282,085 research outputs found
Bayesian Inference for Jump-Diffusion Approximations of Biochemical Reaction Networks
Biochemical reaction networks are an amalgamation of reactions where each
reaction represents the interaction of different species. Generally, these
networks exhibit a multi-scale behavior caused by the high variability in
reaction rates and abundances of species. The so-called jump-diffusion
approximation is a valuable tool in the modeling of such systems. The
approximation is constructed by partitioning the reaction network into a fast
and slow subgroup of fast and slow reactions, respectively. This enables the
modeling of the dynamics using a Langevin equation for the fast group, while a
Markov jump process model is kept for the dynamics of the slow group. Most
often biochemical processes are poorly characterized in terms of parameters and
population states. As a result of this, methods for estimating hidden
quantities are of significant interest. In this paper, we develop a tractable
Bayesian inference algorithm based on Markov chain Monte Carlo. The presented
blocked Gibbs particle smoothing algorithm utilizes a sequential Monte Carlo
method to estimate the latent states and performs distinct Gibbs steps for the
parameters of a biochemical reaction network, by exploiting a jump-diffusion
approximation model. The presented blocked Gibbs sampler is based on the two
distinct steps of state inference and parameter inference. We estimate states
via a continuous-time forward-filtering backward-smoothing procedure in the
state inference step. By utilizing bootstrap particle filtering within a
backward-smoothing procedure, we sample a smoothing trajectory. For estimating
the hidden parameters, we utilize a separate Markov chain Monte Carlo sampler
within the Gibbs sampler that uses the path-wise continuous-time representation
of the reaction counters. Finally, the algorithm is numerically evaluated for a
partially observed multi-scale birth-death process example
Finding Multiple Reaction Pathways of Ligand Unbinding
Searching for reaction pathways describing rare events in large systems
presents a long-standing challenge in chemistry and physics. Incorrectly
computed reaction pathways result in the degeneracy of microscopic
configurations and inability to sample hidden energy barriers. To this aim, we
present a general enhanced sampling method to find multiple diverse reaction
pathways of ligand unbinding through non-convex optimization of a loss function
describing ligand-protein interactions. The method successfully overcomes large
energy barriers using an adaptive bias potential, and constructs possible
reaction pathways along transient tunnels without the initial guesses of
intermediate or final states, requiring crystallographic information only. We
examine the method on the T4 lysozyme L99A mutant which is often used as a
model system to study ligand binding to proteins, provide a previously unknown
reaction pathway, and show that using the bias potential and the tunnel widths
it is possible to capture heterogeneity of the unbinding mechanisms between the
found transient protein tunnels
Fast, Robust, and Versatile Event Detection through HMM Belief State Gradient Measures
Event detection is a critical feature in data-driven systems as it assists
with the identification of nominal and anomalous behavior. Event detection is
increasingly relevant in robotics as robots operate with greater autonomy in
increasingly unstructured environments. In this work, we present an accurate,
robust, fast, and versatile measure for skill and anomaly identification. A
theoretical proof establishes the link between the derivative of the
log-likelihood of the HMM filtered belief state and the latest emission
probabilities. The key insight is the inverse relationship in which gradient
analysis is used for skill and anomaly identification. Our measure showed
better performance across all metrics than related state-of-the art works. The
result is broadly applicable to domains that use HMMs for event detection.Comment: 8 pages, 7 figures, double col, ieee conference forma
An immune network approach to learning qualitative models of biological pathways
ACKNOWLEDGMENT GMC is supported by the CRISP project (Combinatorial Responses In Stress Pathways) funded by the BBSRC (BB/F00513X/1) under the Systems Approaches to Biological Research (SABR) Initiative. WP and GMC are also supported by the partnership fund from dot.rural, RCUK Digital Economy research.Postprin
Penta-quark states with hidden charm and beauty
More and more hadron states are found to be difficult to be accommodated by
the quenched quark models which describe baryons as 3-quark states and mesons
as antiquark-quark states. Dragging out an antiquark-quark pair from the gluon
field in hadrons should be an important excitation mechanism for hadron
spectroscopy. Our recent progress on the penta-quark states with hidden charm
and beauty is reviewed.Comment: Plenary talk at the 5th Asia-Pacific Conference on Few-Body Problems
in Physics 2011 (APFB2011), 22-26 Aug., 2011, Seoul, Kore
- …