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  • 1
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    A Data Dropout Compensation Algorithm Based on the Iterative Learning Control Methodology for Discrete-Time Systems (2015)
    Hindawi
    Details
    Publication Date: 2015-05-07
    Description: This paper deals with the convergence of a remote iterative learning control system subject to data dropouts. The system is composed by a set of discrete-time multiple input-multiple output linear models, each one with its corresponding actuator device and its sensor. Each actuator applies the input signals vector to its corresponding model at the sampling instants and the sensor measures the output signals vector. The iterative learning law is processed in a controller located far away of the models so the control signals vector has to be transmitted from the controller to the actuators through transmission channels. Such a law uses the measurements of each model to generate the input vector to be applied to its subsequent model so the measurements of the models have to be transmitted from the sensors to the controller. All transmissions are subject to failures which are described as a binary sequence taking value 1 or 0. A compensation dropout technique is used to replace the lost data in the transmission processes. The convergence to zero of the errors between the output signals vector and a reference one is achieved as the number of models tends to infinity.
    Print ISSN: 1024-123X
    Electronic ISSN: 1563-5147
    Topics: Mathematics , Technology
    Published by Hindawi
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  • 2
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    On the Stability and Equilibrium Points of Multistaged Epidemic Models (2015)
    Hindawi
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    Publication Date: 2015-05-15
    Description: This paper relies on the concept of next generation matrix defined ad hoc for a new proposed extended SEIR model referred to as -model to study its stability. The model includes successive stages of infectious subpopulations, each one acting at the exposed subpopulation of the next infectious stage in a cascade global disposal where each infectious population acts as the exposed subpopulation of the next infectious stage. The model also has internal delays which characterize the time intervals of the coupling of the susceptible dynamics with the infectious populations of the various cascade infectious stages. Since the susceptible subpopulation is common, and then unique, to all the infectious stages, its coupled dynamic action on each of those stages is modeled with an increasing delay as the infectious stage index increases from 1 to . The physical interpretation of the model is that the dynamics of the disease exhibits different stages in which the infectivity and the mortality rates vary as the individual numbers go through the process of recovery, each stage with a characteristic average time.
    Print ISSN: 1026-0226
    Electronic ISSN: 1607-887X
    Topics: Mathematics
    Published by Hindawi
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  • 3
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    Observer-Based Vaccination Strategy for a True Mass Action SEIR Epidemic Model with Potential Estimation of All the Populations (2011)
    Hindawi
    Details
    Publication Date: 2011-10-28
    Description: This paper presents a simple continuous-time linear vaccination-based control strategy for a SEIR (susceptible plus infected plus infectious plus removed populations) propagation disease model. The model takes into account the total population amounts as a refrain for the illness transmission since its increase makes more difficult contacts among the susceptible and infected. The control objective is the asymptotically tracking of the removed-by-immunity population to the total population while achieving simultaneously the remaining population (i.e., susceptible plus infected plus infectious) to asymptotically converge to zero. A state observer is used to estimate the true various partial populations of the susceptible, infected, infectious, and immune which are assumed to be unknown. The model parameters are also assumed to be, in general, unknown. In this case, the parameters are replaced by available estimates to implement the vaccination action.
    Print ISSN: 1026-0226
    Electronic ISSN: 1607-887X
    Topics: Mathematics
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  • 4
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    Robust Sliding Control of SEIR Epidemic Models (2014)
    Hindawi
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    Publication Date: 2014-03-14
    Description: This paper is aimed at designing a robust vaccination strategy capable of eradicating an infectious disease from a population regardless of the potential uncertainty in the parameters defining the disease. For this purpose, a control theoretic approach based on a sliding-mode control law is used. Initially, the controller is designed assuming certain knowledge of an upper-bound of the uncertainty signal. Afterwards, this condition is removed while an adaptive sliding control system is designed. The closed-loop properties are proved mathematically in the nonadaptive and adaptive cases. Furthermore, the usual sign function appearing in the sliding-mode control is substituted by the saturation function in order to prevent chattering. In addition, the properties achieved by the closed-loop system under this variation are also stated and proved analytically. The closed-loop system is able to attain the control objective regardless of the parametric uncertainties of the model and the lack of a priori knowledge on the system.
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    Electronic ISSN: 1563-5147
    Topics: Mathematics , Technology
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  • 5
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    Potential Effects of Host Height and Phenology on Adult Susceptibility to Foliar Attack in Tropical Dry Forest Grass (2011)
    Hindawi
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    Publication Date: 2011-01-01
    Description: Identifying the sources of variation in plant susceptibility to herbivore and pathogen attack is critical to understand ecological processes determining species abundance and diversity in tropical forests. We assessed the potential effect of tiller height and phenology on standing levels of herbivore and pathogen damage on adults of the woody perennial grass Lasiacis ruscifolia in the tropical dry forest of Chamela, Mexico. Analyses revealed that adult susceptibility to pathogens was greater in small and fruiting tillers than in taller and leaf flushing tillers. Adult susceptibility to herbivores, on the other hand, varied greatly among plants and had no relationship with tiller height and phenology. Our findings suggest that adults highly susceptible to pathogen attack could augment the negative density and distance dependence effects predicted by the Janzen-Connell hypothesis, with potential consequences for the local distribution of the studied species in the forest.
