No abstract

Elevated exposure to Ultra-Violet Radiation (UVR) from the sun has led to adverse effects on human skin and foods, and therefore, the need for materials that offer resistance to Ultra-Violet (UV) penetration for protection. Some building window and non-window-materials, car-glasses, Linear Low Density Polyethylene (LLDPE) and Polyethylene Terephthalate (PET) rubber and plastic materials have been investigated to determine their transparencies and suitability for use as shields against UVR. These were studied by directly measuring scattered solar radiation through the optical window of a spectrometer and then measuring the scattered light when the window was completely covered with the material to be examined. Wavelengths of light that were not absorbed when sunlight was incident on the samples and the transmitted intensity of sunlight at each wavelength through each sample as compared to the transmitted intensity through air were determined in the UVB and UVA spectral regions. The results showed that the building window-glasses were opaque to UVB but transparent to UVA while the non-window-glasses exhibited transparency in the UVB and UVA spectral regions. The car-glass (laminated), used as windscreen, was opaque to UVB and UVA while the side-glass (non-laminated) was opaque to UVB but transparent to UVA. Perspex, sometimes used as an alternative to windscreen and side-glass in cars, exhibited transparency in UVB and UVA spectral regions. The LLDPE materials used for food storage were transparent to UVB and UVA while the PET plastic materials used for water, fruit juice and beverage storage was opaque to UVB but transparent to UVA.

To enhance the current understanding of mechanisms contributing to magnetic hyperfine interactions in excited states of atomic systems, in particular, alkali-metal atom systems, the hyperfine fields in the excited 5 2 S 1/2 -8 2 S 1/2 states of potassium and 8 2 S 1/2 -12 2 S 1/2 states of francium atoms have been studied using the relativistic linked-cluster many-body perturbation procedure. The net theoretical values of the hyperfine fields for the excited states studied are in excellent agreement with available experimental data for both atoms. There is a significant decrease in importance of the correlation contribution in going from the ground state to the excited states, the correlation contributions as ratios of the direct contribution decreasing rapidly as one moves to the higher excited states. However, the contribution from the exchange core polarization ͑ECP͒ effect is nearly a constant fraction of the direct effect for all the excited states considered. Physical explanations are offered for the observed trends in the contributions from the different mechanisms. A comparison is made of the different contributing effects to the hyperfine fields in potassium and francium to those in the related system, rubidium, studied earlier. Extrapolating from our results to the highly excited states of alkali-metal atoms, referred to as the Rydberg states, it is concluded that in addition to the direct contribution from the excited valence electron to the hyperfine fields, a significant contribution is expected from the ECP effect arising from the influence of exchange interactions between electrons in the valence and core states.

We report on a computational technique that recovers Raman peaks embedded in highly fluorescent contaminated spectra. The method uses a second derivative technique to identify the most intense Raman peak, and a modified Savisty Golay algorithm to filter and recover the embedded Raman peaks iteratively. This technique is an improvement on existing background removal algorithms in both performance and user objectivity.

A first-principles relativistic many-body investigation of magnetic hyperfine fields has been carried out for the ground states 4 2 S 1/2 of the alkali atom K and doubly charged ion Sc 2ϩ completing the investigation over the three members of the isoelectronic series K, Ca ϩ , and Sc 2ϩ with a single valence electron in the 4s state, since Ca ϩ had been investigated by us previously. This allows one to study both the nature of agreement with experiment over this series as the charge increases and the trends in the contributions from the major mechanisms responsible for the hyperfine fields in these systems. The calculated magnetic hyperfine fields in tesla for K, Ca ϩ , and Sc 2ϩ are 56.81, 135.90, and 239.29, respectively. These agree very well with the measured values of 58.02 T for K and 140.30 T for Ca ϩ. No experimental data are available for the Sc 2ϩ system. The exchange core polarization ͑ECP͒ and correlation contributions, as fractions of the valence contribution, are found to decrease rapidly as one goes to systems with higher ionic charges, the decrease being more drastic for correlation effects. The trend of the ratios of ECP and correlation contributions to the valence contribution for both K and Sc 2ϩ were compared with those calculated for the neighboring alkali-metal systems, sodium and rubidium. The physical explanations for the results and the observed trends in the contributions from the different mechanisms are discussed. ͓S1050-2947͑97͒04603-9͔