Energy levels in 40Ca up to 10.2 MeV have been studied in the neutron pickup reaction 41Ca(τ, α)40Ca with 20 MeV bombarding energy. Thirty excited states have been identified and angular distributions have been measured in the interval from 5° to 40° by means of a split-pole magnetic spectrometer. The angular distributions together with DW calculations have been used to extract ln values and spectroscopic factors. The ln = 2 strength distribution for the particle-hole levels is compared to the lp = 3 strength distribution from pr stripping data. 相似文献
Samples of rock, soil and seepage were collected from Yucca Mountain, USA, and analyzed for 36Cl/Cl ratios by accelerator mass spectrometry (AMS). Rock excavated from the Drill Hole Wash fault at repository horizon depths
produced a ratio suggesting that small amounts of water with “bomb-pulse” 36Cl had percolated to that site over the past 50 years. Rock from four other sites within the exploratory studies facility
did not yield bomb-pulse ratios. Ratios in the soil varied depending on depth and location, with some samples producing bomb-pulse
signatures. Ratios for seep water were slightly elevated above the present cosmogenic background value. This paper also discusses
results from a column study mimicking the passage of 36Cl through volcanic rock and from an experiment using bromide instead of chloride as a carrier in sample preparation for AMS. 相似文献
The CuNi binary alloy can be significant as a catalyst for nitrogen‐doped (N‐doped) graphene growth considering controllable solubility of both carbon and nitrogen atoms. Here, we report for the first time the possibility of synthesizing substitutional N‐doped bilayer graphene on the binary alloy catalyst. Raman spectroscopy, atomic force microscopy and transmission electron microscopy analysis confirm the growth of bilayer and few‐layer graphene domains. X‐ray photoelectron spectroscopy analysis shows the presence of around 5.8 at% of nitrogen. Our finding shows that large N‐doped bilayer graphene domains can be synthesized on the CuNi binary alloy.
While arsenic(III) compounds can exert profound toxicological and pharmacological effects, their modes of action and, in particular, the structural consequences of their binding to cysteinyl side chains in proteins, remain poorly understood. To gain an understanding of how arsenic binding influences beta-structure, pairs of cysteines were introduced into a model monomeric beta-hairpin to yield a family of peptides such that coordination occurs either across the strands or within the same strand of the beta-hairpin. Circular dichroism, NMR, UV-vis spectroscopy, and rapid-reaction studies were used to characterize the binding of monomethylarsonous acid or p-succinylamidephenyl arsenoxide (PSAO) to these peptides. Placement of cysteines at non-hydrogen bond (NHB) positions across the beta-hairpin, such that they occupy the same face of the sheet, was found to enhance the structure as assessed by CD. Cross-strand cysteine residues that project on opposite faces close to the termini of the hairpin can still bind arsenic tightly and show modestly increased beta-sheet content. NMR and modeling studies suggest that arsenic can be accommodated at this locus without disrupting the core interactions stabilizing the turn. However, As(III) binding to nonopposed cysteines, or to cysteines at HB and NHB positions along one strand of the hairpin, caused loss of structure. UV-vis titrations show that all these hairpin peptides bind PSAO stoichiometrically with K(d) values from 13 to 106 nM. Further, binding is moderately rapid, with second-order rate constants for association of 10,000-22,000 M(-1) s(-)1 irrespective of the placement of the cysteines within the hairpin and the consequent extent of structural reorganization required as a result of binding. These studies complement recent work with alpha-helices and further demonstrate that capture of a pair of thiols by As(III) may result in significant changes in local secondary structure in the protein targets of these potent bioactive agents. 相似文献
The numerical approximation of the semiintegral and semiderivative of a function f by the RL algorithm of Oldham and Spanier [1] is examined. An error analysis is given for the case when f has a continuous second derivative. The performance of the algorithm when applied to experimental data is also discussed. Numerical examples are presented to illustrate the theory. 相似文献