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521.
The subthreshold fission cross section of neutron induced fission of237Np has been measured between 20 and 60 eV with the CBNM time-of-flight spectrometer. The resonances in this energy range have been analysed with a single level shape fitting computer program. The result is interpreted in the frame of Strutinsky's theory of nuclear deformation. 相似文献
522.
Patrik R. Callis 《Chemical physics letters》1979,61(3):568-570
Polarized fluorescence spectra are presented for thymine, cytosine, adenine and guanine in neutral aqueous solution and in rigid neutral ethylene glycol-water (6:4) at ca. ?125°C. For thymine and cytosine at 25°C the polarization is nearly as high as in rigid media. Analysis yields fluorescence lifetime (τf) estimates of ?2 ps. This limits the likelihood that emission is from a minor species or via a forbidden transition. The lower room temperature polarization for adenine and guanine indicates τf's of ≈ 10 ps which allows for emission from a fluorescent tautomer or via a slightly forbidden transition. 相似文献
523.
Zeitschrift für Physik B Condensed Matter - The ground state properties of the nondegenerate periodic Anderson model, which includes an external magnetic field, are studied variationally. We... 相似文献
524.
Sandra Biedermann Patrik Tschudin Koni Grob 《Analytical and bioanalytical chemistry》2010,398(1):571-576
Of 13 thermal printing papers analyzed, 11 contained 8–17 g/kg bisphenol A (BPA). When taking hold of a receipt consisting
of thermal printing paper for 5 s, roughly 1 μg BPA (0.2–6 μg) was transferred to the forefinger and the middle finger if
the skin was rather dry and about ten times more if these fingers were wet or very greasy. This amount transferred to dry
skin was neither significantly increased when taking hold of the paper at up to 10 sites, nor reduced when BPA-free paper
was contacted afterwards. After 60–90 min, BPA applied to the skin as a solution in ethanol was only partially or no longer
at all extractable with ethanol, whereas BPA transferred to the skin by holding thermal printer paper remained largely extractable
after 2 h. This suggests that penetration of the skin depends on the conditions. Extractability experiments did not enable
us to conclude whether BPA passes through the skin, but indicated that it can enter the skin to such a depth that it can no
longer be washed off. If this BPA ends up in the human metabolism, exposure of a person repeatedly touching thermal printer
paper for 10 h/day, such as at a cash register, could reach 71 μg/day, which is 42 times less than the present tolerable daily
intake (TDI). However, if more than just the finger pads contact the BPA-containing paper or a hand cream enhances permeability
of the skin, this margin might be smaller. 相似文献
525.
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527.
The fluorescence excitation spectra of 12 nucleic acid components in ethylene-glycol-H2O solution at 160 K show quantum yields which are 2 to 10 times higher when excitation is near the 0-0 energy than at the first absorption maximum. Discussion leads to the conclusion that internal conversion which competes with vibrational relaxation is generally responsible. 相似文献
528.
Patrik Önnerfjord Sergei A Eremin Jenny Emnéus György Marko-Varga 《Journal of chromatography. A》1998,800(2):1585-230
A flow immunodetection system with high sample throughput capacity is described for the screening of various analytes. The immunochemical detection principle is based on the chromatographic separation of the formed immunocomplex (AbAg or AbAg*) and the free antigen (Ag) by a restricted access (RA) column, utilising size-exclusion and reversed-phase mechanism. A fluorescein labelled analyte (Ag*) was used in the competitive assay format with fluorescence detection. The speed and simplicity of the assay were the greatest advantages, allowing measurement of the analyte to be carried out in less than 1 min. The biocompatibility and capacity of the restricted access material allowed multiple injections of up to 5000, without any breakthrough of the fluorescent tracer molecule and thus need for regeneration. The flow immunoassay was developed using the well-known atrazine herbicide and some transformation products as model compounds, due to their human toxicity and widespread use. The sample throughput was 80 samples per hour and the detection limits were 1.4 nM (300 pg/ml) for atrazine (Ab I) and 2.3 nM (500 pg/ml) for the sum of triazines (Ab II–III). Different sample matrices, PBS buffer, creek water, and urine were successfully applied in the flow system without the need for any sample handling step. For plasma samples an additional clean-up step using solid-phase extraction had to be included. The resulting detection limits for atrazine in plasma and water samples using this clean-up and trace enrichment procedure were found to be 2 ng/ml and 20 pg/ml, respectively. The analysis could be performed at a sample throughput rate of 400 per 6-h working shift. 相似文献
529.
530.
The chemical properties and synthetic modifications of the natural lignan hydroxymatairesinol in basic and acidic nucleophilic media were studied. Hydroxymatairesinol presumably reacts via a quinone methide and a carbonium ion mechanism under basic and acidic conditions, respectively. In these conditions the benzylic hydroxyl group was displaced by nucleophiles yielding new 7-substituted butyrolactone lignans. Reactions in alcoholic basic solutions yielded the 7-alkoxy ethers diastereoselectively. Several previously known lignans as well as new lignans and lignan derivatives were synthesised. The transformations were monitored and the products identified by HPLC-MS and NMR. 相似文献