Global exponential convergence to variational traveling waves in cylinders

We prove, under generic assumptions, that the special variational traveling wave that minimizes the exponentially weighted Ginzburg-Landau functional associated with scalar reaction-diffusion equations in infinite cylinders is the long-time attractor for the solutions of the initial value problems with front-like initial data. The convergence to this traveling wave is exponentially fast. The obtained result is mainly a consequence of the gradient flow structure of the considered equation in the exponentially weighted spaces and does not depend on the precise details of the problem. It strengthens our earlier generic propagation and selection result for "pushed" fronts.Comment: 23 page

The effects of liquid-phase oxidation of multiwall carbon nanotubes on their surface characteristics

The development of new sorbents based on nanostructured carbon materials recently became a perspective field of research. Main topic of current study is to investigate the effect of different regimes of multiwall carbon nanotubes (MWCNT) surface modification process on their structural characteristics. MWCNT samples were treated with nitric acid at high temperature. Structural properties were studied using low temperature nitrogen adsorption and acid-base back titration methods. The study showed that diluted nitric acid does not affect MWCNT structure. Concentrated nitric acid treatment leads to formation of 2.8 carboxylic groups per 1 nm{2} of the sample surface

Scenarios of domain pattern formation in a reaction-diffusion system

We performed an extensive numerical study of a two-dimensional reaction-diffusion system of the activator-inhibitor type in which domain patterns can form. We showed that both multidomain and labyrinthine patterns may form spontaneously as a result of Turing instability. In the stable homogeneous system with the fast inhibitor one can excite both localized and extended patterns by applying a localized stimulus. Depending on the parameters and the excitation level of the system stripes, spots, wriggled stripes, or labyrinthine patterns form. The labyrinthine patterns may be both connected and disconnected. In the the stable homogeneous system with the slow inhibitor one can excite self-replicating spots, breathing patterns, autowaves and turbulence. The parameter regions in which different types of patterns are realized are explained on the basis of the asymptotic theory of instabilities for patterns with sharp interfaces developed by us in Phys. Rev. E. 53, 3101 (1996). The dynamics of the patterns observed in our simulations is very similar to that of the patterns forming in the ferrocyanide-iodate-sulfite reaction.Comment: 15 pages (REVTeX), 15 figures (postscript and gif), submitted to Phys. Rev.

Современные тенденции в создании бесклеточных алло- и ксенотканей для реконструкции структур сердца

Tissue engineering has significant potential for solving the problems of durability of biological tissues when used in cardiac and vascular reconstructive surgery. A decellularization technology has been proposed for obtaining a biomaterial, morphologically and functionally similar to the damaged human heart tissue. This review discusses various aspects and models of biological tissue decellularization, including the modern technology of using supercritical carbon dioxide as the most eco-friendly and promising method. Тканевая инженерия обладает значительным потенциалом для решения проблем долговечности биологических тканей при использовании в реконструктивной хирургии структур сердца и сосудов. В целях получения биоматериала, морфологически и функционально близкого к поврежденной ткани сердца человека, была предложена технология децеллюляризации. В обзоре рассматриваются различные аспекты и модели децеллюляризации биологических тканей, в том числе современная технология использования сверкритического диоксида углерода как наиболее экологичного и перспективного метода

Parametric generation of second sound in superfluid helium: linear stability and nonlinear dynamics

We report the experimental studies of a parametric excitation of a second sound (SS) by a first sound (FS) in a superfluid helium in a resonance cavity. The results on several topics in this system are presented: (i) The linear properties of the instability, namely, the threshold, its temperature and geometrical dependencies, and the spectra of SS just above the onset were measured. They were found to be in a good quantitative agreement with the theory. (ii) It was shown that the mechanism of SS amplitude saturation is due to the nonlinear attenuation of SS via three wave interactions between the SS waves. Strong low frequency amplitude fluctuations of SS above the threshold were observed. The spectra of these fluctuations had a universal shape with exponentially decaying tails. Furthermore, the spectral width grew continuously with the FS amplitude. The role of three and four wave interactions are discussed with respect to the nonlinear SS behavior. The first evidence of Gaussian statistics of the wave amplitudes for the parametrically generated wave ensemble was obtained. (iii) The experiments on simultaneous pumping of the FS and independent SS waves revealed new effects. Below the instability threshold, the SS phase conjugation as a result of three-wave interactions between the FS and SS waves was observed. Above the threshold two new effects were found: a giant amplification of the SS wave intensity and strong resonance oscillations of the SS wave amplitude as a function of the FS amplitude. Qualitative explanations of these effects are suggested.Comment: 73 pages, 23 figures. to appear in Phys. Rev. B, July 1 st (2001

