Density Functional Theory and Molecular Dynamics Studies on Energetics and Kinetics for Electro-Active Polymers: PVDF and P(VDF-TrFE)

We use first principles methods to study static and dynamical mechanical properties of the ferroelectric polymer Poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoro ethylene (TrFE). We use density functional theory [within the generalized gradient approximation (DFT-GGA)] to calculate structures and energetics for various crystalline phases for PVDF and P(VDF-TrFE). We find that the lowest energy phase for PVDF is a non-polar crystal with a combination of trans (T) and gauche (G) bonds; in the case of the copolymer the role of the extra (bulkier) F atoms is to stabilize T bonds. This leads to the higher crystallinity and piezoelectricity observed experimentally. Using the MSXX first principles-based force field (FF) with molecular dynamics (MD), we find that the energy barrier necessary to nucleate a kink (gauche pairs separated by trans bonds) in an all-T crystal is much lower (14.9 kcal/mol) in P(VDF-TrFE) copolymer than in PVDF (24.8 kcal/mol). This correlates with the observation that the polar phase of the copolymer exhibits a solid-solid a transition to a non-polar phase under heating while PVDF directly melts. We also studied the mobility of an interface between a polar and non-polar phases under uniaxial stress; we find a lower threshold stress and a higher mobility in the copolymer as compared with PVDF. Finally, considering plastic deformation under applied shear, we find that the chains for P(VDF-TrFE) have a very low resistance to sliding, particularly along the chain direction. The atomistic characterization of these "unit mechanisms" provides essential input to mesoscopic or macroscopic models of electro-active polymers.Comment: 15 pages 9 figures Electro-active polyme

A look into the factor model black box: publication lags and the role of hard and soft data in forecasting GDP

We derive forecast weights and uncertainty measures for assessing the role of individual series in a dynamic factor model (DFM) to forecast euro area GDP from monthly indicators. The use of the Kalman filter allows us to deal with publication lags when calculating the above measures. We find that surveys and financial data contain important information beyond the monthly real activity measures for the GDP forecasts. However, this is discovered only, if their more timely publication is properly taken into account. Differences in publication lags play a very important role and should be considered in forecast evaluation. JEL Classification: E37, C53Dynamic Factor Models, filter weights, forecasting

FUBAR: Flow utility based routing

We present FUBAR, a system that reduces congestion and maximizes the utility of the entire network by installing new routes and changing the traffic load on existing ones. FUBAR works offline to periodically adjust the distribution of traffic on paths. It requires neither changes to end hosts nor precise prior knowledge of the traffic matrix. We demonstrate that even in the presence of traffic from all network devices to all other devices, FUBAR can optimize a real-world core-level network in a matter of minutes

Master of Science

thesisThe electrical induced polarization (EIP) method has been used in mineral exploration for over half a century, but its application was limited due to the relatively high cost involved and a requirement of using a galvanic source and receivers having a direct contact with the ground. In order to overcome these limitations, the magnetic induced polarization (MIP) method was introduced. However, interpretation of the MIP data in a complex three-dimensional (3D) environment represents a very challenging problem. In this thesis, a new method of interpretation of 3D MIP data was introduced based on the generalized effective medium theory of induced polarization (GEMTIP). The GEMTIP model was established to describe the induced polarization (IP) effect in complex heterogeneous rock samples. I have incorporated the GEMTIP model with the integral equation (IE) method to simulate the magnetic field caused by the IP effect. I have also developed an inversion algorithm based on the regularized conjugate gradient method. The inversion produces a 3D distribution of the four parameters of the GEMTIP model-matrix conductivity (σ0) (or DC resistivity ρ0= 1/σ0), fraction volume (f), time constant (t), and relaxation parameter (C). The developed methods and computer codes were tested on synthetic MIP data. I have also applied this new method for interpretation of the synthetic MIP data computer simulated for the real geological structure of the Silver Bell area in Arizona

Density functional theory and molecular dynamics studies of the energetics and kinetics of electroactive polymers: PVDF and P(VDF-TrFE)

We used first principles methods to study static and dynamical mechanical properties of the ferroelectric polymer poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoro ethylene (TrFE). We use density functional theory [within the generalized gradient approximation (DFT-GGA)] to calculate structure and energetics for various crystalline phases for PVDF and P(VDF-TrFE). We find that the lowest energy phase for PVDF is a nonpolar crystal with a combination of trans (T) and gauche (G) bonds; in the case of the copolymer the role of the extra (bulkier) F atoms is to stabilize T bonds. This leads to the higher crystallinity and piezoelectricity observed experimentally. Using the MSXX first principles-based force field (FF) with molecular dynamics (MD), we find that the energy barrier necessary to nucleate a kink (gauche pairs separated by trans bonds) in an all-T crystal is much lower (14.9 kcal/mol) in P(VDF-TrFE) copolymer than in PVDF (24.8 kcal/mol). This correlates with the observation that the polar phase of the copolymer exhibits a solid-solid transition to a nonpolar phase under heating while PVDF directly melts. We also studied the mobility of an interface between polar and nonpolar phases under uniaxial stress; we find a lower threshold stress and a higher mobility in the copolymer as compared with PVDF. Finally, considering plastic deformation under applied shear, we find that the chains for P(VDF-TrFE) have a very low resistance to sliding, particularly along the chain direction. The atomistic characterization of these "unit mechanisms" provides essential input to mesoscopic or macroscopic models of electro-active polymers

Sistema didático de uma unidade industrial de processos discretos

Os sistemas didáticos, que têm como principal objetivo a resolução de desafios semelhantes aos que existem no contexto real, são um recurso amplamente utilizado no contexto prático do ensino, permitindo simular o funcionamento de um sistema real na segurança de um laboratório.Esta dissertação é baseada no sistema didático de uma unidade industrial de processos discretos, existente no Laboratório de Automação Industrial no Departamento de Engenharia Eletrotécnica e de Computadores (DEEC) da Faculdade de Engenharia da Universidade do Porto (FEUP).Inicialmente é realizado um estudo de diferentes soluções de sistemas didáticos presentes no mercado e a forma como se podem dividir quanto à finalidade, tangibilidade e forma de controlo.Após o estudo das soluções existentes, é feita a análise das especificações e arquitetura do sistema didático, de forma a identificar pontos de melhoria a partir dos quais é proposta e implementada uma nova arquitetura. A dissertação termina com as conclusões obtidas a partir dos resultados da implementação

Instalación eléctrica de baja tensión y centro de transformación de una nave industrial

En este PFC se va a describir la Instalación eléctrica en baja tensión de una nave industrial dedicada a la fabricación de tornillos y tuercas. La instalación eléctrica constará de: - Instalación de alumbrado general tanto interior como exterior, de emergencia y de señalización. - Instalación de fuerza y tomas de corriente. - Centro de transformación de media a baja tensión. - Protección eléctrica de las líneas que alimentan todas las instalaciones. - Puestas a tierra del centro de transformación, y de la instalación eléctrica de la nave. - Corrección del factor de potencia del centro de transformación (en caso necesario).Ingeniería Técnica IndustrialIndustria Ingeniaritza Tekniko