Variational Calculation on A = 3 and 4 Nuclei with Non-Local Potentials

The application of the hyperspherical harmonic approach to the case of non-local two-body potentials is described. Given the properties of the hyperspherical harmonic functions, there are no difficulties in considering the approach in both coordinate and momentum space. The binding energies and other ground-state properties of A = 3 and 4 nuclei are calculated using the CD Bonn 2000 and N3LO two-body potentials. The results are shown to be in excellent agreement with corresponding ones obtained by other accurate techniques.     

Changes in ultraviolet absorbance and hence in protective efficacy against lipid peroxidation of organic sunscreens after UVA irradiation

Owing to the spectral distribution of solar UV, the UVA component of sunlight is now believed to be the main cause of photoaging and photocarcinogenesis and is much more effective than UVB in inducing peroxidative damage. Consequently, most skin care cosmetic products now include UVA filters in their formulations along with UVB filters. These modern sunscreens should provide and maintain their initial absorbance, hence protection, throughout the entire period of exposure to sunlight. However, not all UVA and UVB filters are sufficiently photostable. In this study, we examine the correlation between the photochemical degradation of sunscreen agents under UVA irradiation, with particular reference to the UVA-absorber 4-tert-butyl-4'-methoxydibenzoylmethane, alone and in combination with other organic UV filters (2-ethylhexyl 4 methoxycinnamate and 2-ethylhexyl 2-cyano-3,3-diphenylacrylate) and their ability to prevent UVA-induced lipid peroxidation. Since antioxidants are also added to formulations to deactivate free radicals generated during UVA exposure, vitamin E and the synthetic antioxidant, bis(2,2,6,6-tetramethyl-1-oxyl-piperidine-4-yl)sebacate, a nitroxide derivative, were also included in this study. By using simple in vitro tests, the results show that a decrease in spectral absorbance of the UV filters correlates in most cases with increased UVA-induced lipid peroxidation; this depends on the specific UV absorber analysed and also on whether they are alone or in combination. Furthermore, the combined presence or absence of antioxidants has a profound effect on this oxidative event. In particular, the nitroxide appears to be a more efficient photo-antioxidant than vitamin E. Similar experiments were also performed under natural sunlight and the results obtained did not differ substantially from those performed under UVA. The results presented and discussed in this work may help in understanding the effects of UVA/UVB absorbers and antioxidants upon the level of UV-induced ROS generated under UVA exposure and in natural sunlight which could be relevant for improving the photoprotection and efficacy of skin care cosmetic formulations.     

Chiral effective field theory predictions for muon capture on deuteron and {3}He

The muon-capture reactions {2}H(μ{-},ν{μ})nn and {3}He(μ{-},ν{μ}){3}H are studied with nuclear potentials and charge-changing weak currents, derived in chiral effective field theory. The low-energy constants (LECs) c{D} and c{E}, present in the three-nucleon potential and (c{D}) axial-vector current, are constrained to reproduce the A=3 binding energies and the triton Gamow-Teller matrix element. The muon-capture rates on deuteron and {3}He are predicted to be 399±3 sec{-1} and 1494±21 sec{-1}, respectively. The spread accounts for the cutoff sensitivity, as well as uncertainties in the LECs and electroweak radiative corrections. By comparing the calculated and precisely measured rates on {3}He, a value for the induced pseudoscalar form factor is obtained in good agreement with the chiral perturbation theory prediction.     

High-Precision Calculation of the Triton Ground State Within the Hyperspherical-Harmonics Method

The problem of calculating the three-nucleon bound-state properties in the case of realistic nucleon-nucleon potentials is studied by means of the hyperspherical-harmonics approach. Important aspects of the method are the inclusion of all relevant channels in the wave function and the use of large expansion bases. Results are presented for some of the local nucleon-nucleon potentials most frequently used. The conclusion is that, in these cases, the hyperspherical-harmonics approach allows at present for the results of highest precision. Moreover, the extension of the calculation technique to larger systems appears feasible and very promising. Received September 18, 1996; accepted in final form November 22, 1996     

Yield of electronically excited N2 molecules from the dissociative recombination of N2H+ with e-

Quantitative spectroscopic observations of the N2 first positive band system (N2(B 3Pig-A 3Sigmau+))/electron in a recombining N2H+ flowing-afterglow plasma indicate that a substantial fraction of the product N2 molecules are formed in one or more of the low-lying triplet states, B 3Pig, A 3Sigmau+, and W 3Deltau. The total measured N2(B-A) emission intensity from N2(B,v' > or = 1) is equivalent to a yield of (19 +/- 8)%. The effect of rapid collision-induced transitions between states of the triplet manifold is discussed..     

Euler and correlated harmonic-oscillator wave function for the trinucleon bound-state

The trinucleon bound-state properties have been calculated by means of an Euler variational procedure, subsequently improved by the addition of correlated harmonic-oscillator wave functions. Three realistic model interactions containing only two-body forces have been considered. The results obtained show a satisfactory accuracy when compared with the corresponding estimates from Faddeev theory. The extension to larger nuclei of the method here investigated is a possible goal.Dedicated to Profs. Erich Schmid and Ivo laus on the occasion of their 60th birthdays     

Radiation-induced polymerization of 2,3-dimethyl-1,3-butadiene clathrate in deoxycholic acid

Poly(dimethylbutadiene) (PDMB) was synthesized through the inclusion polymerization technique, by γ-irradiation of a clathrate of 2,3-dimethyl-1,3-butadiene in deoxycholic acid (DOCA) at 75, 150, 320 and 430 kGy. The resulting inclusion complexes PDMB@DOCA were studied by FTIR spectroscopy and by thermal analysis (DTA, TGA and DTG). Pure PDMB was isolated by extracting the complex PDMB@DOCA with ethanol. The best sample in terms of purity was that prepared at 75 kGy, while the other samples prepared at higher doses suffered of DOCA grafting on PDMB chains. Pure PDMB isolated from PDMB@DOCA complex was studied by FT-IR spectroscopy and by thermal analysis in comparison to a reference highly crystalline and ≈=100% trans-1,4-PDMB prepared by inclusion polymerization in thiourea and in comparison to PDMB prepared by emulsion polymerization. A lower degree of regularity and crystallinity has been found on the PDMB sample prepared as inclusion compound in DOCA in comparison to the reference PDMB obtained by inclusion polymerization in thiourea.