scholarly journals Brain MRI Segmentation with Multiphase Minimal Partitioning: A Comparative Study

2007 ◽  
Vol 2007 ◽  
pp. 1-15 ◽  
Author(s):  
Elsa D. Angelini ◽  
Ting Song ◽  
Brett D. Mensh ◽  
Andrew F. Laine
Keyword(s):  
Quantitative Evaluation ◽  
Level Set ◽  
Markov Random Fields ◽  
Initial Conditions ◽  
A Priori ◽  
Brain Mri ◽  
Three Dimensional ◽  
Error Rates ◽  
Adult Brain ◽  
Set Up

This paper presents the implementation and quantitative evaluation of a multiphase three-dimensional deformable model in a level set framework for automated segmentation of brain MRIs. The segmentation algorithm performs an optimal partitioning of three-dimensional data based on homogeneity measures that naturally evolves to the extraction of different tissue types in the brain. Random seed initialization was used to minimize the sensitivity of the method to initial conditions while avoiding the need fora prioriinformation. This random initialization ensures robustness of the method with respect to the initialization and the minimization set up. Postprocessing corrections with morphological operators were applied to refine the details of the global segmentation method. A clinical study was performed on a database of 10 adult brain MRI volumes to compare the level set segmentation to three other methods: “idealized” intensity thresholding, fuzzy connectedness, and an expectation maximization classification using hidden Markov random fields. Quantitative evaluation of segmentation accuracy was performed with comparison to manual segmentation computing true positive and false positive volume fractions. A statistical comparison of the segmentation methods was performed through a Wilcoxon analysis of these error rates and results showed very high quality and stability of the multiphase three-dimensional level set method.

scholarly journals Assessing biases, relaxing moralism: On ground-truthing practices in machine learning design and application

2021 ◽  
Vol 8 (1) ◽  
pp. 205395172110135
Author(s):  
Florian Jaton
Keyword(s):  
Machine Learning ◽  
William James ◽  
A Priori ◽  
Learning Algorithms ◽  
Three Dimensional ◽  
Ground Truth ◽  
Machine Learning Algorithms ◽  
Ground Truthing ◽  
Set Up ◽  
The Moment

This theoretical paper considers the morality of machine learning algorithms and systems in the light of the biases that ground their correctness. It begins by presenting biases not as a priori negative entities but as contingent external referents—often gathered in benchmarked repositories called ground-truth datasets—that define what needs to be learned and allow for performance measures. I then argue that ground-truth datasets and their concomitant practices—that fundamentally involve establishing biases to enable learning procedures—can be described by their respective morality, here defined as the more or less accounted experience of hesitation when faced with what pragmatist philosopher William James called “genuine options”—that is, choices to be made in the heat of the moment that engage different possible futures. I then stress three constitutive dimensions of this pragmatist morality, as far as ground-truthing practices are concerned: (I) the definition of the problem to be solved (problematization), (II) the identification of the data to be collected and set up (databasing), and (III) the qualification of the targets to be learned (labeling). I finally suggest that this three-dimensional conceptual space can be used to map machine learning algorithmic projects in terms of the morality of their respective and constitutive ground-truthing practices. Such techno-moral graphs may, in turn, serve as equipment for greater governance of machine learning algorithms and systems.

scholarly journals Direct numerical simulation of the autoignition of a hydrogen plume in a turbulent coflow of hot air

2013 ◽  
Vol 720 ◽  
pp. 424-456 ◽  
Author(s):  
S. G. Kerkemeier ◽  
C. N. Markides ◽  
C. E. Frouzakis ◽  
K. Boulouchos
Keyword(s):  
Complex Dynamics ◽  
Mixture Fraction ◽  
A Priori ◽  
Three Dimensional ◽  
Scalar Dissipation ◽  
Detailed Chemistry ◽  
History Of ◽  
Reactive Mixture ◽  
Set Up ◽  
Flame Sheet

