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1.
Solid‐State NMR Study of Mn2+ for Ca2+ Substitution in Thermally Processed Hydroxyapatites 下载免费PDF全文
Joanna Kolmas Mateusz Jabłoński Anna Ślósarczyk Waclaw Kolodziejski 《Journal of the American Ceramic Society》2015,98(4):1265-1274
In the present study calcium hydroxyapatites enriched at 0.08 wt% in Mn2+ ions (Mn–HA) and their unsubstituted forms (HA) were synthesized using the same standard wet chemical route. Mn‐HA and HA were both calcined at 800°C to give Mn‐HAc and HAc, respectively or sintered at 1250°C, to give Mn‐HAs and HAs, respectively. The influence of the heat treatment on physicochemical properties of Mn‐HA was investigated using powder X‐ray diffraction (PXRD), scanning, and transmission electron microscopy (SEM and TEM), and solid‐state nuclear magnetic resonance (ssNMR). Mn‐HAc and Mn‐HAs were compared to each other and to HAc and HAs, respectively. Assignment of the proton ssNMR peaks from high‐temperature‐treated apatites has been revised. It was found that Mn–HAc and HAc were nanocrystalline, while Mn‐HAs and HAs comprised micrometer sized, partially fused particles (SEM and TEM). PXRD and ssNMR demonstrated that the incorporation of Mn2+ into the crystal lattice of hydroxyapatite significantly facilitates its dehydroxylation and decomposition to oxyhydroxyapatite during calcination at 800°C, and induces its transformation to tetracalcium phosphate (TTCP) and alpha‐tricalcium phosphate (α‐TCP) at 1250°C. Contamination by CaO has also been detected. The 1H→31P NMR cross‐polarization experiments have indicated that the Mn2+ ions preferentially occupied the Ca(I) position in the crystallographic unit cell of Mn‐HAc. In Mn‐HAs, the Mn2+ ions were evenly distributed between the Ca(I) and Ca(II) positions. 相似文献
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The metalorganic molecular beam epitaxial growth of ZnSe using diethylzinc and/or diethylselenium gas sources results in an
abnormally low growth rate of several hundred angstroms per hour. Experiments with dimethylzinc or elemental zinc with elemental
selenium confirm that adsorbed ethyl-based radicals contribute to the low growth rate. Surface sites for incorporation of
the metal atom are saturated by the chemisorbed ethyl radicals or by an ethyl molecule that is postulated to cause the growth
rate limitation. It is observed that laser and electron beam irradiation overcome the site blockage phenomenon under appropriate
growth conditions. For beam-assisted growth, significant increases over the unilluminated growth rate are measured. Experiments
designed to investigate the wavelength dependence of the photon-enhanced growth rate provide evidence that photo-generated
electron/hole pairs are necessary to assist in releasing the ethyl radical from the unpyrolyzed DEZn molecule that is adsorbed
to the surface. 相似文献
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Byun H Sander MY Motamedi A Shen H Petrich GS Kolodziejski LA Ippen EP Kärtner FX 《Applied optics》2010,49(29):5577-5582
We demonstrate a high-repetition-rate soliton fiber laser that is based on highly doped anomalously dispersive erbium-doped fiber. By splicing an 11 mm single-mode fiber to the erbium-doped fiber, the thermal damage of the butt-coupled saturable Bragg reflector (SBR) is overcome. The laser generates 187 fs pulses at a repetition rate of 967 MHz with a measured long-term stability of more than 60 h. 相似文献
8.
Carl-Magnus Persson Andrei Fokau Ivan Serafimovich Victor Bournos Yurii Fokov Christina Routkovskaia Hanna Kiyavitskaya Waclaw Gudowski 《Annals of Nuclear Energy》2008
A subcritical zero-power source-driven coupled core, the YALINA-Booster, has been constructed for experimental investigations of neutron kinetics of source-driven systems. In this study, the reactivity of two subcritical configurations has been determined by the area ratio method. The prompt neutron decay constants have been evaluated through slope fitting of the prompt neutron decay as well as through the pulsed Rossi-α method. It is shown that the slope fitting method and the pulsed Rossi-α method give stable results whereas the area ratio method results show spatial dependence. The reasons for the spatial spread are addressed. 相似文献
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At the beginning of the present century it has been demonstrated that nanocrystalline titanium (NC-Ti) can be fabricated by hydrostatic extrusion (HE) which is one of the severe plastic deformation method. NC-Ti obtained in such a way exhibited excellent mechanical properties. The influence of HE on the microstructure and mechanical properties of titanium Grade 2 was first analyzed in 2005. In this study the progress in HE of titanium has been described. However, there are tribological and technological challenges encountered in HE of titanium. They can practically be eliminated by modifying the surface of Ti billets with aluminum coatings. Another important issue in extrusion is the optimum value of the accumulated strain necessary for grain refinement of titanium. Our results have shown that this value must exceed 3 to obtain nanocrystalline Ti. The results obtained indicate that HE permits producing NC-Ti rods with the diameter up to 10 mm. 相似文献
10.
Rakich PT Dahlem MS Tandon S Ibanescu M Soljacić M Petrich GS Joannopoulos JD Kolodziejski LA Ippen EP 《Nature materials》2006,5(2):93-96
Diffraction, a fundamental process in wave physics, leads to spreading of the optical beams as they propagate. However, new photonic crystal (PhC) meta-materials can be nano-engineered to generate extreme anisotropy, resulting in apparent propagation of light without diffraction. This surprising phenomenon, called supercollimation, effectively freezes the spatial width of a light beam inside a PhC, observed over a few isotropic diffraction-lengths. However, using such experiments to predict the behaviour for longer propagation lengths is difficult, as a tiny error in a measured width can extrapolate to order unity uncertainty in the width at distances over hundreds of diffraction-lengths. Here, supercollimation is demonstrated in a macroscopic PhC system over centimetre-scale distances, retaining spatial width confinement without the need for waveguides or nonlinearities. Through quantitative studies of the beam evolution in a two-dimensional PhC, we find that supercollimation possesses unexpected but inherent robustness with respect to short-scale disorder such as fabrication roughness, enabling supercollimation over 600 isotropic diffraction-lengths. The effects of disorder are identified through experiments and understood through rigorous simulations. In addition, a supercollimation steering capability is proposed. 相似文献