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Probabilistic Safety Analysis of Sensor-Driven Hybrid Automata + (The control programs of complex autonomous … The control programs of complex autonomous systems that have conditional branching can be modeled as linear hybrid systems. When the state knowledge is perfect, linear hybrid systems with state-based transition conditions can be verified against a specified unsafe set using existing model checking software. This paper introduces a formal method for calculating the failure probability due to state estimation uncertainty of these sensor-driven hybrid systems. Problem complexity is described and some reduction techniques for the failure probability calculation are given. An example goal-based control program is given and the failure probability for that system is calculated.probability for that system is calculated.)
Just-in-time synthesis for motion planning with temporal logic + (The cost of the great expressivity of moti … The cost of the great expressivity of motion planning subject to temporal logic formulae is intractability. Recent advances in sampling-based methods seem to be only applicable to âlow-levelâ control. The problem of realizing âhigh-levelâ controllers that satisfy a temporal logic specification does not readily admit approximations, unless the notion of correctness is relaxed as might be achieved with probabilistic variants of temporal logics. In this paper, we argue that not all possible environment (uncontrolled) behaviors need to be explicitly planned for, but rather short-time strategies can be generated online while maintaining global correctness. We achieve this by separating feasibility from controller synthesis, using a metric from the underlying continuous state space to ensure short-time strategies chained together provide globally correct behavior.ogether provide globally correct behavior.)
Autonomous Driving in Urban Environments: Approaches, Lessons and Challenges + (The development of autonomous vehicles for … The development of autonomous vehicles for urban driving has seen rapid progress in the past 30 years. This paper provides a summary of the current state of the art in autonomous driving in urban environments, based primarily on the experiences of the authors in the 2007 DARPA Urban Challenge (DUC). The paper briefly summarizes the approaches that different teams used in the DUC, with the goal of describing some of the challenges that the teams faced in driving in urban environments. The paper also highlights the long term research challenges that must be overcome in order to enable autonomous driving and points to opportunities for new technologies to be applied in improving vehicle safety, exploiting intelligent road infrastructure and enabling robotic vehicles operating in human environments. vehicles operating in human environments.)
Optimal Experiment Design and Leveraging Competition for Shared Resources in Cell-free Extracts + (The fact that genes compete for shared cel … The fact that genes compete for shared cellular resources poses a fundamental challenge when identifying pa- rameters of synthetic gene circuits. A recently developed model of gene expression tackles this problem by explicitly accounting for resource competition. In addition to accurately describing experimental data, this model only depends on a handful of easily identifiable parameters with clear physical interpretation. Based on this model, we outline a procedure how to select the optimal set of experiments to characterize biomolecular parts in synthetic biology. Additionally, we reveal the role competition for shared resources plays, provide guidelines how to minimize its detrimental effects, and how to leverage this phenomenon to extract the most information about unknown parameters. To illustrate the results, we consider the case of part characterization in cell-free extracts, treat plasmid DNA concentrations as decision variables, and demonstrate the significant performance difference between na ̈ıve and optimal experiment design.een na ̈ıve and optimal experiment design.)
Future Directions in Control in an Information-Rich World + (The field of control provides the principl … The field of control provides the principles and methods used to design physical and information systems that maintain desirable performance by sensing and automatically adapting to changes in the environment. As we begin the 21st Century, the opportunities to apply control principles and methods are exploding. New developments in this increasingly information rich world will require a significant expansion of the basic tool sets of control. This article summarizes the main findings and recommendations of the Panel on Future Directions in Control, Dynamics, and Systems, which has recently released its report. The report spells out some of the prospects for control in the current and future technological environment, describes the role the field will play in military, commercial, and scientific applications over the next decade, and recommends actions required to enable new breakthroughs in engineering and technology through application of control research.y through application of control research.)
Model Predictive Control for an Uncertain Smart Thermal Grid + (The focus of this paper is on modeling and … The focus of this paper is on modeling and control of Smart Thermal Grids (STGs) in which the uncertainties in the demand and/or supply are included. We solve the corre- sponding robust model predictive control (MPC) optimization problem using mixed-integer-linear programming techniques to provide a day-ahead prediction for the heat production in the grid. In an example, we compare the robust MPC approach with the robust optimal control approach, in which the day-ahead production plan is obtained by optimizing the objective function for entire day at once. There, we show that the robust MPC approach successfully keeps the supply-demand balance in the STG while satisfying the constraints of the production units in the presence of uncertainties in the heat demand. Moreover, we see that despite the longer computation time, the performance of the robust MPC controller is considerably better than the one of the robust optimal controller. the one of the robust optimal controller.)
POD Based Models of Self-Sustained Oscillations in the Flow Past an Open Cavity + (The goal of this work is to provide accura … The goal of this work is to provide accurate dynamical models of oscillations in the flow past a rectangular cavity, for the purpose of bifurcation analysis and control. We have performed an extensive set of direct numerical simulations which provide the data used to derive and evaluate the models. Based on the method of Proper Orthogonal Decomposition (POD) and Galerkin projection, we obtain low-order models (from 6 to 60 states) which capture the dynamics very accurately over a few periods of oscillations, but deviate for long time.f oscillations, but deviate for long time.)
Reactive Protocols for Aircraft Electric Power Distribution + (The increasing complexity of electric powe … The increasing complexity of electric power sys- tems leads to integration and verification challenges. We consider the problem of designing a control protocol for the aircraft electric power system that meets these system requirements and reacts dynamically to changes in internal system states. We formalize these requirements by translating them into a temporal logic specification language describing the correct behaviors of the system, and apply formal methods to automatically synthesize a controller protocol that satisfies these overall properties and requirements. Through an example, we perform a design exploration to show the benefits and tradeoffs between centralized and distributed control architectures.zed and distributed control architectures.)
