Quasi-Topological Field Theories in Two Dimensions as Soluble Models

We study a class of lattice field theories in two dimensions that includes gauge theories. Given a two dimensional orientable surface of genus $g$, the partition function $Z$ is defined for a triangulation consisting of $n$ triangles of area $\epsilon$. The reason these models are called quasi-topological is that $Z$ depends on $g$, $n$ and $\epsilon$ but not on the details of the triangulation. They are also soluble in the sense that the computation of their partition functions can be reduced to a soluble one dimensional problem. We show that the continuum limit is well defined if the model approaches a topological field theory in the zero area limit, i.e., $\epsilon \to 0$ with finite $n$. We also show that the universality classes of such quasi-topological lattice field theories can be easily classified. Yang-Mills and generalized Yang-Mills theories appear as particular examples of such continuum limits.Comment: 23 pages, 16 figures, uses psbox.te

Transformerless series active power filter to compensate voltage disturbances

This paper presents a transformerless topology of series active power filter with capability to protect sensitive loads against harmonics, sags, swells and unbalances of the power system voltages. The proposed topology is constituted by three isolated H-bridge with a voltage source at the DC side. The series active power filter has been studied with the help of PSIM (Power Simulation software) and simulation results are presented. A laboratory prototype is under development and experimental results are shown.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/EEA-EEL/104569/200

Single-phase series active conditioner active power flow in a harmonic free electrical system during sag and swell events

This paper presents a Single-Phase Active Conditioner, which primal function is regulate load voltage, thus protecting the most sensitive loads from sags, swells, flicker and voltage harmonics. It is constituted by two back-to-back H-bridge converters. One regulates load voltage, the other DC-link voltage. This paper will focus essentially on the active power flow during sag and swell events, in a harmonic free Electrical System. It is shown that, ideally, during a sag or swell event, the active power consumed from the AC mains, is the same that is delivered to the load. It also shows how this is achieved, by analyzing the working principle of the Single-Phase Series Active Converter, and, particularly, the crucial action of the DC link capacitor. The control strategy of the proposed custom power device is also presented in a brief form, for contextualization with the operating principle for the compensation of voltage variation events. Simulation results are presented, showing transient and steady state waveforms of the Single-phase Series Active Conditioner with a purely resistive load. The controller of Series Active Conditioner was implemented on a TMS320F2812F from Texas Instruments. Experimental results are also presented, and for better understanding of the active power flow in the Single-Phase Series Active Conditioner, the implemented electrical system has only a resistive load.Fundação para a Ciência e a Tecnologia (FCT

Simulations of a Current-Source Shunt Active Power Filter with Carrier-Based PWM and Periodic Sampling modulation techniques

Bruno Exposto, Helder Carneiro, J. G. Pinto, Carlos Couto, João L. Afonso, "Simulations of a current-source Shunt Active Power Filter with Carrier-Based PWM and Periodic Sampling Modulation Techniques" Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011), pp.1-8, 30 Aug. – 1 Sept., 2011.This paper presents a Shunt Active Power Filter that is built using a current-source inverter. The control of the Active Filter relies in the p-q Theory with the “Sinusoidal Currents at Source” algorithm implemented. The Active Power Filter was simulated using two modulation techniques: Periodic Sampling and Carrier-Based Pulse Width Modulation (CBPWM). To assess the performance of the Active Filter, the simulations were made using two different loads. The first load was a RL balanced load. The second was a non-linear load, namely a full bridge rectifier with a RL load in the DC side. These loads allowed determining the performance of the Active Filter when compensating current harmonics and power factor, using the two modulation techniques.This work is financed by FEDER Funds, through the Operational Programme for Competitiveness Factors – COMPETE, and by National Funds through FCT – Foundation for Science and Technology of Portugal, under the project PTDC/EEA-EEL/104569/2008

