| 1. |
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| 2. |
- Wade, G. A., et al.
(författare)
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The MiMeS survey of magnetism in massive stars : introduction and overview
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 456:1, s. 2-22
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties of O- and early B-type stars. Initiated in 2008 and completed in 2013, the project was supported by three Large Program allocations, as well as various programmes initiated by independent principal investigators, and archival resources. Ultimately, over 4800 circularly polarized spectra of 560 O and B stars were collected with the instruments ESPaDOnS (Echelle SpectroPolarimetric Device for the Observation of Stars) at the Canada-France-Hawaii Telescope, Narval at the Telescope Bernard Lyot and HARPSpol at the European Southern Observatory La Silla 3.6 m telescope, making MiMeS by far the largest systematic investigation of massive star magnetism ever undertaken. In this paper, the first in a series reporting the general results of the survey, we introduce the scientific motivation and goals, describe the sample of targets, review the instrumentation and observational techniques used, explain the exposure time calculation designed to provide sensitivity to surface dipole fields above approximately 100 G, discuss the polarimetric performance, stability and uncertainty of the instrumentation, and summarize the previous and forthcoming publications.
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| 3. |
- Aldeghi, Nausica, 1993-
(författare)
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Eigenvalues and eigenfunctions of Laplacians and Schrödinger operators with mixed boundary conditions
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of three papers, all concerned with the eigenvalue problem for the Schrödinger operator -Δ+V, and in particular the Laplacian -Δ, on bounded, connected, Lipschitz domains with mixed boundary conditions, where a Dirichlet boundary condition is imposed on a subset of the boundary and a Neumann boundary condition on its complement. Given different such choices of boundary conditions on the same domain, we compare the resulting mixed Dirichlet-Neumann eigenvalues by establishing inequalities between them, and prove a variant of the hot spots conjecture for the lowest mixed Dirichlet-Neumann eigenfunction of the Laplacian. Our approach is purely variational and relies on both classical and novel variational principles; the geometric features of the underlying domain, such as convexity or curvature of the boundary, play a crucial role in our results.In Paper I we consider the Laplacian on planar, convex domains and compare the lowest eigenvalues corresponding to different choices of mixed boundary conditions in the case in which the boundary contains a straight line segment. The proof relies on estimating the Rayleigh quotient of the derivative of a certain eigenfunction in the unique direction normal to this segment; as a result the established inequalities depend on the geometry of the boundary with respect to this direction, as well as on the convexity of the domain.In Paper II we also compare the lowest mixed eigenvalues of the Laplacian on simply connected planar domains, but instead rely on a novel variational principle where the minimizers are gradients of eigenfunctions. To the best of our knowledge, this variational principle has not appeared in the literature before. This allows to replace the convexity assumption with a more general assumption regulating the normal directions to the boundary, and to drop the assumption that the boundary contains a straight line segment. Using this novel variational principle we also prove a version of the hot spots conjecture for mixed Dirichlet-Neumann boundary conditions.In Paper III we extend the eigenvalue inequalities of Paper I to Schrödinger operators on both planar and higher-dimensional domains by generalizing the variational approach therein established; in this case we require the boundary to contain a subset of a hyperplane. The inequalities rely again on the convexity of the domain and on the geometry of both the boundary and the potential V with respect to the unique direction normal to this hyperplane. Further, we prove an inequality between higher order mixed Dirichlet-Neumann eigenvalues and pure Dirichlet eigenvalues of Schrödinger operators.
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| 4. |
- Barrio, Isabel C., et al.
(författare)
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Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome
- 2017
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Ingår i: Polar Biology. - : Springer. - 0722-4060 .- 1432-2056. ; 40:11, s. 2265-2278
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Tidskriftsartikel (refereegranskat)abstract
- Chronic, low intensity herbivory by invertebrates, termed background herbivory, has been understudied in tundra, yet its impacts are likely to increase in a warmer Arctic. The magnitude of these changes is however hard to predict as we know little about the drivers of current levels of invertebrate herbivory in tundra. We assessed the intensity of invertebrate herbivory on a common tundra plant, the dwarf birch (Betula glandulosa-nana complex), and investigated its relationship to latitude and climate across the tundra biome. Leaf damage by defoliating, mining and gall-forming invertebrates was measured in samples collected from 192 sites at 56 locations. Our results indicate that invertebrate herbivory is nearly ubiquitous across the tundra biome but occurs at low intensity. On average, invertebrates damaged 11.2% of the leaves and removed 1.4% of total leaf area. The damage was mainly caused by external leaf feeders, and most damaged leaves were only slightly affected (12% leaf area lost). Foliar damage was consistently positively correlated with mid-summer (July) temperature and, to a lesser extent, precipitation in the year of data collection, irrespective of latitude. Our models predict that, on average, foliar losses to invertebrates on dwarf birch are likely to increase by 6-7% over the current levels with a 1 degrees C increase in summer temperatures. Our results show that invertebrate herbivory on dwarf birch is small in magnitude but given its prevalence and dependence on climatic variables, background invertebrate herbivory should be included in predictions of climate change impacts on tundra ecosystems.
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| 5. |
- Barrio, Isabel C., et al.
(författare)
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Publisher Correction to : Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome (vol 40, pg 2265, 2017)
- 2018
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Ingår i: Polar Biology. - : Springer. - 0722-4060 .- 1432-2056. ; 41:8, s. 1653-1654
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Tidskriftsartikel (refereegranskat)abstract
- The above mentioned article was originally scheduled for publication in the special issue on Ecology of Tundra Arthropods with guest editors Toke T. Hoye . Lauren E. Culler. Erroneously, the article was published in Polar Biology, Volume 40, Issue 11, November, 2017. The publisher sincerely apologizes to the guest editors and the authors for the inconvenience caused.
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| 6. |
- Fomenko, L.S., et al.
