9,343 research outputs found

    Neutron scattering studies of heterogeneous catalysis

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    Understanding the structural dynamics/evolution of catalysts and the related surface chemistry is essential for establishing structure–catalysis relationships, where spectroscopic and scattering tools play a crucial role. Among many such tools, neutron scattering, though less-known, has a unique power for investigating catalytic phenomena. Since neutrons interact with the nuclei of matter, the neutron–nucleon interaction provides unique information on light elements (mainly hydrogen), neighboring elements, and isotopes, which are complementary to X-ray and photon-based techniques. Neutron vibrational spectroscopy has been the most utilized neutron scattering approach for heterogeneous catalysis research by providing chemical information on surface/bulk species (mostly H-containing) and reaction chemistry. Neutron diffraction and quasielastic neutron scattering can also supply important information on catalyst structures and dynamics of surface species. Other neutron approaches, such as small angle neutron scattering and neutron imaging, have been much less used but still give distinctive catalytic information. This review provides a comprehensive overview of recent advances in neutron scattering investigations of heterogeneous catalysis, focusing on surface adsorbates, reaction mechanisms, and catalyst structural changes revealed by neutron spectroscopy, diffraction, quasielastic neutron scattering, and other neutron techniques. Perspectives are also provided on the challenges and future opportunities in neutron scattering studies of heterogeneous catalysis

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    The future of cosmology? A case for CMB spectral distortions

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    This thesis treats the topic of CMB Spectral Distortions (SDs), which represent any deviation from a pure black body shape of the CMB energy spectrum. As such, they can be used to probe the inflationary, expansion and thermal evolution of the universe both within Λ\LambdaCDM and beyond it. The currently missing observation of this rich probe of the universe makes of it an ideal target for future observational campaigns. In fact, while the Λ\LambdaCDM signal guarantees a discovery, the sensitivity to a wide variety of new physics opens the door to an enormous uncharted territory. In light of these considerations, the thesis opens by reviewing the topic of CMB SDs in a pedagogical and illustrative fashion, aimed at waking the interest of the broader community. This introductory premise sets the stage for the first main contribution of the thesis to the field of SDs: their implementation in the Boltzmann solver CLASS and the parameter inference code MontePython. The CLASS+MontePython pipeline is publicly available, fast, it includes all sources of SDs within Λ\LambdaCDM and many others beyond that, and allows to consistently account for any observational setup. By means of these numerical tools, the second main contribution of the thesis consists in showcasing the versatility and competitiveness of SDs for several cosmological models as well as for a number of different mission designs. Among others, the results cover features in the primordial power spectrum, primordial gravitational waves, non-standard dark matter properties, primordial black holes, primordial magnetic fields and Hubble tension. Finally, the manuscript is disseminated with (20) follow-up ideas that naturally extend the work carried out so far, highlighting how rich of unexplored possibilities the field of CMB SDs still is. The hope is that these suggestions will become a propeller for further interesting developments.Comment: PhD thesis. Pedagogical review of theory, experimental status and numerical tools (CLASS+MontePython) with broad overview of applications. Includes 20 original follow-up idea

    Novel 129Xe Magnetic Resonance Imaging and Spectroscopy Measurements of Pulmonary Gas-Exchange

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    Gas-exchange is the primary function of the lungs and involves removing carbon dioxide from the body and exchanging it within the alveoli for inhaled oxygen. Several different pulmonary, cardiac and cardiovascular abnormalities have negative effects on pulmonary gas-exchange. Unfortunately, clinical tests do not always pinpoint the problem; sensitive and specific measurements are needed to probe the individual components participating in gas-exchange for a better understanding of pathophysiology, disease progression and response to therapy. In vivo Xenon-129 gas-exchange magnetic resonance imaging (129Xe gas-exchange MRI) has the potential to overcome these challenges. When participants inhale hyperpolarized 129Xe gas, it has different MR spectral properties as a gas, as it diffuses through the alveolar membrane and as it binds to red-blood-cells. 129Xe MR spectroscopy and imaging provides a way to tease out the different anatomic components of gas-exchange simultaneously and provides spatial information about where abnormalities may occur. In this thesis, I developed and applied 129Xe MR spectroscopy and imaging to measure gas-exchange in the lungs alongside other clinical and imaging measurements. I measured 129Xe gas-exchange in asymptomatic congenital heart disease and in prospective, controlled studies of long-COVID. I also developed mathematical tools to model 129Xe MR signals during acquisition and reconstruction. The insights gained from my work underscore the potential for 129Xe gas-exchange MRI biomarkers towards a better understanding of cardiopulmonary disease. My work also provides a way to generate a deeper imaging and physiologic understanding of gas-exchange in vivo in healthy participants and patients with chronic lung and heart disease

