Encontrado(s) 2243790 resultado(s)
Encontrada(s) 224379 página(s)
Encontrada(s) 224379 página(s)
- De Sousa Serrano, Laura
Des del seu origen a la primera meitat del segle XX, els plàstics han anat prenent cada cop més protagonisme a les nostres vides, generant en conseqüència cada cop més quantitat de residus plàstics arreu del món. Una de les principals problemàtiques que aquests presenten és la seva incapacitat de degradar-se, fet que provoca la seva acumulació a diferents medis i espais naturals. En vista d'aquesta problemàtica, avui en dia hi ha una forta tendència en invertir recursos en la recerca de nous polímers que generin un menor impacte mediambiental. Una nova important línia d'investigació és la dels biopolímers, que consisteixen en materials polimèrics sintetitzats a partir de matèries primes naturals, els quals són, generalment, degradables. En aquest treball s'ha presentat l'estudi de la degradació de dos tipus de polímers biodegradables: un policarbonat natural i un àcid polilàctic amb estructura estereocomplexa. L'estudi se centra en l'avaluació de la biodegradació per compostatge seguint la norma ISO 14855 durant un temps d'uns 40 dies. Per altra banda, s'ha estudiat la degradació hidrolítica del PLA estereocomplexe a temperatures diferents, amb la finalitat d'avaluar la resistència a l'aigua d'aquest grau de PLA. El seguiment de la biodegradació s'ha dut a terme mesurant la generació de CO2 en el procés de compostatge i la pèrdua de pes molecular en la degradació hidrolítica. El policarbonat natural ha mostrat capacitat de degradació després d'un període d'inducció de 20 dies, fins arribar a uns nivells de degradació entre el 27 i el 50%. L'àcid polilàctic PLA s'ha degradat un 43% i l'estereocomplex de PLA ha tingut un període d'inducció de 15 dies i s'ha descompost fins a un 29%. La degradació hidrolítica de l'estereocomplex de PLA s'ha dut a terme a tres temperatures (36, 58 i 80ºC). Els resultats indiquen que aquest polímer es degrada hidrolíticament a qualsevol temperatura, però a velocitats diferents en funció d'aquesta. D'acord amb la teoria d'Arrhenius, s'ha calculat que l'energia d'activació és de 95,0 kJ/mol, la qual és lleugerament superior a la determinada pel PLA convencional, que és de 82,2 kJ/mol. El resultat és coherent amb el que es pot esperar de la degradació hidrolítica d'un PLA altament cristal·lí contra un PLA normal (és a dir, Easc-PLA > EaPLA). El pressupost del treball s'ha estimat en 15.431 euros.
A framework for artificial data generation based on anatomical differences for electroencephalography-based brain-computer interfaces, Enhancing subject-independent classification by forcing anatomical invariance
- Rapp, Rachel Elizabeth
One of the major limitations of brain-computer interfaces (BCI) is the need for a long and tedious calibration period in order for a subject to become proficient with the system. A principal challenge in training a BCI classifier that should work without user-specific calibration is that the training set is not large enough to capture the spectrum of potential signals. In this thesis, a new method to reduce BCI calibration time is proposed. Since one cause for subject-to-subject variability is the anatomical differences between subjects, we aimed to generate artificial data which would resemble the signals obtained from a new subject with a different cortical anatomy. This would allow for a large expansion of the training set size. To generate the artificial data we begin by decomposing the original signals, localizing the most prominent sources and shifting their orientation relative to the cortex. New signals are then regenerated using different head models. Training a classifier on the enriched training set should result in better generalizability. Although inter-subject classification ultimately fell outside the scope of this thesis, we consider intra-subject classification as a starting point for consideration of the methods applied. This ultimately lays the foundation for a much greater field of research involving the use of artificial data generation to combat the calibration time issue for BCIs.
