Vaguery + theoretical-biology   12

[1102.2359] A Phyllotactic Approach to the Structure of Collagen Fibrils
"… We examine here how the algorithm of phyllotaxis could contribute to the analysis of the structure of collagen fibrils. Such an algorithm indeed leads to organizations giving to each element of the assembly the most homogeneous and isotropic dense environment in a situation of cylindrical symmetry. The scattered intensity expected from a phyllotactic distribution of triple helices in collagen fibrils well agrees with the major features observed along the equatorial direction of their X ray patterns. Following this approach, the aggregation of triple helices in fibrils should be considered within the frame of soft condensed matter studies rather than that of molecular crystal studies."
self-assembly  nanotechnology  molecular-design  molecular-machinery  theoretical-biology  structural-biology  crystallography  condensed-matter  from delicious
april 2011 by Vaguery
A dynamical model of genetic networks describes cell differentiation : Nature Precedings
"…The model is based on the emergent properties of generic genetic networks, it does not refer to specific control circuits and it can therefore hold for a wide class of lineages. The model points to a peculiar role of cellular noise in differentiation, which has never been hypothesized so far, and leads to non trivial predictions which could be subject to experimental testing."
cellular-biology  boolean-networks  artificial-life  Stuart-Kauffman  theoretical-biology 
august 2010 by Vaguery
[1006.4265] Modeling capsid self-assembly: Design and analysis
"A series of simulations aimed at elucidating the self-assembly dynamics of spherical virus capsids is described. This little-understood phenomenon is a fascinating example of the complex processes that occur in the simplest of organisms. The fact that different viruses adopt similar structural forms is an indication of a common underlying design, motivating the use of simplified, low-resolution models in exploring the assembly process. Several versions of a molecular dynamics approach are described. Polyhedral shells of different sizes are involved, the assembly pathways are either irreversible or reversible, and an explicit solvent is optionally included. …Among the key observations are that efficient growth proceeds by means of a cascade of highly reversible stages, and that while there are a large variety of possible partial assemblies, only a relatively small number of strongly bonded configurations are actually encountered."
molecular-design  virus  biochemistry  self-assembly  simulation  nudge-targets  theoretical-biology  biological-engineering 
june 2010 by Vaguery
[1006.2960] Imitation, internal absorption and the reversal of local drift in stochastic evolutionary games
"Evolutionary game dynamics in finite populations is typically subject to noise, inducing effects which are not present in deterministic systems, including fixation and extinction. In the first part of this paper we investigate the phenomenon of drift reversal in finite populations, taking into account that drift is a local quantity in strategy space. Secondly, we study a simple imitation dynamics, and show that it can lead to fixation at internal mixed-strategy fixed points even in finite populations. Imitation in infinite populations is adequately described by conventional replicator dynamics, and these equations are known to have internal fixed points. Internal absorption in finite populations on the other hand is a novel dynamic phenomenon. Due to an outward drift in finite populations this type of dynamic arrest is not found in other commonly studied microscopic dynamics, not even in those with the same deterministic replicator limit as imitation."
theoretical-biology  game-theory  complexology  agent-based  RPS  evolutionary-game-theory  genetic-drift 
june 2010 by Vaguery
[1002.4273] Mutual information in time-varying biochemical systems
ME: what would 'well-designed' biochemical nets look like, if you evolved them in silico?

