The effect of self-absorption in hollow cathode lamp on its temperature

It has been shown experimentally that even a small error in the calculation of the temperature inside the hollow-cathode lamp (HCL) and the current applied to the lamp, may cause a tremendous error in determination of the absorption ratio in optical resonance absorption (ORA) method. This effect is intensified nonlinearity for large absorption ratios. If a higher current is applied to a copper hollow cathode lamp, the copper density inside the lamp is increasing rapidly. Due to the cylindrical (axisymmetric) form of the lamp, the density of atoms around the main axis of the lamp becomes greater than that near the internal wall. In this case the auto-absorption (or self-absorption) is occurred and as its result, the emission spectrum produced by copper atoms is locally absorbed before going out from the lamp. This absorption is stronger near the main axis compared with the areas near the wall because of the Gaussian profile of the spectral line. Two different Cu atoms ground state lines with the similar lower state (327.4 nm and 324.7 nm) are used in this work as optical resonance absorption and the absorption coefficient is obtained for three different pressures (0.6, 4.5 and 14 µbar). The best values for copper HCL temperature and for maximum HCL current were found respectively 450 K, and 5mA.

Vibration of Hemi-Ellipsoidal Axisymmetric Domes Submerged in Water

Ten thin-walled domes, of hemi-ellipsoidal form, were vibrated in air and while partially and fully submerged in water. The domes varied in shape from oblate ones of aspect ratio (AR) 0.25 to prolate ones of aspect ratio 4. The fundamental modal patterns for the oblate domes tended to be of axisymmetric form, while the fundamental modal patterns of the hemispherical and prolate domes tended to be of asymmetric or lobar form. The theoretical analysis was carried out by the finite element method, where the motion of the shell structure was represented by three different types of element and the motion of the water was represented by a solid annular element. Comparison between theory and experiment was found to be good.

Numerical solutions and laser-Doppler measurements of spin-up

The spin-up flow in a cylinder of homogeneous fluid has been examined both experimentally and numerically. The primary motivation for this work was to check numerical solution schemes by comparing the numerical results with laboratory measurements obtained with a rotating laser-Doppler velocimeter. The laser-Doppler technique is capable of high accuracy with small space and time resolution, and disturbances of the flow are virtually negligible. A series of measurements was made of the zonal flow over a range of Ekman numbers (1·06 × 10−3≤E≤ 3·30 × 10−3) and Rossby numbers (0·10 [les ]|ε| [les ] 0·33) at various locations in the interior of the flow. These measurements exceed previous ones in accuracy. The weak inertial modes excited by the impulsive start are detectable. The numerical simulations used the primitive equations in axisymmetric form and employed finite-difference techniques on both constant and variable grids. The number of grid points necessary to resolve the Ekman layers was determined. A thorough comparison of the simulations and the experimental measurements is made which includes the details of the amplitude and frequency of the inertial modes. Agreement to within the experimental tolerance is achieved. Analytical results for conditions identical to those in the experiments are not available but some similar linear and nonlinear theories are also compared with the experiments.