Olusegun J. Ilegbusi

Gas–Liquid Two-Phase Flow

Bubble and liquid flow characteristics of bubble-driven gas–liquid two-phase flows observed in various types of reactors in materials processing operations are introduced with many exercises. Heat and mass transfer from a solid body immersed in a molten metal bath is also discussed.

Biocompatibility and Conductometric Property of Sol-Gel Derived ZnO/PVP Nanocomposite Biosensor Film

Nanocrystalline ZnO and ZnO/PVP nanocomposite films have been prepared by the sol-gel dip-coating technique from zinc acetate precursor on silicon wafer and Pyrex glass substrates. The films were characterized using atomic force microscopy for morphology, and X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy for chemical analysis. Thermally untreated and annealed films were studied in order to analyze the influence of temperature on the formation and properties of the films. The films have a uniform void-free surface and the grain size increases with the annealing temperature. The cell viability assays indicate that the growth rate of BPH cells incubated in the presence of ZnO was significantly reduced (35% of the control) compared to that of untreated controls, indicating antibacterial activity of ZnO as a result of the generation of hydrogen peroxide. The sensor characteristic of ZnO/PVP nanocomposite was also demonstrated by measuring the change in conductivity upon exposure to superoxide anion radical.

Modeling Reaction Front Propagation and Porosity in Pressure-Assisted Combustion Synthesis of Porous NiTi Intermetallics

A mathematical model is developed to investigate the effect of various processing parameters on pressure-assisted combustion synthesis of NiTi intermetallics. Specifically, preheat and ambient temperature, particle size, initial porosity, and pressure differential are studied to determine their influence on propagation behavior and final porosity. The governing equations are solved using a high-order-implicit numerical scheme capable of accommodating the steep spatial and temporal gradients of properties. The predicted results appear plausible and consistent with the trends presented in the available literature.

A 5mm catheter for constant resolution probing in Fourier domain optical coherence endoscopy

A 5mm biophotonic catheter was conceived for optical coherence tomography (OCT) with collimation optics, an axicon lens, and custom design imaging optics, yielding a 360 degree scan aimed at imaging within concave structures such as lung lobes. In OCT a large depth of focus is necessary to image a thick sample with a constant high transverse resolution. There are two approaches to achieving constant lateral resolution in OCT: Dynamic focusing or Bessel beam forming. This paper focuses on imaging with Bessel beams. A Bessel beam can be generated in the sample arm of the OCT interferometer when axicon optics is employed instead of a conventional focusing lens. We present a design for a 5mm catheter that combines an axicon lens with imaging optics and the coupling of a MEMS mirror attached to a micromotor that allow 360 degree scanning with a resolution of about 5 microns across a depth of focus of about 1.2mm.

Patient-specific model of lung deformation using spatially dependent constitutive parameters

Breathing-induced spatially dependent lung deformation is predicted using patient-specific elastic properties with the contact–impact analysis model. The lung geometry is derived from 4D CT scan data of real patients. The spatially varying Young’s modulus for the patient is obtained from a previous study that used inverse deformation of the lung. The compact–impact analysis is implemented using the finite element method. The predicted lung deformation is compared with the results based on linear elasticity. The results are consistent with physiology, indicating large deformations near the diaphragm and smaller values at remote locations on the lobe. The effect of non-linearity of elastic property is most significant at the remote locations where the diaphragm-induced deformation is significantly attenuated.

Modeling airflow using subject-specific 4DCT-based deformable volumetric lung models

Lung radiotherapy is greatly benefitted when the tumor motion caused by breathing can be modeled. The aim of this paper is to present the importance of using anisotropic and subject-specific tissue elasticity for simulating the airflow inside the lungs. A computational-fluid-dynamics (CFD) based approach is presented to simulate airflow inside a subject-specific deformable lung for modeling lung tumor motion and the motion of the surrounding tissues during radiotherapy. A flow-structure interaction technique is employed that simultaneously models airflow and lung deformation. The lung is modeled as a poroelastic medium with subject-specific anisotropic poroelastic properties on a geometry, which was reconstructed from four-dimensional computed tomography (4DCT) scan datasets of humans with lung cancer. The results include the 3D anisotropic lung deformation for known airflow pattern inside the lungs. The effects of anisotropy are also presented on both the spatiotemporal volumetric lung displacement and the regional lung hysteresis.

Modeling of Aerosol Spray Characteristics for Synthesis of Mixed-Oxide Nanocomposite Sensor Film

A model is developed of aerosol synthesis of mixed metal oxide nanocomposite film for sensor applications. The synthesis technique involves atomization of a solution of mixed salts in water, spraying of solution droplets, droplet deposition on a heated substrate, evaporation and chemical reaction to produce the mixed oxides, and film growth. The precise control of oxide nanoparticle size distribution and inter-particle spacing in the film is crucial to achieving high sensitivity. These in turn largely depend on the droplet characteristics prior to impingement on the substrate. This paper focuses on development of a model to describe the atomization and spray processes before the film growth. Specifically, a mathematical model is developed utilizing Computational Fluid Dynamics solution of the equations governing the transport of atomized droplets from the nozzle to predict droplet characteristics in flight. The predictions include spatial distribution of droplet size and concentration, and the effect on these characteristics of swirling inlet flow at the spray nozzle.Copyright

Droplet Evaporation and Chemical Reaction in a Single Multi-Component Droplet to Synthesis Mixed-Oxide Film Using Spray Pyrolysis Method

This paper describes mathematical modeling of transport and chemical reaction phenomena in a single droplet on a heated substrate deposited by spray pyrolysis. The droplet contains mixed salt solution which reacts on the heated substrate to produce mixed oxides and water residue. The water is subsequently evaporated, leaving a thin film of the mixed oxides for sensor application. The droplet, containing solvent and precursors is modeled using Computational Fluid Dynamics (CFD) technique. The variety of stages is predicted of the evolution of droplet morphology associated with surface energy and evaporation. The transient distribution is also predicted of the concentration of various species in the droplet.Copyright

A fluid-structure interaction index of coronary plaque rupture

The impact of coupled blood flow and structural dynamics on coronary plaque is investigated with the objective of defining a unique index for characterizing plaque rupture. Two-dimensional non-circular lumen models of native, moderate and severely stenosed human coronary arteries are investigated. The flow and structural analyses are performed simultaneously using well-validated commercial software. New flow–structure interaction (FSI) indices are defined by normalizing the predicted hemodynamic shear stress with the structural stresses. The results predict that the plaques investigated are potentially vulnerable to rupture at 40-45% stenosis levels. The predicted trend is consistent with clinical observations, indicating that the selected FSI index has the potential to characterize plaque rupture when properly established.

2mm catheter design for endoscopic optical coherence tomography

A biophotonics catheter was conceived with collimation optics, an axicon lens, and custom design imaging optics yielding a 360 degree scan aimed at imaging within concave structures such as arteries and lung lobes. The large depth of focus is necessary to image a long-depth-range sample with constant transverse resolution in optical coherence tomography (OCT). There are two approaches to achieving constant invariant resolution in OCT: Dynamic focusing or Bessel beam formation. This paper focuses on imaging with Bessel beams. The Bessel beams may be created with axicon optics which can be used instead of a conventional focusing lens in the sample arm of the OCT interferometer. In this paper we present the design of a 2mm catheter for optical coherence endoscopy with resolution of about 5 micron across a depth of focus of about 1.6mm. Importantly, we investigated the fabrication of a 800μm diameter axicon lens and the associated lateral resolution obtained over a long depth range in our OCT system, compared to the same OCT system using a conventional lens.