Partial branching ratios have been measured in six lepton momentum bins between 120 and 180 MeV/c. From these, six relations between the form factor slopes λ+ and λ0 have been derived. Using the world average value λ+ = 0.029 ± 0.003 and combining the six partial results on λ0, we obtain λ0 = 0.019 ± 0.010. This value is in agreement with the Callan-Treiman relation and other predictions. Together with recent K30 results, it supports the rule. The agreement of our result with the value of λ0 obtained from Kμ3 Dalitz-plot studies supports muon-electron universality. 相似文献
The decay K+ → e+υγ has been investigated. For the structure-dependent part with positive γ-helicity (SD+) the branching ratio is obtained from 51 ± 3 events observed in the kinematical region Ee ? 235 MeV, Eγ > 48 MeV and θeγ > 140°. For the corresponding part with negative γ-helicity we obtain an upper limit Γ(SD?)/Γ(SD+) < 11 (90% CL) from the sample of electrons with energies 220 MeV ? Ee < 230 MeV and with no γ in the backward direction. This upper limit implies that the ratio of structure-dependent axial vector amplitudes lies outside the region .For the decay the limit 90% confidence level) was found. 相似文献
PtCl(2) constitutes an efficient and practical catalyst for a set of different atom economical rearrangement reactions of enynes. This includes (i) a formal enyne metathesis reaction delivering 1,3-dienes, (ii) the formation of polycyclic vinylcyclopropane derivatives, and (iii) an unprecedented O-->C allyl shift reaction if unsaturated ethers are employed. Although these transformations produce significantly different structural motifs, they share a common mechanism comprising a cationic manifold triggered by the pi-complexation of Pt(II) onto the alkyne unit of the substrates. Strong experimental support for the proposed mechanism comes from deuterium-labeling studies, a careful analysis of the product distribution pattern, and the fact that in some cases PtCl(2) can be replaced by simple Lewis or Br?nsted acids as the catalysts. 相似文献
Abstract Amino acids containing functionalized aromatic substituents are of considerable interest as building blocks for the syntheses and the design of new types of proteins and pharmacologically active compounds. In contrast to amino acids bearing phosphonated phenyl substituents [1], phosphinophenyl derivatives have been reported only very recently[2]. We have been able to synthesize phosphinophenyl amino acids of type 1 or 2 by nucleophilic phosphination [3] of the potassium salts of 2-and 4-fluoro-a-phenylglycine and-alanine with potassium phosphides Ph(R')PK in high yields. 相似文献
A set of poly(2‐oxazoline)‐derived (co‐)polymers was prepared by microwave‐assisted polymerizations and acid‐mediated hydrolysis and tested for antimicrobial activity in 50 × 50 × 2 mm PP compound plates containing 5 wt% of the polymers. Antimicrobial activity against gram‐negative E. coli and P. aeruginosa as well as C. albicans depended only on the degree of hydrolysis, while antimicrobial activity against gram‐positive S. aureus was only observed for hydrolyzed poly(2‐nonyl‐2‐oxazoline)s. The surface energies of the compound plates compared to pure PP were hardly altered, and the compounds can be considered as alternatives for PP. The presence of the biocide additives at the surface of the PP compound plates could be shown by combined ATR‐IR, zeta potential, and SEM‐EDX measurements. Antimicrobial activity was maintained during double incubation as well as for lowered amounts of the biocide additive of 1% in PP compound plates.
Events with 2, 3 and 4 heavy-fragments (A≧20) have been detected in the reactions100Mo+100Mo atE/A =18.7, 23.7 MeV and120Sn+120Sn atE/A=18.4 MeV. The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilitiesP3 andP4 of producing 3- and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of theP3 andP4 curves at high energy losses. Small deviations of theP3 andP4 curves at 23.7A · MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter. 相似文献
A new microscope combines optical sectioning by fluorophore excitation using a single light sheet with structured illumination. Several images with laterally intensity-modulated light sheets are recorded from scattering fluorescent specimens. By applying a simple data processing scheme, the nonmodulated volumes are identified. The blurred features become dark, and the resultant images are improved in terms of contrast and resolution. Hence, the instrument is capable of discriminating against contributions to the image that are induced by the optical properties of the specimen. The new microscope's capabilities are demonstrated by imaging the internals of the head of an adult Drosophila melanogaster (fruit fly) expressing green fluorescent protein-labeled polycomb proteins. 相似文献