Converting Smooth, Time-Varying, Asymptotic Stabilizers for Driftless Systems to Homogeneous, Exponential Stabilizers + (The main result of this paper is a theorem … The main result of this paper is a theorem that allows smooth,time-varying controllers which asymptotically stabilize a driftlessnonlinear system to be converted to homogeneous, time-varyingcontrollers which provide {\em exponential} stability. The resultingcontrollers are smooth everywhere except the origin and are easilycomputed given the original asymptotic stabilizer. We illustrate theresult with experimental results on a simple mobile robot.rimental results on a simple mobile robot.)
Impact of Chemical Dynamics of Commercial PURE Systems on Malachite Green Aptamer Fluorescence + (The malachite green aptamer (MGapt) is kno … The malachite green aptamer (MGapt) is known for its utility in RNA measurement in vivo and lysate-based cell-free protein systems. However, MGapt fluorescence dynamics do not accurately reflect mRNA concentration. Our study finds that MGapt fluorescence is unstable in commercial PURE systems. We discovered that the chemical composition of the cell-free reaction strongly influences MGapt fluorescence, which leads to inaccurate RNA calculations. Specific to the commercial system, we posit that MGapt fluorescence is significantly affected by the system’s chemical properties, governed notably by the presence of dithiothreitol (DTT). We propose a model that, on average, accurately predicts MGapt measurement within a 10% margin, leveraging DTT concentration as a critical factor. This model sheds light on the complex dynamics of MGapt in cell-free systems and underscores the importance of considering environmental factors in RNA measurements using aptamers.actors in RNA measurements using aptamers.)
Engineering Logical Inflammation Sensing Circuit for Modulating Gut Conditions + (The mammalian gut contains trillions of mi … The mammalian gut contains trillions of microbes that interact with host cells and monitor changes in the environment. Opportunistic pathogens exploit environmental conditions to stimulate their growth and virulence, leading to a resurgence of chronic disorders such as inflammatory bowel disease (IBD). Current therapies are effective in less than 30% of patients due to the lack of adherence to prescription schedules and overall, off-target effects. Smart microbial therapeutics can be engineered to colonize the gut, providing in situ surveillance and conditional disease modulation. However, many current engineered microbes can only respond to single gut environmental factors, limiting their effectiveness. In this work, we implement the previously characterized split activator AND logic gate in the probiotic E. coli strain Nissle 1917. Our system can respond to two input signals: the inflammatory biomarker tetrathionate and a second input signal, IPTG. We report 4-6 fold induction with minimal leak when both signals are present. We model the dynamics of the AND gate using chemical reaction networks, and by tuning parameters in silico, we identified perturbations that affect our circuit's selectivity. We anticipate that our results will prove useful for designing living therapeutics for spatial targeting and signal processing in complex environments.signal processing in complex environments.)
Resource usage and gene circuit performance characterization in a cell-free âbreadboardâ + (The many successes of synthetic biology ha … The many successes of synthetic biology have come in a manner largely different from those in other en- gineering disciplines; in particular, without well-characterized and simplified prototyping environments to play a role analogous to wind-tunnels in aerodynamics and breadboards in electrical engineering. However, as the complexity of synthetic circuits increases, the benefitsÂin cost savings and design cycle timeÂ of a more traditional engineering approach can be significant. We have recently developed an in vitro ÂbreadboardÂ prototyping platform based on E. coli cell extract that allows biocircuits to operate in an environment considerably simpler than but functionally similar to in vivo. The simplicity of the cell-free transcription-translation breadboard makes it a promising tool for rapid biocircuit design and testing, as well as for probing the fundamentals of gene circuit functions that are normally masked by cellular complex- ity. In this work we characterize the cell-free breadboard using real-time and simultaneous measurements of transcriptional and translational activities of a small set of reporter genes and a transcriptional activation cascade. We determine the effects of promoter strength, gene and nucleoside triphosphate concentrations on biocircuits properties, and we isolate contributions of the essential componentsÂcore RNA polymerase, housekeeping sigma factor, and ribosomesÂto overall performance. Importantly, we show how limits on essential resources, particularly those involved in translation steps, manifest themselves in the form of reduced expression in the presence of orthogonal genes as load processes.nce of orthogonal genes as load processes.)
Experimental Demonstration of the Dynamics and Stability of a Low Reynolds Number Swimmer Near a Plane Wall + (The motion of microorganisms as well as of … The motion of microorganisms as well as of tiny robotic swimmers for biomedical applications is governed by low Reynolds number (Re) hydrodynamics, where viscous effects dominate and inertial effects are negligible. This paper presents experimental results that verify theoretical predictions of our recent work which analyzed the dynamics and stability of a low-Re swimmer near a plane wall. The experimental setup uses macro-scale swimmer prototypes which are propelled by rotating cylinders in highly viscous silicone oil. The motion was recorded by a video camera and position measurements were taken by an optical tracking system. The results show good qualitative agreement with our recent theoretical predictions.t with our recent theoretical predictions.)
Simple Delay-Based Implementation of Continuous-Time Controllers + (The objective of this work is to study the … The objective of this work is to study the benefits that delay can provide in simplifying the control process of large-scale systems, motivated by the availability of different types of delays in man-made and biological systems. We show that a continuous-time linear time-invariant (LTI) controller can be approximated by a simple controller that mainly uses delay blocks instead of integrators. More specifically, three methods are proposed to approximate a pre-designed stabilizing LTI controller arbitrarily precisely by a simple delay-based controller composed of delay blocks, a few integrators and possibly a unity feedback. Different problems associated with the developed approximation procedures, such as finding the optimal number of delay blocks or studying the robustness of the designed controller with respect to delay values, are then addressed.spect to delay values, are then addressed.)
Observability of a Class of Hybrid Systems on Bounded Lattices + (The observability properties of a class of … The observability properties of a class of hybridsystems whose continuous variables are available for measurementare considered. We show that the discrete variables'dynamics can be always extended for observable systems toa lattice in such a way that the extended system has theproperties that allow the construction of the LU discretestate estimator. Such an estimator updates two variables ateach step, namely the upper and lower bound of the setof all possible discrete variables' values compatible with theoutput sequence. We give an estimate of the complexity of theestimator in the worst case.lexity of the estimator in the worst case.)
