ALBERT

Description: A 2665-year ring-width chronology was developed based on Qilian juniper from the upper treeline of the Animaqin Mountains on the eastern Tibetan Plateau. Correlation analysis results showed that the chronology was significantly negatively correlated with April–June maximum temperature at nearby meteorological stations, indicating that maximum temperature is the factor that limits tree growth in this area. Accordingly, we reconstructed the average April–June maximum temperature variations since 261 BC. Our regression model explained 37.9% of the total variance for the whole calibration period of 1960–2012. Our reconstruction revealed that the maximum temperature started to increase from approximately 1750 without a rapid warming trend, and the warmest period was from AD 890 to 947, as opposed to the recent period, whereas the period from AD 351–483 was the coldest. Significant periods in the wavelet power spectrum were approximately 2–8 years, 20–30 years, 30–60 years, and 60–130 years, as well as some long-term periods (more than 200 years). Comparisons with other temperature series from neighboring regions and the Northern Hemisphere as a whole support the validity of our reconstruction and suggest that it provides a representation of the temperature change for the Animaqin area, although asymmetric variation patterns in minimum and maximum temperatures were found.

Description: Bentonite is considered as an ideal buffer/backfill material for preparing an engineering barrier for high-level radioactive waste (HLW) disposal. During initial sample preparation, the tendency of wet bentonite powder to gather into large agglomerates and the water to be spread unevenly in the traditional water content adjustment process decreases the homogeneity of compacted bentonite. The main purpose of this study was to solve this problem by applying a new wetting method, which mixes ice powder with bentonite powder (the ice-bentonite mixing method). This new method was used to adjust the water distribution in Gaomiaozi County, China (GMZ) bentonite powder and was compared to the traditional spray method. The screening method was used to separate macro-agglomerates (〉= 0.25 mm) from the water and bentonite mixture. The properties, the content of the various size agglomerates in loose mixtures, and the heterogeneity defects observed in compacted bentonite were compared. An index (P) was defined to quantitatively evaluate the water distribution in a loose bentonite/water mixture. Macro-agglomerates in loose mixtures produced heterogeneities in water content, density, and shrinkage. By using the ice-bentonite mixing method, fewer macro-agglomerates were formed and a homogeneous distribution of water was produced in the compacted bentonite. A homogeneous water distribution had the tendency to decrease the number of shrinkage cracks after the drying process and to maintain high mechanical strength in the compacted bentonite. Although the production of ice powder was laborious, the ice-bentonite mixing method has workability advantages: (i) a high mixing efficiency, (ii) a low mass loss rate, and (iii) a small deviation between measured water content and target water content. The low thawing efficiency of ice-bentonite mixtures can be solved by using a microwave-assisted thawing method. This research can improve the sample preparation method used to produce compacted buffer/backfill materials for HLW disposal.