A New Method for Computing the Gravitational Force in Particle Simulations

1983 ◽  
Vol 5 (2) ◽  
pp. 182-183 ◽  
Author(s):  
J. J. Monaghan
Keyword(s):  
Gravitational Force ◽  
Mass Density ◽  
Standard Procedure ◽  
Equal Mass ◽  
New Method ◽  
Average Mass ◽  
Gravitational Forces ◽  
Particle Simulations

A standard procedure for the simulation of galaxies is to replace the ∼ 1011 stars by ∼ 104 particles. These particles are assumed to have equal mass and their distribution in space produces a mass density ϱ which mimics the average mass density of the stars. From the mass density of the particles the gravitational forces between the particles can be computed. In the literature two methods have been used to compute these forces.

Particle energization inside plasmoids: numerical and analytical investigations

2021 ◽  
Author(s):  
Xiaozhou Zhao ◽  
Rony Keppens ◽  
Fabio Bacchini
Keyword(s):  
Test Particle ◽  
Large Scale ◽  
Mass Density ◽  
Magnetic Islands ◽  
Chaotic Flow ◽  
Reynolds Decomposition ◽  
Particle Simulations ◽  
Particle Energization ◽  
Periodic Setting ◽  
A Current

<div> <div> <div> <p>In an idealized system where four magnetic islands interact in a two-dimensional periodic setting, we follow the detailed evolution of current sheets forming in between the islands, as a result of an enforced large-scale merging by magnetohydrodynamic (MHD) simulation. The large-scale island merging is triggered by a perturbation to the velocity field, which drives one pair of islands move towards each other while the other pair of islands are pushed away from one another. The "X"-point located in the midst of the four islands is locally unstable to the perturbation and collapses, producing a current sheet in between with enhanced current and mass density. Using grid-adaptive resistive magnetohydrodynamic (MHD) simulations, we establish that slow near-steady Sweet-Parker reconnection transits to a chaotic, multi-plasmoid fragmented state, when the Lundquist number exceeds about 3×10<sup>4</sup>, well in the range of previous studies on plasmoid instability. The extreme resolution employed in the MHD study shows significant magnetic island substructures. Turbulent and chaotic flow patters are also observed inside the islands. We set forth to explore how charged particles can be accelerated in embedded mini-islands within larger (monster)-islands on the sheet. We study the motion of the particles in a MHD snapshot at a fixed instant of time by the Test-Particle Module incorporated in AMRVAC (). The planar MHD setting artificially causes the largest acceleration in the ignored third direction, but does allow for full analytic study of all aspects leading to the acceleration and the in-plane, projected trapping of particles within embedded mini-islands. The analytic result uses a decomposition of the test particle velocity in slow and fast changing components, akin to the Reynolds decomposition in turbulence studies. The analytic results allow a complete fit to representative proton test particle simulations, which after initial non-relativistic motion throughout the monster island, show the potential of acceleration within a mini-island beyond (√2/2)c≈0.7c, at which speed the acceleration is at its highest efficiency. Acceleration to several hundreds of GeVs can happen within several tens of seconds, for upward traveling protons in counterclockwise mini-islands of sizes smaller than the proton gyroradius.</p> </div> </div> </div><div></div><div></div>

Topology Optimization Considering Gravitational and Centrifugal Forces

2006 ◽  
Author(s):  
Bin Zheng ◽  
Hae Chang Gea
Keyword(s):  
Topology Optimization ◽  
Kinetic Energy ◽  
Structural Design ◽  
Gravitational Force ◽  
Body Force ◽  
Optimization Problems ◽  
Sensitivity Analyses ◽  
Centrifugal Forces ◽  
Gravitational Forces ◽  
Mean Compliance

In this paper, topology optimization problems with two types of body force are considered: gravitational force and centrifugal force. For structural design under both external and gravitational forces, a total mean compliance formulation is used to produce the stiffest structure. For rotational structural design with high angular velocity, one additional design criteria, kinetic energy, is included in the formulation. Sensitivity analyses of the total mean compliance and kinetic energy are derived. Finally, design examples are presented and compared to show the effects of body forces on the optimized results.

Seed coat specific weight in Lupinus angustifolius: influence of genotype and environment and relationship with seed coat proportion

2004 ◽  
Vol 55 (11) ◽  
pp. 1189 ◽  
Author(s):  
M. Mera ◽  
R. Jerez ◽  
H. Miranda ◽  
J. L. Rouanet
Keyword(s):  
Seed Coat ◽  
Seed Weight ◽  
Mass Density ◽  
Selection Criterion ◽  
Specific Weight ◽  
Equal Mass ◽  
Lupinus Angustifolius ◽  
Broad Sense ◽  
Broad Sense Heritability ◽  
Selection For

