The purpose of this study is to propose a unified model integrating the technology acceptance model (TAM), task fit technology (TTF) model, MOOCs features and social motivation to investigate ...continuance intention to use MOOCs. A sample of 252 participants in China that have already used MOOCs took part in this study. Structural equation modeling implemented via partial least squares (PLS) is conducted to test the research hypotheses. The results show that research framework for integrating the TAM for the adoption and TTF model for utility provides a more comprehensive understanding of the behaviors related to this context: (1) perceived usefulness and attitude are critical to the continuance intention to use MOOCs; (2) perceived usefulness is a significant mediator of the effects of perceived ease of use, task-technology fit, reputation, social recognition and social influence on continuance intention; (3) perceived ease of use, task-technology fit, reputation, social recognition and social influence are found to play important roles in predicting continuance intention; (4) individual-technology fit, task-technology fit, and openness affect the perceived ease of use; (5) unexpectedly, perceived ease of use and social influence have no significant effect on attitude, and individual-technology and openness do not affect perceived usefulness.
•Integrating the TAM and TTF model provides a better understanding of MOOCs.•Perceived usefulness and attitude are critical to the continuance intention.•Perceived usefulness is a significant mediator for continuance intention.•Perceived ease of use and social influence do not influence attitude.•Task-technology fit and reputation predict continuance intention.
This paper studies inference for the mean vector of a high-dimensional U-statistic. In the era of big data, the dimension d of the U-statistic and the sample size n of the observations tend to be ...both large, and the computation of the U-statistic is prohibitively demanding. Data-dependent inferential procedures such as the empirical bootstrap for U-statistics is even more computationally expensive. To overcome such a computational bottleneck, incomplete U-statistics obtained by sampling fewer terms of the U-statistic are attractive alternatives. In this paper, we introduce randomized incomplete U-statistics with sparse weights whose computational cost can be made independent of the order of the U-statistic. We derive nonasymptotic Gaussian approximation error bounds for the randomized incomplete U-statistics in high dimensions, namely in cases where the dimension d is possibly much larger than the sample size n, for both nondegenerate and degenerate kernels. In addition, we propose generic bootstrap methods for the incomplete U-statistics that are computationally much less demanding than existing bootstrap methods, and establish finite sample validity of the proposed bootstrap methods. Our methods are illustrated on the application to nonparametric testing for the pairwise independence of a high-dimensional random vector under weaker assumptions than those appearing in the literature.
The mechanical and corrosion properties of gas metal arc additive manufacturing (GMA-AM) 316L could be optimized by modifying the volume fractions of sigma (σ) and delta-ferrite (δ) phases through ...heat treatment. Results show that the heat treatment at 1000°C to 1200°C for one hour will not obvious influence the morphology of grains in steel but largely influence the contents of σ and δ phases. The heat treatment at 1000°C effectively increases the amount of σ phase in steel, causing both increase of UTS and YS but decrease of El and RA. The heat treatment at 1100°C to 1200°C completely eliminates σ phase, leading to the decrease of UTS and YS but increase of El and RA. The σ phase has better strengthening effect than δ phase, but which may degrade ductility and increase the possibility for cracks generation in steel. Meanwhile, limiting the number of both σ and δ phases through heat treatment can improve the corrosion resistance of steel. And σ phase appears more detrimental impact on degradation the corrosion resistance of steel than δ phase.
The austenitic stainless steel 316L was fabricated by gas metal arc additive manufacturing (GMA-AM) and its microstructure and room temperature tensile properties were investigated. Results show that ...in the GMA-AM 316L plate, a large number of well-aligned austenitic dendrites vertically orient, forming large columnar grains in the middle and some dendrites bent toward the plate surfaces, forming small columnar grains near the edges. The microstructure of GMA-AM 316L consists of δ, γ and σ phases. After one layer was deposited, the δ phase exhibited reticular morphology within austenitic dendrites. The δ phase redissolved in austenite with the intermetallic σ phases forming at γ/δ interfaces under the thermal cycles influence of subsequent three deposition layers. And under the thermal influence after the fourth layers, both δ and σ phases turned into fine vermicular morphologies within austenitic dendrites. The tensile properties of GMA-AM 316L steel are comparable to wrought 316L and exceed the industry requirements for 316L. Its fracture type is ductile fracture due to the obvious fracture surface dimples. The microcracks initiate at the interior of σ phases and grow into large cracks leading to materials failure.
