Within recent times there has been much interest generated in the area of high powered lasers and their interaction with materials. As a result, lasers are very well characterized for their industrial applications. However, when materials are subjected to intense levels of laser radiation beyond the range for controlled processing operations, complicated physical and mechanical phenomenon such as melting, vaporization, and electro-dissociation can occur. Failure prediction under such extreme loading conditions becomes an increasingly difficult task due to the rapid deposition of energy that occurs within the heat affected zone A cohesive zone model is developed to simulate the effects of laser irradiation on aluminum specimens that are simultaneously subjected to displacement controlled loading. However, the current interface cohesive element formulation is only applicable under isothermal conditions. In order to make these elements temperature dependent, a technique is developed in this study that allows the key parameters used in the constitutive model for defining the response of these cohesive elements, to be calibrated for the thermal field induced by a high powered CO2 laser / acase@tulane.edu

Writing is an intricate grapho-motor skill whose early attainment is fundamental to a child's future academic and occupational success. It has been posited that humans rely heavily on the perceptual medium of vision to plan and carry out writing activities. It has also been suggested that the development of early literacy skills, such as those necessary for reading (i.e. phonemic awareness and phonological processing) may impact the cognitive planning and motor execution of writing. In order to examine these positions, this study utilized eye-tracking technology to examine the eye-gaze behavior of 5 - 6 year-old kindergarten children and 19 - 33 year-old adults who completed a copying task. This task required participants to copy a series of single letters, real words, and nonsense strings from a visually presented stimulus onto a white board easel. To examine the cognitive planning of writing, the number of visual fixations made to the stimulus to be copied, current writing area, and future writing area were coded. Results indicate that when copying single letters, real words, and nonsense letter strings adults efficiently obtain the visual information necessary to copy the stimulus prior to beginning to write. Young kindergarten children only utilize this efficient method when copying single letters, while older kindergarten utilize the efficient method exhibited by adult writers for all stimuli. Additionally, the phonemic and phonological properties of the stimulus of be copied influenced the role of vision in the copying behavior of both children and adults. And lastly, this study revealed that both children and adults utilize online visual guidance more than prospective cognitive control to guide their writing actions / acase@tulane.edu

This dissertation presents original research into the melting process of a downward facing cryogenic solid hydrogen surface subject to a two dimensional axisymmetric jet impingement flow of superheated hydrogen vapor. The motivation for the study is to investigate concepts of storing rocket propellants as a solid and rapidly melting the solid for liquid propellant delivery to a rocket engine. The present study considers a more favorable liquid removal arrangement than prior (1970s) experiments which melted solid hydrogen at the bottom of a cryostat This is a numerical study that involves computation fluid dynamic (CFD) simulation of four distinct physical phenomena: (1) melting, (2) jet impingement heat transfer (JIHT), (3) multiphase transport, and (4) film breakup/droplet formation. The volume of fluid (VOF) method is used with the V2F turbulence model in a commercial CFD Navier-Stokes solver (FLUENT) to investigate the multiphase nature of melt transport and its interaction with the vapor stream; i.e., the phenomena relevant to effective heat transfer between the vapor and the melting interface. The goal of the research is: (1) to develop a numerical method to study the problem and (2) evaluate several simple configurations to begin investigating relevant phenomena for the purpose of enhancing melting rate. Many options exist for the vapor to interact with the solid surface. The scope of this initial research is limited to a steady jet of single phase superheated hydrogen vapor at fixed jet exit conditions (T = 525 R and Re = 11,000) at a fixed jet standoff ( H/D = 1.0). Condensation/vaporization are not considered. Although film breakup/droplet formation is a phenomenon where two dimensional features evolve into three dimensional events, this phenomenon is approximated as two dimensional to allow a computationally tractable problem for this initial study Calculations are performed validating the numerical method for melting and JIHT against known results. Validation of film breakup/droplet formation is cited in the literature. A numerical method is developed to model the four physical phenomena. Four simple configurations are evaluated and a fundamental understanding is obtained of the multiphase melt transport and vapor interaction / acase@tulane.edu

