Màster en Física Avançada i Matemàtica Aplicadahttp://hdl.handle.net/11201/1455882024-05-18T16:50:21Z2024-05-18T16:50:21ZAlfvén wave heating in partially ionised thin threads of solar prominencesMelis Sánchez, Llorençhttp://hdl.handle.net/11201/1566342022-01-11T12:11:02Z2020-10-13T00:00:00ZAlfvén wave heating in partially ionised thin threads of solar prominences
Melis Sánchez, Llorenç
[eng] Quiescent solar filaments and prominences are clouds of cool and dense plasma in the solar
corona suspended against gravity by forces which are supposed to be of magnetic origin. Prominences are highly dynamic structures that display oscillations that seem to be ubiquitous, as
shown in observations. These oscillations are magnetohydrodynamic waves from a wide range
of frequencies that are probably driven by motions in the underlying solar photosphere and may
transport energy up to prominences suspended in the above corona. Dissipation of wave energy
can lead to heating of the cool prominence plasma, thereby contributing to the local energy
balance within the prominence.
In this work we analyse the effect of Alfv´en wave dissipation as a heating mechanism in thin
threads of solar prominences. We consider a 1D prominence thread model with a constant
magnetic field, while the density and temperature vary along the thread in a fashion that mimics
the observations. We consider Ohm’s and ambipolar diffusions and we use two different relations
between the temperature and the ionisation degree. We investigate the standing and propagating
modes cases using a semi-analytical approach.
The results show that for the standing modes, the damping is almost negligible unless very high
harmonics are considered, and the heating produced by the Alfv´en wave dissipation does not
compensate the radiative cooling. For the propagating modes we have seen that the injected
energy flux in the thread has relative minimums for the frequencies that correspond to the
eigenfrequencies of the standing modes, which suggests the existence of resonances. For the
energy balance, a broadband spectrum of propagating modes provides enough heating at the
centre of the thread to compensate the cooling, but wave heating is inefficient in the hot coronal
part.
2020-10-13T00:00:00ZAnálisis multifractal de correlaciones en series temporales de sistemas económicosDomínguez Monterroza, Andy Rafaelhttp://hdl.handle.net/11201/1464932018-10-23T10:44:48Z2018-05-31T00:00:00ZAnálisis multifractal de correlaciones en series temporales de sistemas económicos
Domínguez Monterroza, Andy Rafael
[spa] El presente trabajo ofrece un estudio emp´ırico de la multifractalidad de las series de tiempo
financieras, y sus correlaciones, del Mercado de Valores de Colombia. Se discute la pertinencia
de estos resultados en la construcci´on de nuevos modelos predictivos, a la luz de los
enfoques principales de la teor´ıa financiera de los mercados. Se han aplicado dos m´etodos, el
Multifractal Detrended Fluctuation Analysis y el Multifractal Detrended Cross-Correlation
Analysis a las series de precios de las principales empresas del Mercado Burs´atil de Colombia
en el periodo comprendido entre 2011 a 2014. Los resultados reportan la presencia de
multifractalidad en las series, como en sus correlaciones, sugiriendo el cumplimiento de la
Hip´otesis del Mercado Fractal y la ineficiencia del mercado.; [eng] In this thesis we present a empirical study of multifractality in financial time series on
Colombian Stock Market. We have applied two methods, theMultifractal Detrended Fluctuation
Analysis and Multifractal Detrended Cross-Correlation Analysis for stock series of
the largest companies of Colombia from 2011 to 2014. Our results suggest the presence of
multifractality properties for all time series analyzed and to provide an evidence that confirm
Fractal Market Hipothesis and market ine!ciency.
2018-05-31T00:00:00ZAproximación regional a la inundación y erosión de las playas de Baleares en el siglo XXILuque Lozano, Pauhttp://hdl.handle.net/11201/1573392022-02-08T09:55:37Z2020-10-07T00:00:00ZAproximación regional a la inundación y erosión de las playas de Baleares en el siglo XXI
Luque Lozano, Pau
abstract not available
2020-10-07T00:00:00ZBeyond the Stationary Phase Approximation: an alternative approach to model gravitational waves from precessing compact binaries in the Fourier DomainPlanas Llompart, Maria de Lluchttp://hdl.handle.net/11201/1588472022-04-27T07:26:51Z2021-07-20T00:00:00ZBeyond the Stationary Phase Approximation: an alternative approach to model gravitational waves from precessing compact binaries in the Fourier Domain
Planas Llompart, Maria de Lluc
[eng] The first detection of gravitational waves of a black hole binary [1] opened the current
observational era of gravitational wave astronomy. Several gravitational waves from
merging compact binaries have already been observed during the three observational “runs”
[2, 3], with the expectation of increasing the detection rate with upgraded and upcoming
detectors.
Sophisticated data analysis methods are indispensable for the detection of gravitational
waves and it requires theoretical models to estimate the source parameters. Through
the “matched filtering” method, the theoretical templates are cross correlated against the
observed signal at the detector, so one can infer the source parameters using Bayesian
inference. In order to sample the posterior probability distribution of the parameters,
Bayesian inference requires at least millions of evaluations of the likelihood function. The
better the sensitivity of the detectors, the more accurate and computationally efficient the
signal templates need to be. This is why one of the main efforts of the gravitational wave
group at the UIB is to improve the current Inspiral-Merger-Ringdown (IMR) waveforms in
the Fourier domain, which describe the amplitude and phase needing a low computational
cost to evaluate them and hence, making them a reasonable template for applications in
Bayesian inference.
In this work I focus on the challenging effect that a complete representation of the
spins implies on waveform models, known as spin precession. In case of having a black
hole binary with misaligned spins, i.e. when the angular momenta of the individual black
holes are not orthogonal to the orbital plane, the spin-orbit and the spin-spin couplings
induce a precession of the orbital plane and of the spins themselves. This precession leads
to a modulation of the signal as seen by the observer, and increases the dimensionality of
the problem, which makes it difficult to cover the large parameter space with numerical
relativity simulations. However, the fact that the acceleration due to the orbital motion
dominates and the power radiated due to precession can be neglected in the inspiral gives
rise to a fruitful approach to modelling this effect [4–7]: One can use a (non-inertial)
co-precessing frame in which the decomposed waveform is similar to a non-precessing one,
performing a time-dependent rotation that follows the precession of the orbital plane. In
order to create efficient Fourier domain models, one needs to understand how to translate
the time rotation from an inertial frame to the co-precessing one into a Fourier domain
transfer function.
Our purpose is thus to implement the formalism developed in [8] in order to process
the time domain modulation necessary to treat precession in the Fourier domain, while
retaining the compactness of a Fourier domain amplitude and phase representation of the
signal. This new formalism, based on the separation of time-scales between precession and
orbital motion directly in the Fourier domain, seeks to overcome the limitations of the
Stationary Phase Approximation (SPA) [9]. This method can only be applied to compute
the Fourier transform of non-precessing systems, i.e. with aligned spins, during the inspiral,
and hence, it is not applicable to IMR precessing waveforms. A better approach than
SPA is crucial to deal with the challenging events we may detect with the upgraded and
upcoming detectors.
2021-07-20T00:00:00Z