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  • 1
    Electronic Resource
    Electronic Resource
    The structure of small nickel clusters. II. Ni16–Ni28 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7377-7389 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The molecular adsorption of nitrogen on nickel clusters is used to probe the clusters' geometrical structures. The application of nitrogen binding rules derived from earlier studies of both larger and smaller nickel clusters allows a determination of structure from nitrogen uptake patterns. In the 16- and 28-atom size region cluster structure is dominated by local pentagonal symmetry, a consequence of a preference for close packing of atoms on clusters with curved surfaces. In most cases, the structures that result can be derived from the 13-atom icosahedron, the polyicosahedral 19-, 23-, and 26-atom clusters, and the 55-atom icosahedron, by adding or removing atoms. Icosahedral and polyicosahedral clusters often have substantial surface strain, which in some cases is relieved by deviations from the ideal geometry. Structures are proposed for all clusters in the Ni16 to Ni28 size range, with the exception of Ni27. Generally, there is no evidence for structural changes as a consequence of nitrogen binding, so that the proposed structures are those of the bare as well as the nitrogenated clusters. Where possible, comparison with existing theoretical calculations of nickel cluster structure is made. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469050
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  • 2
    Electronic Resource
    Electronic Resource
    EXAFS and magnetic characterization of inverted ball milled zinc ferrite powders (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5431-5431 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Divalent zinc is commonly used as a replacement cation in ferrites, as it increases the material magnetization when substituted in moderate amounts. However, pure zinc ferrite (ZnFe2O4) is a normal spinel, as zinc has a strong preference for the tetrahedral (A) site in the spinel structure, with Fe occupying the octahedral (B) sites. Then antiferromagnetic B–B coupling dominates the magnetic behavior yielding a material with a Neel temperature near 10 K. It is typically difficult to produce inverted zinc ferrite due to this strong site preference, but recently we produced fine zinc ferrite powders having an inversion parameter of 0.20 using an aerogel process. Ball milling these powders increased the inversion parameter to 0.55, and the median particle size from 14 to 40 nm. To confirm the x-ray diffraction inversion parameters, extended x-ray absorption fine structure (EXAFS) measurements were taken on these powders and ZnFe2O4 standards for both the Fe Kα and Zn Kα absorption edges. Fourier transformed results were fingerprinted against theroretical radial distrubtion functions generated from multiple-scattering FEFF codes for scattering atoms located on the tetrahedral and octahedral sites. Qualitatively, the zinc ferrite standard appears as a normal spinel, while both the iron and zinc radial distributions for the ball milled sample showed large site occupation of both A and B sites. This sample shows superparamagnetic behavior at room temperature, with some ferrimagnetic particles exceeding the critical volume, as indicated by a 15 Oe coercive field. The saturation magnetization of the metastable ball milled powder exceeds 2100 G. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361853
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic properties of Zn–Mg ferrite fine powders (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5435-5435 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several fine powder samples of ZnxMg1−xFe2O4, 0≤x≤1, were prepared by the supercritical sol-gel (aerogel) process, and were annealed at 500 °C for 2 h. The structure, crystallite size and inversion parameter were determined by x-ray diffraction. The crystallite diameter of the as-prepared powders ranged from 6.5 to 8.5 nm. The minimum size was achieved for the samples with 0.25≤x≤0.50. After annealing the crystallite size increased by an average of 3 nm. The values of the inversion parameters, before and after annealing, reflect roughly the chemical preference of Zn cations to the tetrahedral sites and Mg cations to the octahedral sites of the spinel structure. However, these values indicate that the as-prepared materials were not in the equilibrium state. The magnetic properties were studied by 57Fe Mössbauer spectroscopy over a temperature range of 25 K to room temperature. Taking advantage of their sensitivity to the superparamagnetic behavior induced by the size effects, the Mössbauer spectra were used to determine the blocking temperatures. The calculated values peaked at x=0.50 for both the as-prepared and annealed powders. SQUID magnetometry measurements are currently underway. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362330
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  • 4
    Electronic Resource
    Electronic Resource
    Gas dynamics and radiation heat transfer in the vapor plume produced by pulsed laser irradiation of aluminum (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7205-7215 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of pulsed laser irradiation of nanosecond duration with a metal surface is studied by numerical simulation. The heat transfer in the solid substrate and the melted liquid is modeled as one-dimensional transient heat conduction using the enthalpy formulation for the solution of phase change problems. A discontinuity layer is assumed just above the liquid surface. Mass, momentum, and energy conservation are expressed across this layer, while the vapor across the discontinuity is modeled as an ideal gas. The compressible gas dynamics is computed numerically by solving the system of Euler equations for mass, momentum, and energy, supplemented with an isentropic equation of state in a two-dimensional axisymmetric system of coordinates. The excimer laser-beam absorption and radiation transport in the vapor phase are modeled using the discrete ordinates method. The rates for ionization are computed using the Saha–Eggert equation assuming conditions of local thermal equilibrium. The inverse bremsstrahlung mechanism is considered as the main mechanism of plasma absorption. Results show that a thin, submicron vapor layer is formed above the target surface in the duration of laser pulse while thermal radiation plays the key role for plume cooling during the period of strong absorption by the plasma. The release of a very strong shock wave, propagating with a speed of 104 m/s, is observed in the evaporating plume. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361436
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  • 5
