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71.
M. Tang K.S. Holliday J.A. Valdez P.O. Dickerson Y. Wang K.E. Sickafus 《Journal of solid state chemistry》2010,183(4):844-848
Polycrystalline uranium-bearing compounds Y6U1O12, Gd6U1O12, Ho6U1O12, Yb6U1O12, and Lu6U1O12 samples were irradiated with various ions species (300 keV Kr++, 400 keV Ne++, and 100 keV He+) at cryogenic temperature (∼100 K), and the microstructures were examined following irradiation using grazing incidence X-ray diffraction and transmission electron microscopy. The pristine samples are characterized by an ordered, fluorite derivative structure, known as the delta phase. This structure possesses rhombohedral symmetry. Amorphization was not observed in any of the irradiated samples, even at the highest dose ∼65 dpa (displacement per atom). On the other hand, some of these compounds experienced an order-to-disorder (O-D) phase transformation, from an ordered rhombohedral to a disordered fluorite structure, at ion doses between 2.5 and 65 dpa, depending on ion irradiation species. Factors influencing the irradiation-induced O-D transformation tendencies of these compounds are discussed in terms of density functional theory calculations of the O-D transformation energies. 相似文献
72.
73.
Nornicotine, a native component of tobacco and minor nicotine metabolite, was found to catalyze the chemoselective reduction of alpha,beta-unsaturated aldehydes under homogeneous aqueous conditions. 相似文献
74.
Stefaniak AB Brink CA Dickerson RM Day GA Brisson MJ Hoover MD Scripsick RC 《Analytical and bioanalytical chemistry》2007,387(7):2411-2417
Complete digestion of all chemical forms and sizes of particulate analytes in environmental samples is usually necessary to
obtain accurate results with atomic spectroscopy. In the current study, we investigate the physicochemical properties of beryllium
particles likely to be encountered in samples collected from different occupational environments and present a hypothesis
that a dissolution theory can be used as a conceptual framework to guide development of strategies for digestion procedures.
For monodisperse single-chemical constituent primary particles, such as those encountered when handling some types of beryllium
oxide (BeO) powder, theory predicts that a digestion procedure is sufficient when it completely dissolves all primary particles,
independent of cluster size. For polydisperse single-chemical constituent particles, such as those encountered during the
handling of some types of beryllium metal powder, theory predicts that a digestion procedure is sufficient only when it completely
dissolves the largest particle in the sample. For samples with unknown or multi-chemical constituent particles and with particles
having undefined sizes, e.g., fume emissions from a copper–beryllium alloy furnace operation or dust from a beryl ore crushing
operation, a surface area-limited and single-constituent-dependent dissolution theory may not predict complete dissolution,
thereby requiring non-routine robust treatment procedures with post-digestion filtration, followed by examination of residual
particulate material. Additionally, for beryllium, and likely other poorly soluble materials, particulate reference materials
of various chemical forms and size distributions are needed to better evaluate and harmonize analytical digestion procedures.
Figure Generation of aerosol particles during machining of beryllium oxide
The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National
Institute for Occupational Safety and Health. 相似文献
75.
This paper obtains solitons as well as other solutions to a few nonlinear evolution equations that appear in various areas of mathematical physics. The two analytical integrators that are applied to extract solutions are tan–cot method and functional variable approaches. The soliton solutions can be used in the further study of shallow water waves in (1+1) as well as (2+1) dimensions. 相似文献
76.
77.
John R Dickerson Paul A Erickson 《Journal of Mathematical Analysis and Applications》1974,47(3):513-519
The behavior of an infinite sequence of ordinary differential equations of the form: , , where Xn(t) is a vector valued function of R+, is studied in spaces of infinite sequences of vectors. In particular, sufficient conditions for asymptotic stability of this sequence of linear equations are established and applied to the stability analysis of a string of vehicles with a simple form of automatic control. 相似文献
78.
79.
80.
Gambs C Dickerson TJ Mahajan S Pasternack LB Janda KD 《The Journal of organic chemistry》2003,68(9):3673-3678
The success of organic reactions performed on a gel-phase resin is highly dependent on the accessibility of solvents, catalysts, and reagents to the interior of the resin. A variety of techniques including EPR, fluorescence, and Hildebrand solubility parameters (delta) have been used to probe reaction capabilities and in particular the microenvironment of a gel-phase resin. To provide a more detailed picture of the matrix in question, researchers have turned to NMR for the determination of the diffusion coefficients of solvents and small molecules in swollen beads to provide a means to compare the microenvironment of swollen beads. Since Merrifield and JandaJel resins display different swelling properties and have significantly different kinetic behavior, we undertook a comparative study of the diffusion coefficients of solvents and small molecules in both resins by high-resolution (1)H DOSY NMR. Our results show the following: (1) diffusion values for all studied solvents and small molecules are 20-30% higher in JandaJel compared to Merrifield resins, (2) in the absence of interactions between the resin and a given molecule, the diffusion values mirror the swelling properties of the resin, and (3) in the presence of strong intermolecular interactions between the gel and the considered molecule, the diffusion behavior in the gel is primarily influenced by the strength of the interactions and secondarily by the swelling properties of the resin. These results clearly show that the microenvironment of JandaJels is more "solution-like" than that of Merrifield resins, presumably due to the higher swelling capacity. 相似文献