Outward Motion Research Articles

Horizontal flow fields in and around a small active region

Aims. Combining high-resolution and synoptic observations aims to provide a comprehensive description of flux emergence at photospheric level and of the growth process that eventually leads to a mature active region. Methods. Small active region NOAA 12118 was observed on 2014 July 18 with the 1.5-meter GREGOR solar telescope on 2014 July 18. High-resolution time-series of blue continuum and G-band images acquired in the blue imaging channel (BIC) of the GREGOR Fabry-P\'erot Interferometer (GFPI) were complemented by LOS magnetograms and continuum images obtained with the HMI onboard the SDO. Horizontal proper motions and horizontal plasma velocities were computed with local correlation tracking (LCT) and the differential affine velocity estimator, respectively. Morphological image processing was employed to measure the photometric/magnetic area, magnetic flux, and the separation profile of the EFR during its evolution. Results. The computed growth rates for photometric area, magnetic area, and magnetic flux are about twice as high as the respective decay rates. The space-time diagram using HMI magnetograms of five days traces a leaf-like structure, which is determined by the initial separation of the two polarities, a rapid expansion phase, a time when the spread stalls, and a period when the region slowly shrinks again. The separation rate of 0.26 km\s is highest in the initial stage, and it decreases when the separation comes to a halt. Horizontal plasma velocities computed at four evolutionary stages indicate a changing pattern of inflows. In LCT maps we find persistent flow patterns such as outward motions in the outer part of the two major pores, a diverging feature near the trailing pore marking the site of upwelling plasma and flux emergence, and low velocities in the interior of pores. We detected many elongated rapidly expanding granules between the two major polarities.

Radial migration in numerical simulations of Milky‐Way sized galaxies

AbstractWe show that in rmN ‐body simulations of isolated spiral discs, spiral arms appear to transient, recurring features that co‐rotate with the stellar disc stars at all radii. As a consequence, stars around the spiral arm continually feel a tangential force from the spiral and gain/lose angular momentum at all radii where spiral structure exists, without gaining significant amounts of random energy. We demonstrate that the ubiquitous radial migration in these simulations can be seen as outward (inward) systematic streaming motions along the trailing (leading) side of the spiral arms. We characterise these spiral induced peculiar motions and compare with those of the Milky Way obtained from APOGEE red clump data. We find that transient, co‐rotating spiral arms are consistent with the data, in contrast with density wave‐like spirals which are qualitatively inconsistent. In addition, we show that, in our simulations, radial migration does not change the radial metallicity gradient significantly, and broadens the metallicity distribution function at all radii, similar to some previous studies.

A sequence of flux transfer events potentially generated by different generation mechanisms

AbstractFlux transfer events (FTEs) are magnetic structures generated by time‐varying reconnection at the dayside magnetopause. Understanding their generation mechanism is important, because it is necessary in order to understand the global contribution of FTEs to the convection process. We present observations of several FTEs sequentially observed by Cluster at the subsolar magnetopause. Cluster detected also several reconnection jets, which seem to be systematically associated with the trailing edge of the FTEs. This association is expected only in the FTEs formed by single X line reconnection but could be compatible also with the multiple X line model, when reconnection at one X line is dominant. Instead, it does not seem compatible with original mechanism proposed by Russell and Elphic (1978). For a large FTE, not associated with any reconnection jet, the Grad‐Shafranov reconstruction obtained from Cluster 1 data recovers a flux rope, indicative of multiple X line reconnection. This same FTE was detected also by Cluster 3, which observed an asymmetric signature in the magnetic field component normal to the magnetopause. We show that this asymmetric signature was caused by an outward motion of the magnetopause. The orientation of the other FTEs, obtained from a Grad‐Shafranov optimization, shows considerable spread, despite the relatively steady conditions. Our interpretation is that a combination of single and multiple X line reconnection generated these FTEs. The FTEs in the first part of the crossing, associated with reconnection jets, are generated by the single X line model and may therefore not satisfy the Grad‐Shafranov assumptions so well. Instead, the last FTE, slower, bigger, and well separated from the previous ones, may be formed by multiple X line reconnection.

Digitalized K(+) Occupancy in the Nanocavity Holds and Releases Queues of K(+) in a Channel.

