NUCLEAR FISSION WITHIN THE MEAN-FIELD APPROACH

2009 ◽  
Vol 18 (04) ◽  
pp. 798-807 ◽  
Author(s):  
J. SKALSKI
Keyword(s):  
Simple Model ◽  
Density Matrix ◽  
Hermitian Operator ◽  
Mean Field ◽  
Nuclear Fission ◽  
Decay Rates ◽  
Instanton Action ◽  
Field Approach ◽  
The Mean

We discuss the mean-field instanton method for calculating decay rates of the sponteneous fission. Based on our recent work, we stress the role of the velocity-momentum relations which make the instanton action minimal, and the choice of a time-even density matrix and a time-odd hermitian operator as special variables making the adiabatic limit transparent. We also present an analytic study of a simple model of barrier tunneling, which illustrates the importance of the velocity-momentum constraints.

scholarly journals Paradox of integration — mean field approach

2017 ◽  
Vol 28 (11) ◽  
pp. 1750133 ◽  
Author(s):  
Krzysztof Kułakowski ◽  
Piotr Gronek ◽  
Alfio Borzì
Keyword(s):  
Social Status ◽  
Positive Emotions ◽  
Mean Field ◽  
Computational Approach ◽  
Transient Time ◽  
Field Approach ◽  
The Social ◽  
The Mean ◽  
High Social Status

Recently, a computational model has been proposed of the social integration, as described in sociological terms by Blau. In this model, actors praise or critique each other, and these actions influence their social status and raise negative or positive emotions. The role of a self-deprecating strategy of actors with high social status has also been discussed there. Here, we develop a mean field approach, where the active and passive roles (praising and being praised, etc.) are decoupled. The phase transition from friendly to hostile emotions has been reproduced, similarly to the previously applied purely computational approach. For both phases, we investigate the time dependence of the distribution of social status. There we observe a diffusive spread, which — after some transient time — appears to be limited from below or from above, depending on the phase. As a consequence, the mean status flows.

scholarly journals Non-linear and chaotic dynamo regimes

2012 ◽  
Vol 8 (S294) ◽  
pp. 387-398
Author(s):  
Axel Brandenburg
Keyword(s):  
Mean Field ◽  
Rotation Frequency ◽  
Magnetic Activity ◽  
Current Status ◽  
Small Scale ◽  
Field Approach ◽  
Magnetic Prandtl Number ◽  
The Mean ◽  
Open Question

AbstractAn update is given on the current status of solar and stellar dynamos. At present, it is still unclear why stellar cycle frequencies increase with rotation frequency in such a way that their ratio increases with stellar activity. The small-scale dynamo is expected to operate in spite of a small value of the magnetic Prandtl number in stars. Whether or not the global magnetic activity in stars is a shallow or deeply rooted phenomenon is another open question. Progress in demonstrating the presence and importance of magnetic helicity fluxes in dynamos is briefly reviewed, and finally the role of nonlocality is emphasized in modeling stellar dynamos using the mean-field approach. On the other hand, direct numerical simulations have now come to the point where the models show solar-like equatorward migration that can be compared with observations and that need to be understood theoretically.

scholarly journals Role of tolerance to resource demand - supply mismatch in a model of annual plants

2017 ◽  
Vol 4 (4) ◽  
pp. 191-201
Author(s):  
Michel Droz ◽  
Andrzej Pękalski
Keyword(s):  
Mean Field ◽  
Spatial Arrangement ◽  
Annual Plants ◽  
Trade Off ◽  
Field Approach ◽  
Nearest Neighbours ◽  
Different Types ◽  
The Mean ◽  
Number Of Seeds

We propose and discuss a simulation model of annual plants competing for a single resource. Plants are characterised by their tolerance to a surplus of this resource and the maximum number of seeds a plant can produce in a year. Interaction among plants is reduced to blocking a part of the resource by the plant’s nearest neighbours. Spatial and temporal conditions are homogeneous. There are no trade-off mechanisms nor immigrants. Plants may suffer from both a lack and too much of the resource. We consider two systems - plants of one type (target plants) and a mixture of two types, where the second type differs from the target ones only by the tolerance to surplus of the resource. We show how the life cycle of a plant depends on its tolerance, on supply of the resource and on how it is affected by the presence of the second type of annuals. We demonstrate that even in such a simple system coexistence of the two species is possible, and we determine the conditions for this. We present also a mean field type approach to the problem, showing that the results from simulations and mean field are quite similar. However the mean field approach cannot answer questions concerning spatial arrangement of plants, like possible formation of niches for different types of plant.