(författare)
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Low temperature microhardness of Xe-intercalated fullerite C60
- 2005
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 31:5, s. 454-458
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Tidskriftsartikel (refereegranskat)abstract
- The Vickers microhardness of Xe-intercalated polycrystalline fullerite C60 (XexC60, x~=0.35) is measured in a moderately low temperature range of 77 to 300 K. A high increase in the microhardness of the material (by a factor of 2 to 3) as compared to that of pure C60 single crystals is observed. It is shown that the step-like anomaly in the temperature dependences of the microhardness of pure C60 single crystals recorded under the orientational fcc-sc phase transition (Tc~=260 K) is also qualitatively retained for XexC60, but its onset is shifted by 40 K towards lower temperatures and the step becomes less distinct and more smeared. This behavior of H-barV(T) correlates with x-ray diffraction data, the analysis of which revealed a considerable influence of xenon interstitial atoms on the peculiar features of fullerite thermal expansion due to orientational phase transitions (see the paper by A.I. Prokhvatilov et al. in this issue).
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| 7. |
- Gurevich, A.M., et al.
(författare)
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Low temperature heat capacity of fullerite C60 doped with nitrogen
- 2006
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 32:10, s. 967-969
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Tidskriftsartikel (refereegranskat)abstract
- The heat capacity C-m of polycrystalline fullerite C-60 doped with nitrogen is measured in the temperature interval 2-13 K. The contributions to the heat capacity from translational lattice vibrations (Debyc contribution), from orientational vibrations of the C-60 molecules (Einstein contribution), and from the motion of the N-2 molecules in the octahedral cavities of the C-60 lattice are estimated. However, no indications of the first-order phase transformation detected earlier in a dilatometric investigation of the N-2-C-60 orientational glass are found (beyond the experimental error limits). A possible explanation for this fact is proposed.
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| 8. |
- Lindén, Elin, et al.
(författare)
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Circum-Arctic distribution of chemical anti-herbivore compounds suggests biome-wide trade-off in defence strategies in Arctic shrubs
- 2022
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Ingår i: Ecography. - : John Wiley & Sons. - 0906-7590 .- 1600-0587. ; :11
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Tidskriftsartikel (refereegranskat)abstract
- Spatial variation in plant chemical defence towards herbivores can help us understand variation in herbivore top–down control of shrubs in the Arctic and possibly also shrub responses to global warming. Less defended, non-resinous shrubs could be more influenced by herbivores than more defended, resinous shrubs. However, sparse field measurements limit our current understanding of how much of the circum-Arctic variation in defence compounds is explained by taxa or defence functional groups (resinous/non-resinous). We measured circum-Arctic chemical defence and leaf digestibility in resinous (Betula glandulosa, B. nana ssp. exilis) and non-resinous (B. nana ssp. nana, B. pumila) shrub birches to see how they vary among and within taxa and functional groups. Using liquid chromatography–mass spectrometry (LC–MS) metabolomic analyses and in vitro leaf digestibility via incubation in cattle rumen fluid, we analysed defence composition and leaf digestibility in 128 samples from 44 tundra locations.We found biogeographical patterns in anti-herbivore defence where mean leaf triterpene concentrations and twig resin gland density were greater in resinous taxa and mean concentrations of condensing tannins were greater in non-resinous taxa. This indicates a biome-wide trade-off between triterpene- or tannin-dominated defences. However, we also found variations in chemical defence composition and resin gland density both within and among functional groups (resinous/non-resinous) and taxa, suggesting these categorisations only partly predict chemical herbivore defence. Complex tannins were the only defence compounds negatively related to in vitro digestibility, identifying this previously neglected tannin group as having a potential key role in birch anti-herbivore defence.We conclude that circum-Arctic variation in birch anti-herbivore defence can be partly derived from biogeographical distributions of birch taxa, although our detailed mapping of plant defence provides more information on this variation and can be used for better predictions of herbivore effects on Arctic vegetation.
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| 9. |
- Liu, Bingbing, et al.
(författare)
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Synthesis and characterization of single-walled nanotubes produced with Ce as catalyst
- 2000
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Ingår i: Molecular Materials: Molecular Crystals and Liquid Crystals Section C, vol. 13. - : Overseas Publishers Association N.V.. ; , s. 75-80
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Konferensbidrag (refereegranskat)abstract
- We have studied the effect of using rare-earth elements C (typically +4 oxide state) and Eu (typically +2 oxide state) together with nanometer Ni as catalysts to synthesize SWNT in high yield by arc evaporation. A black collar deposit containing mainly SWNT was formed in the presence of Ce/Ni while only nanometer carbon particles were formed using Eu/Ni, as identified by SEM, TEM and Raman spectra. The Raman spectra of our SWNT mats show difference from spectra shown in the literature in a low frequency range, indicating that our mats contain chiral tubes. The temperature dependent resistance of SWNT mats was also measured. A semiconducting behaviour was observed with a negative dR/dT and no resistance minimum from 2 to 350 K. The resistance follows a 2D variable range hopping behaviour.
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| 10. |
- Prager, C. M., et al.
(författare)
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Climate and multiple dimensions of plant diversity regulate ecosystem carbon exchange along an elevational gradient
- 2021
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Ingår i: Ecosphere. - : Wiley. - 2150-8925. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- The impacts of warming on communities and ecosystems are predicted to be significant in mountain ecosystems because physiological processes, including rates of carbon (C) cycling, are often more temperature-sensitive in colder environments. Plant biodiversity can also influence C exchange, yet few studies integrate how biotic and abiotic factors may directly or interactively impact ecosystem C flux. Here, we examine the link between simultaneous changes in multiple dimensions of plant diversity and peak growing season ecosystem C uptake across a climatic gradient in the Rocky Mountains, Colorado, USA. We found that taxonomic diversity (species richness), functional diversity (functional evenness), and phylogenetic diversity (mean pairwise distance) were significantly and positively related to peak growing season ecosystem C uptake (i.e., net ecosystem exchange) when considered independently. However, when abiotic and biotic factors were integrated in a structural equation model, only plant phylogenetic diversity was significantly related to C uptake. In addition, we found that actual evapotranspiration (AET-a measure that integrates precipitation and temperature) affected ecosystem C exchange indirectly via its impact on the three dimensions of plant diversity that we examined. These findings highlight complex relationships among key measures of biodiversity and ecosystem C uptake in a rapidly warming ecosystem, and the possible mechanisms that underlie relationships between biodiversity and ecosystem functioning. They also point to the need for integrating multiple dimensions of biodiversity into studies of community and ecosystem ecology.
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| 11. |
- Siefert, Andrew, et al.
