TFAW: wavelet-based signal reconstruction to reduce photometric noise in time-domain surveys

There have been many efforts to correct systematic effects in astronomical light curves to improve the detection and characterization of planetary transits and astrophysical variability. Algorithms like the Trend Filtering Algorithm (TFA) use simultaneously-observed stars to remove systematic effects, and binning is used to reduce high-frequency random noise. We present TFAW, a wavelet-based modified version of TFA. TFAW aims to increase the periodic signal detection and to return a detrended and denoised signal without modifying its intrinsic characteristics. We modify TFA's frequency analysis step adding a Stationary Wavelet Transform filter to perform an initial noise and outlier removal and increase the detection of variable signals. A wavelet filter is added to TFA's signal reconstruction to perform an adaptive characterization of the noise- and trend-free signal and the noise contribution at each iteration while preserving astrophysical signals. We carried out tests over simulated sinusoidal and transit-like signals to assess the effectiveness of the method and applied TFAW to real light curves from TFRM. We also studied TFAW's application to simulated multiperiodic signals, improving their characterization. TFAW improves the signal detection rate by increasing the signal detection efficiency (SDE) up to a factor ~2.5x for low SNR light curves. For simulated transits, the transit detection rate improves by a factor ~2-5x in the low-SNR regime compared to TFA. TFAW signal approximation performs up to a factor ~2x better than bin averaging for planetary transits. The standard deviations of simulated and real TFAW light curves are ~40x better than TFA. TFAW yields better MCMC posterior distributions and returns lower uncertainties, less biased transit parameters and narrower (~10x) credibility intervals for simulated transits. We present a newly-discovered variable star from TFRM.Comment: Accepted for publication by A&A. 13 pages, 16 figures and 5 table

On the Design of a Novel Joint Network-Channel Coding Scheme for the Multiple Access Relay Channel

This paper proposes a novel joint non-binary network-channel code for the Time-Division Decode-and-Forward Multiple Access Relay Channel (TD-DF-MARC), where the relay linearly combines -- over a non-binary finite field -- the coded sequences from the source nodes. A method based on an EXIT chart analysis is derived for selecting the best coefficients of the linear combination. Moreover, it is shown that for different setups of the system, different coefficients should be chosen in order to improve the performance. This conclusion contrasts with previous works where a random selection was considered. Monte Carlo simulations show that the proposed scheme outperforms, in terms of its gap to the outage probabilities, the previously published joint network-channel coding approaches. Besides, this gain is achieved by using very short-length codewords, which makes the scheme particularly attractive for low-latency applications.Comment: 28 pages, 9 figures; Submitted to IEEE Journal on Selected Areas in Communications - Special Issue on Theories and Methods for Advanced Wireless Relays, 201

The Turn of the Screw and the Slide of the Skyrmion

The experimental discovery of magnetic skyrmions in 2009 opened the door to the development of a new exciting field of physics: skyrmionics. Skyrmions are just one phase of the broader class of chiral magnets, which are characterised by broken inversion symmetry and twisting spin textures. Controlling chiral magnets is of fundamental interest if we want to use them in the technological devices of the future. One way of achieving this is to drive a chiral magnet out of equilibrium with time-oscillating magnetic fields. Even for weak fields, such driving universally activates the rotational and translational Goldstone modes of the magnet. For example, the helical phase starts to turn like an Archimedean screw, while a single skyrmion starts to slide at constant velocity. In this thesis we present a fully analytical theory of this effect for the first time. We also investigate what happens as we drive stronger. Above a critical driving strength, we observe the formation of a Floquet time quasicrystal, where a cascade of magnons carrying incommensurate frequencies and spatial momenta start populating the system. We show that this is triggered by magnon laser instabilities in the driven Floquet magnon spectrum. Finally, we show how the magnetic Archimedean screw can be used to pump electrons, generating large, in principle easily detectable DC currents. Because of their non-collinearity, chiral magnets can host topological charge. In the last part of the thesis, we consider what happens when this topological charge becomes fractional. We show firstly that this phenomenon is real, occurring for example at the meeting points of cubic magnets, or in the remains of exploding skyrmions. Finally, we discuss the physical properties of fractional charges, in particular their ability to act as strong scatterers for low energy magnons

Design, synthesis and characterization of inks based in waterborne polyurethane urea dispersions suitable for direct ink writing 3D-printing.

330 p.A series of waterborne polyurethane urea dispersions were prepared to study their viability as inks for direct ink writing 3D-printing. In this context, waterborne polyurethane urea dispersions were successfully synthesized using a hydrophilic polyethylene glycol (PEG) and a hydrophobic polycaprolactone (PCL) as soft segment to ease the physical gelation of the inks. The PCL/PEG ratio as well as the molar mass of the PEG has been modified and the resulting dispersions, as well as the films prepared from the dispersions, were characterized from the physicochemical, mechanical, thermomechanical and morphological viewpoints to select the better formulation that fulfils with the required end-use properties, particularly for 3D-printing process. Once the selection of the composition of the waterborne polyurethane urea was stablished, inks with different solid content were prepared, analysed by means of rheology and subsequently printed so as to establish relationships between the rheological behaviour and the 3D-printing performances.To pilot the rheological behaviour and the printing performances, cellulose nanocrystals were used as viscosity modulator. Different cellulose contents were added to the waterborne polyurethane urea ink using two different methods called the in situ and the ex situ methods which differ in the moment of the addition of the nanoentities. The composites prepared from both methods were analysed from the rheological viewpoint and printed in the aim to select the best compositions, as well as to compare both incorporation methods. Additionally, the physicochemical, mechanical and thermomechanical properties of the printed pieces were studied to ensure the successful reinforcement of the cellulose nanocrystals into the composites. It was seen that the different addition methods resulted in different disposition of the cellulose nanocrystals leading to the obtain of nanocomposites presenting different rheological, mechanical and thermomechanical properties.Two potential applications were studied to demonstrate their viability. In the first one, shape customized scaffolds were prepared via 3D-printing and freeze drying using a previously developed waterborne polyurethane urea ink with in situ addition of different contents of cellulose nanocrystals, as well as crosslinking by immersion in CaCl2 before freeze drying. The morphology, mechanical and physicochemical properties of the prepared scaffolds were evaluated and tested as an absorption material against cationic methylene blue dye presenting an interesting absorption capacity. For the second application, inks based on a waterborne polyurethane urea with Salvia extracts incorporated by in situ method and different contents of ex situ added cellulose nanocrystals were developed in order to prepare scaffolds with antimicrobial properties. The antimicrobial activity of the scaffolds was tested successfully against Gram positive Staphylococcus aureus and Gram negative Escherichia coli. Additionally, the influence of the inclusions of Salvia extracts on the rheological properties of the inks and the properties of the dispersion were studied.IPREM: Institut des sciences analytiques et de physics-chimie pour l'environnement et les matériaux. GMT Msterials Technologies Research Grou

