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101.
The weak compactness of the composition operator C(f) = f acting on the uniform algebra of analytic uniformly continuousfunctions on the unit ball of a Banach space with the approximationproperty is characterized in terms of . The relationship betweenweak compactness and compactness of these composition operatorsand general homomorphisms is also discussed. 2000 MathematicsSubject Classification 46J15 (primary), 46E15, 46G20 (secondary). 相似文献
102.
Use of INAA,PGAA, and RNAA to determine 30 elements for certification of an SRM: Tomato Leaves, 157a
D. A. Becker D. L. Anderson R. M. Lindstrom R. R. Greenberg K. M. Garrity E. A. Mackey 《Journal of Radioanalytical and Nuclear Chemistry》1994,179(1):149-154
Analyses for certification have been made for the determination of 30 elements in the National Institute of Standards and Technology (NIST) Tomato Leaves renewal reference material, SRM 1573a. Three of the analytical techniques used were instrumental neutron activation analysis (INAA), radiochemical neutron activation analysis (RNAA), and prompt gamma activation analysis (PGAA). These techniques provided data on 19 elements by INAA, 10 elements by PGAA, and 7 elements by RNAA, with some overlap between techniques. For example, INAA was able to obtain overall analytical uncerainties (at the 95% confidence level) averaging ±2.2% for major and minor constituents (Ca, Mg, K), ±3.3% for constituents from 1 to 1000 g/g (Na, Fe, Al, Mn, Ba, Zn, Rb, La, Cr), and ±6.4% for elements between 10 and 1000 ng/g (Co, V, Se, Th, Sc, Sb), using sample dry weights of approximately 150 mg. These analyses represent the most extensive use to date of nuclear analytical techniques in the certification of a trace element SRM at NIST. 相似文献
103.
104.
Sofia M. Eriksson Elizabeth A. Mackey Richard M. Lindstrom George P. Lamaze Kelly P. Grogan Dennis E. Brady 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(3):1819-1822
An automated delayed-neutron activation analysis system has been installed at the NIST research reactor. This work involved characterization of the transfer time of the system, evaluation of blanks, and tests of the system’s analytical capabilities through quantitative analysis for uranium in several natural matrix standard reference materials (SRMs). The calibration curve was shown to be linear up to at least 20 μg of uranium, and the well-thermalized reactor irradiation position makes the system insensitive to thorium and oxygen. For SRMs 1646a Estuarine Sediment and 2710a Montana Soil the values determined for this work agree with the reference and certified values, respectively. The mass fraction of uranium in SRM 695 Multi-Nutrient Fertilizer is the first reported for this material. For this system and the irradiation, transfer, and counting times used, the limit of detection for natural uranium is 20 ng, which corresponds to approximately 200 pg of 235U. 相似文献
105.
Richard M. Lindstrom 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):897-900
In an attempt to improve the accuracy of neutron activation analysis, gamma-ray spectrometry and least-squares methods developed for other nuclides have been applied to redetermine the decay constants of 90mY and 97Ru. Several irradiated samples of each pure element were counted continually through several half-lives, acquiring up to 100 spectra with good statistics. Photopeaks from each nuclide were evaluated with a region of interest integration routine, and each data point corrected for rate-related losses before fitting to an exponential function by a nonlinear least-squares procedure. The half-lives found are 3.204 ± 0.008 h for 90mY and 2.836 ± 0.014 days for 97Ru, where the uncertainty is an estimate of the 95 % confidence level. Although (by Chi squared criteria) the fits to the decay curves were very good and the uncertainty of the resulting half-lives an order of magnitude smaller than the previously published uncertainty, care is necessary before assigning a best value with a totally defensible uncertainty to the overall data set. 相似文献
106.
We probe the electronic structure of alkanethiolate self-assembled monolayers (SAMs) on Au(111) using two-photon photoemission spectroscopy. We observe a dispersive unoccupied resonance close to the vacuum level with a lifetime shorter than 30 fs. The short lifetime and the insensitivity of the energy level and dispersion to molecular length (and thus layer thickness) suggest that the probability density of the electron wave function is concentrated inside the molecular layer close to the SAM/Au interface. Such an interfacial resonance results from the image like potential at the SAM/Au interface. 相似文献