Vaporizing Microdroplet Inhalation,Transport, and Deposition in a Human Upper Airway Model

Evaluation of injuries from inhalation exposure to toxic fuel requires detailed knowledge of inhaled aerosol transport and deposition in human airways. Focusing on highly toxic, easily volatized JP-8 fuel droplets, the three-dimensional airflow, temperature distributions, and fluid-particle thermodynamics, i.e., droplet motion as well as evaporation, are simulated and analyzed for laminar as well as locally turbulent flow conditions.

Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler-Lagrange approach for the fluid-particle thermodynamics is employed with: (1) a low Reynolds number k-ω model for laminar-to-turbulent airflow, and (2) a stochastic model for random fluctuations in the droplet trajectories with droplet evaporation. Presently, the respiratory system consists of two major segments of a simplified human cast replica, i.e., a representative oral airway from mouth to trachea (Generation 0) and a symmetric four-generation upper bronchial tree model (G0 to G3). Experimentally validated computational fluid-particle thermodynamics results show that evaporation of JP-8 fuel droplets is greatly affecting deposition in the human airway. Specifically, droplet deposition fractions due to vaporization decrease with increasing ambient temperatures and decreasing inspiratory flow rates. It is also demonstrated that assuming idealized velocity profiles and particle distributions in or after the trachea may greatly overpredict particle deposition efficiencies in the upper bronchial tree.     

Computational Fluid Dynamic Predictions and Experimental Results for Particle Deposition in an Airway Model

An area identified as having a high priority by the National Research Council (NRC 1998) relating to health effects of exposure to urban particulate matter is the investigation of particle deposition patterns in potentially-susceptible subpopulations. A key task for risk assessment is development and refinement of mathematical models that predict local deposition patterns of inhaled particles in airways. Recently, computational fluid dynamic modeling (CFD) has provided the ability to predict local airflows and particle deposition patterns in various structures of the human respiratory tract. Although CFD results generally agree with available data from human studies, there is a need for experimental particle deposition investigations that provide more detailed comparisons with computed local patterns of particle deposition. Idealized 3-generation hollow tracheo-bronchial models based on the Weibel symmetric morphometry for airway lengths and diameters (generations 3-5) were constructed with physiologically-realistic bifurcations. Monodisperse fluorescent polystyrene latex particles (1 and 10 mu m aerodynamic diameter) were deposited in these models at a steady inspiratory flow of 7.5 L /min (equivalent to heavy exertion with a tracheal flow of 60 L /min). The models were opened and the locations of deposited particles were mapped using fluorescence microscopy. The particle deposition predictions using CFD for 10 mu m particles correlated well with those found experimentally. CFD predictions were not available for the 1 mu m diameter case, but the experimental results for such particles are presented.     

Development of an Aerosol Dynamics Model for Dry Deposition Process Using the Moment Method

An aerosol dynamics model for dry deposition process is developed based on the moment method. Since it is hard to fully apply the moment method to the widely used dry deposition velocity expressions based on the resistance theory, the dry deposition velocity expression by Raupach et al. (2001) Raupach, M. R., Briggs, P. R., Ahmad, N. and Edge, V. E. 2001. Endosulfan Tansport: II. Modeling airborne Dispersal and Deposition by Spray and Vapor. J. Environ. Qual., 30: 729–740. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar] is used. Detailed deposition mechanisms such as Brownian diffusion, gravitational settling, and impaction are considered in the expression. To verify the validity of the derived dynamic equation, aerosol dynamics for the dry deposition process is estimated with the expressions of Raupach et al. (2001) Raupach, M. R., Briggs, P. R., Ahmad, N. and Edge, V. E. 2001. Endosulfan Tansport: II. Modeling airborne Dispersal and Deposition by Spray and Vapor. J. Environ. Qual., 30: 729–740. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar], of Wesely (1989) Wesely, M. L. 1989. Parameterizations of Surface Resistance to Gaseous Dry Deposition in Regional-Scale, Numerical Models. Atmos. Environ., 23: 1293–1304. [Crossref], [Web of Science ®] , [Google Scholar] modified for particles (Seinfeld and Pandis 1998 Seinfeld, J. H. and Pandis, S. N. 1998. Atmospheric Chemistry and Physics, 958–996. New York, , USA: Wiley.  [Google Scholar]), in CMAQ, and with constant value used in RAINS-ASIA. Those expressions give different dynamics. Generally, the result for this study is between the result of modified Wesely's expression and CMAQ. When using the modified Wesely's expression with the number of sections being equal or smaller than 10, the resultant size distribution does not give the peak shape accurately.     

