Runaway electron flows in magnetized coaxial gas diodes

This paper presents the experimental results on applying a strong magnetic field (B) to increase the uniformity and density of a picosecond runaway electron flow (RAEF) formed in an air coaxial diode with a tubular cathode. A uniform longitudinal field Bz allows to confine RAEF similarly to the electron beam in a magnetically insulated coaxial vacuum diode. Dependence of the spatial discreteness of RAEF emission and the transverse size of the emitting plasma regions on Bz has been demonstrated. For the cathode diameter of 8 mm, a current density was significantly increased from 40 A/cm2 (at Bz = const) to 100 A/cm2 by applying B-field with converging field lines. In the region of B maximum (5 T) the RAEF diameter was squeezed by ≈ 4 times.

Linear Morphometric Parameters of the Liver in Children and Adolescents according to Intravital Imaging Findings

The aim of the study is to define age and gender regularities of the linear morphometric parameters of the liver in children and adolescents on the basis of intravital imaging findings.Material and methods. The authors analyzed computed tomograms of the abdominal cavity in 75 children without visible pathology. All patients were divided into 4 groups depending on their age: early childhood, first childhood, second childhood, adolescence. The transverse, anteroposterior and vertical dimensions of the right and left hepatic lobes were investigated on 16-slice computed tomographs. The obtained findings were processed using variational statistical analysis, the mean value (M), standard error (m) and the statistical significance were defined using the Student's t-test.Results. There was a significant increase in the anteroposterior size of the right hepatic lobe in separate sections at different age periods. A statistical significance between the parameters of the anteroposterior size of the right hepatic lobe was registered in girls and boys within the following groups: on one section in the 2nd group of patients, on two sections in the 4th group of patients. A statistical significance between the parameters of the transverse size of the right hepatic lobe was registered on one section (ThXII) in the 2nd and 3rd groups, and on two (ThXI and LI) and three (ThXI, ThXII and LI) sections in the 3rd and 4th groups of girls and boys, respectively. A statistical significance between the parameters of the transverse size of the right hepatic lobe in girls and boys were recorded only in the 4th group on three sections (ThXI, ThXII and LI). The vertical size of the right hepatic lobe was significantly higher in the 2nd and 4th groups, and the differences in the parameters between girls and boys were noted only among adolescents. A significant increase in the anteroposterior size of the left hepatic lobe was registered only in girls of the 2nd and 3rd groups on two sections (ThXII and LI); a significant increase in the transverse size was only registered at the LI level in these groups of patients. A significant increase in the vertical size of the left hepatic lobe was only detected in girls of the first childhood compared with girls of the early childhood. No statistical significance was registered for any of the linear parameters of the left hepatic lobe between girls and boys of the same groups.Conclusion. Thus, there was a significant increase in the anteroposterior and transverse dimensions of the right hepatic lobe in separate sections and an increase in the vertical size between individual groups of the studied patients, as well as a statistical significance between girls and boys of the same group. A significant increase in the anteroposterior and transverse dimensions of the left hepatic lobe was detected only in girls of the 2nd and 3rd groups if compared with the girls of the 1st group. No significant differences were registered between girls and boys of the same groups for any of the linear parameters of the left hepatic lobe.

Emergence of transverse size in electric streamers

<p>The accurate determination of parameters of electric streamer propagation in air, such as their velocity, transverse size (radius) and the maximum field at the tip, is extremely important, e.g., for the studies of further lightning development and acceleration of electrons at the tip, which may lead to generation of x-rays. Relations between these parameters produce a family of streamer-shaped solutions, while the radius remains undetermined. We hypothesize that all these solutions are, in fact, valid solutions of hydrodynamic equations, but the physical radius emerges when one solution is selected by the condition of being maximally unstable, i.e., having the highest velocity.</p><p>Direct verification of this hypothesis by hydrodynamic simulations is complicated by the fact that the streamer length is one of the background conditions which determine its parameters, and in a propagating streamer the length is constantly changing. To circumvent this, we simulate a `steady-state' streamer, such that its length is kept constant by synchronizing the motion of the electrode to which it is attached. We show that the predicted maximally-unstable selected solution does, in fact, emerge in the infinite time limit of the simulation. We note, however, that we were yet unable to test the first part of the hypothesis, i.e. to produce the non-selected solutions in the predicted family, as they are quickly replaced by the selected one.</p><p>We present the calculated streamer parameter dependence on external uniform field and streamer length for an isolated streamer and streamers propagating parallel to each other. In the latter case, the field of neighboring streamers makes the streamer propagation independent of its length when it exceeds the inter-streamer distance. We draw parallels of this situation to the selected solution for a viscous Saffman-Taylor finger of infinite length in a narrow channel [Luque et al, 2008, doi:10.1103/PhysRevE.78.016206].</p><p>The practical interest of this work lies in reducing the complexity of streamer propagation modeling, by avoiding detailed simulation of the streamer head, if we can calculate the parameters by a simpler algorithm.</p>