La provincia jesuítica de Castilla en el Archivum Romanun Societatis Iesu.

Sin resume

Design, synthesis and characterization of inks based in waterborne polyurethane urea dispersions suitable for direct ink writing 3D-printing.

330 p.A series of waterborne polyurethane urea dispersions were prepared to study their viability as inks for direct ink writing 3D-printing. In this context, waterborne polyurethane urea dispersions were successfully synthesized using a hydrophilic polyethylene glycol (PEG) and a hydrophobic polycaprolactone (PCL) as soft segment to ease the physical gelation of the inks. The PCL/PEG ratio as well as the molar mass of the PEG has been modified and the resulting dispersions, as well as the films prepared from the dispersions, were characterized from the physicochemical, mechanical, thermomechanical and morphological viewpoints to select the better formulation that fulfils with the required end-use properties, particularly for 3D-printing process. Once the selection of the composition of the waterborne polyurethane urea was stablished, inks with different solid content were prepared, analysed by means of rheology and subsequently printed so as to establish relationships between the rheological behaviour and the 3D-printing performances.To pilot the rheological behaviour and the printing performances, cellulose nanocrystals were used as viscosity modulator. Different cellulose contents were added to the waterborne polyurethane urea ink using two different methods called the in situ and the ex situ methods which differ in the moment of the addition of the nanoentities. The composites prepared from both methods were analysed from the rheological viewpoint and printed in the aim to select the best compositions, as well as to compare both incorporation methods. Additionally, the physicochemical, mechanical and thermomechanical properties of the printed pieces were studied to ensure the successful reinforcement of the cellulose nanocrystals into the composites. It was seen that the different addition methods resulted in different disposition of the cellulose nanocrystals leading to the obtain of nanocomposites presenting different rheological, mechanical and thermomechanical properties.Two potential applications were studied to demonstrate their viability. In the first one, shape customized scaffolds were prepared via 3D-printing and freeze drying using a previously developed waterborne polyurethane urea ink with in situ addition of different contents of cellulose nanocrystals, as well as crosslinking by immersion in CaCl2 before freeze drying. The morphology, mechanical and physicochemical properties of the prepared scaffolds were evaluated and tested as an absorption material against cationic methylene blue dye presenting an interesting absorption capacity. For the second application, inks based on a waterborne polyurethane urea with Salvia extracts incorporated by in situ method and different contents of ex situ added cellulose nanocrystals were developed in order to prepare scaffolds with antimicrobial properties. The antimicrobial activity of the scaffolds was tested successfully against Gram positive Staphylococcus aureus and Gram negative Escherichia coli. Additionally, the influence of the inclusions of Salvia extracts on the rheological properties of the inks and the properties of the dispersion were studied.IPREM: Institut des sciences analytiques et de physics-chimie pour l'environnement et les matériaux. GMT Msterials Technologies Research Grou

Skyrmion Jellyfish in Driven Chiral Magnets

Chiral magnets can host topological particles known as skyrmions which carry an exactly quantised topological charge $Q=-1$. In the presence of an oscillating magnetic field ${\bf B}_1(t)$, a single skyrmion embedded in a ferromagnetic background will start to move with constant velocity ${\bf v}_{\text{trans}}$. The mechanism behind this motion is similar to the one used by a jellyfish when it swims through water. We show that the skyrmion's motion is a universal phenomenon, arising in any magnetic system with translational modes. By projecting the equation of motion onto the skyrmion's translational modes and going to quadratic order in ${\bf B}_1(t)$ we obtain an analytical expression for ${\bf v}_{\text{trans}}$ as a function of the system's linear response. The linear response and consequently ${\bf v}_{\text{trans}}$ are influenced by the skyrmion's internal modes and scattering states, as well as by the ferromagnetic background's Kittel mode. The direction and speed of ${\bf v}_{\text{trans}}$ can be controlled by changing the polarisation, frequency and phase of the driving field ${\bf B}_1(t)$. For systems with small Gilbert damping parameter $\alpha$, we identify two distinct physical mechanisms used by the skyrmion to move. At low driving frequencies, the skyrmion's motion is driven by friction, and $v_{\text{trans}}\sim\alpha$, whereas at higher frequencies above the ferromagnetic gap the skyrmion moves by magnon emission and $v_{\text{trans}}$ becomes independent of $\alpha$.Comment: 16 pages (including references), 5 figures. Supplementary: 8 pages. v2: small typos corrected, two references added. v3: minor revisions to the text in response to referee reports, six references adde