Mobile edge computing (MEC) is an emerging paradigm that mobile devices can offload the computationintensive or latency-critical tasks to the nearby MEC servers, so as to save energy and extend battery life. Unlike the cloud server, MEC server is a small-scale data center deployed at a wireless access point, thus it is highly sensitive to both radio and computing resource. In this paper, we consider an Orthogonal Frequency-Division Multiplexing Access (OFDMA) based multi-user and multi-MEC-server system, where the task offloading strategies and wireless resources allocation are jointly investigated. Aiming at minimizing the total energy consumption, we propose the joint offloading and resource allocation strategy for latencycritical applications. Through the bi-level optimization approach, the original NP-hard problem is decoupled into the lower-level problem seeking for the allocation of power and subcarrier and the upper-level task offloading problem. Simulation results show that the proposed algorithm achieves excellent performance in energy saving and successful offloading probability (SOP) in comparison with conventional schemes.Index Terms-Mobile edge computing(MEC), task offloading scheduling, subcarrier allocation, bi-level optimization.

Despite the proposed climate–human connection in the West Liao River Basin during the Bronze Age, the question of how climate change could have affected the subsistence strategies, and consequently, the cultural transformation from the Lower Xiajiadian to the Upper Xiajiadian periods, has never been systematically explored. Based on radiocarbon dating and the analysis of plant remains recovered by flotation, as well as the spatial distribution of archaeological sites, this study investigates the subsistence strategies of ancient people and their influence on cultural development in the West Liao River Basin during the Lower Xiajiadian (3900–3400 cal. yr BP) and Upper Xiajiadian periods (3000–2500 cal. yr BP). Carbonized seeds collected from 13 archaeological sites reveal that people engaged in millet-based agriculture in this area throughout the Bronze Age. Favorable climate during the Holocene Optimum promoted millet farming among the Lower Xiajiadian Culture. The end of the Holocene Optimum and its associated climate deterioration led to agricultural shrinkage in the Upper Xiajiadian period, which is revealed by the reduced amount of carbonized millet seeds and the ratio between foxtail millet and broomcorn millet. Climate deterioration led to diverse subsistence strategies, resulting in the dispersal of human settlements and the differentiation of the spatial distributions of different groups. People with millet-based subsistence strategies retreated southward, while people with animal husbandry and hunting-based subsistence strategies migrated westward. The above findings may offer insights in comprehending how climate deterioration could have affected the multi-facets of human societies in the West Liao River Basin, which is a climatically sensitive region, in Chinese prehistory.

Carbon-based materials generated from biomass have been studied extensively. However, to the best of our knowledge, there is no report of any hollow structured carbon nanospheres directly derived from biomass without the use of templates. In this research, a green route to directly convert biomass to nitrogen-doped hollow carbon nanospheres (N-HCSs) was reported, where only glucose and glucosamine were used as the precursors and an aerosol-assisted process was employed. In the process, amino groups of glucosamine triggered the coassembly between glucose and glucosamine, resulting in the structural evolution of hollow structures. The aerosol-based technology ensures the obtained particles have a spherical morphology and are in the nanoscale size range. The as-prepared materials have been thoroughly characterized by SEM, TEM, HAADF-STEM, EELS mapping, XPS, XRD, Raman, and nitrogen adsorption. Owing to the unique structural and surface properties, the resultant N-HCSs exhibited excellent electrochemical properties for energy storage, including a high specific capacitance of 266 F g −1 at 0.2 A g −1 , long cycling stability with 96.8% of capacitance retained after 3000 cycles, and a fast charge−discharge process. This discovery could be adapted to guide the design and synthesis of a variety of hollow materials from biomass for wider applications in the environment and energy fields.

The transitions from ignition to flames as well as the combustion dynamics in stratified nheptane and toluene mixtures are numerically modeled by a correlated dynamic adaptive chemistry method coupled with a multi-timescale method (CO-DAC/MTS) in a onedimensional constant volume chamber. The study attempts to answer how the kinetic difference between n-alkanes and aromatics leads to different ignition to flame transitions and knocking-like acoustic wave formation at low temperature and engine pressure conditions with fuel stratification. It is found that the low temperature chemistry (LTC) and fuel stratification of n-heptane leads to the formation of multiple ignition fronts. Four different combustion wave fronts, a low temperature ignition (LTI) front followed by a high temperature ignition (HTI) front, a premixed flame (PF) front, and a diffusion flame (DF) front, are demonstrated. The fast LTI and HTI wave front propagation leads to a shock-like strong acoustic wave propagations, thus strongly modifying the dynamics of the subsequent diffusion and premixed flame fronts. On the other hand, for the toluene mixture, due to the lack of LTC, only two combustion wave fronts are formed, a HTI front and a premixed flame front, exhibiting stable flow field and no formation of shocklike acoustic wave. The dynamics of transition from combustion to shock waves is further analyzed by using a modified Burgers' equation. The analysis for n-heptane/air mixture indicates that both the onset of LTI and the strong dependency of HTI on the equivalence ratio can either promote or attenuate the transition from strong acoustic wave to shock wave. However, the toluene/air mixture exhibits no coupling with acoustic wave, suggesting that the rich LTC reactivity with fuel stratification, specific to the n-alkane chemistry, can lead to knocking and acoustic formation.

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The industrial cyber-physical system enables collaboration between distributed nodes across industrial clouds and edge devices. Flexibility and interoperability could be enhanced significantly by introducing the service-oriented architecture to industrial edge devices. From the industrial edge computing perspective, software components shall be dynamically composed across heterogeneous edge devices to perform various functionalities. In this paper, a knowledge-driven Microservice-based architecture to enable plug-and-play software components is proposed for industrial edges. These software components can be dynamically configured based on the orchestration of microservices with the support of the knowledge base and the reasoning process. These semantically enhanced plug-and-play microservices could provide rapid online reconfiguration without any programming efforts. The use of the plug-and-play software components is demonstrated by an assembly line example. INDEX TERMS Service-oriented architecture, industrial automation, IEC 61499 function blocks, plug and play, microservices, interoperability, REST API, SQWRL, OWL.

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