Narrow Layer Research Articles

Observation of Nongyrotropic Electron Distribution Across the Electron Diffusion Region in the Magnetotail Reconnection

AbstractUsing measurements by the Magnetospheric Multiscale spacecraft in the magnetotail, we studied electron distribution functions across an electron diffusion region. The dependence of the nongyrotropic distribution on the energy and vertical distance from the electron diffusion region midplane was revealed for the first time. The nongyrotropic distribution was observed everywhere except for an extremely narrow layer right at the electron diffusion region midplane. The energy of the nongyrotropic distribution increased with growth of the vertical distance from the midplane. For the electrons within certain energy range, they exhibited the nongyrotropic distribution at the distance further away from the midplane than that expected from the meandering motion. The correlation between the crescent‐shaped distribution with multiple stripes and the large Hall electric field was established. It appears that the measured nongyrotropic distribution and the crescent‐shaped distribution were caused by the meandering motion and the Hall electric field together.

Dynamics of Fast Electrons in an Inhomogeneous Plasma with Plasma Beam Instability

The results of numerical simulation of the one-dimensional propagation of fast electrons in a plasma with Langmuir turbulence are presented. The resonant interaction of fast electrons with Langmuir waves and Coulomb collisions with particles of the background plasma are taken into account. It is shown that an increase in plasma density along the direction of the propagation of the electron beam leads to the transformation of the Langmuir turbulence spectrum into a region of high phase velocities and “spreading” of the velocity distribution function of accelerated electrons. For a Gaussian electron beam with an energy of 30 keV at its peak and a characteristic scale of an increase in plasma density of 107 cm, the electron spectrum expands; some of the electrons are accelerated to 1.3 of their initial velocity. In addition, a narrow (~105 cm) layer with an increased turbulence level forms in the plasma. As the electrons move deeper into the plasma, Coulomb collisions restore the inverse over velocity part of the electron distribution function, which leads to the formation of a turbulent layer at a distance from the plasma boundary of ~107 cm–108 cm; however, the energy density of Langmuir turbulence in this layer is ~(10–6–10–7) of the plasma thermal energy.

Anatomical, Histological, and Histochemical Analyses of the Scent Glands of the Scorpion Mud Turtle (Kinosternon scorpioides scorpioides).

Fossil evidence suggests that scent glands are basal features of Testudines. However, we know little about the structure of these glands in the Brazilian Kinosternidae. In this study, we described the macroscopic anatomy, histology, and histochemistry of the scent glands of three males and three females of Kinosternon scorpioides scorpioides from the Marajó mesoregion, Pará State, Brazil. In all of the specimens analyzed, regardless of sex, we found four scent glands, including two axillary and two inguinal glands that were structurally similar to each other. Each gland consisted of a single holocrine secretory lobule, a large lumen surrounded by relatively thin glandular secretory epithelium, an adjacent narrow layer of loose connective tissue, and a thick layer of skeletal striated muscle tissue surrounded by a serous tunic. The secretory epithelium produced a characteristic malodorous yellowish substance that was passed via a single duct through a bone channel in the bridge connecting the carapace to the plastron and excreted through an outer pore in the plate of each respective gland. Histologically, the secretory epithelium presented cells with two types of secretory vacuoles. Type 1 vacuoles stained red were the largest and most frequently found, and stained positively with Periodic acid-Schiff (PAS), suggesting they contained glycoproteic complexes. Type 2 vacuoles were translucent, smaller in size and fewer in number, and negative for PAS staining. Because they are very primitive structures, scent glands must play important roles in the lives of chelonians, but their real function remains unknown. Several hypotheses suggest that they can act as protection against ectoparasites, as a repellent of predators, in addition to attracting mates and eliciting other pheromonal responses. In this study, all animals reacted by exuding malodorous substances when handled, as a form of defense. However, these are just assumptions that need to be clarified with additional studies on animal behavior. Anat Rec, 303:1489-1500, 2020. © 2019 American Association for Anatomy.

The interplay of an external torque and E×B structure formation in tokamak plasmas

The interplay between an external torque and spontaneously occurring mesoscale structures, known as staircases, is investigated. Gyrokinetic simulations show that the E × B shear connected with the external torque does not simply add to the shear of the mesoscale structures. A positive (negative) externally forced E × B shear leads to a broadening of the positive (negative) region of the staircase but does not significantly change the plateau value or the narrow zero shear layer. In consequence, while the space and time averaged shearing rate is enhanced by the external torque, there is little or no effect on the turbulent transport. This raises doubts about the importance of driven or intrinsic rotation as a means to improve plasma confinement close to the stability threshold.

