Steady-State Control Reference and Token Conservation Laws in Continuous Petri Net Systems

This paper addresses several questions related to the control of timed continuous Petri nets under infinite server semantics. First, some results regarding equilibrium states and control actions are given. In particular, it is shown that the considered systems are piecewise linear, and for every linear subsystem the possible steady states are characterized. Second, optimal steady-state control is studied, a problem that surprisingly can be computed in polynomial time, when all transitions are controllable and the objective function is linear. Third, an interpretation of some controllability aspects in the framework of linear dynamic systems is presented. An interesting finding is that noncontrollable poles are zero valued.     

Comparative analysis of passive algorithms in adaptive control

Representative passive adaptive algorithms have been developed with a wide variety of applications. However, to the best of our knowledge, the attempt to unify or to compare them has not been clearly established in literature. In this article, we provide a passive adaptive framework which encompasses all those algorithms including the recently developed proportional‐integral (PI) adaptive scheme. A comparative analysis among performances of the passive algorithms is carried out by means of simulations considering the problem of passivity‐based adaptive tracking control of a simple pendulum. In addition, passivity property for PI algorithm is rigorously shown in case of linear parametrization. Copyright © 2013 John Wiley & Sons, Ltd.     

Going beyond energy intensity to understand the energy metabolism of nations: The case of Argentina

The link between energy consumption and economic growth has been widely studied in the economic literature. Understanding this relationship is important from both an environmental and a socio-economic point of view, as energy consumption is crucial to economic activity and human environmental impact. This relevance is even higher for developing countries, since energy consumption per unit of output varies through the phases of development, increasing from an agricultural stage to an industrial one and then decreasing for certain service based economies.In the Argentinean case, the relevance of energy consumption to economic development seems to be particularly important. While energy intensity seems to exhibit a U-Shaped curve from 1990 to 2003 decreasing slightly after that year, total energy consumption increases along the period of analysis. Why does this happen? How can we relate this result with the sustainability debate? All these questions are very important due to Argentinean hydrocarbons dependence and due to the recent reduction in oil and natural gas reserves, which can lead to a lack of security of supply.In this paper we study Argentinean energy consumption pattern for the period 1990–2007, to discuss current and future energy and economic sustainability. To this purpose, we developed a conventional analysis, studying energy intensity, and a non conventional analysis, using the Multi-Scale Integrated Analysis of Societal and Ecosystem Metabolism (MuSIASEM) accounting methodology. Both methodologies show that the development process followed by Argentina has not been good enough to assure sustainability in the long term. Instead of improving energy use, energy intensity has increased. The current composition of its energy mix, and the recent economic crisis in Argentina, as well as its development path, are some of the possible explanations.     

Synthesis and characterization of a titanium phosphate-tellurite glass for Faraday rotators

This work is focused on investigation of thermal, structural, optical, magnetic, and magneto-optical properties of novel titanium phosphate-tellurite glass applied as Faraday rotators. The glass belonging to the system 35Li₂O–10Al₂O₃–5TiO₂–45P₂O₅–5TeO₂ was prepared by a nonconventional wet route of raw materials processing, followed by melting-quenching-annealing steps. Some important physical properties of the investigated glass have been measured and calculated, providing knowledge related to glass compactness, electronic structure, glass forming capability, etc. XRD analysis evidenced an amorphous network structure of the investigated glass. The optical absorption in the Vis domain is mainly due to Ti³⁺ ions and Te₂ clusters formed during the glass melting process. A relatively low optical absorption is noticed over 600 nm that activates a significant Faraday magneto-optical effect. Photoluminescence bands in the blue, red, and infrared domains are observed, caused by Te₂ clusters formed during the glass melting process. The magnetization in dependency on applied magnetic field reveals a complex behavior of the glass, depending on temperature. Thus, it is found a ferromagnetic behavior up to 2000 Oe, a paramagnetic component up to 40 000 Oe, followed by a diamagnetic one over 40 000 Oe. Faraday rotation angle and Verdet constant values in the visible domain are correlated with the reduced TeO₂ content of the glass.     

Pictures in Dispute: Documentary photography in Sandinista Nicaragua

The need for political participation felt in the aftermath of the Cuban revolution, and the widespread mobilization of photography to political ends during this period intersected with postmodern theory in a global arena. While US-based critiques of the documentary genre have been duly analyzed in the relevant literature, related conversations taking place in Latin America have only been marginally explored. This article posits that so-called postmodern discourses in fact created the basis for a horizontal, transnational and multi-centered, rather than vertical (North?South) dynamic between these photographic communities. Through their commitment to politics, and to avant-garde aesthetics, documentary photographers performed gestures of cultural and visual appropriation, fitting their itinerant context. This article analyzes the work of Claudia Gordillo, taking as a case study Nicaragua during the 1980s.     

冷却水中的腐蚀和腐蚀控制

热交换器上的固体沉积作为热量剂导致了非常重要的困难，由于沉积会减少能量交换效率，因此，特别引起技术人员的兴趣。固体沉积具有复杂的结构，含有：方解石、磁铁矿、褐铁矿、纤铁矿和石英。报告了腐蚀产物的存在；进行了X-射线衍射研究。     

A simple strategy to generate light-responsive azobenzene-containing epoxy networks

Azobenzene containing epoxy networks are a class of photosensitive materials characterized by high thermal, optical and mechanical stability, promising for reversible optical storage applications. Here, we propose an encouraging two-step method to fabricate crosslinked coatings by simply reacting an amine-functionalized azobenzene and an epoxy resin in bulk for specified times to get soluble products (network precursors). Thin films based on these precursors were prepared, and thermally crosslinked in order to obtain high-T_g materials. The optical response of the materials was determined, both before and after crosslinking. In the case of the samples as prepared, the dynamic time response of the system is fast, as well as the relaxation of the photoinduced birefringence, as expected due to the high mobility of the chromophore. On the other hand, crosslinked systems have a slightly slower response, but higher values of remnant birefringence, providing stability of the photoinduced orientation, what makes them promising materials to use in optical storage applications. Besides, further analysis on the effect of temperature on the induced birefringence of the polymeric networks was also conducted to help optimization of material design. Finally, we had presented some preliminary investigations of surface relief grating recording in the obtained new materials.