Implementation And Simulation Of Phosphorylation-Based Insulator In Transcription-Translation Platform + (The operational amplifier (OPAMP) is a ver … The operational amplifier (OPAMP) is a very useful insulation module in electric circuits to avoid loading effect (retroactivity). In synthetic biological circuits, we also have the same retroactivity problem, in which the biomolecular systems are not always modular due to downstream components. The output of the upstream component will be affected as the downstream component sequesters that output, which in turn impedes the process of constructing more complex biocircuits. To address this obstacle, the retroactivity needs to be attenuated by implementing a similar OPAMP device using biocircuits. Previous theoretical papers suggested a potential function of a phosphorylation based circuit in providing the feature of atten- uating retroactivity. Here we presented a successful prototyping and implementation of such a phosphorylation-based insulator (PBI) in an in vitro cell-free transcription-translation system (TX- TL). We demonstrated that retroactivity also exists in TX-TL system, if not stronger, by testing a simple negative regulation circuit. Besides we showed that the TX-TL system contains all the protein, DNA components and other resources required for the PBI circuit to work properly. We then demonstrated that the PBI circuit helps minimizing the loading effect to less than 10% compared to control circuit. With this preliminary PBI circuit design, attenuation of retroactivity while connecting two modules in vitro becomes possible. In concert with another paper from our group (E. Yeung, S. Guo, R. Murray QBIO2014) which used system identification to estimate all three essential parameters in a simplified PBI model, we showed that the simulations based on these parameters match the experimental data very well and provide an interesting insight into future designs.n interesting insight into future designs.)
Geometric trajectory filtering via numerical conformal mapping + (The paper studies the problem which we ref … The paper studies the problem which we refer to as geometric trajectory filtering, where only trajectories that satisfy the local safety constraints are selected from a library of trajectories. The goal is to speed up primitive-based motion planning while still maintaining a relatively a large collection of motion primitives. One way to solve this problem is to obtain a proper (preferably smooth) function, referred to as the containment indicator function, that describes the shape of the free space. To construct the containment indicator function for an arbitrary shape, the paper uses conformal mapping to transform the original shape of interest to a simpler target shape (e.g. disk, rectangle), which can then be characterized by elementary functions. Computational methods for finding the desired conformal maps are studied. It is shown that they can be formulated as convex optimization problems, whose solution can be obtained efficiently.hose solution can be obtained efficiently.)
Learning diffeomorphism models of robotic sensorimotor cascades + (The problem of bootstrapping consists in d … The problem of bootstrapping consists in designing agents that can learn from scratch the model of their sensori- motor cascade (the series of robot actuators, the external world, and the robot sensors) and use it to achieve useful tasks. In principle, we would want to design agents that can work for any robot dynamics and any robot sensor(s). One of the difficulties of this problem is the fact that the observations are very high dimensional, the dynamics is nonlinear, and there is a wide range of "representation nuisances" to which we would want the agent to be robust. In this paper, we model the dynamics of sensorimotor cascades using diffeomorphisms of the sensel space. We show that this model captures the dynamics of camera and range-finder data, that it can be used for long-term predictions, and that it can capture nonlinear phenomena such as a limited field of view. Moreover, by analyzing the learned diffeomorphisms it is possible to recover the "linear structure" of the dynamics in a manner which is independent of the commands representation.ndependent of the commands representation.)
Discrete State Estimators for a Class of Nondeterministic Hybrid Systems on a Lattice + (The problem of estimating the discrete var … The problem of estimating the discrete variablesin nondeterministic hybrid systems where the continuousvariables are available for measurement is considered. Usingpartial order and lattice theory, we construct a discrete stateestimator, the LU estimator, which updates two variables ateach step. Namely, it updates the lower (L) and upper (U)bounds of the set of all possible discrete variables valuescompatible with the output sequence and with the systems'dynamics. If the system is weakly observable, we show thatthere always exist a lattice on which to construct the LUestimator. For computational issues, some partial orders are tobe preferred to others.We thus show that nondeterminism maybe added to a system so as to obtain a new system that satisfiesthe requirements for the construction of the LU estimator ona chosen lattice. These ideas are applied to a nondeterministicmulti-robot system. to a nondeterministic multi-robot system.)
Nonlinear Trajectory Generation for Unmanned Air Vehicles with Multiple Radars + (The problem of finding a real time optimal … The problem of finding a real time optimaltrajectory to minimize the probability of detection (to maximizethe probability of notbeingdetected, pnd, function) ofunmanned air vehicles by opponent radar detection systemsis investigated. This paper extends our preliminary resultson low observable trajectory generation in three ways. First,trajectory planning in the presence of detection by multipleradar systems, rather than single radar systems, is considered.Second, an overall probability of detection function isdeveloped for the multiple radar case. In previous work, bothprobability of detection by a single radar and signature weredeveloped in the theory section, but the examples used onlysignature constraints. In this work, the use of the overallprobability of detection function is used, both because itaids in the extension to multiple radar systems and becauseit is a more direct measure of the desirable optimizationcriteria. The third extension is the use of updated signatureand probability of detection models. The new models have agreater number of sharp gradients than the previous models,with low detectability regions for both a cone shaped areascentered around the nose as in the previous paper, as well as acone-shaped area centered around rear of the air vehicle. TheNonlinear Trajectory Generation method (NTG), developedat Caltech, is used and motivated by the ability to providereal time solutions for constrained nonlinear optimizationproblems. Numerical simulations of multiple radar scenariosillustrate UAV trajectories optimized for both detectability andtime.optimized for both detectability and time.)
