scholarly journals Streaming instability on different scales – I. Planetesimal mass distribution variability

2020 ◽  
Vol 500 (1) ◽  
pp. 520-530
Author(s):  
J J Rucska ◽  
J W Wadsley
Keyword(s):  
Numerical Simulations ◽  
Mass Distribution ◽  
Formation Process ◽  
Total Mass ◽  
Density Field ◽  
Dust Density ◽  
Streaming Instability ◽  
Novel Approach ◽  
Self Gravity ◽  
Linear Nature

ABSTRACT We present numerical simulations of dust clumping and planetesimal formation initiated by the streaming instability (SI) with self-gravity. We examine the variability in the planetesimal formation process by employing simulation domains with large radial and azimuthal extents and a novel approach of re-running otherwise identical simulations with different random initializations of the dust density field. We find that the planetesimal mass distribution and the total mass of dust that is converted into planetesimals can vary substantially between individual small simulations and within the domains of larger simulations. Our results show that the non-linear nature of the developed SI introduces substantial variability in the planetesimal formation process that has not been previously considered and suggests larger scale dynamics may affect the process.

Impedance Control of Dual-Arm Systems Based on the Object with Senseless Force

2013 ◽  
Vol 765-767 ◽  
pp. 1920-1923
Author(s):  
Li Jiang ◽  
Yang Zhou ◽  
Bin Wang ◽  
Chao Yu
Keyword(s):  
Numerical Simulations ◽  
Relative Position ◽  
Position Control ◽  
Impedance Control ◽  
Force Sensors ◽  
Operational Space ◽  
Novel Approach ◽  
Control Scheme ◽  
Statics And Dynamics ◽  
Dual Arm

A novel approach to impedance control based on the object is proposed to control dual-arm systems with senseless force. Considering the motion of the object, the statics and dynamics of the dual-arm systems are modeled. Extending the dynamics of dual-arm system and the impedance of object to the operational space, impedance control with senseless force is presented. Simulations on a dual-arm system are carried out to demonstrate the performance of the proposed control scheme. Comparing with position control, results of numerical simulations show that the proposed scheme realizes suitable compliant behaviors in terms of the object, and minimizes the error of the relative position between the manipulators even without force sensors.

scholarly journals Bondgraph modelling and simulation of the dynamic behaviour of above-knee prostheses

1987 ◽  
Vol 11 (2) ◽  
pp. 65-70 ◽  
Author(s):  
P. G. Van De Veen ◽  
W. Van Der Tempel ◽  
J. De Vreiss
Keyword(s):  
Mathematical Model ◽  
Computer Simulation ◽  
Mass Distribution ◽  
Total Mass ◽  
Dynamic Behaviour ◽  
Step Length ◽  
Swing Phase ◽  
Knee Prostheses ◽  
Prosthetic Foot ◽  
Walking Velocity

A mathematical model was used to investigate the dynamic behaviour of an above-knee (AK) prosthesis in the swing phase and to analyse the influence of mass and mass distribution on the maximal stump load and the required energy. The model consists of a bondgraph model of the prosthesis and a “walking” model which predicts the walking velocity, step length and the femoral trajectory. Equipment was developed to measure the inertial properties of the components of the prosthesis. Through computer simulation, stickdiagrams of the swing phase and graphs of the variation with time of the hip and stump forces were obtained. It was found that for a normal AK prosthesis with a knee-lock mechanism the axial stump load is greatest at the beginning and at the end of the swing phase. At a walking velocity of 5 km/hr the maximum axial stump load amounts to 2.1 times the static weight of the prosthesis. The maximum axial stump force appeared to be almost directly proportional to the total mass of the prosthesis but independent of the mass distribution. The required energy also increased with the mass of the prosthesis but is' dependent on mass distribution. Because of their comparable weights the influence of the shoe is almost equal to the influence of the prosthetic foot. Thus lightweight shoes should be used with lightweight prosthetic feet in order to add to their advantages.

