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  1. Book ; Online: Buoyancy and Marangoni Effects on Horizontal Ribbon Growth

    Bagheri-Sadeghi, Nojan / Helenbrook, Brian T.

    2022  

    Abstract: Unsteady simulations of horizontal ribbon growth of silicon were performed that included both Marangoni and buoyancy effects. A chaotic flow was observed dominated by strong Marangoni-driven jets emerging near the local temperature minima on the free ... ...

    Abstract Unsteady simulations of horizontal ribbon growth of silicon were performed that included both Marangoni and buoyancy effects. A chaotic flow was observed dominated by strong Marangoni-driven jets emerging near the local temperature minima on the free surface. This oscillatory flow caused the vertical position of the leading edge of the sheet to fluctuate, resulting in corrugations on the top surface of the ribbon. Additionally, larger amplitude and wavelength nonuniformities appeared on the bottom of the sheet resulting in a sheet with varying thickness. Lastly, the unsteady flow caused temporal variations in growth rate, which when converted to distance using the pull speed, matched the wavelengths observed on the top surface. All three of these phenomena have been observed experimentally: The median of the surface wavelengths and amplitudes decreased with increasing temperature sensitivity of surface tension and had wavelengths on the same order as experiments for a sensitivity corresponding to uncontaminated silicon. Oscillations in growth rate have been observed using passive antimony demarcation and thickness variations have been measured after sheet removal. These results indicate that the chaotic flow makes producing thin uniform sheets using HRG challenging.

    Comment: Added Acknowledgments, added links to videos, fixed a few references
    Keywords Physics - Fluid Dynamics ; Condensed Matter - Materials Science
    Subject code 551
    Publishing date 2022-05-02
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article: Influence of two-dimensional expiratory airflow variations on respiratory particle propagation during pronunciation of the fricative [f].

    Mofakham, Amir A / Helenbrook, Brian T / Erath, Byron D / Ferro, Andrea R / Ahmed, Tanvir / Brown, Deborah M / Ahmadi, Goodarz

    Journal of aerosol science

    2023  Volume 173, Page(s) 106179

    Abstract: Propagation of respiratory particles, potentially containing viable viruses, plays a significant role in the transmission of respiratory diseases (e.g., COVID-19) from infected people. Particles are produced in the upper respiratory system and exit the ... ...

    Abstract Propagation of respiratory particles, potentially containing viable viruses, plays a significant role in the transmission of respiratory diseases (e.g., COVID-19) from infected people. Particles are produced in the upper respiratory system and exit the mouth during expiratory events such as sneezing, coughing, talking, and singing. The importance of considering speaking and singing as vectors of particle transmission has been recognized by researchers. Recently, in a companion paper, dynamics of expiratory flow during fricative utterances were explored, and significant variations of airflow jet trajectories were reported. This study focuses on respiratory particle propagation during fricative productions and the effect of airflow variations on particle transport and dispersion as a function of particle size. The commercial ANSYS-Fluent computational fluid dynamics (CFD) software was employed to quantify the fluid flow and particle dispersion from a two-dimensional mouth model of sustained fricative [f] utterance as well as a horizontal jet flow model. The fluid velocity field and particle distributions estimated from the mouth model were compared with those of the horizontal jet flow model. The significant effects of the airflow jet trajectory variations on the pattern of particle transport and dispersion during fricative utterances were studied. Distinct differences between the estimations of the horizontal jet model for particle propagation with those of the mouth model were observed. The importance of considering the vocal tract geometry and the failure of a horizontal jet model to properly estimate the expiratory airflow and respiratory particle propagation during the production of fricative utterances were emphasized.
    Language English
    Publishing date 2023-04-11
    Publishing country England
    Document type Journal Article
    ZDB-ID 1499134-2
    ISSN 1879-1964 ; 0021-8502
    ISSN (online) 1879-1964
    ISSN 0021-8502
    DOI 10.1016/j.jaerosci.2023.106179
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  3. Article ; Online: Variability in expiratory trajectory angles during consonant production by one human subject and from a physical mouth model: Application to respiratory droplet emission.

