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81.
82.
E L Dorwin A A Shaw K Hom P Bethel M D Sheltar 《Journal of photochemistry and photobiology. B, Biology》1988,2(2):265-278
The photoinduced exchange reactions of cytosine (Ia) and 5-methylcytosine (IIa) with N alpha-acetyl-L-lysine, a derivative of the common amino acid L-lysine, were studied. These reactions of Ia and IIa at pH 7.5 produce, respectively, 2-N-acetylamino-6-(1-cytosinyl)hexanoic acid (Ib) and 2-N-acetylamino-6-(1-(5-methylcytosinyl]hexanoic acid (IIb) as major final products. In addition, small amounts of the corresponding deamination products were formed in the 5-methylcytosine-N alpha-acetyl-L-lysine and cytosine-N alpha-acetyl-L-lysine systems, namely 2-N-acetylamino-6-(1-thyminyl)-hexanoic acid and 2-N-acetylamino-6-(1-uracilyl)hexanoic acid. The compounds Ib and IIb were deacetylated by acid hydrolysis to yield the corresponding lysine products: 2-amino-6-(1-cytosinyl)hexanoic acid (Ic) and 2-amino-6-(1-(5-methylcytosinyl]hexanoic acid (IIc). The compound Ic was identified as a product in the photoreaction of cytosine with L-lysine at near neutral pH, while IIc is found as a product in the corresponding reaction of 5-methylcytosine. The occurrence of the above photoexchange reactions at pH values near those found in physiological systems could have biological implications; in particular, our observations suggest that cytosine and 5-methylcytosine residues, contained in DNA, might react with the epsilon-amino groups of lysine residues in proteins upon UV irradiation of nucleosomes and other DNA-protein complexes under physiological conditions. 相似文献
83.
Th. Frommhold F. Steiper W. Henkel U. Kneissl J. Ahrens R. Beck J. Peise M. Schmitz I. Anthony J. D. Kellie S. J. Hall G. J. Miller 《Zeitschrift für Physik A Hadrons and Nuclei》1994,350(3):249-261
The total photofission cross section ,F
for235U and238U has been measured in the energy range 50E
800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4 arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section F
, which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections ,F
normalized to the atomic numberA for both isotopes coincide, and agree in the-resonance region, within the systematic errors, with the socalledUniversal Curve ,T
/A of the total photon absorption cross section ,T
. At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there isno resonance-like shape near the D13 resonance (at 710 MeV) as observed for the free proton. This complete suppression of the D13 resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.Excerpt from D26 Supported by the Deutsche Forschungsgemeinschaft, SFB 201 Mainz 相似文献
84.
A Hünger J Peise A Robbiano J Ahrens I Anthony H.-J Arends R Beck G.P Capitani B Dolbilkin H Falkenberg G Galler S.J Hall J.D Kellie R Kondratjev R Kordsmeier V Lisin A.I L'vov G.J Miller C Molinari P Ottonello A.R Reolon M Sanzone M Schmitz M Schneider M Schumacher O Selke Th Walcher F Wissmann S Wolf A Zucchiatti 《Nuclear Physics A》1997,620(4):601
Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θcms = 75° and θcms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the amplitude at the resonance energy of 320 MeV is: . 相似文献
85.
F. A. Gooch D. U. Hill W. Fresenius J. L. M. van der Hom van den Bos O. B. Winter L. G. Willis W. H. Me Intire J. Großfeld M. H. Corten I. Estermann L. W. Winkler P. Nicolardot F. Dandurand P. L. Hibbard N. Busvold F. S. Hammett E. T. Adams J. M. Kolthoff V. Fortini und F. W. Bruckmiller 《Fresenius' Journal of Analytical Chemistry》1930,79(10):403-411
Ohne Zusammenfassung 相似文献
86.