A passivity-based observer for neural mass models

2018 ◽  
Vol 36 (3) ◽  
pp. 701-711
Author(s):  
Xian Liu ◽  
Cheng-Xia Sun ◽  
Qing Gao ◽  
Zhi-Wang Chen
Keyword(s):  
System Theory ◽  
Linear Matrix Inequality ◽  
Numerical Simulations ◽  
Linear Matrix ◽  
Matrix Inequality ◽  
Structure Characteristics ◽  
Novel Approach ◽  
Neural Mass ◽  
Passive Theory

Abstract This paper presents a novel approach of designing a stabilizing observer for neural mass models which can simulate distinct rhythms in electroencephalography (EEG). Due to the structure characteristics, neural mass models are expressed as Lurie systems. The stabilizing observer is designed by using the Lurie system theory and the passive theory. The observer matrices are constructed via solutions of some linear matrix inequality (LMI) conditions. Numerical simulations are used to demonstrate the efficiency of the results.

scholarly journals Growth after the streaming instability

2019 ◽  
Vol 624 ◽  
pp. A114 ◽  
Author(s):  
Beibei Liu ◽  
Chris W. Ormel ◽  
Anders Johansen
Keyword(s):  
Dynamical Evolution ◽  
Bimodal Distribution ◽  
Stokes Number ◽  
Volume Density ◽  
Mass Star ◽  
Type I ◽  
Solar Mass ◽  
Streaming Instability ◽  
Two Component ◽  
Self Gravity

Context. Streaming instability is a key mechanism in planet formation, clustering pebbles into planetesimals with the help of self-gravity. It is triggered at a particular disk location where the local volume density of solids exceeds that of the gas. After their formation, planetesimals can grow into protoplanets by feeding from other planetesimals in the birth ring as well as by accreting inwardly drifting pebbles from the outer disk. Aims. We aim to investigate the growth of planetesimals into protoplanets at a single location through streaming instability. For a solar-mass star, we test the conditions under which super-Earths are able to form within the lifetime of the gaseous disk. Methods. We modified the Mercury N-body code to trace the growth and dynamical evolution of a swarm of planetesimals at a distance of 2.7 AU from the star. The code simulates gravitational interactions and collisions among planetesimals, gas drag, type I torque, and pebble accretion. Three distributions of planetesimal sizes were investigated: (i) a mono-dispersed population of 400 km radius planetesimals, (ii) a poly-dispersed population of planetesimals from 200 km up to 1000 km, (iii) a bimodal distribution with a single runaway body and a swarm of smaller, 100 km size planetesimals. Results. The mono-dispersed population of 400 km size planetesimals cannot form protoplanets of a mass greater than that of the Earth. Their eccentricities and inclinations are quickly excited, which suppresses both planetesimal accretion and pebble accretion. Planets can form from the poly-dispersed and bimodal distributions. In these circumstances, it is the two-component nature that damps the random velocity of the large embryo through the dynamical friction of small planetesimals, allowing the embryo to accrete pebbles efficiently when it approaches 10−2 M⊕. Accounting for migration, close-in super-Earth planets form. Super-Earth planets are likely to form when the pebble mass flux is higher, the disk turbulence is lower, or the Stokes number of the pebbles is higher. Conclusions. For the single site planetesimal formation scenario, a two-component mass distribution with a large embryo and small planetesimals promotes planet growth, first by planetesimal accretion and then by pebble accretion of the most massive protoplanet. Planetesimal formation at single locations such as ice lines naturally leads to super-Earth planets by the combined mechanisms of planetesimal accretion and pebble accretion.

scholarly journals Some Problems of Feedback Control Strategies and It’s Treatment

2017 ◽  
Vol 9 (1) ◽  
pp. 39 ◽  
Author(s):  
Maysoon M. Aziz ◽  
Saad Fawzi AL-Azzawi
Keyword(s):  
Dynamical Systems ◽  
Feedback Control ◽  
Numerical Simulations ◽  
Positive Feedback ◽  
Control Strategies ◽  
Novel Approach

This paper extends and improves the feedback control strategies. In detailed, the ordinary feedback, dislocated feedback, speed feedback and enhancing feedback control for a several dynamical systems are discussed here. It is noticed that there some problems by these strategies. For this reason, this Letter proposes a novel approach for treating these problems. The results obtained in this paper show that the strategies with positive feedback coefficients can be controlled in two cases and failed in another two cases. Theoretical and numerical simulations are given to illustrate and verify the results.

scholarly journals Energy optimization in extrasolar planetary systems: the transition from peas-in-a-pod to runaway growth

2020 ◽  
Vol 493 (4) ◽  
pp. 5520-5531 ◽  
Author(s):  
Fred C Adams ◽  
Konstantin Batygin ◽  
Anthony M Bloch ◽  
Gregory Laughlin
Keyword(s):  
Binary Stars ◽  
Total Mass ◽  
Extrasolar Planets ◽  
Energy State ◽  
Critical Mass ◽  
Energy Optimization ◽  
Planetary Systems ◽  
Equal Mass ◽  
Wide Range ◽  
Self Gravity

