179 research outputs found
Control of scroll wave turbulence using resonant perturbations
Turbulence of scroll waves is a sort of spatio-temporal chaos that exists in
three-dimensional excitable media. Cardiac tissue and the Belousov-Zhabotinsky
reaction are examples of such media. In cardiac tissue, chaotic behaviour is
believed to underlie fibrillation which, without intervention, precedes cardiac
death. In this study we investigate suppression of the turbulence using
stimulation of two different types, "modulation of excitability" and "extra
transmembrane current". With cardiac defibrillation in mind, we used a single
pulse as well as repetitive extra current with both constant and feedback
controlled frequency. We show that turbulence can be terminated using either a
resonant modulation of excitability or a resonant extra current. The turbulence
is terminated with much higher probability using a resonant frequency
perturbation than a non-resonant one. Suppression of the turbulence using a
resonant frequency is up to fifty times faster than using a non-resonant
frequency, in both the modulation of excitability and the extra current modes.
We also demonstrate that resonant perturbation requires strength one order of
magnitude lower than that of a single pulse, which is currently used in
clinical practice to terminate cardiac fibrillation. Our results provide a
robust method of controlling complex chaotic spatio-temporal processes.
Resonant drift of spiral waves has been studied extensively in two dimensions,
however, these results show for the first time that it also works in three
dimensions, despite the complex nature of the scroll wave turbulence.Comment: 13 pages, 12 figures, submitted to Phys Rev E 2008/06/13. Last
version: 2008/09/18, after revie
How to infer gene networks from expression profiles
Inferring, or ‘reverse-engineering', gene networks can be defined as the process of identifying gene interactions from experimental data through computational analysis. Gene expression data from microarrays are typically used for this purpose. Here we compared different reverse-engineering algorithms for which ready-to-use software was available and that had been tested on experimental data sets. We show that reverse-engineering algorithms are indeed able to correctly infer regulatory interactions among genes, at least when one performs perturbation experiments complying with the algorithm requirements. These algorithms are superior to classic clustering algorithms for the purpose of finding regulatory interactions among genes, and, although further improvements are needed, have reached a discreet performance for being practically useful
Elucidation of Directionality for Co-Expressed Genes: Predicting Intra-Operon Termination Sites
We present a novel framework for inferring regulatory and sequence-level
information from gene co-expression networks. The key idea of our methodology
is the systematic integration of network inference and network topological
analysis approaches for uncovering biological insights. We determine the gene
co-expression network of Bacillus subtilis using Affymetrix GeneChip time
series data and show how the inferred network topology can be linked to
sequence-level information hard-wired in the organism's genome. We propose a
systematic way for determining the correlation threshold at which two genes are
assessed to be co-expressed by using the clustering coefficient and we expand
the scope of the gene co-expression network by proposing the slope ratio metric
as a means for incorporating directionality on the edges. We show through
specific examples for B. subtilis that by incorporating expression level
information in addition to the temporal expression patterns, we can uncover
sequence-level biological insights. In particular, we are able to identify a
number of cases where (i) the co-expressed genes are part of a single
transcriptional unit or operon and (ii) the inferred directionality arises due
to the presence of intra-operon transcription termination sites.Comment: 7 pages, 8 figures, accepted in Bioinformatic
On the Integrability, B\"Acklund Transformation and Symmetry Aspects of a Generalized Fisher Type Nonlinear Reaction-Diffusion Equation
The dynamics of nonlinear reaction-diffusion systems is dominated by the
onset of patterns and Fisher equation is considered to be a prototype of such
diffusive equations. Here we investigate the integrability properties of a
generalized Fisher equation in both (1+1) and (2+1) dimensions. A Painlev\'e
singularity structure analysis singles out a special case () as
integrable. More interestingly, a B\"acklund transformation is shown to give
rise to a linearizing transformation for the integrable case. A Lie symmetry
analysis again separates out the same case as the integrable one and
hence we report several physically interesting solutions via similarity
reductions. Thus we give a group theoretical interpretation for the system
under study. Explicit and numerical solutions for specific cases of
