From this review, a FORTRAN code was developed that generates time and position dependent distributed loads based on linear wave theory for shallow water conditions. The routine was integrated into to the Abaqus finite element analysis framework, and used to evaluate the structural response of a representative bridge section impacted by tidal surge.

No description available.

The DLVO theory states that the interaction between two lyophobic particles in aqueous media can be predicted by the sum of two surface forces, i.e., the electrical double-layer and van der Waals forces. This theory, which was developed 50 years ago, served as a backbone for colloid chemistry. However, various experiments conducted in recent years showed that it is applicable only to those particles whose advancing water contact angles (qa) are in the range of 15-60o. For example, direct surface force measurements conducted between silica substrates, whose qa values are less than 15o, exhibited the existence of repulsive hydration forces at relatively short separation distances. On the other hand, substrates, for which qa is greater than 60o, exhibit long-range attractive hydrophobic forces not considered in the DLVO theory . These extraneous attractive forces play important roles in many industrial applications. It is, therefore, the objective of the present study to measure the hydrophobic and hydration forces under different conditions. The measurements were conducted using both the Surface Forces Apparatus (SFA) and the Atomic Force Microscope (AFM). Mica and Silica were used as substrates, and the effects of dioctylammonium-hydrochloride (DOAHCl), octanol, methanol, ethanol, trifluoroethanol (TFE), pyridine, CaCl2, MgCl2 and sodium oleate were studied. A Mark IV SFA was used to conduct force measurements between mica surfaces in aqueous solutions of DOAHCl, which is a secondary amine. At 7x10-6M DOAHCl, the mica surfaces were rendered electrically neutral, and net attractive hydrophobic forces were observed. The measured forces can be represented by a double-exponential function with the larger decay length (D2) of 5.1 nm. The measured hydrophobic forces are substantially stronger than those reported in literature between self-assembled monolayers of soluble single-chain surfactants such as dodeylammonium hydrochloride (DAHCl) and cetyltrimethylammonium bromide (CTAB). Appearance of the strong hydrophobic forces is due to the likelihood that the double-chain cationic surfactant can create a higher hydrocarbon chain packing density than the single-chain cationic surfactants such as DAHCl and CTAB. Force measurements were also conducted using the AFM between a silica plate and a glass sphere in aqueous solutions of methanol, ethanol, TFE and pyridine to study their effect on the hydration force. It was observed that in Nanopure water, silica surfaces exhibit a strong short-range hydration repulsion, which can be represented by a double-exponential function with its longer decay length (D2) of 2.4 nm. In solutions containing 15% methanol, however, the hydration force disappears completely. This observation can be attributed to the displacement of the water molecules H-bonded to the silanol group by methanol, which in turn destroys the water structure in the vicinity of the silica surface. Methanol can displace water from the silanol group because it is more basic than the water. Ethanol, on the other hand, cannot cause the hydration forces to disappear, suggesting that it is less effective than methanol in displacing the H-bonded water molecules from the silanol groups, possibly due to steric hindrance. In the presence of triflouroethanol (TFE) and pyridine, hydration forces change little, which suggest that they are not effective in disturbing the water structure in the vicinity of silica. Finally, an AFM was used to measure the hydrophobic forces between silica surfaces coated with oleate. Since this surfactant is anionic, and the silica surface is negatively charged in alkaline solutions, it was necessary to reverse the charge of the silica substrate. In the present work, CaCl2 and MgCl2 were used as activators. It was found that hydrophobic forces are observed at pHs where the CaOH+ or MgOH+ ion concentrations reach maximum, suggesting that the singly charged hydroxo-complexes are the activating species. A model developed in the proposed work suggests that a significant part of the free energy of adsorption comes from the lateral interactions between neighboring hydroxo-complexes on the surface. It is also suggested that oleate adsorbs on silica as basic calcium oleate and basic magnesium oleate. These species may be H-bonded to the silanol groups on surface. The force measurements were also conducted between hydrophobic (silanated) silica surfaces in CuCl2 solutions. The results show that the hydrophobic force decreases most significantly at the pH where the concentration of the CuOH+ ions reaches maximum, which suggests that the singly charged hydroxo-complexes are more surface-active than their unhydrolyzed counterpart. The driving forces for the adsorption of the CaOH+ ions may include the electrostatic attraction from the surface and the lateral interaction between neighboring hydroxo-complexes on the surface. / Ph. D.