Large Scale Distribution of Galaxies in The Field HS 47.5-22. I. Data Analysis Technique

We present the results of methodological works on automated analysis of the large scale distribution of galaxies. Selecting candidates for clusters and groups of galaxies was carried out using two complementary methods of determining the density contrast maps in the narrow layers of the three-dimensional large scale distribution of galaxies: the filtering algorithm with an adaptive core and the Voronoi tesselation. The developed algorithms were tested on 10 data sets of the MICE model catalog; additionally, we determined the statistical parameters of the obtained results (completeness, sample purity, etc.). The constructed density contrast maps were also used to determine voids.

Asymptotics of the Solution of a Differential Equation in a Saddle–Node Bifurcation

A second-order semilinear differential equation with slowly varying parameters is considered. With frozen parameters, the corresponding autonomous equation has fixed points: a saddle point and stable nodes. Upon deformation of the parameters, the saddle–node pair merges. An asymptotic solution near such a dynamic bifurcation is constructed. It is found that, in a narrow transition layer, the principal terms of the asymptotics are described by the Riccati and Kolmogorov–Petrovsky–Piskunov equations. An important result is finding the dragging out of the stability: the moment of disruption significantly shifts from the moment of bifurcation. The exact assertions are illustrated by the results of numerical experiments.

Geometric quantization of localized surface plasmons

Abstract We consider the quasi-static problem governing the localized surface plasmon modes and permittivity eigenvalues $\epsilon $ of smooth, arbitrarily shaped, axisymmetric inclusions. We develop an asymptotic theory for the dense part of the spectrum, i.e. close to the accumulation value $\epsilon =-1$ at which a flat interface supports surface plasmons; in this regime, the field oscillates rapidly along the surface and decays exponentially away from it on a comparable scale. With $\tau =-(\epsilon +1)$ as the small parameter, we develop a surface-ray description of the eigenfunctions in a narrow boundary layer about the interface; the fast phase variation, as well as the slowly varying amplitude and geometric phase, along the rays are determined as functions of the local geometry. We focus on modes varying at most moderately in the azimuthal direction, in which case the surface rays are meridian arcs that focus at the two poles. Asymptotically matching the diverging ray solutions with expansions valid in inner regions in the vicinities of the poles yields the quantization rule \begin{equation*}\frac{1}{\tau} \sim \frac{\pi n }{\varTheta}+\frac{1}{2}\left(\frac{\pi}{\varTheta}-1\right)+o(1),\end{equation*}where $n\gg 1$ is an integer and $\varTheta $ a geometric parameter given by the product of the inclusion length and the reciprocal average of its cross-sectional radius along its symmetry axis. For a sphere, $\varTheta =\pi $, whereby the formula returns the exact eigenvalues $\epsilon =-1-1/n$. We also demonstrate good agreement with exact solutions in the case of prolate spheroids.

Physics basis for the first ITER tungsten divertor

Abstract On the eve of component procurement, this paper discusses the present physics basis for the first ITER tungsten (W) divertor, beginning with a reminder of the key elements defining the overall design, and outlining relevant aspects of the Research Plan accompanying the new “staged approach” to ITER nuclear operations which fixes the overall divertor lifetime constraint. The principal focus is on the main design driver, steady state power fluxes in the DT phases, obtained from simulations using the 2-D SOLPS-4.3 and SOLPS-ITER plasma boundary codes, assuming the use of the low Z seeding impurities nitrogen (N) and neon (Ne). A new perspective on the simulation database is adopted, concentrating purely on the divertor physics aspects rather than on the core-edge integration, which has been studied extensively in the course of the divertor design evolution and is published elsewhere. Emphasis is placed on factors which may increase the peak steady state loads: divertor target shaping for component misalignment protection, the influence of fluid drifts, and the consequences of narrow scrape-off layer heat flux channels. All tend to push the divertor into an operating space at higher sub-divertor neutral pressure in order to remain at power flux densities acceptable for the target material. However, a revised criterion for the maximum tolerable loads based on avoidance of W recrystallization, sets an upper limit potentially ∼50% higher than the previously accepted value of ∼10 MW m−2, a consequence both of the choice of material and the finalized component design. Although the simulation database is currently restricted to the 2-D toroidally symmetric situation, considerable progress is now also being made using the EMC3-Eirene 3-D code suite for the assessment of power loading in the presence of magnetic perturbations for ELM control. Some new results for low input power corresponding to the early H-mode operation phases are reported, showing that even if realistic plasma screening is taken into account, significant asymmetric divertor heat fluxes may arise far from the unperturbed strike point. The issue of tolerable limits for transient heat pulses is an open and key question. A new scaling for ELM power deposition has shown that whilst there may be more latitude for operation at higher current without ELM control, the ultimate limit is likely to be set more by material fatigue under large numbers of sub-threshold melting events.

