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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 5145-5148 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3715-3721 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the unrestricted Hartree–Fock procedure, we have studied the numbers and locations of water molecules in the second hydration shells of the Mn+2–aquoion system. Two arrangements for the second hydration shell were considered, one involving 8 water molecules located along the body diagonals of a cube with Mn+2 ion at the body center and the other with 12 water molecules located in the directions of the lines joining the Mn+2 ion and the midpoints of the sides of the cube. Both these arrangements of the second hydration shells were considered in the presence of the octahedral arrangement of six water molecules in the first hydration shell. The total energies of the composite clusters were minimized with respect to the metal–oxygen distance for the second shell of water molecules to determine the equilibrium geometries in the two cases. From a consideration of the hydration energies, the eight-molecule configuration was found to be the more likely one for the second hydration shell, the metal–oxygen distance for the second shell being 3.75 A(ring) as compared to 2.19 A(ring) for the first. A physical reason associated with steric effects within the second shell water molecules and between the first and second shell molecules is suggested for the greater stability of the 8-member hydration shell as compared to the 12-member one. Using the calculated geometry, the contribution to the proton relaxivity in aqueous solution from the second hydration shell was determined to be 9.9% of that from the first hydration shell in the dipolar interaction regime, in magnetic fields of 0.25 T (corresponding to proton resonance frequency of about 10 MHz) and above and progressively smaller in importance as one went to lower fields corresponding to the contact interaction regime.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7740-7748 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic structures of aquoions involving the divalent paramagnetic ion Mn+2 and the two trivalent ions Fe+3 and Cr+3 have been studied using the unrestricted Hartree–Fock procedure, with six H2O molecules surrounding the metal ion. From the results of our investigations, good agreement is found between the metal–oxygen distances obtained from the present calculation and those from hydrated ionic crystals and aqueous solutions. From the analysis of the charges on the various atoms of the cluster, the covlaent bonding between the metal ion and water molecules is found to be negligible in the Mn+2 system and significant for Fe+3 and Cr+3. The spin populations however indicate strong localization on the metal ions in all three cases. Very good agreement is found between the calculated contact proton hyperfine constants for all three systems and measured values and for the 17O hyperfine constant in the Mn+2 aquoion system, the only one of those systems for which it is available. The contributions of the dipolar hyperfine fields at the proton sites to the proton relaxivities are studied and it is shown that in all three cases, the use of the point dipole model in earlier literature to explain the data on these relaxivities is well justified. Physical reasons for the various features of our results are discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1200-1208 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The unrestricted Hartree–Fock cluster procedure has been applied to the Cu2+–(H2O)6 complex to study both its geometry and the hyperfine properties of protons and 17O nuclei in the water molecules of the first hydration sphere. The geometry was studied to understand the Jahn–Teller effect expected for this complex and to explain the observed tetragonal distortion of an elongated nature from extended x-ray absorption fine structure measurements involving four of the H2O molecules being closer to the Cu2+ ion than the other two. The hyperfine properties were studied to attempt to explain observed data in this respect from nuclear magnetic resonance measurements. Our results for the situation in which there is a hole in the dx2–y2 type of state do explain the elongated nature of the tetragonal distortion. The calculated electronic wave functions provide a satisfactory explanation of the 17O hyperfine interaction. For the protons, our results demonstrate the validity of the point ion model commonly used for the dipolar interaction between protons of the hydrated H2O molecules and the unpaired spins in explaining proton nuclear magnetic resonance relaxation data for aquoions. For the proton contact interaction however, theory appears to lead to a higher value than experiment. Possible sources that can lead to an improvement in the predicted proton hyperfine interaction constant are discussed.
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 9051-9055 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 89 (1980), S. 295-298 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 83 (1979), S. 417-420 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-2234
    Keywords: Hemin ; Hyperfine properties ; First-principles UHF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary As part of a program for first-principles quantitative study of hyperfine properties of large biological molecules, we have applied the Self-Consistent Field Unrestricted Hartree-Fock procedure to investigate the electronic structure of hemin, the associated charge and unpaired spin population distributions and the hyperfine constants of57Fe,14N,13C,1H and35Cl nuclei. The results of the present work indicate significantly more localized charge and spin distributions than were found earlier by the semi-empirical Self-Consistent Charge Extended Hückel procedure. The theoretical values of the57Fe,14N and methene proton hyperfine constants, the only nuclei for which experimental data are available, are found to be −34.99, 11.89 and −1.50 MHz in satisfactory agreement with the experimental values of −26.47, 7.55 and −1.014 MHz, respectively. The contact and dipolar contributions to the hyperfine constants and their breakdowns into direct and exchange polarization contributions are analyzed. Possible sources that could bridge the remaining gap between experiment and theory will be analyzed.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-0630
    Keywords: 78.65.Jd ; 78.20.Dj ; 77.55. + f
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The influence of different evaporation process parameters on the optical properties and constants of thin Sb2O3 films in the ultraviolet and visible region from 250 to 800 nm has been investigated. The most dominant parameters, namely the substrate temperature, rate of evaporation, and ambient oxygen pressure used during the deposition process and the post-annealing temperatures were optimised which resulted in low loss, dense and homogeneous Sb2O3 films. The optical constants and band gaps of these films were evaluated using their interference modulated transmittance spectra in case of both homogeneous and inhomogeneous conditions. Optimized films have been successfully used in developing multilayer high reflecting coatings for Fabry-Perot etalons along with the cryolite (Na3AlF6) films.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 59 (1994), S. 317-326 
    ISSN: 1432-0630
    Keywords: 42.80 ; 77.55 ; 78.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A new computer design program based on the modified-complex method has been developed for constrained optimization and refinement of optical thin-film multilayer devices. This program is having a provision to include both limiting constraints as well as constraint equations. Constraints are suitably accommodated to generate designs which are practicable and withstand high laser power. Various rapid convergent processes like dynamic contraction and expansion of feasible vertices are incorporated for efficient scanning of the constraint parametric space. A broad band IR antireflection coating has been designed to test its relative efficiency with respect to other available methods. A wide varieties of highly useful multilayer devices have been successfully developed using this method.
    Type of Medium: Electronic Resource
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