Haematopoietic stem cells (HSCs) are capable of self-renewing and multi-lineage reconstitution of the haematopoietic system of irradiated recipient mice. In the mouse embryo, HSCs originate in a step-wise manner from the haematogenic endothelium. The first HSC precursor has been detected at E9.5 in the dorsal aorta, while HSCs emerge in the aorta-gonad-mesonephros (AGM) region around E11. To date, the molecular mechanisms regulating these events are poorly characterized. Through the activating role of Angiopoietin1 (Ang1) on Tie2 receptor, the Ang-Tie signalling pathway plays a critical role in HSC maintenance in the adult bone marrow niche. Tie2 ligand Angiopoietin2 (Ang2) is described as being a Tie2 inhibitor, however its role is unknown. The aim of this thesis was to characterise the role of Ang-Tie signalling pathway in HSC formation in the mouse embryo. First, I used an ex vivo aggregate system to culture with angiopoietins cells derived from the AGM region at stages of development preceding HSC formation (E9.5-E11). Ang2- treated cells were able to reconstitute the peripheral blood of recipient mice to a higher extent compared to control, indicating a role for Ang2 in promoting HSC maturation. Then, I characterized the expression pattern of Ang-Tie molecules in the AGM region. Ang2-expressing cells were identified as perivascular and sub-aortic mesenchymal cells located in the ventral side of the aorta and in proximity of intra-aortic haematopoietic clusters. Finally, I performed an RNA-seq analysis with the aim of unravelling the molecular mechanisms involved in Ang2-mediated HSC maturation. Pre-HSC-I were cultured in presence or absence of Ang2 and their transcriptional profiles were compared, revealing a number of genes and pathways up-regulated or down-regulated in presence of Ang2, which might indicate a role for Ang2 in increasing cell proliferation, favouring cell migration, and regulation of other signalling pathways involved in HSC development. All together, these data support Ang2 as a novel regulator for HSC formation.

Corrosion of reinforcing steel is a major problem facing infrastructures owners with billions of dollars spent in repairing our aging infrastructure. One of the first steps in the repair process is to quantify the strength degradation in a reinforced concrete element caused by the corrosion of reinforcing steel. An understanding of the forces involved in the load carrying mechanisms is imperative; the transfer of shear forces in reinforced concrete beams is one of these load carrying mechanisms. The shear transfer mechanism is different near the end of beams, adjacent to point loads, and near changes in cross section. These regions are known as disturbed regions. Structural engineers have a good understanding of the shear transfer mechanism in disturbed regions. However, the effects of corroded shear reinforcement in these regions have not been widely investigated. The current study is comprised of an experimental program and analytical strut and tie modeling aimed at quantifying the strength reduction that occurs in disturbed regions of reinforced concrete beams with corroded shear reinforcement. The feasibility of strengthening a beam with dry lay-up carbon fibre reinforced polymer (CFRP) to repair the damage caused by corrosion of the shear reinforcement was also investigated. In the experimental study, a total of 16 reinforced concrete beams were cast. The specimens were 350 mm deep, 125 mm wide and 1850 mm long. Three shear-span to depth ratios (1.0, 1.5, 2.0) were selected. Each specimen was reinforced in flexure with two 25M bars and the shear reinforcement was 10M spaced at 150 mm on centre. The specimens were corroded for 21 days, 60 days, and 120 days corresponding to low, medium, and high corrosion levels. In addition, three specimens were constructed without shear reinforcement in the shear-span in order to compare the results from the corroded specimens. One specimen was also corroded to a high level and repaired with dry lay-up CFRP. The specimens were corroded using an accelerated corrosion technique. There was evidence of cracking of the cover concrete in all specimens, and in the more severely corroded specimens delamination of the cover concrete was recorded. The stiffness of the corroded specimens was less than their corresponding control specimen, and a strength reduction was evident in most specimens. The maximum recorded strength reduction was 52% compared to the companion uncorroded specimen. It was revealed that a more critical case occurs when the corroded shear reinforcement was shifted during placement or was inclined closer to the direction of the compressive force flow. Also, it was observed that the corroded shear reinforcement still provides limited ductility in comparison to the un-corroded reinforcement. A strut and tie model was developed based on the experiments to explain the behaviour of disturbed regions with corroded shear reinforcement. The model consisted of direct and indirect struts. The effects of corrosion were expressed in terms of a reduction in the stirrup cross-section, a reduction of compressive strength due to corrosion cracking, and a reduction in the concrete cross section width. It was hypothesized that the corrosion crack width influences the concrete compressive strength in the strut; consequently, a mathematical model was developed that related the reduction in concrete compressive strength with corrosion crack width. Also, a relationship between reinforcing steel mass loss and corrosion crack width was utilized from the published literature. An effective cross section width was obtained by reducing the width by the damaged concrete cover. The results from these models were input into a strut and tie model as a reduction in concrete compressive strength. The output from the strut and tie model was the ultimate shear strength of the specimen. The developed models were compared with a model from the literature and compared with the experimental results. The major contribution of this research is to allow designers to analyze disturbed regions with corroded shear reinforcement and determine the strength degradation; subsequently, one can determine what strengthening procedure would be most appropriate.