Model reduction of interconnected linear systems + (The problem of model reduction of linear s … The problem of model reduction of linear systems with certain interconnection structure is considered in this paper. To preserve the interconnection structure between subsystems in the reduction, special care needs to be taken. This problem is important and timely because of the recent focus on complex networked systems in control engineering. Two different model-reduction methods are introduced and compared in the paper. Both methods are extensions to the well-known balanced truncation method. Compared to earlier work in the area these methods use a more general linear fractional transformation framework, and utilize linear matrix inequalities. Furthermore, new approximation error bounds that reduce to classical bounds in special cases are derived. So-called structured Hankel singular valueso-called structured Hankel singular values)
Formal Test Synthesis for Safety-Critical Autonomous Systems based on Control Barrier Functions + (The prolific rise in autonomous systems ha … The prolific rise in autonomous systems has led to questions regarding their safe instantiation in real-world scenarios. Failures in safety-critical contexts such as human-robot interactions or even autonomous driving can ultimately lead to loss of life. In this context, this paper aims to provide a method by which one can algorithmically test and evaluate an autonomous system. Given a black-box autonomous system with some operational specifications, we construct a minimax problem based on control barrier functions to generate a family of test parameters designed to optimally evaluate whether the system can satisfy the specifications. To illustrate our results, we utilize the Robotarium as a case study for an autonomous system that claims to satisfy waypoint navigation and obstacle avoidance simultaneously. We demonstrate that the proposed test synthesis framework systematically finds those sequences of events (tests) that identify points of system failure.s) that identify points of system failure.)
Engineering Transcriptional Regulator Effector Specificity Using Computational Design and In Vitro Rapid Prototyping: Developing a Vanillin Sensor + (The pursuit of circuits and metabolic path … The pursuit of circuits and metabolic pathways of increasing complexity and robustness in synthetic biology will require engineering new regulatory tools. Feedback control based on relevant molecules, including toxic intermediates and environmental signals, would enable genetic circuits to react appropriately to changing conditions. In this work, variants of qacR, a tetR family repressor, were generated by computational protein design and screened in a cell-free transcription-translation (TX-TL) system for responsiveness to a new targeted effector. The modified repressors target vanillin, a growth-inhibiting small molecule found in lignocellulosic hydrolysates and other industrial processes. Promising candidates from the in vitro screen were further characterized in vitro and in vivo in a gene circuit. The screen yielded two qacR mutants that respond to vanillin both in vitro and in vivo. While the mutants exhibit some toxicity to cells, presumably due to off-target effects, they are prime starting points for directed evolution toward vanillin sensors with the specifications required for use in a dynamic control loop. We believe this process, a combination of the generation of variants coupled with in vitro screening, can serve as a framework for designing new sensors for other target compounds.ng new sensors for other target compounds.)
Engineering Transcriptional Regulator Effector Specificity using Computational Design and In Vitro Rapid Prototyping: Developing a Vanillin Sensor + (The pursuit of circuits and metabolic path … The pursuit of circuits and metabolic pathways of increasing complexity and robustness in synthetic biology will require engineering new regulatory tools. Feedback control based on relevant molecules, including toxic intermediates and environmental signals, would enable genetic circuits to react appropriately to changing conditions. In this work, variants of qacR, a tetR family repressor, were generated by compu- tational protein design and screened in a cell-free transcription-translation (TX-TL) system for responsiveness to a new targeted effector. The modified repressors target vanillin, a growth-inhibiting small molecule found in lignocellulosic hydrolysates and other industrial processes. Promising candidates from the in vitro screen were further characterized in vitro and in vivo in a gene circuit. The screen yielded two qacR mutants that respond to vanillin both in vitro and in vivo. We believe this process, a combination of the generation of variants coupled with in vitro screening, can serve as a framework for designing new sensors for other target compounds.ng new sensors for other target compounds.)
Engineering Transcriptional Regulator Effector Specificity Through Rational Design and Rapid Prototyping + (The pursuit of circuits and metabolic path … The pursuit of circuits and metabolic pathways of increasing complexity and robustness in synthetic biology will require engineering new regulatory tools. Feedback control based on relevant molecules, including toxic intermediates and environmental signals, would enable genetic circuits to react appropriately to changing conditions. In this work, computational protein design was used to create functional variants of qacR, a tetR family repressor, responsive to a new targeted effector. The modified repressors target vanillin, a growth-inhibiting small molecule found in lignocellulosic hydrolysates and other industrial processes. A computatio ally designed library was screened using an in vitro transcription-translation (TX-TL) system. Leads from the in vitro screen were characterized in vivo. Preliminary results demonstrate dose-dependent regulation of a downstream fluorescent reporter by vanillin. These repressor designs provide a starting point for the evolution of improved variants. We believe this process can serve as a framework for designing new sensors for other target compounds.ng new sensors for other target compounds.)

(The pursuit of circuits and metabolic pathways of increasing complexity)

Timing molecular motion and production with a synthetic transcriptional clock + (The realization of artificial biochemical … The realization of artificial biochemical reaction networks with unique functionality is one of the main challenges for the development of synthetic biology. Due to the reduced number of components, biochemical circuits constructed in vitro promise to be more amenable to systematic design and quantitative assessment than circuits embedded within living organisms. To make good on that promise, effective methods for composing subsystems into larger systems are needed. Here we used an artificial biochemical oscillator based on in vitro transcription and RNA degradation reactions to drive a variety of âloadâ processes such as the operation of a DNA-based nanomechanical device (âDNA tweezersâ) or the production of a functional RNA molecule (an aptamer for malachite green). We implemented several mechanisms for coupling the load processes to the oscillator circuit and compared them based on how much the load affected the frequency and amplitude of the core oscillator, and how much of the load was effectively driven. Based on heuristic insights and computational modeling, an âinsulator circuitâ was developed, which strongly reduced the detrimental influence of the load on the oscillator circuit. Understanding how to design effective insulation between biochemical subsystems will be critical for the synthesis of larger and more complex systems.thesis of larger and more complex systems.)
