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241.
We observe a yield to the 1+T = 1 level in 12C at 15.11 MeV in the isospin forbidden 12C(d, d') and 10B(α, d) reactions at about 1 % of the yield to the 1+T = 0 level at 12.71 MeV. Observed yields to the T = 12+ level at 16.11 MeV in both reactions at about half the yield to the 15.11 MeV level preclude attributing this observed isospin violation entirely to final state mixing. From the ratios of the spectroscopic factors for the 12.71 and 15.11 MeV levels in 12C and the ground state of 12B from the 13C(d, t) and 13C(d, 3He) reactions, we find a charge dependent matrix element between the 1+ states in 12C of 179 ± 75 keV. 相似文献
242.
D. A. Lind 《Israel Journal of Mathematics》1974,17(2):162-168
We show that ergodic algebraic automorphisms of the infinite torus are measure isomorphic to Bernoulli shifts. Using the same techniques, we also show that the existence of such an automorphism with finite entropy is equivalent to an open problem in algebraic number theory. 相似文献
243.
244.
A basic design is outlined for the conversion of the aggregate spectral properties of an organic compound of unknown structure to a set of compatible alternative molecular structures which is small in number anal exhaustive in scope. The process is built around a precisely defined unit of substructure. A procedure is described for the exhaustive generation of the set of these fragments from any specified group of elements and allowed valences. A versatile, user-friendly data-management system (FOCISS) provides a convenient means of manipulating these fragments and correlating their structure and properties. Extensive carbon-13 n.m.r. data are in place and applications of FOCISS to fragment-oriented searches are illustrated. The creation of a subset of chemically-stable fragments is also described. 相似文献
245.
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247.
Let be an action of by continuous automorphisms of a compact abelian group . A point in is called homoclinic for if as . We study the set of homoclinic points for , which is a subgroup of . If is expansive, then is at most countable. Our main results are that if is expansive, then (1) is nontrivial if and only if has positive entropy and (2) is nontrivial and dense in if and only if has completely positive entropy. In many important cases is generated by a fundamental homoclinic point which can be computed explicitly using Fourier analysis. Homoclinic points for expansive actions must decay to zero exponentially fast, and we use this to establish strong specification properties for such actions. This provides an extensive class of examples of -actions to which Ruelle's thermodynamic formalism applies. The paper concludes with a series of examples which highlight the crucial role of expansiveness in our main results.
248.
The determination of iron isotope ratios in blood, without prior sample preparation, using inductively coupled plasma mass spectrometry (ICP-MS) with sample introduction by electrothermal vaporisation (ETV) is described. Following oral administration of 5 mg of enriched 54FeSO4 and intravenous administration of 200 micrograms of 57FeSO4 to non-pregnant women, the 54Fe: 56Fe and 57Fe: 56Fe isotope ratios in serum were measured reliably within 20 min per sample in quintuplicate. Changes in the fractional absorption of iron during human pregnancy could therefore be assessed. 相似文献
249.
The monocyclic beta-lactam antibiotic nocardicin A is related structurally and biologically to the bicyclic beta-lactams comprised of penicillins/cephalosporins, clavams, and carbapenems. Biosynthetic gene clusters are known for each of the latter, but not for monocyclic beta-lactams. A previously cloned gene encoding an enzyme specific to the biosynthetic pathway was used to isolate the nocardicin A cluster from Nocardia uniformis. Sequence analysis revealed the presence of 14 open reading frames involved in antibiotic production, resistance, and export. Among these are a two-protein nonribosomal peptide synthetase system, p-hydroxyphenylglycine biosynthetic genes, an S-adenosylmethionine-dependent 3-amino-3-carboxypropyl transferase (Nat), and a cytochrome P450. Gene disruption mutants of Nat, as well as an activation domain of the NRPS system, led to loss of nocardicin A formation. Several enzymes involved in antibiotic biosynthesis were heterologously overproduced, and biochemical characterization confirmed their proposed activities. 相似文献
250.
G Lundblad M Elander J Lind 《Acta chemica Scandinavica. Series B: Organic chemistry and biochemistry》1976,(9):889-894
A beta-N-acetylglucosaminidase from Helix pomatia digestive juice was separated and partly purified by gel chromatography. The optimal pH for the degradation of p-nitrophenyl-N-acetyl-beta-D-glucosaminide was 3.4. The molecular weight was around 160 000 and the pI = 4.95. In the same gel chromatography run two chitinase active peaks were also obtained. These chitinase active peaks were also obtained. These chitinases, with molecular weights around 26 000 and 13 000, had somewhat different pH activity curves with optima at 4.2 and 4.3. By isoelectric focusing the first peak with molecular weight around 26 000 was divided in two chitinase active regions with pI at 5.7 and 3.5. The second peak with molecular weight around 13 000 had a pI at 7.3. 相似文献