Generalizing Multi-agent Graph Exploration Techniques

International Journal of Control, Automation and Systems - The system of multiple agents working in coordination for a given task has several advantages on faster completion, fault-tolerance, etc....     

Finite‐time posture stabilization of the unicycle mobile robot using only position information: A discrete‐time sliding mode approach

The posture stabilization of a unicycle mobile robot is useful in executing parking and docking maneuvers. It becomes more advantageous to guarantee the posture stabilization in finite time for a battery operated robot, especially in an application involving multiple robots. This paper addresses the posture stabilization of the unicycle mobile robot in finite time, especially when only the position information is available. We adopt the reaching law approach and design a discrete‐time sliding mode (DSM) controller by finitely discretizing the chained form of the unicycle, using the notion of multirate input sampling. Finite‐time stabilization of the equilibria is achieved by using multirate piecewise continuous inputs. Furthermore, the control inputs are realized using multirate output‐feedback (MROF) technique, wherein the states are estimated using the knowledge of the past fast output samples and immediate past control inputs. The proposed MROF‐DSM strategy avoids undesirable chatter in the system response owing to the nonswitching‐type controller and guarantees the stabilization in finite time. Simulations demonstrate the efficacy of the proposed method.     

New nonlinear residual feedback observer for fault diagnosis in nonlinear systems

The increased complexity of plants and the development of sophisticated control systems have necessitated the parallel development of efficient Fault Detection and Isolation (FDI) systems. This paper discusses a model based technique, viz., observers for detecting and isolating parametric and sensor faults. In this paper, a novel diagonal nonlinear residual feedback observer is proposed which is valid for a certain class of nonlinear systems where, subject to other conditions, the state depends nonlinearly on the fault. A number of typical chemical engineering systems can be represented by models of this form. The structure of the observer ensures that the residuals are diagonally affected by the faults. Conditions for exact decoupling of residuals are presented and convergence of the observer in the presence of step faults is proved using Lyapunov like analysis. Multiple observers and a decision logic module are used for FDI when there are un-monitored faults. Results are presented from numerical simulations of an illustrative example and a typical chemical engineering system: a counter-current heat exchanger.     

Robust and reliable estimation via Unscented Recursive Nonlinear Dynamic Data Reconciliation

The quality of process data in a chemical plant significantly affects the performance and benefits gained from activities like performance monitoring, online optimization and control. Since many chemical processes often exhibit nonlinear dynamics, techniques like Extended Kalman Filter (EKF) and Nonlinear Dynamic Data Reconciliation (NDDR) have been developed to improve the data quality. There are various issues that arise with the use of either of these techniques: EKF cannot handle inequality or equality constraints, while the NDDR has high computational cost. Recently a recursive estimation technique for nonlinear dynamic processes has been proposed which combines the merits of EKF and NDDR techniques. This technique, named as Recursive Nonlinear Dynamic Data Reconciliation (RNDDR), provides state and parameter estimates that satisfy bounds and other constraints imposed on them. However, the estimate error covariance matrix in RNDDR is computed in the same manner as in EKF, that is, the effects of both nonlinearity and constraints are neglected in the computation of the estimate error covariance matrix.

A relatively new method known as the Unscented Kalman Filter has been developed for nonlinear processes, in which the statistical properties of the estimates are computed without resorting to linearization of the nonlinear equations. This leads to improved accuracy of the estimates. In this paper, we combine the merits of the Unscented Kalman Filter and the RNDDR to obtain the Unscented Recursive Nonlinear Dynamic Data Reconciliation (URNDDR) technique. This technique addresses all concerns arising due to the presence of nonlinearity and constraints within a recursive estimation framework, resulting in an efficient, accurate and stable method for real-time state and parameter estimation for nonlinear dynamic processes.     

Innovation and the Post‐Original: On Moral Stances and Reproduction

This article represents an inquiry into the ontology of innovation, that is, the foundational issues of innovation and how we conceive of the nature of innovation and creativity. By juxtaposing the notions of novelty and copying, the article introduces the concept of ‘post‐originality’ as a way to understand how time and reproductive acts can be understood in relation to the innovative. Looking at how innovation and creativity are hailed as the highest forms of economic action, while copying and derivation have often been viewed as somewhat lesser forms, the article thus discusses how moralizations affect the way in which we view the economic. Specifically building on the works of German polymath Walter Benjamin and his theories of time, ruin and redemption, the article connects with the philosophy of history, and by way of three mini‐cases, presents three tentative modes of the post‐original (derivation, knock‐offs and remixes), showing how these can each in their own way raise interesting issues regarding the role of copying in creating the new. We end with a reflection on the notion of the event in innovation, inspired by the French philosopher Alain Badiou and his engagement with the truth of the event.     

