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The publication deals with the results of archaeological research in 2019 of a number of sites near the village Rzhavets in the Spassk district of the Republic of Tatarstan. The first archaeological sites were discovered here by exploration study in 1961. In subsequent years only some sites of the Rzhavets group of sites were visited, no excavations were carried out on them. The excavations in 2019 were fulfilled due to the destruction of the cultural layer of sites by reason of natural and anthropogenic impact. Cultural strata and two pits of the settlement, presumably dating from the Bronze Age, have been found on the eroded coastline of the Rzhavets I settlement by excavation I with an area of 68 sq . m, in addition to deposits and objects of the modern village. These deposits were covered by a layer of the settlement of the Imenkovo culture, processed by the arable land of the second half of the XIX – first half of the XX centuries. On the Rzhavets V–VI settlement, the research was carried out by excavation I with an area of 160 sq. m. Here cultural strata was destroyed by long–term plowing of the XIX – early XXI centuries, just objects deepened into the virgin soil were preserved. They are represented by three household and two tar pits. Based on the analysis of the few finds and radiocarbon dating of charcoal samples from the filling in one of the pits, the existence of the settlement is dated by the authors back to the pre–Mongol period of Volga Bulgaria, namely to the XI-XII centuries. Thanks to research on sites in the central regions of Volga Bulgaria, the objects associated with the tar industry have been identified for the first time.

The publication deals with the results of archaeological studies at Balymery V settlement in 2019. The work was carried out in relation to the destruction of the site’s cultural layer by the branched ravine network of the left bank of the Volga river. The first archaeological excavations at Balymery V settlement were carried out in 1955 under the supervision of A.M. Efimova by the Kuibyshev archaeological expedition. Two excavations by A.M. Efimova allowed to identify hearths, economic, residential and “sacrificial” pits, and establish the existence of the settlement in the Imenkovo and Bolgar Pre-Mongol periods. In her opinion, settlement of the Volga Bolgars ceases to exist by the end of the 11th – early 12th centuries. The studies of 2019 made it possible to clarify the dating of the site. Based on study results, the development of the territory of Balymery V settlement began in the Imenkovo period (4th–7th cc.). In the Volga Bolgaria period, the territory of the Imenkovo settlement was developed as a result of economic activity and plowing. The existence period of the Volga Bolgars settlement was determined as the interval from the 11th (most likely, its second half) – mid-13th centuries as a result of the studies. After the Mongol conquest, the settlement continued to exist in the Ulus of Jochi’s formation period, as evidenced by the coins of the 1240s discovered both in the cultural layer and in one of the objects.

Experimental study of unsteady swirling flows generated by special diverters in closed toroidal channels with different curvatures was carried out. The formation of a swirling flow in a toroidal channel is crucially different from the case of a straight cylindrical channel. It essentially depends on the curvature and is hindered by its increasing. The complex dynamics of swirling flow tightly connects with the interaction of jets after the diverter. Measurements of flow velocity using tracer's tracks showed that the evolution of the toroidal component in torus with one diverter can be divided into two-time intervals with different power laws. The evolution of the poloidal component is rather characterized by one slope "-2/3". [ABSTRACT FROM AUTHOR]

Important role of helicity was theoretically predicted for the generation of large-scale magnetic fields and atmospheric vortices. Helicity can lead to a reduction of turbulent dissipation in the atmosphere or in a specific constrained flow, e.g. in pipe. We use the TomoPIV data (42 cube of grid points, resolution 0.84 mm) to measure 3D velocity field of turbulent swirling flows. We study spatial distribution of the mean and fluctuating components of energy and helicity. We find that helical turbulence excitation and decay along stream of the jet strongly depend on the inflow swirl. We observe spatial separation of turbulent flow with different sign of helicity while integrated values are conserves. It is shown that large scale swirling flow induces helicity at the small scales. Our results bring valuable materials for benchmark the modern numerical simulations with turbulent closure technique.

