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With the development of mobile communication technology and the widespread popularization of mobile devices, mobile learning (m-learning) as a new learning model has achieved rapid development in many fields. Therefore, it is essential to clearly describe the knowledge development trajectory and research topics in the field of m-learning. This paper reviews 1396 articles associated with m-learning since 1992 to explore the knowledge trajectories. The global main path and the key-route main path reveal that higher education has become the leading research field of m-learning. The majority of researches focus on personalized guidance and acceptance and adoption of m-learning. Multiple main paths obtain three subareas, including "design and development of m-learning," "factors affecting the acceptance and adoption of m-learning," and "comprehensive application of m-learning." This paper contributes to the m-learning domain by providing research directions and making implications for future researchers.

Photodetectors based on semiconducting materials are vital building blocks for modern systems containing optoelectronic modules. Although commercial semiconductors have established good performances, they are plagued by complex processing procedures and stalled performances. Recently, lead halide perovskites with superior semiconducting attributes have achieved stunning progress in optoelectronics including photodetectors. However, the toxicity of lead and the ill stability significantly handicap their practical use. Great efforts thus have been devoted to developing lead-free alternatives with improved stability and uncompromised traits. In this review, we thoroughly summarize recent progress in photodetectors based on lead-free halide perovskite variants. The substitution of lead with new elements usually induces a change in structure and ensuingly optoelectronic particularities, which afford unique suitability for a collection of functionality-specified photodetectors. Especially, the family of lead-free variants witnesses a range of bandgaps that construct a broadband photon detection spanning from near-infrared (NIR) to visible regimes. Besides, stress is laid on the X-ray detection capability based on especially bismuth-type lead-free perovskites, of which the strong X-ray absorption, large bulk resistance, suppressed ion migration, and efficient charge collection enable superior X-ray sensitivities and ultralow detection limits. Finally, the challenges and visions are discussed.

Owing to their remarkable and adjustable optoelectronic properties, halide perovskites (HPs) have been regarded as a class of promising materials for various optoelectronic applications based on different energy conversion reactions, including photovoltaic cell, photocatalysis, electrocatalysis, and photoelectrochemical (PEC) systems. However, the low stability of HPs upon exposure to ambient conditions (e.g., water, heat, light, electricity) greatly hinders the practical applications of HPs. In the past few years, significant efforts have been devoted to enhancing the eventual stability of the perovskite‐based optoelectronic systems, mainly focusing on delivering improvements in the stabilities of halide perovskite materials and the relevant operation conditions of optoelectronic systems, which deserve in‐depth and systematic summaries. In this comprehensive review, the in‐depth environment‐induced decomposition mechanisms of typical HPs are elucidated. Simultaneously, the strategies for addressing the instability issues of halide perovskite materials are critically reviewed, including dimension control, compositional engineering, ligand passivation, and encapsulation engineering. Furthermore, the photoelectric applications based on the modified HPs and operation conditions are discussed systematically. In the last part of this review, future perspectives and outlooks toward the stability of HPs and their photoelectric applications are envisaged respectively. [ABSTRACT FROM AUTHOR]

In the era of the Internet and big data, the PageRank (PR) algorithm is a constantly evolving research field. However, there is no systematic research to explore the overall development trend of the PR domain. This article evaluates 1446 articles related to the PR algorithm and provides a thorough understanding of the PR field through the main path analysis (MPA). Through two basic main paths, a number of papers that play a leading role have been identified, which outline the backbone of the PR domain. Based on the analysis of multiple main paths, four main subareas have been investigated. There are accelerating the computation of PR, comprehensive applications of PR, researches on academic impact assessment and age preference in network evolution. Finally, this article discusses the research findings and the future directions of the PR field. It is the first attempt to identify the development trend of the PR domain through MPA, thus providing an insight into the knowledge evolution of the PR field over the past two decades. [ABSTRACT FROM AUTHOR]