查看更多>>摘要：The above paper addresses the critical topic of CFD simulation of flow in the upper airway and down into the lungs, an area that is researched widely and is of particular importance since the COVID 19 pandemic. In their simulations, the authors use the two-equation transition SST turbulence model in Ansys Fluent. They justify its use with the following sentences: 'In the work, the built-in transition SST model in ANSYS Fluent was adopted to solve the Reynolds stress term. This model has been demonstrated to be able to capture unsteady velocity fluctuations especially transitional flows reasonably well (Ball et al., 2008; Menon et al., 1984). As the flow in the airways was predominately transitional, this model was well suited for modelling continuous phase flow through the airway models.'
查看更多>>摘要：In a previous paper, computational results for drag and diffusion coefficients for particle aggregates virus like particles were reported. In this work we explore similar computations for torque on particle aggregates and virus like particles. In the free-molecular regime we have used a Monte Carlo technique, and in the continuum regime we solved relevant boundary integral equations with a numerical technique. Our test results agree with those available in the literature and provide values that are exact within numerical tolerance. Furthermore, we use our results in the free-molecular and the continuum limits for the construction of approximations, including a modified Sherman approximation, applicable over the full range of Knudsen numbers.
查看更多>>摘要：In addition to topical delivery, nasal sprays offer an alternative drug administration route to the systemic circulation, therefore avoiding the need for painful, invasive delivery techniques. Studies on the efficacy of nasal drug delivery to date have been conflicting despite its potential. In particular computational studies, e.g. Computational Fluid Dynamics (CFD), of nasal spray deposition require realistic initial spray conditions, which are lacking in the literature. This study aims to provide benchmark experimental data for CFD inputs by characterizing four different types of commercially available nasal sprays used in an ENT (Ear Nose Throat) clinic. Spray characteristics were obtained via high-speed videography, while droplet size distribution (DSD) measurements were obtained with laser diffraction. Three actuation forces were evaluated, representing the use-case of an average adult, average child and the maximum force applied to the spray device. The results demonstrated that actuation force influenced spray velocity, spray duration, DSD, and breakup length. Quantitative data of Rosin-Rammler diameter distributions, spray cone angles, dispersion angles and breakup lengths were found, assisting computational models with realistic values, thereby improving future CFD studies of nasal spray drug delivery in the nasal cavity.
查看更多>>摘要：Acoustic agglomeration as a promising preconditioning process for fine particle removal has been proven to be inefficient for submicron particles. In order to enhance the performance of acoustic agglomeration, large seed particles have been introduced into the flue gas. To understand the influence of seed particles on acoustic agglomeration, a nondimensional model of particle interaction was developed by taking into account all important particle interaction mechanisms. The simulated particle trajectories were validated against experimental data. The interaction dynamics of a seed particle and its neighboring fine particles was examined, and the dimen-sionless first collision time under different conditions was obtained. The results suggest that the enhancement of acoustic agglomeration with seed particle is mainly due to the acoustic wake effect. The overall collision kernel for the acoustic agglomeration was referred from the collision time. The results reveal that the dimensionless collision kernel almost increases linearly with the Stokes number of the seed particle, whereas its dependence on the Schmidt number of the fine particle varies significantly. The collision kernel for acoustic agglomeration was further compared with traditional collision kernels based on differential sedimentation, Brownian diffusion, laminar shear and turbulent shear. The results demonstrate that acoustic field indeed remarkably enhances the collision rate.
