range is investigated through the use of a kinetic growth model. The molecular components included are sulfuric acid, ammonia, water, a non-volatile organic compound, and a semi-volatile organic compound. Molecular composition and growth rate are compared for particles that grow by partitioning alone vs. those that grow by a combination of partitioning and an accretion reaction in the particle phase between two organic molecules. Particle-phase chemistry causes a change in molecular composition that is particle diameter dependent, and when the reaction involves semi-volatile molecules, the particles grow faster than by partitioning alone. These effects are most pronounced for particles larger than about 20 nm in diameter. The modeling results provide a fundamental basis for understanding recent experimental measurements of the molecular composition of secondary organic aerosol showing that accretion reaction product formation increases linearly with increasing aerosol volume-to-surface-area. They also allow initial estimates of the reaction rate constants for these systems. For secondary aerosol produced by either OH oxidation of the cyclic dimethylsiloxane (D₅) or ozonolysis of β-pinene, oligomerization rate constants on the order of 10⁻³ to 10⁻¹ M⁻¹ s⁻¹ are needed to explain the experimental results. These values are consistent with previously measured rate constants for reactions of hydroperoxides and/or peroxyacids in the condensed phase. 

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5. Temperature dependence of on–off ratio and reverse recovery time in NiO/β-Ga ₂ O ₃ heterojunction rectifiers

   https://doi.org/10.1116/6.0002186  

   Li, Jian-Sian; Chiang, Chao-Ching; Xia, Xinyi; Ren, Fan; Pearton, S. J. (December 2022, Journal of Vacuum Science & Technology A)

   The temperature-dependent behavior of on/off ratio and reverse recovery time in vertical heterojunction p-NiO/β n-Ga 2 O/n + Ga 2 O 3 rectifiers was investigated over the temperature range of 25–300 °C. The device characteristics in forward bias showed evidence of multiple current transport mechanisms and were found to be dependent on the applied bias voltages and temperatures. The on–off ratio decreased from 3 × 10 6 at 25 °C to 2.5 × 10 4 at 300 °C for switching to 100 V reverse bias. For 200  μm diameter rectifiers, the reverse recovery time of ∼21 ns was independent of temperature, with the I rr monotonically increasing from 15.1 mA at 25 °C to 25.6 mA at 250 °C and dropping at 300 °C. The dI/dt increased from 4.2 to 4.6 A/ μs over this temperature range. The turn-on voltage decreased from 2.9 V at 25 °C to 1.7 V at 300 °C. The temperature coefficient of breakdown voltage was negative and does not support the presence of avalanche breakdown in NiO/β-Ga 2 O 3 rectifiers. The energy loss during switching from 100 V was in the range 23–31  μJ over the temperature range investigated. 

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