Kellie O. Gutman 《Mathematical Intelligencer》2005,27(1):32-36
in the history of mathematics, the story of the solution to the cubic equation is as convoluted as it is significant. When
I first read an account of it in William Dunham’s Journey Through Genius1 in 2000, I was captivated by the personalities, the intrigues, and the controversies that were part of mathematics in sixteenth-century
Italy. For those unfamiliar with it, the story runs as follows: 相似文献
87.
A broad range of fundamental free radical reactions such as hydrogen atom transfer, radical deoxygenations, and radical cyclizations utilizing quaternary ammonium salts of phosphinic acids as chiral and achiral hydrogen donors at room temperature are investigated. The reactions proceed in good to excellent yields with some degree of enantioselectivity. 相似文献
88.
U. Siodlaczek P. Achenbach J. Ahrens H.-J. Arends R. Beck R. Bilger H. Clement V. Hejny J.D. Kellie M. Kotulla B. Krusche V. Kuhr R. Leukel J.C. McGeorge V. Metag R. Novotny V. Olmos de León F. Rambo M. Schepkin A. Schmidt H. Ströher G.J. Wagner Th. Walcher J. Weiß F. Wissmann M. Wolf 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):309-311
The reaction γd↦π0
X has been measured with TAPS at MAMI in the energy range E
γ = 140-300 MeV. Using the Glasgow tagging spectrometer a photon energy resolution of 0.8 MeV was achieved. The energy excitation
functions of integral and differential total cross-sections show no structures of statistical significance > 2σ. Upper limits
for the production of narrow isoscalar or isovector dibaryons with masses m? 2100 MeV/c2 were deduced. They are in the range 2-5 μb averaged over the 0.8 MeV energy resolution.
Received: 25 October 2000 / Accepted: 24 November 2000 相似文献
89.
M. Wolf J. Ahrens R. Beck V. Hejny J.D. Kellie M. Kotulla B. Krusche V. Kuhr R. Leukel V. Metag J.C. Nacher R. Novotny V. Olmos de León R.O. Owens F. Rambo A. Schmidt M. Schumacher U. Siodlaczek H. Ströher J. Weiß F. Wissmann 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):5-8
Double neutral pion photoproduction from the proton has been measured at MAMI for photon energies between threshold and 820
MeV. The reaction was identified by an invariant mass and missing mass analysis. From threshold up to 370 MeV the total cross-section
does not exceed 30 nb. For higher energies it shows a smooth rise until it reaches a maximum of about 10 μb at E
γ = 740 MeV. Dalitz plots of m
2(π0π0) versus
m
2(p,π0) for seven bins of incident photon energy have been analysed. For E
γ > 610 MeV, a strong contribution of a sequential decay is observed with the Δ(1232)-resonance as intermediate state. A comparison
to model calculations shows that these sequential decays presumably originate from the D
13(1520) and also the P
11(1440)-resonance.
Received: 6 June 2000 / Accepted: 18 August 2000 相似文献
90.
V. Kleber P. Achenbach J. Ahrens R. Beck V. Hejny J.D. Kellie M. Kotulla B. Krusche V. Kuhr R. Leukel V. Metag R. Novotny V. Olmos de León R.O. Owens F. Rambo A. Schmidt M. Schumacher U. Siodlaczek H. Ströher J. Weiß F. Wissmann M. Wolf 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):1-4
The photoproduction of two neutral pions from the deuteron has been studied for incident photon energies from 200 MeV to
820 MeV with the TAPS spectrometer at MAMI (Mainz Microtron). The total cross-section was determined and used to deduce the
cross-section from the neutron. Due to the good statistical quality of the data Dalitz plots for the three particles in the
exit channel (π0π0
N) could be constructed. The invariant mass distributions derived from them are presented in this paper. They indicate that
the important reaction mechanism in the second resonance region is a sequential decay pattern involving the population of
the Δ(1232)-resonance as an intermediate state.
Received: 5 June 2000 / Accepted: 4 September 2000 相似文献