Computational Approaches to Characterizing Online Health Communities

Online health communities (OHCs) have been increasingly popular among patients with chronic or life-threatening illnesses for the exchange of social support. Contemporary research of OHCs relies on methods and tools to handle analytics of massive user-generated content at scale to complement traditional qualitative analysis. In this thesis, we aim at advancing the area of research by providing computational tools and methods which facilitate automated content analysis, and by presenting applications of these tools to investigating member characteristics and behaviors. We first provide a framework of conceptualization to systematically describe problems, challenges, and existing solutions for OHCs from a social support standpoint, to bridge the knowledge gap between health psychology and informatics. With this framework in hand, we define the landscape of online social support, summarize current research progress of OHCs, and identify research questions to investigate for this thesis. We then build a series of computational tools for analyzing OHC content, relying on techniques of machine learning and natural language processing. Leveraging domain-specific features, our tools are tailored to handle content analysis tasks on OHC text effectively. Equipped with computational tools, we demonstrate how characteristics of OHC members can be identified at scale in an automated fashion. In particular, we build up multi-dimensional descriptions for patient members, consisting of what topics they focus on, what sentiment they express, and what treatments they discuss and adopt. Patterns of how these member characteristics change through time are also investigated longitudinally. Finally, relying on computational analytics, members' behaviors of engagement such as debate and dropping-out are identified and characterized. Studies presented in this thesis discover static and longitudinal patterns of member characteristics and engagement, which are potential research hypotheses to be explored by health psychologists and clinical researchers. The thesis also contributes to the informatics community by making computational tools, lexicons, and annotated corpora available to facilitate future research

Sampled in Pairs and Driven by Text: A New Graph Embedding Framework

In graphs with rich texts, incorporating textual information with structural information would benefit constructing expressive graph embeddings. Among various graph embedding models, random walk (RW)-based is one of the most popular and successful groups. However, it is challenged by two issues when applied on graphs with rich texts: (i) sampling efficiency: deriving from the training objective of RW-based models (e.g., DeepWalk and node2vec), we show that RW-based models are likely to generate large amounts of redundant training samples due to three main drawbacks. (ii) text utilization: these models have difficulty in dealing with zero-shot scenarios where graph embedding models have to infer graph structures directly from texts. To solve these problems, we propose a novel framework, namely Text-driven Graph Embedding with Pairs Sampling (TGE-PS). TGE-PS uses Pairs Sampling (PS) to improve the sampling strategy of RW, being able to reduce ~99% training samples while preserving competitive performance. TGE-PS uses Text-driven Graph Embedding (TGE), an inductive graph embedding approach, to generate node embeddings from texts. Since each node contains rich texts, TGE is able to generate high-quality embeddings and provide reasonable predictions on existence of links to unseen nodes. We evaluate TGE-PS on several real-world datasets, and experiment results demonstrate that TGE-PS produces state-of-the-art results on both traditional and zero-shot link prediction tasks.Comment: Accepted by WWW 2019 (The World Wide Web Conference. ACM, 2019

Experimental and kinetic study on the laminar burning speed, Markstein length and cellular instability of oxygenated fuels

The laminar burning speed, Markstein length and cellular instability of three oxygenated fuels, polyoxymethylene dimethyl ether 3 (PODE3), dimethyl carbonate (DMC) and n-butanol (NB), were experimentally studied using spherical flame propagation method. Both of the three fuels are potential alternatives for petrochemical gasoline and diesel. Laminar burning speeds and Markstein lengths were measured at ambient pressure and elevated temperature (363 K-423 K) with three extrapolation models including linear and non-linear employed to extract the unstretched flame speed. Onset of flame cellular instability of the three fuels was determined at high pressure (0.5–0.75 MPa) which was favored to the occurrence of cellular instability. Three well-validated mechanisms for PODE3, DMC and NB respectively were used to numerically analyze the flame structure and then understand the underlying effect of the molecular structure of oxygenated fuels on laminar flame propagation. Results show that PODE3 has the highest laminar burning speed among the three, supporting by both thermal effect and kinetic effect. While the laminar burning speed of NB is higher than that of DMC, which is due to the combined effect of thermal factor and kinetic factor. The molecular structure of oxygenated fuels exerts an influence on the laminar flame propagation through the fuel-specific cracking pathway and resulting formed intermediates with different reactivity. The absence of C–C bond within PODE3 and DMC leads to the formation of substantial oxy-intermediates (CH2O) with high reactivity during fuel decomposition. PODE3 has the most stable flame among the three because of the strong stretching of PODE3 flame. The flame stability of DMC and NB is approximately similar especially at high initial pressure

An experimental investigation of wide distillation fuel based on CTL on the combustion performance and emission characteristics from a CI engine

