1,206 research outputs found
Soil carbon stock increases in the organic layer of boreal middle-aged stands
Changes in the soil carbon stock can potentially have a large influence on global carbon balance between terrestrial ecosystems and atmosphere. Since carbon sequestration of forest soils is influenced by human activities, reporting of the soil carbon pool is a compulsory part of the national greenhouse gas (GHG) inventories. Various soil carbon models are applied in GHG inventories, however, the verification of model-based estimates is lacking. In general, the soil carbon models predict accumulation of soil carbon in the middle-aged stands, which is in good agreement with chronosequence studies and flux measurements of eddy sites, but they have not been widely tested with repeated measurements of permanent plots. The objective of this study was to evaluate soil carbon changes in the organic layer of boreal middle-aged forest stands. Soil carbon changes on re-measured sites were analyzed by using soil survey data that was based on composite samples as a first measurement and by taking into account spatial variation on the basis of the second measurement. By utilizing earlier soil surveys, a long sampling interval, which helps detection of slow changes, could be readily available. <br><br> The range of measured change in the soil organic layer varied from −260 to 1260 g m<sup>−2</sup> over the study period of 16–19 years and 23 &plusmn; 2 g m<sup>−2</sup> per year, on average. The increase was significant in 6 out of the 38 plots from which data were available. Although the soil carbon change was difficult to detect at the plot scale, the overall increase measured across the middle-aged stands agrees with predictions of the commonly applied soil models. Further verification of the soil models is needed with larger datasets that cover wider geographical area and represent all age classes, especially young stands with potentially large soil carbon source
Electronic-structure-induced deformations of liquid metal clusters
Ab initio molecular dynamics is used to study deformations of sodium clusters
at temperatures K. Open-shell Na cluster has two shape
isomers, prolate and oblate, in the liquid state. The deformation is stabilized
by opening a gap at the Fermi level. The closed-shell Na remains magic also
at the liquid state.Comment: REVTex, 11 pages, no figures, figures (2) available upon request
(e-mail to hakkinen at jyfl.jyu.fi), submitted to Phys. Rev.
Stability of conductance oscillations in monatomic sodium wires
We study the stability of conductance oscillations in monatomic sodium wires
with respect to structural variations. The geometry, the electronic structure
and the electronic potential of sodium wires suspended between two sodium
electrodes are obtained from self-consistent density functional theory
calculations. The conductance is calculated within the framework of the
Landauer-B\"utttiker formalism, using the mode-matching technique as formulated
recently in a real-space finite-difference scheme [Phys. Rev. B \textbf{70},
195402 (2004)]. We find a regular even-odd conductance oscillation as a
function of the wire length, where wires comprising an odd number of atoms have
a conductance close to the quantum unit , and even-numbered
wires have a lower conductance. The conductance of odd-numbered wires is stable
with respect to geometry changes in the wire or in the contacts between the
wire and the electrodes; the conductance of even-numbered wires is more
sensitive. Geometry changes affect the spacing and widths of the wire
resonances. In the case of odd-numbered wires the transmission is on-resonance,
and hardly affected by the resonance shapes, whereas for even-numbered wires
the transmission is off-resonance and sensitive to the resonance shapes.
Predicting the amplitude of the conductance oscillation requires a
first-principles calculation based upon a realistic structure of the wire and
the leads. A simple tight-binding model is introduced to clarify these results.Comment: 16 pages, 20 figure
Structure and Magnetism of Neutral and Anionic Palladium Clusters
The properties of neutral and anionic Pd_N clusters were investigated with
spin-density-functional calculations. The ground state structures are
three-dimensional for N>3 and they are magnetic with a spin-triplet for 2<=N<=7
and a spin nonet for N=13 neutral clusters. Structural- and spin-isomers were
determined and an anomalous increase of the magnetic moment with temperature is
predicted for a Pd_7 ensemble. Vertical electron detachment and ionization
energies were calculated and the former agree well with measured values for
anionic Pd_N clusters.Comment: 5 pages, 3 figures, fig. 2 in color, accepted to Phys. Rev. Lett.
(2001
Close-Packing of Clusters: Application to Al_100
The lowest energy configurations of close-packed clusters up to N=110 atoms
with stacking faults are studied using the Monte Carlo method with Metropolis
algorithm. Two types of contact interactions, a pair-potential and a many-atom
interaction, are used. Enhanced stability is shown for N=12, 26, 38, 50, 59,
61, 68, 75, 79, 86, 100 and 102, of which only the sizes 38, 75, 79, 86, and
102 are pure FCC clusters, the others having stacking faults. A connection
between the model potential and density functional calculations is studied in
the case of Al_100. The density functional calculations are consistent with the
experimental fact that there exist epitaxially grown FCC clusters starting from
relatively small cluster sizes. Calculations also show that several other
close-packed motifs existwith comparable total energies.Comment: 9 pages, 7 figure
Spectroscopy with random and displaced random ensembles
Due to the time reversal invariance of the angular momentum operator J^2, the
average energies and variances at fixed J for random two-body Hamiltonians
exhibit odd-even-J staggering, that may be especially strong for J=0. It is
shown that upon ensemble averaging over random runs, this behaviour is
reflected in the yrast states. Displaced (attractive) random ensembles lead to
rotational spectra with strongly enhanced BE2 transitions for a certain class
of model spaces. It is explained how to generalize these results to other forms
of collectivity.Comment: 4 pages, 4 figure
Broken Symmetry in Density-Functional Theory: Analysis and Cure
We present a detailed analysis of the broken-symmetry mean-field solutions
using a four-electron rectangular quantum dot as a model system. Comparisons of
the density-functional theory predictions with the exact ones show that the
symmetry breaking results from the single-configuration wave function used in
the mean-field approach. As a general cure we present a scheme that
systematically incorporates several configurations into the density-functional
theory and restores the symmetry. This cure is easily applicable to any
density-functional approach.Comment: 4 pages, 4 figures, submitted to PR
Actively open-minded thinking : development of a shortened scale and disentangling attitudes towards knowledge and people
Actively open-minded thinking (AOT) is often used as a proxy for reflective thinking in research on reasoning and related fields. It is associated with less biased reasoning in many types of tasks. However, few studies have examined its psychometric properties and criterion validity. We developed a shortened, 17-item version of the AOT for quicker administration. AOT17 is highly correlated with the original 41-item scale and has highly similar relationships to other thinking dispositions, social competence and supernatural beliefs. Our analyses revealed that the AOT is not a unitary construct, but comprises four distinct dimensions, some of which concern attitudes towards knowledge, and others concern attitudes towards people. This factor structure was replicated in another data-set, and correlations with other measures in four data-sets (total N = 3345) support the criterion validity of these dimensions. Different dimensions were responsible for the AOT's relationships with other thinking dispositions.Peer reviewe
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