387 research outputs found
Periodic solutions with nonconstant sign in Abel equations of the second kind
The study of periodic solutions with constant sign in the Abel equation of
the second kind can be made through the equation of the first kind. This is
because the situation is equivalent under the transformation ,
and there are many results available in the literature for the first kind
equation. However, the equivalence breaks down when one seeks for solutions
with nonconstant sign. This note is devoted to periodic solutions with
nonconstant sign in Abel equations of the second kind. Specifically, we obtain
sufficient conditions to ensure the existence of a periodic solution that
shares the zeros of the leading coefficient of the Abel equation. Uniqueness
and stability features of such solutions are also studied.Comment: 10 page
Second-order odd-harmonic repetitive control and its application to active filter control
High order repetitive control has been introduced toovercomeperformance decay of repetitive control systems undervarying frequency of the signals to be tracked/rejected orimproving the interhamonic behavior. However, most highorder repetitive internal models used to improve frequencyuncertainty are unstable, as a consequence practicalimplementations are more difficult. In this work a stable,second order odd-harmonic repetitive control system ispresented and studied.The proposed internal model has been implemented andvalidated in a shunt active filter current controller. Thishigh order controller allows dealing with the gridfrequency variations without using adaptive schemes
Novel slow-fast behaviour in an oscillator driven by a frequency-switching force
When an oscillator switches abruptly between different frequencies, there is
some ambiguity in deciding how the system should be modelled at the switch.
Here we describe two seemingly natural models of a switch in a simple
periodically-forced harmonic oscillator, which disagree starkly in their
predictions of its long time behaviour. Attempting to resolve the disagreement
by `regularizing' the switch not only preserves the disagreement, but shows it
increases with time. One of the models corresponds to a conventional `Filippov'
description of a nonsmooth system, while the second exhibits a structure that
irreversibly ages, developing a number of novel multi-scale behaviours that we
believe have not been reported before. These include slow-fast staircases,
novel mixed-mode oscillations, and a synchronized canard explosion. These
features are proven to exist using asymptotic analysis, but as they involve a
slow-fast time-scale separation that increases with time, they lie beyond the
reach of numerical methods
Ageing of an oscillator due to frequency switching
If an oscillator is driven by a force that switches between two frequencies,
the dynamics it exhibits depends on the precise manner of switching. Here we
take a one-dimensional oscillator and consider scenarios in which switching
occurs: (i) between two driving forces which have different frequencies, or
(ii) as a single forcing whose frequency switches between two values. The
difference is subtle, but entirely changes the long term behaviour, and
concerns whether the switch can be expressed linearly or nonlinearly in terms
of a discontinuous quantity (such as a sign or Heaviside step function that
represents the switch between frequencies). In scenario (i) the oscillator has
a stable periodic orbit, and the system can be described as a Filippov system.
In scenario (ii) the oscillator exhibits hidden dynamics, which lies outside
the theory of Filippov's systems, and causes the system to be increasingly (as
time passes) dominated by sliding along the frequency-switching threshold, and
in particular if periodic orbits do exist, they too exhibit sliding. We show
that the behaviour persists, at least asymptotically, if the systems are
regularized (i.e. if the switch is modelled as a smooth transition in the
manner of (i) or (ii))
Polynomial Interrupt Timed Automata
Interrupt Timed Automata (ITA) form a subclass of stopwatch automata where
reachability and some variants of timed model checking are decidable even in
presence of parameters. They are well suited to model and analyze real-time
operating systems. Here we extend ITA with polynomial guards and updates,
leading to the class of polynomial ITA (PolITA). We prove the decidability of
the reachability and model checking of a timed version of CTL by an adaptation
of the cylindrical decomposition method for the first-order theory of reals.