(författare)
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A global meta-analysis of the relative extent of intraspecific trait variation in plant communities
- 2015
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 18:12, s. 1406-1419
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Forskningsöversikt (refereegranskat)abstract
- Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.
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| 12. |
- Sundqvist, Hanna S., et al.
(författare)
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Arctic Holocene proxy climate database - new approaches to assessing geochronological accuracy and encoding climate variables
- 2014
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 10:4, s. 1605-1631
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Tidskriftsartikel (refereegranskat)abstract
- We present a systematic compilation of previously published Holocene proxy climate records from the Arctic. We identified 170 sites from north of 58 degrees N latitude where proxy time series extend back at least to 6 cal ka (all ages in this article are in calendar years before present - BP), are resolved at submillennial scale (at least one value every 400 +/- 200 years) and have age models constrained by at least one age every 3000 years. In addition to conventional meta-data for each proxy record (location, proxy type, reference), we include two novel parameters that add functionality to the database. First, climate interpretation is a series of fields that logically describe the specific climate variable(s) represented by the proxy record. It encodes the proxy-climate relation reported by authors of the original studies into a structured format to facilitate comparison with climate model outputs. Second, geochronology accuracy score (chron score) is a numerical rating that reflects the overall accuracy of C-14-based age models from lake and marine sediments. Chron scores were calculated using the original author-reported C-14 ages, which are included in this database. The database contains 320 records (some sites include multiple records) from six regions covering the circumpolar Arctic: Fennoscandia is the most densely sampled region (31% of the records), whereas only five records from the Russian Arctic met the criteria for inclusion. The database contains proxy records from lake sediment (60 %), marine sediment (32 %), glacier ice (5 %), and other sources. Most (61 %) reflect temperature (mainly summer warmth) and are primarily based on pollen, chironomid, or diatom assemblages. Many (15 %) reflect some aspect of hydroclimate as inferred from changes in stable isotopes, pollen and diatom assemblages, humification index in peat, and changes in equilibrium-line altitude of glaciers. This comprehensive database can be used in future studies to investigate the spatio-temporal pattern of Arctic Holocene climate changes and their causes. The Arctic Holocene data set is available from NOAA Paleoclimatology.
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| 13. |
- Aleksandrovskii, A.N., et al.
(författare)
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On the polyamorphism of fullerite-based orientational glasses.
- 2005
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 31:5, s. 429-444
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Tidskriftsartikel (refereegranskat)abstract
- The dilatometric investigation in the temperature range of 2–28 K shows that a first-orderpolyamorphous transition occurs in the orientational glasses based on C60 doped with H2, D2 andXe. A polyamorphous transition was also detected in C60 doped with Kr and He. It is observed thatthe hysteresis of thermal expansion caused by the polyamorphous transition (and, hence, the transitiontemperature) is essentially dependent on the type of doping gas. Both positive and negativecontributions to the thermal expansion were observed in the low-temperature phase of the glasses.The relaxation time of the negative contribution occurs to be much longer than that of the positivecontribution. The positive contribution is found to be due to phonon and libron modes, whilst thenegative contribution is attributed to tunneling states of the C60 molecules. The characteristictime of the phase transformation from the low-T phase to the high-T phase has been found for theC60–H2 system at 12 K. A theoretical model is proposed to interpret these observed phenomena.The theoretical model proposed, includes a consideration of the nature of polyamorphism inglasses, as well as the thermodynamics and kinetics of the transition. A model of noninteractingtunneling states is used to explain the negative contribution to the thermal expansion. The experimentaldata obtained is considered within the framework of the theoretical model. From the theoreticalmodel the order of magnitude of the polyamorphous transition temperature has been estimated.It is found that the late stage of the polyamorphous transformation is described well by theKolmogorov law with an exponent of n = 1. At this stage of the transformation, the two-dimensionalphase boundary moves along the normal, and the nucleation is not important.
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| 14. |
- Blank, Vladimir D., et al.
(författare)
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Electric resistivity and magnetoresistance of some superhard and ultrahard fullerites in the range 300-2K
- 1999
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Ingår i: AIP Conference Proceedings vol. 486. - Melville, NY : American Institute of Physics (AIP). - 1563969009 ; , s. 416-420
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Konferensbidrag (refereegranskat)abstract
- Electric resistivity and magnetoresistance were measured on samples with disordered structure synthesized from pure C60 and C70 at pressures in the range 8 - 12.5 GPa and temperature 900 - 1500 K. Different type of behaviour were observed: semimetallic and semiconducting, depending on the particular short-range order of the structure.
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| 15. |
- Blank, Vladimir D., et al.
(författare)
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High-pressure polymerized phases of C60
- 1998
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Ingår i: Carbon. - 0008-6223 .- 1873-3891. ; 36:4, s. 319-343
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Forskningsöversikt (övrigt vetenskapligt/konstnärligt)abstract
- Data from recent experimental studies of C60 under high pressures are collected and analyzed, concentrating on the polymerized states where covalent intermolecular bonds have been formed through treatment of molecular C60 at high pressures and temperatures at or above room temperature. We give an overview of the observed phase transformations and the structures of metastable polymeric phases, both crystalline and disordered, as analyzed under ambient conditions, and we present and discuss a pressure-temperature diagram showing which synthesis conditions result in which final phases in the pressure range up to 20 GPa (200 kbar) and at temperatures up to 2300 K. The physical properties of the various phases are discussed whenever enough data are available. The pressure-temperature stability limits for C60 and the conditions for the transformation of C60 into graphite, diamond and chaoite-type carbon are derived.
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| 16. |
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| 17. |
- Bredin, CG, et al.
