The strontium ruthenate Sr3Ru2O 7 is a strongly correlated electron system with intriguing electronic and magnetic properties. Though structurally similar to the widely studied unconventional superconductor Sr2RuO4, its properties are quite different: its ground state appears to be close to a ferromagnetic instability. Moderate applied magnetic fields can induce a metamagnetic transition into a ferromagnetic-like state, defined as a superlinear rise in magnetization at a given value of applied field; there is good evidence that this transition is a zero-temperature quantum phase transition with features distinctly different than ordinary phase transitions. We have taken three avenues towards better understanding the electronic and magnetic properties of Sr3Ru 2O7 and its behavior under magnetic fields: single particle tunneling, doping with nonmagnetic Ti impurities, and critical current measurements of a Sr2RuO4-Sr3Ru2O7 intergrowth Our tunneling measurements reveal an unusual oscillation in tunneling magnetoresistance under applied magnetic fields. This behavior is unexpected within our existing understanding of Sr3Ru2O7, and likely indicates the presence of an unusual surface state on this material. Our studies of Ti doped Sr3Ru2O7 suggest that the ground state of this material is characterized by competing short-range ferromagnetic and antiferromagnetic interactions; nonmagnetic Ti impurities appear to alter the band structure in such a way to reduce the antiferromagnetism, leaving the system in a state dominated by 2D ferromagnetic fluctuations. Finally, our studies of the Sr2RuO4-Sr3Ru 2O7 solid mixture suggest that large regions of Sr3 Ru2O7 may become superconducting when intergrown in this fashion; this finding may also shed light on the pairing mechanism of the unconventional superconductor Sr2RuO4 These three approaches to studying the ground state of the itinerant metamagnet Sr3Ru2O7 reveal the great diversity of electronic and magnetic properties possible in this material. In addition to confirming key issues related to the magnetic ground state, our results suggest several new directions for further study of Sr3Ru 2O7 and related strontium ruthenate materials / acase@tulane.edu

The goal of this research is to study the structural transitions in self-assembled surfactant systems and the use of such systems for materials synthesis. The anionic surfactant AOT, when contacted with an acidic phenol at a stoichiometric ratio in a non polar solvent, spontaneously forms an organogel. This system, mainly intervened by hydrogen bonding between the phenol and the surfactant, is strictly organic with low water tolerance. The organogel consists of entangled fibers when formed in the bulk. This dissertation explores the process of gel growth and presents a method to generate straight, unidirectional, densely packed gel fibers. The use of the organogel as a reverse template to synthesize porous polymerized divinylbenzene films is also discussed A second study describes the addition of a series of phenols of different hydrophobicities to a solution of CTAB micelles, which alters the shape of the surfactant assemblies from spherical micelles to elongated micelles, discs and later vesicles at progressively higher phenol concentrations. These different surfactant assemblies are exploited as templates for inorganic silica synthesis to create novel nanostructured phenolic silica composites. The shape changes of the surfactant assemblies have tremendous implications on membrane selection and design for micellar enhanced ultrafiltration A preliminary cryo-SEM study of a rigid AOT+Lecithin surfactant mesophase formed in isooctane is also presented. This surfactant mesophase allows incorporation of significant amounts of water and transforms from hexagonal columnar structure to lamellar structure as the water content is progressively increased. Through cryo-SEM, several interesting microstructural features of the surfactant mesophase are reported / acase@tulane.edu

