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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.
1

Comparing various characteristics of oven-cured and field-cured prime coat materials applied to granular bases

Okuyucu, Osman 12 September 2014 (has links)
A prime coat is defined as a low-viscosity bituminous material such as cutback, asphalt emulsions, or polymer-based chemicals applied onto the surface of road bases in order to protect the base from the penetration of moisture into the base layer. Other functions of prime coat include (1) providing good adhesion between a granular base and the bituminous surface, (2) strengthening the surface of the base by binding the fine particles, and (3) sealing against any voids along the base surface in order to reduce water absorption. To achieve these functions, a prime coat should successfully penetrate the granular base and should cure fully. In this study, field-curing data on selected prime coats was collected during March 12th-18th, 2014 and April 12th-18th, 2014. Oven-curing data was also collected in a laboratory using an adjustable oven. Identical prime coats including the four most commonly used prime coats by TxDOT ((1) Cutback MC-30, (2) asphalt emulsions and cutback mixture AEP, (3) polymer emulsions EC-30 and (4) asphalt emulsions SS-1H and CSS-1H) and base materials were divided into the two types of testing environments, one field-cured, and one in an accelerated and controlled indoor, oven-curing environment. Once the specimens were fully cured, evaluation of the engineering properties of the specimens were carried out in order to determine if oven-cured specimens can be expected to exhibit the same engineering characteristics as the field-cured specimens. Evaluation of water absorption tests, indirect indicator of relative strength, and penetration tests were performed on all specimens for both field-cured and oven-cured specimens. Importantly, a comparison of these results shows the viability of using accelerated, laboratory curing procedures. Prime coat field-testing procedures will be suggested using oven-curing rather than field-curing, reducing the amount of time required for sample preparation. Prime coat testing could conceivably be completed in a single day due to the accelerated curing rates. This advantage would reduce cost and man-hours of new prime coat material testing. / text
2

Characterisation of a factor required for specific gene expression during Dictyostelium development

Gibson, Fernando January 1988 (has links)
No description available.
3

Thin film encapsulants for gallium arsenide

Abid, Adil R. January 1987 (has links)
The problems associated with the use of ion implantation during the preparation of compound semiconductors have been examined. In particular, the use of an encapsulant as protection during annealing was considered and the properties and ease of preparation of the ideal encapsulant were studied. Among the experimental techniques used to study the surface of thin film coatings on the semiconductors materials, reflection high energy electron diffraction (RHEED) was extremely useful in allowing the study of thin layers. Other techniques used in the work included scanning electron microscopy (SEM), Rutherford backscattering (RBS), rapid thermal annealing using a graphite strip heater and thin film deposition by evaporation and sputtering. Among the encapsulants studied were aluminium nitride and the zirconium nitride the former being the most important. A study was also made of the chemical reactivity of aluminium nitride to oxidation and hydration. It was found that AlN was resistant to oxidation in air up to about 1000°C and in an inert atmosphere up to at least 1400°C. It was shown that aluminium nitride reacts readily with water to form AlOOH. The reproducibility of a good quality evaporated AlN film as an encapusulant was found to be difficult to control, but a combination of AlN and Si[3]N[4] in a "sandwich" proved to be more successful. Zirconium nitride was found to be useful as a passivation layer up to 700°C. Sputtered AlN coatings seemed to offer the best hope of success but further work is needed to improve the sputtering techniques so that free Al, or Al[2]O[3] is not present in the AlN layers.
4

Exploring Caffeyl-Lignin Biosynthesis in Cleome hassleriana and Polymerization of Caffeyl Alcohol in Arabidopsis thaliana