Abstract. The relatively high seed coat proportion of the narrow-leafed lupin reduces its economic value. This character has been shown to be affected by seed weight, and this limits the use of seed coat proportion as a selection criterion. We examined the variation for seed coat specific weight, a potential alternative selection criterion, and tested its relationship with seed coat proportion and seed weight. Seeds were sampled from mainstem pods of 14 winter-sown genotypes of Lupinus angustifolius L. grown at 4 southern Chile sites over 2 years. Seed coat specific weight had an overall mean of 30.1 mg/cm2. Highly significant genotypic effects were found (range 28.9–32.1 mg/cm2). The ranges for sites and years were 29.1–31.1 and 28.9–31.2 mg/cm2, respectively. Genotypes interacted significantly with years, but not with sites. Broad-sense heritability was 0.59, a value that predicts a good response to selection for this character. Seed coat specific weight was weakly correlated (rph = 0.11*) with seed coat proportion, and was not associated with mean seed weight. Seed coat proportion was negatively correlated with mean seed weight (rph = –0.75***) and had high broad-sense heritability (0.95). The correlation between seed coat specific weight and a theoretical seed coat thickness, calculated under the assumptions of equal mass density of seed coat, cotyledons, and embryo, and a spherical-shaped seed, was r = 0.14*. Phenotypic and genotypic correlations between seed coat specific weight and number of seeds per pod were 0.41 and 0.84, respectively. Our results indicate that selection for low seed coat proportion will lead to larger seeded genotypes, but will not reduce seed coat specific weight. Selection for low seed coat proportion after crosses would presumably be effective in reducing seedcoat specific weight if all segregating materials were uniformly large seeded, but that scenario is unrealistic. The evidence presented here suggests that selection for low seed coat specific weight (or measures correlated with it) in segregating populations will be necessary in order to increase the proportion of higher value kernels in seeds and to improve the economic yield of lupins.

scholarly journals Using depolarization to quantify ice nucleating particle concentrations: a new method

2017 ◽  
Vol 10 (12) ◽  
pp. 4639-4657 ◽  
Author(s):  
Jake Zenker ◽  
Kristen N. Collier ◽  
Guanglang Xu ◽  
Ping Yang ◽  
Ezra J. T. Levin ◽  
...  
Keyword(s):  
Standard Procedure ◽  
Diffusion Chamber ◽  
Operating Conditions ◽  
Ice Crystals ◽  
New Method ◽  
State University ◽  
Analysis Method ◽  
Colorado State University ◽  
Nominal Size ◽  
Wide Range

Abstract. We have developed a new method to determine ice nucleating particle (INP) concentrations observed by the Texas A&M University continuous flow diffusion chamber (CFDC) under a wide range of operating conditions. In this study, we evaluate differences in particle optical properties detected by the Cloud and Aerosol Spectrometer with POLarization (CASPOL) to differentiate between ice crystals, droplets, and aerosols. The depolarization signal from the CASPOL instrument is used to determine the occurrence of water droplet breakthrough (WDBT) conditions in the CFDC. The standard procedure for determining INP concentration is to count all particles that have grown beyond a nominal size cutoff as ice crystals. During WDBT this procedure overestimates INP concentration, because large droplets are miscounted as ice crystals. Here we design a new analysis method based on depolarization ratio that can extend the range of operating conditions of the CFDC. The method agrees reasonably well with the traditional method under non-WDBT conditions with a mean percent error of ±32.1 %. Additionally, a comparison with the Colorado State University CFDC shows that the new analysis method can be used reliably during WDBT conditions.

Penetrating Resistance of the Laminated Composite with Stepwise Graded Foam

2010 ◽  
Vol 139-141 ◽  
pp. 72-75
Author(s):  
Feng Huan Sha
Keyword(s):  
Mass Density ◽  
Laminated Composite ◽  
Areal Density ◽  
Equal Mass ◽  
Composite Target ◽  
Perfectly Plastic ◽  
Cellular Target ◽  
Expansion Theory ◽  
The Difference ◽  
Cavity Expansion Theory

The present study focuses on the penetrating resistance of the laminated composite with stepwise graded foam target struck normally by conical-nosed projectiles. The dynamic cavity expansion theory is applied to formulate analytical model. Experimental results verify that this model on account of rigid-perfectly plastic-locking model is suitable for analyzing penetration depth of the projectile into a cellular target. The difference types of foam configurations, with identical areal density, were arranged according to the density of the respective foam. The penetrating process can be divided into 7 stages. Penetrating depth; the effect of mass density and the change of graded/layered core structures of the difference configurations are analyzed. It is found that composite target have a higher penetrating resistance than the monolithic foam material target of equal mass. The analytical results show great potential to reasonable structures for absorbing the dynamics energy and improving the overall penetrating resistance.

