Determination of two-dimensional magnetostatic equilibria and analogous Euler flows

1993 ◽  
Vol 246 ◽  
pp. 569-591 ◽  
Author(s):  
D. Linardatos
Keyword(s):  
Variational Problem ◽  
Energy State ◽  
Local Equilibrium ◽  
Minimum Energy ◽  
Saddle Points ◽  
Infinite Family ◽  
Finite Energy ◽  
Equilibrium Solutions ◽  
Energy Field ◽  
Field Lines

The equivalence of the method of magnetic relaxation to a variational problem with an infinity of constraints is established. This variational problem is solved in principle and approximations to the exact solution are compared to results obtained by numerical relaxation of fields with a single stationary elliptic point. In the case of a finite energy field of the above topology extending to infinity, we show that the minimum energy state is the one in which all field lines are concentric circles and that this state is topologically accessible from the original one. This state is used as a reference state for understanding the relaxation of fields constrained by finite boundaries. We then consider the relaxation of fields containing saddle points and confirm the tendency of the saddle points to collapse and form two Y-points. An infinite family of local equilibrium solutions each describing a Y-point is provided.

ALPHA-HELIX FORMATION IN C-PEPTIDE RNASE-A INVESTIGATED BY PARALLEL TEMPERING SIMULATIONS

2007 ◽  
Vol 18 (01) ◽  
pp. 91-98 ◽  
Author(s):  
GÖKHAN GÖKOĞLU ◽  
TARIK ÇELİK
Keyword(s):  
Energy State ◽  
Minimum Energy ◽  
Alpha Helix ◽  
Salt Bridge ◽  
Rnase A ◽  
Parallel Tempering ◽  
Implicit Solvent ◽  
C Peptide ◽  
Helix Formation ◽  
Α Helix

We have performed parallel tempering simulations of a 13-residue peptide fragment of ribonuclease-A, c-peptide, in implicit solvent with constant dielectric permittivity. This peptide has a strong tendency to form α-helical conformations in solvent as suggested by circular dichroism (CD) and nuclear magnetic resonance (NMR) experiments. Our results demonstrate that 5th and 8–12 residues are in the α-helical region of the Ramachandran map for global minimum energy state in solvent environment. Effects of salt bridge formation on stability of α-helix structure are discussed.

scholarly journals Generation of Coronal Currents by the Solar Convection Zone

2001 ◽  
Vol 18 (4) ◽  
pp. 329-335 ◽  
Author(s):  
D. J. Galloway ◽  
Y. Uchida ◽  
N. O. Weiss
Keyword(s):  
Convection Zone ◽  
Energy State ◽  
Minimum Energy ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Poynting Flux ◽  
Available Energy ◽  
Order Of Magnitude ◽  
The Right ◽  
Right Order

AbstractSolar flares are thought to be caused by reconnection of magnetic fields and their associated electric currents in the solar corona. The currents have to be there to provide available energy over and above the current-free minimum energy state, but what generates them has been little discussed. This paper investigates the idea that twisting motions in the turbulent convection zone below may provide a natural source for the currents and explain some of their properties. The twists generate upward-propagating Alfvén waves with a Poynting flux of the right order of magnitude to power a flare. Depending on the depth it takes place, the twisting event that initiates a particular flare may occur hours, days or even months before the flare itself.

scholarly journals Micromagnetic Simulation of Thermal Effects in Magnetic Nanostructures

2002 ◽  
Vol 746 ◽  
Author(s):  
Rok Dittrich ◽  
Thomas Schrefl ◽  
Vassilios Tsiantos ◽  
Hermann Forster ◽  
Dieter Suess ◽  
...  
Keyword(s):  
Minimum Energy ◽  
Saddle Points ◽  
Time Integration ◽  
Magnetic Nanostructures ◽  
Integration Scheme ◽  
Thermally Induced ◽  
Thermally Activated ◽  
Time Integration Scheme ◽  
Stochastic Time ◽  
Finding Method

ABSTRACTA path finding method and a stochastic time integration scheme for the simulation of thermally activated magnetization processes are introduced. The minimum energy path and the saddle points for the thermally induced transitions between the ground states of NiFe magnetic nano-elements are calculated.