This work addresses the effect of travelling thermal waves applied at the fluid layer surface, on the formation of global flow structures in two-dimensional (2-D) and 3-D convective systems. For a broad range of Rayleigh numbers ($10^3\leq Ra \leq 10^7$) and thermal wave frequencies ($10^{-4}\leq \varOmega \leq 10^{0}$), we investigate flows with and without imposed mean temperature gradients. Our results confirm that the travelling thermal waves can cause zonal flows, i.e. strong mean horizontal flows. We show that the zonal flows in diffusion dominated regimes are driven purely by the Reynolds stresses and end up always travelling retrograde. In convection dominated regimes, however, mean flow advection, caused by tilted convection cells, becomes dominant. This generally leads to prograde directed mean zonal flows. By means of direct numerical simulations we validate theoretical predictions made for the diffusion dominated regime. Furthermore, we make use of the linear stability analysis and explain the existence of the tilted convection cell mode. Our extensive 3-D simulations support the results for 2-D flows and thus provide further evidence for the relevance of the findings for geophysical and astrophysical systems. [ABSTRACT FROM AUTHOR]

Values and linear fits of the published and improved current data, displayed over the MULTIMAG nominal voltage Uin. Erratum: Generating a tide-like flow in a cylindrical vessel by electromagnetic forcing [Phys. At low power and frequency, the values show the strongest bias of up to 30% at 1.845 A. Fortunately, the average difference of about 3% is small and does not change the qualitative results, especially for high currents where the tide-like flow is most clearly expressed. [Extracted from the article]

We show and compare the numerical and experimental results on the electromagnetic generation of a tide-like flow structure in a cylindrical vessel, which is filled with the eutectic liquid metal alloy GaInSn. Fields of various strengths and frequencies are applied to drive liquid metal flows. The impact of the field variations on amplitude and structure of the flow is investigated. The results represent the basis for a future Rayleigh–Bénard experiment, in which a modulated tide-like flow perturbation is expected to synchronize the typical sloshing mode of the large-scale circulation and the helicity oscillation connected with it. A similar entrainment mechanism might play a role in the synchronization of stellar dynamos by tidal forces. [ABSTRACT FROM AUTHOR]

Using direct numerical simulation of hydrodynamic turbulence with helicity forcing applied at all scales, a near-maximum helical turbulent state is obtained, with an inverse energy cascade at scales larger than the energy forcing scale and a forward helicity cascade at scales smaller than the energy forcing scale. In contrast to previous studies using decimated triads, our simulations contain all possible triads. By computing the shell-to-shell energy fluxes, we show that the inverse energy cascade results from weakly non-local interactions among homochiral triads. Varying the helicity injection range of scales leads to necessary conditions to obtain an inverse energy cascade. [ABSTRACT FROM AUTHOR]

Guided by the working hypothesis that the Schwabe cycle of solar activity is synchronized by the 11.07‐year alignment cycle of the tidally dominant planets Venus, Earth, and Jupiter, we reconsider the phase diagrams of sediment accumulation rates in Lake Holzmaar and of methanesulfonate data in the Greenland ice core Greenland Ice Sheet Project 2 (GISP2), which are available for the period 10000–9000 cal. BP. As some half‐cycle phase jumps appearing in the output signals are, very likely, artifacts of applying a biologically substantiated transfer function, the underlying solar input signal with a dominant 11.04‐year periodicity can be considered to be mainly phase‐coherent over the 1,000‐year period in the early Holocene. For more recent times, we show that the reintroduction of a hypothesized "lost cycle" at the beginning of the Dalton minimum would lead to a real phase jump. Similarly, by analyzing various series of 14C and 10Be data and comparing them with Schove's historical cycle maxima, we support the existence of another "lost cycle" around 1565, also connected with a real phase jump. Viewed synoptically, our results lend greater plausibility to the starting hypothesis of a tidally synchronized solar cycle, which at times can undergo phase jumps, although the competing explanation in terms of a nonlinear solar dynamo with increased coherence cannot be completely ruled out. [ABSTRACT FROM AUTHOR]