Quantitative Modeling of Integrase Dynamics Using a Novel Python Toolbox for Parameter Inference in Synthetic Biology + (The recent abundance of high-throughput da … The recent abundance of high-throughput data for biological circuits enables data-driven quantitative modeling and parameter estimation. Common modeling issues include long computational times during parameter estimation, and the need for many iterations of this cycle to match data. Here, we present BioSCRAPE (Bio-circuit Stochastic Single-cell Reaction Analysis and Parameter Estimation) - a Python package for fast and flexible modeling and simulation for biological circuits. The BioSCRAPE package can be used for deterministic or stochastic simulations and can incorporate delayed reactions, cell growth, and cell division. Simulation run times obtained with the package are comparable to those obtained using C code - this is particularly advantageous for computationally expensive applications such as Bayesian inference or simulation of cell lineages. We first show the package's simulation capabilities on a variety of example simulations of stochastic gene expression. We then further demonstrate the package by using it to do parameter inference for a model of integrase dynamics using experimental data. The BioSCRAPE package is publicly available online along with more detailed documentation and examples. more detailed documentation and examples.)
Identification of Decision Rules in a Human-controlled System: Vehicles at a Traffic Intersection + (The rules that govern decision making in s … The rules that govern decision making in systemscontrolled by humans are often simple to describe. However,deriving these rules from the actions of a group can be verydifficult, making human behavior hard to predict. We developan algorithm to determine the rules implemented by driversat a traffic intersection by observing the trajectories of theircars. We applied such algorithm to a traffic intersection scenarioreproduced in the Caltech multi-vehicle lab, with human subjectsremotely driving kinematic robots. The results obtained on thesedata suggest that this kind of human behavior is to some extentpredictable on our data set, and different subjects implementsimilar rules.ifferent subjects implement similar rules.)
Nonlinear Control of Rotating Stall and Surge with Axisymmetric Bleed and Air Injection on Axial Flow Compressors + (The study of compressor instabilities in g … The study of compressor instabilities in gas turbine engines has receivedmuch attention in recent years. In particular, rotating stall and surgeare major causes of problems ranging from component stress and lifespanreduction to engine explosion. In this thesis, modeling and control ofrotating stall and surge using bleed valve and air injection is studied andvalidated on a low speed, single stage, axial compressor at Caltech.Bleed valve control of stall is achieved only when the compressorcharacteristic is actuated, due to the fast growth rate of the stall cellcompared to the rate limit of the valve. Furthermore, experimental resultsshow that the actuator rate requirement for stall control is reduced by afactor of fourteen via compressor characteristic actuation. Analyticalexpressions based on low order models (2--3 states) and a high fidelitysimulation (37 states) tool are developed to estimate the minimum raterequirement of a bleed valve for control of stall. A comparison of thetools to experiments show a good qualitative agreement, with increasingquantitative accuracy as the complexity of the underlying model increases.Air injection control of stall and surge is also investigated.Simultaneous control of stall and surge is achieved using axisymmetric airinjection. Three cases with different injector back pressure are studied.Surge control via binary air injection is achieved in all three cases.Simultaneous stall and surge control is achieved for two of the cases, butis not achieved for the lowest authority case. This is consistent withprevious results for control of stall with axisymmetric air injectionwithout a plenum attached.Non--axisymmetric air injection control of stall and surge is also studied.Three existing control algorithms found in literature are modeled andanalyzed. A three--state model is obtained for each algorithm. For twocases, conditions for linear stability and bifurcation criticality oncontrol of rotating stall are derived and expressed in terms ofimplementation--oriented variables such as number of injectors. For thethird case, bifurcation criticality conditions are not obtained due tocomplexity, though linear stability property is derived. A theoreticalcomparison between the three algorithms is made, via the use of low--ordermodels, to investigate pros and cons of the algorithms in the context ofoperability.The effects of static distortion on the compressor facility at Caltech ischaracterized experimentally. Results consistent with literature areobtained. Simulations via a high fidelity model (34 states) are alsoperformed and show good qualitative as well as quantitative agreement toexperiments. A non--axisymmetric pulsed air injection controller for stallis shown to be robust to static distortion.n controller for stall is shown to be robust to static distortion.)
Temporal Logic Control of POMDPs via Label-based Stochastic Simulation Relations + (The synthesis of controllers guaranteeing … The synthesis of controllers guaranteeing linear temporal logic specifications on partially observable Markov decision processes (POMDP) via their belief models causes computational issues due to the continuous spaces. In this work, we construct a finite-state abstraction on which a control policy is synthesized and refined back to the original belief model. We introduce a new notion of label- based approximate stochastic simulation to quantify the deviation between belief models. We develop a robust synthesis methodology that yields a lower bound on the satisfaction probability, by compensating for deviations a priori, and that utilizes a less conservative control refinement.es a less conservative control refinement.)
Real-time trajectory generation for constrained nonlinear dynamical systems using non-uniform rational B-spline basis functions + (The thesis describes a new method for obta … The thesis describes a new method for obtaining minimizers for optimal control problems whose minima serve as control policies for guiding nonlinear dynamical systems to achieve prescribed goals under imposed trajectory and actuator constraints. One of the major contributions of the present work resides in the approximation of such minimizers by piecewise polynomial functions expressed in terms of a linear combination of non-uniform rational B-spline (NURBS) basis functions and the judicious exploitation of the properties of the resulting NURBS curves to improve the computational effort often associated with solving optimal control problems for constrained dynamical systems. In particular, by exploiting the two structures combined in a NURBS curve, NURBS basis functions and an associated union of overlapping polytopes constructed from the coefficients of the linear combination, we are able to separate an optimal control problem into two subproblemstimal control problem into two subproblems)
Counter-example Guided Learning of Bounds on Environment Behavior + (There is a growing interest in building au … There is a growing interest in building autonomous systems that interact with complex environments. The difficulty associated with obtaining an accurate model for such environments poses a challenge to the task of assessing and guaranteeing the system’s performance. We present a data-driven solution that allows for a system to be evaluated for specification conformance without an accurate model of the environment. Our approach involves learning a conservative reactive bound of the environment’s behavior using data and specification of the system’s desired behavior. First, the approach begins by learning a conservative reactive bound on the environment’s actions that captures its possible behaviors with high probability. This bound is then used to assist verification, and if the verification fails under this bound, the algorithm returns counter-examples to show how failure occurs and then uses these to refine the bound. We demonstrate the applicability of the approach through two case-studies: i) verifying controllers for a toy multi-robot system, and ii) verifying an instance of human-robot interaction during a lane-change maneuver given real-world human driving data.euver given real-world human driving data.)
