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21.
J. Carrasquilla-Alvarez R. Castaneda J. Garcia-Sucerquia M.A. Schofield M. Beleggia Y. Zhu G. Matteucci 《Optik》2008,119(3):127-133
The possibility to characterize the coherence properties of an electron source is presented. The method, based on the determination of centered-reduced moments of the beam spot, allows the evaluation of both amplitude and phase of the complex degree of spatial coherence. The experimental results are in agreement with a different approach based on the Fourier analysis and with calculations according to the Van Cittert—Zernike theorem. 相似文献
22.
A fluid of spheroids, ellipsoids of revolution, is among the simplest models of the disordered matter, where positional and rotational degrees of freedom of the constituent particles are coupled. However, while highly anisometric rods, and hard spheres, were intensively studied in the last decades, the structure of a fluid of spheroids is still unknown. We reconstruct the structure of a simple fluid of spheroids, employing direct confocal imaging of colloids, in three dimensions. The ratio t between the polar axis and the equatorial diameter for both our prolate and oblate spheroids is not far from unity, which gives rise to a delicate interplay between rotations and translations. Strikingly, the measured positional interparticle correlations are significantly stronger than theoretically predicted, indicating that further theoretical attention is required, to fully understand the coupling between translations and rotations in these fundamental fluids. 相似文献
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van't Zand DD Schofield AB Thijssen JH Clegg PS 《Langmuir : the ACS journal of surfaces and colloids》2011,27(22):13436-13443
The addition of sterically stabilized colloidal particles to a phase-separating microemulsion leads to dramatic changes in its demixing behavior, especially during the later stages. Our microemulsion is composed of reverse micelles of sodium dodecyl sulfate, pentanol, and water in a dodecane continuous phase which separates into micelle-rich and micelle-poor phases above a lower critical solution temperature. The poly(methyl methacrylate) particles preferentially partition into the less structured, micelle-poor phase. Nucleation of the minority phase or spinodal decomposition close to criticality continue to occur in the presence of particles, albeit with pronounced pretransitional clustering of particles when the micelle-poor phase is in the minority. The coalescence of micelle-poor droplets and the coarsening of micelle-rich domains are both strongly modified due to the presence of colloidal particles. We use our observations of the early stages of phase separation to understand these late stage changes. 相似文献
24.
White KA Schofield AB Wormald P Tavacoli JW Binks BP Clegg PS 《Journal of colloid and interface science》2011,359(1):126-135
Using a system of modified silica particles and mixtures of water and 2,6-lutidine to form particle-stabilized emulsions, we show that subtle alterations to the hydration of the particle surface can cause major shifts in emulsion structure. We use fluorescence confocal microscopy, solid state nuclear magnetic resonance (NMR) and thermo-gravimetric analysis (TGA) to explore this sensitivity, along with other shifts caused by modifications to the silica surface chemistry. The silica particles are prepared by a variant of the St?ber procedure and are modified by the inclusion of 3-(aminopropyl)triethoxysilane and the dye fluorescein isothiocyanate. Treatment prior to emulsification consists of gently drying the particles under carefully controlled conditions. In mixtures of water and 2,6-lutidine of critical composition, the particles stabilize droplet emulsions and bijels. Decreasing particle hydration yields an inversion of the emulsions from lutidine-in-water (L/W) to water-in-lutidine (W/L), with bijels forming around inversion. So dependent is the emulsion behavior on particle hydration that microscopic differences in drying within a particle sample can cause differences in the wetting behavior of that sample, which helps to stabilize multiple emulsions. The formation of bijels at emulsion inversion is also crucially dependent on the surface modification of the silica. 相似文献
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Canepa P Schofield E Chadwick AV Alfredsson M 《Physical chemistry chemical physics : PCCP》2011,13(28):12826-12834
Comparison and prediction of the experimental XANES spectrum is a good measurement of the quality of the electronic structure calculations employed, and their ability to predict electronic transitions in solids. Here we present a comparison between BLYP + U and hybrid-BLYP calculations regarding the geometric, magnetic and electronic structures of α-Fe(2)O(3) (hematite). Several values of U and different percentages of Fock-exchange have been screened to see how their contributions affect different properties of hematite, paying particular attention to the electronic structure. To estimate the quality of the various methods the calculated density-of-states were compared to the experimentally collected XANES spectrum of the iron K-edge, providing information about the orbitals describing the conduction band. We find that in agreement with previous studies DFT + U and hybrid-functional simulations can correctly predict the character of the valence band, but only Fock-exchange higher than 30% or U-values equal or larger than 6 eV properly reproduce the order between the t(g) and e orbitals in the conduction band, and can, therefore, be used to study and predict XANES spectra and electronic transitions in hematite. 相似文献
27.
D. Stavorinus F. Daniels W. Swientoslawski E. Cohen A. L. Th. Moesveld W. D. Helderman F. F. Flanders F. H. Schofield C. V. Boys S. W. Parr W. A. Roth W. Kohen G. Bruhns P. E. Verkade J. Coops Jr. F. Henning P. F. Hoots H. Ginsberg R. Lassé H. v. Wartenberg W. Husen M. Padoa B. Foresti Englisches Handelsamt 《Analytical and bioanalytical chemistry》1925,67(10):401-408
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Reduction of pertechnetate [(99m)TcO(-)(4)] by controlled-potential coulometry in the presence of 1-hydroxy-1,1-ethanediphosphonate (HEDP) leads to the formation of (99m) Tc complexes which are suitable for bone imaging. The complex radiopharmaceutical mixtures can be separated into their respective components by anion-exchange high-performance liquid chromatography. The distribution of the complexes in the mixtures is dependent on the cell potential, pH, technetium concentration, and presence or absence of air. A single component formed in high yield and isolated from the mixture by HPLC was investigated as a potential bone-imaging agent. This particular complex is produced only in low yields when prepared by chemical reduction of (99m) TcO(-)(4). Thus electrochemistry shows promise in aiding in the development of a more efficacious bone-imaging agent by allowing selective generation of individual (99m) Tc-HEDP complexes. 相似文献