• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 268
  • 76
  • 51
  • 32
  • 15
  • 8
  • 8
  • 8
  • 8
  • 8
  • 8
  • 8
  • 6
  • 5
  • 5
  • Tagged with
  • 571
  • 72
  • 66
  • 61
  • 55
  • 51
  • 47
  • 44
  • 44
  • 43
  • 42
  • 40
  • 40
  • 33
  • 32
  • 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.
51

A mechanistic study of the oxidation of Na[VO(O₂)₂(bpy)] by HOCI and its DNA-cleavage activity

Chong, Wai Kwok Sammel 01 January 2000 (has links)
No description available.
52

Intermediate oxides of vanadium and titanium

Khan, A. S. January 1968 (has links)
No description available.
53

Biospeciation and antidiabetic effects of oxidovanadium(IV) complexes

Ugirinema, Vital January 2014 (has links)
The syntheses of bis(1R-imidazole-2/4-carboxylato)oxidovanadium(IV) complexes was successfully carried out and the complexes were isolated in the solid state. The coordinated water was confirmed by elemental analyses, and single crystal XRD. The complexes were therefore distorted octahedral rather than square planar due to the coordination of water at the sixth position. The reaction of the vanadyl ion (VO2+) with imidazole-4-carboxylic acid (Im4COOH), imidazole-2-carboxylic acid (Im2COOH) and methylimidazole-2-carboxylic acid (MeIm2COOH), respectively, in the presence of small bioligands (bL) [oxalate (Ox), lactate (Lact), and phosphate (Phos)] and high molecular weight (HMM) human serum proteins [albumin (HSA) and transferrin (hTf)] were studied in aqueous solution using potentiometric acid base titrations under oxygen and carbon dioxide–free conditions. The data obtained from these titrations was used to calculate the binary and ternary stability constants using the programme HYPERQUAD. The overall stability constants for VO2+-L-Ox system (log β1111 = 18.9, 18.79 and 19.86), VO2+-L-Lact system (log β1111 = 21.83, 20.98 and 22.86), and VO2+-L-Phos system (log β1111 = 27.35, 24.16 and 27.42) (for L= Im4COOH, Im2COOH and MeIm2COOH, respectively) were obtained. The species distribution diagrams showed that under physiological pH the following ternary and quaternary species; [(VO)L(bL)], and [VO(L)(bL)(OH)], would dominate provided that the competition with serum proteins is not too strong. These species were also confirmed by HPLC, LC-MS and EPR. The overall stability constants for the VO2+-L-HSA system (log β2,1,1,0 = 24.3, 23.7 and 24.7), and for the VO2+-L-hTf system (log β2,2,1,0 = 31.1, 30.8, 36.4 for L = Im4COOH, Im2COOH and MeIm2COOH, respectively), suggesting stronger binding of transferrin. The formation constants for the formation of binary (VO(IV) and the proteins) were 9.1 and 13 for log β11, and 20.9 and 25.2 for β12, for human serum albumin and human serum transferrin respectively. The species distribution diagrams for the proteins (HMM) with oxidovanadium(IV) under physiological pH was dominated by VO(HMM)2, VOL(HMM) for unsubstituted Im4COOH and Im2COOH, however, for the N-substituted MeIm2COOH, the species distribution diagrams under physiological pH, were dominated by VOL2, VO(HMM)2 and VO2L2(HMM). These species were further confirmed by HPLC, MALDI-TOF-MS and EPR. The glucose stimulated insulin secretion (GSIS) action of the complexes was investigated using INS-1E cells at 1μM concentration which was established through cytotoxicity studies via the MTT assay. The vanadium salt (VOSO4), cationic vanadium(IV) complex ([VO(MeImCH2OH)2]2+) were also included in the GSIS study in addition to the three neutral complexes [VO(Im4COO)2, VO(Im2COO)2 and VO(MeIm2COO)2] for comparison. The neutral complexes, especially VO(MeIm2COO)2, showed promising results in the stimulation of insulin secretion than the cationic complex and the vanadium salt.
54