Modeling and Control of Epitaxial Thin Film Growth + (Thin ﬁlm deposition is a manufacturing pro … Thin ﬁlm deposition is a manufacturing process in which tolerances may approachthe size of individual atoms. The ﬁnal film is highly sensitive to the processingconditions, which can be intentionally manipulated to control film properties. Alattice model of surface evolution during thin film growth captures many importantfeatures, including the nucleation and growth of clusters of atoms and thepropagation of atomic-height steps. The dimension of this probabilistic masterequation is too large to directly simulate for any physically realistic domain, andinstead stochastic realizations of the lattice model are obtained with kinetic MonteCarlo simulations.In this thesis simpler representations of the master equation are developed foruse in analysis and control. The static map between macroscopic process conditionsand microscopic transition rates is ﬁrst analyzed. In the limit of fast periodicprocess parameters, the surface responds only to the mean transition rates, and,since the map between process parameters and transition rates is nonlinear, neweffective combinations of transition rates may be generated. These effective ratesare the convex hull of the set of instantaneous rates.The map between transition rates and expected film properties is also studied.The dimension of a master equation can be reduced by eliminating or groupingconﬁgurations, yielding a reduced-order master equation that approximates theoriginal one. A linear method for identifying the coefficients in a master equationis then developed, using only simulation data. These concepts are extended togenerate low-order master equations that approximate the dynamic behavior seenin large Monte Carlo simulations. The models are then used to compute optimaltime-varying process parameters.The thesis concludes with an experimental and modeling study of germaniumfilm growth, using molecular beam epitaxy and reflection high-energy electrondiffraction. Growth under continuous and pulsed flux is compared in experiment,and physical parameters for the lattice model are extracted. The pulsing accessiblein the experiment does not trigger a change in growth mode, which is consistentwith the Monte Carlo simulations. The simulations are then used to suggest othergrowth strategies to produce rougher or smoother surfaces.ce rougher or smoother surfaces.)
Reduction Strategies for Kinetic Monte Carlo Models of Thin Film Growth + (Thin film deposition encompasses a variety … Thin film deposition encompasses a variety of physical processes,which occur over a wide range of length and time scales. A major challenge in modeling and simulating thin film deposition is this disparityin scales. In this study we focus on an atomic-scale lattice model ofsurface processes. Kinetic Monte Carlo simulations provide stochasticrealizations of the surface evolution, which may then inform a reacting flow or heat transfer model. Unfortunately, these simulations areextremely computationally intensive, particularly for design and optimization studies in which many cases are considered.We develop reduced-order models of thin film growth using two techniques: balanced truncation and eigensystem realization. After identifying the underlying structure of the lattice model as a linear differentialequation, we apply the reduction techniques to obtain reduced-ordermodels of root-mean-square roughness and step edge density. Threemodes are needed for a very small model system, while only five modescapture the evolution of a 200x200-site system over a range of growthmodes, from stochastic roughening to island nucleation and coalescence.roughening to island nucleation and coalescence.)
Effective Transition Rates for Epitaxial Growth Using Fast Modulation + (Thin film deposition is an industrially-im … Thin film deposition is an industrially-important process that is highly dependent on the processconditions. Most films are grown under constant conditions, but a few studies show that modifiedproperties may be obtained with periodic inputs. However, assessing the effects of modulationexperimentally becomes impractical with increasing material complexity. Here we consider periodicconditions in which the period is short relative to the time-scales of growth. We analyze a stochasticmodel of thin film growth, computing effective transition rates associated with rapid periodicprocess parameters. Combinations of effective rates may exist which are not attainable understeady conditions, potentially enabling new film properties. An algorithm is presented to constructthe periodic input for a desired set of effective transition rates. These ideas are first illustratedby two simple examples using kinetic Monte Carlo simulations and are then compared to existingdeposition techniques.ompared to existing deposition techniques.)
Modeling and Control of Thin Film Morphology Using Unsteady Processing Parameters: Problem Formulation and Initial Results + (Thin film deposition is an industrially-im … Thin film deposition is an industrially-important process to which control theory has not historically been applied. The need for control is growing as the size of integratedcircuits shrinks, requiring increasingly tighter tolerances in the manufacture of thin films. Our contributions in this study are two-fold: we formulate a model of thin filmgrowth as a control system and we examine the effects of fast periodic forcing.We choose a lattice formulation of crystal growth as our physical model, which captures atomic length scale effects at a time scale compatible with film growth. We focus on the control of film morphology, or surface height profile. Although the systemdimension is high, the structure is simple: the dynamics and the output are linear in the state. We consider the process conditions as inputs, which alter the transition ratefunctions. In the evolution equation, each of these nonlinear functions is multiplied by a linear vector field, yielding a system with a structure similar to a bilinear system.The process conditions in some deposition methods are inherently unsteady, whichproduces films with altered morphology. We use the model developed in this study to analyze the effects of fast periodic forcing on thin film evolution. With the method ofaveraging we develop new effective transition rates which may produce film propertiesunattainable with constant inputs. We show that these effective rates are the convexhull of the set of rates associated with constant inputs. We present conditions onthe convex hull for which the finite-time and infinite-time reachability sets cannot beexpanded with fast periodic forcing. An example in which this forcing increases thereachability set and produces more desirable morphology is also presented. produces more desirable morphology is also presented.)
