3 resultados para Arc flash hazards

em Helda - Digital Repository of University of Helsinki


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Most countries of Europe, as well as many countries in other parts of the world, are experiencing an increased impact of natural hazards. It is often speculated, but not yet proven, that climate change might influence the frequency and magnitude of certain hydro-meteorological natural hazards. What has certainly been observed is a sharp increase in financial losses caused by natural hazards worldwide. Eventhough Europe appears to be a space that is not affected by natural hazards to such catastrophic extents as other parts of the world are, the damages experienced here are certainly increasing too. Natural hazards, climate change and, in particular, risks have therefore recently been put high on the political agenda of the EU. In the search for appropriate instruments for mitigating impacts of natural hazards and climate change, as well as risks, the integration of these factors into spatial planning practices is constantly receiving higher attention. The focus of most approaches lies on single hazards and climate change mitigation strategies. The current paradigm shift of climate change mitigation to adaptation is used as a basis to draw conclusions and recommendations on what concepts could be further incorporated into spatial planning practices. Especially multi-hazard approaches are discussed as an important approach that should be developed further. One focal point is the definition and applicability of the terms natural hazard, vulnerability and risk in spatial planning practices. Especially vulnerability and risk concepts are so many-fold and complicated that their application in spatial planning has to be analysed most carefully. The PhD thesis is based on six published articles that describe the results of European research projects, which have elaborated strategies and tools for integrated communication and assessment practices on natural hazards and climate change impacts. The papers describe approaches on local, regional and European level, both from theoretical and practical perspectives. Based on these, passed, current and future potential spatial planning applications are reviewed and discussed. In conclusion it is recommended to shift from single hazard assessments to multi-hazard approaches, integrating potential climate change impacts. Vulnerability concepts should play a stronger role than present, and adaptation to natural hazards and climate change should be more emphasized in relation to mitigation. It is outlined that the integration of risk concepts in planning is rather complicated and would need very careful assessment to ensure applicability. Future spatial planning practices should also consider to be more interdisciplinary, i.e. to integrate as many stakeholders and experts as possible to ensure the sustainability of investments.

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Viime aikoina yleistyneet flash-muistiin perustuvat tallennusvälineet ovat monessa suhteessa kiintolevyä parempia. Flash-muistissa on kuitenkin useita erityispiirteitä, jotka vaikeuttavat sen käyttöönottoa tietokantajärjestelmässä. Flash-muistissa kirjoittaminen on hitaampaa kuin lukeminen. Erityisesti hajanaisten sivujen päivittäminen on hidasta. Hajaluku flash-muistista on huomattavasti nopeampaa kuin kiintolevyltä. Näiden erityispiirteiden vuoksi tietokannan hallintajärjestelmä on optimoitava erikseen flash-muistia varten. Tässä optimoinnissa lähes kaikki tietokannan hallintajärjestelmän osa-alueet on toteutettava uudelleen flash-muistin näkökulmasta. Flash-muistin nopean hajaluvun ansiosta relaatioiden tiedot voidaan sijoitella flash-muistiin vapaammin kuin kiintolevylle. Yleisin tietokannoissa käytetty hakemistorakenne B+-puu ei toimi tehokkaasti flash-muistissa hajapäivitysten suuren määrän vuoksi. Flashmuistia varten on kehitetty useita B+-puun muunnelmia, joissa hajapäivitysten määrää on onnistuttu vähentämään. Puskurin hallintaa voidaan optimoida flash-muistia varten vähentämällä hitaiden kirjoitusten määrää nopeiden lukujen määrän kustannuksella sekä muuttamalla hitaita hajakirjoituksia nopeammiksi peräkkäisten sivujen kirjoituksiksi. B.3 (hardware, memory structures) H.2.2 (database management, physical design)

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The main obstacle for the application of high quality diamond-like carbon (DLC) coatings has been the lack of adhesion to the substrate as the coating thickness is increased. The aim of this study was to improve the filtered pulsed arc discharge (FPAD) method. With this method it is possible to achieve high DLC coating thicknesses necessary for practical applications. The energy of the carbon ions was measured with an optoelectronic time-of-flight method. An in situ cathode polishing system used for stabilizing the process yield and the carbon ion energies is presented. Simultaneously the quality of the coatings can be controlled. To optimise the quality of the deposition process a simple, fast and inexpensive method using silicon wafers as test substrates was developed. This method was used for evaluating the suitability of a simplified arc-discharge set-up for the deposition of the adhesion layer of DLC coatings. A whole new group of materials discovered by our research group, the diamond-like carbon polymer hybrid (DLC-p-h) coatings, is also presented. The parent polymers used in these novel coatings were polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE). The energy of the plasma ions was found to increase when the anode-cathode distance and the arc voltage were increased. A constant deposition rate for continuous coating runs was obtained with an in situ cathode polishing system. The novel DLC-p-h coatings were found to be water and oil repellent and harder than any polymers. The lowest sliding angle ever measured from a solid surface, 0.15 ± 0.03°, was measured on a DLC-PDMS-h coating. In the FPAD system carbon ions can be accelerated to high energies (≈ 1 keV) necessary for the optimal adhesion (the substrate is broken in the adhesion and quality test) of ultra thick (up to 200 µm) DLC coatings by increasing the anode-cathode distance and using high voltages (up to 4 kV). An excellent adhesion can also be obtained with the simplified arc-discharge device. To maintain high process yield (5µm/h over a surface area of 150 cm2) and to stabilize the carbon ion energies and the high quality (sp3 fraction up to 85%) of the resulting coating, an in situ cathode polishing system must be used. DLC-PDMS-h coating is the superior candidate coating material for anti-soiling applications where also hardness is required.