in solution, [28-30] and at the interfaces [31,32] features the unique microstructures and varied applications (Figure 1C). Janus bottlebrush polymers are a class of special molecular brushes, which have two incompatible side chains on the same repeating unit of the backbone. [33] "Janus" is the god in ancient Roman religion and myth with two faces looking to the past and the future. [34] In scientific community, the phrases containing Janus, such as "Janus nanoparticles," [35-38] "Janus beads," [39,40] and "Janus polymerization," [41-43] indicate something consisting of counterparts. [44-46] The design of Janus bottlebrush polymers was inspired by Janus particles. [35,47-49] The characteristic of Janus bottlebrush polymers is that the repeating unit of the backbone possesses two immiscible side chains. [50-52] Core-shell bottlebrush polymers with block copolymers as the side chains are usually not Janus-type unless the block side chains are unsymmetrical. [6] An emerging Janus core-shell bottlebrush polymer has been developed by transferring the side chains from homo polymers to two different block copolymers. [53] Design, synthesis, and self-assembly of Janus bottlebrush polymers have arouse much interest in polymer chemistry and material science. [54,55] In general, Janus bottlebrush polymers could be prepared via backbone-first [50] (grafting-to and graftingfrom) or side-chain-first [56] (grafting-through) strategy. Most of Janus bottlebrush polymers were reported via grafting-through approach. Macromonomers are first designed and subsequently polymerizations occur to form the backbone. [23] Backbonefirst route also allows for the synthesis of Janus bottlebrush polymers by using combined grafting-to and grafting-from approach. [57] The special unsymmetrical architectures enable Janus bottlebrush polymers to achieve ideal phase separation in bulk, [58,59] in solution, [52] and at the interface. [32] The preorganized interface can promote self-assembly process and avoid the distorted phase separation. [32,33] The self-assembly of Janus bottlebrush polymers achieves small domain size and tunable bulk property, [58,59] which is challenging for the traditional linear or bottlebrush polymers. [60,61] Therefore, Janus bottlebrush polymers have great potential applications in nanolithography, [58] photonic crystals, [62] biomedicine, [53] surfactants, [63] etc. The big families of bottlebrush polymers have been nicely reviewed by Grubbs and co-workers, [64] Müllner and coworkers, [65-67] Rzayev and co-workers, [7] Verduzco and coworkers, [6] and Matyjaszewski and co-workers [2]. As a young but significant class, Janus bottlebrush polymers have achieved remarkable advances in recent years. Therefore, this review attempts to focus on Janus bottlebrush polymers, covering Janus bottlebrush polymers are a class of special molecular brushes, which have two immiscible side chains on the repeating unit of the backbone. The characteristic architectures of Janus bottlebrush polymers enable unique selfassembly properties and br...

No abstract

No abstract

Polymer gears have shown potential in power transmission by their comprehensive mechanical properties. One of the significant concerns with expanding their applications is the deficiency of reliability evaluation methods considering small data set circumstances. This work conducts a fair number of polyoxymethylene (POM) gear durability tests with adjustable loading and lubrication conditions via a gear durability test rig. A novel machine learning-based reliability model is developed to evaluate contact fatigue reliability for the POM gears with such a data set. Results reveal that the model predicts reasonable POM gear contact fatigue curves of reliability–stress–number of cycles with 2.0% relative error and 18.8% reduction of test specimens compared with the large sample data case. In contrast to grease lubrication, the oil-lubricated POM gear contact fatigue strength improves by 10.4% from 52.1 to 57.6 MPa.

In general the ordering of join-operations is quite sensitive and has a devastatingly negative effect on the efficiency of the DBMS.  Scheufele and Moerkotte proved that join-ordering is NP-complete in the general case [1]. The dynamic programming algorithm has a worst case running time, thus for queries with more than 10 joins, it becomes infeasible. To resolve this problem, random strategies are used.  Simulated annealing is an intelligent algorithm of developing very fast. In this paper, we introduce the traditional simulated annealing algorithm through discussing its theory and process, analyzes its shortcoming in detail, simple describe influence of key parameters to simulated annealing algorithm and provided feasible improvement. Especially, in order to avoid the deficiency resulted by the neighbors of state, and make the query optimization support complex non-inner join, the improved algorithm gives a semantics expression of query and a method of constructing the connected join pairs. Experimental results show that the improved algorithm outperforms the original algorithm in terms of both output quality and running time.