Fault-Tolerant Controller Design with Applications in Power Systems and Synthetic Biology + (This paper deals with fault-tolerant contr … This paper deals with fault-tolerant controller design for linear time-invariant (LTI) systems with multiple actuators. Given some critical subsets of the actuators, it is assumed that every combination of actuators can fail as long as the set of the remaining actuators includes one of these subsets. Motivated by electric power systems and biological systems, the goal is to design a controller so that the closed-loop system satisfies two properties: (i) stability under all permissible sets of faults and (ii) better performance after clearing every subset of the existing faults in the system. It is shown that a state-feedback controller satisfying these properties exists if and only if a linear matrix inequality (LMI) problem is feasible. This LMI condition is then transformed into an optimal-control condition, which has a useful interpretation. The results are also generalized to output-feedback and decentralized control cases. The efficacy of this work is demonstrated by designing fault-tolerant speed governors for a power system. The results developed here can be extended to more general types of faults, where each fault can possibly affect all state-space matrices of the system.ct all state-space matrices of the system.)
Control education for societal-scale challenges: A community roadmap + (This article focuses on extending, dissemi … This article focuses on extending, disseminating and interpreting the findings of an IEEE Control Systems Society working group looking at the role of control theory and engineering in solving some of the many current and future societal challenges. The findings are interpreted in a manner designed to give focus and direction to both future education and research work in the general control theory and engineering arena, interpreted in the broadest sense. The paper is intended to promote discussion in the community and also provide a useful starting point for colleagues wishing to re-imagine the design and delivery of control-related topics in our education systems, especially at the tertiary level and beyond.pecially at the tertiary level and beyond.)
Synthesis of Control Protocols for Autonomous Systems + (This article provides a review of control … This article provides a review of control protocol synthesis techniques that incorporate methodologies from formal methods and control theory to provide correctness guarantee for different types of autonomous systems, including those with discrete and continuous state space. The correctness of the system is defined with respect to a given specification expressed as a formula in linear temporal logic to precisely describe the desired properties of the system. The formalism presented in this article admits non-determinism, allowing uncertainties in the system to be captured. A particular emphasis is on alleviating some of the difficulties, e.g., heterogeneity in the underlying dynamics and computational complexity, that naturally arise in the construction of control protocols for autonomous systems. control protocols for autonomous systems.)
Robotic Control and Nonholonomic Motion Planning + (This dissertation addresses the problem of … This dissertation addresses the problem of control and kinematicplanning for constrained robot systems. An example of a system ofthis type is a multifingered robot hand grasping an object. Theindividual fingers act as robot manipulators and are constrained bytheir contact with the object. If the contacts allow rolling betweenthe object and the fingertips, it is possible for the constraints tobe nonholonomic. That is, the constraints may not restrict thereachable configurations of the system, but rather, constrain only theallowable velocities of the system.Using the multifingered hand as a motivating example, thisdissertation presents a detailed analysis of the kinematics, dynamics,and control of robot systems with contact constraints. In particular,it presents a unified derivation of the dynamics of robot manipulatorswith Pfaffian velocity constraints, including the nonholonomic case.This derivation allows control laws to be specified which are provablystable for an entire class of systems, including unconstrained robots,robot hands, and other systems of multiple robots performing acoordinated task. A method for building complex controllers whichrespects this class of constraints is also developed using a set ofsimple primitives which allow hierarchical control structures to becreated in an organized fashion.Finally, the nonholonomic motion planning problem is introduced anddiscussed in detail. Using tools from differential geometric controltheory, it is possible to classify and analyze systems withnonholonomic constraints. A brief review of the necessary tools alongwith a review of the current literature is presented. A practicalmethod for steering nonholonomic systems using sinusoids is derivedand applied to several kinematic systems with contact constraints.to several kinematic systems with contact constraints.)
Exponential Stabilization of Driftless Nonlinear Control Systems + (This dissertation lays the foundation for … This dissertation lays the foundation for practical exponentialstabilization of driftless control systems. Driftless systems havethe form $$\dot x = X_1(x)u_1+\cdots +X_m(x)u_m, \quad x\in\real^n$$.Such systems arise when modeling mechanical systems with nonholonomicconstraints. In engineering applications it is often required tomaintain the mechanical system around a desired configuration. Thistask is treated as a stabilization problem where the desiredconfiguration is made an asymptotically stable equilibrium point. Thecontrol design is carried out on an approximate system. Theapproximation process yields a nilpotent set of input vector fieldswhich, in a special coordinate system, are homogeneous with respect toa non-standard dilation. Even though the approximation can be given acoordinate-free interpretation, the homogeneous structure is useful toexploit: the feedbacks are required to be homogeneous functions andthus preserve the homogeneous structure in the closed-loop system.The stability achieved is called {\em $\rho$-exponential stability}.The closed-loop system is stable and the equilibrium point isexponentially attractive. This extended notion of exponentialstability is required since the feedback, and hence the closed-loopsystem, is not Lipschitz. However, it is shown that the convergencerate of a Lipschitz closed-loop driftless system cannot be bounded byan exponential envelope.The synthesis methods generate feedbacks which are smooth on\rminus. The solutions of the closed-loop system are proven to beunique in this case. In addition, the control inputs for manydriftless systems are velocities. For this class of systems it ismore appropriate for the control law to specify actuator forcesinstead of velocities. We have extended the kinematic velocitycontrollers to controllers which command forces and still$\rho$-exponentially stabilize the system.Perhaps the ultimate justification of the methods proposed in thisthesis are the experimental results. The experiments demonstrate thesuperior convergence performance of the $\rho$-exponential stabilizersversus traditional smooth feedbacks. The experiments also highlightthe importance of transformation conditioning in the feedbacks. Otherdesign issues, such as scaling the measured states to eliminatehunting, are discussed. The methods in this thesis bring thepractical control of strongly nonlinear systems one step closer.rol of strongly nonlinear systems one step closer. )
Model-Based Estimation of Off-Highway Road Geometry using Single-Axis LADAR and Inertial Sensing + (This paper applies some previously studied … This paper applies some previously studied extendedKalman filter techniques for planar road geometryestimation to the domain of autonomous navigation of offhighwayvehicles. In this work, a clothoid model of the roadgeometry is constructed and estimated recursively based onroad features extracted from single-axis LADAR range measurements.We present a method for feature extraction of theroad centerline in the image plane, and describe its applicationto recursive estimation of the road geometry. We analyzethe performance of our method against simulated motion ofvaried road geometries and against recorded data from previousautonomous navigation runs. Our method accomodates full 6DOF motion of the vehicle as it navigates, constructs consistentestimates of the road geometry with respect to a fixed globalreference frame, and requires an estimate of the sensor posefor each range measurement.he sensor pose for each range measurement.)