Microwave‐Assisted Synthesis of Pyrazino[2,1‐b]quinazolines and 3‐Indolyl‐2(1H)‐pyrazinones Employing a Chemoselective Silver(I)‐ and Gold(I)‐Catalyzed Reaction

Novel microwave‐assisted syntheses of pyrazino[2,1‐b]quinazolines and 3‐indolyl‐2(1H)‐pyrazinones employing silver(I)‐ or gold(I)‐catalyzed protocols have been elaborated. The scope and limitations of these processes have been investigated.     

Human monocyte binding to fibronectin enhances IFN-gamma-induced early signaling events

Leukocyte integrins are fundamentally important in modulating adhesion to extracellular matrix components and to other cells. This integrin-mediated adhesion controls leukocyte arrest and extravasation during the onset of inflammatory responses. Moreover, integrin-ligand interactions trigger signaling pathways that may influence leukocyte phenotype and function at sites of inflammation. In the current studies, we evaluated the combinatorial effects of monocyte adhesion and IFN-gamma on intracellular signaling pathways. IFN-gamma triggers a well-defined signal transduction pathway, which although not directly stimulated by monocyte adherence to fibronectin or arginine-glycine-aspartate (RGD)-coated substrata, was enhanced significantly in these matrix-adherent cells. Compared with monocytes in suspension or adherent on plastic surfaces, monocytes adherent to fibronectin or RGD exhibited a greater than threefold increase in steady state levels of IFN-gamma-induced mRNA for the high affinity Fc gammaRI receptor. By electrophoretic mobility shift assays, this increase in mRNA was associated with a 5- to 10-fold increase in the STAT1-containing DNA-binding complex that binds to Fc gammaRI promoter elements. Furthermore, the tyrosine phosphorylation of STAT1 and the tyrosine kinases JAK1 and JAK2 was enhanced significantly in RGD-adherent monocytes compared with control cells. These results suggest a novel mechanism by which integrin-mediated cell adhesion can modulate the magnitude of cytokine-induced signal transduction pathways, thereby amplifying cellular events leading to monocyte activation and inflammation.     

Multi-Robot Graph Exploration and Map Building with Collision Avoidance: A Decentralized Approach

This paper proposes a decentralized multi-robot graph exploration approach in which each robot takes independent decision for efficient exploration avoiding inter-robot collision without direct communication between them. The information exchange between the robots is possible through the beacons available at visited vertices of the graph. The proposed decentralized technique guarantees completion of exploration of an unknown environment in finite number of edge traversals where graph structure of the environment is incrementally constructed. New condition for declaring completion of exploration is obtained. The paper also proposes a modification in incidence matrix so that it can be used as a data structure for information exchange. The modified incidence matrix after completion represents map of the environment. The proposed technique requires either lesser or equal number of edge traversals compared to the existing strategy for a tree exploration. A predefined constant speed change approach is proposed to address the inter-robot collision avoidance using local sensor on a robot. Simulation results verify the performance of the algorithm on various trees and graphs. Experiments with multiple robots show multi-robot exploration avoiding inter-robot collision.     

Effect of the continuous stiffness measurement on the mechanical properties extracted using spherical nanoindentation

The effects of the superimposed oscillating load while using the continuous stiffness measurement (CSM) technique on the extracted indentation stress–strain (ISS) curves were systematically investigated using spherical nanoindentation tests performed on a variety of samples, using probes of 1 and 100 μm radii. Particular care was afforded to the corrections that were needed on the load, displacement and stiffness signals to account for the effect of the superimposed oscillations. A decrease in the oscillation frequency from the commonly used 45 Hz caused the measured stiffness values to decrease. This resulted in questionable high strain hardening values in the ISS curves. The noise levels in the recorded stiffness signal were significantly higher while using an oscillation amplitude of 1 nm. It was concluded that these observations are artifacts of the machine dynamic control systems and do not represent the material’s true behavior. The CMS signal with a 45 Hz oscillation frequency and 2 nm amplitude appears to produce most reasonable values of stiffness values and is therefore the best choice for reliably extracting ISS curves for the materials studied.     

Hardware-Efficient Prediction-Correction-Based Generalized-Voronoi-Diagram Construction and FPGA Implementation

Sensor-based construction of different geometric structures has been an important development in the domain of autonomous robot navigation. This paper presents a hardware-efficient scheme to construct one such geometric structure, namely, the generalized Voronoi diagram (GVD), using a prediction-and- correction strategy. In this paper, an architecture to construct the GVD for an indoor environment with multiple obstacles whose geometry and location are not known beforehand is presented. A feature of the proposed approach is that it does not involve operations that are expensive in hardware. Furthermore, no explicit angle computation circuitry is needed. An efficient architecture based on hardware reuse is presented. The design is shown to be space efficient and fits in a low-end field-programmable gate-array (FPGA) device (with a small number of system gates). Detailed experiments with a mobile robot fabricated locally with a Xilinx XC2S200E FPGA and eight ultrasonic sensors onboard validate the efficacy of the proposed approach for static as well as dynamic environments.