Maximally nonabelian Toda systems

A detailed consideration of the maximally nonabelian Toda systems based on the classical semisimple Lie groups is given. The explicit expressions for the general solution of the corresponding equations are obtained.Comment: 28 pages, LaTeX file. A few references and appendix B are added; this version will appear in Nuclear Physics

Возрастные зависимости длин теломер клеток мышечной ткани хищных видов рыб с потенциально различным механизмом старения

The mechanisms of aging differ and have their own features both mammals, and in different species groups of fish. Telomere length is an indicator of the theoretical number of cell cycles that cells of a particular tissue can go through; therefore, the age-related dynamics of telomere length characterizes changes in the tissue's ability to regenerate and is necessary to describe the mechanism of tissue aging. In this work, age-related linear regressions of the telomere lengths of muscle tissue of northern pike (Esox lucius) and zander (Sander lucioperca) were empirically obtained for the wide age groups of individuals of both sexes. The identified significant difference in the dependences on their slope values indicates different degrees of decrease in the ability to regenerate muscle tissue with age, which is consistent with the previously discovered physiological characteristics of the muscle tissue of pike. In both fish species studied, telomere length in females decreases with age much more slowly than in males, which is a common feature in the aging mechanisms of most vertebrates.Механизмы старения отличаются и имеют свои особенности как у рыб и млекопитающих, так и у различных видовых групп рыб, поэтому представляют научный интерес. Длина теломер является показателем теоретического числа клеточных циклов, которые могут пройти клетки той или иной ткани, следовательно, возрастная динамика длины теломер характеризует изменение способности ткани к регенерации и необходима для описания механизма старения. В данной работе эмпирически получены линейные зависимости длин теломер мышечной ткани щуки (Esox lucius) и судака (Sander lucioperca) от возраста рыбы для широких возрастных выборок особей обоих полов. Достоверно выявленная разница зависимостей длины теломер от возраста по угловым коэффициентам свидетельствует о разной степени снижения способности к регенерации мышечной ткани со временем, что согласуется с обнаруженными ранее физиологическими особенностями этой ткани у щуки. У обоих исследуемых видов рыб длина теломер у самок уменьшается с возрастом значительно медленнее, чем у самцов, что является общей чертой в механизмах старения большинства позвоночных

Способность экстракта икры окуня и лиофилизата овариальной жидкости осетра ускорять восстановление фибробластов после стресс-индуцированного преждевременного старения

Ovarian liquid and fish roe are valuable sources of biologically active compounds. In order to study mechanisms of aging and also to search for biologically active compounds capable of inhibiting aging, we have modelled premature senescence in human embryonic fibroblasts by incubating of cells with H2O2. Cell senescence was assessed by staining for β-galactosidase (SA-β-Gal) at pH 6.0; cell proliferation was further evaluated by the optical method. The dried ovarian liquid of the Siberian sturgeon and the extract of the perch roe were able to enhance recovery of the cells after induction of their premature senescence caused by oxidative stress. In contrast to the extract from perch roe and the extracts from fish muscle, dried ovarian fluid gave such an effect without the growth of proliferation.Овариальная жидкость и икра рыб представляют собой ценные источники биологически активных соединений. С целью изучения механизмов старения, а также обнаружения биологически-активных соединений, способных ему препятствовать, производили моделирование данного процесса in vitro, инкубируя культуры эмбриональных фибробластов человека с пероксидом водорода. Индуцированное клеточное старение оценивали путём окрашивания на β-галактозидазу (SA-β-Gal) при рН 6.0, пролиферацию клеток - оптическим методом. Лиофилизат овариальной жидкости осетра сибирского (Acipenser baerii) и экстракт икры окуня обыкновенного (Perca fluviatilis) способны усиливать восстановление клеток после индукции их преждевременного старения, вызванного окислительным стрессом. В отличие от экстракта икры окуня и экстрактов из мышечной ткани рыб, высушенная овариальная жидкость оказывала такой эффект без роста пролиферации

The pion transition form factor and the pion distribution amplitude

Recent BaBaR data on the pion transition form factor, whose Q^2 dependence is much steeper then predicted by asymptotic Quantum Chromodynamics (QCD), have caused a renewed interest in its theoretical description. We present here a formalism based on a model independent low energy description and a high energy description based on QCD, which match at a scale Q_0. The high energy description incorporates a flat pion distribution amplitude, phi(x)=1, at the matching scale Q_0 and QCD evolution from Q_0 to Q>Q_0. The flat pion distribution is connected, through soft pion theorems and chiral symmetry, to the pion valance parton distribution at the same low scale Q_0. The procedure leads to a good description of the data, and incorporating additional twist three effects, to an excellent description of the data.Comment: 11 pages, 5 postscript figures, uses epsfig.sty and 1 appendi

