Magnetic Retention of LOX in an Off-Axis Accelerating Environment

2005 ◽  
Author(s):  
B. D. Simmons ◽  
J. I. Hochstein ◽  
J. G. Marchetta ◽  
S. H. Collicott
Keyword(s):  
Magnetic Field ◽  
Potential Energy ◽  
Computational Simulation ◽  
Minimum Energy ◽  
Surface Evolver ◽  
Magnetic Retention ◽  
Cryogenic Propellants ◽  
Energy Configurations ◽  
Constant Gradient ◽  
Propellant Management

Magnetic positive propellant positioning (MP3) of cryogenic propellants in spacecraft tanks may outperform existing technologies and, unlike some of the competing technologies, MP3 can be an adaptive management system that optimizes performance for the entire mission profile. Surface Evolver, (SE), a public domain program that seeks minimum energy configurations for modeled systems, provided a foundation on which to build a computational simulation to begin investigating the promise of MP3. Energies modeled include surface tension, potential energy due to background acceleration, and the change in potential energy due to the presence of a fluid in a magnetic field. A detailed development of these models is presented as well as specific expressions that other researchers can use with SE to study MP3. Verification and validation of the comprehensive model has been performed using several “known” solutions, three of which are reported herein: a constant gradient, a current carrying wire, and a dipole magnetic field. The computational tool is then used to study the ability of a magnet to retain a pool of LO2 about it when subjected to background acceleration. Results from this study, presented herein, indicate the promise of MP3 for adaptive cryogenic propellant management systems for future spacecraft and fuel depot applications.

scholarly journals Effects of electrical stimulation on isolated rodent gastric smooth muscle cells evaluated via a joint computational simulation and experimental approach

2009 ◽  
Vol 297 (4) ◽  
pp. G672-G680 ◽  
Author(s):  
P. Du ◽  
S. Li ◽  
G. O'Grady ◽  
L. K. Cheng ◽  
A. J. Pullan ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Electrical Stimulation ◽  
Pulse Train ◽  
Pulse Width ◽  
Computational Simulation ◽  
Minimum Energy ◽  
Experimental Studies ◽  
Single Pulse ◽  
Plateau Phase ◽  
Wide Range

Gastric electrical stimulation (GES) involves the delivery of electrical impulses to the stomach for therapeutic purposes. New GES protocols are needed that are optimized for improved motility outcomes and energy efficiency. In this study, a biophysically based smooth muscle cell (SMC) model was modified on the basis of experimental data and employed in conjunction with experimental studies to define the effects of a large range of GES protocols on individual SMCs. For the validation studies, rat gastric SMCs were isolated and subjected to patch-clamp analysis during stimulation. Experimental results were in satisfactory agreement with simulation results. The results define the effects of a wide range of GES parameters (pulse width, amplitude, and pulse-train frequency) on isolated SMCs. The minimum pulse width required to invoke a supramechanical threshold response from SMCs (defined at −30 mV) was 65 ms (at 250-pA amplitude). The minimum amplitude required to invoke this threshold was 75 pA (at 1,000-ms pulse width). The amplitude of the invoked response beyond this threshold was proportional to the stimulation amplitude. A high-frequency train of stimuli (40 Hz; 10 ms, 150 pA) could invoke and maintain the SMC plateau phase while requiring 60% less power and accruing ∼30% less intracellular Ca2+ concentration during the plateau phase than a comparable single-pulse protocol could in a demonstrated example. Validated computational simulations are an effective strategy for efficiently identifying effective minimum-energy GES protocols, and pulse-train protocols may also help to reduce the power consumption of future GES devices.

The energy and helicity of knotted magnetic flux tubes

1995 ◽  
Vol 451 (1943) ◽  
pp. 609-629 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Minimum Energy ◽  
Circular Cross Section ◽  
Parametric Representation ◽  
Energy Functional ◽  
Helical Axis ◽  
Torus Knots ◽  
Flux Tubes ◽  
Kink Mode

Magnetic relaxation of a magnetic field embedded in a perfectly conducting incompressible fluid to minimum energy magnetostatic equilibrium states is considered. It is supposed that the magnetic field is confined to a single flux tube which may be knotted. A local non-orthogonal coordinate system, zero-framed with respect to the knot, is introduced, and the field is decomposed into toroidal and poloidal ingredients with respect to this system. The helicity of the field is then determined; this vanishes for a field that is either purely toroidal or purely poloidal. The magnetic energy functional is calculated under the simplifying assumptions that the tube is axially uniform and of circular cross-section. The case of a tube with helical axis is first considered, and new results concerning kink mode instability and associated bifurcations are obtained. The case of flux tubes in the form of torus knots is then considered and the ‘ground-state’ energy function ͞m ( h ) (where h is an internal twist parameter) is obtained; as expected, ͞m ( h ), which is a topological invariant of the knot, increases with increasing knot complexity. The function ͞m ( h ) provides an upper bound on the corresponding function m ( h ) that applies when the above constraints on tube structure are removed. The technique is applicable to any knot admitting a parametric representation, on condition that points of vanishing curvature are excluded.

scholarly journals Pitch angle scattering of an energetic magnetized particle by a circularly polarized electromagnetic wave

2021 ◽  
Author(s):  
Paul M. Bellan
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Wave ◽  
Kinetic Energy ◽  
Potential Energy ◽  
Pitch Angle ◽  
Energetic Electron ◽  
Circularly Polarized ◽  
Angle Scattering ◽  
Background Magnetic Field ◽  
Pseudo Potential

