Search

In recent years, polymeric microcarriers have drawn great attention because of their potential applications in medical, cosmetic and some other industries. A variety of materials, preparation techniques have been explored to endow these microcarriers the desired properties. In spite of encouraging improvements in other properties, the low permeability of microcarriers remains a challenge which results in massive amount of cargo loss due to fast release. This work aimed to develop microcarriers with reduced permeability by coating with biocompatible and hydrophobic polymers via different techniques such as Layer-by-Layer, surface-initiated atom transfer radical polymerization and emulsion methods. This thesis starts with an introduction and literature review, which present the background of this work, followed by the description of materials as well as methods used in this work in chapter 3. Chapter 4 studied various parameters for fabricating structurally intact Poly(lactic acid) stereocomplex microcapsules, and demonstrated that heat treatment could significantly reduce the permeability of PLA microcapsules. In chapter 5, Layer-by-Layer and surface-initiated atom transfer radical polymerization techniques were combined to fabricate PMMA coated microparticles with low permeability. A polyelectrolyte macroinitiator and Poly(sodium 4-styrenesulfonate) were first deposited onto CaCO3 particles through LbL process, followed by growing PMMA brush layer via ATRP from the polyelectrolyte precursor. Chapter 6 introduced a simple emulsion method to prepare PLA coated CaCO3 microparticles with low permeability, which can retain bioactive molecules within the particles. It was found that 0.8 was the optimal CaCO3/PLA mass ratio in terms of the low permeability of microparticles as well as high-usage of polymers. In chapter 7, PLA films were synthesized from two different types of macroinitiators, with one being polyelectrolyte based and the other one being Poly(2-hydroxyethyl methacrylate) polymer brush precursor. The kinetics of PLA film growth from different precursors was compared whilst degradation of PLA films was also studied.

Bone fOlmation is an exquisitely coordinated process involving both chondrogenic and osteogenic differentiation. SOX9 is the best-known master regulator for chondrocyte differentiation and cartilage formation. Herein we demonstrate that SOX9 also participates in osteogenic differentiation;bone formation, and the action is interlocked with cAMPIPKA signaling at multilevel. Together with osteogenic markers such as Runx2, ColI a I and osteopontin, SOX9 was up-regulated in the early osteogenic stage of primary MSCs as well as in BMP-2-indued osteoblast differentiation ofC3HlOTl/2 and C2C12 cells. Overexpression of wild-type SOX9 in the progenitor cells efficiently propelled expression of multiple osteogenic marker genes such as ALP activity, type I collagen and osteocalcin expression. The promoter of the type I collagen gene was activated by SOX9. However, pathogenic mutants showed impaired osteogenesis. Furthermore, SOX9 knockdown in the bone progenitor cells inhibited osteogenic differentiation. In vivo, SOX9 overexpression in C3HIOTl12 cells slightly increased bone formation quantity, while SOX9 knockdown significantly blocked development of bone. During signaling investigation, we found the removal of PKA-phosphorylation sites of SOX9 deprived it of stimulatory effect. Chemicals specifically activating or inhibiting PKA signaling and the cognate inhibitor of PKA, PKIy, distinctly affected the SOX9 action. Fmihennore, we provide evidence that through i,ts carboxyl tenninal domain, SOX9 physically and functionally interacts with CREB, the prototypical PKA-downstream transcription factor. Thus, these results suggest that in addition to the predominate role in driving chondrogenesis, SOX9 also plays a novel role by promoting osteogenesis, which is, at both the nuclear and cytoplasmic levels, orchestrated with the PKA pathway during bone formation.

The purpose of the research conducted is to investigate the effects of local managers' education and training on corporate culture in foreign companies in the People's Republic of China. In order to realise the purpose, the project sets up three corresponding aims. First, an examination of corporate values and the corresponding cross-cultural issues in Western companies in a Chinese context is given. Second, a prescription of various adaptation forms of these companies is provided. Finally, the effects of the training on the corporate culture are evaluated and presented. The study employs a qualitative methodology for the exploration. Foreign companies covering the main fields of business activities in China were selected with an emphasis on the two countries: the United Kingdom and the United States. Thirty participants from those sample companies were interviewed face-to-face with semi-structured questions. The fieldwork was carried out mainly in Shanghai, which is the biggest city and an economic zone in China. At the same time, documentation was used as a complementary method in terms of providing relevant information. Data were also collected from two Asian foreign enterprises in China for benchmark. Final results in light of the research purpose and aims indicate that a foreign company in China, which is internationally accepted, is likely to apply a corporate culture that accommodates both similarities and differences between the local culture and the original culture of the foreign parent company. Such a corporate culture is not judged by its form, for it is neither a typical culture of a Western organisation nor typical one of a Chinese enterprise. It allows the corporation to keep international standards and simultaneously be capable of cultivating local managers to accept it emotionally. In this sense, local managers' education and training need to be perceived as a cultural process and delivered in a flexible way. The effects of the training upon the corporate culture are identified.

