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[Objectives] The aim of the HISPANIAS (HyperperfusIon Syndrome Post-carotid ANgIoplasty And Stenting) study was to define CHS rates and develop a clinical predictive model for cerebral hyperperfusion syndrome (CHS) after carotid artery stenting (CAS)., [Background] CHS is a severe complication following CAS. The presence of clinical manifestations is estimated on the basis of retrospective reviews and is still uncertain., [Methods] The HISPANIAS study was a national prospective multicenter study with 14 recruiting hospitals. CHS was classified as mild (headache only) and moderate-severe (seizure, impaired level of consciousness, or development of focal neurological signs)., [Results] A total of 757 CAS procedures were performed. CHS occurred in 22 (2.9%) patients, in which 16 (2.1%) had moderate-severe CHS and 6 (0.8%) had mild CHS (only headache). The rate of hemorrhages was 0.7% and was associated with high mortality (20%). Pre-operative predictors of moderate-severe CHS in multivariate analysis were female sex (odds ratio [OR]: 3.24; 95% confidence interval [CI]: 1.11 to 9.47; p = 0.03), older patients (OR: 1.09; 95% CI: 1.01 to 1.17; p = 0.02), left carotid artery treated (OR: 4.13; 95% CI: 1.11 to 15.40; p = 0.03), and chronic renal failure (OR: 6.29; 95% CI: 1.75 to 22.57; p = 0.005). The area under the curve of this clinical and radiological model was 0.86 (95% CI: 0.81 to 0.92; p = 0.001)., [Conclusions] The rate of CHS in the HISPANIAS study was 2.9%, with moderate-severe CHS of 2.1%. CHS was independently associated with female sex, older age, history of chronic kidney disease, and a treated left carotid artery. Although further investigations are needed, the authors propose a model to identify high-risk patients and develop strategies to decrease CHS morbidity and mortality in the future., This study was supported by a Spanish grant from the Instituto de Salud Carlos III (ISCIII-FIS IP14/00971, 2014–2017). The ITRIBIS project has the registration number REGPOT-2013-1. Cooperative Cerebrovascular Disease Research Network (INVICTUS+) (RD16/0019/0015). Dr. Mancha is supported by a Río Hortega contract (CM16/00015). Abbott and Grifols have partial financial supported the conduction of the HISPANIAS project but had no role in the design of the study, interpretation of the data, or manuscript approval.

The aim of the HISPANIAS (HyperperfusIon Syndrome Post-carotid ANgIoplasty And Stenting) study was to define CHS rates and develop a clinical predictive model for cerebral hyperperfusion syndrome (CHS) after carotid artery stenting (CAS). CHS is a severe complication following CAS. The presence of clinical manifestations is estimated on the basis of retrospective reviews and is still uncertain. The HISPANIAS study was a national prospective multicenter study with 14 recruiting hospitals. CHS was classified as mild (headache only) and moderate-severe (seizure, impaired level of consciousness, or development of focal neurological signs). A total of 757 CAS procedures were performed. CHS occurred in 22 (2.9%) patients, in which 16 (2.1%) had moderate-severe CHS and 6 (0.8%) had mild CHS (only headache). The rate of hemorrhages was 0.7% and was associated with high mortality (20%). Pre-operative predictors of moderate-severe CHS in multivariate analysis were female sex (odds ratio [OR]: 3.24; 95% confidence interval [CI]: 1.11 to 9.47; p = 0.03), older patients (OR: 1.09; 95% CI: 1.01 to 1.17; p = 0.02), left carotid artery treated (OR: 4.13; 95% CI: 1.11 to 15.40; p = 0.03), and chronic renal failure (OR: 6.29; 95% CI: 1.75 to 22.57; p = 0.005). The area under the curve of this clinical and radiological model was 0.86 (95% CI: 0.81 to 0.92; p = 0.001). The rate of CHS in the HISPANIAS study was 2.9%, with moderate-severe CHS of 2.1%. CHS was independently associated with female sex, older age, history of chronic kidney disease, and a treated left carotid artery. Although further investigations are needed, the authors propose a model to identify high-risk patients and develop strategies to decrease CHS morbidity and mortality in the future.

