118,246 research outputs found
Multilevel comparison of large urban systems
For the first time the systems of cities in seven countries or regions among
the largest in the world (China, India, Brazil, Europe, the Former Soviet Union
(FSU), the United States and South Africa) are made comparable through the
building of spatio-temporal standardised statistical databases. We first
explain the concept of a generic evolutionary urban unit ("city") and its
necessary adaptations to the information provided by each national statistical
system. Second, the hierarchical structure and the urban growth process are
compared at macro-scale for the seven countries with reference to Zipf's and
Gibrat's model: in agreement with an evolutionary theory of urban systems,
large similarities shape the hierarchical structure and growth processes in
BRICS countries as well as in Europe and United States, despite their positions
at different stages in the urban transition that explain some structural
peculiarities. Third, the individual trajectories of some 10,000 cities are
mapped at micro-scale following a cluster analysis of their evolution over the
last fifty years. A few common principles extracted from the evolutionary
theory of urban systems can explain the diversity of these trajectories,
including a specific pattern in their geographical repartition in the Chinese
case. We conclude that the observations at macro-level when summarized as
stylised facts can help in designing simulation models of urban systems whereas
the urban trajectories identified at micro-level are consistent enough for
constituting the basis of plausible future population projections.Comment: 14 pages, 9 figures; Pumain, Denise, et al. "Multilevel comparison of
large urban systems." Cybergeo: European Journal of Geography (2015
Zipf's law, Hierarchical Structure, and Shuffling-Cards Model for Urban Development
A new angle of view is proposed to find the simple rules dominating complex
systems and regular patterns behind random phenomena such as cities. Hierarchy
of cities reflects the ubiquitous structure frequently observed in the natural
world and social institutions. Where there is a hierarchy with cascade
structure, there is a rank-size distribution following Zipf's law, and vice
versa. The hierarchical structure can be described with a set of exponential
functions that are identical in form to Horton-Strahler's laws on rivers and
Gutenberg-Richter's laws on earthquake energy. From the exponential models, we
can derive four power laws such as Zipf's law indicative of fractals and
scaling symmetry. Research on the hierarchy is revealing for us to understand
how complex systems are self-organized. A card-shuffling model is built to
interpret the relation between Zipf's law and hierarchy of cities. This model
can be expanded to explain the general empirical power-law distributions across
the individual physical and social sciences, which are hard to be comprehended
within the specific scientific domains.Comment: 28 pages, 8 figure
Hierarchical mutual information for the comparison of hierarchical community structures in complex networks
The quest for a quantitative characterization of community and modular
structure of complex networks produced a variety of methods and algorithms to
classify different networks. However, it is not clear if such methods provide
consistent, robust and meaningful results when considering hierarchies as a
whole. Part of the problem is the lack of a similarity measure for the
comparison of hierarchical community structures. In this work we give a
contribution by introducing the {\it hierarchical mutual information}, which is
a generalization of the traditional mutual information, and allows to compare
hierarchical partitions and hierarchical community structures. The {\it
normalized} version of the hierarchical mutual information should behave
analogously to the traditional normalized mutual information. Here, the correct
behavior of the hierarchical mutual information is corroborated on an extensive
battery of numerical experiments. The experiments are performed on artificial
hierarchies, and on the hierarchical community structure of artificial and
empirical networks. Furthermore, the experiments illustrate some of the
practical applications of the hierarchical mutual information. Namely, the
comparison of different community detection methods, and the study of the
consistency, robustness and temporal evolution of the hierarchical modular
structure of networks.Comment: 14 pages and 12 figure
Hierarchy Theory of Evolution and the Extended Evolutionary Synthesis: Some Epistemic Bridges, Some Conceptual Rifts
Contemporary evolutionary biology comprises a plural landscape of multiple co-existent conceptual frameworks and strenuous voices that disagree on the nature and scope of evolutionary theory. Since the mid-eighties, some of these conceptual frameworks have denounced the ontologies of the Modern Synthesis and of the updated Standard Theory of Evolution as unfinished or even flawed. In this paper, we analyze and compare two of those conceptual frameworks, namely Niles Eldredgeâs Hierarchy Theory of Evolution (with its extended ontology of evolutionary entities) and the Extended Evolutionary Synthesis (with its proposal of an extended ontology of evolutionary processes), in an attempt to map some epistemic bridges (e.g. compatible views of causation; niche construction) and some conceptual rifts (e.g. extra-genetic inheritance; different perspectives on macroevolution; contrasting standpoints held in the âexternalismâinternalismâ debate) that exist between them. This paper seeks to encourage theoretical, philosophical and historiographical discussions about pluralism or the possible unification of contemporary evolutionary biology
A Hierarchical Allometric Scaling Analysis of Chinese Cities: 1991-2014
The law of allometric scaling based on Zipf distributions can be employed to
research hierarchies of cities in a geographical region. However, the
allometric patterns are easily influenced by random disturbance from the noises
in observational data. In theory, both the allometric growth law and Zipf's law
are related to the hierarchical scaling laws associated with fractal structure.
In this paper, the scaling laws of hierarchies with cascade structure are used
to study Chinese cities, and the method of R/S analysis is applied to analyzing
the change trend of the allometric scaling exponents. The results show that the
hierarchical scaling relations of Chinese cities became clearer and clearer
from 1991 to 2014 year; the global allometric scaling exponent values
fluctuated around 0.85, and the local scaling exponent approached to 0.85. The
Hurst exponent of the allometric parameter change is greater than 0.5,
indicating persistence and a long-term memory of urban evolution. The main
conclusions can be reached as follows: the allometric scaling law of cities
represents an evolutionary order rather than an invariable rule, which emerges
from self-organized process of urbanization, and the ideas from allometry and
fractals can be combined to optimize spatial and hierarchical structure of
urban systems in future city planning.Comment: 28 pages, 10 figures, 5 table
Class movement and re-location: An empirical study of Java inheritance evolution
This is the post-print version of the final paper published in Journal of Systems and Software. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2009 Elsevier B.V.Inheritance is a fundamental feature of the Object-Oriented (OO) paradigm. It is used to promote extensibility and reuse in OO systems. Understanding how systems evolve, and specifically, trends in the movement and re-location of classes in OO hierarchies can help us understand and predict future maintenance effort. In this paper, we explore how and where new classes were added as well as where existing classes were deleted or moved across inheritance hierarchies from multiple versions of four Java systems. We observed first, that in one of the studied systems the same set of classes was continuously moved across the inheritance hierarchy. Second, in the same system, the most frequent changes were restricted to just one sub-part of the overall system. Third, that a maximum of three levels may be a threshold when using inheritance in a system; beyond this level very little activity was observed, supporting earlier theories that, beyond three levels, complexity becomes overwhelming. We also found evidence of âcollapsingâ hierarchies to bring classes up to shallower levels. Finally, we found that larger classes and highly coupled classes were more frequently moved than smaller and less coupled classes. Statistical evidence supported the view that larger classes and highly coupled classes were less cohesive than smaller classes and lowly coupled classes and were thus more suitable candidates for being moved (within an hierarchy)
- âŠ