Exceedance frequency of appearance of extreme internal waves in the World Ocean
Statistical estimates of internal waves in different
regions of theWorld Ocean are discussed. It is found that the
observed exceedance probability of large-amplitude internal
waves in most cases can be described by the Poisson law,
which is one of the typical laws of extreme statistics. Detailed
analysis of the statistical properties of internal waves in several
regions of theWorld Ocean has been performed: tropical
part of the Atlantic Ocean, northwestern shelf of Australia,
the Mediterranean Sea near the Egyptian coast, and the Yellow
In this paper for the explain of the mechanism of formation of smooth strips (slicks) on the sea surface under the action of internal waves are used the film of surface-active substances, attendees everywhere in the sea. Experimental data on the real characteristics of marine films of surface-active substances are used for the calculation of histograms of contrast in the spectrum of wind ripples in the centimeter range for various parameters of the internal wave and wind wave lengths within the "film" mechanism of the effects of internal waves on the spectrum of wind-generated waves. It is shown that the ripple in the wavelength range 2-3 cm contrast weakly depends on the parameters of the internal waves (although with increasing internal wave amplitude), and the average number of 6-7 dB. For greater lengths ripple contrast is strongly dependent on the ratio of the rate of flow of water particles in the internal waves to the phase velocity of the internal wave. This dispersion deviations from average contrast values around the average value, which indicates a strong variation of contrast in each case. Nevertheless, it can be concluded relatively low sensitivity of "film" mechanism of action internal waves on the sea surface to a particular type of surface-active substances.
Simulation of abnormally large internal waves generated by the baroclinic tide is now quite important due to the increased number of offshore platforms installed on offshore oil and gas fields. The height of the internal waves in many areas of the oceans can be up to 100 m, and these waves become really dangerous. All of this points to the need to study the possible dynamic and catastrophic phenomena accompanying the propagation of internal waves of large amplitude. In terms of the computational analysis of transient wave motion is a very complex task. There was designed widely used numerical code MIT, decisive full hydrodynamic equations with the real bottom topography, the Earth's rotation and turbulent processes. However, this model requires a lot of computing resources, a number of viable solutions to the practical problems of Oceanology. However, even such a complete model is not yet take into account the current practice relatively stable background horizontal - nonuniform stratification, which is typical for the real ocean conditions. That is why the research and analysis of new phenomena is widely used asymptotic model based on the Korteweg–de Vries equation and its generalizations. In this paper we use the asymptotic model for the analysis of the two most important effects in the bottom layer, induced by internal waves: the change in pressure at the bottom and sediment transport. Moving the sediment and erosion of the bottom near the supports are well known to storm surges in the coastal zone. The specifics of the internal waves is their greater length (a few kilometers), so that such waves are always "get" to the bottom, even far from the coast and can lead to erosion of supports oil platforms in deep water. Particularly dangerous abnormally large waves, since the characteristics of erosion is proportional to the cube of the amplitude of the internal wave. In our country, yet the effects of internal waves on the stability of marine structures are not regulated. What is needed is an active study of this problem in theoretical terms, and the accumulation of data on the hazards of internal waves in areas where there are oil and gas platforms.
Purpose: Numerical modeling of internal baroclinic disturbances of different shapes in a model lake with variable depth, analysis of velocity field of wave-induced current, especially in the near-bed layer.
Approach: The study is carried out with the use of numerical full nonlinear nonhydrostatic model for stratified fluid.
Findings: The full nonlinear numerical modeling of internal wave dynamics in a stratified lake is carried out. The calculated distributions of near-bed velocities are analyzed; the significance of 3D effects for the velocity fields is emphasized; the regions of maximal (where internal waves are the main driving factor for sediment resuspension and erosion processes on the bed) and minimal velocities are marked out.
Originality: The results are new and can have practical application for many applied problems, especially ecological and economical, concerned with the processes of propagation of natural and anthropogenic pollutions in natural basins and the investigation of water quality, as well as with influence upon engineering structures and sediment transport.
