1,409 research outputs found
Adaptively Biased Molecular Dynamics for Free Energy Calculations
We present an Adaptively Biased Molecular Dynamics (ABMD) method for the
computation of the free energy surface of a reaction coordinate using
non-equilibrium dynamics. The ABMD method belongs to the general category of
umbrella sampling methods with an evolving biasing potential, and is inspired
by the metadynamics method. The ABMD method has several useful features,
including a small number of control parameters, and an numerical cost
with molecular dynamics time . The ABMD method naturally allows for
extensions based on multiple walkers and replica exchange, where different
replicas can have different temperatures and/or collective variables. This is
beneficial not only in terms of the speed and accuracy of a calculation, but
also in terms of the amount of useful information that may be obtained from a
given simulation. The workings of the ABMD method are illustrated via a study
of the folding of the Ace-GGPGGG-Nme peptide in a gaseous and solvated
environment.Comment: Revised version to appear in Journal of Chemical Physic
Simulation Modeling and Analysis of Adjustable Service-Rate Queueing Models that Incorporate Feedback Control
Research shows that in a system model, when the production rate is adjusted based on the number of items in queue, the nature of the model changes from an open-loop queueing system to a closed-loop feedback control system. Service-rate adjustment can be implemented in a discrete event simulation model, but the effect of this adjustment has not been thoroughly analyzed in the literature. This research considers the design of feedback signals to generate realistic simulation models of production system behavior. A series of simulation experiments is conducted to provide practical guidance for simulation modelers on how adding a service-rate adjustment feedback loop to a queueing system affects system performance
Relativistic point dynamics and Einstein formula as a property of localized solutions of a nonlinear Klein-Gordon equation
Einstein's relation E=Mc^2 between the energy E and the mass M is the
cornerstone of the relativity theory. This relation is often derived in a
context of the relativistic theory for closed systems which do not accelerate.
By contrast, Newtonian approach to the mass is based on an accelerated motion.
We study here a particular neoclassical field model of a particle governed by a
nonlinear Klein-Gordon (KG) field equation. We prove that if a solution to the
nonlinear KG equation and its energy density concentrate at a trajectory, then
this trajectory and the energy must satisfy the relativistic version of
Newton's law with the mass satisfying Einstein's relation. Therefore the
internal energy of a localized wave affects its acceleration in an external
field as the inertial mass does in Newtonian mechanics. We demonstrate that the
"concentration" assumptions hold for a wide class of rectilinear accelerating
motions
Giant Coulomb broadening and Raman lasing on ionic transitions
CW generation of anti-Stokes Raman laser on a number of blue-green argon-ion
lines (4p-4s, 4p-3d) has been demonstrated with optical pumping from metastable
levels 3d'^2G, 3d^4F. It is found, that the population transfer rate is
increased by a factor of 3-5 (and hence, the output power of such Raman laser)
owing to Coulomb diffusion in the velocity space. Measured are the excitation
and relaxation rates for the metastable level. The Bennett hole on the
metastable level has been recorded using the probe field technique. It has been
shown that the Coulomb diffusion changes shape of the contour to exponential
cusp profile while its width becomes 100 times the Lorentzian one and reaches
values close to the Doppler width. Such a giant broadening is also confirmed by
the shape of the absorption saturation curve.Comment: RevTex 18 pages, 5 figure
Effect of Specially Programmed Physical and Health Education on Motor Fitness of Seven-Year-Old School Children
The efficacy of specially programmed physical and health education on the motor development
of first-grade pupils was analyzed in a sample of 633 children aged 7 years.
Pupils have been divided into control group consisting of 140 boys and 137 girls attending
standard program of physical and health education, and in experimental group
consisting of 184 boys and 172 girls attending specially programmed physical and health
education. A battery of 12 motor tests has been used on two occasions separated by nine
-month interval. Analysis of time-changes (by using the model of differences) pointed to
the significantly greater quantitative changes in experimental group compared with control
group of children. In boys, the changes are obtained for the tests of aerobic endurance,
static strength, flexibility, speed, explosive strength of sprint and throw type, and equilibrium,
and in girls, they are for aerobic endurance, static strength, explosive strength of
throw and sprint type, flexibility, repetitive strength, speed, and equilibrium
Effect of Specially Programmed Physical and Health Education on Motor Fitness of Seven-Year-Old School Children
The efficacy of specially programmed physical and health education on the motor development
of first-grade pupils was analyzed in a sample of 633 children aged 7 years.
