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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
571

Rock Salt vs. Wurtzite Phases of Co1-xMnxO: Control of Crystal Lattice and Morphology at the Nanoscale

Walsh, Sean 24 July 2013 (has links)
Diamond cuboid-, rhombohedron- and hexagon-shaped nanocrystals as well as branched rods of the solid solution Co1-xMnxO have been synthesized via a solvothermal synthetic route from manganese formate and cobalt acetate at elevated temperature. Rhombohedra and hexagons have dimensions no larger than 50 nm on the longest axis, rods have branches up to 150 nm long and cuboids grow up to 250 nm on a side. X-ray and electron diffraction and transmission electron microscopy analyses show that these nanoparticles are single crystals of wurtzite-type and rock salt-type Co1-xMnxO. Varying the surfactant, water and precursor ratios allows control of particle size, morphology and stoichiometry. Extending growth time at high temperatures (>370°C) leads to the disappearance of the wurtzite phase due to Ostwald ripening. Longer reaction times at temperatures between 345-365°C lead to more crystalline wurtzite-lattice particles. These results show that nanoparticle morphologies and crystal lattices arise from crystal growth and Ostwald ripening at different rates selecting for either small, smooth-surfaced wurtzite lattice particles or large, dendritically-grown rock salt lattice particles.
572

A Molecular Phylogenetic Study of Historical Biogeography and the Evolution of Self-Incompatibility RNases in Indian Ocean Coffea (Rubiaceae)

Nowak, Michael Dennis January 2010 (has links)
<p>A fundamental goal in the diverse field of evolutionary biology is reconstructing the historical processes that facilitated lineage diversification and the current geographic distribution of species diversity. Oceanic islands provide a view of evolutionary processes that may otherwise be obscured by the complex biogeographic histories of continental systems, and have thus provided evolutionary biology with some of its most lasting and significant theories. The Indian Ocean island of Madagascar is home to an extraordinarily diverse and endemic biota, and reconstructing the historical processes responsible for this diversity has consumed countless academic careers. While the flowering plant genus <italic>Coffea</italic> is but one lineage contributing to Madagascar's staggering floral diversity, it is representative of the common evolutionary theme of adaptive radiation and local endemism on the island. In this dissertation, I employ the genus <italic>Coffea</italic> as a model for understanding historical biogeographic processes in the Indian Ocean using methods of molecular phylogenetics and population genetics. In the molecular phylogenetic study of <italic>Coffea</italic> presented in chapter 2, I show that Madagascan <italic>Coffea</italic> diversity is likely the product of at least two independent colonization events from Africa, a result that contradicts current hypotheses for the single origin of this group. </p><p>Species of <italic>Coffea</italic> are known to exhibit self-incompatibly, which can have a dramatic affect on the geographic distribution of plant genetic diversity. In chapter 3, I identify the genetic mechanism of self-incompatibility in <italic>Coffea</italic> as homologous to the canonical eudicot S-RNase system. Baker's Rule suggests that self-incompatible lineages are very unlikely to colonize oceanic islands, and in chapter 4, I test this hypothesis by characterizing the strength of self-incompatibility and comparing S-RNase polymorphism in <italic>Coffea</italic> populations endemic to isolated Indian Ocean islands (Grande Comore and Mauritius) with that of Madagascan/African species. My findings suggest that while island populations show little evidence for genetic bottleneck in S-RNase allelic diversity, Mauritian endemic <italic>Coffea</italic> may have evolved a type of "leaky" self-incompatibility allowing self-fertilization at some unknown rate. Through the application of traditional phylogenetic methods and novel data from the self-incompatibly locus, my dissertation contributes a wealth of new information regarding the evolutionary and biogeographic history of <italic>Coffea</italic> in the Indian Ocean.</p> / Dissertation
573