Human categorization performance has been studied extensively during the past sixty years. Shepard, Hovland, and Jenkins (1961) conducted a seminal study in which they examined and established the learning difficulty ordering of the family of six structures with four positive examples defined over three binary dimensions (aka, the 32[4] structures family). This empirical ordering has proven robust whenever the experimental stimuli are defined over separable dimensions under both compact and distributed representations. Since the advent of this ordering, researchers utilizing this constraint have assumed that individuals allocate their attention to dimensions of stimuli optimally to categorize. In order to test this assumption, Rehder and Hoffman (2005a) performed an eye tracking version of the SHJ study with the 32[4] structure family and found evidence in support of the selective attention optimality assumption. However, in arriving to their conclusions, these researchers studied only four out of the six structure types in the family and only tested one instance of each structure type in the family.In this study, we comprehensively investigated all six structures for the first time from the standpoint of eye tracking behavior and did so more thoroughly by examining more than one instance per structure. First, we found that the learning difficulty ordering of the 32[4] structure family is: I < II < [III, IV, V] < VI, when the dimensions of experimental stimuli are separated with the distributed representation. There was a statistically significant improvement from the first to the second instance, regarding the classification behavior. Second, we found evidence that participants used the selective attention mechanism during the concept learning and categorization process by examining participants’ eye tracking performance (e.g., number of dimensions fixated, dwell time, saccades, similarity of scanpaths, etc.). In addition, we observed that individuals tend to use the decreasing pattern of attention allocation during the classification task. Third, we compared the degree of similarity of scanpaths in different structure types, and found that there were statistically significant differences among the types III, IV, and V structures, regarding participants’ scanpaths. Last, the fitness of two leading categorization models (i.e., the Generalized Context Model (GCM; Nosofsky, 1984, 1986) and Generalized Invariance Structure Theory Model (GISTM; Vigo, 2013a, 2014)) was tested. The results showed that GCM and GISTM can account for 70.51% and 95.36% of the variance of the degrees of learning difficulty, respectively. In addition, the attentional weights predicted by the GCM were not consistent with the attentional distribution in the empirical data. However, the dimensional binding cognitive mechanism on which GISTM is based, was presented in all six structure types.

Human categorization performance has been studied using two fundamentally different empirical approaches: the “parainformative” approach and the “serioinformative” approach. Under the “parainformative” approach (Vigo, 2013), all objects in the target category are presented to participants for a certain amount of time before the classification phase begins (Feldman, 2000; Vigo, 2013; Vigo, Evans, & Owens, 2015; Vigo, Zeigler, & Halsey, 2013). In contrast, under the “serioinformative” approach, participants do not have prior knowledge of the target category. Instead, single object-stimuli from the target category are presented one at a time from the start, thereby forcing participants to gradually learn the associated concept on a trial by trial basis (Kruschke, 1992; Love & Medin, 1998; Nosofsky, Gluck, Palmeri, Mckinley, & Glauthier, 1994; Nosofsky & Palmeri, 1996). Both of these approaches have been used to test the robustness of the learning difficulty ordering of categories with four objects defined over three binary separable dimensions known as the “SHJ ordering” (Shepard, Hovland, & Jenkins, 1961). The corresponding category structures are called the SHJ category structures. Using the serioinformative approach, only Nosofsky and Palmeri (1996) studied these structures with integral dimensions. In their study, they found a learning difficulty ordering that was significantly different from the well-known SHJ ordering. The present study fills a gap in the extant literature by seeking to further understand how humans conceptualize and categorize the SHJ category structures involving integral dimensions using a parainformative approach, instead of using the serioinformative approach. It employed two different experiment methods for generating the dimensional values of stimuli—the multidimensional scaling (MDS) procedure and the Munsell Color System (MCS). To explore the different mechanisms of concept learning and categorization behavior when information is defined over separable dimensions and integral dimensions, two concept learning models were tested and compared to account for the data from the two experiments: the generalized context model (GCM; Nosofsky, 1984, 1986) and the generalized invariance structure theory model (GISTM; Vigo, 2013, 2014).