Pancreatic ductal adenocarcinoma, as one of the most aggressive cancers, is characterized by rich desmoplastic stroma that forms a physical barrier for anticancer drugs. To address this issue, we ...herein report a two-step sequential delivery strategy for targeted therapy of pancreatic cancer with gemcitabine (GEM). In this sequential strategy, metformin (MET) was first administrated to disrupt the dense stroma, based on the fact that MET downregulated the expression of fibrogenic cytokine TGF-β to suppress the activity of pancreatic stellate cells (PSCs), through the 5'-adenosine monophosphate-activated protein kinase pathway of PANC-1 pancreatic cancer cells. In consequence, the PSC-mediated desmoplastic reactions generating α-smooth muscle actin and collagen were inhibited, which promoted the delivery of GEM and pH (low) insertion peptide (pHLIP) comodified magnetic nanoparticles (denoted as GEM-MNP-pHLIP). In addition, pHLIP largely increased the binding affinity of the nanodrug to PANC-1 cells. The targeted delivery and effective accumulation of MET/GEM-MNP-pHLIP in vivo were confirmed by magnetic resonance imaging enhanced by the underlying magnetic nanoparticles. The tumor growth inhibition of the sequential MET and GEM-MNP-pHLIP treatment were investigated on both subcutaneous and orthotopic tumor mice models. A remarkably improved therapeutic efficacy, for example, up to 91.2% growth inhibition ratio over 30 d of treatment, well-exemplified the novel cascade treatment for pancreatic cancer and the innovative use of MET.
Joint optimization models were developed combining group preventive maintenance of a series system and production scheduling. In this paper, we propose a joint optimization model to minimize the ...total cost including production cost, preventive maintenance cost, minimal repair cost for unexpected failures and tardiness cost. The total cost depends on both the production process and the machine maintenance plan associated with reliability. For the problems addressed in this research, any machine unavailability leads to system downtime. Therefore, it is important to optimize the preventive maintenance of machines because their performance impacts the collective production processing associated with all machines. Too lengthy preventive maintenance intervals may be associated with low scheduled machine maintenance cost, but may incur expensive costs for unplanned failure due to low machine reliability. Alternatively, too frequent preventive maintenance activities may achieve the desired high reliability machines, but unacceptably high scheduled maintenance cost. Additionally, product scheduling plans affect tardiness and maintenance cost. Two results are obtained when solving the problem; the optimal group preventive maintenance interval for machines, and the assignment of each job, including the corresponding start time and completion time. To solve this non-deterministic polynomial-time problem, random keys genetic algorithms are used, and a numerical example is solved to illustrate the proposed model.
•Group preventive maintenance (PM) planning and production scheduling are jointed.•Maintenance interval and assignment of jobs are decided by minimizing total cost.•Relationships among system age, PM, job processing time are quantified.•Random keys genetic algorithms (GA) are used to solve the NP-hard problem.•Random keys GA and Particle Swarm Optimization (PSO) are compared.
Theranostics referring to the ingenious integration of diagnostics and therapeutics has garnered tremendous attention in these years as it provides a promising opportunity for modern personalized and ...precision medicine. By virtue of the good biocompatibility, outstanding fluorescence property, easy processability and functionalization, promoted photosensitizing efficiency, as well as facile construction of multi‐modality theranostics, fluorophores with aggregation‐induced emission (AIE) characteristics exhibit inexhaustible and vigorous vitality in the field of theranostics. Numerous significant breakthroughs and state‐of‐the‐art progression have been witnessed in the past few years. This review highlights the tremendous aggregation‐enhanced superiorities of AIE luminogens (AIEgens) in disease theranostics mainly involving diagnostic imaging (fluorescence and room temperature phosphorescence), therapeutic intervention (photodynamic therapy), and feasibility in construction of multi‐modality theranostics based on the experimental measurements and theoretical simulations. Additionally, the latest and advanced developments of AIEgens in disease theranostics in the aspect of corresponding strategies to design highly effective AIE‐active theranostics through triggering aggregation formation are comprehensively summarized. Moreover, a brief conclusion with the discussion of current challenges and future perspectives in this area is further presented.
