Quantifying blood flow and wall shear stresses in the outflow tract of chick embryonic hearts

Wall shear stresses (WSS) exerted by blood flow on cardiac tissues modulate growth and development of the heart. To study the role of hemodynamic conditions on cardiac morphogenesis, here, we present a methodology that combines imaging and finite element modeling to quantify the in vivo blood flow dynamics and WSS in the cardiac outflow tract (OFT) of early chicken embryos (day 3 out of 21-day incubation period). We found a distinct blood flow field and heterogeneous distribution of WSS in the chicken embryonic heart OFT, which have physiological implications for OFT morphogenesis.     

Coarse particulate matter and airborne endotoxin within wood stove homes

Emissions from indoor biomass burning are a major public health concern in developing areas of the world. Less is known about indoor air quality, particularly airborne endotoxin, in homes burning biomass fuel in residential wood stoves in higher income countries. A filter‐based sampler was used to evaluate wintertime indoor coarse particulate matter (PM_10‐2.5) and airborne endotoxin (EU/m³, EU/mg) concentrations in 50 homes using wood stoves as their primary source of heat in western Montana. We investigated number of residents, number of pets, dampness (humidity), and frequency of wood stove usage as potential predictors of indoor airborne endotoxin concentrations. Two 48‐h sampling events per home revealed a mean winter PM_10‐2.5 concentration (± s.d.) of 12.9 (± 8.6) μg/m³, while PM_2.5 concentrations averaged 32.3 (± 32.6) μg/m³. Endotoxin concentrations measured from PM_10‐2.5 filter samples were 9.2 (± 12.4) EU/m³ and 1010 (± 1524) EU/mg. PM_10‐2.5 and PM_2.5 were significantly correlated in wood stove homes (r = 0.36, P < 0.05). The presence of pets in the homes was associated with PM_10‐2.5 but not with endotoxin concentrations. Importantly, none of the other measured home characteristics was a strong predictor of airborne endotoxin, including frequency of residential wood stove usage.     

Penetration of Particles into Buildings and Associated Physical Factors. Part I: Model Development and Computer Simulations

The PM_2.5 standard proposed by the U.S. Environmental Protection Agency (EPA) has stimulated research on the relationships between particulate matter concentrations and the exposures and subsequent health responses of sensitive subpopulations, such as the elderly. Since individuals in these subpopulations may spend more than 90% of their time indoors, understanding the relationship between outdoor particle concentrations and those found in indoor microenvironments is critical. This research resulted in a time-dependent indoor air quality model incorporating all potential particle sources and loss mechanisms. Monte Carlo simulations of the model identified the mechanisms, such as particle loss during penetration through the building envelope, that modify the outdoor particle size distribution during transport into the interior of a building, calculated indoor-to-outdoor (I/O) concentration ratios, and estimated penetration factors as a function of particle size. Indoor particle generation and transport of outdoor particles through the HVAC system were the most important contributors to the indoor concentration in residential and commercial buildings, respectively. The most significant removal mechanisms included ventilation through and particle removal by the HVAC filter if an HVAC system was present, or particle deposition on indoor surfaces if an HVAC system was not present. The modeled I/O concentration ratios varied between 0.05 and 0.5, depending on particle size and type of ventilation system, and agreed well with published experimental results. Penetration factors less than unity were calculated for particles with aerodynamic diameters larger than 0.2 θ m if the air exchange rate and steady-state I/O concentration ratio were correlated during the simulations. An additional correlation between the air exchange rate and particle deposition velocity is required if penetration factors less than unity are to be modeled for particles with aerodynamic diameters smaller than 0.2 θ m. These results     

Resuspension of Particulate Matter from Carpet Due to Human Activity

This work investigated the resuspension and subsequent translocation of particulate matter (PM) from carpeted flooring surfaces due to walking. In addition, the effect of HVAC systems and ceiling fans on mixing and/or translocation of resuspended PM was studied. Testing took place both in a residence with a well-worn, soiled carpet and in an environmental test chamber. Prescribed walking occurred with PM measurements taken at multiple sampling heights. Scanning electron microscopy (SEM) of carpet fibers was used to determine the fraction of dust available for resuspension. These data, in conjunction with resuspended mass concentrations from this study, were used to generate emission factors by particle size for walking on both new and worn carpet.

Carpet loading does not affect the emission factor, indicating that the amount of resuspended PM is directly proportional to the available PM in the carpet. While relative humidity (RH) plays an important role in resuspension from new carpets, with high RH enhancing resuspension, it has the opposite affect with old carpets, with increased RH decreasing resuspension. With the HVAC system on, translocated particles 1.2 m horizontally from the source had number concentrations of approximately 20–40% of those at the source. With a ceiling fan on, extensive mixing was noted with little difference seen in particle resuspension by height. With the ceiling fan off, there was very little mixing present and particle size varied substantially by height.     

Automatic unstructured grid generation based on iterative point insertion

Unstructured grid generation is concerned with discretizing surfaces and volumes in 3D space by triangles and tetrahedra. The tetrahedra discretize a volume in a surface's interior or surrounding a surface on its outside. This paper presents a new technique for unstructured grid generation based on intersecting lines with a given geometry and inserting grid points yielding an adapted grid whose point density decreases with increasing distance to the geometry. The technique is completely automatic.