The magnetorotational instability (MRI) is thought to be a powerful source of turbulence and momentum transport in astrophysical accretion discs, but obtaining observational evidence of its operation ...is challenging. Recently, laboratory experiments of Taylor-Couette flow with externally imposed axial and azimuthal magnetic fields have revealed the kinematic and dynamic properties of the MRI close to the instability onset. While good agreement was found with linear stability analyses, little is known about the transition to turbulence and transport properties of the MRI. We here report on a numerical investigation of the MRI with an imposed azimuthal magnetic field. We show that the laminar Taylor-Couette flow becomes unstable to a wave rotating in the azimuthal direction and standing in the axial direction via a supercritical Hopf bifurcation. Subsequently, the flow features a catastrophic transition to spatio-temporal defects which is mediated by a subcritical subharmonic Hopf bifurcation. Our results are in qualitative agreement with the PROMISE experiment and dramatically extend their realizable parameter range. We find that as the Reynolds number increases defects accumulate and grow into turbulence, yet the momentum transport scales weakly.
The study of the mechanical properties of materials based on titanium nickelide arising during thermoelastic martensitic transformations, including reactive stresses, is of great interest. The effect ...of generating reactive stresses in shape memory materials has an impact on various fields of technology. So, in materials with a shape-memory effect acting as mechanical energy converters and as power elements of drives, conditions are used under which deformation is fixed. This use assumes the stability of properties and operating parameters in this type of device. In this work, reactive stresses that arise in samples of alloys based on titanium nickelide when the strain is fixed, which prevents the shape-memory effect from occurring during the cycling of martensitic transformations, were studied. It is assumed that the cycling of martensitic transformations can lead to a change in reactive stresses due to the structural rearrangement of the material, which, in turn, will affect the performance of units and assemblies made of alloys based on titanium nickelide. It is shown that the level of reactive stresses developed in the sample in the heating–cooling cycle decreases in subsequent cycles. The observed hardening from cycle to cycle, under the action of reactive stresses, can characterize the phenomenon of phase hardening.
The proper functioning and assembly of the sperm flagella structures contribute significantly to spermatozoa motility and overall male fertility. However, the fine mechanisms of assembly steps are ...poorly studied due to the high diversity of cell types, low solubility of the corresponding protein structures, and high tissue and cell specificity. One of the open questions for investigation is the attachment of longitudinal columns to the doublets 3 and 8 of axonemal microtubules through the outer dense fibers. A number of mutations affecting the assembly of flagella in model organisms are known. Additionally, evolutionary genomics data and comparative analysis of flagella morphology are available for a set of non-model species. This review is devoted to the analysis of diverse ultrastructures of sperm flagellum of Metazoa combined with an overview of the evolutionary distribution and function of the mammalian fibrous sheath proteins.
Since its initial detection in Africa, the West Nile virus has disseminated widely across all continents, becoming endemic in numerous countries, including the Russian Federation. A substantial ...expansion of the West Nile virus range was observed in the European part of the Russian territory in 1999. In light of this epidemiological trend, research endeavours focusing on monitoring West Nile virus circulation activity in endemic regions of the country have gained paramount significance. A substantial dataset has been accrued from 2007 onwards regarding genomic variability and dissemination dynamics across the country throughout the entire monitoring period for the West Nile fever pathogen. The objective of this study was to characterise West Nile virus isolates that have been circulating in the Russian Federation and identify their molecular and genetic characteristics. A phylogenetic analysis of 55 complete genome sequences revealed that the West Nile virus population within the Russian Federation is genetically heterogeneous and is represented by four major clades. One of these clades is currently exhibiting extensive spread into new regions of the country.
