Results 1 - 10 of 54956
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[en] We present a method to determine the magnitude of the uncorrelated background distribution obtained with the event mixing technique, through the simultaneous observation of the projectile elastic scattering in different detectors, which correspond to random coincidences. The procedure is tested with α-d angular correlation data from the 6Li+59Co reaction at Elab=29.6MeV. We also show that the method can be applied using the product of singles events, when singles measurements are available.
[en] In the present paper a new experimental method to measure nuclear reaction time in the 10-15-10-10 s region is presented. Measurements of the lifetimes of low-lying and long-lived states of 19F and 20Ne decaying via α-channel were carried out with the aim of checking the feasibility of the method. The results obtained in this way are compared with the lifetimes known from different techniques. ((orig.))
[en] A plot of delta13C against delta15N for all lunar soils and breccias for which both values are available indicates that the 30% change in delta15N previously observed is accompanied by a change in delta13C about one-tenth as large. The correlation remains when the data are broken down into sub-sets according to soil maturity. The correlation therefore is not due to maturation effects or non-selective sample contamination and must represent concurrent changes in the isotope ratios of both elements at their source. A rough calculation of the relative production rates of 13C and 15N indicates that spallation reactions in the sun could lead to the observed ratio of the delta13C to delta15N variations. (orig.)
[en] We report on interferometric studies of 3He-4He liquid mixtures. Anomalous wetting phenomena were observed in phase separated mixture films: the upper 3He-rich phase did not wet the lower 4He-rich phase under a small continuous feed of 4He atoms to the vapor phase. Instead, under this dynamic situation, floating pools of the 3He-rich phase were stabilized with a contact angle on the order of 10 mrad. In equilibrium, the concentrated 3He-rich phase was found to nucleate uniformly on the free surface, consistent with Antonow's rule. (orig.)
[en] The osmotic pressure of 3He-4He mixtures was measured along the phase separation curve at temperatures up to 500 mK by balancing it with the fountain pressure of pure 4He. The usefullness of the secondary osmotic pressure thermometer was reinvestigated. (Auth.)
[en] Aromatic side chains are attractive probes of protein dynamics on the millisecond time scale, because they are often key residues in enzyme active sites and protein binding sites. Further they allow to study specific processes, like histidine tautomerization and ring flips. Till now such processes have been studied by aromatic 13C CPMG relaxation dispersion experiments. Here we investigate the possibility of aromatic 1H CPMG relaxation dispersion experiments as a complementary method. Artifact-free dispersions are possible on uniformly 1H and 13C labeled samples for histidine δ2 and ε1, as well as for tryptophan δ1. The method has been validated by measuring fast folding–unfolding kinetics of the small protein CspB under native conditions. The determined rate constants and populations agree well with previous results from 13C CPMG relaxation dispersion experiments. The CPMG-derived chemical shift differences between the folded and unfolded states are in good agreement with those obtained directly from the spectra. In contrast, the 1H relaxation dispersion profiles in phenylalanine, tyrosine and the six-ring moiety of tryptophan, display anomalous behavior caused by 3J 1H–1H couplings and, if present, strong 13C–13C couplings. Therefore they require site-selective 1H/2H and, in case of strong couplings, 13C/12C labeling. In summary, aromatic 1H CPMG relaxation dispersion experiments work on certain positions (His δ2, His ε1 and Trp δ1) in uniformly labeled samples, while other positions require site-selective isotope labeling. Graphical abstract: .
[en] The foundation of the Strutinsky method within the Hartree-Fock (HF) framework is discussed. Both the basic energy theorem and the energy averaging method are investigated theoretically and numerically. The equivalence of the averaging method with semiclassical expansions is exhibited. Numerical tests of the basic assumptions of the shell-correction approach are presented, which make use of the results of constrained HF calculations for various nuclei and with different effective interactions. The HF energy is decomposed into a smooth part which is shown to be very close to a liquid drop model energy, a first order shell-correction defined in the usual way, and higher order corrections which usually are neglected in standard Strutunsky calculations. These higher order terms are shown not to contribute more than approximately 1-2 MeV to the total energy in medium and heavy nuclei. New results for the nucleus 40Ca show that this is no longer the case for light nuclei. Alternative ways of defining the smooth part of the energy are also considered. It is particularly found that if the Strutinsky averaging is performed selfconsistently, the sum of the average energy plus the first order shell-correction extracted from the average potential reproduces perfectly well the exact HF energy. (Auth.)