Spectrophotometric methods of analysis

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Model electrodes for the electrooxidation of simple alcohols : a DEMS study

Pt is considered as a model for fuel cell electrocatalysts. In the present thesis, I stud-ied the electrooxidation mechanisms of methanol (chapter 3) and ethanol (chapter 4) on different Pt surfaces, using a dual thin-layer flow through cell combined with the mass spectrometer. In chapter 5, Ru quasi single crystal films on different bead Pt surfaces were formed using the resistive heating in a stream of nitrogen. The Ru films were exam-ined by cyclic voltammetry in sulfuric acid and by structure-sensitive underpotential deposition of Cu. Finally, in chapter 6, in order to use bead single crystal in the right ar-rangement (hanging meniscus) on DEMS, a new DEMS flow cell was manufactured and improved for that purpose. The electrooxidation of methanol proceeds via the dual pathway mechanism. The path involving the formation of soluble intermediates such as formaldehyde and formic acid is the direct pathway, while the dehydrogenation of methanol to adsorbed CO fol-lowed by its oxidation to CO2 is referred to as indirect pathway. Methylformate is one of the volatile products formed during the electrooxidation of methanol at Pt surfaces. In all previous articles it is assumed that methylformate formation results from the reaction of formic acid and the excess of methanol, i.e. the detection of methylformate is an indirect way to determine the amount of formic acid produced during the oxidation reaction. However, the probability of esterification reaction is very small because the fast diffusion of the soluble products away from DEMS cell under effect of continuous electrolyte flow. A simple kinetic study of methanol esterification and methylformate hydrolysis in acid media was performed since literature data for the rate of this esterification reaction were not available. The reaction rate constant of methylformate formation was found to be far too low (τ ≈ 40 h at 0.1 mol L-1 methanol), while the time constant of dual-thin layer flow through cell at 1.6 µL s-1 is 5 s. Methylformate therefore is directly formed during oxida-tion of methanol at the electrode surface and not in the solution phase as believed before, with a current efficiency about 1%. The suggested mechanism for methylformate formation, is the nucleophilic attack of adsorbed methanol with another methanol molecule from the solu-tion; note that the nucleophilic power of the oxygen in methanol is higher than that in the water molecule. The current efficiency with respect to CO2 and the surface coverage with methanol adsorbate (COad) have been shown to be independent of the electrolyte flow rate (from 1.6–30 µL s-1); this confirms the parallel pathway mechanism. Poisoning of the catalyst with adsorbed CO is one of the main problems in fuel cells. Ru as a catalyst with Pt promotes the electrooxidation of adsorbed CO according to bi-functional and the electronic mechanism. On such bimetallic surfaces, Ru is preferentially deposited at steps. Using deliberately stepped Pt surfaces as model electrodes, it could be shown that the complete coverage of the step sites with Ru has an inhibiting effect for methanol and ethanol oxidation due to the blockage of the most active sites, i.e. the free step sites are necessary for the first step of C1 and C2 alcohols adsorption and oxidation. For ethanol, the cleavage of C–C bond is the most difficult step in the complete oxi-dation of ethanol to CO2. Also ethanol electrooxidation at Pt surfaces occurs according to different pathways depending on the surface structure. During the electrooxidation under controlled convection, where there is no further oxidation of soluble products at the sur-face, acetaldehyde