Opioids acting at the mu (morphine) receptor represent the vast majority of clinically used opioids and remain the most effective analgesics for treating moderate to severe pain. The use of morphine and similar compounds for the management of pain is limited by adverse side effects including respiratory depression, abuse potential, motor impairment and cognitive deficits. Novel mu opioid receptor agonists developed in our laboratory are based on the structure of the endogenous ligands (endomorphins) and provide potent antinociception. Studies from our laboratory indicate that these endomorphin (EM) analogs produce fewer adverse side-effects in rodents than morphine, including reduced respiratory depression, motor impairment, tolerance, and abuse potential. Recent studies have indicated that repeated injection of morphine, for as little as a few days, can induce glial activation, an inflammatory response that can led to a “paradoxical” morphine-induced pain (Watkins et al, 2005, 2007). Morphine is recognized by glia cells similarly to a foreign antigen via toll-like receptor 4 (Hutchinson et al., 2010; Watkins et al., 2009). Since endomorphin analogs are more similar in structure to endogenous peptides, we hypothesized that they would not be recognized by the immune system as pathogenic. In support of this hypothesis, our laboratory showed activation of microglia in the spinal cord after treatment with morphine, but not endomorphin analogs (Zadina et al., 2012). This may be of particular importance in the treatment of pain in patients already vulnerable to inflammation-induced pathologies, including during older adulthood and after traumatic brain injury (TBI). The focus of this project was to evaluate the cognitive effects of morphine and endomorphin analogs using aging and TBI models. Morphine impaired cognition after both acute and chronic drug administration but EM analogs did not, despite equal or greater duration of antinociception relative to morphine. Chronic studies using young, middle-aged, and old rats revealed that middle-aged rats were more susceptible to cognitive deficits caused by morphine than younger or older rats. Likewise, morphine exacerbated cognitive deficits produced by TBI. Electrophysiology experiments revealed that morphine altered hippocampal long-term potentiation to a greater extent than an EM analog. Immunohistochemistry of the hippocampus indicated that astrocytes are activated after treatment with morphine, but not an EM analog. In TBI studies, morphine treatment led to a reduction in the number of neurons in the dentate gyrus despite an increase in volume, which may be due to increased glial activation. Thus, EM analogs may serve as safer analgesics as indicated by several models, and differential effects of morphine and EM analogs are likely mediated, in part, by alterations in glial activation. / acase@tulane.edu

The endomorphins are peptides isolated from the brain with high affinity and selectivity for the mu opioid receptor (MOR) (Nature 386:499, 1997). At least two paradigms illustrate differences in the effects of endomorphin-1 (Tyr-Pro-Trp-Phe) (EM1) and morphine. In contrast to morphine, the respiratory and cardiovascular effects of EM1 are not reached at doses capable of inducing antinociception (Czapla et al., 2001). In addition, at antinociceptive doses, morphine was shown to produce conditioned place preference (CPP), while EM1 did not (Wilson et al., 2000). These findings indicate that compounds similar to EM1 may (1) produce a different profile of effects at the MOR and (2) provide a favorable 'therapeutic ratio' of analgesic action relative to unwanted side effects such as respiratory depression and reward Because native peptides are rapidly degraded, a series of endomorphin analogs were synthesized in this lab. One of these compounds, a cyclized (c) D-lysine (k)-containing analog of EM1 (Tyr-c[DLys-Trp-Phe]) (ck1/CYT-1010), showed higher affinity than the parent EM1 and morphine for the MOR. In addition, it showed greater selectivity for the MOR, relative to delta and kappa receptors, than morphine. ck1/CYT-1010 is being used in our laboratory as a tool to investigate differential actions of MOR agonists in paradigms where a peptide-based MOR agonist can show a profile of effects distinct from that of morphine This dissertation characterizes the dose-dependent antinociception induced by the analog after intracerebroventricular (ICV) injections, and its effects on reward. The metabolic stability of the analog enabled us to carefully match the antinociceptive effects of morphine and the analog across the time period of exposure to the CPP apparatus. This provides a conceptually valid comparison of the compounds for their antinociceptive properties relative to their rewarding potential. At doses of the analog and morphine that produced antinociception of virtually identical maximal effect and duration, morphine induced a significant place preference while the analog did not. Given that CPP has been correlated with abuse potential, our results show promise for the development of novel opioids with less abuse potential relative to morphine at equally effective analgesic doses / acase@tulane.edu

