Single-Grid Spectral Collocation for the Navier-Stokes Equations

The aim of the paper is to study a collocation spectral methodto approximate the Navier-Stokes equations: only one grid isused, which is built from the nodes of a Gauss-Lobatto quadratureformula, either of Legendre or of Chebyshev type. The convergenceis proved for the Stokes problem provided with inhomogeneusDirichlet conditions, then thoroughly analysed for the Navier-Stokesequations. The practical implementation algorithm is presented,together with numerical results.     

FTIR spectroscopy of the 2v3 overtone band for different BrCN isotopomers: an improved evaluation of the anharmonic force field of cyanogen bromide

The 2v₃ overtone band of six different isotopomers of cyanogen bromide has been recorded in the range from 4200 to 4400 cm^?1 with a resolution of 0.02 cm^?1 using a Fourier transform infrared (FTIR) spectrometer. This allowed us to achieve complete knowledge of the energies for all levels corresponding to double vibrational excitation. An improved evaluation of the quartic force field of cyanogen bromide has been performed using the new data obtained together with those already known from previous works. Theoretical values derived from a recent ab initio calculation have been used to constrain the potential terms which cannot be determined with sufficient precision by the least-squares analysis of the available experimental data.     

In vivo SPECTROPHOTOMETRIC EVALUATION OF NEOPLASTIC AND NON-NEOPLASTIC SKIN PIGMENTED LESIONS–I. REFLECTANCE MEASUREMENTS

Reflectance spectrophotometry from 400 to 800 nm on different cutaneous pigmented lesions, including primary and metastatic malignant melanoma, pigmented nevi, lentigo and seborrhoeic keratosis, has been performed by using an external integrating sphere coupled to a spectrophotometer. Measurements show that reflectance spectra of the different lesions manifest dissimilar patterns, particularly in the near IR region. Comparison of reflectance of nevi with that of malignant melanomas results in a highly significant difference (P less than 10(-6)) between the two samples. Though interpretation of the spectra remains difficult as a result of the complexity of the optical processes of scattering and absorption, our results suggest that a detailed analysis of the reflectance spectrum may give clinically useful information, and could be utilized as an aid in clinical diagnosis of cutaneous pigmented lesions, especially where malignant melanoma is concerned.     

Millimetre-wave and diode laser spectroscopy of IC 15N: anharmonic force field of cyanogen iodide from spectroscopic data and ab initio calculations

(Molecular Physics, 1998, 93, 95–106)     

Neutronic simulation of a research reactor core of (232Th, 235U)O 2 fuel using MCNPX2.6 code

The small reactor design for the remote and less developed areas of the user countries should have simple features in view of the lack of infra-structure and resources. Many researchers consider long core life with no on-site refuelling activity as a primary feature for the small reactor design. Long core life can be achieved by enhancing internal conversion rate of fertile to fissile materials. For that purpose, thorium cycle can be adopted because a high fissile production rate of ²³³U converted from ²³²Th can be expected in the thermal energy region. A simple nuclear reactor core arranged 19 assemblies in hexagonal structure, using thorium-based fuel and heavy water as coolant and moderator was simulated using MCNPX2.6 code, aiming an optimized critical assembly. Optimized reflector thickness and gap between assemblies were determined to achieve minimum neutron leakage and void reactivity. The result was a more compact core, where assemblies were designed having 19-fuel pins in 1.25 pitch-to-diameter ratio. Optimum reflector thickness of 15 cm resulted in minimal neutron leakage in view of economic limitations. A 0.5 cm gap between assembles achieved more safety and 2.2% enrichment requirements. The present feasibility study suggests a thermal core of acceptable neutronic parameters to achieve a simple and safe core.     

A benchmark study on uncertainty of ALICE ASH 1.0, TALYS 1.0 and MCNPX 2.6 codes to estimate production yield of accelerator-based radioisotopes

Radioisotopes find very important applications in various sectors of economic significance and their production is an important activity of many national programmes. Some deterministic codes such as ALICE ASH 1.0 and TALYS 1.0 are extensively used to calculate the yield of a radioisotope via numerical integral over the calculated cross-sections. MCNPX 2.6 stochastic code is more interesting among the other Monte Carlo-based computational codes for accessibility of different intranuclear cascade physical models to calculate the yield using experiment-based cross-sections. A benchmark study has been proposed to determine the codes’ uncertainty in such calculations. ¹⁰⁹Cd, ⁸⁶Y and ⁸⁵Sr production yields by proton irradiation of silver, rubidium chloride and strontium carbonate targets are studied. ¹⁰⁹Cd, ⁸⁶Y and ⁸⁵Sr cross-sections are calculated using ALICE ASH 1.0 and TALYS 1.0 codes. The evaluated yields are compared with the experimental yields. The targets are modelled using MCNPX 2.6 code. The production yields are calculated using the available physical models of the code. The study shows acceptable relative discrepancies between theoretical and experimental results. Minimum relative discrepancy between experimental and theoretical yields is achievable using ISABEL intranuclear model in most of the targets simulated by MCNPX 2.6. The stochastic code utilization can be suggested for calculating ¹⁰⁹Cd, ⁸⁶Y and ⁸⁵Sr production yields. It results in more valid data than TALYS 1.0 and ALICE ASH 1.0 in noticeably less average relative discrepancies.