Determination of the total attenuation coefficient for six contact lens materials using the Beer-Lambert law

The Beer-Lambert law has been used to determine the total attenuation coefficient, mu t, of three hard and three soft contact lens materials. The three hard contact lens materials were PMMA, Polycon II and Boston IV whereas the 3 soft materials were chosen with differing water contents of 38, 55 and 70%, respectively. The total attenuation coefficients of all six materials were obtained from measurements of the axial transmission at 632.8 nm of a series of plano powered lenses varying in axial thickness from 0.5 to 3.5 mm. The value of the total attenuation coefficient depends on both scattering and absorption and hence PMMA and Boston IV, which both incorporated a handling tint, showed significantly higher values (P < 0.0001) of mu t (0.562 +/- 0.010 mm-1 and 0.820 +/- 0.008 mm-1, respectively) than Polycon II (mu t = 0.025 +/- 0.005 mm-1). A comparison between Polycon II and the three hydrated soft contact lens materials showed a significant increase (P < 0.02) in the total attenuation coefficients for the 38% and 55% water content materials, and a weakly significant increase for the 70% water content soft lens material (P < 0.1). On the assumption that the absorption coefficients of these four materials are approximately constant, then this change would be due to an increase in the scattering coefficient of the material and could contribute to an increase in intraocular scatter. No significant difference (P > 0.5) was found between any of the hydrated soft contact lens materials tested.     

经济型数控车床两用机构

目前国内在车床数控化改造中,其结构形式不外乎有两种。一种是去掉“两箱”(溜板箱、进给箱),换上滚珠丝杠;另一种是保留两箱,但只能用滑动丝杠。本文提出一种两用机构,使得在保留两箱功用的同时,采用滚珠丝杠传动,从而使经济型数控车床既具有滚珠丝杠传动精确、摩擦力小的优点,又可以保留原机床进给传动系统,获得数控、普车两用功能。     

Depth-profiling of beryllium on graphite with ion beams

The surface layer of beryllium-coated graphite was analysed by backscattering and nuclear reaction methods using a 2.5 MeV accelerator. For the Be analysis the nuclear reactions ⁹Be(p, d)⁸Be, ⁹Be(p, )⁶Li, ⁹Be(d, p)¹⁰Be, ⁹Be(d, t)⁸Be, ⁹Be(d, )⁷Li and ⁹Be(³He, p)¹¹B are compared with backscattering of ⁴He⁺ and protons. For the analysis of carbon, which provides complementary information to the depth profiling of Be, and for the analysis of oxygen, which is the third element of importance in the system, elastic backscattering of ⁴He⁺ and protons is applied. It turns out that the backscattering analysis with protons of 1.3 MeV presents the best compromise for a quick and straightforward measurement of all three elements. The other methods have their merits for a more detailed analysis.     

Superconducting gap function and upper critical field in the presence of inhomogeneous magnetic order

Rare earth ternary superconductors are known to exhibit oscillatory magnetic orders below their superconducting transition temperatures. The study of behaviour of superconducting electrons in an inhomogeneous magnetic field is therefore important for such systems. We report here the results of our theoretical study of superconducting gap function Δ(T) and upper critical fieldH _c2 (T). The results are applied to analyse and explain the variation of Δ(T) andH _c2 (T) in case of NdRh₄B₄.