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1.
The angular variations of the five-fold differential cross section obtained by using different wave functions of helium are
compared with experimental data. It is found that in the coplanar geometry two kinematical arrangements, (i) equal energy
sharing between the two ejected electrons with one of them ejected along the momentum transfer direction and the other along
varying direction and (ii) the Bethe ridge condition with fixed sum of ejected electron energies and varying angle between
them, are very sensitive to e-e correlations contained in the target wave function. This comparison has been used to show
that open-shell class of wave functions better incorporate e-e correlations than the closed-shell class. 相似文献
2.
Nicolas Gaillard Alain Guyot Jerome Claverie 《Journal of polymer science. Part A, Polymer chemistry》2003,41(5):684-698
Amphiphilic block copolymers of poly(acrylic acid‐b‐butyl acrylate) were prepared by reversible addition–fragmentation chain transfer polymerization in a one‐pot reaction. These copolymers were characterized by NMR, static and dynamic light scattering, tensiometry, and size exclusion chromatography. The aggregation characteristics of the copolymers corresponded to those theoretically predicted for a star micelle. In a butyl acrylate and methyl methacrylate emulsion polymerization, low amounts of these copolymers could stabilize latices with solid contents up to 50%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 684–698, 2003 相似文献
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David G. Whitten Mohammad S. Farahat Elizabeth R. Gaillard 《Photochemistry and photobiology》1997,65(1):23-32
Abstract— Characterization of short-lived intermediates in homogeneous and microheterogeneous systems has been carried out using time-resolved spectroscopic techniques. The data obtained from these techniques have been analyzed in a relatively unconventional manner to elucidate complex transient behavior for two reactive systems. The highly nonexponential fluorescence decay for a series of fraws-stilbene-derivatized amphiphiles that readily form bilayer systems in aqueous media has been analyzed using a distribution of lifetimes analysis (DLA). The utility of DLA for quantitative studies was first determined by simulation of artificial decay data. Despite some limitations in DLA, qualitative conclusions as to the nature of the fluorescing species may be drawn when supplementary information such as steady-state spectroscopic data are also considered. The results indicate that the observed fluorescence originates from different types of excited-state species that consist of two or more trans-stilbene units; one of the emissions is attributed to the excited state of a ground-state aggregate while the other is assigned to an excimer that may arise from a 'defect'in the bilayer. The nonexponential nature of the decays is attributed to distributions of environments experienced by the fluorescing species. Electron transfer (ET) reactions between several excited pinacols and carbon tetrachloride in solution have been found to yield products with quantum yields that are higher than unity in the presence of oxygen, suggesting a chain mechanism for product formation. In these systems both the donor and the acceptor undergo bond fragmentation following the initial ET step. The individual steps involved in the proposed mechanism for these systems have been investigated in part using different steady-state and time-resolved laser spectroscopic techniques. However, it was also necessary to utilize pulse radiolysis in order to confirm the involvement of certain radical intermediates that were not observable by the usual flash photolysis techniques. 相似文献
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We study issues arising in attempts to unify strong and other elementary particle interactions. The proton lifetime is estimated in theories with second-order baryon number violation, and found to be O(103–104) longer than naive dimensional counting suggested. The renormalization of quark and lepton masses below the grand unification mass is considered in some detail. Application is made to the SU(5) model of Georgi and Glashow, and we find strange and bottom quark masses: . Inputs are the values of the strong interactions coupling constant favoured by electroproduction and charmonium analyses, and the observed muon and heavy lepton (τ) masses. These estimates are substantially increased if there are more than six flavours of quark. Symmetry breaking in the SU(5) model is studied, including radiative corrections to the effective Higgs potential. 相似文献
8.
The photophysical properties of all-trans-retinal (RAL) have been extensively studied because of the importance of the retinoids in the visual process. However, little information is available regarding the participation of RAL in photochemical transformations such as photoxidation. RAL is one of several native chromophores that have been suggested to act as photosensitizers of damage in the human retina, and this damage would likely occur through oxidative pathways. Time-resolved and steady state techniques have been used to examine the photoreactivity of RAL toward several suitable substrates. The lifetime of the RAL triplet excited state is observed to decrease with increasing concentration of the well-known electron and hydrogen atom donors, 2,3,5,6-tetramethyl-1,4-phenylenediamine (DAD), hydroquinone (HQ), methylhydroquinone (MHQ), 2,3-dimethylhydroquinone (DMHQ) and trimethylhydroquinone (TMHQ), although the bimolecular rate constants for the reaction are much less than that of diffusion controlled (2.9 x 10(7) M-1 s-1, 1.2 x 10(5) M-1 s-1, 1.2 x 10(5) M-1 s-1, 1.5 x 10(5) M-1 s-1 and 1.6 x 10(6) M-1 s-1, for DAD, HQ, MHQ, DMHQ and TMHQ, respectively). In the presence of the donors, new absorptions grow concomitant with the decay of the triplet excited state, and for DAD and TMHQ, the observed spectra are similar to the spectra of p-phenylenediamine and TMHQ radicals. Irradiation of RAL in argon-saturated methanol results in fairly efficient photobleaching of RAL and in the formation of two new compounds having absorption spectra that are shifted below 300 nm. Irradiation of RAL in argon-saturated acetonitrile also results in photobleaching of RAL, but the reaction proceeds at a slower rate. 相似文献
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M. Bourquin R. M. Brown Y. Chatelus J. C. Chollet A. Degré D. Froidevaux A. R. Fyfe J. -M. Gaillard C. N. P. Gee W. M. Gibson R. J. Gray P. Igo-Kemenes P. W. Jeffreys B. Merkel R. Morand R. J. Ott H. Plothow J. -P. Repellin B. J. Saunders G. Sauvage B. Schiby H. W. Siebert V. J. Smith K. -P. Streit R. Strub J. J. Thresher 《Zeitschrift fur Physik C Particles and Fields》1982,12(4):307-321
The charged hyperon beam at the CERN Super Proton Synchrotron (SPS) has been used to collect data on semileptonic decays ofΣ ?,Ξ ? andΛ. A magnetic channel selects 100 GeV/c negatively charged particles produced in the forward direction by interaction of the 200 GeV/c SPS proton beam on a BeO target. TheΣ ? andΞ ? hyperons are concurrently identified in a DISC ?erenkov counter, and their decay products are analysed by a magnetic spectrometer. Electron-hadron discrimination is achieved by the combined use of lead-glass and lead/scintillator counters, transition radiation detectors, and a ?erenkov counter. In this article we report results on the \(\Sigma ^ - \to \Lambda e^ - \bar v\) decay mode. Measurements of the Λ polarization and of the centre-of-mass distributions (baryon kinetic energy, electron-neutrino correlation, and Dalitz plot distributions) yield the vector to axialvector form factor ratiof 1/g 1=+0.034±0.080, in agreement with the value expected from the conserved vector current hypothesis (f 1/g 1=0). TheΣ ?→Λe ? v→ branching ratio measurement gives a value of (5.41±0.30)×10?5. The effects of radiative corrections are not included in these results. They are discussed in the text. Results on the otherΞ ?,Σ ?, andΛ semileptonic decays are reported in separate articles. 相似文献