Cardiovascular disease is the leading cause of morbidity and mortality in developed countries and is the number one cause of death in the United States. Current treatments include drug therapy, gene therapy, surgical interventions, heart transplants, and tissue engineering. The goal of this dissertation was to combine the sciences of genetic and tissue engineering to create a three dimensional (3D) engineered construct with cardiomyocytes derived from genetically selected embryonic stem (ES) cells that could be used as an in vitro model to study the effects of mechanical and electrical stimulation on the differentiation of ES cells. To investigate this, two custom devices were built to deliver precise, reproducible, and long-term mechanical and electrical stimulation regiments to the constructs To optimize construct constituents and test the efficacy of these devices. 3D scaffolds containing HL-1 cells were studied. These experiments showed that an optimal ratio of cells and ECM proteins (0.2 mg collagen, 0.01 mg fibronectin, and 6 x 106 cells) was necessary to create constructs with the structural integrity necessary for use in the devices. Also, the mechanical loading device was shown to be efficacious by encouraging cellular alignment with distinct sarcomeric structures, development of dense cell boundary layers and homogeneous cell distributions throughout the construct's central regions Parallel experiments using constructs containing ES cells revealed that 0.4 mg collagen, 0.01 mg fibronectin and 6 x 106 cells were optimal. These experiments led to the discovery of a synergistic relationship between mechanical and electrical stimulation. A sequential regiment of electrical stimulation, followed by mechanical loading, resulted in the most significant switch from the expression of fetal genes (alpha-skeletal actin and beta-MHC) to adult cardiac genes (alpha-cardiac actin and alpha-MHC). Also, these constructs contained myofiber like structures, organized sarcomeric structures and distinct gap junctions similar to those found in the native neonatal heart This dissertation takes steps toward the development of a 3D model of the developing heart using a renewable cell source embedded in a defined ECM scaffold and exposed to mechanical and electrical stimuli, and provides the experimental foundation for those developing alternative treatments for those suffering from heart disease / acase@tulane.edu

Rodents rely on spatial learning and memory to efficiently navigate a complex environment. Distinct brain areas mediate different types of spatial learning strategies. The hippocampus-dependent place strategy utilizes spatial cues in the environment to guide the rodent to a goal, while striatum-dependent response and stimulus-response strategies rely on proprioceptive cues or cues proximal to a goal, respectively, to guide the rodent to a goal. The spatial strategy employed to learn a task is influenced by a range of factors including biological sex, age, and anxiety. Previous reports have found that high levels of natural, or trait, anxiety tend to bias prepubertal male rats towards a stimulus-response learning strategy. The effect of reduced transient, or state, anxiety on spatial strategy preference in prepubertal rats is yet to be determined. In the present study, an anxiolytic agent, diazepam, was administered to prepubertal male rats to determine its effect on expression of anxiety-like behaviors on an open field test and spatial learning strategy preference on a visible platform water maze (VPWM) task. Prepubertal male rats treated with a low dose of diazepam (2.5 mg/kg) displayed reduced anxiety in comparison to prepubertal male rats treated with vehicle or a high dose of diazepam (5 mg/kg). A separate sample of prepubertal male rats treated with vehicle displayed a significant preference for a stimulus-response learning strategy as reported previously, while males treated with either a low or high dose of diazepam displayed no spatial learning strategy preference. Taken together, these results support previous findings that higher levels of anxiety bias prepubertal male rats towards a stimulus-response learning strategy, indicating that reduction of anxiety shifts strategy preference away from a stimulus-response learning strategy. / acase@tulane.edu

The blood and lymphatic vascular systems coordinate to play critical roles in tissue fluid homeostasis and immune function and are fundamentally associated with diseases including inflammation, wound healing, edema, and tumor progression and metastasis. Their coordination during vascular growth and remodeling represents an under-investigated area of research in which a better understanding will provide insights into future therapeutic approaches. Angiogenesis and lymphangiogenesis are the growth of new blood or lymphatic vessels, respectively, from pre-existing vessels. The comprehensive goal of this work was to provide a new perspective on the relationships between angiogenesis and lymphangiogenesis in microvascular networks and develop tools needed to probe the mechanisms involved in lymphatic/blood vessel patterning and identity. The first aim of this study was to characterize the spatiotemporal relationships between lymphatic and blood vessel growth in response to an inflammatory stimulus. We found that lymphangiogenesis temporally lagged angiogenesis during inflammation and that the presence of lymphatic vessels attenuated angiogenesis. We also identified increased lymphatic/blood endothelial cells connections and a novel lymphatic marker. These results motivated the need for a system to probe the multicellular and multisystem interactions suggested by these findings. Our lab recently developed the rat mesentery culture model as an ex vivo model for investigating angiogenesis in the context of intact microvascular networks. The second aim was to determine whether this model can be used to study lymphangiogenesis. We found that vascular endothelial growth factor C stimulated lymphatic sprout formation in the rat mesentery culture model and confirmed the ability to observe angiogenesis and lymphangiogenesis simultaneously in an ex vivo environment. This suggests the rat mesentery culture model can be used to investigate the dynamics of lymphatic/blood vessel patterning and plasticity motivated by our in vivo work. The final aim of this work was to investigate the ability to induce phenotypic plasticity in intact vasculature by using lysophosphatidic acid, an agonist suggested to cause blood-to-lymphatic endothelial cell transition. We demonstrated that while lysophosphatidic acid stimulated angiogenesis, it was not sufficient to reprogram blood vessels to acquire a lymphatic phenotype. These results underscore the necessity of investigating these multisystem relationships in the context of intact microvascular networks. These studies as a whole demonstrate the coordination that exists between blood and lymphatic vessels and reinforce the need for novel models that incorporate the complexities of the entire microvasculature. / acase@tulane.edu

