scholarly journals A quantitative model of the planetary Na<sup>+</sup> contribution to Mercury’s magnetosphere

2003 ◽  
Vol 21 (8) ◽  
pp. 1723-1736 ◽  
Author(s):  
D. C. Delcourt ◽  
S. Grimald ◽  
F. Leblanc ◽  
J.-J. Berthelier ◽  
A. Millilo ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Spatial Scales ◽  
Direct Consequence ◽  
Quantitative Model ◽  
Photon Flux ◽  
Field Variation ◽  
Chaotic Scattering ◽  
Loss Cone ◽  
Wide Range ◽  
Order Of Magnitude

Abstract. We examine the circulation of heavy ions of planetary origin within Mercury’s magnetosphere. Using single particle trajectory calculations, we focus on the dynamics of sodium ions, one of the main species that are ejected from the planet’s surface. The numerical simulations reveal a significant population in the near-Mercury environment in the nightside sector, with energetic (several keV) Na + densities that reach several tenths cm-3 at planetary perihelion. At aphelion, a lesser (by about one order of magnitude) density contribution is obtained, due to weaker photon flux and solar wind flux. The numerical simulations also display several features of interest that follow from the small spatial scales of Mercury’s magnetosphere. First, in contrast to the situation prevailing at Earth, ions in the magnetospheric lobes are found to be relatively energetic (a few hundreds of eV), despite the low-energy character of the exospheric source. This results from enhanced centrifugal acceleration during E × B transport over the polar cap. Second, the large Larmor radii in the mid-tail result in the loss of most Na + into the dusk flank at radial distances greater than a few planetary radii. Because gyroradii are comparable to, or larger than, the magnetic field variation length scale, the Na + motion is also found to be non-adiabatic throughout most of Mercury’s equatorial magnetosphere, leading to chaotic scattering into the loss cone or meandering (Speiser-type) motion in the near-tail. As a direct consequence, a localized region of energetic Na + precipitation develops at the planet’s surface. In this region which extends over a wide range of longitudes at mid-latitudes ( ~ 30°–40°), one may expect additional sputtering of planetary material.Key words. Magnetospheric physics (planetary magnetospheres) – Space plasma physics (charged particle motion and acceleration; numerical simulation studies)

scholarly journals On the concentration of near-inertial waves in anticyclones

2015 ◽  
Vol 773 ◽  
Author(s):  
Eric Danioux ◽  
Jacques Vanneste ◽  
Oliver Bühler
Keyword(s):  
Numerical Simulations ◽  
Wave Field ◽  
Conservation Law ◽  
Spatial Scales ◽  
Direct Consequence ◽  
Inertial Waves ◽  
Background Flow ◽  
Homogeneous Wave ◽  
New Perspective ◽  
Scaling Arguments

An overlooked conservation law for near-inertial waves (NIWs) propagating in a steady background flow provides a new perspective on the concentration of these waves in regions of anticyclonic vorticity. The conservation law implies that this concentration is a direct consequence of the decrease in spatial scales experienced by an initially homogeneous wave field. Scaling arguments and numerical simulations of a reduced-gravity model of mixed-layer NIWs confirm this interpretation and elucidate the influence of the strength of the background flow relative to the dispersion.

Scanning-tunneling spectroscopy on conjugated polymer films

2003 ◽  
Vol 771 ◽  
Author(s):  
M. Kemerink ◽  
S.F. Alvarado ◽  
P.M. Koenraad ◽  
R.A.J. Janssen ◽  
H.W.M. Salemink ◽  
...  
Keyword(s):  
Polymer Films ◽  
Conjugated Polymer ◽  
Three Dimensional ◽  
Field Enhancement ◽  
Direct Consequence ◽  
Scanning Tunneling Spectroscopy ◽  
Tunneling Spectroscopy ◽  
Band Alignment ◽  
Scanning Tunneling ◽  
Order Of Magnitude

AbstractScanning-tunneling spectroscopy experiments have been performed on conjugated polymer films and have been compared to a three-dimensional numerical model for charge injection and transport. It is found that field enhancement near the tip apex leads to significant changes in the injected current, which can amount to more than an order of magnitude, and can even change the polarity of the dominant charge carrier. As a direct consequence, the single-particle band gap and band alignment of the organic material can be directly obtained from tip height-voltage (z-V) curves, provided that the tip has a sufficiently sharp apex.

scholarly journals Energetics of magnetic transients in a solar active region plage

2019 ◽  
Vol 623 ◽  
pp. A176 ◽  
Author(s):  
L. P. Chitta ◽  
A. R. C. Sukarmadji ◽  
L. Rouppe van der Voort ◽  
H. Peter
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Flux ◽  
Numerical Simulations ◽  
Extreme Ultraviolet ◽  
Spatial Scales ◽  
Coronal Loops ◽  
The Sun ◽  
Flux Emergence ◽  
Transient Events

