An Approximation of the Customer Waiting Time for Online Restaurants Owning Delivery System

Online restaurants, which receive online orders and deliver food directly to the customer's residence, are becoming increasingly popular. To be successful, online restaurants need to provide reliable and prompt deliveries. Careful design of the meal preparation and order delivery systems is needed to avoid excessive customer waiting time between ordering and delivery. This paper considers the meal preparation and delivery processes simultaneously to approximate average customer waiting time for deliveries. The authors first discuss the system performance with one cook and unit-capacity delivery vehicles, using an M/G/1 queue and a GI/G/1 queue. Numerical experiments show that our approximation can adequately describe real waiting times. Then, series queues with multiple cooks and multi-capacity delivery vehicles, e.g., an M/G/n queue and a GI/G~n/1 queue, are examined.Results show that except for situations with a large meal preparation time and a small vehicle capacity,compared with the result of simulation, the approximation in this paper is acceptable with a deviation of less than 20%. The marginal decrease in waiting time associated with hiring more vehicles is estimated under different meal preparation speeds, sizes of service area and vehicle capacities.     

含形状记忆合金支撑的框架结构的动力特性

利用有限元法分析了谐激励下含形状记忆合金（SMA）支撑的框架结构的位移响应和频谱特性，并从SMA的初始预应变、激振力力幅和操作温度3个方面讨论了SMA的伪弹阻尼特性对结构位移响应的影响．结果表明，伪弹性SMA能够比较有效地抑制结构振动.     

Electrochemical characterization of the Pt /PEDOT electrode in DMFC

Poly-(3, 4-ethylenedioxythiophene) (PEDOT) was applied in making electrodes and gas diffusion layer for direct methanol fuel cells (DMFC). Electrochemical characterizations of Pt/PEDOT electrodes, made by two different methods, were investigated by cyclic voltammetry, methanol oxidation tests and DMFC performance. The platinum particle structure in PEDOT/PSS (poly?styrene sulfonic acid) films was investigated by SEM and TEM. Our research work showed that PEDOT influenced the catalytic activity behavior in three different ways when it was applied to the anode, cathode and the gas diffusion layer. The DMFC performance agreed with the cyclic voltammetry and methanol oxidation test results.