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41.
Wave energy is a renewable source, which has so far not been exploited widely. Many of the various schemes in the past consist of large mechanical structures, often located near the sea surface. This article presents a range of systems with point absorbers on the surface and linear generators placed on the seabed, converting the wave motion into electrical power. Electrical power components are combined in different ways to obtain solutions suitable for various conditions. Different topologies for the electrical system transmitting power to the grid are discussed. Qualitative case studies are used to exemplify system options and connection schemes. 相似文献
42.
Ulla Kokfelt Nina Reuss Eric Struyf Mats Sonesson Mats Rundgren G?ran Skog Peter Rosén Dan Hammarlund 《Journal of Paleolimnology》2010,44(1):327-342
Permafrost in peatlands of subarctic Sweden is presently thawing at accelerated rates, which raises questions about the destiny
of stored carbon and nutrients and impacts on adjacent freshwater ecosystems. In this study we use peat and lake sediment
records from the Stordalen palsa mire in northern Sweden to address the late Holocene (5,000 cal BP-present) development of
the mire as well as related changes in carbon and nutrient cycling. Formation, sediment accumulation and biogeochemistry of
two studied lakes are suggested to be largely controlled by the development of the mire and its permafrost dynamics. Peat
inception took place at ca. 4,700 cal BP as a result of terrestrialisation. Onset of organic sedimentation in the adjacent
lakes occurred at ca. 3,400 and 2,650 cal BP in response to mire expansion and permafrost aggradation, respectively. Mire
erosion, possibly due to permafrost decay, led to re-deposition of peat into one of the lakes after ca. 2,100 cal BP, and
stimulated primary productivity in the other lake at ca. 1,900–1,800 cal BP. Carbonate precipitation appears to have been
suppressed when acidic poor fen and bog (palsa) communities dominated the catchment mire, and permafrost-induced changes in
hydrology may further have affected the inflow of alkaline water from the catchment. Elevated contents of biogenic silica
and diatom pigments in lake sediments during periods of poor fen and bog expansion further indicate that terrestrial vegetation
influenced the amount of nutrients entering the lake. Increased productivity in the lake likely caused bottom-water anoxia
in the downstream lake and led to recycling of sediment phosphorous, bringing the lake into a state of self-sustained eutrophication
during two centuries preceding the onset of twentieth century permafrost thaw. Our results give insight into nutrient and
permafrost dynamics in a subarctic wetland and imply that continued permafrost decay and related vegetation changes towards
minerotrophy may increase carbon and nutrient storage of mire deposits and reduce nutrient fluxes in runoff. Rapid permafrost
degradation may on the other hand lead to widespread mire erosion and to relatively short periods of significantly increased
nutrient loading in adjacent lakes. 相似文献
43.
Response of the North Atlantic subpolar gyre to persistent North Atlantic oscillation like forcing 总被引:2,自引:1,他引:1
The response of the North Atlantic subpolar gyre (SPG) to a persistent positive (or negative) phase of the North Atlantic oscillation (NAO) is investigated using an ocean general circulation model forced with idealized atmospheric reanalysis fields. The integrations are analyzed with reference to a base-line integration for which the model is forced with idealized fields representing a neutral state of the NAO. In the positive NAO case, the results suggest that the well-known cooling and strengthening of the SPG are, after about 10 years, replaced by a warming and subsequent weakening of the SPG. The latter changes are caused by the advection of warm water from the subtropical gyre (STG) region, driven by a spin-up of the Atlantic meridional overturning circulation (AMOC) and the effect of an anomalous wind stress curl in the northeastern North Atlantic, which counteracts the local buoyancy forcing of the SPG. In the negative NAO case, however, the SPG response does not involve a sign reversal, but rather shows a gradual weakening throughout the integration. The asymmetric SPG-response to the sign of persistent NAO-like forcing and the different time scales involved demonstrate strong non-linearity in the North Atlantic Ocean circulation response to atmospheric forcing. The latter finding indicates that analysis based on the arithmetic difference between the two NAO-states, e.g. NAO+ minus NAO?, may hide important aspects of the ocean response to atmospheric forcing. 相似文献
44.
The thermogravimetric measurements on fayalite reported by Nakamura and Schmalzried (1983) have been reassessed using the compound-energy model and computer calculations which eliminate much mathematical manipulation and subjective choice. The calculated phase field for fayalite differs somewhat from the one obtained by Nakamura and Schmalzried (1983) but there is satisfactory agreement in the experimental range. 相似文献
45.
Marcel Nicolaus Caixin Wang Sebastian Gerland LI Na LI Zhijun Bin Cheng Don K Perovich Mats A Granskog SHI Liqiong LEI Ruibo LI Qun LU Peng 《极地研究(英文版)》2015,(2)
In recent decades, significant changes of Arctic sea ice have taken place. These changes are expected to influence the surface energy balance of the ice-covered Arctic Ocean. To quantify this energy ba... 相似文献
46.