Ultra-wideband (UWB) technology and its use in imaging and sensing have drawnsignicant interest in the last two decades. Extensive studies have contributed toutilize UWB transient scattering for automated target recognition and imagingpurposes. In this thesis a near-eld UWB synthetic aperture radar (SAR) imagingalgorithm is presented.It is shown with measurements and simulation, that it is possible to reconstruct an imageof an object in the near eld region using UWB technology and SAR imaging algorithm.However the nal SAR image is highly aected by unwanted scattered elds at each pixelusually observed as an image artifact in the nal image. In this study these artifactsare seen as a smile around the main object. Two methods are suggested in this thesiswork to suppress this artifact. The rst method combines the scattered eld informationreceived from both rear and front of the object to reconstruct two separate images, onefrom rear view and one from front view of the object respectively. Since the scatteredelds from behind the object are mirrored, the pixel by pixel multiplication of thesetwo images for objects with simple geometry will cancel the artifact. This method isvery simple and fast applicable to objects with simple geometry. However this methodcannot be used for objects with rather complex geometry and boundaries. Thereforethe Range Point Migration (RPM) method is used along with the global characteristicsof the observed range map to introduce a new artifact rejection method based on thedirectional of arrival (DOA) of scattered elds at each pixel. DOA information can beused to calculate an optimum theta for each antenna. This optimum angle along withthe real physical direction of arrival at each position can produce a weighting factor thatlater can be used to suppress the eect of undesired scattered elds producing the smileshaped artifact. Final results of this study clearly show that the UWB SAR accompaniedwith DOA can produce an image of an object free of undesired artifact from scatteredeld of adjacent antennas.

