Oleksandr O. Sudakov

Chimera states in three dimensions

The chimera state is a recently discovered dynamical phenomenon in arrays of nonlocally coupled oscillators, that displays a self-organized spatial pattern of coexisting coherence and incoherence. In this paper, the first evidence of three-dimensional chimera states is reported for the Kuramoto model of phase oscillators in 3D grid topology with periodic boundary conditions. Systematic analysis of the dependence of the spatiotemporal dynamics on the range and strength of coupling shows that there are two principal classes of the chimera patterns which exist in large domains of the parameter space: (I) oscillating and (II) spirally rotating. Characteristic examples from the first class include coherent as well as incoherent balls, tubes, crosses, and layers in incoherent or coherent surrounding; the second class includes scroll waves with incoherent, randomized rolls of different modality and dynamics. Numerical simulations started from various initial conditions indicate that the states are stable over the integration time. Videos of the dynamics of the chimera states are presented in supplementary material. It is concluded that three-dimensional chimera states, which are novel spatiotemporal patterns involving the coexistence of coherent and incoherent domains, can represent one of the inherent features of nature.

CHPOX: Transparent Checkpointing System for Linux Clusters

Paper presents design, implementation, features and applications of kernel based process checkpointing system CHPOX (checkpointing for Linux). Comparison of CHPOX to other Linux checkpointing systems is given. Conclusions about CHPOX advantages, shortcomings and future work directions are made.

Ukrainian Grid Infrastructure: Practical Experience

In 2006 National Academy of Sciences of Ukraine approved the project for development of grid technologies in Ukraine. Since then an extensive work is carried out in order to build a full-scale grid infrastructure for scientific and educational institutions. This article deals with the aspects of building such infrastructure, its organization and peculiarities of implementation in Ukraine, shows the current status of project, describes scientific tasks which benefit from using grid.

Integrated grid environment for massive distributed computing in neuroscience

Automation methods for huge amount of computations in grid environment and their applications in Ukrainian National Grid (UNG) are described. Proposed methods are based on asynchronous job submission and control. Methods has solved the problems of job data staging in, description preparing, job submission, job status monitoring and staging out results. Methods are implemented for building integrated environment for investigations in neuroscience. Running thousands non-interacting jobs with different input data sets primarily suitable for grid computing. Using portal web-interface, you can handle those thousands of jobs in “one-click”. The first application results in neuroscience are obtained. Simulations covers Kuramoto phenomeno-logical phase oscillators model and Hodgkin-Huxley-Katz realistic neurons model. Proposed integrated environment can be extended to solve other scientific problems.

User clients for working with medical images in Ukrainian Grid infrastructure

Design and application of web service and desktop user client for working with medical DICOM-images in Ukrainian Grid infrastructure are described. Web-service provides transparent replication of data in grid storage elements. Client consists of graphical front-end, network back-end and provides functions of image anonymization-deanonymization, searching, visualizing, archiving etc. Clients are easily extensible so new data transfer protocols, image procession functions, grid job submission and results retrieving may be easily integrated. Proposed clients are developed, tested and deployed in several Ukrainian institutions for testing and pre-production operation.

Multiple scroll wave chimera states

Abstract We report the appearance of three-dimensional (3D) multiheaded chimera states that display cascades of self-organized spatiotemporal patterns of coexisting coherence and incoherence. We demonstrate that the number of incoherent chimera domains can grow additively under appropriate variations of the system parameters generating thereby head-adding cascades of the scroll wave chimeras. The phenomenon is derived for the Kuramoto model of N3 identical phase oscillators placed in the unit 3D cube with periodic boundary conditions, parameters being the coupling radius r and phase lag α. To obtain the multiheaded chimeras, we perform the so-called ‘cloning procedure’ as follows: choose a sample single-headed 3D chimera state, make appropriate scale transformation, and put some number of copies of them into the unit cube. After that, start numerical simulations with slightly perturbed initial conditions and continue them for a sufficiently long time to confirm or reject the state existence and stability. In this way it is found, that multiple scroll wave chimeras including those with incoherent rolls, Hopf links and trefoil knots admit this sort of multiheaded regeneration. On the other hand, multiple 3D chimeras without spiral rotations, like coherent and incoherent balls, tubes, crosses, and layers appear to be unstable and are destroyed rather fast even for arbitrarily small initial perturbations.

Distributed system for sampling and analysis of electroencephalograms

Distributed system for sampling and analysis of electroencephalograms is proposed and implemented in alpha state. The system is based on the previously developed database for archiving of the electroencephalograms in Ukrainian National Grid infrastructure. The new components of the system include EEG sensors for laboratory animals, simulations software and data procession algorithms. The first application of the system for data sampling, analysis and simulations of epileptic seizures is performed.

Rainbow framework: Running virtual machines on demand as a grid jobs

Rainbow is the system for running hardware accelerated virtual machines with an interactive access capability as grid jobs submitted to the Advanced Resource Connector (ARC) [1] powered infrastructure. Methods for running virtual machine as a grid jobs as well as Rainbow architecture has been proposed and implemented for practical use in the Ukrainian National Grid (UNG). Rainbow framework had been successfully applied in the MedGrid project for visualization and analysis of ECG stored on UNG resources by means of running proprietary software developed for OS Windows [2].

Artificial Neural Network for Multiclass Recognition and its Application to the Thyroid Functional State

Background. Development of automated diagnostic requires selection and improvement of appropriate machine learning methods, in particular multiclass recognition. Artificial Neural Networks (ANN) of various architecture are considered as an approach to the problem. Objective. The goal is to analyze and compare performance of ANN-based classifiers on various datasets for further improvement of model selection strategy. Methods. ANN-based models of the distribution of class labels in terms of predictor features are constructed, trained and validated for datasets of clinical records. Varying training algorithms for multi-layer perceptrons, Kohonen neural network, linear functional strategy with multi-parameters regularization are considered. Results. Performance of the classifiers is compared in terms of accuracy, sensitivity, and specificity. Linear functional strategy classifier outperforms the other with more complex ANN-architecture and exhibits relative steadiness to overfitting. Performance of Kohonen neural network on large dataset exceeds 90 % in terms of specificity for each class, withal sensitivity for distinct classes is more than 95 %. Conclusions. The understanding of the strengths and limitations of each method is crucial for careful choice of ANN-based classifier, particularly its architecture, regularization and training algorithm.