Joint Modelling of Competing Risks and Time-Dependent Covariates

In this thesis we propose a joint model for competing risks and longitudinal data. Our joint model provides a flexible approach to handle longitudinal data with complicated structures. Our model consists of a multi-state model for the competing risks and a general mixed model for the longitudinal outcomes, linked together by some latent random effects. For the joint model of one longitudinal outcome, we obtain the estimates of the parameters by maximising the marginal likelihood. We also extend the joint model to take into account multiple longitudinal outcomes simultaneously. To alleviate the 'curse of dimensionality' in integration, we propose to use Bayesian inference and use the posterior means as the estimates of the parameters. The joint models are applied to two datasets, the English Longitudinal Study of Ageing (ELSA) and the clinical data from the PhysioNet/Computing in Cardiology Challenge 2019. For the second dataset, we also propose a two-stage framework for disease early diagnosis. We construct a time-dependent loss function, and make diagnosis by minimising the expected loss

Graphic

When I was young, I was attracted by Animate and Comics, started drawing childish colorful lines on blanket paper. I can easily draw those cartoon characters vividly, which has plant an art seed deeply inside of my heart. As I get older, I was being trained in school to draw much more professional ways. I work hard to invest in as many kinds of media as I can, but still focus on graphic design and digital drawing, especially for video games and movies, which brought me to art area. I want to do concept design mostly in the future, like design characters and environment. In the past several years, I tried a lot to practice my physical skills on digital drawings, but I noticed that, compared with brilliant concept designers like Martin Deschambault, I still lack ability on the “design” part, that I don’t have good enough feeling of “two-dimensional shape”, and creating atmosphere. However, I was trying to increase my weakness a little bit. In my recent editorial illustration work, I use blue-tone to create a peaceful atmosphere. There’s a skeleton sitting in a computer station, on the middle of the water surface inside of a cave. It’s indicates myself when I was a child, sitting in front of my computer during mid-night to do digital drawings. That’s my most productive time, and I’m always trying to find the feeling about that time. What’s more, for my final project in illustration class, I used two different shapes – triangle and circle, to design two different kinds of amour sets for male warrior. Because of the difference of shapes, they gave the audience totally different feelings. It was also a challenge for me to draw an elder man, since I drew young woman all the time while practice skills in the past. If “concept design” is my dream, then graphic design is my choice of reality. To get better sense of “shape”, I concentrated on graphic design a lot in college study as well. When I was in China, even though I was not an art major student, I was asked to help organizations in school to make posters or PowerPoint stuff all the time, which had practiced me a lot in the past few years. When I attended to Murray State University, during the study in graphic design class, I learnt many new, especially more professional skills about design. One of the most obvious change is, my taste of design became better. My final project of graphic design II class is a zoo poster, but the first version was ugly, just like what non-art student did in Chinese college. My last version is very graphic and neat, which I like a lot. Now, most of my graphic design project need me to make it several versions to get a relatively satisfying one, nevertheless, I believe this is the tough but necessary step to develop my skill and taste to create professional art work, and I’m on the right way to change my style. I’ll keep learning and practicing for my design and illustration skills, and the taste of my design style in the future, in order to make stuff that also amuse myself.https://digitalcommons.murraystate.edu/art399/1056/thumbnail.jp

System as a living organism

This is cross-disciplinary research in urban systems, architecture, bio-systems, agriculture, energy supplies, circular economy, and sustainability

Modelling the mechanical response of Japanese lacquer (urushi) to varying environmental conditions

Urushi is a complex natural polymer that has been used to protect and decorate objects for many hundreds of years. Urushi is an important material as decorated objects can obtain great value and historical worth. A star item of urushi lacquerwares, the Mazarin Chest, property of Victoria & Albert (V&A) Museum in London, is famous as one of the finest pieces of Japanese lacquerware in the world, dating back to as early as the late 1630s. These urushi lacquerwares are often exposed to environments that are detrimental to both their aesthetic appeal and structural performance, and restoration and conservation procedures are needed to preserve these objects over long periods of time. However, the precise behaviour of urushi lacquers is not sufficiently understood to allow accurate prediction of the material response to environmental effects or of the effectiveness of any proposed conservation procedure. Thus a need exists for a comprehensive understanding of this material and a finite element (FE) model to predict the mechanical response to varying environmental conditions. The aim of this research was to model the hygro-mechanical effects during the environmental ageing process of urushi films by means of FE modelling, which will help to make decisions about the environmental conditions required for storage and exhibition. This was achieved by a combination of experimental and computational methods. A synthetic thermosetting (crosslinked) lacquer, polyurethane (PU), was initially studied to develop the methodology of the experimental and numerical studies and to provide a comparison to the natural lacquer. Experimental work was carried out to characterise the material behaviour of both materials, such as hygroscopic expansion, moisture diffusion kinetics and mechanical behaviour under various environmental conditions. Moisture diffusion in the two lacquer films was well described by Fick s law. However, different sorption isotherm models, Flory-Huggins model for PU and Guggenheim-Anderson-de-Boer (GAB) model for urushi, were required to model the equilibrium sorption of these two materials. The mechanical properties of the lacquer films were found to have a complex dependence on environmental conditions. The tensile properties of both lacquer films were shown to change significantly after UV ageing. With increasing time of ultraviolet (UV) irradiation, Young s Modulus and tensile strength increased dramatically, but the maximum strain decreased. With water absorption, both Young s modulus and tensile strength decreased, and maximum strain increased. The two lacquer films were found to behave with a non-linear viscoelasticity, which was highly dependent on environmental conditions. A modified Burger s model was found to provide a good fit to experimental creep data for the PU lacquer well at different stress levels, suggesting this is a satisfactory method for characterising PU rheological behaviour. A novel modified generalized Kelvin fluid (MGKF) model was found to be a powerful non-linear viscoelastic model capable of representing the rheological behaviour of the urushi below the yield stress. However, in order to include the post yield behaviour a visco-elastic-plastic model is required. A hygro-mechanical model of the urushi behaviour based on the MGKF viscoelastic model was developed and tested. Through careful determination of the mechanical behaviour the constitutive properties of a thin layer of lacquer were determined and used as an input to a FE based model of the deformation and stresses that develop in response to changes in the environmental conditions. The model was validated using experimental results that showed the depth averaged stress in a thin layer deposited on a glass substrate, which allowed insight into the time dependent and spatially varying stresses within the layer. It was shown that the regions of highest stress were found in areas of highest moisture ingress, emphasising the need for control of the environment in which urushi covered artefacts are stored. In order to perform a predictive study on the bending behaviour of urushi films with cracks, as can be seen in aged lacquers, a model with a grooved urushi film on an aluminium substrate was created and subjected to bending loads. The time-dependency of the urushi material properties seems to hardly affect the bending behaviour of the model, however, the profile of the displacement field around the groove was found to be considerably affected by the geometry of the groove. To evaluate the effectiveness of a traditional Japanese consolidation method for lacquerware objects, known as urushi-gatame, a strain-based progressive damage failure model was used to model the continuum failure in the bi-material strip under an increasing bending load. The behaviour of damage initiation and evolution was modelled for an unfilled groove, a filled groove with fresh filler and filled groove with UV aged filler. From the finite element analysis (FEA) results, the introduction of the filler, as a simple mimic of the consolidation method, does enable the strip to sustain a higher bending load. However, this effectiveness is weakened as the material is aged, with it behaving similar to a groove without any filler

