Tensile bond strength of composite to air-abraded enamel.

PURPOSE: The purpose of this study was to test the tensile bond strength of composite resin to enamel surfaces treated with kinetic cavity preparation (KCP) and acid etching, respectively. MATERIALS AND METHODS: Plane labial surfaces of 280 human maxillary central incisors were treated with either KCP by varying treatment conditions or phosphoric acid gel. Composite samples were bonded to the pretreated surfaces with a bonding resin. After 24 hours specimens were loaded in tension in an Instron testing machine until bond failure. A two-way analysis of variance was used to determine significant differences. The failure sites were qualitatively evaluated by SEM. RESULTS: The determined tensile bond strengths and observed failure modes demonstrated that acid-etched enamel has a significantly higher bond strength to composite resin than KCP-treated enamel surfaces. CONCLUSION: KCP-prepared enamel has to be acid etched before bonding to composite resin.

In situ measurements of optical parameters in Lake Baikal with the help of a Neutrino telescope.

We present results of an experiment performed in Lake Baikal at a depth of approximately 1 km. The photomultipliers of an underwater neutrino telescope under construction at this site were illuminated by a distant laser. The experiment not only provided a useful cross-check of the time calibration of the detector but also allowed us to determine inherent optical parameters of the water in a way that was complementary to standard methods. In 1997 we measured an absorption length of 22 m and an asymptotic attenuation length of 18 m. The effective scattering length was measured as 480 m. By use of (cos theta) = 0.95 (0.90) for the average scattering angle, this length corresponds to a geometric scattering length of 24 (48) m.

Optical properties of deep ice at the South Pole: absorption.

We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800-1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410-610 nm. At the shortest wavelength our value is approximately a factor 20 below previous values obtained for laboratory ice and lake ice; with increasing wavelength the discrepancy with previous measurements decreases. At ~415 to ~500 nm the experimental uncertainties are small enough for us to resolve an extrinsic contribution to absorption in ice: submicrometer dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.