Introduction Mechanical thrombectomy (MT) is the mainstay of treatment for major artery occlusion in stroke patients. It is not known whether there is a limit to the number of passes after which is no longer effective and becomes counterproductive. Parenchymal hematoma (PH) is a serious complication in these patients with unclear underlying mechanisms. We have examined whether the number of passes correlates with a significant increase in PH. Methods We retrospectively analyzed the impact of the number of passes on patients treated between January 2017 and April 2020 in our centre. The main objective was to assess the correlation of the number of passes with the percentage of PH assessed by CT 24 h after endovascular treatment. Successful recanalization was defined as TICIm 2b-3. A good clinical outcome was defined as 90-day mRS ≤ 2. Results 369 patients were included in the study. Successful recanalization was achieved in 85.09%. Recanalization rates decreased sequentially as the number of passes increased, but the rate achieved by ≥ 6 passes was still 31.25%. ≥ 3 passes had a significantly higher incidence of PH (p = 0.026). In a multivariate analysis, the ASPECTS scale, the number of passes, and arterial puncture to recanalization time, were independent predictors related to PH. Of the 18 parenchymal hematomas, 5 occurred in patients with ≥ 6 passes. Conclusions The increase in PH risk for patients undergoing ≥ 3 passes becomes significant when ≥ 6 passes are performed. At this point it is important to ponder the risk of parenchymal hematoma and a possible negative treatment outcome.

[EN]: Scanning tunneling microscope (STM) lleva revolucionando el campo de la materia condensada desde hace unos años. Esta técnica ofrece tanto una gran resolución espacial como energética, permitiendo la manipulación atómica gracias a un control de la punta a nivel subatómico. Sin embargo, desde 2015, una nueva técnica con mayor resolución energética e igual espacial apareció: Electrón Spin Resonance (ESR). La gran diferencia con STM viene de modular la diferencia de potencial entre la punta y el substrato a través de un voltaje alterno AC. Cuando la frecuencia de este campo eléctrico coincide con la separación enérgica (frecuencia de Larmor) entre dos estados de un momento magnético localizado en una superficie aislante, la corriente sufre un cambio brusco. De esta forma, el espín del momento magnético empieza a precesar. Algunas de las aplicaciones más interesantes que ofrece esta técnica han sido la identificación de distintos isotopos de Ti y Fe, así como obtener información de átomos con electrones tipo f como el Ho. También, recientemente, se está intentado hacer manipulación coherente entre átomos magnéticos. De esta forma, se podrían realizar operaciones cuánticas que tendrían un gran impacto en el campo de la información cuántica. Sin embargo, un marco teórico de predicción todavía no ha sido descubierto. La gran dificultad recae en como puede afectar un campo eléctrico alterno al espín atómico. Las propuestas han sido varias: desde excitaciones de fonones en la superficie hasta desplazamientos del átomo magnético, entre otras. El objetivo de esta tesis es arrojar un poco de luz a este asunto y obtener un modelo teórico que pueda predecir y simular experimentos. Inicialmente aplicaremos Density Functional Theory (DFT) para intentar sacar algunas primeras conclusiones de como el sistema magnético (Fe sobre MgO/Ag(001)) reacciona ante un campo eléctrico. Para ello, primero, debemos seguir un procedimiento estándar de relajación de los sistemas bulk del MgO y Ag. Extrayendo los parámetros de red correspondientes y construyendo la superficie MgO/Ag en la que colocaremos el átomo magnético sobre un O. La exposición a un campo eléctrico estático nos permite ver que cambios hay en la PDOS y en el planar average potential (PAP). Las conclusiones resultan inmediatas: el campo eléctrico afecta mucho más el PAP, lo que implica que se este modulando la barrera de potencial. Es interesante apreciar que en otros