9,081 research outputs found

    GEE Training Manual on Use of Earth Observation data and Google Earth Engine monitoring and early warning of floods and droughts in Zambia

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    This training manual supported participants in learning the pre-processing tool to provide the user with enhanced time-series processing capabilities and access to various open-source satellite data, learning basic scripts in Google Earth Engine for activities related to floods and drought in showcasing the application of water resource management. Specifically, the experts will give more focus to Google’s Earth Engine platform to showcase large- and small-scale scientific analysis and visualization of geospatial datasets. The codes and step by step procedure are given in the manual

    The role of unpredictability in maintaining control of the security forces in The Gambia

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    Increased lifetime of Organic Photovoltaics (OPVs) and the impact of degradation, efficiency and costs in the LCOE of Emerging PVs

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    Emerging photovoltaic (PV) technologies such as organic photovoltaics (OPVs) and perovskites (PVKs) have the potential to disrupt the PV market due to their ease of fabrication (compatible with cheap roll-to-roll processing) and installation, as well as their significant efficiency improvements in recent years. However, rapid degradation is still an issue present in many emerging PVs, which must be addressed to enable their commercialisation. This thesis shows an OPV lifetime enhancing technique by adding the insulating polymer PMMA to the active layer, and a novel model for quantifying the impact of degradation (alongside efficiency and cost) upon levelized cost of energy (LCOE) in real world emerging PV installations. The effect of PMMA morphology on the success of a ternary strategy was investigated, leading to device design guidelines. It was found that either increasing the weight percent (wt%) or molecular weight (MW) of PMMA resulted in an increase in the volume of PMMA-rich islands, which provided the OPV protection against water and oxygen ingress. It was also found that adding PMMA can be effective in enhancing the lifetime of different active material combinations, although not to the same extent, and that processing additives can have a negative impact in the devices lifetime. A novel model was developed taking into account realistic degradation profile sourced from a literature review of state-of-the-art OPV and PVK devices. It was found that optimal strategies to improve LCOE depend on the present characteristics of a device, and that panels with a good balance of efficiency and degradation were better than panels with higher efficiency but higher degradation as well. Further, it was found that low-cost locations were more favoured from reductions in the degradation rate and module cost, whilst high-cost locations were more benefited from improvements in initial efficiency, lower discount rates and reductions in install costs

    Early Neanderthal social and behavioural complexity during the Purfleet Interglacial: handaxes in the latest Lower Palaeolithic.

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    Only a handful of ‘flagship’ sites from the Purfleet Interglacial (Marine Isotope Stage 9, c. 350-290,000 years ago) have been properly examined, but the archaeological succession at the proposed type-site at Purfleet suggests a period of complexity and transition, with three techno-cultural groups represented in Britain. The first was a simple toolkit lacking handaxes (the Clactonian), and the last a more sophisticated technology presaging the coming Middle Palaeolithic (simple prepared core or proto-Levallois technology). Sandwiched between were Acheulean groups, whose handaxes comprise the great majority of the extant archaeological record of the period – these are the focus of this study. It has previously been suggested that some features of the Acheulean in the Purfleet Interglacial were chronologically restricted, particularly the co-occurrence of ficrons and cleavers. These distinctive forms may have exceeded pure functionality and were perhaps imbued with a deeper social and cultural meaning. This study supports both the previously suggested preference for narrow, pointed morphologies, and the chronologically restricted pairing of ficrons and cleavers. By drawing on a wide spatial and temporal range of sites these patterns could be identified beyond the handful of ‘flagship’ sites previously studied. Hypertrophic ‘giants’ have now also been identified as a chronologically restricted form. Greater metrical variability was found than had been anticipated, leading to the creation of two new sub-groups (IA and IB) which are tentatively suggested to represent spatial and perhaps temporal patterning. The picture in the far west of Britain remains unclear, but the possibility of different Acheulean groups operating in the Solent area, and a late survival of the Acheulean, are both suggested. Handaxes with backing and macroscopic asymmetry may represent prehensile or ergonomic considerations not commonly found on handaxes from earlier interglacial periods. It is argued that these forms anticipate similar developments in the Late Middle Palaeolithic in an example of convergent evolution

    Physical phenomena controlling quiescent flame spread in porous wildland fuel beds

