Evolution and stabilization of subnanometric metal species in confined space by in situ TEM

Understanding the behavior and dynamic structural transformation of subnanometric metal species under reaction conditions will be helpful for understanding catalytic phenomena and for developing more efficient and stable catalysts based on single atoms and clusters. In this work, the evolution and stabilization of subnanometric Pt species confined in MCM-22 zeolite has been studied by in situ transmission electron microscopy (TEM). By correlating the results from in situ TEM studies and the results obtained in a continuous fix-bed reactor, it has been possible to delimitate the factors that control the dynamic agglomeration and redispersion behavior of metal species under reaction conditions. The dynamic reversible transformation between atomically dispersed Pt species and clusters/nanoparticles during CO oxidation at different temperatures has been elucidated. It has also been confirmed that subnanometric Pt clusters can be stabilized in MCM-22 crystallites during NO reduction with CO and H2

PALEOHYDROLOGY OF LAKE SELIGER (VALDAI UPLAND, RUSSIA)

50-5

Finite time singularities in a class of hydrodynamic models

Models of inviscid incompressible fluid are considered, with the kinetic energy (i.e., the Lagrangian functional) taking the form ${\cal L}\sim\int k^\alpha|{\bf v_k}|^2d^3{\bf k}$ in 3D Fourier representation, where $\alpha$ is a constant, $0<\alpha< 1$. Unlike the case $\alpha=0$ (the usual Eulerian hydrodynamics), a finite value of $\alpha$ results in a finite energy for a singular, frozen-in vortex filament. This property allows us to study the dynamics of such filaments without the necessity of a regularization procedure for short length scales. The linear analysis of small symmetrical deviations from a stationary solution is performed for a pair of anti-parallel vortex filaments and an analog of the Crow instability is found at small wave-numbers. A local approximate Hamiltonian is obtained for the nonlinear long-scale dynamics of this system. Self-similar solutions of the corresponding equations are found analytically. They describe the formation of a finite time singularity, with all length scales decreasing like $(t^*-t)^{1/(2-\alpha)}$, where $t^*$ is the singularity time.Comment: LaTeX, 17 pages, 3 eps figures. This version is close to the journal pape

Instabilities in the two-dimensional cubic nonlinear Schrodinger equation

The two-dimensional cubic nonlinear Schrodinger equation (NLS) can be used as a model of phenomena in physical systems ranging from waves on deep water to pulses in optical fibers. In this paper, we establish that every one-dimensional traveling wave solution of NLS with trivial phase is unstable with respect to some infinitesimal perturbation with two-dimensional structure. If the coefficients of the linear dispersion terms have the same sign then the only unstable perturbations have transverse wavelength longer than a well-defined cut-off. If the coefficients of the linear dispersion terms have opposite signs, then there is no such cut-off and as the wavelength decreases, the maximum growth rate approaches a well-defined limit.Comment: 4 pages, 4 figure

Collapse dynamics of trapped Bose-Einstein condensates

We analyze the implosion and subsequent explosion of a trapped condensate after the scattering length is switched to a negative value. Our results compare very well qualitatively and fairly well quantitatively with the results of recent experiments at JILA.Comment: 4 pages, 3 figure

Search for exoplanets in M31 with pixel-lensing and the PA-99-N2 event revisited

Several exoplanets have been detected towards the Galactic bulge with the microlensing technique. We show that exoplanets in M31 may also be detected with the pixel-lensing method, if telescopes making high cadence observations of an ongoing microlensing event are used. Using a Monte Carlo approach we find that the mean mass for detectable planetary systems is about $2 M_{\rm {J}}$. However, even small mass exoplanets ($M_{\rm P} < 20 M_{\oplus}$) can cause significant deviations, which are observable with large telescopes. We reanalysed the POINT-AGAPE microlensing event PA-99-N2. First, we test the robustness of the binary lens conclusion for this light curve. Second, we show that for such long duration and bright microlensing events, the efficiency for finding planetary-like deviations is strongly enhanced with respect to that evaluated for all planetary detectable events.Comment: 14 pages, 8 figures. Paper presented at the "II Italian-Pakistani Workshop on Relativistic Astrophysics, Pescara, July 8-10, 2009. To be published in a special issue of General Relativity and Gravitation (eds. F. De Paolis, G.F.R. Ellis, A. Qadir and R. Ruffini

