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Core Size (core + size)
Selected AbstractsInfluence of stability on the acute toxicity of CdSe/ZnS nanocrystals to Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2010Heather E. Pace Abstract The acute toxicity of polymer-coated CdSe/ZnS quantum dots (QDs) to Daphnia magna was investigated using 48-h exposure studies. The principal objective was to relate the toxicity of QDs to specific physical and chemical aspects of the QD. As such, two different CdSe core diameters, 2,nm QDs (green-emitting) and 5,nm QDs (red-emitting), and two different surface coatings, polyethylene oxide (PEO) and 11-mercaptoundecanoic acid (MUA) were studied. The QDs were characterized before and after the 48-h exposure using fluorescence, ultrafiltrations (3 kDa), and inductively coupled plasma-atomic emission spectrometry (ICP-AES) metal analysis. In addition, flow field flow fractionation-inductively coupled plasma-mass spectrometry (Fl FFF-ICP-MS) was used as a more extensive characterization technique to determine particle size and composition as well as identify other potential constituents in the QD solutions. The more stable QDs (PEO) were found to be less acutely toxic than the QDs with accelerated dissolution (MUA), suggesting QD stability has significant impact on the nanoparticles' short-term toxicity. The emergence of dissolved Cd2+ in solution indicates that the toxicity of the MUA QDs is likely due to Cd poisoning, and a mass-based dose response occurred as a consequence of this mode of action. Alternatively, the PEO QDs caused acute toxicity without observed particle dissolution (i.e., no detectable metals were solubilized), suggesting an alternative mode of toxic action for these nanoparticles. Results of the present study suggest that using particle number, instead of mass, as a dose metric for the PEO QDs, produces markedly different conclusions, in that smaller core size does not equate to greater toxicity. Environ. Toxicol. Chem. 2010;29:1338,1344. © 2010 SETAC [source] Thin-tube vortex simulations for sinusoidal instability in a counter-rotating vortex pairINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2002Z. C. ZhengArticle first published online: 22 MAY 200 Abstract A thin-tube vortex method is developed to investigate the intrinsic instability within a counter-rotating vortex pair system and the effects from the core size and the wavenumbers (or wavelengths). The numerical accuracy and the advantages of the scheme are theoretically estimated. A nearest-neighbour-image method is employed in this three-dimensional vortex simulation. Agreement with Crow's instability analysis has been achieved numerically for the long-wave cases. A short-wave instability for the zeroth radial mode of bending instability has also been found using the thin-tube vortex simulations. Then, the combinations of long- and short-wave instability are investigated to elucidate the non-linear effects due to the interactions of two different modes. It is shown that instability is enhanced if both long- and short-wave instabilities occur simultaneously. Although the method used in the paper is not capable of including effects such as axial flow, vortex core deformation and other complicated viscous effects, it effectively predicts and clarifies the first-order factor that dominates the sinusoidal instability behaviour in a vortex pair. Copyright © 2002 John Wiley & Sons, Ltd. [source] The application of distance distribution functions to structural analysis of core,shell particlesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Oleksandr O. Mykhaylyk The structure of core,shell latex particles of polymethylmethacrylate (the core) and polyurethane (the shell) have been investigated by methods of small-angle X-ray scattering (SAXS) and atom-force microscopy. A set of SAXS patterns has been obtained using contrast variation method. Indirect methods have been used to follow the evolution of distance distribution functions from SAXS for lattices in various sucrose solutions over a range of solution density, yielding structural parameters of the particles such as core size, shell thickness and density of the polymers including density deviations within the particle's core and shell. A model for an ensemble of core,shell particles with a normal distribution of average electron density of both the core and the shell has been developed to fit the distance distribution functions using a random search algorithm. The effects of nanophase separation in the polyurethane is estimated using Monte Carlo simulations of the distance distribution functions where the phase-separated polyurethane is represented by spherical truncated cones in a shell simulating the location of hard and soft polyurethane blocks, respectively. [source] Comparison of lipid-rich necrotic core size in symptomatic and asymptomatic carotid atherosclerotic plaque: Initial resultsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2008Vincent C. Cappendijk MD Abstract Purpose To investigate the potential difference in the size of the lipid-rich necrotic core (LRNC) in carotid plaques of symptomatic patients versus asymptomatic patients. Pathological studies established that a large LRNC is an important feature of vulnerable atherosclerotic plaque. Previously, we have demonstrated a high correlation between semiquantitative analysis of the LRNC size in T1-weighted (w) turbo field echo (TFE) MR images and histology. Materials and Methods Thirty-seven patients with carotid stenosis >70% with (n = 26) or without (n = 11) symptoms were included. Three independent MR readers quantified the amount of LRNC with a T1w TFE pulse sequence. The relative amount of LRNC (LRNC score) was defined as sum of cross-sectional area percentages LRNC per carotid plaque. Results Interreader agreement for the three MR readers was good, with an intraclass correlation coefficient (ICC, 95% confidence interval [CI]) of 0.72 (0.57,0.83). All three MR readers on average found a larger LRNC in the symptomatic group of patients, although