Towards Optimally Decentralized Multi-Robot Collision Avoidance via Deep Reinforcement Learning

Developing a safe and efficient collision avoidance policy for multiple robots is challenging in the decentralized scenarios where each robot generate its paths without observing other robots' states and intents. While other distributed multi-robot collision avoidance systems exist, they often require extracting agent-level features to plan a local collision-free action, which can be computationally prohibitive and not robust. More importantly, in practice the performance of these methods are much lower than their centralized counterparts. We present a decentralized sensor-level collision avoidance policy for multi-robot systems, which directly maps raw sensor measurements to an agent's steering commands in terms of movement velocity. As a first step toward reducing the performance gap between decentralized and centralized methods, we present a multi-scenario multi-stage training framework to find an optimal policy which is trained over a large number of robots on rich, complex environments simultaneously using a policy gradient based reinforcement learning algorithm. We validate the learned sensor-level collision avoidance policy in a variety of simulated scenarios with thorough performance evaluations and show that the final learned policy is able to find time efficient, collision-free paths for a large-scale robot system. We also demonstrate that the learned policy can be well generalized to new scenarios that do not appear in the entire training period, including navigating a heterogeneous group of robots and a large-scale scenario with 100 robots. Videos are available at https://sites.google.com/view/drlmac

Comparison of Two Models for Temperature Observation of Miniature PEM Fuel Cells Under Dry Conditions

Water and thermal management have been identified as technical hurdles to the successful implementation of low-temperature polymer electrolyte membrane (PEM) fuel cell (PEMFC) power systems. In low-power applications, miniature PEMFCs show significant promise as a competitor to lithium-ion batteries. Significant design work is underway to improve the specific power and energy densities of these fuel cells. However, little attention has been given to characterizing transient response in these miniature applications to enable gains in system design, optimization, and control. This work develops, calibrates, and experimentally validates two different dynamic control-oriented models for open-loop temperature state observation in miniature PEMFCs. Of critical importance, these estimators target operation under dry conditions with no reactant pretreatment. Operational conditions are then identified for which each model architecture is more suitable, specifically targeting minimal model complexity. A sensitivity analysis was completed that indicates necessary sensor measurements with sensor frugality in mind. The dynamic responses under changes in load and fuel stoichiometry are well captured over a range of operating conditions

The impact of regional financial development on economic growth in Beijing-Tianjin-Hebei region:a spatial econometric analysis

The Beijing–Tianjin–Hebei (BTH) integration project in China is ambitious which offers great potential with its promotion of sustainable and inclusive development. This study investigates the impact of regional financial development on economic growth in the BTH region, with panel data collected from 2007 to 2016. Two indicators namely, CREDIT (denoted as regional financial development depth) and BRANCH (denoted as regional financial intermediaries accessibility) are used to construct an integrated regional financial development indicator through the spatial econometrics approach. The spatio-temporal distribution characteristics of regional financial development and economic growth are analyzed. Afterward, the global Moran’s I and local Getis–Ord Gi* statistics are applied to detect the presence of spatial autocorrelation. Finally, a spatial Durbin model (SDM) is utilized to examine spatial distribution and spatial association. The research findings of this study suggest that the CREDIT has a positive effect on regional economic growth, while the BRANCH has no impact on regional economic growth. Moreover, it is found that the spatial autocorrelation of CREDIT and BRANCH are statistically significant. The CREDIT of the neighboring areas has a negative spatial spillover effect on economic growth of one area, while the BRANCH in the neighboring areas has a positive effect on the one area. The results and research findings reported in this article highlight the role of regional financial development in improving the economic growth not only for Chinese policy makers but also for other countries’ researchers and practitioners in this field