5,312 research outputs found

    Organically Structured Control of Large-Scale Systems with Expanding Construction Based on State Observation

    Get PDF
    This paper presents a new method on the problem of organically structured control based on state observation for a class of large-scale systems with expanding construction. This problem is to design a local state feedback controller and an observer for a new subsystem which is added to a large-scale system without changing the decentralized state feedback control laws of the original construction, so that both the new subsystem and the resulting expanded system are robustly connectively stable. Firstly, based on state observers, the mathematical model of a large-scale system with expanding construction is reestablished and analyzed. In addition, the sufficient condition for robust decentralized connective stabilization of the expanded construction of large-scale systems is deduced by taking an LMI approach, which is further relaxed by removing the square matrix condition on the output matrix. This problem is transformed into solving an LMI problem. The new design method of an organically structured controller and observer for the expanded construction is also given. Finally, the simulation examples show the effectiveness of the proposed method

    Towards real-world complexity: an introduction to multiplex networks

    Full text link
    Many real-world complex systems are best modeled by multiplex networks of interacting network layers. The multiplex network study is one of the newest and hottest themes in the statistical physics of complex networks. Pioneering studies have proven that the multiplexity has broad impact on the system's structure and function. In this Colloquium paper, we present an organized review of the growing body of current literature on multiplex networks by categorizing existing studies broadly according to the type of layer coupling in the problem. Major recent advances in the field are surveyed and some outstanding open challenges and future perspectives will be proposed.Comment: 20 pages, 10 figure

    Cortex, countercurrent context, and dimensional integration of lifetime memory

    Get PDF
    The correlation between relative neocortex size and longevity in mammals encourages a search for a cortical function specifically related to the life-span. A candidate in the domain of permanent and cumulative memory storage is proposed and explored in relation to basic aspects of cortical organization. The pattern of cortico-cortical connectivity between functionally specialized areas and the laminar organization of that connectivity converges on a globally coherent representational space in which contextual embedding of information emerges as an obligatory feature of cortical function. This brings a powerful mode of inductive knowledge within reach of mammalian adaptations, a mode which combines item specificity with classificatory generality. Its neural implementation is proposed to depend on an obligatory interaction between the oppositely directed feedforward and feedback currents of cortical activity, in countercurrent fashion. Direct interaction of the two streams along their cortex-wide local interface supports a scheme of "contextual capture" for information storage responsible for the lifelong cumulative growth of a uniquely cortical form of memory termed "personal history." This approach to cortical function helps elucidate key features of cortical organization as well as cognitive aspects of mammalian life history strategies

    Robust Decentralized Control of Power Systems: A Matrix Inequalities Approach

    Get PDF
    This dissertation presents an extension of robust decentralized control design techniques for power systems, with special emphasis on design problems that can be expressed as minimizing a linear objective function under linear matrix inequality (LMI) in tandem with nonlinear matrix inequality (NMI) constraints. These types of robust decentralized control design problems are generally nonconvex optimizations, and are proven to be computationally challenging. Therefore, this dissertation proposes alternative computational schemes using: i) bordered-block diagonal (BBD) decomposition algorithm for designing LMI based robust decentralized static output feedback controllers, ii) sequential LMI programming method for designing robust decentralized dynamic output feedback controllers, and, iii) generalized parameter continuation method involving matrix inequalities for designing reduced-order decentralized dynamic output feedback controllers. First, this dissertation considers the problem of designing robust decentralized static output feedback controllers for power systems that guarantee connective stability despite the presence of uncertainties among the interconnected subsystems. The design problem is then solved using BBD decomposition algorithm that clusters the state, input and output structural information for the direct computation of the appropriate gain matrices. Moreover, the approach is flexible enough to allow the inclusion of additional design constraints such as the size of the gain matrices and the degree of robust stability while at the same time maximizing the tolerable upper bounds on the class of perturbations. Second, this research considers the problem of designing a robust decentralized fixed-order dynamic output feedback controller for power systems that is formulated as a nonconvex optimization problem involving LMIs coupled through bilinear matrix equation. In the design, the robust connective stability of the overall system is guaranteed while the upper bounds of the uncertainties arising from the interconnection of the subsystems as well as nonlinearities within each subsystem are maximized. The (sub)-optimal robust decentralized dynamic output feedback control design problem is then solved using sequential LMI programming method. Moreover, the local convergence property of this algorithm has shown the effectiveness of the proposed approach for designing (sub)-optimal robust decentralized dynamic output feedback controllers for power systems. Third, this dissertation considers the problem of designing a robust decentralized structure-constrained dynamic output feedback controller design for power systems using LMI-based optimization approach. The problem of designing a decentralized structure-constrained H2/Hinf controller is first reformulated as an extension of a static output feedback controller design problem for the extended system. The resulting nonconvex optimization problem which involves bilinear matrix inequalities (BMIs) is then solved using the sequentially LMI programming method. Finally, the research considers the problem of designing reduced-order decentralized Hinf controllers for power systems. Initially a fictitious centralized Hinf robust controller, which is typically high-order controller, is designed to guarantee the robust stability of the overall system against unstructured and norm bounded uncertainties. Then the problem of designing a reduced-order decentralized controller is reformulated as an embedded parameter continuation problem that homotopically deforms from the centralized controller to the decentralized controller as the continuation parameter monotonically varies. The design problem, which guarantees the same robustness condition of the centralized controller, is solved using a two-stage iterative matrix inequality optimization algorithm. Moreover, the approach is flexible enough to allow designing different combinations of reduced-order controllers between the different input/output channels. The effectiveness of these proposed approaches are demonstrated by designing realistic power system stabilizers (PSSs) for power system, notably so-called reduced-order robust PSSs that are linear and use minimum local-feedback information. Moreover, the nonlinear simulation results have confirmed the robustness of the system for all envisaged operating conditions and disturbances. The proposed approaches offer a practical tool for engineers, besides designing reduced-order PSSs, to re-tune PSS parameters for improving the dynamic performance of the overall system

