344 research outputs found
Second generation diffusion model of interacting gravity waves on the surface of deep fluid
We propose a second generation phenomenological model for nonlinear interaction of gravity waves on the surface of deep water. This model takes into account the effects of non-locality of the original Hasselmann diffusion equation still preserving important properties of the first generation model: physically consistent scaling, adherence to conservation laws and the existence of Kolmogorov-Zakharov solutions. Numerical comparison of both models with the original Hasselmann equation shows that the second generation models improves the angular distribution in the evolving wave energy spectrum
Second generation diffusion model of interacting gravity waves on the surface of deep fluid
International audienceWe propose a second generation phenomenological model for nonlinear interaction of gravity waves on the surface of deep water. This model takes into account the effects of non-locality of the original Hasselmann diffusion equation still preserving important properties of the first generation model: physically consistent scaling, adherence to conservation laws and the existence of Kolmogorov-Zakharov solutions. Numerical comparison of both models with the original Hasselmann equation shows that the second generation models improves the angular distribution in the evolving wave energy spectrum
Self-similarity of wind-driven seas
International audienceThe results of theoretical and numerical study of the Hasselmann kinetic equation for deep water waves in presence of wind input and dissipation are presented. The guideline of the study: nonlinear transfer is the dominating mechanism of wind-wave evolution. In other words, the most important features of wind-driven sea could be understood in a framework of conservative Hasselmann equation while forcing and dissipation determine parameters of a solution of the conservative equation. The conservative Hasselmann equation has a rich family of self-similar solutions for duration-limited and fetch-limited wind-wave growth. These solutions are closely related to classic stationary and homogeneous weak-turbulent Kolmogorov spectra and can be considered as non-stationary and non-homogeneous generalizations of these spectra. It is shown that experimental parameterizations of wind-wave spectra (e.g. JONSWAP spectrum) that imply self-similarity give a solid basis for comparison with theoretical predictions. In particular, the self-similarity analysis predicts correctly the dependence of mean wave energy and mean frequency on wave age Cp / U10. This comparison is detailed in the extensive numerical study of duration-limited growth of wind waves. The study is based on algorithm suggested by Webb (1978) that was first realized as an operating code by Resio and Perrie (1989, 1991). This code is now updated: the new version is up to one order faster than the previous one. The new stable and reliable code makes possible to perform massive numerical simulation of the Hasselmann equation with different models of wind input and dissipation. As a result, a strong tendency of numerical solutions to self-similar behavior is shown for rather wide range of wave generation and dissipation conditions. We found very good quantitative coincidence of these solutions with available results on duration-limited growth, as well as with experimental parametrization of fetch-limited spectra JONSWAP in terms of wind-wave age Cp / U10
Coexistence of Weak and Strong Wave Turbulence in a Swell Propagation
By performing two parallel numerical experiments -- solving the dynamical
Hamiltonian equations and solving the Hasselmann kinetic equation -- we
examined the applicability of the theory of weak turbulence to the description
of the time evolution of an ensemble of free surface waves (a swell) on deep
water. We observed qualitative coincidence of the results.
To achieve quantitative coincidence, we augmented the kinetic equation by an
empirical dissipation term modelling the strongly nonlinear process of
white-capping. Fitting the two experiments, we determined the dissipation
function due to wave breaking and found that it depends very sharply on the
parameter of nonlinearity (the surface steepness). The onset of white-capping
can be compared to a second-order phase transition. This result corroborates
with experimental observations by Banner, Babanin, Young.Comment: 5 pages, 5 figures, Submitted in Phys. Rev. Letter
Токсичність МАРК у карциномах щитоподібної залози. Механізми пригнічення сигнального каскаду (огляд літератури та власних даних)
The aim of the work: to study the activity and expression of the main effector protein kinase cascade in tumors of thyroid gland.
There is a strong evidence that the Ras/Raf/MEK/ERK (МАРК) signaling cascade promotes cell proliferation and malignancy by stimulating cell growth and division, as well as inhibiting apoptosis. The mitogenic MAPK cascade associates growth factor signals at cell surface receptors with the transcription factors AP-1, NF-κB, Ets, leading to the induction of c-Fos, cyclin D1 and c-Myc. These factors regulate the expression of genes that control survival, angiogenesis, growth, proliferation, and cell motility. However, the hyperactivity of this cascade in tumor tissues can lead to sensescence, growth retardation, apoptosis or increased autophagy. This phenomenon was called "oncogenic toxicity".Цель работы: исследование в опухолях щитовидной железы активности и экспрессии главной эффекторной протеинкиназы каскада – ERK1/2.
Получены убедительные доказательства того, что сигнальный каскад Ras/Raf/MEK/ERK (МАРК) способствует пролиферации и злокачественной трансформации клеток путем стимуляции клеточного роста и деления, а также подавления апоптоза. Митогенный МАРК-каскад связывает сигналы факторов роста на рецепторах клеточной поверхности с транскрипционными факторами АР-1, NF-κB, Ets, что приводит к индукции с-Fos, циклина D1 и с-Мус. Эти факторы регулируют экспрессию генов, контролирующих выживание, ангиогенез, рост, пролиферацию и подвижность клеток. Однако гиперактивность этого каскада в опухолевых тканях может привести к сенесценции, задержке роста, апоптозу или усилению аутофагии. Этот феномен назвали “токсичностью онкогенов”.Мета роботи: дослідження в пухлинах щитоподібної залози (ЩЗ) активності та експресії головної ефекторної протеїнкінази каскаду – ERK1/2.