Harkleroad, Aaron Djuanell 12 1900 (has links)
C-lignin (caffeyl-lignin) is a novel linear lignin polymer found in the seed coats of several non-crop plants, notably Vanilla planifolia (Vanilla), Jatropha Curcas (Jatropha), and Cleome hassleriana (Cleome). C-lignin has several advantages over normal G/S-lignin, found in the majority of lignocellulosic biomass, for valorization in the context of bioprocessing: less cross-linking to cell wall polysaccharides (less recalcitrant biomass), ordered linkages between monomers (homogeneous polymer), and no branching points (linear polymer). These properties make C-lignin an attractive replacement for native lignin in lignocellulosic biomass crops. The seed coats of Cleome hassleriana (Cleome) synthesize G-lignin during early seed maturation, then switch to synthesis of C-lignin during late maturation. This switch to C-lignin in Cleome seed coats is accompanied by loss of caffeoyl-CoA 3-O-methyltransferase (CCoAOMT) and caffeic acid 3-O-methyltransferase (COMT) activities, along with changes in transcript abundance of several lignin related genes. The focus of this research thesis is to understand the biochemical changes leading to C-lignin deposition in Cleome hassleriana seed coats, and to explore the ability of Arabidopsis thaliana seedlings to polymerize caffeyl alcohol to C-lignin. In this thesis, candidate transcripts were implicated in C-lignin biosynthesis by differential gene expression analysis of transcripts in seed coat tissues at 8-18 days after pollination (DAP) and in non-seed coat tissues. Three candidate genes were selected for recombinant expression and their in vitro kinetic properties were measured with potential substrates. Of the three candidates, a cinnamyl alcohol dehydrogenase (ChCAD5) was found to have high transcript levels during C-lignin formation and have a novel preference for converting caffealdehyde to caffeyl alcohol, the precursor of C-lignin. To determine if accumulation of caffeyl alcohol is sufficient for polymerization of C-lignin, Arabidopsis seedlings grown in a xylem induction system were supplied caffeyl alcohol. Polymerization of caffeyl alcohol was not found to occur in this Arabidopsis system, suggesting the need for a C-lignin specific polymerization mechanism.
5

Molecular biology of maize streak virus movement in maize

Liu, Huanting January 1997 (has links)
No description available.
6

Evaluation of traits associated with bucking bull performance and behavior

Romero, Natasha Elizabeth 15 May 2009 (has links)
Video and industry data were used to assess the inter-relationships of aggression, delivery, coat color, year of birth, number of outs, buckoff percent and score in rodeo bulls. An evaluation of laterality based on observations of how the individual animals were loaded into chutes at 11 bull riding events showed 63% left-handed delivery and 37% right-handed delivery across all observations (n = 525). There was a similar distribution for aggressiveness (based on whether or not the bull charged after the rider dismounted) with 64% of bulls being non-aggressive and 36% of bulls being aggressive. Significant linear relationships existed between score and number of outs and score and buckoff percentage indicating that experience impacted performance. The correlation between number of outs and buckoff percentage was low to moderate (0.06 to 0.30), depending upon the subset of data evaluated. The r-square value for the analysis of score among all bulls was 0.14; however, the r-square value in the subset of bulls with known sires with more than one son was 0.68 when sire was included in the model. Similar increases in r-square values were observed for 2006 average score, career average score, buckoff percentage, and career buckoff percentage, indicating important genetic influences on these traits and/or their component traits. Investigations into the relationship between performance and aggression may help bucking stock producers improve the selection criteria they use. The current trend within the industry is for several breeders to breed ‘hot’ or flighty, nervous cattle to achieve higher performing offspring. Given that there was no association between aggression and score based on chi-square test, aggression may be removed from the criteria for using certain animals for breeding purposes. Based on results from this work, if bucking stock breeders want to make genetic changes in these traits, documentation of pedigree information is vital.
7

Early Endocytosis Pathways in SSN-1 Cells Infected by Dragon Grouper Nervous Necrosis Virus

