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Selected AbstractsA new method for the aqueous functionalization of superparamagnetic Fe2O3 nanoparticlesCONTRAST MEDIA & MOLECULAR IMAGING, Issue 6 2008Fernando Herranz Abstract A new methodology for the synthesis of hydrophilic iron oxide nanoparticles has been developed. This new method is based on the direct chemical modification of the nanoparticles' surfactant molecules. Using this methodology both USPIO (ultrasmall super paramagnetic iron oxide) (hydrodynamic size smaller than 50,nm) and SPIO (super paramagnetic iron oxide) (hydrodynamic size bigger than 50,nm) were obtained. In addition, we also show that it is possible to further functionalize the hydrophilic nanoparticles via covalent chemistry in water. The magnetic properties of these nanoparticles were also studied, showing their potential as MRI contrast agents. Copyright © 2008 John Wiley & Sons, Ltd. [source] Powder Metallurgical Near-Net-Shape Fabrication of Porous NiTi Shape Memory Alloys for Use as Long-Term Implants by the Combination of the Metal Injection Molding Process with the Space-Holder Technique,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Manuel Köhl Abstract A new method was developed for producing highly porous NiTi for use as an implant material. The combination of the space-holder technique with the metal injection molding process allows a net-shape fabrication of geometrically complex samples and the possibility of mass production for porous NiTi. Further, the porosity can be easily adjusted with respect to pore size, pore shape, and total porosity. The influence of the surface properties of powder metallurgical NiTi on the biocompatibility was first examined using human mesenchymal stem cells (hMSCs). It was found that pre-alloyed NiTi powders with an average particle size smaller than 45,,m led to the surface properties most suitable for the adhesion and proliferation of hMSCs. For the production of highly porous NiTi, different space-holder materials were investigated regarding low C- and O-impurity contents and the reproducibility of the process. NaCl was the most promising space-holder material compared to PMMA and saccharose and was used in subsequent studies. In these studies, the influence of the total porosity on the mechanical properties of NiTi is investigated in detail. As a result, bone-like mechanical properties were achieved by the choice of Ni-rich NiTi powder and a space-holder content of 50,vol% with a particle size fraction of 355,500,,m. Pseudoelasticity of up to 6% was achieved in compression tests at 37,°C as well as a bone-like loading stiffness of 6.5,GPa, a sufficient plateau stress ,25 of 261,MPa and a value for ,50 of 415,MPa. The first biological tests of the porous NiTi samples produced by this method showed promising results regarding proliferation and ingrowth of mesenchymal stem cells, also in the pores of the implant material. [source] The preservation of seismic anisotropy in the Earth's mantle during diffusion creepGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2009J. Wheeler SUMMARY Seismic anisotropy in the Earth, particularly in the mantle, is commonly interpreted as the result of solid-state deformation by dislocation creep that induces a lattice preferred orientation (LPO). Diffusion creep operates where stress levels are lower and/or grain sizes smaller. It is often assumed that diffusion creep induces grain rotations that eventually destroy any existing LPO. A new numerical test of this assumption shows that it is not necessarily the case: diffusion creep will create some relative grain rotations, but rotation rates decrease through time. Hence, when microstructural change due to diffusion creep dominates that due to grain growth, defined here as ,type P' behaviour (the converse being ,type O' behaviour), the model indicates that LPO will be weakened but preserved (for a variety of strain paths including both pure and simple shear). One measure of anisotropy is the proportional difference in shear wave velocities for different polarization vectors (AVs). A model olivine microstructure with equant grains and initial maximum AVs of 10.0 percent has this value reduced to 6.7 per cent when ,rotational steady state' is attained. Other models with different initial maximum AVs values exhibit final maximum AVs values more than half the initial values. If the grains are initially elongate by a factor of 2, maximum AVs is reduced just slightly, to 8.5 per cent. Thus, when grain growth plays a subordinate role to the deformation, diffusion creep weakens seismic anisotropy by a factor of less than 2 (using maximum AVs as a measure and olivine as an example). Consequently, the link between seismic anisotropy and deformation mechanism in the mantle requires reappraisal: regions with LPO may comprise material which once deformed by dislocation creep, but is now deforming by diffusion creep in a rotational steady state. [source] Characterization of combustion-derived individual fine particulates by computer-controlled scanning electron microscopyAICHE JOURNAL, Issue 11 2009Lian Zhang Abstract Particulate matter (PM) emission from the combustion of solid fuels potentially poses a severe threat to the environment. In this article, a novel approach was developed to examine the properties of individual particles in PM. With this method, PM emitted from combustion was first size-segregated. Subsequently, each size was characterized by computer-controlled scanning electron microscopy (CCSEM) for both bulk property and single particle analysis. Combustion of bituminous coal, dried sewage sludge (DSS) and their mixture were conducted at 1200°C in a laboratory-scale drop tube furnace. Three individual sizes smaller than 2.5 ,m were investigated. The results indicate that a prior size-segregation can greatly minimize the particle size contrast and phase contrast on the backscattered images during CCSEM analysis. Consequently, high accuracy can be achieved for quantifying the sub-micron particles and their inherent volatile metals. Regarding the PM properties as attained, concentrations of volatile metals including Na, K, and Zn have a negative relationship with particle size; they are enriched in the smallest particles around 0.11 ,m as studied here. Strong interactions can occur during the cofiring of coal and DSS, leading to the distinct properties of PM emitted from cofiring. The method developed here and results attained from it are helpful for management of the risks relating to PM emission during coal-fired boilers. