Time filter

Source Type

Koch C.T.,Max Planck Institute for Intelligent Systems (Stuttgart)
Ultramicroscopy | Year: 2011

The application of convergent beam electron diffraction (CBED) to determine symmetry, refine structure factors, and measure specimen thickness requires rather thick specimen and is very difficult or even impossible in the case of large unit cell materials. The large-angle rocking-beam electron diffraction (LARBED) technique introduced in this paper gives access to the kind of experimental data contained in CBED patterns but over a much larger angular range. In addition to symmetry determination and thickness measurement even for thin samples this technique also allows, in principle, very accurate measurements of structure factors. Similar to precession electron diffraction (PED), LARBED uses the illumination tilt coils to sequentially change the angle of incidence of the electron beam over a very large range. I will present results obtained by a recently developed self-calibrating acquisition software which compensates for aberration-induced probe shifts during the acquisition of LARBED patterns and keeps the probe within a few nm, while covering a tilt range from 0 to 100. mrad. This paper is dedicated to Prof. John C. H. Spence on the occasion of his 65th birthday. © 2010 Elsevier B.V. Source

Fahnle M.,Max Planck Institute for Intelligent Systems (Stuttgart)
Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2011

For metallic magnets we review the experimental and electron-theoretical investigations of fast magnetization dynamics (on a timescale of ns to 100 ps) and of laser-pulse-induced ultrafast dynamics (few hundred fs). It is argued that for both situations the dominant contributions to the dissipative part of the dynamics arise from the excitation of electron-hole pairs and from the subsequent relaxation of these pairs by spin-dependent scattering processes, which transfer angular momentum to the lattice. By effective field theories (generalized breathing and bubbling Fermi-surface models) it is shown that the Gilbert equation of motion, which is often used to describe the fast dissipative magnetization dynamics, must be extended in several aspects. The basic assumptions of the Elliott-Yafet theory, which is often used to describe the ultrafast spin relaxation after laser-pulse irradiation, are discussed very critically. However, it is shown that for Ni this theory probably yields a value for the spin-relaxation time T(1) in good agreement with the experimental value. A relation between the quantity α characterizing the damping of the fast dynamics in simple situations and the time T(1) is derived. © 2011 IOP Publishing Ltd Source

Roke S.,Institute of Bioengineering IBI | Roke S.,Max Planck Institute for Intelligent Systems (Stuttgart) | Gonella G.,Temple University
Annual Review of Physical Chemistry | Year: 2012

Nano -and microparticles have optical, structural, and chemical properties that differ from both their building blocks and the bulk materials themselves. These different physical and chemical properties are induced by the high surface-to-volume ratio. As a logical consequence, to understand the properties of nano- and microparticles, it is of fundamental importance to characterize the particle surfaces and their interactions with the surrounding medium. Recent developments of nonlinear light scattering techniques have resulted in a deeper insight of the underlying light-matter interactions. They have shed new light on the molecular mechanism of surface kinetics in solution, properties of interfacial water in contact with hydrophilic and hydrophobic particles and droplets, molecular orientation distribution of molecules at particle surfaces in solution, interfacial structure of surfactants at droplet interfaces, acid-base chemistry on particles in solution, and vesicle structure and transport properties. Copyright © 2012 by Annual Reviews. All rights reserved. Source

Palagi S.,Max Planck Institute for Intelligent Systems (Stuttgart)
Nature Materials | Year: 2016

Microorganisms move in challenging environments by periodic changes in body shape. In contrast, current artificial microrobots cannot actively deform, exhibiting at best passive bending under external fields. Here, by taking advantage of the wireless, scalable and spatiotemporally selective capabilities that light allows, we show that soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions. We realize continuum yet selectively addressable artificial microswimmers that generate travelling-wave motions to self-propel without external forces or torques, as well as microrobots capable of versatile locomotion behaviours on demand. Both theoretical predictions and experimental results confirm that multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa, can be achieved with single microswimmers. The principle of using structured light can be extended to other applications that require microscale actuation with sophisticated spatiotemporal coordination for advanced microrobotic technologies. © 2016 Nature Publishing Group Source

Garcia-Saez A.J.,Max Planck Institute for Intelligent Systems (Stuttgart) | Garcia-Saez A.J.,German Cancer Research Center
Cell Death and Differentiation | Year: 2012

The Bcl-2 family of proteins is formed by pro-and antiapoptotic members. Together they regulate the permeabilization of the mitochondrial outer membrane, a key step in apoptosis. Their complex network of interactions both in the cytosol and on mitochondria determines the fate of the cell. In the past 2 decades, the members of the family have been identified and classified according to their function. Several competing models have been proposed to explain how the Blc-2 proteins orchestrate apoptosis signaling. However, basic aspects of the action of these proteins remain elusive. This review is focused on the biophysical mechanisms that are relevant for their action in apoptosis and on the challenging gaps in our knowledge that necessitate further exploration to finally understand how the Bcl-2 family regulates apoptosis. © 2012 Macmillan Publishers Limited. All rights reserved. Source

Discover hidden collaborations