• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 34
  • 10
  • 9
  • 7
  • 5
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 87
  • 31
  • 13
  • 12
  • 11
  • 10
  • 9
  • 9
  • 9
  • 8
  • 7
  • 6
  • 6
  • 6
  • 6
  • 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

Excited state properties of 1-naphthol and its sulphonates

Henson, Robert M. C. January 1973 (has links)
The transient absorption spectrum of 1-naphthol was first sought by flash photolysis at higher acidities than had been previously investigated. While no transient absorption was observed for l-naphthol itself, strong transient absorptions were observed for l-naphthol-2 and -4-sulphonates even in aqueous solution. This enabled pK(T1) for the protonation of the naphtholate ions to be measured directly from the strength of triplet-triplet absorptions and this value was compared with the pK(T1) obtained from Forster Cycle calculations on phosphorescence maxima,. Values of pK(S1) and pK(S0) were also obtained and the order of the pK values was found to be pK(S0) > pK(T1) >> pK(S1), It is likely that this order is the same for l-naphthol and therefore disagrees with the results of some recent quantum mechanical calculations, A strong fluorescence was also observed for l-naphthol-2- sulphonate in aqueous acidic solutions, in contrast with the weak fluorescence observed for 1-naphthol and l-naphthol-4-sulphonate. This is explained in terms of intramolecular hydrogen bonding in l-naphthol-2-sulphonate which prevents quenching of the first excited singlet state by hydrogen bonding with solvent water molecules. The fluorescence intensity of 1-naphthol, l-naphthol-2-sulphonate, and l~naphthol-4-sulphonate in aqueous acidic solutions is also found to increase as the water concentration is effectively reduced by the addition of certain solutes in large quantities, A corresponding increase in the triplet yield is also found for l-naphthol-2-sulphonate in acidic solutions. These increases are also explained in terms of reducing the hydrogen bonding to solvent water molecules and hence reducing the deactivation of the state, l-Naphthol sulphonates and protonates in concentrated sulphuric acid and it is deduced that protonation occurs at a carbon atom in the naphthalene ring, A value of pK(S0 ) was determined for this protonation.
2

The Snf2 Domain SnAC binds specifically to the Interior of Histone H3

Jones, Megan Ashely 01 August 2015 (has links)
Combined with the data showing that the analogous section of BRG1 has histone binding properties, the second proposed model, where the SnAC domain acts as a histone anchor required for remodeling and directly binds to a location on the histone surface, was pursued. This was supported by Fe-BABE targeted cleavage that showed a cleavage site located within the SnAC domain as well as crosslinking data that showed there was a 2-3 fold reduction of Snf2 crosslinking upon deletion of the SnAC domain [62]. In order to find which histones SnAC binds to specifically and the regions of the histone(s) involved, a recombinant SnAC domain protein was generated and used in pull down assays with histones H2A, H3, and H4 in order to show binding and specificity. Finally gH3, a tailless histone H3, was purified to determine if the interaction between the SnAC domain and the histone occurred in either the tail, or core domain of the protein.
3

Influence of Penicillium simplicissimum (Oud.) Thom and Penicillium citrinum Thom on growth, chemical composition and root exudation of axenic marigold

