1,221 research outputs found

    Photophysics, electronic structure and picosecond excited-state dynamics of boron-nitrogen-bridged ferrocene-donor organic-acceptor charge-transfer compounds

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    Im Rahmen dieser Dissertation wurde die Photophysik und die elektronische Struktur einer Klasse neuartiger Donator-Akzeptor-Ladungstransfer-Komplexe untersucht. Im Wesentlichen bestehen diese Verbindungen aus einem Ferrocen-Donator (Fc) und organischen Akzeptoren, die über B-N-Bindungen verbrückt sind, welche sich bei dieser Art von makromolekularen Systemen spontan bilden. Zentraler Gegenstand dieser Arbeit war die spektroskopische Untersuchung des Metall-zu-Ligand-Ladungstransfers (engl. Abkürzung: MLCT) im elektronischen Anregungszustand dieser kationischen Komplexverbindungen, die im Weiteren als „Fc-B-bpy“-Verbindungen bezeichnet werden. Die vorliegende Arbeit analysiert eine Vielzahl miteinander verwandter Fc-B-bpy-Derivate. Die Arbeit ist gegliedert in 1.) die Analyse der Absorptionsspektren vom UV- bis zum nahen Infrarot-Spektralbereich (250-1000 nm) von Lösungen, dotierten Polymer-Dünnfilmen und Einkristallen, 2.) die zeitaufgelöste optische Spektroskopie des angeregten Zustands auf der Pikosekunden-Zeitskala, 3.) die Analyse elektrochemischer Messungen an Lösungen, und 4.) die Auswertung quantenchemischer Berechnungen. Für die zeitaufgelösten Messungen wurde ein komplexes optisches Spektroskopie-System mit breitbandigen Femtosekunden-Pulsen sowie den entsprechenden zeitaufgelösten Detektionsmethoden (spektral gefilterte Weißlicht-Detektion) aufgebaut. Die Ergebnisse dieser Arbeit beweisen die Existenz eines MLCT-Übergangs mit fast vollständigem Übergang eines Fc-Donator-Elektrons zum B-bpy-Akzeptor bei optischer Anregung. Die vergleichenden Untersuchungen der spektroskopischen Eigenschaften verschiedener Derivate liefern wichtige Information für die Entwicklung neuartiger Derivate, einschließlich verwandter Polymere, mit verbesserten spektroskopischen Eigenschaften. Es wurden transiente Absorptionsmessungen bestimmter Fc-B-bpy-Derivate in Lösung nach gepulster Anregung der MLCT-Bande (bei 500 nm) über einen Zeitbereich von 0,1-1000 ps und einen Wellenlängenbereich von 460-760 nm vorgenommen. Aus den Messergebnissen geht hervor, dass die Relaxation aus dem angeregten MLCT-Zustand in den Grundzustand auf verschiedenen Zeitskalen geschehen kann, welche im Bereich zwischen ~18 und 900 ps liegen. Ein Vergleich verschiedener Derivate mit unterschiedlicher Flexibilität in der Konformation zeigt, dass die Starrheit der Bindungen zwischen Donatoren und Akzeptoren ein wesentlicher Faktor für die Lebensdauer des angeregten Zustands ist. Wenn die Akzeptorgruppen relativ frei rotieren können, ist es der Verbindung möglich, eine Geometrie einzunehmen, von der aus ein effizienter, strahlungsfreier Übergang in den Grundzustand erfolgen kann. Dieser Befund zeigt einen Weg auf, wie neuartige, verwandte Verbindungen mit größerer Lebensdauer das angeregten Zustands synthetisiert werden können, indem darauf geachtet wird, daß eine starre molekulare Architektur zwischen Donator und Akzeptor verwirklicht wird

    Optimizing astrophotonic spatial reformatters using simulated on-sky performance

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    One of the most useful techniques in astronomical instrumentation is image slicing. It enables a spectrograph to have a more compact angular slit, whilst retaining throughput and increasing resolving power. Astrophotonic components like the photonic lanterns and photonic reformatters can be used to replace bulk optics used so far. This study investigates the performance of such devices using end-to-end simulations to approximate realistic on-sky conditions. It investigates existing components, tries to optimize their performance and aims to understand better how best to design instruments to maximize their performance. This work complements the recent work in the field and provides an estimation for the performance of the new components.Comment: Conference proceedings in SPIE 2018 Austin Texa

