• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 127
  • 47
  • 13
  • 10
  • 4
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 244
  • 244
  • 37
  • 36
  • 34
  • 28
  • 25
  • 25
  • 23
  • 22
  • 22
  • 21
  • 17
  • 17
  • 16
  • 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

The decomposition of hydrogen sulphide ...

Pickett, Charles Francis. January 1900 (has links)
Thesis (Ph. D.)--New York University, 1927. / Reprinted from the Journal of physical chemistry, v.31.
2

Investigation leading to a process for the synthesis of hydrogen sulphide from sulphur and certain lubricating oils derived from petroleum

Schauder, H January 1952 (has links)
The primary object of the present study was to provide a process adaptable to prevailing South African conditions, for the manufacture of hydrogen sulphide. Such a process would also be suitable for use in other countries where the gas is not obtainable naturally or from refinery operations or as a by-product from other industries. Early in the study it was found that the literature embodying prior work was very scattered in character and had to be sought in many different fields of research. It was therefore decided to make the record of prior work as comprehensive as possible so as to provide, at the same time, a starting point tor future workers on related subjects. Intro., p. 1.
3

Synthesis of polymers with the potential to release H2S: polydicyclopentadiene nanoporous membranes

Long, Tyler Richard 01 May 2014 (has links)
This thesis discuses two very different projects. In the first project, synthesizing a polymer with the potential to release H2S. This was accomplished through the copolymerization of L-lactide and lactide monomers that has been functionalized with 4-hydroxythiobenzamide which is known to release H2S in vivo. The synthesis of the functionalized monomer required the development of a new method to attach functional groups to a derivative of L-lactide, which involved the addition of a thiol to an alpha- beta-unsaturated lactide using catalytic I2. After polymerization, the molecular weight of the copolymers ranged from 8 to 88 kg mol-1 with PDIs below 1.50. These polymers have the ability to be loaded with different amounts of thiobenzamide by controlling the ratio of the functionalized monomer with L-lactide during polymerization. The copolymers were fabricated into two sizes of microparticles with average diameters of 0.52 and 12 µm. The degradation of the smaller microparticles was studied in a PBS buffered solution at pH 7.4 which showed the slow release of the thiobenzamide over a 4 week period. These microparticles are the first to show potential to deliver H2S over a period of weeks. This research addresses a critical need in the field of H2S in medicine where no method exists to release H2S in vivo at times over a few hours. In the second project dicyclopentadiene was polymerized with Grubbs first generation catalyst and fabricated into highly cross-linked membranes with a thickness of 100 µm. The flux of twenty-one molecules with varying polarities and molecular weights ranging from 101 to 583 g mol-1 were studied. Molecules that permeated these membranes had flux rates of 10-5 to 10-6 mol cm-2 h-1 but molecules that did not permeate these membranes had flux rates 104 to 105 times slower. The large difference in flux did not have a strong correlation to molecular weight or solubility in the membrane. However, there was a strong correlation to the cross-sectional areas of the molecules. Cross-sectional area is the smallest two-dimensional rectangle determined by molecular modeling. The cross-sectional area cut-off of the membranes was determined to be between 0.38 and 0.50 nm2. This property gives these membranes the selectivity to successfully separate constitutional isomers, such as tributylamine and triisobutylamine. The membranes have also been used to separate organic products from expensive catalyst and ligands as well as different fatty acids from each other as their respective amine salts.
4

The Effects of Chronic Hydrogen Sulfide Treatment on Hemodynamics and Vasomotor Function in Adult Spontaneously Hypertensive Rats

