Strong non-Oberbeck–Boussinesq (OB) effects in turbulent convection were investigated experimentally in SF6 in the vicinity of its gas-liquid critical point (CP). The temperature and density dependencies of the thermodynamic and kinetic properties of SF6 near its CP and at the average critical density lead to strong but symmetric vertical variations of the main physical properties, which enter into the control parameters of turbulent convection. This produces an up-down symmetry in the temperature drops across the upper and lower half of the cell, while the temperature in the middle of the cell remains equal to the average value. Thus, in spite of the strong variations of the fluid properties across the cell height, the up-down symmetry remains like in the OB case. The distinctive feature of the symmetric non-OB turbulent convection is that the heat transport scales with the Rayleigh number Ra like in the OB turbulent convection. At the same time, it shows a much stronger dependence on the Prandtl number Pr. We singled out the influence of the non-OB effect on the heat transport and found that, for the same Pr, an eightfold larger non-OB effect does not alter either the value of the Nusselt number, Nu, nor its scaling with respect to the Rayleigh number, Nu∝Raγ. The conclusion is that the strong symmetric non-OB effect by itself is not responsible for the strong Pr dependence of the heat transport near CP. The possible source of this Pr dependence is the strongly enhanced isothermal compressibility in the vicinity of CP, which can affect the dynamics of plumes and so the heat transport close to the CP, and manifests itself in a dependence of Nu on Pr much steeper than in the OB case.

We report the experimental studies of the statistical and scaling properties of the fully developed turbulent regime in von Karman swirling flow between counter-rotating disks with and without blades using the only global measurements of the spatially averaged torque Γ and pressure p fluctuations in water and water-sugar solutions of different viscosities in the same cell geometry. We show that for all fluids under investigation probability distribution functions (PDFs) of the torque fluctuations δΓ/Γrms are Gaussian in both the laminar and turbulent regimes and for the both types of the stirrers. On the contrary, PDFs of the pressure fluctuations change from Gaussian in the laminar regime into the skewed shape with the exponential tails toward low-pressure events for both the entrainment methods. Both the friction coefficient Cf and normalized rms of the pressure fluctuations Cp are independent of Re in the fully developed turbulent regime for all fluids under study and found in a good quantitative agreement with the previous results. We also observe that the internal flow variables such as the normalized torque \documentclass[12pt]{minimal}\begin{document}$\bar{\Gamma }/Vp_{rms}$\end{document}Γ¯/Vprms versus the “internal” Reynolds number Rerms = (prms/ρ)1/2Rρ/η instead of the global variables Cf, Cp versus Re show sharp transition into the well developed turbulent regime. We find that the scaling exponents of the fundamental characteristics based only on Γ and p measurements in the range of fully developed turbulent flow, namely, the integral, Taylor, and Kolmogorov dissipation lengths, as well as the Taylor-based Reynolds number Rλ, are in rather fair agreement with the predictions. We would like to emphasize that scaling of the main turbulent parameters Rλ, λ, ηd obtained via the global variables is a very non-trivial result. It is not obvious that measurements based on the global quantities will provide the predicted scaling relations. The result on such scaling obtained previously strongly disagrees with the scaling predictions. Indeed, both \documentclass[12pt]{minimal}\begin{document}$\bar{\Gamma }$\end{document}Γ¯ and prms are averaged over the cell volume as well as all spatial scales, whereas the swirling flow is neither isotropic nor homogeneous. So the global variables being averaged over all spatial scales get contributions from the scales larger and smaller than those from the inertial range of scales. And finally, the normalized characteristic frequencies fp/frot found in both the torque and pressure frequency power spectra in the fully developed turbulent regime have close values, are independent of Re, and associated with either the rotation or oscillation frequency of the main vortex.

Background: Transcranial magnetic stimulation (TMS) is a rapidly expanding technology utilized in research and neuropsychiatric treatments. Yet, conventional TMS configurations affect primarily neurons that are aligned parallel to the induced electric field by a fixed coil, making the activation orientationspecific. A novel method termed rotational field TMS (rfTMS), where two orthogonal coils are operated with a 90 phase shift, produces rotation of the electric field vector over almost a complete cycle, and may stimulate larger portion of the neuronal population within a given brain area. Objective: To compare the physiological effects of rfTMS and conventional unidirectional TMS (udTMS) in the motor cortex. Methods: Hand and leg resting motor thresholds (rMT), and motor evoked potential (MEP) amplitudes and latencies (at 120% of rMT), were measured using a dual-coil array based on the H7-coil, in 8 healthy volunteers following stimulation at different orientations of either udTMS or rfTMS. Results: For both target areas rfTMS produced significantly lower rMTs and much higher MEPs than those induced by udTMS, for comparable induced electric field amplitude. Both hand and leg rMTs were orientation-dependent. Conclusions: rfTMS induces stronger physiologic effects in targeted brain regions at significantly lower intensities. Importantly, given the activation of a much larger population of neurons within a certain brain area, repeated application of rfTMS may induce different neuroplastic effects in neural networks, opening novel research and clinical opportunities.

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A neuron will fire an action potential when its membrane potential exceeds a certain threshold. In typical activity of the brain, this occurs as a result of chemical inputs to its synapses. However, neurons can also be excited by an imposed electric field. In particular, recent clinical applications activate neurons by creating an electric field externally. It is therefore of interest to investigate how the neuron responds to the external field and what causes the action potential. Fortunately, precise and controlled application of an external electric field is possible for embryonic neuronal cells that are excised, dissociated and grown in cultures. This allows the investigation of these questions in a highly reproducible system. In this paper some of the techniques used for controlled application of external electric field on neuronal cultures are reviewed. The networks can be either one dimensional, i.e. patterned in linear forms or allowed to grow on the whole plane of the substrate, and thus two dimensional. Furthermore, the excitation can be created by the direct application of electric field via electrodes immersed in the fluid (bath electrodes) or by inducing the electric field using the remote creation of magnetic pulses.