Hameed, Khalid Majid January 1971 (has links)
Axenic marigold (Tagetes erecta L.) were grown in quartz sand free of organic compounds and one-half strength Hoagland and Arnon nutrient solution plus chelated iron, in individual plant containers, designed for collecting root exudates, inside sterile gnotobiotic flexible plastic isolators. Plant roots were treated with washed conidiospores of Penicillium simplicissimum (Oud.) Thom (7 to 8 x 10⁶ per plant) or Penicillium citrinum Thom (4 x 10⁶ conidiospores per plant), citrinin (0.1, 1.0 and 10 mg/l), and extracts of 80 g axenic or P. simplicissimum-colonized roots. Experiments were harvested 20 days (prior to flowering) and 34 days (flowering) after inoculation. Root exudates were collected at the end of experiments or also weekly obtained for 5 weeks. Inoculated plants were larger in size, contained more dry matter and flowered earlier than the axenic plants. Concentration of 1.0 mg/l citrinin stimulated plant growth and 10 mg/l citrinin had no effect. Extract of P. simplicissimum-colonized roots suppressed plant growth. Roots exhibited 40-60% degradation 34 days after inoculation. Fresh weight of P. citrinum-inoculated plants was lower than the noninoculated. Total water soluble carbohydrates and reducing sugars were significantly higher in the foliage of root colonized plants 34 days after inoculation. Total organic matter and protein were decreased in root exudates 20 days after inoculation. These variations were attributed to reabsorption of organic compounds by the plants and immobilization of those compounds by the mycelial growth. Thirty-four days after inoculation there was increased amounts of organic compounds in the exudates as root colonization progressed. Analyses of periodically obtained exudates indicated a decrease in exudates at flowering from axenic plants only. This phenomenon was not detected in the presence of P. simplicissimum. Percentages of P and K in dried leaves were decreased 20 days after inoculation. However, N, P and K concentrations were not affected 34 days after inoculation. Calcium concentration was significantly increased at the latter stage. Germination of conidiospores occurred in the root hair region, but no direct penetration of intact living cells was observed. There was extensive mycelial growth from infection centers at weakened root hai:rs, damaged epidermal cells and sloughed tissues. Macerating enzyme, polygalacturonase, and cellulase were detected in extracts of P. simplicissimum-colonized roots. / Ph. D.
4

Some physiological characteristics of wild, caged-stressed, and shock-comatose gray squirrels

Hanson, Jeffrey C. January 1966 (has links)
This project was undertaken to determine the effects of continued close confinement on the normal physiological characteristics of the gray squirrel. A total of 46 squirrels divided into three groups: normal, confined-stressed, and confined-shocked were sampled within a period of 10 months from September 15, 1965 to June 30, 1966. The confined-shocked squirrels exhibited acute hypoglycemia, hypolacticemia, and hypothermia indicating a general breakdown in the overall homeostatic processes. The adrenal glands from the confined-shocked individuals were approximately 6-8 mg heavier than either the normal or confined-stressed animals. Packed-cell-volumes averaged from 31-36% higher than normal in both the confined-stressed and confined-shocked animals indicating a polycythemic condition which developed due to the increased stress of confinement. Normal adult liver glycogen levels were approximately 17.2 mg/g of liver tissue higher than immature squirrels. Death from shock could have been caused by the acute reduction of plasma glucose, plasma lactic acid, or body temperature or any combination of these three physiological characteristics. High PCV may have been an additive factor to the shock syndrome evident in this study. However, further intensive study must be conducted before we can contribute the observed shock losses to any specific physiological mechanism. / Master of Science
5

A comparison of sludge properties and kinetic differences between a pure oxygen system and a conventional system

Haas, Scott Trethaway January 1973 (has links)
The objective of this research was to analyze a pure oxygen activated sludge process and its claimed advantages. The major emphasis of both the claims and this research was the settleability of the sludge and the biological kinetics. An identical conventional air activated sludge unit was also operated as a direct comparison. Settling tests were run in three different cylinders with increasing diameters to collect data on the sidewall effects in addition to the settling rates. The settling velocities were also calculated and the average values for the oxygen and the air sludges were 95.0 ml/min and 104.0 ml/min, respectively. The results indicated there was no significant difference in the settling rates and the mixed liquor solids concentration did not affect these rates. The mass settling rate, a new parameter obtained by multiplying the settling velocity times the mixed liquor solids concentration, indicated the oxygen sludge settled more mass in a given time period than the air sludge and therefore compacted to a greater degree. The substrate utilization rate of the oxygen process was found to be 2.8 times greater than that of the conventional air process. This finding is comparable to other published reports. The oxygen utilization rate for the sludge from the air unit was slightly higher than that of the oxygen sludge. The coefficients of the kinetic formula did indicate that the oxygen system had a greater degree of endogenous stabilization occurring than did the air. The oxygen unit used in this study consistently had better BOD removal efficiencies than did the air. The oxygen unit averaged 94%, while the air unit averaged 85%. This investigation also indicates that an air unit will not operate at the identical parameters utilized in an oxygen process. This is due primarily to hydraulic difficulties encountered. / Master of Science
6

