			Home About us Contact

Rotational Dynamics (rotational + dynamics)

Distribution by Scientific Domains

Chemistry	40%

Selected Abstracts

Singularity-Free Brownian Dynamics Analyses of Rotational Dynamics: Non-Spherical Nanoparticles in Solution

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2005
Stine Nalum Naess
Abstract Summary: From kinetic theory we have rigorously derived singularity-free Brownian dynamics analyses of nanoparticle rotational dynamics. The rigid non-spherical nanoparticles incorporate all three rotational degrees of freedom. This was achieved by using the components of Cartesian rotation vectors as the generalized coordinates describing angular orientation. The new results constitute an important advance compared to the situation when Eulerian angles specify angular orientation. Our finding eliminates one of the main longstanding obstacles to detailed studies of nanoparticle rotational dynamics in the diffusion time domain. The described formalism is applicable to a wide range of nanoparticle systems including liquid crystals, biopolymers, and colloids. [source]

Closed-loop identification of the time-varying dynamics of variable-speed wind turbines

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2009
J. W. van Wingerden
Abstract The trend with offshore wind turbines is to increase the rotor diameter as much as possible to decrease the costs per kWh. The increasing dimensions have led to the relative increase in the loads on the wind turbine structure. Because of the increasing rotor size and the spatial load variations along the blade, it is necessary to react to turbulence in a more detailed way: each blade separately and at several separate radial distances. This combined with the strong nonlinear behavior of wind turbines motivates the need for accurate linear parameter-varying (LPV) models for which advanced control synthesis techniques exist within the robust control framework. In this paper we present a closed-loop LPV identification algorithm that uses dedicated scheduling sequences to identify the rotational dynamics of a wind turbine. We assume that the system undergoes the same time variation several times, which makes it possible to use time-invariant identification methods as the input and the output data are chosen from the same point in the variation of the system. We use time-invariant techniques to identify a number of extended observability matrices and state sequences that are inherent to subspace identification identified in a different state basis. We show that by formulating an intersection problem all states can be reconstructed in a general state basis from which the system matrices can be estimated. The novel algorithm is applied on a wind turbine model operating in closed loop. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Singularity-Free Brownian Dynamics Analyses of Rotational Dynamics: Non-Spherical Nanoparticles in Solution

Cyclodextrin-Based Bimodal Fluorescence/MRI Contrast Agents: An Efficient Approach to Cellular Imaging

CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2010
Zuzana Kotková Dr.
Abstract A novel bimodal fluorescence/MRI probe based on a cyclodextrin scaffold has been synthesized and characterized. The final agent employs the fluorescein (F) functionality as a fluorescence marker and the GdIII complex of a macrocyclic DOTA-based ligand (GdL) having one aminobenzyl-phosphinic acid pendant arm as an MRI probe, and has a statistical composition of (GdL)6.9 -F0.1 -,-CD. Slow rotational dynamics (governed by a very rigid cyclodextrin scaffold) combined with fast water exchange (ensured by the chosen macrocyclic ligand) resulted in a high relaxivity of ,22,s,1,mM,1 per GdIII or ,150,s,1,mM,1 per molecule of the final conjugate (20,MHz, 25,°C). In vitro labelling of pancreatic islets (PIs) and rat mesenchymal stem cells has been successfully performed. The agent is not cytotoxic and is easily internalized into cells. The labelled cells can be visualized by MRI, as proved by the detection of individual labelled PIs. A fluorescence study performed on mesenchymal stem cells showed that the agent stays in the intracellular space for a long time. [source]

Oriented Ensembles in Ultrafast Electron Diffraction

CHEMPHYSCHEM, Issue 7 2006
J. Spencer Baskin
Abstract Electron scattering expressions are presented which are applicable to very general conditions of implementation of anisotropic ultrafast electron diffraction (UED) experiments on the femto- and picosecond time scale. "Magic angle" methods for extracting from the experimental diffraction patterns both the isotropic scalar contribution (population dynamics) and the angular (orientation-dependent) contribution are described. To achieve this result, the molecular scattering intensity is given as an expansion in terms of the moments of the transition-dipole distribution created by the linearly polarized excitation laser pulse. The isotropic component (n=0 moment) depends only on population and scalar internuclear separations, and the higher moments reflect bond angles and evolve in time due to rotational motion of the molecules. This clear analytical separation facilitates assessment of the role of experimental variables in determining the influence of anisotropic orientational distributions of the molecular ensembles on the measured diffraction patterns. Practical procedures to separate the isotropic and anisotropic components of experimental data are evaluated and demonstrated with application to reactions. The influence of vectorial properties (bond angles and rotational dynamics) on the anisotropic component adds a new dimension to UED, arising through the imposition of spatial order on otherwise randomly oriented ensembles. [source]