A new concept of aggregation‐enhanced theranostics (AET) is put forward on the basis of tremendous aggregation‐enhanced superiorities of AIEgens in terms of diagnostic imaging, therapeutic intervention, and feasibility in construction of multi‐modality one‐for‐all theranostics. Additionally, the latest and advanced developments in the fields of AET based on AIEgens referring to strategies to trigger aggregation formation are comprehensively summarized.
Photovoltaic (PV) systems have witnessed a rapid increment, the yield mainly relies on the working condition. In most cases, it is hard to obtain the optimal yield. Therefore, Maximum Power Point ...Tracking (MPPT) controllers witness much attention as an important optimization field of PV systems. These controllers employ different algorithms and they vary in their efficiency, performance, modernity, complexity, and tracking speed. MPPT controllers have witnessed a rapid improvement, they can be generally classified as conventional and advanced methods. Conventional methods are relatively simple but they can't distinguish between the local and global peaks if partial shading occurs, therefore, their efficiency is relatively low. Advanced tracking methods are widely used due to their superior efficiency. Due to the limitation of the singular conventional and advanced methods, hybrid methods find their way to solve these limitations. Selecting the finest MPPT method is still an open issue, this issue can be solved by implementing a survey of the applied methods. This study gives a concise classification and evaluation review of all the applied MPPT methods. This study also provides an accessible reference to undertake mass research works in MPPT in the near future.
Abundant desmoplastic stroma, which typically exists in pancreatic ductal adenocarcinoma (PDAC), can act as a natural protective physical barrier rendering insufficient drug delivery and penetration. ...To address this issue, we herein report a two-step sequential delivery strategy for enhanced pancreatic cancer therapy. In this sequential strategy, the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) loaded liposomes (Lip-SNAP) were firstly delivered to pancreatic stellate cells (PSCs) in tumor tissue to inhibit the production of dense stroma, by inhibiting the expression of TGF-β1 and its downstream profibrotic signal transduction. Therefore, the PSC-mediated desmoplastic reaction could be suppressed by inhibiting the expression of fibronectin, α-SMA and collagen. The gemcitabine (GEM) loaded liposomes (Lip-GEM) were administrated subsequently. The enhanced intratumoral penetration of Lip-GEM was then achieved due to the stromal disruption in consequence of NO treatment, thus significantly improving the drug delivery efficiency. The tumor growth inhibition of the two-step sequential delivery of Lip-SNAP and Lip-GEM was investigated on both subcutaneous and orthotopic tumor mouse models, to show the remarkably improved therapeutic efficacy of GEM. Such NO-induced stromal depletion provides a general strategy to overcome the blockage of desmoplastic stroma on other therapeutic agents.
Cigarette smoking is a major risk factor for atherosclerosis and other cardiovascular diseases. Increasing evidence has demonstrated that nicotine impairs the cardiovascular system by targeting ...vascular endothelial cells, but the underlying mechanisms remain obscure. It is known that cell death and inflammation are crucial processes leading to atherosclerosis. We proposed that pyroptosis may be implicated in nicotine-induced atherosclerosis and therefore conducted the present study. We found that nicotine resulted in larger atherosclerotic plaques and secretion of inflammatory cytokines in ApoE
mice fed with a high-fat diet (HFD). Treatment of human aortic endothelial cells (HAECs) with nicotine resulted in NLRP3-ASC inflammasome activation and pyroptosis, as evidenced by cleavage of caspase-1, production of downstream interleukin (IL)-1β and IL-18, and elevation of LDH activity and increase of propidium iodide (PI) positive cells, which were all inhibited by caspase-1 inhibitor. Moreover, silencing NLRP3 or ASC by small interfering RNA efficiently suppressed nicotine-induced caspase-1 cleavage, IL-18 and IL-1β production, and pyroptosis in HAECs. Further experiments revealed that the nicotine-NLRP3-ASC-pyroptosis pathway was activated by reactive oxygen species (ROS), since ROS scavenger (N-acetyl-cysteine, NAC) prevented endothelial cell pyroptosis. We conclude that pyroptosis is likely a cellular mechanism for the pro-atherosclerotic property of nicotine and stimulation of ROS to activate NLRP3 inflammasome is a signaling mechanism for nicotine-induced pyroptosis.
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