Collection Efficiencies in an Aerodyne Aerosol Mass Spectrometer as a Function of Particle Phase for Laboratory Generated Aerosols

The Aerodyne Aerosol Mass Spectrometer (AMS) is a useful tool to study ambient particles. To be quantitative, the mass or (number) of particles detected by the AMS relative to the mass (or number) of particles sampled by the AMS, or the AMS collection efficiency (CE), must be known. Here we investigated the effect of particulate phase on AMS CE for ammonium nitrate, ammonium sulfate, mixed ammonium nitrate/ammonium sulfate, and ammonium sulfate particles coated with an organic liquid. Dry, solid ammonium sulfate particles were sampled with a CE of 24 ± 3%. Liquid droplets and solid particles that were thickly coated with a liquid organic were collected with a CE of 100%. Mixed phase particles, solid particles thinly coated with liquid organic, and metastable aqueous ammonium sulfate droplets had intermediate CEs. The higher CEs for liquid particles compared with solid particles were attributed to wet or coated particles tending to stick upon impact with the AMS vaporizer, while a significant fraction of solid particles bounced prior to vaporization/detection. The consistency of single particle signals indicated that the phase (and hence CE) of mixed component particles did not affect the AMS sensitivity to a particular chemical species once volatilization occurred. Particle phase might explain a significant fraction of the variable AMS CEs reported in the literature. For example, ambient particles that were liquid (e.g., composition dominated by ammonium nitrate or acidic sulfate) have been reported to be sampled with 100% CE. In contrast, most ambient particle measurements report CEs of < 100% (typically~ 50%).     

A Plug Flow Model for Chemical Reactions and Aerosol Nucleation and Growth in an Alkali-Containing Flue Gas

The paper presents a numerical model for the simulation of gas to particle conversion and the chemical changes during cooling of a flue gas from the combustion of fuels rich in volatile alkali species. For the homogeneous nucleation of alkali species the model uses the classical theory modified by the Tolman coefficient for the size dependent surface tension. A special adaptation of the theory to the nucleation of seeds of chloride salt from an equilibrium mixture of monomer and dimer chloride vapor molecules is also made. The growth of particles occurs by condensation and agglomeration. Different multicomponent growth models are treated. The local gas phase composition is determined from a gas phase chemical equilibrium calculation combined with finite reaction rate kinetics for slower reactions. The model is useful in the analysis of boiler operation with respect to the formation of particles, HCl, SO₂, and deposits.     

MADMS: Modal Aerosol Dynamics model for multiple Modes and fractal Shapes in the free-molecular and near-continuum regimes