查看更多>>摘要：Primary biological aerosol particles (PBAPs) are important air pollutants because they are ubiquitous in the atmosphere; influence human health, air quality, atmospheric chemistry and physics; and play important roles in regulating atmospheric processes. In investigations of the effects of PBAPs in ambient environments, it is necessary to distinguish them from other particles. In this study, flow cytometry (FCM) was utilized in combination with permeant (SYBR Green dyes) and impermeant (Propidium Iodide, PI) nucleic acid fluorescent stains, to characterize and quantify the viable and dead airborne PBAPs in ambient aerosol in Beijing, China. The number concentrations of viable and dead PBAPs showed a consistent trend and correlated well with one another (R~2 = 0.72, p < 0.01). However, no relationship was found between the number concentration of PBAPs and non-biological particles. The mean number concentrations of total particulate matter, dead PBAPs and viable PBAPs were 5.78 x 10~6 m~(-3), 1.11 x 10~6 m~(-3) and 7.09 x 10~5 m~(-3), respectively. The median PBAPs number concentrations (the sum of dead and viable) exhibited a seasonal cycle, i.e., highest in summer and autumn, lowest during winter and spring. Despite a lower median PBAPs number concentration during winter compared with other seasons, the viability peaked during winter, coinciding with the winter flu season. Stable synoptic conditions, polluted southwesterly air mass and long-range transported dust from the northwest desert region all contributed to the occurrence of explosive fluorescent PBAP episodes in Beijing, China.
查看更多>>摘要：This study investigated the distribution and transmission of bacteria and antibiotic resistance genes (ARGs) in aerosol environments during the process of waste recycling in the stock landfill, including the excavation site, drying field, screening workshop and office area, to identify potential hazards to people and the surrounding environment. Results revealed that aerosols released during waste recycling had a significant impact on composition of environmental microorganisms and may affect nearby areas by diffusion. Eleven potential human pathogenic bacteria (HPB) from different sampling sites were observed and the predominant HPB genera in each sample were Acinetobacter, Pantoea and Klebsiella, especially the extremely high abundance of Acinetobacter (50.43%) in the screening workshop may be a threat to the staff. Four resistance genes and three mobile genetic elements (MGEs) in aerosols were detected by droplet digital PCR, and the most kinds and high concentrations of resistance gene subtypes were detected in screening workshop and office area. A significant positive correlation was observed between intll and up to 3 resistance gene subtypes (P < 0.05), while the correlation between ARGs and bacterial communities was weak. The study measured and evaluated the resulting risk of aerosols released during waste cycling to guide the necessary pollution control measures especially in the closed and humid environment when subsequent such projects are implemented.
查看更多>>摘要：Accurate and realistic predictions of the fate of nasally inhaled generic drugs provide new physical insight which can be of great importance to toxicologists, drug developers and federal regulators alike. To understand the dynamics of mucociliary clearance (MCC) and subsequent absorption of the dissolved drug by the nasal epithelium, it becomes necessary to model the air-particle-mucus dynamics accurately. The MCC process, including particle dissolution, transport and absorption for a 3-D representative nasal cavity, were established by Chari et al. (2021). In this study, the effects of inter-subject variability of three representative nasal cavities (subjects A, B, C) on deposition and subsequent uptake of the dissolved drug in the nasal epithehum are analyzed for three generic drugs: Mometasone furoate (MF), Flunisolide (FN), and Ribavirin (RB). The computational fluid-particle dynamics (CF-PD) results indicate that smaller sized particles (3 祄) deposit more in the ciliated portion of the nasal cavity where the columnar cells responsible for uptake are present. In contrast, larger particles (10 祄) tend to deposit in the unciliated anterior third of the nose. The epithelial uptake in case of subject A was considerably higher than that in subjects B and C because of the unique anatomical characteristics of subject A. Also, FN and RB were found to have a higher rate of uptake compared to MF due to their considerably higher partition coefficient. As a visualization tool, concentration contours are used to explain regional trends in cumulative drug uptake for all three cases.