"The reliability with which a network can transmit a particular frequency component of the input signal tra- jectory is determined by the gain-to-noise ratio of the net- work as a function of frequency. For systems that obey the spectral addition rule [32], that is those for which downstream reactions do not affect the input signal, the gain-to-noise ratio is an intrinsic property of the processing network. For networks that do not obey the spectral addition rule the gain-to-noise ratio will be dependent on the statistics of the input signal. The mutual information between input and output signals, which quantifies the information which can be transmitted about a particular input ensemble, also depends on the particular choice of the input signal.…"
biochemistry  theoretical-biology  molecular-design  biological-engineering  network-theory  complexology  nudge-targets 
june 2010 by Vaguery
[1006.2307] Exploring the randomness of Directed Acyclic Networks
"The feed-forward relationship naturally observed in time-dependent processes and in a diverse number of real systems -such as some food-webs and electronic and neural wiring- can be described in terms of so-called directed acyclic graphs (DAGs). An important ingredient of the analysis of such networks is a proper comparison of their observed architecture against an ensemble of randomized graphs, thereby quantifying the {\em randomness} of the real systems with respect to suitable null models. This approximation is particularly relevant when the finite size and/or large connectivity of real systems make inadequate a comparison with the predictions obtained from the so-called {\em configuration model}. In this paper we analyze four methods of DAG randomization as defined by the desired combination of topological invariants (directed and undirected degree sequence and component distributions) aimed to be preserved.…"
networks  network-theory  graph-theory  algorithms  statistics  complexology  theoretical-biology 
june 2010 by Vaguery
[1006.0079] Modeling the mobility of living organisms in heterogeneous landscapes: Does memory improve foraging success?
"Thanks to recent technological advances, it is now possible to track with an unprecedented precision and for long periods of time the movement patterns of many living organisms in their habitat. The increasing amount of data available on single trajectories offers the possibility of understanding how animals move and of testing basic movement models. Random walks have long represented the main description for micro-organisms and have also been useful to understand the foraging behaviour of large animals. Nevertheless, most vertebrates, in particular humans and other primates, rely on sophisticated cognitive tools such as spatial maps, episodic memory and travel cost discounting. These properties call for other modeling approaches of mobility patterns. We propose a foraging framework where a learning mobile agent uses a combination of memory-based and random steps. We investigate how advantageous it is to use memory for exploiting resources in heterogeneous and changing environments.…"
theoretical-biology  ecology  ethology  simulation  agent-based  algorithms  strategies  complexology 
june 2010 by Vaguery
[1005.4342] The effect of scale-free topology on the robustness and evolvability of genetic regulatory networks
"… We find that SF networks generate oscillations much more easily than ER networks do, and this may explain why SF networks are more evolvable than ER networks are for oscillatory phenotypes. In spite of their greater evolvability, we find that networks with SFout topologies are also more robust to mutations than ER networks. Furthermore, the SFout topologies are more robust to changes in initial conditions (environmental robustness). For both topologies, we find that once a population of networks has reached the target state, further neutral evolution can lead to an increase in both the mutational robustness and the environmental robustness to changes in initial conditions."
small-world  network-theory  evolvability  genetic-regulatory-network  theoretical-biology  physics 
may 2010 by Vaguery
[1005.2107] Efficient parameter search for qualitative models of regulatory networks using symbolic model checking
"Investigating the relation between the structure and behavior of complex biological networks often involves posing the following two questions: Is a hypothesized structure of a regulatory network consistent with the observed behavior? And can a proposed structure generate a desired behavior? Answering these questions presupposes that we are able to test the compatibility of network structure and behavior. We cast these questions into a parameter search problem for qualitative models of regulatory networks…. We develop a method based on symbolic model checking that avoids enumerating all possible parametrizations, and show that this method performs well on real biological problems, using the IRMA synthetic network and benchmark experimental data sets. We test the consistency between the IRMA network structure and the time-series data, and search for parameter modifications that would improve the robustness of the external control of the system behavior."
complexology  theoretical-biology  bioinformatics  modeling-is-not-mathematics  nudge-targets 
may 2010 by Vaguery
[1005.1191] Living on the edge of chaos: minimally nonlinear models of genetic regulatory dynamics
"…We analyze the Lyapunov spectrum, determine the probability to find stationary oscillating solutions, demonstrate the effect of the nonlinearity on the effective in- and out-degree of the active interaction network and study how the frequency distributions of oscillatory modes of such system depend on the average connectivity."
origin-of-life  autocatalysis  biochemistry  theoretical-biology  models  nudge-targets 
may 2010 by Vaguery
[1005.1311] The Beauty Contest Game, a population-centric approach
"The beauty contest game concept originated with John Maynard Keynes [5] and has been studied in [3,7] and many other articles and experiments as a simple model of cognition and behavior. In a beauty contest game, all players guess a number within a given interval, with the goal of guessing p times the average of all other guesses, where p is a number in the interval (0, 1). For instance, for p = 1/2 and an interval of [0, 100], a player attempts to guess what will be half of the average of all guesses (including the player’s guess).…"
nudge-targets  game-theory  theoretical-biology  models  agent-based  theory-and-practice-sitting-in-a-tree 
may 2010 by Vaguery

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