Arctic tundra ecosystems will play a key role in future climate change due to
intensifying permafrost thawing, plant growth and ecosystem carbon exchange,
but monitoring these changes may be ...challenging due to the heterogeneity of
Arctic landscapes. We examined spatial variation and linkages of soil and
plant attributes in a site of Siberian Arctic tundra in Tiksi, northeast
Russia, and evaluated possibilities to capture this variation by remote
sensing for the benefit of carbon exchange measurements and landscape
extrapolation. We distinguished nine land cover types (LCTs) and to
characterize them, sampled 92 study plots for plant and soil attributes in
2014. Moreover, to test if variation in plant and soil attributes can be
detected using remote sensing, we produced a normalized difference vegetation
index (NDVI) and topographical parameters for each study plot using three
very high spatial resolution multispectral satellite images. We found that
soils ranged from mineral soils in bare soil and lichen tundra LCTs to soils
of high percentage of organic matter (OM) in graminoid tundra, bog, dry fen
and wet fen. OM content of the top soil was on average 14 g dm−3 in bare
soil and lichen tundra and 89 g dm−3 in other LCTs. Total moss biomass
varied from 0 to 820 g m−2, total vascular shoot mass from 7 to 112 g m−2
and vascular leaf area index (LAI) from 0.04 to 0.95 among LCTs. In
late summer, soil temperatures at 15 cm depth were on average 14 ∘C in bare soil and lichen tundra, and varied from 5 to 9 ∘C in
other LCTs. On average, depth of the biologically active, unfrozen soil layer
doubled from early July to mid-August.
When contrasted across study plots,
moss biomass was positively associated with soil OM % and OM content and
negatively associated with soil temperature, explaining 14–34 % of
variation. Vascular shoot mass and LAI were also positively associated with
soil OM content, and LAI with active layer depth, but only explained 6–15 %
of variation. NDVI captured variation in vascular LAI better than in
moss biomass, but while this difference was significant with late season
NDVI, it was minimal with early season NDVI. For this reason, soil attributes
associated with moss mass were better captured by early season NDVI.
Topographic attributes were related to LAI and many soil attributes, but not
to moss biomass and could not increase the amount of spatial variation
explained in plant and soil attributes above that achieved by NDVI. The LCT
map we produced had low to moderate uncertainty in predictions for plant and
soil properties except for moss biomass and bare soil and lichen tundra LCTs.
Our results illustrate a typical tundra ecosystem with great fine-scale
spatial variation in both plant and soil attributes. Mosses dominate plant
biomass and control many soil attributes, including OM % and temperature,
but variation in moss biomass is difficult to capture by remote sensing
reflectance, topography or a LCT map. Despite the general accuracy of
landscape level predictions in our LCT approach, this indicates challenges in
the spatial extrapolation of some of those vegetation and soil attributes
that are relevant for the regional ecosystem and global climate models.
Evidence for chiral doublet bands has been observed for the first time in the even-even nucleus Nd136. One chiral band was firmly established. Four other candidates for chiral bands were also ...identified, which can contribute to the realization of the multiple pairs of chiral doublet bands (MχD) phenomenon. The observed bands are investigated by the constrained and tilted axis cranking covariant density functional theory (TAC-CDFT). Possible configurations have been explored. The experimental energy spectra, angular momenta, and B(M1)/B(E2) values for the assigned configurations are globally reproduced by TAC-CDFT. Calculated results support the chiral interpretation of the observed bands, which correspond to shapes with maximum triaxiality induced by different multiquasiparticle configurations in Nd136.
