A Systematic Exploration of InGaN/GaN Quantum Well-Based Light Emitting Diodes on Semipolar Orientations -=SUP=-*-=/SUP=-

Light-emitting diodes (LEDs) based on group III-nitride semiconductors (GaN, AlN, and InN) are crucial elements for solid-state lighting and visible light communication applications. The most widely used growth plane for group III-nitride LEDs is the polar plane (c-plane), which is characterized by the presence of a polarization-induced internal electric field in heterostructures. It is possible to address long-standing problems in group III-nitride LEDs, by using semipolar and nonpolar orientations of GaN. In addition to the reduction in the polarization-induced internal electric field, semipolar orientations potentially offer the possibility of higher indium incorporation, which is necessary for the emission of light in the visible range. This is the preferred growth orientation for green/yellow LEDs and lasers. The important properties such as high output power, narrow emission linewidth, robust temperature dependence, large optical polarization ratio, and low-efficiency droop are demonstrated with semipolar LEDs. To harness the advantages of semipolar orientations, comprehensive studies are required. This review presents the recent progress on the development of semipolar InGaN/GaN quantum well LEDs. Semipolar InGaN LED structures on bulk GaN substrates, sapphire substrates, free-standing GaN templates, and on Silicon substrates are discussed including the bright prospects of group III-nitrides. Keywords: Group III-nitride semiconductor, semipolar, light-emitting diodes, InGaN/GaN quantum well.

3D Curve Generation Using Spherical Polar Piecewise Interpolation in CAD and CAM

In this paper a newly 3D path planning approach and curve generation for design and manufacturing efficiency is considered. The 3D path is generated by a combination of piecewise interpolating curves - along a given number of via-points - created via a spherical coordinate system specified by the polar angles, radial distances and the associated azimuthal angles. Each piecewise interpolating curve is constructed using Hermite polar interpolation in the projective polar plane and the rotating azimuthal plane. To verify the proposed approach, numerical simulations for the generation of a helix design, a 4 and 6 leaf design and a trajectory planning of a picking robot arm are conducted.

Flow pattern of accelerated cometary ions inside and outside the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko

Analyzing data from the Ion Composition Analyzer on board the Rosetta spacecraft, we studied a flow pattern of accelerated cometary ions (40–80 eV) inside and outside the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko (67P). We found that the accelerated ions are intermittently observed and are ten times more frequently observed outside the cavity than inside, and they mainly flow tailward with an aberration (~20–40°). We suggest that they are accelerated by the tailward polarization electric field upstream of the comet. Because their occurrence frequency becomes lowest near perihelion where the water production rate is highest at 67P, ion-neutral collisions and/or charge exchange may play a role in controlling the occurrence frequency. The aberration pattern is different inside and outside the cavity in the cometocentric solar equatorial (CSEQ) frame but it is consistent in the comet-Sun electric (CSE) frame; the latter is rotated from the CSEQ frame about the comet-Sun line so that the Z-axis is aligned with the local motional electric field. Because the flow pattern of the accelerated ions inside the cavity in the CSE frame is the same as outside, we suggest that the flow pattern inside is determined by the flow outside, depending on the local plasma and magnetic field. Near the CSE polar plane the aberration is in the opposite direction of the motional electric field, while it is in the anti-cometward direction near the CSE equator plane. The aberration in the anti-electric-field direction near the CSE polar plane suggests that the accelerated ions are mass-loaded by local cold cometary ions, just like the mass-loading of the solar wind by cold cometary ions. The cause of the anti-cometward aberration near the CSE equator plane is still unknown, but this may indicate that the tailward-flowing cometary ions are deflected across the upstream boundaries or by an outward-pointing ambipolar electric field.

