Daily Archives: March 16, 2012

Fluoride attacks certain dental alloys

Cheng, W., H. Yu, X. Lin, X. Han, L. Liu, T. Ding, and P. Ji. [The effect of fluoride on dental alloys in different concentrations of fluoride artificial saliva]. Hua Xi Kou Qiang Yi Xue Za Zhi. 2012 Feb;30(1):18-21. [Article in Chinese]

OBJECTIVE: To study the changes in surface morphology of cobalt-chromium alloy, pure titanium and high-cobalt chromium molybdenum alloy immersed in artificial saliva with different concentrations of fluoride, and to analyze the corrosion resistance of these metals.

METHODS: The three kinds of metal were polished and then were immersed in artificial saliva with different concentrations of fluoride (0%, 0.05%, 0.2%). All specimens were immersed for 3 weeks at (37.0 +/- 1.0) degrees C. Metal surface roughness before and after immersion were measured and analyzed by scanning electron microscope (SEM).

RESULTS: Metal surface roughness was increased with the concentration of fluoride. The surface roughness of the Co-Cr group and Ti group had a statistically significant difference between before and after immersion at the fluoride concentration of 0.05% (P<0.01), and the difference between Co-Cr group and vitallium2000 group, Ti group and vitallium2000 group were statistically significant difference (P<0.01). The differences of three groups before and after immersion were statistically significant at the fluoride concentration of 0.2% (P<0.01), and the difference among three groups was statistically significant (P<0.01).

CONCLUSION: Patients who frequently use fluoride products should not use pure titanium or cobalt-chromium alloy prosthesis. Patients with these three metal prostheses are not advised to use high concentration fluoride products.

East Antarctica ice sheet stable, climate models in error

Study author quote:

“it is extremely unlikely the East Antarctic ice sheet can melt catastrophically in a slightly warmer climate”. click here

Raymo, M.E., and J.X. Mitrovica. Collapse of polar ice sheets during the stage 11 interglacial. Nature (2012)  doi:10.1038/nature10891

Abstract: Contentious observations of Pleistocene shoreline features on the tectonically stable islands of Bermuda and the Bahamas have suggested that sea level about 400,000 years ago was more than 20 metres higher than it is today1, 2, 3, 4. Geochronologic and geomorphic evidence indicates that these features formed during interglacial marine isotope stage (MIS) 11, an unusually long interval of warmth during the ice age1, 2, 3, 4. Previous work has advanced two divergent hypotheses for these shoreline features: first, significant melting of the East Antarctic Ice Sheet, in addition to the collapse of the West Antarctic Ice Sheet and the Greenland Ice Sheet1, 2, 3; or second, emplacement by a mega-tsunami during MIS 11 (ref. 4, 5). Here we show that the elevations of these features are corrected downwards by ~10 metres when we account for post-glacial crustal subsidence of these sites over the course of the anomalously long interglacial. On the basis of this correction, we estimate that eustatic sea level rose to ~6–13 m above the present-day value in the second half of MIS 11. This suggests that both the Greenland Ice Sheet and the West Antarctic Ice Sheet collapsed during the protracted warm period while changes in the volume of the East Antarctic Ice Sheet were relatively minor, thereby resolving the long-standing controversy over the stability of the East Antarctic Ice Sheet during MIS 11.

Click here for the full paper (fee). Click here for futher discussion.

American Southeast droughts not unprecedented…..

These researchers conclude that the era in which state water supply decisions were made were among the wettest since at lease 1665. Meaning there has been much less water in the past….we should not be surprised if there are periods of less water in the future…. 

Pederson, N., A.R. Bell, T.A. Knight, C. Leland, N. Malcomb, K.J. Anchukaitis, K. Tackett, J. Scheff, A. Brice, B. Catron, W. Blozan, and J. Riddle. A long-term prespective on a modern drought in the American Southeast. 2012 Environ. Res. Lett. 7, 014034 doi:10.1088/1748-9326/7/1/014034

Abstract: The depth of the 2006–9 drought in the humid, southeastern US left several metropolitan areas with only a 60–120 day water supply. To put the region’s recent drought variability in a long-term perspective, a dense and diverse tree-ring network—including the first records throughout the Apalachicola–Chattahoochee–Flint river basin—is used to reconstruct drought from 1665 to 2010 CE. The network accounts for up to 58.1% of the annual variance in warm-season drought during the 20th century and captures wet eras during the middle to late 20th century. The reconstruction shows that the recent droughts are not unprecedented over the last 346 years. Indeed, droughts of extended duration occurred more frequently between 1696 and 1820. Our results indicate that the era in which local and state water supply decisions were developed and the period of instrumental data upon which it is based are amongst the wettest since at least 1665. Given continued growth and subsequent industrial, agricultural and metropolitan demand throughout the southeast, insights from paleohydroclimate records suggest that the threat of water-related conflict in the region has potential to grow more intense in the decades to come.

 Click here for the full paper (open source).