Background: Impedance cardiography (ICG) is an inexpensive, noninvasive technique for estimating hemodynamic parameters. ICG can be used to obtain the ejection fraction of the left atrium and to monitor systolic time intervals. Traditional ICG technique does not enable unambiguous detection of the left ventricle ejection time (LVET) and the time relationships between specific marker points.Objective: This work aims to approbate a new approach for ICG signal processing using wavelet transform (WT) and to investigate the possibilities of this approach for determination of the parameters which are related to the stroke volume (SV), in particular LVET.Methods: Thoracic tetrapolar polyrheocardiography method for simultaneous registration of ECG, ICG and phonocardiograms has been used. A control group consisted of eight healthy men aged 20-25 years. In addition, four patients with essential hypertension participated in the study. Wavelet representation of the ICG data produced local maxima in a two dimensional distribution of the wavelet coefficient. Each extremum point was characterized by the amplitude, scale and time, which determine SV.Results: LVET was defined as the scale corresponding to the E-wave maximum related to the systolic phase of the cardiac cycle. Also, we defined the initial systolic time interval (ISTI) as the time interval between R peak in the ECG and E-wave maximum on the wavelet plane. During functional test LVET and ISTI values defined by WT demonstrated a proper hemodynamic response to loading for the control group and patients with essential hypertension.Conclusion: The proposed approach demonstrates the ability of ICG-WT technique for adequate assessment of SV parameters, including cardiac time intervals. [ABSTRACT FROM AUTHOR]

Skin microvessels have proven to be a model to investigate the mechanisms of vascular disease; in particular, endothelial dysfunction. To analyze skin blood flow, high-resolution thermometry can be used because low-amplitude skin temperature oscillations are caused by changes in the tone of skin vessels. The aim of our study was to test the possibilities of wavelet analysis of skin temperature (WAST) for the diagnosis of impaired regulation of microvascular tone in patients with type 2 diabetes. A local heating functional test was used for the assessment of microvascular tone regulation. A control group consisted of healthy male and female volunteers (n = 5 each), aged 39.1 ± 5.3 years. A group of patients with type 2 diabetes comprised thirteen people, seven men and six women, aged 36 to 51 years old (43.2 ± 3.4 years). The diagnosis of diabetes was made according to the criteria of the World Health Organization (WHO). The mean disease duration was 7.36 ± 0.88 years. Skin temperature oscillations, reflecting intrinsic myogenic activity (0.05–0.14 Hz), neurogenic factors (0.02–0.05 Hz) and endothelial activity (0.0095–0.02 Hz) increase greatly during local heating for healthy subjects. In the group of patients with type 2 diabetes, no statistically significant differences in the amplitudes in the endothelial range were observed. Relative changes in the oscillation amplitudes in patients with type 2 diabetes were markedly lower compared to the control group. The latter indicates that the WAST method enables assessment of the state of vascular tone and the effects of mechanisms responsible for regulation of blood flow in the microvasculature. [ABSTRACT FROM AUTHOR]

The energy spectral density E(k), where k is the spatial wave number, is a well-known diagnostic of homogeneous turbulence and magnetohydrodynamic turbulence. However, in most of the curves plotted by different authors, some systematic kinks can be observed at k=9, 15, and 19. We claim that these kinks have no physical meaning and are in fact the signature of the method that is used to estimate E(k) from a three-dimensional spatial grid. In this paper we give another method in order to get rid of the spurious kinks and to estimate E(k) much more accurately. [ABSTRACT FROM AUTHOR]

Using one-dimensional models, we show that a helical magnetic field with an appropriate sign of helicity can compensate the Faraday depolarization resulting from the superposition of Faraday-rotated polarization planes from a spatially extended source. For radio emission from a helical magnetic field, the polarization as a function of the square of the wavelength becomes asymmetric with respect to zero. Mathematically speaking, the resulting emission occurs then either at observable or at unobservable (imaginary) wavelengths. We demonstrate that rotation measure (RM) synthesis allows for the reconstruction of the underlying Faraday dispersion function in the former case, but not in the latter. The presence of positive magnetic helicity can thus be detected by observing positive RM in highly polarized regions in the sky and negative RM in weakly polarized regions. Conversely, negative magnetic helicity can be detected by observing negative RM in highly polarized regions and positive RM in weakly polarized regions. The simultaneous presence of two magnetic constituents with opposite signs of helicity is shown to possess signatures that can be quantified through polarization peaks at specific wavelengths and the gradient of the phase of the Faraday dispersion function. Similar polarization peaks can tentatively also be identified for the bi-helical magnetic fields that are generated self-consistently by a dynamo from helically forced turbulence, even though the magnetic energy spectrum is then continuous. Finally, we discuss the possibility of detecting magnetic fields with helical and non-helical properties in external galaxies using the Square Kilometre Array. [ABSTRACT FROM AUTHOR]