<p>The interaction between a circularly polarized electromagnetic wave and an energetic gyrating particle is described [1] using a relativistic pseudo-potential that is a function of the frequency mismatch,  a measure of the extent to which ω-k<sub>z</sub>v<sub>z</sub>=Ω/γ is not true. The description of this wave-particle interaction involves a sequence of relativistic transformations that ultimately demonstrate that the pseudo potential energy of a pseudo particle adds to a pseudo kinetic energy giving a total pseudo energy that is a constant of the motion. The pseudo kinetic energy is proportional to the square of the particle acceleration (compare to normal kinetic energy which is the square of a velocity) and the pseudo potential energy is a function of the mismatch and so effectively a function of the particle velocity parallel to the background magnetic field (compare to normal potential energy which is a function of position). Analysis of the pseudo-potential provides a means for interpreting particle motion in the wave in a manner analogous to the analysis of a normal particle bouncing in a conventional potential well.  The wave-particle  interaction is electromagnetic and so differs from and is more complicated than the well-known Landau damping of electrostatic waves.  The pseudo-potential profile depends on the initial mismatch, the normalized wave amplitude, and the initial angle between the wave magnetic field and the particle perpendicular velocity. For zero initial mismatch, the pseudo-potential consists of only one valley, but for finite mismatch, there can be two valleys separated by a hill. A large pitch angle scattering of the energetic electron can occur in the two-valley situation but fast scattering can also occur in a single valley. Examples relevant to magnetospheric whistler waves are discussed. Extension to the situation of a distribution of relativistic particles is presented in a companion talk [2].</p><p>[1] P. M. Bellan, Phys. Plasmas 20, Art. No. 042117 (2013)</p><p>[2] Y. D. Yoon and P. M. Bellan, JGR 125, Art. No. e2020JA027796 (2020)</p>

scholarly journals Onset of superconductivity and retention of magnetic fields in cooling neutron stars

2017 ◽  
Vol 13 (S337) ◽  
pp. 213-216
Author(s):  
Wynn C. G. Ho ◽  
Nils Andersson ◽  
Vanessa Graber
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
Minimum Energy ◽  
Meissner Effect ◽  
Energy Conditions ◽  
Field Diffusion ◽  
Neutron Star Cooling ◽  
Proton Pairing

AbstractA superconductor of paired protons is thought to form in the core of neutron stars soon after their birth. Minimum energy conditions suggest that magnetic flux is expelled from the superconducting region due to the Meissner effect, such that the neutron star core retains or is largely devoid of magnetic fields for some nuclear equation of state and proton pairing models. We show via neutron star cooling simulations that the superconducting region expands faster than flux is expected to be expelled because cooling timescales are much shorter than timescales of magnetic field diffusion. Thus magnetic fields remain in the bulk of the neutron star core for at least 106 − 107yr. We estimate the size of flux free regions at 107yr to be ≲ 100m for a magnetic field of 1011G and possibly smaller for stronger field strengths.

scholarly journals On the stability of a general magnetic field topology in stellar radiative zones

2019 ◽  
Vol 82 ◽  
pp. 365-371
Author(s):  
K. Augustson ◽  
S. Mathis ◽  
A. Strugarek
Keyword(s):  
Magnetic Field ◽  
Global Change ◽  
Magnetic Fields ◽  
Potential Energy ◽  
Massive Stars ◽  
Spherical Geometry ◽  
Stable Region ◽  
Magnetic Field Topology ◽  
The Stability ◽  
The Magnetic Field

This paper provides a brief overview of the formation of stellar fossil magnetic fields and what potential instabilities may occur given certain configurations of the magnetic field. One such instability is the purely magnetic Tayler instability, which can occur for poloidal, toroidal, and mixed poloidal-toroidal axisymmetric magnetic field configurations. However, most of the magnetic field configurations observed at the surface of massive stars are non-axisymmetric. Thus, extending earlier studies in spherical geometry, we introduce a formulation for the global change in the potential energy contained in a convectively-stable region for both axisymmetric and non-axisymmetric magnetic fields.

Modelling of interactions in solutions: alkali halides in DMSO

1979 ◽  
Vol 57 (5) ◽  
pp. 538-551 ◽  
Author(s):  
Peeter Kruus ◽  
Barbara E. Poppe
Keyword(s):  
Reasonable Agreement ◽  
Minimum Energy ◽  
Alkali Halides ◽  
Ion Pair ◽  
Point Of View ◽  
Ion Solvation ◽  
Solvation Energies ◽  
Solvent Molecules ◽  
A Charge ◽  
Energy Configurations

A model of solutions of alkali halides in DMSO is developed. Each ion is described by a radius, a charge, a polarizability, and an exponential repulsion parameter. Each molecule is described by a polarizability, charges, 6-12 energy parameters, and 6-12 distance parameters centered on each of the 10 atoms in the molecule. The model is applied to calculate (i) the vaporization energy of solvent molecules, (ii) single ion solvation energies and configurations of the solvating molecules, and (iii) the energy as a function of reaction coordinate for the formation of an ion pair. The energies and configurations are obtained by allowing the systems to relax to minimum energy configurations by allowing motion of the molecules. The results of (i) give a vaporization energy 60% of the experimental. The results of (ii) give solvation energies in reasonable agreement with the experimental, and configurations which are reasonable from the point of view of mobilities of ions. The results of (iii) show the presence of a distinct solvent separated ion pair which actually has an energy lower than the contact ion pair. Advantages and problems involved in using this approach to model solutions are discussed.

scholarly journals Clusters, columns, and lamellae—minimum energy configurations in core softened potentials

Soft Matter ◽  
2008 ◽  
Vol 4 (7) ◽  
pp. 1396 ◽  
Author(s):  
Gernot J. Pauschenwein ◽  
Gerhard Kahl
Keyword(s):  
Minimum Energy ◽  
Energy Configurations
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