194 research outputs found
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
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 in 3D Fourier representation, where
is a constant, . Unlike the case (the usual Eulerian
hydrodynamics), a finite value of 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 ,
where 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 .
However, even small mass exoplanets () 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
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