Due to spatial and temporal variations of environmental, loading conditions, material properties, and geometries of large-scale reinforced concrete (RC) structures, spatial reliability analysis of corroded RC structures is crucial to perform informed decision-making in maintenance, retrofitting and serviceability enhancement of existing infrastructure. In reality, the probability of collapse of the entire structure is much less than that of local failures that may require interruption or delay of service that may result in more substantial loses of opportunity costs. Therefore, precise maintenance and decision-making require estimations of local and spatial reliability in the level of components rather than in the level of structures. In this thesis, in order to overcome current challenges faced by the spatial reliability analysis of large-scale corroded reinforced concrete structures, first, analytical corrosion models and numerical simulations have been implemented to simulate initiation of corrosions, reductions of rebar diameters, corrosion-induced crack propagations, and eventually toward degradation of elastic moduli properties of RC structures. In the established analytical and numerical analysis, critical environmental and geometrical variables are modeled as spatially varying random fields to simulate uncertainty propagation and predict service life of structures according to the limit state functions defined based on reduction of rebar diameter, crack width and degradation of elastic modulus. As an example, this study uses the established analysis method to probabilistically predict the service life of a reinforced concrete slab subjected to corrosion-induced cracks. The results are analyzed and insights on probabilistic service life are provided. Also, the sensitivity of statistical parameters (mean, coefficient of variation etc.) for selected corrosion damage related spatially random variables on the service life prediction are examined. In addition, a new spatial reliability updating framework based on incomplete monitoring data is proposed in order to realize more accurate probabilistic service life prediction of structures during structure service period. In this proposed spatial reliability updating framework, a recently developed self-optimizing inverse parameter identification method (Stochastic SELF-OPTIM) is used to identify the material parameters of structure from the incomplete monitoring data. The pre-established analytical and numerical analysis model of corrosion-induced reinforced concrete degradation and the Bayesian updating method are also incorporated so that the spatial reliability of structure can be updated.

Abstract: Approximately 70% of patients infected with hepatitis C virus (HCV) develop chronic infection, which has been reported to be due to impaired specific T cell responses. Myeloid dendritic cells (mDCs) are potent antigen-presenting cells that regulate T cell responses, however their role during chronic hepatitis C (CHC) is not fully understood. My hypothesis was that the activity of mDCs to regulate T-cell response against HCV might be changed during CHC infection, and this change might contribute to the impaired T-cell responses that lead to the persistence of HCV infection. The objectives of my thesis were to compare the immunogenic activity (which stimulates T-cell proliferation), tolerogenic activity (which kills T cells), and apoptosis of mDCs from CHC patients and healthy donors. In this thesis, I found that mDCs from CHC patients expressed lower level of activating molecules, HLA-DR and CD86, compared to mDCs from healthy volunteers. When mDCs were cocultured with T cells, there were fewer T cells proliferating in the patient group than in the healthy group. This result indicated that the ability of mDCs to stimulate T cell proliferation was impaired in CHC patients. Moreover, mDCs from CHC patients underwent spontaneous apoptosis at a higher rate than mDCs from healthy donors. Nuclear factor-kappa B (NF-κB) activity, which is critical for mDC function and prevention of apoptosis, was diminished in mDCs from CHC patients. I further studied the tolerogenic activity of mDCs during CHC infection. mDCs from CHC patients expressed up-regulated levels of Fas ligand and the ligand 2 of PD-1 compared to mDCs from healthy volunteers. mDCs from CHC patients can kill T cells, while mDCs from healthy volunteers could not. This result indicated that the tolerogenic activity of mDCs was up-regulated in CHC patients. In conclusion, mDCs from CHC patients demonstrated functional changes with increased apoptosis, and diminished NF-κB activity. mDCs from CHC patients have impaired immunogenic activity to stimulate T-cell proliferation, and have up-regulated tolerogenic activity to kill T cells. These changes might be additional novel mechanisms of immune evasion by HCV, and contribute to the impaired specific T-cell responses observed in CHC patients.