    Ahmed, Tanvir / Wendling, Hannah E / Mofakham, Amir A / Ahmadi, Goodarz / Helenbrook, Brian T / Ferro, Andrea R / Brown, Deborah M / Erath, Byron D

    Indoor air

    2021  Volume 31, Issue 6, Page(s) 1896–1912

    Abstract: The COVID-19 pandemic has highlighted the need to improve understanding of droplet transport during expiratory emissions. While historical emphasis has been placed on violent events such as coughing and sneezing, the recognition of asymptomatic and ... ...

    Abstract The COVID-19 pandemic has highlighted the need to improve understanding of droplet transport during expiratory emissions. While historical emphasis has been placed on violent events such as coughing and sneezing, the recognition of asymptomatic and presymptomatic spread has identified the need to consider other modalities, such as speaking. Accurate prediction of infection risk produced by speaking requires knowledge of both the droplet size distributions that are produced, as well as the expiratory flow fields that transport the droplets into the surroundings. This work demonstrates that the expiratory flow field produced by consonant productions is highly unsteady, exhibiting extremely broad inter- and intra-consonant variability, with mean ejection angles varying from ≈+30° to -30°. Furthermore, implementation of a physical mouth model to quantify the expiratory flow fields for fricative pronunciation of [f] and [θ] demonstrates that flow velocities at the lips are higher than previously predicted, reaching 20-30 m/s, and that the resultant trajectories are unstable. Because both large and small droplet transport are directly influenced by the magnitude and trajectory of the expirated air stream, these findings indicate that prior investigations of the flow dynamics during speech have largely underestimated the fluid penetration distances that can be achieved for particular consonant utterances.
    MeSH term(s) Aerosols ; Air Pollution, Indoor ; COVID-19 ; Humans ; Mouth/physiology ; Research Subjects ; SARS-CoV-2 ; Speech/physiology
    Chemical Substances Aerosols
    Language English
    Publishing date 2021-07-23
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1081722-0
    ISSN 1600-0668 ; 0905-6947
    ISSN (online) 1600-0668
    ISSN 0905-6947
    DOI 10.1111/ina.12908
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    Z 7724: Show issues

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  4. Article ; Online: Characterizing respiratory aerosol emissions during sustained phonation.

    Ahmed, Tanvir / Rawat, Mahender Singh / Ferro, Andrea R / Mofakham, Amir A / Helenbrook, Brian T / Ahmadi, Goodarz / Senarathna, Dinushani / Mondal, Sumona / Brown, Deborah / Erath, Byron D

    Journal of exposure science & environmental epidemiology

    2022  Volume 32, Issue 5, Page(s) 689–696

    Abstract: Objective: To elucidate the role of phonation frequency (i.e., pitch) and intensity of speech on respiratory aerosol emissions during sustained phonations.: Methods: Respiratory aerosol emissions are measured in 40 (24 males and 16 females) healthy, ... ...

    Abstract Objective: To elucidate the role of phonation frequency (i.e., pitch) and intensity of speech on respiratory aerosol emissions during sustained phonations.
    Methods: Respiratory aerosol emissions are measured in 40 (24 males and 16 females) healthy, non-trained singers phonating the phoneme /a/ at seven specific frequencies at varying vocal intensity levels.
    Results: Increasing frequency of phonation was positively correlated with particle production (r = 0.28, p < 0.001). Particle production rate was also positively correlated (r = 0.37, p < 0.001) with the vocal intensity of phonation, confirming previously reported findings. The primary mode (particle diameter ~0.6 μm) and width of the particle number size distribution were independent of frequency and vocal intensity. Regression models of the particle production rate using frequency, vocal intensity, and the individual subject as predictor variables only produced goodness of fit of adjusted R
    Significance: The results suggest there remain unexplored effects (e.g., biomechanical, environmental, behavioral, etc.) that contribute to the high variability in respiratory particle production rates, which ranged from 0.2 particles/s to 142 particles/s across all trials. This is evidenced as well by changes in the distribution of participant particle production that transitions to a more bimodal distribution (second mode at particle diameter ~2 μm) at higher frequencies and vocal intensity levels.
    MeSH term(s) Female ; Humans ; Male ; Phonation ; Respiratory Aerosols and Droplets ; Speech
    Language English
    Publishing date 2022-03-29
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 2218551-3
    ISSN 1559-064X ; 1559-0631
    ISSN (online) 1559-064X
    ISSN 1559-0631
    DOI 10.1038/s41370-022-00430-z
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    In stock of ZB MED Bonn / Germany

    Z 7529: Show issues

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