(författare)
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Integrin dependent migration of lung cancer cells to extracellular matrix components
- 1998
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Ingår i: The European respiratory journal. - : European Respiratory Society (ERS). - 0903-1936 .- 1399-3003. ; 11:2, s. 400-407
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Tidskriftsartikel (refereegranskat)abstract
- Since tumour progression is dependent on the ability of malignant cells to interact with the extracellular matrix (ECM), we have investigated the significance of beta1 and beta3 integrins for migration of lung cancer cells to components of the ECM. In an in vitro hapto- and chemotactic assay system, five cell lines representing the major types of lung cancer were examined: adenocarcinoma (WART); squamous cell carcinoma (U-1752); small cell lung cancer (SCLC) (U-1906, 054 A) and large cell lung cancer (LCLC) (U-1810). Flow cytometric analyses were performed to characterize their integrin expression. U-1906, 054 A, WART and U-1752 all expressed beta1 integrins whereas U-1810 did not. However, U-1810 and U-1752 expressed beta3 integrins. All cell lines except U-1810 and U-1752 showed hapto- and chemotactic motility to fibronectin, laminin and type IV collagen and this motility was beta1 integrin-dependent except in the case of U-1810. However, the hapto- and chemotactic responses differed markedly between the separate cell lines and there was no distinct pattern to separate non-small cell lung cancer (NSCLC) from SCLC. No or very little migration was seen in control experiments with bovine serum albumin (BSA) or serum-free medium alone, indicating that the migration of the lung cancer cells require adhesion molecules, soluble or substratum bound. We have found the involvement of beta1 integrins in lung cancer cell migration in vitro towards fibronectin, laminin and type IV collagen except in the case of U-1810. The U-1810 cell line clearly differed from the rest of the cell lines by lacking expression of beta1 integrins.
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| 18. |
- Buga, Sergei G., et al.
(författare)
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Dissociation energy of 3D-polymeric C60 : Calorimetric study and structural analysis
- 2001
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Ingår i: Electronic Properties of Novel Materials - Science and Technology of Molecular Nanostructures. - Melville, NY : American Institute of Physics. - 0735400334 ; , s. 49-53
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Konferensbidrag (refereegranskat)abstract
- Annealing of 2D- and 3D-polymeric C[sub60] fullerene obtained under pressures of 9.5 and 12.5 GPa and temperatures of 670 and 770 K has been investigated by DSC in the range 240–640 K. An endothermal heat effect was observed with a peak maximum just below 540 K, a temperature characteristic for breakdown of (2+2) intermolecular links in dimers, 1D and 2D polymers. Exothermal effects, starting from 380 K, were observed for the first time in polymeric fullerenes. These effects are attributed to relaxation processes and to breakdown of other types of intermolecular bonds such as common four-sided rings and (3+3) interlinks.
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| 19. |
- Buga, Sergei G., et al.
(författare)
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DSC study of annealing and phase transformations of C60 and C70 polymerized under pressures in the range 9.5 - 13 GPa.
- 2002
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Ingår i: Journal of Physics and Chemistry of Solids. - : Elsevier B.V.. - 0022-3697 .- 1879-2553. ; 63:2, s. 331-343
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Tidskriftsartikel (refereegranskat)abstract
- C60 and C70 fullerenes polymerized under pressures between 9.5 and 13 GPa and temperatures between 670 and 1850 K were investigated by differential scanning calorimetry (DSC) in the range 240–640 K. Endothermal heat effects were observed with a peak maximum just below 540 K, a temperature characteristic for breakdown of (2+2) intermolecular links in dimers, 1D and 2D polymers. Exothermal effects, starting from 380 K, were observed for the first time in polymeric fullerenes. These effects are attributed to relaxation processes and to breakdown of other types of intermolecular bonds such as common four-sided rings and (3+3) interlinks.
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| 20. |
- Buga, Sergei G., et al.
(författare)
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Electrical properties of 3D-polymeric crystalline and disordered C60 and C70 fullerites.
- 2005
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Ingår i: Diamond and Related Materials vol. 14, special Issue (3-7). - : Elsevier B.V.. ; , s. 896-901
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Konferensbidrag (refereegranskat)abstract
- Crystalline and disordered 3D-polymeric C60 and C70 with different lattice parameters and with densities in the range of 2.2÷3.25 g cm−1 were obtained by high-pressure-high-temperature treatment at P=11.5÷15 GPa, T=670÷1800 K. Their d.c. electrical conductivity was investigated at temperatures 30÷350 K. The variable range hopping mechanism dominates in all samples up to room temperature. A temperature activated conductivity via delocalized states was observed at T>160÷260 K in crystalline C60 samples and in some samples with disordered structure. The evaluated band gap value is Eg=0.28÷0.54 eV for different crystalline structures and 0.06÷0.25 eV for disordered ones
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| 21. |
- Buga, Sergei G., et al.
(författare)
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Pressure effect on electrical properties and photoluminescence spectra of solid C60 and C70 fullerenes
- 2001
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Ingår i: Frontiers of High Pressure Research II: Application of High Pressure to Low-Dimensional Novel Electronic Materials. - Dordrecht : Springer/Kluwer. - 9781402001604 ; , s. 483-491
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Konferensbidrag (refereegranskat)abstract
- Electrical resistivity of crystalline and disordered fullerite samples obtained by static high-pressure-high-temperature treatment of C-60 and C-70 at P = 12.5 GPa and T = 820-1500 K was investigated in the temperature range of 2.4-300 K, Room-temperature activation energy of charge carriers was found to be in the range 40-200 meV. T-3/2 and T-4 dependencies of conductivity versus temperature were revealed both in crystalline and disordered structures. Photoluminescence spectra of C-60 samples treated at P = 13 GPa. T = 770-1470 K show 50 nm short-wave length shift of characteristic 750 nm PL band.
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| 22. |
- Buga, Sergei G., et al.
(författare)
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Semimetallic and semiconductor properties of some superhard and ultrahard fullerites in the range 300-2 K
- 2000
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Ingår i: Proceedings of the 5th IUMRS International Conference on Advanced Materials, Beijing 1999. - : Elsevier B.V.. ; , s. 1009-1015
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Konferensbidrag (refereegranskat)abstract
- Electrical resistivity and magnetoresistance were measured on samples with disordered structures synthesized from pure C60 and C70 at pressures in the range 8–12.5 GPa and temperatures of 900–1500 K. Different types of behaviour were observed: semimetallic, VRH and semiconducting, depending on the degree of disorder and the particular short-range order of the samples. A negative magnetoresistance was observed at T<10 K on samples with a semimetallic type of conductivity synthesized at 8 GPa pressure. The temperature dependence of resistivity in the sample with a disordered crystalline structure based on 3D-polymerized C60 molecules fits Mott's law for hopping conductivity. T3/2, T2 and T4 dependencies of conductivity are observed for samples with densities of 2.8 and 3.05 g/cm3 synthesized at a pressure of 12.5 GPa. The effect of hydrostatic pressure on the resistivity of cross-linked layered carbon structures obtained from C60 at P=8 GPa, T=1600 K was investigated up to 0.6 GPa at room temperature. An approximately linear decrease of resistivity was observed with a very small value of the derivative d ln ρ/dp=0.06 /GPa, which correlates with a very low compressibility of the material.