Receding Horizon Temporal Logic Planning for Dynamical Systems + (This paper bridges the advances in compute … This paper bridges the advances in computer science and control to allow automatic synthesis of complex dynamical systems which are guaranteed, by construction, to satisfy the desired properties even in the presence of adversary. The desired properties are expressed in the language of temporal logic. With its expressive power, a wider class of properties than safety and stability can be specified. The resulting system consists of a discrete planner which plans, in the abstracted discrete domain, a set of transitions of the system to ensure the correct behaviors and a continuous controller which continuously implements the plan. For a system with certain structure, we present an approach, based on a receding horizon scheme, to overcome computational difficulties in the synthesis of a discrete planner and allow more complex problems to be solved. allow more complex problems to be solved.)
Exponential Stabilization of Driftless Nonlinear Control Systems via Time-varying, Homogeneous Feedback + (This paper brings together results from a … This paper brings together results from a number of different areas incontrol theory to provide an algorithm for the synthesis of locallyexponentially stabilizing control laws for a large class of driftlessnonlinear control systems. The exponential stabilization relies on theuse of feedbacks which render the closed loop vector field homogeneouswith respect to a dilation. These feedbacks are generated from amodification of Pomet's algorithm for smooth feedbacks. ConverseLiapunov theorems for time-periodic homogeneous vector fieldsguarantee that local exponential stability is maintained in thepresence of higher order (with respect to the dilation) perturbingterms.ect to the dilation) perturbing terms. )
Real-valued average consensus over noisy quantized channels + (This paper concerns the average consensus … This paper concerns the average consensus problem with the constraint of quantized communication between nodes. A broad class of algorithms is analyzed, in which the transmission strategy, which decides what value to communicate to the neighbors, can include various kinds of rounding, probabilistic quantization, and bounded noise. The arbitrariness of the transmission strategy is compensated by a feedback mechanism which can be interpreted as a self-inhibitory action. The result is that the average of the nodes state is not conserved across iterations, and the nodes do not converge to a consensus; however, we show that both errors can be made as small as desired. Bounds on these quantities involve the spectral properties of the graph and can be proved by employing elementary techniques of LTI systems analysis.entary techniques of LTI systems analysis.)
Decentralised minimal-time dynamic consensus + (This paper considers a group of agents tha … This paper considers a group of agents that aim to reach an agreement on individually measured time-varying signals by local communication. In contrast to static network averaging problem, the consensus we mean in this paper is reached in a dynamic sense. A discrete-time dynamic average consensus protocol can be designed to allow all the agents tracking the average of their reference inputs asymptotically. We propose a minimal-time dynamic consensus algorithm, which only utilises minimal number of local observations of randomly picked node in a network to compute the final consensus signal. Our results illustrate that with memory and computational ability, the running time of distributed averaging algorithms can be indeed improved dramatically using local information as suggested by Olshevsky and Tsitsiklis. as suggested by Olshevsky and Tsitsiklis.)
Stability and Performance of Non-Homogeneous Multi-Agent Systems on a Graph + (This paper considers distributed control o … This paper considers distributed control of interconnected multi-agent systems. The dynamics of the individual agents are not required to be homogeneous and the interaction topology is described by an arbitrary directed graph. We derive the sensitivity transfer functions between every pair of agents and we analyze stability and performance of non-homogeneous systems, showing that the low frequency behavior is influenced not only by topology, but also by static gain and poles of the agents.so by static gain and poles of the agents.)
On Decentralized Classification using a Network of Mobile Sensors + (This paper considers how a team of mobile … This paper considers how a team of mobile sensorsshould cooperatively move so as to optimally categorize asingle moving target from their noisy sensor readings. Thecooperative control procedure is based on the development ofa cost function that quantifies the teamâs classification error.The robotsâ motions are then chosen to minimize this function.We particularly investigate the case where the sensor noise andclass distributions are Gaussian. In this case, we can derive aduality principle which states that optimal classification will berealized when the covariance of the target estimate is minimized.That is, in this case, optimal estimation leads naturally tooptimal classification. We extend previous work to develop adistributed discrete-gradient search algorithm that guides theteamâs location motions for purposes of optimal estimation andclassification. The concepts developed are validated throughnumerical studies.d are validated through numerical studies.)
Nonlinear Control Methods for Planar Carangiform Robot Fish + (This paper considers the design of motion … This paper considers the design of motion control algorithms for robot fish. We present modeling, control design, and experimental trajectory tracking results for a planar robotic fish that is propelled using the carangiform style of locomotion. Our experimental apparatus consists of a freely translating and rotating flat plate and a two-link actuated tail. We develop a model for the fish's propulsion that is based on quasi-steady fluid flow. Using this model, we predict system response to sinusoidal motions of the tail joints andcompare these predictions to the experimental results. We then propose gaits for forward and turning trajectories and analyze system response under such control strategies. Our models and predictions are verified by experiment.nd predictions are verified by experiment.)
A Testbed for Nonlinear Flight Control Techniques: The Caltech Ducted Fan + (This paper considers the fundamental desig … This paper considers the fundamental design and modeling of the Caltech ducted fan.The Caltech ducted fan is a scaled model of the longitudinal axis of a flight vehicle. Thepurpose of the ducted fan is the research and development of new nonlinear flight guidanceand control techniques for Uninhabited Combat Aerial Vehicles. It is shown that criticaldesign relations must be satisfied in order that the ducted fan's longitudinal dynamicsbehave similar to those of an flight vehicle. Preliminary flight test results illustratethe flying qualities of the ducted fan.te the flying qualities of the ducted fan.)

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