238 research outputs found
Electron vortices in crystals
The propagation of electron beams carrying angular momentum in crystals is
studied using a multislice approach for the model system Fe. It is found that
the vortex beam is distorted strongly due to elastic scattering. Consequently,
the expectation value of the angular momentum as well as the local vortex
components change with the initial position of the vortex and the propagation
depth, making numerical simulations indispensable when analyzing experiments
Comment on "Quantized Orbital Angular Momentum Transfer and Magnetic Dichroism in the Interaction of Electron Vortices with Matter"
It was claimed (Lloyd et al., PRL 108 (2012) 074802) that energy loss
magnetic chiral dichroism (EMCD) with electron vortex beams is feasible, and
has even advantages over the standard setup with Bragg diffracted waves. In
this Comment, we show that Lloyd et al. ignored an important constraint on the
proposed selection rule for the transfer of angular momentum in the
interaction, namely that it is only valid for an atom located in the very
center of the vortex. As an experimental consequence, the EMCD signal will only
be strong for extremely small nanoparticles of 1 to 2 nm diameter.Comment: Submitted to Physical Review Letters 11 July 2012. Accepted for
publication 3 April 2013. "Copyright (2013) by the American Physical
Society." http://prl.aps.org
Image Difference Metrics for High-Resolution Electron Microscopy
Digital image comparison and matching brings many advantages over the
traditional subjective human comparison, including speed and reproducibility.
Despite the existence of an abundance of image difference metrics, most of them
are not suited for high-resolution transmission electron microscopy (HRTEM)
images. In this work we adopt two image difference metrics not widely used for
TEM images. We compare them to subjective evaluation and to the mean squared
error in regards to their behaviour regarding image noise pollution. Finally,
the methods are applied to and tested by the task of determining precipitate
sizes of a model material.Comment: 15 pages, 4 figure
Role of Endothelin-1 in the Brown Adipose Tissue
ET-1 was shown to inhibit adipogenesis in murine mesenchymal stem cells derived from new-born brown adipose tissue in vitro and antagonism of Endothelin-1 (ET-1) signaling at the respective level of the Endothelin-1 receptor A (ETA) enhanced differentiation of brown adipocytes in vitro, which was quantified by increased brown adipocyte-marker expression. Based on in vitro data, in vivo studies were conducted in order to put the therapeutic strategy of ETA-antagonism to the test. In the conducted studies two approaches were taken to realize whether or not beneficial effects arise from ETA-antagonism: First, ETA was antagonized pharmacologically with BQ-123. Secondly, ETA was genetically deleted (Ednra-ATKO) in the adipose tissue using the cre-lox system. Both approaches were tested in a setting of diet-induced obesity and chronic cold-exposure. In the settings of diet-induced obesity, neither pharmacological inhibition nor genetic ablation proved to be clearly beneficial. The pharmacological antagonism upon BQ-123-treatment induced a minor but significant upregulation of the functional marker Ucp1 in brown adipose tissue after chronic cold-exposure
Magnetic properties of single nanomagnets: EMCD on FePt nanoparticles
Energy-loss magnetic chiral dichroism (EMCD) allows for the quantification of
magnetic properties of materials at the nanometer scale. It is shown that with
the support of simulations that help to identify the optimal conditions for a
successful experiment and upon implementing measurement routines that
effectively reduce the noise floor, EMCD measurements can be pushed towards
quantitative magnetic measurements even on individual nanoparticles. With this
approach, the ratio of orbital to spin magnetic moments for the Fe atoms in a
single L ordered FePt nanoparticle is determined to be . This finding is in good quantitative agreement with the results of
XMCD ensemble measurements.Comment: 35 pages, 10 figure
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