ОТДАЛЕННЫЕ РЕЗУЛЬТАТЫ ИМПЛАНТАЦИИ КСЕНОПЕРИКАРДИАЛЬНЫХ ПРОТЕЗОВ «БИОЛАБ» В ПОЗИЦИЮ КЛАПАНОВ ЛЕВЫХ КАМЕР СЕРДЦА

Background Heart valve replacement with mechanical prostheses in elderly patients is associated with increased risk of bleeding due to the need of lifelong indirect anticoagulant therapy. Therefore, biological heart valve prosthesis is an option of choice. Aim To estimate long-term results of aortic and mitral valve replacement with xenopericardial prosthesis «BioLAB». Methods 150 stented biological prostheses «BioLAB» were implanted into the aortic and mitral position in the Department of Emergency Surgery for Acquired Heart Disease in the period from January 1993 to December 2008. 50 stentless biological prostheses «BioLAB» were implanted in the aortic position in the period from January 2008 to December 2012. Results 1-, 5- and 10-years survival in the recipients of stented xenopericardial prostheses «BioLAB» implanted in aortic position was 91.1±2.9%, 85.3±6.1% and 85.3±6.1%, respectively. 5-, 10- and 15-years survival among those who received mitral valve replacement was 72.31%±5.56%, 55.18%±6.61%, and 22.77%±12.13%, respectively. There were no cases of redo surgeries for valve tissue degeneration among the recipients of stented and stentless aortic valve prostheses within the follow-up. 10-, 12- and 15-years freedom from mitral valve degeneration was 61.08±7.32%, 50.21±9.56%, and 43.6±10.65%. Conclusion Stented xenopericardial bioprostheses «BioLAB» implanted in the aortic position provide good and encouraging hemodynamic results in the long-term period time. There were no signs of tissue degeneration of the stented heart valves within the 10-years follow-up. Similar results were obtained for the stentless bioprosthesis within the 7-years follow-up. The period of 8.5 years after mitral valve replacement with «BioLAB» is critical for tissue degeneration of bioprosthesis.Актуальность Имплантация механического протеза возрастным пациентам сопряжена с повышенным риском кровотечений из-за необходимости пожизненного приема непрямых антикоагулянтов, альтернативой может быть биологический протез. Цель Анализ отдаленных результатов операций имплантации ксеноперикардиальных протезов «БиоЛАБ» в позицию клапанов левых камер сердца. Материалы и методы В отделении неотложной хирургии приобретенных пороков сердца с января 1993 года по декабрь 2008 года было имплантировано 150 каркасных ксенобиопротезов серии «БиоЛАБ» в позицию левых камер сердца и в период с января 2008 по декабрь 2012 г. – 50 бескаркаркасных ксеноперикардиальных протезов в позицию аортального клапана. Результаты Отдаленная выживаемость в группе пациентов с каркасным ксеноперикардиальным протезом «БиоЛАБ» в аортальной позиции к первому, 5 и 10 году составила 91,1±2,9%, 85,3±6,1% и 85,3±6,1% соответственно. В митральной позиции к 5 – 72,31 %± 5,56%, 10 – 55,18% ± 6,61%, и 15 году – 22,77%±12,13% соответственно. После имплантации каркасных и бескаркасных протезов «БиоЛАБ» в аортальную позицию реопераций, связанных с дегенерацией ткани биопротеза за весь период наблюдения не было. Свобода от дегенерации протеза в митральной позиции составила к 10 году 61,08±7,32 %, к 12-му 50,21±9,56% и к 15-му 43,6±10,65%. Заключение Ксеноперикардиальные каркасные протезы «БиоЛАБ» в аортальной позиции обеспечивают хорошие гемодинамические показатели в отдаленном периоде и отсутствие дегенерации при сроках наблюдения до 10 лет, а бескаркасные при сроках наблюдения до 7 лет. Период 8,5 лет после имплантации протеза «БиоЛАБ» в митральную позицию является критической для возникновения дегенерации ткани биопротеза