Intracellular distribution of nitrogen during synchronous growth of Chlorella pyrenoidosa

Hare, Theodore Arthur January 1967 (has links)
A continuous dilution method for the mass culture of microorganisms was developed which yielded 3x as much cellular material as previous culturing methods for <i>C. pyrenoidosa</i> in the same time period and in less than one-tenth the culture volume. Cellular growth parameters increased exponentially throughout the cell cycle of <i>C. pyrenoidosa</i> when the new mass culturing technique was utilized. The levels of nitrogen in different cellular fractions were estimated during the cell cycle (i.e. lipid-plus chlorophyll-N; TCA soluble-N; individual free-, peptide-, and protein-amino acid residues; nucleotide-N; DNA-N; RNA-N). The amino acid distribution within the cellular protein remained nearly constant during cellular development. Protein-N accounted for approximately 60% of the total cellular-N throughout the cell cycle. The free amino acids exhibited a variety of trends in change of level during the cell cycle. Free-alanine, -lysine, -serine, -glycine, -arginine, and -glutamate were present at relatively high levels. Increase in level of peptide-N during early cellular development resulted largely from increase in levels of peptide-arginine, -glutamate, and -lysine. The other peptide amino acids exhibited a variety of different trends. RNA-N demonstrated exponential accumulation throughout cellular development with a reduced rate of accumulation during cellular division. DNA-N increased during most of the cell cycle at a lower exponential rate; however, the rate of DNA-N accumulation increased abruptly at the onset of nuclear division. Reduced glutathione (GSH) was found to be the predominant acid-soluble sulfhydryl-containing compound throughout the cell cycle. Its trend (as % of total cellular-N) was similar to that of TCA-soluble sulfhydryl-containing compounds in synchronized sea urchin eggs. GSH exhibited properties similar to certain compounds tentatively identified as sulfur-containing nucleotide-peptides by previous workers. Norit-A adsorption studies indicated that nucleotide-peptides were not present in the TCA extracts of <i>C, pyrenoidosa.</i> During the period 0.4-0.9 fraction of the cell cycle GSH was synthesized at the expense of cellular protein. A hypothetical scheme was presented to account for both the origin of GSH prior to nuclear division and the proposed regulation of mitotic apparatus formation through acid-soluble sulfhydryl compounds. / Ph. D.
7

Studium rekombinace molekulárních iontů s elektrony za nízkých teplot / Recombination of molecular ions with electrons at low temperatures

Kálosi, Ábel January 2015 (has links)
The aim of this work is the experimental study of recombination of molecular ions with electrons at low temperatures (< 300 K). The work gives an overview of the diagnostic methods, modelling of chemical kinetics, and experimental ap- paratuses Cryo-FALP II and SA-CRDS used in the undertaken measurements. Two processes were studied in the course of this work: state-selective binary disso- ciative recombination of H+ 3 ions in para-H+ 3 and ortho-H+ 3 states, and H2-assisted ternary recombination of H+ 3 . The main result of the state-selective dissociative recombination study is that the rate of recombination in the para-H+ 3 state is at least three times higher than in the ortho-H+ 3 state at 60 K. The study of H2- assisted recombination gave a better understanding of ternary processes of H+ 3 ions and removed further discrepancies between results of afterglow experiments.
8