Отримано переконливі докази того, що сигнальний каскад Ras/Raf/MEK/ERK (МАРК) сприяє проліферації і злоякісній трансформації клітин шляхом стимуляції клітинного росту і ділення, а також пригнічення апоптозу. Мітогенний МАРК-каскад пов’язує сигнали факторів росту на рецепторах клітинної поверхні з транскрипційними факторами АР-1, NF-κB, Ets, що приводить до індукції с-Fos, цикліну D1 і с-Мус. Ці фактори регулюють експресію генів, що контролюють виживання, ангіогенез, ріст, проліферацію і мобільність клітин. Однак гіперактивність цього каскаду в пухлинних тканинах може привести до сенесценції, затримки росту, апоптозу або посилення автофагії. Цей феномен назвали “токсичністю онкогенів”
Entanglement entropy in de Sitter: no pure states for conformal matter
In this paper, we consider the entanglement entropy of conformal matter for
finite and semi-infinite entangling regions, as well as the formation of
entanglement islands in four-dimensional de Sitter spacetime partially reduced
to two dimensions. We analyze complementarity and pure state condition of the
entanglement entropy of pure states and show that they never hold in the given
setup. We consider two different types of Cauchy surfaces in the extended
static patch and flat coordinates, correspondingly. For former, we found that
entanglement entropy of a pure state is always bounded from below by a constant
and never becomes zero, as required by quantum mechanics. In turn, the
difference between the entropies for some region and its complement, which
should be zero for a pure state, in direct calculations essentially depends on
how the boundaries of these regions evolve with time. Regarding the flat
coordinates, it is impossible to regularize spacelike infinity in a way that
would be compatible with complementarity and pure state condition, as opposed,
for instance, to two-sided Schwarzschild black hole. Finally, we discuss the
information paradox in de Sitter and show that the island formula does not
resolve it. Namely, we give examples of a region with a time-limited growth of
entanglement entropy, for which there is no island solution, and the region,
for which entanglement entropy does not grow, but the island solution exists.Comment: v1: 25 pages, 10 figures; v2: 25 pages, 10 figures, references added,
notation clarifie
Spontaneous and induced ferroelectricity in the BiFe1−xScxO3 perovskite ceramics
High-pressure synthesis method allows obtaining single-phase perovskite
BiFe1-xScxO3 ceramics in the entire concentration range. As-prepared compositions with x from 0.30 to 0.55 have the antipolar orthorhombic Pnma structure
but can be irreversible converted into the polar rhombohedral R3c or the polar
orthorhombic Ima2 phase via annealing at ambient pressure. Microstructure
defects and large conductivity of the high-pressure-synthesized ceramics make it
difficult to study and even verify their ferroelectric properties. These obstacles can
be overcome using piezoresponse force microscopy (PFM) addressing ferroelectric behavior inside single grains. Herein, the PFM study of the BiFe1-xScxO3
ceramics (0.30 ≤ x ≤ 0.50) is reported. The annealed samples show a strong PFM
contrast. Switching of domain polarity by an electric field confirms the ferroelectric nature of these samples. The as-prepared BiFe0.5Sc0.5O3 ceramics
demonstrate no piezoresponse in accordance with the antipolar character of the
Pnma phase. However, application of a strong enough electric field induces
irreversible transition to the ferroelectric state. The as-prepared BiFe0.7Sc0.3O3
ceramics show coexistence of ferroelectric and antiferroelectric grains without
poling. It is assumed that mechanical stress caused by the sample polishing can
be also a driving force of phase transformation in these materials alongside
temperature and external electric field.publishe
Entanglement Islands and Infrared Anomalies in Schwarzschild Black Hole
In this paper, island formation for entangling regions of finite size in the
asymptotically flat eternal Schwarzschild black hole is considered. We check
the complementarity property of entanglement entropy which was implicitly
assumed in previous studies for semi-infinite regions. This check reveals the
emergence of infrared anomalies after regularization of a Cauchy surface. A
naive infrared regularization based on ``mirror symmetry'' is considered and
its failure is shown. We introduce an improved regularization that gives a
correct limit agreed with the semi-infinite results from previous studies. As
the time evolution goes, the endpoints of a finite region compatible with the
improved regularization become separated by a timelike interval. We call this
phenomenon the ``Cauchy surface breaking''. Shortly before the Cauchy surface
breaking, finite size configurations generate asymmetric entanglement islands
in contrast to the semi-infinite case. Depending on the size of the finite
regions, qualitatively new behaviour arises, such as discontinuous evolution of
the entanglement entropy and the absence of island formation. Finally, we show
that the island prescription does not help us to solve the information paradox
for certain finite size regions.Comment: v1: 55 pages, 19 figures; v2: 57 pages, 19 figures, references added,
Sec. 5 presentation improve
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