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    Despite well-developed solid surface flame spread theories, we still lack a coherent theory to describe flame spread through porous wildland fuel beds. This porosity results in additional complexity, reducing the thermal conductivity of the fuel bed, but allowing in-bed radiative and convective heat transfer to occur. While previous studies have explored the effect of fuel bed structure on the overall fire behaviour, there remains a need for further investigation of the effect of fuel structure on the underlying physical phenomena controlling flame spread. Through an extensive series of laboratory-based experiments, this thesis provides detailed, physics-based insights for quiescent flame spread through natural porous beds, across a range of structural conditions. Measurements are presented for fuel beds representative of natural field conditions within an area of the fire-prone New Jersey Pinelands National Reserve, which compliment a related series of field experiments conducted as part of a wider research project. Additional systematic investigation across a wider range of fuel conditions identified independent effects of fuel loading and bulk density on the spread rate, flame height and heat release rate. However, neither fuel loading nor bulk density alone provided adequate prediction of the resulting fire behaviour. Drawing on existing structural descriptors (for both natural and engineered fuel beds) an alternative parameter ασΎ was proposed. This parameter (incorporating the fuel bed porosity (α), fuel element surface-to-volume ratio (σ), and the fuel bed height (ÎŽ)) was strongly correlated with the spread rate. One effect of the fuel bed structure is to influence the heat transfer mechanisms both above and within the porous fuel bed. Existing descriptions of radiation transport through porous fuel beds are often predicated on the assumption of an isotropic fuel bed. However, given their preferential angle of inclination, the pine needle beds in this study may not exhibit isotropic behaviour. Regardless, for the structural conditions investigated, horizontal heat transfer through the fuel bed was identified as the dominant heating mechanism within this quiescent flame spread scenario. However, the significance of heat transfer contributions from the above-bed flame generally increased with increasing ασΎ value of the fuel bed. Using direct measurements of the heat flux magnitude and effective heating distance, close agreement was observed between experimentally observed spread rates and a simple thermal model considering only radiative heat transfer through the fuel bed, particularly at lower values of ασΎ. Over-predictions occurred at higher ασΎ values, or where other heat transfer terms were incorporated, which may highlight the need to include additional heat loss terms. A significant effect of fuel structure on the primary flow regimes, both within and above these porous fuel beds, was also observed, with important implications for the heat transfer and oxygen supply within the fuel bed. Independent effects of fuel loading and bulk density on both the buoyant and buoyancy-driven entrainment flow were observed, with a complex feedback cycle occurring between Heat Release Rate (HRR) and combustion behaviour. Generally, increases in fuel loading resulted in increased HRR, and therefore increased buoyant flow velocity, along with an increase in the velocity of flow entrained towards the combustion region. The complex effects of fuel structure in both the flaming and smouldering combustion phases may necessitate modifications to other common modelling approaches. The widely used Rothermel model under-predicted spread rate for higher bulk density and lower ασΎ fuel beds. As previously suggested, an over-sensitivity to fuel bed height was observed, with experimental comparison indicating an under-prediction of reaction intensity at lower fuel heights. These findings have important implications particularly given the continuing widespread use of the Rothermel model, which continues to underpin elements of the BehavePlus fire modelling system and the US National Fire Danger Rating System. The physical insights, and modelling approaches, developed for this low-intensity, quiescent flame spread scenario, are applicable to common prescribed fire activities. It is hoped that this work (alongside complimentary laboratory and field experiments conducted by various authors as part of a wider multi-agency project (SERDP-RC2641)) will contribute to the emerging field of prescribed fire science, and help to address the pressing need for further development of fire prediction and modelling tools

    Karttatypografia: luettavuuden parantaminen kirjainmuotoilun keinoin topografisissa kartoissa