is the main product at polycrystalline Pt and Pt stepped single crystal surfaces vicinal to the (100) plane. Acetaldehyde is formed at these surfaces over the po-tential range with a current efficiency close to 100%. At Pt stepped single crystals vicinal to the (111) plane, the formation of acetic acid proceeds at lower potentials than that of acetaldehyde production due to the direct reac-tion between adsorbed ethanol and adsorbed hydroxide species. At higher potentials, due the blockage of the surface with adsorbed anions, e.g. acetate and sulfate, only the dehydrogenation of ethanol takes place at (111) planes to produce acetaldehyde. In practical applications, the formation of acetic acid should be avoided because of its inertness whereas, in principle, acetaldehyde can be oxidized to CO2. Therefore, it might be advantageous to use nanoparticles without a large degree of (111) facets as electro-catalyst in fuel cells. Another kind of model electrode would be Ru single crystals modified by Pt. How-ever, since Ru is oxidized by atmospheric oxygen very fast, the usual flame annealing method in air does not work. Attard and co-workers developed a new method for Ru quasi single crystal preparation by forced deposition of Ru multilayer on Pt single crystals followed by resistive heating in a nitrogen atmosphere. In order to characterize this Ru film on different Pt single crystals, Cu UPD is the suitable technique. For Pt(100), the charge density of Cu UPD stripping from Ru quasi-single-crystal electrode is in agreement with the charge density of Cu UPD stripping from clean Pt(100); this suggests the formation of an epitaxial Ru film on the Pt(100) electrode. For the Ru films formed on Pt(111) and Pt(110) surfaces, Cu UPD deposition is inhibited due to strongly adsorbed oxygen species. For Ru films deposited on stepped Pt single crystal vicinal to the (100) plane, it was found that: Because the characteristic Cu UPD stripping peak related to the free Pt sites is absent, the stepped Pt single crystal surfaces are completely covered with Ru film. The charge density for the peak at 185 mV related to Cu UPD stripping from (100) terrace sites decreases linearly with increasing the step density of the Pt single crystal substrate, which confirms the formation of epitaxial Ru films on the Pt surfaces. Preliminary results show that the deposition of a Pt sub-monolayer on the Ru film is pos-sible by galvanic replacement of Cu UPD. In order to be able to use bead single crystals in the hanging meniscus configuration, a new DEMS cell was constructed. The recorded cyclic voltammogrames for different bead Pt single crystals in supporting electrolyte, under hanging meniscus arrangement and at constant flow of electrolyte, are in agreement with literature profiles. This and the calibration constant and corresponding ionic signals for organic molecules oxidation sug-gest that this new cell is well suited for bead single crystals. Compared with the dual thin layer flow through cell, it has the advantage that cleanliness is easier achieved and that less expensive single crystals can be used. The K* values are reproducible and typical to that of the dual thin layer flow through cell under the same experimental conditions. For the electrooxidation of bulk methanol at polycrystalline Pt in the new flow cell, the current efficiency with respect to CO2 is high-er than that in the previous cell design. The reason might be the further oxidation of the soluble intermediates because of a less efficient electrolyte flow in the thin layer between the electrode surface and the glass capillary. Also, the ionic signal of methylformate is not detected under the same experimental conditions due to the small surface area of the working electrode resulting in a small amount of product.</p