- Sánchez Sepúlveda, Mónica
- Fonseca, David
- Calvo Figueras, Xavier
- Navarro Delgado, Isidro
- Franquesa Sànchez, Jordi
- Redondo Domínguez, Ernesto
- Gener, Marc
How can we incorporate into our educational system the emerging technologies, new processes and new habits of society to improve public motivation, implication, and satisfaction in urban decision-making processes? New technology implementations in the teaching field largely extend to all types of levels and educational frameworks. However, these innovations require approval validation and evaluation by the final users. The premise is that the technology used in Virtual Reality (VR), is familiar to the Architecture students, which preview to work on specific parameters and outcome, and on the contrary, citizens with a profile not related to the field get more excited and perceive the technology as a more efficient tool. To prove this, we use a quantitative method to evaluate the satisfaction of citizens related and not related to the Architecture field. Using an interactive visualization process in a real environment, we obtained adequate feedback that allowed the optimization of this type of experiment in future iterations. The results show that the degree of satisfaction when using an advanced visualization technology was satisfactory with a differentiation between user’s profiles, Peer Reviewed
Noise-reversed stability of Turing patterns versus Hopf oscillations near codimension-two conditions
- Alonso Muñoz, Sergio
- Sagués Mestres, Francesc
Pattern formation induced by noise is a celebrated phenomenon in diverse reaction-diffusion systems. Here we report numerical simulations with the Lengyel-Epstein model for the chlorine dioxide-iodine-malonic acid reaction when perturbed with an external spatiotemporal stochastic forcing in the vicinity of the Hopf and Turing codimension-two bifurcation. Competition between Turing and Hopf modes gives rise to the generation of transient Turing patterns evolving to stationary global oscillations. This situation is reversed by the introduction of external fluctuations and Turing patterns become dominant in this case. The increase in the spatial coherence is found for intermediate noise intensity and small correlation length., Peer Reviewed
- Confalonieri, Federica
- Perego, Umberto
This work is devoted to the formulation of a new cohesive model for mixed-mode delamination. The model is based on a thermodynamically consistent isotropic damage formulation, with consideration of an internal friction mechanism that governs the interaction between normal and shear opening modes.
Macroscopic fe-simulation of residual stresses in thermo-mechanically processed steels considering phase transformation effects
- Behrens, B. A.
- Chugreev, A.
- Kock, C.
Residual stresses are an important issue as they affect both the manufacturing processes as well as the performance of the final parts. Taking into account the whole process chain of hot forming, the integrated heat treatment provided by a defined temperature profile for cooling of the parts offers a great potential for the targeted adjustment of the desired residual stress state. However, in addition to elastic, plastic and linear thermal strain components, the complex material phenomena arising from phase transformation effects of the polymorphic steels have to be considered in order to predict the residual stresses. These transformation strains account for the plastic deformation at the phase boundary between the emerging and the parent phase. In addition, they are strongly related to the transformation induced plasticity (TRIP) phenomena which depend on the stress state. The aim of this study is the investigation of TRIP effects and their impact on residual stresses regarding the typical hot forming steels 1.7225 (DIN: 42CrMo4) and 1.3505 (DIN: 100Cr6) by means of an experimental-numerical approach. The TRIP behaviour of the materials under consideration is integrated into an FE simulation model in the commercial software Simufact.forming for the purpose of residual stress prediction. The experimental thermo-mechanical investigations are carried out using a quenching and forming dilatometer. These experiments are numerically modelled by means of FEM which allows TRIP coefficients to be determined phasespecifically by numerical identification. For validation of the improved FE-model, an experimental thermo-mechanical reference process is considered, in which cylindrical specimens with an eccentric hole are hot formed and subsequently cooled by different temperature routes. Finally, the numerical model is validated by means of a comparison between residual stress states determined with X-ray diffraction and predicted residual stresses from the simulation.