We discuss inverse problem of detection turbulence magnetic field helical properties using radio survey observations statistics. In this paper, we present principal solution which connects magnetic helicity and correlation between Faraday rotation measure and polarization degree of radio synchrotron emission. The effect of depolarization plays the main role in this problem and allows to detect magnetic helicity for certain frequency range of observable radio emission. We show that the proposed method is mainly sensitive to a large-scale magnetic field component. [ABSTRACT FROM PUBLISHER]

A turbulent screw flow (with Reynolds number exceeding 106) is generated by the sudden stop of a toroidal channel. The working fluid is a gallium alloy and velocity measurements are performed using a dual-axis potential probe. We describe the onset of motion, the development of strongly anisotropic fluctuations, and the final homogenization and decay of turbulence. Our observations are relevant for the relaxation of anisotropic turbulence; they are also in agreement with measurements of magnetohydrodynamic induction processes in this type of flow. [ABSTRACT FROM AUTHOR]

The Hall effect occurs in strongly magnetized conductive media and results in non-dissipative currents perpendicular to the electric field. We discuss its influence on the magnetic field dynamics ignoring fluid motion and ambipolar diffusion. The magnetic field evolution can then be basically similar to that of the velocity field in hydrodynamic turbulence resulting in a magnetic turbulence. Shell models for the induction equation with Hall effect are constructed on the basis of the conservation of magnetic energy and helicity in the dissipation-free limit. Numerical simulations of these models indicate that a magnetic energy cascade does occur, but the time behaviour and spatial spectrum of the magnetic field are very different from those of the velocity in shell models of hydrodynamic turbulence. [ABSTRACT FROM AUTHOR]

We investigate the dynamo problem in the limit of small magnetic Prandtl number ( Pm ) using a shell model of magnetohydrodynamic turbulence. The model is designed to satisfy conservation laws of total energy, cross helicity and magnetic helicity in the limit of inviscid fluid and null magnetic diffusivity. The forcing is chosen to have a constant injection rate of energy and no injection of kinetic helicity nor cross helicity. We find that the value of the critical magnetic Reynolds number ( Rm ) saturates in the limit of small Pm . Above the dynamo threshold we study the saturated regime versus Rm and Pm . In the case of equipartition, we find Kolmogorov spectra for both kinetic and magnetic energies except for wave numbers just below the resistive scale. Finally the ratio of both dissipation scales (viscous to resistive) evolves as Pm -3/4 for Pm [ABSTRACT FROM AUTHOR]

In an experiment in the Institute of Continuous Media Mechanics in Perm (Russia) a non-stationary screw dynamo is intended to be realized with a helical flow of liquid sodium in a torus. The flow is necessarily turbulent, that is, may be considered as a mean flow and a superimposed turbulence. In this study, the induction processes of the turbulence are investigated within the framework of mean-field electrodynamics. They imply, of course, a part which leads to an enhanced dissipation of the mean magnetic field. As a consequence of the helical mean flow there are also helical structures in the turbulence. They lead to some kind of α-effect, which might basically support the screw dynamo. The peculiarity of this α-effect explains measurements made at a smaller version of the device envisaged for the dynamo experiment. The helical structures of the turbulence lead also to other effects, which in combination with a rotational shear are potentially capable of dynamo action. A part of them can basically support the screw dynamo. Under the conditions of the experiment all induction effects of the turbulence prove to be rather weak in comparison to that of the main flow. Numerical solutions of the mean-field induction equation show that all the induction effects of the turbulence together let the screw dynamo threshold slightly, at most by a few percent, rise. The numerical results also give some insights into the action of the individual induction effects of the turbulence. [ABSTRACT FROM AUTHOR]

