11,339 research outputs found
Theory of Interface: Category Theory, Directed Networks and Evolution of Biological Networks
Biological networks have two modes. The first mode is static: a network is a
passage on which something flows. The second mode is dynamic: a network is a
pattern constructed by gluing functions of entities constituting the network.
In this paper, first we discuss that these two modes can be associated with the
category theoretic duality (adjunction) and derive a natural network structure
(a path notion) for each mode by appealing to the category theoretic
universality. The path notion corresponding to the static mode is just the
usual directed path. The path notion for the dynamic mode is called lateral
path which is the alternating path considered on the set of arcs. Their general
functionalities in a network are transport and coherence, respectively. Second,
we introduce a betweenness centrality of arcs for each mode and see how the two
modes are embedded in various real biological network data. We find that there
is a trade-off relationship between the two centralities: if the value of one
is large then the value of the other is small. This can be seen as a kind of
division of labor in a network into transport on the network and coherence of
the network. Finally, we propose an optimization model of networks based on a
quality function involving intensities of the two modes in order to see how
networks with the above trade-off relationship can emerge through evolution. We
show that the trade-off relationship can be observed in the evolved networks
only when the dynamic mode is dominant in the quality function by numerical
simulations. We also show that the evolved networks have features qualitatively
similar to real biological networks by standard complex network analysis.Comment: 59 pages, minor corrections from v
Mapping tori of small dilatation irreducible train-track maps
We prove that for every P there is a bound B depending only on P so that the
mapping torus of every P--small irreducible train-track map can be obtained by
surgery from one of B mapping tori. We show that given an integer P>0 there is
a bound depending only on P, so that there exists a presentation of the
fundamental group of the mapping torus of a P--small irreducible train-track
map with less than M generators and M relations.Comment: Some figures in colo
The composition of Event-B models
The transition from classical B [2] to the Event-B language and method [3] has seen the removal of some forms of model structuring and composition, with the intention of reinventing them in future. This work contributes to thatreinvention. Inspired by a proposed method for state-based decomposition and refinement [5] of an Event-B model, we propose a familiar parallel event composition (over disjoint state variable lists), and the less familiar event fusion (over intersecting state variable lists). A brief motivation is provided for these and other forms of composition of models, in terms of feature-based modelling. We show that model consistency is preserved under such compositions. More significantly we show that model composition preserves refinement
Modularity for Security-Sensitive Workflows
An established trend in software engineering insists on using components
(sometimes also called services or packages) to encapsulate a set of related
functionalities or data. By defining interfaces specifying what functionalities
they provide or use, components can be combined with others to form more
complex components. In this way, IT systems can be designed by mostly re-using
existing components and developing new ones to provide new functionalities. In
this paper, we introduce a notion of component and a combination mechanism for
an important class of software artifacts, called security-sensitive workflows.
These are business processes in which execution constraints on the tasks are
complemented with authorization constraints (e.g., Separation of Duty) and
authorization policies (constraining which users can execute which tasks). We
show how well-known workflow execution patterns can be simulated by our
combination mechanism and how authorization constraints can also be imposed
across components. Then, we demonstrate the usefulness of our notion of
component by showing (i) the scalability of a technique for the synthesis of
run-time monitors for security-sensitive workflows and (ii) the design of a
plug-in for the re-use of workflows and related run-time monitors inside an
editor for security-sensitive workflows
Shapes of topological RNA structures
A topological RNA structure is derived from a diagram and its shape is
obtained by collapsing the stacks of the structure into single arcs and by
removing any arcs of length one. Shapes contain key topological, information
and for fixed topological genus there exist only finitely many such shapes. We
shall express topological RNA structures as unicellular maps, i.e. graphs
together with a cyclic ordering of their half-edges. In this paper we prove a
bijection of shapes of topological RNA structures. We furthermore derive a
linear time algorithm generating shapes of fixed topological genus. We derive
explicit expressions for the coefficients of the generating polynomial of these
shapes and the generating function of RNA structures of genus . Furthermore
we outline how shapes can be used in order to extract essential information of
RNA structure databases.Comment: 27 pages, 11 figures, 2 tables. arXiv admin note: text overlap with
arXiv:1304.739
PLTL Partitioned Model Checking for Reactive Systems under Fairness Assumptions
We are interested in verifying dynamic properties of finite state reactive
systems under fairness assumptions by model checking. The systems we want to
verify are specified through a top-down refinement process. In order to deal
with the state explosion problem, we have proposed in previous works to
partition the reachability graph, and to perform the verification on each part
separately. Moreover, we have defined a class, called Bmod, of dynamic
properties that are verifiable by parts, whatever the partition. We decide if a
property P belongs to Bmod by looking at the form of the Buchi automaton that
accepts the negation of P. However, when a property P belongs to Bmod, the
property f => P, where f is a fairness assumption, does not necessarily belong
to Bmod. In this paper, we propose to use the refinement process in order to
build the parts on which the verification has to be performed. We then show
that with such a partition, if a property P is verifiable by parts and if f is
the expression of the fairness assumptions on a system, then the property f =>
P is still verifiable by parts. This approach is illustrated by its application
to the chip card protocol T=1 using the B engineering design language
Quick-cast: A method for fast and precise scalable production of fluid-driven elastomeric soft actuators
Fluid-driven elastomeric actuators (FEAs) are among the most popular
actuators in the emerging field of soft robotics. Intrinsically compliant, with
continuum of motion, large strokes, little friction, and high power-to-weight
ratio, they are very similar to biological muscles, and have enabled new
applications in automation, architecture, medicine, and human-robot
interaction. To foster future applications of FEAs, in this paper we present a
new manufacturing method for fast and precise scalable production of complex
FEAs of high quality (leak-free, single-body form, with <0.2 mm precision). The
method is based on 3d moulding and supports elastomers with a wide range of
viscosity, pot life, and Young's modulus. We developed this process for two
different settings: one in laboratory conditions for fast prototyping with 3d
printed moulds and using multi-component liquid elastomers, and the other
process in an industrial setting with 3d moulds micromachined in metal and
applying compression moulding. We demonstrate these methods in fabrication of
up to several tens of two-axis, three-chambered soft actuators, with two types
of chamber walls: cylindrical and corrugated. The actuators are then applied as
motion drivers in kinetic photovoltaic building envelopes
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