Context. Densely packed coronal loops are rooted in photospheric plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plage areas are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. Aims. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in the active region plage using high spatial resolution observations and numerical simulations. Methods. We used photospheric Fe I 6173 Å spectropolarimetric observations of a decaying active region obtained from the Swedish 1-m Solar Telescope (SST). These data were inverted to retrieve the photospheric magnetic field underlying the plage as identified in the extreme-ultraviolet emission maps obtained from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). To obtain better insight into the evolution of extended unidirectional magnetic field patches on the Sun, we performed 3D radiation magnetohydrodynamic simulations of magnetoconvection using the MURaM code. Results. The observations show transient magnetic flux emergence and cancellation events within the extended predominantly unipolar patch on timescales of a few 100 s and on spatial scales comparable to granules. These transient events occur at the footpoints of active region plage loops. In one case the coronal response at the footpoints of these loops is clearly associated with the underlying transient. The numerical simulations also reveal similar magnetic flux emergence and cancellation events that extend to even smaller spatial and temporal scales. Individual simulated transient events transfer an energy flux in excess of 1 MW m−2 through the photosphere. Conclusions. We suggest that the magnetic transients could play an important role in the energetics of active region plage. Both in observations and simulations, the opposite-polarity magnetic field brought up by transient flux emergence cancels with the surrounding plage field. Magnetic reconnection associated with such transient events likely conduits magnetic energy to power the overlying chromosphere and coronal loops.

scholarly journals On the generation of internal waves by river plumes in subcritical initial conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
R. Mendes ◽  
J. C. B. da Silva ◽  
J. M. Magalhaes ◽  
B. St-Denis ◽  
D. Bourgault ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Internal Waves ◽  
Coastal Waters ◽  
Initial Conditions ◽  
Spatial Scales ◽  
River Plumes ◽  
Wide Range ◽  
Near Shore ◽  
Generation Mechanisms ◽  
Douro River

AbstractInternal waves (IWs) in the ocean span across a wide range of time and spatial scales and are now acknowledged as important sources of turbulence and mixing, with the largest observations having 200 m in amplitude and vertical velocities close to 0.5 m s−1. Their origin is mostly tidal, but an increasing number of non-tidal generation mechanisms have also been observed. For instance, river plumes provide horizontally propagating density fronts, which were observed to generate IWs when transitioning from supercritical to subcritical flow. In this study, satellite imagery and autonomous underwater measurements are combined with numerical modeling to investigate IW generation from an initial subcritical density front originating at the Douro River plume (western Iberian coast). These unprecedented results may have important implications in near-shore dynamics since that suggest that rivers of moderate flow may play an important role in IW generation between fresh riverine and coastal waters.

scholarly journals The Impact of Initial Conditions in N-Body Simulations of Debris Discs

2015 ◽  
Vol 32 ◽  
Author(s):  
E. Thilliez ◽  
S. T. Maddison
Keyword(s):  
Numerical Simulations ◽  
Initial Conditions ◽  
Parent Body ◽  
Dust Trapping ◽  
Physical Context ◽  
Disc Width ◽  
Wide Range ◽  
Belt Width ◽  
New Generation ◽  
The Impact

AbstractNumerical simulations are a crucial tool to understand the relationship between debris discs and planetary companions. As debris disc observations are now reaching unprecedented levels of precision over a wide range of wavelengths, an appropriate level of accuracy and consistency is required in numerical simulations to confidently interpret this new generation of observations. However, simulations throughout the literature have been conducted with various initial conditions often with little or no justification. In this paper, we aim to study the dependence on the initial conditions of N-body simulations modelling the interaction between a massive and eccentric planet on an exterior debris disc. To achieve this, we first classify three broad approaches used in the literature and provide some physical context for when each category should be used. We then run a series of N-body simulations, that include radiation forces acting on small grains, with varying initial conditions across the three categories. We test the influence of the initial parent body belt width, eccentricity, and alignment with the planet on the resulting debris disc structure and compare the final peak emission location, disc width and offset of synthetic disc images produced with a radiative transfer code. We also track the evolution of the forced eccentricity of the dust grains induced by the planet, as well as resonance dust trapping. We find that an initially broad parent body belt always results in a broader debris disc than an initially narrow parent body belt. While simulations with a parent body belt with low initial eccentricity (e ~ 0) and high initial eccentricity (0 < e < 0.3) resulted in similar broad discs, we find that purely secular forced initial conditions, where the initial disc eccentricity is set to the forced value and the disc is aligned with the planet, always result in a narrower disc. We conclude that broad debris discs can be modelled by using either a dynamically cold or dynamically warm parent belt, while in contrast eccentric narrow debris rings are reproduced using a secularly forced parent body belt.

