Differentiation is an important task in control, observation, and fault detection. Levant's differentiator is unique, since it is able to estimate exactly and robustly the derivatives of a signal ...with a bounded high-order derivative. However, the convergence time, although finite, grows unboundedly with the norm of the initial differentiation error, making it uncertain when the estimated derivative is exact. In this article, we propose an extension of Levant's differentiator so that the worst-case convergence time can be arbitrarily assigned independently of the initial condition, i.e., the estimation converges in fixed time . We propose also a family of continuous differentiators and provide a unified Lyapunov framework for analysis and design.
We propose a family of smooth explicit Lyapunov functions (LF) for Levant's differentiator, which is a discontinuous real-time robust and exact differentiator. These LF allow the analysis of the ...convergence and performance properties and the design of appropriate gains for the differentiator.
Zoonoses in a changing world García-Moreno, Jaime
BioScience/Bioscience,
10/2023, Letnik:
73, Številka:
10
Journal Article
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Abstract
Animals are continuously exposed to pathogens but rarely get infected, because pathogens must overcome barriers to establish successful infections. Ongoing planetary changes affect factors ...relevant for such infections, such as pathogen pressure and pathogen exposure. The replacement of wildlife with domestic animals shrinks the original host reservoirs, whereas expanding agricultural frontiers lead to increased contact between natural and altered ecosystems, increasing pathogen exposure and reducing the area where the original hosts can live. Climate change alters species’ distributions and phenology, pathogens included, resulting in exposure to pathogens that have colonized or recolonized new areas. Globalization leads to unwilling movement of and exposure to pathogens. Because people and domestic animals are overdominant planetwide, there is increased selective pressure for pathogens to infect them. Nature conservation measures can slow down but not fully prevent spillovers. Additional and enhanced surveillance methods in potential spillover hotspots should improve early detection and allow swifter responses to emerging outbreaks.
An arbitrary order differentiator that, in the absence of noise, converges to the true derivatives of the signal after a finite time independent of the initial differentiator error is presented. The ...only assumption on a signal to be differentiated (n−1) times is that its n-th derivative is uniformly bounded by a known constant. The proposed differentiator switches from a newly designed uniform differentiator to the classical High-Order Sliding Mode (HOSM) differentiator. The Uniform part drives the differentiation error trajectories into a compact neighborhood of the origin in a time that is independent of the initial differentiation error. Then, the HOSM differentiator is used to bring the differentiation error to zero in finite-time.
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•Sources, fate and occurrence of phthalates and BPA in aquifers have been reviewed.•Phthalates and BPA have been globally detected in groundwater reservoirs.•Landfills, sewage sludge ...and wastewater are the main sources to groundwater pollution.•Some phthalate and BPA features and soil conditions promote the transport to aquifers.•Worldwide guidelines values for drinking water vary in a wide range of concentrations.
Phthalic acid esters (PAEs) or phthalates and bisphenol A (BPA) are emerging organic contaminants (EOCs) that may harm biota and human health. Humans can be exposed to these contaminants by drinking water consumption from water sources such as groundwater. Before their presence in aquifer systems, phthalates and BPA can be found in many matrices due to anthropogenic activities, which result in long-term transport to groundwater reservoirs by different mechanisms and reaction processes. The worldwide occurrence of phthalates and BPA concentrations in groundwater have ranged from 0.1 × 10−3 to 3 203.33 µg L−1 and from 0.09 × 10−3 to 228.04 µg L−1, respectively. Therefore, the aim of this review is to describe the groundwater contamination pathways of phthalates and BPA from the main environmental sources to groundwater. Overall, this article provides an overview that integrates phthalate and BPA environmental cycling, from their origin to human reception via groundwater consumption. Additionally, in this review, the readers can use the information provided as a principal basis for existing policy ratification and for governments to develop legislation that may incorporate these endocrine disrupting compounds (EDCs) as priority contaminants. Indeed, this may trigger the enactment of regulatory guidelines and public policies that help to reduce the exposure of these EDCs in humans by drinking water consumption.
A method to construct a family of strict Lyapunov functions, i.e., with negative definite derivative, for the super-twisting algorithm, without or with perturbations, is provided. This second order ...sliding modes algorithm is widely used to design controllers, observers and exact differentiators. The proposed Lyapunov functions ascertain finite time convergence, provide an estimate of the convergence time, and ensure the robustness of the finite-time or ultimate boundedness for a class of perturbations wider than the classical ones for this algorithm. Since the Lyapunov functions and their derivatives are quadratic forms, the operation with them is as simple as for linear time invariant systems.
In this paper, an output feedback stabilization of perturbed double-integrator systems using super-twisting control (STC) is studied. It is shown that when STC is implemented based on super-twisting ...observer (STO), then it is not possible to achieve second-order sliding mode (SOSM) using continuous control on the chosen sliding surface. Two methodologies are proposed to circumvent the above-mentioned problem. In the first method, control input is discontinuous, which may not be desirable for practical systems. In the second method, continuous STC is proposed based on higher order sliding mode observer (HOSMO) that achieves SOSM on the chosen sliding surface. For simplicity, we are considering here only the perturbed double integrator, which can be generalized for an arbitrary-order systems. Numerical simulations and experimental validation are also presented to show the effectiveness of the proposed method.
Abstract
For arbitrary multiple‐input multiple‐output linear time invariant systems with unknown inputs this article provides sufficient conditions to estimate linear functionals of the state ...variables. When the unknown input is uniformly bounded these conditions are strictly weaker than the classical conditions for functional unknown input observers, well‐known in the literature, and generalize previous results using discontinuous differentiators. Furthermore, a general methodology is proposed to design functional observers, that are able to estimate the functionals, when possible, exactly and in finite‐time or fixed‐time. Instead of using a cascade of Luenberger observers and high‐order sliding‐mode differentiators, standard in the literature for this problem, a bi‐homogeneous observer of reduced order is proposed in the article. Proofs of the convergence are provided using smooth Lyapunov functions and an academic example illustrates the behavior of the proposed observer for a system not tractable with the available methods.
Summary
In this article, we propose a finite‐time output‐feedback control scheme for a class of nonlinear systems. The dynamic part of the controller consists of an extended order observer, which is ...based on the higher order sliding‐mode exact differentiator. With such an observer, the states of the system are exactly estimated in finite‐time; moreover, the additional state in the observer estimates exactly and in finite‐time Lipschitz disturbances in the system. Such an estimation is used by the static part of the controller to compensate the disturbances. The static part of the controller can be chosen from a class of homogeneous controllers. The whole control scheme allows to recover in finite‐time several useful properties of homogeneous systems despite the additional and uncertain nonlinear terms. The effect of the noise in the measurement is also studied.
When the nth derivative of a signal to be differentiated is bounded by a known constant, Levant's arbitrary-order differentiator provides, in the absence of noise, for an exact estimation of all ...derivatives up to order (n − 1) in finite time. Recently, Levant has shown that if the nth derivative is bounded by a known time-varying function, the same differentiator with a time-varying gain is also able to estimate in finite time all derivatives, if the initial condition of the differentiation error is sufficiently small. In this paper, we find, using a smooth Lyapunov function, under which conditions the same result is valid globally.
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