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Abstract— Measurements of epidermal hyperplasia induced by UV in albino mice, using an improved method of sampling and counting of cells, show wide variability attributable largely to basic uncertainty rather than experimental error. Factors are analyzed that may contribute to the infeasibility of determining simultaneously the size of cell population and rate of cell duplication, including recovery of cell activity enhanced by photoreactivation. A hyperplasia-inducing factor is isolated from epidermis exposed to UV. 相似文献
274.
Individual components that make up different grades of gasoline - or gasolines of the same grade produced by different manufacturers - are resolved and identified by gas chromatography using packed columns and a flame ionization detector. Contaminants at levels as low as 0.5 mu1/1 may be identified by the method if samples of gasoline from the source of contamination can be obtained for comparison. The uniqueness of this method is that it can be applied for routine analysis without the use of sophisticated complements for the gas chromatograph. 相似文献
275.
Ferroelastic LuNbO4 single crystals containing 0.3 at. % Cr3+ ions have been grown by the floating zone technique, and their EPR spectra have been studied at a frequency of 9.8 GHz at room temperature. The lines on the spectra are due to the transitions caused by three paramagnetic centers formed as a result of the replacement of one isovalent position of a Lu3+ ion and two nonisovalent positions of Nb5+ions by Cr3+-ions. As a result of twinning, the line number is doubled and four principal directions arise along which the same spectra are obtained. The spectra of these centers were described by a spin Hamiltonian with S = 3/2, the D and E parameters ranging from 0.024 to 0.17 cm?1, and the g-factors g ∥ = 1.75–2.20 and g ⊥ = 1.90–2.13. 相似文献
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Aleš Marek Robert Pepin Bo Peng Kenneth J. Laszlo Matthew F. Bush František Tureček 《Journal of the American Society for Mass Spectrometry》2013,24(11):1641-1653
Gas-phase conformations and electron transfer dissociations of pentapeptide ions containing the photo-Leu residue (L*) were studied. Exhaustive conformational search including molecular dynamics force-field, semi-empirical, ab initio, and density functional theory calculations established that the photo-Leu residue did not alter the gas-phase conformations of (GL*GGK? + ?2H)2+ and (GL*GGK-NH2?+?H)+ ions, which showed the same conformer energy ranking as the unmodified Leu-containing ions. This finding is significant in that it simplifies conformational analysis of photo-labeled peptide ions. Electron transfer dissociation mass spectra of (GL*GGK? + ?2H)2+, (GL*GGK-NH2?+?2H)2+,(GL*GGKK?+?2H)2+, (GL*GLK?+?2H)2+, and (GL*LGK?+?2H)2+ showed 16 %–21 % fragment ions originating by radical rearrangements and cleavages in the diazirine ring. These side-chain dissociations resulted in eliminations of N2H3, N2H4, [N2H5], and [NH4O] neutral fragments and were particularly abundant in long-lived charge-reduced cation-radicals. Deuterium labeling established that the neutral hydrazine molecules mainly contained two exchangeable and two nonexchangeable hydrogen atoms from the peptide and underwent further H/D exchange in an ion–molecule complex. Electron structure calculations on the charge-reduced ions indicated that the unpaired electron was delocalized between the diazirine and amide π* electronic systems in the low electronic states of the cation-radicals. The diazirine moiety in GL*GGK-NH2was calculated to have an intrinsic electron affinity of 1.5 eV, which was further increased by the Coulomb effect of the peptide positive charge. Mechanisms are proposed for the unusual elimination of hydrazine from the photo-labeled peptide ions. Figure
? 相似文献
278.
A. S. Nogai S. Yu. Stefanovich A. A. Bush D. E. Uskenbaev A. A. Nogai 《Physics of the Solid State》2018,60(1):23-30
The aspects of structure, dipole ordering, and ionic conductivity of the Na3Cr2(PO4)3 crystal with the four polymorphic phases (α, α', β, and γ) have been investigated. The features of the α-Na3Cr2(PO4)3 crystal structure and its dipole ordering and relaxation polarization in the low-temperature α and α' phases have been refined. The occurrence of Na3Cr2(PO4)3 dipole ordering in the α and α' phases and high ionic conductivity in the β and γ phases is attributed to the structural changes in the rhombohedral [Me2(PO4)3]–33∞ crystal frame upon phase transformations α → α', α' → β, and β → γ. A model for explaining the dipole ordering and ionic conductivity phenomena in Na3Cr2(PO4)3 is proposed. 相似文献
279.