Fast plasma sheet flows and X line motion in the Earth's magnetotail: results from a global hybrid-Vlasov simulation

Fast plasma flows produced as outflow jets from reconnection sites or X lines are a key feature of the dynamics in the Earth's magnetosphere. We have used a polar plane simulation of the hybrid-Vlasov model Vlasiator, driven by steady southward interplanetary magnetic field and fast solar wind, to study fast plasma sheet ion flows and related magnetic field structures in the Earth's magnetotail. In the simulation, lobe reconnection starts to produce fast flows after the increasing pressure in the lobes has caused the plasma sheet to thin sufficiently. The characteristics of the earthward and tailward fast flows and embedded magnetic field structures produced by multi-point tail reconnection are in general agreement with spacecraft measurements reported in the literature. The structuring of the flows is caused by internal processes: interactions between major X points determine the earthward or tailward direction of the flow, while interactions between minor X points, associated with leading edges of magnetic islands carried by the flow, induce local minima and maxima in the flow speed. Earthward moving flows are stopped and diverted duskward in an oscillatory (bouncing) manner at the transition region between tail-like and dipolar magnetic fields. Increasing and decreasing dynamic pressure of the flows causes the transition region to shift earthward and tailward, respectively. The leading edge of the train of earthward flow bursts is associated with an earthward propagating dipolarization front, while the leading edge of the train of tailward flow bursts is associated with a tailward propagating plasmoid. The impact of the dipolarization front with the dipole field causes magnetic field variations in the Pi2 range. Major X points can move either earthward or tailward, although tailward motion is more common. They are generally not advected by the ambient flow. Instead, their velocity is better described by local parameters, such that an X point moves in the direction of increasing reconnection electric field strength. Our results indicate that ion kinetics might be sufficient to describe the behavior of plasma sheet bulk ion flows produced by tail reconnection in global near-Earth simulations. Keywords. Magnetospheric physics (magnetospheric configuration and dynamics; plasma sheet) – space plasma physics (numerical simulation studies)

A possible source mechanism for magnetotail current sheet flapping

The origin of the flapping motions of the current sheet in the Earth's magnetotail is one of the most interesting questions of magnetospheric dynamics yet to be solved. We have used a polar plane simulation from the global hybrid-Vlasov model Vlasiator to study the characteristics and source of current sheet flapping in the center of the magnetotail. The characteristics of the simulated signatures agree with observations reported in the literature. The flapping is initiated by a hemispherically asymmetric magnetopause perturbation, created by subsolar magnetopause reconnection, that is capable of displacing the tail current sheet from its nominal position. The current sheet displacement propagates downtail at the same pace as the driving magnetopause perturbation. The initial current sheet displacement launches a standing magnetosonic wave within the tail resonance cavity. The travel time of the wave within the local cavity determines the period of the subsequent flapping signatures. Compression of the tail lobes due to added flux affects the cross-sectional width of the resonance cavity as well as the magnetosonic speed within the cavity. These in turn modify the wave travel time and flapping period. The compression of the resonance cavity may also provide additional energy to the standing wave, which may lead to strengthening of the flapping signature. It may be possible that the suggested mechanism could act as a source of kink-like waves that have been observed to be emitted from the center of the tail and to propagate toward the dawn and dusk flanks.

A source mechanism for magnetotail current sheet flapping

The origin of the flapping motions of the current sheet in the Earth's magnetotail is one of the most interesting questions of magnetospheric dynamics yet to be solved. We have used a polar plane simulation from the global hybrid-Vlasov model Vlasiator to study the characteristics and source of current sheet flapping in the center of the magnetotail. The characteristics of the simulated signatures agree with observations reported in the literature. The flapping is initiated by a hemispherically asymmetric magnetopause perturbation, created by subsolar magnetopause reconnection, that is capable of displacing the tail current sheet from its nominal position. The current sheet displacement propagates downtail at the same pace as the driving magnetopause perturbation. The initial current sheet displacement launches a standing magnetosonic wave within the tail resonance cavity. The travel time of the wave within the local cavity determines the period of the subsequent flapping signatures. Compression of the tail lobes due to added flux affects the cross-sectional width of the resonance cavity as well as the magnetosonic speed within the cavity. These in turn modify the wave travel time and flapping period. The compression of the resonance cavity may also provide additional energy to the standing wave, which may lead to strengthening of the flapping signature. The suggested mechanism could act as a source for kink-like waves that have been observed to be emitted from the center of the tail and to propagate toward the dawn and dusk flanks.