Recent MMS observations have discovered electron‐scale super‐thin current sheets (STCSs) with a partial electron demagnetization, which distinguishes them from the ion‐scale TCSs traditionally ...observed by the Cluster mission. Our investigation focuses on the dynamics of STCSs and reveals new aspects influencing their stability. We use the earlier proposed 1D collisionless self‐consistent equilibrium STCS model and show that the free parameters of this model, such as the relative part of demagnetized electrons, their flow velocity and the pressure anisotropy of magnetized electron population, can contribute to the development of tearing instability. With the growth of these parameters, the STCS becomes thinner, which leads to the accumulation excess of a free energy. Stabilizing energy decreases due to the increase of a relative part of demagnetized electrons. Thus, demagnetized electrons in STCSs can provide the development of fast and short‐wavelength electron tearing modes.
Plain Language Summary
Recent MMS observations in space plasma have discovered extremely thin current sheets having the transverse electron scales. These sheets are different from the thicker current sheets usually observed by the Cluster mission. The electrons in these sheets are partially demagnetized, that is, they are not affected by magnetic fields. The presence of demagnetized electrons can lead to the development of a fast tearing mode with the shorter wavelengths in comparison with corresponding modes observed in the thicker current configurations. Our investigation focuses on the understanding of the dynamics of these super‐thin current sheets and the identification of factors that influence their stability.
Key Points
Demagnetized electrons supporting STCSs can initiate the fast electron tearing instability at short wavelengths
Fast growth of small‐scale magnetic perturbation results in the formation of magnetic islands, that is, plasmoids
Development of fast tearing mode is followed by strong inductive electric fields
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2.
Current sheets in planetary magnetospheres Zelenyi, Lev; Malova, Helmi; Grigorenko, Elena ...
Plasma physics and controlled fusion,
05/2019, Volume:
61, Issue:
5
Journal Article
Peer reviewed
Open access
In this article we aim to highlight the problems related to the structure and stability of the comparatively thin current sheets that were relatively recently discovered by space missions in the ...magnetospheres of the Earth and planets, as well as in the solar wind. These magnetoplasma structures are universal in collisionless cosmic plasmas and can play a key role in the processes of storage and release of energy in the space environment. The development of a self-consistent theory for these sheets in the Earth's magnetosphere, where they were first discovered, has a long and dramatic history. Solution of the problem of the thin current sheet structure and stability become possible in the framework of a kinetic quasi-adiabatic approach required to explain their embedding and metastability properties. It was found that the structure and stability of current structures are completely determined by the nonlinear dynamics of plasma particles. Theoretical models have been developed to predict many properties of these structures and interpret many experimental observations in planetary magnetospheres and the heliosphere.
With wavelength tunability, free-electron lasers (FELs) are well-suited for generating orbital angular momentum (OAM) beams in a wide photon energy range. We report here the first experimental ...demonstration of OAM beam generation using an oscillator FEL with the tens of picosecond pulse duration. Lasing around 458 nm, we have produced the four lowest orders of superposed Laguerre-Gaussian beams using a very long FEL resonator of 53.73 m. The produced beams have good beam quality, excellent stability, and substantial average power. We have also developed a pulsed operation mode for these beams with a highly reproducible temporal structure for a range of repetition rate of 1-30 Hz. This development can be extended to short wavelengths, for example to x-rays using a future x-ray FEL oscillator. The OAM operation of such a storage-ring FEL also paves the way for the generation of OAM gamma-ray beams via inverse Compton scattering.
Glia selectively approach synapses on thin dendritic spines Medvedev, Nikolai; Popov, Victor; Henneberger, Christian ...
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
10/2014, Volume:
369, Issue:
1654
Journal Article
Peer reviewed
Open access
This paper examines the relationship between the morphological modality of 189 dendritic spines and the surrounding astroglia using full three-dimensional reconstructions of neuropil fragments. An ...integrative measure of three-dimensional glial coverage confirms that thin spine postsynaptic densities are more tightly surrounded by glia. This distinction suggests that diffusion-dependent synapse–glia communication near ‘learning’ synapses (associated with thin spines) could be stronger than that near ‘memory’ synapses (associated with larger spines).
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This study conducted in an EFL setting investigates students’ perception of the thesis proposal presentation in an online format due to safety concerns during the Covid-19 pandemic. Fifty-five ...students aged 20-22 years old, level B2-C1 in English, in their fourth year of a Business Informatics Bachelor’s programme at HSE University, Moscow, were surveyed regarding their end-of-course assessment experience, which involved a Skype online presentation, rather than the usual face-to-face presentation. Data were collected using a researcher-made questionnaire consisted of 3 sections and 12 items. A mixed-method approach using quantitative and qualitative data was employed. The findings indicate that emergency transition to the new format did not affect students’ satisfaction or results of the presentation. Overall, students were more than satisfied with the online format, and the results were similar, if not better, than in previous years. To minimise the disadvantages of this format, recommendations for teachers and students were offered. This study might offer new insight on the most appropriate and beneficial oral testing system for students and staff.
