Modeling of Ironless Permanent Magnet Planar Motor Structures

In this paper, finite element analysis is used to develop a fast model that includes end-effects and allows performance and controllability analysis without specifying a commutation scheme or control method is for ironless permanent magnet planar motor structures

Contactless Planar Actuator with Manipulator

The accuracy and reliability of high-precision machines is compromised by friction and disturbances due to cables to moving machine parts. These problems can be solved by applying three contactless techniques in one system: contactless generation of forces and torques, contactless energy transfer to a moving load and wireless control. This paper presents an overview of the research performed at Eindhoven University of Technology to create a contactless planar actuator with manipulator, a system which combines all three contactless techniques

Performance of the Vignale-Kohn functional in the linear response of metals

Recently the linear response of metallic solids has been formulated within the time-dependent current-density-functional approach [Romaniello and de Boeij, Phys. Rev. B 71, 155108 (2005)]. The implementation, which originally used only the adiabatic local density approximation for the exchange-correlation kernel is extended in order to include also the Vignale-Kohn current functional. Within this approximation the exchange-correlation kernel is frequency dependent, thus relaxation effects due to electron-electron scattering can now be taken into account and some deficiencies of the adiabatic local density approximation (ALDA), as the absence of the low-frequency Drude-like tail in absorption spectra, can be cured. We strictly follow the previous formulation of the linear response of semiconductors by using the Vignale-Kohn functional [Berger, de Boeij, and van Leeuwen, Phys. Rev. B 71, 155104 (2005)]. The self-consistent equations for the interband and intraband contributions to the induced density and current density, which are completely decoupled within the ALDA and in the long-wavelength limit, now remain coupled. We present our results calculated for the optical properties of the noble metals Cu, Ag, and Au and we compare them with measurements found in literature. In the case of Au we treat the dominant scalar relativistic effects using the zeroth-order regular approximation in the ground-state density-functional-theory calculations, as well as in the time-dependent response calculations

Spatially resolved electronic structure of twisted graphene

We have used scanning tunneling microscopy and spectroscopy to resolve the spatial variation of the density of states of twisted graphene layers on top of a highly oriented pyrolytic graphite substrate. Owing to the twist a moire pattern develops with a periodicity that is substantially larger than the periodicity of a single layer graphene. The twisted graphene layer has electronic properties that are distinctly different from that of a single layer graphene due to the nonzero interlayer coupling. For small twist angles (about 1-3.5 degree) the integrated differential conductivity spectrum exhibits two well-defined Van Hove singularities. Spatial maps of the differential conductivity that are recorded at energies near the Fermi level exhibit a honeycomb structure that is comprised of two inequivalent hexagonal sub-lattices. For energies |E-E_F|>0.3 eV the hexagonal structure in the differential conductivity maps vanishes. We have performed tight-binding calculations of the twisted graphene system using the propagation method, in which a third graphene layer is added to mimic the substrate. This third layer lowers the symmetry and explains the development of the two hexagonal sub-lattices in the moire pattern. Our experimental results are in excellent agreement with the tight-binding calculations.Comment: To appear in Phys. Rev.

Reduced protein diffusion rate by cytoskeleton in vegetative and polarized Dictyostelium cells

Fluorescence recovery after photobleaching measurements with high spatial resolution are performed to elucidate the impact of the actin cytoskeleton on translational mobility of green fluorescent protein (GFP) in aqueous domains of Dictyostelium discoideum amoebae. In vegetative Dictyostelium cells, GFP molecules experience a 3.6-fold reduction of their translational mobility relative to dilute aqueous solutions. In disrupting the actin filamentous network using latrunculin-A, the intact actin cytoskeletal network is shown to contribute an effective viscosity of 1.36 cP, which accounts for 53% of the restrained molecular diffusion of GFP. The remaining 47% of hindered protein motions is ascribed to other mechanical barriers and the viscosity of the cell liquid. A direct correlation between the density of the actin network and its limiting action on protein diffusion is furthermore established from measurements under different osmotic conditions. In highly locomotive polarized cells, the obstructing effect of the actin filamentous network is seen to decline to 0.46 cP in the non-cortical regions of the cell. Our results indicate that the meshwork of actin filaments constitutes the primary mechanical barrier for protein diffusion and that any noticeable reorganization of the network is accompanied by altered intracellular protein mobility

Moiré-modulated band gap and van Hove singularities in twisted bilayer germanene

Twisting bilayers of two-dimensional topological insulators has the potential to create unique quantum states of matter. Here, we successfully synthesized a twisted bilayer of germanene on Ge2Pt(101) with a 21.8° twist angle, corresponding to a commensurate (√7×√7) structure. Using scanning tunneling microscopy and spectroscopy, we unraveled the structural and electronic properties of this configuration, revealing a moiré-modulated band gap and a well-defined edge state. This band gap opens at AB/BA stacked sites and closes at AA stacked sites, a phenomenon attributed to the electric field induced by the scanning tunneling microscopy tip. Our study further revealed two van Hove singularities at −0.8 eV and +1.04 eV, resulting in a Fermi velocity of (8 ± 1) × 105 m s−1. Our tight-binding results uncover a unique quantum state, where the topological properties could be regulated through an electric field, potentially triggering two topological phase transitions.</p