Pupils have been divided into control group consisting of 140 boys and 137 girls attending
standard program of physical and health education, and in experimental group
consisting of 184 boys and 172 girls attending specially programmed physical and health
education. A battery of 12 motor tests has been used on two occasions separated by nine
-month interval. Analysis of time-changes (by using the model of differences) pointed to
the significantly greater quantitative changes in experimental group compared with control
group of children. In boys, the changes are obtained for the tests of aerobic endurance,
static strength, flexibility, speed, explosive strength of sprint and throw type, and equilibrium,
and in girls, they are for aerobic endurance, static strength, explosive strength of
throw and sprint type, flexibility, repetitive strength, speed, and equilibrium
Electrodynamics of balanced charges
In this work we modify the wave-corpuscle mechanics for elementary charges
introduced by us recently. This modification is designed to better describe
electromagnetic (EM) phenomena at atomic scales. It includes a modification of
the concept of the classical EM field and a new model for the elementary charge
which we call a balanced charge (b-charge). A b-charge does not interact with
itself electromagnetically, and every b-charge possesses its own elementary EM
field. The EM energy is naturally partitioned as the interaction energy between
pairs of different b-charges. We construct EM theory of b-charges (BEM) based
on a relativistic Lagrangian with the following properties: (i) b-charges
interact only through their elementary EM potentials and fields; (ii) the field
equations for the elementary EM fields are exactly the Maxwell equations with
proper currents; (iii) a free charge moves uniformly preserving up to the
Lorentz contraction its shape; (iv) the Newton equations with the Lorentz
forces hold approximately when charges are well separated and move with
non-relativistic velocities. The BEM theory can be characterized as
neoclassical one which covers the macroscopic as well as the atomic spatial
scales, it describes EM phenomena at atomic scale differently than the
classical EM theory. It yields in macroscopic regimes the Newton equations with
Lorentz forces for centers of well separated charges moving with
nonrelativistic velocities. Applied to atomic scales it yields a hydrogen atom
model with a frequency spectrum matching the same for the Schrodinger model
with any desired accuracy.Comment: Manuscript was edited to improve the exposition and to remove noticed
typo
Neoclassical Theory of Elementary Charges with Spin of 1/2
We advance here our neoclassical theory of elementary charges by integrating
into it the concept of spin of 1/2. The developed spinorial version of our
theory has many important features identical to those of the Dirac theory such
as the gyromagnetic ratio, expressions for currents including the spin current,
and antimatter states. In our theory the concepts of charge and anticharge
relate naturally to their "spin" in its rest frame in two opposite directions.
An important difference with the Dirac theory is that both the charge and
anticharge energies are positive whereas their frequencies have opposite signs
Intermittency and regularity issues in 3D Navier-Stokes turbulence
Two related open problems in the theory of 3D Navier-Stokes turbulence are
discussed in this paper. The first is the phenomenon of intermittency in the
dissipation field. Dissipation-range intermittency was first discovered
experimentally by Batchelor and Townsend over fifty years ago. It is
characterized by spatio-temporal binary behaviour in which long, quiescent
periods in the velocity signal are interrupted by short, active `events' during
which there are violent fluctuations away from the average. The second and
related problem is whether solutions of the 3D Navier-Stokes equations develop
finite time singularities during these events. This paper shows that Leray's
weak solutions of the three-dimensional incompressible Navier-Stokes equations
can have a binary character in time. The time-axis is split into `good' and
`bad' intervals: on the `good' intervals solutions are bounded and regular,
whereas singularities are still possible within the `bad' intervals. An
estimate for the width of the latter is very small and decreases with
increasing Reynolds number. It also decreases relative to the lengths of the
good intervals as the Reynolds number increases. Within these `bad' intervals,
lower bounds on the local energy dissipation rate and other quantities, such as
\|\bu(\cdot, t)\|_{\infty} and \|\nabla\bu(\cdot, t)\|_{\infty}, are very
large, resulting in strong dynamics at sub-Kolmogorov scales. Intersections of
bad intervals for are related to Scheffer's potentially singular set
in time. It is also proved that the Navier-Stokes equations are conditionally
regular provided, in a given `bad' interval, the energy has a lower bound that
is decaying exponentially in time.Comment: 36 pages, 3 figures and 6 Table
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