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  • 1
    Publication Date: 2010-11-01
    Print ISSN: 0015-5632
    Electronic ISSN: 1874-9356
    Topics: Biology
    Published by Springer
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  • 2
    Publication Date: 1984-10-01
    Description: In the recent past, specific gravity of tubers has been considered an easy means of estimating yield potential of sweet potato cultivars (Bryant, 1979) and their quality characters like starch value and dry-matter content (Ishikawa & Sakai, 1973). Bryant (1979) separated sweet potato tubers with low and high specific gravity at planting time by determining whether or not they floated in water, and observed that the floaters gave 20% higher yield than the sinkers. As this simple test claimed to hold promise for selecting higher-yielding sweet potato genotypes, it was decided to scan its usefulness at the College of Agriculture, Dholi, where a large collection of sweet potato germ plasm is being maintained for research needs.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 3
    Publication Date: 2011-01-04
    Print ISSN: 1073-5623
    Electronic ISSN: 1543-1940
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of a series of Ce2Fe17−xSix solid solutions with x equal to 0.0, 0.23, 0.4, 0.6, 0.8, 1.02, 1.98, and 3.20 have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. An x-ray-diffraction study indicates that the compounds adopt the rhombohedral Th2Zn17-type structure. The substitution of silicon for iron in Ce2Fe17 leads to a contraction of the a axis by 0.2%, an expansion of the c axis by 0.2%, and a consequent reduction of the unit-cell volume by about 0.2% per substituted silicon. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17 to 455 K for Ce2Fe14Si2. Powder neutron-diffraction results, obtained at 295 K, indicate both that the silicon atoms preferentially occupy the 18h sites and that the iron moments increase with increasing silicon content, an increase which is related to the increase in Curie temperature. The Mössbauer spectra have been fit with a binomial distribution of the near-neighbor environments in terms of a maximum hyperfine field Hmax for an iron with zero silicon near neighbors, and a decremental field ΔH per silicon near neighbor. The compositional independence of both the weighted average maximum hyperfine field and of the decremental field indicates that the silicon acts as a magnetic hole, a hole which does not perturb the magnetic moments at the iron sites. The compositional dependence of the weighted average isomer shift is explained in terms of an interband mixing of the iron 4s and silicon 2p bands, due to the reduction of the iron 18h bond lengths. This interband mixing affects the charge but not the spin distribution at the iron sites. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6700-6702 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nature of the Verwey transition in magnetite (Fe3O4) within a three-band spinless model Hamiltonian is examined. These bands, which arise from the minority-spin t2g orbitals on the Fe(B) sublattice, are occupied by half an electron per Fe(B) atom. The Verwey order–disorder transition is studied as a function of the ratio of the intersite Coulomb repulsion U1 and the bandwidth W. It is found that the electrons are ordered beyond the critical value of U1/W≈0.25 in essential agreement with the results of the one-band Cullen–Callen model. For larger values of U1/W, a Verwey-like order is exhibited where the electrons occupy alternate (001) planes. The model predicts a transition from the metallic to the semiconducting state with the band gap increasing linearly with U1 beyond the transition point.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An x-ray diffraction study of the substitution of gallium in Tb2Fe17 to form the Tb2Fe17−xGax solid solutions indicates that the compounds adopt the rhombohedral Th2Zn17 structure. The unit cell volume and the a-axis lattice parameter increase linearly with increasing gallium content. The c-axis lattice parameter increases linearly from x=0 to 6 and then decreases between x=7 and 8. Magnetic studies show the Curie temperature increases by ∼150° above that of Tb2Fe17 to reach a maximum between x=3 and 4, and then decreases with further increases in x. Neutron diffraction studies of Nd2Fe15Ga2 and Tb2Fe17−xGax, with x equal to 5, 6, and 8, indicate that the gallium completely avoids the 9d site, occupies the 6c "dumbell'' site only at high values of x and strongly prefers the 18f site at high values of x. The magnetic neutron scattering indicates both that the terbium sublattice magnetization couples antiferromagnetically with the iron sublattice and that there is a change in easy magnetization direction from planar to axial with increasing gallium concentration. This change in easy magnetization direction is explained in terms of a sign reversal of the second-order crystal field parameter, A02, the most important parameter responsible for determining the terbium sublattice anisotropy. The Mössbauer effect spectra indicate a larger room-temperature average hyperfine field at the iron site in the Tb2Fe17−xGax solid solutions than in several related R2Fe17 compounds. The large observed increase in the isomer shift with increasing gallium content results from interatomic charge transfer and intraatomic s-d charge redistribution in the presence of gallium.