Compared to previous approaches, our procedure handles parameters and clocks in
a unified way. Moreover, we show that PolITA are incomparable with stopwatch
automata. Finally additional features are introduced while preserving
decidability
Program transformations using temporal logic side conditions
This paper describes an approach to program optimisation based on transformations, where temporal logic is used to specify side conditions, and strategies are created which expand the repertoire of transformations and provide a suitable level of abstraction. We demonstrate the power of this approach by developing a set of optimisations using our transformation language and showing how the transformations can be converted into a form which makes it easier to apply them, while maintaining trust in the resulting optimising steps. The approach is illustrated through a transformational case study where we apply several optimisations to a small program
Control adaptativo por modelo de referencia para un inversor basado en LCL con síntesis de controlador mínima
[Resumen] Un Control Adaptativo por Modelo de Referencia (MRAC) con Síntesis de Controlador Mínima (MCS), es desarrollado con el objetivo de controlar un Inversor monofásico basado en un Filtro LCL conectado a la Red Eléctrica y adaptar el inductor de la red, que es un parámetro desconocido y que genera incertidumbre, manteniendo las prestaciones y la robustez del sistema. Para ello primero se revisara el algoritmo de MCS y en función de este, se muestran todos los pasos a seguir y el desarrollo de los componentes necesarios para el funcionamiento de MCS en tiempo continuo. Se desarrolla un modelo de simulación promediado y se presentan los resultados obtenidos.Este trabajo ha sido realizado gracias al apoyo de la Secretaría Nacional de Educación Superior, Ciencia y Tecnología e Innovación del Ecuador (SENESCYT), a la Universidad de Cuenca, y a los proyectos DPI2013-41224-P y DPI2015-69286-C3-2-R (MINECO/FEDER) y 2014 SGR 267 de la agencia AGAUR de la Generalitat de CatalunyaGeneralitat de Catalunya; 2014 SGR 267https://doi.org/10.17979/spudc.978849749808
Characterising Probabilistic Processes Logically
In this paper we work on (bi)simulation semantics of processes that exhibit
both nondeterministic and probabilistic behaviour. We propose a probabilistic
extension of the modal mu-calculus and show how to derive characteristic
formulae for various simulation-like preorders over finite-state processes
without divergence. In addition, we show that even without the fixpoint
operators this probabilistic mu-calculus can be used to characterise these
behavioural relations in the sense that two states are equivalent if and only
if they satisfy the same set of formulae.Comment: 18 page
The role of ethanol oxidation during carboxydotrophic growth of clostridium autoethanogenum
The WoodLjungdahl pathway is an ancient metabolic route used by acetogenic carboxydotrophs to convert CO into acetate, and some cases ethanol. When produced, ethanol is generally seen as an end product of acetogenic metabolism, but here we show that it acts as an important intermediate and co-substrate during carboxydotrophic growth of Clostridium autoethanogenum. Depending on CO availability, C. autoethanogenum is able to rapidly switch between ethanol production and utilization, hereby optimizing its carboxydotrophic growth. The importance of the aldehyde ferredoxin:oxidoreductase (AOR) route for ethanol production in carboxydotrophic acetogens is known; however, the role of the bifunctional alcohol dehydrogenase AdhE (AldAdh) route in ethanol metabolism remains largely unclear. We show that the mutant strain C. autoethanogenum adhE1a, lacking the Ald subunit of the main bifunctional aldehyde/alcohol dehydrogenase (AdhE, CAETHG\_3747), has poor ethanol oxidation capabilities, with a negative impact on biomass yield. This indicates that the AdhAld route plays a major role in ethanol oxidation during carboxydotrophic growth, enabling subsequent energy conservation via substrate-level phosphorylation using acetate kinase. Subsequent chemostat experiments with C. autoethanogenum show that the wild type, in contrast to adhE1a, is more resilient to sudden changes in CO supply and utilizes ethanol as a temporary storage for reduction equivalents and energy during CO-abundant conditions, reserving these stored assets for more CO-limited conditions. This shows that the direction of the ethanol metabolism is very dynamic during carboxydotrophic acetogenesis and opens new insights in the central metabolism of C. autoethanogenum and similar acetogens.info:eu-repo/semantics/publishedVersio
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