AbstractThe autoignition of an axisymmetric nitrogen-diluted hydrogen plume in a turbulent coflowing stream of high-temperature air was investigated in a laboratory-scale set-up using three-dimensional numerical simulations with detailed chemistry and transport. The plume was formed by releasing the fuel from an injector with bulk velocity equal to that of the surrounding air coflow. In the ‘random spots’ regime, autoignition appeared randomly in space and time in the form of scattered localized spots from which post-ignition flamelets propagated outwards in the presence of strong advection. Autoignition spots were found to occur at a favourable mixture fraction close to the most reactive mixture fraction calculated a priori from considerations of homogeneous mixtures based on inert mixing of the fuel and oxidizer streams. The value of the favourable mixture fraction evolved in the domain subject to the effect of the scalar dissipation rate. The hydroperoxyl radical appeared as a precursor to the build-up of the radical pool and the ensuing thermal runaway at the autoignition spots. Subsequently, flamelets propagated in all directions with complex dynamics, without anchoring or forming a continuous flame sheet. These observations, as well as the frequency of and scatter in appearance of the spots, are in good agreement with experiments in a similar set-up. In agreement with experimental observations, an increase in turbulence intensity resulted in a downstream shift of autoignition. An attempt is made to understand the key processes that control the mean axial and radial locations of the spots, and are responsible for the observed scatter. The advection of the most reactive mixture through the domain, and hence the history of evolution of the developing radical pools were considered to this effect.

scholarly journals Learning High-Order Geometric Flow Based on The Level Set Method

2021 ◽  
Author(s):  
Chun Li ◽  
Yunyun Yang ◽  
Hui Liang ◽  
Boying Wu
Keyword(s):  
Neural Networks ◽  
Level Set Method ◽  
Level Set ◽  
Input Data ◽  
Initial Conditions ◽  
High Order ◽  
Geometric Flow ◽  
Set Up ◽  
Almost All ◽  
Physical Phenomena

Abstract Recently, the development of deep learning (DL), which has accomplished unbelievable success in many fields, especially in scientific computational fields. And almost all computational problems and physical phenomena can be described by partial differential equations (PDEs). In this work, we proposed two potential high-order geometric flows. Motivation by the physical-information neural networks (PINNs) and the traditional level set method (LSM), we have integrated deep neural networks (DNNs) and LSM to make the proposed method more robust and efficient. Also, to test the sensitivity of the system to different input data, we set up three sets of initial conditions to test the model. Furthermore, numerical experiments on different input data are implemented to demonstrate the effectiveness and superiority of the proposed models compared to the state-of-the-art approach.

scholarly journals QUASI-INVARIANTS OF CHEMICAL REACTIONS IN DISTRIBUTED SYSTEMS WITH DIFFUSION

2020 ◽  
Vol 64 (1) ◽  
pp. 41-46
Author(s):  
Nikolay I. Kol'tsov
Keyword(s):  
Distributed Systems ◽  
Chemical Reactions ◽  
Initial Conditions ◽  
A Priori ◽  
Three Dimensional ◽  
Radial Diffusion ◽  
Time And Space ◽  
Temperature Changes ◽  
Isothermal System ◽  
Temporal And Spatial Characteristics

For reactions occurring in distributed systems with longitudinal and radial diffusion, the relations between the concentrations of reagents and temperature remaining practically constant in time and space (space-time kinetic quasi-invariants) are found. A method for determining such quasi-invariants for chemical reactions occurring in the mixing reactor taking into account the diffusion of reagents and temperature changes in the longitudinal and radial directions has been developed and tested. The quasi-invariants found relate nonequilibrium concentrations of diffusing reagents and temperatures measured in two or more experiments with different initial conditions (multi-experiments), and practically do not change throughout the reaction both in length and in radius of the reactor. Analytical expressions for quasi-invariants are obtained, allowing a priori to estimate the corresponding constants (initial values). It is shown that the number of basic quasi-invariants is determined by the number of reagents. The application of the method is illustrated by the reaction of isomerization A=B in a non-isothermal system with diffusion of reagents. Found for this reaction quasiinvariant based on three-dimensional (surface) matched with three-dimensional variations of concentrations and temperature given the diffusivity in the course of the reaction. It is shown that quasi-invariants change in a smaller spatial range than their corresponding concentrations and temperatures in different experiments, i.e. remain practically constant in time and space. Visually, quasi-invariants are four-dimensional structures, three-dimensional projections of which are similar to "recumbent" waves, pillows, lenses, etc. Elaborated method for determining quasi-invariants of chemical reactions in systems with diffusion develops D.A. Frank-Kamenetsky's macrokinetic methods for approximate study of temporal and spatial characteristics of distributed dynamic systems. The obtained results can be used to solve inverse problems and optimize the operation modes of chemical mixing reactors with longitudinal and radial diffusion of reagents and temperature changes.

