Mimetic Finite Difference methods for Hamiltonian wave equations in 2D

In this paper we consider the numerical solution of the Hamiltonian wave equation in two spatial dimension. We use the Mimetic Finite Difference (MFD) method to approximate the continuous problem combined with a symplectic integration in time to integrate the semi-discrete Hamiltonian system. The main characteristic of MFD methods, when applied to stationary problems, is to mimic important properties of the continuous system. This approach, associated with a symplectic method for the time integration yields a full numerical procedure suitable to integrate Hamiltonian problems. A complete theoretical analysis of the method and some numerical simulations are developed in the paper.Comment: 26 pages, 8 figure

Holographic Relaxation of Finite Size Isolated Quantum Systems

We study holographically the out of equilibrium dynamics of a finite size closed quantum system in 2+1 dimensions, modelled by the collapse of a shell of a massless scalar field in AdS4. In global coordinates there exists a variety of evolutions towards final black hole formation which we relate with different patterns of relaxation in the dual field theory. For large scalar initial data rapid thermalization is achieved as a priori expected. Interesting phenomena appear for small enough amplitudes. Such shells do not generate a black hole by direct collapse, but quite generically an apparent horizon emerges after enough bounces off the AdS boundary. We relate this bulk evolution with relaxation processes at strong coupling which delay in reaching an ergodic stage. Besides the dynamics of bulk fields, we monitor the entanglement entropy, finding that it oscillates quasi-periodically before final equilibration. The radial position of the traveling shell is brought into correspondence with the evolution of the entanglement pattern in the dual field theory. The entanglement entropy is not only able to portrait the streaming of entangled excitations, but it is also a useful probe of interaction effects.Comment: 37 pages, 27 figure

From the bitterness of lemons to the sweet taste of lemonade: three essays in entrepreneurship

To critically evaluate the constraints faced by entrepreneurs, scholars have lean on two fundamental research questions. First, why doesn’t everyone who pursues his/her entrepreneurial aspirations actually succeed? Second, what are the most effective strategies entrepreneurs lean on to manage their ventures in such turbulent environments? Answering to the first question provides knowledge about how entrepreneurs react to constraints and what fuels/inhibits their behavior in the face of adversity. Furthermore, getting knowledge about how entrepreneurs act, disentangles the nuances of their activity and helps to explain what management practices foster and/or deters the development of a new business. In three studies, using different samples and methodologies, we highlight the importance of understanding the effect of constraints on entrepreneurial behavior, as well as the implications that the strategies used to manage such demands have for the venture development. Our findings deliver contributions for both research and practice. For scholars, this research provides a more granular view about the impact of constraints in entrepreneurial behavior. For entrepreneurs, we provide evidence about the effectiveness of some management practices for venture high-performance. Our findings also help policy makers to elaborate more effective propositions to stimulate entrepreneurial activity

Interacting fermions and domain wall defects in 2+1 dimensions

We consider a Dirac field in 2+1 dimensions with a domain wall like defect in its mass, minimally coupled to a dynamical Abelian vector field. The mass of the fermionic field is assumed to have just one linear domain wall, which is externally fixed and unaffected by the dynamics. We show that, under some general conditions on the parameters, the localized zero modes predicted by the Callan and Harvey mechanism are stable under the electromagnetic interaction of the fermions

Métodos de alimentación alternativa para recién-nacidos prematuros

OBJECTIVE: To present a literature review about the use of glass/cup as an alternative method of feeding premature newborns and to identify if there is a consensus on its indication for this population. DATA SOURCE: A narrative review of the literature. Articles were selected from Medline, Lilacs, SciELO, and Cochrane databases, regardless of year, using the following specific key-words: feeding, premature newborn, breastfeeding, feeding methods. DATA SYNTHESIS: Although some studies showed that feeding premature and term newborns using the glass/cup is safe and efficient, most of them did not apply an objective evaluation of the swallowing to identify the effect of the method in this population. CONCLUSIONS: There is no consensus in the literature about feeding premature newborn infants by glass/cup. Controlled studies should be conducted in order to evaluate risks and benefits of alternative feeding methods in preterm newborn infants.OBJETIVO: Presentar revisión de literatura sobre el uso de vaso/taza como método alternativo de alimentación para recién-nacidos prematuros y verificar si hay consenso sobre su indicación para esta población. FUENTES DE DATOS: Revisión de literatura narrativa, habiendo sido seleccionados artículos en las bases de datos Medline, Lilacs, SciELO y Cochrane, independientemente del año, usando descriptores específicos: alimentación artificial, recién-nacido prematuro, lactancia materna, métodos de alimentación. SÍNTESIS DE LOS DATOS: Aunque algunos estudios afirmen que el método vaso/taza es eficaz y seguro para alimentar a recién-nacidos pre-término y a término, tales estudios no evalúan de modo objetivo el efecto del método sobre la deglución de estos pacientes. CONCLUSIONES: Se verificó que no hay consenso en la literatura respecto a la complementación de la alimentación de recién-nacidos prematuros mediante vaso/taza. Se debe realizar estudios controlados con la finalidad de rever riesgos y beneficios del uso de métodos alternativos en la alimentación del recién-nacido prematuro.OBJETIVO: Apresentar revisão de literatura sobre o uso do copo/xícara como método alternativo de alimentação para recém-nascidos prematuros e verificar se há consenso sobre sua indicação para essa população. FONTES DE DADOS: Revisão de literatura narrativa, tendo sido selecionados artigos nas bases de dados Medline, Lilacs, SciELO e Cochrane, independentemente do ano, usando descritores específicos: alimentação artificial, recém-nascido prematuro, aleitamento materno, métodos de alimentação. SÍNTESE DOS DADOS: Apesar de alguns estudos afirmarem que o método do copo/xícara é eficaz e seguro para alimentar recém-nascidos pré-termo e a termo, tais estudos não avaliam de forma objetiva o efeito do método sobre a deglutição desses pacientes. CONCLUSÕES: Verificou-se não haver consenso na literatura quanto à complementação da alimentação de recém-nascidos prematuros por meio do copo/xícara. Estudos controlados devem ser realizados com a finalidade de rever riscos e benefícios do uso de métodos alternativos na alimentação do recém-nascido prematuro.Universidade Federal de São Paulo (UNIFESP)Universidade Estadual Paulista Júlio de Mesquita Filho Departamento de FonoaudiologiaUNIFESPSciEL