查看更多>>摘要：The purpose of this tutorial is to teach the method of digital in-line holography (DIH) as a means to characterize aerosol particles in an in-sitti manner. The scope is limited to the simplest, yet powerful, lens-less implementation, which is the most intuitive and forgiving of the varieties of digital holography. By illuminating free-flowing aerosol particles with a pulsed, expanded, collimated laser beam, one can record the interference pattern of scattered and unscattered light on an image sensor. The resulting digital hologram can then be used in a diffraction calculation to render a silhouette-like image of the particle, or particles, present in the beam. A key advantage of imaging with DIH over conventional imaging, e.g. microscopy, is that particles located at different positions can be brought into focus from a single hologram measurement. Useful information can be obtained from such images including the number of particles present, their size, shape, and orientation. Notably, this is all achieved without the need to collect or otherwise trap particles. The inherent motion of aerosol particles imposes specific constraints on the design and performance of DIH imaging, and in particular, restricts the resolution in comparison to applications involving stationary or otherwise controlled particles. As such, DIH is currently most effective for particles larger than several micrometers in size. The tutorial will explain the theoretical basis of DIH, illustrate how particle images are generated computationally from hologram measurements, provide code in the Mathematica language to do so, and discuss several limitations imposed by hardware. Also reviewed will be a method to approximate a particle's extinction cross section and two-dimensional angular light scattering pattern.
Kaleb J. DuelgeGeorge W. MulhollandAntonio R. Montoro Bustos
16页
查看更多>>摘要：Implementation of hybrid nanoparticles (HNPs), consisting of two different metal components, into applied systems has been hindered by an incomplete understanding of structural and chemical properties responsible for their enhanced, yet inconsistent performance. To address this persistent need, our work focused on using the electrospray differential mobility analyzer hyphenated to inductively coupled plasma mass spectrometry (ES-DMA-ICP-MS) to determine mass distributions across the entire NP distribution. Although previous work had applied similar hyphenated measurements to HNP systems, no efforts to develop accurate calibration methods for quantifying NP, and especially HNP, masses have been reported. We chose gold titania catalyst HNPs (Au@TiO2: 4 ran gold NPs adsorbed on 100 nm-300 nm TiO2 NPs) as a representative system because a large body of research exists on this topic. When we used ionic standards and compared it to our Au@TiO2 control, a reproducible difference in the slope was observed that led to an overestimation of both gold (Au) and titanium (Ti) by nearly a factor of four for the HNPs, demonstrating the complexity of quantification and the need to both develop a validated calibration method and identify the major sources for uncertainty in quantification. We determined the mass quantification discrepancy derived from the metal oxide NPs (independent of the presence of Au) and was caused by the DMA and ES (not the ICP-MS). Corrections were made for multiple charging that significantly improved the agreement between the ionic standard and Au@TiO2 metal quantification. Discussion on material properties for improved accuracy across different shapes, sizes, compositions, and surface chemistries is also included to demonstrate the general utility of the calibration across a broad number of fields. ES-DMA-ICP-MS is a powerful technique that provides statistically significant data for simultaneous determination of mass distributions of multi-element HNP systems across the entire sample population and should enhance characterization and development of HNPs when coupled with current core methods.
查看更多>>摘要：Estimation of fungal spore emission from various sources, which is a necessary input for the estimation of their effects on health and climate using mathematical models, relies on realistic quantification of fungal spores. Different quantification techniques have been used in various studies of fungal spore emission. For the purposes of model development, validation and application, the various methods must be correlated. In this study, we compare the commonly used methods - fluorescence microscopy, haemocytometer and fluorescence spectroscopy, in in relation to fungal spore emission estimation using Penitillium chrysogenum as a test fungal species. In addition, we also compare an offline and online technique - Biosampler~R and Optical particle sizer (OPS) respectively. It was found that haemocytometer shows up to 50% higher average spore count than fluorescence microscopy in the range of 10~4-10~7 spores/ml. The effect of sampling volume, artifacts and image magnification on sample representativeness was also studied using fluorescence microscopy as the basis. Statistical analysis of these effects shows that at spore concentrations lower than 10~4/mL, the uncertainty is significant. The comparison between emission measurement using OPS and Biosampler/fluorescence microscopy techniques were reasonably similar. The quantitative comparison also provides a basis for other users to choose methods for their research objectives using appropriate quantitative correction and correlation factors.
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