- Prats Soler, Clara
- Alonso Muñoz, Sergio
- Álvarez Lacalle, Enrique
- Marchena Angos, Miquel
- López Codina, Daniel
- Català Sabaté, Martí
- Cardona Iglesias, Pere Joan
The present report aims to provide a comprehensive picture of the pandemic situation of COVID-19 in the EU countries, and to be able to foresee the situation in the next coming days. We employ an empirical model, verified with the evolution of the number of confirmed cases in previous countries where the epidemic is close to conclude, including all provinces of China. The model does not pretend to interpret the causes of the evolution of the cases but to permit the evaluation of the quality of control measures made in each state and a short-term prediction of trends. Note, however, that the effects of the measures’ control that start on a given day are not observed until approximately 7-10 days later. The model and predictions are based on two parameters that are daily fitted to available data: a: the velocity at which spreading specific rate slows down; the higher the value, the better the control. K: the final number of expected cumulated cases, which cannot be evaluated at the initial stages because growth is still exponential. We show an individual report with 8 graphs and a table with the short-term predictions for different countries and regions. We are adjusting the model to countries and regions with at least 4 days with more than 100 confirmed cases and a current load over 200 cases. The predicted period of a country depends on the number of datapoints over this 100 cases threshold, and is of 5 days for those that have reported more than 100 cumulated cases for 10 consecutive days or more. For short-term predictions, we assign higher weight to last 3 points in the fittings, so that changes are rapidly captured by the model. The whole methodology employed in the inform is explained in the last pages of this document. In addition to the individual reports, the reader will find an initial dashboard with a brief analysis of the situation in EU-EFTA-UK countries, some summary figures and tables as well as long-term predictions for some of them, when possible. These long-term predictions are evaluated without different weights to datapoints. We also discuss a specific issue every day., These reports are funded by the European Commission (DG CONNECT, LC-01485746) PJC and MC received funding from “la Caixa” Foundation (ID 100010434), under agreement LCF/PR/GN17/50300003; CP, DL, SA, MC, received funding from Ministerio de Ciencia, Innovación y Universidades and FEDER, with the project PGC2018-095456-B-I00
Sensitive thermal transitions of nanoscale polymer samples using the bimetallic effect: Application to ultra-thin polythiophene
- Ahumada Heredero, Óscar
- Pérez Madrigal, Maria del Mar
- Ramírez García, Jorge
- Curcó Cantarell, David
- Esteves, Carina
- Armelín Diggroc, Elaine Aparecida
- Luongo, Giovanni
- Puiggalí Bellalta, Jordi
- Alemán Llansó, Carlos
- Salvador Matar, Antonio
A sensitive nanocalorimetric technology based on microcantilever sensors is presented. The tech- nology, which combines very short response times with very small sample consumption, uses the bimetallic effect to detect thermal transitions. Specifically, abrupt variations in the Young’s modu- lus and the thermal expansion coefficient produced by temperature changes have been employed to detect thermodynamic transitions. The technology has been used to determine the glass transition of poly(3-thiophene methyl acetate), a soluble semiconducting polymer with different nanotechno- logical applications. The glass transition temperature determined using microcantilevers coated with ultra-thin films of mass = 10 − 13 gis5.2 ◦ C higher than that obtained using a conventional differential scanning calorimeter for bulk powder samples of mass = 5 × 10 − 3 g. Atomistic molecular dynamics simulations on models that represent the bulk powder and the ultra-thin films have been carried out to provide understanding and rationalization of this feature. Simulations indicate that the film-air in- terface plays a crucial role in films with very small thickness, affecting both the organization of the molecular chains and the response of the molecules against the temperature., Peer Reviewed
Ver en: http://hdl.handle.net/2117/20028
Low-complexity interference variance estimation methods for coded multicarrier systems: application to SFN
- Caus López, Marius
- Pérez Neira, Ana Isabel
- Renfors, Markku
For single-frequency network (SFN) transmission, the echoes coming from different transmitters are superimposed at the reception, giving rise to a frequency selective channel. Although multicarrier modulations lower the dispersion, the demodulated signal is sensitive to be degraded by inter-symbol interference (ISI) and inter-carrier interference (ICI). In view of this, we use channel coding in conjunction either with filter bank multicarrier (FBMC) modulation or with orthogonal frequency division multiplexing (OFDM). To deal with the loss of orthogonality, we have devised an interference-aware receiver that carries out a soft detection under the assumption that the residual interference plus noise (IN) term is Gaussian-distributed. To keep the complexity low, we propose to estimate the variance of the IN term by resorting to data-aided algorithms. Experimental results show that regardless of the method, FBMC provides a slightly better performance in terms of coded bit error rate than OFDM, while the spectral efficiency is increased when FBMC is considered., Peer Reviewed
Ver en: http://hdl.handle.net/2117/21817
- Hernández-Machado, Aurora
- Lacasta Palacio, Ana María
- Mayoral, E.
- Corvera Poiré, E.
A one-sided phase-field model is proposed to study the dynamics of unstable interfaces of Hele-Shaw flows in the high viscosity contrast regime. The corresponding macroscopic equations are obtained by means of an asymptotic expansion from the phase-field model. Numerical integrations of the phase-field model in a rectangular Hele-Shaw cell reproduce finger competition with the final evolution to a steady-state finger., Peer Reviewed
Ver en: http://hdl.handle.net/2117/2517