Phenotypic and Genetic Diversity in the Sea Urchin Lytechinus Variegatus

Wise, Maria L. January 2011 (has links)
<p>Diversity in coloration is a common phenomenon in marine invertebrates, although the ecological significance of the diversity is often unknown. Patterns of geographic variability, particularly with respect to color phenotypes, are evident in many organisms and may provide visual evidence of natural selection. </p><p>This dissertation examined the geographic and genetic variability of color patterns and morphology of the sea urchin <italic>Lytechinus variegatus </italic>. This study had 3 objectives: 1) to describe and quantify phenotypic diversity--color and morphology--throughout the geographic range; 2) to determine the heritability of color in genetic crosses between individuals with similar and differing phenotype; 3) to assess the degree of genetic divergence between and within the regions and congruence between the phylogenetic mitochondrial COI data and color phenotypes seen in the field.</p><p>The distribution of color phenotypes in the field is highly variable across the geographic range which stretches from Beaufort NC to southern Brazil and throughout the Gulf of Mexico and Caribbean. Urchins in each of the 5 regions sampled (Beaufort, Gulf, Keys, Panama and Brazil) have a distinct phenotypic composition despite the presence of similar color morphs. The two regions at the extremes--Beaufort and Brazil--demonstrate the most homogeneous phenotypes, each with a single dominant color morph. The Keys has the most heterogeneous composition with all 14 color morphs present. Morphological diversity mirrors color diversity in being highly variable across the range. Urchins in Beaufort are significantly different morphologically from urchins in the central portion of the range, with thicker, flatter tests and longer more robust spines.</p><p>The heritability of color phenotypes and morphology suggests that genes rather than environment have a major role in color phenotype and patterning as well as morphology in test, spines and lanterns. F<sub>1</sub> and F<sub>2</sub> offspring of Beaufort and Tavernier Key crosses resemble the parental phenotypes in both morphology and color phenotype. Hybrids from crosses between regions have a mixed color palette and intermediate morphological characteristics. The crosses establish that in <italic>L. variegatus </italic>the white phenotype is a dominant autosomal trait and green and purple are recessive and co-expressed. Patterning of the test and spines is dominant to non-patterning. </p><p>Analysis of the mitochondrial COI gene in urchins from Beaufort, Gulf and Keys regions revealed two clades. Clade 1 composed exclusively of Keys urchins differed significantly (F<sub>ST</sub> = 0.89, <italic>P</italic> < 0.001) from Clade 2 composed of urchins from Beaufort, Gulf and Keys. Genetic differentiation within Clade 2 was zero, indicating that urchins in these regions are genetically identical. The genetic split between phenotypically indistinguishable Keys urchins suggests cryptic species. Genetic differentiation does not concord with phenotypic and morphological differentiation. No structure was detected with regards to color phenotype in either clade or region of origin in Clade 2.</p> / Dissertation
574

Single Nucleotide Polymorphism Analysis of the Metastasis Supressor RECK Gene Promoter and It¡¦s Clinical Significance

Wu, Nein-chi 09 August 2011 (has links)
Reversion-inducing cysteine-rich with Kazal motif (RECK) is a cell surface anchoring protein, which known for the ability to inhibit matrix metalloproteinases (MMPs) and participate in angiogenesis regulation. The inhibition of membrane type-1 matrix metalloproteinase (MT1-MMP), MMP-2, MMP-7 and, MMP-9 by RECK has been demonstrated. Our previous studies show that RECK expression is suppressed by Ras and Her-2/neu oncogene. In addition, oncogenic Ras activates downstream ERK signaling pathway to increase Sp1/HDAC promoter binding affinity which results in reduction of RECK gene transcription and increase of tumor progression and metastasis. From the clinical investigation, RECK expression is down-regulated in a number of cancer types. In breast cancer, RECK expression is associated with the prognosis of the patients. Recently, single nucleotide polymorphisms (SNPs) of RECK promoter have been suggested to be linked with survival rate and prognosis of breast cancer patients. Whether SNP of the RECK promoter has any effect on RECK expression and its clinical significance is still unclear. . In this study, we investigate -402 SNP at RECK promoter and find this SNP directly affects RECK expression through progesterone receptor binding. Additionally, we also address the -402 SNP in the sample collected from patients and analyze its association with clinicopathological parameters to clarify its clinical significance. Our results suggest that RECK SNP may be an valuable prognosis factor for breast cancer.
575