Low back disorders (LBDs) comprise one of the major health issues in the United States. Previous research used isometric studies to understand the mechanisms that cause LBDs. Occupational tasks involving dynamic trunk movements, muscle fatigue, and spinal instability are identified as major risk factors for developing low back pain. Dynamic stability and muscle forces during trunk flexion-extension movements are studied in this dissertation. Torso muscle fatigue is known to affect the neuromuscular muscle recruitment that influences spinal stability. The first part of this dissertation investigates the effect of muscle fatigue on the stability of dynamic trunk flexion-extension movements. Participants with no self-reported low back pain history performed repetitive trunk flexion-extension exercises before and after extensor muscle fatigue. The extensor muscles were fatigued to 60% of their unfatigued isometric maximum voluntary exertion force. The maximum finite-time Lyapunov exponent, λ_Max, was used to quantify the dynamic stability. Values of λ_Max increased with fatigue, suggesting dynamic stability of the torso decreases with muscle fatigue. Fatigue-by-task asymmetry interactions did not influence spinal stability. The purpose of the second part of this dissertation was to predict time-dependent muscle forces and spinal loads during symmetric flexion-extension movements. A 2-dimensional sagittal plane, lumped parameter model was built with one thorax and five lumbar vertebrae stacked upon a stationary pelvis. Kinematics driven optimization was used to estimate time-dependent muscle forces. Muscle forces were determined by minimizing the metabolic power while satisfying the equations of motion. Spinal loads were calculated as the vector sum of the muscle forces and the trunk weight. Abdominal activity was observed at the onset of flexion and at the end of extension. The multifidus and psoas muscles played a major role in the spine dynamics. The compressive spinal loads were found to reach highest values at the onset of flexion, while the shear loads reached the highest values at large flexion angles. / Ph. D.

At the molecular level the entropic “hydrophobic effect” is responsible for high interfacial energies between hydrophobic solids and aqueous liquids, the low solubility of apolar solutes in aqueous solvents, and self-assembly in biological processes, such as vesicle formation and protein folding. Although it is known that a strong attraction between apolar molecules exists at the molecular level, it is not clear how this force scales up to objects with dimensions in the range 100 nm–1 m. This work sets out to measure the forces between particles with a radius of about 10 µm. Because we can only measure the total force, which includes the van der Waals force and the electrostatic forces, it is important to isolate the effect of “hydrophobicity”. We do this by measuring for systems where the particles are very hydrophobic (water contact angle, θ ~110°) and the van der Waals and electrostatic forces are very small. Under these conditions we find that the total force is very small: it is similar to the van der Waals force at separations exceeding 5 nm. Many early works on the hydrophobic force reported surface force at over 100 nm of separation. However, many of these strong, long-ranged attractive forces are likely caused by submicron interfacial bubbles, known as nanobubbles. Nanobubbles were imaged with an atomic force microscope to better understand their stability and dependence on solution properties, such as initial concentration of dissolved gas and changes in gas concentration. We found that nanobubbles still formed in degassed solutions and that lowering the dissolved gas concentration did not reduce the bubble size, implying that nanobubbles do not form from dissolved gas in the liquid phase or do not contain gas and are instead water vapor. Furthermore, addition of an oxygen scavenger agent, sodium sulfite, to a liquid phase that had been pressured with oxygen did not reduce bubble size which could be evidence that nanobubbles are impermeable to gas diffusion across the gas liquid interface, do not form from the dissolved gas in the surrounding liquid, or do not contain gas and are instead water vapor. / Ph. D.

