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The development of massive open online courses (MOOCs) has proceeded through three generations, and in all three, online discussions have been considered a critical component. Although discussions in MOOCs have the potential to promote learning, instructors have faced challenges facilitating learners' knowledge inquiry, construction, and management through social interaction. In addition, understanding various aspects of learning calls for more mixed-method studies to provide both quantitative, generalized analysis and qualitative, detailed descriptions of learning. This study fills these practice and research gaps. We designed a Chinese MOOC with the support of a pedagogical strategy, a learning analytic tool, and a social learning environment in order to foster learner engagement in discussions. Mixed methods were used to explore learners' discussion patterns, perceptions, and preferences. Results indicated that learners demonstrated varied patterns, perceptions, and preferences, which implies a complex learning process due to the interplay of multiple factors. Based on the results, this research provided theoretical, pedagogical, and analytical implications for MOOC design, practice, and research.

ABSTRACT The tribological properties of lubricants containing the same additives often vary with varying hardness and composition of the frictional parts. This means that, in terms of the effectiveness of lubricant additives, most of current researches using GCr15 steel to assemble the frictional pair could not be directly cited by the moving parts made of other materials. Aiming at verifying if RNS‐1A‐PIBSA (referring to amino‐functionalized silica nanoparticle [RNS‐1A] after secondary surface‐capping by polyisobutylene succinic anhydride [PIBSA]) is suitable for multiple frictional parts made of different materials with varying hardness and composition, herein we investigate its applicability an additive in poly‐alpha‐olefin 6 (PAO6) base oil to three types of sliding pairs constructed from GCr15 steel, #45 steel, and ductile iron with much different hardness and composition by SRV‐5. A series of analyses of worn surface morphology and composition demonstrate that, independent of the composition and hardness of the frictional pairs, RNS‐1A‐PIBSA added in PAO6 base oil can form silica deposition film on the rubbed surfaces of the three kinds of sliding pairs, thereby effectively reducing friction and wear. Besides, we also examine the effect of RNS‐1A‐PIBSA on the thermal stability of the PAO6 base oil, and found the nano‐additive RNS‐1A‐PIBSA can delay the thermal decomposition of PAO6 base oil to some extent, which is favourable for its application in lubrication engineering. [ABSTRACT FROM AUTHOR]

This work demonstrates high-performance AlN/GaN double-barrier resonant tunneling diodes (RTDs) with high peak current density grown by plasma-assisted molecular beam epitaxy on c-plane free-standing GaN substrates, featuring stable and repeatable negative differential resistance (NDR) characteristics at room temperature. By scaling down the barrier thickness of AlN barrier and the lateral mesa size of collector, the record peak current density of 1551 kA/cm2 is achieved along with a peak-to-valley current ratio (PVCR) of 1.24, which is attributed to the reduced resonant tunneling time under thinner AlN barrier and the suppressed external incoherent valley current by reducing the dislocation number contained in the RTD device with the smaller size of collector. By statistically analyzing the NDR performance of RTD devices with different thicknesses of AlN barrier, the average peak current density increases from 145.7 to 1215.1 kA/cm2, while the average PVCR decreases from 1.45 to 1.1, correspondingly, accompanying with a decreased peak voltage from 6.89 to 5.49 V, with downscaling the AlN barrier thickness from 1.5 to 1.25 nm. The peak current density obtained in this work is the highest value among all the reported nitride-based RTDs up until now while maintaining high PVCR value simultaneously, which illustrates that ultra-scaled RTD based on vertical quantum-well structure and lateral collector size is a valuable approach for the development of nitride-based RTDs with excellent NDR characteristics and reveals their great potential applications in high-frequency oscillation sources and high-speed switch circuits. [ABSTRACT FROM AUTHOR]

Here, we present a systematical investigation of AlN/GaN double-barrier resonant tunneling diodes (RTDs) grown by plasma-assisted molecular beam epitaxy on metal-organic chemical vapor deposition GaN-on-sapphire templates. The processed devices featured an active region composed of 2.5 nm GaN quantum well sandwiched by two 1.5 nm AlN barriers and RTD mesa diameter ranging from 1 to 20 μm. Room temperature current–voltage characteristics exhibited a repeatable negative differential resistance (NDR) free of degradation and hysteresis after 1000 times subsequently up-to-down voltage sweeps across different sizes. High peak-to-valley current ratios of 1.93 and 1.58 were obtained at room temperature for 1 and 12 μm diameter devices, respectively, along with peak current densities of 48 and 36 kA/cm2 corresponding to peak voltages of 4.65 and 5.9 V. The peak current density decreased quickly initially and then was less susceptible to this averaging effect with increasing the device diameter. Temperature-dependent measurements revealed that the valley current density displayed a positive relationship to the temperature, and an abruptly increasement was observed for the devices with a diameter of 20 μm when the temperature rose over 230 K. We attributed this abnormal phenomenon to the increased contribution from acoustic and longitudinal optical (LO) phonon scattering, especially for the LO phonon scattering. The area dependence of electrical performance suggested that the leakage pathway through dislocations played a vital role for charge transport and there existed a threshold of dislocation density for NDR characteristics. These results promote further study for future implementation of III-nitride-based RTD oscillators into high-frequency and high-power terahertz radiation. [ABSTRACT FROM AUTHOR]