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We have examined how some major catchment disturbances may affect the aquatic greenhouse gas fluxes in the boreal zone, using gas flux data from studies made in 1994–1999 in the pelagic regions of ...seven lakes and two reservoirs in Finland. The highest pelagic seasonal average methane (CH
4) emissions were up to 12 mmol
m
−2
d
−1 from eutrophied lakes with agricultural catchments. Nutrient loading increases autochthonous primary production in lakes, promoting oxygen consumption and anaerobic decomposition in the sediments and this can lead to increased CH
4 release from lakes to the atmosphere. The carbon dioxide (CO
2) fluxes were higher from reservoirs and lakes whose catchment areas were rich in peatlands or managed forests, and from eutrophied lakes in comparison to oligotrophic and mesotrophic sites. However, all these sites were net sources of CO
2 to the atmosphere. The pelagic CH
4 emissions were generally lower than those from the littoral zone. The fluxes of nitrous oxide (N
2O) were negligible in the pelagic regions, apparently due to low nitrate inputs and/or low nitrification activity. However, the littoral zone, acting as a buffer for leached nitrogen, did release N
2O. Anthropogenic disturbances of boreal lakes, such as increasing eutrophication, can change the aquatic greenhouse gas balance, but also the gas exchange in the littoral zone should be included in any assessment of the overall effect. It seems that autochthonous and allochthonous carbon sources, which contribute to the CH
4 and CO
2 production in lakes, also have importance in the greenhouse gas emissions from reservoirs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
One new pair of positive-parity chiral doublet bands have been identified in the odd-A nucleus Nd-135 which together with the previously reported negative-parity chiral doublet bands constitute a ...third case of multiple chiral doublet (M chi D) bands in the A approximate to 130 mass region. The properties of the M chi D bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed M chi D bands in Nd-135 represents an important milestone in supporting the existence of M chi D in nuclei.
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The rotational band structure of 255Lr has been investigated using advanced in-beam gamma-ray spectroscopic techniques. To date, 255Lr is the heaviest nucleus to be studied in this manner. One ...rotational band has been unambiguously observed and strong evidence for a second rotational structure was found. The structures are tentatively assigned to be based on the 1/2-521 and 7/2-514 Nilsson states, consistent with assignments from recently obtained alpha decay data. The experimental rotational band dynamic moment of inertia is used to test self-consistent mean-field calculations using the Skyrme SLy4 interaction and a density-dependent pairing force.
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The nature of two high-spin bands in Nd-136 built on the two-quasiparticle configuration pi h(11/2)(2), predicted by the triaxial projected shell model as good candidates of transverse wobbling ...bands, are investigated experimentally. The mixing ratio of one Lambda I = 1 transition connecting the one-phonon and the zero-phonon wobbling bands is established from a high-statistics JuroGam II gamma-ray spectroscopy experiment by using the combined angular correlation and linear polarization method. The resulting wobbling excitation energy and ratios of reduced electromagnetic transition probabilities are in good agreement with results of a new particle-rotor model which rigidly couples the total angular momentum of two quasiparticles to a triaxial core in an orthogonal geometry, confirming thus the transverse wobbling nature of the bands.
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58.
Nuclear Data Sheets for A=188 Kondev, F. G.; Juutinen, S.; Hartley, D. J.
Nuclear data sheets,
05/2018, Volume:
150, Issue:
C
Journal Article
Peer reviewed
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We present the first experimental evidence of the scissors mode in the superheavy nucleus 254No produced in the 208Pb(48Ca, ))254No reaction. The spectrum of γ rays emitted by the excited 254No ...nuclei shows an enhanced γ-ray yield for transition energies of ≈2.5 MeV. By measuring the linear polarization properties of the emitted γ rays, we confirm that the transitions in the enhancement region are predominantly of magnetic-dipole character, characteristic for the scissors mode. To further characterize the enhanced γ-ray yield, simulations of the electromagnetic decay of 254No were performed. The observed enhancement is reproduced by including an M1 component in the γ strength function with total strength . This is in good agreement with the integrated M1 strength from sum-rule estimates and new calculations within the quasi-particle random-phase approximation presented here. Our results provide a stringent test of phenomenological formulae for the scissors mode currently used in stellar nucleosynthesis calculations. We find that those formulae are not satisfactory, and we recommend using sum-rule estimates assuming a rigid-body moment of inertia instead for describing the scissors mode in superheavy nuclei. (Elsevier B.V.)
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Lifetimes of the first excited 2þ and 4þ states in the extremely neutron-deficient nuclide 172Pt have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging ...techniques. An unusually low value of the ratio BðE2∶4þ 1 → 2þ 1 Þ=BðE2∶2þ 1 → 0þ gsÞ ¼ 0.55ð19Þ was found, similar to a handful of other such anomalous cases observed in the entire Segr´e chart. The observation adds to a cluster of a few extremely neutron-deficient nuclides of the heavy transition metals with neutron numbers N ≈ 90–94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low BðE2∶4þ 1 → 2þ 1 Þ=BðE2∶2þ 1 → 0þ gsÞ ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of BðE2∶4þ 1 → 2þ 1 Þ=BðE2∶2þ 1 → 0þ gs) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N ≈ 90–94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.
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