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Six samples of Ce2Fe17−xGax with nominal Ga content x equal to 0, 0.3, 0.5, 0.7, 1.0, 2.0 have been studied by powder neutron diffraction at room temperature. Both crystalline and magnetic refinements have been carried out. All six samples adopt the Th2Zn17-type rhombohedral structure. The only additional phase found is α-iron. Gallium atoms are found to have high affinity for the iron 18h site, and are absent from the 9d and 18f sites. The Ga substitution for Fe leads to an expansion of both the a and c axes. The Curie temperature increases from 238 K for Ce2Fe17 to 406 K for Ce2Fe15Ga2. Magnetic refinements on the samples with x=0.3, 0.5, 0.7, 1.0, and 2.0 reveal that the magnetic moments of the four Fe sites are in the basal plane and that their values increase with increasing Ga content. © 1996 American Institute of Physics.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of a series of Tb2Fe17−xAlx solid solutions, with nominal x compositions of 0, 2, 3, 4, 5, 6, 7, and 8, have been studied by neutron diffraction and Mössbauer spectroscopy. Neutron-diffraction data indicate that the compounds all crystallize with the Th2Zn17 structure and that the aluminum atoms are excluded from the 9d site and show a distinct preference for the 6c site only for an aluminum content greater than 6. The unit-cell volume increases by approximately 1% per aluminum atom substituted in the formula unit. The magnetic moment per formula unit, measured at 295 K, shows very little change for x less than or equal to 4, but decreases rapidly with increasing aluminum content for higher values of x. Mössbauer spectral results indicate that all the samples are ferromagnetically ordered at 85 K. However, at 295 K Tb2Fe9Al8 is paramagnetic and Tb2Fe10Al7 is either paramagnetic or has at most very small ferromagnetic moments. An analysis of the magnetic spectra with a basal magnetic model is successful for x values of 5 or less; however, at higher x values an axial model for the magnetization is required, indicating the presence of a spin reorientation with increasing aluminum content and decreasing temperature. The weighted average hyperfine field decreases approximately linearly by 21 kOe per substituted aluminum atom at 85 K and more rapidly at 295 K. As expected, the isomer shifts increase with increasing aluminum content as a result of interatomic charge transfer and intraatomic iron 4s-3d electronic redistribution.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5994-5996 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Mössbauer spectra of Sm2Fe17 and Ho2Fe17 and their nitrides have been measured between 295 and 85 K and analyzed with a model which is consistent with our earlier work on R2Fe17 and R2Fe17Nx compounds, where R is Pr, Nd, and Th. This model is completely consistent throughout these rare-earth compounds and is in agreement with the crystallographic changes occurring upon nitrogenation and with the prediction of band structure calculations. The dramatic increase in Curie temperature in the nitrides results from the expansion of the crystallographic lattice, an expansion which is mainly centered on the 9d and 18h iron sites as is indicated by the increase of their Wigner–Seitz cell volumes upon nitrogenation. The 9d and 18h sites show a larger enhancement of their hyperfine fields as compared to the 6c and 18f sites as a result of improved ferromagnetic exchange between these sites and their near neighbors because of the lattice expansion and the consequent reduced iron 3d-iron 3d overlap.
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of a series of Ce2Fe17−xAlx solid solutions with x equal to 0.00, 0.88, 2.06, 2.81, 3.98, 5.15, 6.08, 7.21, 8.20, 9.08, 9.84, and 10.62 have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. The compounds crystallize in the rhombohedral Th2Zn17-type structure. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17 to 384 K for Ce2Fe14Al3 and then decreases at higher aluminum content. Powder neutron diffraction results, obtained at 295 K, indicate that aluminum avoids the 9d site for all x values and preferentially occupies the 18h site at low aluminum content. Aluminum shows a marked preference for the 6c site for x(approximately-greater-than)6. The room-temperature iron magnetic moments increase from x=0 to 2 and then decrease for x(approximately-greater-than)2. The Mössbauer spectra have been fit with a binomial distribution of the near-neighbor environments in terms of a maximum hyperfine field, Hmax, for an iron with zero aluminum near neighbors, and a decremental field, ΔH, per aluminum near neighbor. The compositional dependence of the decremental field indicates the influence of aluminum on the long-range magnetic ordering in the compound.The compositional dependence of the weighted average maximum hyperfine fields and the weighted average isomer shifts in Ce2Fe17−xAlx may be understood in terms of a mixing of the 3d conduction band electrons with the 3p valence band electrons of aluminum, a mixing which is more extensive than that associated with silicon in the Ce2Fe17−xSix solid solutions. We conclude that this mixing has a larger influence on the magnetic properties of these solid solutions than does the presence of a short iron–iron bond or the expansion or contraction of the lattice parameters and unit cell volume. © 1996 American Institute of Physics.
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