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| 23. |
- Buga, Sergei G., et al.
(författare)
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Synthesis of superhard 3D-polymeric C60 fullerites from rhombohedral 2D-polymer by high-pressure-high-temperature treatment.
- 2003
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Ingår i: High Pressure Research vol. 23, issue 3. - London : Taylor & Francis. ; , s. 259-264
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Konferensbidrag (refereegranskat)abstract
- Rhombohedral C60 polymer was subjected to high-pressure-high-temperature treatment at P =13 GPa, T =620-1620 K. After quenching, crystalline and disordered structures with densities in the range of 2.1-2.9 g cm-1 were obtained. The structures of the samples have been investigated by powder X-ray diffraction and Raman scattering. DSC analysis showed a transformation of the polymeric structure into monomeric on annealing in the range 400-640 K. The temperature dependence of the electrical resistance of samples with disordered structure was measured in the range 2.5-300K. For different samples, the conductivity was proportional to T1/2, T3/2, T4 and exp(-1/T1/4).
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| 24. |
- Denev, Iliya D., et al.
(författare)
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Organization of protochlorophyllide oxidoreductase in prolamellar bodies isolated from etiolated carotenoid-deficient wheat leaves as revealed by fluorescence probes
- 2005
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Ingår i: Biochimica et Biophysica Acta (BBA) - Biomembranes. - : Elsevier BV. - 0005-2736. ; 1716:2, s. 97-103
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Tidskriftsartikel (refereegranskat)abstract
- Carotenoid importance for membrane organization of NADPH protochlorophyllide oxidoreductase (POR) was studied by comparing interaction of two membrane fluorescent probes with proteins in prolamellar bodies isolated from norflurazon-treated wheat plants (cdPLBs) to those isolated form plants with normal carotenoid amount (oPLBs). The tryptophan fluorescence quenching by 1-anilino-8-naphthalene sulfonate (attached to the surface of membrane lipid phase) and pyrene (situated deep into the fatty acid region of membrane lipids) was used to locate the position of POR molecules toward lipid phase, to analyze their supramolecular organization and the light-induced structural transitions. Our results showed that the pigment-protein complexes of cdPLBs were larger than those of oPLBs. Upon flash irradiation the aggregates of both types of PLB dissociated into smaller units but in cdPLBs this process was accompanied by reorientation of the POR molecules closer to the lipid surface and/or dissociation from the lipids. These results revealed that carotenoid deficiency led to a looser attachment of POR to the lipid phase and its early (in comparison with oPLBs) dissociation from the membranes during the light-induced transformation of cdPLBs. This might be one of the reasons for the inability of carotenoid-deficient plants to form functional plastids. (c) 2005 Elsevier B.V. All rights reserved
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| 25. |
- Dolbin, Alexander V., et al.
(författare)
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Specific features of thermal expansion and polyamorphism in CH4 – C60 solutions at low temperatures
- 2007
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 33:12, s. 1068-1072
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the linear thermal expansion coefficient alpha(T) is investigated in the temperature range of 2.5 to 23 K for two different CH4-C-60 solutions in which CH4 molecules occupy 24 and 50% of the octahedral interstitial sites of the C-60 lattice. In both cases, alpha(T) exhibits hysteresis, suggesting the existence of two types of orientational glass associated with these solutions. The temperature of the first-order phase transition between these two glasses is estimated, and the behavior of these two glasses is compared. The characteristic times of thermalization tau(1), reorientation of the C-60 molecules tau(2), and of the phase transformation between the glasses tau('), are estimated for these solutions. Both the temperature dependence of alpha(T) and the characteristic thermalization time tau(1) are found to have features near the phase transition temperature, and an explanation is put forward to explain these observed features.
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| 26. |
- Dolbin, Alexander V., et al.
(författare)
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The effect of the noncentral impurity-matrix interaction upon the thermal expansion and polyamorphism of solid CO-C60 solutions at low temperatures
- 2008
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Ingår i: Fizika Nizkikh Temperatur. - : AIP Publishing. - 0132-6414. ; 34:6, s. 592-598
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Tidskriftsartikel (refereegranskat)abstract
- Orientational glasses with CO molecules occupying 26 and 90% of the octahedral interstitial sites in the C60 lattice have been investigated by the dilatometric method in a temperature interval of 2.5–22 K. At temperatures 4–6 K the glasses undergo a first-order phase transition which is evident from the hysteresis of the thermal expansion and the maxima in the temperature dependences of the linear thermal expansion coefficients a(T), and the thermalization times t1(T) of the samples. The effect of the noncentral CO–C60 interaction upon the thermal expansion and the phase transition in these glasses was clarified by comparing the behavior of the properties of the CO–C60 and N2–C60 solutions.
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| 27. |
- Dolbin, Alexander V., et al.
(författare)
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Thermal expansion of solutions of deuteromethane in fullerite C60 at low temperature : Isotopic effect
- 2009
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics. - 1063-777X .- 1090-6517. ; 35:3, s. 226-231
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Tidskriftsartikel (refereegranskat)abstract
- The thermal expansion of CD4 solutions in the orientational glass C60 with molar concentration of deuteromethane 20 and 50% has been investigated in the temperature range 2.5–23 K. The orientational glass CD4–C60 undergoes a first-order phase transition in the temperature interval 4.5–55 K. This transition is manifested as hysteresis of the linear thermal expansion coefficient alpha as well as maxima in the temperature dependences alpha(T) and tau1(T), where tau1 is the characteristic thermalization time of the experimental samples. The characteristic re-orientation times of the C60 molecules and the characteristic phase transformations occurring in the experimental solutions are determined. The results of the present study are compared with the results of a similar study of the solution CH4–C60. It is concluded that tunneling rotation of the CH4 and CD4 molecules occupying interstitial positions in the fullerite C60 lattice occurs.
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| 28. |
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| 29. |
- Figdor, D, et al.
