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Due to the huge number of objects/things connected to the Internet of Things (IoT) which are embedded with electronics, software, and sensors, the IoT creates many exciting applications such as smart grids, smart homes, and smart cities. In the IoT, the sensing and control of objects/things can be abstracted as a task, in which many sensing devices sense and collect data. However, the substantial case studies show that by simply connecting them without further collaboration among the objects/things will lead to the bad performance of the system. With the number of sensing devices connected to the IoT increases, the collaboration for completing the task is becoming more and more urgent. In this paper, a Collaborative Multi-Tasks Data Collection Scheme (CMDCS) is proposed to solve the problem by constructing a collaborative platform for task publisher and data reporter. The main contribution of CMDCS includes the following two aspects: (1) a Task Unit Bid-based task selection strategy is proposed to select the task which can bring higher profits to the system, in which the Task Unit Bid is the ratio of task bid to the amount of data which are needed to collect sensing tasks; and (2) a greedy contributed density-based data collector set selection method is proposed to reduce the cost of data collection so as to maximize system profit, in which the contribution density is used to measure the contribution of a single data collector to a specific sensing task. A large number of experiments have been carried out to verify the effectiveness of our proposed strategy. The experiments show that compared to the traditional data collection strategy Random Task selection with Coverage First Reporter selection, in which the Task Unit Bid and Contribution Density are not used, the profit of the system is improved by 92.08%. INDEX TERMS Mobile crowdsourcing, task and data report selection, task unit bid, contribution density.

In this work, two series of linear-comb and star-comb well defined graft poly(L-lactide) (PLLA) have been synthesized conveniently by one-pot ring-opening polymerization (ROP) of L-lactide using functionalized polybutadiene macroinitiators. The used organocatalyst of 1, 8-diazabicyclo[5,4,0]undec-7-ene (DBU) allows the polymerization of L-lactide proceeds rapidly at room temperature. Kinetic studies of the ROP reaction in this system indicate a first-order kinetic in monomer concentration.1 H NMR and GPC techniques are employed to characterize the synthesized polymers, validating the formation of desired comb structures with controllable chain length. Linear-comb and star-comb graft PLLA were comparatively studied as well as with linear PLLA by DSC and POM. The results reveal that comb structure makes a remarkable improvement of PLLA crystallization ability in both crystallinity and growth rate of spherulites. Furthermore, the more compacted star-comb structure imposes restriction on chain mobility, which weakens the growth effect to some extent. It is found that the glass transition temperature (Tg) and melting temperature (Tm) significantly depend on the side chain length and backbone structure. Rheological studies of both melt and instinct viscosity of the solution show that star-comb PLLA has the lowest hydrodynamic volume compared with linear-comb PLLA and linear PLLA.Polylactide (PLA) derived from renewable resources has drawn significant attention due to its well biodegradable/biocompatible properties and the other concerns associated with the use of petroleum-based products. 1-3 High molecular weight PLA and its copolymers are one of the most widely utilized polymers in the field of biomedical materials 4-8 . Due to the extremely high mechanical strength, it has been used as commodity and industrial materials as well as clinically in medical applications, 9-10 orthopaedic screw, 11-12 scaffolds, 13-15 etc.PLA can be directly prepared from lactic acid by polycondensation under azeotropic distillation conditions referred as poly(lactic acid) [16][17][18] . Ring-opening polymerization (ROP) of lactide is another effective route to synthesize PLA with higher molecular weight and lower polydispersity 19 . Stannous octoate (Sn(Oct)2) is the most common catalyst for ROP of lactide 20 . However, tin based catalysts are less than ideal from both chemical and biological perspective. The organic catalysts now appear as viable substitutes for classical metallic catalysts 21-23 .Non-metallic ROP processes are demanded for sustainable and environmentally friendly products, especially in microelectronic 24 and biomedical 25-26 applications. In 2001, Hedrick et al. first reported N-heterocyclic carbenes as novel metal-free nucleophilic catalysts for the ROP of cyclic ester monomers 27 . Among those catalysts, the commercial available amidine and guanidine (such as 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU)) provide better control of molecular weight and highly efficient at room...

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