One of the key advances in genome assembly that has led to a significant improvement in contig lengths has been improved algorithms for utilization of paired reads (mate-pairs). While in most assemblers, mate-pair information is used in a post-processing step, the recently proposed Paired de Bruijn Graph (PDBG) approach incorporates the mate-pair information directly in the assembly graph structure. However, the PDBG approach faces difficulties when the variation in the insert sizes is high. To address this problem, we first transform mate-pairs into edge-pair histograms that allow one to better estimate the distance between edges in the assembly graph that represent regions linked by multiple mate-pairs. Further, we combine the ideas of mate-pair transformation and PDBGs to construct new data structures for genome assembly: pathsets and pathset graphs.
Papers about natural protection territories
Many environmental stimuli present a quasi-rhythmic structure at different timescales that the brain needs to decompose and integrate. Cortical oscillations have been proposed as instruments of sensory de-multiplexing, i.e., the parallel processing of different frequency streams in sensory signals. Yet their causal role in such a process has never been demonstrated. Here, we used a neural microcircuit model to address whether coupled theta–gamma oscillations, as observed in human auditory cortex, could underpin the multiscale sensory analysis of speech. We show that, in continuous speech, theta oscillations can flexibly track the syllabic rhythm and temporally organize the phoneme-level response of gamma neurons into a code that enables syllable identification. The tracking of slow speech fluctuations by theta oscillations, and its coupling to gamma-spiking activity both appeared as critical features for accurate speech encoding. These results demonstrate that cortical oscillations can be a key instrument of speech de-multiplexing, parsing, and encoding.
Neuronal nicotinic acetylcholine receptors (NNRs) of the α7 subtype have been shown to contribute to the release of dopamine in the nucleus accumbens. The site of action and the underlying mechanism, however, are unclear. Here we applied a circuit modeling approach, supported by electrochemical in vivo recordings, to clarify this issue. Modeling revealed two potential mechanisms for the drop in accumbal dopamine efflux evoked by the selective α7 partial agonist TC-7020. TC-7020 could desensitize α7 NNRs located predominantly on dopamine neurons or glutamatergic afferents to them or, alternatively, activate α7 NNRs located on the glutamatergic afferents to GABAergic interneurons in the ventral tegmental area. Only the model based on desensitization, however, was able to explain the neutralizing effect of coapplied PNU-120596, a positive allosteric modulator. According to our results, the most likely sites of action are the preterminal α7 NNRs controlling glutamate release from cortical afferents to the nucleus accumbens. These findings offer a rationale for the further investigation of α7 NNR agonists as therapy for diseases associated with enhanced mesolimbic dopaminergic tone, such as schizophrenia and addiction
Let k be a field of characteristic zero, let G be a connected reductive algebraic group over k and let g be its Lie algebra. Let k(G), respectively, k(g), be the field of k- rational functions on G, respectively, g. The conjugation action of G on itself induces the adjoint action of G on g. We investigate the question whether or not the field extensions k(G)/k(G)^G and k(g)/k(g)^G are purely transcendental. We show that the answer is the same for k(G)/k(G)^G and k(g)/k(g)^G, and reduce the problem to the case where G is simple. For simple groups we show that the answer is positive if G is split of type A_n or C_n, and negative for groups of other types, except possibly G_2. A key ingredient in the proof of the negative result is a recent formula for the unramified Brauer group of a homogeneous space with connected stabilizers. As a byproduct of our investigation we give an affirmative answer to a question of Grothendieck about the existence of a rational section of the categorical quotient morphism for the conjugating action of G on itself.
Let G be a connected semisimple algebraic group over an algebraically closed field k. In 1965 Steinberg proved that if G is simply connected, then in G there exists a closed irreducible cross-section of the set of closures of regular conjugacy classes. We prove that in arbitrary G such a cross-section exists if and only if the universal covering isogeny Ĝ → G is bijective; this answers Grothendieck's question cited in the epigraph. In particular, for char k = 0, the converse to Steinberg's theorem holds. The existence of a cross-section in G implies, at least for char k = 0, that the algebra k[G]G of class functions on G is generated by rk G elements. We describe, for arbitrary G, a minimal generating set of k[G]G and that of the representation ring of G and answer two Grothendieck's questions on constructing generating sets of k[G]G. We prove the existence of a rational (i.e., local) section of the quotient morphism for arbitrary G and the existence of a rational cross-section in G (for char k = 0, this has been proved earlier); this answers the other question cited in the epigraph. We also prove that the existence of a rational section is equivalent to the existence of a rational W-equivariant map T- - - >G/T where T is a maximal torus of G and W the Weyl group.