Development of the mammalian female reproductive tract (FRT), including the oviduct, uterus, cervix and vagina, starts during embryogenesis and lasts after birth. This process requires orchestrated and complex interactions among molecules involved in signaling transduction, cell cycle regulation, apoptosis, and differentiation. As a sex organ, FRT development is also tightly controlled by hormones. Deregulation of endogenous hormones and/or ectopic exposure to synthetic hormones, particularly during critical developmental period, can cause a spectrum of FRT abnormalities from infertility to cancers in human. In this body of work, I used a well established mouse model to investigate the effects of estrogens, especially diethylstilbestrol (DES), on genetic pathways governing FRT development Neonatal DES exposure in the mouse resulted in suppression of uterine cell proliferation and apoptosis. Global gene profiling analysis of neonatal mouse uterus revealed many genes whose expression was perturbed by DES. Among them, small proline-rich protins, epidermal keratins and placental alkaline phosphatase were ectopically induced by DES in the uterine epithelium, indicating precocious differentiation of these cells. Msx2, a homeobox transcription factor, was identified as a key factor mediating estrogenic effects of DES on FRT development, since Msx2-/- uterus exhibited differential gene regulation and altered tissue responsiveness to DES compared to the wild-type controls. Birc1 genes, a family of anti-apoptosic genes, were identified as potential estrogen targets to suppress uterine apoptosis. These genes were potently induced by estrogens in an ER-alpha-dependent manner, and mutation of Birc1a led to incomplete apoptosis suppression in the uterine epithelium by DES. Not only is Msx2 involved in uterine responsiveness to DES, but it is also indispensable for normal FRT patterning. Msx2-/- vaginal epithelium showed abnormal cytostructure and altered gene expression. Mutation of Msx2 also hindered caudal Wolffian duct regression, possibly due to its pro-apoptotic function. As in the uterus, Msx2 appeared to counter-act the DES effects in the vagina, as mutation of the gene rendered the vagina more susceptible to DES. These results suggest the possibility that protective mechanisms exist in our body to dampen the effects of any environmental hormones that might influence development or physiology / acase@tulane.edu

There is a clinical need for large numbers of phenotypes which are suitable for tissue engineering and cell therapy applications. Pluripotent stem cells (PSCs) are readily expanded in vitro and can differentiate into any somatic phenotype, making them a potential cell source. However, generating clinically-relevant numbers of phenotypes requires culture in stir-based bioreactor systems which expose cells to shear stress. Here we use a parallel plate bioreactor as a surrogate model system to better understand the effects of shear stress on pluripotent embryonic stem cells (ESCs). Initial studies examined the impact of cell deformation by shear stress during early ESC differentiation. Shear-treatment regulated specification into the three germ lineages and promoted mesodermal differentiation. Next we examined the response to shear stress during later specification events. The application of shear stress was found to promote mesodermal differentiation towards both definitive hematopoietic and mature endothelial phenotypes, although delayed applications were less effective at promoting hematopoietic specification. The next studies used low oxygen treatment to study the impact of another differentiation cue in the presence and absence of shear stress. Hypoxia promoted mesodermal phenotypes but the response was highly dependent on the physical microenvironment such as the culture method and the presence of shear stress. The next group of studies examined the impact of shear stress on ESC expansion. ESCs expanded under flow conditions maintained pluripotency but mesodermal specification was regulated in a manner that was dependent on the presence or absence of a ROCK inhibitor. The final studies used small molecule inhibitors to determine the role of specific signaling molecules during the shear-mediated differentiation of ESCs. Although inhibition of ROCK had little effect, inhibition c-SRC, JNK, or ERK modulated the shear-response. These studies highlight the important effects of shear stress during PSC culture and increase the basic science understanding of stem cell regulation by the physical microenvironment. The systematic approach to analyze multiple parameters allows for an improved translation of techniques from the bench-top into large-scale bioprocessing systems. Altogether these studies can inform large-scale differentiation techniques and bioreactor design in order to help establish the cell banks needed for clinical applications. / acase@tulane.edu