To explore the intervention effect of exoskeleton robot training on anxiety of stroke patients. Methods 24 stroke patients with hemiplegia were randomly divided into experimental group and control group, with 12 cases in each group. Moreover, the robot group took the walking training with UGO 210, a lower limb exoskeleton walking rehabilitation, once per day, 30 minutes per time, a total of 20 times of treatment. Before the trial and at the end of the trial cycle, patients’ emotions were assessed using the Self-rating Anxiety scale (SAS), and the efficacy of the two groups was compared. Results: The scores of anxiety scale decreased in both groups (P

In this Letter, we present the excellent negative differential resistance (NDR) characteristics of AlN/GaN double-barrier resonant tunneling diodes (RTDs) in which the active layers are grown by molecular beam epitaxy on thick GaN-on-sapphire templates manufactured by metal-organic chemical vapor deposition. Here, indium flux is introduced as surfactant to reduce the interface roughness and improve the sharpness of heterointerface during epitaxial growth of AlN/GaN/AlN quantum well. The processed device with a top collector diameter of 1 μm size demonstrates a record peak current density of 1039 kA/cm2 while simultaneously featuring a peak-to-valley current ratio of 1.23 at room temperature, excellent achievements among all the reported GaN-based RTDs on any substrates. In addition, no degradation of device performance together with free of hysteresis is observed for the 1000 times consecutive up-to-down voltage sweeps under forward bias. These remarkable achievements are attributed to the marked improvement in heterointerface quality of AlN/GaN/AlN double-barrier quantum well by adopting indium as surfactant during epitaxial growth as clarified by transmission electron microscopy analysis, which dramatically suppresses the interface roughness scattering and elements interdiffusion, thus significantly improving the NDR signatures in current–voltage curves. The obtained results in this work illustrate that indium-surfactant added epitaxy technique turns out to be a promising approach for the modulation of vertical electron resonant tunneling in III-nitride heterostructures and realization of highly reproducible and reliable AlN/GaN double-barrier RTDs, in favor of implementation for future high-power solid-state electronics operating in terahertz spectra. [ABSTRACT FROM AUTHOR]

Highlights: Using NiFe2O4 quantum dots (QDs) as additive substitutes, the total carbon content in cathodes is sharply reduced from original ~ 26% (in traditional S/C cathodes) to a low mass ratio of ~ 5%. The as-built S@CB ⊆ QDs demonstrate more appropriate tap density (~1.32 g cm−3) and specific surface area (~19.9 m2 g−1) values than S@CB counterparts. NiFe2O4 QDs additives possess superb chemisorption interactions with Li2Sn molecules and proper charge-transfer/catalytic features to strengthen redox kinetics of overall cathode systems.Smart combination of manifold carbonaceous materials with admirable functionalities (like full of pores/functional groups, high specific surface area) is still a mainstream/preferential way to address knotty issues of polysulfides dissolution/shuttling and poor electrical conductivity for S-based cathodes. However, extensive use of conductive carbon fillers in cell designs/technology would induce electrolytic overconsumption and thereby shelve high-energy-density promise of Li–S cells. To cut down carbon usage, we propose the incorporation of multi-functionalized NiFe2O4 quantum dots (QDs) as affordable additive substitutes. The total carbon content can be greatly curtailed from 26% (in traditional S/C cathodes) to a low/commercial mass ratio (~ 5%). Particularly, note that NiFe2O4 QDs additives own superb chemisorption interactions with soluble Li2Sn molecules and proper catalytic features facilitating polysulfide phase conversions and can also strengthen charge-transfer capability/redox kinetics of overall cathode systems. Benefiting from these intrinsic properties, such hybrid cathodes demonstrate prominent rate behaviors (decent capacity retention with ~ 526 mAh g−1 even at 5 A g−1) and stable cyclic performance in LiNO3-free electrolytes (only ~ 0.08% capacity decay per cycle in 500 cycles at 0.2 A g−1). This work may arouse tremendous research interest in seeking other alternative QDs and offer an economical/more applicable methodology to construct low-carbon-content electrodes for practical usage. [ABSTRACT FROM AUTHOR]