The mechanisms of ion permeation through potassium channels have been extensively examined. Molecular dynamics (MD) simulations have demonstrated that rapidly permeating ions collide near the selectivity filter (SF) ("knock-on" mechanism), but this oversimplified mechanism is insufficient to account for the experimentally observed single-channel current amplitudes. Here, we analyzed the MD-simulated ion trajectories through a Kv1.2 potassium channel using an event-oriented analysis method, and surprisingly, we found that the nanocavity (NC) governs ion permeation in a digital fashion. The NC has a maximal diameter of 10 Å and stands between the intracellular bulk solution and the SF, which holds only up to one K(+) during permeation. Accordingly, the K(+) concentration in the intracellular solution is translated as a digitalized zero or one K(+) in the NC. When the ion number in the NC is zero, the multiple ions in the SF are mostly immobilized. By contrast, when the number of ions in the NC is one, the structured water in the NC mediates the ion-occupied status to the queueing ions in the SF, and the ions then initiate a collective outward motion. Accordingly, the one ion in the NC serves as a catalytic intermediate for permeation, which quantitatively accounts for the experimentally obtained conductance-concentration relationships. We conclude that the ion movements are coherent across the entire pore.

Multipoint MMS observations of fine‐scale SAPS structure in the inner magnetosphere

AbstractWe present detailed observations of dynamic, fine‐scale inner magnetosphere‐ionosphere coupling at ∼3.9 RE in the Region 2 Birkeland field‐aligned current (FAC). We find that observed electrodynamic spatial/temporal scales are primarily characteristic of magnetically mapped ionospheric structure. On 15 September 2015, conjugate Magnetospheric Multiscale (MMS) spacecraft and Millstone Hill radar observations show plasmasphere boundary region subauroral polarization stream (SAPS) electric fields at L = 4.0–4.2 near 21 MLT. MMS observations reveal high‐altitude ∼1 mV/m fine‐scale radial and azimuthal electric field perturbations over ≤0.15 L with high spatial coherence over ≥2–3 min and show outward motion within a broader FAC of ∼0.12 μA/m2. Our analysis shows that MMS electric field fluctuations are most likely reflective of SAPS ionospheric structure at scales of ∼22 km and with ionospheric closure of small‐scale filamentary FAC perturbations. The results highlight the ionosphere's importance in regulating fine‐scale magnetosphere‐ionosphere structure.

A 17 June 2011 polar jet and its presence in the background solar wind

AbstractHigh‐speed jet responses in the polar solar wind are enigmatic. Here we measure a jet response that emanates from the southern polar coronal hole on 17 June 2011 at the extreme speed of over 1200 km/s. This response was recorded from the Sun‐Earth line in Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) and Large Angle and Spectrometric Coronagraph/C2 and both Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager and COR2 coronagraphs when the three spacecraft were situated ~90° from one another. These certify the coronal 3‐D location of the response that is associated with an existing solar plume structure and show its high speed to distances of over 14 RS. This jetting is associated with magnetic flux changes in the polar region as measured by the SDO/Helioseismic and Magnetic Imager instrumentation over a period of several hours. The fastest coronal response observed can be tracked to a time near the period of greatest flux changes and to the onset of the brightest flaring in AIA. This high‐speed response can be tracked directly as a small patch of outward moving brightness in coronal images as in Yu et al. (2014) where three slower events were followed from the perspective of Earth. This accumulated jet response has the largest mass and energy we have yet seen in 3‐D reconstructions from Solar Mass Ejection Imager observations, and its outward motion is certified for the first time using interplanetary scintillation observations. This jet response is surrounded by similar high‐speed patches, but these are smoothed out in Ulysses polar measurements, we speculate about how these dynamic activities relate to solar wind acceleration.

Three-dimensional DEM Study of Coal Distribution in the Melter Gasifier of COREX

COREX is one of the commercialized smelting reduction ironmaking processes. It mainly includes two reactors: a reduction shaft and a melter gasifier (MG). Lump coal is used in the MG to generate reducing agents, and hence its distribution plays an important role in determining the temperature distribution and the reduction of iron ores. To understand the formation of burden profiles, a three-dimensional discrete element method (DEM) model is established and validated against experimental tests. The effects of key operational parameters such as the chute angle and the rotational speed are investigated, and the underlying mechanisms in the formation of an asymmetrical pile are analyzed. The results show that the asymmetrical pile is intrinsic to the discharge system due to the outward motion of lump coal. The results also reveal a significant size segregation of lump coal along the radial direction. Small particles tend to accumulate in the inner side of the pile while the large ones have large fractions in the outer side. The effect of the rotational speed is minor within the range from 3 to 12 rpm. These findings are helpful for the control and optimization of the MG to improve its energy efficiency.