(författare)
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A big role for the very small : understanding endodontic microbial flora
- 2007
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Ingår i: Australian dental journal. - Sydney : Australian dental association. - 0045-0421 .- 1834-7819. ; 52:Suppl 1, s. S38-S51
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Forskningsöversikt (refereegranskat)abstract
- Apical periodontitis, an inflammatory process around the apex of a tooth root, is primarily a sequel to microbial infection of the pulp space. The microbial flora is composed of a restricted group of the total oral flora, selected by environmental pressures of anaerobiosis, nutrition and competition with other species and inhabits the root canal as a biofilm of coaggregated communities in an extracellular matrix. The untreated infected canal is generally composed of a polymicrobial mix with approximately equal proportions of Gram-positive and Gram-negative species, dominated by obligate anaerobes. The type of microbial flora in the root-filled tooth with persistent apical periodontitis has very different characteristics. These infections are characterized by one or just a few species, predominantly Grampositive micro-organisms with an equal distribution of facultative and obligate anaerobes. Enterococcus faecalis has been a conspicuous finding in most studies. Because the primary aetiological problem is infection, endodontic treatment is directed at control and elimination of the root canal flora by working in a sterile way. Based on current knowledge, the best available method for obtaining clean, microbe-free root canals is by instrumentation with antimicrobial irrigation reinforced by an intracanal dressing with calcium hydroxide.
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| 30. |
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| 31. |
- Flowers, Sarah A., et al.
(författare)
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Decrease of core 2 O-glycans on synovial lubricin in osteoarthritis reduces galectin-3 mediated crosslinking
- 2020
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 295:47, s. 16023-16036
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Tidskriftsartikel (refereegranskat)abstract
- The synovial fluid glycoprotein lubricin (also known as proteoglycan 4) is a mucin-type O-linked glycosylated biological lubricant implicated to be involved in osteoarthritis (OA) development. Lubricin's ability to reduce friction is related to its glycosylation consisting of sialylated and unsialylated Tn-antigens and core 1 and core 2 structures. The glycans on lubricin have also been suggested to be involved in crosslinking and stabilization of the lubricating superficial layer of cartilage by mediating interaction between lubricin and galectin-3. However, with the spectrum of glycans being found on lubricin, the glycan candidates involved in this interaction were unknown. Here, we confirm that the core 2 O-linked glycans mediate this lubricin-galectin-3 interaction, shown by surface plasmon resonance data indicating that recombinant lubricin (rhPRG4) devoid of core 2 structures did not bind to recombinant galectin-3. Conversely, transfection of Chinese hamster ovary cells with the core 2 GlcNAc transferase acting on a mucin-type O-glycoprotein displayed increased galectin-3 binding. Both the level of galectin-3 and the galectin-3 interactions with synovial lubricin were found to be decreased in late-stage OA patients, coinciding with an increase in unsialylated core 1 O-glycans (T-antigens) and Tn-antigens. These data suggest a defect in crosslinking of surface-active molecules in OA and provide novel insights into OA molecular pathology.
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| 32. |
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| 33. |
- Frölander, Hans-Erik, 1966-, et al.
(författare)
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Theory-of-mind in adolescents and young adults with Alström Syndrome
- 2014
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Ingår i: International Journal of Pediatric Otorhinolaryngology. - : Elsevier. - 0165-5876 .- 1872-8464. ; 78:3, s. 530-537
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The study focuses on theory-of-mind in adolescents and young adults with Alström syndrome (ALMS). ALMS, an autosomal recessive syndrome causes juvenile blindness, sensorineural hearing loss, cardiomyopathy, endocrinological disorders and metabolic dysfunction. Theory-of-mind (ToM) refers to the ability to impute mental states to one self and to others. Clinical observations have revealed an increased occurence of deviances in mental state understanding in ALMS. In the present study ToM will be examined and related to working memory (WM), verbal ability and sensory loss.Methods: Twelve young individuals (16-37 years) with ALMS and 24 nondisabled individuals matched on age, gender and educational level participated. ToM was assessed by means of a multiple task that taxes the ability to understand thoughts and feelings of story chraracters´. WM was examined by means of a reading span task and verbal ability by means of a vocabulary test.Results: The ALMS group performed at significantly lower levels in ToM tasks and displayed a higher variability in performance than the control group. Individuals with ALMS and a relatively poor level performance provided fewer correct mental state inferences in ToM tasks than ALMS individuals with relatively higher performance levels. ALMS individuals with relatively high performance levels made as many correct inferences in ToM tasks as the control group, but their inferences were more often incomplete. Vocabulary skills and educational level, but not WM-capacity predicted ToM performance. Degree of deafblindness did not have an impact on ToM. Age of onset of visual loss but not hearing loss related to ToM.Conclusions: The individuals with ALMS display a high degree of heterogeneity in terms of ToM, where some individuals reached performance levels comparable to nondisabled individuals. The results are discussed with respect to how cognitive and verbal abilities and factors related to the disability affect ToM.
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| 34. |
- Galtsov, N. N., et al.
(författare)
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Intercalation of fullerite C60 with N2 molecules : an investigation by X-ray powder diffraction
- 2007
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics (AIP). - 1063-777X .- 1090-6517. ; 33:10, s. 881-885
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Tidskriftsartikel (refereegranskat)abstract
- The lattice parameter a of fullerite C60 intercalated with N2 molecules is investigated in the temperature interval 6–295K by x-ray diffraction. It is found that the interstitial molecular N2 has a considerable effect on both the orientational phase transition temperature Tc and the orientational glass formation temperature Tg. Hysteresis of a(T) in the Tc and Tg regions is detected, along with an abrupt change in volume over the region defining Tc. Complete intercalation of C60 with N2 molecules results in a 0.2% increase in the lattice parameter, which persists over the whole temperature range. Evidence is also obtained that the interstitial guest molecular N2 induces a slight deformation of the cubic symmetry of the C60 host lattice.
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| 35. |
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
- Hislop, P. D., et al.
