SAR Tomography as an Add-On to PSI: Detection of Coherent Scatterers in the Presence of Phase Instabilities

We present an analytical study on the stability of distorted hexagonal patterns. From a general amplitude equation we calculate the instabilities with respect to homogeneous and longwave perturbations. The latter lead to the phase equations that permit to determine the stability regions. Slightly squeezed hexagons are locally stable in a full range of distortion angles. The stability regions obtained from the phase equation are similar to those obtained numerically by other authors [Gunaratne et al., 1994].

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An Advanced Frequency-Domain Code for BWR Stability Analysis and Design

Volume 8C: Heat Transfer and Thermal Engineering ◽

10.1115/imece2013-65245 ◽

2013 ◽

Author(s):

Behrooz Askari ◽

George Yadigaroglu

Keyword(s):

Steady State ◽

Frequency Domain ◽

Transfer Functions ◽

Density Wave ◽

System Stability ◽

Reactor Kinetics ◽

Analysis And Design ◽

Drift Flux ◽

Reactor Transfer ◽

Phase Instabilities

Density Wave Oscillations in BWRs are coupled with the reactor kinetics. A new analytical, frequency-domain tool that uses the best available models and methods for modeling BWRs and analyzing their stability is described. The steady state of the core is obtained first in 3D with two-group diffusion equations and spatial expansion of the neutron fluxes in Legendre polynomials. The time-dependent neutronics equations are written in terms of flux harmonics (nodal-modal equations) for the study of “out-of-phase” instabilities. Considering separately all fuel assemblies divided into a number of axial segments, the thermal-hydraulic conservation equations are solved (drift-flux, non-equilibrium model). The thermal-hydraulics are iteratively fully coupled to the neutronics. The code takes all necessary information from plant files via an interface. The results of the steady state are used for the calculation of the transfer functions and system transfer matrices using extensively symbolic manipulation software (MATLAB). The resulting very large matrices are manipulated and inverted by special procedures developed within the MATLAB environment to obtain the reactor transfer functions that enable the study of system stability. Applications to BWRs show good agreement with measured stability data.

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Dependence of Phase Instabilities on Bunch Length at the CEA

IEEE Transactions on Nuclear Science ◽

10.1109/tns.1973.4327236 ◽

1973 ◽

Vol 20 (3) ◽

pp. 765-767 ◽

Cited By ~ 3

Author(s):

R. Averill ◽

R. Eddy ◽

A. Hofmann ◽

R. Little ◽

H. Mieras ◽

...

Keyword(s):

Bunch Length ◽

Phase Instabilities

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Instabilities of Coulomb phases and the Gribov picture of confinement

International Journal of Modern Physics A ◽

10.1142/s0217751x1645024x ◽

2016 ◽

Vol 31 (28n29) ◽

pp. 1645024

Author(s):

Manuel Asorey ◽

Alessandro Santagata

Keyword(s):

First Principles ◽

Critical Value ◽

Coupling Constants ◽

Quark Confinement ◽

Abelian Gauge ◽

Vacuum Decay ◽

Coulomb Phase ◽

A Value ◽

Analytic Derivation ◽

Phase Instabilities

A new picture of quark confinement based on the instability of Coulomb phase at low energy was introduced by Volodya Gribov in the early nineties. In QCD the effective [Formula: see text] coupling constant can reach very large values in the infrared regime what generates Coulomb phase instabilities. In the Gribov picture the instability leads to a vacuum decay into light quarks for coupling constants [Formula: see text] larger than a critical value [Formula: see text], for SU(N) gauge theories. The instability of Coulomb phase can be derived from first principles in any non-Abelian gauge theory for [Formula: see text], a value which is larger than the Gribov critical value. In this paper we review the analytic derivation of the Gribov mechanism from first principles and analyze the effects of dynamical quarks in the instability of the Coulomb phase. The instabilities associated to light quarks turn out to appear at larger values of [Formula: see text] than the ones induced from pure gluon dynamics, unlike it is expected in the standard Gribov scenario. The analytic results confirm the consistency of the picture where quark confinement is mainly driven by gluonic fluctuations.

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