EVALUATING EFFECTS OF MOLECULAR HETEROGENEITY ON THE NON-LINEAR MECHANICAL BEHAVIOR OF EPOXY NETWORKS

This thesis describes synthetic and processing strategies to formulate epoxies resins with molecular heterogeneity to achieve enhanced engineering properties. The network heterogeneities include chemical differences in stiffness and crosslink density, as well as mechanical difference in baseline energy state. The focus is to understand the fundamental structure-process-property relationships in these unusual network polymers, especially the post-yield responses and fracture toughness. The main characterization techniques to probe the complex network architectures are dynamic mechanical spectroscopy and compression tests. Ductility and governing parameters are also proposed to describe the relationships between molecular structures and physical properties. Three different staged fabrication strategies are studied, with increasing complexity in network architectures. In the Topologically Heterogeneous Network approach, a rigid multi-functional prepolymer is prepared first and then reacted with flexible reagents to generate within the resulting materials regions of varying stiffness and crosslink density. In the Prestressed Double Network approach, deformation is imposed between cure reactions to alter the energy state of the resulting materials. In the Asymmetric Double Network approach, lightly crosslinked aliphatic network and highly crosslinked aromatic network are introduced as the major and minor components. All three strategies produce macroscopically homogeneous epoxies with improved toughness. Combinations of the approaches are also evaluated. The observed changes in the dynamic mechanical spectra include broadening and shifting of the transitions with imposed molecular heterogeneity. A ductility parameter based on mechanical spectroscopy is proposed to quantify the influence of segmental mobility on large strain deformation. Compression test is also investigated to extract intrinsic network characteristics of thermosets. A second ductility parameter based on equilibrium and kinematic considerations is proposed to correlate with fracture toughness. Both the glass transition temperature and cohesive energy density are correlated with the non-linear mechanical behavior, including rejuvenated stress and strain hardening modulus

On the relative Morrison-Kawamata cone conjecture

We relate the Morrison-Kawamata cone conjecture for Calabi-Yau fiber spaces to the existence of Shokurov polytopes. For K3 fibrations, the existence of (weak) fundamental domains for movable cones is established. The relationship between the relative cone conjecture and the cone conjecture for its geometric or generic fibers is studied.Comment: 30 page

The Effects of Cardiometabolic Factors on the Association Between Serum Uric Acid and Chronic Kidney Disease in Chinese Middle-Aged and Older Population: A Mediation Analysis

IntroductionTo explore whether dyslipidemia, hyperglycemia or hypertension has mediating effect on the association between serum uric acid (SUA) and the development of chronic kidney disease (CKD).MethodsWe conducted a mediation analysis to explore the potential mediating effects of systolic blood pressure (SBP), diastolic blood pressure (DBP), blood glucose, triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) on the association between SUA and estimated glomerular filtration rate (eGFR). The data were obtained from China Health and Retirement Longitudinal Study (CHARLS), covering 5,762 individuals.ResultsSUA had a negative dose-response total effect on eGFR (β -3.11, 95% CI -3.40 to -2.82, P-value<0.001). The linear regression between SUA and seven potential mediators indicated that blood glucose (β 0.80, 95% CI 0.18 to 1.42, P-value=0.012), TG (β 10.01, 95% CI 8.22 to 11.79, P-value<0.001), TC (β 2.64, 95% CI 1.83 to 3.45, P-value<0.001), HDL-C (β -0.27, 95% CI -0.52 to -0.02, P-value=0.034) and LDL-C (β 1.15, 95% CI 0.49 to 1.80, P-value=0.001) all had significant dose-response association with SUA, but SBP and DBP showed no significant association with SUA. In terms of the association between potential mediators and eGFR, only TG (β 0.003, 95% CI -0.001 to 0.01, P-value=0.117) and HDL-C (β 0.01, 95% CI -0.02 to 0.04, P-value=0.444) did not have significant linear association with eGFR. The linear regression showed that SUA was directly associated with eGFR (P-value<0.001).ConclusionsThis study supported that the association between SUA and the risk of CKD was not mediated by hypertension, hyperglycemia or dyslipidemia

The latest Ordovician Hirnantia brachiopod fauna of Myanmar: Significance of new data from the Mandalay Region