We present a concept for using long-wavelength broadband radio continuum observations of spiral galaxies to isolate magnetic structures that were only previously accessible from short-wavelength observations. The approach is based on combining the RM Synthesis technique with the 2D continuous wavelet transform. Wavelet analysis helps to isolate and recognize small-scale structures which are produced by Faraday dispersion. We find that these structures can trace galactic magnetic arms as illustrated by the case of the galaxy NGC 6946 observed at λ = 17 − 22 cm. We support this interpretation through the analysis of a synthetic observation obtained using a realistic model of a galactic magnetic field. [ABSTRACT FROM AUTHOR]

We calculate the relative magnitudes of the fluctuations in total synchrotron intensity in the interstellar medium, both from observations and from theory under various assumptions about the correlation or anticorrelation between cosmic rays and interstellar magnetic fields. The results are inconsistent with local energy equipartition between cosmic rays and magnetic fields. The distribution of cosmic rays must be rather uniform at scales of order 1 kpc, whereas interstellar magnetic fields vary at much smaller scales. [ABSTRACT FROM PUBLISHER]

The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest, for the first time, a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore, the energy is accumulated and redistributed so that the efficiency of nonlinear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum. [ABSTRACT FROM AUTHOR]

We solve the Navier-Stokes equations with two simultaneous forcings. One forcing is applied at a given large scale and it injects energy. The other forcing is applied at all scales belonging to the inertial range and it injects helicity. In this way we can vary the degree of turbulence helicity from nonhelical to maximally helical. We find that increasing the rate of helicity injection does not change the energy flux. On the other hand, the level of total energy is strongly increased and the energy spectrum gets steeper. The energy spectrum spans from a Kolmogorov scaling law k-5/3 for a nonhelical turbulence, to a non-Kolmogorov scaling law k-7/3 for a maximally helical turbulence. In the latter case we find that the characteristic time of the turbulence is not the turnover time but a time based on the helicity injection rate. We also analyze the results in terms of helical modes decomposition. For a maximally helical turbulence one type of helical mode is found to be much more energetic than the other one, by several orders of magnitude. The energy cascade of the most energetic type of helical mode results from the sum of two fluxes. One flux is negative and can be understood in terms of a decimated model. This negative flux, however, is not sufficient to lead an inverse energy cascade. Indeed, the other flux involving the least energetic type of helical mode is positive and the largest. The least energetic type of helical mode is then essential and cannot be neglected. [ABSTRACT FROM AUTHOR]

The free decay of a strong flow of liquid sodium (at Reynolds number defined via the maximal mean velocity and the radius of the channel cross section up to Re &ap; 3 × 106 and the corresponding magnetic Reynolds number up to Rm &ap; 30) generated by the sudden stop of a rapidly rotating toroidal channel is studied experimentally. The toroidal and poloidal components of velocity are measured using a potential probe. We describe the onset of motion, the evolution of strongly anisotropic fluctuations, and the homogenization and decay of turbulence in the final period. We analyze the statistical characteristics of velocity fields in relation to the behavior of effective magnetic diffusivity estimated from measurements of the phase shift between the induced and applied magnetic fields. For the late (self-similar) decay of turbulent flow, turbulent viscosity is shown to be dependent on the root-mean-square velocity pulsations and can be expressed as νt ∼ νRe1,3. The behavior of turbulent magnetic diffusivity depends on the magnetic Reynolds number defined in terms of the root-mean-square velocity pulsations. At low magnetic Reynolds numbers (Rmrms < 1), turbulent magnetic diffusivity grows rapidly with increasing velocity pulsations (ηt ∼ ηRm2rms). If the magnetic Reynolds number exceeds unity, the behavior of turbulent magnetic diffusivity becomes similar to the behavior of turbulent viscosity. The highest values of turbulent magnetic diffusivity are achieved at the end of braking, which corresponds to the transient stage oi' a strongly anisotropic turbulent flow in which the poloidal velocity oscillations prevail. [ABSTRACT FROM AUTHOR]

The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest, for the first time, a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore, the energy is accumulated and redistributed so that the efficiency of nonlinear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum.

