Principal Sub-manifolds

We revisit the problem of finding principal components to the multivariate datasets, that lie on an embedded nonlinear Riemannian manifold within the higher-dimensional space. Our aim is to extend the geometric interpretation of PCA, while being able to capture the non-geodesic form of variation in the data. We introduce the concept of a principal sub-manifold, a manifold passing through the center of the data, and at any point on the manifold, it moves in the direction of the highest curvature in the space spanned by eigenvectors of the local tangent space PCA. Compared to the recent work in the case where the sub-manifold is of dimension one (Panaretos, Pham and Yao 2014)--essentially a curve lying on the manifold attempting to capture the one-dimensional variation--the current setting is much more general. The principal sub-manifold is therefore an extension of the principal flow, accommodating to capture the higher dimensional variation in the data. We show the principal sub-manifold yields the usual principal components in Euclidean space. By means of examples, we illustrate how to find, use and interpret principal sub-manifold with an extension of using it in shape analysis

Estimation of Sand Production Rate Using Geomechanical and Hydromechanical Models

This paper aims to develop a numerical model that can be used in sand control during production phase of an oil and gas well. The model is able to predict not only the onset of sand production using critical bottom hole pressure inferred from geomechanical modelling, but also the mass of sand produced versus time as well as the change of porosity versus space and time using hydromechanical modelling. A detailed workflow of the modelling was presented with each step of calculations. The empirical parameters were calibrated using laboratory data. Then the modelling was applied in a case study of an oilfield in Cuu Long basin. In addition, a sensitivity study of the effect of drawdown pressure was presented in this paper. Moreover, a comparison between results of different hydromechanical models was also addressed. The outcome of this paper demonstrated the possibility of modelling the sand production mass in real cases, opening a new approach in sand control in petroleum industry

Power Allocation in Wireless Relay Networks

This thesis is mainly concerned with power allocation issues in wireless relay networks where a single or multiple relays assist transmission from a single or multiple sources to a destination. First, a network model with a single source and multiple relays is considered, in which both cases of orthogonal and non--orthogonal relaying are investigated. For the case of orthogonal relaying, two power allocation schemes corresponding to two partial channel state information (CSI) assumptions are proposed. Given the lack of full and perfect CSI, appropriate signal processing at the relays and/or destination is also developed. The performance behavior of the system with power allocation between the source and the relays is also analyzed. For the case of non-orthogonal relaying, it is demonstrated that optimal power allocation is not sufficiently effective. Instead, a relay beamforming scheme is proposed. A comprehensive comparison between the orthogonal relaying with power allocation scheme and the non-orthogonal relaying with beamforming scheme is then carried out, which reveals several interesting conclusions with respect to both error performance and system throughput. In the second part of the thesis, a network model with multiple sources and a single relay is considered. The transmission model is applicable for uplink channels in cellular mobile systems in which multiple mobile terminals communicate with the base station with the help of a single relay station. Single-carrier frequency division multiple access (SC-FDMA) technique with frequency domain equalization is adopted in order to avoid the amplification of the multiple access interference at the relay. Minimizing the transmit power at the relay and optimizing the fairness among the sources in terms of throughput are the two objectives considered in implementing power allocation schemes. The problems are visualized as water-filling and water-discharging models and two optimal power allocation schemes are proposed, accordingly. Finally, the last part of the thesis is extended to a network model with multiple sources and multiple relays. The orthogonal multiple access technique is employed in order to avoid multiple access interference. Proposed is a joint optimal beamforming and power allocation scheme in which an alternative optimization technique is applied to deal with the non-convexity of the power allocation problem. Furthermore, recognizing the high complexity and large overhead information exchange when the number of sources and relays increases, a relay selection scheme is proposed. Since each source is supported by at most one relay, the feedback information from the destination to each relay can be significantly reduced. Using an equal power allocation scheme, relay selection is still an NP-hard combinatorial optimization problem. Nevertheless, the proposed sub-optimal scheme yields a comparable performance with a much lower computational complexity and can be well suited for practical systems