A new, latest Ordovician brachiopod fauna is systematically described from the Hwe Mawng Purple Shale Member (Hirnantian) of the Naungkangyi Group of the Pa-thin area, Mandalay Region, Myanmar, revealing one of the most diverse representatives of the typical Hirnantia Fauna. Rhynchonelliformean, craniiformean and linguliformean brachiopods studied belong to 23 genera and a few indeterminate taxa, among which the most abundant genus Kinnella, along with the four common genera (Paromalomena, Pseudopholidops, Fardenia, and Dalmanella), and other genera (such as Cliftonia, Draborthis, Hindella, Hirnantia, Leptaena, Mirorthis, Plectothyrella, Skenidioides, and Xenocrania) are recorded for the first time. This high diversity Hirnantia Fauna represents an ecological differentiation within the benthos of the Sibumasu Terrane during the end Ordovician global crisis. The palaeoeco-unit named herein as the Kinnella-Paromalomena Association is assigned to lower BA3. This paper includes a taxonomic revision with the following conclusions: 1) Sinomena Zeng et al. and Yichangomena Zeng et al. are treated as junior synonyms of Eostropheodonta Bancroft; 2) Hubeinomena Zeng et al. is regarded as a juvenile form of Coolinia Bancroft; 3) Paramirorthis Zeng et al. is considered an immature growth stage of Mirorthis Zeng; 4) Shanomena Cocks and Fortey is treated as a junior synonym of Paromalomena Rong; 5) Scenidium? medlicotti Reed is redesignated as the type species of Kinnella Bergström to replace Hirnantia? kielanae Temple. The distribution of the Hirnantia Fauna in Myanmar, Thailand and western Yunnan of the Sibumasu Terrane highlights the distinctive nature of the Mandalay fauna, and the analyses of the Hirnantia Fauna and others of Sibumasu shows that Sibumasu was not located far from the South China and Lhasa palaeoplates during late Middle and Late Ordovician

Multi-threshold Segmentation for Color Image Based on Pyramid Evolution Strategy

In view of the fact that traditional intelligent optimization algorithms for multi-threshold segmentation of color images fall to consider the competition and cooperation between populations,which results in local optimization problems that affect the segmentation effect.In order to improve the segmentation effect,an improved pyramid evolution strategy (IPES) is proposed.The algorithm designs an adaptive search operator suitable for the multi-threshold segmentation problem of color images;expands the search space at all levels,improves the optimization ability of the algorithm;takes Otsu as the optimization goal and uses the competition and cooperation relationship between populations to solve the local optimization problem,thereby improving the accuracy of the solution and the effect of segmentation.The performance of IPES is tested on existing standard test images and compared with other eight algorithms.Experimental results show that the peak signal-to-noise ratio of the image segmented by IPES algorithm is between 28~35 dB,which is at least 10 dB higher than that of the improved tree-seed algorithm and traditional particle swarm algorithm and differential evolution algorithm;the structural similarity is between 89%~97%,increased by at least 3%.The image quality after segmentation is better and the structural similarity is higher.Therefore,the algorithm has good perfor-mance in solving multi-threshold segmentation problem of color images

Pore structure characterization of Chang-7 tight sandstone using MICP combined with N2GA techniques and its geological control factors

Understanding the pore networks of unconventional tight reservoirs such as tight sandstones and shales is crucial for extracting oil/gas from such reservoirs. Mercury injection capillary pressure (MICP) and N(2) gas adsorption (N(2)GA) are performed to evaluate pore structure of Chang-7 tight sandstone. Thin section observation, scanning electron microscope, grain size analysis, mineral composition analysis, and porosity measurement are applied to investigate geological control factors of pore structure. Grain size is positively correlated with detrital mineral content and grain size standard deviation while negatively related to clay content. Detrital mineral content and grain size are positively correlated with porosity, pore throat radius and withdrawal efficiency and negatively related to capillary pressure and pore-to-throat size ratio; while interstitial material is negatively correlated with above mentioned factors. Well sorted sediments with high debris usually possess strong compaction resistance to preserve original pores. Although many inter-crystalline pores are produced in clay minerals, this type of pores is not the most important contributor to porosity. Besides this, pore shape determined by N(2)GA hysteresis loop is consistent with SEM observation on clay inter-crystalline pores while BJH pore volume is positively related with clay content, suggesting N(2)GA is suitable for describing clay inter-crystalline pores in tight sandstones