Compressional perturbations of the dayside magnetosphere during high‐speed‐stream‐driven geomagnetic storms

AbstractThe quasi‐DC compressions of the Earth's dayside magnetic field by ram‐pressure fluctuations in the solar wind are characterized by using multiple GOES spacecraft in geosynchronous orbit, multiple Los Alamos spacecraft in geosynchronous orbit, global MHD simulations, and ACE and Wind solar wind measurements. Owing to the inward‐outward advection of plasma as the dayside magnetic field is compressed, magnetic field compressions experienced by the plasma in the dayside magnetosphere are greater than the magnetic field compressions measured by a spacecraft. Theoretical calculations indicate that the plasma compression can be a factor of 2 higher than the observed magnetic field compression. The solar wind ram‐pressure changes causing the quasi‐DC magnetospheric compressions are mostly owed to rapid changes in the solar wind number density associated with the crossing of plasma boundaries; an Earth crossing of a plasma boundary produces a sudden change in the dayside magnetic field strength accompanied by a sudden inward or outward motion of the plasma in the dayside magnetosphere. Superposed epoch analysis of high‐speed‐stream‐driven storms was used to explore solar wind compressions and storm time geosynchronous magnetic field compressions, which are of particular interest for the possible contribution to the energization of the outer electron radiation belt. The occurrence distributions of dayside magnetic field compressions, solar wind ram‐pressure changes, and dayside radial plasma flow velocities were investigated: all three quantities approximately obey power law statistics for large values. The approximate power law indices for the distributions of magnetic compressions and ram‐pressure changes were both −3.

Radial gas motions in The H i Nearby Galaxy Survey (THINGS)

The study of 21cm line observations of atomic hydrogen allows detailed insight into the kinematics of spiral galaxies. We use sensitive high-resolution VLA data from The HI Nearby Galaxy Survey (THINGS) to search for radial gas flows primarily in the outer parts (up to $3\times r_{25}$) of ten nearby spiral galaxies. Inflows are expected to replenish the gas reservoir and fuel star formation under the assumption that galaxies evolve approximately in steady state. We carry out a detailed investigation of existing tilted ring fitting schemes and discover systematics that can hamper their ability to detect signatures of radial flows. We develop a new Fourier decomposition scheme that fits for rotational and radial velocities and simultaneously determines position angle and inclination as a function of radius. Using synthetic velocity fields we show that our novel fitting scheme is less prone to such systematic errors and that it is well suited to detect radial inflows in disks. We apply our fitting scheme to ten THINGS galaxies and find clear indications of, at least partly previously unidentified, radial gas flows, in particular for NGC 2403 and NGC 3198 and to a lesser degree for NGC 7331, NGC 2903 and NGC 6946. The mass flow rates are of the same order but usually larger than the star formation rates. At least for these galaxies a scenario in which continuous mass accretion feeds star formation seems plausible. The other galaxies show a more complicated picture with either no clear inflow, outward motions or complex kinematic signatures.

Effect of surfactant concentration and viscosity of outer phase during the coalescence of a surfactant-laden drop with a surfactant-free drop

This work focuses on the coalescence of two water drops, one of which contains surfactant. The coalescence was carried out in surrounding silicone oils of various viscosities. It has been found that, in all the studied cases, the outward motion of the liquid neck follows the power scaling law with exponent ∼0.5 with the pre-factor dependent upon the surfactant concentration and viscosity of outer phase. Interfacial Marangoni flows arising at coalescence were visualised and quantified. Considerable convective bulk motion was observed by coalescence of surfactant-laden and surfactant-free drops with patterns depending on viscosity of outer phase. No noticeable convection was observed during the coalescence of two surfactant-free drops or similar surfactant-laden drops. It was confirmed that the rate of growth of the liquid bridge was reduced when the surfactant was present in the drops due to the lower interfacial tension in the bridge. Dependence of the reduction on surfactant concentration and viscosity of surrounding liquid is discussed. For the coalescence of a surfactant-free drop and a surfactant-laden drop, the curvature of the meniscus was different on either side of the growing bridge.