Corrosion of reinforcing steel is a major problem facing infrastructures owners with billions of dollars spent in repairing our aging infrastructure. One of the first steps in the repair process is to quantify the strength degradation in a reinforced concrete element caused by the corrosion of reinforcing steel. An understanding of the forces involved in the load carrying mechanisms is imperative; the transfer of shear forces in reinforced concrete beams is one of these load carrying mechanisms. The shear transfer mechanism is different near the end of beams, adjacent to point loads, and near changes in cross section. These regions are known as disturbed regions. Structural engineers have a good understanding of the shear transfer mechanism in disturbed regions. However, the effects of corroded shear reinforcement in these regions have not been widely investigated. The current study is comprised of an experimental program and analytical strut and tie modeling aimed at quantifying the strength reduction that occurs in disturbed regions of reinforced concrete beams with corroded shear reinforcement. The feasibility of strengthening a beam with dry lay-up carbon fibre reinforced polymer (CFRP) to repair the damage caused by corrosion of the shear reinforcement was also investigated. In the experimental study, a total of 16 reinforced concrete beams were cast. The specimens were 350 mm deep, 125 mm wide and 1850 mm long. Three shear-span to depth ratios (1.0, 1.5, 2.0) were selected. Each specimen was reinforced in flexure with two 25M bars and the shear reinforcement was 10M spaced at 150 mm on centre. The specimens were corroded for 21 days, 60 days, and 120 days corresponding to low, medium, and high corrosion levels. In addition, three specimens were constructed without shear reinforcement in the shear-span in order to compare the results from the corroded specimens. One specimen was also corroded to a high level and repaired with dry lay-up CFRP. The specimens were corroded using an accelerated corrosion technique. There was evidence of cracking of the cover concrete in all specimens, and in the more severely corroded specimens delamination of the cover concrete was recorded. The stiffness of the corroded specimens was less than their corresponding control specimen, and a strength reduction was evident in most specimens. The maximum recorded strength reduction was 52% compared to the companion uncorroded specimen. It was revealed that a more critical case occurs when the corroded shear reinforcement was shifted during placement or was inclined closer to the direction of the compressive force flow. Also, it was observed that the corroded shear reinforcement still provides limited ductility in comparison to the un-corroded reinforcement. A strut and tie model was developed based on the experiments to explain the behaviour of disturbed regions with corroded shear reinforcement. The model consisted of direct and indirect struts. The effects of corrosion were expressed in terms of a reduction in the stirrup cross-section, a reduction of compressive strength due to corrosion cracking, and a reduction in the concrete cross section width. It was hypothesized that the corrosion crack width influences the concrete compressive strength in the strut; consequently, a mathematical model was developed that related the reduction in concrete compressive strength with corrosion crack width. Also, a relationship between reinforcing steel mass loss and corrosion crack width was utilized from the published literature. An effective cross section width was obtained by reducing the width by the damaged concrete cover. The results from these models were input into a strut and tie model as a reduction in concrete compressive strength. The output from the strut and tie model was the ultimate shear strength of the specimen. The developed models were compared with a model from the literature and compared with the experimental results. The major contribution of this research is to allow designers to analyze disturbed regions with corroded shear reinforcement and determine the strength degradation; subsequently, one can determine what strengthening procedure would be most appropriate.

Online group-buying is one of the popular online business models recently. Both the initiator and participants hope to recruit more consumers to join order to aggregate larger orders and thus get cheaper price. Traditionally, consumers always invite their friends or families to join group-buying in order to collect more orders. Hope the relationship could affect their behavior. As the communication and coordination through the Internet are getting more convenient, it is easy and popular to recruit friends in larger range to join group-buying via e-mail. Further, the increasing virtual communities result from that, members have same interest, concern, and needs. It is quite possible that the members have same needs and therefore initiate a group-buying activity to fulfill many members¡¦ needs. Since information sharing is a major activity between members of virtual communities, the degree of the interactions will impact the tie strength between them. If members can send peer-to-peer recommendation email to other members who may be interested in the group-buying transaction, it may improve the group-buying performance. In addition, marketing via e-mail is getting common. The different marketing appeal results in different effect. Rational appeals focus on product itself while emotional appeal makes consumer¡¦s feeling change. The purpose of this research is to explore the difference in advertisement attitude between consumers clicking the peer-to-peer recommendation e-mail and consumers not clicking it. We also examined if these two groups have different cognition of tie strength with the e-mail sender. The result shows the group clicking the recommendation mail has better advertisement attitude than the group not clicking. Further, emotional appeal induces the subjects¡¦ better cognition of reliability of the appeal

This study examines the effects of social tie strength, value fit and affect-based trust of overseas workers on their cultural knowledge acquisition in foreign countries. Based on the assumption that cultural knowledge is acquired through social interactions, the research model encompassed 3 social-related independent variables and tested empirically from 536 interpersonal relationships reported by 136 respondents. The results revealed that social tie strength and value fit have positive impacts on cultural knowledge acquisition not only directly but also indirectly, through the mediation role of affect-based trust. However, the mediation effect differs between relationships with local nationals and relationships with non-local nationals. Specifically, affect-based t rust is essential for the effect of social tie strength to local nationals instead of that to non-local nationals; moreover, the mediation effect is sufficient on value fitted non-local nationals but is incomplete on value fitted local nationals. The implications of the findings and the need for future research were also discussed.