The first direct measurements of effective magnetic diffusivity in turbulent flow of electroconductive fluids (the so-called β effect) under the magnetic Reynolds number Rm≫1 are reported. The measurements are performed in a nonstationary turbulent flow of liquid sodium, generated in a closed toroidal channel. The peak level of the Reynolds number reached Re≈3×10(6), which corresponds to the magnetic Reynolds number Rm≈30. The magnetic diffusivity of the liquid metal was determined by measuring the phase shift between the induced and the applied magnetic fields. The maximal deviation of magnetic diffusivity from its laminar value reaches about 50%.

A phenomenology of isotropic magnetohydrodynamic (MHD) turbulence subject to both rotation and applied magnetic field is presented. It is assumed that the triple correlation decay time is the shortest between the eddy turn-over time and the ones associated to the rotating frequency and the Alfvén wave period. For Pm=1 it leads to four kinds of piecewise spectra, depending on four parameters: injection rate of energy, magnetic diffusivity, rotation rate, and applied field. With a shell model of MHD turbulence (including rotation and applied magnetic field), spectra for Pm ≤ 1 are presented, together with the ratio between magnetic and viscous dissipations.

We demonstrate that flows of conducting fluid along a Möbius strip and related surfaces are hydromagnetic dynamos, i.e., they can produce an exponentially growing magnetic field from an infinitesimal seed. The critical magnetic Reynolds number in one of our models is as low as about 16. Together with other attractive features, this makes this flow an interesting candidate for a laboratory dynamo experiment.

The evolution of the large-scale magnetic field in a turbulent flow of conducting fluid is considered in the framework of a multiscale alpha2-dynamo model, which includes the poloidal and the toroidal components for the large-scale magnetic field and a shell model for the small-scale magnetohydrodynamical turbulence. The conjugation of the mean-field description for the large-scale field and the shell formalism for the small-scale turbulence is based on strict conformity to the conservation laws. The model displays a substantial magnetic contribution to the alpha effect. It was shown that a large-scale magnetic field can be generated by current helicity even solely. The alpha quenching and the role of the magnetic Prandtl number (Pm) are studied. We have determined the dynamic nature of the saturation mechanism of dynamo action. Any simultaneous cross correlation of alpha and large-scale magnetic field energy EB is negligible, whereas coupling between alpha and EB becomes substantial for moderate time lags. An unexpected result is the behavior of the large-scale magnetic energy with variation of the magnetic Prandtl number. Diminishing of Pm does not have an inevitable ill effect on the magnetic field generation. The most efficient large-scale dynamo operates under relatively low Prandtl numbers--then the small-scale dynamo is suppressed and the decrease of Pm can lead even to superequipartition of the large-scale magnetic field (i.e., EB>Eu). In contrast, the growth of Pm does not promote the large-scale magnetic field generation. A growing counteraction of the magnetic alpha effect reduces the level of mean large-scale magnetic energy at the saturated state.

The mean electromotive force caused by turbulence of an electrically conducting fluid, which plays a central part in mean-field electrodynamics, is calculated for a rotating fluid. Going beyond most of the investigations on this topic, an additional mean motion in the rotating frame is taken into account. One motivation for our investigation originates from a planned laboratory experiment with a Ponomarenko-type dynamo. In view of this application the second-order correlation approximation is used. The investigation is of high interest in astrophysical context, too. Some contributions to the mean electromotive are revealed which have not been considered so far, in particular contributions to the effect and related effects due to the gradient of the mean velocity. Their relevance for dynamo processes is discussed. In a forthcoming paper the results reported here will be specified to the situation in the laboratory and partially compared with experimental findings.

The kinematic dynamo problem is investigated for the flow of a conducting fluid in a cylindrical, periodic tube with conducting walls. The methods used are an eigenvalue analysis of the steady regime, and the three-dimensional solution of the time-dependent induction equation. The configuration and parameters considered here are close to those of a dynamo experiment planned in Perm, which will use a torus-shaped channel. We find growth of an initial magnetic field by more than three orders of magnitude. A marked field growth can be obtained if the braking time is less than 0.2 s and only one diverter is used in the channel. The structure of the seed field has a strong impact on the field amplification factor. Generation properties can be improved by adding ferromagnetic particles to the fluid in order to increase its relative permeability, but this will not be necessary for the success of the dynamo experiment. For higher magnetic Reynolds numbers, the nontrivial evolution of different magnetic modes limits the value of simple "optimistic" and "pessimistic" estimates.