Trade-off between environmental benefits and time costs for public bicycles: An empirical analysis using streaming data in China.

In recent years, bicycle sharing has become more popular in cities and towns around the world. Public bicycles are one of the important forms of bicycle sharing. The use of public bicycles instead of motor vehicles has brought about changes in environmental benefits for the society, and at the same time, it has also changed the travel time of residents. Because these changes are potential and cannot be measured directly, we put forward the calculation methods of environmental benefits and time costs of public bicycles according to the concept of opportunity cost. Taking Hohhot, the capital city of Inner Mongolia, as an example, according to the streaming data of 9.76×106 valid orders of public bicycle trips in 2016, we found that the use of public bicycles could reduce consumption of standard coal by as much as 5,796.11 tons (accounting 0.16‱ of the total coal consumption in Inner Mongolia) and carbon emissions were reduced by 4,381.28 tons (accounting 0.30‱ of the total carbon emissions in Inner Mongolia). However, the promotion of public bicycles is not without disadvantages. The use of public bicycles has increased the average travel time of residents by 0.06 hours, which is neglected in previous studies. The contribution of public bicycles to saving 1kg standard coal corresponds to 0.10 hours of travel time waste. Thus, reducing 1kg of carbon emissions is corresponding to a waste of 0.14 hours of travel time. The use of public bicycles varies among different income groups, which is caused by the value of travel time. Low-income groups use more frequently than high-income groups. Generally speaking, low-income groups bring more environmental benefits to society through the use of public bicycles, but bear more time costs. Therefore, we propose a carbon tax on high-carbon transportation modes to encourage green travel and balance the environmental benefits and time costs of public bicycles.

Brønsted Acid-Catalyzed Tandem Cyclizations of Tryptamine-Ynamides Yielding 1H-Pyrrolo[2,3-d]carbazole Derivatives.

Ynamides, as versatile synthetic precursors, have attracted much attention from synthetic chemists and sparked the development of a number of methodologies for the construction of various structures. 1H-Pyrrolo[2,3-d]carbazole is a core scaffold of a series of monoterpene indole alkaloids found in Kopsia, Strychnos, and Aspidosperma, for example. In this study, 1H-pyrrolo[2,3-d]carbazole derivatives were synthesized by a Brønsted acid-catalyzed tandem cyclization starting from tryptamine-based ynamides. This strategy prevented Wagner-Meerwein rearrangement by instantaneous intramolecular nucleophilic trapping of the indoleninium to afford a tetracyclic indoline via an in situ-formed enol species induced by the formation of a more stable conjugate diene moiety. The functional group tolerances were investigated by using a series of readily available substrates. A plausible mechanism has been proposed based on the evidence of the capture of the hemiaminal intermediate. Lastly, a Büchi ketone, which is the pivotal intermediate in the synthesis of the indole alkaloid vindorosine, was synthesized by utilizing our newly developed methodology.