Reid, Eric Benjamin January 2013 (has links)
The endothelial layer of blood vessels is able to produce a number of vasoactive substances, and these substances can work to either relax or contract the underlying vascular smooth muscle. A hallmark of hypertension is the development of endothelial dysfunction, a shift in the balance of these substances to a state of increased contraction. Hydrogen sulfide (H2S) has recently garnered much interest as a gaseous signaling molecule with the discoveries that is can relax isolated blood vessels and lower blood pressure in young spontaneously hypertensive rats (SHR). Here we investigate whether chronic H2S treatment (56 μmol/kg of the H2S donor sodium hydrosulfide (NaHS), once daily for 5 weeks) can lower the blood pressure of adult aged SHR when compared to normotensive control Wistar Kyoto rats (WKY), and whether there are changes in the endothelium-dependent relaxation and contraction pathways. Invasive hemodynamic measurements including systolic, diastolic, and mean blood pressure, as well as heart rate were measured. Isolated vessel myography was performed on the common carotid artery to determine whether there were changes in the endothelium-dependent and independent relaxation and contraction pathways. This was achieved using a number of dose response curves. Changes in endothelium dependent dilation to ACh, VSM sensitivity to NO and H2S, and NO bioavailability were tested with dose response curves using ACh, SNP (an NO donor), H2S and indomethacin, respectively. TP receptor sensitivity, as well as COX-mediated constriction in quiescent vessels was also examined by using the TP receptor agonist U46619 and L-NAME (eNOS inhibitor), respectively. Biochemical analyses included Western blotting to assess protein levels of CSE (H2S generating enzyme) and eNOS (NO generating enzyme) as well as determining prostacyclin production. Determination of H2S concentration in the blood via a sulfide electrode was also performed to confirm that the H2S treatment was effective. There were no main effects of H2S treatment in any of the hemodynamic measurements taken. ACh dose response revealed a blunting in the recontraction at 10-5 and 10-4.5 log M concentrations (p<0.05) in SHR treated with H2S. No effects were observed, however, in any other myography protocol. Western blot analysis revealed no difference in the protein expression of CSE or eNOS with H2S treatment, and there were no differences in prostacyclin production with H2S treatment. In conclusion, these data suggest that H2S may not be an effective treatment for hypertension in adult SHR, in contrast to previous work finding a similar dosing regimen to be effective at lowering blood pressure in young SHR. Further work must be completed to ascertain the mechanism for the alteration in the ACh dose response curve and to determine at what time point the H2S treatment becomes ineffective.
5

Desulfurization by Metal Oxide/Graphene Composites

Song, Hoon Sub January 2014 (has links)
Desulfurization of liquid and gas phase sulfur compounds has been receiving dramatic attention since sulfur compounds cause environmental damages (especially acid rain) and pose industrial challenges (i.e. corrosion of equipment and deactivation of catalysts). This thesis has focused on the removal of liquid phase aromatic sulfur compounds (i.e. thiophene or dibenzothiophene (DBT)), as well as on the removal of gas phase hydrogen sulfide (H2S) through adsorption method by metal oxide/graphene composites. More specifically, the effects of graphene (or reduced graphite oxide) as a substrate were thoroughly investigated. For liquid phase sulfur removal, graphene which possesses π orbitals can adsorb aromatic sulfur compounds through π-π interactions. In addition, depending on the synthesis methods, higher quality graphene (i.e. thinner or larger graphene) could be obtained; and it improved the amount of DBT adsorption. For gas phase desulfurization (i.e. H2S adsorption), zinc oxide (ZnO) and reduced graphite oxide (rGO) composites have been studied. This study highlights the critical role of rGO as a substrate to enhance the H2S adsorption capacity. The presence of rGO with ZnO increases the surface area compared with pure ZnO since the oxygen functional groups on rGO prevent the aggregation of nano-sized ZnO particles for mid temperature sulfidation processes. The average particle size for pure ZnO was increased from 110 nm to 201 nm during the adsorption process while that for ZnO/rGO was maintained as 95 nm even after adsorption at 300°C. This contributes to explain that the presence of rGO with ZnO can enhance the H2S adsorption capacity from 31.7 mg S/g ads (for pure ZnO) to 172.6 mg S/g ads (for ZnO/rGO), that is more than a 5-fold increase. Morever, the presence of rGO with ZnO considerably improves the stability of the adsorbent; for multiple regeneration cycles at 600°C (in N2 environment), the adsorption capacity for ZnO/rGO stabilized at 93.1 mg S/g ads after the 8th cycle, while that for pure ZnO was nil after 5 cycles. The effects of copper (5, 10, 15, 20 and 25 mol%) with zinc oxide (ZnO) and reduced graphite oxide (rGO) composite on the hydrogen sulfide (H2S) adsorption capacity have also been studied. It was found that depending on the copper loading, the H2S adsorption capacity has been increased by up to 18 times compared to pure ZnO. In order to investigate the oxidation changes on copper and zinc oxides, crystallite analysis by XRD and chemical state analysis by XPS were performed. It was confirmed that the 2D rGO substrate, containing abundant oxygen functional groups, promoted the metal oxide dispersion and increased the H2S adsorption efficiency by providing loosely bonded oxygen ions to the sulfur molecules. In addition, it was determined that the optimum content of copper was 15 mol% relative to ZnO for maximizing the H2S adsorption. The 15% copper with ZnO/rGO led to the highest portion of zinc ions located in the Zn-O lattice; and led to the co-existence of Cu1+ and Cu2+ ions with ZnO. The H2S exposure at 300°C produces metal sulfides (i.e. zinc sulfide and copper sulfide) and sulfate ions.
6