nonintegrable systems are also given. In particular, the system is found to
exhibit different types of travelling wave solutions and patterns, static
structures and localized structures. Besides the Lie symmetry analysis,
nonclassical and generalized conditional symmetry analysis are also carried
out.Comment: 30 pages, 10 figures, to appear in Int. J. Bifur. Chaos (2004
Oxidation resistance of nano-reinforced PC-refractories modified with phenol formaldehyde resin. Part 4. Thermodynamic evaluation of phase formation within Mg–O–C–Al, Mg–O–C–Ni and МgO‒Al₂O₃‒NiO‒SiO₂ systems using SiC + Al + Ni (NiO) complex antioxidant
Results are given for the synthesis and co-existence of phases formed from components of complex organic-
inorganic antioxidant formed during modification of phenol-formaldehyde resin (PFR) and graphite with silica alkoxide and inorganic or organic nickel precursors. Thermodynamic analysis is given for the Mg–Al–C and Mg–O–Ni–C systems. It is shown that the periclase and carbon can coexist with aluminum and nickel, and also that oxidized antioxidants Al₂O₃ and NiO can interact respectively with the periclase and with the synthesized SiC formed during modification of PFR with silica. In considering the NiO‒MgO‒Al₂O₃‒SiO₂ system it is established that during service noble spinel will be synthesized from the complex antioxidant components, facilitating an increase in PC-refractory durability in service
GENETIC POLYMORPHISM OF INFLAMMATORY FACTORS IS ASSOCIATED WITH THROMBOEMBOLIC COMPLICATIONS OF ATRIAL FIBRILLATION
Aim. To reveal the association of hereditary specifics of inflammatory factors with the adverse risk in atrial fibrillation (AF).Material and methods. Totally 258 patients studied (68,5±0,67 y. o.) with nonvalvular AF, recording the events as ischemic stroke, myocardial infarction, venous and arterial thromboembolism. Mean follow-up was 455±11,71 days.Results. Factors that are independently associated with ischemic stroke development in patients not receiving anticoagulants (n=101), were the allele C of polymorphic marker rs2228145(А/С) of gene IL-6 receptor (OR 13,25 CI 1,57112,18, р=0,018), age ?75 y. o. (OR 1,1, CI 1,008-1,2, р=0,032) and EF LV (OR 0,97 CI 0,94-0,99 р=0,027), with a “thrombotic endpoint” development — DM (OR 4,3 CI 1,46-12,45 р=0,008), EF LV (OR 0,96 CI 0,94-0,98, р<0,0001) and carriage of allele C of polymorphic marker rs2228145(А/С) of receptor to IL-6 gene (OR 4,03 CI 1,0715,26, р=0,04). There was no association with adverse outcomes in genes IL-6 polymorphisms as (G(-174)C and G(-572)C), ИЛ-10 (C(-819)T), ФНО (G(-238)A, G(-308)A and ФНО? rs180630). In those receiving adequate anticoagulant therapy (n=157) there was no significant association of IL-6 receptor gene polymorphism with adverse outcomes.Conclusion. Therefore, the carriage of allele C of polymorphic marker rs2228145(А/С) of the IL-6 receptor gene might be an independent risk marker for adverse outcome in non-valvular AF, potentially, being a selection tool for those patients not having enough high risk according to common scores
Evolution of spiral and scroll waves of excitation in a mathematical model of ischaemic border zone
Abnormal electrical activity from the boundaries of ischemic cardiac tissue
is recognized as one of the major causes in generation of ischemia-reperfusion
arrhythmias. Here we present theoretical analysis of the waves of electrical
activity that can rise on the boundary of cardiac cell network upon its
recovery from ischaemia-like conditions. The main factors included in our
analysis are macroscopic gradients of the cell-to-cell coupling and cell
excitability and microscopic heterogeneity of individual cells. The interplay
between these factors allows one to explain how spirals form, drift together
with the moving boundary, get transiently pinned to local inhomogeneities, and
finally penetrate into the bulk of the well-coupled tissue where they reach
macroscopic scale. The asymptotic theory of the drift of spiral and scroll
waves based on response functions provides explanation of the drifts involved
in this mechanism, with the exception of effects due to the discreteness of
cardiac tissue. In particular, this asymptotic theory allows an extrapolation
of 2D events into 3D, which has shown that cells within the border zone can
give rise to 3D analogues of spirals, the scroll waves. When and if such scroll
waves escape into a better coupled tissue, they are likely to collapse due to
the positive filament tension. However, our simulations have shown that such
collapse of newly generated scrolls is not inevitable and that under certain
conditions filament tension becomes negative, leading to scroll filaments to
expand and multiply leading to a fibrillation-like state within small areas of
cardiac tissue.Comment: 26 pages, 13 figures, appendix and 2 movies, as accepted to PLoS ONE
2011/08/0
Buckling of scroll waves
A scroll wave in a sufficiently thin layer of an excitable medium with
negative filament tension can be stable nevertheless due to filament rigidity.