Thin current sheets as key structures in space plasma

<p>Plasma structures with extremely small transverse size (named thin current sheets or TCSs) have been discovered and investigated by spacecraft observations in the Earth's magnetotail, then in other planetary magnetospheres and the solar wind. Their formation is related with complicated dynamic processes in collisionless space plasma near the magnetic reconnection regions. The proposed models describing TCSs in space plasma, based on the assumption of a quasi-adiabatic proton dynamics and magnetized electrons were successful. Various modifications of the initial equilibrium allowed describing such current sheets as the system of current sheets where the central sheet is supported by magnetized electron drifts, and the external sheets are supported by quasi-adiabatic protons and sometimes oxygen ions. Such current configurations are shown to have properties that are completely different from the well-known Harris model, particularly the multiscale structure, embedding and metastability. The structure and evolution of TCSs under the tearing mode as well as the related paradox of complete tearing mode stabilization in configurations with a nonzero normal magnetic field component is highlighted.</p><p>This work is supported by the Russian Science Foundation grant № 20-42-04418.</p>

Наноструктурирование при наклонном напылении алюминия

Formation of regular arrays of nanorods with high aspect ratio (length to transverse size) has been found in the process of Al thin film growth at oblique angle deposition on silicon substrate by the method of electron beam evaporation. It was found that the optimal conditions for nanostructuring are realized at the inclination angle larger than 80 degrees.

Measurement of the Transverse Size of the Eyeball by B-Scanning Using a Linear Probe

Purpose. To evaluate the feasibility of measuring the transverse size of the eyeball by B-scan with a linear probe in patients with horizontal strabismus. Material and Methods. The study included 56 children (56 eyes) aged 2 to 15 years with previously not operated horizontal strabismus. Two independent operators used B-scan method to measure the axial length (for comparison with A-scan data) and the transverse size of the eyeball according to the proposed method. The accuracy of measurements was estimated by calculating the reproducibility limit, and indirectly by the forecast accuracy of the software system STRABO, which used the obtained values of the transverse size of the eyeball for individual dosing operations. Results. The B-scan technique was developed for measuring the transverse size of the eyeball using a contact linear probe. The measurement reproducibility limit was 0.22 mm (95% confidence interval is 0.18–0.25 mm), which does not exceed 1% of the average transverse size of the eyeball (22.03 mm). The results of the operations confirmed the accuracy of the prediction by the software system STRABO, since the correct eye position was obtained within 6 months in all cases, excluding 4 patients in whom the second stage of the surgery was postponed. That gave an indirect confirmation of the measurement accuracy of the transverse size of the eyeball using the proposed technique. Conclusion. The proposed ultrasound B-scan technique with a linear contact probe provides high accuracy and reproducibility of measurements of the transverse size of the eyeball and can be used in pediatric ophthalmological practice for calculating surgical procedures for strabismus using the individual dosing software system STRABO. Key words: transverse size of the eyeball, axial length, ultrasound B-scan, linear probe, horizontal strabismus, dosing.

On the transverse size of hadrons at asymptotically high energies

We show that Gribov diffusion of the partons in the impact parameter plane, which leads to the square-root-of-logarithmic growth of the transverse size of the hadrons, can occur only simultaneously with a similar diffusion in the transverse-momentum space. At the same time, a restriction of the partons in the transverse momenta entails an increase in their propagation in the impact parameter plane. Ultimately this leads to a logarithmic growth of the transverse size of hadrons at asymptotically high energies.