The Effects of Chronic Hydrogen Sulfide Treatment on Hemodynamics and Vasomotor Function in Adult Spontaneously Hypertensive Rats

Reid, Eric Benjamin January 2013 (has links)
The endothelial layer of blood vessels is able to produce a number of vasoactive substances, and these substances can work to either relax or contract the underlying vascular smooth muscle. A hallmark of hypertension is the development of endothelial dysfunction, a shift in the balance of these substances to a state of increased contraction. Hydrogen sulfide (H2S) has recently garnered much interest as a gaseous signaling molecule with the discoveries that is can relax isolated blood vessels and lower blood pressure in young spontaneously hypertensive rats (SHR). Here we investigate whether chronic H2S treatment (56 μmol/kg of the H2S donor sodium hydrosulfide (NaHS), once daily for 5 weeks) can lower the blood pressure of adult aged SHR when compared to normotensive control Wistar Kyoto rats (WKY), and whether there are changes in the endothelium-dependent relaxation and contraction pathways. Invasive hemodynamic measurements including systolic, diastolic, and mean blood pressure, as well as heart rate were measured. Isolated vessel myography was performed on the common carotid artery to determine whether there were changes in the endothelium-dependent and independent relaxation and contraction pathways. This was achieved using a number of dose response curves. Changes in endothelium dependent dilation to ACh, VSM sensitivity to NO and H2S, and NO bioavailability were tested with dose response curves using ACh, SNP (an NO donor), H2S and indomethacin, respectively. TP receptor sensitivity, as well as COX-mediated constriction in quiescent vessels was also examined by using the TP receptor agonist U46619 and L-NAME (eNOS inhibitor), respectively. Biochemical analyses included Western blotting to assess protein levels of CSE (H2S generating enzyme) and eNOS (NO generating enzyme) as well as determining prostacyclin production. Determination of H2S concentration in the blood via a sulfide electrode was also performed to confirm that the H2S treatment was effective. There were no main effects of H2S treatment in any of the hemodynamic measurements taken. ACh dose response revealed a blunting in the recontraction at 10-5 and 10-4.5 log M concentrations (p<0.05) in SHR treated with H2S. No effects were observed, however, in any other myography protocol. Western blot analysis revealed no difference in the protein expression of CSE or eNOS with H2S treatment, and there were no differences in prostacyclin production with H2S treatment. In conclusion, these data suggest that H2S may not be an effective treatment for hypertension in adult SHR, in contrast to previous work finding a similar dosing regimen to be effective at lowering blood pressure in young SHR. Further work must be completed to ascertain the mechanism for the alteration in the ACh dose response curve and to determine at what time point the H2S treatment becomes ineffective.
7

Isotopic exchange reactions in liquid hydrogen sulfide /

Smith, Robert Clifford. January 1952 (has links)
Thesis (M.S.)--Oregon State College, 1952. / Typescript. Includes bibliographical references (leaves 69-70). Also available on the World Wide Web.
8

Volatile sulfur compounds in periodontal pockets

Persson, Sten. January 1993 (has links)
Thesis (doctoral)--Umeå University, Sweden, 1993. / Added t.p. with thesis statement inserted. Includes bibliographical references.
9

Removal of hydrogen sulfide from groundwater using ozone and iron oxide-coated sand /

Chaudhuri, Mahua. January 2004 (has links)
Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 54-58). Also available on the Internet.
10

Volatile sulfur compounds in periodontal pockets

Persson, Sten. January 1993 (has links)
Thesis (doctoral)--Umeå University, Sweden, 1993. / Added t.p. with thesis statement inserted. Includes bibliographical references.

Page generated in 0.0489 seconds