29 research outputs found
Motif Dynamics in Signed Directional Complex Networks
Complex networks evolve and vary their structure as time goes by. In
particular, the links in those networks have both a sign and a directionality.
To understand their structural principles, we measure the network motifs, which
are patterns that appear much more than one would expect in randomized
networks, considering both link properties. We propose motif dynamics, which is
a study to investigate the change in the number of motifs, and applied the
motif dynamics to an open evolving network model and empirical data. We confirm
that a non-cyclic motif has a greater correlation with the system size than a
cyclic structural motif. Furthermore, the motif dynamics can give us insight
into the friendship between freshmen in a university
Invasion and Interaction Determine Population Composition in an Open Evolving System
It is well-known that interactions between species determine the population
composition in an ecosystem. Conventional studies have focused on fixed
population structures to reveal how interactions shape population compositions.
However, interaction structures are not fixed, but change over time due to
invasions. Thus, invasion and interaction play an important role in shaping
communities. Despite its importance, however, the interplay between invasion
and interaction has not been well explored. Here, we investigate how invasion
affects the population composition with interactions in open evolving systems
considering generalized Lotka-Volterra-type dynamics. Our results show that the
system has two distinct regimes. One is characterized by low diversity with
abrupt changes of dominant species in time, appearing when the interaction
between species is strong and invasion slowly occurs. On the other hand,
frequent invasions can induce higher diversity with slow changes in abundances
despite strong interactions. It is because invasion happens before the system
reaches its equilibrium, which drags the system from its equilibrium all the
time. All species have similar abundances in this regime, which implies that
fast invasion induces regime shift. Therefore, whether invasion or interaction
dominates determines the population composition.Comment: 15 pages (including supplementary material), 8 figures (4 figures in
main, 4 figures in SI
Exactly solvable charged dilaton gravity theories in two dimensions
We find exactly solvable dilaton gravity theories containing a U(1) gauge
field in two dimensional space-time. The classical general solutions for the
gravity sector (the metric plus the dilaton field) of the theories coupled to a
massless complex scalar field are obtained in terms of the stress-energy tensor
and the U(1) current of the scalar field. We discuss issues that arise when we
attempt to use these models for the study of the gravitational back-reaction.Comment: The introductory part is changed. a version to appear in Class.
Quant. Grav. 6 pages, RevTe
Magnetically charged solutions via an analog of the electric-magnetic duality in (2+1)-dimensional gravity theories
We find an analog of the electric-magnetic duality, which is a
transformation between magnetic and electric sectors of the static and
rotationally symmetric solutions in a class of (2+1)-dimensional
Einstein-Maxwell-Dilaton gravity theories. The theories in our consideration
include, in particular, one parameter class of theories continuously connecting
the Banados-Teitelboim-Zanelli (BTZ) gravity and the low energy string
effective theory. When there is no charge, we have or
symmetry, depending on a parameter that specifies each theory. Via the
transformation, we obtain exact magnetically charged solutions from the known
electrically charged solutions. We explain the relationship between the
transformation and symmetry, and comment on the -duality of the
string theory.Comment: 10 pages, RevTe
General Static Solutions of 2-dimensional Einstein-Dilaton-Maxwell-Scalar Theories
General static solutions of effectively 2-dimensional
Einstein-Dilaton-Maxwell-Scalar theories are obtained. Our model action
includes a class of 2-d dilaton gravity theories coupled with a gauge
field and a massless scalar field. Therefore it also describes the spherically
symmetric reduction of -dimensional Einstein-Scalar-Maxwell theories. The
properties of the analytic solutions are briefly discussed.Comment: 16 pages, Latex fil