Adult mouse digit tip regeneration is a level specific response. After amputation, the P3 phalangeal element, which is composed of the most distal phalangeal bone, the nail, soft connective tissue in between and the ventral skin, can regenerate back into a functional digit tip. The P2 phalangeal element, which is the tissue associated with the phalangeal bone immediate behind P3, cannot regenerate after amputation and, instead undergoes a wound healing response and forms scar tissue. Fibroblasts have long been implicated as the cell population that both bears positional information and constitutes a potential cell source that can be reprogrammed. In order to understand the different functions of fibroblasts in a regenerative event and a non-regenerative event, we designed a series of experiments to compare fibroblasts from the regenerative site (P3) and the non-regenerative site (P2) using in vitro culture models and in vivo regeneration models In the first chapter, we isolated P3 and P2 fibroblasts and characterized them as distinct progenitor populations that carry positional information and also share some stem cell characteristics. We also established a cell engraftment method to introduce labeled P3 and P2 fibroblasts into the mouse digits. Using engraftment, we learned that both P3 and P2 fibroblasts can participate in the adult P3 level digit blastema in vivo, and both failed to promote regeneration at the P2 level. The first chapter introduces the idea that the wound environment, rather than the intrinsic properties of the cell, is a major factor in determining whether regeneration occurs or not. In the second chapter, we further investigated the participation of P3 and P2 fibroblasts in the P3 level regeneration response by evaluating their survival and differentiation. P3 cells showed better survival and differentiation than P2 cells both in engraftment and during regeneration. Thus, even though the environment plays a major role in regeneration, the cells maintain intrinsic properties that affect their responsiveness to the local environment during a regeneration event. In the third chapter, we further introduced both P3 and P2 fibroblasts into a P2 level neonatal BMP2 induced regeneration model to test whether they would participate in endochondral ossification. We found that while both P3 and P2 fibroblasts were recruited by SDF-1 chemotaxis, neither cell type differentiated into chondrocytes. Instead they interfered with the endogenous endochondral ossification event by competing for the space where endogenous cells should be recruited. The data suggests that recruitment itself is not the answer to promote regeneration, but recruiting the right population is The experimental approach is based on the current knowledge of stem cell biology and cell therapy. The detailed fundamental comparisons based on proliferation, survival and differentiation set a good standard in promoting cell therapy based regenerative medicine. The results suggest that in order to fully utilize the cell population in regenerative medicine, we must learn the balance between intrinsic properties of the cell and influences from the environment / acase@tulane.edu

The purpose of the present study was to examine the impact of approach and avoidant coping strategies on the relation between exposure to Hurricane Katrina-related trauma (defined as either degree of exposure or subsequent disruption) and symptoms of posttraumatic stress disorder (PTSD). In addition, the differential importance of these coping strategies based on developmental level was also examined. Participants included 690 predominantly Caucasian females in grades eight through twelve at a private school in St. Tammany Parish, Louisiana. Regression analyses indicated that high approach coping served as a protective-stabilizing factor for younger adolescents but as a risk factor for older adolescents exposed to hurricane-related trauma. For younger adolescents, low avoidance coping appeared to be more adaptive and was related to less PTSD symptoms, while higher avoidance coping appeared to be a risk factor related to higher PTSD symptoms (although less so at higher levels of trauma exposure). For older adolescents, low avoidance coping served as a protective factor while high avoidance coping served as a significant risk factor for PTSD symptoms. With regard to trauma disruption which followed Hurricane Katrina, for younger adolescents low avoidance coping seemed to be a protective factor while high avoidance coping appeared to be a risk factor for PTSD symptoms. Finally, for older adolescents, both high and low avoidance coping was related to increasing PTSD symptoms, however lower avoidance coping was related to fewer PTSD symptoms. Overall, findings revealed that the impact and aftermath of Hurricane Katrina posed a significant risk factor for PTSD symptoms for those affected by this disaster. In addition, various coping mechanisms appeared to function differently depending upon the age of the participant in impacting the relation between trauma exposure and PTSD symptoms / acase@tulane.edu

This research project focused on the synthesis of a small library of linear and branched (1→3-beta-D-. beta-Glucans, isolated from various microorganisms, are polysaccharides composed of anhydro-D-glucose units joined together by beta-glycosidic linkages. In addition to linear beta-(1→3)-linkages, glucans can also be branched with side chains of varying length via beta-(1→6)-glycosidic bond along the backbone. beta-Glucans are known as biological response modifiers (BRMs) and they have attracted great attention in recent years as non-specific immune stimulants with low toxicity. However, the results of physiological studies can sometimes give contradictory results mainly due to purification difficulties and the lack of structurally well-defined, pure glucans. Therefore, a synthetic strategy for the production of structurally well-defined glucans is still in great need Recently, we utilized the C-2 acyl protecting group 4-acetoxy-2,2-dimethylbutanoate (ADMB), as the neighboring participation group in making beta-glucosyl linkages with high diastereoselectivity. Using a stepwise synthetic strategy with a disaccharide acceptor as the reducing terminus, reiterative glycosylation with a disaccharide donor (linear or branched with C-2 ADMB ester) and selective deprotection of the C-3 silyl ether, we have successfully prepared a small library of linear and branched glucans. During the course of this work, we have obtained a single crystal of a fully protected linear hexasaccharide. By the X-ray structure of the hexasaccharide, we are able to explain the abnormalities of the 1H NMR. Also, we have employed a convergent block-wise approach to synthesize a linear hexadecasaccharide by using an 8 + 8 glycosylation / acase@tulane.edu