this was not statistically significant. The mean LRNC score was 116 ± 129 and 59 ± 62 for symptomatic and asymptomatic patients, respectively (P = 0.13). Symptomatic patients showed wide ranges in LRNC scores (0,424), while the range was much lower in the asymptomatic group (0,170). Conclusion Single-sequence T1w TFE may be a promising technique to study atherosclerotic plaque at risk of stroke. Larger studies are warranted to confirm these promising results. J. Magn. Reson. Imaging 2008;27:1356,1361. © 2008 Wiley-Liss, Inc. [source] Electrochemical synthesis and stabilization of cobalt nanoparticlesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006A. Ledo-Suárez Abstract Cobalt nanoparticles (NPs) were synthesized via an electrochemical method in the presence of tetraalkylammonium salt. The nanometer dimensions of the NPs can be controlled in a simple way by adjustment of the current density. From these particles stable colloidal suspensions are prepared in the presence of a fatty acid (oleic acid) and triphenylphosphine. The colloidal system is stable against oxidation when they are kept in heptane (C7H16). Transmission electron microscopy (TEM) was employed to determine the core size and the shape of metal nanoparticles. The chemical interaction of the surfactant with the Co nanoparticles was studied by using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Thermogravimetric analysis (TGA) was used to study the thermal stability and the composition of the capped cobalt nanoparticles. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic properties of bimetallic Co-Pd nanostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2005Javier Guevara Abstract We study the dependence of the magnetic properties of Co-Pd nanoclusters (Co cores coated by Pd atoms) on size and relative composition. We consider Co-Pd clusters having closed shell cubo-octahedral structure with an increasing Co core size. The electronic and magnetic properties are calculated with a parametrized Hubbard Hamiltonian within the unrestricted Hartree-Fock approximation. We show that, depending on the relative composition, the Pd coating can give rise to an enhancement of the average magnetic moment of the Co core. We compare with results from slabs by using an ab initio calculation method. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation and cytotoxic properties of goethite-based nanoparticles covered with decyldimethyl(dimethylaminoethoxy) silane methiodideAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2010Izolda Segal Abstract The present work describes the synthesis, physico-chemical and biological properties of the first water-soluble goethite nanoparticles covered with biologically active components: oleic acid and cytotoxic decyldimethyl(dimethylaminoethoxy)silane methiodide. The structure of initial goethite nanoparticles synthesized was proved by XRD analysis and the rough estimation of nanoparticles core size gave the value of 8 nm. The size of colloidal water-soluble nanoparticles, determined by dynamic light scattering, was within 19,35 nm. Magnetic properties and cytotoxicity (against HT-1080 and MG-22A tumor cell lines) of the nanoparticles obtained were investigated. Copyright © 2009 John Wiley & Sons, Ltd. [source] Superparamagnetic iron oxide particles: contrast media for magnetic resonance imaging,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2004Rüdiger Lawaczeck Abstract The mainstream magnetic iron oxide particles used as contrast media for magnetic resonance (MR) imaging are composed of a magnetic iron oxide core surrounded by a dextran or carboxydextran coat. The core size ranges from 2 nm to less than 10 nm, and the hydrodynamic diameter ranges from 20 nm to about 120 nm. The coat prevents aggregation and sedimentation of the particles in aqueous solutions, achieves high biological tolerance, and prevents toxic side effects. Two kinds of particles are considered: (i) large particles (>30 nm), called superparamagnetic iron oxide particles (SPIOs) for liver imaging; (ii) smaller particles (<30 nm hydrodynamic diameter), called ultrasmall SPIOs (USPIOs), e.g. for MR angiography. To characterize the particles, Mössbauer spectra are presented for the two particle ensembles. These spectra allow insight into the magnetic coupling, the valency of the iron ions and a rough estimate of the core size to be deduced. On the basis of the concentration dependence of the MR signal intensities, two applications are discussed together with two representative clinical examples. Future indications for MR diagnostics, e.g. the labeling and tracking of stem cells during stem-cell therapy control, are outlined. Copyright © 2004 John Wiley & Sons, Ltd. [source] A Convergent Approach to Biocompatible Polyglycerol "Click" Dendrons for the Synthesis of Modular Core,Shell Architectures and Their Transport BehaviorCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2008Monika Wyszogrodzka Dipl.-Ing. Abstract Dendrimers are an important class of polymeric materials for a broad range of applications in which monodispersity and multivalency are of interest. Here we report on a highly efficient synthetic route towards bifunctional polyglycerol dendrons on a multigram scale. Commercially available triglycerol (1), which is highly biocompatible, was used as starting material. By applying Williamson ether synthesis followed by an ozonolysis/reduction procedure, glycerol-based dendrons up to the fourth generation were prepared. The obtained products have a reactive core, which was further functionalized to the corresponding monoazido derivatives. By applying copper(I)-catalyzed 1,3-dipolar cycloaddition, so-called "click" coupling, a library of core,shell architectures was prepared. After removal of the 1,2-diol protecting groups, water-soluble core,shell architectures 24,27 of different generations were obtained in high yields. In the structure,transport relationship with Nile red we observe a clear dependence on core size and generation of the polyglycerol dendrons. [source] | |||||||||||||