Thalchemy (United States)

The data science system at Udemy1, a global online education marketplace, is described. This data science system currently supports recommendation and search, but will be extended to support e-learning as well. The motivations behind and the approach to the system are explained, which allows multiple individual data scientists to all become ‘full stack’, taking control of their own destinies from the exploration and research phase, through algorithm development, experiment setup, and deep experiment analytics. Algorithms tested and deployed in 2015 are described, as well as some key insights obtained from experiments leading to the launch of the new recommender system at Udemy. Finally, current areas of research in applied computing are outlined, which include search, personalization, and algorithmic topic generation.

The polysilylenes exhibit complex solid-state structures and electronic properties. In this report the solid-state conformational structures of symmetrically substituted poly(di-n-alkylsilylenes) are described. Comparisons between the different structures and their respective UV absorption characteristics demonstrate that the relationship is complex and aspects of molecular geometry beyond chain conformation must be considered. The thermochromic and piezochromic behavior of several of these polysilylenes is discussed. The all-trans conformation of the silicon backbone is associated with both phenomena. The properties of several polysilylene copolymers have also been investigated. We find that some of the copolymers form a well-ordered structure and exhibit absorption characteristics similar to the crystalline phases of the corresponding homopolymers.

Electronic transport of photoinjected holes in high molecular weight linear polymers with silicon and germanium backbone displays a familiar pattern of electric field and temperature dependence similar to behavior already reported in a very diverse collection of glassy molecular solids. At fixed electric fields, during both rate and step heating, the mobility activation energy e in all these polymers changes abruptly and reversibly at a temperature Tc, which is specific for each polymer, without concurrent abrupt changes in mobilities. These temperatures coincide with the respective glass transition temperatures Tg. In all cases, the below-Tg activation is higher than above Tg. In polymers with aliphatic side groups, e(t > t g) is extremely low, practically approaching zero. The change of activation near Tg is similar to that observed in amorphous charge-transporting polymers and other glasses including selenium and its alloys. Polymers such as poly(di-n-hexylsilylene) (PDHS) which undergo conformational transitions at temperatures TTr due to side chain crystallization and melting, also experience a change in mobility and its activation energy at TTr. The change in the transport behavior and the association with the bathochromic shift in the uv spectra is demonstrated.