A Comparison of Petri Net Semantics under the Collective Token Philosophy

In recent years, several semantics for place/transition Petri nets have been proposed that adopt the collective token philosophy. We investigate distinctions and similarities between three such models, namely configuration structures, concurrent transition systems, and (strictly) symmetric (strict) monoidal categories. We use the notion of adjunction to express each connection. We also present a purely logical description of the collective token interpretation of net behaviours in terms of theories and theory morphisms in partial membership equational logic

Two Algebraic Process Semantics for Contextual Nets

We show that the so-called 'Petri nets are monoids' approach initiated by Meseguer and Montanari can be extended from ordinary place/transition Petri nets to contextual nets by considering suitable non-free monoids of places. The algebraic characterizations of net concurrent computations we provide cover both the collective and the individual token philosophy, uniformly along the two interpretations, and coincide with the classical proposals for place/transition Petri nets in the absence of read-arcs

State space c-reductions for concurrent systems in rewriting logic

We present c-reductions, a state space reduction technique. The rough idea is to exploit some equivalence relation on states (possibly capturing system regularities) that preserves behavioral properties, and explore the induced quotient system. This is done by means of a canonizer function, which maps each state into a (non necessarily unique) canonical representative of its equivalence class. The approach exploits the expressiveness of rewriting logic and its realization in Maude to enjoy several advantages over similar approaches: exibility and simplicity in the definition of the reductions (supporting not only traditional symmetry reductions, but also name reuse and name abstraction); reasoning support for checking and proving correctness of the reductions; and automatization of the reduction infrastructure via Maude's meta-programming features. The approach has been validated over a set of representative case studies, exhibiting comparable results with respect to other tools

On the galloping instability of two-dimensional bodies having elliptical cross sections.

Galloping, also known as Den Hartog instability, is the large amplitude, low frequency oscillation of a structure in the direction transverse to the mean wind direction. It normally appears in the case of bodies with small stiffness and structural damping, when they are placed in a flow provided the incident velocity is high enough. Galloping depends on the slope of the lift coefficient versus angle of attack curve, which must be negative. Generally speaking this implies that the body is stalled after boundary layer separation, which, as it is known in non-wedged bodies, is a Reynolds number dependent phenomenon. Wind tunnel experiments have been conducted aiming at establishing the characteristics of the galloping motion of elliptical cross-section bodies when subjected to a uniform flow, the angles of attack ranging from 0° to 90°. The results have been summarized in stability maps, both in the angle of attack versus relative thickness and in the angle of attack versus Reynolds number planes, where galloping instability regions are identified

An experimental study of the breakage of liquid bridges at stability limit of minimum volume

An experimental apparatus to study the breaking process of axisymmetric liquid bridges has been developed, and the breaking sequences of a large number of liquid bridge configurations at minimum-volume stability limit have been analyzed. Experimental results show that very close to the breaking moment the neck radius of the liquid bridge varies as t1/3, where t is the time to breakage, irrespective of the value of the distance between the solid disks that support the liquid column

Growth and formation of inverse GaP and InP opals

Opals consist of an ordered array of SiO2 spheres. This leads to a modulation of the refractive index and hence photonic stop bands behaviour over the visible/IR range of the electro-magnetic spectrum. The exact position of the stop bands depends on the size of the silica spheres. However, the refractive index contrast between the SiO2 spheres and air spaces is not great enough to open up a full photonic band gap (PBG), only the pseudogap. To increase the contrast the air spaces are filled with a material of high refractive index such as InP or GaP. To further increase the contrast the SiO2 is removed leaving a III-V framework as the inverse opal structure. By use of MOCVD we have been able to infill opals with InP and GaP to such a level that has supported the inversion of the composite forming a structure of air holes within a III-V lattice. XRD and Raman confirmed the quality of the III-V infill, while the extent of the infill was studied by SEM and reflectance measurements

Estudio de la nueva torre de control del aeropuerto de Tenerife-Norte

Aunque el criterio fundamental de diseño de la torre de control de un aeropuerto es obviamente que esta instalación satisfaga los requisitos funcionales propios del control del tráfico aéreo (suministrar los servicios de control de tránsito aéreo a tránsito de aeródromo), el hecho de que este elemento de la arquitectura aeroporLuaria deba ocupar, precisamente debido a los req ui sitos específicos de vis ibilidad, un lugar destacado dentro del complejo aeroportuario, ha ocasionado que con el tiempo en las construcciones se hayan convertido en elementos singulares y emblemáticos, diseñados tanto para cumplir la batería de requisitos operativos, constructivos y de equipamiento que asegurcn el cumplimiento de su misión, como para, en muchos casos, servir de signo identificador de l aeropuerto. Todo ello ha ocasionado que en los últimos años se haya vertido mucha imaginación en el diseño de tales torres de control, pudiéndose encontrar en los aeropuertos las torres de control de las más variadas formas y aspectos

On linear instability mechanisms in incompressible open cavity flow

A theoretical study of linear global instability of incompressible flow over a rectangular spanwise-periodic open cavity in an unconfined domain is presented. Comparisons with the limited number of results available in the literature are shown. Subsequently, the parameter space is scanned in a systematic manner, varying Reynolds number, incoming boundary-layer thickness and length-to-depth aspect ratio. This permits documenting the neutral curves and leading eigenmode characteristics of this flow. Correlations constructed using the results obtained collapse all available theoretical data on the three-dimensional instabilities

Stability of liquid bridges between twisted elliptical disks

The influence in the stability of long liquid bridges supported between two elliptical-shaped disks of their main axis relative orientation is investigated. A numerical continuation method capable of finding equilibrium shapes, both stable and unstable, is used to calculate a series of equilibrium shapes supported by disks of increasing eccentricity for different relative orientation of the disks axis. The stable or unstable character of each of the shapes is calculated to determine the position of the stability limit and its characte

Tales effect in real and perceived aquatic: Competence in preschoolers

Pese a existir un interés creciente en los estudios por la renovación de los contenidos lúdicos tradicionales, así como en la utilización del medio acuático como recurso educativo, en la actualidad existen muy pocas investigaciones que relacionen ambos aspectos. Por ello, el objetivo de este estudio cuasi-experimental fue comprobar el efecto de los cuentos motores acuáticos sobre la competencia motriz percibida y la capacidad motriz real. Los participantes fueron 16 infantes de 3 a 5 años a los que se le midió la competencia motriz real y percibida acuática. Tras una prueba no paramétrica los resultados mostraron que la administración del programa de cuentos motores contribuyó de manera positiva y significativa sobre la competencia motriz percibida del grupo experimental. Se discuten los resultados en pro de incluir en los programas educativos acuáticos los cuentos motores de cara a fomentar el autoconcepto infantilEven though a growing interest exists in the study of the renewal of the traditional ‘play’ curriculum, as well as the utilization of the aquatic medium as an educational resource, at present, very few studies link both areas. For this reason, the objective of this quasi-experimental study was to confirm the effect of aquatic motor tales over perceived motor competency and real motor capacity. We studied 16 preschoolers among 3 to 5 years of age for their real and perceived aquatic motor competency. After a non-parametric test was administered, the results show that administration of aquatic mobility stories contributed positively and significantly on the perceived motor competence of the experimental group. The results are discussed in favor of inclusion of aquatic educational programs in order to promote the self-esteem of this age-group