Large Eddy Simulations of Staggered Parallel-Plate Flows

2005 ◽  
Author(s):  
M. V. Pham ◽  
F. Plourde ◽  
S. K. Doan
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Heat Transfer Enhancement ◽  
Parallel Plate ◽  
Large Scale ◽  
Primary Objective ◽  
Transfer Enhancement ◽  
Turbulent Structures ◽  
Wide Range ◽  
Large Eddy

Heat transfer enhancement is a subject of major concern in numerous fields of industry and research. Having received undivided attention over the years, it is still studied worldwide. Given the exponential growth of computing power, large-scale numerical simulations are growing steadily more realistic, and it is now possible to obtain accurate time-dependent solutions with far fewer preliminary assumptions about the problems. As a result, an increasingly wide range of physics is now open for exploration. More specifically, it is time to take full advantage of large eddy simulation technique so as to describe heat transfer in staggered parallel-plate flows. In fact, from simple theory through experimental results, it has been demonstrated that surface interruption enhances heat transfer. Staggered parallel-plate geometries are of great potential interest, and yet many numerical works dedicated to them have been tarnished by excessively simple assumptions. That is to say, numerical simulations have generally hypothesized lengthwise periodicity, even though flows are not periodic; moreover, the LES technique has not been employed with sufficient frequency. Actually, our primary objective is to analyze turbulent influence with regard to heat transfers in staggered parallel-plate fin geometries. In order to do so, we have developed a LES code, and numerical results are compared with regard to several grid mesh resolutions. We have focused mainly upon identification of turbulent structures and their role in heat transfer enhancement. Another key point involves the distinct roles of boundary restart and the vortex shedding mechanism on heat transfer and friction factor.

Numerical simulations of wet snow avalanches: interplay between cohesion and friction

2021 ◽  
Author(s):  
Guillaume Chambon ◽  
Thierry Faug ◽  
Mohamed Naaim
Keyword(s):  
Numerical Simulations ◽  
Flow Regimes ◽  
Liquid Water Content ◽  
Snow Avalanches ◽  
Shallow Flow ◽  
Distinctive Features ◽  
Wide Range ◽  
Wet Snow ◽  
Sensitivity Studies ◽  
Avalanche Flow

&lt;p&gt;Wet snow avalanches present distinctive features such as unusual trajectories, peculiar deposit shapes, and a rheological behavior displaying a combination of granular and pasty features depending on the actual snow liquid water content. Complex transitions between dry (cold) and wet (hot) flow regimes can also occur during a single avalanche flow. In an attempt to account for this complexity, we report on numerical simulations of avalanches using a frictional-cohesive rheology implemented in a depth-averaged shallow-flow model. Through extensive sensitivity studies on synthetic and real topographies, we show that cohesion plays a key role to enrich the physics of the simulated flows, and to represent realistic avalanche behaviors. First, when coupled to a proper treatment of the yielding criterion, cohesion provides a way to define objective stopping criteria for the flow, independently of the issues incurred by artificial diffusion of the numerical scheme. Second, and more importantly, the interplay between cohesion and friction gives raise to a variety of nontrivial physical effects affecting the dynamics of the avalanches and the morphology of the deposits. The relative weights of frictional and cohesive contributions to the overall stress are investigated as a function of space and time during the propagation, and related to the formation of specific features such as lateral lev&amp;#233;es, hydraulic jumps, etc. This study represents a first step towards robust avalanches simulations, spanning the wide range of possible flow regimes, through shallow-flow approaches. Future improvements involving more refined cohesion parameterizations will be discussed.&lt;/p&gt;

Influence of Longitudinal Roughness on Friction in EHL Contacts

2004 ◽  
Vol 126 (3) ◽  
pp. 473-481 ◽  
Author(s):  
B. Jacod ◽  
C. H. Venner ◽  
P. M. Lugt
Keyword(s):  
Numerical Simulations ◽  
Operating Conditions ◽  
Simplified Approach ◽  
Curve Fit ◽  
Longitudinal Roughness ◽  
Wide Range ◽  
Equivalent Wave ◽  
Harmonic Components ◽  
Comparison Of The Results ◽  
Relative Friction