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    This thesis examines the legibility of type on maps and aims to find out ways to improve it through type design. As type often is an integral part of maps – something that helps the map user navigate, understand, and perceive a wide range of information in an effective way – type design and legibility must be regarded as important design elements. However, even though cartography and typography have extensive theoretical bases, the subject of legibility has not been comprehensively researched in cartographic context. Thus, by combining type design theory and scientific legibility studies with cartographic theory, the legibility of type on maps could be improved. The topic is first studied by an extensive literature review to cover existing concepts and theories of cartography, cartographic typography, and typography. After a competent knowledge basis of these concepts and theories is acquired, the findings are utilised in the design component. The design component is a type family designed specifically to be used with topographic maps: it consists of two elements, a project description that follows the design process of the type family, relating design choices to the theoretical findings and perspectives presented in the literary review, and the finished type family. In conclusion of the design component, several visual studies are made both to compare the design component (type family) to other relevant typefaces, and to validate the possible functionality of the design component in the chosen cartographic application (topographic map). A broad understanding of the topics of the literature review was formed. Cartographic theory observed the overall nature of maps and specified the various map elements and their intended uses. Cartographic typography deepened the understanding of type on maps – it highlighted the specific needs that must be taken into consideration, demonstrated the diversity of typographic situations that might occur, and presented a large set of guidelines to help the mapmaker to achieve better results. Typography and type design focused on the micro-level of type: how the minor design choices affect the whole, and furthermore, through legibility studies, validated certain views and brought new topics into consideration. By combining theoretical literature from these domains, this thesis helped to form a foundation for an improved framework for type de-sign for (topographic) maps. Furthermore, the domains of cartographic typography and typography and type design gave clear suggestions on how the legibility of type on topographic maps can be improved: legibility of type in this context constitutes from multiple components that must be both taken into consideration and be applied to processes of mapmaking and type design.TĂ€ssĂ€ opinnĂ€ytetyössĂ€ tutkitaan karttatypografiaa ja pyritÀÀn löytĂ€mÀÀn keinoja parantaa luettavuutta kirjainmuotoilun keinoin. Teksti on usein elimellinen osa karttoja: se helpottaa kartan kĂ€yttĂ€jÀÀ navigoimaan ja sisĂ€istĂ€mÀÀn suuren mÀÀrĂ€n informaatiota tehokkaasti. SiispĂ€ kirjainmuotoilua ja luettavuutta tulee pitÀÀ tĂ€rkeinĂ€ karttasuunnittelun työkaluina. Vaikka sekĂ€ kartografiassa ettĂ€ typografiassa on olemassa laajat teoreettiset perustat, luettavuutta ei ole kattavasti tutkittu kartografisessa kontekstissa. YhdistĂ€mĂ€llĂ€ kirjainmuotoilun ja tieteelliset luettavuustutkimukset kartografiseen teoriaan, karttatekstien luettavuutta voidaan parantaa. Aluksi tutustutaan olemassa oleviin konsepteihin ja kartografisiin teorioihin kattavan kirjallisuuskatsauksen avulla. Kun tarpeellinen tietopohja on rakennettu, saavutettua tietĂ€mystĂ€ hyödynnetÀÀn opinnĂ€ytetyön projektiosassa, joka tĂ€ssĂ€ tapauksessa on topografisten karttojen yhteydessĂ€ kĂ€ytettĂ€vĂ€ kirjainperhe. Projektiosio on kaksijakoinen ja pitÀÀ sisĂ€llÀÀn sekĂ€ valmiin kirjainperheen, ettĂ€ projektikuvauksen. Projektikuvaus seuraa suunnitteluprosessia ja peilaa tehtyjĂ€ valintoja kirjallisuuskatsauksessa esiteltyihin löydöksiin. Projektiosion pÀÀtelmĂ€ssĂ€ tutkitaan visuaalisesti kirjainperheen toimintaa ja kĂ€yttökelpoisuutta topografisessa karttaympĂ€ristössĂ€, sekĂ€ verrataan kirjainperheen toimivuutta suhteessa muihin kirjaintyyppeihin. Tutkimuksen perusteella muodostuu laaja ymmĂ€rrys aiheesta. Kartografinen teoria valottaa yleisesti karttojen olemusta ja toimintaa, sekĂ€ esittelee erilaisia karttalementtejĂ€ ja niiden toimintatapoja. Karttatypografian teoria syventÀÀ ymmĂ€rrystĂ€ tekstin kĂ€yttĂ€ytymisestĂ€ karttaympĂ€ristössĂ€, esittelee karttatypografian erityispiirteitĂ€, ja tarjoaa laajan karttatypografisen ohjeiston. Typografian ja kirjainmuotoilun teoria keskittyy mikrotason aiheisiin: kuinka vĂ€hĂ€pĂ€töisiltĂ€ vaikuttavat suunnitteluvalinnat vaikuttavat kokonaisuuteen, ja kuinka luettavuustutkimukset auttavat nĂ€kemÀÀn asioita uudessa valossa. TĂ€mĂ€ opinnĂ€ytetyö auttaa parantamaan kirjainmuotoilua (topografisessa) karttaympĂ€ristössĂ€ yhdistĂ€mĂ€llĂ€ edellĂ€ mainittujen alojen teorioita keskenÀÀn ja pohjustamalla paranneltuja suunniteluvalintoja. Yhdistetty teoria viittaa selkeĂ€sti siihen, ettĂ€ luettavuus karttaympĂ€ristössĂ€ koostuu lukuisista osatekijöistĂ€ – nĂ€mĂ€ osatekijĂ€t tulee ymmĂ€rtÀÀ, ottaa huomioon, ja soveltaa sekĂ€ karttojen ettĂ€ niille suunniteltujen kirjaintyyppien suunnitteluprosesseissa

    Optical coherence tomography methods using 2-D detector arrays

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    Optical coherence tomography (OCT) is a non-invasive, non-contact optical technique that allows cross-section imaging of biological tissues with high spatial resolution, high sensitivity and high dynamic range. Standard OCT uses a focused beam to illuminate a point on the target and detects the signal using a single photodetector. To acquire transverse information, transversal scanning of the illumination point is required. Alternatively, multiple OCT channels can be operated in parallel simultaneously; parallel OCT signals are recorded by a two-dimensional (2D) detector array. This approach is known as Parallel-detection OCT. In this thesis, methods, experiments and results using three parallel OCT techniques, including full -field (time-domain) OCT (FF-OCT), full-field swept-source OCT (FF-SS-OCT) and line-field Fourier-domain OCT (LF-FD-OCT), are presented. Several 2D digital cameras of different formats have been used and evaluated in the experiments of different methods. With the LF-FD-OCT method, photography equipment, such as flashtubes and commercial DSLR cameras have been equipped and tested for OCT imaging. The techniques used in FF-OCT and FF-SS-OCT are employed in a novel wavefront sensing technique, which combines OCT methods with a Shack-Hartmann wavefront sensor (SH-WFS). This combination technique is demonstrated capable of measuring depth-resolved wavefront aberrations, which has the potential to extend the applications of SH-WFS in wavefront-guided biomedical imaging techniques
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