The discovery of the ancient city of Loulan in Xinjiang, China, at the beginning of the 20th century was of great significance for understanding the evolution of culture and civilization in Inner Asia. However, due to the lack of systematic chronological studies, the history of this ancient city remains unclear, particularly the date of its construction and abandonment. Here, we present the results of the first systematic radiocarbon (14C) dating carried out on artifacts from ancient Loulan. Our results show that human activity began as early as 350 cal BC, flourished during the interval from the 1st to 4th centuries AD, and completely disappeared around 600 AD. Most of the buildings in the city were constructed during the Eastern Han Dynasty rather than in Wei/Jin Dynasty, as previously indicated by excavated documents and letters (Hedin 1898; Xiao 2006). The development and flourishing of Loulan coincided with the interval of high ice accumulation and meltwater supply from surrounding mountains. The city began to decline and was finally abandoned following an abrupt decrease in ice accumulation and meltwater supply (Yao et al. 1996; Lauterbach et al. 2014), suggesting that natural climate change was the major factor responsible for the abandonment of Loulan.
States differ substantially in higher education policies. Little is known about the effects of state policies on the performance of public colleges and universities, largely because no clear measures of college quality exist. In this paper, I estimate the average quality of public colleges of US states based on the value-added to individuals' early career earnings. I explicitly deal with the problem of self-selection in both where to go to college and where to work. I find considerable variation in the quality of states' public college systems. Using this quality measure, I then explore how various aspects of state higher education policy are associated with college outcomes. I find that states with better faculty quality and with more diversity among public colleges tend to have higher value-added to student earnings.
Blending poly(L-lactic-acid) (PLLA) and thermoplastic polyurethane (TPU) has been performed in an effort to toughen PLLA without compromising its biodegradability and biocompatibility. The mixing enthalpy calculation of PLLA and TPU predicted that the blend was a thermodynamic miscible system. The viscoelastic properties and phase morphologies of PLLA/TPU blends were investigated further by dynamic mechanical analysis and scanning electron microscopy. It was found that the blend was a partially miscible system. The dynamic mechanical analysis showed that T g of PLLA and TPU shifted toward with TPU content increasing. Scanning electron microscopy photos showed that the morphologies of the blends changed from a sea island structure to a bicontinuous structure as an increment in TPU content, which suggested that the miscibility of PLLA and TPU was enhanced when the TPU increased. PLLA/TPU blend fibers were fabricated. With the TPU content increasing from 0 wt% to 30 wt%, the tensile strength and initial modulus of blend fibers decreased first then increased, while elongation at break and fracture work gradually increased. The change of tensile properties indicated the toughening effects of TPU on PLLA fibers, also suggested that the formation of blend fibers was influenced by the blend rheological behavior other than the compatibility.
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