sistemas como Cu2N/Cu o ClCu/Cu no se tiene una respuesta tan notable con el campo eléctrico. Con la conclusión anterior, empezamos a aplicar ciertos modelos teóricos que podrían permitir simular los experimentos. El primero es el llamado cotunneling. Inicialmente se parte de un Hamiltoniano total que contiene el Hamiltoniano del entorno, el del sistema central o impureza magnética (modelo de Anderson generalizado) y la conexión entre ambos, llamado tunneling. Dicho Hamiltioniano resulta demasiado complejo de tratar por lo que se aplica teoría de perturbaciones a segundo orden en el término tunneling. El objetivo detrás de esta aproximación es conseguir escribir el llamado Hamiltoniano de cotunneling, cuya forma permite usar la teoría Bloch-Redfield. Dicha teoría aplica un lenguaje de matrices de densidad muy práctico para problemas de sistemas abiertos pero, además, es fácilmente extensible al regimen con dependencia temporal que nos interesa. Teniendo en cuenta ciertas consideraciones, el producto final de mezclar cotunneling con dependencia temporal nos lleva a una ecuación de los elementos de la matriz de densidad reducida que presenta un nuevo parámetro. Este parámetro resulta estar asociado a la precesión del espín y se le llama frecuencia de Rabi. Los resultados del modelo de cotunneling muestran que la frecuencia de Rabi es el pilar fundamental de la teoría. Sin este parámetro, no es posible inducir resonancia ya que la altura del pico en la corriente es directamente proporcional al cuadrado de la Rabi. Aunque los cálculos con la teoría son bastante satisfactorios, los valores de la frecuencia de Rabi resultan ser un factor 10-20 más grandes que los experimentales. Un rápido vistazo al modelo y las ecuaciones empleadas nos dice que hemos tendido a sobresimplificar demasiado los cálculos. Varias estrategias pueden ejecutarse para mejorar estos pero, sin duda, la más destacable es usar Wannier para conocer mejor la hibridación entre el sistema y el entorno. Sin embargo, esto es algo que escapa del contenido de la tesis. La siguiente teoría que empleamos, en un intento de mejorar los resultados de cotunneling, es la de Floquet combinada con funciones de Green fuera del equilibrio. La teoría de Floquet estudia la estabilidad de sistema de ecuaciones diferenciales periódicos y permite reescribirlos como uno algebraico mediante el uso del teorema de Floquet. En nuestro caso, partimos de un Hamiltoniano total parecido al no perturbado del cotunneling y aplicamos funciones de Green junto con operadores Hubbard. Así, llegamos a una ecuación diferencial en los elementos reducidos de la matrix de la densidad que cumple la forma requerida para aplicar Floquet. De esta forma, podemos transformar dicho sistema de ecuaciones en uno algebraico, resolverlo y calcular la corriente junto con cualquier otro observable del sistema. La forma en la que definimos el Hamiltoniano del sistema nos permite introducir interacciones entre espines y simular otros experimentos ESR más recientes. De las ecuaciones master de Floquet que derivamos podemos calcular todos los parámetros que afectan a la señal ESR tales como los tiempos de vida, de decoherencia o la frecuencia de Rabi de forma natural. En cualquier caso, en el momento de escribir la tesis, este último modelo aún no ha sido totalmente explorado. Por tanto, tenemos margen de mejora de cara a los resultados. Sin embargo, cabe destacar que estos resultan ser bastante satisfactorios., [EN]: Scanning tunneling microscope (STM) has revolutionized the field of condensed matter physics since years. The reason why comes from offering an amazing spatial and energy resolutions, which allows to manipulate atoms thank to a precise control of the tip. However, since 2015, a new technique emerged with a better energy resolution and the same amazing spatial one. The technique is called Electron Spin Resonance (ESR). The ESRSTM technique consists in modulating the tip-surface bias potential with a radiofrequency (AC) component. When the frequency matches the Larmor frequency