    El surgimiento de un esquema de pagos móviles: el caso de Movii

    Get PDF
    Las billeteras móviles replican a las billeteras físicas en un dispositivo móvil, con las que los usuarios pueden utilizar diferentes instrumentos de pago (e.g., tarjetas, transferencias) para realizar pagos móviles. Con la adopción de la billetera móvil surge un esquema de pagos móviles, en el que sus usuarios son elementos de una red de transferencias. En este artículo se estudia el esquema de pagos móviles de Movii—la primera fintech en Colombia que opera bajo una licencia financiera (no bancaria) de depósitos y pagos electrónicos. Con base en una base de datos de transferencias bilaterales entre usuarios de la billetera móvil de Movii, se construye, visualiza y analiza la red de Movii, diaria, desde noviembre 18 de 2017 hasta noviembre 25 de 2020. Además del esperado incremento en el número de usuarios y el valor de las transferencias, se encuentra que la complejidad visual y cuantitativa de la red de transferencias se incrementa a través del tiempo. Este aumento en la complejidad tiene que ver con la adopción de la billetera móvil de Movii, lo cual resulta en que los usuarios encuentran nuevas maneras de utilizar los pagos móviles más allá de transferencias persona a persona, incluyendo pagos de persona a negocio y de negocio a negocio. Así mismo, es evidente que la pandemia por Covid-19 aceleró la evolución del esquema de pagos móviles de Movii.Mobile wallets replicate physical wallets on a mobile device, in which users can store different payment instruments (e.g., cards, transfers) to make mobile payments. As the mobile wallet is adopted, a mobile payment scheme emerges, with its users as elements in a network of transfers. In this article, I study the mobile payment scheme of Movii— the first fintech firm in Colombia operating under a financial non-banking license for electronic deposits and payments. Based on a unique dataset of bilateral transfers between Movii’s mobile wallet users, I build, visualize and analyze Movii’s network, daily from November 18, 2017, to November 25, 2020. Besides the anticipated increase in the number of users and the value of transfers, the visual and quantitative complexity of the network of transfers increases over time. This increase in complexity is likely to be linked to the adoption of Movii’s mobile wallet, which results in users finding new ways to use mobile payments beyond person-to-person transfers, including person-to-business and business-to-business. Also, results suggest the Covid-19 pandemic accelerated the evolution of Movii’s mobile payments scheme.El surgimiento de un esquema de pagos móviles: el caso de Movii Enfoque El rápido crecimiento de la industria fintech se explica—en parte—por la demanda insatisfecha por servicios financieros. En el caso de América Latina, la literatura señala que esta demanda insatisfecha resulta de la inadecuada oferta de servicios bancarios, de pagos y transferencias. En cuanto a la industria paytech (i.e. segmento de la industria fintech orientado a los pagos) se refiere, las billeteras móviles permiten a los usuarios utilizar sus dispositivos móviles (e.g., teléfono móvil, tableta) para realizar pagos a través de transferencias entre cuentas y compras en línea y presenciales. Es decir, una billetera móvil replica a una billetera física en un dispositivo móvil, con lo cual permite a un usuario guardar y utilizar diferentes instrumentos de pago para realizar pagos móviles. De acuerdo con la literatura, factores tales como la penetración de la telefonía móvil, la falta de alternativas frente al efectivo, los costos de las transferencias bancarias, así como la facilidad de uso de las billeteras móviles, han incentivado su adopción en países en desarrollo. El estudio de la adopción de las billeteras móviles apenas empieza. Sin embargo, la literatura sobre la adopción de tecnologías y servicios de pago no es nueva. En esa literatura se ha identificado un importante vacío, el cual consiste en la utilización de variables en extremo agregadas (e.g., valor y número de pagos, número de usuarios) que no capturan los cambios en el comportamiento de los usuarios y el consiguiente cambio en los patrones de utilización. Es decir, no existe una perspectiva de usuario en el estudio de servicios de pago. Contribución En este artículo se estudia el esquema de pagos de la billetera móvil de Movii—la primera fintech en Colombia que opera bajo una licencia financiera (no bancaria) de depósitos y pagos electrónicos. A diferencia de la literatura sobre adopción de tecnologías y servicios de pago, se utilizan las transferencias bilaterales entre usuarios de Movii para construir, visualizar y analizar las redes de transferencias de la billetera móvil. Con esto se consigue estudiar la evolución de los patrones de transferencias entre los usuarios de la billetera móvil, desde el día en que ocurrió la primera operación (noviembre 18 de 2017) hasta noviembre 25 de 2020. En la literatura no existe antecedente de un estudio de este tipo. Los resultados son útiles para los agentes de la industria paytech, ya que permiten examinar la evolución de un esquema de pagos desde la perspectiva del usuario. Para los gobiernos, esta perspectiva y los resultados permiten estudiar de mejor manera las billeteras móviles. Adicionalmente, dadas las transferencias de los gobiernos a la población durante la pandemia por el Covid-19, esta perspectiva permite explorar cómo los usuarios utilizaron esos recursos. Resultados Además del esperado incremento en el número de usuarios y el valor y número de transferencias, se observa que el patrón de transferencias entre usuarios de la billetera móvil de Movii se torna más complejo a través del tiempo. La evolución de las redes de transferencia muestra—visual y cuantitativamente—que los usuarios encuentran nuevas maneras de utilizar los pagos móviles más allá de transferencias persona a persona, presumiblemente incluyendo pagos de persona a negocio y de negocio a negocio. Esto puede explicarse por la bien conocida dificultad que tienen los negocios pequeños para recibir instrumentos de pago diferentes al efectivo; en este caso, la billetera móvil no solo facilita las transferencias entre personas sino también aquellas entre personas y negocios. Los resultados también muestran que la pandemia por Covid-19 aceleró la evolución del esquema de pagos móviles de Movii. Frase destacada: Los resultados permiten examinar la evolución de un esquema de pagos desde la perspectiva del usuario. Para los gobiernos, esta perspectiva y los resultados permiten estudiar de mejor manera las billeteras móviles

