52 research outputs found
Heat-conserving three-temperature model for ultrafast demagnetization of 3d ferromagnets
We study the ultrafast magnetization dynamics of bcc Fe and fcc Co using the
recently suggested heat-conserving three-temperature model (HC3TM), together
with atomistic spin- and lattice dynamics simulations. It is shown that this
type of Langevin-based simulation is able to reproduce observed trends of the
ultrafast magnetization dynamics of fcc Co and bcc Fe, in agreement with
previous findings for fcc Ni. The simulations are performed by using parameters
that to as large extent as possible are obtained from electronic structure
theory. The one parameter that was not calculated in this way, was the damping
term used for the lattice dynamics simulations, and here a range of parameters
were investigated. It is found that this term has a large influence on the
details of the magnetization dynamics. The dynamics of iron and cobalt is
compared with previous results for nickel and similarities and differences in
the materials' behavior are analysed following the absorption of a femtosecond
laser pulse. Importantly, for all elements investigated so far with this model,
we obtain a linear relationship between the value of the maximally demagnetized
state and the fluence of the laser pulse, which is in agreement with
experiments.Comment: 9 pages, 9 figures, Submitted to Physical Review
Trait‐based analysis of subpolar North Atlantic phytoplankton and plastidic ciliate communities using automated flow cytometer
Plankton are an extremely diverse and polyphyletic group, exhibiting a large range in morphological and physiological traits. Here, we apply automated optical techniques, provided by the pulse‐shape recording automated flow cytometer—CytoSense—to investigate trait variability of phytoplankton and plastidic ciliates in Arctic and Atlantic waters of the subpolar North Atlantic. We used the bio‐optical descriptors derived from the CytoSense (light scattering [forward and sideward] and fluorescence [red, yellow/green and orange from chlorophyll a, degraded pigments, and phycobiliproteins, respectively]) and translated them into functional traits to demonstrate ecological trait variability along an environmental gradient. Cell size was the master trait varying in this study, with large photosynthetic microplankton (> 20 μm in cell diameter), including diatoms as single cells and chains, as well as plastidic ciliates found in Arctic waters, while small‐sized phytoplankton groups, such as the picoeukaryotes (< 4 μm) and the cyanobacteria Synechococcus were dominant in Atlantic waters. Morphological traits, such as chain/colony formation and structural complexity (i.e., cellular processes, setae, and internal vacuoles), appear to favor buoyancy in highly illuminated and stratified Arctic waters. In Atlantic waters, small cell size and spherical cell shape, in addition to photo‐physiological traits, such as high internal pigmentation, offer chromatic adaptation for survival in the low nutrient and dynamic mixing waters of the Atlantic Ocean. The use of automated techniques that quantify ecological traits holds exciting new opportunities to unravel linkages between the structure and function of plankton communities and marine ecosystems
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