Some thermal properties of transition metal alloys

Howe, D. R. January 1967 (has links)
No description available.
55

High resolution spectroscopy of niobium nitride and vanadium oxide

Huang, Gejian January 1988 (has links)
This thesis reports the spectroscopic studies of two gaseous molecules, niobium nitride (NbN) and vanadium oxide (VO). The ³∏ — ³∆ electronic transition of NbN was recorded by laser-induced fluorescence at Doppler-limited resolution as well as at sub-Doppler resolution. Two almost identical branch features are observed in the ³∏₀ — ³∆₁ sub-band because the A-doubling in the ³∏₀ sub-state is large and almost J-independent. The ³∏₁ — ³∆₂ transition is shifted 600 cm⁻¹ to the red of its central first-order position as a result of very large second-order spin-orbit interaction effects. The shift is believed to be caused principally by the coupling of the ³∏₁ component with the ¹∏ state from the same electron configuration, with a smaller contribution from coupling of the ³∆₂ component of the ground state with the low-lying ¹∆ state. The ³∏ and ¹∏ states are unusual in that their zero-order energies are calculated to be within 100 cm⁻¹, based on the newly observed ¹∏₁ - ³∆₂ (1,0) transition; this means that they form a very fine example of a "super-multiplet", where the spin-orbit effects within and between the states of a particular electron configuration are larger than their separations. The spin-orbit interactions are so extensive that the fine structure can only be fitted using effective rotational and hyperfine Hamiltonians for the individual sub-states, as in case (c) coupling. From the determined hyperfine constants h and C⍳ for the three ³∏(v — 0) components, the Fermi contact constant b was found to be negative, which is consistent with the configuration πδ. Rotational analysis gave the ³∏ and ³∆ bond lengths as 1.6705 Å and 1.6622 Å, respectively. The near-infrared electronic system of VO has been recorded in emission at Doppler-limited resolution with the 1-m FT spectrometer at Kitt Peak National Observatory. The spectrum in the 4000-14000 cm⁻¹ region consists of numerous transitions with most of them extensively analyzed. Two isolated sub-bands at 7200 cm⁻¹ have been assigned as the two spin components of a ²∏ — ²∆ transition and rotationally analyzed. The rotational constant for the lower state is found to be larger than that for the σδ² X ⁴∑⁻ ground state, indicating that the ²∆ state arises from the electron configuration σ²δ. The configuration assignment was confirmed by the derived spin-orbit coupling constant for the ²∆ state. Similar reasoning applied to the ²∏ upper state suggests that it may arise from the configuration σ²π, though the preliminary study of the hyperfine structure argues against this assignment. / Science, Faculty of / Chemistry, Department of / Graduate
56

A mechanistic study of the protein photocleavage activities of vanadate(V) and vanadium(V)-peroxo complexes towards aldolase

Leung, Wing Chi 01 January 2011 (has links)
No description available.
57

Obtenção, caracterização e estudos das propriedades de compósitos formados por xerogéis de pentóxido de vanádio e óxido de tungstênio / Preparation, structural and electrochemical properties of V2O5-WO3 xerogel composite

Bolsoni, Aline Turini 29 August 2007 (has links)
O xerogel de pentóxido de vanádio possui estrutura bi-dimensional que viabiliza a intercalação de diferentes espécies como íons, compostos orgânicos e espécies poliméricas. E, quando associeado a outros óxidos de metais transição, tais como, WO3 e MoO3 apresenta uma importância em reações de catálise, pois estes óxidos atuam como promotores em reações como, por exemplo, a redução catalítica seletiva do NOx a NH3 e a oxidação de hidrocarbonetos. Além disso, estes óxidos melhoram as propriedades eletroquímicas e eletrocrômicas, favorecendo assim sua utilização em células fotoquímicas, células para conversão de energia solar e cátodos de baterias e lítio. Dentre estes óxidos, o óxido de tungstênio hidratado foi escolhido não somente por favorecer a dissociação ácida das moléculas, mas também por apresentar uma estrutura lamelar que favorece reações de intercalação sem afetar significativamente sua estrutura original. Neste contexto, o xerogel de óxido misto V2O5/WO3 foi sintetizado e suas propriedades eletroquímicas bem como sua capacidade de intercalação foi investigada. em relação ao comportamento eletroquímico, a melhor resposta foi obtida para o óxido misto com menor concentração de WO3, ao passo que para os óxidos com alta quantidade de óxido de tungstênio, a intercalação dos íons Li+ não foi eficiente. Estudos de voltametria cíclica revelaram que a resposta eletroquímica do óxido misto é similar à encontrada para o xerogel de pentóxido de vanádio. Em adição, outros resultados revelaram a dependência da resposta eletroquímica com a natureza do eletrólito suporte. Também foi verificado que é possível intercalar anilina e agentes tensoativos (Brometo de Cetiltrimetilamônio - CTAB), mantendo o caráter bi-dimensional. Neste trabalho, o compósito V2O5/WO3/SiO2 foi preparado pelo método sol-gel. A metodologia usada possibilitou a preparação de microesferas de sílica cobertas por xerogel de V2O5/WO3, conservando não somente a estrutura, mas também as propriedades eletroquímicas. A atividade catalítica avaliou a oxidação do estireno em fase líquida. / Vanadium pentoxide xerogel has a bi-dimensional structure which is suitable for intercalation of a variety of ions, organic compounds, and even polymeric species. In addition, when associated with other metal oxides such as WO3 and MoO3, it presents an important role in catalysis, since the resulting oxides act as promoters in catalytic reduction of the NOx to NH3 and hydrocarbons oxidation. Besides, these oxides improve electrochemical and electrochromic properties, leading to their use in photochemical cells, cathodes and in solar energy cells. Among several metal oxides, hydrated tungsten oxide was chosen not only because of favor the acid dissociation of molecles but also because of its lamellar structure that allows intercalation reactions without affect significantly the original structure. In this context, V2O5/WO3 xerogel mixed oxides were synthesized and electrochemical properties as well as intercalation capacity were investigated. Concerning the electrochemical behavior, the best response was obtained for the mixed oxides with low concentration of WO3, whereas for the oxides with high amount of tungsten oxide, the lithium ions intercalation was not efficient. Cyclic voltammetric studies revealed that the electrochemical response of mixed oxide is similar to that found for the vanadium pentoxide xerogel. In addition, our results reveal the dependence of the electrochemical response on the nature of the supporting electrolyte. It was also verified that it is possible to intercalate aniline and surfactant molecules (N-cetyl-N,N,N,-trimethyl-ammonium bromide - CTAB), maintaining the bi-dimensional character. In this work, V2O5/WO3/SiO2 composite was prepared by sol-gel method. The methodology used enables the preparation of silica microspheres covered by V2O5/WO3 xerogel mixed oxides, retaining not only its structure but also the electrochemical properties. the catalytic activity evaluated in the oxidation of the styrene in liquidphase.
58

