Jose Alvarez-Ramirez

Multifractal Hurst analysis of crude oil prices

Daily records of international crude oil prices are studied using multifractal analysis methods. Rescaled range Hurst analysis provides evidence that the crude oil market is a persistent process with long-run memory effects. On the other hand, height–height correlation analysis reveals evidence of multifractal structures in the sense that the crude oil dynamics displays mixing of (rough) Hurst exponents. The existence of two characteristic time scales in the order of weeks and quarters is discovered and the corresponding prices dynamics are extracted using moving-average-based filtering. These results seem to demonstrate that the crude oil market is consistent with the random-walk assumption only at time scales of the order of days to weeks. A plausible oil price formation mechanism is discussed in terms of the market dynamics at three different time scales.

Linear systems with bounded inputs: global stabilization with eigenvalue placement

This work presents a technique for obtaining a bounded continuous feedback control function which stabilizes a linear system in a certain region. If the open-loop system has no eigenvalues with positive real part, the region of attraction of the resulting closed-loop system is all ℝn, i.e., the feedback control is a global stabilizer; otherwise, the region contains an invariant (‘cylindric-like’) set where the controller does not saturate. The proposed control is a linear-like feedback control with state-dependent gains. The gains become implicitly defined in terms of a nonlinear scalar equation. The control function coincides in an ellipsoidal neighbourhood of the origin with a linear feedback law which is a solution of a linear quadratic regulator problem. This design allows eigenvalue placement in a specified region.

On the PID tracking control of robot manipulators

We consider the problem of PID tracking control of robotics manipulators. Our objective is to prove that under classical PID control, semiglobal stability can be assured with arbitrary small output tracking error. This means that, for any given set of initial conditions Wx, there exist PID control gains such that all trajectories starting in Wx converge to a residual set of arbitrary size. A novel PID control configuration is developed in terms of a parameter that is directly related with the size of the region of attraction and the size of the residual set. Tuning guidelines are extracted from the stability analysis.

Adaptive synchronization of high-order chaotic systems: a feedback with low-order parametrization

Abstract In this work, an adaptive strategy for chaos synchronization is developed. The proposed scheme allows the synchronization of high-order chaotic systems. Only one tuning parameter is required to perform the chaos synchronization. The nonidentical chaotic synchronization can be attained. Computer simulations are provided to verify the operation of the designed synchronization scheme. The proposed controller is implemented to secure communication and synchronization of inhomogeneous oscillators chain. Nevertheless, other practical applications can be physically carried out.

A stable design of PI control for DC-DC converters with an RHS zero

The stability of boost and buck-boost DC-DC power converters under proportional plus integral (PI) control is discussed in this paper. A novel PI control configuration is proposed, which reveals the effect that the right-hand-side zero has on PI control stability. Tuning rules in terms of the converter parameters are derived and illustrated via numerical and experimental simulations.

Brief Semiglobal stability of saturated linear PID control for robot manipulators

This paper addresses the position regulation problem of robot manipulators under control input constraints. It is proven that the robot system under a saturated linear PID control is semiglobally asymptotically stable, if the torque bounds are larger than gravitational torques, and if the proportional gain is large enough and the integral gain is small enough. The stability analysis makes use of singular perturbation tools and the results are illustrated via numerical simulations.

PID regulation of robot manipulators: stability and performance

Position control of robot manipulators using a novel PID control configuration derived from modeling error compensation ideas is introduced. The PID control law stability depends only on the inertial parameters of the robot. A simple proof of semiglobal PID stabilization of robot manipulators is provided. It is shown that the performance of the inverse dynamics control can be recovered by the PID control in the high-gain limit. Simple tuning guidelines derived from the proposed PID control configuration and closed-loop stability analysis are presented.

SYNCHRONIZATION OF A CLASS OF STRICTLY DIFFERENT CHAOTIC OSCILLATORS

Abstract The synchronization of two different chaotic oscillators is studied. First, this problem is understood in terms of chaos suppression. Next, a robust asymptotic controller is used in the chaos control. The robust controller comprises an uncertainty estimator and a linearizing control law. In this way, synchronization is obtained despite the master model being strictly different from the slave model. In fact, the controller does not know the master oscillator model.

Stability of Robot Manipulators Under Saturated PID Compensation

The joint position regulation problem for robot manipulators under a standard saturated proportional-integral differential (PID) compensator is studied in this brief. The main result states the existence of PID control gains yielding semiglobal asymptotic stability if the control torque bounds are larger than gravitational torques. Energy shaping plus damping injection methods, as well as singular perturbation analysis, are used to establish stability conditions to achieve regulation at any desired position. Some experiments are carried out to illustrate the stability results.

Acid hydrolysis of native corn starch: Morphology, crystallinity, rheological and thermal properties

The acid hydrolysis of native corn starch at 35 °C was monitored during 15 days. After this time, the residual solids were about 37.0 ± 3.0%. First-order kinetics described the hydrolysis data, giving a constant rate of kH = 0.18 ± 0.012 days(-1). Amylose content presented a sharp decrement of about 85% and X-ray diffraction results indicated a gradual increase in crystallinity during the first 3 days. SEM micrographs showed that hydrolysis disrupted granule morphology from an initial regular shape to increasingly irregular shapes. Fractal analysis of SEM images revealed an increase in surface roughness. Fast changes in the thermal effects were caused by molecular rearrangements after fast hydrolysis of amylose in the amorphous regions in the first day. Steady shear rate and oscillatory tests showed a sharp decrease of the apparent viscosity and an increase of the damping factor (tan(δ)) caused by amylose degradation.