Dynamic wettability properties of a soft contact lens hydrogel

The wettability of poly[2-hydroxyethyl methacrylate-co-methacrylic acid] (pHEMA-MAA) soft contact lenses was investigated in the absence and presence of block copolymer surfactants and lysozyme using the sessile drop method. The advancing dynamic contact angles (Thetaw/a) values are reported for water as a function of sequential wetting and drying cycles. The Thetaw/a values for the pHEMA-MAA in the absence of surfactant and lysozyme increased from approximately 20 degrees to 100 degrees as the number of cycles increased from two to ten, and they were independent of the pHEMA-MAA bulk water content. The change from the highly hydrophilic to hydrophobic pHEMA-MAA surface could not be reversed using the sequential wetting and drying cycles even under repeated exposures to saline solution. The effect of block copolymer surfactants with different molecular weights (MW) and hydrophilic-lipophilic balance (HLB) values on the pHEMA-MAA wettability were also studied. Low Theta(w/a) values were observed for pHEMA-MAA hydrogels that were treated with T1304 (MW 10500, HLB 14) and T904 (MW 6700, HLB 15). The surface tension data indicated that these surfactants were incompletely desorbed from the pHEMA-MAA and that the rate of desorption was slow in the timescale of the cycling experiments. Comparatively, poor wettability was observed for pHEMA-MAA surfaces presoaked in T304 (MW 1650, HLB 16) and T1107 (MW 15000, HLB 24) as Thetaw/a values greater than 90 degrees were measured for these surfactants. The surface tension data indicated that the rate of desorption of T304 and T1107 from the pHEMA-MAA was rapid and that they had a low affinity to the pHEMA-MAA. High contact angles were observed for the pHEMA-MAA hydrogels treated with lysozyme and also for the T1107 presoaked pHEMA-MAA that was also treated with lysozyme. Zero wetting angles throughout the sequential cycling were observed for the T1304 pre-treated pHEMA-MAA that had been treated with lysozyme. These results suggested that the adsorbed lysozyme on the pHEMA-MAA hydrogel had no significant influence on its wetting properties when the hydrogel was pre-treated with T1304.     

The choice of composition variable for comparing the Walker and Vause model to binary liquid mixtures having closed-loop coexistence curves

By using unconventional composition variables, we have extended the application of the Walker and Vause model to include binary liquid mixtures having highly asymmetric closed-loop coexistence curves. We offer a plausibility argument supporting the use of these composition variables.     

A robust forecasting system,based on the combination of two simple moving averages

For series with negligible growth and seasonality, simple moving averages are frequently used to estimate the current level of a process, and the resultant value projected as a forecast for future observations. This paper shows that a linear combination of two simple moving averages (SMA) can provide an improved estimate of the underlying level of the process. The proposition is demonstrated by simulation, and good combinations are listed. The theory underlying the improvement is developed. The general rules are then illustrated through an application in an inventory situation.     

The Solid-state Structure of a 4,13-Diaza-18-crown-6 NaI Complex: A Unique Chain-link Assembly

Abstract  Reported within is the crystal structure of 4,13-diaza-18-crown-6 and NaI (P21/c; a = 7.0732(5) ?, b = 15.4058(10) ?, c = 9.9605(6) ?, b = 96.7950(10)°, V = 1077.75(12) ?³, Z = 2). The structure was obtained serendipitously from a crystallization attempt of these two components in the presence of indole. There are two non-equivalent sodium cations, one encapsulated within the diazacrown, and a second cation linking two adjacent diazacrowns and coordinating to both. The sodium cations are also linked through a water bridge. This leads to the formation of infinite 1–D chains in which iodide counterions occupy the space between the chains. This is the first reported example of an unsubstituted 4,13-diaza-18-crown-6 encapsulating Na⁺. The first structure of 4,13-diaza-18-crown-6 and NaI containing two symmetrically inequivalent Na⁺ ions, only one of which is encapsulated by the diazacrown, is reported. Index Abstract  The first structure of 4,13-diaza-18-crown-6 and NaI containing two symmetrically inequivalent Na+ ions, only one of which is encapsulated by the diazacrown, is reported

Observation of color-transparency in diffractive dissociation of pions

We have studied the diffractive dissociation into dijets of 500 GeV/c pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where t(min)-->0), we find that when the per-nucleus cross section for this process is parametrized as sigma = sigma0Aalpha, alpha has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.     

Direct measurement of the pion valence-quark momentum distribution, the pion light-cone wave function squared

We present the first direct measurements of the pion valence-quark momentum distribution which is related to the square of the pion light-cone wave function. The measurements were carried out using data on diffractive dissociation of 500 GeV/c pi(-) into dijets from a platinum target at Fermilab experiment E791. The results show that the /q&q> light-cone asymptotic wave function describes the data well for Q2 approximately 10 (GeV/c)(2) or more. We also measured the transverse momentum distribution of the diffractive dijets.     

The atmospheres of the Earth and the terrestrial planets: Their origin and evolution

The stability of the Earth's atmosphere is reviewed, and the importance of the hydrosphere and biosphere in the development of the atmosphere is emphasized. Although the Earth's atmosphere has naturally been investigated in the greatest detail, the atmospheres of other terrestrial planets may have had a simpler developmental history. The atmospheres of the Earth, Venus and Mars are compared, and it is shown that a consistent model of their evolution can be obtained on the basis of degassing from the solid planet.