13 research outputs found
Near-optimal experimental design for model selection in systems biology
Motivation:âBiological systems are understood through iterations of modeling and experimentation. Not all experiments, however, are equally valuable for predictive modeling. This study introduces an efficient method for experimental design aimed at selecting dynamical models from data. Motivated by biological applications, the method enables the design of crucial experiments: it determines a highly informative selection of measurement readouts and time points. Results:âWe demonstrate formal guarantees of design efficiency on the basis of previous results. By reducing our task to the setting of graphical models, we prove that the method finds a near-optimal design selection with a polynomial number of evaluations. Moreover, the method exhibits the best polynomial-complexity constant approximation factor, unless P = NP. We measure the performance of the method in comparison with established alternatives, such as ensemble non-centrality, on example models of different complexity. Efficient design accelerates the loop between modeling and experimentation: it enables the inference of complex mechanisms, such as those controlling central metabolic operation. Availability:âToolbox âNearOED' available with source code under GPL on the Machine Learning Open Source Software Web site (mloss.org). Contact:â[email protected] Supplementary information:âSupplementary data are available at Bioinformatics onlin
Biological Networks
Networks of coordinated interactions among biological entities govern a myriad of biological functions that span a wide range of both length and time scalesâfrom ecosystems to individual cells and from years to milliseconds. For these networks, the concept âthe whole is greater than the sum of its partsâ applies as a norm rather than an exception. Meanwhile, continued advances in molecular biology and high-throughput technology have enabled a broad and systematic interrogation of whole-cell networks, allowing the investigation of biological processes and functions at unprecedented breadth and resolutionâeven down to the single-cell level. The explosion of biological data, especially molecular-level intracellular data, necessitates new paradigms for unraveling the complexity of biological networks and for understanding how biological functions emerge from such networks. These paradigms introduce new challenges related to the analysis of networks in which quantitative approaches such as machine learning and mathematical modeling play an indispensable role. The Special Issue on âBiological Networksâ showcases advances in the development and application of in silico network modeling and analysis of biological systems
Scalable Front End Designs for Communication and Learning
In this work we provide three examples of estimation/detection problems, for which customizing the Front End to the specific application makes the system more efficient and scalable. The three problems we consider are all classical, but face new scalability challenges. This introduces additional constraints, accounting for which results in front end designs that are very distinct from the conventional approaches. The first two case studies pertain to the canonical problems of synchronization and equalization for communication links. As the system bandwidths scale, challenges arise due to the limiting resolution of analog-to-digital converters (ADCs). We discuss system designs that react to this bottleneck by drastically relaxing the precision requirements of the front end and correspondingly modifying the back end algorithms using Bayesian principles. The third problem we discuss belongs to the field of computer vision. Inspired by the research in neuroscience about the mammalian visual system, we redesign the front end of a machine vision system to be neuro-mimetic, followed by layers of unsupervised learning using simple k-means clustering. This results in a framework that is intuitive, more computationally efficient compared to the approach of supervised deep networks, and amenable to the increasing availability of large amounts of unlabeled data. We first consider the problem of blind carrier phase and frequency synchronization in order to