1,186 research outputs found
Gold in graphene: in-plane adsorption and diffusion
We study the bonding and diffusion of Au in graphene vacancies using
density-functional theory. Energetics show that Au adsorbs preferably to double
vacancies, steadily in-plane with graphene. All diffusion barriers for the
complex of Au in double vacancy are above 4 eV, whereas the barriers for larger
vacancies are below 2 eV. Our results support the main results of a recent
experiment [Gan et al., Small 4, 587 (2008)], but suggest that the observed
diffusion mechanism is not thermally activated, but radiation-enhanced.Comment: 3 pages, 3 figure
Conductance through atomic point contacts between fcc(100) electrodes of gold
Electrical conductance through various nanocontacts between gold electrodes
is studied by using the density functional theory, scalar-relativistic
pseudopotentials, generalized gradient approximation for the
exchange-correlation energy and the recursion-transfer-matrix method along with
channel decomposition. The nanocontact is modeled with pyramidal fcc(100) tips
and 1 to 5 gold atoms between the tips. Upon elongation of the contact by
adding gold atoms between the tips, the conductance at Fermi energy E_F evolves
from G ~ 3 G_0 to G ~ 1 G_0 (G_0 = 2e/h^2). Formation of a true one-atom point
contact, with G ~ 1 G_0 and only one open channel, requires at least one atom
with coordination number 2 in the wire. Tips that share a common vertex atom or
tips with touching vertex atoms have three partially open conductance channels
at E_F, and the symmetries of the channels are governed by the wave functions
of the tips. The long 5-atom contact develops conductance oscillations and
conductance gaps in the studied energy range -3 < E-E_F < 5 eV, which reflects
oscillations in the local density of electron states in the 5-atom linear "gold
molecule" between the electrodes, and a weak coupling of this "molecule" to the
tips
Prevalence of tail biting in pigs and associations to carcass condemnations - a Finnish pilot study
The aim of this study was to investigate the prevalence of tail biting in Finland and the relationship between tail biting and carcass condemnation
Unexplained limits on species distributions: how important is climate in defining species’ range edges?
The study of species’ range margins has a long history of academic interest, but is of particular relevance today due to its applications in modelling species range shifts induced by climate change, and predicting the spread of invasive species. Climate has long been assumed to structure species’ ranges over broad scales, but this consensus has recently been challenged by work on non-climatic factors, such as dispersal, biotic interactions and gene flow. It remains unclear how and where non-climatic factors can structure species’ ranges, and to what extent species’ ranges will consistently match sets of climatic conditions. In this thesis I investigate what can lead to a species underfilling its climatic niche (when a species fails to colonise all climatically suitable areas), or expanding its climatic niche (when a species is able to colonise new types of climate). I find evidence that several non-climatic factors can slow or prevent non-native species colonising all climatically suitable areas in their naturalised regions, including dispersal, fragmentation of climatically suitable areas and the area of introduction. I also find that species will readily spread into new precipitation regimes with which they have not been previously associated. This suggests that species ranges can be constrained by non-climatic factors in the wettest part of their native range, and these constraints are frequently lifted in their naturalised range. I find evidence that species range limits set by temperature, in particular temperature maxima and minima, are more conserved and species will rarely expand into new thermal regimes. I also find evidence that species have different phenotypic responses to temperature across their range. Together these results indicate that a species’ current range frequently does not indicate its overall climatic tolerance, particularly in relation to precipitation, hence predictions that rely on associations between occurrence and environmental variables will frequently be flawed. Future work should consider a systematic way of detecting and including non-climatic factors that constrain the edges of species’ ranges
Formation and propagation of great salinity anomalies
North Atlantic/Arctic ocean and sea ice variability for the period 1948–2001 is studied using a global Ocean General Circulation Model coupled to a dynamic/thermodynamic sea ice model forced by daily NCEP/NCAR reanalysis data [Kalnay et al., 1996]. Variability of Arctic sea ice properties is analysed, in particular the formation and propagation of sea ice thickness anomalies that are communicated via Fram Strait into the North Atlantic. These export events led to the Great Salinity Anomalies (GSA) of the 1970s, 1980s and 1990s in the Labrador Sea (LS). All GSAs were found to be remotely excited in the Arctic, rather than by local atmospheric forcing over the LS. Sea ice and fresh water exports through the Canadian Archipelago (CAA) are found to be only of minor importance, except for the 1990s GSA. Part of the anomalies are tracked to the Newfoundland Basin, where they enter the North Atlantic Current. The experiments indicate only a minor impact of a single GSA event on the strength of the North Atlantic Thermohaline Circulation (THC)
Results of Russian geomagnetic observatories in the 19th century: magnetic activity, 1841–1862
Hourly (spot readings) magnetic data (H- and D-components) were digitized from
Russian yearbook tables for the years 1850–1862 from four observatories. The
pdf pictures for digitization were taken by a normal digital camera. The
database obtained consists of about 900 000 single data points. The time
series of hourly magnetic values reveal slow secular variations (declination
only) as well as transient and regular geomagnetic variations of external
origin. The quality and homogeneity of the data is satisfactory. Daily
Ak-indices were calculated using the index algorithm that has been earlier
applied to 19th century data from Helsinki (Finland) as well as modern
magnetic observatory recordings. The activity index series derived from the
Russian data is consistent with earlier activity index series for 1850–1862.
