Construction of stability multipliers for non-linear feedback systems

This paper is concerned with the analysis of the absolute stability of a non-linear autonomous system which consists of a single non-linearity belonging to a particular class, in an otherwise linear feedback loop. It is motivated from the earlier Popovlike frequency-domain criteria using the ' multiplier ' eoncept and involves the construction of ' stability multipliers' with prescribed phase characteristics. A few computer-based methods by which this problem can be solved are indicated and it is shown that this constitutes a stop-by-step procedure for testing the stability properties of a given system.

Stability of Switched Feedback Time-Varying Dynamic Systems Based on the Properties of the Gap Metric for Operators

The stabilization of dynamic switched control systems is focused on and based on an operator-based formulation. It is assumed that the controlled object and the controller are described by sequences of closed operator pairs (L, C) on a Hilbert space H of the input and output spaces and it is related to the existence of the inverse of the resulting input-output operator being admissible and bounded. The technical mechanism addressed to get the results is the appropriate use of the fact that closed operators being sufficiently close to bounded operators, in terms of the gap metric, are also bounded. That philosophy is followed for the operators describing the input-output relations in switched feedback control systems so as to guarantee the closed-loop stabilization.

Zero miss distance guidance using feedforward and periodic control

There have been attempts at obtaining robust guidance laws to ensure zero miss distance (ZMD) for interceptors with parametric uncertainties. All these laws require the plant to be of minimum phase type to enable the overall guidance loop transfer function to satisfy strict positive realness (SPR). The SPR property implies absolute stability of the closed loop system, and has been shown in the literature to lead to ZMD because it avoids saturation of lateral acceleration. In these works higher order interceptors are reduced to lower order equivalent models for which control laws are designed to ensure ZMD. However, it has also been shown that when the original system with right half plane (RHP) zeros is considered, the resulting miss distances, using such strategies, can be quite high. In this paper, an alternative approach using the circle criterion establishes the conditions for absolute stability of the guidance loop and relaxes the conservative nature of some earlier results arising from assumption of in�nite engagement time. Further, a feedforward scheme in conjunction with a lead-lag compensator is used as one control strategy while a generalized sampled hold function is used as a second strategy, to shift the RHP transmission zeros, thereby achieving ZMD. It is observed that merely shifting the RHP zero(s) to the left half plane reduces miss distances signi�cantly even when no additional controllers are used to ensure SPR conditions.

Charge and color breaking constraints in MSSM after the Higgs discovery at LHC

We revisit the constraints on the parameter space of the Minimal Supersymmetric Standard Model (MSSM), from charge and color breaking minima in the light of information on the Higgs from the LHC so far. We study the behavior of the scalar potential keeping two light sfermion fields along with the Higgs in the pMSSM framework and analyze the stability of the vacuum. We find that for lightest stops a parts per thousand(2) 1 TeV and small mu a parts per thousand(2) 500 GeV, the absolute stability of the potential can be attained only for . The bounds become stronger for larger values of the mu parameter. Note that this is approximately the value of Xt which maximizes the Higgs mass. Our bounds on the low scale MSSM parameters are more stringent than those reported earlier in literature. We reanalyze the stau sector as well, keeping both staus. We study the connections between the observed Higgs rates and vacuum (meta)stability. We show how a precision study of the ratio of signal strengths, (mu (gamma gamma) /mu (ZZ) ) can shed further light.

On Bounded Strictly Positive Operators of Closed Range and Some Applications to Asymptotic Hyperstability of Dynamic Systems

The problem discussed is the stability of two input-output feedforward and feedback relations, under an integral-type constraint defining an admissible class of feedback controllers. Sufficiency-type conditions are given for the positive, bounded and of closed range feed-forward operator to be strictly positive and then boundedly invertible, with its existing inverse being also a strictly positive operator. The general formalism is first established and the linked to properties of some typical contractive and pseudocontractive mappings while some real-world applications and links of the above formalism to asymptotic hyperstability of dynamic systems are discussed later on.