On the Criterion for the Determination Transition Onset and Breakdown to Turbulence in Wall-Bounded Flows1

2004 ◽  
Vol 126 (4) ◽  
pp. 626-633 ◽  
Author(s):  
J. Jovanovic´ ◽  
M. Pashtrapanska
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Local Equilibrium ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Correlation Technique ◽  
Equilibrium Solutions ◽  
Onset Of Turbulence ◽  
Transition Criterion ◽  
Flat Plate Boundary Layer

Starting from the basic conservation laws of fluid flow, we investigated transition and breakdown to turbulence of a laminar flat plate boundary layer exposed to small, statistically stationary, two-component, three-dimensional disturbances. The derived equations for the statistical properties of the disturbances are closed using the two-point correlation technique and invariant theory. By considering the equilibrium solutions of the modeled equations, the transition criterion is formulated in terms of a Reynolds number based on the intensity and the length scale of the disturbances. The deduced transition criterion determines conditions that guarantee maintenance of the local equilibrium between the production and the viscous dissipation of the disturbances and therefore the laminar flow regime in the flat plate boundary layer. The experimental and numerical databases for fully developed turbulent channel and pipe flows at different Reynolds numbers were utilized to demonstrate the validity of the derived transition criterion for the estimation of the onset of turbulence in wall-bounded flows.

ENERGETICS AND STABILITY OF DISCRETE CHARGE DISTRIBUTION ON THE SURFACE OF A SPHERE

2001 ◽  
Vol 12 (02) ◽  
pp. 293-305 ◽  
Author(s):  
HÜSEYIN OYMAK ◽  
ŞAKIR ERKOÇ
Keyword(s):  
Energy Distribution ◽  
Coulomb Potential ◽  
Energy State ◽  
Minimum Energy ◽  
Energy Distributions ◽  
Tangential Forces ◽  
Energy Consideration ◽  
Minimum Energy State ◽  
A Charge ◽  
Discrete Charge

We have investigated the minimum-energy distribution of N, 3 ≤ N ≤ 97, equal point charges confined to the surface of a sphere. Charges interact with each other via the Coulomb potential of the form 1/r. Minimum-energy distributions have been determined by minimizing the tangential forces on each charge. Further numerical evidence shows that in the minimum-energy state of N charges on the sphere, it is not possible to place a charge at the geometrical center. Besides, it has been found that the most and reliable information about the relative stability properties of the distributions can be obtained with the help of second difference energy consideration.

Dynamical, spectroscopic and computational imaging of bond breaking in photodissociation: roaming and role of conical intersections

2015 ◽  
Vol 177 ◽  
pp. 77-98 ◽  
Author(s):  
Masaaki Nakamura ◽  
Po-Yu Tsai ◽  
Toshio Kasai ◽  
King-Chuen Lin ◽  
Federico Palazzetti ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Potential Energy Surfaces ◽  
Minimum Energy ◽  
Saddle Points ◽  
Integrated Approach ◽  
Computational Imaging ◽  
Ion Imaging ◽  
Structural Investigations ◽  
Alternative Pathways ◽  
Fragmentation Threshold

Recent experimental and theoretical advances in the study of the dissociation of excited molecules are revealing unexpected mechanisms, when their outcomes are tackled by combining (i) space-time ion imaging of translational features, with (ii) spectroscopic probing of rotational and vibrational distributions; crucial is the assistance of (iii) the quantum chemistry of structural investigations of rearrangements of chemical bonds, and of (iv) the simulations of molecular dynamics to follow the evolution of selective bond stretching and breaking. Here we present results of such an integrated approach to methyl formate, HCOOCH3, the simplest of esters; the main focus is on the rotovibrationally excited CO (v = 1) product and in general on the energy distribution in the fragments. Previous laser studies of dissociation into CO and CH3OH at a sequence of various wavelengths discovered signatures of a roaming mechanism by the late arrival of CO (v = 0) products in time-of-flight ion imaging. Subsequent detailed investigations as a function of excitation energy provided the assessment of the threshold, which opens for triple breakdown into CO and further fragments H and CH3O, as spectroscopically characterized by ion imaging and FTIR respectively. Accompanying quantum mechanical electronic structure calculations and classical molecular dynamics simulations clarify the origin of these fragments through “roaming” pathways involving incipient radical intermediates at energies below the triple fragmentation threshold: a specific role is played by nonadiabatic transitions at a conical intersection between ground and excited states; alternative pathways focalize our attention to regions of the potential energy surfaces other than those in the neighbourhoods of saddle points along minimum energy paths: eventually this leads us to look for avenues in reaction kinetics beyond those of venerable transition state theories.

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