Magnetorotational instability (MRI) is one of the fundamental processes in astrophysics, driving angular momentum transport and mass accretion in a wide variety of cosmic objects. Despite much ...theoretical/numerical and experimental efforts over the last decades, its saturation mechanism and amplitude, which sets the angular momentum transport rate, remains not well understood, especially in the limit of high resistivity, or small magnetic Prandtl numbers typical to interiors (dead zones) of protoplanetary disks, liquid cores of planets and liquid metals in laboratory. Using direct numerical simulations, in this paper we investigate the nonlinear development and saturation properties of the helical magnetorotational instability (HMRI)-a relative of the standard MRI-in a magnetized Taylor-Couette flow at very low magnetic Prandtl number (correspondingly at low magnetic Reynolds number) relevant to liquid metals. For simplicity, the ratio of azimuthal field to axial field is kept fixed. From the linear theory of HMRI, it is known that the Elsasser number, or interaction parameter determines its growth rate and plays a special role in the dynamics. We show that this parameter is also important in the nonlinear problem. By increasing its value, a sudden transition from weakly nonlinear, where the system is slightly above the linear stability threshold, to strongly nonlinear, or turbulent regime occurs. We calculate the azimuthal and axial energy spectra corresponding to these two regimes and show that they differ qualitatively. Remarkably, the nonlinear state remains in all cases nearly axisymmetric suggesting that this HMRI-driven turbulence is quasi two-dimensional in nature. Although the contribution of non-axisymmetric modes increases moderately with the Elsasser number, their total energy remains much smaller than that of the axisymmetric ones.
Crowdsourcing works by distributing many small tasks to large numbers of workers, yet the true potential of crowdsourcing lies in workers doing more than performing simple tasks-they can apply their ...experience and creativity to provide new and unexpected information to the crowdsourcer. One such case is when workers not only answer a crowdsourcer's questions but also contribute new questions for subsequent crowd analysis, leading to a growing set of questions. This growth creates an inherent bias for early questions since a question introduced earlier by a worker can be answered by more subsequent workers than a question introduced later. Here we study how to perform efficient crowdsourcing with such growing question sets. By modeling question sets as networks of interrelated questions, we introduce algorithms to help curtail the growth bias by efficiently distributing workers between exploring new questions and addressing current questions. Experiments and simulations demonstrate that these algorithms can efficiently explore an unbounded set of questions without losing confidence in crowd answers.
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t—The (1 –
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3
–
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SiO
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composites where the silicon oxide mole fraction is
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≤ 0.5 were manufactured by the solid-phase method. The phase compositions of the composites and ...their thermodynamic stability were verified by X-ray powder diffraction and thermogravimetry, respectively, in combination with differential scanning calorimetry (DSC). The morphology of the composites was studied by scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis. The electrical conductivity of the composites measured by electrochemical impedance was studied as functions of temperature, oxygen vapor pressure, and the amount of silicon oxide (the dispersed additive). The sums of ion transference numbers were studied as a function of temperature by the EMF method; the ionic character of conduction in the composites was found. The composite-conductivity effect was found to occur in the studied system: additions of 30 mol % nanosized silica to neodymium tungstate increased the ionic conductivity by more than two orders of magnitude.
Since 2012 the territory of Moscow has increased by two times with the annexation of the Troitskii and Novomoskovskii administrative districts (TiNAO) into Moscow. Due to the fact that earlier this ...territory was part of the Moscow region, detailed studies of the ecological state of the soils were not carried out. In the period from 2019 to 2020, to assess the soil pollution with heavy metals of certain areas of New Moscow, both in forest areas and near man-made objects that are potential sources of pollution, samples were taken up to 10 cm deep and analyzed by X-ray fluorescence analysis for the content of V, Ni, Pb, Cu, and Zn. It was revealed that at present the surveyed areas are characterized by an acceptable level of pollution, no excess beyond the maximum permissible concentrations was detected. It is shown that anthropogenic activity contributes to soil pollution. It is recommended to conduct annual environmental monitoring for the purpose of early detection of pollution sources.
We investigate the effect of controlling large-scale, logarithmic-layer turbulent structures, which have a characteristic size and aspect ratio that scale with the distance from the wall. The aim is ...to quantify the effect of suppressing these structures while leaving the near-wall turbulent dynamics unaltered. By affecting only the logarithmic-layer structures, it might be possible to isolate their contribution to the drag from that of the other scales in the flow. We conduct direct numerical simulations of turbulent channel flows at friction Reynolds number ReT ?s 500-1000 and artificially remove certain streamwise and spanwise wavelengths of the wall-normal velocity across a range of heights. The wavelengths chosen depend on the target height (and size) of the structures that we wish to target. When these wavelengths are removed, we observe a positive, outward shift of the mean velocity profile above the target height, due to a local reduction in Reynolds shear stress, and a subsequent increase in viscous stress. Our preliminary results suggest that this shift in the mean velocity profile scales in outer units.
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