对流扩散方程的绝对稳定高阶中心差分格式

将作者提出的数值摄动算法改进为区分离散单元内上游和下游并分别对通量进行高精度重构的双重数值摄动算法,与原(单重)摄动算法相比,双重摄动算法既提高了格式精度又明显扩大了格式的稳定域范围,利用双重摄动算法,即分别利用上游和下游基点变量的摄动重构将高阶流体力学关系及迎风机制耦合进二阶中心格式之中,由此构建了对流扩散方程的对网格Reynolds数的任意值均稳定(绝对稳定)高精度(四阶和八阶精度)三基点中心TVD差分格式,通过解析分析以及3个算例计算证实了构建格式的优良性能;3个算例包括一维线性、非线性(Burgers方程)和二维变系数对流扩散方程,数值计算表明:构建的格式在粗网格下不振荡,构建格式在粗网格时的最大误差L∞和均方误差L2与二阶中心格式在细网格时的相应误差一致,对线性方程,构建格式在细网格下可达到L2精度阶

Le soutien maternel à l’autonomie : stabilité et relation avec le développement des fonctions exécutives à l'âge préscolaire

Bien qu’il y ait de plus en plus d’études sur le soutien maternel à l’autonomie, de nombreuses questions restent à éclaircir dans le domaine. Notamment, on en sait très peu sur ses relations avec le développement cognitif de l’enfant, sa stabilité temporelle et les antécédents de celle-ci. La thèse est composée de trois articles empiriques. Le premier explore le rôle médiateur du langage dans la relation entre le soutien maternel à l'autonomie et les fonctions exécutives de l'enfant. Le deuxième examine la stabilité relative et absolue du soutien maternel à l'autonomie entre la petite enfance et l’âge préscolaire en fonction des représentations d'attachement de la mère, des évènements de vie stressants et du sexe de l'enfant. Le troisième article se penche sur le rôle du soutien maternel à l’autonomie mesuré à la petite enfance et à l’âge préscolaire dans la prédiction des fonctions exécutives de l’enfant, ainsi que sur l’impact de différents patrons de stabilité du soutien maternel à l’autonomie sur les fonctions exécutives. 70 dyades mère-enfant ont participé à 5 visites à domicile. Lorsque l’enfant était âgé de 7-8 mois, les représentations d’attachement de la mère ont été mesurées à l’aide de l’entrevue d’attachement à l’âge adulte (George, Kaplan, & Main, 1996). Le soutien maternel à l’autonomie a été mesuré à 15 mois et à 3 ans à l’aide du système de codification de Whipple, Bernier, et Mageau (2011). Les évènements de vie stressants ont été mesurés à 3 reprises entre l’âge de 15 mois et 3 ans à l’aide de l’inventaire des expériences de vie (Sarason, Johnson, & Siegel, 1978). À 2 ans, le langage de l’enfant a été évalué à l’aide des inventaires MacArthur du développement de la communication (Dionne, Tremblay, Boivin, Laplante, & Pérusse, 2003). Les fonctions exécutives de l’enfant ont quant à elles été mesurées à l’âge de 3 ans à l’aide d’une batterie de tâches (Carlson, 2005). Les résultats du premier article indiquent que le langage de l’enfant joue un rôle médiateur dans la relation entre le soutien maternel à l’autonomie et une composante des fonctions exécutives de l’enfant, l’inhibition volontaire. Les résultats du deuxième article démontrent que le soutien maternel à l’autonomie est stable de façon relative, mais non absolue. Les résultats démontrent aussi que les mères qui ont une fille, qui ont vécu peu d’évènements de vie stressants ou qui ont des représentations d’attachement sécurisées sont plus stables dans leur degré de soutien à l’autonomie. Le troisième article démontre d’abord que la moyenne de soutien maternel à l’autonomie entre 15 mois et 3 ans est un prédicteur plus efficace des fonctions exécutives de l’enfant que ne l’est le soutien à l’autonomie à 15 mois ou à 3 ans pris séparément. De plus, les enfants dont les mères conservent un degré élevé de soutien à l’autonomie entre 15 mois et 3 ans performent mieux aux tâches d’inhibition que les enfants dont les mères conservent un faible degré de soutien à l’autonomie. Les résultats présentés dans les articles sont discutés ainsi que leurs implications.

Uniform estimates of attracting sets of extended Lurie systems using LMIs

This research presents a systematic procedure to obtain estimates, via extended Lyapunov functions, of attracting sets of a class of nonlinear systems, as well as an estimate of their stability regions. The considered class of nonlinear systems, called in this note the extended Lurie system, consists of nonlinear systems like those of the Lurie problem where one of the nonlinear functions can violate the sector conditions of the Lurie problem around the origin. In case of nonautonomous systems the concept of absolute stability is extended and uniform estimates of the attracting set are obtained. Two classical nonlinear systems, the forced duffing equation and the Van der Pol system, are analyzed with the proposed procedure.

