2,019 research outputs found
An innovative method for highly-efficient fabrication of carbon fiber precursors via acrylonitrile emulsion copolymerization coupled to a chemical oscillator
No full textA new synthetic protocol to produce the carbon fiber precursor polyacrylonitrile (PAN) and its block copolymers with polyethylene glycol (PEG) is proposed here. The constant flux of radical species produced at low concentrations during the oscillating Belousov-Zhabotinsky (BZ) reaction was properly exploited to initiate the radical polymerization reaction. Compared with conventional methods, this oscillating initiation decreases the probability of chain termination, thus favouring the production of high molecular weight polymers, and it does not require an inert atmosphere and elevated temperatures to be produced. The solubility of the polymeric chains during the polymerization reaction was improved by adding the anionic micelle-forming surfactant sodium dodecyl sulphate (SDS). Following the initiation step, short oligomer chains are able to overcome the micellar
interface, thereby reaching a favourable environment for the increase of the polymeric chains, thus strongly contributing to the increase of the molecular weight of the fibers’ precursors. The synthesis was conducted by adding the monomer acrylonitrile (AN) to the unperturbed and PEG-perturbed BZ system after the onset of the oscillations, in the absence and presence of increasing amounts of the SDS surfactant. The potentiometric
technique was utilized to detect the dynamics of the oscillatory reaction. Preliminarily, the response of the BZ system to the monomer addition was investigated. Additional information was provided from the study of the effect of the SDS and PEG concentration on the dynamics of the BZ reaction during AN polymerization, thus obtaining a deepening in the understanding of the BZ mechanism. The characterization of the obtained polymers and copolymers, by melting point measurements, molecular weight determinations, Fourier Transform Infrared (FTIR), X-ray diffraction (XRD) analyses, and thermal treatments, indicated that the proposed synthetic method produces carbon fiber precursors with high molecular weight and good thermal stability. The addition of the surfactant was revealed as a good method to improve and/or finely tune the precursor molecular weight. The proposed synthetic protocol represents a valuable alternative to conventional methods to produce highperformant precursors of carbon fibers
Multi-Agent Reinforcement Learning using Centralized Critics in Collaborative Environments
No full textAgents trained through single-agent reinforcement learning methods such as self-play can provide a good level of performance in multi-agent settings and even in fully cooperative environments. However, most of the time, training multiple agents together using single-agent self-play yields poor results as each agent tries to learn how to perform their task while their teammates are also learning. Thus, training models to reach an optimal behaviour in such situations becomes a challenging, if not impossible issue to overcome. One possible solution to deal with this problem is to facilitate a centralized training process in which the policies of all agents are evaluated by a centralized critic that has access to the observations and actions of all the agents in the environment. By using this approach, the environment becomes stationary and the agents learn in a similar way to using a single-agent algorithm in settings where only one agent needs to be trained. In this paper, we test whether by using a multi-agent reinforcement learning algorithm with centralized critics, as opposed to single-agent ones, we would obtain an agent that generalizes better to new partners in a collaborative environment such as Overcooked, where coordination is critical for good performance. The results display a similar performance between the two algorithms when evaluated through self-play and slightly better or worse results when paired with the human model, representing a mediocre agent, depending on the map. Thus, the multi-agent, centralized critics algorithm used in this study did not train agents that generalize better to new partners. However, the training metrics clearly indicate that the centralized critics method makes the agents learn and converge twice as fast as its single-agent version.https://github.com/andrei-07/rp-overcooked-centralized-critics Link to GitHub repositoryCSE3000 Research ProjectComputer Science and Engineerin
Andrei Tarkovsky:
No full textThe author studies the originality of the film language of Andrei Tarkovsky, one of the great filmmakers of the twentieth century. For this purpose he considers the symbolic, poetic, technical and mystical elements of Tarkovsky’s seven films. Beyond the standard critics, he builds an unitary language for the interpretation of a work reputedly tight.El autor estudia la originalidad del lenguaje cinematográfico de Andrei Tarkovsky, uno de los grandes directores de cine del siglo XX. Para este propósito considera los aspectos simbólicos, poéticos, técnicos y místicos de sus siete películas. Desecha el formato de ficha crítica y construye un lenguaje unitario para la interpretación de una obra reputada como hermética
História e Documentário no Cinema de Andrei Tarkóvski
No full textIn the article, the author discuses the Cinematic history and documentary of Andrei Tarkóvski
Vogel-Fulcher analysis of relaxor dielectrics with the tetragonal tungsten bronze structure : Ba6MNb9O30 (M = Ga, Sc, In)
No full textIn-depth analysis of the relaxor behaviour of Ba6MNb9O30 (M= Ga, Sc, In) tetragonal tungsten bronze (TTB) ceramics was carried out. Powder x-ray diffraction and scanning electron microscopy were performed in order to confirm the formation of desired phases and to determine the microstructure. Low-temperature dielectric spectroscopy was used in order to characterise the dielectric properties of these materials; the degree of relaxor behaviour were investigated in relation with the increase of ionic radius of the M-cation on the B-site of the TTB structure. The dynamics of dielectric relaxation of dipoles was studied by fitting the dielectric permittivity data to the Vogel-Fulcher (VF) model in order to monitor the reproducibility and validity of the physical results. Restrictions to the VF fit were attempted besides the regular “free-fit” by constraining some of the fundamental relaxation parameters to physically sensible values. We show that Vogel-Fulcher fits are very sensitive to the fitting range resulting in a large range of fundamental parameters for the dielectric relaxation processes, and that the restriction of the frequency domain due to experimental noise or to instrumentation limits has a dramatic influence on the values obtained.Peer reviewe
Andrei Tarkovsky:: devolver a la naturaleza sus enigmas
No full textThe author studies the originality of the film language of Andrei Tarkovsky, one of the great filmmakers of the twentieth century. For this purpose he considers the symbolic, poetic, technical and mystical elements of Tarkovsky’s seven films. Beyond the standard critics, he builds an unitary language for the interpretation of a work reputedly tight.El autor estudia la originalidad del lenguaje cinematográfico de Andrei Tarkovsky, uno de los grandes directores de cine del siglo XX. Para este propósito considera los aspectos simbólicos, poéticos, técnicos y místicos de sus siete películas. Desecha el formato de ficha crítica y construye un lenguaje unitario para la interpretación de una obra reputada como hermética
Fotografia ca apropiere și distanțare la Andrei Codrescu / Photography as distance and nearness to Andrei Codrescu
No full textThe present study is part of a PhD thesis titled “Space in Andrei Codrescu’s prose – between reality and imaginary”, analysing the religious space, the virtual space, the photo studio, the American space and the library, as reflected in the above mentioned writer’s prose. The chapter dedicated to the photo studio depicts the manner in which the professional environment of the writer’s parents and close relatives influence the perception of the Self and of the Other, passing from the hypostasis of photographed subject to that of photographer “withtheeyes”, starting from the postmodern statement: “I am a camera”. Our study presents the travel literature of the author, “Ay, Cuba!” and “Prof pe drum” (Road Scholar), the last one also an autobiographical volume, illustrated by photos as a completion of the text. We also discuss the transformation of Road Scholar into a documentary, well received by the critics. The second part of our study presents the text written by Andrei Codrescu for several photobooks, as Walker Evans’ “Cuba” and “Signs”, David Graham’s “Land of the free: What makes Americans different” and others. If, in thefirst part of the study, Andrei Codrescu needs the production of a photo camera to deepen the understanding of the words, we discover him in the second part as a verbalising agent helping the rounding and the guiding of a Weltanschauung for other viewers, the public of the images from the photo books
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