Gaseous vanadium, vanadium oxide and hydroxide clusters from clusters to model catalysts

Feyel, Sandra January 2008 (has links)
Zugl.: Berlin, Techn. Univ., Diss., 2008
59

Vanadium oxide anion clusters their abundances, structures and reactions with SO₂ /

Wyrwas, Richard Ben, January 2004 (has links) (PDF)
Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2005. / Whetten, Robert L., Committee Chair ; First, Phillip N, Committee Member ; Sherrill, C. David, Committee Member ; Wine, Paul H., Committee Member ; El-Sayed, Mostafa A, Committee Member. Includes bibliographical references.
60

Ablation laser impulsionnelle : source de nanoparticules en vol et de films minces : Développement de matériaux nanostructurés à base d'argent, de vanadium et de dioxyde de vanadium / Pulsed laser ablation : a source of in-flight nanoparticles and thin films : Development of nanostructured composites made of silver, vanadium, and vanadium dioxide

Gaudin, Michael 09 June 2017 (has links)
Ces travaux de thèse portent sur le développement d’un dispositif de synthèse de nanoparticules (NPs) par une voie physique basée sur la pulvérisation laser d’une cible suivie d’une trempe du panache plasma ainsi formé. L’association de cette source à une enceinte d’ablation laser conventionnelle a permis de synthétiser des NPs d’argent et de vanadium empilées sur des substrats ou noyées dans des matrices synthétisées par ablation laser. Des analyses par microscopie électronique en transmission (MET) et microscope à force atomique (AFM) ont révélé des NPs cristallisées en vol, de forme sphérique et de tailles relativement monodisperses (~ 3 nm de diamètre) fonction de leur temps de séjour dans la cavité de nucléation. La réalisation de nanocomposites Al2O3 amorphe dopée par des NPs d’argent métallique de différentes tailles a montré l’influence de la taille de ces entités nanométriques sur la position et la largeur de la résonance plasmon de surface (RPS) du matériau nanostructuré. Les NPs gardent leur forme originelle après impact sur le substrat ce qui conduit à des empilements de nanoparticules fortement poreux (de l’ordre de 50%). Des NPs de dioxyde de vanadium ont pu être synthétisées par recuit d’empilements de NPs de vanadium. Du fait de leur individualité, les NPs de VO2 présentent une température de transition plus faible (~50°C) et une largeur d’hystérésis plus importante (~10-30°C) qu’un film mince (température de transition d’environ 68°C et largeur d’hystérésis d’environ 3°C). En associant un film mince synthétisé par PLD à un empilement de NPs il est alors possible de combiner leurs propriétés et d’obtenir un matériau nanocomposite présentant une transition par palier. / The work presented in this thesis is focused on the development of an experimental setup for the synthesis of nanoparticles (NPs) by a physical route, based on the laser vaporization of a target and followed by the rapid quenching of the plasma plume. Combining such a NP source with conventional laser ablation makes possible to synthesize silver and vanadium NPs in stacks on substrates or embedded in different matrices synthesized by laser ablation. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis revealed crystallized spherical NPs relatively monodisperse in size (~ 3 nm in diameter) depending on the residence time in the nucleation cavity. The synthesis of amorphous Al2O3 nanocomposites doped with metallic silver NPs of different sizes showed the influence of the size on the position and the width of the surface plasmon resonance (SPR) of the nanostructured material. The NPs keep their original shape during impact on the substrate, leading to highly porous NPs stacks (approximately 50%). Vanadium dioxide nanoparticles (VO2 NPs) have been synthesized by annealing vanadium NPs stacks. Due to their individual behaviour, VO2NPs exhibit lower transition temperature (~ 50°C) and larger hysteresis width (~ 10-30°C) than thin films (transition temperature around 68°C and hysteresis width around 3°C). By coupling a PLD thin film and a NPs stack, it is possible to combine their properties and obtain a nanostructured material having a step transition.

Page generated in 0.0498 seconds