An experimental study of recirculating flow through fluid–sediment interfaces

1999 ◽  
Vol 383 ◽  
pp. 229-247 ◽  
Author(s):  
A. KHALILI ◽  
A. J. BASU ◽  
U. PIETRZYK ◽  
M. RAFFEL
Keyword(s):  
Fluid Layer ◽  
Saturated Porous Medium ◽  
A Priori ◽  
Three Dimensional ◽  
Solid Matrix ◽  
Permeable Sediments ◽  
Recirculating Flow ◽  
Positron Emission ◽  
Dye Transport ◽  
Set Up

We report here visualizations and quantitative measurements of scalar transport, under the influence of rotation, through permeable sediments with an overlying fluid layer. The experimental set-up considered here is a stationary cylinder containing a fluid-saturated porous medium up to its midheight, with supernatant water on top. A rotating lid generates, in the upper fluid region, a flow that partially percolates into the porous layer below. The velocity field in the fluid layer is obtained using particle image velocimetry (PIV). Further, dye transport from the sediment is studied using two different techniques. The first one is positron emission tomography (PET), a non-invasive method which allowed us to ‘see’ through the opaque solid matrix, and to obtain full three-dimensional pictures of dye transport through the sediment. The second one is digital photographic visualization from outside, and subsequent image processing in order to obtain the near-wall dye-washout depth. The experimental data suggest that the temporal evolution of washout depth for different sediments follows near-logarithmic behaviour. This finding is of importance for the a priori estimation of the transport of fluid and other solute substances in sandy aquatic sediments.

scholarly journals On Kaufmann's theory of the impact of the pianoforte hammer

1920 ◽  
Vol 97 (682) ◽  
pp. 99-110 ◽  
Keyword(s):  
Initial Conditions ◽  
Practical Importance ◽  
Prima Facie ◽  
Point Of View ◽  
Infinite Length ◽  
Modes Of Vibration ◽  
Rigorous Treatment ◽  
The Subject ◽  
Set Up ◽  
The Impact

The theory of the vibrations of the pianoforte string put forward by Kaufmann in a well-known paper has figured prominently in recent discussions on the acoustics of this instrument. It proceeds on lines radically different from those adopted by Helmholtz in his classical treatment of the subject. While recognising that the elasticity of the pianoforte hammer is not a negligible factor, Kaufmann set out to simplify the mathematical analysis by ignoring its effect altogether, and treating the hammer as a particle possessing only inertia without spring. The motion of the string following the impact of the hammer is found from the initial conditions and from the functional solutions of the equation of wave-propagation on the string. On this basis he gave a rigorous treatment of two cases: (1) a particle impinging on a stretched string of infinite length, and (2) a particle impinging on the centre of a finite string, neither of which cases is of much interest from an acoustical point of view. The case of practical importance treated by him is that in which a particle impinges on the string near one end. For this case, he gave only an approximate theory from which the duration of contact, the motion of the point struck, and the form of the vibration-curves for various points of the string could be found. There can be no doubt of the importance of Kaufmann’s work, and it naturally becomes necessary to extend and revise his theory in various directions. In several respects, the theory awaits fuller development, especially as regards the harmonic analysis of the modes of vibration set up by impact, and the detailed discussion of the influence of the elasticity of the hammer and of varying velocities of impact. Apart from these points, the question arises whether the approximate method used by Kaufmann is sufficiently accurate for practical purposes, and whether it may be regarded as applicable when, as in the pianoforte, the point struck is distant one-eighth or one-ninth of the length of the string from one end. Kaufmann’s treatment is practically based on the assumption that the part of the string between the end and the point struck remains straight as long as the hammer and string remain in contact. Primâ facie , it is clear that this assumption would introduce error when the part of the string under reference is an appreciable fraction of the whole. For the effect of the impact would obviously be to excite the vibrations of this portion of the string, which continue so long as the hammer is in contact, and would also influence the mode of vibration of the string as a whole when the hammer loses contact. A mathematical theory which is not subject to this error, and which is applicable for any position of the striking point, thus seems called for.

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