Laminar and turbulent generation states of different parity-time symmetry properties in coupled Raman fiber lasers

We employ an orthogonal decomposition technique with unique space–time symmetry properties to analyze a network of thalamo–cortical oscillators. A small number of thalamic "cells" are used to drive a network of cortical cells structured on a two-dimensional lattice. Two Bonhoeffer–van der Pol (BVP) based models of cortical neurons are compared at the network level in an attempt to reproduce some features of the thalamo–cortical system. It is shown that with the addition of a slowly varying term to the classical two-dimensional BVP model, the network can exhibit both periodic and irregular space–time behavior, along with changes in the temporal coherence and spatial frequency resembling the 8–12 Hz alpha rhythm.

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Spin-Flavour Symmetry and Contractions Towards Classical Space-Time Symmetry

International Journal of Modern Physics A ◽

10.1142/s0217751x97000190 ◽

1997 ◽

Vol 12 (01) ◽

pp. 147-152

Author(s):

Rolf Dahm

Keyword(s):

Classification Scheme ◽

Dynamical Symmetry ◽

Approximate Symmetry ◽

Hadron Spectrum ◽

Time Symmetry ◽

Flavour Symmetry ◽

Symmetry Properties ◽

Low Energies ◽

Exact Symmetry ◽

Conceptual Problems

A classification scheme of hadrons is proposed on the basis of the division algebra H of quaternions and an appropriate geometry. This scheme suggests strongly to understand flavour symmetry in another manner than from standard symmetry schemes. In our approach, we do not start from "exact" symmetry groups like SU(2) × SU(2) chiral symmetry and impose various symmetry breaking mechanisms which collide with theorems wellknown from quantum field theory. On the contrary, the approximate symmetry properties of the hadron spectrum at low energies, usually classified by "appropriately" broken compact flavour groups, emerge very naturally as a low energy reduction of the noncompact (dynamical) symmetry group Sl(2,H). This quaternionic approach not only avoids most of the wellknown conceptual problems of Chiral Dynamics but it also allows for a general treatment of relativistic flavour symmetries as well as it yields a direct connection towards classical relativistic symmetry.

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Semi-automated methods for 3-D reconstruction of macromolecular complexes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136581 ◽

1995 ◽

Vol 53 ◽

pp. 42-43

Author(s):

B. Carragher ◽

M. Whittaker

Keyword(s):

Three Dimensional ◽

Time Saving ◽

Macromolecular Complexes ◽

Symmetry Properties ◽

Dimensional Reconstruction ◽

Experienced Operator ◽

Projection Images ◽

The Individual ◽

Natural Symmetry

Techniques for three-dimensional reconstruction of macromolecular complexes from electron micrographs have been successfully used for many years. These include methods which take advantage of the natural symmetry properties of the structure (for example helical or icosahedral) as well as those that use single axis or other tilting geometries to reconstruct from a set of projection images. These techniques have traditionally relied on a very experienced operator to manually perform the often numerous and time consuming steps required to obtain the final reconstruction. While the guidance and oversight of an experienced and critical operator will always be an essential component of these techniques, recent advances in computer technology, microprocessor controlled microscopes and the availability of high quality CCD cameras have provided the means to automate many of the individual steps.During the acquisition of data automation provides benefits not only in terms of convenience and time saving but also in circumstances where manual procedures limit the quality of the final reconstruction.

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