Precision-cut tissue slices: a novel ex vivo model for fibrosis research

Pathological scar formation, i.e. fibrosis, is characterized by a disproportionate production and deposition of extracellular matrix proteins in tissues resulting in loss of organ function. Fibrotic diseases account for up to 45% of worldwide mortality, yet there are no effective antifibrotic therapies currently available. To improve and accelerate antifibrotic drug discovery, there is an urgent need for reliable and reproducible (human) in vitro methods that reflect the cellular diversity that epitomize specific organs. This thesis delineates the successful development of a novel ex vivo/in vitro model for intestinal and renal fibrosis, namely precision-cut intestinal slices (PCIS) and precision-cut kidney slices (PCKS) prepared from murine, rat and human tissue. Our results demonstrated that the slices remain viable during culture and maintain their organ-specific phenotype. Moreover, in both PCIS and PCKS we observed that fibrosis could be induced by either culture activation or treatment with a profibrotic stimulus. Based on these findings, both models were subsequently used to evaluate the efficacy of various putative antifibrotic drugs. Using PCIS, we demonstrated that pirfenidone, LY2109761 and sunitinib could mitigate fibrogenesis on a gene level, warranting further evaluation of these compounds for the treatment of intestinal fibrosis. In addition, we demonstrated that IFNγ could be used to halt renal fibrogenesis. Furthermore, studies with precision-cut liver and intestinal slices revealed that rosmarinic acid elicited organ- and species-specific effects, illustrating the pressing need for good translational models for drug discovery. Taken together, this thesis delineates that precision-cut tissue slices can be used to unravel fibrosis and evaluate the antifibrotic potential of therapeutics

A study into the cause of drug abuse amongst the Vietnamese youth: An environmental perspective

This study describes the environmental causes of alcohol and other drug misuse amongst the Vietnamese street youth. It explores how factors of migration affected the Vietnamese family life, mainly language difficulty, employment, racial bias, and ill-image of the Vietnamese community reported by the media. The study further outlines three atmospheres: family, school and media that contribute to the problems of alcohol and other drug misuse by the Vietnamese youth. Conflict and tension issues between parents and children are discussed in terms of cultural differences, communication and lack of effective parenting skills. Problems at schools faced by the Vietnamese students are discussed in terms of racism, language difficulties and lack of appropriate services. The study highlighted that "very easy" and "easy" to get drug was an added factor to increase drug use amongst this target group. To date there is no existing intervention and prevention programs initiated by the government and the community to deal with racism and schooling issues. The paper suggests some practical strategies that can be employed to deal with these issues in relation of cross-cultural training, racism prevention, parenting skills and increase in employment rates amongst the Vietnamese community

In vitro Fermentation Patterns of Rice Bran Components by Human Gut Microbiota

The prevalence of colorectal cancer (CRC) has been increasing in recent years worldwide. In the United States, it is ranked the second leading cause of cancer death. Risks of CRC increase with age and are associated with several lifestyle factors such as diet, drinking and smoking habits, and levels of physical activity. There is an abundance of scientific literature demonstrating the protective roles of several dietary components including fibers and polyphenolic compounds. These compounds have been shown to be able to positively modulate gastrointestinal ecology by increasing the production of short-chain fatty acids (SCFA) and promoting the population of beneficial bacteria. Whole grain cereals such as wheat, corn, sorghum, and rice are rich sources of these components. However, they are more abundant in the cereal bran layer which is typically removed during polishing. Research have shown that feruloylated arabinoxylan oligosaccharides (FAXO) isolated from cereals such as wheat, corn, and sorghum exerted prebiotic-like properties by increasing SCFA production and selectively promote microbiota population. Polyphenolic compounds have also been demonstrated to be able to modulate gut microbiota ecology. However, rice bran FAXO and rice bran polyphenolics (RBPP) have not been studied for such properties. Therefore, two rice bran components including FAXO and RBPP are hypothesized to have positive impacts on human gut microbiota. In this study, prebiotic-like properties of FAXO and RBPP were assessed by determining the fermentation patterns of FAXO and RBPP to increase SCFA production and by evaluating the impacts of FAXO and RBPP on the composition of human gut microbiota