Polarized gamma-ray beams are a precise and selective probe for studying fundamental questions about nuclear structure and hadron properties. Improvements to this probe require new experimental ...approaches that can produce high-flux gamma-ray beams with easily switchable pure polarization states. Here, we report an optics-free method to precisely control the polarization of a Compton gamma-ray beam. Using a free-electron laser (FEL) oscillator with two helical undulator magnets of opposite helicities, we have produced a linearly polarized FEL beam with a variable polarization direction and an unprecedented degree of linear polarization, PLin = 0.997. With this FEL as a photon drive, we are able to generate Compton gamma-ray beams having either left/right-circular polarization or rotatable linear polarization. The linearly polarized gamma-ray beam has been characterized and shows PLin = 0.97. This demonstrated polarization control technique is well suited for high-flux gamma-ray production with any level of FEL power.
We synthesize colloidal HgSe quantum dots and characterize their nonlinear refraction and nonlinear absorption using a Nd:YAG laser and its second harmonic. The 7.5 nm quantum dots were synthesized ...using the hot-injection method. The nonlinear absorption (
β
= 9×10
−7
cm W
-1
) and negative nonlinear refraction (
γ
= -5×10
−12
cm
2
W
-1
) coefficients of colloidal quantum dots were determined using the 10 ns, 532 nm laser radiation. The joint influence of above processes was realized at a higher intensity of probe pulses. In the case of 10 ns, 1064 nm radiation, only negative nonlinear refraction dominated during z-scans of these quantum dots. The studies of optical limiting using two laser sources demonstrated the effectiveness of this process at 532 nm. The role of nonlinear scattering is analyzed. We discuss the mechanisms responsible for the nonlinear refraction processes in colloidal HgSe quantum dots.
The process of innovative transformations at an industrial enterprise is studied. The main features of the introduction of innovations into the production process are considered. A general model for ...carrying out innovative transformations at an industrial enterprise with a large share of high-tech production is proposed. The main elements of the proposed three-dimensional model include the basic processes of change, project and innovation management. Additionally, the models include such processes as: increasing innovation potential, improving internal communications through the introduction of digital technologies, increasing the efficiency of the production process by improving the production system. The applicability of the proposed model under real production conditions is investigated on the basis of Sorbent JSC, and the impact of the implementation of the innovation process on the overall economic efficiency of the enterprise is assessed.
AbstractManganese mud (MnM) is a manganese oxide petal-like nanostructured precipitate that accumulates on the inner surface of pipes transferring reclaimed effluent from the Shafdan soil aquifer ...treatment system to irrigation fields in southern Israel. It was found that Mn2+ adsorbs on the MnM sediment, and under aerobic conditions, rapid Mn(II) oxidation takes place. The MnM exhibited superior Mn(II) adsorption capacity compared to other commercially available manganese oxide catalysts. A filter loaded with anthracite-supported MnM was developed and used as a highly efficient, reagentless catalyst for the continuous oxidative removal of dissolved Mn. A 10–13 m3·h−1 pilot plant was constructed for Mn removal from Mn-rich effluent by atmospheric oxygen oxidation. The system operated continuously for more than two years with minimal maintenance, without oxidative regeneration. No ripening period was required, and the fixed bed exhibits exceptionally high catalytic efficiency. The proposed filter is superior to synthetic supported manganese oxide reactors because it does not require periodic regeneration by strong oxidizers; it is superior to filtration units for manganese removal because it does not require ripening time. A possible explanation for the superior catalytic activity based on the delicate, two-dimensional structure of MnM is presented.
Acceleration of single‐ and multicharged oxygen ions in the perturbed Earth's magnetotail is investigated as the possible source of energetic heavy ions in the ring current. The numerical model is ...developed that allows evaluating the acceleration of oxygen ions O+‐O+8 in two possible scenarios of characteristic perturbations: (A) passage of multiple dipolarization fronts in the magnetotail; (B) passage of fronts followed by electromagnetic turbulence. It is shown that acceleration processes depend on particle charges as well as characteristic time scales of induced electric field variations. Maximum energies gained by oxygen ions correlate with values of their charges. Our simulations show that all kinds of single‐ and multiply charged heavy particles can be efficiently accelerated during multiple dipolarizations processes of the type (A) from initial energies 12 keV to maximum energies about several MeV. The gain of energies of heavy ions under the (B) scenario of magnetospheric perturbations is about 10% higher than in (A) scenario. The shapes of obtained in the model energy spectra were shown to be in agreement with experimental spectra in the range of L‐shells corresponding to ring/radiation belts. Therefore, we conclude that the Earth's magnetotail can play the role of the depot where oxygen ions of both ionospheric and solar wind origin can be effectively accelerated during magnetic substorms to energies about several MeV and then populate the ring current and radiation belts of the Earth.
Key Points
Mechanisms of multicharged oxygen ion acceleration in the Earth's magnetosphere are investigated
Simulation results have been compared with experimental energy spectra of oxygen ions in the ring current and proton radiation belt
It is shown that substorm dynamics of the magnetotail contributes to the transfer of accelerated ions in the radiation belts
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