scholarly journals Two-term expansion of the ground state one-body density matrix of a mean-field Bose gas

2021 ◽  
Vol 60 (3) ◽  
Author(s):  
Phan Thành Nam ◽  
Marcin Napiórkowski
Keyword(s):  
Density Matrix ◽  
Ground State ◽  
Mean Field ◽  
Interaction Strength ◽  
Bose Gas ◽  
Body Density ◽  
The Mean ◽  
The One ◽  
Mean Field Regime ◽  
Number Of Particles

AbstractWe consider the homogeneous Bose gas on a unit torus in the mean-field regime when the interaction strength is proportional to the inverse of the particle number. In the limit when the number of particles becomes large, we derive a two-term expansion of the one-body density matrix of the ground state. The proof is based on a cubic correction to Bogoliubov’s approximation of the ground state energy and the ground state.

scholarly journals Filaments and the Solar Dynamo

1998 ◽  
Vol 167 ◽  
pp. 406-414
Author(s):  
N. Seehafer
Keyword(s):  
Mean Field ◽  
Decisive Role ◽  
Dynamo Theory ◽  
Simultaneous Generation ◽  
Alpha Effect ◽  
Generation Region ◽  
The Mean ◽  
Numerical Bifurcation ◽  
Dynamo Effect

AbstractFilaments are a global phenomenon and their formation, structure and dynamics are determined by magnetic fields. So they are an important signature of the solar magnetism. The central mechanism in traditional mean-field dynamo theory is the alpha effect and it is a major result of this theory that the presence of kinetic or magnetic helicities is at least favourable for the effect. Recent studies of the magnetohydrodynamic equations by means of numerical bifurcation-analysis techniques have confirmed the decisive role of helicity for a dynamo effect. The alpha effect corresponds to the simultaneous generation of magnetic helicities in the mean field and in the fluctuations, the generation rates being equal in magnitude and opposite in sign. In the case of statistically stationary and homogeneous fluctuations, in particular, the alpha effect can increase the energy in the mean magnetic field only under the condition that also magnetic helicity is accumulated there. Generally, the two helicities generated by the alpha effect, that in the mean field and that in the fluctuations, have either to be dissipated in the generation region or to be transported out of this region. The latter may lead to the appearance of helicity in the atmosphere, in particular in filaments, and thus provide valuable information on dynamo processes inaccessible to in situ measurements.

NUCLEAR MATTER WITH CONSTITUENT MESON QUANTA

1990 ◽  
Vol 05 (17) ◽  
pp. 3391-3399 ◽  
Author(s):  
AMRUTA MISHRA ◽  
H. MISHRA ◽  
S.P. MISRA
Keyword(s):  
Field Theory ◽  
Nuclear Matter ◽  
Mass Shell ◽  
Mean Field ◽  
S Wave ◽  
Field Approach ◽  
Physical Insight ◽  
The Mean

We discuss here some nonperturbative techniques of field theory, where we dress nuclear matter as a whole with off-mass-shell pions. Here s-wave pion pairs simulate the effect of σ-meson of the mean field approach of Walecka. The signatures are in agreement with earlier results along with new physical insight.

Queueing networks with mobile servers: The mean-field approach

2016 ◽  
Vol 52 (2) ◽  
pp. 178-199 ◽  
Author(s):  
F. Baccelli ◽  
A. N. Rybko ◽  
S. B. Shlosman
Keyword(s):  
Queueing Networks ◽  
Mean Field ◽  
Field Approach ◽  
The Mean

PHENOMENOLOGICAL THEORY OF HIGH Tc SUPERCONDUCTORS

1987 ◽  
Vol 01 (03n04) ◽  
pp. 997-1000 ◽  
Author(s):  
M.P. Das ◽  
A.G. Saif
Keyword(s):  
Electrical Conductivity ◽  
Mean Field ◽  
Phenomenological Theory ◽  
Phenomenological Approach ◽  
Order Parameters ◽  
High Tc Superconductors ◽  
High Tc ◽  
Field Approach ◽  
Superconducting Ceramics ◽  
The Mean

We present a phenomenological approach in terms of two coexisting macroscopic order parameters correponding to the superconducting and the insulating states relevant to the high. temperature superconducting ceramics. On using the mean field approach we discuss the electrodynamical responses and from the fluctuations of the order parameters we obtain results for the electrical conductivity, which is shown to possess anomalies as in the granular materials.

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