A comparative study of juvenile delinquency and its treatment in Egypt and Massachusetts.

Thesis (M.A.)--Boston Universit

QTL Analysis for Drought Tolerance Related to Root and Shoot Traits in Barley (<em>Hordeum vulgare </em>L.)

Enhancement of drought tolerance of cultivated barley via identifying the potential and beneficial QTL alleles of wild species (H. vulgare ssp. spontaneum C. Koch) is a great target in barley breeding. Therefore, the overall objectives of the proposed study were: 1) to assess variations in shoot, root and physiological traits of BC2DH lines under control and drought stress conditions. 2) to localize and characterize the QTLs underlying drought tolerance related to shoot, root and physiological traits. Mapping was conducted using a combination of phenotypic data of three investigated years and 371 DNA markers. This investigation was done under control and drought stress conditions. Components of variance revealed a wide range of variability for majority of the investigated traits. In total, 79 putative QTLs for 15 studied traits were detected among 5,565 marker by trait combinations in the population S42 under study. They can be divided into 55 QTLs for shoot traits, 15 QTLs for root traits and 9 QTLs for physiological traits. Overall 27 (34.1 %) QTLs showed favorable effects derived from the presence of exotic alleles. Most of putative QTLs were located on chromosomes 1H, 2H, 4H and 5H. For instance, two QTLs (QWS.S42.1H and QWS.S42.4H) had favorable effects due to the presence of the exotic alleles (Hsp) that were responsible for decreasing plant wilting score by 17%. The SSR markers GMS3 [2H], HvNAM2 [2H] and M1o [4H] were associated with QTLs are likely to be dominating number of tillers/plant and number of spikes/plant and the introgressions from wild barley may increase both traits in S42 population. Also for root length, the vernalisation gene VrnH1[5H] was associated significantly with the QTL (QRL.S42.5H). The presence of exotic alleles at this marker locus led to increase root length by 9.17 % under drought conditions. For proline accumulation, the superior performance of exotic allele at marker locus MGB338 on chromosome 5H suggests a transgression effect of the exotic alleles and led to increase proline content BC2DH lines carrying Hsp alleles by 53% under drought conditions. The majority of the digenic epistatic interaction pairs which were detected in current study had favorable effects in enrich the phenotypic values of the studied traits. Interesting, these exotic QTL alleles responded favorably under drought conditions only that indicates the possibility of underlying a novel drought inducible gene. This study has highlighted the role of the exotic alleles for the detection of favorable leads for drought tolerance. Subsequently, a combinatory approach for the selection of favorable exotics alleles can be employed to develop a better shield against the adverse effects of drought.QTL-Analyse für Trockentoleranz relevante Wurzel-und Sproßmerkmale bei Gerste (Hordeum vulgare L.) Die Verbesserung der Trockentoleranz von Kulturgerste durch die Identifizierung positiver QTL-Allele von Wildgersten (H. vulgare ssp. spontaneum C. Koch) ist ein großes Ziel in der Gerstenzüchtung. Daher waren die übergeordneten Ziele der geplanten Studie: 1) Variation in Sproß, Wurzel und physiologischen Eigenschaften von BC2DH-Linien unter kontrollierten und trockengestressten Bedingungen zu beurteilen. 2) Lokalisierung und Charakterisierung QTLs bezüglich Trockentoleranz . Die Kartierung wurde unter Verwendung von phänotypischen Daten aus drei Versuchsjahren und 371 DNA-Marker durchgeführt. Die phänotypischen Daten wurden unter kontrollierten und trockenstressbedingten Bedingungen durchgeführt. Die Varianzkomponentenanalyse zeigt ein breites Spektrum an Variabilität für die Mehrheit der untersuchten Merkmale. Insgesamt konnten 79 putative QTLs für 15 untersuchte Merkmale unter 5565 Marker x Merkmal Kombination in der Gerstenpopulation S42 nachgewiesen werden. Diese könne in 55 QTLs für Sproßlmerkmale, 15 QTLs für Wurzelmerkmale und 9 QTLS für physiologische Merkmale unterteilt werden. Insgesamt 27 QTLs zeigten positive Effekte aufgrund der Anwesenheit von exotischen Allelen. Die meisten der vermutlichen QTLs wurden auf den Chromosomen 1H, 2H, 4H und 5H lokalisiert. Zum Beispiel hatten zwei QTLs (QWS.S42.1H und QWS.S42.4H) positive Effekte durch exotische Allele bezüglich verminderte Welke um 17%. Die SSR-Marker GMS2 (2H), HvNAM2(2H) und M1o(4H) sind assoziiert mit QTls bezüglich Anzahl Triebe/Pflanze und Anzahl Ähren/Pflanze und die Introgression des Wildgerstenalleles ermöglicht die Erhöhung beider Merkmale in der S42 Population. Für das Merkmal Wurzellänge und das Vernalisationsgen VrnHi[5H] ergaben sich Signifikanzen mit dem QTL (QRL.S42.5H). Die Anwesenheit des exotischen Allels an diesem Markerlocus bewirkte eine Zunahme des Wurzelwachstums um 9,17% unter Trockenstress Die Anwesenheit des exotischen Allels für Marker MGB338 auf Chromosom 5H führte zu erhöhten Prolingehalten in den Hsp-tragenden BC2DH-Linien um 53%. Die Mehrheit der epistatischen Effekte, die in dieser Studie nachgewiesen wurden, hatten positive Auswirkungen auf den phänotypischen Wert. Interessanterweise reagierten die exotischen Allele nur positiv bei trockengestressten Bedingungen, welches auf Trockenstress induzierbare Gene schließen lässt. Die Studie unterstreicht die Bedeutung von exotischen Allelen im Zusammenhang mit Trockenstress. Anschließend kann ein kombinatorischer Ansatz für die Selektion auf exotische Allele für die negativen Auswirkungen des Trockenstresses angewendet werden