Stable vortex and dipole vector solitons in a saturable nonlinear medium

We study both analytically and numerically the existence, uniqueness, and stability of vortex and dipole vector solitons in a saturable nonlinear medium in (2+1) dimensions. We construct perturbation series expansions for the vortex and dipole vector solitons near the bifurcation point where the vortex and dipole components are small. We show that both solutions uniquely bifurcate from the same bifurcation point. We also prove that both vortex and dipole vector solitons are linearly stable in the neighborhood of the bifurcation point. Far from the bifurcation point, the family of vortex solitons becomes linearly unstable via oscillatory instabilities, while the family of dipole solitons remains stable in the entire domain of existence. In addition, we show that an unstable vortex soliton breaks up either into a rotating dipole soliton or into two rotating fundamental solitons.Comment: To appear in Phys. Rev.

Stability of trapped Bose-Einstein condensates

In three-dimensional trapped Bose-Einstein condensate (BEC), described by the time-dependent Gross-Pitaevskii-Ginzburg equation, we study the effect of initial conditions on stability using a Gaussian variational approach and exact numerical simulations. We also discuss the validity of the criterion for stability suggested by Vakhitov and Kolokolov. The maximum initial chirp (initial focusing defocusing of cloud) that can lead a stable condensate to collapse even before the number of atoms reaches its critical limit is obtained for several specific cases. When we consider two- and three-body nonlinear terms, with negative cubic and positive quintic terms, we have the conditions for the existence of two phases in the condensate. In this case, the magnitude of the oscillations between the two phases are studied considering sufficient large initial chirps. The occurrence of collapse in a BEC with repulsive two-body interaction is also shown to be possible.Comment: 15 pages, 11 figure

Transverse instability and its long-term development for solitary waves of the (2+1)-Boussinesq equation

The stability properties of line solitary wave solutions of the (2+1)-dimensional Boussinesq equation with respect to transverse perturbations and their consequences are considered. A geometric condition arising from a multi-symplectic formulation of this equation gives an explicit relation between the parameters for transverse instability when the transverse wavenumber is small. The Evans function is then computed explicitly, giving the eigenvalues for transverse instability for all transverse wavenumbers. To determine the nonlinear and long time implications of transverse instability, numerical simulations are performed using pseudospectral discretization. The numerics confirm the analytic results, and in all cases studied, transverse instability leads to collapse.Comment: 16 pages, 8 figures; submitted to Phys. Rev.

Применение тест-системы «Лайн-Блот Сифилис» в диагностикесифилиса методом линейного иммуноблотинга

ZAO ECOlab (Russia) developed Line Blot Syphilis, a new test system on the basis of the linear immunoblotting method using Treponema рallidum recombinant antigens. The article assessed the diagnostic value of the Line Blot Syphilis test system in the form of a confirmatory test. As a part of the conducted study, the test system demonstrated its absolute sensitivity and specificity to serum-positive (n = 237) and serum-negative (n = 114) samples, in which the presence or absence of Т.pallidum antibodies was confirmed by two treponemal tests. As a result of examining 14 samples attributed to doubtful analytes based on two test results (passive hemagglutination test and immunofluorescence test with absorption), the data compliance between the Line Blot Syphilis test system and data from INNO-LIA Syphilis Score amounted to 100% (14/14) or 93% (13/14) for the immune-enzyme assay and 57% (8/14) for the immunofluorescence test with absorption. It is recommended to use the Line Blot Syphilis test system (ZAO ECOlab) as a confirmatory syphilis test.Разработана новая отечественная тест-система «Лайн-Блот Сифилис» (ЗАО «ЭКОлаб») на основе метода линейного иммуноблотинга с использованием рекомбинантных антигенов Treponema рallidum. В представленной работе диагностическая значимость диагностикума «Лайн-Блот Cифилис» оценивалась в формате подтверждающего теста. В рамках проведенного исследования тест-система показала абсолютную чувствительность и специфичность по отношению к серопозитивным (n = 237) и серонегативным (n = 114) образцам, в которых наличие или отсутствие антител к Т.pallidum было установлено двумя трепонемными тестами. При исследовании 14 образцов, отнесенных на основании результатов двух тестов (РПГА и РИФабс) в группу сомнительных аналитов, соответствие данных, полученных в тест-системе «Лайн-Блот Cифилис», данным «INNO-LIA Syphilis score» составило 100% (14/14), ИФА - 93% (13/14), РИФабс - 57% (8/14). Рекомендовано использовать тест-систему «Лайн-Блот Сифилис» (ЗАО «ЭКОлаб») в качестве подтверждающего теста на сифилис