A new method for orthoscopic adjustment with the Fedorov stage

1959 ◽  
Vol 32 (246) ◽  
pp. 245-250
Author(s):  
A. F. Hallimond
Keyword(s):  
Standard Procedure ◽  
Symmetry Plane ◽  
Maximum Sensitivity ◽  
New Method ◽  
Wide Range

SummaryA new method is described to replace the standard procedure for completing the adjustment of an optical symmetry plane, with conditions for the accurate use of the biquartz. Extinction measurements are plotted to show the wide range of sensitivity (for the adjustment of A1 and A2) at various directions in the symmetry planes of a plagioclase. It is proposed that A1 and A2should be adjusted at different settings of A4 so as to obtain maximum sensitivity for each of those axes.

scholarly journals FREE CURVILINEAR SPACE WITH TORSION

Globus ◽  
2021 ◽  
Vol 7 (6(63)) ◽  
pp. 27-33
Author(s):  
Y.A. Sharin
Keyword(s):  
Field Theory ◽  
Mass Density ◽  
Classical Field Theory ◽  
Classical Field ◽  
Field Equations ◽  
Curved Space ◽  
Astronomical Observations ◽  
Average Mass ◽  
Cosmological Solutions ◽  
The Universe

Under the classical field theory, a variant unification of gravity and electromagnetism on the basis of four-dimensional curved space with torsion is proposed. The connection between electromagnetic field and torsion of space is discovered, a physical interpretation of the space scalar curvature as the density of matter mass is proposed. The solution for the eigenstate of a curved space with torsion, corresponding to the electron is obtained. The identification of the field equations as the Schrodinger equation for the hydrogen atom is shown. Cosmological solutions for the expanding Universe are found, the average mass density in the Universe is estimated, and the results corresponding to the data of astronomical observations are obtained.

Influence of microgravity on crystal formation in biomineralization

2000 ◽  
Vol 89 (4) ◽  
pp. 1601-1607 ◽  
Author(s):  
Wilhelm Becker ◽  
Julia Marxen ◽  
Matthias Epple ◽  
Oliver Reelsen
Keyword(s):  
Gravitational Force ◽  
Space Shuttle ◽  
Organic Matrix ◽  
Essential Elements ◽  
Model System ◽  
Inorganic Materials ◽  
Crystal Formation ◽  
Shell Material ◽  
Gravitational Forces ◽  
Building Process

Biomineralized tissues are widespread in animals. They are essential elements in skeletons and in statocysts. The function of both can only be understood with respect to gravitational force, which has always been present. Therefore, it is not astonishing to identify microgravity as a factor influencing biomineralization, normally resulting in the reduction of biomineralized materials. All known biominerals are composite materials, in which the organic matrix and the inorganic materials, organized in crystals, interact. If, during remodeling and turnover processes under microgravity, a defective organization of these crystals occurs, a reduction in biomineralized materials could be the result. To understand the influence of microgravity on the formation of biocrystals, we studied the shell-building process of the snail Biomphalaria glabrataas a model system. We show that, under microgravity (space shuttle flights STS-89 and STS-90), shell material is built in a regular way in both adult snails and snail embryos during the beginning of shell development. Microgravity does not influence crystal formation. Because gravity has constantly influenced evolution, the organization of biominerals with densities near 3 must have gained independence from gravitational forces, possibly early in evolution.

A Method of Calculating Radiative Heat Diffusion in Particle Simulations

1985 ◽  
Vol 6 (2) ◽  
pp. 207-210 ◽  
Author(s):  
L. Brookshaw
Keyword(s):  
Boundary Conditions ◽  
Radiative Heat ◽  
Three Dimensional ◽  
Heat Diffusion ◽  
New Method ◽  
Particle Simulations

AbstractA new method for solving heat diffusion in three dimensional particle simulations is described. The difficulties encounted by other authors is discussed, in particular the difficulty of including boundary conditions in particle simulations. One and three dimensional tests of the method are described.

scholarly journals Surrounding matter theory

2018 ◽  
Vol 182 ◽  
pp. 03006
Author(s):  
Frederic Lassiaille
Keyword(s):  
Galaxy Formation ◽  
Large Scale ◽  
Gravitational Force ◽  
Mass Density ◽  
Critical Density ◽  
Fine Tuning ◽  
Newtonian Potential ◽  
Alternative Theory ◽  
De Sitter ◽  
Matter Theory

S.M.T. (Surrounding Matter Theory), an alternative theory to dark matter, is presented. It is based on a modification of Newton's law. This modification is done by multiplying a Newtonian potential by a given factor, which is varying with local distribution of matter, at the location where the gravitational force is exerted. With this new equation the model emphasizes that a gravitational force is roughly inversely proportional to mass density at the location where this force is applied. After presentation of the model, its dynamic is quickly applied to cosmology and galaxy structure. Some possible caveats of the model are identified. But the simple mechanism described above suggests the idea of a straightforward solution to the following issues: virial theorem mystery, the bullet cluster (“1E 0657-56” galaxy clusters) issue, the strong relative velocity of its subclusters, the value of cosmological critical density, the fine tuning issue, and expansion acceleration. Nucleosynthesis is not explained and would require a different model for radiation era. But a de Sitter Universe is predicted, this means that the spatial curvature, K, is 0, and today's deceleration parameter, q, is -1. The predicted time since last scattering is 68 h-1Gyr. With this value SMT explains heterogeneities of large scale structure and galaxy formation. Each kind of experimental speed profiles are retrieved by a simulation of a virtual galaxy. In the simulations, ring galaxies are generated by SMT dynamic itself, without the help of any particular external event. Those studies give motivation for scientific comparisons with experimental data.

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