Carbon-carbon double and triple bonds are very common in organic chemistry whereas the multiple bonds between silicon atoms are rare. Much of our knowledge about simple disilynes like dimethyldisilyne and diphenyldisilyne are based on theoretical calculations. The obstacles that prevent the synthesis and observation of simple disilynes are (i) the existence of a more stable isomer (for example in the case dimethyldisilyne, the dimethyldisilavinylidene isomer) (ii) the small energy barriers for isomerization, (iii) their intrinsically high reactivity. Therefore the generation of these simple disilynes is a great challenge and of great value for silicon chemistry. Reactive laser ablation coupled with molecular beam techniques is a powerful tool to study this type of highly reactive species. Potential precursors to the generation of disilynes are highly strained bis(silirane)s (Me4C2SiR)2 A series of strained three membered substituted bis(silirane)s (Me 4C2SiR)2 (where R = tert-butyl, Me, Ph) were synthesized. The tert-butyl substituted bis(silirane) has conformational rigidity in solution in contrast with its methyl and phenyl analogs which was observed by the appearance of four distinct methyl groups of the silirane ring in its 1H and 13C{ 1H} NMR spectra. This is consistent with a high rotational barrier of 30 kcal/mol along the Si-Si bond as determined by density functional theory calculations Preliminary laser ablation experiments on the tert-butylsubstituted bis(silirane) suggested that tBuSi≡Si tBu as well as a four membered cyclic disilene Me4C 2(SitBu)2 could be gas-phase intermediates An interesting silirane Me4C2Si(SiMe2Ph) 2 was synthesized, to investigate its decomposition pathway since it may form either the bis(dimethylphenylsilyl)silylene (Me2PhSi) 2Si: and tetramethylethylene or the cyclic silylene (Me2C) 2Si: and Me2PhSiSiMe2Ph. This silirane photochemically as well as thermally extrude the (Me2PhSi)2Si: quantitatively. The extruded silylene was intercepted with triethylsilane, trimethylmethoxysilane and bis(trimethylsilyl)acetylene The reaction of CH3(SiPcnBu8)Cl with KC8 or alkali metals to generate Wurtz coupling product CH 3(SiPcnBu8)2CH3, a cofacial phthalocyanine dimer with a direct Si-Si bond was studied. The failure of this reaction was studied by examining the electrochemistry and spectroelectrochemistry of CH3(SiPcnBu8)Cl. The failure of this compound to undergo reductive coupling is attributed to the stability of the anions produced by reduction / acase@tulane.edu