Material flow behaviours during friction stir spot welding of lightweight alloys using pin and pinless tools

This study investigated material flow behaviour in similar aluminium alloy and magnesium alloy sheet lap welds produced by friction stir spot welding. The material flows around the tool pin and shoulder were visualised through the tracer material technique, and schematic illustrations were made to clarify the induced material flow direction and intensity. The material flow observations described that the pin part provided the outward spinning motion of the material, while the shoulder part generated a centrifugal effect at the edge for downward flow/hooking. Induced material flow intensity suggested that dominant flow patterns near the shoulder edge were observed for the similar Al welds, whereas high intensity outward spinning flows at the pin periphery for the similar Mg welds. As a result, the material flow under the pin and shoulder of the tool explained that the morphology of the failure mode was highly dependent on the tool geometry and the alloy material adopted.

Post-buckling relaxation of an elastic layer and its geological relevance: Insights from analogue experiments in pure shear

By physical modelling we investigated the buckling and post-buckling behaviour of an elastic layer hosted in a viscous medium, as analogue of the elastic response of crustal rocks. The experiments were performed by embedding thin elastic layers of finite length in a linear viscous medium, and in two successive stages: a first stage of layer-parallel shortening in pure shear, followed by a second stage of post-buckling unfolding with zero velocity at the bounding walls. The experimental results show that the fold wavelength varies inversely with applied piston velocity, following an exponential function for which the higher the piston velocity the higher the number of waves. With cessation of layer-parallel shortening, the buckled layers underwent post-buckling relaxation in response to the elastic strain accumulated during the buckling stage. Such relaxation reduces the number of waves by successive elimination of the lower amplitude folds. The relaxation process gives rise to larger folds of higher amplitude in the centre of the elastic layer, concomitantly with the production of a train of gentle folds in the outer domains by outward motion of the ends of the elastic layer. This means that relaxation is more efficient away from the central domain. Comparison of our experimental results with available analytical solutions reveals significant discrepancies. Finally, we suggest that a similar process of relaxation of the elastic strain, although of lower amplitude, may explain the late stage open folding and the formation of overlying extensional basins observed in past orogens like the Caledonides in western Norway.

Dynamical Model-Based Aerobics Upper Limb Inward and Outward Rotation Motion Sports Injured Part Research

In the flourishing society, aerobics as a sport event that can build one's body and cultivate one's taste, is popular among ordinary people, but due to professional knowledge deficiency, mass may unconsciously generate injuries in body when taking aerobics exercise, in order to reduce occurrence rate of such injuries, the paper firstly gets dynamics relations and arms rotational inertia when aerobics athletes exercise upper limb inward and outward rotation motion by researching, gets that aerobics athletes' arms potential energy size when exercise upper limb inward and outward rotation motion, and according to momentum theory of transmitting from near-end to far-end, athletes can strengthen elbow joint momentum through shoulder joint effective braking effect, and then transfer momentum to wrist joint by elbow joint braking to have end acceleration effects. It also gets forearm angular speed should be bigger than that of upper arm so that can more beneficial to elbow joint acceleration. And it gets that when aerobics athletes take upper limb inward and outward rotation motion, due to it should let forearm angular speed to be bigger than upper arm's angular speed to drive elbow joint acceleration, athletes should let elbow joint speed to be more faster than shoulder joint in the process, and then shoulder joint is likely to suffer injuries because of braking, by comparing, elbow joint injury extent is far less than that of shoulder joint, athlete can take some corresponding prevention measures by referencing the result.