    Print ISSN: 2090-4614
    Electronic ISSN: 2090-4622
    Topics: Biology
    Published by Hindawi
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  • 6
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    Fish Species Richness in Lowland Streams with a Geothermal Input Phenomenon, Sarapiquí de Heredia, Costa Rica (2011)
    Hindawi
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    Publication Date: 2011-01-01
    Description: Lowland streams of the Caribbean Costa Rican slope are naturally enriched by minerals and solutes such as phosphorus, a phenomenon known as geothermal input. The resulting stream phosphorus gradient affects the food web by altering primary production, leading to complex biotic and abiotic interactions. The objective of this study was to describe fish species richness patterns in relation to a naturally occurring phosphorus gradient in three lowland streams. We hypothesized that phosphorus input in La Selva Biological Station streams is correlated with species richness. 354 individuals were identified at 4 sites: Surá, El Salto, Sábalo and Jaguar, using a cast net, a total of 150 throws were made, distributed in 10 samplings, at each site. An estimation of species richness along with alpha and beta diversity indices were calculated in order to describe fish community structure. Species richness was estimated to be higher at Jaguar but presents a lower phosphorus enrichment. Jaguar and Sábalo, differed the most while Salto and Surá were the most similar as indicated by species turnover among streams. There is a non significant relationship between phosphorus levels and diversity; however, this interesting trend encourages further studies on species richness patterns and natural nutrient enrichment of streams.
    Print ISSN: 2090-4614
    Electronic ISSN: 2090-4622
    Topics: Biology
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  • 7
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    A Data Dropout Compensation Algorithm Based on the Iterative Learning Control Methodology for Discrete-Time Systems (2015)
    Hindawi
    Details
    Publication Date: 2015-01-01
    Description: This paper deals with the convergence of a remote iterative learning control system subject to data dropouts. The system is composed by a set of discrete-time multiple input-multiple output linear models, each one with its corresponding actuator device and its sensor. Each actuator applies the input signals vector to its corresponding model at the sampling instants and the sensor measures the output signals vector. The iterative learning law is processed in a controller located far away of the models so the control signals vector has to be transmitted from the controller to the actuators through transmission channels. Such a law uses the measurements of each model to generate the input vector to be applied to its subsequent model so the measurements of the models have to be transmitted from the sensors to the controller. All transmissions are subject to failures which are described as a binary sequence taking value 1 or 0. A compensation dropout technique is used to replace the lost data in the transmission processes. The convergence to zero of the errors between the output signals vector and a reference one is achieved as the number of models tends to infinity.
    Print ISSN: 1024-123X
    Electronic ISSN: 1563-5147
    Topics: Mathematics , Technology
    Published by Hindawi
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  • 8
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    PID Based on Attractive Ellipsoid Method for Dynamic Uncertain and External Disturbances Rejection in Mechanical Systems (2015)
    Hindawi
    Details
    Publication Date: 2015-01-01
    Description: This paper presents a stability analysis for LNDS (Lagrangian nonlinear dynamical systems) with dynamic uncertain using a PID controller with external disturbances rejection based on attractive ellipsoid methods, since the PID-CT (proportional integral derivative computed torque) compensator has been used for the nonlinear trajectory tracking of an LNDS, when there are external perturbations and system uncertainties. The global system convergence of the trivial solution has not been proved. In this sense, we propose an approach to find the gains of the nonlinear PID-CT controller to guarantee the boundedness of the trivial solution by means of the concept of the UUB (uniform-ultimately bounded) stability. In order to show the effectiveness of the methodology proposed, we applied it in a real 2-DoF robot system.
    Print ISSN: 1024-123X
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    Topics: Mathematics , Technology
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  • 9
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    Robustly stable multiestimation scheme for adaptive control and identification with model reduction issues (2005)
    Hindawi
    Details
    Publication Date: 2005-01-01
    Description: A discrete pole-placement-based and multiestimation-based adaptive control scheme involving a relative adaptation dead zone is presented for a plant with known poles and unknown zeros. The basic usefulness of the proposed multiestimation scheme is related to the use of a set of models of reduced order associated with the multiestimation scheme instead of a high-order one. Depending on the frequency spectrum characteristics of the input and on the estimates evolution, the multiestimation scheme selects on-line the most appropriate model and its related estimation scheme in order to improve the identification and control performances. Robust closed-loop stability is proved even in the presence of unmodeled dynamics of sufficiently small sizes as it has been confirmed by simulation results. The scheme chooses in real time the estimator/controller associated with a particular reduced model possessing the best performance according to an identification performance index by implementing a switching rule between estimators. The switching rule is subject to a minimum residence time at each identifier/adaptive controller parameterization for closed-loop stabilization purposes. A conceptually simple higher-level supervisor, based on heuristic updating rules which estimate on-line the weights of the switching rule between estimation schemes, is discussed.
    Print ISSN: 1026-0226
    Electronic ISSN: 1607-887X
    Topics: Mathematics
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  • 10
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    Robust Adaptive Stabilization of Linear Time-Invariant Dynamic Systems by Using Fractional-Order Holds and Multirate Sampling Controls (2010)
    Hindawi
    Details
    Publication Date: 2010-01-01
    Description: This paper presents a strategy for designing a robust discrete-time adaptive controller for stabilizing linear time-invariant (LTI) continuous-time dynamic systems. Such systems may be unstable and noninversely stable in the worst case. A reduced-order model is considered to design the adaptive controller. The control design is based on the discretization of the system with the use of a multirate sampling device with fast-sampled control signal. A suitable on-line adaptation of the multirate gains guarantees the stability of the inverse of the discretized estimated model, which is used to parameterize the adaptive controller. A dead zone is included in the parameters estimation algorithm for robustness purposes under the presence of unmodeled dynamics in the controlled dynamic system. The adaptive controller guarantees the boundedness of the system measured signal for all time. Some examples illustrate the efficacy of this control strategy.
    Print ISSN: 1026-0226
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    Topics: Mathematics
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