Repositorio USM (Universidad Técnica Federico Santa María)
Not a member yet
423 research outputs found
Sort by
Cimientos Casa Rector, 1 julio 1930
No full textCimientos de la Casa del Rector con vista hacia la bahía (Campus Casa Central
Edificio C Talleres, Altillo Fundición, 30 abril 1930
No full textAltillo de la Fundición en edificio C Talleres, Los Placeres (Campus Casa Central
Integrating machine learning and physiological modeling tools for the assessment of vocal function using neck surface acceleration
No full textThis thesis is dedicated to advancing the ambulatory assessment of vocal func tion by utilizing a neck-surface accelerometer attached directly to the skin surface of the neck. The motivation lies in the fact that a fully developed ambulatory method, capable of precisely identifying the underlying pathophysiological char acteristics of both normal and pathological vocal functions, could revolutionize clinical practices in monitoring, evaluating, and treating common voice disorders. Accordingly, this work exploits the advantages of a low-order voice production model to introduce a non-invasive technique for estimating relevant vocal func tion metrics, such as subglottal pressure, vocal fold collision pressure, and intrin sic laryngeal muscle activation of the cricothyroid and thyroarytenoid muscles, based on signals from an accelerometer sensor. In the first stage, a Bayesian framework based on a constrained extended Kalman filter is proposed to link a low-order voice production model with either a glottal area waveform extracted from high-speed video recordings or glottal airflow estimated from Rothenberg mask measurements. The results provide new insights into the capacity of the selected voice production model to replicate different phonation conditions and highlight the feasibility of using this method to estimate clinical measures that are difficult to ascertain in a clinical setting. The second stage of the thesis focuses on an alternate solution: a neural network trained exclusively with simulations from a voice production model. This nonlinear regressor maps seven input features, which can be extracted from an accelerometer signal, to the target measures of vocal function. The efficacy of this method, particularly in terms of subglottal pressure, was validated through in vivo recordings, which included synchronous measurements of oral volume velocity, intraoral pressure, microphone, and ac celerometer. This method was applied to healthy and disordered voices (unilateral vocal fold paralysis and both phonotraumatic and nonphonotraumatic vocal hy perfunction). Participants were prompted to articulate /p/-vowel syllable strings, varying loudness, vowels, pitch, and voice quality. The neural network, trained with synthetic data, demonstrated subglottal pressure estimation comparable to that of previous studies for subjects without voice disorders. However, this non linear mapping was found to be less robust in cases of pathology. In the search for more accurate subject-specific models, the final research stage focuses on re fining the neural network regressor, initially trained solely with simulations from a synthetic voice production model. This refinement is carried out by employing a domain adaptation strategy from synthetic to in vivo laboratory data, result ing in an improved estimate of subglottal pressure. This method yielded a set of subject-specific models that provided the most accurate estimation of subglottal pressure to date for both normal and disordered voices using an accelerometer. Additionally, through a case study—which, alongside the previously mentioned in vivo synchronous measurements, also incorporates fine-wire laryngeal electromyo graphy—it is demonstrated that the performance of the subject-specific regressor in estimating subglottal pressure is maintained while concurrently estimating mus cle activation of the cricothyroid and thyroarytenoid muscles. Overall, this thesis advances the field of vocal function assessment through a series of significant contributions. The proposed Bayesian framework reduces the need for multiple observations while yielding robust and reliable estimates of features that are diffi cult to measure in clinical practice. It also innovatively combines machine learning techniques with the voice production model to estimate physiologically relevant features such as subglottal pressure, vocal fold collision pressure, and laryngeal muscle activation from neck-surface accelerometers. Furthermore, this work in troduces a subject-specific nonlinear regression enhanced by transfer learning, significantly improving the estimation of subglottal pressure from neck-surface vi bration signals, with promising potential for application to other vocal function paraDoctorado en Ingeniería Electrónic
Magnetic field generation in white dwarfs: comparing model predictions with the observations of close double white dwarfs
No full textDurante numerosos años, ha persistido la pregunta sobre por qué ciertas enanas blancas poseen campos magnéticos fuertes mientras que otras no. Se han formulado varias teorías para explicar la generación de estos campos magnéticos. El escenario de campo fósil postula que los campos magnéticos observados en enanas blancas se originaron durante las etapas anteriores de las estrellas Ap o Bp. Otra propuesta implica fusiones de núcleos doblemente degenerados, donde la fusión de dos enanas blancas resultan en la creación de campos magnéticos robustos. Una teoría alternativa sugiere que se genera un dínamo durante la fase de envoltura común de un sistema binario. En este escenario, la rotación diferencial en la envoltura común que rodea a las dos estrellas puede impulsar un dínamo, dando lugar al campo magnético de la enana blanca. En la última década, ha surgido una nueva teoría como una explicación posible para los campos magnéticos en enanas blancas. Según esta teoría, el dínamo es impulsado por la cristalización de la enana blanca junto
con una rotación rápida.
Tan pronto como una enana blanca de carbono/oxígeno (C/O) está cristalizando, el núcleo sólido se enriquece en oxígeno, mientras que las zonas exteriores ricas en carbono se vuelven convectivas. Esta situación se asemeja a la de la Tierra, en la cual un núcleo de hierro sólido rodeado por una zona de convección líquida junto con la rotación impulsa un dínamo magnético que se supone genera el campo magnético de la Tierra. Basándose en esta analogía, se ha propuesto que un mecanismo de dínamo similar es responsable del desarrollo de campos magnéticos fuertes en enanas blancas.