    Electronic Resource
    Electronic Resource
    Inhibition of caspase-1 slows disease progression in a mouse model of Huntington's disease (1999)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 399 (1999), S. 263-267 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Huntington's disease is an autosomal-dominant progressive neurodegenerative disorder resulting in specific neuronal loss and dysfunction in the striatum and cortex. The disease is universally fatal, with a mean survival following onset of 15–20 years and, at present, there is no ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/20446
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  • 6
    Electronic Resource
    Electronic Resource
    Computational study of heat transfer and gas dynamics in the pulsed laser evaporation of metals (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4696-4709 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pulsed laser irradiation of nanosecond duration is used in a variety of applications, including laser deposition of thin films and micromachining. Of fundamental interest is the prediction of the evaporative material removal rates, as well as the velocity, density, and temperature distributions of the ejected particles as functions of the laser-beam pulse energy, temporal distribution, and irradiance density on the target material surface. In order to address these issues, the present work establishes a new computational approach for the thorough treatment of the heat transfer and fluid flow phenomena in pulsed laser processing of metals. The heat conduction in the solid substrate and the liquid melt is solved by a one-dimensional transient heat transfer model. The ejected high-pressure vapor generates shock waves against the ambient background pressure. The compressible gas dynamics is computed numerically by solving the system of Euler equations for mass, momentum, and energy, supplemented by an isentropic gas equation of state. The aluminum, copper, and gold targets considered were subjected to pulsed ultraviolet excimer laser irradiation of nanosecond duration. Results are given for the temperature distribution, evaporation rate, and melting depth in the target, as well as the pressure, velocity, and temperature distributions in the vapor phase. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359817
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  • 7
    Electronic Resource
    Electronic Resource
    Low temperature heat capacities of Ti3Al1.1C1.8, Ti4AlN3, and Ti3SiC2 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3609-3611 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the binary Ti–Al system, an ordering transformation in Ti3Al has been shown to result in a significant lowering of the electronic heat-capacity coefficient, γ, by removing electrons from conducting states. When γ is normalized to a per Ti atom basis, the same tendency is found in low temperature calorimetric studies of the conducting ternary carbides Ti3Al1.1C1.8, Ti4AlN3, and Ti3SiC2 reported herein. As a consequence of C- or N-induced covalent-like bond formation, the Debye temperatures in these ternaries are in excess of 700 K. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371267
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  • 8
    Electronic Resource
    Electronic Resource
    Low temperature heat capacity of Ti3SiC2 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 7970-7971 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Calorimetric measurements between 2 and 10 K have been made on Ti3SiC2. The molar heat capacity, c, data can be fitted to the sum of an electronic and a lattice contribution: c=γT+βT3. The β value of 0.049 mJ/mol K4 yields a Debye temperature of 620 K, typical of high stiffness and hardness ceramic materials such as TiC. This value is significantly higher than the Debye temperature measured from elastic measurements. The γ value of 5.21 mJ/mol K2 is a measure of the density of states at the Fermi level. This value, when normalized to a per Ti atom basis, is higher than that of TiC0.97, but roughly half that of Ti metal, implying that covalent-type bonding induced electron localization increases in going from Ti to Ti3SiC2 to TiC. It also partially explains the excellent electrical and thermal conductivities of Ti3SiC2. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370618
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic properties of partially-inverted zinc ferrite aerogel powders (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 1851-1857 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fine powders of ZnFe2O4 with an average particle size of 10 nm and inversion parameter of 0.21 were synthesized by the aerogel procedure. Portions of the powders were calcined in air at 500 and 800 °C and other portions were ball-milled for 10 h. The materials were characterized by x-ray diffractometry, vibrating sample, and SQUID magnetometry, Mössbauer spectrometry, and low temperature calorimetry. Upon calcination the powders underwent significant changes in grain size, inversion parameter, and hence magnetic properties. The magnetic state of the as-produced and calcined samples is best described as disordered and highly dependent on temperature. Upon ball-milling the grain size varied widely and the inversion parameter attained a value of 0.55. The magnetic properties of the ball-milled sample are similar to those of ferrimagnetic MgFe2O4 powders having comparable grain size and inversion parameters. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364068
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic properties of Ni–Co–Cr-base Elgiloy (1999)
    Springer
    Journal of materials science 10 (1999), S. 555-560 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The Ni–Co–Cr-base Elgiloy is one of the commonly used engineering materials. Most applications rely on its high strength, ductility, corrosion resistance and excellent fatigue life over a wide temperature range. However, in the medical application of cerebral aneurysm clips, the alloy is often subjected to strong magnetic fields associated with magnetic resonance imaging (MRI). Its paramagnetic behavior meets MRI safety requirements, but is the source of relatively large artifacts and thus less MRI-compatible for MRI procedure involving the brain. This article reports superconducting quantum interference device (SQUID) measurements on the magnetic properties of a series of Elgiloy wires in either as-drawn or heat-treated conditions. Furthermore, low-temperature calorimetry was employed to reveal the existence of submicroscopic clusters containing ferromagnetic elements such as Ni or Co in the macroscopically paramagnetic matrix. © 1999 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008920415237
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