Role of Fiber Orientation in Atrial Arrythmogenesis

Electrical wave-front propagation in the atria is determined largely by local fiber orientation. Recent study suggests that atrial fibrillation (AF) progresses with enhanced anisotropy. In this work, a 3D rabbit atrial anatomical model at 20 × 20 × 20 μm3 resolution with realistic fiber orientation was constructed based on the novel contrast-enhanced micro-CT imaging. The Fenton-Karma cellular activation model was adapted to reproduce rabbit atrial action potential period of 80 ms. Diffusivities were estimated for longitudinal and transverse directions of the fiber orientation respectively. Pacing was conducted in the 3D anisotropic atrial model with a reducing S2 interval to facilitate initiation of atrial arrhythmia. Multiple simulations were conducted with varying values of diffusion anisotropy and stimulus locations to evaluate the role of anisotropy in initiating AF. Under physiological anisotropy conditions, a rapid right atrial activation was followed by the left atrial activation. Excitation waves reached the atrio-ventricular border where they terminated. Upon reduction of conduction heterogeneity, re-entry was initiated by the rapid pacing and the activation of both atrial chambers was almost simultaneous. Myofiber orientation is an effective mechanism for regulating atrial activation. Modification of myoarchitecture is proarrhythmic

Studying Ion Channel Dysfunction and Arrythmogenesis in the Human Atrium: A Computational Approach

Non

HCN and SCN5A Channel Mutations: Implications for Impaired Atrioventricular Nodal Conduction in a Heterogeneous Computer Model of the Whole Mouse Heart

Abstract The atrioventricular (AV

BeatBox - HPC simulation environment for biophysically and anatomically realistic cardiac electrophysiology

The BeatBox simulation environment combines flexible script language user interface with the robust computational tools, in order to setup cardiac electrophysiology in-silico experiments without re-coding at low-level, so that cell excitation, tissue/anatomy models, stimulation protocols may be included into a BeatBox script, and simulation run either sequentially or in parallel (MPI) without re-compilation. BeatBox is a free software written in C language to be run on a Unix-based platform. It provides the whole spectrum of multi scale tissue modelling from 0-dimensional individual cell simulation, 1-dimensional fibre, 2-dimensional sheet and 3-dimensional slab of tissue, up to anatomically realistic whole heart simulations, with run time measurements including cardiac re-entry tip/filament tracing, ECG, local/global samples of any variables, etc. BeatBox solvers, cell, and tissue/anatomy models repositories are extended via robust and flexible interfaces, thus providing an open framework for new developments in the field. In this paper we give an overview of the BeatBox current state, together with a description of the main computational methods and MPI parallelisation approaches.Comment: 37 pages, 10 figures, last version submitted to PLOS ON

Towards understanding the myometrial physiome: approaches for the construction of a virtual physiological uterus

Premature labour (PTL) is the single most significant factor contributing to neonatal morbidity in Europe with enormous attendant healthcare and social costs. Consequently, it remains a major challenge to alleviate the cause and impact of this condition. Our ability to improve the diagnosis and treatment of women most at risk of PTL is, however, actually hampered by an incomplete understanding of the ways in which the functions of the uterine myocyte are integrated to effect an appropriate biological response at the multicellular whole organ system. The level of organization required to co-ordinate labouring uterine contractile effort in time and space can be considered immense. There is a multitude of what might be considered mini-systems involved, each with their own regulatory feedback cycles, yet they each, in turn, will influence the behaviour of a related system. These include, but are not exclusive to, gestational-dependent regulation of transcription, translation, post-translational modifications, intracellular signaling dynamics, cell morphology, intercellular communication and tissue level morphology. We propose that in order to comprehend how these mini-systems integrate to facilitate uterine contraction during labour (preterm or term) we must, in concert with biological experimentation, construct detailed mathematical descriptions of our findings. This serves three purposes: firstly, providing a quantitative description of series of complex observations; secondly, proferring a database platform that informs further testable experimentation; thirdly, advancing towards the establishment of a virtual physiological uterus and in silico clinical diagnosis and treatment of PTL

Non-standard Abilities of PostgreSQL

Import 22/07/2015Cílem bakalářské práce je prozkoumat nadstandardní vlastnosti databázového systému PostgreSQL nad rámec standardu SQL, respektive konkurečních databázových systémů a následně pro ně najít situace, ve kterých se dají vhodně uplatnit. V práci jsou nejprve postupně vyčteny možnosti uživatelské rozšířitelnosti PostgreSQL databáze a následně vybrány, zdokumentovány a zdůvodněny právě ty, které jsou jen obtížně nahraditelné vlastnostmi standardu SQL. Další část práce se soustředí na postup vytvoření jednoho praktického uživatelského rozšíření datábaze. Tato část podrobně popisuje, co všechno bylo při implementaci tohoto rozšíření nutno provést. Závěrečná část práce se pak stručně zabývá srovnáním dvou konkurečních SŘBD z hlediska rozšířitelnosti.The goal of this bachelor thesis is to explore non-standard abilities of PostgreSQL database system beyond the SQL standard respectively beyond other competitive database systems and to find situations of practical applications for these non-standard abilities subsenquently. As first there are listed user-defined extensibility options of the PostgreSQL database and then there are picked those that are difficult to replace with abilities of SQL standard. Next part of the thesis is focused on process of creating one practical user-defined extension of the database system. This part in detail describes what was needed for the implementation of that user-defined extension. Final part then briefly compares PostgreSQL database with two other database managements systems from the point of extensibility.460 - Katedra informatikyvelmi dobř

Cryptanalysis of Dedicated Cryptographic Hash Functions

In this thesis we study the security of a number of dedicated cryptographic hash functions against cryptanalytic attacks. We begin with an introduction to what cryptographic hash functions are and what they are used for. This is followed by strict definitions of the security properties often required from cryptographic hash functions. FSB hashes are a class of hash functions derived from a coding theory problem. We attack FSB by modeling the compression function of the hash by a matrix in GF(2). We show that collisions and preimages can easily be found in FSB with the proposed security parameters. We describe a meet-in-the-middle attack against the FORK-256 hash function. The attack requires 2^112.8 operations to find a collision, which is a 38000-fold improvement over the expected 2^128 operations. We then present a method for finding slid pairs for the compression function of SHA-1; pairs of inputs and messages that produce closely related outputs in the compression function. We also cryptanalyse two block ciphers based on the compression function of MD5, MDC-MD5 and the Kaliski-Robshaw "Crab" encryption algorithm. VSH is a hash function based on problems in number theory that are believed to be hard. The original proposal only claims collision resistance; we demonstrate that VSH does not meet the other hash function requirements of preimage resistance, one-wayness, and collision resistance of truncated variants. To explore more general cryptanalytic attacks, we discuss the d-Monomial test, a statistical test that has been found to be effective in distinguishing iterated Boolean circuits from real random functions. The test is applied to the SHA and MD5 hash functions. We present a new hash function proposal, LASH, and its initial cryptanalysis.The LASH design is based on a simple underlying primitive, and some of its security can be shown to be related to lattice problems