El objetivo de esta tesis es contrastar dos teorías: una que propone la generación de un dínamo dentro de la envoltura común y la teoría alternativa que sugiere un dínamo impulsado por los procesos de cristalización y rotación rápida. Este trabajo implicará un análisis comparativo con datos observacionales.
Para llevar a cabo este proyecto, se utilizó un código BSE modificado para generar una población significativa de sistemas binarios de enanas blancas cercanas que se formaron a través de dos fases de envoltura común. Posteriormente, se utilizaron ecuaciones proporcionales simples para la
fuerza del campo magnético generado por un dínamo dentro de la envoltura común y el dínamo de cristalización para predecir la fracción y las fuerzas de campo de enanas blancas en binarias dobles cercanas. Al comparar la predicción de nuestro modelo de población con las observaciones de enanas blancas dobles, obtenemos los siguientes resultados.
Primero, dos fases de envoltura común no pueden representar la principal vía de formación para la población actual de enanas blancas dobles observadas, ya que las masas predichas difieren sustancialmente. Para una comprensión completa de la población de enanas blancas dobles en general y de sus campos magnéticos en particular, se requieren modelos de población que incluyan
transferencia de masa estable.
En segundo lugar, la teoría del dínamo de envoltura común predice muchas enanas blancas fuertemente magnéticas en comparación con las observaciones, así como una relación entre el período orbital y la fuerza del campo que no se observa. Incluso si solo una pequeña fracción de enanas blancas dobles se forma a través de dos fases de envoltura común, el dínamo de envoltura común en su forma actual no puede describir adecuadamente la generación de campos magnéticos en enanas blancas dobles.
En tercer lugar, las predicciones del dínamo impulsado por la cristalización podrían estar en acuerdo con las observaciones si la eficiencia de la envoltura común, que describe cuán eficientemente se utiliza la energía orbital durante la evolución de la envoltura común para expulsar la envoltura, es pequeña y si los sesgos observacionales afectan la muestra observada.
Concluyo que el dínamo impulsado por la cristalización es probablemente el escenario más plausible para la generación del campo magnético en enanas blancas, pero se requieren simulaciones más detalladas que incluyan transferencia de masa estable para poner a prueba esta hipótesis.For numerous years, the question has persisted regarding why certain white dwarfs possess strong magnetic fields while others do not. Several theories have been formulated to explain the generation of these magnetic fields. The fossil field scenario postulates that magnetic fields observed in white dwarfs originated during the prior stages of Ap or Bp stars. Another proposal involves double degenerate core mergers, where the merging of two white dwarfs results in the creation of robust magnetic fields. An alternative theory suggests that a dynamo is generated during the common envelope phase of a binary system. In this scenario, the differential rotation in the common envelope
surrounding the two stars is able to drive a dynamo, thereby giving rise to the white dwarf magnetic field. Over the past decade, a new theory has emerged as a plausible explanation for magnetic fields in white dwarfs. According to this theory, the dynamo is driven by the crystallization of the white dwarf coupled with rapid rotation. As soon as a carbon/oxygen (C/O) white dwarf is crystallizing, the solid core becomes rich in oxygen while the carbon rich outer zones become convective. This situation resembles that of the Earth, in which a solid iron core surrounded by a liquid convection zone together with rotation drives a magnetic dynamo that is supposed to generate the Earth’s magnetic field. Based on this analogy it has been proposed that a similar dynamo mechanism is responsible for the development of strong magnetic fields in white dwarfs.
The aim of this thesis is to contrast two theories: one proposing the generation of a dynamo within the common envelope, and the alternative theory suggesting a dynamo driven by the processes of crystallization and rapid rotation. This examination will involve a comparative analysis with observational data.
To accomplish this project, a modified BSE code was employed to generate a significant population of close white dwarf binary systems that formed through two common envelope phases. Subsequently, simple scaling equations for the strength of the magnetic field generated through a dynamo within the common envelope and the crystallization dynamo were used to predict the fraction and field strengths of white dwarfs in close double white dwarf binaries. Comparing the prediction of our population model with the observations of double white dwarfs, we obtain the following results. First, two common envelope phases cannot represent the main formation channel for the currently observed double white dwarf population because the predicted white dwarf masses differ substantially. For a full understanding of the double white dwarf population in general and their magnetic fields in particular, population models that include stable mass transfer are highly required. Second, the common envelope dynamo theory predicts far too many strongly magnetic white dwarfs compared to the observations as well as a relation between orbital period and field strength which is not observed. Even if only a relatively small fraction of double white dwarfs form through two common envelope phases, the common envelope dynamo in its current form can be
excluded to properly describe the generation of magnetic fields in double white dwarfs. Third, the predictions of the crystallization driven dynamo could be in agreement with the observations if the common envelope efficiency, which describes how efficiently orbital energy is used during common envelope evolution to expel the envelope, is small and if observational biases affect the observed sample.
I conclude that the crystallization driven dynamo is probably the most plausible scenario for the magnetic field generation in white dwarfs but that more detailed simulations including stable mass transfer are required to further test this hypothesis.Magíster en Ciencias, mención Físic
Cantera El Bosque, camino de acceso
No full textCamino de acceso, Cantera El Bosque desde donde se extraían las piedras para la construcción de muros y edificios de la Universidad (Campus Casa Central
Edificio C Talleres, muro interior de la fachada norte, extremo poniente, 5 marzo 1930
No full textMuro interior de la fachada norte extremo poniente de edificio C Tallere
