12 research outputs found
Hybrid silicon nanostructures with conductive ligands and their microscopic conductivities
Silicon nanoparticles (SiNPs) functionalized with conjugated molecules promise a potential pathway to generate a new category of thermoelectric materials. While the thermoelectric performance of materials based on phenyl-acetylene capped SiNPs has been proven, their low conductivity is still a problem for their general application. A muon study of phenyl-acetylene capped SiNPs has been recently carried out using the HiFi spectrometer at the Rutherford Appleton Laboratory, measuring the ALC spectra as a function of temperature. The results show a reduction in the measured line width of the resonance above room temperature, suggesting an activated behaviour for this system. This study shows that the muon study could be a powerful method to investigate microscopic conductivity of hybrid thermoelectric materials
Long-term forest composition and its drivers in taiga forests in NW Russia
Understanding the processes behind long-term
boreal forest dynamics can provide information that assists
in predicting future boreal vegetation under changing
environmental conditions. Here, we examine Holocene
stand-scale vegetation dynamics and its drivers at the
western boundary of the Russian taiga forest in NW Russia.
Fossil pollen and conifer stomata records from four small
hollow sites and two lake sites are used to reconstruct local
vegetation dynamics during the Holocene. Variation partitioning
is used to assess the relative importance of the
potential drivers (temperature, forest fires and growing site
wetness) to the long-term stand-scale dynamics in taiga
forest. All the main tree taxa, including the boreal keystone
species Picea abies (Norway spruce) and Larix sibirica
(Siberian larch), have been locally present since 10,000 cal
yr BP. The constant Holocene presence of L. sibirica at
three small hollow sites suggests a fast postglacial immigration
of the species in northern Europe. Picea was present
but not dominant at all study sites until its expansion
between 8,000 and 7,000 cal yr BP markedly changed the
forest structure through the suppression of Betula (birch),
Pinus (pine) and Larix. Our results demonstrate that in
general, the Holocene forest dynamics in our study region
have been driven by temperature, but during short intervals
the role of local factors, especially forest fires, has been
prominent. The comparison between sites reveals the
importance of local factors in stand-scale dynamics in taiga
forests. Therefore, the future responses of taiga forest to
climate change will be predominantly modulated by the
local characteristics at the site