MR Spectroscopy Shows Long Propylene Glycol Half-Life in Neonatal Brain

<b><i>Introduction:</i></b> Neonatal propylene glycol (PG) clearance is low with long plasma half-life. We hypothesized that neonatal brain PG clearance is diminished and may be related to perinatal asphyxia, infection, or stroke, via different blood-brain barrier permeability. This study aimed to estimate cerebral PG half-life with a clearance model including PG measured with MR spectroscopy (MRS) in neonates that received phenobarbital as the only PG source and to evaluate whether PG clearance was related to intracerebral pathology, for example, perinatal asphyxia, infection, or stroke. <b><i>Methods:</i></b> In this retrospective cohort study, 45 neonates receiving any dose of phenobarbital underwent MRS (short echo time single-voxel MRS at 1.5 T). Cumulative phenobarbital/PG doses were calculated. MRS indications were perinatal asphyxia (<i>n</i> = 22), infection (<i>n</i> = 4), stroke (<i>n</i> = 10), metabolic disease (<i>n</i> = 4), and others (<i>n</i> = 5). <b><i>Results:</i></b> Medians (interquartile range) included gestational age 39.4 (3.1) weeks, birth weight 3,146 (1,340) g, and cumulative PG dose 700 (1,120) mg/kg. First-order kinetics with mono-exponential decay showed cerebral PG half-life of 40.7 h and volume of distribution of 1.6 L/kg. Zero-order kinetics showed a rate constant of 0.048 mM/h and a volume of distribution of 2.3 L/kg, but the fit had larger residuals than the first-order model. There were no differences in ΔPG (i.e., PG estimated with clearance model minus PG observed with MRS) in infants with perinatal asphyxia, infection, or stroke. <b><i>Discussion/Conclusion:</i></b> This study showed a long cerebral PG half-life of 40.7 h in neonates, unrelated to perinatal asphyxia, infection, or stroke. These findings should increase awareness of possible toxic PG concentrations in neonatal brain due to intravenous PG-containing drugs.

Study of tip clearance model effects on computational simulation costs for NASA rotor 37.

The computational time and resources required to calculate an accurate solution is the key concern in the field of CFD. Especially in the CFD analysis of turbomachines many simulations are required to validate the CFD code and to predict the performance of the turbomachines. In this thesis, the typical computational domain was remodelled and the best computational settings were identified to compute the flows. By modifying the numerical domain, improved grid distribution with less number of nodes was achieved and the results predicted were within the limits specified by NASA for the validation of CFD codes. The modified model with the best computational settings required 28.3% less computational time and 20.5% less computer memory than the typical model and baseline methods.

Study of tip clearance model effects on computational simulation costs for NASA rotor 37.

The computational time and resources required to calculate an accurate solution is the key concern in the field of CFD. Especially in the CFD analysis of turbomachines many simulations are required to validate the CFD code and to predict the performance of the turbomachines. In this thesis, the typical computational domain was remodelled and the best computational settings were identified to compute the flows. By modifying the numerical domain, improved grid distribution with less number of nodes was achieved and the results predicted were within the limits specified by NASA for the validation of CFD codes. The modified model with the best computational settings required 28.3% less computational time and 20.5% less computer memory than the typical model and baseline methods.

A CFD-Based Prediction Method for Tip Clearance Losses and Deviations in Axial Turbines

Accurate loss models are crucial for reliable turbine performance predictions using low-fidelity tools. However, the complex flow structure of the blade tip gap flow impedes an experimental deduction of a realistic tip clearance loss model. In this work, validated, high-fidelity CFD simulations are used to substitute the cost- and time-consuming experiments of a parameter study and to develop a modern, flexible and universal tip clearance model. The CFD model is based on a single stage high-pressure turbine. Inflow conditions and geometry of the rotor were specifically varied to separately study the effects of the significant parameters on the tip clearance loss and deviation. Partial correlations were formulated for each effect and combined to a new tip clearance model. Apart from commonly considered parameters such as gap height, blade loading and solidity, other parameters that are well known to have an effect but are still disregarded in most conventional loss correlations are also investigated, such as incidence, Reynolds number, rotor speed and boundary layer thickness. Furthermore, a downstream progression model is presented that reflects the local conditions of the incompletely mixed out wake flow. Interrelations between the effects are modeled by a Kriging surrogate model, which was refined by the space filling technique. The new model was validated by additional CFD simulations at unprobed operation conditions. In addition, the new model was implemented into a through flow method. Performance calculations were performed for a four-stage air turbine and compared with experimental data. In comparison with the conventional tip clearance correlations, the new model improves the performance predictions at all operation points.

Simulation of the effect of mucociliary clearance on the bronchial distribution of inhaled radon progenies and related cellular damage using a new deposition and clearance model for the lung

Most of the current dosimetry models of inhaled short-lived radon decay products assume uniform activity distributions along the bronchial airways. In reality, however, both deposition and clearance patterns of inhaled radon progenies are highly inhomogeneous. Consequently, a new deposition-clearance model has been developed that accounts for such inhomogeneities and applied together with biophysical models of cell death and cell transformation. The scope of this study was to apply this model which is based on computational fluid and particle dynamics methods, in an effort to reveal the effect of mucociliary clearance on the bronchial distribution of deposited radon progenies. Furthermore, the influence of mucociliary clearance on the spatial distribution of biological damage due to alpha-decay of the deposited radon progenies was also studied. The results obtained demonstrate that both deposition and clearance of inhaled radon progenies are highly non-uniform within a human airway bifurcation unit. Due to the topology of the carinal ridge, a slow clearance zone emerged in this region, which is the location where most of the radio-aerosols deposit. In spite of the slow mucus movement in this zone, the initial degree of inhomogeneity of the activity due to the nonuniform deposition decreased by a factor of about 3 by considering the effect of mucociliary clearance. In the peak of the airway bifurcation, the computed cell death and cell transformation probabilities were lower when considering deposition and clearance simultaneously, compared to the case when only deposition was considered. However, cellular damage remained clustered.