Nanoparticle application for heat transfer and irreversibility analysis in an air conditioning unit

Charging of PCM with incorporating copper oxide nanomaterial has been modeled in current article. Unsteady simulation for reporting thermal irreversibility was performed. Nanoparticles have been dispersed into paraffin to achieve greater efficiency and reach the match between demand and supply of energy. To increase the stored energy, volume fraction of copper oxide should be increased. Outputs revealed that narrow melt layer near the inner duct has been formed in initial time and it expanded as time progressed. Melting time and volume fraction of copper oxide has reverse relation and dispersing nanoparticles make entropy generation to decline.

Assessing the role of planetary and gravity waves in the vertical structure of ozone over midlatitudinal Europe

Abstract. Planetary and gravity waves play an important role in the dynamics of the atmosphere. They are present in the atmospheric distribution of temperature, wind, and ozone content. These waves are detectable also in the vertical profile of ozone and they cause its undulation. One of the structures occurring in the vertical ozone profile is laminae, which are narrow layers of enhanced or depleted ozone concentrations in the vertical ozone profile. They are connected with the total amount of ozone in the atmosphere and with the activity of the planetary and gravity waves. The aim of this paper is to quantify these processes in midlatitudinal Europe. We compare the occurrence of laminae induced by planetary waves (PL) with the occurrence of these induced by gravity waves (GL). We show that the PL are 10–20 times more frequent than that of GL. There is a strong annual variation of PL, while GL exhibit only a very weak variation. With the increasing lamina size the share of GL decreases and the share of PL increases. The vertical profile of lamina occurrence is different for PL and GL smaller than 2 mPa. For laminae greater than 2 mPa this difference is smaller.

Effects of the Action of Particle Fluxes and Geomagnetic Variations on Low-Orbital Spherical Satellites

The paper theoretically studies the process of formation of volume charge in a spacecraft body under action of electron fluxes of Earth’s radiation belts and other cosmic particles, as well as the generation of induction currents caused by geomagnetic variations. The BLITS and BLITS-M satellites, which have a spherical configuration manufactured entirely of dielectric materials as well as the metal WESTPAC satellite, are considered. The relative simplicity of the form of a dielectric satellite allows one to obtain an analytical solution to the problem and calculate the distribution of fields and charges inside and on its surface. This solution shows that after the establishment of the stationary mode, charges accumulate mainly in a narrow layer near the satellite surface. According to the obtained estimates for low orbits, the electric field strength in this layer is below the threshold value corresponding to the breakdown of uniform dielectric in laboratory conditions. Nevertheless, one can expect the appearance of local electrical breakdowns and microdestructions in the dielectric during increasing solar activity accompanied by an increase in cosmic-ray fluxes. From this point of view, space experiments, in which dielectric destruction was observed during long-term exposure to radiation, can be interpreted as the result of accumulation of microdestructions similarly to fatigue destruction of materials under long-term load. For passive satellites similar to WESTPAC manufactured of conductive materials, the magnetic moment of induction currents in the spacecraft body is estimated. According to these estimates, the interaction of this moment with the geomagnetic field leading to the precession of the axis of the satellite’s rotation is most significant for Pc5 geomagnetic pulsations.

A ring of fire in the pulsar magnetosphere

Contopoulos 2019 proposed that a dissipation zone develops in the magnetosphere of young pulsars at the edge of the closed-line region beyond the light cylinder. This is necessary in order to supply the charge carriers that will establish current closure through the equatorial and separatrix current-sheets. In the present work, we propose to investigate in greater detail this region with a simplified model that we would like to call the `ring-of-fire'. According to this simple model, the dissipation zone is a narrow reconnection layer where electrons and positrons are accelerated inwards and outwards respectively along Speiser orbits that are deflected in the azimuthal direction by the pulsar rotation. After they exit the reconnection layer, the accelerated positrons form the positively charged equatorial current-sheet, and the accelerated electrons form the negatively charged separatrix current-sheet along the boundary of the closed-line region. During their acceleration, particles lose only a small part of their energy to radiation. Most of their energy is lost outside the dissipation region, in the equatorial and separatrix current sheets. Our simple model allows us to obtain high-energy spectra and efficiencies. The radiation emitted by the positrons in the equatorial current-sheet forms a very-high energy tail that extends up to the TeV range.

Thin Ti adhesion layer breaks bottleneck to hot hole relaxation in Au films.