Master of Arts / Department of History / David A. Graff / The central highlands of Vietnam were of vital strategic importance during the Second Indochina War (1955-1975); the collapse of South Vietnamese forces in this region in March 1975 led to the fall of Saigon just one month later. Despite this area’s importance, most central highlands historiography addresses large military campaigns, such as the 1972 Nguyen Hue “Easter Offensive” and the 1975 Ho Chi Minh Offensive. Micro-histories are of great value in examining the implementation of national programs, yet all province case studies examine events in the more heavily populated and ethnically homogeneous Saigon and Mekong Delta regions of the Republic of Vietnam (RVN). This thesis examines Lam Dong province, at the southern end of the Vietnamese central highlands. Focusing on the territorial forces initiative and RVN policy toward ethnic minority Montagnards in the highlands—two vital yet under-studied topics in Vietnam War historiography—this study demonstrates the operational success of the former and the strategic failure of the latter. The thesis is organized chronologically and concentrates on the final six years of the war, when South Vietnamese officials were increasingly promulgating and executing policy. The first part of the study details background information and outlines the war through 1967, when the National Liberation Front (NLF) held the advantage. The middle section scrutinizes the late 1960s and early 1970s and describes the factors that led to increased province security. The final section analyzes the final two years of the war following the departure of U.S. troops. In this period, South Vietnamese forces held the advantage against a weakened NLF, yet ordinary citizens’ discontent reached a climax. In-depth study of both province- and national-level documents from this period demonstrates that local officials, both American and Vietnamese, often attempted to address challenges but were hindered by the centralized nature of the Saigon bureaucracy. The inability and unwillingness of the RVN to address adequately issues such as highlands refugee policy led to the gradual dissatisfaction of many Montagnards in the highlands. This study elucidates RVN initiatives such as the territorial force, Main Living Area, and Return to Village programs—seldom-mentioned yet key facets of the Saigon government’s attempt to mollify ethnic tensions and counter the threat posed by the NLF.

Abstract Some gender scholars who have studied Western welfare regimes have argued that dominant cultural assumptions about women (ideational forces) should be examined in order to understand the development of these regimes. On the other hand, gender scholars working on Iran’s social policy argue that religious assumptions and institutions have shaped the position of women in Iran’s welfare regime. However, none of these researchers have thoroughly and explicitly examined the role of ideas in the development of Iran’s social policy. In contrast, this thesis studies the role of ideational forces in the formation of the only Iranian social assistance program designed exclusively for women, Empowering Women Without Guardians (EWWG). It also examines the connection of these forces to non-ideational factors in order to further elucidate their impact on policymaking. As argued, multiple cultural assumptions influence policymaking on women’s issues in Iran. Traditional cultural assumptions reinforce and legitimize the unequal position of women in society, whereas reformist and secularist ideas assume that men and women are equal. As claimed, the interaction of these assumptions with institutional and structural forces empowers some of these ideas over others at different stages of policymaking regarding the formation of EWWG: Iran’s laws (institutional forces) have reinforced previously dominant traditional assumptions about women (ideational forces) in the problem stream; in contrast, reformist interpretations of structural factors challenged previously prevailing traditional ideas and resulted in the adoption of a policy, which is more consistent with reformist and secularist ideas. The relative power of these assumptions helps explain both policy continuity and change in Iran’s context of policymaking on women’s issues.

Thesis (Ph. D.)--American University, 2006. / Includes bibliographical references (leaves 597-628).

This study is a conceptual analysis of power-sharing. It applies power-sharing in the context of Mozambique. The study is informed on the premise that components of power sharing contribute to the duration of peace. However, findings from empirical investigations show that certain types of power sharing are associated with more durable peace than others, primarily through their positive effects on governance and public service delivery. The specific objectives of the study were to contextualize the concept of military power sharing arrangement; to explore the challenges faced in implementing the military power sharing arrangement in Mozambique; to explore the strategies used to manage the Mozambique peace process; to ascertain the challenges faced by the BDF during the reintegration standardized training of FRELIMO and RENAMO forces; and to propose recommendations for future interventions. In order to achieve these objectives, the study used a purposive sampling technique to assemble participants that provided useful data for the study. The target population was made up of members of the Botswana Defence Force (BDF) who participated in the United Nations Peace Mission in Mozambique dubbed UNOMOZ; and those who conducted the reintegration standardized training of FRELIMO and RENAMO military personnel Thematic analysis of the participants’ responses from the interviews was used to address the objectives of the study. The findings of the study reveal that poorly trained military personnel were a challenge to the implementation of power sharing deal in Mozambique. Also, there was a lack of trust and confidence between constituent parties, and a lack of transitional authority in holding forth power until the power sharing deal was fully implemented. In addition, the study found out that there was the problem of language barrier, and that very little counselling was offered to those who were traumatized by the conflict. Also, there was a kind of unwillingness by civilians to accept former combatants in their midst and a lack of logistics for both the peace keepers and the combatants. Among others, the study recommended that NGOs, civil society organizations, and churches should be more pro-active in engaging the government and not only ensuring that every party involved in the power-sharing deal fulfills its role, but also organizing and carrying out counselling sessions for ex-combatants as part of reintegration process.

Doctorat en sciences sociales, politiques et économiques / info:eu-repo/semantics/nonPublished