MOOC learners are generally divided into two categories according to whether they finish the courseor drop out. This binary classification is an oversimplified portrait of MOOC learners. For example, peoplemay be only...MOOC learners are generally divided into two categories according to whether they finish the courseor drop out. This binary classification is an oversimplified portrait of MOOC learners. For example, peoplemay be only interested in certain parts of a MOOC, hence ignoring ＇irrelevant＇ activities, or they may beactively engaged in a MOOC but with no desire to obtain a course certificate, hence skipping assess-ment assignments. These learners are often classified into the ＇drop-out＇ category, which, nevertheless,fails to explain why they ＇drop out＇ and to effectively capture the heterogeneity of MOOCacteristics.展开更多
We demonstrate a proposal for making an ultrastable laser referenced to a multi-cavity, enabling a lower thermal noise limit due to the averaging effect. In comparison with a single-cavity system, relative frequency i...We demonstrate a proposal for making an ultrastable laser referenced to a multi-cavity, enabling a lower thermal noise limit due to the averaging effect. In comparison with a single-cavity system, relative frequency instability of the synthesized laser can be improved by a factor of the square root of the cavity number. We perform an experiment to simulate a two-cavity system with two independent ultrastable lasers. Experimental results show that the relative frequency instability(Allan deviation) of the synthesized laser is 5 × 10^(-16), improved by a factor of √2 from a single-cavity-stabilized laser.展开更多
文摘MOOC learners are generally divided into two categories according to whether they finish the courseor drop out. This binary classification is an oversimplified portrait of MOOC learners. For example, peoplemay be only interested in certain parts of a MOOC, hence ignoring ＇irrelevant＇ activities, or they may beactively engaged in a MOOC but with no desire to obtain a course certificate, hence skipping assess-ment assignments. These learners are often classified into the ＇drop-out＇ category, which, nevertheless,fails to explain why they ＇drop out＇ and to effectively capture the heterogeneity of MOOCacteristics.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.91536217and 91336101)the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2015334)the Special Funds for Scientific Equipment Development(No.YZ201518) from the Chinese Academy of Sciences for the use of the developed equipment
文摘We demonstrate a proposal for making an ultrastable laser referenced to a multi-cavity, enabling a lower thermal noise limit due to the averaging effect. In comparison with a single-cavity system, relative frequency instability of the synthesized laser can be improved by a factor of the square root of the cavity number. We perform an experiment to simulate a two-cavity system with two independent ultrastable lasers. Experimental results show that the relative frequency instability(Allan deviation) of the synthesized laser is 5 × 10^(-16), improved by a factor of √2 from a single-cavity-stabilized laser.