Atmospheric particles vary in size and shape. Moment Dynamics Equations (MDEs) of the Modal Aerosol Dynamics (MAD) approach were extended to simulate the Brownian coagulation process of multimodal aerosols covering full size ranges and arbitrary fractal dimensions for implementation in three-dimensional atmospheric aerosol chemical transport and climate models. The proposed approach is referred as the Modal Aerosol Dyanmics 'model' for multiple Modes and fractal Shapes (MADMS). The approximation of Otto, Fissan, Park, and Lee (1997) for intramodal coagulation in the free-molecular regime was for the first time extended to intermodal coagulation with different geometric standard deviations (σ) and geometric mean diameters (D_g) for arbitrary mass fractal dimensions (D_f). To evaluate the accuracy of the MADMS model and to examine temporal evolution of coagulating aerosol modes under atmospheric conditions, simple one-box simulations using the model were performed and compared with rigorous numerical solutions obtained using the difference (bin) method. Deviations of MADMS from the accurate bin method (BIN100, d log D=3.01×10^?2, 100 bins between 1 nm and 1 μm and 100 between 1 μm and 1 mm) are smaller than 5% in number and volume concentrations and smaller than 2% in σ and D_g during the period for 30% of the initial number concentration to coagulate (t₃₀). The MADMS model is four to six orders of magnitude faster than BIN100 with respect to CPU time. It was found to be sometimes comparable in accuracy to, but generally one order of magnitude more accurate than, the bin method with a coarse bin-grid resolution (BIN10, d log D=3.01×10^?1, 10 bins between 1 nm and 1 μm), which is commonly used for 3-D simulations, as well as two to four orders of magnitude faster than BIN10.     

Particle Deposition in Replicate Casts of the Human Upper Tracheobronchial Tree Under Constant and Cyclic Inspiratory Flow. II. Experimental Model

Data obtained in a study of the deposition of monodisperse particles in replicate casts of the human upper bronchial tree were used to develop an empirical model for prediction of bronchial deposition under both constant and cyclic inspiratory flow conditions. The model incorporates specific morphometric factors which affect deposition.     

A One-Dimensional Model for Particulate Deposition and Hydrocarbon Condensation in Exhaust Gas Recirculation Coolers

Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine out NO_x (oxides of nitrogen) emissions. A portion of the exhaust gases is recirculated into the intake manifold of the engine after cooling it through a heat exchanger. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface. This adversely affects the combustion process, engine durability, and emissions. In this study, a 1-D model was developed to simulate soot deposition, soot removal, and condensation of several hydrocarbon (HC) species in a circular tube with turbulent gas flow at constant wall temperature. The circular tube, which makes up the computational domain in the model, represents a single channel from any EGR cooler geometry. The model takes into account soot particle deposition due to thermophoresis, diffusion, turbulent impaction, and gravitational drift. However, thermophoresis was found to be the most dominant deposition mechanism for boundary conditions at which EGR coolers typically operate. Soot removal was modeled by considering a force balance between the drag and van der Waals forces. A lognormal distribution of particles was assumed at the tube inlet. The evolution of the particle distribution in the bulk flow along the tube as well as the mass distribution in the deposit layer on the tube walls is predicted by the model. Condensation of six HC species between C₁₅-C₂₄ alkanes was also modeled. Predictions made by the model are in reasonably good agreement with experimental data obtained from a laboratory reactor under the same boundary conditions. There are several assumptions and simplifications built into the model, which can be refined further to improve it.

Copyright 2012 American Association for Aerosol Research     

Transmission Efficiency of an Aerodynamic Focusing Lens System: Comparison of Model Calculations and Laboratory Measurements for the Aerodyne Aerosol Mass Spectrometer

The size-dependent particle transmission efficiency of the aerodynamic lens system used in the Aerodyne Aerosol Mass Spectrometer (AMS) was investigated with computational fluid dynamics (CFD) calculations and experimental measurements. The CFD calculations revealed that the entire lens system, including the aerodynamic lens itself, the critical orifice which defines the operating lens pressure, and a valve assembly, needs to be considered. Previous calculations considered only the aerodynamic lens. The calculations also investigated the effect of operating the lens system at two different sampling pressures, 7.8 × 10⁴ Pa (585 torr) and 1.0 × 10⁵ Pa (760 torr). Experimental measurements of transmission efficiency were performed with size-selected diethyl hexyl sebacate (DEHS), NH₄NO₃, and NaNO₃ particles on three different AMS instruments at two different ambient sampling pressures (7.8 × 10⁴ Pa, 585 torr and 1.0 × 10⁵ Pa, 760 torr). Comparisons of the measurements and the calculations show qualitative agreement, but there are significant deviations which are as yet unexplained. On the small size end (30 nm to 150 nm vacuum aerodynamic diameter), the measured transmission efficiency is lower than predicted. On the large size end (> 350 nm vacuum aerodynamic diameter) the measured transmission efficiency is greater than predicted at 7.8 × 10⁴ Pa (585 torr) and in good agreement with the prediction at 1.0 × 10⁵ Pa (760 torr).     