    Analysis of Hippo pathway signalling in schwannoma and meningioma

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    Images from Figures 3.7.1, 3.7.2, 3.7.3, 3.9.3 and 3.11.2 and quantification data from Figures 3.7.5, 3.9.4 and 3.11.4 published in Laraba et al. 2022 in the scientific journal BrainThis project focuses on two tumours of the nervous system, schwannoma and meningioma. A large group of schwannomas and meningiomas display the inactivation of the NF2 gene. The NF2 gene codes for the tumour suppressor protein Merlin and its loss is associated with a multitude of pro-tumourigenic mechanisms leading to the occurrence of schwannomas and meningiomas. The loss of Merlin function causes augmented Hippo signaling i.e. interaction of YAP and TAZ, both co-activators of gene expression and the two main effectors of the Hippo signalling pathway, and TEAD, a group of transcription factors binding to YAP and TAZ. There resulting gene expression is associated with increased proliferation and evasion of cell death. This makes the YAP/TAZ-TEAD complex an excellent therapeutic target. Since therapy options for schwannomas and meningiomas are limited to surgery and radiosurgery, both carrying additional risks for the patient, new therapy approaches are desperately needed. Therefore, we explored if a schwannoma mouse model and cell culture and primary meningioma cells would be suitable systems to allow the testing of two potential new therapy options. Macrophages, especially tumour associated macrophages (TAMs), have been shown to promote tumour growth in various ways. Therefore, macrophage depletion is considered a promising therapy option. To see whether elimination of macrophages could be effective in our chosen schwannoma mouse model, a connection between increased TAM numbers and equally heightened proliferation within the developing schwannomas would need to be and was established. Additionally, Nf2 gene knockout and the additional knockout of either Yap or Taz genes also had distinct effects on proliferation, TAM numbers and overall schwannoma structure and cell numbers. Macrophage infiltration and resulting support of tumour growth has also been shown to be partly YAP/TAZ-TEAD signaling dependent. Therefore, in order to simultaneously reduce TAM-derived growth support and directly impair tumour cell proliferation, the second approach targets the Hippo signaling pathway using TEAD S-autopalmitoylation inhibitors by Vivace Therapeutics which interfere with YAP/TAZ-TEAD interaction. I could show that these TEAD palmitoylation inhibitors efficiently inhibit cell proliferation of human meningioma cell lines and primary human meningioma cells.Peninsula Schools of Medicine and DentistryBrain Tumour Researc

    Modified Theories of Gravity and Cosmological Applications

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    This reprint focuses on recent aspects of gravitational theory and cosmology. It contains subjects of particular interest for modified gravity theories and applications to cosmology, special attention is given to Einstein–Gauss–Bonnet, f(R)-gravity, anisotropic inflation, extra dimension theories of gravity, black holes, dark energy, Palatini gravity, anisotropic spacetime, Einstein–Finsler gravity, off-diagonal cosmological solutions, Hawking-temperature and scalar-tensor-vector theories

    Investigating optical absorption in organic semiconductors using a coarse-grained approach