obtain insight into the performance limitations imposed by severe quantization constraints. We adopt a mixed signal analog front end that coarsely quantizes the phase and employs a digitally controlled feedback that applies a phase shift prior to the ADC, this acts as a controllable dither signal and aids in the estimation process. We propose a control policy for the feedback and show that combined with blind Bayesian algorithms, it results in excellent performance, close to that of an unquantized system.Next, we take up the problem of channel equalization with severe limits on the number of slicers available for the ADC. We find that the standard flash ADC architecture can be highly sub-optimal in the presence of such constraints. Hence we explore a ``space-time'' generalization of the flash architecture by allowing a fixed numberof slicers to be dispersed in time (sampling phase) as well as space (i.e., amplitude). We show that optimizing the slicer locations, conditioned on the channel, results in significant gains in the bit error rate (BER) performance. Finally, we explore alternative ways of learning convolutionalnets for machine vision, making it easier to interpret and simpler to implement than currently used purely supervised nets. In particular, we investigate a framework that combines a neuro-mimetic front end (designed in collaboration with the neuroscientists from the psychology department at UCSB) together with unsupervised feature extraction based on clustering. Supervised classification, using a generic support vector machine (SVM), is applied at the end.We obtain competitive classification results on standard image databases, beating the state of the art for NORB (uniform-normalized) and approaching it for MNIST
Simplification de modÚles mathématiques représentant des cultures cellulaires
Lâutilisation de cellules vivantes dans un procĂ©dĂ© industriel tire profit de la complexitĂ© inhĂ©rente au vivant pour accomplir des tĂąches complexes et dont la comprĂ©hension est parfois limitĂ©e. Que ce soit pour la production de biomasse, pour la production de molĂ©cules dâintĂ©rĂȘt ou pour la dĂ©composition de molĂ©cules indĂ©sirables, ces procĂ©dĂ©s font appel aux multiples rĂ©actions formant le mĂ©tabolisme cellulaire. Afin de dĂ©crire lâĂ©volution de ces systĂšmes, des modĂšles mathĂ©matiques composĂ©s dâun ensemble dâĂ©quations diffĂ©rentielles sont utilisĂ©s. Au fur et Ă mesure que les connaissances du mĂ©tabolisme se sont dĂ©veloppĂ©es, les modĂšles mathĂ©matiques le reprĂ©sentant se sont complexifiĂ©s. Le niveau de complexitĂ© requis pour expliquer les phĂ©nomĂšnes en jeu lors dâun procĂ©dĂ© spĂ©cifique est difficile Ă dĂ©finir. Ainsi, lorsquâon tente de modĂ©liser un nouveau procĂ©dĂ©, la sĂ©lection du modĂšle Ă utiliser peut ĂȘtre problĂ©matique. Une des options intĂ©ressantes est la sĂ©lection dâun modĂšle provenant de la littĂ©rature et adaptĂ© au procĂ©dĂ© utilisĂ©. Lâinformation contenue dans le modĂšle doit alors ĂȘtre Ă©valuĂ©e en fonction des phĂ©nomĂšnes observables dans les conditions dâopĂ©ration. Souvent, les modĂšles provenant de la littĂ©rature sont surparamĂ©trĂ©s pour lâutilisation dans les conditions dâopĂ©ration des procĂ©dĂ©s ciblĂ©es. Cela fait en sorte de causer des problĂšmes dâidentifiabilitĂ© des paramĂštres. De plus, lâensemble des variables dâĂ©tat utilisĂ©es dans le modĂšle nâest pas nĂ©cessairement mesurĂ© dans les conditions dâopĂ©ration normales. Lâobjectif de ce projet est de cibler lâinformation utilisable contenue dans les modĂšles par la simplification mĂ©thodique de ceux-ci. En effet, la simplification des modĂšles permet une meilleure comprĂ©hension des dynamiques Ă lâoeuvre dans le procĂ©dĂ©. Ce projet a permis de dĂ©finir et dâĂ©valuer trois mĂ©thodes de simplification de modĂšles mathĂ©matiques servant Ă dĂ©crire un procĂ©dĂ© de culture cellulaire. La premiĂšre mĂ©thode est basĂ©e sur lâapplication de critĂšres sur les diffĂ©rents Ă©lĂ©ments du modĂšle, la deuxiĂšme est basĂ©e sur lâutilisation dâun critĂšre dâinformation du type dâAkaike et la troisiĂšme considĂšre la rĂ©duction dâordre du modĂšle par retrait de variables dâĂ©tat. Les rĂ©sultats de ces mĂ©thodes de simplification sont prĂ©sentĂ©s Ă lâaide de quatre modĂšles cellulaires provenant de la littĂ©rature