Surface properties of various single-crystalline SnO2 surfaces were studied and the growth of palladium was investigated in the low-coverage regime. Metal - oxide structures play an important role in microelectronics and nanotechnology. They are also widely used in catalysis. Small catalytically-active metal particles on metal oxide substrates are key features in the gas sensing mechanism: they dramatically increase the sensitivity and selectivity of solid-state gas sensors towards target gases. Tin Oxide is widely used in solid-state gas sensors for detection of combustible and toxic gases. Its sensitivity and selectivity strongly depends on catalytic dopants, such as Pd or Pt, on the surface of the material. Thus, the characterization of Pd growth on tin oxide may give new insights into the catalytic and gas sensing mechanisms, and also help to understand fundamental steps that lead to various metal-on-oxide growth modes Upon deposition of Pd onto the reduced (101) surface of a SnO2 single crystal, 1D cluster growth was observed. Starting from very low coverages, one-dimensional Pd clusters grow on the terraces, which indicates that the Pd wets the reduced tin oxide surface. Pd deposition on the oxidized surface results in randomly distributed three-dimensional Pd clusters. The clusters are distributed at step edges and on terraces without any apparent preferential adsorption sites The one-dimensional clusters are imaged in scanning tunneling microscopy (STM) as straight, parallel nanostructures oriented along the [-101] direction, all with the same characteristic width of 0.5 nm and a height of 1 monolayer (ML). X-ray photoelectron spectroscopy (XPS) experiments show no sign of Pd oxidation; i.e. Pd grows as a metal. There is a 0.5 eV shift in the Pd 3d 5/2 core level peak position to lower binding energy that occurs during the initial stages of the growth on the reduced surface. This is an indication of charge transfer from the Pd clusters to the substrate. Coverage-dependent Ultraviolet Photoelectron Spectroscopy (UPS) spectra show that, at submonolayer Pd coverages, a Pd 4d-derived peak appears at the same position (3eV from Fermi edge) in the band gap as the Sn surface state and shifts towards the Fermi edge as coverage increases. Angular resolved photoemission data of the valence band of the clean reduced SnO2 surface and the Pd dosed reduced surface shows a strong correlation between the Sn 5s derived surface state and the Pd 4d state. The position, as well as the shape of Pd 4d peak closely follows the position and the shape of the 5s derived Sn peak in both low-index directions. This is a sign of a strong electronic interaction, hybridization between Pd 4d and Sn 5s derived states Scanning tunneling microscopy experiments on a clean, reduced SnO 2 (100)-(1x1) surface reveal surface defects with zero, one, and two dimensions. Point defects consist of missing SnO/SnO2 units. Line defects are probably crystallographic shear planes that extend to the surface and manifest themselves as rows of atoms, shifted half a unit cell along the [010] direction. Their ends act as preferential nucleation sites for the formation of Pd clusters upon vapor-deposition. Submonolayer coverages of Pd deposited on the reduced surface at room temperature by vapour deposition result in the formation of three-dimensional clusters nucleating on the terraces. Areas of a more reduced surface phase, i.e. elongated 'holes', observed at the surface after annealing to higher temperatures, still with a (1x1) structure and a half-unit-cell deep, form at [001]-oriented step edges Recently, the use of nanobelts and nanoribbons has been suggested as novel materials for gas sensing applications. The large surface-to-volume ratio of the semiconducting metal oxide nanobelts and the congruence of the carrier screening length with their lateral dimensions make them highly sensitive and efficient transducers of surface chemical processes into electrical signal The surface morphology of an individual nanobelts (NB) was studied with STM. Atomically resolved STM images of NBs reveal an 1x1 (101) SnO2 structure on the top surface of the NB. To the best of the author's knowledge, this is the first atomically resolved STM image of SnO2 nanobelts. The thermal stability of the NBs was studied with SEM. The critical temperatures were determined, where structural changes occur in UHV, O2, and air. XPS was used to characterize chemical composition and monitor the cleanness of the NB material. Ca and C contamination was detected on as-grown SnO 2 nanobelts. O plasma, ozone treatment, and annealing in oxygen were used to remove the contaminants / acase@tulane.edu

This dissertation is devoted to the study of the question of stable equivalence. That is, given two nonhomeomorphic topological spaces X and Y, does there exist some integer k > 0 such that the products X x Rk and Y x Rk are homeomorphic. In the case of closed manifolds M and N it is a known result that there exists a k ≥ 0 such that M x Rk and N x Rk are homeomorphic if and only if M and N are tangentially homotopy equivalent (i.e. there is a homotopy equivalence f : M → N such that the pullback of the stable tangent bundle of N is the stable tangent bundle of M). Therefore, given two tangentially homotopy equivalent manifolds M and N, we ask: what is the least value of k ≥ 0 such that M x Rk and N x Rk are homeomorphic? Qualitatively, we describe results to such an optimal value question in terms a concept called tangential thickness, loosely defined to be the least k ≥ 0 such that M x Rk and N x Rk are homeomorphic. In our analysis, we will consider the tangential thickness of spherical spaceforms; manifolds of the form S n/G for G a finite group acting freely on Sn. If the group action is linear, we call the resulting manifold a linear spherical spaceform. If the group action is nonlinear, we call the resulting manifold a fake spherical spaceform. Specifically, we will consider the case of quaternionic spaceforms in which the group G is the generalized quaternion group First, we shall show that the tangential thickness of linear quaternionic spaceforms is 3. In the case of fake quaternionic spaceforms, one can have varying thicknesses. Thus, we shall classify those fake quaterionic spaceforms with tangential thickness 1, 2 or 3. We shall also prove the existence of fake quaternionic spaceforms with tangential thickness ≥ 4 / acase@tulane.edu

