83,929 research outputs found
Transitions between nonsymmetric and symmetric steady states near a triple eigenvalue
We examine the existence of nonuniform steady-state solutions of a certain class of reaction-diffusion
equations. Our analysis concentrates on the case where the first bifurcation is near a triple eigenvalue. We derive the conditions for a continuous transition between nonsymmetric and symmetric solutions when the bifurcation parameter progressively increases from zero. Finally, we give an example of a four variables model which presents the possibility of a triple eigenvalue
Imperfect Bifurcation Near a Double Eigenvalue: Transitions Between Nonsymmetric and Symmetric Patterns
We examine the existence of nonsymmetric and symmetric steady state solutions of a general class of reaction-diffusion equations.
Our study consists of two parts: (i) By analyzing the bifurcation from a uniform reference state to nonuniform regimes, we demonstrate the existence of a unique symmetric solution (basic wave number two) which becomes linearly stable when it surpasses a critical amplitude. (We assume that the first bifurcation point corresponds to the emergence of the simplest nonsymmetric steady state solutions.) (ii) This result is not affected when a parameter is nonuniformly distributed in the system. However, one of the two possible branches of nonsymmetric solutions may disappear from the bifurcation diagram.
Our analysis is motivated by the fact that experimental observations of pattern transitions during morphogenesis are interpreted in terms of the dynamics of stable concentration gradients. We have shown that in addition to the values of the physico-chemical parameters, these structures can be selected by two different mechanisms: (i) the linear stability of the nonuniform patterns, (ii) the effects of a small and nonuniform variation of a parameter in the spatial domain
Reports on crustal movements and deformations
This Catalog of Reports on Crustal Movements and Deformation is a structured bibliography of scientific papers on the movements of the Earth crust. The catalog summarizes by various subjects papers containing data on the movement of the Earth's surface due to tectonic processes. In preparing the catalog we have included studies of tectonic plate motions, spreading and convergence, microplate rotation, regional crustal deformation strain accumulation and deformations associated with the earthquake cycle, and fault motion. We have also included several papers dealing with models of tectonic plate motion and with crustal stress. Papers which discuss tectonic and geologic history but which do not present rates of movements or deformations and papers which are primarily theoretical analyses have been excluded from the catalog. An index of authors cross-referenced to their publications also appears in the catalog. The catalog covers articles appearing in reviewed technical journals during the years 1970-1981. Although there are citations from about twenty journals most of the items come from the following publications: Journal of Geophysical Research, Tectonophysics, Geological Society of America Bulletin of the Seismological Society of America, Nature, Science, Geophysical Journal of the Royal Astronomical Society, Earth and Planetary Science Letters, and Geology
Information Flow in an R and D Laboratory
Statistical analysis of hypotheses concerning roles of technological gatekeeper and primary groups in flow of information in small research and development laborator
Diquarks, Pentaquarks and Dibaryons
We explore the connection between pentaquarks and dibaryons composed of three
diquarks in the framework of the diquark model. With the available experimental
data on H dibaryon, we estimate the Pauli blocking and annihilation effects and
constrain the pentaquark singlet mass. Using the
pentaquark mass, we estimate dibaryon mass
Regularization, Renormalization and Range: The Nucleon-Nucleon Interaction from Effective Field Theory
Regularization and renormalization is discussed in the context of low-energy
effective field theory treatments of two or more heavy particles (such as
nucleons). It is desirable to regulate the contact interactions from the outset
by treating them as having a finite range. The low energy physical observables
should be insensitive to this range provided that the range is of a similar or
greater scale than that of the interaction. Alternative schemes, such as
dimensional regularization, lead to paradoxical conclusions such as the
impossibility of repulsive interactions for truly low energy effective theories
where all of the exchange particles are integrated out. This difficulty arises
because a nonrelativistic field theory with repulsive contact interactions is
trivial in the sense that the matrix is unity and the renormalized coupling
constant zero. Possible consequences of low energy attraction are also
discussed. It is argued that in the case of large or small scattering lengths,
the region of validity of effective field theory expansion is much larger if
the contact interactions are given a finite range from the beginning.Comment: 7 page
Optimization of Network Robustness to Waves of Targeted and Random Attack
We study the robustness of complex networks to multiple waves of simultaneous
(i) targeted attacks in which the highest degree nodes are removed and (ii)
random attacks (or failures) in which fractions and respectively of
the nodes are removed until the network collapses. We find that the network
design which optimizes network robustness has a bimodal degree distribution,
with a fraction of the nodes having degree k_2= (\kav - 1 +r)/r and the
remainder of the nodes having degree , where \kav is the average
degree of all the nodes. We find that the optimal value of is of the order
of for
The Skyrmion strikes back: baryons and a new large limit
In the large limit of QCD, baryons can be modeled as solitons, for
instance, as Skyrmions. This modeling has been justified by Witten's
demonstration that all properties of baryons and mesons scale with
in the same way as the analogous meson-based soliton model scales with a
generic meson-meson coupling constant . An alternative large limit
(the orientifold large limit) has recently been proposed in which quarks
transform in the two-index antisymmetric representation of . By
carrying out the analog of Witten's analysis for the new orientifold large
limit, we show that baryons and solitons can also be identified in the
orientifold large limit. However, in the orientifold large limit,
the interaction amplitudes and matrix elements scale with in the
same way as soliton models scale with the generic meson coupling constant
rather than as as in the traditional large limit.Comment: 10 pages, 26 figure
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