(författare)
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Band functions in the presence of magnetic steps
- 2016
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Ingår i: Mathematical Models and Methods in Applied Sciences. - 1793-6314. ; 26:1, s. 161-161
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Tidskriftsartikel (refereegranskat)abstract
- We complete the analysis of the band functions for two-dimensional magnetic Schrodinger operators with piecewise constant magnetic fields. The discontinuity of the magnetic field can create edge currents that flow along the discontinuity, which have been described by physicists. Properties of these edge currents are directly related to the behavior of the band functions. The effective potential of the fiber operator is an asymmetric double well (eventually degenerated) and the analysis of the splitting of the bands incorporates the asymmetry. If the magnetic field vanishes, the reduced operator has essential spectrum and we provide an explicit description of the band functions located below the essential spectrum. For non-degenerate magnetic steps, we provide an asymptotic expansion of the band functions at infinity. We prove that when the ratio of the two magnetic fields is rational, a splitting of the band functions occurs and has a natural order, predicted by numerical computations.
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| 41. |
- Idelevich, E. A., et al.
(författare)
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Microbiological diagnostics of bloodstream infections in Europe-an ESGBIES survey
- 2019
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Ingår i: Clinical Microbiology and Infection. - : Elsevier. - 1198-743X .- 1469-0691. ; 25:11, s. 1399-1407
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: High-quality diagnosis of bloodstream infections (BSI) is important for successful patient management. As knowledge on current practices of microbiological BSI diagnostics is limited, this project aimed to assess its current state in European microbiological laboratories.Methods: We performed an online questionnaire-based cross-sectional survey comprising 34 questions on practices of microbiological BSI diagnostics. The ESCMID Study Group for Bloodstream Infections, Endocarditis and Sepsis (ESGBIES) was the primary platform to engage national coordinators who recruited laboratories within their countries.Results: Responses were received from 209 laboratories in 25 European countries. Although 32.5% (68/209) of laboratories only used the classical processing of positive blood cultures (BC), two-thirds applied rapid technologies. Of laboratories that provided data, 42.2% (78/185) were able to start incubating BC in automated BC incubators around-the-clock, and only 13% (25/192) had established a 24-h service to start immediate processing of positive BC. Only 4.7% (9/190) of laboratories validated and transmitted the results of identification and antimicrobial susceptibility testing (AST) of BC pathogens to clinicians 24 h/day. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry from briefly incubated sub-cultures on solid media was the most commonly used approach to rapid pathogen identification from positive BC, and direct disc diffusion was the most common rapid AST method from positive BC.Conclusions: Laboratories have started to implement novel technologies for rapid identification and AST for positive BC. However, progress is severely compromised by limited operating hours such that current practice of BC diagnostics in Europe complies only partly with the requirements for optimal BSI management.
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| 42. |
- Idh, Jonna, et al.
(författare)
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Resistance to First-Line Anti-TB Drugs is Associated with Reduced Nitric Oxide Susceptibility in Mycobacterium tuberculosis
- 2012
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 7:1, s. e39891-
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Tidskriftsartikel (refereegranskat)abstract
- Background and objective: The relative contribution of nitric oxide (NO) to the killing of Mycobacterium tuberculosis in human tuberculosis (TB) is controversial, although this has been firmly established in rodents. Studies have demonstrated that clinical strains of M. tuberculosis differ in susceptibility to NO, but how this correlates to drug resistance and clinical outcome is not known.Methods: In this study, 50 sputum smear- and culture-positive patients with pulmonary TB in Gondar, Ethiopia were included. Clinical parameters were recorded and drug susceptibility profile and spoligotyping patterns were investigated. NO susceptibility was studied by exposing the strains to the NO donor DETA/NO.Results: Clinical isolates of M. tuberculosis showed a dose- and time-dependent response when exposed to NO. The most frequent spoligotypes found were CAS1-Delhi and T3_ETH in a total of nine known spoligotypes and four orphan patterns. There was a significant association between reduced susceptibility to NO (>10% survival after exposure to 1mM DETA/NO) and resistance against first-line anti-TB drugs, in particular isoniazid (INH). Patients infected with strains of M. tuberculosis with reduced susceptibility to NO showed no difference in cure rate or other clinical parameters, but a tendency towards lower rate of weight gain after two months of treatment.Conclusion: There is a correlation between resistance to first-line anti-TB drugs and reduced NO susceptibility in clinical strains of M. tuberculosis. Further studies including the mechanisms of reduced NO susceptibility are warranted and could identify targets for new therapeutic interventions.
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| 43. |
- Iwasiewicz-Wabnig, Agnieszka, et al.
(författare)
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Investigations of N@C60 and N@C70 stability under high pressure and high temperature conditions
- 2009
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Ingår i: Physica Status Solidi B vol. 246, issue 11-12. - : Wiley. ; , s. 2767-2770
-
Konferensbidrag (refereegranskat)abstract
- Endohedral fullerenes encapsulating single nitrogen atoms (N@C60 and N@C70) are spin active, due to the presence of unpaired nitrogen electron spins. High reactivity of nitrogen leads to a poor stability of these molecules at elevated temperatures, drastically restricting possibilities of their chemical treatment. In this study, N@C60 and N@C70 in toluene solutions were subjected to high pressure (HP) up to 0.8 GPa and annealed for 1, 2, 10 or 24 h, at either room or elevated temperatures. In each case the number of surviving molecules was evaluated based on the relative spin counts of ex situ EPR spectra obtained before and after the treatment. The enhanced thermal stability of N@C60 and N@C70 under HP conditions is attributed to inhibited formation of azabridges, which under normal pressure facilitate the escape of nitrogen from the fullerene cage.
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| 44. |
- Landberg, Anna, 1988-, et al.
(författare)
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Validation of data quality in the National Swedish Kidney Cancer Register
- 2021
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Ingår i: Scandinavian Journal of Urology. - : Medical Journals Sweden AB. - 2168-1805 .- 2168-1813. ; 55:2, s. 142-148
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Tidskriftsartikel (refereegranskat)abstract
- Introduction The National Swedish Kidney Cancer Register (NSKCR) was launched in 2005. It is used for health care quality improvement and research. The aim of this study was to validate the register's data quality by assessing the timeliness, completeness, comparability and validity of the register. Material and Methods To assess timeliness we evaluated the number of days between date of diagnosis and date of reporting the patient to the NSKCR. For completeness, we used data on number of cancer cases reported to the NSKCR compared to cases reported to the Swedish Cancer Register. Comparability was evaluated by reviewing coding routines and comparing data collected in the NSKCR to national and international guidelines. Validity was assessed by reabstraction of data from medical charts from 431 randomly selected patients diagnosed in 2007, 2010, 2013 and 2016. Results Timeliness has improved since the register started. In 2016, 76.9% and 96.5% of the patients were reported within 6 and 12 months respectively. Completeness was high, with a 99.5% coverage between 2008 and 2017. Registration forms and manuals were updated according to national and European guidelines. Improvements have been made continuously to decrease the risk of reporting mistakes and misunderstandings. Validity was high where a majority of the variables demonstrated an exact agreement >90% and few missing values. Conclusion Overall, the data quality of the NSKCR is high. Completeness, comparability and validity is high. Timeliness can be further improved, which will make it easier to follow changes and improve the care and research of RCC patients.