Eulerian Model for Prediction of Particle Transport and Deposition in Turbulent Duct Flows with Thermophoresis

The Reynolds-averaged equations for turbulent particle population/transport in an Eulerian framework must be closed by specifying models for several terms: a turbophoretic force; a turbulent thermophoretic force; and a turbulent particle-diffusion term. In this article, new models are proposed for the turbophoretic term, as a particle-size dependent extrapolation of the corresponding turbulent fluid-velocity correlation, and for the turbulent thermophoretic term as an eddy-viscosity-scaled multiple of the corresponding mean thermophoretic term, appropriate for small low-inertia particles with τ⁺_p < 10. When the turbophoresis model is incorporated in a system of equations that describes particle motion within the surrounding fluid, it predicts particle deposition velocities that are in good agreement with experimental data over a range of particle sizes. When this equation system is included in a computational model to predict particle transport in turbulent pipe flows, the efficiency of particle deposition in pipes with upstream heating and downstream cooling is found to be in fair agreement with experimental measurements at two different Reynolds numbers, and over a range of particle sizes and temperature differences.

Copyright 2015 American Association for Aerosol Research     

Ion Densities and Particle Charges for Alpha Ionization in an Aerosol Atmosphere: Columnar Recombination Corrections

Ionization by alpha sources in an environment containing small aerosol particles is of interest in aerosol neutralizes, particle chargers and atmospheric electricity. It is known that the conventional ion-balance equation is inadequate in describing the bulk ion densities for alpha sources in view of the columnar recombination process. An earlier self-consistent formulation to include this effect is extended to the case of unequal ionic mobilities and the consequent asymmetric charging of particles. Calculations for medium (Radon-222) and low (Thorium-232) energy sources commonly encountered indicate that the columnar recombination corrections lower the ion densities and the particle mean charges by a factor of about 2 for weak sources (strength < 10³ ions cm^?3 s^?1) and by a factor of 1.2 for strong sources (strength = 10⁹ ions cm^?3 s^?1). The paper presents a detailed study of the dependence of the correction factors as a function of particle concentration and the strength of the alpha sources.     

Role of Flaxseed Meal Feeding for Different Durations in the Lipid Deposition and Meat Quality in Broiler Chickens

This study investigated the role of flaxseed meal (FSM), a rich terrestrial source of ω-3 fatty acids, in the alteration of the fatty acid profile and metabolism, health indices, physicochemical properties, and sensory quality of broiler chicken meat. The broiler chickens were fed 100 g FSM kg⁻¹ diet for different time periods (1, 2, 3, 4, and 5 weeks). The results revealed that 100 g FSM feeding in broiler chickens for at least 3 weeks increased (P < 0.01) the EPA, DHA, MUFA, PUFA, ω-3 PUFA, and ω-6 PUFA of broiler chicken meat with the corresponding decrease in palmitic acid, stearic acid, and SFA content. 100 g FSM feeding up to 3 weeks has increased the Δ⁹-desaturases (P < 0.05), thioesterase index (P < 0.01), and Δ⁵-desaturase + Δ⁶-desaturase activity (P < 0.01) along with an improvement in health indices (P < 0.01) of chicken meat. Similarly, a reduction in meat cholesterol and fat content of thigh meat (P < 0.01) was observed by feeding 100 g FSM for at least 3 weeks with no effect on the pH, color scores, and sensory evaluation of broiler chicken meat. The water-holding capacity (WHC) and extract release volume (ERV) decreased, whereas, drip loss of meat increased (P < 0.01) due to the feeding of 100 g FSM beyond 3 weeks. Thus, this study concluded that 100 g FSM feeding for 3 weeks in broiler chickens significantly improves the fatty acid profile, lipid metabolism, and health indices of meat, without compromising the physicochemical properties of broiler chicken meat.     