Coal to liquid (CTL) has promising application prospects as an alternative diesel fuel, but the direct application of coal-based synthetic diesel with high cetane number (CN) in compression ignition (CI) engines also has problems. Therefore, the CTL is blended with gasoline to adjust the physicochemical properties of the fuel, which is expected to meet the requirements of efficient and clean combustion. From the perspective of fuel design and combustion boundary condition control, the effects of CTL/gasoline blends on the combustion performance and emission characteristics in a CI engine are investigated in this study. Meanwhile, the variation in the start of injection (SOI) along with the addition of exhaust gas recirculation (EGR) permit achieving clean combustion with CTL/gasoline blends. Experimental results present that the wide distillation fuel (WDF) formed by adding gasoline to CTL, which is conducive to reducing the required mixing timescale and lengthening the chemical preparation timescale. CTL/gasoline blends bring in a higher premixed combustion ratio (PCR) and keep NOx and soot emissions at the lowest level after introducing EGR. Simultaneously, the inhibition effects of CTL/gasoline blends on particulate emissions are apparent with or without EGR due to prolonged ignition delay (ID) and improved mixing quality of fuel-air mixture, and the mass of the total particulates for CG60 is significantly reduced above 90% compared to pure CTL. In addition, the CTL/gasoline blends show refined engine characteristics for broad SOI, and the addition of gasoline to CTL is valid to alleviate the deterioration of combustion processes and emissions caused by EGR. In brief, Coupling EGR and gasoline addition is an effective way to break the trade-off relationship between NOx and particulate emissions for CTL

Comparative assessment of n-butanol addition in CTL on performance and exhaust emissions of a CI engine

Coal to liquid (CTL) is a diesel alternative fuel based on Fischer-Tropsch (FT) process, which has shown promising application value. Besides, as an oxygenated biofuel with high oxygen content and volatility, n-butanol can be blended with hydrocarbon fuels to improve engine performance. This study aims to investigate the effects of CTL/n-butanol blends on the performance of the compression-ignition (CI) engine, and to reveal the influence of combustion boundary conditions such as n-butanol blending ratio, the start of injection (SOI), and exhaust gas recirculation (EGR) on the combustion and emissions characteristics. The results show that blending n-butanol with CTL is beneficial to improve the fuel-gas mixture distribution in the cylinder, and the premixed combustion ratio (PCR) increases by 13.66% as the energy ratio of n-butanol increases to 30% (B30) compared with the pure CTL. CTL/n-butanol blends make particulate emission tend to be shifted towards nucleation mode and the particulate mass emission significantly reduced, especially the particulate mass of B30 reduce by 68.6%; meanwhile, the NOx emission shows an upward trend. Compared with n-butanol blended, adjusting the SOI impacts NOx emissions significantly, while its influence on the indicated thermal efficiency (ITE) and particulate emissions is relatively slight. Moreover, through the synergistic control of n-butanol addition and EGR, the trade-off relationship between NOx and particles is mitigated

Optical diagnostic study of internal and external EGR combined with oxygenated fuels of n-butanol, PODE3 and DMC to optimize the combustion process of FT synthetic diesel

With the introduction of carbon neutrality target, Fischer-Tropsch (FT) synthetic fuels are coming back into the limelight as a kind of carbon–neutral fuel. However, the mismatch between the overly high cetane number (CN) and the relatively low vaporability of FT synthetic diesel is unfavorable to the soot emission control, which will make it difficult to meet more stringent fuel consumption and emission regulations in future applications. To investigate the potential of oxygenated fuels combined with different exhaust gas recirculation (EGR) introduction schemes to achieve high-efficiency and clean combustion of FT synthetic diesel, an optical diagnostic study was carried out based on high-speed photography and the two-color method. The results show that all three kinds of oxygenated fuels could suppress soot emissions via self-carrying oxygen and adjusting the physicochemical properties of the fuel blend. Compared with the combustion characteristics of FT synthetic diesel, the flame area and luminosity of oxygenated blends are reduced, and the in-cylinder temperature and soot KL factor are lowered. Among them, n-butanol exhibits a greater capability of soot control compared to polyoxymethylene dimethyl ethers (PODE3) and dimethyl carbonate (DMC). In addition, introducing internal and external EGR to the engine fueled by n-butanol/FT synthetic diesel blend shows that with the increase of EGR rate, the external EGR exhibits a gradually stronger inhibiting effect on the heat release process and soot KL factor, while the internal EGR exhibits an inhibiting and then promoting effect. Moreover, the high ratio internal EGR shortens the ignition delay (ID) significantly due to the strong heating effect, which is unfavorable to the control of soot emission. The combination of oxygenated fuels and internal/external EGR could effectively optimize the combustion process of FT synthetic diesel and inhibit soot generation, but the EGR rate needs to be controlled within a proper range

Optical diagnostic study of ammonia-kerosene dual-fuel engine combustion process

In this study, the differences in the combustion process of ammonia-premixed ignition with conventional diesel and kerosene as pilot fuels were investigated based on flame chemiluminescence, and further study on the effects of ammonia ratio (AMR) and direct injection timing (DIT) on the ammonia-kerosene dual-fuel combustion (AKDC) process was carried out. The results show that the kerosene with stronger volatility is more conducive to promoting rapid and stable combustion of ammonia. A composite flame structure is observed in dual-fuel modes. With the increase of AMR, the capacity to ignite ammonia is lessened, the flame area and luminosity are stabilized and then reduced, and the flame hue is transformed from blue-green to yellow. Higher combustion rates are observed when the DIT lies between −9° and −12° CA ATDC, resulting in higher flame area and luminosity. The overly advanced or delayed DIT leads to the deterioration of ammonia combustion