6,835 research outputs found
Dynamic Influence Networks for Rule-based Models
We introduce the Dynamic Influence Network (DIN), a novel visual analytics
technique for representing and analyzing rule-based models of protein-protein
interaction networks. Rule-based modeling has proved instrumental in developing
biological models that are concise, comprehensible, easily extensible, and that
mitigate the combinatorial complexity of multi-state and multi-component
biological molecules. Our technique visualizes the dynamics of these rules as
they evolve over time. Using the data produced by KaSim, an open source
stochastic simulator of rule-based models written in the Kappa language, DINs
provide a node-link diagram that represents the influence that each rule has on
the other rules. That is, rather than representing individual biological
components or types, we instead represent the rules about them (as nodes) and
the current influence of these rules (as links). Using our interactive DIN-Viz
software tool, researchers are able to query this dynamic network to find
meaningful patterns about biological processes, and to identify salient aspects
of complex rule-based models. To evaluate the effectiveness of our approach, we
investigate a simulation of a circadian clock model that illustrates the
oscillatory behavior of the KaiC protein phosphorylation cycle.Comment: Accepted to TVCG, in pres
Causal machine learning for single-cell genomics
Advances in single-cell omics allow for unprecedented insights into the
transcription profiles of individual cells. When combined with large-scale
perturbation screens, through which specific biological mechanisms can be
targeted, these technologies allow for measuring the effect of targeted
perturbations on the whole transcriptome. These advances provide an opportunity
to better understand the causative role of genes in complex biological
processes such as gene regulation, disease progression or cellular development.
However, the high-dimensional nature of the data, coupled with the intricate
complexity of biological systems renders this task nontrivial. Within the
machine learning community, there has been a recent increase of interest in
causality, with a focus on adapting established causal techniques and
algorithms to handle high-dimensional data. In this perspective, we delineate
the application of these methodologies within the realm of single-cell genomics
and their challenges. We first present the model that underlies most of current
causal approaches to single-cell biology and discuss and challenge the
assumptions it entails from the biological point of view. We then identify open
problems in the application of causal approaches to single-cell data:
generalising to unseen environments, learning interpretable models, and
learning causal models of dynamics. For each problem, we discuss how various
research directions - including the development of computational approaches and
the adaptation of experimental protocols - may offer ways forward, or on the
contrary pose some difficulties. With the advent of single cell atlases and
increasing perturbation data, we expect causal models to become a crucial tool
for informed experimental design.Comment: 35 pages, 7 figures, 3 tables, 1 bo
Modelling & analysis of hybrid dynamic systems using a bond graph approach
Hybrid models are those containing continuous and discontinuous behaviour. In constructing dynamic systems models, it is frequently desirable to abstract rapidly changing, highly nonlinear behaviour to a discontinuity. Bond graphs lend themselves to systems modelling by being multi-disciplinary and reflecting the physics of the system. One advantage is that they can produce a mathematical model in a form that simulates quickly and efficiently. Hybrid bond graphs are a logical development which could further improve speed and efficiency. A range of hybrid bond graph forms have been proposed which are suitable for either simulation or further analysis, but not both. None have reached common usage.
A Hybrid bond graph method is proposed here which is suitable for simulation as well as providing engineering insight through analysis. This new method features a distinction between structural and parametric switching. The controlled junction is used for the former, and gives rise to dynamic causality. A controlled element is developed for the latter. Dynamic causality is unconstrained so as to aid insight, and a new notation is proposed.
The junction structure matrix for the hybrid bond graph features Boolean terms to reflect the controlled junctions in the graph structure. This hybrid JSM is used to generate a mixed-Boolean state equation. When storage elements are in dynamic causality, the resulting system equation is implicit.
The focus of this thesis is the exploitation of the model. The implicit form enables application of matrix-rank criteria from control theory, and control properties can be seen in the structure and causal assignment. An impulsive mode may occur when storage elements are in dynamic causality, but otherwise there are no energy losses associated with commutation because this method dictates the way discontinuities are abstracted.
The main contribution is therefore a Hybrid Bond Graph which reflects the physics of commutating systems and offers engineering insight through the choice of controlled elements and dynamic causality. It generates a unique, implicit, mixed-Boolean system equation, describing all modes of operation. This form is suitable for both simulation and analysis
Causality in Economics: A Menu of Approaches
Causality is a notion that occurs often in economics. In using the words ‘cause' and ‘effect,' economists seek to distinguish causation from association, recognizing that causes are responsible for producing effects, whereas non-causal associations are not. The identification of causes is accorded a high priority because it is viewed as the basis for understanding economic phenomena and developing policy implications. In this survey we look at different approaches to causality in economics and set out the general principles of each approach, so as to assist in the communication and teaching role. Specifically, we confine attention to five approaches to causality in economics (narrative, comparative statics, theoretical, structural, and experimentalist) and elucidate their distinctive characteristics without entering into philosophical discussions. In particular, we pay close attention to the debate between the structuralist and experimentalist schools because this controversy has been extremely useful to clarify a number of fundamental points concerning causality in economic
Aspects of bond graph modelling in control
Abstract available: p. i
Muscleless Motor synergies and actions without movements : From Motor neuroscience to cognitive robotics
Emerging trends in neurosciences are providing converging evidence that cortical networks in predominantly motor areas are activated in several contexts related to ‘action’ that do not cause any overt movement. Indeed for any complex body, human or embodied robot inhabiting unstructured environments, the dual processes of shaping motor output during action execution and providing the self with information related to feasibility, consequence and understanding of potential actions (of oneself/others) must seamlessly alternate during goal-oriented behaviors, social interactions. While prominent approaches like Optimal Control, Active Inference converge on the role of forward models, they diverge on the underlying computational basis. In this context, revisiting older ideas from motor control like the Equilibrium Point Hypothesis and synergy formation, this article offers an alternative perspective emphasizing the functional role of a ‘plastic, configurable’ internal representation of the body (body-schema) as a critical link enabling the seamless continuum between motor control and imagery. With the central proposition that both “real and imagined” actions are consequences of an internal simulation process achieved though passive goal-oriented animation of the body schema, the computational/neural basis of muscleless motor synergies (and ensuing simulated actions without movements) is explored. The rationale behind this perspective is articulated in the context of several interdisciplinary studies in motor neurosciences (for example, intracranial depth recordings from the parietal cortex, FMRI studies highlighting a shared cortical basis for action ‘execution, imagination and understanding’), animal cognition (in particular, tool-use and neuro-rehabilitation experiments, revealing how coordinated tools are incorporated as an extension to the body schema) and pertinent challenges towards building cognitive robots that can seamlessly “act, interact, anticipate and understand” in unstructured natural living spaces
- …