Performance of Hollow Bar Micropiles Under Axial and Lateral Loads in Cohesive Soils

The use of hollow core bars in micropiles has greatly increased over the past ten years. Hollow core construction, also known as “self drilled”, is becoming a popular option because it allows a faster installation processes and ground improvement at the same time. Despite the growing demand for hollow bar micropiles, little work has been devoted to evaluating the nominal bond strength between the micropile grout and the surrounding soil, especially in clayey soils. Moreover, the performance of such micropiles under different kinds of loading is still largely unknown and needs to be investigated. In this study, a research methodology encompassing two primary elements is adopted. The first element is a series of full scale field studies on hollow bar micropiles installed in cohesive soils, while the second is numerical investigations on hollow bar micropiles. To accomplish the study, four hollow core micropiles were installed using an air flushing technique employing large drilling carbide bits. Twenty-two load tests were conducted on the four hollow bar micropiles. The hollow bar micropiles were loaded in four consecutive phases, which included; five axial monotonic, five axial cyclic load tests on single micropiles, four axial monotonic tests on pairs of hollow bar micropiles, two monotonic and six cyclic lateral tests on single micropiles. The results of each set of tests were utilized to validate a numerical model. Parametric studies were conducted on the calibrated model to provide design guide lines for hollow bar micropiles under different loads. An equation is proposed to estimate the axial capacity of hollow bar micropiles in cohesive soils depending on the installation method adopted. In addition, an equation for the stiffness degradation under axial cyclic loading is proposed. It reveals that the group efficiency factor for hollow bar micropiles should be taken equal to 1, despite the spacing to diameter ratio employed. Moreover, a family of interaction factor diagrams is established to estimate the settlement of hollow bar micropiles group. Finally, the study demonstrated that hollow bar micropiles can carry moderate lateral loads with proper reinforcement configurations and pile head fixity condition

The Interaction of Water and Salt Flow in Unsaturated Soils

The movements of salt and water, particularly in fairly dry soils or compacted shales, are important processes in both agronomic studies and hydraulics of deep ground water which is important in the location of oil

Improvement of Kojic Acid Production by a Mutant strain of Aspergillus flavus

The ability of 58 different strains of Aspergillus, Mucor, and Penicillium to form kojic acid has been studied. Four Aspergillus species and Penicillium cryzogenum local isolates with high activity of kojic acid synthesis were screened for kojic acid production on five proposed kojic acid producing synthetic medium. Aspergillus flavus (AF) was found to be the highly active one for kojic acid production. The highest level of kojic acid productivity (0.234 g/ l.h) obtained by A. flavus using fermentation medium of 100g/l glucose, and 5.0 g/l yeast extract, and incubated at 30°C and 180rpm for 9 days. The study implicated the optimization of different carbon and nitrogen source of fermentation medium. Among the carbon sources tested, glucose gave the highest kojic acid yield (50.27 g/l) followed by sucrose (48.95 g/l). The use of 5g/l yeast extract resulted in the highest kojic acid production (50.21g/l) compared with the other nitrogen sources. Improvement of Aspergillus flavus by natural selection and random mutagenesis by using UV (for 5, 10, 20, 40 and 60 min) and various doses of gamma irradiation (20, 40, 60, 80, 100, 120, 140 and 160 Gy) has been done to obtain a potential mutant which produce kojic acid higher than its parent strain. Some of wastes hydrolyzates were used as carbon and nitrogen source, potato starch, and rice bran hydrolyzates were the best carbon and nitrogen source, respectively. Key words: Kojic acid, Aspergillus flavus, mutation, UV, Gamma radiatio