The nature of the γ-ray flare associated with blazar 3C 454.3

We have studied the simultaneous spectral energy distributions (SEDs) of the 2009 December flare and those of the quiescent state of blazar 3C 454.3 by constructing a multi-component model. We find that all six SEDs can be explained by a one-zone leptonic model involving synchrotron self-Compton (SSC) plus external Compton emission from an accretion disk (ECD) and that from a broad-line region (ECC). X-ray emission is dominated by the SSC mechanism, and the γ-ray spectrum is well represented by a combination of ECD and ECC processes. Our results indicate that the energy density of the magnetic field and electrons decrease with distance from the central engine, and the Doppler factor increases with the blob moving outward in the development of the 2009 December flare. The increase in the observed flux density is possibly due to the increase in the Doppler factor of the blob. The relation between the Doppler factor δb and the distance from the central black hole suggests the magnetically driven jets span a sub-pc scale, and the relation between the magnetic field B' and the dimension of the emission region R'b is in good agreement with what is required by conservation of magnetic flux. The weak “harder-when-brighter” behavior of the γ-ray spectrum could be a result of the increase in Doppler factor during the outward motion of the blob. The parameters during the quiescent state obviously deviate from those during the flare state. We propose that the flare was likely caused by the ejection of a new blob. The gamma-ray emissions in different states are associated with the evolution of the blob.

Weakly nonlinear Bell-Plesset effects for a uniformly converging cylinder

In this research, a weakly nonlinear (WN) model has been developed considering the growth of a small perturbation on a cylindrical interface between two incompressible fluids which is subject to arbitrary radial motion. We derive evolution equations for the perturbation amplitude up to third order, which can depict the linear growth of the fundamental mode, the generation of the second and third harmonics, and the third-order (second-order) feedback to the fundamental mode (zero-order). WN solutions are obtained for a special uniformly convergent case. WN analyses are performed to address the dependence of interface profiles, amplitudes of inward-going and outward-going parts, and saturation amplitudes of linear growth of the fundamental mode on the Atwood number, the mode number (m), and the initial perturbation. The difference of WN evolution in cylindrical geometry from that in planar geometry is discussed in some detail. It is shown that interface profiles are determined mainly by the inward and outward motions rather than bubbles and spikes. The amplitudes of inward-going and outward-going parts are strongly dependent on the Atwood number and the initial perturbation. For low-mode perturbations, the linear growth of fundamental mode cannot be saturated by the third-order feedback. For fixed Atwood numbers and initial perturbations, the linear growth of fundamental mode can be saturated with increasing m. The saturation amplitude of linear growth of the fundamental mode is typically 0.2λ–0.6λ for m < 100, with λ being the perturbation wavelength. Thus, it should be included in applications where Bell-Plesset [G. I. Bell, Los Alamos Scientific Laboratory Report No. LA-1321, 1951; M. S. Plesset, J. Appl. Phys. 25, 96 (1954)] converging geometry effects play a pivotal role, such as inertial confinement fusion implosions.

Polarization dependent micro-structuring of silicon with a femtosecond laser

We experimentally demonstrate formation of a sub-micron rim around femtosecond laser ablated crater on silicon whose height and width were sensitive to laser polarization. Except for circularly polarized light we show that the rim height and width were asymmetric – larger along the direction of the laser polarization for n-type and intrinsic silicon, while in p-type silicon the asymmetry was perpendicular. Polarization dependent rim formation is attributed to the transient light–plasma interaction that gives rise to local-field enhancements resulting in an asymmetric electron density and energy deposition. Picoseconds later when the electron energy is transferred to the lattice, the asymmetry is retained in the temperature distribution within the interaction region. The temperature distribution eventually leads to non-symmetric radial outward fluid motion of a thin layer of molten material from the centre of the ablation crater that subsequently re-solidifies on a nanosecond timescale.

CONTRIBUTION OF VELOCITY VORTICES AND FAST SHOCK REFLECTION AND REFRACTION TO THE FORMATION OF EUV WAVES IN SOLAR ERUPTIONS

We numerically study the detailed evolutionary features of the wave-like disturbance and its propagation in the eruption. This work is a follow-up to Wang et al., using significantly upgraded new simulations. We focus on the contribution of the velocity vortices and the fast shock reflection and refraction in the solar corona to the formation of the EUV waves. Following the loss of equilibrium in the coronal magnetic structure, the flux rope exhibits rapid motions and invokes the fast-mode shock forward of the rope, which then produces the type II radio burst. The expansion of the fast shock, which is associated with outward motion, takes place in various directions, and the downward expansion shows the reflection and the refraction as a result of the non-uniform background plasma. The reflected component of the fast shock propagates upward and the refracted component propagates downward. As the refracted component reaches the boundary surface, a weak echo is excited. The Moreton wave is invoked as the fast shock touches the bottom boundary, so the Moreton wave lags the type II burst. A secondary echo occurs in the area where reflection of the fast shock encounters the slow-mode shock, and the nearby magnetic field lines are further distorted because of the interaction between the secondary echo and the velocity vortices. Our results indicate that the EUV wave may arise from various processes that are revealed in the new simulations.