Wireless Connectivity of a Ground-and-Air Sensor Network

This paper shows that, when considering outdoor scenarios and wireless communications using the IEEE 802.11 protocol with dipole antennas, the ground reflection is a significant propagation mechanism. This way, the Two-Ray model for this environment allows predicting, with some accuracy, the received signal power. This study is relevant for the application in the communication between overflying Unmanned Aerial Vehicles (UAVs) and ground sensors. In the proposed Wireless Sensor Network (WSN) scenario, the UAVs must receive information from the environment, which is collected by sensors positioned on the ground, and need to maintain connectivity between them and the base station, in order to maintain the quality of service, while moving through the environment.Comment: 8 pages, 11 figure

Three Dimensional de Sitter Gravity and the Correspondence

Certain aspects of three dimensional asymptotically de Sitter spaces are studied, with emphasis on the mapping between gravity observables and the representation of the conformal symmetry of the boundary. In particular, we show that non-real conformal weights for the boundary theory correspond to space-times that have non-zero angular momentum. Some miscellaneous results on the role of the holonomies and isometry groups are also presented.Comment: 10 pages, 1 figure, uses epsf. Added references and a discussion on the (dis)similarities with previous work

Active Flexible Films for Food Packaging: A Review

This article belongs to the Special Issue Active and Intelligent Food Packaging Polymers.Active food packaging is a dynamic area where the scientific community and industry have been trying to find new strategies to produce innovative packaging that is economically viable and compatible with conventional production processes. The materials used to develop active packaging can be organized into scavenging and emitting materials, and based on organic and inorganic materials. However, the incorporation of these materials in polymer-based flexible packaging is not always straightforward. The challenges to be faced are mainly related to active agents' sensitivity to high temperatures or difficulties in dispersing them in the high viscosity polymer matrix. This review provides an overview of methodologies and processes used in the production of active packaging, particularly for the production of active flexible films at the industrial level. The direct incorporation of active agents in polymer films is presented, focusing on the processing conditions and their effect on the active agent, and final application of the packaging material. Moreover, the incorporation of active agents by coating technologies and supercritical impregnation are presented. Finally, the use of carriers to help the incorporation of active agents and several methodologies is discussed. This review aims to guide academic and industrial researchers in the development of active flexible packaging, namely in the selection of the materials, methodologies, and process conditions.Conducted under the project “MobFood-Mobilizing scientific and technological knowledge in response to the challenges of the agri-food market” (POCI-01-0247-FEDER-024524), by “Mob Food” Consortium, and financed by European Regional Development Fund (ERDF), through the Incentive System to Research and Technological development, within the Portugal2020 Competi tiveness and Internationalization Operational Program. IPC researchers acknowledge also funding by National Funds through FCT-Portuguese Foundation for Science and Technology, References UIDB/05256/2020 and UIDP/05256/2020.info:eu-repo/semantics/publishedVersio

Active flexible films for food packaging: a review

Active food packaging is a dynamic area where the scientific community and industry have been trying to find new strategies to produce innovative packaging that is economically viable and compatible with conventional production processes. The materials used to develop active packaging can be organized into scavenging and emitting materials, and based on organic and inorganic materials. However, the incorporation of these materials in polymer-based flexible packaging is not always straightforward. The challenges to be faced are mainly related to active agents’ sensitivity to high temperatures or difficulties in dispersing them in the high viscosity polymer matrix. This review provides an overview of methodologies and processes used in the production of active packaging, particularly for the production of active flexible films at the industrial level. The direct incorporation of active agents in polymer films is presented, focusing on the processing conditions and their effect on the active agent, and final application of the packaging material. Moreover, the incorporation of active agents by coating technologies and supercritical impregnation are presented. Finally, the use of carriers to help the incorporation of active agents and several methodologies is discussed. This review aims to guide academic and industrial researchers in the development of active flexible packaging, namely in the selection of the materials, methodologies, and process conditions.Financed by European Regional Development Fund (ERDF), through the Incentive System to Research and Technological development, within the Portugal2020 Competitiveness and Internationalization Operational Program. IPC researchers acknowledge also funding by National Funds through FCT-Portuguese Foundation for Science and Technology, References UIDB/05256/2020 and UIDP/05256/2020