Self-bound interacting QCD matter in compact stars

The quark gluon plasma (QGP) at zero temperature and high baryon number is a system that may be present inside compact stars. It is quite possible that this cold QGP shares some relevant features with the hot QGP observed in heavy ion collisions, being also a strongly interacting system. In a previous work we have derived from the QCD Lagrangian an equation of state (EOS) for the cold QGP, which can be considered an improved version of the MIT bag-model EOS. Compared to the latter, our EOS reaches higher values of the pressure at comparable baryon densities. This feature is due to perturbative corrections and also to nonperturbative effects. Here we apply this EOS to the study of neutron stars, discussing the absolute stability of quark matter and computing the mass-radius relation for self-bound (strange) stars. The maximum masses of the sequences exceed two solar masses, in agreement with the recently measured values of the mass of the pulsar PSR J1614-2230, and the corresponding radii of around 10-11 km.

Nonlinear constrained and saturated control of power electronics and electromechanical systems

Power electronic converters are extensively adopted for the solution of timely issues, such as power quality improvement in industrial plants, energy management in hybrid electrical systems, and control of electrical generators for renewables. Beside nonlinearity, this systems are typically characterized by hard constraints on the control inputs, and sometimes the state variables. In this respect, control laws able to handle input saturation are crucial to formally characterize the systems stability and performance properties. From a practical viewpoint, a proper saturation management allows to extend the systems transient and steady-state operating ranges, improving their reliability and availability. The main topic of this thesis concern saturated control methodologies, based on modern approaches, applied to power electronics and electromechanical systems. The pursued objective is to provide formal results under any saturation scenario, overcoming the drawbacks of the classic solution commonly applied to cope with saturation of power converters, and enhancing performance. For this purpose two main approaches are exploited and extended to deal with power electronic applications: modern anti-windup strategies, providing formal results and systematic design rules for the anti-windup compensator, devoted to handle control saturation, and “one step” saturated feedback design techniques, relying on a suitable characterization of the saturation nonlinearity and less conservative extensions of standard absolute stability theory results. The first part of the thesis is devoted to present and develop a novel general anti-windup scheme, which is then specifically applied to a class of power converters adopted for power quality enhancement in industrial plants. In the second part a polytopic differential inclusion representation of saturation nonlinearity is presented and extended to deal with a class of multiple input power converters, used to manage hybrid electrical energy sources. The third part regards adaptive observers design for robust estimation of the parameters required for high performance control of power systems.

On stable uniqueness in linear semi-infinite optimization

This paper is intended to provide conditions for the stability of the strong uniqueness of the optimal solution of a given linear semi-infinite optimization (LSIO) problem, in the sense of maintaining the strong uniqueness property under sufficiently small perturbations of all the data. We consider LSIO problems such that the family of gradients of all the constraints is unbounded, extending earlier results of Nürnberger for continuous LSIO problems, and of Helbig and Todorov for LSIO problems with bounded set of gradients. To do this we characterize the absolutely (affinely) stable problems, i.e., those LSIO problems whose feasible set (its affine hull, respectively) remains constant under sufficiently small perturbations.

Acontecimentos Traumáticos, Sentimentos de Vergonha na Relação com os Sintomas Depressivos na Adolescência: estudo longitudinal