TARC Genetic Polymorphism and Expression in Kawasaki Disease

Lee, Chiu-Ping 08 September 2011 (has links)
Kawasaki disease (KD) is characterized by a systemic vasculitis of unknown etiology. More research indicates that KD is related to genetic. In 2003, Sekiya et al. studied the correlation of Th2-related genes and the KD in Japan. They found out that -431T allele would increase the concentration of Thymus and activation-regulated chemokine (TARC)/ CCL17 protein in serum by single nucleotide polymorphism (SNP) -431 C>T of chemokine TARC/ CCL17 operon 5¡¦-flanking region , which suggests that SNP has functionality. Therefore, this study explored the polymorphism and relationship between the regulation of chemokine of TARC/ CCL17 and KD. Firstly, we performed polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) to detect TARC/CCL17 -431 C>T genotype. Then enzyme immunoassay was used to detect TARC/CCL17 chemokine¡¦s expression. The results showed that the performance of TARC -431 C/T SNP, the alleles from KD patients with -431 T, were significantly less than the non-KD control group. It was observed that the -431 T alleles had a lower chance to occur in KD with aneurysms, but independent with coronary artery lesions (CAL). In addition, the acute stage of KD has a higher TARC protein expression, which gradually decreases during IVIG treatment period. However, the up-regulation of TARC protein may not be the direct consequence caused by the single nucleotide polymorphism of TARC -431 C>T.
576

The gene-gene interactions on IgE production from prenatal stage to 6 years of age

Chang, Jen-Chieh 22 August 2012 (has links)
Prevalence of childhood asthma in Taiwan has increased 9 times from 1.3% to 10-14% in the past 4 decades. Many studies worldwide have demonstrated that many genes in different chromosomes are implicated in childhood asthma in different ethnic populations. A growing body of evidence suggests that allergic sensitization could occur in perinatal stage and correlate to the development of childhood asthma. Epidemiological studies, however, indicate that prevalence of childhood asthma is much higher in developed countries than that in developing countries; and prevalence of childhood asthma in metropolitan area is higher than that in country sites. This suggests that certain genes can interact with the environmental factors in developed countries to promote the development of childhood atopic disorders. Interests are now increasing on what is (are) the real pathogenic gene-gene interaction(s) for childhood atopic disorders under influence of age, gender and environmental factors? In a large perinatal cohort study with 1,211 pregnant women and their offspring from the obstetrics and pediatrics of Kaohsiung Chang Gung Memorial Hospital, we analyzed 159 allergy candidate genes with 384 single nucleotide polymorphisms and showed that 14 genes over 22 somatic and X chromosomes risk to or protective from cord blood immunoglobulin E (CBIgE) elevation are different from those genes associated with IgE elevation in children under 1.5, 3 and 6 years of age (12, 15 and 12 genes, respectively). CX3CL1, IL13, PDGFRA and FGF1 polymorphisms were associated with elevated IgE at earlier ages (newborn, 1.5 and 3 years); HLA-DPA1, HLA-DQA1, CCR5 and IL5RA polymorphisms were associated with IgE production at 6 years of age. Further analysis by multifactor dimensionality reduction (MDR) developed from data reduction strategy, we found that there are interactions among innate immunity, adaptive immunity, and response and remodeling genes on IgE production begin in prenatal stage. For example, The gene-gene interaction among IL13, rs1800925, CYFIP2, rs767007 and PDE2A, rs755933 was significantly associated with IgE production at 3 years of age. This suggests that different genotypes of genes interact one another on the IgE production contributing to the development of allergic diseases. Since the concentration of IgE is an important indicator of atopic disorders and allergic sensitization, we believe after clarifying the natural course of the genomic profiles on IgE elevation, certain early predictor(s) and preventive regimens for allergic sensitization or atopic disorders may be made possible.
577