Tie-down systems are used to fasten drilling rigs to the deck of offshore structures during harsh environmental conditions such as hurricanes. During Hurricane Ivan (2004) and Katrina (2005), a number of offshore structures were moved and several tie-down systems were damaged. In the present study, the reaction force and connection capacity of tie-down systems for a TLP and SPAR are investigated. The environmental conditions are taken from the API Bulletin 2INT-MET which has been updated after several major storms during 2004-2005. The hydrodynamic coefficients of the TLP and SPAR are obtained using a 3D diffraction/radiation panel method. The motions of the TLP and SPAR are then simulated in the time domain by using the hull-mooring-riser coupled dynamic analysis tool CHARM3D. Based on the simulated motion and acceleration time series, the inertial and gravity loads on derrick and skid base footing are calculated. In addition to the inertial-gravity loads, wind forces exerted on the derrick are also calculated. All the external forces and resultant hull motions are simulated for 100-year, 200-year and 1000-year storms to observe the derrick structural integrity with increasing environmental intensity. Various environmental headings are also considered to find the maximum reaction forces. In the present method, the phase differences between gravity-inertia forces and wind forces are taken into consideration to obtain more realistic loads on derrick and skid base footings. This research shows that the maximum and minimum load values are appreciably higher for the SPAR. In addition, the direction of external forces is also important to determine maximum reaction forces on footings. The capacities of the clamps in slip, bolt tension, and bolt shear can be also analyzed using the resultant data to provide guidance on appropriate design values.

A compatibility-based strut-and-tie model C-STM is proposed for analyzing deep beams and disturbed regions with particular emphasis on reinforced concrete bridge piers. In addition to the normal strut-and-tie force equilibrium requirements the model accounts for non-linear behavior through displacement compatibility using inelastic constitutive laws of cracked reinforced concrete. The model is implemented into widely used commercial structural analysis software and validated against results from previously conducted large scale experiments. A near full-scale experiment on a reinforced concrete sub-assemblage that represents cantilevered and straddle pier bents is conducted to investigate the shear-flexure performance of deep (disturbed) regions. Insights into the development of nonlinear behavior and the final collapse failure mechanism are then evaluated and accurately modeled using the C-STM. It is concluded that the proposed C-STM serves as an advanced method of analysis that can predict with suitable accuracy the force-deformation response of both D- and B- regions, deep beams, and beam-columns. This provides engineers with a supplementary analysis tool that can be used to assess the nonlinear behavior of bridge piers with stocky members and/or large disturbed regions.

Most of previous word of mouth studies focused on marketing and consumer behavior issues. However, for job applicants, word of mouth could be a significant reference when applicants are looking for jobs. The present study tried to find out if word of mouth will influence organizational attractiveness perceived by potential applicants and under what situations related to word of mouth have the stronger effect. Hence, the study examined if the impact of word of mouth and if these impacts are moderated by the situational variables of tie strength with presenters and expertise of presenters and moderated by individual-difference variables of self-monitoring, self-esteem, and risk-taking. Results indicated that word of mouth has significant impact on organizational attractiveness. The moderation effects of potential applicants¡¦ tie strength with presenters, expertise of presenters, and self-esteem are also supported.

Building upon Granovetters well-known study of the job search behaviors of white males, this research extended the degree to which his findings apply across cultures to Chinese minorities, and across time to the Internet age. Using quantitative and qualitative data collected through systematic observation, questionnaire surveys, and in-depth interviews, this research investigated the impact of culture, Internet usage, gender and age on the communication patterns of foreign-born Chinese jobseekers in the U.S. It is found that jobseekers adopt either one or a combination of traditional (printed publications and direct application), institutional (the Internet, job fairs, and employment agencies), and personal (personal network) approaches. Within the institutional approach, the Internet job search strategy is a rsing preference among younger jobseekers. Through the personal approach, jobseekers enjoy four benefits of personal networks: information, trust building, position creation, and job market expansion. Across culture, guanxi, the Chinese version of the personal network is compared and contrasted with its American counterpart. Further, Granovetters argument about the strength of weak ties holds true in todays Internet age. Job-leading weak ties are usually those infrequently contacted professional and social connections working in targeted organizations at the time of a job search. Meanwhile, Chinese jobseekers mainly encounter six obstacles in the U.S.: racial discrimination, cultural obstacle, linguistic obstacle, insufficient network, immigration background, and an intercultural communication gap.