Introdução: As experiências adversas na infância, tal como a exposição a acontecimentos traumáticos e vivências de vergonha, podem ter um contributo importante na vida dos adolescentes moldando a forma estes se percecionam a si próprios e aos outros, e como lidam com as adversidades, podendo aumentar a sua vulnerabilidade para desenvolver uma perturbação depressiva. Este estudo, de desenho longitudinal, consistiu em estudar os factores preditores (acontecimentos de vida traumáticos e sentimentos de vergonha) no desenvolvimento de psicopatologia depressiva a seis meses. Método: A amostra é constituída por 325 adolescentes, com idades compreendidas entre os 12 e os 18 anos a frequentar o 3º ciclo do ensino básico e ensino secundário. Para o estudo das variáveis referidas, foram utilizados os seguintes instrumentos de medida: o Child Depression Inventory, o Childhood Trauma Questionaire e a Escala de Vergonha Externa. Resultados: Os resultados obtidos relativamente à estabilidade absoluta das variáveis demonstram diferenças significativas entre os valores médios do 1ºmomento de avaliação e do 2º momento de avaliação (após 6 meses) para a variável vergonha. Ao longo do estudo, verificou-se uma associação positiva entre as variáveis relacionadas com o trauma e os sentimentos de vergonha avaliados no primeiro tempo (T1) e a variável sintomas depressivos (T2). O modelo de regressão linear múltipla, explicou 63% da variância dos sintomas depressivos no tempo 2, mostrando que o facto de pertencer ao sexo feminino, experienciar mais vivências de vergonha, e mais experiências traumáticas de abuso afetivo, abuso sexual e de negligência emocional permitem predizer mais sintomas depressivos na adolescência. Conclusão: Podemos concluir com a presente investigação, que o impacto de acontecimentos traumáticos, do tipo abuso/negligência, bem como de sentimentos de vergonha durante a fase da adolescência pode ser nocivo para o desenvolvimento harmonioso posterior, nomeadamente no desenvolvimento de sintomatologia depressiva. / Introduction: The adverse experiences in childhood, such as an exhibition of traumatic events and experiences of sham can have important contribution in teenager’s life shaping the way they perceive themselves and the others and how they deal with adversity, increasing their vulnerability to develop a depressive disorder. This study, longitudinal design, it was consisted in study of the predictive factors (traumatic life events and feelings of shame) in the development of depressive psychopathology in six months. Method: The sample consisted of 325 adolescents aged between 12 and 18 years attending the 3rd cycle of basic education and secondary education. To the study of the variables mentioned, the following measuring instruments were used: the Child Depression Inventory, the Childhood Trauma Questionnaire and External Shame Scale. Results: The results obtained regarding the absolute stability of the variables showed significant differences between the mean values of the evaluation 1st moment and 2nd moment of evaluation (after 6 months) for the variable shame. Throughout the study, there was a positive association between variables related to the trauma and feelings of shame evaluated at the first time (T1) and the variable depressive symptoms (T2). The multiple linear regression model explained 63% of variance in depressive symptoms at time 2 , showing that the fact of being female experience more shame experiences, and most traumatic experiences of emotional abuse, sexual abuse and emotional neglect permit predict more depressive symptoms in adolescence. Conclusion: We can conclude with this research, that the impact of traumatic events, the type abuse/neglect, as well as feelings of shame during adolescence can be harmful to the subsequent harmonious development, including the development of depressive symptoms.

El despido ineficaz en la legislación ecuatoriana

La publicación de una nueva ley, trae consigo la derogatoria total o parcial de otra ley y con ello, la imperiosa necesidad de conocer aquella reforma que cambia la realidad jurídica respecto de la materia que rige. Tal es el caso de la Ley Orgánica de Justicia Laboral y Reconocimiento del Trabajo en el Hogar, publicada en abril de 2015, que modificó el Código de Trabajo y la Ley de Seguridad Social, siendo uno de los temas más relevantes de esta reforma, el despido ineficaz. El tema de estabilidad laboral absoluta en Ecuador, era únicamente una ilusión para los trabajadores, y a palabras de un gran catedrático de la Facultad de Jurisprudencia de la Universidad de Cuenca, Doctor Jorge Morales, la estabilidad absoluta era “simples mariposas amarillas”; sin embargo, desde abril del 2015, la estabilidad absoluta pasó de la teoría a la praxis, aunque únicamente para un grupo mínimo de trabajadores, representantes sindicales y mujeres embarazadas o asociadas a su condición de maternidad;debido que, por su condición de vulnerabilidad en el marco laboral, la Reforma transformala estabilidad relativa manifestada en el despido intempestivo de estos trabajadores en ineficaz. “La ley, una vez publicada se presume conocida por todos y no podrá alegarse ignorancia por ninguna persona”, todos los ciudadanos dentro de la circunscripción para la cual rige la nueva norma, tenemos la obligación de informarnos sobre tal, siendo este, el motivo y objetivo principal de la presente investigación, otorgar a la ciudadanía un análisis profundo de la reforma laboral precisamente sobre las disposiciones que regulan la aplicación, alcance, causas y efectos del despido ineficaz.