    Reorganization of columnar architecture in the growing visual cortex

    Full text link
    Many cortical areas increase in size considerably during postnatal development, progressively displacing neuronal cell bodies from each other. At present, little is known about how cortical growth affects the development of neuronal circuits. Here, in acute and chronic experiments, we study the layout of ocular dominance (OD) columns in cat primary visual cortex (V1) during a period of substantial postnatal growth. We find that despite a considerable size increase of V1, the spacing between columns is largely preserved. In contrast, their spatial arrangement changes systematically over this period. While in young animals columns are more band-like, layouts become more isotropic in mature animals. We propose a novel mechanism of growth-induced reorganization that is based on the `zigzag instability', a dynamical instability observed in several inanimate pattern forming systems. We argue that this mechanism is inherent to a wide class of models for the activity-dependent formation of OD columns. Analyzing one member of this class, the Elastic Network model, we show that this mechanism can account for the preservation of column spacing and the specific mode of reorganization of OD columns that we observe. We conclude that neurons systematically shift their selectivities during normal development and that this reorganization is induced by the cortical expansion during growth. Our work suggests that cortical circuits remain plastic for an extended period in development in order to facilitate the modification of neuronal circuits to adjust for cortical growth.Comment: 8+13 pages, 4+8 figures, paper + supplementary materia

    A Parallelizable Algorithm for Stabilizing Large Sparse Linear Systems With Uncertain Interconnections

    Get PDF
    This paper proposes a new method for permuting sparse matrices into an upper block triangular from. The algorithm is highly parallelizable, which makes it suitable for large-scale systems with uncertain interconnection patterns. In such cases, the proposed decomposition can be used to develop flexible decentralized control strategies that produce a different gain matrix whenever the configuration changes. Applications to interconnected microgrids and supply and demand networks are provided to illustrate the versatility of the proposed approach
    corecore