Liu, Wang-ta 23 January 2006 (has links)
Many fish undergo betanodavirus infection. To study the infection process of dragon grouper nervous necrosis virus (DGNNV), native virus and E. coli-produced virus-like particles (VLPs) were used to analyze the binding and internalization in SSN-1 cells. The binding of DGNNV and VLPs to SSN-1 cells was demonstrated using Western blotting and indirect enzyme-linked immunosorbent assay (ELISA). As estimated by ELISA, the DGNNV particles bound SSN-1 cells in a dose-dependent manner up to 8 ¡Ñ 104 particles per cell. The binding of VLPs was sensitive to neuraminidase and tunicamycin, suggesting that cell-surface sialic acid is involved in binding. The recombinant VLPs block attachment of native virus to the surface of cultured fish nerve cells, blocking infection by the native virus. It is suggesting that the outer shell of DGNNV VLPs is structurally indistinguishable from native virus. The penetration of DGNNV into cells, which was monitored by electron microscopy, appeared mainly to occur via the spherical pit and membrane ruffling pathways. Occasionally, a spherical pit was engulfed by membrane ruffling so as to form a large figure 8-shaped vesicle with an open connection. Our observations suggest that DGNNV utilizes both micro- and macro-pinocytosis pathways to enter SSN-1 cells. Both of nucleotide and amino acid sequences of MGNNV protein A were comparison with all of Nodaviridae members, revealed that MGNNV were most closely related to RGNNV. No correlation of sequences of betanodavirus with geographical habitat was detected. All thirteen nodavirus protein A amino acid sequences contained canonical RNA polymerase motifs in their C-terminal halves and conserved elements of predicted secondary structure throughout. By Phyre web server identification, the BVDV RdRp as the best template for fold recognition of the RdRp domain of MGNNV and allowed the construction of a congruent 3D model.
8

A Study on Seed Morphology of Melastomataceae in Taiwan

Huang, Yu-Feng 23 July 2007 (has links)
The seed external morphology and seed coat pattern of 11 genera and 22 species of Melastomataceae in Taiwan were studied by dissecting microscopey and scanning electron microscopey. According to the seed size, the result showed that the length and width of seed is different inter-generically. The biggest size is the seed of Memecylon while contrast to those of the other genera. The seed shapes could be divided into 8 types. They are liner-lanceolate, cuneate, fusiform, reniform, cochleate, triangular, obovoid and parallelogram respectively. Except that of the Sarcopyramis, the seed shape is rather stable intra-generically. The seed coat could be classified into 6 patterns. They are verrucate, rugose, smooth, tuberculate, granulate, and colliculate respectively. The seed colors are egg-yellow, brown, nut-brown and reddish brown. The difference of seed morphology is obvious inter-generically, and the difference of seed coat patterns is extinctive intra-generically.
9

Study of bond coats for thermal barrier coating applications

Chen, Ying January 2015 (has links)
Bond coats used in thermal barrier coatings (TBCs) for gas-turbine engine applications are studied in this thesis, with a focus on oxidation behaviour, surface rumpling and stress evolution. Bond coats made of γ/γ’ Ni-Al-Pt alloys have been widely used in TBCs and it has been found that addition of platinum greatly improves the oxidation resistance of the coatings. The mechanisms behind this benefit, however, are not well understood. For this reason, the oxidation behaviour of four γ/γ’ Ni-20Al-xPt (x= 0, 5, 10 and 15 at. %) alloys at 1150 °C is studied and compared in terms of oxide spallation, oxide microstructure and growth, residual stress in the oxide scale and oxide/alloy interface morphology. The progressive increase of platinum addition into the alloys results in (1) greater resistance to oxide spallation, (2) reduction in oxidation of nickel, (3) lower stresses in the α-Al2O3 scale and (4) more planar oxide/alloy interfaces. It is found that the selective oxidation of aluminium promoted by platinum plays a central role in the evolution of the oxidation behaviour of the alloys. Surface rumpling of a NiCoCrAlY bond coat deposited on a Ni-base superalloy during cyclic oxidation at 1150 °C is studied. The extent of rumpling is found to depend on thermal history, coating thickness and exposure atmosphere. While the coating surface progressively roughens with cyclic oxidation, bulk NiCoCrAlY alloys with the same nominal composition show a much less tendency to rumple under the same thermal cycling condition. The coatings, especially the thin ones, experience substantial degradation (e.g. β to γ phase transformation and exhaustion of yttrium) induced by oxidation and coating/substrate interdiffusion during thermal exposure. The observations together suggest that rumpling is driven by the lateral growth of the thermally grown oxide (TGO) and the coating deforms in compliance with the TGO. While the dependence of rumpling development on experimental conditions is generally in agreement with the prediction of the existing model, it is suggested that the degradation of the NiCoCrAlY coating and its dependence on coating thickness need to be taken into consideration when predicting the rumpling development of NiCoCrAlY coatings. The residual stresses in a NiCoCrAlY bond coat deposited on a Ni-base superalloy are studied by X-ray diffraction using the sin2Ψ technique. The stresses at room temperature are found to be tensile; they first increase and then decrease with oxidation time. The stress develops and builds up upon cooling, predominantly within the temperature range from 1150 °C to 600 °C. Due to the limited penetration depth into the bond coat, the X-ray only probes the stress in a thin surface layer consisting of a single γ-phase formed through aluminium depletion during oxidation. Above 600 °C, the volume fraction of the β-phase in the bond coat increases with decreasing temperature. The mechanisms of stress generation in the coating are examined and discussed based on experiments designed to isolate the contribution of possible stress generation factors. It is found that the measured bond coat stresses are mainly induced by the volume change of the bond coat associated with the precipitation of the β-phase upon cooling.
10