The digitized index data series derived in this study was extended back to
1841 by including magnetic <I>C</I>9 activity index data available from a Russian
observatory (St. Petersburg). Magnetic data rescued here is well suitable
for various reconstructions for studies of the long-term variation of the
space weather in the 19th century
Comparison of Raman spectra and vibrational density of states between graphene nanoribbons with different edges
Vibrational properties of graphene nanoribbons are examined with density
functional based tight-binding method and non-resonant bond polarization
theory. We show that the recently discovered reconstructed zigzag edge can be
identified from the emergence of high-energy vibrational mode due to strong
triple bonds at the edges. This mode is visible also in the Raman spectrum.
Total vibrational density of states of the reconstructed zigzag edge is
observed to resemble the vibrational density of states of armchair, rather than
zigzag, graphene nanoribbon. Edge-related vibrational states increase in energy
which corroborates increased ridigity of the reconstructed zigzag edge.Comment: 4 pages, 4 figure
Supported magnetic nanoclusters: Softlanding of Pd clusters on a MgO surface
Low-energy deposition of neutral Pd_N clusters (N=2-7 and 13) on a MgO(001)
surface F-center (FC) was studied by spin-density-functional molecular dynamics
simulations. The incident clusters are steered by an attractive "funnel"
created by the FC, resulting in adsorption of the cluster, with one of its
atoms bonded atop of the FC. The deposited Pd_2-Pd_6 clusters retain their
gas-phase structures, while for N>6 surface-commensurate isomers are
energetically more favorable. Adsorbed clusters with N > 3 are found to remain
magnetic at the surface.Comment: 5 pages, 2 figs, Phys.Rev.Lett., accepte
Increased interleukin-6 and C-reactive protein levels after instrumented lumbar spine fusion in older patients
Purpose: Interleukin 6 (IL-6) and the acute phase C-reactive protein (CRP) blood concentrations after lumbar spine fusion may be affected by age. The purpose of this prospective observational study was to assess postoperative serum levels of pro-inflammatory IL-6 and CRP after instrumented lumbar spine fusion surgery. We hypothesized that older patients would have increased levels of IL-6 and CRP after surgery. Methods: IL-6 and high-sensitive CRP biochemical marker levels were measured before instrumented spinal fusion, and postoperatively at 1 and 3 days, 6 weeks, and 3 months. The 49 patients in this sample were divided into two groups: age 60 years (n = 26). Results: Acute changes in IL-6 high-sensitivity and CRP from preoperative levels to postoperative day (POD) 1 increased with age. Mean (95% CI) difference between the age-groups in changes of IL-6 at PODs 1 and 3 was 45 pg/ml (10-83, p = 0.014) and 20 pg/ml (5-36, p = 0.021), respectively. Mean (95% CI) difference between groups in changes of CRP at PODs 1 and 3 was 9.6 mg/l (-3.5 to 22.7, p = 0.47) and 24.8 mg/l (-17 to 67, p = 0.33), respectively. Both groups had decreased IL-6 and CRP levels at 6 weeks after surgery compared to the preoperative level. Conclusions: Elevation of IL-6 and CRP is stronger in patients over 60 years old after instrumented lumbar spinal fusion. The CRP and IL-6 are sensitive markers for acute postoperative inflammation. Even high acute CRP values do not necessarily indicate postoperative infection.Peer reviewe
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.
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