Nonaxisymmetric MHD instabilities of Chandrasekhar states in Taylor-Couette geometry

We consider axially periodic Taylor-Couette geometry with insulating boundary conditions. The imposed basic states are so-called Chandrasekhar states, where the azimuthal flow $U_\phi$ and magnetic field $B_\phi$ have the same radial profiles. Mainly three particular profiles are considered: the Rayleigh limit, quasi-Keplerian, and solid-body rotation. In each case we begin by computing linear instability curves and their dependence on the magnetic Prandtl number Pm. For the azimuthal wavenumber m=1 modes, the instability curves always scale with the Reynolds number and the Hartmann number. For sufficiently small Pm these modes therefore only become unstable for magnetic Mach numbers less than unity, and are thus not relevant for most astrophysical applications. However, modes with m>10 can behave very differently. For sufficiently flat profiles, they scale with the magnetic Reynolds number and the Lundquist number, thereby allowing instability also for the large magnetic Mach numbers of astrophysical objects. We further compute fully nonlinear, three-dimensional equilibration of these instabilities, and investigate how the energy is distributed among the azimuthal (m) and axial (k) wavenumbers. In comparison spectra become steeper for large m, reflecting the smoothing action of shear. On the other hand kinetic and magnetic energy spectra exhibit similar behavior: if several azimuthal modes are already linearly unstable they are relatively flat, but for the rigidly rotating case where m=1 is the only unstable mode they are so steep that neither Kolmogorov nor Iroshnikov-Kraichnan spectra fit the results. The total magnetic energy exceeds the kinetic energy only for large magnetic Reynolds numbers Rm>100.Comment: 12 pages, 14 figures, submitted to Ap

Transition to magnetorotational turbulence in Taylor-Couette flow with imposed azimuthal magnetic field

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 experi-ments 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 ex-periment 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

Dynamo action in a quasi-Keplerian Taylor-Couette flow

We numerically compute the flow of an electrically conducting fluid in a Taylor-Couette geometry where the rotation rates of the inner and outer cylinders satisfy \Omega_o/\Omega_i=(r_o/r_i)-3/2. In this quasi-Keplerian regime a non-magnetic system would be Rayleigh-stable for all Reynolds numbers Re, and the resulting purely azimuthal flow incapable of kinematic dynamo action for all magnetic Reynolds numbers Rm. For Re=10^4 and Rm=10^5 we demonstrate the existence of a finite-amplitude dynamo, whereby a suitable initial condition yields mutually sustaining turbulence and magnetic fields, even though neither could exist without the other. This dynamo solution results in significantly increased outward angular momentum transport, with the bulk of the transport being by Maxwell rather than Reynolds stresses

Karelian Seaside in a Linguistic Context

The current state of the study of Russian dialects in Karelian Seaside is analyzed, the territory of the studied region, which coincides with the boundaries of the dialectal division of the Russian language in 1915 is indicated. It is shown that the exclusion of Karelian Seaside from the dialectal division of 1965, which was an indirect reason for the lack of proper research attention to this region is unjustified. An overview of linguistic works devoted to the study of various language levels (phonetic, grammatical, lexical) is presented. The review of dictionaries, including the vocabulary of Russian dialects of the Karelian Seaside, is carried out. The prospects and objectives of the study are determined. In particular, future research is associated with comparative work on the study of the preservation / change of linguistic phenomena at each level, including the lexical one, which is the most stable in its main core. It is primarily due to extralinguistic reasons. Particular attention is paid to the use of digital technologies when creating a textual database, tested on the materials of the Karelian Seaside. It is noted that the electronic resource will make it possible to constantly introduce new data into scientific circulation, connecting them to various aspects of research, both linguistic and broader humanitarian

Gas metallicity diagnostics in star-forming galaxies

Generally the gas metallicity in distant galaxies can only be inferred by using a few prominent emission lines. Various theoretical models have been used to predict the relationship between emission line fluxes and metallicity, suggesting that some line ratios can be used as diagnostics of the gas metallicity in galaxies. However, accurate empirical calibrations of these emission line flux ratios from real galaxy spectra spanning a wide metallicity range are still lacking. In this paper we provide such empirical calibrations by using the combination of two sets of spectroscopic data: one consisting of low-metallicity galaxies with a measurement of [OIII]4363, and the other one consisting of galaxies in the SDSS DR4 whose metallicity has been determined from various strong emission lines in their spectra. This combined data set constitutes the largest sample of galaxies with information on the gas metallicity available so far and spanning the widest metallicity range. Our empirical diagrams show that the line ratio [OIII]/[OII] is a useful tool to break the degeneracy in the R_23 parameter when no information on the [NII] line is available. The line ratio [NeIII]/[OII] also results to be a useful metallicity indicator for high-z galaxies. Finally, we compare these empirical relations with photoionization models. We find that the empirical R_23-metallicity sequence is strongly discrepant with respect to the trend expected by models with constant ionization parameter, which is interpreted as a consequence of a strong metallicity dependence of the average ionization parameter in galaxies. This result should warn about the use of theoretical models with constant ionization parameter to infer metallicities from observed line ratios. (abbreviated)Comment: 27 pages, 19 figures, Astronomy and Astrophysics, in press. (Replaced with the accepted version.

Genetically modified human umbilical cord blood mononuclear cells as potential stimulators of neuroregeneration in degenerative disorders of central nervous system

Gene-cell therapy is a new step for the treatment of different human disorders including central nervous system degenerative diseases. In this review we focused on the last challenges in the field of human umbilical cord blood mononuclear cells transplantation - An attempt to support neuronal cells survival and to stimulate the neuroregeneration. As a potential therapy for the treatment of neurodegenerative diseases we reviewed the latest advances in gene modification of human umbilical cord blood mononuclear cells as a novel tool for the effective delivery of neuroprotective factors and growth factors in the injured or degenerative areas of the central nervous system under pathological conditions. The main topic of this review is the potential therapy of the amyotrophic lateral sclerosis - The progressive neurodegenerative disorder affecting primarily upper and lower motoneurons - by using genetically modified human umbilical cord blood mononuclear cells. The results from the up-to-date experiments indicated the opportunity to obtain differentiated macrophages, endothelial cells, or astrocytes from the genetically modified human umbilical cord blood mononuclear cells after their transplantation in the mouse model of the amyotrophic lateral sclerosis. Taken together, these data build the high-capacity platform for the supporting of degenerating neurons, structural and functional recovery of the brain and spinal cord after trauma, ischemia and other neurodegenerative disorders. © Human stem cells institute, 2013

Selective opposition-like control of large-scale structures in wall-bounded turbulence

Abstract 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.</jats:p

On a possibility of inelasticity partial coefficient K sub gamma determination in pi C and pi Pb interactions at 10 to the 14th power eV (experiment PAMIR 1)

The investigation of hadron-nuclear interactions in Pamir experiment is carried out by means of X-ray emulsion chambers of two types: carbon (C) and lead (Pb). While comparing the results from the chambers of both types it was found a discrepancy in n sub h and E sub h(1)R values. The observed discrepancy in C and Pb chambers is connected with the difference in values of effective coefficients of energy transfer to the soft component K sub eff for C and Pb chambers