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51.
Richard N. Peterson John A. Breier Lindsay R. Harmon Jamie Brusa Patrick R. Hutchins 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(2):1347-1357
Radon-222 has become a widely used tracer of submarine groundwater discharge. However, remote field studies are often limited by the need to pump water to a spray chamber which degasses dissolved radon for subsequent analysis in the gaseous phase. We develop here a new method of degassing dissolved 222Rn, utilizing a stream of bubbles driven by the internal air pump of a commercial radon analyzer to achieve air:water partitioning equilibrium, eliminating the need to pump water. This system utilizes a sparging chamber, comprised of a slotted vertically-oriented pipe with bubbles produced in the bottom. A non-slotted section of the pipe at the top of the chamber forms a sealed headspace, allowing air to be circulated in a closed loop between the sparging chamber and a radon-in-air monitor. We found that such a sparging chamber needs to allow bubbles to rise through at least 45 cm of water column to function at equal efficiency as the standard protocol of the spray chamber. Under our optimized configuration, the sparging chamber operates as efficiently as the standard protocol at measuring dissolved 222Rn activities when encountering increasing 222Rn activities, and offers even greater gas exchange efficiency when dissolved 222Rn activities decrease. The sparging chamber offers a more field-friendly alternative to measuring 222Rn activities, as it eliminates the need to maintain a submersible pump throughout the measurement and it offers increased temporal resolution when variable 222Rn activities are expected. 相似文献
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We propose the projected BCS wave function as the ground state for the doped Mott insulator SrCu2(BO3)2 on the Shastry-Sutherland lattice. At half filling this wave function yields the exact ground state. Adding mobile charge carriers, we find a strong asymmetry between electron and hole doping. Upon electron doping an unusual metal with strong valence bond correlations forms. Hole doped systems are d-wave resonating valence bond superconductors in which superconductivity is strongly enhanced by the emergence of spatially varying plaquette bond order. 相似文献
55.
In this article, we report on the formation of a photocatalytic porphyrin crystalline structure using two oppositely charged commercially available low cost porphyrins, [meso-tetra(N-methy-4-pyridyl)porphyrin tetratosylate (TMPyP) and zinc-tetrakis(4-sulfonatophenyl)porphyrin (Zn-TPPS)], by self-assembly at room temperature without acidification. Using optical microscopy, the crystals were determined to have a length of 30–55 μm and width of 2–50 μm, depending on the molar ratio of the porphyrins in the starting solution. The porphyrin crystals were characterized by means of powder X-ray diffraction and UV–Vis, fluorescence, and optical microscopic techniques. The UV–Vis absorbance spectrum of the crystalline structure is different than those of the monomer solutions, involving a broadened Soret band that is split into two blue-shifted and red-shifted peaks and broadened red-shifted Q-bands. The crystals exhibit a different emission spectrum from those of the porphyrin solutions in that they are red-shifted, split, and show a dramatic decrease in intensities. A hypothetical model for the crystal structure of the porphyrin crystals is developed. Illumination of the crystals in a 2,4,6-trinitrotoluene solution with a tungsten lamp results in TNT reduction to 1,3,5-trinitrobenzene and 4-amino-2,6-dinitrotoluene. 相似文献
56.
Jennifer L. Gottfried Russell S. Harmon Frank C. De Lucia Jr. Andrzej W. Miziolek 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009,64(10):1009
A large suite of natural carbonate, fluorite and silicate geological materials was studied using laser-induced breakdown spectroscopy (LIBS). Both single- and double-pulse LIBS spectra were acquired using close-contact benchtop and standoff (25 m) LIBS systems. Principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were used to identify the distinguishing characteristics of the geological samples and to classify the materials. Excellent discrimination was achieved with all sample types using PLS-DA and several techniques for improving sample classification were identified. The laboratory double-pulse LIBS system did not provide any advantage for sample classification over the single-pulse LIBS system, except in the case of the soil samples. The standoff LIBS system provided comparable results to the laboratory systems. This work also demonstrates how PCA can be used to identify spectral differences between similar sample types based on minor impurities. 相似文献
57.
K-doping dependence of the Fermi surface of the iron-arsenic Ba1-xKxFe2As2 superconductor using angle-resolved photoemission spectroscopy 总被引:1,自引:0,他引:1
Liu C Samolyuk GD Lee Y Ni N Kondo T Santander-Syro AF Bud'ko SL McChesney JL Rotenberg E Valla T Fedorov AV Canfield PC Harmon BN Kaminski A 《Physical review letters》2008,101(17):177005
We use angle-resolved photoemission spectroscopy to investigate the electronic properties of the newly discovered iron-arsenic superconductor Ba_(1-x)K_(x)Fe_(2)As_(2) and nonsuperconducting BaFe_(2)As_(2). Our study indicates that the Fermi surface of the undoped, parent compound BaFe_(2)As_(2) consists of hole pocket(s) at Gamma (0,0) and larger electron pocket(s) at X (1,0), in general agreement with full-potential linearized plane wave calculations. Upon doping with potassium, the hole pocket expands and the electron pocket becomes smaller with its bottom approaching the chemical potential. Such an evolution of the Fermi surface is consistent with hole doping within a rigid-band shift model. Our results also indicate that the full-potential linearized plane wave calculation is a reasonable approach for modeling the electronic properties of both undoped and K-doped iron arsenites. 相似文献
58.
At 10–20 K the broad room temperature IR bands of the hydrogen bonded cluster anions in tetramethylammonium fluoride and hydroxide monohydrates and monohydrates-dn are resolved into a number of components. The band patterns are consonant with distortion of formally tetrahedral H4F2O22? and H6O42? ions of Td point group to C2v and S4, respectively in a C4h5 unit cell isomorphous with tetramethylammonium hexafluorosilicate. A lattice mode has been identified for each monohydrate. 相似文献
59.
The energy bands of the semiconductor ZrSe3 have been evaluated using the KKR method. The general features of the electronic structure are expected to pertain to other transition metal trichalcogenides which have similar trigonal prismatic coordination. The calculated density of states agrees well with X-ray photoemission spectra for the valence band. The joint density of states has been evaluated and is discussed in terms of optical measurements. 相似文献
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