of a local magnetic moment, the current changes rapidly and the spin precesses. Some of the most interesting application have been the identification of isotopes of Ti and Fe, and to gather information on the elusive f-electron of Ho atoms. Recently, STM-ESR has been used to make coherence manipulation of local magnetic atoms. In this way, quantum operations could be possible and it could revolutionize the field of quantum information. However, the mechanism is still not perfectly understood. The challenge is to fully comprehend how the electric field can alter a magnetic moment. Different mechanisms have been proposed: phonons excitations, displacement of the magnetic atom etc. The aim of this thesis is light up this questions and trying to come up with a theoretical model that can simulate and predict experiments. Initially, we will apply Density Functional Theory (DFT) in order to gather information on the magnetic system (Fe on MgO/Ag(001)) when an electric field is applied. To this end, we follow the standard procedure of relaxation of the bulk system MgO and Ag. After extracting the lattice parameter, we build the surface MgO/Ag(001) and place the Fe on the top O. If we now compute the PDOS and planar average potential (PAP) for different electric fields, we can easily see that PAP feel it significantly more. Therefore, we can conclude that the electric field is modulating the tunneling barrier. It is worthy to notice that the surface Cu2N/Cu o ClCu/Cu feels the electric field much less compare to the MgO/Ag surface. With this information, we can start applying certain theories that could allow us to simulate the experiments. We first try the cotunneling approach. We use a Hamiltonian that contains the reservoirs, the impurity Hamiltonian (generalized Anderson model) and the connection between both, called tunneling Hamiltonian. This last contribution is approximated by perturbation theory up to second order. The objective is to derive a cotunneling Hamiltonian from this approximation and apply Bloch Redfield theory. This theory is extremely useful for open quantum system such that ESR because it uses a density matrix language. The theory can be easily expanded to time dependent problems too. Combining cotunneling and Bloch-Redfield lead master equation that contains a new parameter: the Rabi frequency. Rabi frequency becomes essential to explain the ESR. Without it, the spin do not precess since the resonance peak is proportional to the square of the Rabi frequency. Even though the cotunneling results are quite satisfactory, the Rabi frequency is still a factor 10-20 larger than the one we find in the experiments. A quick look at the expression we are using gives us the reason of this discrepancy: we are oversimplifying the calculations. To improve the results one could apply Wannier but we are not going to talk about it in this thesis. The next theory we apply, in order to improve our results, is the Floquet theory together with non equilibrium Green’s function. Floquet theory is the study of the stability of linear periodic systems in continuous time. It allows us to transform a time differential system of equation into an algebraic one, using the so called Floquet theorem. If we use a total Hamiltonian similar to the one we talked early, while introducing Hubbard operator and Green’s Function, we arrive to a master equation of the reduced density matrix. This master equation satisfies the Floquet condition so that we transform the system into a simpler algebraic one to compute the density matrix element, current or any other observable. The master equation contains all the ESR important parameter such as lifetime, decoherence times or Rabi frequencies. Moreover, since we also introduce an exchange interaction between spins, we can simulate other experimental situations. In any case, at the moment of writing the thesis, Floquet Green’s function model is still quite unexplored. Therefore, it can be greatly improved and extended even though the results are already quite satisfactory.