Slow relaxation of highly excited (hot) charge carriers can be used to increase efficiencies of solar cells and related devices as it allows hot carriers to be extracted and utilized before they relax and lose energy. Using a combination of real-time density functional theory and nonadiabatic molecular dynamics, we demonstrate that nonradiative relaxation of excited holes in an Au film slows down 30-fold as holes relax across the energy range -2 to -1.5 eV below the Fermi level. This effect arises due to sharp decreases in density of states (DOS) and reduced hole-phonon coupling in this energy range. Furthermore, to improve adhesion, a thin film of transition metal, such as Ti, is often inserted between the noble metal layer and its underlying substrate; we demonstrate that this adhesion layer completely eliminates the hot-hole bottleneck because it significantly, 7-fold per atom, increases the DOS in the critical energy region between -1.5 eV and the Fermi level, and because Ti atoms are 4-times lighter than Au atoms, high frequency phonons are introduced and increase the charge-phonon coupling. The detailed ab initio analysis of the charge-phonon scattering emphasizes the nonequilibrium nature of the relaxation processes and provides important insights into the energy flow in metal films. The study suggests that energy losses to heat can be greatly reduced by judicious selection of adhesion layers that do not involve light atoms and have relatively low DOS in the relevant energy range. Inversely, narrow Ti adhesion layers assist heat dissipation needed in electronics applications.

Two dimensional electron transports for terahertz emission fromIn0.53Ga0.47As/In0.52Al0.48Asmultilayer structures illuminated by 1.55 μm-laser

Two dimensional electron gas (2DEG) transports in In0.53Ga0.47As/In0.52Al0.48As multilayer structure (MLS) illuminated by an ultrashort optical pulse with the central wavelength at 1.55 μm is investigated by ensemble Monte Carlo simulations. Terahertz (THz) pulses are calculated according to the transient photocurrent in the InGaAs layers. It is found that InGaAs/InAlAs MLS with narrower InGaAs layers has an advantage in generating large temporal change in the transient photocurrent, which thereby is able to increase the intensity of THz emission. Beryllium (Be)-doping in InGaAs layers provides a scattering channel to speed the decay of photocurrent, and is shown to be a factor in shaping the bipolar structure of THz temporal waveforms. Bandwidth of the generated THz emission is found to be mainly controlled by the laser pulse duration at low doping level, but at high doping level, the bandwidth is determined together by laser pulse duration and doping density.

Computer Simulation of Zr0.8Sc0.2O1.9/Ce0.9Gd0.1O1.95 Heterostructure

A two-layer Zr0.8Sc0.2O1.9/Ce0.9Gd0.1O1.95 heterostructure has been modeled by the molecular dynamics method in a box containing about 27 thousand atoms. It is shown that this system retains on the whole the crystallographic characteristics of layers doped with zirconia and ceria, having a fluorite structure. Crystal structure distortions are observed in a narrow boundary layer with a thickness of few angstrom. An analysis of pair correlation functions indicates that the oxygen sublattice in the heterostructure is disordered. The calculated values of the layer-by-layer diffusion coefficient of oxygen and the diffusion activation energy are compared with the data of both direct physical and computer experiments.

Ion Transport Behavior through Thermally Reduced Graphene Oxide Membrane for Precise Ion Separation

The cation transport behavior of thermally treated reduced graphene oxide membranes (GOMs) is reported. The GOMs were reduced by heat treatment at 25, 80, and 120 °C and then characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy to determine oxygen group content, C/O ratio, and layer spacing. The permeation rates of various cations with different sizes and charge numbers through these membranes were measured to understand the effect of the cations on transport behavior. The results indicated that the cation transport through the membranes depended on the layer spacing of the membrane and ion size and charge. Cations of the same valence permeating through the same GOM could be differentiated by their hydration radius, whereas the same type of cation passing through different GOMs could be determined by the spacing of the GOM layers. The cation valence strongly affected permeation behavior. The GOM that was prepared at 120 °C exhibited a narrow layer spacing and high separation factors for Mg/Ca, Mg/Sr, K/Ca, and K/Fe. The cations moving through the membrane could insert into the membrane lamellas, which neutralized the negative charge of the membrane, enlarged the layer spacing of the GOMs, and affected cation permeation.