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Verifying the RTE model: ortho-positronium lifetime measurement on controlled pore glassesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007S. Thraenert Abstract In porous media, the vacuum lifetime of ortho-positronium (o-Ps) of , = 142 ns can be reduced markedly by pick-off annihilation (interaction with electrons of the host material). So the o-Ps lifetime is determined by the pore size which can be extracted by utilising approved models like the Tao-Eldrup model for pore sizes smaller than 1 nm and the Tokyo model or RTE model for larger pore sizes. The RTE model contains an explicit temperature dependence of the o-Ps lifetime. Experiments on controlled pore glasses (CPG) with different pore sizes (2-70 nm) at different temperatures (50-500 K) were performed to verify the RTE model. A general agreement for T = 300 K could be found. The temperature dependence of the lifetime, especially for low temperatures, could not be approved sufficiently. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of die temperature on the morphology of microcellular foamsPOLYMER ENGINEERING & SCIENCE, Issue 6 2003Xiangmin Han A study on the extrusion of microcellular polystyrene foams at different foaming temperatures was carried out using CO2 as the foaming agent. The contraction flow in the extrusion die was simulated with FLUENT computational fluid dynamics code at two temperatures (150°C and 175°C) to predict pressure and temperature profiles in the die. The location of nucleation onset was determined based on the pressure profile and equilibrium solubility. The relative importance of pressure and temperature in determining the nucleation rate was compared using calculations based on classical homogeneous nucleation theory. Experimentally, the effects of die temperature (i.e., the foaming temperature) on the pressure profile in the die, cell size, cell density, and cell morphology were investigated at different screw rotation speeds (10 , 30 rpm). Experimental results were compared with simulations to gain insight into the foaming process. Although the foaming temperature was found to be less significant than the pressure drop or the pressure drop rate in deciding the cell size and cell density, it affects the cell morphology dramatically. Open and closed cell structures can be generated by changing the foaming temperature. Microcellular foams of PS (with cell sizes smaller than 10 ,m and cell densities greater than 10 cells/cm3) are created experimentally when the die temperature is 160°C, the pressure drop through the die is greater than 16 MPa, and the pressure drop rate is higher than 109 Pa/sec. [source] Small scale mixing processes at the top of a marine stratocumulus,a case studyTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 622 2007Krzysztof E. Haman Abstract A layer of intensive mixing (entrainment interface layer, [EIL]) at the top of marine stratocumulus under a strong inversion has been investigated with 10 cm resolution using an ultrafast thermometer (UFT-F; temperature), a particle volume monitor PVM,100A (liquid water content), and a fast forward scattering spectrometer probe (FFSSP; droplet spectra). Measurements were collected on board the NCAR C-130 aircraft during research flight RF05 of DYCOMS-II field study. The EIL consists of mutual filaments of cloudy and clear air at different stages of stirring, mixing, and homogenization. Borders between these filaments are often very sharp, with the 10 cm resolution of the instruments being insufficient to characterize them properly in many cases. Certain classifications of these filaments and hypotheses about the mechanisms of their formation have been proposed. The common occurrence of filaments of sizes smaller than the resolution of instruments has been indirectly confirmed. This is in agreement with the observed cloud droplet spectra showing variations of droplet number concentration without significant change of the mean droplet diameter and spectrum width. Copyright © 2007 Royal Meteorological Society [source] Direct Volumetric Measurement of Gas Oversolubility in Nanoliquids: Beyond Henry's LawCHEMPHYSCHEM, Issue 12 2009Marc Pera-Titus Dr. Abstract The properties of condensed matter are strongly affected by confinement and size effects at the nanoscale. Herein, we measured by microvolumetry the increased solubility of H2 in a series of solvents (CHCl3, CCl4, n -hexane, ethanol, and water) when confined in the cavities of mesoporous solids (,-alumina, silica, and MCM-41). Gas/liquid solubilities are enhanced by up to 15 times over the corresponding bulk values for nanoliquid sizes smaller than 15 nm as long as gas/liquid interfaces are mesoconfined in a porous network. Although Henry's law constant apparently no longer applies under these confinement, the concentration of dissolved H2 still increases linearly with increasing pressure in the range 1,5 bar. We discuss the role and main implications of surface excess concentrations at mesoconfined gas/liquid interfaces in enhancing gas solubility. [source] | ||||||||||||||||