Mona Hedfeldt Mats Lundmark 《Norsk geografisk tidsskrift. Norwegian journal of geography》2015,69(2):90-101
The article examines new firm formation in the old industrial region (OIR) of Bergslagen in Sweden, and in particular the role of in-migrants. The study is based on longitudinal georeferenced microdata (1993–2008) compiled by Statistics Sweden and providing information on individuals' attachments to the Swedish labour market, as well as workplaces and firms, education, income, and family composition. This specially commissioned database enabled the characterization and analysis of emerging forms of entrepreneurship and self-employment, as well as the socio-economics of the labour market. The longitudinal data allowed the authors to trace actions taken by individuals over time. The results indicate that new firm formation is related to private services, rather than to the traditional manufacturing sector and public services that currently dominate the regional labour market. Self-employed in-migrants are active in other sectors than non-migrants, and show some distinct features in terms of their lower age, better education, and more often non-Nordic background. The study showed that both in-migration and return migration had a positive, significant, and substantial effect on migrants' decision to start a business when a number of other individual characteristics had been controlled for. 相似文献
47.
Assessment of marine benthic quality change in gradients of disturbance: Comparison of different Scandinavian multi-metric indices 总被引:1,自引:0,他引:1
Alf B. Josefson Mats Blomqvist Jrgen L.S. Hansen Rutger Rosenberg Brage Rygg 《Marine pollution bulletin》2009,58(9):1263-1277
Three multi-metric benthic macrofauna indices were used to assess marine benthic ecological quality status (EcoQS) according to the European Water Framework Directive, in seven pollution gradients mainly, western Scandinavia. The impacts included organic load, hypoxia, metals, urban effluents and physical disturbance. The indices responded in a similar threshold fashion, irrespective of impact factor identity. Usually, the border between Good and Moderate EcoQS (G/M), is determined as some deviation from a reference situation. References, however, are difficult to find. An alternative procedure is described to estimate the G/M border, not requiring reference data. Thresholds, where faunal structure deterioration commences, were identified from non-linear regressions between indices and impact factors. Index values from the less impacted side of the thresholds were assumed to come from environments of Good and High EcoQS, and the 5th percentile of these data, was defined as the G/M border. Estimated G/M borders compared well with previous studies. 相似文献
48.
Mats Leijon Cecilia Boström Oskar Danielsson Stefan Gustafsson Kalle Haikonen Olivia Langhamer Erland Strömstedt Magnus Stålberg Jan Sundberg Olle Svensson Simon Tyrberg Rafael Waters 《Surveys in Geophysics》2008,29(3):221-240
This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider? buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system. 相似文献
49.
Effects of ozone depletion and increased ultraviolet-B radiation on northern vegetation 总被引:2,自引:0,他引:2
Lars Olof Björn Terry V. Callaghan Carola Gehrke Dylan Gwynn-Jones John A. Lee Ulf Johanson Mats Sonesson Nicholas D. Buck 《Polar research》1999,18(2):331-337
The stratospheric ozone layer has been depleted at high and mid-latitudes as a consequence of man's pollution of the atmosphere, and this results in increasing ultraviolet-B radiation at ground level. We investigate the effects of further radiation increases on plants and ecosystems by irradiating natural sub-Arctic and Arctic vegetation with artificial UV-B radiation in field experiments extending over several years. Our experimental sites are located at Abisko, in northern Sweden (68°N), and Adventdalen, on the island of Spitsbergen (78°N). Additional UV-B induced interspecific differences in plant response in terms of reduced (or, in one case, increased) growth, changed morphology and changed pigment content. In some cases effects seem to be accumulated from one year to another. Plant litter decomposition is retarded. We are also studying how UV-B enhancement may affect the interaction between species. In some experiments we combine UV-B enhancement with changes in other factors: carbon dioxide concentration, water availability, and temperature. In some cases the effect of radiation enhancement is modified, or even reversed, by such changes. Over a four year period we did not find any significant radiation induced change in species composition, but based on the effects on individual plant species, such changes can be expected to take place over a longer time. 相似文献
50.
Abundance, Sources and Speciation of Trace Elements in Humus-Rich Streams Affected by Acid Sulphate Soils 总被引:3,自引:0,他引:3
The behaviour of trace elements (Al, As, Cd, Co, Cr,Cu, Fe, Mn, Ni, V, Zn) was studied in five humus-richstreams (dissolved organic carbon = 14–40 mg/L)impacted by acid sulphate soils developed in marinesulphide-bearing fine-grained sediments. During heavyrainfalls in autumn, on which the study focusses, themetals Al, Cd, Co, Cu, Mn, Ni and Zn are extensivelyleached from these acidic soils (pH = 2.5–4.5), whileAs, Cr, Fe and V are not leached more strongly fromthis soil type than from areas of till and peat. Aspeciation experiment, based on anion and cationexchange of the stream waters in the field, showedthat (1) the metals Al, Cd, Co, Mn, Ni and Zn aretransported in the streams mainly as inorganiccations, (2) Cu exists mainly in cationic form but isalso to a significant extent associated with dissolvedhumic substances, (3) Fe occurs mainly in the anionicfraction explained by organic coating on colloidal Feoxyhydoxides and (4) the hydrochemistry of As, Cr andV is complex as these elements may exist in severalunquantified anionic fractions and to a minor extentin cationic species/forms. Whereas the proportion ofacid sulphate soils in the catchments had a largeimpact on concentrations levels of several elements inthe stream waters, these soils did not have a largeaffect on the speciation of elements in water. 相似文献