    Advanced Kidney Disease Patient Portal:Implementation and Evaluation with Haemodialysis Patients

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    Patients on haemodialysis face complex care pathways, a high treatment burden and lower quality-of-life. Working with multidisciplinary domain experts, we have conducted several iterative development cycles to design, develop and evaluate a portal for patients on haemodialysis that can help them better understand and navigate their care pathways. A key functionality of the portal is to improve data and information sharing with clinicians, including on key aspects of quality-of-life through Patients Reported Outcome Measures. A case study was conducted with multidisciplinary experts and patients in the NHS Greater Glasgow and Clyde health board (Scotland), using interviews combined with the System Usability Scale (n=26). Patients' feedback and system use observations were used to further refine the system design requirements and functionalities. Key lessons include: a wide preference for tablet-based input vs paper, identification of case-specific accessibility issues and situational impairment, benefits of self-completed digital data collection in overcoming such issues and promoting patient independence and privacy, with considerations for maintaining perceived value and engagement with such systems and when to offer alternatives

    Skeletal muscle and the maintenance of vitamin d status

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    © 2020 by the authors. Licensee MDPI, Basel, Switzerland. Vitamin D, unlike the micronutrients, vitamins A, E, and K, is largely obtained not from food, but by the action of solar ultraviolet (UV) light on its precursor, 7-dehydrocholesterol, in skin. With the decline in UV light intensity in winter, most skin production of vitamin D occurs in summer. Since no defined storage organ or tissue has been found for vitamin D, it has been assumed that an adequate vitamin D status in winter can only be maintained by oral supplementation. Skeletal muscle cells have now been shown to incorporate the vitamin D-binding protein (DBP) from blood into the cell cytoplasm where it binds to cytoplasmic actin. This intracellular DBP provides an array of specific binding sites for 25-hydroxyvitamin D (25(OH)D), which diffuses into the cell from the extracellular fluid. When intracellular DBP undergoes proteolytic breakdown, the bound 25(OH)D is then released and diffuses back into the blood. This uptake and release of 25(OH)D by muscle accounts for the very long half-life of this metabolite in the circulation. Since 25(OH)D concentration in the blood declines in winter, its cycling in and out of muscle cells appears to be upregulated. Parathyroid hormone is the most likely factor enhancing the repeated cycling of 25(OH)D between skeletal muscle and blood. This mechanism appears to have evolved to maintain an adequate vitamin D status in winter

    Environmental interventions to reduce fear of crime: systematic review of effectiveness

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    Background: Fear of crime is associated with negative health and wellbeing outcomes, and may mediate some impacts of the built environment on public health. A range of environmental interventions have been hypothesized to reduce the fear of crime. Methods: This review aimed to synthesize the literature on the effectiveness of interventions in the built environment to reduce the fear of crime. Systematic review methodology, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidance, was used. Studies of environmental interventions which reported a fear of crime outcome and used any prospective evaluation design (randomized controlled trial (RCT), trial or uncontrolled before-and-after study) were included. Eighteen databases were searched. The Hamilton tool was used to assess quality. A narrative synthesis of findings was undertaken. Results: A total of 47 studies were included, 22 controlled and 25 uncontrolled, with total sample sizes ranging from n = 52 to approximately n = 23,000. Thirty-six studies were conducted in the UK, ten studies in the USA and one study in the Netherlands. The quality of the evidence overall is low. There are some indications that home security improvements and non-crime-related environmental improvements may be effective for some fear of crime outcomes. There is little evidence that the following reduce fear of crime: street lighting improvements, closed-circuit television (CCTV), multi-component environmental crime prevention programs or regeneration programs. Conclusions: There is some evidence for the effectiveness of specific environmental interventions in reducing some indicators of fear of crime, but more attention to the context and possible confounders is needed in future evaluations of complex social interventions such as these

    Metastable structural transformations and pressure-induced amorphization in natural (Mg,Fe)2SiO4 olivine under static compression: A Raman spectroscopic study

