• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 718
  • 425
  • 180
  • 84
  • 38
  • 28
  • 21
  • 11
  • 9
  • 8
  • 8
  • 7
  • 7
  • 5
  • 5
  • Tagged with
  • 2207
  • 926
  • 428
  • 376
  • 340
  • 213
  • 199
  • 178
  • 175
  • 164
  • 157
  • 156
  • 145
  • 145
  • 121
  • 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

Scattering of he+ ions by noble gases at high energies

Taylor, George Ormsbee 12 1900 (has links)
No description available.
52

The separation of samarium from rare earth mixtures by means of ion-exchange

Turner, Max Allen 08 1900 (has links)
No description available.
53

The separation of neodymium and praseodymium by ion exchange : I. Effect of column length, loading, and ph of eluent

Johnson, William Nelson 08 1900 (has links)
No description available.
54

The heat content, specific heat and entropy of La[subscript]20[subscript]3, Pr[subscript]60[subscript]11 and Nd[subscript]20[subscript]3 between 30[superscript]0 and 900[superscript]0C

Blomeke, John Otis 12 1900 (has links)
No description available.
55

The heat content, heat capacity and entropy of Ce0[subscript]2 between 30[superscript]0 and 900[superscript]0

Ligon, Walter Madison 12 1900 (has links)
No description available.
56

Preparation and dielectric measurements of the rare earth green phases R₂BaCuO₅₋x (R= Y, Sm, Gd, Dy, Ho, Er, Yb)

Gonzalez-Titman, Carlos 05 1900 (has links)
No description available.
57

Laser Spectroscopy of Eu Centres in MBE Grown CaF₂:Eu-CdF₂ Superlattices and CaF₂:Eu Thin Films

Choi, Joon Koo January 2009 (has links)
Molecular beam epitaxy (MBE) grown CaF₂-CdF₂ superlattices (SLs) and CaF₂ thin films doped with Eu ions were investigated by laser spectroscopic techniques. Eu ions were selectively doped into CaF₂ layers and were used as an optical probe to the SLs and thin films. Physical properties of the SLs and thin films were inferred from optical transitions of divalent and trivalent Eu centres. The 4ƒ⁶5d → 4ƒ⁷ transition of Eu²⁺ has shown strain dependent peak shifts of the zero phonon line. These shifts were thought to be a result of deformation in the crystal structure primarily due to the lattice mismatch with the Si substrate. Based on the amount of shifts, the strains associated with the MBE samples were calculated. Photoluminescence (PL) bleaching and its recovery of the same transition of Eu²⁺ in SLs were also explored. At low temperature the bleaching is best described as bi-exponential decay. Localisation of the liberated electrons from the 4ƒ⁶5d absorption band was considered for the bleaching effect. It was observed that at elevated temperatures the PL intensity of the 4ƒ⁶5d → 4ƒ⁷ transition was recovered. Combined excitation-emission spectroscopy (CEES) was employed to investigate trivalent Eu centres in SLs. The strong ⁷F₀ → ⁵D₁ excitation and the ⁵D₀ → ⁷F₁ emission of Eu³⁺ were studied. A novel centre, which is assigned as I, of Eu³⁺ in SL was observed and investigated in comparison with the cubic centre (O centre) of Eu³⁺. Relative to the O centre the I centre has shown a strong thickness dependent PL which can be demonstrated with a mono layer (1 ML = 3.15 Å) resolution. Possible transformation of the I centre to the O centre was also observed by additional thermal and UV excitations. The I and the O centres are proposed as the same centre except for having an electron in the vicinity of the I centre.
58

Complexes of the lanthanides with group V donor ligands

Tillotson, Martin Robert January 1996 (has links)
No description available.
59

Carbonatite-related rare-earth mineralization in the Bear Lodge alkaline complex, Wyoming: Paragenesis, geochemical and isotopic characteristics

Moore, Meghan January 2014 (has links)
The Bear Lodge alkaline complex in northeastern Wyoming (USA) is host to potentially economic rare-earth mineralization in carbonatite and carbonatite-related veins and dikes that intrude heterolithic diatreme breccias in the Bull Hill area of the Bear Lodge Mountains. The deposit is zoned and consists of pervasively oxidized material at and near the surface, which passes through a thin transitional zone at a depth of ~120-183m, and grades into unaltered carbonatites at depths greater than ~183-190m. Carbonatites in the unoxidized zone consist of coarse and fine-grained calcite that is Sr-, Mn- and inclusion-rich and are characterized by the presence of primary burbankite, early-stage parisite and synchysite with minor bastnäsite that have high (La/Nd)cn and (La/Ce)cn values. The early minerals are replaced with polycrystalline pseudomorphs consisting of secondary rare-earth fluorocarbonates and ancylite with minor monazite. Different secondary parageneses can be distinguished on the basis of the relative abundances and composition of individual minerals. Variations in key element ratios, such as (La/Nd)cn, and chondrite-normalized profiles of the rare-earth minerals and calcite record multiple stages of hydrothermal deposition involving fluids of different chemistry. A single sample of primary calcite shows mantle-like δ18O V-SMOW and δ13C V-PDB values, whereas most other samples are somewhat depleted in 13C (δ13C V-PDB ≈ –8 to –10‰) and show a small positive shift in δ18O V-SMOW due to degassing and wall-rock interaction. Isotopic re-equilibration is more pronounced in the transitional and oxidized zones; large shifts in δ18O V-SMOW (to ~ 18‰) reflect input of meteoric water during pervasive hydrothermal and supergene oxidation. The textural relations, mineral chemistry, and C and O stable-isotopic variations record a polygenetic sequence of rare-earth mineralization in the deposit. With the exception of one Pb-poor sample showing an appreciable positive shift in 208Pb/204Pb value (~39.2), the Bear Lodge carbonatites are remarkably uniform in their Nd, Sr and Pb isotopic composition: (143Nd/144Nd)i=0.512591-0.512608; εNd=0.2-0.6; (87Sr/86Sr)i=0.704555-0.704639; εSr=-1.5-2.7; (206Pb/204Pb)i=18.071-18.320; (207Pb/204Pb)i=15.543-15.593; (208Pb/204Pb)i=38.045-39.165. These isotopic characteristics indicate that the source of the carbonatitic magma was in the subcontinental lithospheric mantle, and modified by subduction-related metasomatism. Carbonatites are interpreted to be generated from small degrees of partial melt that may have been produced via interaction of upwelling asthenosphere giving a small depleted MORB component, with an EM1 component likely derived from subducted Farallon crust.
60

Aspects of the ecology and conservation of the rare plant species Phyteuma spicatum L (Campanulaceae) in the British Isles

Wheeler, Belinda Ruth January 1997 (has links)
No description available.

Page generated in 0.047 seconds