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    Organic semiconductors have attracted great interest as candidate materials for solar cells, light-emitting diodes and other photonic applications. The performance of such devices depends upon the spectral range and strength of the optical absorption, as well as other material properties. Optical transition energies and strengths are controlled in turn by the chemical structure of the (macro)molecule and its conformation; however, the large conformational phase space of conjugated polymers means that the chemical structure – optical property relationship is not trivial to determine. In the solid state, the conformations and interactions of the molecules are a function of process conditions and hard to control, and yet they control the optoelectronic properties of the material. Whilst many studies have sought to develop and validate computationally efficient methods for prediction of transition energies, relatively few have addressed prediction of transition strength. Methods such as time dependent density functional theory are widely used to complement experimental studies but are too computationally expensive to access the length scales required to fully explain the observed structure-property relationships, especially for polymers with large repeat units or complex phase behaviour. Coarse-grained models of optical properties such as tight-binding exciton models can be used to examine the structure-property relationships at longer length scales, but these use approximations to the electron-hole interactions that do not accurately reproduce the experimentally observed trends in absorption strength as a function of molecular structure. I therefore implement a coarse-grained model using parameters from ab initio calculations as a tool to further our understanding of the relationship between the conformation of pi-conjugated macromolecules and their optical properties. I apply this approach to study two conjugated polymers and show how effects of conformational changes on their optical absorption spectra can be linked to changes in the parameters that characterise the electronic intermonomer interactions in the model.Open Acces

    Optimization of passive ultrafast fiber lasers based on indium nitride for novel applications

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    Los láseres ultrarrápidos en fibra constituyen una de las fuentes de luz más utilizadas actualmente debido a su fiabilidad y flexibilidad, convirtiéndose en la pieza clave de múltiples aplicaciones, como las comunicaciones ópticas, el procesamiento de materiales o la espectroscopía. Entre ellos, los láseres en fibra anclado en modos basados en el uso de absorbentes saturables demuestran características superiores de estabilidad, simplicidad y bajo coste, capaces de emitir pulsos ultracortos con potencias extremadamente altas en un amplio rango espectral. En las últimas décadas, se han probado varios absorbentes saturables, donde los materiales de semiconductor destacan por su amplia profundidad de modulación, su elevada absorción no lineal y su baja intensidad de saturación. Sin embargo, presentan algunas limitaciones como un estrecho ancho de banda y un bajo umbral de daño. Por tanto, en este trabajo se propone el uso de un semiconductor de InN en un láser todo en fibra anclado en modos para la generación de láseres ultrarrápidos de alta potencia en la región del infrarrojo cercano. Esta configuración ha demostrado trenes de pulsos Gaussianos en el rango de los femtosegundos mediante un sistema sencillo y de bajo coste. En esta tesis, el objetivo es optimizar las características de un láser de fibra anclado en modos basado en un absorbente saturable de InN, y desarrollar un novedoso dispositivo espectroscópico para aplicaciones de detección. Primeramente, se estudia la mejora de las propiedades del absorbente saturable de semiconductor mediante un mayor control del dopaje residual así como del crecimiento de material, demostrando el máximo comportamiento no lineal para este tipo de absorbentes saturables en un láser en fibra. También se discute como estas características podrían mejorarse mediante el desarrollo de un nuevo diseño de láser totalmente en fibra, capaz de contrarrestar las limitaciones actuales de ruido y perdidas de inserción dentro de la cavidad láser. De este modo, se demuestra la duración de pulso más corta y la máxima potencia óptica, conservando una configuración sencilla, lo que allana el camino hacia el desarrollo de sistemas láser comerciales en aplicaciones de alta potencia. A continuación, se introducen nuevas aplicaciones potenciales del sistema láser de fibra: en la detección de gases, mediante la generación de supercontinuo del pulso láser ultrarrápido en fibras monomodo capaces de cubrir espectros de absorción más amplios; y en la caracterización de moléculas biológicas mediante el uso de una novedosa estructura espectroscópica SF-CARS conectada a la fuente láser totalmente en fibra. Además, se exponen las implicaciones del chirp-matching en el rendimiento de la medición de la absorción, y el impacto de la dispersión y los efectos no lineales generados por diferentes fibras ópticas en la compresión y el ensanchamiento de los pulsos de fibra ultrarrápidos. La configuración láser propuesta supera la máxima resolución medible y la cobertura espectral, las limitaciones más importantes a las que se enfrenta la espectroscopía moderna. Finalmente, se resumen los objetivos alcanzados en esta tesis, evaluando el potencial de las aplicaciones propuestas, así como futuras líneas de investigación basadas en dichos hallazgos
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