Epigenetic Effects of Arsenite in HeLa Cells

Burgos, Rosa M January 2007 (has links)
Mechanisms of arsenic toxicity are not yet clear. Arsenite has effects on methylation pathways, by decreasing expression of DNA methylases and depletion of S-adenosylmethionine. Histones are DNA packing proteins that regulate gene expression modulating chromatin accessibility. Methylation at Lysine 9 of Histone H3 (K9H3) is a hallmark of heterochromatin. Dimethyl K9H3 is a mark of facultative heterochromatin and trimethyl K9H3 is present on constitutive heterochromatin. HeLa cells exposed for 24 hrs to 1 uM or 5 uM Sodium Arsenite were fixed and different posttranslational modifications of histones were detected by indirect immunofluorescence. Images were analyzed to assess the change on average methylated species of K9H3 in cell nuclei. Interestingly Arsenite (1 uM and 5 uM) treated cells had a significant increase in the trimethylated and dimethylated of K9H3, evaluated throught the comparison of average nuclei brightness and pixel value analysis between treatments.
9

An investigation into the nature of perceptual style and body awareness in relation to perceptual-motor abilities

Head, Andrew S. January 1988 (has links)
The thesis is an account of an investigative study into the nature of perceptual-motor abilities. Part one considers Witkin's construct of cognitive style, using it to predict the relationships between three tests of perceptual functioning from widely varying areas of psychology and sports science. To some extent the results were as predicted; that is, those people demonstrating high levels of perceptual acuity on one test also showed similar acuity on one or more of the other perceptual tests. These results, however, only applied to the male subjects and then only when the opposite poles of one test-dimension were partitioned out and compared. The female subjects demonstrated no significant relationships between the three tests. As a result, it was proposed that the tests were indeed linked but by an array of underlying perceptual abilities rather than by a single, overlying cognitive or perceptual style. In the ensuing search for these abilities, 76 measures of perceptual and perceptual-motor skills were factor analysed to reveal 8 oblique perceptual-motor factors of which one was interpreted as being perceptual style. The nature of perceptual-motor abilities is discussed both in relation to clumsiness and to sports training with the emphasis being on whether such abilities are amenable to alteration. The thesis puts forward the proposal that an upper limit to each ability is fixed for each individual in early childhood but that this potential may be maximised through relevant training. The Perceptual-Motor Ability Profile was devised as a tool with which to indicate the aptitude a person evidenced for a particular sport or physical activity and was used in demonstration to describe the group abilities of four dancers with respect to the requirements of their chosen activity. Finally, a model of perceptual-motor functioning, relating the eight factors extracted, is suggested.
10

Theoretical And Computational Studies Of Dissociative Recombination Of H3+ With Low Kinetic Energy Electrons: Time-independent A

Santos, Samantha 01 January 2009 (has links)
Dissociative recombination of molecular ions by collisions with electrons is a reactive collision, in which the electronic kinetic energy is transferred to the excitation of the molecule that, then, dissociates. The goals of this dissertation was (1) to improve existing approaches in theory of DR of triatomic ions in the time-independent framework developed in recent years by Kokoouline and Greene, and (2) to develop a time-dependent theoretical framework for DR treatment based on quantum defect theory. The theoretical method developed by Kokoouline and Greene is based on multichannel quantum defect theory and accounts for the major non-Born-Oppenheimer Jahn-Teller interaction between electronic and vibrational motions of the molecule. The study of this dissertation is partially based on this method but improved, extended, and systematically applied in the framework of my thesis. This dissertation presents the calculated DR rate coefficient for H3+ within the time-independent framework and the description of the method used to obtain the (qualitative) flux with time-dependent method. The time-independent results show good agreement with experimental data from storage ring experiments. The DR rate coefficients for ortho- and para-H3+ were calculated separately and show a significant difference at very low electronic energies; a result that agrees with recent storage ring experiments. Also, it is discussed results for other isotopologues of H3+ (H2D+, D2H+, and D3+) and the results for vibrationally-excited initial states of H3+. It was found that the DR rate coefficients for vibrationally-excited initial states are larger than the rates for the ion initially in the ground vibrational state. At the end, this dissertation discuss the time-dependent calculations done with a diatomic model system.

Page generated in 0.0191 seconds