Molecular and Genetic Analysis of Adaptive Evolution in the Rare Serpentine Endemic, Caulanthus amplexicaulis var. barbarae (J. Howell) Munz

Burrell, Anna Mildred 2010 August 1900 (has links)
In the interest of understanding the genetic basis of adaption to environment, we developed F2 lines from an F1 interspecific cross between the rare serpentine endemic, Caulanthus amplexicaulis var. barbarae and the non-serpentine Caulanthus amplexicaulis var. amplexicaulis. Using genomic DNA from Caulanthus amplexicaulis var. barbarae, we developed a suite of microsatellite markers. In addition, we developed gene specific markers for genes known in Arabidopsis to be ecologically important. Our suite of markers was used to genotype 186 F2 plants, the basis for our F2 linkage map. In order to further resolve evolutionary relationships among related taxa, we constructed a molecular phylogeny for 52 taxa within the related genera Caulanthus, Guillenia, Sibaropsis, Streptanthella, and Streptanthus, using the sequences from the ribosomal ITS region and two chloroplast regions. To create a useful system to enable comparative genomics within the related taxa of the ecologically and morphologically diverse Streptanthoid Complex, we demonstrated that our molecular tools are portable across a large group of ecologically significant taxa. To use the significant genomic resources available in Arabidopsis, we constructed a collinear comparative map of Caulanthus and the model plant Arabidopsis thaliana based on ancestral linkage blocks with the Brassicaceae family. This comparative map acted as a guide for candidate gene selection in the mapping of sepal color. We identified a region of MYB transcription factors in an orthologous region of Arabidopsis. Sequence data from Caulanthus amplexicaulis var. barbarae and Caulanthus amplexicaulis var. amplexicaulis in this MYB region showed significant sequence divergence between the two taxa. To determine the genetic basis for the tolerance of high concentrations of magnesium in Caulanthus amplexicaulis var. barbarae, we phenotyped multiple individuals from 88 F2:3 families under two nutrient treatments, differing in the ratio of calcium to magnesium. Through QTL analysis, using our F2 linkage map as a framework for the analysis, we identified one major effect QTL on Caulanthus Linkage Group 8 and another QTL on Caulanthus Linkage Group 3. We identified candidate genes for the QTLs using our collinear comparative map to Arabidopsis.
578

Crystallization Behavior of Syndiotactic Polystyrenes

Su, Chiou-Huen 20 July 2004 (has links)
Reported is a study of the crystallization behavior of syndiotactic polystyrene (sPS) and its copolymers (with 4-bromostyrene as the comonomer or with atactic polystyrene arms grafted on the comonomer sites) via three sets of experiments. The first involves the study of structural identification of negatively birefringent spherulites by means of polarized light microscopy (PLM) and scanning electron microscopy (SEM). Results indicated that the optically positive and optically negative spherulites have same morphological features. Differences in the optical texture are due entirely to differences in orientation of the (anisotropic) sheaf-like precursors: the rigid nature of crystalline lamellae renders incomplete development of spherical symmetry even at the axialitic size of tens of microns. In the second part, we propose a modified approach for more precise determination of the Tm* value by taking advantage of the dual-mode distribution of crystalline lamellae in analyzing small-angle X-ray scattering (SAXS) profiles. This method should be generally applicable to other semi-crystalline polymers with dual-mode distribution in lamellar thickness. Results from wide-angle X-ray diffraction (XRD) suggest the presence of ?'-to-?" phase transformation at ca. 264 oC; no indications for the previously proposed ?-to-? transformation are identified. We therefore conclude that the ?' form is truly metastable; the ?"-form is the entropically favored high temperature phase (with Tm* = 300 oC) whereas the more ordered ?' phase (with Tm* = 288 oC) is enthalpically favored at lower temperatures. In the third set of experiments, identification of effects of copolymerization has been studied via a combination of PLM, differential scanning calorimetry (DSC), XRD, SAXS, and transmission electron microscopy (TEM). Results show that the equilibrium melting temperatures (determined via either Hoffman¡VWeeks or Gibbs¡VThomson plots) of the copolymers are significantly lower than that of the corresponding sPS homopolymer. The PLM observations indicate that the axialitic growth rates in copolymers are drastically lower than that of the corresponding homopolymer at comparable backbone length and supercooling. Both XRD and TEM results indicate preferred formation of the ?" phase upon melt crystallization in the bulk state; however, the ?" phase (instead of ?' phase that is the more commonly observed for sPS homopolymers in the bulk state) is dominant in thin films.
579