Domain wall kinetics of lithium niobate single crystals near the hexagonal corner

A mesospheric approach based on a simple microscopic 2D Ising model in a hexagonal lattice plane is proposed to explain macroscopic “asymmetric in-out domain wall motion” observation in the (0001) plane of MgO-doped stoichiometric lithium niobate. Under application of an electric field that was higher than the conventional coercive field (Ec) to the ferroelectric crystal, a natural hexagonal domain was obtained with walls that were parallel to the Y-axis of the crystal. When a fraction of the coercive field of around 0.1Ec is applied in the reverse direction, this hexagonal domain is shrunk (moved inward) from the corner site into a shape with a corner angle of around 150° and 15° wall slopes to the Y-axis. A flipped electric field of 0.15Ec is then applied to recover the natural hexagonal shape, and the 150° corner shape changes into a flat wall with 30° slope (moved outward). The differences in corner domain shapes between inward and outward domain motion were analyzed theoretically in terms of corner and wall site energies, which are described using the domain corner angle and wall slope with respect to the crystal Y-axis, respectively. In the inward domain wall motion case, the energy levels of the evolving 150° domain corner and 15° slope walls are most competitive, and could co-exist. In the outward case, the energy levels of corners with angles >180° are highly stable when compared with the possible domain walls; only a flat wall with 30° slope to the Y-axis is possible during outward motion.

External circuit integration with electromagnetic particle in cell modeling of plasma focus devices

The pinch performance of a plasma focus (PF) device is sensitive to the physical conditions of the breakdown phase. It is therefore essential to model and study the initial phase in order to optimize device performance. An external circuit is self consistently coupled to the electromagnetic particle in cell code to model the breakdown and initial lift phase of the United Nations University/International Centre for Theoretical Physics (UNU-ICTP) plasma focus device. Gas breakdown during the breakdown phase is simulated successfully, following a drop in the applied voltage across the device and a concurrent substantial rise in the circuit current. As a result, the plasma becomes magnetized, with the growing value of the magnetic field over time leading to the gradual lift off of the well formed current sheath into the axial acceleration phase. This lifting off, with simultaneous outward sheath motion along the anode and vertical cathode, and the strong magnetic fields in the current sheath region, was demonstrated in this work, and hence validates our method of coupling the external circuit to PF devices. Our method produces voltage waveforms that are qualitatively similar to the observed experimental voltage profiles of the UNU-ICTP device. Values of the mean electron energy before and after voltage breakdown turned out to be different, with the values after breakdown being much lower. In both cases, the electron energy density function turned out to be non-Maxwellian.

OUTWARD MOTION OF POROUS DUST AGGREGATES BY STELLAR RADIATION PRESSURE IN PROTOPLANETARY DISKS

We study the dust motion at the surface layer of protoplanetary disks. Dust grains in surface layer migrate outward due to angular momentum transport via gas-drag force induced by the stellar radiation pressure. In this study, we calculate mass flux of the outward motion of compact grains and porous dust aggregates by the radiation pressure. The radiation pressure force for porous dust aggregates is calculated using the T-Matrix Method for the Clusters of Spheres. First, we confirm that porous dust aggregates are forced by strong radiation pressure even if they grow to be larger aggregates in contrast to homogeneous and spherical compact grains to which efficiency of radiation pressure becomes lower when their sizes increase. In addition, we find that the outward mass flux of porous dust aggregates with monomer size of 0.1 $\mu$m is larger than that of compact grains by an order of magnitude at the disk radius of 1 AU, when their sizes are several microns. This implies that large compact grains like calcium-aluminum rich inclusions (CAIs) are hardly transported to outer region by stellar radiation pressure, whereas porous dust aggregates like chondritic-porous interplanetary dust particles (CP-IDPs) are efficiently transported to comet formation region. Crystalline silicates are possibly transported in porous dust aggregates by stellar radiation pressure from inner hot region to outer cold cometary region in the protosolar nebula.