Study of Different Delivery Modes of Chondroitin Sulfate Using Microspheres and Cryogel Scaffold for Application in Cartilage Tissue Engineering

This study focuses on the development of an efficient delivery modes designed for chondroitin sulfate (CS) for application in cartilage tissue engineering. Novel three-dimensional (3-D) scaffold fabricated from natural polymers such as chitosan and gelatin blended with chondroitin sulfate (CGC) were synthesized using cryogelation technology. Other methods to deliver CS were also tried, which included incorporation into microparticles for sustained release and embedding the CS loaded microparticles in CG (chitosan-gelatin) cryogel scaffold. Novel CGC scaffolds were characterized by rheology, scanning electron microscopy (SEM), and mechanical assay. Scaffolds exhibited compression modulus of 50 KPa confirming the utility of these scaffolds for cartilage tissue engineering. Primary goat chondrocytes were used for the in vitro testing of all the delivery modes. So this study shows that CS microparticles when given freely with matrix (chitosan–gelatin) or embedded into scaffold has potential to enhance chondrocyte proliferation together with improved matrix production than in control without microspheres.     

Different Effects of RNAi-Mediated Downregulation or Chemical Inhibition of NAMPT in an Isogenic IDH Mutant and Wild-Type Glioma Cell Model

The IDH1^R132H mutation in glioma results in the neoenzymatic function of IDH1, leading to the production of the oncometabolite 2-hydroxyglutarate (2-HG), alterations in energy metabolism and changes in the cellular redox household. Although shifts in the redox ratio NADPH/NADP⁺ were described, the consequences for the NAD⁺ synthesis pathways and potential therapeutic interventions were largely unexplored. Here, we describe the effects of heterozygous IDH1^R132H on the redox system in a CRISPR/Cas edited glioblastoma model and compare them with IDH1 wild-type (IDH1^wt) cells. Besides an increase in 2-HG and decrease in NADPH, we observed an increase in NAD⁺ in IDH1^R132H glioblastoma cells. RT-qPCR analysis revealed the upregulation of the expression of the NAD⁺ synthesis enzyme nicotinamide phosphoribosyltransferase (NAMPT). Knockdown of NAMPT resulted in significantly reduced viability in IDH1^R132H glioblastoma cells. Given this dependence of IDH1^R132H cells on NAMPT expression, we explored the effects of the NAMPT inhibitors FK866, GMX1778 and GNE-617. Surprisingly, these agents were equally cytotoxic to IDH1^R132H and IDH1^wt cells. Altogether, our results indicate that targeting the NAD⁺ synthesis pathway is a promising therapeutic strategy in IDH mutant gliomas; however, the agent should be carefully considered since three small-molecule inhibitors of NAMPT tested in this study were not suitable for this purpose.     

Heat and Mass Flow Control in an Interconnected Multiphase CFD Model for Chemical Looping Combustion

Chemical looping combustion is a feasible option for carbon capture from fossil fuels. Within the process, the oxygen necessary for combustion is provided by a solid carrier material which alternately undergoes oxidation and reduction reactions. Features of the process are that the oxidation reaction of the particulate carrier in the air reactor is strongly exothermic and that the conversion of both oxidation and reduction reactions has to be in balance for stable operation. Simulations of the transient behavior of chemical looping combustion systems are possible through multiphase CFD. To allow for the modeling of chemical looping at steady state, cooling of the reactors and mass flow between fuel and air reactor must be adequately adjusted. Therefore, an interconnected multiphase CFD model was extended by an adjustment control. In this extended modeling framework variations of the operational load, control set points and carrier materials were performed. These simulations allow detailed insight into the dynamic behavior of chemical looping systems.     

