An Enhanced Approach for Segmentation of Liver from Computed Tomography Images

287-293An accurate segmentation of liver from Computed Tomography (CT) scans is essential for liver tumor research as it offers valuable information for clinical diagnosis and treatment. However, it is challenging to achieve an accurate segmentation of the liver because of the blurred edges, low contrast and similar intensity of the organs in the CT scan. In this paper, an automated model which will segment the liver from CT images using a hybrid algorithm has been used. The segmentation of liver from CT scan is done with the help of Particle Swarm Optimization (PSO) followed by level set algorithm. The ultimate aim of using this hybrid algorithm is to improve the accuracy of liver segmentation. Computer aided classification of liver CT into healthy and tumorous images aids in diagnosis of liver diseases. It can help a great deal in diagnosis of liver disorders. In order to achieve better classification results, it is of high importance to segment the liver accurately without an error of over or under segmentation. The results obtained indicate that the approach used in this work is faster and has 98.62% accuracy, 99.2% specificity, 97.1% sensitivity, 97.8% F-measure, 96.6% Matthews Coefficient Constant (MCC), 99.08% precision, 97.8% dice coefficient and 95.7% jaccard coefficient in segmenting the liver

Numerical and analytical investigations of non-isothermal fluids

Theoretical and numerical techniques are used to investigate three different problems involving non-isothermal fluid flow. The first part of the dissertation investigates flame dynamics in a strained mixing layer established between two-dimensional counterflowing streams of fuel and oxidizer. When a one-step Arrhenius chemistry model is employed for the chemistry description, the numerical computations for small values of the stoichiometric mixture fraction yield a C-shaped premixed front with a trailing diffusion flame attached to one of its ends, a structure that is markedly different to the tri-brachial structure found in previous studies. Analytic predictions from the G equation are found to agree well with the numerical results. An explanation for these unexpected shapes is obtained by analyzing the variation with dilution of the burning velocity of planar premixed flames. Detailed-chemistry results are presented next for H$_2$-O$_2$-N$_2$ systems with high degrees of N$_2$ dilution, such that the resulting flame temperature lies close to the crossover value. Under these near-critical conditions, the flame dynamics is found to be strongly dependent on the initial conditions. A bifurcation diagram is presented in the stoichiometric mixture-fraction vs. strain-rate plane that identifies six different combustion regimes involving four different flame types, namely, one-dimensional diffusion flames, propagating/retreating edge flames, broken flame tubes, and isolated flame tubes. A spherically symmetric heterogeneous fuel-oxidizer system is investigated next as an ignition model for hypergolic gelled propellants. Depending on the conditions, the fuel-oxidizer system may approach an explosive mode or it may settle into a steady-state mode. The critical condition defining the transition between these two states is determined analytically and the ignition time for the explosive mode is approximated by solving an integral equation for the interface temperature, employing activation-energy asymptotics. A non-Boussinesq stability analysis of natural-convection boundary-layer flows over hot inclined surfaces is presented in the last part of the dissertation. Depending on the inclination angle, the disturbances are seen to evolve into either streamwise vortices or spanwise traveling waves. The critical inclination angle at which transition between the two instability modes occurs is calculated as a function of wall-to-ambient temperature ratio. For sufficiently large values of this ratio, wave modes are found to be always predominant, regardless of the inclination angle

Tricritical point as a crossover between type-Is and type-IIs bifurcations

A tricritical point as a crossover between (stationary finite-wavelength) type-Is and (stationary longwave) type-IIs bifurcations is identified in the study of diffusive-thermal (Turing) instability of flames propagating in a Hele-Shaw channel in a direction transverse to a shear flow. Three regimes exhibiting different scaling laws are identified in the neighbourhood of the tricritical point. For these three regimes, sixth-order partial differential equations are obtained governing the weakly nonlinear evolution of unstable solutions near the onset of instability. These sixth-order PDES may be regarded as the substitute for the classical fourth-order Kuramoto­­­­­­–­­Sivashinsky equation which is not applicable near the tricritical point

Premixed flame stability under shear-enhanced diffusion: Effect of the flow direction

In the presence of shear-enhanced diffusion (Taylor dispersion), flame propagation is effectively anisotropic. This study focuses on the influence of the direction of a shear flow relative to the direction of propagation on the diffusional-thermal instabilities of premixed flames. The problem is addressed analytically using large activation energy asymptotics, complemented by numerical simulations, in the framework of a constant density two-dimensional model. The model, obtained by depth averaging of the governing equations in a Hele-Shaw configuration, accounts for shear-enhanced diffusion. A linear stability analysis is carried out analytically, leading to a dispersion relation involving three parameters: the Lewis number Le; the Taylor-dispersion coefficient p, which is proportional to the Péclet number; and the angle φ between the direction of propagation of the unperturbed planar flame and the flow direction. Based on the dispersion relation, stability diagrams are determined in terms of the parameters, along with bifurcations curves identifying the nature of the instabilities observed. It is shown that cellular instabilities expected when Le < 1 can now occur as a result of Taylor dispersion in Le > 1 mixtures, provided the angle φ exceeds a critical value approximately equal to 75◦. In general, it is found that an increase in φ from 0◦ to 90◦ has a stabilizing effect in subunity Lewis number mixtures Le < 1 and a destabilizing effect when Le > 1. Particular attention is devoted to the cellular long-wave instability encountered, which is found to be described by a modified Kuramoto-Sivashinsky equation. The equation involves the three aforementioned parameters and includes a dispersion term (a third-order spatial derivative) as well a drift term (first-order derivative) whenever φ = 0◦ and φ = 90◦, which is whenever the direction of the shear flow is neither parallel nor perpendicular to the direction of flame propagation