Artificial Aurora Experiments and Application to Natural Aurora

A review is given of the effects observed during injections of powerful electron beams from sounding rockets into the upper atmosphere. Data come from in situ particle and wave measurements near a beam emitting rocket and ground-based optical, wideband radiowave, and radar observations. The overall data cannot be explained solely by collisional degradation of energetic electrons but require collisionless beam plasma interactions (BPI) be taken into account. The beam-plasma discharge theory describes the features of the region near a beam-emitting rocket, where the beam-excited plasma waves energize plasma electrons, which then ignite the discharge. The observations far beneath the rocket reveal a double-peak structure of artificial auroral rays, which can be understood in terms of the beam-excited strong Langmuir turbulence being affected by collisions of ionospheric electrons. This leads to the enhanced energization of ionospheric electrons in a narrow layer termed the plasma turbulence layer (PTL), which explains the upper peak. Similar double-peak structures or a sharp upper boundary in rayed auroral arcs have been observed in the auroral ionosphere by optical, radar, and rocket observations, and called Enhanced Aurora. A striking resemblance between Enhanced and Artificial Aurora altitude profiles indicates that they are created by the above BPI process which results in the PTL.

Collisional alpha transport in a weakly rippled magnetic field

To properly treat the collisional transport of alpha particles due to a weakly rippled tokamak magnetic field the tangential magnetic drift due to its gradient (the $\unicode[STIX]{x1D735}B$ drift) and pitch angle scatter must be retained. Their combination gives rise to a narrow boundary layer in which collisions are able to match the finite trapped response to the ripple to the vanishing passing response of the alphas. Away from this boundary layer collisions are ineffective. There the $\unicode[STIX]{x1D735}B$ drift of the alphas balances the small radial drift of the trapped alphas caused by the ripple. A narrow collisional boundary layer is necessary since this balance does not allow the perturbed trapped alpha distribution function to vanish at the trapped–passing boundary. The solution of this boundary layer problem allows the alpha transport fluxes to be evaluated in a self-consistent manner to obtain meaningful constraints on the ripple allowable in a tokamak fusion reactor. A key result of the analysis is that collisional alpha losses are insensitive to the ripple near the equatorial plane on the outboard side where the ripple is high. As the high field side ripple is normally very small, collisional $\sqrt{\unicode[STIX]{x1D708}}$ ripple transport is unlikely to be a serious issue.

Collisional alpha transport in a weakly non-quasisymmetric stellarator magnetic field

Alpha particle confinement is a serious concern in stellarators and provides strong motivation for optimizing magnetic field configurations. In addition to the collisionless confinement of trapped alphas in stellarators, excessive collisional transport of the trapped alpha particles must be avoided while they tangentially drift due to the magnetic gradient (the $\unicode[STIX]{x1D735}B$ drift). The combination of pitch angle scatter off the background ions and the $\unicode[STIX]{x1D735}B$ drift gives rise to two narrow boundary layers in the trapped region. The first is at the trapped–passing boundary and enables the finite trapped response to be matched to the vanishing passing response of the alphas. The second layer is a region that encompasses the somewhat more deeply trapped alphas with vanishing tangential $\unicode[STIX]{x1D735}B$ drift. Away from (and between) these boundary layers, collisions are ineffective and the alpha $\unicode[STIX]{x1D735}B$ drift simply balances the small radial drift of the trapped alphas. As this balance does not vanish as the trapped–passing boundary is approached, the first collisional boundary layer is necessary and gives rise to $\surd \unicode[STIX]{x1D708}$ transport, with $\unicode[STIX]{x1D708}$ the collision frequency. The vanishing of the tangential drift results in a separate, somewhat wider boundary layer, and significantly stronger superbanana plateau transport that is independent of collisionality. The constraint imposed by the need to avoid significant energy depletion loss in the slowing down tail distribution function sets the allowed departure of a stellarator from an optimal quasisymmetric configuration.

Thermally Controllable High-Efficiency Unidirectional Coupling in a Double-Slit Structure Filled With Phase Change Material

We present the realization of a high-efficiency, compact, and thermally tunable unidirectional launcher of surface plasmon polaritons (SPPs) in a double-slit structure filled with phase change materials (PCMs). PCMs such as VO2 provide a feasible way for tailoring optical properties, particularly refractive index as a function of heat. By introducing a narrow hybrid dielectric layer beneath the slits, SPPs couple efficiently into waveguide mode and propagate within the slot waveguide with considerably high intensity. Our simulation results revealed up to 80% coupling efficiency into the slot waveguide with extinction ratio of 1:800 between the left and the right slots can be achieved at telecommunication wavelength for normally incident P-polarized light. By heating the coupler above the VO2 phase transition temperature, the coupling and consequently the crosstalk approaches zero. Propagation length and other properties of the structure are characterized to confirm the feasibility of the coupler. This approach of unidirectional coupling into slot waveguides may lead to the development of integrated plasmonic circuits and on-chip applications.