843 research outputs found
Heavy Hadrons and QCD Instantons
Heavy hadrons are analyzed in a random and dilute gas of instantons. We
derive the instanton-induced interactions between heavy and light quarks at
next to leading order in the heavy quark mass and in the planar approximation,
and discuss their effects on the hadronic spectrum. The role of these
interactions in the formation of exotic hadrons is also discussed.Comment: 26 pages, REVTeX, 2 tables, 5 figures, uses FEYNMAN.st
Field-induced decay dynamics in square-lattice antiferromagnet
Dynamical properties of the square-lattice Heisenberg antiferromagnet in
applied magnetic field are studied for arbitrary value S of the spin. Above the
threshold field for two-particle decays, the standard spin-wave theory yields
singular corrections to the excitation spectrum with logarithmic divergences
for certain momenta. We develop a self-consistent approximation applicable for
S >= 1, which avoids such singularities and provides regularized magnon decay
rates. Results for the dynamical structure factor obtained in this approach are
presented for S = 1 and S = 5/2.Comment: 12 pages, 11 figures, final versio
Using the simulation modeling with stochastic estimation of trafficability of forest transport systems
Forecasting trafficability of logging and forest transport systems on the ground, which have a multi-sectional layout solution is considered in the paper. Trafficability problems are evaluated from the point of view of the stochastic character of indicators of traction properties - the forces of resistance to movement and the adhesion force of the driving wheels with the supporting surface. With the stochastic estimation of trafficability the law of Gaussian distribution for random values of the rolling resistance coefficient and the two-parameter Weibull distribution law with a negative asymmetry coefficient or values of the shape parameter greater than 4 for the cohesion coefficient was adopted. A stochastic approach to the evaluation of trafficability allows to ensure a rational distribution of the power flows between propulsors of the transport-technological system, which is shown in this paper. Β© 2019 Published under licence by IOP Publishing Ltd
Using the simulation modeling with stochastic estimation of trafficability of forest transport systems
Forecasting trafficability of logging and forest transport systems on the ground, which have a multi-sectional layout solution is considered in the paper. Trafficability problems are evaluated from the point of view of the stochastic character of indicators of traction properties - the forces of resistance to movement and the adhesion force of the driving wheels with the supporting surface. With the stochastic estimation of trafficability the law of Gaussian distribution for random values of the rolling resistance coefficient and the two-parameter Weibull distribution law with a negative asymmetry coefficient or values of the shape parameter greater than 4 for the cohesion coefficient was adopted. A stochastic approach to the evaluation of trafficability allows to ensure a rational distribution of the power flows between propulsors of the transport-technological system, which is shown in this paper. Β© 2019 Published under licence by IOP Publishing Ltd
Acoustic instability of a circular vortex with a smoothed vorticity profile
It is known that a localized vortex can have two specific mechanisms of
interaction with the ambient flow. The first mechanism is associated with
acoustic radiation, which is accompanied by a loss of energy and causes
instability in the case of negative energy of vortex disturbances. The second
is a Miles mechanism of interaction of the vortex core oscillations with
disturbances in the vicinity of the critical layer (where the phase velocity of
the disturbances coincides with the velocity of the mean flow), accompanied by
an energy flux from the critical layer vicinity, which leads to damping in the
case of negative energy of the oscillations. For the first time, the flow with
both of these mechanisms is considered. The problem is solved from the first
principles. It is shown that the Miles mechanism can completely suppress
acoustic instability, however, in the case of a stronger loss of energy due to
acoustic radiation, acoustic instability will dominate. The role of various
parameters is analyzed and a quantitative criterion for the acoustic
instability of a vortex with a smoothed vorticity profile is obtained
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