Magnetic domains are at the core of most data storage technologies. Material science is fundamental in the design of new devices, with a continuous search for devices with smaller domain sizes, which enables higher storage density, together with new protocols for more efficient manipulation. The route for new materials and implementation can be more efficiently addressed in a bottom-up approach, where optimal atomic species, crystal structures, and stackings are analyzed systematically. Thin insulating layers act as stabilizers of the magnetic domains, which suffer the impact of interactions such as phonon scattering, electronic scattering with nearby metals, or the interaction with the probe tunnel current. With this idea in mind, in this work, we study the magnetic properties of some transition metal atoms, usually employed in magnetic domains, deposited on an atomically thin insulating layer of NaCl, a substrate that has been used by some experimental groups in the search for alternative and viable technologies. With the aid of an electronic multiplet calculation, which allows us to treat precisely the essential electronic correlations in the d-shell of the transition metal atom, we describe the magnetic degrees of freedom of the local spins of isolated impurities. The analysis of the spectral properties permits us to describe essential properties, such as the magnetic anisotropy, the energy scale responsible of the stabilization of the magnetic moments versus thermal or quantum fluctuations. We first use cobalt as a model adatom, and we use it to explore the robustness and limitations of our results. The analysis of structural and absorption properties is beyond the scope of the present work. Thus, it should be understood as a guide for future and more elaborate studies, concentrating just on the possible adatoms which could display the most advantageous magnetic properties. The results are then extended to other transition metal atoms such as Fe or Ni.

[EN]: We combine density functional theory (DFT) calculations and a multiorbital many-body Hamiltonian approach to shed light on magnetic properties of Co adsorbed on h-BN depending on the adsorption site. These methods reveal an out-of-plane easy axis anisotropy for atop N site and hard axis for hollow site, with an electronic configuration close to 3d8, corresponding to a spin S = 1. Then, we compare our results with x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) measurements on Co/h-BN/Ir(111) and Co/h-BN/Ru(0001). XAS and XMCD data show large (14 meV) out-of-plane anisotropy for Co/h-BN/Ru(0001) and almost isotropic for Co/h-BN/Ir(111), while both have an electronic structure compatible with spin S = 1. We use this information to determine the atop N adsorption of Co on h-BN/Ru(0001) and hollow for the Co on h-BN/Ir(111). XMLD data together with DFT and multiorbital Hubbard model results suggest that the different adsorption sites induce dissimilar anisotropy of Co. Finally, we explain from DFT calculations the counterintuitive downward shift of the Au(111) surface state measured by angle resolved photo-emission spectroscopy (ARPES) when two homothetic Co-coordinated metal-organic nanoporous networks (MONN) are self-assembled. We associate this effect to the weak Co-substrate hybridization and show that it appears with different adatoms and substrates., [ES]: El rápido avance tecnológico de las ultimas décadas y el gran impacto que tiene la informacion en la sociedad actual crean la necesidad de buscar nuevas formas mas efi cientes de almacenar la informacion. La cantidad total de informacion almacenada en el mundo ha pasado de 1 ZB (1021 B) en 2009 a alrededor de 20 ZB en 2017, y se espera que siga creciendo, superando los 160 ZB en 2025. Este aumento se ha visto enormemente favorecido por la aparición de nuevas tecnologías como los coches autónomos, la inteligencia art ficial y electrodomésticos inteligentes. Todos estos avances necesitan procesar una cantidad enorme de informacion que tiene que ser almacenada de alguna forma. Hoy en día, la informacion se almacena en tres tipos de dispositivos: ópticos, eléctricos y magnéticos. Los dispositivos más comunes y de más capacidad son los dispositivos de almacenamiento magnéticos. Estos almacenan la informacion en forma de dominios magnéticos localizados en un material magnético. La informacion de estos dominios se lee y escribe mediante una cabeza que detecta y modi fica la magnetización de dicho dominio. Este tipo de tecnología se emplea en los discos duros, las bandas magnéticas (tarjetas de crédito) y las memorias RAM (random access memory) magnéticas o MRAM. Generalmente, la capacidad de un dispositivo magnetice aumenta cuanto más pequeño sean los dominios. Los dispositivos convencionales tienen la capacidad de almacenar alrededor de 1 Pbit/m2 (1016 bit/m2), lo que signi fica que cada dominio ocupa unos 100 nm2 de la superfi cie magnética. En ultima instancia, el tamaño límite de estos dominios sera el límite atómico. El objetivo de esta tesis es estudiar estos dominios magnéticos en el limite atómico. Para ello es necesario estudiar como son las interacciones magnéticas a escala atómica.