Model for parallel surface and pore diffusion of an adsorbate in a spherical adsorbent particle

A model is presented to describe the rate of uptake of a species by a spherical adsorbent particle when intraparticle transport can occur by parallel diffusion through the pore space and along the surfaces of pore walls. Although the conventional shrinking core model (SCM) has been applied to such systems previously, its use is valid only when adsorption onto the pore walls is described by a rectangular isotherm. As with the SCM, the new model differs from homogeneous models by envisaging the advance of the adsorbate to be marked by a distinct inward-moving interface, but it generalizes the SCM to allow for an incompletely saturated adsorbed shell behind the front governed by any Langmuir isotherm. The model has been applied to previously published experimental data for the uptake of bovine serum albumin by chitosan beads and compared to the results obtained when the same data are analysed using the corresponding homogeneous model. The fit of the two models to the convension-time data yields comparable results, but significant differences in the predicted absorbate concentration profiles within adsorbent particles are observed, particularly at high conversions.     

鼓泡床内气液两相流动的二阶矩模型与代数应力模型的模拟比较

A full second-order moment(FSM) model and an algebraic stress (ASM) two-phase turbulence model are proposed and applied to predict turbulent bubble-liquid flows in a 2D rectangular bubble column.Predication gives the bubble and liquid velocities,bubble volume fraction,bubble and liquid Reynolds stresses and bubble-liquid velocity correlation.For predicted two-phase velocities and bubble volume fraction the is only silight difference between these two models,and the simulation results using both two models are in good agreement with the particle image velocimetry(PIV) measurements.Although the predicted two-phase Reynolds stresses using the FSM are in somewhat better agreement with the PIV measurements than those predicted using the ASM,the Reynolds stresses predicted using both two models are in general agreement with the experiments.Therefore,it is suggested to use the ASM two-phase turbulence model in engineering application for saving the computation time.     

Development and Validation of a Flowsheet Simulation Model for Neptunium Extraction in an Advanced PUREX Process

An Advanced PUREX process has been developed for separation and recycling of neptunium from spent nuclear fuel. This work presents a new flowsheet simulation model for the extraction of neptunium using centrifugal contactors, where mass transfer is modeled using two-film theory and a linear driving force. Distribution coefficients and neptunium redox reactions are modeled using published models. Mass transfer between the organic and aqueous phases in the phase separation zone is shown to have a negligible effect. The model is applied to a previously tested flowsheet and its predictions are shown to be in good agreement with the experimental results.     

The Zebrafish,an Outstanding Model for Biomedical Research in the Field of Melatonin and Human Diseases

The zebrafish has become an excellent model for the study of human diseases because it offers many advantages over other vertebrate animal models. The pineal gland, as well as the biological clock and circadian rhythms, are highly conserved in zebrafish, and melatonin is produced in the pineal gland and in most organs and tissues of the body. Zebrafish have several copies of the clock genes and of aanat and asmt genes, the latter involved in melatonin synthesis. As in mammals, melatonin can act through its membrane receptors, as with zebrafish, and through mechanisms that are independent of receptors. Pineal melatonin regulates peripheral clocks and the circadian rhythms of the body, such as the sleep/wake rhythm, among others. Extrapineal melatonin functions include antioxidant activity, inducing the endogenous antioxidants enzymes, scavenging activity, removing free radicals, anti-inflammatory activity through the regulation of the NF-κB/NLRP3 inflammasome pathway, and a homeostatic role in mitochondria. In this review, we introduce the utility of zebrafish to analyze the mechanisms of action of melatonin. The data here presented showed that the zebrafish is a useful model to study human diseases and that melatonin exerts beneficial effects on many pathophysiological processes involved in these diseases.