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| 45. |
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| 46. |
- Liu, Q., et al.
(författare)
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Functional characteristics of circulating granulocytes in severe congenital neutropenia caused by ELANE mutations
- 2019
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Ingår i: Bmc Pediatrics. - : Springer Science and Business Media LLC. - 1471-2431. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundNeutrophils and eosinophils are multifunctional granulocytes derived from common myelocytic-committed progenitor cells. Severe congenital neutropenia 1 (SCN1) caused by ELANE mutations is a rare disease characterized by very low numbers of circulating neutrophils. Little is known about the functional characteristics of the SCN1 granulocytes, except that eosinophilia has been noticed in both bone marrow and peripheral blood. In this study, we profiled the number and function of granulocytes in patients suffering from SCN1.MethodsNine patients diagnosed with SCN1 were enrolled in this study and absolute counts of eosinophils and neutrophils from bone marrow aspirates and peripheral blood samples were analysed. In addition, Ficoll-Paque enriched granulocytes from patients and healthy controls were analysed for specific eosinophil and neutrophil markers using flow cytometry and for NADPH-oxidase activity-profile by chemiluminescence.ResultsOur data demonstrate a skewed granulocyte population in SCN1 patients dominated by eosinophils in both bone marrow and peripheral blood. The latter was detected only by blood smear examination, but not by automated blood analysers. Furthermore, we show that the SCN1 eosinophils exerted normal production of reactive oxygen species generated by the NADPH-oxidase, however the response was profoundly different from that of healthy control neutrophils.ConclusionsSCN1 patients with ELANE mutations suffer from neutropenia yet display eosinophilia in the bone marrow and blood, as revealed by smear examination but not by automatic blood analysers. The SCN1 eosinophils are functionally normal regarding production of reactive oxygen species (ROS). However, the ROS profile produced by eosinophils differs drastically from that of neutrophils isolated from the same blood donor, implying that the eosinophilia in SCN1 cannot compensate forthe loss of neutrophils regarding ROS-mediated functions.
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| 47. |
- Manzhelii, V.G., et al.
(författare)
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Thermal expansion and polyamorphism of N2 – C60 solutions
- 2006
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 32:7, s. 695-699
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Tidskriftsartikel (refereegranskat)abstract
- The linear coefficients alpha(T) of N-2-C-60 solutions with 9.9% and 100% of the C-60 lattice thermal expansion interstitials filled with N-2 are investigated in the interval 2.2-24 K. The dependence alpha(T) has a hysteresis suggesting co-existence of two types of orientational glasses in these solutions. The features of the glasses are compared. The characteristic times of phase transformations in the solutions and reorientation of C-60 molecules are estimated.
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| 48. |
- Mayor, Jordan, et al.
(författare)
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Elevation alters ecosystem properties across temperate treelines globally
- 2017
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Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 542:7639, s. 91-95
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Tidskriftsartikel (refereegranskat)abstract
- Temperature is a primary driver of the distribution of biodiversity as well as of ecosystem boundaries(1,2). Declining temperature with increasing elevation in montane systems has long been recognized as a major factor shaping plant community biodiversity, metabolic processes, and ecosystem dynamics(3,4). Elevational gradients, as thermoclines, also enable prediction of long-term ecological responses to climate warming(5-7). One of the most striking manifestations of increasing elevation is the abrupt transitions from forest to treeless alpine tundra(8). However, whether there are globally consistent above-and belowground responses to these transitions remains an open question(4). To disentangle the direct and indirect effects of temperature on ecosystem properties, here we evaluate replicate treeline ecotones in seven temperate regions of the world. We find that declining temperatures with increasing elevation did not affect tree leaf nutrient concentrations, but did reduce ground-layer community-weighted plant nitrogen, leading to the strong stoichiometric convergence of ground-layer plant community nitrogen to phosphorus ratios across all regions. Further, elevation-driven changes in plant nutrients were associated with changes in soil organic matter content and quality (carbon to nitrogen ratios) and microbial properties. Combined, our identification of direct and indirect temperature controls over plant communities and soil properties in seven contrasting regions suggests that future warming may disrupt the functional properties of montane ecosystems, particularly where plant community reorganization outpaces treeline advance.
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| 49. |
- Metcalfe, Daniel B., et al.
(författare)
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Patchy field sampling biases understanding of climate change impacts across the Arctic
- 2018
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Ingår i: Nature Ecology and Evolution. - : Springer Science and Business Media LLC. - 2397-334X. ; 2:9, s. 1443-1448
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Tidskriftsartikel (refereegranskat)abstract
- Effective societal responses to rapid climate change in the Arctic rely on an accurate representation of region-specific ecosystem properties and processes. However, this is limited by the scarcity and patchy distribution of field measurements. Here, we use a comprehensive, geo-referenced database of primary field measurements in 1,840 published studies across the Arctic to identify statistically significant spatial biases in field sampling and study citation across this globally important region. We find that 31% of all study citations are derived from sites located within 50 km of just two research sites: Toolik Lake in the USA and Abisko in Sweden. Furthermore, relatively colder, more rapidly warming and sparsely vegetated sites are under-sampled and under-recognized in terms of citations, particularly among microbiology-related studies. The poorly sampled and cited areas, mainly in the Canadian high-Arctic archipelago and the Arctic coastline of Russia, constitute a large fraction of the Arctic ice-free land area. Our results suggest that the current pattern of sampling and citation may bias the scientific consensuses that underpin attempts to accurately predict and effectively mitigate climate change in the region. Further work is required to increase both the quality and quantity of sampling, and incorporate existing literature from poorly cited areas to generate a more representative picture of Arctic climate change and its environmental impacts.
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| 50. |
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