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    [EN] Raman spectroscopic data were obtained for (Mg,Fe)(2)SiO4 samples during compression to 57 GPa. Single crystals of San Carlos olivine compressed hydrostatically above 41 GPa showed appearance of a new "defect" peak in the 820-840 cm(-1) region associated with SiOSi linkages appearing between adjacent SiO44- tetrahedra to result in five- or sixfold-coordinated silicate species. Appearance of this feature is accompanied by a broad amorphous background. The changes occur at lower pressure than metastable crystalline transitions of end-member Mg2SiO4 forsterite (Fo-I) into Fo-II and Fo-III phases described recently. We complemented our experimental study using density functional theory (DFT) calculations and anisotropic ion molecular dynamics (AIMD) simulations to study the Raman spectra and vibrational density of states (VDOS) of metastably compressed Mg2SiO4 olivine, Fo-II and Fo-III, and quenched melts at high and low pressures. By 54 GPa all sharp crystalline peaks disappeared from observed Raman spectra indicating complete pressure-induced amorphization (PIA). The amorphous (Mg,Fe)(2)SiO4 spectrum contains Si-O stretching bands at lower wavenumber than expected for SiO44- indicating high coordination of the silicate units. The amorphous spectrum persisted on decompression to ambient conditions but with evidence for reappearance of tetrahedrally coordinated units. Non hydrostatic compression of polycrystalline olivine samples showed similar appearance of the defect feature and broad amorphous features between 43-44 GPa. Both increased in intensity as the sample was left at pressure overnight but they disappeared during decompression below 17 GPa with recovery of the starting olivine Raman signature. A hydrated San Carlos olivine sample containing 75-150 ppm OH was also studied. Significant broadening of the SiO44- stretching peaks was observed above 43 GPa but without immediate appearance of the defect or broad amorphous features. However, both of these characteristics emerged after leaving the sample at 47 GPa overnight followed by complete amorphization that occurred upon subsequent pressurization to 54 GPa. During decompression the high-density amorphous spectrum was retained to 3 GPa but on final pressure release a spectrum similar to thermally quenched low-pressure olivine glass containing isolated SiO44- groups was obtained. Leaving this sample overnight resulted in recrystallization of olivine. Our experimental data provide new insights into the metastable structural transformations and relaxation behavior of olivine samples including material recovered from meteorites and laboratory shock experiments.Our work was supported by the U.K. NERC via Grant NE/K002902/1 and Spanish MINECO under projects MAT2014-46649-C4-1/2-P.Santamaría Pérez, D.; Thomson, A.; Segura, A.; Pellicer Torres, J.; Manjón, F.; Cora, F.; Mccoll, K.... (2016). Metastable structural transformations and pressure-induced amorphization in natural (Mg,Fe)2SiO4 olivine under static compression: A Raman spectroscopic study. American Mineralogist. 101(7):1642-1650. https://doi.org/10.2138/am-2016-5389CCBYS16421650101

    Validation of a vascular access specific quality of life measure (VASQoL)

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    Background: A self-administered 11 item vascular access specific quality of life measure (VASQoL) was previously derived from detailed qualitative interviews with adult patients with kidney failure who have experienced vascular access using the Capabilities Approach as a theoretical base. This study reports the psychometric validation of the VASQoL measure including its reliability, content validity and responsiveness to change. Methods: Cognitive interviews were conducted with 23 adult patients with kidney failure after completion of the VASQoL measure. Focus group discussion with a vascular access professional multidisciplinary team was undertaken (n = 8) and subsequently a further 101 adult kidney failure patients with vascular access (TCVC, AVF or AVG) completed the digital VASQoL measure, EQ-5D and SF-36 questionnaires in a longitudinal study with prospectively recorded vascular access events. Results: Transcript analysis of cognitive interviews after VASQoL completion indicated that the content was comprehensive and well understood by participants. Assessment of Internal reliability for the VASQoL measure was high (Cronbach’s alpha 0.858). Test-retest reliability of the overall VASQoL measure was high (intra class correlation coefficient 0.916). In those patients who experienced a vascular access event, significant differences were observed in paired analysis of the VASQoL physical domain questions and vascular access function domain questions and in the EQ-5D usual activities, pain and anxiety domains. In those with no vascular access event, variation was observed in longitudinal analysis in VASQoL questions relating to worry about VA function and capability domains, whilst no variation was observed in the EQ5D measure. Conclusion: The VASQoL measure has good internal consistency, test-retest reliability, convergent validity and responsiveness to change for clinically relevant vascular access outcomes. This provides a validated, vascular access specific quality of life measure that can be used in future trials of vascular access, evaluation of new technologies and routine use as a patient reported outcome measure (PROM)
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