The effect of longitudinal roughness on the friction in EHL contacts is investigated by means of numerical simulations. In the theoretical model the Eyring equation is used to describe the rheological behavior of the lubricant. First the relative friction variation caused by a single harmonic roughness component is computed as a function of the amplitude and wavelength for a wide range of operating conditions. From the results a curve fit formula is derived for the relative friction variation as a function of the out-of-contact geometry of the waviness and a newly derived parameter characterizing the response of the lubricant to pressure variations. Subsequently, the case of a superposition of two harmonic components is considered. It is shown that for the effect on friction such a combined pattern can be represented by a single equivalent wave. The amplitude and the wavelength of the equivalent wave can be determined from a nonlinear relation in terms of the amplitudes and wavelengths of the individual harmonic components. Finally the approach is applied to the prediction of the effect of a real roughness profile (many components) on the friction. From a comparison of the results with full numerical simulations it appears that the simplified approach is quite accurate.

scholarly journals Persistent magnetic vortex flow at a supergranular vertex

2018 ◽  
Vol 610 ◽  
pp. A84 ◽  
Author(s):  
Iker S. Requerey ◽  
Basilio Ruiz Cobo ◽  
Milan Gošić ◽  
Luis R. Bellot Rubio
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Vortex Flow ◽  
Spatial Scales ◽  
Magnetic Vortex ◽  
Magnetic Feature ◽  
Magnetic Element ◽  
Flow Maps ◽  
Wide Range ◽  
Intensity Images

Context. Photospheric vortex flows are thought to play a key role in the evolution of magnetic fields. Recent studies show that these swirling motions are ubiquitous in the solar surface convection and occur in a wide range of temporal and spatial scales. Their interplay with magnetic fields is poorly characterized, however. Aims. We study the relation between a persistent photospheric vortex flow and the evolution of a network magnetic element at a supergranular vertex. Methods. We used long-duration sequences of continuum intensity images acquired with Hinode and the local correlation-tracking method to derive the horizontal photospheric flows. Supergranular cells are detected as large-scale divergence structures in the flow maps. At their vertices, and cospatial with network magnetic elements, the velocity flows converge on a central point. Results. One of these converging flows is observed as a vortex during the whole 24 h time series. It consists of three consecutive vortices that appear nearly at the same location. At their core, a network magnetic element is also detected. Its evolution is strongly correlated to that of the vortices. The magnetic feature is concentrated and evacuated when it is caught by the vortices and is weakened and fragmented after the whirls disappear. Conclusions. This evolutionary behavior supports the picture presented previously, where a small flux tube becomes stable when it is surrounded by a vortex flow.

scholarly journals A comprehensive Monte Carlo study to design a novel multi-nanoparticle loaded nanocomposites for augmentation of attenuation coefficient in the energy range of diagnostic X-rays

2021 ◽  
Vol 27 (4) ◽  
pp. 279-289
Author(s):  
Elahe Sayyadi ◽  
Asghar Mesbahi ◽  
Reza Eghdam Zamiri ◽  
Farshad Seyyed Nejad
Keyword(s):  
Monte Carlo ◽  
Energy Range ◽  
Radiation Protection ◽  
Experimental Studies ◽  
Rubber Matrix ◽  
Photon Flux ◽  
Monte Carlo Code ◽  
X Rays ◽  
Wide Range ◽  
Shielding Properties

Abstract Introduction: The present study aimed to investigate the radiation protection properties of silicon-based composites doped with nano-sized Bi2O3, PbO, Sm2O3, Gd2O3, WO3, and IrO2 particles. Radiation shielding properties of Sm2O3 and IrO2 nanoparticles were investigated for the first time in the current study. Material and methods: The MCNPX (2.7.0) Monte Carlo code was utilized to calculate the linear attenuation coefficients of single and multi-nano structured composites over the X-ray energy range of 10–140 keV. Homogenous distribution of spherical nanoparticles with a diameter of 100 nm in a silicon rubber matrix was simulated. The narrow beam geometry was used to calculate the photon flux after attenuation by designed nanocomposites. Results: Based on results obtained for single nanoparticle composites, three combinations of different nano-sized fillers Sm2O3+WO3+Bi2O3, Gd2O3+WO3+Bi2O3, and Sm2O3+WO3+PbO were selected, and their shielding properties were estimated. In the energy range of 20-60 keV Sm2O3 and Gd2O3 nanoparticles, in 70-100 keV energy range WO3 and for photons energy higher than 90 keV, PbO and Bi2O3 nanoparticles showed higher attenuation. Despite its higher density, IrO2 had lower attenuation compared to other nanocomposites. The results showed that the nanocomposite containing Sm2O3, WO3, and Bi2O3 nanoparticles provided better shielding among the studied samples. Conclusions: All studied multi-nanoparticle nanocomposites provided optimum shielding properties and almost 8% higher attenuation relative to single nano-based composites over a wide range of photon energy used in diagnostic radiology. Application of these new composites is recommended in radiation protection. Further experimental studies are suggested to validate our findings.

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