Porous silica, carbon, titania and carbon/silica composite micro- or nano-materials have been synthesized by the templated self-assembly approaches through an aerosol-assisted process or hydrothermal technique Porous silica particles with controllable hierarchical pore structure (from hexagonal to lamellar or hierarchical) have been prepared through tuning the hydrophilic and hydrophobic balance among silicate, cetyltrimethylammonium bromide (CTAB), and hydrophobic poly(propylene oxide) (PPO, H[OCH(CH 3)CH2nOH) additives during a dynamic aerosol-assisted process Aerosol-assisted self-assembly of hollow silica microspheres with microporous shell (HSMMS) are prepared by utilizing the block copolymer F127's aggregating behavior in basic solution and the self-assembly between silicate and amphiphilic tetrapropylammonium hydroxide (TPAOH) molecules. Interactions of TPAOH with both F127 and silicate are necessary for avoiding the phase separation between silicate and F127 aggregates because of the lack of hydrogen bonding interactions. Therefore, F127 aggregates with various sizes act as the core template while TPAOH molecules or TPAOH aggregates formed by excessive TPAOH molecules stay in the silica shell. Removal of F127 and TPAOH by solvent extraction results in the HSMMS materials Mesoporous carbon/silica composite with both meso- and molecular ordering has been synthesized by carbonization of as-synthesized phenylene/silica/surfactant hybrid by co-assembly of BTEB and Pluronic surfactant P123. Removal of silica from carbon/silica composite results in the mesoporous carbon which retains some of the meso-ordering and has many worm-like pores due to silica dissolution. This mesoporous carbon has potential applications in such field as hydrogen storage, catalysis, and other areas Hollow carbon microspheres with micropores in the shell and carbon nanotubes on the outer surface have been prepared using resols as the carbon precursor and hydrophobic PPO additives as template. An aerosol process with the heating temperature of 1000°C and an intermediate carbonization process result in the carbon material with the aforementioned structure Mesoporous titania materials with anatase wall are synthesized templated by nano-sized colloidal silica in an aerosol-assisted process. And titanate nanosheets are also obtained by treating materials with concentrated NaOH solution / acase@tulane.edu

This thesis presents trajectory-tracking control of flexible-link robots, overhead cranes, and multiple mobile robots in formation. Firstly, a new model-based trajectory control is proposed for the control of one-link flexible robots. The proposed control guarantees asymptotic stability with all internal signals bounded. Next, a distributed-parameter dynamic model, consisting of two ordinary differential equations and one partial differential equation, is derived using the extended Hamilton's principle for a two-link rigid/flexible robot. A collocated trajectory-tracking control scheme is designed based on the distributed-parameter dynamic model. With only two joint actuators, the proposed control guarantees stability throughout the entire trajectory control and asymptotic stability at desired goal positions. The proposed control is free from the so-called spillover instability Secondly, a sliding-mode anti-swing trajectory control is proposed for overhead cranes with high-speed load hoisting. In association with a new anti-swing motion-planning scheme, the proposed control realizes a typical anti-swing trajectory control in practice, allowing high-speed load-hoisting motion and sufficient damping of load swing. Lyapunov stability theorem is applied for the stability analysis of all of the above theoretical results, and the effectiveness is evaluated with control experiments Thirdly, a new formation control scheme is proposed for a group of mobile robots based on multi-objective potential forces. The angle of the potential force, with respect to the global coordinate system, is used to generate trajectories for the navigation of a group of nonholonomic mobile robots. A smooth and continuous control law is designed to reduce the global orientation error asymptotically to zero while maintaining proper formation for a target configuration. Finally, a trajectory-tracking control is designed for a group of nonholonomic mobile robots in a virtually structured formation. A real-time trajectory modification scheme is presented such that the center of the mobile robots tracks a desired trajectory. Lyapunov stability theorem is applied as the mathematical design tool. Moreover, an obstacle avoidance mechanism is designed based on a formation controller such that a mobile robot can escape from concave-shaped obstacles / acase@tulane.edu