Pion-photon transition form factor. Living on the QCD frontier

An analysis of all available data (CELLO, CLEO, \babar) in the range $[1\div 40]$ GeV$^2$ for the pion-photon transition form factor in terms of light-cone sum rules with next-to-leading-order accuracy is discussed, including twist-four contributions and next-to-next-to-leading order and twist-six corrections---the latter two via uncertainties. The antithetic trend between the \babar data for the $\gamma^*\gamma\pi^0$ and those for the $\gamma^*\gamma\eta(\eta')$ transition is pointed out, emphasizing the underlying antagonistic mechanisms: endpoint enhancement for the first and endpoint-suppression for the second---each associated with pseudoscalar meson distribution amplitudes with distinct endpoint characteristics.Comment: 6 pages, 3 figures; needs style files svglov2.clo, svjour2.cls (supplied). Presented at LIGHTCONE 2011, 23 - 27 May, 2011, Dallas, USA. Accepted for publication in Few-Body Systems. In v2 name of second author in [28] corrected. V3 is final version, published online 23. Sep 201

Hard exclusive electroproduction of two pions and their resonances

We study the hard exclusive production of two pions in the virtual photon fragmentation region with various invariant masses including the resonance region. The amplitude is expressed in terms of two-pion light cone distribution amplitudes ($2\pi$DA's). We derive dispersion relations for these amplitudes, which enables us to fix them completely in terms of $\pi\pi$ scattering phases and a few low-energy subtraction constants determind by the effective chiral lagrangian. Quantitative estimates of the resonance as well $\pi\pi$ background DA's at low normalization point are made. We also prove certain new soft pion theorem relating two-pion DA's to the one-pion DA. Crossing relations between $2\pi$DA's and parton distributions in a pion are discussed. We demontrate that by studying the shape of the $\pi\pi$ mass spectra (not absolute cross section!) in a diffractive electroproduction one can extract the deviation of the meson ($\pi,\rho,$ etc.) wave functions from their asymptotic form $6 z(1-z)$ and hence to get important information about the structure of mesons. Also we discuss how the moments of quark distributions in a pion can be measured in the hard diffraction. We suggest (alternative to S\"oding's) parametrization of $\pi\pi$ spectra which is suitable for large photon virtuality.Comment: 30 pages, one figure. Discussion of crossing relations between meson distribution amplitudes and quark densities is adde

Model analysis of the world data on the pion transition form factor

We discuss the impact of recent Belle data on our description of the pion transition form factor based on the assumption that a perturbative formalism and a nonperturbative one can be matched in a physically acceptable manner at a certain hadronic scale $Q_{0}$. We discuss the implications of the different parameters of the model in comparing with world data and conclude that within experimental errors our description remains valid. Thus we can assert that the low $Q^2$ nonperturbative description together with an additional $1/Q^2$ term at the matching scale have a strong influence on the $Q^2$ behavior up to very high values of $Q^2$ .Comment: 6 pages and 3 figures. Contains a comparison with other models and additional reference

Infinitely many local higher symmetries without recursion operator or master symmetry: integrability of the Foursov--Burgers system revisited

We consider the Burgers-type system studied by Foursov, w_t &=& w_{xx} + 8 w w_x + (2-4\alpha)z z_x, z_t &=& (1-2\alpha)z_{xx} - 4\alpha z w_x + (4-8\alpha)w z_x - (4+8\alpha)w^2 z + (-2+4\alpha)z^3, (*) for which no recursion operator or master symmetry was known so far, and prove that the system (*) admits infinitely many local generalized symmetries that are constructed using a nonlocal {\em two-term} recursion relation rather than from a recursion operator.Comment: 10 pages, LaTeX; minor changes in terminology; some references and definitions adde

Activation transport under quantum Hall regime in HgTe-based heterostructure

We have measured the temperature (2.9 K < T < 50 K) and magnetic field (0 T < B < 9 T) dependences of longitudinal and Hall resistivities for HgCdTe/HgTe/HgCdTe system with HgTe quantum well width of 20.3 nm. The activation analysis of the experimental magnetoresistivity traces has been used as a quantitative tool to probe inter-Landau level distances. The activation energies were determined from the temperature dependence of the longitudinal resistivity in the regions of quantized Hall plateaus (for the filling factors ν of 1, 2 and 3) and the indications of the large values of the g factor ≅ 30–75 were found

Spectral quark model and low-energy hadron phenomenology

We propose a spectral quark model which can be applied to low energy hadronic physics. The approach is based on a generalization of the Lehmann representation of the quark propagator. We work at the one-quark-loop level. Electromagnetic and chiral invariance are ensured with help of the gauge technique which provides particular solutions to the Ward-Takahashi identities. General conditions on the quark spectral function follow from natural physical requirements. In particular, the function is normalized, its all positive moments must vanish, while the physical observables depend on negative moments and the so-called log-moments. As a consequence, the model is made finite, dispersion relations hold, chiral anomalies are preserved, and the twist expansion is free from logarithmic scaling violations, as requested of a low-energy model. We study a variety of processes and show that the framework is very simple and practical. Finally, incorporating the idea of vector-meson dominance, we present an explicit construction of the quark spectral function which satisfies all the requirements. The corresponding momentum representation of the resulting quark propagator exhibits only cuts on the physical axis, with no poles present anywhere in the complex momentum space. The momentum-dependent quark mass compares very well to recent lattice calculations. A large number of predictions and relations can be deduced from our approach for such quantities as the pion light-cone wave function, non-local quark condensate, pion transition form factor, pion valence parton distribution function, etc.Comment: revtex, 24 pages, 3 figure