The influence of seed coat and cotyledon structure on cooking characteristics of cowpeas

Penicela, Luisa 29 June 2011 (has links)
Cowpea (Vigna unguiculata L. Walp) is an important legume mainly used for human consumption worldwide, particularly in developing countries. Cowpea legume is rich in protein (25%), carbohydrates (70%), dietary fibre, minerals and vitamins. Cowpea comprises a range of varieties that breeders release based primarily on agronomic characteristics, such as yield, early maturity and drought tolerance. However, consumers do not always adopt all the released cowpea varieties. Cooking characteristics such as cooking time and sensory properties (i.e. appearance, texture, flavour) of cooked cowpeas are believed to be quality characteristics for legume acceptability by consumers. Physicochemical characteristics are known to influence cooking characteristics of cowpeas. These characteristics may be influenced by seed coat and cotyledon structure. The present study focuses on the effect of seed coat and cotyledon structure on cooking and sensory characteristics of cowpeas and how this in turn influences consumer acceptability of cowpeas. The influence of seed coat thickness and cotyledon compactness on cooking characteristics of four cowpea types (thick seed coat/compact cotyledon (Bechuana White), thick seed coat/porous cotyledon (IT82E 18), thin seed coat/compact cotyledon (Black Eye) and thin seed coat/porous cotyledon (California Black) was studied. Seed coat thickness was found to influence water absorption during soaking. Cowpeas with thin seed coats had higher rates of water absorption during soaking due to its amorphous cell layer that rendered the seed coat more permeable compared to the palisade cell layer found in cowpeas with thick seed coats. Cotyledon compactness influenced cooking time of cowpeas. Cowpeas with porous cotyledons cooked faster compared to cowpeas with compact cotyledon probably because of the structural arrangement of porous cotyledon cells that provide more intercellular spaces for rapid water entry, cell expansion and separation favouring a faster cooking process compared to compact cotyledon. Seed coat and cotyledon structures directly influenced very few of the cooking and sensory characteristics. Sensory attributes such as cooked cowpea flavour, degree of sweetness, degree of sweet aftertaste, and degree of mushiness positively contributed to consumers’ liking of cowpeas. Raw cowpea flavour, bitter taste, degree of bitter aftertaste and degree of firmness contributed to consumers’ disliking of cowpeas. Chemical composition of cowpeas probably influences sensory characteristics of cowpeas more than seed coat and cotyledon structures. It is recommended that breeders work together with food scientists in order to release cowpeas types that are preferred by consumers (i.e. cowpeas with good appearance (low percentage of splitting), good flavour and soft texture upon cooking. Please cite as follows: Penicela, L 2010, The influence of seed coat and cotyledon structure on cooking characteristics of cowpeas, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-06292011-154445/ > E11/438/gm / Dissertation (MSc)--University of Pretoria, 2010. / Food Science / unrestricted

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