ABSTRACT Motivated by the trends found in the observed sample of extrasolar planets, this paper determines tidal equilibrium states for forming planetary systems – subject to conservation of angular momentum, constant total mass, and fixed orbital spacing. In the low mass limit, valid for super-Earth-class planets with masses of order mp ∼ 10 M⊕, previous work showed that energy optimization leads to nearly equal mass planets, with circular orbits confined to a plane. The present treatment generalizes previous results by including the self-gravity of the planetary bodies. For systems with a sufficiently large total mass $m_{\scriptstyle \rm T}$ in planets, the optimized energy state switches over from the case of nearly equal mass planets to a configuration where one planet contains most of the material. This transition occurs for a critical mass threshold of approximately $m_{\scriptstyle \rm T}\gtrsim m_{\scriptstyle \rm C}\sim 40\,{\rm M_\oplus}$ (where the value depends on the semimajor axes of the planetary orbits, the stellar mass, and other system properties). These considerations of energy optimization apply over a wide range of mass scales, from binary stars to planetary systems to the collection of moons orbiting the giant planets in our Solar system.

An approach to congestion analysis in crowd dynamics models

2020 ◽  
Vol 30 (05) ◽  
pp. 867-890 ◽  
Author(s):  
Liang Li ◽  
Hong Liu ◽  
Yanbin Han
Keyword(s):  
Numerical Simulations ◽  
Social Force ◽  
Accurate Analysis ◽  
Multiscale Representation ◽  
Novel Approach ◽  
Generalized Force ◽  
Evacuation Management ◽  
Dynamics Models ◽  
Theoretical Mechanics ◽  
Pressure Propagation

This paper presents a novel approach to quantitatively analyzing pedestrian congestion in evacuation management based on the Hughes and social force models. An accurate analysis of crowds plays an important role in illustrating their dynamics. However, the majority of the existing approaches to analyzing pedestrian congestion are qualitative. Few methods focus on the quantification of the interactions between crowds and individual pedestrians. According to the proposed approach, analytic tools derived from theoretical mechanics are applied to provide a multiscale representation of such interactions. In particular, we introduce movement constraints that illustrate the macroscopic and microscopic states of crowds. Furthermore, we consider pressure propagation and changes in the position of pedestrians during the evacuation process to improve the accuracy of the analysis. The generalized force caused by the varied density of pedestrians is applied to calculate the final congestion. Numerical simulations demonstrate the validity of the proposed approach.

scholarly journals 6.2. Efficiency in nuclear fueling

1998 ◽  
Vol 184 ◽  
pp. 265-266
Author(s):  
M. Noguchi
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Numerical Simulations ◽  
Observational Data ◽  
Formation Process ◽  
Large Body ◽  
Merging Galaxies ◽  
Numerical Studies ◽  
Galactic Astronomy ◽  
Theoretical Side

Starburst phenomena in interacting and merging galaxies have been one of the most widely investigated subjects in today's galactic astronomy. On the theoretical side, a large body of numerical studies have been performed in order to interpret available observational data. Numerical simulations have been advanced to the point where they can include interstellar medium (ISM) and star formation process.

Microstructure, Mass and Chemical Analysis with 8 to 44 Angstrom X-Radiation

1958 ◽  
Vol 2 ◽  
pp. 117-155 ◽  
Author(s):  
Burton L. Henke
Keyword(s):  
High Resolution ◽  
Chemical Analysis ◽  
Mass Distribution ◽  
Total Mass ◽  
Biological Research ◽  
Chemical Information ◽  
Analysis Method ◽  
X Ray

AbstractThe requirement of ultrasoft x-radiation (10 to 100A) for high resolution microradiographic analysis is established. Optimum methods are described for obtaining structure, mass distribution and mass-chemical information for microscopic sample regions as small as a few square microns and for total mass as small as a few micro-micrograms. The details of the techniques and of the instrumentation which are used in high resolution microradiographic analysis are presented.There has been a considerable amount of work reported on low magnification microradiography (up to 100 diameters) using conventional x-ray wavelengths.Relatively little work has been done in high resolution microradiography and with ultra soft x-radiation. Nearly all which has been reported has been in application to biological research where the need for such an analysis method seems to be greatest at this time. Outstanding among this work has been that of Engstrom and his co-workers.Much of the material which is presented in the present paper is intended as a supplement to that presented in the works of Engstrom and Lindstrom and with an emphasis upon the quantitative aspects of microradiographic analysis, using ultrasoft x-radiation.

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