Determination Of Polymorphism Of Pgm, Hk, Pgi, And G6pd In Different Developmental Stages Of Honey Bee (apis Mellifera L.) And Its Relation With Pgm Activity And Glycogen Content

Yeni, Filiz 01 May 2010 (has links) (PDF)
In this study, three subspecies of Apis mellifera L. (A. m. caucasica, A. m. carnica, and A. m. syriaca) from different climatic regions were evaluated electrophoretically at ontogenetic level by means of four enzymes, namely Phosphoglucomutase (PGM), Hexokinase (HK), Phosphoglucose isomerase (PGI) and Glukose-6-phosphate dehydrogenase (G6PD). It is determined that only Pgm and Hk loci were polymorphic. Allele and genotype frequencies at Pgm locus changes seasonally whereas Hk locus does not exhibit seasonal variation. Within the scope of this study we investigated at which developmental stage shifting to heterozygotes prior to winter occurs. It is found that there is a seasonal fluctuation throughout the year in Pgm genotype frequencies at each developmental stage studied and correlated with enzyme activity and glycogen content. As the studied enzymes have crucial v roles in insect energy metabolism, results of this study provided further information about the relationship between carbohydrate metabolism and enzyme polymorphism of honey bees.
580

Dna Repair Genes, Xrcc3 And Rad51, Polymorphisms And Risk Of Childhood Acute Lymphoblastic Leukemia

Tanrikut, Cihan 01 January 2011 (has links) (PDF)
In this study, the role of two DNA repair genes, X-ray repair cross complementing group 3 (XRCC3) Thr241Met and Rad51 G135C polymorphisms were investigated in the risk of development of childhood ALL in Turkish population among 193 healthy controls and 184 ALL patients, by using PCR-RFLP technique. For XRCC3 Thr241Met polymorphism, the frequencies of both heterozygous and homozygous mutant genotypes were found to be higher in the controls compared to ALL patients (OR: 0.59, p = 0.02 / OR: 0.48, p = 0.02, respectively). In addition, either heterozygous (Thr/Met) or homozygous mutant (Met/Met) genotypes were significantly more common in the controls than the ALL patients (OR: 0.55, p =0.005). In case of Rad51 G135C polymorphism, no significant associations have been found with the risk of childhood ALL. Combination of XRCC3 heterozygote and Rad51 heterozygote genotypes increased the protective effect for risk of childhood ALL. (OR=0.35 / p =0.02). Combination of homozygote mutant genotype of XRCC3 with homozygote wild type genotype of Rad51 gave a highly statistically proved protective effect for the development of disease (OR= 0.36 / p= 0.004). To our knowledge, this is the first study showing the protective role of XRCC3 Thr241Met polymorphism either alone or in combination with Rad51 G135C variant on the risk of development of childhood ALL. In addition, interactions of these polymorphisms with non-genetic risk factors were investigated. Only in terms of paternal exposure, the heterozygote (Thr/Met) genotype for XRCC3 gene in children whose father exposed to cigarette smoke demonstrated a significant risk of 3.0 fold (p=0.05). Moreover, the frequency of Rad51 135C allele was determined for the first time in Turkish population. The frequency of the mutant allele was found to be very similar to that observed in other Caucasian populations.

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