This work combines the use of thio effects and site-directed mutagenesis (SDM) to characterize the catalytic mechanisms of phosphatidylinositol-specific phospholipase Cs (PI-PLCs). Eukaryotic PI-PLCs utilize Ca2+ in catalysis, whereas Bacillus thuringiensis PI-PLC (btPLC) uses a spatially conserved guanidinium group. A Ca2+-dependent mutant of btPLC was constructed and characterized to understand the functional differences between these two positively charged moieties. The following results indicate that a true catalytic metal site was created by a single mutation at position 69: (1) R69D was activated by Ca2+. (2) Titration of R69D with Ca2+, monitored by 15N-1H HSQC NMR, showed that addition of Ca2+ to R69D restores the environment of the catalytic site analogous to that attained by WT. (3) Upon Ca2+ activation, the SP-thio effect (kO/kSp = 4.4 E5) approached a value similar to that of WT, suggesting a structural and functional similarity between Arg69 and Asp69-Ca2+. (4) Results from additional SDM suggest that the Ca2+ binding site is comprised of side chains from Asp33, Asp67, Asp69, and Glu117. A natural occurring metal-dependent Streptomyces antibioticus PI-PLC (saPLC1) was cloned, expressed, purified, and characterized. The results enrich the knowledge in application of thio effect and provide useful mechanistic information for metal-dependent PI-PLCs: (1) WT has an extraordinarily high SP-thio effect (kO/kSp = 1.6 E8) in the presence of Ca2+. Substitution of Ca2+ by Cd2+ in WT enhances the activity toward SP-DPPsI by a factor of 400, but does not affect the activity with PI or RP-DPPsI, which are evident that the metal cofactor interacts with the pro-SP oxygen. (2) In the presence of Ca2+, the RP-thio effect of H16A (kO/kRp = 1.1) is lowered from that of WT (kO/kRp = 47). Ca2+/Cd2+ replacement in H16A dramatically increases the RP-thio effect (kO/kRp = 7.9 E3). Tentatively, these results suggest that both Ca2+ and His16 are involved in the interaction with the pro-SP oxygen. (3) WT and most of its mutants demonstrated small bridging thio effects (kO/kS = 0.5 ~ 2), whereas H55A displays an inverse thio effect (kO/kS) of 0.0019, implicating that His55 functions as the general acid in the phosphotransferase reaction. This work combines the use of thio effects and site-directed mutagenesis (SDM) to characterize the catalytic mechanisms of phosphatidylinositol-specific phospholipase Cs (PI-PLCs). Eukaryotic PI-PLCs utilize Ca2+ in catalysis, whereas Bacillus thuringiensis PI-PLC (btPLC) uses a spatially conserved guanidinium group. A Ca2+-dependent mutant of btPLC was constructed and characterized to understand the functional differences between these two positively charged moieties. The following results indicate that a true catalytic metal site was created by a single mutation at position 69: (1) R69D was activated by Ca2+. (2) Titration of R69D with Ca2+, monitored by 15N-1H HSQC NMR, showed that addition of Ca2+ to R69D restores the environment of the catalytic site analogous to that attained by WT. (3) Upon Ca2+ activation, the SP-thio effect (kO/kSp = 4.4 E5) approached a value similar to that of WT, suggesting a structural and functional similarity between Arg69 and Asp69-Ca2+. (4) Results from additional SDM suggest that the Ca2+ binding site is comprised of side chains from Asp33, Asp67, Asp69, and Glu117. A natural occurring metal-dependent Streptomyces antibioticus PI-PLC (saPLC1) was cloned, expressed, purified, and characterized. The results enrich the knowledge in application of thio effect and provide useful mechanistic information for metal-dependent PI-PLCs: (1) WT has an extraordinarily high SP-thio effect (kO/kSp = 1.6 E8) in the presence of Ca2+. Substitution of Ca2+ by Cd2+ in WT enhances the activity toward SP-DPPsI by a factor of 400, but does not affect the activity with PI or RP-DPPsI, which are evident that the metal cofactor interacts with the pro-SP oxygen. (2) In the presence of Ca2+, the RP-thio effect of H16A (kO/kRp = 1.1) is lowered from that of WT (kO/kRp = 47). Ca2+/Cd2+ replacement in H16A dramatically increases the RP-thio effect (kO/kRp = 7.9 E3). Tentatively, these results suggest that both Ca2+ and His16 are involved in the interaction with the pro-SP oxygen. (3) WT and most of its mutants demonstrated small bridging thio effects (kO/kS = 0.5 ~ 2), whereas H55A displays an inverse thio effect (kO/kS) of 0.0019, implicating that His55 functions as the general acid in the phosphotransferase reaction.