Above a certain critical thickness of the medium, such scroll wave will have a
tendency to deform into a buckled, precessing state. Experimentally this will
be seen as meandering of the spiral wave on the surface, the amplitude of which
grows with the thickness of the layer, until a break-up to scroll wave
turbulence happens. We present a simplified theory for this phenomenon and
illustrate it with numerical examples.Comment: 4 pages main text + 5 pages appendix, 4+2 figures and a movie, as
accepted by Phys Rev Letters 2012/09/2
Анкилозирующий спондилоартрит в ревматологической практике Карелии
The paper describes the pathological aspects of an inflammatory process in ankylosing spondyloarthritis (AS), the role of muscle spasm in maintaining the intensity of pain syndrome and stiffness, the need for the early diagnosis of AS, and the significance of the early use of nonster-oidal anti-inflammatory drugs in these patients. The results of clinical trials and the authorsX data demonstrate the high efficacy and good tolerance of nimesulide (nise) in AS.Представлены патоморфологические аспекты воспалительного процесса при анкилозирующем спондилоартрите (АС), роль мышечного спазма в поддержании интенсивности болевого синдрома и скованности, необходимость ранней диагностики АС, значение раннего применения нестероидных противовоспалительных препаратов у таких пациентов. Результаты клинических исследований и собственные данные авторов демонстрируют высокую эффективность и хорошую переносимость нимесулида (найз) при АС
LinkEHR-Ed: A multi-reference model archetype editor based on formal semantics
Purpose
To develop a powerful archetype editing framework capable of handling multiple reference models and oriented towards the semantic description and standardization of legacy data.
Methods
The main prerequisite for implementing tools providing enhanced support for archetypes is the clear specification of archetype semantics. We propose a formalization of the definition section of archetypes based on types over tree-structured data. It covers the specialization of archetypes, the relationship between reference models and archetypes and conformance of data instances to archetypes.
Results
LinkEHR-Ed, a visual archetype editor based on the former formalization with advanced processing capabilities that supports multiple reference models, the editing and semantic validation of archetypes, the specification of mappings to data sources, and the automatic generation of data transformation scripts, is developed.
Conclusions
LinkEHR-Ed is a useful tool for building, processing and validating archetypes based on any reference model.This work was supported in part by the Spanish Ministry of Education and Science under grant TS12007-66S7S-C02; by the Generalitat Valenciana under grant APOSTD/2007/055 and by the program PAID-06-07 de la Universidad Politecnica de Valencia.Maldonado Segura, JA.; Moner Cano, D.; Boscá Tomás, D.; Fernandez Breis, JT.; Angulo Fernández, C.; Robles Viejo, M. (2009). LinkEHR-Ed: A multi-reference model archetype editor based on formal semantics. International Journal of Medical Informatics. 78(8):559-570. https://doi.org/10.1016/j.ijmedinf.2009.03.006S55957078
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